Subscriber RF telephone system for providing multiple speech and/or data signals simultaneously over either a single or a plurality of RF channels

(54) (56) (57)

AGENT

NAME

PATENTHARE Interdigital Technology Corp., 781 Third Avenue King of Prussia PA 19406-1409 US

Eric Paneth, San Diego CA US Mark J Handzel, San Diego CA US

AWAPATENT AB

Digital wireless communication system with multiple access

QUOTED PUBLICATIONS: - - SUMMARY: A system for wireless transmission of a plurality of information signals utilizes digital time-sharing circuits between a base station and a plurality of subscriber stations.

The subscriber stations can be fixed or mobile. The number of time-sharing circuits is determined by the transmission quality of the signals. The base station is connected to an external information network, which can be analog and / or digital. The information signals are selected from a group which includes voice, data, image, video, computer and instrumentation signals. The system is provided with room diversity by using a plurality of spaced-apart antennas to provide relatively good signal reception despite signal fading. The base station operates over a number of RF channel pairs. The drive on each channel pair is performed with a combination of a transmit channel circuit which is arranged to process a plurality of information signals received simultaneously on telephone trunk lines for simultaneous transmission to different subscriber stations over a given RF channel, and a receive channel circuit which is arranged to process a plurality of signals received. simultaneously over a given RF signal from different subscriber stations, to form information signals intended to be transmitted on the trunk lines.

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The numbers in parentheses indicate the INID code.

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SUMMARY

A wireless transmission system for a plurality of information signals utilizes digital time-sharing circuits between a base station and a plurality of subscriber stations. The subscriber stations can be fixed or mobile. The number of time division circuits is determined by the transmission quality of the signals. The base station is connected to an external information network, which can be analog and / or digital. The information signals are selected from a group which includes voice, data, image, video, computer and instrumentation signals. The system is provided with room diversity by using a plurality of spaced-apart antennas to provide relatively good signal reception despite signal fading. The base station operates over a number of RF channel pairs. The drive on each channel pair is performed with a combination of a transmit channel circuit, which is arranged to process a given plurality of information signals received simultaneously on telephone trunk lines for simultaneous transmission to different subscriber stations over a given RF channel, and a receive channel circuit arranged to process a multiple signals received. simultaneously over a given RF signal from different subscriber stations, to form information signals intended to be transmitted on the trunk lines.

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BACKGROUND OF THE INVENTION

The present invention relates generally to communication systems and in particular relates to a subscriber telephone system for simultaneous transmission of multiple information signals over one or more radio frequency channels (RF channels).

Summary of the Invention

The present invention provides a system for wirelessly transmitting a plurality of information signals using digital time-sharing circuits between.

a base station and several subscriber stations. Subscriber stations can be fixed or mobile. The number of time sharing circuits. is determined by the transmission quality of the signals. The base station is connected to an external information network, which can be analog and / or digital. The information signals are selected from a group which includes voice, data, image, video, computer and. instrumentation signals.

The moving subscriber states can individually move relatively quickly and relatively slowly.

The modulation level of the signals and the power applied to the system are set depending on signal error detection in the system.

25th The system is provided with room diversity by using a plurality of spaced-apart antennas to provide relatively good signal reception despite signal fading.

The base station operates over a number of RF channel pairs.

The handling of each of the channel pairs takes place in a combination of a transmit channel circuit which is arranged to process a given plurality of information signals.

526 967 received simultaneously on telephone trunk lines, for transmitting them simultaneously to different subscriber stations over a given RF channel, and a receiving channel circuit arranged to process a plurality of signals received simultaneously over a given RF channel from different subscriber stations, for to form information signals which are intended to be transmitted on the trunk lines.

Separate conversion units are connected to each trunk line to convert the information signals received on the trunk lines into digital signal samples.

The transmit channel circuit comprises, on the one hand, a plurality of separate signal compression units which are arranged to simultaneously compress the digital signal samples received from the conversion units to form the same plurality of separate compressed signals, and the one with the compression units connected to the single signals arranged to sequence sändkanalbitflöde, each compressed signal occupying in the transmit channel bit stream a repetitive sequential slot position associated with a predetermined unit among the separate compression units, and partly a unit adapted to provide a transmit channel signal for transmitting the pre-channel RF in response to the transmit channel bit stream.

A switch is provided to connect each of the separate conversion units to specified units among the separate compression units.

A remote connection processor unit is connected to the trunk lines and arranged in response to an incoming call signal received on one of the trunk lines, to generate a slot allocation signal indicating which of the separate compression units the switch should connect to the separate trunk line connected to said one trunk line. and thereby allocating said one trunk line to the slot in the transmit channel bit stream associated with the separate compression unit 266 thus connected by the switch. The remote connection processor includes a memory in which is stored which slots are assigned in this way, and upon an incoming call, the remote connection processor advises the memory to then generate such a closure allocation signal which provides a connection to a compression unit belonging to the together with one of the gaps that have not been assigned any other trunk line.

A call processor connected to the remote connection processor is arranged to respond in response to the latch assignment signal to complete the switch specified by the latch assignment signal.

The receive channel circuit comprises, on the one hand, a receiving unit which is arranged to receive a receive channel signal and process the receive channel signal to form a receive channel bit stream containing separate compressed signals in different repetitive sequential slot positions, and a given multiple separate signal synthesis units. which are associated with each slot position in the receive channel bit stream and are adapted to reproduce digital signal samples from compressed signals in their own slot positions in the receive channel bit stream, and partly a channel controller, which is arranged to separate the separate compressed signals from the receive channel bit stream and one of the separated signals to the unit of the separate synthesis units associated with the time slot from which the signal has been separated.

Separate retransmission means are connected to their respective trunk lines and arranged to convert digital signal samples into input signals, which are intended to be transmitted on corresponding trunk lines. Each of the separate conversion units is associated with one of the conversion units and is connected to a common trunk line with the associated conversion unit.

The switch connects each of the separate conversion units to specified units among the separate synthesis units.

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The remote connection processor is arranged in response to the incoming call signal received on said one trunk line to generate a slot allocation signal which indicates which unit of the separate synthesis units the switch is to connect to the separate conversion unit associated with said one trunk line. and thereby allocating said one trunk line to the slot in the receiving channel bit stream associated with the unit of the separate synthesis units thus connected by the switch. The remote connection processor contains a memory, in which are stored which gaps in the receive channel bit byte allocated in this way, and consult the memory upon receiving. the incoming call to then · feed the gate allocation signal 15 'to the call processor for making the connection to a synthesis unit associated with one of the slots not assigned to another trunk line.

The system according to the invention utilizes advanced

LS1 electronics techniques to enable cheap, reliable and high quality communications for different market segments. · In a preferred embodiment, a fixed, centrally located base station is used for communication with a large number of subscriber stations located in the base station's geographical proximity. The central base station can be connected to a headphone office via a private branch exchange (PBX), which is connected to incoming telephone trunk lines. The subscriber stations in the system can either be portable or mobile and can operate under either relatively slow or fast movement. The subscriber stations communicate with the base station via UHF radio channels and with the user via a two-wire DTMF push-button telephone, an RS-232C interface or non-standard telephone equipment (eg 4-wire). The system can be used to replace already existing local subscriber wire loops or to provide telephone services in areas where wire connections are not suitable or economical.

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An advantage of the inventive system is the possibility of utilizing time-shared multiple access (TDMA) and digital speech coding to enable simultaneous error use of; frequencies in a given network.

Any suitable number of high-volume voice circuits can operate simultaneously on a given frequency channel (with a channel split of 25 KHz). In the description, four such circuits are used for illustrative purposes. This achieves both a spectral and economic advantage over existing analogue radio-based telephony systems, which can only maintain a single call at a time on a given frequency channel.

The use of digital speech coding at a low rate (less than 16 Kbps) in combination with spectrally efficient digital modulation techniques enables the aforementioned advantages. Using a 14.6 Kbps speech coding technology in combination with a 16-level DPSK modulation allows, for example, four simultaneous full-duplex calls on a single channel pair, whose channels have a 20 KHz bandwidth and are separated by 25 KHz across the spectrum. especially in the areas 400-500 MHz and 800-950 MHz respectively. This combination provides good speech quality over a distance of at least 20 Km.

In order to compete with wired connections, the system must be able to handle a much larger number of subscribers than can be simultaneously handled on a given pair of such 25 KHz channels. For example, a system of 12 channel pairs that transmits 47 simultaneous calls can expand a total population of 500 subscribers (where the maximum value is limited by the desired blocking probability under peak load). A subscriber call set up. systems which provide suitable call connection delays are thus also an important part of the present invention.

Other advantages of the invention will be described by preferred embodiments, with reference to the accompanying drawings.

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Brief description of the drawings

Fig. 1 is a block diagram showing the general structure of an RF subscriber telephone system according to the invention.

Figure 2 is a block diagram of a preferred embodiment of the base station of the system shown in Figure 1.

Fig. 3 is a block diagram of a preferred embodiment of a subscriber station in the system shown in Fig. 1.

Figure 4 illustrates a sequence of messages generated by the subscriber stations and the base station to establish a connection between two subscriber stations.

Figure 5 illustrates various data processing modules included in a remote control processor unit (RPU) in the base station shown in Figure 2.

Figure 6 illustrates how the RPU in the base station shown in Figure 2 processes incoming and outgoing BCC messages.

Fig. 7 illustrates how RPU in the base station shown in Fig. 2 processes incoming and outgoing PBX20 messages. .

Fig. 8 illustrates how the RPU in the base station shown in Fig. 2 processes log messages.

Fig. 9 illustrates the contents of a memory of RPU in the base station shown in Fig. 2.

Figure 10 illustrates how a message processing module (MPM) shown in Figure 5 processes messages relating to the RCC state.

IN

FIG. 11 illustrates how the message processing module (MPM) shown in FIG. 5 processes messages relating to the channel state.

Fig. 12 is a block diagram of a subscriber terminal interface unit (STU) in the subscriber station shown in Fig. 3.

Fig. 13 shows a signal interface between PBX and

VCU in the base station shown in Fig. 2.

Fig. 14 (on sheet 1) shows a signal interface between

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STU and VCU in the subscriber station shown in Fig. 3.

Fig. 15 shows the mutual-ratio relationship between the signals in the PBX-VCU interface of Fig. 13 and the signals in the STU-VCU interface of Fig. 14.

Fig. 16 (on sheet 11) shows a signal interface between VCU and CCU of the base station of Fig. 2 and the subscriber station of Fig. 3.

Fig. 17 shows the mutual coverage ratio of the transmit channel signals in the VCU-CCU signal 10 shown in Fig. 16.

Fig. 18 shows the mutual coverage ratio of receiving channel signals in the VCU-CCU signal interface shown in Fig. 16.

Figures 19A and 19B show the mutual-ratio relationship between the transmit number blocks and receive number blocks transmitted between VCU and CCU at 16-level PSK modulation.

Fig. 20A shows the rate and content of input data and. output for the receive channel between VCU and PBX (or STU.) at 16-level PSK modulation.

Fig. 20B shows the rate and content of the input and output of the transmit channel between VCU and PBX (or STU) at 16-level PSK modulation.

Fig. 21 (on sheet 5) is a block diagram of CCU in the base station of Fig. 2 or the subscriber station of Figs.

3. .

Fig. 22 shows the program-realized, functional architecture of CCU in Fig. 21.

Fig. 23 is a rate diagram for transmitting RCC data and 16-level PSK speech data on the transmission bus of the

22 showed CCU.

Fig. 24 is a rate diagram for transmitting RCC data and 16-level PSK speech data on the receiving bus of the CCU shown in Fig. 22.

Fig. 25 (on leaf 3) is a block diagram of the modem 35 of the base station shown in Fig. 2 and the subscriber station shown in Fig. 3.

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Fig. 26 shows a signal interface between CCU_f the modem and STIMU in the base station shown in Fig. 2.

Fig. 27 shows a signal interface between the modem and RFU in the base station shown in Fig. 2 and the subscriber station shown in Fig. 3.

Fig. 28 is a block diagram of the antenna interface circuit intended for the subscriber station of Fig. 3.

Fig. 29 is a block diagram of the antenna interface circuit intended for the base station of Fig. 2.

<td>ACRONYM LIST</td><td> 526 967 9</td>

List of icons used in the description

<td>ACRONYM</td><td>DEFINITION</td>

<td>A.D</td><td>Analog-to-Digital Converter</td>

<td>ADPCM</td><td>Adaptive Differential Pulse Code Modulation (Adaptive differential pulse code modulation)</td>

<td>AGC</td><td>Automatic Gain Control (Automatic gain control)</td>

<td>AM</td><td>Amplitude Modulation</td>

<td>BCC</td><td>Baseband Control Channel (Basbandsstyrkanal)</td>

<td>BPSK</td><td>Binary Phase Shift Keying Modulation</td>

<td>BW</td><td>Bandwidth (Bandwidth)</td>

<td>CCU</td><td>Channel Control Unit (Channel Control Unit)</td>

<td>The CODEC</td><td>Combined Coder and Decoder (Combined encoder and decoder)</td>

<td>DEMOD</td><td>Receive Portion of Modem (Demodulator, modem receiver part)</td>

<td>D / A</td><td>Digital-to-Analog Converter</td>

<td>dB</td><td>Decibels</td>

<td>DID</td><td>Direct Inward Dial</td>

<td>DMA</td><td>Direct Memory Access (Direct memory access)</td>

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<td></td><td> 10</td>

<td>DPSK</td><td>Differential Phase Shift Keying Modulation</td>

<td>DTMF</td><td>Dual Tone Multi-Frequency signaling Scheme (Multi-frequency two tone signaling system)</td>

<td>ECL</td><td>Emitter-coupled Logic</td>

<td>FCC</td><td>United States Federal Communications Commission</td>

<td>FIFO</td><td>First-in First-out Memory</td>

<td> FIR</td><td>Finite-Duration ImpulserResponse filter (Filter with timed pulse response)</td>

<td>HZ</td><td>Hertz (cycles per second) • (Hertz, periods per second)</td>

<td>IN</td><td>In-phase (In phase)</td>

<td>kbps</td><td>Kilobits per second (Kilobits per second)</td>

<td>KHz</td><td>Kilohertz</td>

<td>km</td><td>• Miles</td>

<td>LSB</td><td>Least Significant Bit</td>

<td>MDPSK</td><td>Multi-phase Differential Phase Shift Keying modulation . (Multiplex type differential phase shift modulation)</td>

<td>MF</td><td>Intermediate Frequency</td>

<td>MHz</td><td>MEGAHERTZ</td>

<td>MODEM</td><td>Combined modulator and Demodulator (Combined modulator and demodulator)</td>

*

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<td></td><td> 11</td>

<td>MPM</td><td>Message Processing Module</td>

<td>ms</td><td>milliseconds (Milliseconds)</td>

<td>OCXO</td><td>Oven Controlled Crystal Oscillator (Thermostat Controlled Crystal Oscillator)</td>

<td>PBX</td><td>Private Branch Exchange or Automatic switch (Private gearbox or automatic switch)</td>

<td>PCM</td><td>Pulsed Coded Modulation (Pulse-code modulation)</td>

<td>PSN</td><td>Public Switched Network (Public switched network)</td>

<td>PSTN</td><td>Public Switched Telephone Network or other interconnecting carrier (typically Telco) (Public switched telephone network or other interconnecting carriers (typically Telco)</td>

<td>Q</td><td>quadrature (Quadrature)</td>

<td>QPSK</td><td>Quadrature phase shift keying modulation (90 ° phase shift modulation)</td>

<td>RBTG</td><td>Ringback Tone Generator</td>

<td>FRAME</td><td>Random Access Memory (Write and read memory)</td>

<td>RCC</td><td>Radio Control Channel</td>

<td>RELP</td><td>Residual Excited Linear Prediction</td>

<td>RF</td><td>Radio Frequency</td>

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<td>RFU</td><td>Radio Frequency Unit</td>

<td>RPU</td><td>Remote-Connection Processor Unit (Remote Connection Processor Unit)</td>

<td>GYPSY</td><td>Read-only Memory (Read-Only Memory)</td>

<td>RX</td><td>Receive (Receive)</td>

<td>SHF</td><td>Super High Frequency (3,000-30,000 MHz (Super High Frequency (3,000-30,000 Mhz))</td>

<td>ITS</td><td>Subscriber Identification Number (Subscriber Identification Number)</td>

<td>SLIC</td><td>Subscriber Loop InterfaceCircuit (Subscriber Loop Interface Circuit)</td>

<td>stimulatory</td><td>System Timing Unit</td>

<td>STU</td><td>Subscriber Station Telephone Interface Unit (Telephone interface unit for subscriber station)</td>

<td>SUBTU</td><td>Subscriber Timing Unit</td>

<td>TDM</td><td>Time Division Multiplexing</td>

<td>TDMA</td><td>Time Division Multiple Access</td>

<td>Telco</td><td>Telephone Company</td>

<td>TX</td><td>Transmitters (Send)</td>

<td>UHF</td><td>Ultra-High Frequency</td>

<td></td><td> 526 967</td>

<td>UTX-250</td><td>13 Switch for message processing and customization and may be and PBX. "</td>

<td>UW</td><td>Unique Word (Unique word)</td>

<td>VCU</td><td>Voice Codec Unit (Talkodekenhet)</td>

<td>VCXO</td><td>Voltage Controller Crystal Oscillator (Voltage Controlled Crystal Oscillator)</td>

<td>VHP</td><td>Very High Frequencies (30-350 MHz) (Very High Frequencies, 30-350 MHz)</td>

526 967

DESCRIPTION OF THE PREFERRED EMBODIMENT

It is noted that although a particular frequency band (for example, 450-460 MHz) is used at certain points in the specification, the invention is likewise useful for at least the entire VHF, UHF and SHF band.

The system of the invention (Fig. 1) provides telephone services for local loops using a UHF radio link between subscriber stations (S) 10 and a base station 11. The base station 11 establishes direct call connections between the radio-based subscriber stations 10 and is connected for calls to or from points outside the system. to the headquarters of a telephone company (Telco) 12.

The system shown works on channel pairs with common carrier frequency in the 454-460 MHz frequency band. This particular frequency set contains 26 specified channels. The channels are 25 KHz apart and have a permitted bandwidth of 20 KHz. The separation between transmitting channels and receiving channels is 5 MHz, whereby transmissions to the base station have been assigned the center frequency of the lower of the two frequencies. As stated above, the system can also operate on other UHF channel pairs.

The transfer from the base station to the subscriber station (broadcast channel) takes place with time-division multiplexing (TDM). The transfer from the subscriber station to the base station (receiving channel) takes place with time-shared multiple access (TDMA).

All systems are designed to meet 47 CFR FCC sections 21, 22 and 90 as well as other relevant rules.

Communication between the base station 11 and the subscriber stations 10 takes place digitally using filtered differential phase shift multiplex modulation (MDPSK) on full duplex channels which are on the 454-460 MHz band and are separated at 25 KHz, thereby requiring a bandwidth of 20 KHz as indicated, for example

526 967 of FCC Rule Sections 21, 22 and 90 (for example, 21.105, 22.105, 22.105, and 90.209) are met. The system can also be used for other bandwidth and channel separation values ​​within all useful parts of the VHF, UHF and SHF bands.

The symbol rate of each one. The 25 KHz FCC channels are 16 kilos oz / sec in each direction. Voice transmission is accomplished through the use of 16-level PSK modulation and voice digitization at a coding rate of 14.6 Kbps. Alternatively, the modulation may be of type 2 level (BPSK) or 4 level (QPSK). A combination of different modulation levels can be used simultaneously on one channel. With time-division multiplexing, the system can handle one call for every 2 multiples of phases at the rate of 14.6 Kbps (4 phases provide 2 calls, 16 phases provide).

s number, etc.) or more for lower speeds. This is obviously just one example, as many different combinations of modem pieces / symbols or phases and codecats can be used, as shown in the diagram below:

SCHEME I

2-way calls or duplex circuits with codecs on

<td>Phase modulation</td><td>14.4 Kbps</td><td>6.4 Kbps</td><td>2.4 Kbps</td>

<td> 4</td><td> 2</td><td> 4</td><td> 8</td>

<td> 8</td><td> 3</td><td> 6</td><td> • 12</td>

<td> 16</td><td> 4</td><td> 8</td><td> 16</td>

<td> 32</td><td> 5</td><td> 10</td><td> 20</td>

<td> 64</td><td> 6</td><td> 12</td><td> 24</td>

<td> 128</td><td> 7</td><td> 14</td><td> 28</td>

<td>The base station</td><td>can transmit</td><td>and receive on</td><td>either one</td>

preferably any or all of the available 25 KHz spaced FCC frequency channels in the 454-460 MHz band containing the selectable channels. The choice of channel frequency for each voice channel is performed automatically by the base station for one channel at a time, but can be overridden at a user console interface at the base station.

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The base station can have a transmitted power of typically 100 watts for each frequency channel.

The base station supplies the subscriber stations with modulation control and allocation of time slots and frequency channels. Furthermore, an adaptive power control of the subscriber stations is performed by the base station to minimize differences between sequential time slots and interference between adjacent channels.

Switching among truncations and the TDM time slots 10 on the selected channel is performed in the base station using preferably a digital switch, although it is possible to use an analog switch instead.

The base station has a threefold room diversity on the 15 reception channels.

The subscriber station can work with a diversity of three different channels. The transmit power is typically adjustable between 0.1 and 25 watts but can also be set to other power ranges. Although voice transmissions through the subscriber station are perceived as being real-time full-duplex, the RP system operates with half-duplex using appropriate time-shared multiplexing.

The subscriber station can be adapted to any telephone device for voice transmission, or the phone can be built into the system. Furthermore, a data connection such as a standard RS-232C 25 pin connection is provided for 9600 baudrate data transmission between subscribers. The base station and the subscriber station can be operated by any suitable internal or external source.

Fig. 2 is a block diagram of one embodiment of the base station performing the simultaneous handling of two pairs of transmit and receive frequency channels. Each channel can handle up to four telephone connections at the same time.

In the preferred embodiment, there are many transmit and receive channel pairs. There are many, time slots in each channel ..

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One of the many available time slots is reserved for a radio control channel1 (RCC).

Connections between the PSTN and the subscriber stations are connected and maintained by a private branch exchange (PBX) in the base station. PBX 15 is a UTX-250 type system, which is a commercially available product developed by the United Technologies Building Systems Group. Many of the capabilities of the general PBX system are utilized in the control of Telco interface10 devices, which are needed in the inventive system.

PBX 15 also converts speech information to / from PSTN into 64 Kbps μ-layer compressed, pulse code modulated (PCM) digital samples. From this point forward, the speech information is processed in digital format through the base station and the subscriber stations up to the interface circuit which connects to the subscriber telephone, or as far as the subscriber transmitter and receiver allow.

Digital speech information from PBX 15 is then processed in a speech compression system or codec 16, which reduces the speech information rate from 64 Kbps to about 14.5 Kbps or less. The codec 16 utilizes either a RELP algorithm or an SBC encoder / decoder to perform this speech rate compression. Typically, four. codecs 16 are arranged in a single speech codec unit (VCU) 17 which is arranged to perform the speech compression for the four or more time slots in each frequency channel.

Each VCU 17 in the base station can handle four or more full duplex voice connections for both the transmit channel and the receive channel of each channel pair. The PBX 15 set up connections determines which call to process in which VCU 17 and which codec 16 in the selected VCU 17. The circuits in each VCU 17 are in such hardware that a call with a certain frequency and slot allocation in the base station is always processed by same VCU codec 16.

Each VCU 17 is connected to a channel controller (CCU) 18. CCU 18 controls the TDMA function and also acts as a link-level protocol processor. Each CCU 18 receives

526 967 transmit channel outputs from codecs 16 in corresponding VCU 17 and transmit the data in the correct time slot and in the correct format to a modem 19. Each CCU 18 is controlled by a remote control processor unit RPU 20 to determine which modulation levels to use for the transmission (e.g., 2 level, 4-level or 16-level PSK ^ modulation).

Each CCU 18 also processes such control information transmitted to the subscriber stations partly through the RCC time slot and partly during initial control bits in the speech channels. Each channel pair includes a serially connected combination of a VCU 17, a CCU 18, and a modem 19.

Properly formatted sand data from each CCU 18 is transmitted at a rate of 16 K symbols / second to the corresponding modem 19. Each modem 19 receives these synchronous symbols and converts them into a Gray coded multi-level PSK format. Modem 19 transmit channel output is a modulated MF signal. This signal is fed to an RF / MF processing unit (RFU) 21, which converts the MF signal to the radio frequency UHF signal in the 450 MHz range.

Control signals for modem 19 and RFU 21 are obtained from the corresponding CCU 18, the operation of which is controlled by RPU 20. The UHF signal amplifier is powered by power amplifiers in RFU 21 and transmitted via an antenna matching unit 22 to a transmitter antenna 23 for wireless transmission.

The base station's reception function is essentially a reverse of the transmit function. Any RFU 21, modem 19, CCU 18, VCU'17 and PBX 15 can work with full duplex.

The remote control processor unit (RPU) 20 is the central control processor that sends connection data and control messages to the CCU. The RPU 20 includes a general purpose computer, which is based on a 6800 microprocessor and which performs the sophisticated system control functions and control mechanisms for connection, disconnection and call maintenance. RPU 20 also communicates with a call processor 24 arranged in PBX 15 which is configured to control the connections established by a switching matrix 25 in PBX 15 between the codecs

526 967 and the trunk lines.

Each subscriber station is a relatively small unit located at each user point in the system. The subscriber station connects via the UHF radio channel to the user's standard telephone apparatus and / or data terminal or an integrated acoustic transmitter / receiver with the base station. The way in which the subscriber station and the base station operate is very similar. However, the base station can operate on one or more frequency channels simultaneously, with each channel supporting multiple speech circuits, whereas the subscriber station normally only operates on one frequency at a time.

Fig. 3 is a block diagram of a subscriber station.

The functional breakdown is very similar to that of the base station (Fig. 2). The user-side customization is accomplished by a subscriber telephone interface unit (STU) in the subscriber station. The corresponding function in the base station is performed by the PBX module. The STU in the subscriber station also performs all control functions in the subscriber station, in the same way as the RPU in the base station. The subscriber stations function as slaves to the master base station in the overall system control architecture. The STU can be connected to an external device or can transmit and receive acoustically.

The path of the data flow through the subscriber station begins with the user's speech or data information being processed in a subscriber terminal unit (STU) 27. The voice signals from the user's telephone are received and digitized in one VCU 28. The format of the digitized voice signals is identical to the format used in PBX 15 in the base station. The subscriber station includes a VCU 28, a CCU 29, a modem 30a, and an RFU 3a1, whose functions are substantially the same as the functions of the same units in the base station architecture described with reference to Figure 2. A difference between the operation of the base station and the subscriber station is that the subscriber station is ordinary. 35 is limited to one voice channel at a time. The subscriber station mainly operates with half duplex, transmitting in part of the TDMA frame and receiving in a

526 another part of the TDM framework. With a frame length of 45 ms, the half-duplex characteristic of the subscriber station is not noticeable to the user who hears a continuous speech input from the user at the other end of the call connection.

Both STU 27 and VCU 28 as well as modem 30a can be duplicated to enable more than one subscriber call.

Because the subscriber station operates with half duplex, it is better to make use of the subscriber station's available hardware. The subscriber station's VCU and CCU operate in much the same way as in the base station, at least in terms of voice data management. However, modem 30a is configured to operate with half duplex so that either the modem's receiver or transmitter portion is used, but not (

both at the same time. The main saving here is that RFU 31a only needs to work with half duplex. This provides a power saving in that the RF power amplifier is not active for more than half the time. Furthermore, an RF transmitter antenna 32a can be switched to operate as a second receiving guarantee antenna during the receiving portion of the frame by using an RF antenna switching function. No duplexes are required either.

Each subscriber station · also includes a diversity network, which includes three modems and a diversity combination circuit 33. The diversity combination circuit

33 collects demodulated reception information from each demodulation unit in three modems 30a, 30b, 30c and combines these three flows to form a single best-guess symbol flow, which is then forwarded to CCU 29 for processing. The demodulation circuits in the three modems 30a, 30b and 30c are connected to each RX RFU 31a, 31c and via these to each antenna 32a, 32b and 32c respectively.

At the base station, three receiver antennas 34a, 34b and 34c are spaced at a suitable distance from each other so that uncorrelated signals of room diversity are handled by a diver site network. The function of CCU is not dependent on the diversity network's working methods, which is why it can

526 967 is replaced with the function of a single modem in case the diversity function is not required.

The base station also includes a room diversity network for each transmit and receive channel pair. Although the diversity network is not shown, the base station diagram shown in Figure 2 is the same as the subscriber station diagram shown in Figure 3, which shows the connection of the diversity network for a single transmit and receive channel pair. Thus, each transmit and receive channel pair in the base station contains three demodulation circuits as well as a modem, which in the manner shown in Fig. 3 is connected to a diversity combination circuit.

Accurate rate synchronization between the base station and the subscriber stations is a critical factor in the overall system. The base station provides master rate base for the entire system. All subscriber units in a given system must be synchronized with this time base in terms of frequency, symbol rate and frame rate.

The base station includes a system clock generating unit (STIMU) .35 which produces a very accurate reference rate signal of 8,000 MHz. This 80 MHz reference clock signal is split to provide a 16 KHz clock signal and a 22.222 Hz (duration 45 ms) frame strobe signal. All transmit rate in the base station is generated from these three master references. The 80 MHz clock signal is utilized by modems 19 and RFU 21 as accurate MF and RF frequency bases. The clock signal at 16 KHz provides symbol dial rate for transmission at all base station frequencies. The 45 ms mark is used to point out the first symbol in a new frame. This marking signal is active during the time of a symbol (62.5 ps = 1/16000 Hz). All frequency channels in the base station use the same time reference for transmission. The three clock signals (80 MHz signal,

The KHz signal as well as the rams takes the t marking signal a {SÖF- '.

the tag signal}) is applied to each of the modems 19 in the base station. Modem 19 transmits the correct clock signals to CCU 18. and RFU 21 on the same serial connected transmit and

526 967 receiving channel pairs. CCU 18 uses the signal at 16 KHz and the SOF marking signal to adapt the transmission of numbers and control symbols to the current frame structure of the frequency.

The receiving rate in the base station is preferably identical to the transmitting rate of the base station. In other words, the SOF marking signal and the symbol clock signals should be precisely aligned between the transmit and receive signals.

Since perfect rate synchronization cannot be expected from subscriber station transmissions, the reception rate in the base station modem 19 must be matched to the incoming symbols from the subscriber station. This is fulfilled so that the sampling period at the reception of the base station modem 19 provides the best estimate of the symbol received from the subscriber station. A small buffer arranged in GCU 18, which cooperates with the reception function of modem 19, compensates for this smaller rate offset.

The subscriber stations in the total system synchronize their time references with the main time base in the base station.

This synchronization is achieved by a step-by-step procedure by which the subscriber station, in a first step, intercepts the base station's branch reference by utilizing the RGC messages from the base station. This procedure is described below.

Once the subscriber station has captured the rate reference from the base station, the subscriber station's receiving rate is kept at exactly the right value by means of a tracking algorithm in the demodulation circuits of subscriber station modems 30a, 30b and 3'0c. The subscriber station advances its

30 °. own transmissions back to the base station with a small interval of time in order to eliminate the round-trip delay of the transmission arising from the distance to the subscriber station. This method results in transmission from all subscriber stations being received by the base station with the correct phase relative to each other.

The system timing unit (STIMU) 35 is the time base for all transmissions in the base station. STIMU 35 includes

5? 6 967 a very accurate (3 x 10) thermostatically controlled crystal oscillator operating at a fixed frequency of 80 MHz. This basic clock frequency is divided into STIMU 35 by 5000 to generate the 16 KHz symbol clock signal and then by 720 to generate the SOF marker signal. These three time references are stored, buffered and fed to each of the base station modems.

A subscriber clock display unit (SUBTU) (not shown in Figure 3) provides a clock signal of 80 MHz, a symbol clock signal of 16 KHz and a frame marking signal of 45 ms for the subscriber stations. These signals are identical to the same signals in the base station STIMU, except that the clock signal of 16 KHz is used for symbol reception rate in the subscriber station. In the base station, the clock signal of 16 KHz is used for transmit rate. The subscriber station's transmission rate is given by a delayed version of the subscriber station's reception rate. The delay is variable and is determined by the distance calculation. which is performed between the base station and the subscriber station.

The rate reference signal for the subscriber station is generated by a voltage controlled crystal oscillator (VCXO) operating at a nominal frequency of 80 MHz. ^ The actual frequency is set by the subscriber station modem in such a way that it is frequency locked to the base station clock reference, which is received at the subscriber station RF input.

Protocol

The following protocol specifies the procedures for system control, collision avoidance and call signaling in the system and specifies the transmitted frame structure.

When reference is made to the components of the system, unless otherwise indicated, the components of the base station described above are referred to.

The system utilizes channels with a bandwidth of 15

KHz and with full duplex in the range of 460 MHz, the channels' center frequencies are 25 KHz apart, and handle multiple simultaneous calls per channel. Each

526 The 967 full-duplex channel consists of a reception frequency and a transmit frequency, which is different from the former at 5 MHz. The base station is assigned for transmission the lower frequency of each channel, which is referred to as the forward frequency. The subscriber station is allocated for broadcasting the upper frequency of each channel, which is referred to as reverse frequency. The base station thus transmits on the forward frequency and receives on the reverse frequency. For the subscriber stations, the relationship is the opposite.

The ability of the system to provide a spectrally efficient method of transmitting multiple speech channels at a single frequency is primarily dependent on the modem's mode of operation. The modem must work in such a way that it has an efficiency of 3.2 bits / hertz when working with 16-level DPSK at a symbol rate of 16K symbols / second.

The modem is, in short, a mechanism adapted to convert the symbols obtained from CCU 18 into 1,

2, 4 or more bits to a phase-modulated MF carrier for transmission and to perform the opposite process on the receiver side. All frame rate and mode selection control is performed by CCU 18. An interface unit between CCU 18 and the modem.19 can consist of two 4-bit one-way, synchronous (16 K symbols / second) data buses (Tx and Rx). An 8-bit status / control bus provides control information to the modem and reports the status of the modem to CCU 18. The modem 19 also supplies CCU 18 with the master symbol clock signal of 16 KHz. In the base station, this clock signal is obtained from the master oscillator in the system clock generating unit 35, with which the entire base station (and therefore the entire system) is synchronized. In the subscriber station, this clock signal is obtained from the incoming symbols received from the base station. All transmissions are therefore related to the time base in the base station. A main task of the subscriber modem is to synchronize the local subscriber clock signal with the base station's time reference by decoding the rate from the received symbols.

The modem's transmitting modulator section utilizes a digital FIR filter to form a digital representation

526 967 is also the waveform used for modulation of the RF carrier. The resulting digital flow is converted to analog format and mixed with an MF transmit frequency of 20.2 MHz. The signal is then transmitted to RFU to be filtered and then converted to RF and amplified before transmission.

The modem's receiving demodulator section receives the MF receive signal from RFU 21 at the MF reception frequency of 20 MHz. This signal is frequency converted to baseband, after which it is digitized by an A / D conversion.

The resulting digital samples are processed by a microprocessor based signal processing unit. This step includes filtering as well as synchronization algorithms on the samples as well as a demodulation of the .PSK signal to generate the symbol flow at 16 K symbols / second. The signal processing unit may also operate in a self-learning state which is utilized to teach the processing unit the imperfections found in the analog filters utilized in the receive flow. Once the signal processing unit has undergone this learning, the demodulator's digital equalization process compensates for these imperfections in the analog filters. This technology allows the use of analog components with lower tolerance and lower cost and gives the overall system the ability to demodulate weak signals or high noise signals.

The modems demodulated by the modem are output with the symbol rate to CCU 18 during reception. Modem 19 provides the rate associated with this symbol flow. Both the base station and the subscriber stations recover the reception rate from the incoming receive signal.

A more detailed description of the modem's functions and performance is given below with reference to Fig. 25.

One TDM / TDMA channel per subscriber provides a total of 16 Kbps in each direction for each call. Of this channel capacity, 1.43 Kbps is needed in each direction for initial control and demodulation. VCU therefore works with a fixed data rate

526 967 at 14.57 Kbps. This corresponds to 328 bits per code frame period, which is defined as half of the modem frame period or 22.5 ms.

To enable multiple calls per channel, each channel is divided into time slots using a time division multiplexing system (TDM system).

These gaps determine the frame size of the system. The entire system frame consists of a predetermined, constant number of symbols. The duration of the system frame has been optimized taking into account the speech coding rate and the number of capture symbols needed by modem 19 at the beginning of each burst. The number of gaps in the system frame depends on the modulation level of the channel. For example, if the channel's modulation level is QPSK, then the system frame consists of two slots per frame.

By increasing the modulation level of the channel, one can increase the number of coded information bits per symbol and thereby the channel's data rate. With the 16-level DPSK, the system frame includes four slots, which handle the voice data for each call. ·

It is important to note that the number of modem synchronization times required for symbol synchronization remains constant even at higher modulation levels.

The format of the system frame ensures that the modem 19 in the subscriber stations never has to work at full duplex (ie transmit and receive at the same time). The hatches on the reverse and forward frequencies are thus time offset by at least the time of a gap.

The system's system frame has a fixed length of 45 ms. Symbol transfer takes place at a fixed rate of 16K symbols / second. Each symbol · is transmitted during equal time intervals, equal to 1/16000 second (62.5 microseconds).

This constantly gives 720 symbols per frame, which symbols are numbered 0-719 from the beginning of the system frame. These 720 symbols may each consist of 1, 2 or 4 bits of information, corresponding to a modulation of 2, 4 or 16 phases.

The system frame time (45 ms) is further divided into 2 or time sharing slots, depending on the modulation format

526 967 for the gaps that form the frame. Each hatch can be one of three different hatch types: (1) radio control channel (RCC), (2) 4-time voice channel, and (3) 16-time voice channel. RCC is always transmitted with binary (2-phase) modulation. RCC gates as well

16-when voice channel hatches each require 180 symbols to be transmitted, that is, a quarter of the length of the system frame. Since the 16-hour voice channel transmits 4 bits of information (ie 2⁴ = 16 phases), 720 information bits per frame are transmitted by the 16-channel voice channel. This gives a bit of a bite

16 Kbps. Some of these bits are utilized for modem startup and control, resulting in a speech bitrate of 14.57 Kbps. 4-when voice channel hatches require 360 ​​symbols to be transmitted, which is equal to half the length of the system frame. Each symbol in this type of slot consists of one of four different phases, so that two bits are transmitted per symbol (2 = 4 phases). The resulting bit rate is 16 Kbps, ie the same as for the 16-minute voice channel. The same number of bits (not symbols) is reserved for modem startup and control, so that the speech information rate is 14.57 Kbps, which is also the case for the 16-hour voice channel type.

The system frame on any given frequency channel can be composed of any combination of these three types of slots, provided that the following five conditions are met:

1st A maximum number of (720) symbols are transmitted for each system frame. For this purpose, combinations of the three types of clocks can be combined at a given frequency. In case the entire channel capacity is not utilized in frame transfer from the base station (ie if less than 720 symbols are transmitted in a frame), zero symbols are inserted to fill the frame capacity. A zero symbol is a symbol that has no transmit energy.

2nd Only one frequency in a multi-frequency base station includes an RCC slot. Only one RCC is active in the entire system at a given time. The frequency

526 967 on which RCC operates is determined by a system startup parameter and changes only when the frequency is not available for any reason. The RCC door is always assigned the first 180 symbols of the system frame (referred to as door 0).

3rd A base station frequency can operate in a constant transmit state. The subscriber station broadcasts no more than half the total frame time. When handling a call in a subscriber station, the subscriber10 transmits the station only under 25% of the frame when operating in the RCC state or 16 when the speech channel state&gt; and below 50% of the frame when operating in the 4 when the speech channel state. A subscriber station that handles a call can only transmit in a slot under any given frame.

4th All 4-time voice channels must start broadcasting at symbol number 0. or 360. Thus, either the first half or the second half of a frame may contain ep 4-time voice channels.

5th Switching between the forward frequency and the reverse frequency is carried out in such a way that the return message for a given slot starts sending 180 symbols after the transmission of the forward frequency message. Thereby, the subscriber station need not transmit on the reverse frequency while receiving on the forward frequency.

With these reservations, up to four calls can be handled on a single frequency, if all four calls have 16-hour voice channel format and are handled by codecs at 14.4 Kbps.

The gaps in the system frame are numbered according to their position in the frame structure. The numbering need not be continuous. When one or more of the hatches in the frame is a 4-inch voice call type, the second gate period is skipped according to the number 5226 967, which is included in the longer 4-close door. The hatch numbering for reverse frequency broadcasts (CD's subscriber broadcasts) is offset relative to the numbering of base station5 or forward frequency broadcasts. Therefore, a subscriber receiving information on slot 2 of the forward frequency transmits on the reverse frequency slot 2, which is time-delayed by half a frame. The following tables 1-5 illustrate possible frame formats and the numbering for each door.

526

967

TABLE 1

Radio control channel structure: BPSK

Forward channel;

k

System frame = 45 ms&gt;

<td> &lt;—11.25—:</td><td>&gt; K 11.25-:</td><td>&gt; K 11.25-:</td><td colspan="2">&gt; K --- 11.25-&gt;</td>

<td> 0</td><td> 1</td><td> 2</td><td colspan="2"> 3</td>

<td> 180</td><td> 180</td><td></td><td colspan="2"></td>

<td>BPSK</td><td>16-PSK</td><td></td><td colspan="2"></td>

<td></td><td colspan="4"></td>

<td></td><td colspan="4"></td>

<td>AM HEELS</td><td>FILTER- START-UP</td><td colspan="2">bit sync PATTERN</td><td>RCP</td>

<td> 8</td><td> 8</td><td colspan="2"> 46</td><td> 112</td>

<td>Back Channel: &lt;--- 11.25-&gt;</td><td> &lt;---11.25—&gt;</td><td> &lt;—11.25—&gt;</td><td colspan="2"> &lt;—11.25—&gt;</td>

<td> 2</td><td> 3.</td><td> 0</td><td colspan="2"> 1</td>

<td></td><td></td><td> 180</td><td colspan="2"> 180</td>

<td></td><td></td><td>BPSK</td><td colspan="2">16-PSK</td>

ms

Lucknr.

Number of symbols

Type of modulation

Feature

Number of symbols ms

Lucknr.

Number of symbols

Type of modulation

<td colspan="6"></td>

<td>delay 1</td><td>FILTER- Startup</td><td>bit sync PATTERN</td><td>'your</td><td>RCP</td><td>DELAY 2</td>

<td>XX</td><td> =8-</td><td> 49</td><td> 8</td><td> 112</td><td>3-x</td>

Feature

Number of symbols = n / i / 9 /?

526 967

TABLE 2

Frame structure for 4-channel voice channel

Forward channel;

k ---------------- System frame = 45 ms

22.5·

22.5·

<td> 0</td><td> 2</td>

<td> 360</td><td> 360</td>

Lucknr.

Number of symbols

<td>FILTER- START-UP</td><td>bit sync PATTERN</td><td>codeword</td><td>VCF 0</td><td>VCF 1</td>

<td> 8</td><td> 18</td><td> 6</td><td> 164</td><td> 164</td>

<td>Back Channel:</td><td rowspan="2"> 22.5---------)</td><td rowspan="2"></td><td colspan="2">- OO C - - v</td>

<td></td><td colspan="2"></td>

<td colspan="2">θ</td><td colspan="3"> 2</td>

<td colspan="2"> 360</td><td colspan="3"> . 360</td>

<td colspan="2"></td><td colspan="3"></td>

Feature

Number of symbols

Lucknr.

Number of symbols

<td>FILTER- START-UP</td><td>bit sync AGC</td><td>codeword</td><td>VCF 0</td><td>VCF 1</td>

<td> 8</td><td>¹⁸</td><td> 6</td><td> 164 ;</td><td> 164</td>

Number of symbols

features

526 967

TABLE 3

Frame structure for 16-channel voice channel

Front Channel:

• System frame = 45 ms

<td rowspan="3"></td><td> &lt;---11.25—</td><td> &gt;|&lt;—11.25 —</td><td colspan="3">X 11.25-&gt;</td><td colspan="3"> &lt;---11.25—&gt;</td>

<td> 0</td><td> 1</td><td colspan="3"> 2</td><td colspan="3"> 3</td>

<td> 180</td><td> 180</td><td colspan="3"> 180</td><td colspan="3"> 180</td>

<td rowspan="2"></td><td></td><td colspan="7">r.</td>

<td></td><td colspan="7"></td>

<td rowspan="6"></td><td>FILTER START-UP</td><td>bit sync PATTERN</td><td colspan="2">codeword</td><td colspan="3">VCF 0</td><td>VCF 1</td>

<td> 8</td><td> 5</td><td colspan="2"> 3</td><td colspan="3"> 82</td><td> 82</td>

<td>Back Channel: &lt;-11.25-&gt;</td><td> &lt;—11.25—&gt;</td><td colspan="3"> &lt;---11.25---&gt;</td><td colspan="3"> &lt;---11.25—&gt;</td>

<td> 2</td><td> 3</td><td colspan="3"> 0</td><td colspan="3"> 1</td>

<td> 180</td><td> 180</td><td colspan="3"> 180</td><td colspan="3"> 180'</td>

<td colspan="2"></td><td colspan="3"></td><td colspan="3"></td>

<td></td><td colspan="2"></td><td colspan="3"></td><td colspan="3"></td>

<td></td><td>FILTER- START-UP</td><td>bit sync AGC</td><td>codeword</td><td colspan="3">VCF • 0</td><td colspan="2">VCF 1</td>

<td></td><td> 8</td><td> 5</td><td> 3</td><td colspan="3"> 82</td><td colspan="2"> 82</td>

ms

Lucknr.

Number of symbols

Feature

Number of symbols ms

Lucknr.

Feature

Quantity

symbols

526 9^7

TABLE 4

Frame structure for blend modulation; 2/16-PSK and 4-PSK

<img file="SE526967C2_D0002.tif" />

Reverse channel;

<td> &lt;--------22.5 —------&gt;</td><td> &lt;---11.25—&gt;</td><td> &lt;---11.25—&gt;</td><td rowspan="4">ms Luåknr. • Type of modulation y Number of symbols</td>

<td> 2</td><td> 0</td><td> 1</td>

<td>4 PSK</td><td>2/16-PSK</td><td>16-PSK</td>

<td> 360</td><td> 180</td><td> 180</td>

For description of each of the lock symbols, refer to Fig. 2-1 t of Fig. 6-3.

TABLE 5

Among Modulation; 4-PSK and 16-PSK

E26 967

Front Channel:

<td> &lt;----</td><td> ----22.5--------&gt;</td><td> &lt;—11.25—&gt;</td><td> &lt;--11.25—&gt;</td>

<td colspan="2"> 0</td><td> 2</td><td> 3</td>

<td colspan="2">4 PSK</td><td>16-PSK</td><td>16-PSK</td>

<td colspan="2"> 360</td><td> .180</td><td> 180</td>

ms

Lucknr.

Type of modulation

Number of symbols

· Reverse channel;

<img file="SE526967C2_D0003.tif" />

The structure of the 16-hour voice dial type with 180 symbols will now be described with reference to Table 3. The first eight symbols in this type of slot are referred to as filter start bits. The filter start-up period, which is included at the beginning of each type of hatch, consists of a time interval within which no energy is transmitted, giving the receiving section of the modem 19 time to clear its filters in preparation for the new hatch. .

• After filter startup, a bit sync period follows. During this time interval, a degenerate 16-near pattern is transmitted, simulating an alternating BPSK signal. The modem

526 967 receive section utilizes this field to establish the phase reference with the transmit section of modem 19.

Then, a 12-bit code word is used to determine synchronization between the subscriber and the base station and to exchange control and status information. The code words are used to exchange information about the current state regarding the connection, link quality and power and clock settings. Each control word is through the use of a Hamming code encoded into ten bits, which enables the correction of single errors. and double fault detection. CCU 18 determines whether synchronization is improved or impaired by following the number correctly or incorrectly in sequence of received code words. CCU 18 sends synchronization changes messages to the RPU 20 in the base station. At the subscriber station, CCU 29 sends messages about synchronization changes to STU 27.

According to the .Hamming code, five parity bits are added to five bits of information to form a 10-bit code. Each parity bit is calculated by a modulo-two addition of all the bit positions in the code word containing the bit represented by the parity bit. Although the codeword is transmitted with all data bits in succession, accompanied by all parity bits, the code can be illustrated below by arranging the parity bits in the positions of the word having only one bit set (the position represented by the bit) and by placing the data bits in the other positions:

bit position: 123456789 10 info: Pl P2 Dl P3 D2 D3 D4 P4 D5 P5

P = parity bit

D = data bit

526 967

<td>Pl = Dl</td><td> +</td><td>D2</td><td> +</td><td>D4 + D5</td>

<td>P2 = D1</td><td> +</td><td>D3</td><td> +</td><td>D4;</td>

<td>P3 = D2</td><td> +</td><td>D3</td><td> +</td><td>D4</td>

P4 = D5

P5 = total

When a code word is received, the parity bits are calculated from the received data bits and the calculated parity bits are compared with the received parity bits. If the calculated total parity bit is not equal to the received total bit, an exceller operation is performed between the calculated parity bit and the received bits to determine the address of the missing bit.

If the calculated and received total bits are equal and the other four bits are not equal, two errors have been detected. If all of the parity bits match, the data has been received correctly.

The remaining slots contain two speech codec packets, each containing 328 bits of information.

Table 2 shows the symbol structure of the 4-close speech channel. The structures of this channel and the 16-close speech channel are very similar. There are some differences because some symbol assignments are dependent on a fixed number of symbols per slot, which is necessary for initial purposes, whereas other bit assignments are made based on a fixed number of bits.

The function of the radio control channel (RCC) is to provide a starting point for the subscriber stations when they initially capture the system rate from the base station and partly to provide out-of-band signaling between the base station and the subscriber stations.

The format of the radio control channel cover is the same for the front and reverse channels, except for the following fields.

The first eight symbols in a control slot transmitted from the base station (front channel) contain an amplitude modulation gap (AM hole), which is a time interval within which no energy is transmitted. Subscriber stations take advantage of this.

526 967

37.

time interval to safely identify the control channel.

At the beginning and at the end of the reverse channel control hatch, some extra symbols have been applied to take into account the fact that the subscriber stations' rate may be offset by some symbols.

All hatches contain eight zero-transmission symbols (the filter boot field), which allow the modem to clear its receiving filters in preparation for the new hatch. The next field in the door is a sync pattern with a fixed number of bits. The transmitted pattern is an alternating BPSK signal. The receiving modem utilizes this field to establish a phase reference and a frequency lock with the transmit modem.

CCU 18 is constantly searching for a unique word (UW), which is a sequence of eight symbols, to identify an incoming RCC message. The base station CCU 18 must continuously search for a valid RCC message in each RCC slot. CCU 18 performs this task through f

to search for the unique word within a window of ± .3 symbols around the nominal UW position, calculated with respect to the master system rate. The search algorithm starts at the nominal UW position and switches a symbol to the right and a symbol to the left until it (1) finds the UW pattern and (2) verifies a correct RCC check sum. The search ends as soon as (1) and (2) are fulfilled or all possibilities are exhausted. The switching information, RCC message and power information were sent to RPU 20 after a successful search.

When the subscriber station CCU 29 receives RCC data, this unit may be in one of two states: frame mount state or monitoring state. The frame search state is utilized to capture reception frame rate from the incoming RCC data and start automatically when RCC synchronization is lost. Monitoring State.

. 35 is initiated as soon as reception frame synchronization is established.

When the subscriber station CCU 29 is in the frame increase state, it must continuously search for

526 967 a valid RCC message as soon as an RCC slot is received at the subscriber station. Similar to the base station CCU 18, CCU 29 performs this task by searching for the unique word within a window of ± 3 symbols around the nominal UW position, based on the rate obtained from the modem's detection of the AM hole. The search algorithm starts at the nominal UW position and switches a symbol to the right and a symbol to the left until it (1) finds the UW pattern and (2) verifies a correct RCC check sum. The search is interrupted as soon as (1) and (2) are met or all possibilities are exhausted. The switching information from a successful search is used to set the receive frame marking signals generated by the CCU. The capture ends when (1) and (2) above are met for three consecutive frames with UW in its nominal position. STU. 27 is informed of frame trapping when this occurs. RCC messages were not sent to STU 27 during frame search mode.

When the frame capture is completed, the subscriber station CCU 29 switches to the monitoring state. To avoid the possibility of capturing fake UW. only the nominal UW position is investigated. If no UW is detected for five consecutive frames, the channel is declared out of sync and the frame search state is initiated (this transition should be highly unlikely as the system performance is otherwise unacceptable). STU 27 is informed of this unsynchronized condition.

In the monitoring state, RCC messages with the correct check sum and subscriber ID number (SIN) are transmitted to STU 27.

The rest of the cover is utilized for information exchange between the base station and the subscriber stations. The data section consists of twelve bytes. The first eight data bits contain a link field, which transmits information regarding system status, collision, detection and reservation.

The purpose of the link level protocol is to detect erroneous messages on the radio control channel. Link Protocol

526 967 ³⁹ also reveals collisions on the RCC hatch.

The link field includes bits for sleep transmission, system busy, collision, transmission detected and slot reservation. These bits are set by the base station

CCU 18 and read by the subscriber station CCU 29.

The sleep transmit bit is set by the base station to indicate that a rest message has been sent. When a subscriber unit receives a slot with this bit set, this unit performs the usual synchronization and error checking, however without passing the message on to the respective

RPU 20 or STU 27 if the message was received without error.

The system busy bit indicates that all the voice channels are busy and that new call attempts should not be made (for any given period of time).

The collision bit reveals collisions between two or more subscriber stations that attempt to transmit in the same control slot.

The transmit-detected bit indicates that the base station has detected a transmission on the reverse control channel.

The lid reservation bit reserves the next door on the reverse control channel.

The remainder of the data section is utilized for addressing and exchanging information during connection and call down. Following the data section follows a 16-bit cyclic redundancy check (CRC) of the door's unique words and data sections. CRC is used to detect any errors that occur during the transmission of RCC messages. The CRC algorithm includes a division of a data block with a predetermined bit sequence and transmission of the division residue as part of the data block. The polynomial for generating

The CRC has the following appearance:

P (x) = 1 + x⁵ + x¹² + x¹⁶ . (Eq. 1)

If the CRC approves a received message, the message is not transmitted from CCU 18 to RPU 21 in the base station 'or by CCU 29 to STU 27 in the subscriber station.

When a subscriber station is switched on and becomes on526 967 line, the subscriber station must capture the system rate from and be synchronized with the base station. This capture is achieved through information exchanges on the radio control channel (RCC) and through a fine tuning of the speech channel. The steps leading to system locking are as follows:

1st When the subscriber station is energized, the system is initiated and the subscriber station CCU 29 issues a series of command to the demodulation circuits of the subscriber station modems 30a, 30b and 30c, leading to RCC capture.

2 · The demodulation circuits in each of modems 30a, 30b and 30c are first set in their learning states. During this time interval, the modem learns its digital reception filters the characteristics of the analog reception filters. The analog filters may be impaired due to age or temperature variations. During the learning condition, each modem automatically sets its digital filter coefficients to compensate for these deteriorations. After CCU 29 has received information from the modem

30a, 30b and 30c demodulation circuits that the learning sequence has been completed sets the CCU reception frequency to the RCC normal frequency. The CCU then orders the modem to capture the RCC frequency and to search for the characteristic amplitude modulation interval (AM hole) of the radio control channel. The AM hole is a 16-symbol long time interval, during which no energy is transmitted, at the beginning of RCC transmission from the base station. All other transmitted clock types include only a zero transmission of eight symbols. The extra eight symbols with zero information at the beginning of a lock burst identify the cut as RCC.

3rd The first task of modem 30a, 30b, 30c demodulation circuits is to provide a rough frequency vein capture. The received signal is processed

526 967 in a digital phase-locked loop, and the subscriber's VCXO is set to the base station's transmit frequency. After frequency capture, the modem begins its search for the AM hole. The modem searches for a sequence of symbols with little or no amplitude. When this sequence has been detected for a number of frames, the modem generates an AM strobe signal for activating the CCU frame timing circuit. If any sequence of AM holes is not detected, the modem returns information to

CCU that the RCC capture was unsuccessful. CCU then begins to search for other RCC frequencies in a similar way.

4th After detecting the AM hole, modem 30a, 30b and 30c demodulation circuits perform a refined frequency capture as well as initial bit synchronization settings. The first symbols of the RCC control door 60 are a sync pattern with a fixed number of bits, which is utilized by the modem for locking to the base station phase. (Bittaktinställning). At this time20 point, the RX clock at the subscriber station is useful as a symbol clock.

5th The subscriber station CCU 29 has received a rough symbol rate setting via the AM strobe signal from the modem. After frequency capture and bit synchronization during 25, the CCU searches for the modem received data and searches the CCU for the unique words of the radio control channel (RCC). This unique word provides an absolute symbol count reference for the frame.

CCU then sets its symbol counter so that the counters are aligned with this reference. The subscriber station is now aligned with and locked to the base station's transmission system rate (both in frequency and symbol rate).

6th During the remainder of the system clock capture, the distance dependent delay between the base station and 5 is determined. subscriber stations. This (one-way) delay

526 967 can be from 0 to 1.2 symbol times in the system.

During a call, the subscriber station sends a message on the RCC to the base station.

7th The base station modem 19 is always looking for new in-.

upcoming subscriber bursts. These bursts can be delayed from 0 to 3 symbol times relative to the base station's SOF master reference. For each slot, the demodulation circuits in the base station modem 30a, 30b and 30c search for transmissions on the reverse direction.

RCC slot. All clock and phase information must be extracted during the first part of the door (introduction), otherwise the door and its information will be lost. There is no other chance of receiving arriving shutters. The arriving control gates are received on the RCC according to the Aloha queuing system, which will be described below after this description of the steps leading to system locking.

Eighth For each slot, the base station modem 19 performs a quick AGC setting and bit rate estimation during · the first symbols of the slot 60. The receiving section clock signals are adjusted to compensate for the subscriber statistic's distance dependent delay. The received data is then output to the base station CCU 18.

'CCU 18 detects the position of the unique word in the flow and. determines the distance dependent full symbol delay between the base station and the subscriber station.

The modem 19 outputs AGC information to CCU 18 for performing settings of the subscriber station TX power. Modem 19 also transmits to CCU 18 information regarding link quality and part-time information.

Link quality is used to determine whether a collision has occurred. A poor value for the link quality indicates that the signal was not of good quality, most likely due to a simultaneous transmission of more than one subscriber to the RCC slot. The part-time estimate is the value of the distance 526 967 calculated by modem 19⁴³ depending on the partial delay between the base station and the subscriber stations.

9th This power and delay information is processed in CCU 18 and transmitted to RPU 20. RPU 20 formats this information into RCC format and transmits the information through the RCC control door to the subscriber station. The subscriber station CCU 29 decodes this information and performs the settings required for transmit power and delay calculators in the modem

19 and CCU 18. CCU 18 updates its own full-symbol-type TX symbol frame counter and updates the modem's TX clock part-time delay counter.

10th During the call setup of a subscriber station, the base station's RPU 20 performs frequency and clock 15. sharing for the call. This information is transmitted on the RCC, and the subscriber station CCU 29 sets the RX frequency and orders the modem to begin detecting the tall hatch. Information regarding AGC, rate and frequency is passed from the RCC operation to the 'speech channel operation'. This is possible because all frequencies in the system are synchronized with the same frame rate reference in the base station. .

11.'To accurately set the subscriber station rate, perform a fine tuning procedure at the beginning of each call setup. During the fine tuning phase, the transmission over the speech channel is the same as on the control channel and is the modulation level BPSK and the messages in RCC format, but no AM hole is generated at the base station. As far as these new RCC messages are concerned, there is only one exchange between

CCU 18 and CCU 29. The modem 19 is in the fine tuning state at the base station and in the receive control state at the subscriber station. During the fine tuning, the CCU 29 of the subscriber station generates a message, which for the most part contains

526 967 a pattern with a fixed number of bits as well as a variable part indicating whether the nearest previous message from the base station has been accepted or rejected. The base station modem 19 transmits information on the clock setting and power setting to the CCU18 from each received slot. Power setting information is continuously sent to the subscriber station. Rate setting information and control information, indicating continuation or completion of the fine tuning state, are transmitted after a calculation period. The base station CCU 18 collects below. 30 frames rate setting information from modem 19, calculates an average value, and then transmits the setting information to the subscriber station

CCU 29. Subsequently, the base station CCU 18 performs a further fine tuning under 30 frames, the result being transmitted again to the subscriber station CCU 29. The fine tuning procedure is terminated by the base station CCU 18 and the call begins when the difference between the tuning information received from the modem is within an acceptable range, such as 1 %, or when fine tuning has exceeded a maximum time.

During connection and disconnection, the subscriber stations communicate with the base station by sending messages over the backward RCC door. The traffic originating from such subscriber stations that attempt to access RCC can be considered stochastic.

When a subscriber station wishes to send a message to the base station, some kind of control mechanism must decide which subscriber station to send, since there may be several subscriber stations trying to transmit in the same slot. The Aloha system with slots is suitable for a large number of subscribers, who relatively rarely and randomly need access to the RCC channel.

The Aloha system allows subscriber stations to broadcast

526 967 messages in the assigned RCC slot completely regardless of whether other subscriber stations are also trying to send in the same control slot. The natural consequence of this independence is that messages from different subscriber stations can be sent at the same time and therefore collide. To cope with collisions, this system requires that the base station, after properly receiving the subscriber station's message, send a positive acknowledgment (Ack).

If the acknowledgment ACK is not received within the maximum time allowed for transmission and processing delay in each direction (approximately 1-2 frame times), the subscriber station must transmit the message. Transmissions may be due to errors when receiving ACK at the subscriber station.

In general, subscriber stations cannot determine the cause of the problem. Therefore, a random delay is selected by the subscriber stations prior to the transmission of the message to avoid repeated collisions with other transmitters, which may have been involved in a previous collision.

One problem that arises with the Aloha system is the fact that the channel can become unstable if random retransmission delays are not long enough. When this happens, the channel is clogged again with retransmission and. the transmitted information falls to zero. One. Backoff technology minimizes this problem by increasing the average value for each subscriber station's randomly selected retransmission delay for successful transmissions.

Collision transmissions and access control stability delay mean that the delays are typically geometrically distributed. In order to avoid large delay variations, the channel must be operated with a utilization rate which is considerably less than 36%.

In particular, an utilization rate of 20.% or · less makes it more likely that more than one retransmission is needed due to collisions. Thus, using a random 35 delay delay of, for example, eight frame times for frames of 45 ms, the total mean delay for a retransmission is thus 450 ms (on average, the delay, thus: includes a frame delay for the original.

526 967 transmission, a frame delay for the receipt and the random delay of eight frames).

To ensure that the utilization rate is not greater than 20%, we consider the mean time T between calls per subscriber, the total number of N subscribers and the frame time F for values ​​less than 36%, whereby the utilization rate is given by NF / T. For F = 45 ms, ti = 1000 subscribers and T = 30 minutes, the utilization rate is 1.5%.

For a utilization rate of 20% of the maximum value, a population of 1000 subscribers making each call on average every half minute can be handled with a frame time of 45 ms with access delays of about 45 ms, when a retransmission is required, and with an average access time of about 70-80 ms. The price that one has to pay for the much shorter average access time is an increased delay variation, which for the utilization rate of 20% or less should rarely exceed the time for two transmissions, ie one second.

The Aloha system is suitable for use with a system with a large number of subscribers, which relatively rarely and randomly need access to the control channel, and should allow the co-structure target with delays of less than one second to be achieved for the expected population parameters. In contrast, interrogation techniques and fixed TDMA techniques give unacceptable delays.

All call processing steps, which include call set-up and disconnection as well as slot connection, require information exchange over the control channel and / or voice channel's control portion. Below, the different steps in call processing are described both in terms of the processing in the subscriber station and in the base station.

The subscriber station subscriber identification number (SIN) and the dialed number are two call control numbers * 5 which must be in a CALL REQUEST message to the base station for each call from a subscriber station.

For a subscriber-to-subscriber call, the dialed is fed

526 967 the number into a register in the subscriber station memory. The user initiates communication with the base station by pressing the transmit button or by waiting for a timeout. The radio channel is only used when the entire number has been dialed and stored in the subscriber station. Thus, the user can dial the number slowly without taking up valuable RCC bandwidth or time.

The sequence of messages generated by the subscriber stations and the base station to establish a connection between two subscriber stations is shown in Fig. 4. The control channel's link level protocol is used to control the various error states that arise due to channel errors. Messages received by the base station on the reverse control frequency are automatically acknowledged in the next control slot on the forward control frequency15. Below is a brief description of a message exchange for establishing a call between two subscriber stations.

When the base station receives a CALL REQUEST message on the control channel from a subscriber station A, it first checks for errors in the received SIN. If SIN is incorrect, the message is rejected. Without a valid SIN. the base station does not know who sent the message. If the dialed number is incorrect or incomplete, the base station sends a CLEAR INDICATION message. on the forward channel frequency of the calling subscriber station A with status information specifying the problem.

If the call attempt is correct and allowed (i.e., the destination unit is not busy), the calling subscriber station A is assigned a voice channel and the base station sends a message PAGE in the form of an incoming call message at the forward control frequency to the destination subscriber station B. If the destination subscriber station B does not respond to PAGE with a CALL ACCEPTED message after two attempts or through a CLEAR REQUEST message returns a busy state indication, the base station sends a CLEAR INDICATION message to the calling subscriber station A with status information

526 967 regarding the busy state (i.e., lift handset or equivalent at the destination unit) or information that the destination subscriber station does not respond to the PAGE message.

If the destination subscriber station B accepts the incoming call, a CALL ACCEPTED message 'is sent back to the base station and' an assignment of the voice channel occurs. When voice channel synchronization is established, the destination subscriber station B generates an audible ring 10 signal which can be intercepted at the destination subscriber station B, and the station B generates a RINGBACK tone over the voice channel to the calling subscriber station A.

When the destination subscriber station B responds, that is, when its clock state changes to answer mode (off15 hook mode), the control portion of the tall hatch is changed from a sync indication to a sync off-hook indication and PROGRESS messages on the voice channel are transmitted through the base station between the two subscriber stations. The destination subscriber station B interrupts the audible ring signal and disconnects the RINGBACK tone from the speech channel at this time.

The crèche is now closed and speech / data exchange can begin.

Connecting a call to an external telephone is done in the same way as a call to another subscriber station. The subscriber station simply dials the desired digits and presses the transmit button or, waiting for a timeout. Hereby a radio call message · is delivered to the base station. The base station decides whether to call another subscriber station or select an external trunk line. In this case, an external trunk line is selected and the dialed number is output on the trunk line. While the numbers are being output, the calling subscriber station is assigned a voice rate. When a subscriber station receives the CALL-CONNECT message, it changes frequency and synchronizes itself with the assigned voice channel.

³⁵ When the speech channel clarification is complete, the subscriber station user apparatus is switched from the locally silent state to the external trunk line. From • this time onwards, all tones are generated during the 526,967 ongoing calls by the destination Telco office.

An incoming external call arrives on a trunk line to the base station. The calling central office transmits from 2-5 digits, which identify the unique digits of the destination subscriber station's SIN, to the base station over a direct trunk line for incoming calls (DIDs). If the dialed subscriber station is not busy, the base station sends a PAGE message on the RCC to the current subscriber station. Three possible situations can occur. In a first case, the subscriber station accepts the incoming call, after which the processing proceeds in the manner described below. In a second case is not obtained. any response. In this case, the base station makes the call two more times. If the base station exceeds a permitted number of retries without receiving any response from the subscriber unit, a RINGBACK tone is generated in the calling unit. The third case is a result of the subscriber station being busy with digit dialing (ie offhook mode) and retransmission of a CLEAR20 REQUEST message on the control channel. In this case, a busy tone is returned to the calling subscriber station.

In the case of a successful PAGE call, an allocation of the voice channel occurs and an external ringtone is generated at the destination subscriber station's telephone apparatus at the same time as an audible

RINGBACK tone is returned from the subscriber station to the calling party. When the destination subscriber station responds to the call (i.e., the base station detects a transition from onhook mode to offhook mode), the external ring tone and the RINGBACK message on the channel are removed. At this point, the voice channel is ready for a call.

A normal call disconnection is initiated by the subscriber putting on the handset, ie switching to on-hook mode. The base station detects this transition from offhook mode to onhook mode via the voice channel control part. When the base station detects this transition, it removes the assignment of the voice channel. The channel must not be used again until the base station observes that subscriber 526 967 station synchronization on the channel is lost. If the disconnected call is a call to another subscriber station, an on-hook indication is transmitted to the other subscriber station in the voice channel control portion.

The subscriber stations resync themselves with the radio control channel (RCC) broadcasts and send CLEARREQUEST messages to the base station.

Disconnection of a call also takes place five seconds after the base station's radio contact with a subscriber10 station is lost.

A call connection may be lost due to fading or channel interference at the destination receiver. To determine if there are any problems in the connection, the subscriber stations and the base station check if any of the following conditions exist: the link quality value returned from the subscriber station or base station is below a predetermined threshold value for several consecutive receipts; an impaired word synchronization has been detected during several consecutive broadcasts.

Messages originating in the base station are sent to all active subscriber stations. These messages are transmitted by the base station over the radio control channel. The purpose of the transmitted message is to note the same all active subscriber stations for changes in the operating mode of the system (ie frequency change in RCC, an instruction to the modem to begin the self-learning state, etc.). These messages are not acknowledged by the subscriber stations.

Remote Controller Processor (RPU)

The RPU works as a control computer in the base station architecture. It communicates partly with CCU 18, which in turn communicates with the radio equipment and partly with PBX 15, as shown in Figure 2.

RPU 20 coordinates the necessary functions for radio call processing. RPU 20 exchanges messages with subscriber stations, PBX 15 and CCU 15 to execute

526 967 connection and disconnection. The assignment and release of the radio channels are included in the call processing functions. RPU 20 also includes a database which reflects the current state of the system. The database contains information regarding the status of the equipment, subscriber stations, connections and the radio channels in the system.

Call setup is started when the RPU receives a message from the PBX call processor 24 for a call on one. external line or a message from a subscriber for a call intended for an external telephone or other subscriber. Communications from subscribers are received on the radio control channel (RCC) via the base station CCU 18. RPU 20 performs an allocation of your voice channel and exchanges messages with the subscriber station, PBX and CCU

18 to establish the connection.

A shutdown is initiated by a message received from PBX or a subscriber indicating that a telephone handset has been placed, or by a message received from CCU &lt;18 indicating that synchronization has been lost on the radio channel. RPU informs CCU 18 and PBX 15 of the shutdown, and RCC is released.

The RPU program performs the following functions:

1st Processes subscriber, CCU and PBX messages that control call connectivity, call disconnection and channel for 11 sharing;

2nd Initiates and maintains a read / write system database.

3rd Supports a system console1 or control unit, which enables system testing and manual system control.

4th Manages the BCC interfaces by supporting the BCC communication protocol over an asynchronous 9600 baud serial interface.

526 967 ⁵²

5th Manages the PBX interface by supporting the PBX message protocol.

6th For a transaction log, which provides diagnostic data and approximate billing data.

The RPU software supports a serial interface to the PBX call processor 24. The software also supports serial interfaces to each CCU 18 in the base station configuration.

The RPU hardware includes a general purpose computer based on the Motorola 68000 computer. This machine is equipped with a 1 Mbyte RAM and a 10 Mbyte non-volatile disk memory. I / O consists of a system console1 and a unit containing eight asynchronous serial data interface units.

As shown in Fig. 5, the RPU program package corresponds to a system comprising a timing module 40, one or more BCC interface modules 41a-41n, a 'PBX interface module 42, a console module 43, a log module 44, a message processing module (MPM) 45, and a database20 module 46.

All modules, except database module 46, are called and executed by time management. module 40. The modules communicate with each other via a system of mailboxes. The database module 46 is based on a collection of subroutines, which are intended to provide access to information in the database.

The timing module 40 provides the main line code for the RPU program. It is responsible for timing and activation of all other modules. It is also responsible for the maintenance of event timers and mailboxes, which enable communication between the modules and external units.

The BCC interface modules 41a-41n support a serial asynchronous interface and a link level protocol.

They also monitor the state of communication with each CCU 18.

526 967

The PBX interface module 42 supports a serial asynchronous interface to the PBX ahrop processor 24.

Console module 43 / constitutes a system user interface, which allows testing and modifications to system status and message exchange between RPU 20 and the rest of the system.

The log module 44 provides approximate transaction information for diagnostic and system analysis purposes.

The message processing module 45 processes all received RCC, BCC and PBX messages. It performs all subscriber call connections and disconnections that are not performed by PBX 15, and performs the radio channel assignment. It also includes a background process that monitors the state of each CCU 18.

Database module 46 provides an interface to all data structures necessary for call processing. It includes a frequency sharing process which assigns the radio channels.

The RPU database contains a structure describing the system configuration, including information on all subscribers and the state of all radio channels. These structures are described below;

The RPU database contains one BCC data structure for each CCU 18 in the system.

A subscriber identification table (SIN table) includes a sorted list of all authorized subscribers. The list is sorted to facilitate the determination of subscriber privileges. The SIN table has one input for each subscriber in the system.

The RPU program performs part of the subscriber unit call processing. This call processing is performed in the message processing module. Call processing is performed through message exchanges between MPM 45, PBX module 42 and all BCC modules 41.

526 967

Initiation of a telephone call from a subscriber station

This section briefly describes the normal call setup procedure for a subscriber-initiated call. A subscriber (the calling subscriber) raises the handset (off-hook state), dials a valid telephone number (the telephone number of the destination) and presses the send button or awaits a timeout. The calling subscriber station sends a CALL REQUEST message over the control channel to the base station. The BCC modules 41 in the RPU receive the RADIO REQUEST message and forward it to MPM 45. MPM 45 performs some simple checks on the validity of the digits and sends a RADIO REQUEST message to the PBX module 42, which forwards the message to the PBX control processor 24 The PBX call processor 24 checks the validity of the dialed digits and returns a PLACE CALL pie partition to RPU 20. MPM 45 assigns a calling slot to the calling subscriber station. MPM 45 generates a CHANGE CHANNEL command to CCU 18, which command contains the speech channel assigned to the calling subscriber station. MPM 45 generates a CALL CONNECT command. to the calling subscriber station therein, which command accomplishes in assigning the voice rate and number cap to the calling subscriber station. MPM 45 generates an ALLOCATE message to the PBX call processor 24, which message instructs the PBX call processor 24 to assign a message channel. At this point, the calling subscriber station is fully connected. It now awaits a connection via the PBX connection matrix 25 to the destination. The destination may be either another subscriber station or a telephone to which access is obtained over a trunk line 14.

526 967

Receiving a call at a subscriber station

This section briefly describes how an incoming call to a subscriber station is handled. The PBX call processor 24 determines that a call is intended for a subscriber station. The PBX call processor 24 generates an INCOMING CALL message. This message contains information about the type of incoming call, especially whether the call comes from an external trunk line or from another subscriber station. The PBX module 42 in rpu receives the PBX message from the PBX call processor 24 and forwards it to the MPU 45. If the call comes from another subscriber station, the MPM 45 sets the subscriber to-subscriber index of both the calling subscriber station and the destination subscriber station, and orders MPM 45 involved CCU 18 to position themselves internally. MPM -45 generates a PAGE message to the subscriber station specified in the INCOMING CALL message.

The current subscriber station responds with a CALL ACCEPT message. In response to the CALL ACCEPT20 message, MPM 45 generates a CHANGE CHANNEL message to its corresponding. CCU 18 and a CALL CONNECT message to the corresponding subscriber station. MPM 45 then generates an ALLOCATE message to the PBX call processor 24, which message causes the PBX switching array 25 to make the final connection for the incoming call.

Feedback on signal failure

This section briefly describes how RPU 20 responds to a channel fade during an ongoing call.

The CCU 18 which handles the speech channel on which the fading

30 °. there are observes that synchronization is lost on the channel. CCU 18 produces one. event message NOSYNC. BCC module 41 receives the event message and forwards it to MPM 45. MPM 45 sends a 0NHOOK message to PBX call processor 24 and sets

526 967 the subscriber in the sleep state and the channel in the onhook state.

Processing of an incoming BCC message

A BCC message is transmitted from CCU 18 via an asynchronous interface of 9600 baud to RPU 20. The BBC module 41 which handles the special CCU interface reads the message and checks the link level information bits to verify the validity of the incoming message. If the BCC module 41 determines that the message is acceptable, an appropriate acknowledgment is returned to the sending CCU 18. Otherwise, a retransmission acknowledgment or negative acknowledgment is returned. The BCC module '41 now sends the message to MPM 45. This message is placed in a message processing mailbox 48 using the mailboxes provided by the timing module 40. (See Figure 6)

If there are no more incoming messages from CCU 18 and a BCC mailbox 49 containing messages to the CCU is empty, the BCC module 41 stops itself, after which the control is handed over to the timing module 40.

The timing module 40 activates the next module in the round-robin timing, and this module runs until it stops itself. The time control module then activates another module, etc. At a later time, the timer module activates MPM 45.

MPM 45 then reads the BCC message together with any other messages that may have queued to MPM 45 in its mailbox 48. The BCC message is identified and processed. Such processing may include changes to the database and generation of new messages.

Fig. 6 shows the data flow for an incoming message.

Generation of an outgoing BCC message

Fig. 6 also shows the data flow for an outgoing BCC526 967 message. An outgoing BCC message is generated by MPM 45 in response to any particular event. The message is formed inside the MPM 45 and posted to the BCC module 41 which handles the current CCU 18. After this and other non-essential messages have been sent and there are no more messages in the MPM mailbox 48, the MPM stops itself after which the control is returned to the time control module .

The BCC module reads the message from its mailbox 49 and adds appropriate link level bits to the outgoing message. It then transmits the message through the serial data port to CCU 18..

Processing of RCC messages

An incoming RCC message is handled in exactly the same way as an incoming BCC message, since an RCC message is a type of BCC message. Similarly, an outgoing RCC message is formed and transmitted in the same way as an outgoing BCC message.

Processing of an incoming PBX message

A PBX message is received from the PBX call processor 24. This message is transmitted via an asynchronous 9660 baud interface to the RPU 20. The PBX module 42 of the RPU (Fig. 7) reads the PBX message and sends it to the MPM mailbox 48. When if there are no more incoming characters and a PBX mailbox 50 containing outgoing PBX messages is empty, the PBX module 42 stops itself after which the control is returned to the timing module 40.

MPM 45 reads the PBX message together with any other messages that may have queued in its mailbox 48. The PBX message is processed depending on the message type and current state of the subscriber specified in the message. The treatment may include

526 967 changes to the database, changes in the subscriber state and generation of new messages.

Figure 7 shows the data flow of the incoming PBX message.

Generating an outbound PBX message

Figure 7 also shows how an outbound PBX message is generated by MPM 45 in response to an event. The message is formed inside MPM 45 and posted to the PBX module 42.

After this and other necessary messages have been sent and there are no more messages in the MPM mailbox, MPM 45 stops itself after which the control is returned to the timing module 40.

The timer module 40 continues to activate other modules in the round robin timer until

The PBX module 42 in the RPU is activated.

The PBX module 42 of the RPU reads the PBX message from its mailbox 50 and then outputs the message through the serial data port to the PBX call processor 24.

Alignment of log messages &lt;

At appropriate times in each of the modules in the RPU program package, a message with relevant information is posted to the log module 44. This information is timed and output to a file. Figure 8 shows data flows for log data.

Console1 I / O module

The console module 43 input section handles command generation and recognition as well as command approval.

Approved console commands can query and update the RPU database as well as send messages to '

RPU modules. Outputs from the console display commands emitted directly on the console port.

526 967

Tidsstymingsmodul

The time control module 40 is to be regarded as a special system module and is responsible for the timing of all the other RPU modules. Tidsstyrningsmodulens⁵ 40 main tasks are to select the next module for execution and to manage communication with internal and external modules.

Although all the different RPU modules can be considered as separate modules, all modules in reality constitute an application process in a Regulus operating system. It is the time management module 40 that handles the rouhd-robin declaration of all the other RPU modules. The time control module 40. handles the stack for each of the pseudo-RPU modules by reserving a given&gt;. storage space for each of the pseudo-modules at startup time. Just before each of the modules is scheduled to be executed, the stack pointer of the timing module 40 is changed to point to the correct stack address of the current module. A memory map of RPU 20 is shown in Figure 9.

Each RPU module runs until it stops itself. When one module stops itself, it returns control to the time management module, which allows another module

J to be executed. A module can stop itself in several ways: by calling GETEVENTi), which forces the module to be inactive until an event is waiting, or by calling WAIT (), which stops for a certain number of seconds, or by calling call BLOCK (), which gives a stop during a review of the "round robin time control loop."

Another main function that the timing module 40 performs is inter-module communication between modules. Mailboxes are the means used for sending or receiving messages to or from other modules. Each module can search for letters in its mailbox using the call MAILREAD (). In the same way

524 967 module sends a letter to another module using the call MAILSEND (). The time control module provides a separate; mailbox for each of the modules contained in the timing loop. When a module sends a message to another module, the message is copied into the destination mailbox. When, at a later date, the destination module's turn becomes executed, the timing module checks its mailbox to determine whether there is a message in the mailbox. If this is the case, the timing module 40 generates an event of type MAIL which forces the module to cancel its stop if it has been stopped by a GETEVENT () call, the module being scheduled in the execution schedule.

The time control module also has an event list for each of the modules in the time control loop. Events can consist of letter events or timed events. Letter events are generated as soon as the time management module determines that messages are waiting for the module that is currently being executed. A module can place a timed event on the event list by calling PUTEVENT () and specify how many seconds the generation of an event should be delayed. At each review of the timing loop, the timing module 40 examines the event list of the module if any specified delay for a timed event has expired. If such an expired delay is detected, the time for execution of the correct module is determined and the event is returned to the module through the call GETEVENT ().

The time control module 40 contains routines that are used to initiate RS-232 interfaces between CCU 18 and RPU 20 and between PBX 15 and RPU 20. These routines, which take over the entire program control over these interfaces, disable the Regulus operating system's normal review of control sequences. Other routines are used for clearing I / O buffers and for reading and writing terminal messages. The time control module 40 upp526 967 also maintains the rate of system time for all RPU modules.

BCC interface module

Each BCC module 41 forms an interface between a CCU 18 and the other program modules in RPU 20. The messages exchanged between CCU 18 and RPU 20 are various long binary data transmitted on an asynchronous communication link. The BCC module 41 is responsible for the complete communication of messages on the communication link, which includes error detection, message sequencing and message acknowledgments.

The hardware interface unit between CCU 18 and RPU 20 consists of an asynchronous RS232 interface unit of 9600 baud.

Inputs to this module 41 include messages received from CCU or from other RPU program modules. Messages are output from this module either to the CCU via the RS-232 interface unit or to other RPU program modules via the corresponding mailboxes.

This module 41 has the task of managing message traffic between RPU 20 and CCU 18. This module 41 constantly searches for messages received from CCU 18 and transmits the messages to the correct RPU program module. Similarly, this module constantly searches for messages addressed to CCU 1.8 from other · RPU program modules. An alternate bit protocol is used to limit unwanted messages to a message in each direction. Sequence and acknowledgment bits are responsible for the flow control necessary to perform this function. The protocol is described in more detail in the next section.

In the ensuing discussion, one entity is called that can process messages with us or us, and the other entity is referred to as them. The minutes can be explained by specifying the measures to be taken when receiving a message. There is

526 967 only four basic measures, which depend on whether each of two conditions is met.

It is determined whether these conditions are met by comparing the sequence and acknowledgment bits of the received message with the expected bits.

For an oncoming message, the ACK bit is as expected if it is equal to the SEQ bit in our last sent message. Similarly, the SEQ bit is as expected if it differs from the SEQ bit in the last received message. In other words, the expected states are that an incoming message acknowledges our last message and that we also expect every new reception to be a new message.

The guards taken on receiving a message are summarized below by four different combinations generated by the above state:

1st ACK as expected and SEQ as expected. Mark that our last sent message has been acknowledged (which allows us to send a new message). Process the most recently received message (acknowledge in the next message we send).

2nd ACK as expected and SEQ not as expected. Mark that our last sent message has been acknowledged (which allows us to send a new message).

'Reject the last received message (do not acknowledge the message). .

3rd ACK not as expected and SEQ as expected.

If we have sent a message that has not yet been acknowledged, return the same. If we do not have such a message.

If there is any error at the destination and we should restore as described below. Process the last received message.

4th ACK not as expected and SEQ not as expected.

Our last message was not received at the destination. Repand this. Reject the most recently received message.

526 967

The reset bit was used to reset the SEQ and ACK bits. When we receive a message with the recovery bit set, this message shall be accepted as a new message regardless of its

SEQ bit, and the message should be acknowledged. Furthermore, the ACK bit of the received message reflects the SEQ bit of the last message they received from us. We should change this bit before sending the next message.

For example, if we receive a message whose ACK / SEQ10 number is '' 4 (reset = 1, ACK = 0, ESQ = .0), then the ACK / SEQ number of the response should be 1^?'(reset = 0, ACK = 0, SEQ = 1). Either side can reset when it suspects that an error has occurred in the protocol.

When we receive a message from them and have no new message waiting and no standard response does not appear shortly, we acknowledge the message by sending a special ACK message. The ACK bit acknowledges the received message, but the SEQ bit does not change compared to the last message sent by us. This will cause them to process the receipt and reject the most recent message. The content of this message is a null message. However, since this message is rejected in any case, the content of the message is immaterial.

PBX Interface Module

The PBX module '42 is the interface between the UTX-250 PBX call processor 24 and the other program modules

RPU 20. The messages exchanged between the two units consist of an ASCII character-oriented message exchange.

The ASCII character is here defined as a 7-bit or 8-bit ASCII character. Both PBX call processor 24 and RPU 20 must be able to accept characters with odd, even or no parity. The message text consists of different long character strings or printable characters.

The hardware interface between the PBX call processor

4 and RPU 20 is a 9600 baud asynchronous interface unit of type RS-232.

526 967

Messages to the PBX module 42 include messages from the PBX call processor 24 or from other RPU program modules. Messages are output from this module either to the PBX call processor 24 or to other RPU program modules via corresponding mailboxes.

The PBX module 42 has the task of managing message traffic between RPU 20 and the PBX call processor 24. This module continuously searches for messages received from the PBX call processor 24, and we end these messages to the correct RPU program module. Likewise, this module continuously scans for messages from other RPU program modules intended for the PBX call processor 24.

Each character received from the PBX call processor 24 undergoes one. test for determining whether the character is similar to the character&gt;, indicating the beginning of a message, or a carriage return character, indicating the end of a message. This module can handle full-duplex messaging traffic.

console Module

The console module 43 is the user's window into the current state of the RPU 20. The console enables the display of information relating to the current state of the subscribers and the radio channels, the change of connections and channel states, and the transmission of messages to the PBX 15 and the units CCU 18. The console processes the inflow from the terminal and execute the desired command.

The console module 43 is the interface to the base station using the terminal. The console module 43 processes the input messages from the terminal and executes the command. Data is read from and entered into the database, image commands are output to the terminal's monitor and messages are sent to other modules. Interface messages for this module include:

(1) Characters entered from the user's keyboard.

(2) Characters output to the user's monitor. -.

526 967 (3) Data read and entered into the database.

(4) Send messages to the PBX, BCG, and message processing modules.

A set of parsing routines (parser routines) enters .5 characters from the user's keyboard. A data entry character is displayed at the beginning of each command line, the data is handled in a buffer, the editing characters are processed, the entered characters are displayed on the screen and the data is divided into control symbols. By providing the analysis routine with a set of data structures that describe all possible commands and valid control symbols in each command, the analysis routine is brought to analyze the entered data, respond to question marks and display keywords for that entry. Each control symbol is checked so that it is of the expected data type. Passwords are compared to the list of acceptable entries and floating numbers are converted to integers. Once the command line input is complete, another verification will take place. Entered floating numbers are checked so that they are within the allowed range. the area, and with some commands the state of the system is checked before the command is executed.

Commands can be divided into the following three categories:

(1) commands that display information from the database, (2) commands that change the database, and (3) commands' that send messages. On-screen information about subscriber, connection, CCU and channel status can be displayed. All display commands require that information be read from the database and that formatted data be output to the user's monitor. Change commands include the ability to invite a subscriber connection to a particular channel and the ability to activate and deactivate channels. Such commands are used in testing the frequency assignment algorithm. All change commands type in the database.

PBX, BCC and RCC messages can be sent from console module 43 to several different modules in the system.

967

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.66

Through a SENDMSG command, the user is instructed to enter all necessary information for the message, which is formatted and forwarded to the specified module. The PBX message is sent to the PBX module 42 arranged in the RPU, which transmits the message further to the PBX call processor 24. The BCC and RCC messages can be sent from the RPU 20. to the CCUs 18 via the BCC modules 41 which add the link level protocol bits to the outgoing messages. Inputs from the CCU units.

are simulated, and messages, including both BCC and RCC messages, are forwarded to MPM 46.

logging Module

The log module 44 is responsible for recording or logging of RPU events or messages. The log module 44 contains the following three disk files: a transaction log containing information corresponding to invoicing information, an error log containing error messages, and a message log containing system warning messages.

The log module 44 consists of a set of subroutines which are called from the other RPU modules. Each subroutine is responsible for timestamping the message and writing it to the correct disk file. Each subroutine has a global flag that determines whether to log the messages. The global flags are set and reset using console commands. Message Processing Module (MPM)

In MPM 45, the high-level call processing functions between the PBX 15 and the subscriber stations are performed.

This module is responsible for call processing functions, such as message initiation, voice channel assignment and call dial tone control for both subscriber and external telephones. MPM 45 also processes status messages that it receives from the CCU 18. The MPM 45 processes, for example, channel status information, which is link quality or. abonnentklyktillstånd.

MPM 45 is organized as a state machine,

526 967 ⁶⁷ where PBX and BCC messages execute messages to the message processing authorization machine. MPM 45 processes the messages by · 'updating the database, outputting required replies and' then moving on to the next state.

MPM 45 utilizes the system's mailboxes provided by the timing module 40 to receive and send messages from and to other RPU modules. Furthermore, MPM utilizes 45 subroutines in the database module to read or update state information in the database.

As described above, MPM 45 is organized as a state machine. A control message that gives rise to a certain processing is made up of a sharing or a timed release. MPM 45 determines the type of control message (ie time trigger, RCC message, PBX message, etc.) and which subscriber station or channel is affected by the control message. MPM 45 processes the control message by generating the correct response messages and by moving to the next state.

MPM 45 is in fact two state tables. The RCC state machine shown in Fig. 10 processes messages from the PBX call processor. 24, or RCC messages from a subscriber's station. The channel state machine shown in Fig. 11 processes messages from a CCU 18.

Initially, all subscribers are in an RCC standby and all channels are in a channel rest state. indicating that no connections are connected or under connection.

The following are the state changes that a typical external call to a subscriber station entails.

An external call message is received from the PBX call processor 24, which message includes the telephone number of the call destination subscriber station.

A message PAGE is sent to the subscriber station and the subscriber station switches to a PAGE state.

526 967

When a message CALL ACCEPT is received from the subscriber station, the subscriber station switches to an ACTIVE state. At this time, a channel is assigned and the PBX call processor 24, CCU 18 and the subscriber station are informed of the channel assignment. The channel is set in a RING SYNC-WAIT state (Fig. 11). When CCU 18 indicates that synchronization has been established, the channel state changes to a SYNC-RING state. Finally, when CCU 18 indicates that the subscriber's clock state has changed to off-hook mode, the channel state changes to a

SYNC OffHook state. The SYNC-OFFHOOK state indicates that a call connection has been established.

A subscriber-to-11 subscriber call begins with a message CALL REQUEST being received from the calling subscriber station. The calling subscriber station is put in a DIAL state, and a message RADIO REQUEST is sent to the PBX call processor 24. The PBX call processor 24 then returns a message called PLACE CALL and a message for the destination subscriber station INCOMING CALL. In response to the message PLACE CALL, a channel is assigned and the PBX call processor is informed; 24, CCU 18 and the calling subscriber station for the signal assignment. The calling subscriber channel state is set to OFFHOOK SYNC WAIT until the channel has been synchronized. When the base station CCU 18 detects the broadcast from the calling subscriber, it generates a channel event message SYNC OFFHOOK. RPU 20 processes the channel event message by changing the channel state to the SYNC OFFHOOK state. An incoming call message intended for the destination subscriber station is processed in the same manner as described above for an external call message. Furthermore, the channels involved in the connection are set in internal mode as soon as both subscribers have been synchronized.

Disconnection starts with one of the parties involved in the connection switching to a ONHOOK clock state.

526 967

When the state of a telephone external to the system is changed to ONHOOK, a message ONHOOK is received by MPM 45 from PBX call processor 24. When a subscriber switches to ONHOOK mode, CCU 18 sends a message indicating that the subscriber station is in ONHOOK mode . In which case, the other party is informed of the disconnection, the channel is set to a DISCONNECT state and the subscriber station is set to a TEARDOWN state.

When CCU 18 indicates that synchronization has been lost, the channel and the subscriber station are brought back to their sleep state.

background Process

A background process routine is realized in MPM 45. The background process initially communicates with the units CCU 18 after a cold start or warm start. Even after the system has been started up, the background process monitors the units CCU 18 in order to keep the database updated and an RCC assigned.

From the BCC modules 41, BCC messages generated are received by both the units CCU 18 and .BCC modules 41. Messages are sent via the BCC modules 41 to the units CCU 18.

Data is entered and read from the database.

Initially, BASEBAND QUERY messages are sent to all CCU 18 so that RPU 20 can determine the current system state. All information received from baseband event or response messages is stored in the RPU database. When RPU 20 receives a baseband event message indicating that CCU 18 is ready and not reset (ie, CCU 18 has just been started), the CCU 20 assigned frequency is marked as busy. CCU 18 then receives messages CHANNEL QUERY to update the database to the current system state. CCU initiation is completed as soon as each CCU 18 has responded to all unanswered QUERY messages or if it has been established that CCU 18 is disconnected. At this time, a frequency is assigned to each CCU

526 967

18, which indicates that it is ready and restored (ie the CCU has just been started). If a CCU 18 has not been assigned a control channel, RPU 20 attempts to achieve the control channel assignment. The first choice is to try to assign the control channel to CCU 18 at the first frequency, since this is where the subscriber first searches for RCC. The next choice is a CCU 18, whose cover 0 was not used, and the last choice is a CCU 18, which has a connection on cover 0. If all active CCU 18 already has a connection on slot 0, one of the connections on slot 0 is interrupted and the control channel is assigned to that slot.

Once RPU 20 has communicated with all CCU 18, the state of the units CCU 18 is monitored via status messages received from the units CCU 18 or

The BCC modules 41. The BCC modules 41 continuously monitor the communication connection with each CCU 18. A CCU 18 is considered out of operation when a baseband event message indicating that CCU 18 is not ready is received. At this point, this CCU 18 is marked as not ready in the database. Furthermore, all connections are disconnected, all channels are returned to the idle state and frequency assignments are removed to this CCU 18. If this CCU · contains the control channel, a new control channel is assigned.

When a baseband event message indicating that a CCU 18 is ready and reset is received, this CCU is assigned. 18 and frequency. If no control channel is currently assigned to any CCU 18, slot 0- of the reset CCU is reserved for the control channel.

If a baseband event message indicating that a CCU 18 has lost its connection to RPU 20 is received, CHANNEL QUERY messages (ie one for each of the four channels) are sent to this CCU 18 for updating the RPU database with the the current state of each of the kahals at CCU. In response to each received CHANNEL QUERY message, the current channel state and the current channel are updated

526 967 connection information in the database. If a channel is in the SYNC WAIT state, it is assumed that the subscriber is no longer involved in the connection and the connection is disconnected.

Initially, the units CCU 18 receive the request from RPU 20 for their initial state. The CCU 18 units also send event messages whenever they start up or change states. The message exchange keeps the RPU database updated with the current state of the system. database Module

Database module 46 contains database interface routines necessary for access to the database. They form a consistent one-thread interface to the database for each module, which needs to access the information in the database. The majority of the access routines concern the SIN table and the BCC table. Access to all fields in these tables is provided by the access routines.

The database module is also responsible for database initiation at startup. All significant fields are initialized to appropriate values ​​by the database module initiation portion.

The database module also provides the following:

(1) TTY initiation support routines;

(2) A subscriber search binary search routine in the SIN table;

(3) Routines and. tables for supporting CCU frequency allocation.

(4) Control of analysis image information;

(5) Frequency assignment.

Database module 46 is a collection of routines that allow other modules to gain controlled access to the database. Because all access to the database takes place via the database routines, the database is essentially hidden from outside modules. This makes it possible to change the database without the need for modifications

526 967 on some other modules. When the database is changed, you only need to change the interface routine associated with the changed part of the database.

Frequency Allocation Process

The frequency assignment process performed by RPU

20, selects a suitable frequency and a suitable slot for a subscriber station which needs a voice channel. The selector algorithm depends on the type of call (ie internal or external) and the modulation level (ie 16-level or

10th Level 4). Although the frequency assignment process is functionally Independent of the database module 46, it is intimately associated with the database structures in the database. Because of this fact, this function is described separately from the database module, although it is technically a routine in the database module 46.

The frequency assignment process is utilized by MPM during call switching. It extends to a large extent the data structures in the database module.

Each frequency assignment request always falls into one of two categories. The first is the external source category and the second is the internal destination category. The Internal Destination category covers the incoming party (that is, the destination) for an internal call. The external source category covers all other cases that include external calls, whether incoming or outgoing, or the calling party of an internal call.

Instances for the frequency assignment process consist of an index to the SIN table of the subscriber station requesting a channel and the index of the SIN table of the calling subscriber station. The calling subscriber station index is only valid when the channel is connected for an internal destination call. At all other times, it is made up³ calling the subscriber's index of a pre-defined, invalid index, called DB NULL. These indexes provide access to all information required for assignment

526 967 ⁷³ of a suitable channel (ie frequency and gap). The frequency assignment routine provides the answer TRUE if a successful assignment or a frequency-gap combination has been performed. In another error, the routine gives the answer FALSE. In the case of a successful allocation, the selected frequency and the selected slot are placed in the SIN table of the subscriber station that requested the frequency assignment.

Each frequency is divided into four TDM slots. The RPU database keeps track of how many gaps are available in each position. When an assignment request falls into the external cold category, a gap is selected from the slot position that has it with respect to the highest count of the vacancy. Once a hatch position is selected, the first frequency that has that hatch vacant is selected.

In fact, it does not matter which gap is selected if a request falls into this category. However, this technology tends to distribute system load evenly across all gaps, and more importantly, it increases the likelihood of optimal door allocation · for both parties in an internal call. This is the case since system rate calculation has shown that the optimum slot allocation for a subscriber-to-subscriber call. should have the base station transmit cover for each subscriber in the same slot at different frequencies. By assigning the calling party to a subscriber-to-subscriber call the most available slot position, the probability is greater, when that time comes, that the destination subscriber station can occupy the same slot position at a different frequency. For example, if position · number 2 is the most accessible position, then this hatch position is selected. When the destination subscriber station allocation request is processed, then it is more likely that another hatch in position # 2 can be chased, so as to achieve the optimal hatch-to-hatch allocation.

When an assignment request falls into the internal destination category, the gap to be assigned from an option table is selected. An option table 526 967 contains lists which are arranged from the most desirable slot position assignments to the least desirable slot position assignments for the destination subscriber. This degree is based on the calling subscriber's slot allocation. The modulation type has not been mentioned so far, as the basic rules for assignment are not different in selecting 4-close and 16-close slots, with the important exception that only slot 0 or slot 2 can be assigned for a 4-time connection. As a result of this exception, and due to the fact that two subscribers may have different modulation types, a total of four different choice tables are needed to cover all possible call combinations. These option tables are as follows:

Table 6

<td>calling hatch</td><td>1st choice</td><td>2nd choice</td><td>3rd choice</td><td>4th choice</td>

<td>hatch 0</td><td> 0</td><td> 1</td><td> 3</td><td> 2</td>

<td>hatch 1</td><td> 1</td><td> 0</td><td> 2</td><td> 3</td>

<td>hatch 2</td><td> 2</td><td> 1</td><td> 3</td><td> 0</td>

<td>hatch 3</td><td> 3</td><td> 0</td><td> 2</td><td> 1</td>

<td>ranking</td><td>(in)</td><td>(2a)</td><td>. (2b)</td><td> (3)</td>

Option table for preferred gaps for an internal call from 16 when (dialing) to 16 when (destination)

Note that each of the columns in each table is ranked. This ranking indicates how desirable one's door is. The most desirable slot has ranking 1, and the least desirable slots have rankings 2, 3, etc. If two or more columns in an option table have the same desirability, they also have the same ranking number, which then. accompanied by

526 967 a letter. For example, if three columns have the rankings 2a, 2b and 2c respectively, then all these three columns have the same desirability, and the mutual order between the columns (a, b, c) can be freely chosen.

Table 7

<td>calling hatch</td><td>1st choice</td><td>2nd choice</td><td>3rd choice</td><td>4th choice</td>

<td>hatch 0</td><td> 0</td><td> 1</td><td> 2</td><td> 3</td>

<td>hatch 2</td><td> 2</td><td> 3</td><td> 0</td><td> 1</td>

<td>ranking</td><td>(la)</td><td>(Lb)</td><td>(2a)</td><td>(2b)</td>

Option table for preferred gaps for an internal call from 4-when (caller) to 16-when (destination).

Table 8

<td>calling hatch</td><td>1 ia choice</td><td>2nd choice</td>

<td>hatch 0</td><td> 0</td><td> 2</td>

<td>hatch 1 </td><td> 0</td><td> 2</td>

<td>hatch 2</td><td> 2</td><td> 0</td>

<td>hatch 3</td><td> 2</td><td> 0</td>

<td>ranking</td><td> (1)</td><td> (2)</td>

Option table for preferred gaps for an internal call from 16-call (caller) to 4-call (destination).

5?6 967

Table 9

<td>calling hatch</td><td>1st choice</td><td>2nd choice</td>

<td>hatch 0</td><td> 0</td><td> 2</td>

<td>hatch 2</td><td> 2</td><td> 0</td>

<td>ranking</td><td> (1)</td><td> (2)</td>

Option table for preferred gaps in an internal call from 4-by (dialer) to 4-by (destination)

The frequency allocation process has two instances. These agencies provide access to crucial information needed for choosing the right frequency and gap.

The first instance is the index in the SIN table of the subscriber station requesting a channel. With this index, the frequency assignment process can determine the normal modulation type of this subscriber. This index also informs the routine of where to place the result from its selector algorithms (ie frequency and slot number).

The second instance of the frequency assignment process specifies which category the frequency and gap request belongs to. The value of the other instance is either an index in the SIN table or the predefined, invalid value DB NULL. If a valid index is received, the frequency allocation request is identified as a request from the landing page in a subscriber-to-subscriber call and the option tables should be used. If DB NULL is received, the request is considered to be in the external source category, and the algorithm is used for the most available slot position.

The frequency assignment process gives the answer TRUE if a successful allocation of a frequency-gap combination · has been obtained, otherwise the answer FALSE is obtained.

526 967

The process also has a desirable side effect. If the allocation appears, the baseband index and gap fields of the SIN table are filled in for the subscriber from whom the request originates.

The frequency assignment algorithm can be divided into two steps. The first step, which is called the classification step, determines the category of the allocation request. The second step, which is called the selector. steps, finds and accomplishes the assignment of a frequency-lock combination using the appropriate algorithm defined by the category to which the assignment request belongs.

The classification step determines · first whether an automatic frequency selection is to be made. ' If the subscriber station from which the request originates has been brought into manual mode, the manually set modulation level, frequency and slot indicate which frequency-slot modulation combination is to be assigned. If the specified combination is available, the subscriber spm request is assigned from this frequency and this slot.

If the specified frequency slot combination is not available, the routine interrupts the treatment and responds the routine with FALSE. If the subscriber that the request comes from has been brought into automatic state, further classification is required.

Once it has been determined that an automatic selection will be made, the frequency allocation algorithm · determines the current request category. These categories are as follows: the external in case a destination subscriber station is called from an external telephone; external-out in case a calling subscriber station calls an external telephone; internally out in case a calling subscriber station calls another subscriber station; and internally in case a destination subscriber station is called from another subscriber station. If the request belongs to the External-In, External-Out or Internal-Out category, a slot position is selected through a search for the most available position. Once the position is selected, it is scanned

526 967 ⁷⁸ all frequencies in succession until a vacant door (or an adjacent door pair for a 4-time request) with the desired position is found. At this point, the routine places the correct values ​​in the SIN table, after which the routine stops the run and gives the answer TRUE. If the request belongs to the last category (internal-in), further information is required.

Two additional information bits are required for an internal-type request. The call subscriber's slot allocation and modulation type (4-when or 16-when) must be determined. When this is done, it is determined which option table1 to use based on the modulation type of both the calling subscriber and the destination subscriber. Once the correct table is selected, the calling subscriber's slot allocation is used to determine the correct row in the option table. Each position in the selected row contains a slot allocation with the same or lower rank nip.

This list is reviewed until the available hatch is found, whereby the review begins at the most desirable position and continues until all hatch positions have been scanned. For each hatch position (or each hatch pair ·; for 4-close connections), the frequencies are scanned one by one until the current hatch (or hatch pair) is found. The resulting frequency and gap values ​​are not entered into the corresponding SIN table, and the routine stops and returns the response TRUE.

A hatch count bar keeps track of the number of hatches available for each hatch position. These counts are stored in the database module and are retrieved by the frequency assignment process.

The SIN table contains relevant information for each of the system subscribers. The following accesses are made to the SIN table.

modulation level (read): The modulation level of the subscriber requesting a frequency is obtained from this table as well as the module52 * 967 ring level of the calling subscriber during the connection of an internal call.

slot number (read): The call divider of the calling subscriber when connecting an internal call · must be read.

slot number (write): Here, the slot allocation is applied to the subscriber requesting a channel.

baseband index (write): Here the frequency assignment is applied to the subscriber requesting a channel.

The BCC table was used for the frequency allocation routine's search for an available frequency-gap combination. The following accesses are made to the BCC table:

channel state (read): The state of a channel is checked for availability.

channel status (read): Channel status is checked for fixed. stating that the specified channel is a speech channel.

channel state (write): The channel state changes when the specified channel is selected for assignment.

channel control (write): The modulation type of the subscriber from which the request comes is entered into the channel control byte.

SIN index (write): Establishes a link from the selected channel to the subscriber from which the request originated.

Frequency assignment routines have direct access

526 967 to the database. This is necessary for speed and efficiency. As soon as possible, database boundary routines are utilized to provide access from the frequency allocation routines to data bases.

Subscriber Telephone Interface Unit (STU)

In its basic state, STU operates as an interface unit, which converts an analog signal received on a 2-wire connection from a standard telephone set into PCM-encoded digital samples at 64 Kbps. As shown in Fig. 12, the STU includes a subscriber line interface circuit (SLIC) 53, which is directly connected to a telephone set via wires 37. · The voltage and impedance of the SLIC 53 are adapted to the operation of the telephone. SLIC 53 further enables a ring current to be fed to the telephone set and also performs an on-hook / off-hook detection (ie detection of changed clock state). The output signals from SLIC 53 on line 54 consist of analog, voice frequencies. (TF) transmit and receive signals. These are then converted by a PCM codec 55 into PCM samples. The PCM codec 55 utilizes. a μ-255 compression algorithm to digitize the speech signals into 8-bit samples at a rate of 8 KHz. PCM codec 55 operates with full duplex. The digitized speech samples are then output on a line

56 to a well-established JUL multiplexer MUX 57. The operating state of the MUX is determined by a subscriber controller SCU 58, which communicates with the MUX 57 via a transmit and receive terminal FIFO mini 59. The SCU 58 contains mainly a microprocessor of model 8031. The SCU is connected to CCU 29 via an interface circuit 60 and controls the operation of SLIC 53.

STU can mainly work in one of three distinct states. The first, and most common, condition is the speech state. In this state, speech samples are transferred from PCM codec 55 via MUX 57 and a VCU drive / receive circuit 61 to VCU 28, where they are further processed to reduce the bit rate from 64 Kbps to 14.6 Kbps.

526 967 after which they were transmitted to be transmitted to the base station.

The second working state is the data state.

In this state, the data stream of 64 Kbps to or from VCU 28 does not contain any voice information. Rather, the information transmitted to the hash station consists of a reformatted data stream, which is obtained from an external data source at a channel data transmission rate of up to 14.6 Kbps. The STU also includes a data port 62 of type RS-232, which enables connection of a data unit (e.g., a terminal) via a conduit 63 using an asynchronous RS-232 standard interface capable of operating up to 9600 baud. The STU includes a · UART and clock circuit 64 (universal asynchronous receiver / transmitter), which is · configured to synchronize the data flow from the data port 62. VCU 28 packets the synchronized data so that it does not exceed the channel limit of 14.6 Kbps. In this state, the data transfer takes place at full duplex.

The third STU state is the call connection state. In this state, no data is transmitted from STU 27 via MUX 57 to VCU 28. However, a response tone generating circuit 65 is connected to MUX 57.

This circuit is configured to digitally form the tones utilized during the call setup procedures, such as busy tones and error indication tones. During call switching, the DTMF digits detected by the user are detected by a DTMF detector circuit · 66, after which the numbers are processed by SCU 58 for connection to the call. The response tone generating circuit 65 returns appropriate tones to the user's apparatus. A ring generator 67 is connected to SLIC 53. A clock generator 68 supplies clock signals to the PCM codec 55, the VCU drive / receive circuit '61, and the response tone generator 65. When the call setup is complete, the STU switches to either the voice state or the data state for communication with the base station.

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Another task of STU is to provide for the extinction of unwanted echo signals from the remote connections. The delay of a forward and return speech signal between the base station and the subscriber station will be well over 100 ms. Any reflected signal that occurs due to a lack of impedance matching at either side results in a disturbing, retransmitted echo.

In the base station, this problem is handled by an echo extinguishing system in the PBX function. In the subscriber station must

STU provide echo cancellation. At least 40 dB echo suppression is expected to be required from this extinguishment. However, the delay of the echo to be eliminated is very small, as the interesting reflection arises between SLIC 53 in STU and the local telephone system. This distance is typically only a few tens of feet, and the delay is essentially zero.

Microprocessor 8031 ​​in SCU 58 has the same function as RPU 20 and PBX call processor 24 in the base station. It communicates with the base station RPU 20 via the radio20 control channel (RCC). Transmits messages and controls all individual functions of STU 27. STU also communicates via the baseband control channel (BCC) with the subscriber station CCU 29.RS-232 interface to CCU 29 operates on 9600 baud and used for transmitting control information between CCU 29 and STU 27 at the subscriber station.

Voice Dialing Unit (VCU)

The speech code unit (VCU) includes four RELP speech compression systems, which operate at full duplex. The VCU structure is identical for the base station and the subscriber stations. In the subscriber station, only one quarter of the total capacity is utilized (ie only one of four channels is utilized). The interface to STU 27 in the subscriber station is identical to the interface used for each of the four PBX channels in the interface to the base station VCU 17. In VCU 17, a fully digital system is implemented to implement the RELP speech algorithm, as further described in U.S. Patent Application No. 667,446 under the title RELP Vocoder Implemented in Digital Signal Processors / which application shall be deemed to form part of the present description. Alternatively, a subband codec can be used. The processed data is transferred to CCU 18/29 on a common parallel bus interface / which is controlled by the CCU program. CCU 18, 29 sends control signals to VCU 17, 28 to determine the work state and configuration of VCU 18, 29. The following describes the working state, function and realization aspects of VCU 17, 28.

The interface between PBX 15 and VCU 17 is illustrated in FIG. 13. The interface between STU 27 and VCU 28 is illustrated in FIG. The rate ratio of the PBX and STU interfaces is identical and is illustrated in Figure 15. Table 10 indicates the significance of the designations used in Figure 15.

596

V Ο

967

Table 10

<td>JSymbol</td><td>Parameter</td><td>My</td><td>Type</td><td>Max</td><td>uNIT</td>

<td>Two</td><td>PBX frame width</td><td> —</td><td> 125</td><td> —</td><td>ps</td>

<td>TWL</td><td>clock pulse width</td><td> 1,8</td><td> 2,0</td><td> 2,2</td><td>Ms.</td>

<td>1 tw2</td><td>idle period gate 0</td><td></td><td> 93,75</td><td> —</td><td>Ms.</td>

<td>TW3</td><td>inactive period gate 0 gate 1</td><td> 5,9</td><td> 7,8</td><td> 9,7</td><td>Ms.</td>

<td>TW4</td><td>inactive period arind 1 gate ISLAND</td><td> 52,8</td><td> 54,7</td><td> 56,6</td><td>Ms.</td>

<td>In tdO</td><td>delay start pulse clock 0</td><td> 0</td><td> 250</td><td> -800</td><td>ns</td>

<td>] tdl</td><td>delay start pulse clock 1</td><td> 0</td><td> 250</td><td> -800</td><td>Nah</td>

<td>TD2</td><td>edge delay: clock 0 gate 0</td><td> 100</td><td> 1000</td><td> 2000</td><td>ns</td>

<td>td3</td><td>flankfördröj- ing: clock 1 gate '1</td><td> • 100</td><td> 1000</td><td> 2000</td><td>ns</td>

<td>Tso</td><td>preparation time - input</td><td> 20</td><td> 1500</td><td> —</td><td>ns</td>

<td>tsl</td><td>clarification time - output -</td><td> 500</td><td> 1800</td><td></td><td>ns</td>

<td>Tho</td><td>hold time output</td><td> 500</td><td> 2200 -</td><td> ——</td><td>ns</td>

526 967

The lines shown in Fig. 13 PBX SDAT 0.1, 2 and 3, which in the figure are designated 70, 71, 72 and 73 respectively, transmit data signals from PBX 15 to VCU 17 in the base station. At the subscriber station, the data signal is transmitted on a STU SDAT marked with 74, from STU 27 to VCU 28 (Fig. 14). 8-bit μ-255 compressed serial data is transmitted to the speech codec during the active portion of PBX / STU GRIND 0 or PBX GRIND 1-3 at a clock rate of 256 KHz. The data is clocked into VCU 17,

28 on the positive edge of the clock signal of 256

KHz.

VCU SDAT 0, 1, 2 and 3, which in the figure are designated 75, 76, 77 and 78 respectively, transmit data signals from VCU to PBX 15 in the base station. Cable 79 VCU SDAT

0 transmits data from VCU 28 to STU 27. in the subscriber station. 8-bit μ-255 compressed serial data is transmitted to PBX 15 or STU 27 from the speech codec during the active or positive portion of PBX / STU GRIND 0 or PBX GRIND 1-3 at a clock rate of 256 KHz. Data is clocked from vcu 17, 28 on the positive edge of the clock signal at 256 KHz.

With 80, 81, 82 and 83, lines designated PBX GRIND 0, 1, 2 and 3 respectively transmit gate signals from PBX 15 to VCU 17 in the base station. One with 84 marked! 5 wire STU GRIND 0 transmits a 'gate signal from STU.

to the VCU 28 Γ subscriber station. The gate signal is • an active high signal, which is used to activate. . The transmission on the lines PBX / STU SDAT 0, PBX SDAT 1-3 and VCU SDAT 0-3. This gate signal is active during⁰ eight consecutive clock periods every 125 ms.

With 85, 86, 87 and 88 designated lines PBX

CLK 0.1,2 and 3 respectively transmit clock signals of 256 KHz from PBX 15 to VCU 17 in the base station. A signal designated 89 STU CLK 0 transmits a clock signal of 256 KHz from STU 27 to VCU 28 at the subscriber station.

A clock signal of 256 KHz is used to clock the signals PBX / STU SDAT 0 and PBX SDAT 1-3 into VCU 17,

526 967 and the signals VCU SDAT 0-3 into PBX or STU

27th However, the clock signals are not synchronized with any of the clock signals generated in VCU 17.

18, CCU 18, 29, or modem 19, 30.

At the base station, the PBX / VCU interface converts four channels of synchronous serial data of 64 Kbps to 8bit parallel data, which is then made accessible to the four transmit codecs 16 at a sampling rate of 8 KHz. In the subscriber station, only one channel (channel 0) is converted by the STU-VCU interface. Required clock and gate signals are provided by PBX 15 and STU 27.

The PBX-VCU interface and the STU-VCU interface also account for the opposite function of the receive speech codecs.

In the base station, 8-bit parallel data received from the four codec channels is converted into four synchronous 64 Kbps serial channels for transmission to PBX 15. In the subscriber station, only one voice channel is transmitted, which is transmitted back to STU 27.

Hardware interfaces between VCU 17, 28 and CCU

18, 29 are illustrated in Fig. 16. The rate ratio of transmit and receive channels between VCU and CCU is shown in Figs. 17 and Fig. 18, respectively. The following Table 11 and Table 12 indicate the significance of the designations used in Figs. 17 and 18.

Note that Figures 17 and 18 show the events that occur during VCBTP in Figures 19A and 19B. The individual interface signal definitions are given in the following. the following section.

526 967

Table 11

<td>Symbol</td><td>Parameter</td><td>My'</td><td>Max</td><td>Unit</td>

<td>TDL</td><td>talkodekblocköver- marketing period</td><td> —</td><td> 750</td><td>ps</td>

<td>TD2</td><td>TCVC response time</td><td> 1,25</td><td> 15</td><td>ps</td>

<td>td3</td><td>CCU DMA response time</td><td></td><td> 1,25</td><td>ps</td>

<td>td4</td><td>delay handshake</td><td></td><td> 15</td><td>ns</td>

<td>. td5</td><td>VC blockperiodför- delay</td><td></td><td> 150</td><td>ps</td>

<td>THL</td><td>s bull data retention hole</td><td></td><td></td><td>ns</td>

<td>th2</td><td>status data retention</td><td></td><td></td><td>ns</td>

<td>th3</td><td>TC data retention</td><td></td><td></td><td>ns</td>

<td>tsl</td><td>control data clarification</td><td></td><td></td><td>ns</td>

<td>TS2</td><td>status data clarification</td><td></td><td></td><td>ns</td>

<td>ts3</td><td>TC data clarification</td><td></td><td> »</td><td>ns</td>

<td>TWL</td><td>write width</td><td></td><td></td><td>ns</td>

<td>Tw2</td><td>läsbredd</td><td></td><td></td><td>ns</td>

<td>TW3</td><td>request block</td><td> 1,5</td><td></td><td>ps</td>

*

526 967

Table 12

<td>Symbol</td><td>Parameter</td><td>My</td><td>Max</td><td>Unit.</td>

<td>TD6</td><td>blocköverförings- period</td><td></td><td> 750</td><td>ps</td>

<td>TD7</td><td>CCU data response time</td><td></td><td> 1,25</td><td>ps</td>

<td>TD8</td><td>VC response time</td><td> 1,25</td><td> 15</td><td>PS</td>

<td>TD9</td><td>handshaking delay</td><td></td><td> 15</td><td>ns</td>

<td>TDLo</td><td>VC blockperiod- delay</td><td></td><td> 150 .</td><td>PS</td>

<td>TH4</td><td>styrdatakvarhål1ning</td><td></td><td></td><td>ns</td>

<td>TH5</td><td>statusdatakvar- demeanor</td><td></td><td></td><td>ns</td>

<td>TH6</td><td>RC datakvarhål1ning</td><td></td><td></td><td>ns</td>

<td>s4</td><td>control data clarification</td><td></td><td></td><td>ns'</td>

<td>TS5</td><td>statusdataklar- attachment</td><td>f</td><td></td><td>ns</td>

<td>TS6</td><td>TC data clarification</td><td></td><td></td><td>ns</td>

<td>TW4</td><td>write width</td><td></td><td></td><td>ns</td>

<td>TW4</td><td>'reading width</td><td></td><td></td><td>ns.</td>

<td>TW6</td><td>request block</td><td> 1,5</td><td></td><td>ps</td>

Figures 19A and 19B show the coverage ratio of the various transmit and receive number blocks transmitted between VCU 17, 18 and CCU 18, 19 for 16-level phase shift modulation At the top of Fig. 19 is shown the system frame rate to which all transmissions are related. This frame rate also applies to Fig. 19B. A modem frame is 45 ms long and includes four tall hatches (or channels). Each number hatch consists of two system number block periods (SVBP) with

526 967 ⁸⁹ speech data, which periods contain 82 symbols each (5,125 ms for each period) and 16 initial data symbols, which take 1.0-ms of frame time.

On the transmit channels, a block of 328 bits (41 bytes) of processed speech data is transmitted from VCU 17, 28 to CCU 18, 29 before the beginning of each SVBP during a speech codec block transmission period (VCBTP). The 64 Kbps 64-bit input flow from VCU 64, which is associated with unprocessed speech blocks, is shown in the figure as divided into 22.5 ms long speech codec block periods (VCBP).

For the transmit channel 0 in Fig. 19A, raw VC input data in VCBP OA1 and 0B1 are associated with processed data in VCBPTP 0A1 and 0B1. Also note that VCBP for channels 0 and 2 is offset by half VCBP (ie, 11.25 ms) relative to VCBP for channels 1 and 3.

For the receiving channels (illustrated in FIG

19B), a block of 328 bits (41 bytes) of processed speech data is transmitted from CCU 18, 29 to VCU 17, 28 at the end of each SVBP during a VCBPT. Like the transmit channels, the time offset of the VCBP relative to the VCBPT is implementation dependent, and in Fig. 19B a (maximum) offset on a VCBP is shown. The relationship between the input and output of the speech codecs is shown in Figures 19A and 19B. For the receive channel 0, compressed speech data transmitted during VCBTP 0A10 and 0B10 is associated with the processed, expanded data stream in the

VCBPS 0A10 and OB.IO.

TCADDR lines 90 transmit broadcast channel address signals from CCU 18, 29 to VCU 17, 28. These three address lines are utilized to select the current broadcast channel address.

A TCDATA bus 91 transmits transmit channel data signals between VCU 17, 28 and CCU 18, 29.

A TCDAV line 92 transfers from VCU 17, 28 to

CCU 18, 29 a signal informing CCU 18, 29 that a data group is available in the TCDATA register. The TCDAV signal is low until a TCDACK signal is activated.

A line TCDACK 93 transmits a transmit data receipt 5226 967 signal from CCU 18, 29 to VCU 17, 28. The TCDACK signal engages the data on the · TCDATA bus and resets the TCDAV signal.

A line TCSCWR 94 transmits a transmit channel status / control write signal from CCU 18, 29 to VCU 17, 28. The TCSCWR signal enters the speech codec word in the correct transmit channel control register, which has been addressed by the signals on the TCADDR lines. Data is entered into the register at the positive edge of the TCSCWR signal.

A line TCSCRD 95 transmits a transmit channel status / control read signal from CCU 18, 29 to VCU 17, 28. The TCSCRD signal connects the stature / byte on the TCDAT Abuse from the voice codec status register that has been addressed by the signals on the TCADDR lines.

A line BLOCKRQ 96 transmits a block request signal from CCU 18, 29 to VCU 17, 28. The task of the BLOCKRQ signal is to initiate a data transmission of a block of 41 bytes from the speech codec (addressed by the signals on the lines TCADDR) to CCU 18, 29 over the TCDÄTÄ bus. The BLOCKRQ signal is used by the speech codec to start the VCBP beat.

Eri line TCVCRST 97 transmits a transmit channel · intended speech code reset signal from CCU 18, 29 to VCU 17, 28. The transmit speech codec addressed by the signals on the TCADDR lines is reset.

Wires RCADDR 98 transmits channel address signals from CCU 18, 29. to VCU 17, 28. These address signals are used to select the current receiving channel address.

A bus RCDATA 99 transmits receive channel data signals between CCU 18, 29 and VCU 17, 28.

A line RCDAV 100 transmits a receive channel data access signal from CCU 18, 29 to VCU 17,

28th The RCDAV signal informs the speech codecs addressed by the RCADDR lines that a data bit group is. accessible in the RCDATA register. The RCDAV signal engages the data on the RCDATA bus and in the RCDATA register and resets the RCDACK line.

526 967

A line RCDACK 101 transmits a receive channel data acknowledgment signal from VCU 17, 2.8 to CCU 18,

29th The RCDACK signal informs CCU 18, 29 that the data is read from the RCDATA register and that a new byte can be transmitted from CCU 18, 29.

A line RCSCWR 102 transmits a receive channel status / control write signal from CCU 18, 29 to VCU 17, 28. The RCSCWR signal enters the control word into the correct speech codec register, which has been addressed by the signals on the RCADDR lines. Data is entered into the register at the positive edge of the RCSCWR signal. .

A line RCSCRD 103 transmits a channel status / readout signal from VCU 17, 28 to CCU 18, 29. The RCSCRD signal engages the speech codec status word on the RCDATA bus from the status register addressed by the RCADDR lines.

A BLOCKRDY 104 line transmits a block-ready signal from CCU 18, 29 to VCU 17, 28. The BLOCKRDY signal is used to initiate a data transfer of a block of 41 bytes from CCU 18, 29 to the speech codec addressed by the RCADDR lines. The speech codec uses the BLOCKRDY signal to stop the VCBP rate. CCU 18, must have an accessible data bit group in the RCDATA register before the positive edge of the BLÖCKRDY signal.

A line RCVCRST 105 transmits a receive channel reset speech code signal. from CCU 18, 29 to VCU 17, 28. The speech codec addressed by the RCADDR lines is reset by the RCVCRST signals.

The receive channel VCU hardware receives input in the form of 41 byte blocks from CCU 18, 29 during a VCBTP, as shown in Figure 20A. After the data has been processed according to the current working state, the compressed 8-bit data with a rate of 8 KHz is transferred to the PBX or STU interface module. Data adaptation is performed in VCU 17, 28, so that the input and output requirements. at CCU 18, 29 is simplified. Control information is transmitted between VCU 17, 28 and CCU 18, 29 via a set

526 967 control and status ports for each receive channel at the beginning of a VCBTP, as shown in Fig. 18. The following operating states are supported by the receive coders:

In the external state, a speech bandwidth expansion is performed with an input rate of 14.6 Kbps (328 bits every 22.5 ms) and an output rate of 64 Kbps. Numbers can also contain DTMF tones.

In the internal state, previously compressed 14.6 Kbps data is transmitted from CCU 18, 29 via VCU 17, 28 to PBX 15 or STU 27. Since PBX 15 or STU 27 is configured to receive data at 64 Kbps, a the data flow is performed. Output (64 Kbps) is a resting bit group pattern (FF hex) until voice data is accessed from CCU 18, 29. Then, a sync bit group (55 hex) is output that is accompanied by the previously processed 41 data bit groups, after which the rest bit pattern is resumed. Figure 20A shows an example of input and output rate and content for 16-level PSK modulation.

In the silent state, input blocks with speech data from CCU 18, 29 are consumed without being utilized. A resting bit group pattern (FF hex) is output to PBX 1.5 or STU 27 to maintain line silence.

In the wait state, hardware diagnostics routines are executed, and the status information obtained is stored in the status register. Block transfers to CCU 18, 29 are not performed until the work state is changed by a block request, corresponding to VCBTPA. The new control word (and working state) is read by the speech codec, and the diagnostic status information is transmitted to CCU 18, 29.

The transmit channel VCU hardware receives an 8-bit μ-layer compressed PCM (at a sampling rate of 8 KHz) from the PBX / STU interface. After the data has been processed according to the current working state, the output is transmitted to CCU 18, 29 in 41 bit bytes during a speech codec block transmission period (VCBTP), as shown in FIG.

526 967 ⁹³

19A. Data adaptation is performed in VCU 17, 28, so that the input and output requirements of CCU 18, 29 are simplified. Control information is transmitted between VCU 17, 28 and CCU 18, 29 via a set of control and status ports for each transmit channel at the beginning of a VCBTP, as shown in Fig. 17. The following operating states are supported by the transmit decoders:

In the external state, a speech bandwidth compression is performed with an output rate of 14.8 Kbps. (328 bits every 22.5 ms) Processed speech data is transmitted in blocks of 41 bytes to CCU 18, 29. Voice data can also internally hold multi-frequency two-tone signals (DTMF signals).

In the internal state, previously processed speech data from PBX 15 or STU 27 is transmitted through VCU 17, 28 to CCU 18, 29. The 64 Kbps input stream contains a rest bit pattern (FF hex), a sync bit group. (55 hex), 41 previously processed, compressed voice data groups as well as additional lobes go upper until, 'the beginning of the next sync bit group. The speech codec searches the input for the sync bit group, which appears on a byte boundary, after which the speech codec adapts the 41 speech data bytes. The speech block is then transferred to CCU 18, 29 during / next VCBTP, as described above. Figure 20B shows an example of the rate and content of input and output for · 16-level PSK modulation. Segment 1 of the transmit channel is a sync bit group, and segment 2 is a processed speech data byte. The shaded segment corresponds to a resting bit pattern. Note that the sync and voice data groups do not extend beyond VCBP boundaries.

IN^;..this state: state is consumed, input speech data from PBX 15 or STU 27 without being used. The 41 bytes of speech output to CCU contain a silent speech pattern.

In the waiting state, continuous hardware · diagnostic routines are executed, and the resulting status information is stored in the status register. Block transfers to

526 967

CCU 18, 29 is not performed until the work state is changed by a block request corresponding to VCBTPA. The new control word (and work permit) is read by VCU 17, 28 and the diagnostic status information is transmitted to CCU

18, 29.

A code frame is defined depending on the realization requirements of the RELP algorithm, but the frame must be an integer sub-multiple of the speech code block period (VCBP), which is 22.5 ms long.

Due to the fact that PBX 15 and STU operate asynchronously in relation to internal system rate, means for detecting, reporting and compensating data failure and data failure must be included in VCU 17, 28. This condition occurs approximately once every 5000 VCBP . Since detection of data failure and / or data failure is implementation dependent, such errors are reported in the status word. Data shortage can be compensated by repeating the last speech sample if required, and data loss can be handled by ignoring one or more speech samples if required.

After a reset of one or more codecs, VCBTPA will be the first block transmitted from CCU 18, 29, as illustrated, for example, in Figure 19A.

Control channel unit (CCU)

The channel controller (CCU) performs the same functions in the subscriber stations and in the base station. The hardware used for the CCU function in the two station types is in fact identical. The software in the subscriber 30 station differs slightly from the software in the base station. CCU performs many functions in connection with information formatting and rate control when transmitting on the time-shared broadcast channels. Important authorities for CCU are received from four sources. The first instance consists of the actual digitized samples to be transmitted. These are transferred to CCU 18, 29 from VCU 17,

29th (Figures 2 and 3) These data may be coded number 5226 967 samples or data samples from RS-232 data port 10 in STU. (Fig. 12) In all cases, the digital channels operate at a rate of 16 'Kbps. Four channels can be processed simultaneously by CCU 18 as it operates in the base station with all four 16-level PSK broadcast channels in operation. The subscriber station CCU 29 handles only one flow, but this flow can be in any of the four slot positions belonging to the TDMA frame system. The second CCU instance comes via the baseband control channel (BCC) · from STU 27 (in the subscriber station) or RPU 20 (in the base station). This second authority provides control messages regarding work permits, status information and control information. Many BCC messages from. CCU 18, 29 are radio control channel messages (RCC15 messages) received by CCU 18, 29. CCU 18, forwards control information from the RCC messages to STU 27 or RPU 20, and in response, CCU receives control messages from RPU 20 or STU 27. This determines what CCU 18, 29 should do with the data from

20th VCU 17, 2.8. The third source of instances to. CCU 'provides clock and status information from modem 19, 30a. The modem 19 provides the master clock signal utilized in the VCU-CCU modem chain. In addition, the modem 19, 30a provides status of accuracy of its bit-tracking synchronization, RF AGC level settings, and other goodness indicators used by CCU 18, 29 to determine whether communication reliability on the channel is acceptable. CCU 18, 29 attempts to control the fine tuning of modem 19, 30a modes of operation through commands to change transmit power levels, AGC levels, and rate / distance calculations. Quality level measurements on modem transmissions are reported to RPU 20 or STU 27. The fourth source of source is the modem data received in the form of symbols of up to four bits each (depending on the modulation level). These symbols are processed in a buffer, multiplexed and output to the receiving circuits in VCU.17, 28 to be decoded.

526 967 ⁹⁶

Fig. 21 is a block diagram of a CCU. The CCU architecture is substantially the same as the architecture of two direct memory access type (DMA) one-way data channels with an intelligent, such as a microprocessor designed controller or controller. The DMA channels have the task of transferring data from the VCU to the modem and vice versa. The CCU interface to the VCU includes two parallel DMA buses, namely a TX bus 107 for the transmit channel (VCU to CCU to modem) and an RX bus 108 for the receive channel (modem to CCU to VCU). Data processed by the VCU transmit circuits is stored in the VCU memory until the CCU requests a DMA transmission. 41 bytes. is transferred to CCU during each block transfer period.

Two of these blocks are transmitted for each active voice channel (up to four voice channels in the base station) per TDMA frame. CCU receives these transmit bytes via a transmit codec interface module (TVCIM) 109 and laws them in a transmit memory module (TMM) 110. Depending on the channel's current operating state, a control / sync lead is added to the coded speech byte groups by a CCU processor included in one. microcontroller module (MCM) 111, whereby a complete speech packet is formatted for transmission to the modem via one transmit modem interface module 112. MCM 111 maintains frame rate information and transmits the data to the modem at the correct time. Before transmitting the transmit data to the modem, it is converted by MCM 111 from the eight-bit bit group format used by the CCU into a symbol format, which, depending on the modulation level of the slot, contains 1, 2 or 4 bits per symbol.

The reverse processing is performed for the receiving data from the modem. The data from the modem is received by a receive modem interface module (RMIM) 114 and stored in a receive memory module (RMM) 115. This data is then converted from the format used by the modem with 1, 2 or 4 bits per symbol to the eight-bit byte format used internally by CCU and all other baseband treatment. MCM 111 removes preamble and guide bits

526 967 from the data flow received on the RX bus 108 based on · its knowledge of frame rate, which is fed from the modem to a frame rate module (FTM) 116, and based on its own identification of different code words in the symbol flow. The converted data is fed via a receive speech codec interface module (RVCIM) 117 to the VCU.

CCU also provides for link level control of radio controlled channel transmissions (RCC transmissions) at both the base station and the subscriber stations. In the base station, only one CCU is activated by the RPU for processing the RCC channel.

The CCU controls the reception and formatting of messages from the RPU in the base station to the STU controller in the subscriber stations. This control function at CCU includes both detection and error checking in RCC messages as well as formatting and packaging of such RCC information intended to be transmitted over the radio link. CCU also detects collisions on the incoming

RCC at the base station. CCU controls the power and distance calculations for the subscriber stations in which initial capture attempts are in progress. The protocol for capture and other RCC functions has been described above.

Fig. 22 shows the program-implemented functional architecture of CCU. The CCU has free separate data paths, namely the TX bus 107 for transmission, the RX bus 108 for reception and a local bus 119 for the microcontroller. The microcontroller 111 shares the TX bus 107 with a DMA controller 20 (direct access to memory controller) and shares the RX bus 108 with a receive DMA controller 121. The microcontroller 111 utilizes these buses to control the DMA peripheral controllers, control and status registers 122 and to access both the transmit buffer memory 110 and partly the receive buffer memory 115. The control and status registers 122, which are located adjacent to the local bus section of the microcontroller 119, to

RFU, modem and CCU hardware. An RS-232C link 123 between RPU and CCU is supported by a UART on the microcontroller chip 111. In the subscriber station, RPU is exchanged

526 967 ⁹⁸ against STU, but the interface is still the same.

The microcontroller 111 has access to three physically separated RAM areas, namely a local RAM, the transmit buffer and the receive buffer. The local RAM can be further divided. in an on-chip RAM and off-chip RAM. The microcontroller has access to the transmit buffer and receive buffer only when the corresponding DMA controller is free.

The transmission buffer 110 is divided into distinct segments. Each segment contains the skeleton of a speech or RCC packet, which is ready to be transmitted over the channel. The introduction and the unique word (RCC only) are constants that are initiated by the microcontroller 111 after a CCU reset. The code word (speech only), voice data and RCC data are • entered into the transmit buffer 110 of the microcontroller just before the DMA transfer to the modem 19, 30a. Since the radio control channel null ACK is a fixed message transmitted at a high frequency, this message is stored as a separate unit in the transmission buffer 110.

The receive buffer 115 is divided into a number of distinct Segments. A segment is intended for storing voice data which is stored in the buffer and transmitted in a VCU block. RCC data is stored in the buffer separate from voice data so that it can be stored for a longer period of time. If required, the microcontroller 111 can keep the RCC history for two frames in the receive buffer 115, thereby making the RCC copy process (from the buffer to the local RAM) less time-critical.

The local RAM contains the work variables used by the microcontroller 111. An important data structure stored in this memory manages the baseband control channel (BCC) between CCU and RPU. A registry bank at the local RAM is intended to provide important queue information to the RS-232C interrupt handler. A pointer and longitude field in this bank defines the active transmit data block (TXDB), from which data is read and transmitted. TXDB contains length and pointer information to the next TXDB in the queue, whereby a linked list is obtained. On the receiving side is utilized

526 967 a circular buffer for storing incoming data bit groups. When a full message is received, the interrupt handler flags the serial code to interpret the message.

The microcontroller 111 has access to the modem, RFU and control and status registers 122 in CCU via its local bus 199. over this bus, the microcontroller 111 can also reach the TX bus 107 and the RX bus 108 via insulating logic circuits 124 and 125, respectively. To avoid collisions, the remote buses 107, 108 are accessible only to the microcontroller 111 when the corresponding DMA controller 120 or 121 is in rest. .

CCU and RPU communicate via a link 123 through a full duplex RS-232C interface, called baseband control channel (BCC). Asynchronous characters are binary bytes · of eight bits and transmitted at a rate of 9600 baud. For a data bit group frame, a start bit and a stop bit are utilized. Messages end with a unique, byte, using a bit-fill technique to avoid getting the unique byte within a message. An alternating bit protocol and an 8-bit checksum are used to ensure link quality. ·.

Two external interruptions are handled by the microcontroller.

One is generated by the transmit DMA controller 120 and the other is generated by the receive DMA controller 121. These interruptions occur when the corresponding controller 120, 121 terminates its block transfer, thereby transferring control of its bus to the microcontroller 111.

The BCC interface is driven by an internal interrupt.

The program is interrupted upon receiving or transmitting a byte.

At the base station, the microcontroller 111 of the CCU is responsible for controlling and monitoring the entire four-channel data path assigned to this controller, which data path.

includes VCU 17, 28, CCU 18, 29, modem 19, 30a, and RFU 20, 31a. The microcontroller 111 of the subscriber station controls and monitors the same hardware but handles only

526 967

100 a data path. CCU is in turn controlled by RPU (in the base station) or by STU (in the subscriber station).

CCU provides VCU with information on work permits. Changes in work permits occur only at boundaries between system gaps. During speech compression, the CCU also provides the VCU with information regarding the position of the VCU block in the system door (there are two VCU blocks' for each system door). VCU addressing is performed by CCU prior to a data transfer, which completes the MUX / DEMUX process. CCU reads VCU status after each block transfer and stores appropriate statistics information. CCU can also initiate a VCU machine reset and / or a VCU.

The microcontroller 111 feeds information about the current modulation level to a symbol-to-byte group converter 126 on the RX bus 108 and to a byte-to-symbol converter 127 of the TX bus 107.

The modem receives information about what type of data is received, ie RCC or speech, because different capture procedures are utilized when receiving RCC20 and voice data. The modem provides the CCU with a partial clock offset value, an AGC level value, and a link quality value for each slot. The CCU frequency assignment is performed by RPU or STU. CCU controls the initiation of modem reset, self-test or a learning state for the received page.

CCU handles full-duplex data flow via transmit and receive buses 107, 108. During a given slot time, transmit speech data is transmitted from the VCU in the form of a block via the transmit DMA controller 121 to the transmit buffer 110. Each block has the length of a VCU block, therefore two such transmissions are required for each voice channel. CCU provides the VCU with the correct channel address prior to transmission, thereby performing the multiplexing operation.

An introduction and a code root, which data is stored in the transmit buffer 110, are transmitted in front of the VCU data at the beginning of each slot. The transmit DMA controller transmits data from the transmit buffer to a re-clocking 526 96?

101

FIFO stack 128, whereby the modem receives data from the FIFO stack 128 if needed. Conversion from byte to symbol is performed during the transmission of the byte-to-symbol converter 127. Control of the transmit DMA peripheral control unit is performed by the microcontroller simultaneously with the formation and insertion of the speech packet codeword.

The receipt side data flow is largely a mirror image of the transmit side's data flow. As data is received from modem 19, 30a, it is written into a feedback FIFO stack 129. The receiving DMA controller 121 empties as needed over the contents of the FIFO stack 129 in the receive buffer 115 Symbol-to-byte conversion is performed by symbol-to-byte converter 126, and frame rate is obtained from a clock circuit 130. Alignment of bit boundaries is performed automatically once the channel has been synchronized. Once a complete VCU block has been received, it · · in the form of a DMA block is sent to the correct VCU. The receiving DMA controller is controlled by the microcontroller 111.

Password word detection is performed for each slot. The microcontroller 111 performs this task by copying the code word byte into the local RAM and comparing it. with one list of valid code words. Under each slot, the modem 19, 30a provides some symbol offset and an AGC value. The microcontroller 111 reads these values ​​and interprets them appropriately. If there are any power or distortion problems, the subscriber station is informed. to this via the transmit password.

RCC transmit data is synthesized in transmit buffer 110 by CCU in accordance with the contents of the RCC message queue. If the RPU has sent an RCC message to the CCU, this message is formatted in the transmission buffer 110. Otherwise, the message NULL KNOWLEDGE is permanently stored in the transmission buffer 110. As soon as the RCC package is complete, the DMA transmits the RCC preamble, the unique word and the RCC data to the modem 19, 30a when needed. CCU performs collision detection and matches the outgoing RCC collision detection bit · with

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102 the result of the detection.

The RCC nine-stroke data manager can operate in two states: frame search and monitoring. In the frame search state, the RCC channel is considered to be out of sync.

Each incoming RCC message must be synchronized using a unique word detection algorithm. In the monitoring state, the RCC channel is synchronized and the algorithm for searching for the unique word is not called. The base station is always in the frame search state, because subscribers at the wrong rate can transmit at any time. At the subscriber station, the RCC data manager is in the monitoring state 11, provided that the station has established RCC synchronization.

In the frame search state, the unique word (UW) is detected after each RCC hatch. The microcontroller .111 performs this task by using a scanning technique to search for the unique word inside a window around the unique word's nominal position.

By successfully detecting the unique word, the CCU receives symbol rate information.

RCC reception data is transmitted from modem 19,

30a to the receive buffer 115. Once the transmission is complete, the RCC data is copied into the local RAM of the microcontroller to be processed. Received RCC packets are filtered by CCU. An RCC packet is only forwarded to the RPU if the -unique word is detected and the CRC is correct.

During RCC operation, the corresponding VCU channel is put in a standby mode. During this channel period, there is no data transfer between the VCU and CCU, neither on the transmit data path 107 nor the receive data path 108.

The program is executed in an Intel 803 microcontroller 111, the program memory is created by an external EPROM on the microcontroller's local bus. The program must be able to respond to every request for DMA service in real time and maintain a data flow of up to 64 Kbps in both directions without data loss. FIFO buffer management

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103 in the stacks 128 and 129 of the modem interface provide the dead time required by the microcontroller 111 to perform the DMA block transmissions and system control functions.

The software is divided into five separate modules:

a monitoring module, a data transfer module, a BCC transmitter receiver module, one BMM control module and an auxiliary module. Each module is designed to have only one input and one output, except for interrupt10 and error states. Another exception to this rule is the auxiliary module, which contains a set of auxiliary routines that are directly accessible from the other modules. In general, inter-module communication takes place using global variables, which are defined in separate data segments.

monitoring modules include an initialization function, provide overall program control, and perform basic self-test functions.

Data transfer module a urider supports the control of data transmission over TX bus 107 and RX bus 108 for both speech and RCC data, performs sync detection for all modulation levels for both speech and RCC data and supports RS-232 communication link 123 between CCU and RPU.

The BCC Transmitter Receiver module performs BCC transmit and receive functions, manages the BCC queues, formulates BCC transmit messages, processes BCC receive data and feeds in and out of the CCU via BCC RCC data.

The BBM control module controls the RFU, modem, VCU and CCU30 hardware via registers, reads and interprets status information from these units (eg modem AGC, link quality and symbol clarity), decodes input code words in the reception speech channel, formats the transmit speech channel codewords, provides a software / hardware real-time clock and performs online self-tests.

The auxiliary module performs various auxiliary procedures, which are called by the other modules.

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The CCU software is divided into four separate processes, operating essentially in parallel. Three of these are BCC data processing, a TX DMA process and an RX DMA process, which processes are interrupted and only called when. a special event calls for attention. All these three event-controlled processes are included in the data transfer module. The remaining process, which is distributed among all the modules, is a background process that initiates, controls and monitors the other three processes.

When BCC messages arrive from the RPU (or STU in the subscriber station), the BCC data process provides reception and buffer processing of these messages. Once a full message has been received, the background process receives information from the BCC data process via a mailbox. ' The background process examines this mailbox during its main loop and thereby detects any new messages. Messages are interpreted by the background process and necessary action is taken. Any replies are entered into the BCC broadcast message queue of the background process, and the BCC data process is notified in.

^v proper order.

BCC messages can initiate a reconfiguration of the CCU data channels. The required control information is written to modem 19, 30a and VCU 17, 28 at appropriate times. The modem responds to a new control word at hatch limits. VCU expects state changes.

takes place on the first VCU block transfer of a slot boundary. The background process is responsible for maintaining the correct control rate.

Status gathering is performed by the background process,

TX DMA process and RX DMA process. The last two collect status words from the TX side and the RX side of the VCU. This is necessary because these status records. Are accessible only via the TX bus 107 and the RX bus

108, which are only available for limited periods of time. The background process collects status information directly

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105 from the modem 19, 30a via the status registers 122 on the local bus 119. Upon completion of collection, all status information is collected by the background process. after which it is stored in specific status variables. Each status request received from the RPU is processed by the background process with this status history as the starting point.

Some of the status information, such as the AGC value and the partial bit offset, may call for CCU action.

In addition to storing such data as status history, the data is also used to correct the power and distance problems on the subscriber side. Regarding RCC messages, power and distance information was transmitted directly to RPU as part of RCC. The background process performs this function by formatting a BCC message containing RCC, AGC and distance data. Once the packet is complete, it is placed in the BCC transmit queue, and the BCC data process is notified. For voice channels, this status information is used for formatting of code words which are included in broadcast speech packets. The background process performs the function of this formatting and controls the transmission of the code word through the speech channel. All code words must be transmitted in five consecutive frames, giving a 5: 1 redundancy coding. The TX DMA path automatically sends the code word selected by the background process.

The background process also provides a software / hardware real time clock. Such a clock is accomplished by scanning and counting the spills of the clocks of one of the 8031 ​​units. This time clock function provides a time base for program time triggers and other time-dependent events. The background process checks that the system rate is maintained by scanning CCU machine error indicators and verifying that data transfer events occur at designated times in the system frame. System frame information is obtained via the system frame 35 start status line and a clock sensor connected at 130 at 16 KHz. Data synchronization is performed by the background process.

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The BCC data process responds to interruptions in the RS-232 port, which can occur both for the port's transmission direction and the receive direction. The process simply outputs another byte on the transmit page or inputs another byte on the input page. Boundary characters for message end on the receive page cause the BCC data routine to notify the background process.

The TX DMA process and the RX DMA process handle the DMA transmit channel and the DMA receive channel.

Below is a step-by-step description of the program-controlled data transfer function. Events in the data transfer process are marked with DMA controller interruptions. The interrupt occurs after the DMA controller completes the assigned block transfer. Each walkthrough starts at the beginning of a hatch data transfer. Attached Figures 23 and 24 may be helpful in reviewing this section. Fig. 23 is a clock diagram showing transmission of RCC data and 16-PSK voice data on the CCU transmission bus. Figure 24 is a rate chart showing transmission of RCC data and 16-PSK voice data on the receiving bus of CCU. Tables 13 and 14. below indicate the significance of the time symbols used in Figures 23 and -24.

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Table1 13

<td>time Symbol</td><td>Operation'</td><td>Max (Ps)</td><td>My (Ps)</td><td>Type (ps)</td>

<td>^fcS</td><td>CCU DMA clarification</td><td> 150</td><td> —</td><td> 100</td>

<td>+ VCB</td><td>VCU DMA transfer</td><td> 600</td><td> —</td><td> 100*</td>

<td>^fcRCC</td><td>RCC transmission from CCU</td><td> —</td><td> —</td><td> 900</td>

<td>^hrsM0</td><td>RCC TX Moderate Blocks</td><td> ---.</td><td> 10350</td><td> 10350</td>

<td>^fcM2</td><td>l: a RX modem block</td><td> —</td><td> 4300</td><td> 4300*</td>

<td>^fcM3</td><td>2nd a.RX modembi also</td><td> -·—</td><td> 4225</td><td> 4825* /</td>

* Based on RELP VCC

Table 14

<td>time Symbol</td><td>Operation</td><td>Max (Ps)</td><td>My (Ps)</td><td>Type (ps)</td>

<td></td><td>CCU DMA clarification</td><td>15Ό</td><td> ——</td><td> 100</td>

<td>^fcVCB</td><td>VCU DMA transmission</td><td> 600</td><td> —</td><td> 100*'</td>

<td>^fcM0</td><td>1st TX modem lock</td><td> —</td><td> 5225</td><td> 5825*</td>

<td>^fcMI</td><td>2nd TX modem block</td><td> —</td><td> 4225</td><td> 4825*</td>

<td>^fcM2</td><td>RCC RX modem block</td><td> —</td><td> 5600</td><td> 5800*</td>

<td>^fcRCC</td><td>RCC transfer to CCU</td><td> —</td><td> —</td><td> 900</td>

* Based on RELP VCU

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Transmission function - RCC

1st Receive TX DMA transfer end interrupt. This indicates that the treatment of the previous hatch has been completed and that treatment of the next hatch can begin. The TX DMA process is called.

a. Print control channel and modulation switching information. This information is required in modem 19, 30a and byte-to-symbol converter 127.

b. Format pending RP.U RCC messages in the transmission buffer 110. Otherwise, prepare and send the zero acknowledgment message.

c. Initiating and activating DMA Transfer from the transmission buffer 110 to the modem 19, 30a under the designation of the RCC introduction, the unique word and the RCC data block.

D. End the interruption and return to back-ground treatment.

Transmission Function - Speech

1st Receive TX DMA transfer end interrupt. This indicates that the treatment of the previous hatch has been completed and that treatment of the next hatch can begin. The TX DMA process is called.

a. Print voice channel and modulation switching information for the next cover. This information is required in modem 19, 30a and in the byte-to-symbol converter 127.

b. Select VCU port address and enable DMA transfer from VCU to transmit buffer 110.

c. Type the VCU control word.

d. Cancel VCU for transfer start.

e. End the interruption and return to background processing.

2nd Receive TX DMA transfer end interrupt. This indicates that the transfer from the VCU from the transmit buffer • 15

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109 has been completed. The TX DMA process is called.

a. Read the VCU status word.

b. Enter the code word for the transmission buffer 110.

c. Initiate and activate DMA transmission from the transmit buffer 110 to the modem 19, 30a under the designation of voice input, code words and speech data blocks.

d. End the interruption and return to background processing.

3rd Receive TX DMA transmission end interrupt. This indicates that the first half of the slot transfer from the transmission buffer 110 to the modem 19, 30a is completed here. The TX DMA process is called.

a. Select VCU port address and enable DMA transfer from VCU to the transmit buffer.

b. Type the VCU control word.

c. Cancel VCU for transfer start.

d. End the interruption and return to background processing.

4th Receive TX DMA transfer loop interrupt. This indicates that the transfer from VCU to the transmit buffer has been completed. The TX DMA process is called.

a.; Position the VCU status word.

b. Initiate and activate DMA controller 120 · for transfer from transmission buffer to modem.

c. End the interruption and return to background processing.

Reception Function - RCC

1st Receive RX DMA transfer end interrupt. This indicates that the treatment of the previous hatch has been completed and that treatment of the next hatch can begin. The RX DMA process is called.

a. Preparation for BPSK modulation. This information is needed in the symbol-to-byte group of the converter 126. Modem 19, 30a has already received this information at this time.

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110

b. Initiate and enable DMA transmission from modem 19, 30a to the receive buffer 115 of the RCC message.

c. End the interruption and return to background processing. AGC calculation and processing of uncertain bit synchronization takes place at this time.

2nd Receive RX DMA transmission end interrupt. This indicates that the RCC transmission from the modem 19, 30a to the receive buffer 115 has been completed. The RX DMA process is called.

a. Copy the RCC into the local RAM.

b. End the interruption and return to background processing. Prepare to forward the received RCC data to the RPU if the unique word is detected and the checksum is correct.

Reception Function - Speech

1st Receive RX DMA transfer end interrupt. This) indicates that processing of the previous hatch has been completed and that treatment of the next hatch can begin. The RX DMA process is called.

a. Preparation for tent data with proper modulation. This information is required in the symbol-byte group converter 126. The modem, at this time, has already received this information.

b. Initiate and enable DMA transmission from modem 19, 30a to the receive buffer for the first half-slot with speech data.

c. End the interruption and return to background processing. AGC computation, incomplete bit synchronization management and password processing should take place at this time.

Receive RX DMA transmission end interrupt. This indicates that the first half of the slot transfer from modem 19, 30a to the receive buffer 115 is complete. The RX DMA process is called.

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111

a. Select VCU port address and enable DMA transfer from receive buffer 115 to VCU. Cancel VCU for transfer start.

b. End the interruption and return to background processing.

3rd Receive RX DMÄ transmission end interrupt. This indicates that the first half of the slot transfer from the receive buffer 115 to the VCU has been completed. The RX DMA process is called.

a. Initiate and activate DMA controller 121 for transfer from the modem to the receive buffer for the other half of the slot.

b. End the interruption and return to background processing.

4th Receive RX DMA transmission end interrupt. This indicates that the transfer of the second half of the modem 19, 30a to the receive buffer 115 has been completed. The TX DMA process is called.

a. Select VCU port address and enable DMA transfer from receive buffer 115 to VCU. Cancel VCU for transfer start.

b. End the interruption and return to background processing.

CCU program execution

Program execution starts as a result of a hardware reset, and the flow begins in the monitoring module. The monitoring module takes care of any hardware and software initialization before starting the main loop. After a hardware reset and upon request from the RPU, the monitoring module performs some basic self-test functions. The main loop gains access to the other modules in succession.

the structure of the monitoring module is such that the processes are divided into less manageable time pieces, which · guarantees that the main loop has an acceptable worst case periodicity. Processes that require real-time response are handled via interrupt assistance routines.

/ 35

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Each interrupt assistance routine performs a minimal processing to fulfill the request for assistance. The purpose of this is to preserve as far as possible the serial property of the program execution and to keep the interrupt queues to a minimum. An interrupt auxiliary routine will typically transfer data to or from an interface and set a boole symbol to indicate that the action has been taken. A serially executed code, to which access has been obtained from the main help loop, then takes over the required information processing.

The microcontroller 111 of the CCU is a data flow machine, in which the program event is controlled by the arrival and departure of data. An accurate system rate is the basis for this data flow. However, program events are obtained directly.

from the data stream and not from sister frame markers.

This method allows the software to respond to real events (such as a data I / O request) instead of artificial events (such as a system clock tick). The software relies on the hardware. to transform the previous asynchronous action into events, stitches are synchronized with the system framework.

In order for this to work, it is necessary that software is guaranteed to have current things initiated and completed before the system framework event occurs.

It is therefore obvious that the CCU software, since it is not heavily loaded, is called in to respond to events and to complete certain tasks within a limited time. This real-time processing is uninterrupted and therefore requires special attention to its.

construction. There are four potentially conflicting real-time events requested by the microcontroller: DMA Transmission Events. DMA reception events, RS-232 broadcast events and RS-232 reception events. RS-232 interruptions have the lowest priority, since they occur with a maximum rate of one interrupt per millisecond. The software is set up so that the time limit of one millisecond is not exceeded. Response times for voice and RCC data management are

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113 more critical, and below is a discussion of these response times.

The relative rate ratios of the data transmissions on the transmit bus and receive bus are shown in Figs. 23 and 24. The diagrams are roughly to scale and show a worst-case rate ratio. The diagrams clearly show the time multiplexed mode of operation of the sending bus and the receiving bus. The dark transverse lines shown on the transmission and reception paths correspond to the activity of the microcontroller on the corresponding bus (t_g, t_R+). During this time, the corresponding DMA controller 120, 121 is at rest. The short periods of time (t_VCB) between the clarifications of the DMA controllers correspond to VCU block transfers. During these time periods, the DMA controller operates against the corresponding VCU. For the rest of the time (t_MQ, t_MI, t_M2, t_M3) the DMA controller 120, 121 operates for the modem interface.

The re-clocking FIFO stacks 128, 129 at the interface of the modem account for the main, in the clock diagrams, implied requirement of the beat. The FIFO stacks can store 16 symbols, giving a buffer time of one millisecond before the stack reaches its upper limit (TX) or its lower limit (RX). During this millisecond, the CCU can utilize the transmission bus 107 or the receive bus 108 to complete block transfers to and from the VCU or to copy RCC data into the local RAM.

The CCU program performs an internal self-test and places the VCU, modem and RFU in their rest state at startup. The microcontroller 111 monitors the system frame and initiates block transmissions to allow the VCU to achieve synchronization. Once data transfers have been initiated, the microcontroller 111 utilizes the DMA block end interrupt to regain the system rate. This interruption is directly linked to the data throughput in the CCU and therefore to the symbol clock 130 at 16 KHz. The VCU implicitly maintains the system rate via each DMA transmission request generated by the microcontroller 111 in response to the block end failure. The microcontroller 111 continues to

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114 monitor the frame rate to ensure that the correct system operation is maintained.

At the subscriber station, the system start-up also entails radio synchronization. This is done by locating RCC and by extracting the system rate from RCC. Once the reception rate has been established, the microcontroller 111 establishes the transmission rate with the base station.

The data transfer module supports real-time and background data transfer events in CCU. This module provides data transfers on the transmit data path, receive data path, transmit BCC and receive BCC. All of these events are interrupted events that require real-time responses. The module also performs synchronization and monitoring as a background process.

The transmit data path manager is called when the transmit DMA controller 120 needs help. This typically occurs after a DMA block transfer, when the DMA peripheral unit triggers a block transfer end interrupt. The interrupt is received on one of the two external interrupt lines of the microcontroller 111 (model 8031). The assistance requested by the interrupt depends on the type of data transfer, ie RCC or speech, and the duration of the data within the slot.

'Transmission data interruptions occur at predictable time periods during each slot period. The times and lengths of the interruptions are illustrated in Figs. 23 and 24. On each occasion, the microcontroller 111 is instructed to initiate the DMA peripheral unit for the next block transfer. This operation must be performed within 150 ps from interrupt request to interrupt completion. Regarding

RCC data, the first auxiliary request orders the microcontroller 111 to format the RCC message in the transmit buffer 110 prior to the DMA transmission. This operation must be completed within 900 ps. Since the operations on the transmission route are usually short and require quick answers, the interruption has been assigned the highest priority.

The only magnitude of the transmit data path interrupt handler is that captured after the VCU block transfer

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115

VCU status word. This status word is analyzed by the program in the BBM control module.

The receive data path manager is called when the receive DMA controller 121 needs help. This typically occurs after a DMA block transfer, when the DMA peripheral triggers a block transfer termination interrupt. The interrupt is received on one of the two external interrupt wires of one of the microcontroller 111 (model 8031). The assistance requested by the interrupt depends on the type of data transfer, ie RCC or speech, and the duration of the data transfer within the slot.

The receive data path interrupt occurs at predictable time periods during each slot period. The times and lengths of the interruptions are illustrated in Figures 23 and 24. At each occasion, the microcontroller 111 is instructed to initiate DMA controller 121 for the next block transfer. This operation must be performed, within 150 microseconds from interrupt request to interrupt completion, if DMA initiation is the only task to be performed. For RCC data, the last auxiliary request orders the microcontroller 111 to copy, after the DMA transmission,

The RCC message from the receive buffer 115 into the local RAM. This operation must also be completed within 900 ps. Since transmit road events can occur during this time, receive path interruptions have lower priority than the transmit interruptions.

The receive data path interrupt manager makes the VCU status word available after each VCU block transfer. This status word is analyzed by the program in the BBM control module. The handler also reads new RCC messages from the channel, which are then interpreted in the BCC transmitter-receiver module.

The BCC receiving module is implemented via the on-chip unit RS 232 UART. UART can generate an internal interrupt, which is triggered whenever a byte is received or transmitted. The BCC manager interrogates a status bit to determine which of the two cases caused the interruption and then continues to 35 manage the corresponding port.

The baud rate generator is programmed to a nominal rate of 9600 baud, resulting in a maximum of 1920

526 967 ¹¹⁶ interrupt per second. Each interruption must be rectified within 1 ms to avoid data loss. Since the typical interrupt frequency is Train and the response time is relatively long, BCC data transmission interrupt has a low priority.

The BCC data transfer manager uses pointers to place data in the queue at reception and to remove • the data from the queue at transmission. Here, only link level processing is performed, including byte fill and message end insertion. These measures are described in the system10 interface specification.

There is very little data processing in the BCC transmitter receiver module. The main task of the module is to queue data and remove data from the queue while handling the transmit, receive, and BCC data paths.

The data synchronization capture and monitoring described below comprises the main functions of this module.

Sync word detection involves a synchronization operation at the symbol level. The term syncord is an 'all20 term', which corresponds to the unique word in

RCC and the code word in the speech channels. The unique word (UW) is a fixed 8-bit pattern, which is placed at the beginning of an RCC message. A code word (CW) is · generally one of eight possible 8-bit patterns, which is applied at the beginning of a speech channel. In addition to its synchronization function, code words are used to indicate connection status, power settings and distance settings.

The base station's CCU must continuously search for a valid RCC message in each slot. CCU performs this task by searching for the unique word within a window of +3 symbols around the nominal UW position, calculated in terms of the master system rate. The search algorithm starts at the nominal UW position and switches a symbol to the right and a symbol to the left until it (1) finds the UW pattern and (2) verifies a correct RCC check sum. The search ends as soon as (1) and (2) are up £ 9 £ &lt;7

117 filled or all possibilities have been exhausted. The switching information, the RCC message and the power information were transmitted to the RPU after one successful search. During each number slot, the base station CCU searches for a valid code5 word in the received speech data. In this case, only the nominal code word mode is scanned, since no active symbol synchronization is performed during speech processing. If any code word is not detected for five consecutive frames, the channel is declared out of sync and informed

RPU on this condition. At this point, it is the RPU's task to take appropriate action. Synchronization is considered to be restored if a successful codeword detection has been obtained during three of five consecutive frames.

When the subscriber station CCU receives RCC data, this unit may be in one of two states: frame search mode or monitoring state. Frame search mode 11 is utilized to capture reception frame rate from the incoming RCC data and begin automatically when receive RCC synchronization is lost. The monitoring state is initiated as soon as the reception frame synchronization has been '-' established.

When the CCU subscriber station is in the paging search state, it must continuously search for a valid RCC message for each RCC slot. On the same . in the manner of the base station CCU, it performs this task of searching for the unique word within a window of ± 3 symbols around the nominal UW position, calculated in terms of the rate obtained from the modem's detection of the AM hole. The search algorithm starts at the nominal UW position and switches a symbol to the right and a symbol to the left until it (1) finds the UW pattern and (2) verifies a correct RCC check sum. The search is interrupted as soon as (1) and (2) are met or all possibilities have been exhausted. The switching information from a successful search is used to set the reception frame cursor generated by the CCU. The capture

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118 • ends when (1) and (2) above are met for three consecutive frames with UW in their nominal position. STU is informed of frame trapping when this occurs.

RCC messages were not forwarded to STU during the frame search state.

When the frame capture is completed, the subscriber station CCU switches to the monitoring state. In order to avoid the possibility of capturing false UW, only the nominal UW position is investigated. If no UW is detected for five consecutive frames, the channel is declared unsynchronized and the frame search mode is initiated. STU is informed of this unsynchronized condition. In the monitoring state, RCC messages with the correct check sum and SIN number are forwarded to STU.

During each number slot, the subscriber station CCU searches for a correct code word in the received speech data. Searching occurs only in the nominal code word mode, since no active symbol synchronization is performed during speech processing. All possible code words are searched in this channel direction. Code words can cause increased values ​​in the subscriber station power and distance values. In fact, an increase in the distance values ​​can cause both the symbol and the partial distance values ​​to change. If no code word is detected for five consecutive frames, the channel is declared out of sync and STU is informed of this condition. Synchronization is considered to be restored if a successful password detection has been obtained during three out of five consecutive frames.

Other CCU considerations

The transmit DMA transfer request between the transmit buffer 110 and the modem 19.30a must be obtained from the bit indicating that the FIFO stack 128 is full. This means that the FIFO stack 128 is always full when a DMA block transfer35 lining is completed.

Receive DMA transfer request between modem 19,

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119

30a and receive buffer 115 must be obtained from the bit indicating that stack 129 is empty. This means that FIFO stack 129 is always empty when a DMA block transfer is completed.

The software in the CCU controller provides the gate function for activating DMA transfers, but external control must be responsible for the handshake for initiating and maintaining the block transfer. This is especially important for the modem interface, where the frame rate is critical.

The microcontroller 111 should be able to freeze a DMA transmission. The program will not attempt to use the DMA bus during a block transfer unless this, control is used or the DMA peripheral is vacant.

The re-clocking FIFO stacks 128, 129 should be cleared (reset) automatically and periodically.

Frame rate information must be available to the microcontroller 111. This information may be a symbol clock input to an internal clock sensor of the microcontroller.

When an RCC or speech packet is received by the synchronized CCU /, no symbol shift is required to apply the packet to a byte boundary. This applies regardless of the level of modulation.

Modem

The modem works in one of three operating states. At the base station, the modem transmits and receives full duplex. At the subscriber station, the modem operates in a half-duplex state, transmitting under one part of the TDMA frame and receiving under another part of the TDMA frame.

The third state is a self-learning state.

A single modem handles all these functions. The modem performs the correct function in response to control signals.

from the governing CCU.

Subscriber station modem 30a and base station

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120 modem 19a is identical. A block diagram of the modem is shown in Fig. 25.

The modem's transmit section includes a TX symbol filter 132, a digital-to-analog converter 133, a 200-KHz bandpass filter 134, a mixer 13.5, and a TX (transmit) clock control circuit 136. The modem's receive section includes a mixer 138, an analog-to-digital converter 139, a FIFO stack 140 and a microprocessor 141 of model TMS 320.

The modem's transmission section transmits the information entered from CCU with 16-level PSK modulation. The data is interpreted as DPSK, QPSK or 16-PSK by CCU on the receiving side.

The modem transmits without knowledge of the modulation level.

The modem's transmission section is fully implemented in hardware and requires no settings. The symbols received from the CCU are coded, and their corresponding waveforms are formed so as to provide good interference characteristics and avoid amplitude or group delay distortion. The motive for this approach is based on the assumption that in the nearby frequency band (within 50-100 KHz) of the used band there are no strong interference signals (power densities of 30-40 dB over the signal). The modem's transmission section utilizes a relatively broad-band MF filtering (100 KHz) so that the transmitted signal does not exhibit amplitude or group delay distortion, and filters out any harmonics generated during the baseband level digital filtering.

The TX symbol filter 132 is a digital FIR filter with fixed coefficients. This filter 132 simulates a β-pole filter with a sampling rate of 50 samples per symbol per symbol time of 6 symbols in the FIR filter.

The modem receives symbols from its respective CCU at a rate of 16 K symbols / second. These symbols are then converted to a DPSK code to be fed to a line 143 to the FIR filter 132. The FIR algorithm necessary 526 967

121 means that every other symbol must be inverted before it is input to the FIR filter. A Gray code is used for the DPSK encoding. This ensures that if a symbol is received incorrectly then it is very likely that only one bit will be incorrect in the two symbols fed to the receive codec.

The pulse response of the FIR filter 132 is truncated at 6T (T = 1/16 KHz). The FIR filter over-samples the symbols at a rate of 800 KHz, so that each symbol is sampled 50 times during its 5T pause in the filter. This corresponds to a sampling rate of 3T / 25, where the sampling period is T / 25, so that the samples are output during periods of 3T / 25. The sampled outputs are so mutually displaced that only the first and fourth, second and fifth or third and sixth sample pairs overlap at any point. Each of these samples having a length of T / 25 is in fact divided into two parts. During the first half of the sampling period the I-part of the output symbol is calculated, and during the second half of the period the Q-part of the output symbol is calculated. The actual steering wheel with. which FIR filter 132 outputs data is thus 50 x 16 KHz = 800 KHz. The I and Q samples are offset by half a sampling period, but this is corrected in the FIR filter 132.

Signals corresponding to the multiplication of symbols and impulse response in the FIR filter 132 and the addition of two of these multiplications are obtained from. an 8Kx8 ROM on a line 144 in response to the symbols received on line 143.

The FIR filter 132 outputs digital 10-bit samples on line 144 at a rate of 800 KHz. These values ​​are input into the digital-analog converter 133 to form an analog waveform on a line 145. This waveform consists of the time-split I and Q waveforms of the symbol to be transmitted. This time-shared waveform on line 145 is filtered by bandpass filter 134 of 200

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122

KHz, after which it is fed on a line 146 to the mixer 135. The input to the mixer's local oscillator is a 20 MHz MF frequency signal on a line 147.

The I and Q components are thus frequency converted to a .MF output signal of 20.2 MHz on a line 148. The output of the line 148 is fed via a 20.2 MHz bandpass filter (not shown) to RFU 21, 31a.

The desired output of digital-to-analog converter 134 is centered around 200 KHz with a bandwidth of about 32 KHz. By multiplying the 200 KHz waveform by 20 MHz, the output waveform I and Q samples are mixed with MP: -f frequency signal SIN and CO5 components. Thus, the output waveform can be obtained by direct multiplication with the signal of 20 MHz, and the exact component multiplications are performed automatically. Therefore, no discrete SIN (MF) / COS (MF) generating circuit is needed to multiply the I / Q samples from the digital analog converter, as is the case in the receive section. This also eliminates · feed through effects in the mixer from its baseband side to its output.

The output stored in the lateral FIR filter 132 is as follows: · calculated that any errors that may occur due to • even the difference of 1/50 T between the I and Q time values ​​are corrected. Furthermore, the MF filter in RFU (Figs. 28 and 29) adds the two values ​​to each other to form the correct one.

- transmitted the waveform, since its bandwidth is relatively small compared to the MF.f frequency one.

In the modem's reception section, mixer 138 mixes an analog waveform received on a line 150 via a 20 MHz bandpass filter (not shown) with a 20.MHz MF signal on a line 151 to frequency convert the analog signal to baseband level on a line 152. The analog signal is then converted. of the analog-to-digital converter 139 into a digital signal on a line 153, which signal is stored in the FIFO stack 140 to be processed by the microprocessor 141. Micro 526 967

123 processor 141 performs frequency and bit tracking on the received digital signal and also performs the FIR filtering and demodulation of the signal to a binary symbol flow which is fed to the CCU on a line 154.

In addition to the analog and digital data signals processed by the modem, a number of control and status signals are transmitted to and from the modem. These signals are generally transmitted to the CCU modem. The modem also sends control signals to the RFU to control such functions.

tions such as transmit power level, frequency, AGC and antenna switching for diversity.

The modem interfaces are shown in Figs. 26 and 27. The modem 'receives most of its input signals from the CCU. other inputs are obtained from RFU and clock generating units.

The modem's input signals will now be described below.

The following wires transmit the described signals to the modem 19, 30a from CCU 18, 29:

Wires TX DATA 156 transmit a 4-bit symbol; to be transmitted by the modem (2 bits for QPSK, 1 bit for BPSK). MOD BUS 157 is a two-way microprocessor bus for transmitting control and status information to and from the modem. A line MOD WR 158 transmits a controller signal for connecting MOD BUS to the modem. A line MOD RD 159 transmits a control signal for applying&gt; 5 modem status and other information on MOD BUS for transmission to CCU 18, 29. A MOD RESET 160 line transmits a control signal for resetting the modem. Wiring MOD ADD 161 transmits address signals to various locations for connecting. values ​​inside the modem. One wire TX⁰ SOS 162 transmits a signal to start transmitting a TX slot. A line RX SOS 163 transmits a signal to start receiving an RX door.

A line MF RECEIVE 165 transmits an MF receive frequency input to the modem 19, 30a from RFU 21, 31a.

The following wires transmit the described signals to modem 19 from STIMU 35. An 80MHZ line 167 transmits an 80 MHz ECL clock signal. A similar signal

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124 is supplied to modem 30a by a clock display unit (not shown) in the subscriber station. A 16 KHz line 168 transmits a master TX CLK signal which is utilized in the base station.

A SOMF line transmits a master5 signal sent from STIMU for frame start in the base station. This signal is not used in the modem, but is forwarded to. CCU.

The following lines transmit the described signals from modem 19, 30a to CCU 18, 29. A line TX CLK 171 transmits a clock signal of 16 KHz which supplies

CCU with symbol transmit the beat. The symbols are clocked into the modem at the positive edge of this clock signal. In the base station, all hatches have the same master-TX CLK. Thus, all signals from the base station are transmitted simultaneously. At the subscriber station, TX CLK is offset by the modem with the partial distance delay, which delay is determined from information from the CCU. A line RX CLK 172 transmits a clock signal of 16 KHz, which is obtained from the received signal.

This signal is always available in the subscriber station, but only occurs during the control switch capture in the · base station. This clock signal clocks out the received symbol to the CCU and provides the CCU with symbol rate. Wires RX DATA. 173 Transmit the received 4-bit symbol that has clock out of the signal RX CLK. MOD BUS 157 'transmits status and data information from the modem. A line MOD SOMF 175 forwards the SOMF signal from STIMU to CCU in the base station. A line AM STROBE 176 transmits a strobe signal on which a high / low transition gives the CCU an approximate frame mark during RCC capture at the subscriber station. This is a one-shot line that is pulsed when microprocessor 141 determines the approximate position of the AM hole.

The following wires transmit the described signals from the modem 19, 30a to each of the RF units 21, 31a. An RF RX BUS 178 is an 8-bit bus between the modem and the RFU section. This bus transmits AGC and frequency selection information to the RF reception section. The modem controls which AGC values ​​are to be transmitted and forwarded

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125

CCU frequency selection information. The frequency selection information is fed to the modem by CCU on MOD BUS 157. In the learning state, the modem controls. RF RX frequency selection. RF TX BUS 179 is an 8-bit bus between the modem and the RFU transmission section. This bus transmits TX power level information and frequency selection information to the RFU transmitting section.

This information does not affect the modem, so the information is only forwarded to the RF transmission section. A line RX 80MHZ REF 180 transmits an 80 MHz ECL reference clock signal to the RFU receiving section. A line TX EN 182 to the RFU transmission section transmits a signal for RF transmission activation. A line RX EN 183 to the RFU receiving section transmits a signal for activating RF reception. A wire AGC WR 184 transmits a write strobe signal for connecting AGC data to the RFU receiving section.

A line RXFREQ WR 185 transmits a write-off frequency signal to the RFU transmit section. A line PWR WR 186 transmits a write strobe signal for connecting power information to the RFU transmission section. A line PWR RD 187 transmits a read strobe signal to re-read the power information from the RFU transmitting section. One line TXFREQ RD 188 transmit read strobe signal for read-back_tTransmission Frequency from the RFU Transmission Section · Lead TXFREQ WR 189 transmits a frequency drop signal to the RFU transmission section. A line MF TRANSMIT 190 transmits the MF transmit signal to the RFU.

The following lines transmit the described signals from modem 19 to STIMU 35. A VCXO BUS 192 is a 20-bit data bus to VCXO in STIMU 35 which transmits frequency tracking information. A line VCXO WR transmits a write pulse to the VCXO circuit for connecting VCXO BUS 192 to VCXO. The same signals are transmitted from modem 30a to the clock unit (not shown) in the subscriber station.

The base station modem operates at a fixed RF frequency.

Communication at the base station takes place with full duplex, which is why the modem's receiver and transmitter work together.

126 early. One of the modems is also configured to serve as a control frequency channel modem and thus transmits and receives information with the radio control channel format (RCC format) during the assigned control lock period. All transmissions from the base station modem are clocked by the .master signal TX

CLK of 16 KHz on line 171. In contrast to the subscriber station modem, the base station modem 19 outputs an output to CCU 18, which output indicates how. a large part of the symbol time which lies between the master signal TX CLK on line 171 and the received signal RX CLK on line 172 in modem 19. This information is then transmitted on the radio control channel (RCC) to the subscriber station so that the subscriber station delays its transmission so that its signal is received at the base station in sync with all other slots.

The base station modem 19 also transmits zero energy signals in the control slot to provide the AM control hole of the radio control channel (which constitutes a frame reference), when the RFU transmits a zero energy signal. This non-information-carrying portion of the RCC transmission is utilized for initial RX capture at the subscriber station.

Modem 19 is unaware of the fact that there are four CCU 18 multiplexed speech codecs in the base station for four 16-PSK subscriber closure assignments.

The modem 19 receives the bit stream from CCU 18 and processes the transmission in the same way as a subscriber station with only a codec.

All operations in the subscriber station modem 30a are controlled based on the received signal RX CLK on line 172, which signal is separated from the received transmission. This clock signal acts as a master clock for the subscriber station. The signal TX CLK on line 171 to CCU 29 is not, as in the base station, a master clock. This signal is calculated from the signal RX CLK on line · 172 and is delayed by a part-time delay selected by CCU. CCU 29 determines the length of the delay based on the RCC. The delay is determined by the distance between

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127 the base station and the subscriber stations. The subscriber station CCU 29 feeds this part-time information via MOD BUS 157 to modem 30a. The modem 30a itself takes into account the partial delay. Modem 30a handles the full symbol delay by inserting the TX SOS signal on line 162 after a delay of the correct number of symbols. In this way, all signals arriving at the base station are directed which are transmitted from subscriber stations located at different distances from the base station.

At the subscriber station, communication takes place with half duplex. Thus, when the transmitter is at rest, it is blocked. When the modem 30a does not transmit actively, it is in its receiving state and can thereby monitor the gain levels of the received signal to prepare for a signal burst from the base station.

The subscriber station modem 30a does not transmit anything

..AM protective band for the RCC door. No such is required since the base station defines the frame. Unlike base station modem 19, which operates only at fixed frequencies, subscriber station modem 30a can also transmit or receive data at any of the 26 frequencies selected in RFU by CCU 29.

There are many sources of delay in the modem that have a clear impact 'on the system rate. Such delays include, for example, delays in analog filters, propagation delays, and delays for processing in FIR filters, etc. These delays offset the TX and RX frames relative to each other, and these delays must be carefully considered.

The delay between the TX SOS signal on the line

162 in the base station and the first received analog symbol peak at the base station are +7.4 symbols. Therefore, there is a shift between TX and RX gaps.

To properly decode the incoming phase, the modem must begin sampling approx. 3.5 symbols before the top arrives. The shift between the TX SOS signal and the beginning of RX sampling is therefore approximately 4 symbols.

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128

At the base station, RX gate start occurs approximately 4 hours after TX gate start. RX slot start is defined as the time when the first analogue sample is taken to detect the first received peak.

The subscriber station clock signals are obtained entirely from a master VCXO · of 80 MHz in the subscriber station clock display unit (not shown). VCXO is controlled with an analog signal on a line from modem 30a. From here, all receive and transmit clock signals are calculated.

The modem 30a then supplies CCU 29 with the 16 KHz signal RX CLK on line 172, which signal is received from the incoming data stream. CC (J 29 itself detects the unique word in the control channel and can determine frame and door markings based on the unique word and signal

RX CLK on line 172. The AM-hole signal from the modem demodulated signal gives CCU 29 the location of this unit to search for the unique word.

During reception of all gaps, modem 19 performs frequency synchronization by capture and tracking.

At the subscriber station, VCXO is directly controlled by microprocessor 141^?via a D / A converter. The microprocessor algorithms for '^;frequency capture and frequency tracking calculates necessary changes in VCXO to maintain synchronization. An OCXO embedded in the base station's STIMU 35 operates at a fixed frequency and acts as a master clock for the system. Therefore, no frequency deviation occurs upon receipt. '.

While receiving all gaps, the modem 19, 30a also performs a bit synchronization on the received bit stream pattern of the received data 30. An algorithm performs a bit tracking loop inside the receiver. Microprocessor 141 controls a variable frequency divider of VCXO of 80 MHz or OCXO (only during demodulation of control slots). In the bit tracking loop, microprocessor 141 sets the frequency division to establish bit synchronization. During reception of a voice channel, the frequency-sharing factors can be changed in 0.1% increments of 16 KHz, but during reception of a

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129 In the control door, the partition factor can be changed more dramatically, eg up to ± 50%.

Frame synchronization) in the base station and in the subscriber stations is handled in completely different ways. In the base station, a master SOMF signal (master signal for modem frames takes t) is transmitted via line 169 and memory 19 to CCU 18 on line 175. This' is the master SOMF signal used for all transmissions from the base station.

From this signal and from the master system symbol clock signal (16 KHz), CCU 18 can produce all the hatch and frame rate.

At the subscriber station, CCU 29 performs frame synchronization by detecting the unique word in the received RCC data stream. At the initial capture, modem 30a outputs an approximate frame marking signal (AM STROBE) on line 176. During capture, modem 30a searches for AM HOLE in RCC. If AM HOLE is detected, modem 30a counts this for a few frames, after which the modem outputs the AM STROBE marking signal one on line 176 to CCU 29 at the AM HOLE frame position. CCU 29 uses this strobe marking signal to set counters for initial frame marking signals (windowing), which counters can be modified by CCU software for _;.exact frame synchronization. This signal also indicates that AM HOLE has been detected and that RCC has been captured. Clock synchronization is controlled by CCU 18, 29. The signals TX SOS on line 162 and RX SOS on line 163 are the commands of the clock and control generator 38 for the start of transmitting or receiving a gap. These signals are synchronized with the signal TX CLK on line 171 and signal RX CLK on line 172, respectively.

The self-learning state is a feedback state that the modem assumes to set the receiver's digital FIR filter coefficients so that they are adapted to such deteriorations in the analog reception filters that may occur due to age or temperature changes. The analysis is performed by feedbacking the transmit data via the RF unit and receiving a known pattern.

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130 in the receiver. The coefficients are optimized with a LaGrangian system with 5 parameters. These parameters are (1) the received data flow? (2) the delayed data flow with O ', O5.T? (3) the 0.05 T data flow?

(4) the data stream from the nearest higher channel; and (5) the data stream from the nearest lower channel.

In the learning state, microprocessor 141 TX FIR filter 131 provides a series of learning patterns of 32 symbols on line 143. This is performed via a FIFO10. stack (not shown), which is activated during the learning state.

By advances and delays, the two flows are shifted by 0.05 T. CCU 18, 29 brings the modem into the learning state to allow the modem's transmission section to read particular learning data from the FIFO stack in the modem. For some of the tests, the demodulator section is advanced or delayed. When the process is complete, the modem sends a status message to CCU 18, 29 that the coefficients have been calculated. At this point, the CCU 18, 29 tests the modem by bringing this Ϊ its normal working state, printing a given pattern, bringing RFU 21, 31a into a feedback state, and reading the feedback data to see if it can be approved. . '^; &lt;

The modem is described in more detail in the US patent application Modem for Subscriber RF Telephone

System, filed the same day in the name of Eric Paneth, David N. Critchlow and Moshe Yehushua, which writing is to be considered part of the present description.

RF / MF unit (RFU) and antenna interface

The RFU subsystem provides the communication channel link between the modem and the antenna in both the base station and the subscriber station. RFU acts as a linear amplitude and frequency converter and is essentially transparent for channel data and modulation properties.

The antenna interface circuit for the subscriber station is shown in Fig. 28. An RFU control logic circuit 192 is connected to the transmit antenna 32 via the antenna interface circuit.

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131 the three receiving antennas 32a ,. 32b and 32c. The RFU control logic circuit 192 is also connected to the transmitting section of modem 30a and the receiving sections of modem 30a, 30b and 30c. In fact, the antennas 32 and 32a are the same antenna.

The transmit section of the antenna interface includes a frequency converter and amplifier circuit 193, a TX synthesizer 194, a power amplifier 196 and a TX / RX state switch 197. A first receiving section RX 1 of the antenna interface comprises a frequency converter 197 and an amplifier RX amplifier 198, preamplifier 200. Each additional diversity receiving section, RXn (n = 2, 3). includes a frequency converter and amplifier 202, an RX synthesizer 203 and a preamplifier 204.

RFU the following signals to the transmit section of the antenna interface circuit in response to the signals received from the transmit section of the modem 30a: (1) a TX enable signal on a line 206, which signal is configured to dial TX / RX switch 197 to enable transmit from transmit. antenna 32; (2) an MF input on a line 207 to the frequency converter and amplifier 193; (3) a power control signal on a line 208 which is fed to the frequency converter and amplifier 193; (4) a clock reference signal on a line 209 to the TX synthesizer 194; and (5) a channel selection signal on a line 210 to the TX synthesizer 194. In response to the channel selection signal on line 210, the TX synthesizer 194 generates a TX frequency selection signal on a line 211 to the frequency converter and amplifier 193, which signal is equal to the difference between the desired transmit frequency and the modem's MF frequency.

RFU control logic circuit 192 outputs the following signals to each of the antenna interface circuit's receiving sections in response to corresponding signals received from the received sections of modem 30a, 30b and 30c:

(1) a TX activation signal on wires 213, Which

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132 signal is provided, to cause the frequency converter and amplifier circuits 198, 202 to operate in the receive states; (2) an AGC signal on wires 214 to the frequency converter and amplifier circuits 198, 202; (3) and. clock reference signal on lines 215 to RX synthesizers 199, 203; and (4) a channel selection signal on wires 216 to RX synthesizers 199, 203 which, in response to the channel selection signal on wires 216, output an RX frequency selection signal on wires 217 to frequency converter and amplifier circuits 198, 202 equal to the difference between the desired receive frequency and IF frequency '. The frequency converter and amplifier circuits 198, 202 output MF outputs on lines 218 to RFU control logic circuit 192 for forwarding to the receiving section of corresponding modems 30a, 30b and 30c.

The frequency converter and amplifier circuit 193 in the transmit section receives the modulated MF signal on line 207, amplifies the signal and converts the signal to the selected RF channel frequency. A combination of filters (not shown), amplifiers 196, 197 and level control circuits (not shown) are then utilized to provide the correct transmit power and to suppress unwanted signals at mirror frequencies and harmonic frequencies.

The. the transmitted frequency is the sum of the modem's MF frequency and a conversion rate, which has been synthesized in 25 KHz increments from the reference frequency supplied from the modem.

The subscriber station's RFU works as a transmitter receiver, which works with half duplex and whose receivers are inoperative during the transmit interview, all. The transmission rate is high enough to simulate a full duplex operation for the user. The assigned frequency channel is the channel selected by the base station RPU.

The antenna interface circuit for the base station is shown in Fig. 29. An RFU control logic circuit 219 is connected to the transmit antenna 23 and via the antenna interface circuit to the three receiving antennas 34a, 34b and 34c. RFU controller526 967

133 logic circuit 219 is also connected to the transmitting section of modem 19 and the receiving sections of modem 19, 19b and 19c. (Modems 19b and 19c are diversity modems and are not illustrated in Figure 2).

The transmit section of the antenna interface includes a frequency converter and amplifier circuit 220, a TX synthesizer 221, a power amplifier 222, a high power amplifier 223, a power amplifier 224, and a bandpass filter 225. A first receive section RX 1 synthesizer 231, a preamplifier 232 and a bandpass filter 233. Each additional diversity receiving section RXn includes a frequency converter and amplifier 234, an RX synthesizer 235, a pre-amplifier 236 and a bandpass filter 237.

RFU control logic circuit 219 outputs the following signals to the transmit section of the antenna interface circuit in response to the signals received from the transmit section of modem 19: (1) a signal TX ON on a line 240 to the frequency converter 20 and the amplifier 220 for switching on the transmit transmitting section 2'3; (2) an MF input on a line 239 to the frequency converter and amplifier 220; (3) a clock reference signal on a line 241 to the TX synthesizer 221;

and (4) a channel selection signal on a line 242 to the TX synthesizer 221. In response to the channel selection signal on line 242, TX synthesizer 221 outputs an RX frequency selection signal on a line 243 to the frequency converter and amplifier 220 equal to the difference between the frequency and the transmitted frequency. modem MP frequency. A level control signal is output on a line 244 from the power detector 224 to the frequency converter and amplifier 220.

RFU control logic circuit 219 outputs the following signals ¹⁵ to each of the antenna interface circuit's receiving sections in response to the signals received from respective reception sections of modems 19, 19b, 19c:

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134 &lt;1) an AGC signal on wires' 245 to the frequency converter and amplifier circuits 230, 234; (2) a clock reference signal on leads 246 to RX synthesizers 231, 235; and (3) a channel selection signal on wires. 247 to RX synthesizers 231, 235. RX synthesizers

231, 235, in response to the channel selection signal on lines 247, output an RX frequency selection signal on lines 248 to the frequency converter and amplifier circuits 230,

234 which is equal to the difference between the desired receive frequency and the modem's MF frequency. Frequency converter and amplifier circuits 230, 231 output MF outputs on lines 249 to RFU control logic circuit 219 for forwarding to the receiving sections of respective modems 19, 19b, 19c.

The RF units RFU in the base station and the subscriber stations are the same, except that an extra high power amplifier 223 is used to increase the transmitted power in the base station's RF sands. The main function of RFU in the base station or the subscriber station

20th is to convert the modulated MF (20.2 MHz) signal from the modem's transmit section to the desired RF transmit frequency in the 450 MHz UHF frequency band. The receiving side of the RF unit performs the opposite function, ie frequency downsizing of the received UHF signals in the 450 MHz band. to an MF signal of 20 MHz. The transmit and receive frequencies are offset by 5 MHz. The RF units are programmed by CCUjn's control function to operate at different frequencies, which are utilized in the total system. Typically, each of the base station RF units is set to a single frequency at system initiation, after which the frequency is not changed. The number of RF units in the base station corresponds to the number of transmit and receive frequency channels handled in the base station. Subscriber stations' RF units typically change their frequency of operation for each new telephone call.

The RF units include means for tuning

AGC and transmit power level. AGC gain coefficients

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135 is obtained from the modem based on a calculation in the receive section of the modem's processor 141. The subscriber station transmit power level is calculated by the CCU based on messages received from the base station on the RCC channel, and other control parameters.

If all the gaps in a frequency channel are not utilized, the RFU transmits a rest pattern, which is applied to the door by the CCU. If a full frequency channel is not utilized, the transmitter for this frequency can be disconnected via the modem of the CCU software.

The switching time for diversity switches should be less than 50 μβ.

Three antennas and three separate RF / MF units are provided (one for transmission and three for reception).

Many of the portions included in the base station RFU and antenna interface are identical to the above described portions of the subscriber station. The differences, however, are clarified in the following sections.

The base station RF array and antenna interface circuits operate at full duplex. All transmitters and receivers usually operate during 100% of the duty cycle. Furthermore, from an economic point of view, it is advantageous for the base station to work with a higher transmit power and to utilize receivers with diversity. The transmitter is designed to operate at the highest permissible power level without dynamic control. Receiving diversity is achieved through the use of a plurality of receiving antennas and a plurality of modems.

The base station does not normally change the operating frequency or transmit power level during normal operation. The transmit and receive sections are fully tunable to each of the 26 channels ·. The transmit section of the base station antenna interface receives the modulated MF input on line 239 from the modem and processes it in the same manner as described above for the subscriber station transmit section. The signal is further amplified to the desired power level and filtered by a bandpass filter 225,

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136 which is arranged to reduce noise at the operating frequencies of adjacent receivers and to reduce incorrect transmission levels.

The receiving section of the base station antenna interface is similar to the described receiving section of the subscriber station, except that the input step is preceded by bandpass filters 233, 237 which help eliminate the decrease in sensitivity caused by adjacent or adjacent transmitters. Low noise preamplifiers are also utilized to lower the limit level for useful signals. All antennas 23, 34a, 34b, 34c are isolated with 30 dB from other antennas. Further isolation is provided in the transmit and receive sections so that an isolation of about 80 dB is obtained between transmitted signals and received signals. The bandpass filter, preamplifiers and amplifiers are placed in the vicinity of the corresponding transmit antenna or receive antenna.

Miscellaneous reception reception treatment

Diversity reception is used to reduce the likelihood of a channel fading that falls below an accepted limit value. The diversity system enables a three-fold diversity from the subscriber stations to the base station and from the base station to the subscriber stations. The diversity hardware at both the base station and the subscriber stations includes a special diversity combination circuit, three modems as well as these associated RF units and antennas. Only one of the modem RFU antenna combinations has transmit characteristics. Although the diversity combination circuit 33 is only illustrated in the subscriber system of FIG. 2, this circuit is also included in the base station, where it is connected to the modem and CCU in the same way as in the subscriber station.

When the base station or the subscriber station operates with diversity reception, the station utilizes three receiving antennas · which are spaced apart sufficiently large to ensure

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137 that the fading characteristics of the received signals will be uncorrelated. These three antennas feed the received signals through three identical receiving sections in the antenna interface to the RFU control logic circuit, the

MF outputs are supplied to separate modems for demodulation &lt;

A TMS 320 type microprocessor in the diversity combination circuit 33 (the diversity processor) receives the outputs from the modem and delivers a more reliable data flow to the rest of the system in a manner corresponding to the data flow from a single modem. The responsibility for the two tasks of performing the diversity combination and for CCU to act as a single modem lies on the diversity processor's hardware and software.

The diversity processor reads from their three modems their data symbols, AGC values, signal + noise, amplitude level and phase error (deviation of the detected phase from the ideal reference vectors of 22.5 °). The algorithm used to determine the demodulated symbol includes a majority decision and signal-to-noise ratio calculations for each modem to identify the modem most likely to transmit the correct symbols.

The diversity processor CCU interface registers are virtually identical to the registers found in the modem, except that the extra registers used in the diversity processing function are not required, so only three address bits are needed.

Since the TMS 320 microprocessor I / O capacity is small and most of the processing can be performed with one type of I / O register at a time, a special register is used which stores the addresses needed at the moment. For example, the AGC value from each modem must be read, the highest value selected and the result * 5 thread written to the diversity processor I / O register, where the result can be read by the CCU. The addressing of these registers is performed most efficiently on the address of the AGC register

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138 is first written to a port where the address is applied to the modem's address lines. Thereafter, the processor only needs to address the dial modem or microprocessor register bank, whereby I / O operations can be performed at greater speed.

In the subscriber station diversity system, each has.

modem's own clocking unit, and the clock signals used by the three modems in the diversity system need not necessarily be in phase. Since the three modem clock signals of the three modems are not synchronized with each other, data barriers are needed to freeze the output data symbols from each modem until the diversity processor reads the symbols.

An important function of the diversity processor is to maintain communications between CCU and the three modems. This communication must be fast enough to meet all the requirements of the CCU, but not so fast as to overload the diversity processor.

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139