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

(42) Date of commencement of the patent: 15. 1.1998 (45) Date of issue: 25. 9.1998

<td>(30) Priority:</td><td>(73) Patent owner:</td>

<td>20. 3.1985 US 7D9Z5.</td><td>INTERDIGITAL TECHNOLOGY CORPORATION 19801 DELAWARE (US).</td>

<td>(56) Documents:</td><td></td>

<td>DE 3118018A CE 2812009A DE 2251650A US 3546684A</td><td></td>

CQ

AT 404 202 (54) DIGITAL TELEPHONE SYSTEM, WHICH MAKES A VARIETY OF INFORMATION SIGNALS (57) Digital Telephone System, which processes a multiplicity of information signals emanating from femalescircuits, the subscriber stations communicating with the base via radio-frequency channels, wherein separate conversion devices (15) for respective connections to the remote intercommunication lines for converting the information signals received via these into digital samples, and a plurality of transmission channel circuits (17) are provided, each of which is assigned to a different one of the predetermined radio frequency channels and each of which comprises a predetermined plurality of signal compression devices (16) for simultaneously compressing the high-compression-rate digital signal samples respectively obtained from the conversion devices (15); a channel controller (18) coupled to the compression devices (16) for sequentially combining the compressed signals into a transmit channel bit stream; a transmitting device (34) for outputting a transmission channel signal, a connection device (25) for connecting the respective transfer devices to the indicated compression devices, an remote connection central processor device (20) connected to the information signals emanating from the female links; which contains a memory (46), a call processor device (24), which is connected to the remote central processor device (20) and makes the indicated connection on a slot allocation signal.

FROM OUTDOOR CIRCUITS

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AT 404 202 Β

The present invention relates to a digital telephone system which processes a plurality of information signals originating from telephone lines, which are then transmitted almost simultaneously over predetermined radio frequency channels from a base station to a plurality of stationary or mobile subscriber stations, wherein the subscriber stations send information signals to the base station via radio frequency channels are sendable.

It is thus a system for the simultaneous wireless transmission of multiple information signals by using digital time interleaving circuits between a base station and a plurality of subscriber stations. The subscriber stations can be fixed or mobile. The number of time interleaving circuits is determined by the quality of transmission of the signals. The base station is usually interconnected with an external information network, which may be analog and / or digital. The information signals are selected from a group consisting of voice, data, facsimile, video and meter signals.

In order to achieve a high quality of connection even under unfavorable conditions, the telephone system according to the invention is characterized by separate conversion devices for respective connections to the telephone lines for converting the information signals received via the telephone lines into digital samples, a plurality of transmit channel circuits, each of which is associated with a different one of the predetermined radio frequency channels and each of which has the following characteristics, a predetermined plurality of separate signal compression devices for simultaneously compressing the high-compression-rate (low-bit-rate) digital signal samples respectively obtained from the conversion devices; to provide the predetermined number of separate compressed signals, a channel controller connected to the compression devices for sequentially combining the compressed signals into a single transmit channel bit stream; wherein each of the compressed signals is associated with a separate compression device, repeating sequential slot position in the transmit channel bit stream, a transmission device for outputting a transmission channel signal for transmission over the predetermined radio-frequency channel in accordance with the transmission channel bit stream, a connection device for connecting the respective separate transfer devices to the displayed ones of the separate compression devices, an remote connection central processor device connected to the information signals originating from the telephone lines, which is on a received from one of the telephone lines, incoming connection request signal responds, by outputting a slot allocation signal, which indicates which transmission channel circuit and which of the separate compression devices in said transmission channel circuit has the connection device to connect to the separate conversion devices connected to the one telephone line and thereby assigns a transmission channel circuit and the slot in the transmitted channel bit stream to a telephone line, which slot is associated with one of the separate compression devices, which is thereby connected by the connecting device, wherein the remote central processor device includes a memory, are allocated from the slots for each of the plurality of transmit channel circuits and which polls the memory upon receipt of an incoming connection request and then dynamically outputs a slot assignment signal, which connects to a given transmit channel circuit, in which not all of the time slots are assigned to another telephone line, and a compression device causes which is associated with the slot not associated with another femalescircuit, a call processor device, which is connected to the remote central processor device and responds to a slot allocation signal, by causing the connection device, to establish the connection indicated by the slot assignment,

Devices for exchanging control signals between the base station and each subscriber station, wherein different ones of the control signals provide power adjustment for improving the connection quality, periodically equalizing signals to compensate for distance changes between the base station and each subscriber station, cause synchronization of frames over different channel frequencies and identify the dynamically assigned channel and slot for each subscriber station.

As a result, the mobile subscriber stations can optionally move relatively quickly and relatively slowly. Furthermore, the modulation level of the signals and the power turned off for the system are adjusted in accordance with the signal error detection in the system. In addition, the system is equipped with room diversity, u.zw. by using a plurality of antennas selectively spaced apart from each other irrespective of the signal fading

AT 404 202 B to provide a relatively high signal reception.

The base station operates in the system according to the invention via a plurality of RF channel pairs. Each function of a channel pair is realized by the combination of a transmitter channel circuit for processing a given plurality of information signals, which are simultaneously received over the telephone company's trunk lines and simultaneously broadcast to different subscriber stations over a given radio frequency (RF) channel, and a receive channel circuit for processing a plurality of signals simultaneously received over a given RF channel from the various subscriber stations, to provide information signals for transmission over the trunk lines.

Separate conversion devices are each connected to a transmission line for converting the information received via the transmission lines into digital signal samples.

The transmitter channel circuit contains a certain number of separate signal compression devices for the simultaneous compression of the digital signal samples, each derived from one of the separate transfer devices, to provide a given number of separate compressed signals; a channel control unit, connected to the compression means for continuously combining the compressed signals into a single bit stream of a transmission channel with each of the respective compressed signals, which occupy a repetitive sequence of slot position in the bit stream of the transmission channel, is associated with a predetermined one of the separate compression means and a unit for outputting a transmission channel signal for transmission over the predetermined RF channel in response to the bit stream of the transmission channel.

An exchange from each of the separate conversion devices couples the designated one to the separate compression devices.

A remote connection processor unit is coupled to the trunk lines and is responsive to an incoming call request signal. which is received via one of the trunk lines, by giving a slot assignment signal, that indicates with which of the separate compression devices the exchange with which of the separate transfer devices, which is connected to the transmission line, to connect and to assign a slot to a transmission line in the bit stream of the transmission channel, associated with the one of the separate compression devices, which is so connected to the exchange. The trunk processor maintains a memory from which the slots are allocated and polls the same memory upon receipt of an incoming call request and then provides the slot allocation signal which causes the connection to a compression device associated with one of the slots which has not yet been assigned to any other trunk is.

A call processor is connected to the trunk processor and is responsive to the slot enable signal, causing the switch to complete the connection indicated by the slot allocation signal.

The receive channel circuit includes a receiver unit for receiving a receive channel signal and for processing the receive channel signal to provide a receive channel bitstream containing separate compressed signals in respective different repeating slot order positions. The circuit further includes a given number of signal synthesis devices, each of which is associated with a different slot position in the received bit stream of the receiving port, to restore the digital signal samples from the separate compressed signals, each contained in the associated slot positions of the receive channel bitstream; Furthermore, the circuit includes a control control unit, to separate the separate compressed signals from the bit stream of the receiving channel and to distribute the eliminated signals to the separate synthesis devices, those with the respective timeslot, from which the signals were eliminated, are associated.

Separate retransformers are connected to each of the trunk lines to convert the digital signal samples into information signals for transmission over the respective trunk. Each of the separate backhaul means is associated with one of the separate translation means and is connected via any of the trunk lines to the associated separate translation means.

The switch couples the respective separate backhaul devices to one of the indicated separate synthesis devices.

The trunk processor responds to the incoming call request signals, which he receives via the trunk, on, by giving a slot allocation signal, to show, which of the separate synthesis devices communicate with one of the separate back-conversion devices, which is connected to the one trunk, has to connect and thus allocates the one line in the slot in the bit stream of the receiving channel associated with one of the separate synthesis devices, which is linked in this way by means of mediation. The trunk processor operates a memory from which slots are allocated in the receive channel bit stream and polls the same memory for receipt of the incoming call request and then provides the slot allocation signal

AT 404 202 B to the call processor to cause the connection to one of the synthesis devices associated with one of the slots not allocated to another trunk.

The system of the present invention thus makes use of the advanced digital and highly-integrated electronic technology to provide cheap, reliable, high-quality communication means for different market segments. A preferred embodiment uses a fixed, centrally located installation of a base station for traffic with a large number of subscriber stations located in the near geographical area. The central base station may be connected to a central office of a public telephone company (Telco) via a private branch exchange (PBX) connected via incoming telephone lines. The subscriber stations of the system may be either portable, fixed location, or mobile in nature, and are operable for both slow and fast movements. The subscriber stations communicate with the base station via UHF radio channels, and with the user via standard two-wire DTMF touch tone telephone equipment or via RS-232C or via non-standard telephone stations (eg 4-wire). The system can be used to replace existing hard-wired local subscriber loops or to provide quality telephone service in areas where wire connections are not feasible or uneconomical.

A feature of the system of the present invention is the ability to use Time Division and Multiple Use (TDMA) and allow digital speech coding simultaneously with the multiple use of frequencies within a given network. An executable number of high quality speech circuits can operate simultaneously in a given speech channel (with 25 kHz channel spacing). Four such circuits are used for illustration purposes. This provides both a spectral and an economical advantage over existing analog radio telephony systems, which at one time allow only one call over a given frequency channel.

Advantageously, the base station and each subscriber station may each transmit a control signal to adjust the power to thereby improve the connection quality between the base station and the subscriber station, the reduction of the connection quality resulting below a level in the closure of the associated transmission channel. Furthermore, an apparatus for transmitting synchronization data from the base station to each subscriber station may be provided, wherein signals received in the base station are periodically adjusted for a subscriber station to compensate for distance changes between the base station and the subscriber station. Moreover, the system can take advantage of echo canceller devices to cancel the unwanted echo signals present in the system, while accommodating large time delays of transmissions resulting from the use of high compression rates and large segments of compressed signals. To accurately set the timing of the subscriber station, frame synchronization devices may be provided for frame synchronization across the various frequency channels, the subscriber stations sending their information signals to the base station at half the duplex rate. Finally, the system may transmit at least two bits per symbol over the high frequency channel and the high compression rate may be less than 16 kbps, with multiple information signals being transmitted on the same channel to achieve spectral efficiency.

Features that go beyond the low fixed costs of moving and portable services are the use of low speed digital voice coding (less than 16 kbps) combined with spectrally effective modulation techniques. For example, the combined use of a 14.6 kbps voice coding technique and a 16-level DPSK modulation allows for four simultaneous full-duplex calls transmitted from a single pair of 20 kHz bandwidth channels spaced 25 kHz apart in the entire spectrum , especially in the sections of 400-500 MHz and 800-950 MHz. This combination provides a good voice quality over a distance of at least 20 km.

To be competitive with the wireless service, a much larger total number of subscribers must be served than can be transmitted simultaneously over a given pair of 25kHz channels. For example, a 12-channel par system with 47 simultaneous calls could have a total of 500 subscribing plus subscribers (with the maximum forced by the desired blocking probability in the peak hour). It is therefore a control scheme for the call requests of subscribers that provides reasonable call waiting times, an essential feature of the present invention.

Additional features of the present invention will be described in conjunction with the description of a preferred embodiment.

AT 404 202 B

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a block diagram generally showing the RF subscriber telephone system.

FIG. 2 is a block diagram of a representative preferred embodiment of the base station of FIG

Systems according to FIG. 1.

FIG. 3 is a block diagram of a preferred embodiment of a subscriber station of the system of FIG. 1. FIG.

Fig. 4 illustrates the sequences of messages generated in the subscriber station and in the base station to establish a connection between two subscriber stations.

FIG. 5 illustrates various data processing modules incorporated in the remote control processor unit (RPU) of the base station of FIG. 2.

FIG. 6 illustrates the processing of incoming and outgoing BCC messages by the RPU in the base station of FIG. 2.

Figure 7 illustrates the processing of incoming and outgoing PBX messages by the RPU in the base station of Figure 2.

Figure 8 illustrates the processing of write messages by the RPU in the bassist of Figure 2.

FIG. 9 illustrates a memory map of the RPU in the base station of FIG. 2.

FIG. 10 illustrates the processing of messages concerning the RCC state by the message processing module (MPM) shown in FIG.

Fig. 11 illustrates the processing of channel status messages by the message processing module MPM shown in Fig. 5.

Figure 12 is a block diagram of the subscriber line interface unit (STU) in the subscriber station of Figure 3.

Figure 13 shows the signal intersections between the PBX and the VCU in the base station of Figure 2. Figure 14 (on sheet 1) shows the signal interface between the STU and the VCU in the subscriber station of Figure 3.

FIG. 15 shows the relationships over time for the PBX-VCU interface signals shown in FIG. 13 and for the STU-VCU interface signals shown in FIG.

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

FIG. 17 shows the relationships over time for the signals in the transmission channel of the VCU-CCU interface shown in FIG.

FIG. 18 shows the relationships over time for the receive channel signals of the VCU-CCU signal interface shown in FIG.

Figures 19A and 19B respectively show the ratios over time for the transmit and receive speech blocks which are passed to the 16-level PSK modulation between VCU and CCU.

Figure 20A shows the timing and contents of the input and output data for the transmit channel between the VCU and the PBX (or STU) for 16-level PSK modulation.

Figure 20B shows the timing and contents of the input and output data for the transmit channel between the VCU and the PBX (or STU) for 16-bit PSK modulation.

Figure 21 (on sheet 5) is a block diagram of the CCU both in the base station of Figure 2 and in the subscriber station of Figure 3.

FIG. 22 shows the functional architecture of the CCU of FIG. 21 executed for the software.

Fig. 23 is a timing chart for transferring the RCC and 16 level PSK voice data to the

Transmission bus of the CCU according to FIG. 22.

Figure 24 is a timing diagram for transferring the RCC and 16-level PSK voice data to the receive bus of the CCU of Figure 23.

Figure 25 (on sheet 3) is a block diagram of the modem of the base station of Figure 2 and the subscriber station of Figure 3.

Figure 26 shows the signal interface between the CCU, the modem and the stimu in the base station of Figure 2.

Figure 27 shows the signal interface between the modem and the RFU in the base station of Figure 2 and in the subscriber station of Figure 3.

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

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

AT 404 202 Β

GLOSSARY OF ACRONYMS

Glossary of acronyms used in the description

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

<td>A / D</td><td>Digitizer</td>

<td>ADPCM</td><td>Adaptive differential pulse code modulation</td>

<td>AGC</td><td>Automatic gain control</td>

<td>AT THE</td><td>amplitude modulation</td>

<td>BCC</td><td>Baseband control channel</td>

<td>BPSK</td><td>binary phase-shift keying modulation</td>

<td>BW</td><td>bandwidth</td>

<td>CCU</td><td>Channel controller</td>

<td>CODEC</td><td>Combined encoder and decoder</td>

<td>DEMOD</td><td>Demodulator {receiver part of the modem)</td>

AT 404 202 Β

<td>THERE</td><td>Digital to analog converter</td>

<td>dB</td><td>decibel</td>

<td>DID</td><td>Direct extension</td>

<td>DMA</td><td>Direct memory access</td>

<td>DPSK</td><td>Differential phase-shift keying modulation</td>

<td>DTMF</td><td>Dual tone multi-frequency signal scheme</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>Filter with time-limited impulse response</td>

<td>Hz</td><td>Heart (periods per second)</td>

<td>1</td><td>In phase</td>

<td>XF</td><td>intermediate frequency</td>

<td>Kbps kHz</td><td>Kilobits per second kilohertz</td>

<td>km</td><td>kilometre</td>

<td>LSB</td><td>least significant bit</td>

<td>MDPSK</td><td>Multiphase differential phase-shifting Tastmodulation</td>

<td>MHZ</td><td>megahertz</td>

<td>MODEM</td><td>Combined modulation and demodulation</td>

<td>MPM</td><td>Message processing module</td>

<td>ms</td><td>milliseconds</td>

<td>OCXO</td><td>Temperature-stabilized quartz oscillator</td>

<td>PBX</td><td>PBX or automatic selector</td>

<td>PCM</td><td>Pulse Code Modulation</td>

<td>PSN</td><td>public telephone network</td>

<td>PSTN</td><td>public New York telephone network or</td>

<td>Q</td><td>Carrier connection (typical Telco) quadrature</td>

<td>QPSK</td><td>Quadrature phase-shift keying modulation</td>

<td>RBTG</td><td>Rtickruf tone generator</td>

<td>R.A.M.</td><td>Memory with direct access</td>

<td>RCC</td><td>Radio control channel</td>

<td>RELP</td><td>remaining excited linear prediction</td>

<td>RF</td><td>high frequency</td>

<td>RFO</td><td>RF unit</td>

<td>RPU</td><td>Remote call processor unit</td>

<td>ROME</td><td>Reading content with fixed content</td>

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<td>RX</td><td>reception</td>

<td>SHF</td><td>Super high frequency (3000 - 30000 MHz)</td>

<td>SIN</td><td>Subscriber code</td>

<td>SLIC</td><td>Interface circuit of the subscriber loop</td>

<td>STIMU</td><td>System timing unit</td>

<td>STU</td><td>Subscriber station-telephone interface unit</td>

<td>SUBTU</td><td>Participants timing unit</td>

<td>TDM</td><td>time division</td>

<td>TDMA</td><td>Time division multiple access</td>

<td>Telco</td><td>telephone company</td>

<td>TX</td><td>Send</td>

<td>UHF</td><td>Ultra-high frequency</td>

<td>UTX-250</td><td>Voter incorporating processing and customization and which can be a PBX, but does not have to be</td>

<td>UW</td><td>Only word</td>

<td>VCU</td><td>Voice coding decode-unit</td>

<td>VCXO</td><td>Voltage controlling quartz oscillator</td>

<td>VHF</td><td>Very high frequencies (30 - 350 MHz)</td>

DESCRIPTION OF THE PREFERRED EMBODIMENT

In this description, it should be noted that a particular band (eg 454 to 460 MHz) is used in the embodiment described, but the invention is equally applicable to at least all VHF, UHF and SHF bands.

Referring to Fig. 1, the system of the present invention provides telephone services via local loopers using VHF radio between the subscriber stations (S) 10 and a base station 11. The base station 11 makes call connections directly between the radio based subscriber stations 10 and is connected to central telephone exchanges 12 (Telco) for calls to or from outside the system.

For example, the illustrated system operates on a pair of common carrier frequency channels within the 454 MHz to 460 MHz band. This special frequency range contains 26 fixed channels. The channels are spaced from each other by 25 kHz with an authorized bandwidth of 20 kHz. The distance between the transmit and receive channels is 5 MHz, with the center frequency of the lowest of the two frequencies assigned to the transmissions of the base station. As mentioned above, the system can also operate on other UHF channel pairs.

The type of transmission from the base station to the subscriber station (the transmission channel) is time-division multiplexed. The transmission from the subscriber station (the receiving channel) is done by time sharing and multiple use (TDMA).

All systems are designed to be compatible with 47 CFR FCC classes 21, 22 and 90 as well as other relevant rules.

Traffic between the base station 11 and the subscriber stations 10 is digitally filtered by multi-phase differential phase-shift keying modulation (MDPSK) on 25 kHz spaced full duplex channels in the 454 to 460 MHz band, satisfying the requirements for a 20 kHz bandwidth as described in the FCC Regulations, Classes 21, 22 and 90 (eg 21.105, 22.105 and 90.209). The system can also be used with other bandwidths and distances within any part of the VHF, UHF and SHF spectrum.

The symbol speed on each 25 kHz FCC channel is 16 kilo symbols / second in each direction. Voice transmission is achieved by using the 16 level PSK modulation and digitizing the

AT 404 202 Β

Speech with a coding speed of 14.6 kBpS. Optionally, the modulation may be bi-level (BPSK) or four-level (QPSK). A mix of different modulation levels can be used simultaneously on the same channel. In time-division multiple use, the system provides one call for each multiple of two phases at a speed of 14.6 kbps (4 phases provide two calls, 16 phases provide four calls, etc.) or more at lower appropriate speeds. Of course, this is just one example because, as shown in the following table, many different combinations of modem bits / symbols or phase and codec speeds can be used.

Table I

<td colspan="4">2-way conversation or duplexing using codec speeds from;</td>

<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>8th</td>

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

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

The base station is capable of transmitting and receiving on any or all available 25 kHz spaced FCC channels in the band between 454 to 460 MHz in which the channels are selectable. The channel frequency selection for each voice channel is automatically performed by the base station, one at a time, but this can be bypassed by means of a console interface provided in the base station.

The base station may have a transmitter output power of typically 100 watts for each channel.

The base station provides the modulation control and timeslot and frequency channel allocation to the subscriber station. In addition, adaptive power control is applied at the subscriber station by the base station to reduce consecutive time slot differences and interference with adjacent channels.

The interconnection of telco (telephone) trunk lines and the TDM slots in the selected channel is performed by the base station, preferably using a digital switch, although it is possible to replace it with an analog switch.

The base station gives the receiving channels a triple spatial diversity capability.

The subscriber station is able to work with three-way diversity. The transmission power is typically adjustable between 0.1 and 25 watts, but it can be adjusted to other power ranges. Although speech connections are perceived by the subscriber station as real-time full duplex, the RF system operates on half-duplex, using appropriate time division multiplexing techniques.

The subscriber station is connected to any telephone apparatus for voice communication, but the telephone can also be built into the system. In addition, a data link, such as an RS232C standard 25 pin connector, is provided for a 9600 band rate data transfer between subscribers. The base station and the subscriber station may receive their work energy from any suitable, internal or external source.

Figure 2 is a block diagram of one embodiment of the base station maintaining the simultaneous operation of two pairs of transmit and receive frequency channels. Each channel can handle up to four telephone connections simultaneously. In the preferred embodiment, there are many transmit and receive channel pairs. Each channel has different time slots.

One of the available different time slots is needed for a Radio Control Channel (RCC).

Connections between the PSTN and the subscriber stations are established and maintained in the private branch exchange (PBX) 15, which is integrated into the base station. The PBX is a model UTX-250 system, a product developed by the United Technologies Building Systems group. Many of the existing features of the general PBX system are used in the control of the Telco interfaces needed in the system of the present invention. The PBX also translates voice information to / from the PSTN into 64 kBpS u-law companded Pulse-Coded Digital Modulation (PCM) samples. From this point on, the voice information in the base station and in the

AT 404 202 Β

Subscriber station through to the circuitry of the interface that connects the participants, or as far as it allows the subscriber transmitter and receiver, processed in a digital format.

Digital voice information from the PBX is first processed by a voice compression system, referred to as codec 16, which reduces the voice information rate from 64 kbps to approximately 14.6 kbps or less. The codec 16 uses either a remaining excited prediction algorithm (RELP) or an SBC coder-decoder to perform this speech rate compression. Typically, in a single voice codec unit (VCU) 17, four codecs 17 are included to perform voice compression for the four or more time slots in each frequency channel. In each base station, the VCU 17 may process four or more full-duplex voice connections for both the transmit and receive channels of each channel pair. PBX 15 connections determine which voice call is being processed at which VCU 17 and by which codec 16 in the selected VCU 17. The circuits of each VCU 17 are cartographically set in the hardware such that a speech request of a specific frequency and slot allocation in the base station is always processed by the same VCU codec 16 in all cases.

Each VCU 17 is connected to a channel control unit (CCU) 18. The CCU controls the TDMA function as well as functions of a link level protocol processor. Each CCU 18 receives the output of the transmission channel of the codec 16 in the corresponding VCU 17 and transmits the data in the associated time slot and in the associated format to a modem unit 19. Each CCU 18 determines the modulation levels which are supplied via a fader RPU 20 for use in broadcasting (those with 2, 4, or 16 level PSK modulation). Each CCU also processes status information in traffic to the subscriber stations over the time slot in the radio frequency control channel (RCC) and during the overflow control bits in the voice channels. Each channel pair contains a series-connected combination of a VCU 17, a CCU 18 and a modem 19.

Transmit data correctly set in the format from each CCU 18 are transferred to the corresponding modem at a speed of 16 K symbols / second. Each modem 19 captures these symbols and translates them into a gray-coded multilevel phase-locked (PSK) format. The output of the transmission channel of the modem 19 is a modulated IF signal. This signal is fed to the RF / IF processor unit (RFU) 21, which then converts the IF signal to the RF UHF signal in the 450 MHz range. Control signals for the modem 19 and the RFU 21 are provided by the corresponding CCU 18, which is under the total control of the RPU 20. The UHF signal is amplified by power amplifiers in the RFU and transmitted via the antenna interface unit 22 to an antenna 23 which radiates into free space.

The reception function of the base station is essentially the reverse of the transmission function. Of course, each RFU 21, each modem 19, each CCU 18, each VCU 17, and the PBX will operate in full duplex mode.

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 based on the 6800 microprocessor model that performs the complex functions of the system, and also operates the call setup, interrupt, and maintenance control mechanisms. The RFU 20 also communicates with a call processor 24 in the PBX 15 to control the connections between the codecs 16 and the Telco trunks performed by a switch matrix 25 in the PBX 15. Each subscriber station is a relatively small unit located in the system at each subscriber. The subscriber station connects to the user the standard set of equipment and / or a data terminal or integrated acoustic transmitter / receiver with the base station via the UHF radio channel. The function of the subscriber station is very similar to that of the base station. However, the base station can operate concurrently on one or more frequency channels, each of which has the ability to offer multiple talk circuits, whereas the subscriber station normally operates at one frequency only at one time.

Figure 3 is a block diagram of a subscriber station. The functional distribution is very similar to that of the base station (Figure 2). The interface function at the subscriber is carried out by the telephone interface unit (STU) in the subscriber station. The corresponding function in the base station is carried out by the PBX module. The STU in the subscriber station also performs all control functions exactly as the RPU works in the base station. The subscriber station operates as a base station child station throughout the architecture of the control system. The STU can be linked to an external device or can send and receive acoustically.

In tracking the flow of data through the subscriber station, the user's voice or data information is first processed by a subscriber terminal (STU) 27. The voice signal inputs from the user's telephone are received in the VCU 28 and digitized. The format for the digitized speech signals is identical to the format used for the PBX 15 in the base station

AT 404 202 Β is used. The subscriber station comprises a VCU 28, a CCU 29, the modem 30a and an RFU 31a which perform similar functions to the above-described units in the description of the architecture of the base station shown in FIG. A difference in the operation of the subscriber station is that it is usually limited to only one voice channel. The subscriber station operates essentially in half duplex mode by transmitting in one subregion of the TDMA frame and receiving in another subrange of the TDMA frame. With a frame size of 45 ms, the half-duplex characteristic of the subscriber station is transparent to the user, who continuously hears the voice input from the subscriber on the other side of the voice connection. The STU 27 and the VCU 28, as well as the modem 30a, may be duplicated to accommodate more than one subscriber call.

The half-duplex operation at the subscriber station provides the opportunity to more effectively use the hardware available at the subscriber station. The VCU and the CCU in the subscriber station essentially operate in an identical manner as in the base station, at least as far as the handling of the voice data is concerned. However, since modem 30a is designed to operate in half duplex mode, both the receiver and the transmitter portion of the modem are used, but never at the same time. The primary saving here is that the RFU 31a only has to work in half duplex mode. This saves performance in that the RF power amplifier is active for no more than half the time. Also, the RF transmitter antenna 32a can be switched to operate as a second receiving antenna during the receiving frame by using an RF antenna shunting function. In addition, no duplexer is required.

Each subscriber station also includes a diversity network including three modems and a diversity combiner circuit 33. Each diversity circuit 33 detects demodulated receive information from each of the demodulators of the three modems 30a, 30b, 30c and combines the three streams to form a single best estimate symbol stream, which is then sent to the CCU 29 for processing. The demodulation circuits or demodulators in the three modems 30a, 30b, 30c are connected to separate RX RFUs 31a, 31b, 31c and thus to the separate antennas 32a, 32b, 32c.

In the base station, three receive antennas 34a, 34b, and 34c are spaced at assigned intervals to provide non-correlated, spatially distinct signals that are processed by a diversity network. The operation of the diversity network is recognizable for the CCU function and therefore can be disabled by a single modem function at any time during which the diversity function is not required.

The base station also includes a spatial diversity network for each transmit and receive channel pair. Although the diversity network is not shown, the circuit of the base station is the same as that of the subscriber station of Figure 3, which circuits show the connection of the diversity network for a single transmit and receive pair. Thus, each transmit and receive channel pair in the base station actually includes three demodulators and a modem connected to a diversity combiner circuit as shown in FIG.

The exact timing synchronization between the base station and the subscriber stations is critical throughout the system. The main timer base for the whole system is supplied by the base station. All subscriber units in a given system must be in sync with this time base in frequency designations, symbol timing, and frame timing.

The base station includes a System Timing Unit (STIMU) 35, which provides a high-precision time-related clock signal of 80,000 MHz. This 80 MHz reference clock signal is stepped down to a 16 kHz clock signal and to a 22,222 Hz (45 ms duration) frame scan flag signal. All time signals transmitted by the base station are generated by these three main synchronous references. The 80 MHz clock signal is used by modem 19 and RFUs 21 as the exact IF and RF frequency base. The 16 kHz clock signal provides the symbol time ratio for all base station frequencies. The 45 ms marker signal determines the first symbol in a new frame. This flag is active for one period of a symbol time (62.5 microseconds, equal to 1/16000 Hz). All frequency channels in the base station use the same reference time for transmission. The three timing signals (80 MHz, 16 kHz and the frame marker (SOF)) are brought to each modem 19 in the base station. The modem 19 distributes the corresponding clock signals to the CCU 18 and the RFU 21 in the same series-connected transmission and reception channel pair. The 16 KHz and the SOF markers are used by the CCU 18 to time the transmission of the speech and control symbols according to the structure of the frame flow on that frequency.

The reception timing in the base station is ideally identical to the transmission timing in the base station. This is only the case if the SOF marker and the symbol clock signals between the transmit and receive signals were exactly aligned. However, there is a perfect time-out11

AT 404 202 B

Synchronization from the transmission of the subscriber station can not be expected, the reception timing of the modem of the base station must mix the arriving from the subscriber station symbols. This is done so that the receive function of the modem 19 in the base station in the sample period is estimated to yield the best symbols received from the subscriber station. A small elastic buffer in the CCU 18 associated with the receive function of the modem 19 compensates for this slight time lag.

In the overall system, the subscriber stations synchronize their time references with the main time base in the base station. This synchronization is carried out by means of a multi-step method, wherein the subscriber station first records the time reference of the base station by using the RCC messages from the base station. This method will be described below.

If the subscriber station has first of all obtained the time reference from the base station, a follow-up algorithm in the demodulator of the subscriber station precisely retains the receive timing. The subscriber station advances its own broadcasts to the base station for a small amount of time to compensate for the round-beam delay due to the location of the station. This method provides the correct phase relationships in the transmission of all subscriber stations received by the base station.

The system timing control unit (STIMU) 35 provides the time base for all transmissions in the base station. The STIMU 35 contains a highly accurate (3 x 10 ~⁹) thermally controlled quartz oscillator operating at a fixed frequency of 80 MHz. This base clock frequency is divided by 5000 in the STIMU 35 to form the 16 kHz symbol clock signal and then 720 again to form a frame start mark (SOF) signal. These three time references are buffered and delivered to each base station modem.

The Subscriber Time Control Unit (SUBTU) (not shown in Figure 3) provides an 80 MHz clock signal, a 16 kHz symbol clock signal, and a 45 millisecond frame marker signal to the subscriber station. These signals are identical to those of the base station, except for the 16 kHz clock signal used as symbol reception timing in the subscriber station. The 16 kHz clock signal is used for the transmission timing in the base station. The transmission timing in the subscriber station is provided by a delayed version of the subscriber reception timing. The delay is a variable that is determined by the calculation of the distance between the base station and the subscriber station.

The timing reference signal for the subscriber station is provided by a Voltage Controlled Crystal Oscillator (VCXO) operating at a nominal frequency of 80 MHz. The actual frequency is frequency locked by the subscriber station modem with the base station timing reference as received at the input of the subscriber RF unit.

logs

The following protocols explain the procedures for controlling the system, preventing multiple allocations and call signaling in the system, as well as the transmitted frame structure. When considering the components of the system, reference will be made to the components of the base station described above in connection with Figure 2, unless otherwise indicated.

The system uses full-duplex channels with a bandwidth BW of 20 kHz in the 450 MHz range at intervals of 25 kHz, while allowing different conversations per channel. Each full-duplex channel has a reception and a transmission frequency at a distance of 5 MHz. The low frequency of each channel is attributed to the base station for transmission and is referred to as the going frequency. The higher frequency of each channel is called the return frequency and is assigned to the subscriber station for transmission. Thus, the base station transmits on the outgoing frequency and receives on the returning frequency. The reverse applies to the subscriber station.

The ability of the system to provide a spectrally effective multichannel broadcasting technique on a single frequency is primarily dependent upon the modems operation. The modem must operate in such a manner that, when operating in a 16-phase DPSK 16-s / s operation, it effectively provides 3.2 bits / Hz.

The modem 19 is, strictly speaking, a mechanism for converting 1, 2, 4 or multi-bit symbols from the CCU 18 into a phase-modulated IF carrier for transmission and to reverse the process at the receiving side. All control for the frame timing and the selection of the mode is performed by the CCU 18. An interface between the CCU 18 and the modem 19 may consist of four-bit, one-way, synchronous (16k symbol / second) data buses (Tx and Rx). In addition, an 8-bit state / control bus provides control information to the modem and reports the state of the modem to the CCU. The modem 19 also supplies the CCU 18 with the 16 kHz

AT 404 202 Β

In the base station, this clock signal is picked up by the master oscillator from the system timing unit 35, with which the entire base station (and thus the whole system) is synchronized. In the subscriber station, this clock is derived from the symbols arriving from the base station. All transmissions are therefore related back to the time base of the base station. A major function of the modus operandi of the subscriber station is to synchronize the local subscriber clock signal with the time standard in the base station by decoding the timing from the received symbols.

The modulator portion of the transmitter of the modem uses a FIR digital filter to produce a digital representation of the waveform used to modulate the RF carrier. The resulting digital stream is converted to an analog format and mixed with an IF transmission frequency of 20.2 MHz. The signal is then fed to the RFU for filtering, further converted to the RF and amplified before transmission.

The demodulator part of the receiver of the modem receives the IF reception signal from the RFU 21 with the IF reception frequency of 20 MHz. This signal is lowered to the baseband and then digitized by means of an A / D converter function. The resulting digital samples are processed by a microprocessor-based signal processing unit. This function performs filter equalization and synchronization algorithm on the input samples and then demodulates the PSK signal to produce the symbol stream at 16 K symbols / second. The signal processing unit also operates in self-training mode, which is used to teach the processing unit the imperfections of the analog filters used in the receiving stream. Once the signal processing unit is trained, the digital equalization process in the demodulator frees the input samples from the imperfections of the components of the analog filter. This technique allows the use of cheap, widely tolerated analog components and gives the entire system the ability to demodulate weak or distorted signals.

The signals demodulated by the modem are output to the CCU 18 at symbol speed during the reception process. The modem 19 provides the timing associated with this symbol stream. Both the base station and the subscriber station derive the timing of the receive function from the incoming signals.

A more detailed description and explanation of modem functions and characteristic operations will be given below with reference to FIG.

The base TDM / TDMA channel per subscriber provides a total of 16 kBpS in each direction intended for each call. Of this channel capacity, 1.43 kbps in each direction is needed to control the parent and demodulation preamplifiers. The VCU works with a fixed data rate of 14.57 kBpS. This is equivalent to 328 bits per codec frame period, defined as one-half the modem period or 22.5 ms.

To accommodate multiple calls per channel, each channel is divided into slots by a Time Division Multiplexing (TDM) scheme. These slots determine the frame format of the system. The length of the system frame consists of a given constant number of symbols. The frame duration of the system has been optimized by taking into account the speech encoding speed and the number of capture symbols necessary for the modem at the start of each burst. The number of slots within the system frame depends on the modulation level of the channel. For example, if the modulation level of the channel is QPSK, then the system frame consists of two slots per frame. As the modulation level of the frame increases, the number of information bits coded per symbol increases and, therefore, the data rate of the channel also increases. At a 16-level DPSK, the system frame splits into four slots, each of which transmits at the speech data rate of a call. It is important to note that even at higher modulation levels, the number of symbol times needed for modem synchronization remains constant.

The format of the system frame ensures that the modem 19 in the subscriber station is never forced to operate in full duplex mode (ie, simultaneous transmit and receive). From now on, the slots on the return and on the outgoing frequency are offset by at most one slot time in time.

The system frame of the system is defined as 45 ms. The symbol transmission speed is set at 16K symbols / second. Each symbol is transmitted in real-time, corresponding to 1/16000 of a second (62.5 microseconds). This gives a fix of 720 symbols per frame, from the start of the system frame numbered from 0 to 719. These 720 symbols can each consist of 1.2 or 4 information bits, corresponding to the degree of modulation of 2, 4 or 16 phases.

The system frame time (45 ms) is further divided into 2 or 4 timeslot slots, depending on the modulation format of the slots composing the frame. Each slot can be one of three

AT 404 202 Β

Slot types: (1) a radio control channel (RCC), (2) a 4-way speech channel, and (3) a 16-channel speech channel. The RCC is always transmitted in a binary (2-phase) modulation mode. The RCC and the 16-voice channel slot each require the transmission of 180 symbols, that is, one quarter of a system frame period. Since the 16-channel voice channel 4 information bits per symbol (which are 2⁴ = 16 phases), the 16-bit voice channel transmits 720 information bits per frame. This corresponds to a bit rate of 16 kBpS. Some of these bits are used for modem monitoring and control purposes, resulting in a voice bit rate of 14.57 kbps. The 4-way voice channel slot requires 360 symbols to transmit, equal to one half of the system frame period. Each symbol in this slot type consists of one of four different phases, so that 2 bits are transmitted per symbol (2² = 4 phases). The resulting bit rate is 16 kBpS, the same as for the 16-bit voice channel. The same number of bits (not symbols) are reserved for modem monitoring and control purposes so that the speech information rate is 14.57 kbps, as it is in the 16-bit voice channel slot type.

The system frame for any given frequency channel may be composed of any combination of these three slot types, subject to the following five limitations:

1. A maximum number (720) of symbols is transmitted with each system frame. Combinations of these three slot types can be combined to perform at a given frequency. In the event that the entire channel capacity is not filled in the transmission of the frame of the base station (ie if fewer than 720 symbols are transmitted in a frame), zero symbols are inserted to fill the frame's 720 symbol capacity. A zero symbol is a symbol that has no transmission energy.

Second Only one frequency in a multi-frequency base station has an RCC slot type. Only one RCC is serviceable throughout the system at a given time. The frequency at which the RCC operates is set by a system initialization parameter and is only changed if that frequency is unusable for some reason. The RCC slot is always allocated to the first 180 symbols of the system frame (referred to as slot 0).

Third The frequency of a base station can operate in a continuous transmission mode. The subscriber station transmits only during half the time of the total frame time. The subscriber station only transmits 25% of the frame when conducting a call when operating in RCC or 16-channel voice channel mode. If the subscriber station operates in 4-channel voice channel mode, it will transmit during 50% of the frame. A subscriber station can only transmit in one slot during a given frame when a call is being made.

4th All 4-channel voice channels must begin their transmission with the symbol number 0 or 360. This is because both the first half or the second half of a frame may contain a 4-way voice channel.

5th The transmissions between the adding and the returning frequencies are allocated so that the returning message of a given slot starts transmission 180 symbols after the transmission of the outgoing frequency message. This prevents the subscriber station from transmitting on the returning frequency while simultaneously receiving on the outgoing frequency.

Given these limitations, up to four calls can be processed on a single frequency if all four calls are from the 16-channel voice format and operate within the 14.4-kbps of the codec.

The slots within the system frame are numbered by their location in the frame structure. The numbering system does not have to be continuous. If one or more of the slots in the frame consists of a 4-channel slot type, the numbering system will jump over the second slot period included in the longer 4-slot. The slot numbering system for the transmissions of the returning frequency (ie Subscriber), is offset from the base station transmission (outgoing frequency). Therefore, a subscriber receiving information from the slot 2 of the outgoing frequency transmits on the return frequency in slot 2, which is half a frame shift in time. Tables 1 to 5 represent possible frame formats and the numbering associated with each slot.

AT 404 202 B

Table 1

Structure of the radio control channel Hinführender Kanal:

l &lt;°

System frame 45 ms «

<td>&lt;-11.25-&gt; 0</td><td>&lt;-11.25-&gt; 1</td><td>&lt;-11.25-&gt; 2</td><td>&lt;-11.25-&gt; 3</td>

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

<td>BPSK</td><td>16-PSK</td><td></td><td></td>

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

ms

Number of slots Number of symbols Modulation type

RCP

<td> on 'lch'</td><td> FILTER "STARTUP</td><td>* BIT SYNCTEMPLATE</td><td rowspan="2"></td>

<td>8th</td><td>8th</td><td>46</td>

<td colspan="3">Returning channel:</td><td></td>

<td>&lt;-11.25-&gt; 2</td><td>&lt;-11.25-&gt; 3</td><td>&lt;-11.25-&gt; 0</td><td>&lt;</td>

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

<td></td><td></td><td>BPSK</td><td></td>

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

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

<td>BEREIOH1</td><td>FILTER THRUST</td><td>BIT SYNC TEMPLATE</td><td rowspan="2"></td>

<td>XX</td><td>8th</td><td>49</td>

112

0 / Ϊ / 2/3 uw

function

Number of symbols

Tfoe

16-PSK

RCP

ΤΪΤ ms

Slot number.

No. of symbols Modulation type

RANGE 2

3-XX

function

Number of symbols

AT 404 202 Β

Table 2

Structure of the 4-channel speech channel frame

Leading channel:

l &lt;

systemframe ^s 45 ms&gt; 1 | &lt;------ 22.5 ms -----&gt; | &lt;------ 22.5 ms -----&gt; |

Slot number Number of symbols

360

360

<td colspan="5"></td><td rowspan="3">function Number of symbols</td>

<td>FILTER THRUST</td><td>BIT SYNC TEMPLATE</td><td>CODE WORDS</td><td>VCF 0</td><td>VCF 1</td>

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

Returning channel:

| &lt;------ 22.5 ms -&gt;! &lt;- 22.5 ms ----&gt; |

slot number

36Ö

360

Number of symbols

<td>FILTER THRUST</td><td>BIT SYNC AGC</td><td>CODE WORDS</td><td>VCF 0</td><td>VCF 1</td>

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

features

Number of symbols

AT 404 202 Β

Table 3

Structure of the 16-channel voice channel frame

Leading channel:

<img file="AT404202B_D0002.tif" />

Return channel;

<td>&lt;-11.25-&gt;</td><td colspan="2">&lt;-11.25-&gt;</td><td>&lt;-11.25-</td><td>&gt;</td><td colspan="2">&lt;-11.25-&gt;</td><td colspan="2">ms</td><td></td>

<td>2</td><td>3</td><td></td><td>0</td><td></td><td>1</td><td></td><td colspan="2">slot</td><td>No.</td>

<td>180</td><td>RSÖ</td><td></td><td>ΠΠΓ "</td><td></td><td colspan="2">180</td><td colspan="2">number</td><td>the symbols</td>

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

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

<td colspan="2">FILTER ÄKiiküF</td><td colspan="2">BIT SYNC AGC</td><td colspan="2">CODE WORDS</td><td colspan="2">VCF 0</td><td>VCF 1</td><td>function</td>

<td>8th</td><td></td><td></td><td>5</td><td></td><td></td><td colspan="2">Si</td><td>8Ϊ</td><td>Number of symbols</td>

AT 404 202 Β

Table 4

Frame structure of mixed modulation: 2/16-PSK and 4-PSK

Leading channel:

&lt;---------- system frame _s 45 ms&gt; l

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

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

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

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

ms

slot number

modulation

Number of symbols

Returning channel:

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

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

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

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

ms

slot number

modulation

Number of symbols

For each slot symbol description, reference is made to Figs. 2-1 to 6-3.

AT 404 202 B

Table 5

Mixed modulation: 4-PSK and 16-PSK

Leading channel:

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

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

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

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

ms

slot number

Modulation type Number of symbols

Returning channel :,

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

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

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

<td>18 &lt;5</td><td>180</td><td>J5Ö</td>

ms

protection count

Modulation type Number of symbols

Referring to Table 3, the structure of the 180 symbol 16-channel voice slot type will be described. The first 8 symbols of this slot type refer to filter start bits. The filter start-up period is included in the beginning of each slot type and is a time in which no power is transmitted and gives the receiving part of the modem 19 time to clear its filters in preparation for the new slot.

The filter startup is followed by a bit synchronization period. During this time, a degenerate 16 pattern is transmitted which simulates an alternating BPSK signal. The receiving part of the modem 19 uses this field to establish the phase reference of the transmission part of the modem 19.

Next, a twelve-bit codeword is used to initiate synchronization between the subscriber and the base station and to exchange control and status information. Codewords are used to interchange the current state of the connection, the quality of the connection, and power and time adjustments. Each control word is coded using the Hamming code in ten bits, allowing for easy error correction and double error detection. The CCU 18 determines the gain and synchronization losses by tracking the number of consecutively correctly or incorrectly received codewords; the CCU 18 transfers changes in synchronization to the RPU in the base station. In the subscriber station, the CCU 29 transfers synchronization changes to the STU 27.

The Hamming code adds five parity bits to five bits of information to produce a ten-bit code. Each parity bit is calculated by performing a modu-two addition of all the bits in the positions within the codeword that contains the bit representing the parity bit. Although the codeword is sent with all its associated data bits followed by all the parify bits, with the parity bits located in positions within the word with exactly one additional bit (the position represented by the bit), and the data bits set to other positions the code is illustrated as follows;

AT 404 202 Β

<img file="AT404202B_D0003.tif" />

When a codeword is received, the parity bits are calculated from the received data bits and compared with the received parity bits. If the calculated additional parity bit is different than the received additional bit, then the calculated bit is exclusive or with the received bit to indicate that the address of the bit is erroneous. If the calculated extra bits are the same and the others are not, then two errors have been detected. If all parity bits are the same, then the data was received correctly.

The rest of the slots contain two voice codec packets, each containing 328 bits of information.

Table 2 shows the Smybol structure for the 4-way voice channel. The structure is very similar to that of the 16-voice channel. Differences exist because certain symbol assignments depend on a fixed number of symbols needed per slot for higher-level purposes where other bit allocations are made with a fixed number of bits.

The Radio Control Channel (RCC) serves a dual purpose in providing a base to the subscriber station to initiate the detection of the system's timing from the base station and to provide native signaling between the base station and the subscriber station.

The format of the radio control channel slot is the same for both the leading and the returning channel, except for the following fields. The first eight symbols of a control slot, transmitted by the base station (on the leading channel), contain an amplitude-modulated (AM HOLE) gap, which is a period in which no energy is transmitted. This slot is used by the subscriber station to uniquely identify the control channel. At the beginning and at the end of the control channel of the returning channel there are extra few signals to account for the fact that the participant could be interrupted in his timing by a few symbols.

All slots contain eight symbols of the ΝυΙΓ transmission, and the filter startup field, which allows the modem to clear its filters for the new slot. The next field of the slot is a fixed bit tracking pattern. The pattern is an alternating BPSK signal. The receive modem uses this field to establish a phase reference and a frequency lock with the sending modem.

The CCU 18 searches to identify an incoming RCC message, constantly for a single word (UW), which is an eight-symbol sequence. The base station CCU must exhaustively check for a valid RCC message in each RCC slot. Based on the system timing, it performs this step by searching around the nominal UW position in a window of ± 3 symbols for the single word. The search algorithm starts with the nominal UW position and inserts a symbol right and left until it (1) finds the UW pattern and (2) determines a correct checksum. The search is completed as soon as (1) and (2) are fulfilled or all possibilities have been exhausted. The shift information, the RCC message and the performance information are sent to the RPU after a successful search.

When the subscriber station CCU 29 receives RCC data, it may be in one of two modes: frame search or monitor. The frame search operation is used to obtain the receive frame timing from the incoming RCC data and is called automatically when the RCC synchronization is lost. The monitor mode is entered as soon as a receive frame synchronization has been detected.

In the frame search mode, the CCU 29 of the subscriber station must immediately after a RCC slot is received at the subscriber station, exhaustively check this for a valid RCC message. As with the CCU 18 of the base station, the CCU 29 performs its steps by sampling for the single word within a window of ± 3 symbols around the nominal UW location based on the timing of the detection of the AM slot is derived by the modem. The search algorithm

AT 404 202 B starts with the nominal UW position and inserts a symbol right and left until it (1) finds the UW pattern and (2) determines a correct checksum. The search ends as soon as (1) and (2) are fulfilled, or all possibilities have been exhausted. The shift information of a successful search is used to set the receive frame markers generated by the CCU. The recording ends when, as above, (1) and (2) satisfy for three successive frames with the UW in its nominal position. The STU 27 will, if this occurs, informed of the frame takeover. During frame search, RCC messages are not forwarded to the STU 27.

When the frame recording is completed, the CCU 29 of the subscriber station turns on the monitor operation. Only the nominal UW position is checked to avoid the possibility of a wrong UW takeover. If no UW is found in five consecutive frames then the channel is declared out of synchronization and the frame search operation is picked up (this transition should be very unlikely or the usability of the system is unacceptable). The STU 27 is informed of this synchronization failure. During monitor operation, RCC messages having a correct checksum and subscriber ID number are routed to the STU 27.

The remainder of the slot is used for information exchange between the base station and the subscriber station. The data section consists of 12 bits. The first eight bits of data contain a link field that provides information regarding the state of the system, the collision, detection, and recovery of information.

The purpose of the Link Level Protocol is to detect bad messages in the Radio Control Channel. The connection protocol also resolves disagreements in the RCC slot.

The connection field contains bits for free transmission. System busy, collision, broadcast detected and slot reservation. These bits are set by the CCU 18 of the base station and read by the CCU 29 of the subscriber station.

The free transfer bit is set by the base station to indicate that an empty message has been transmitted. When a subscriber unit receives a slot with this set of bits, it only performs the usual synchronization and error checks, but does not pass the message on to the respective RPU 20 or STU 27 if the message was received with an error.

The system busy bit indicates that all voice channels should be allocated and no new call requests (for a certain time) should be attempted.

The collision bit resolves entanglements of two or more subscribers attempting to transmit in the same control slot.

The message designating bit indicates that the base station has detected a transmission on the returning control channel.

The slot reservation bit reserves the next slot of the returning control channel.

The remainder of the data portion is used to address and exchange information during call setup and abort operations. The data part is followed by a cyclic 16-bit redundancy check (CRC) on the slot's only word and data parts. The CRC is used to detect errors that may occur during transmission of the RCC message. The CRC algorithm involves dividing a data block by a predefined bit sequence and transmitting the remainder of that division as part of a data block. The polynomial for generating the CRC has the form of P (x) = 1 + x⁵ + x¹² + x^{, s} (Equation 1)

When the CRC realizes this check on a received message, the message is not passed from the CCU 18 to the RPU 21 in the base station, or not from the CCU 29 to the STU 27 in the subscriber station.

When the subscriber station first turns on and goes to the line, the subscriber station must record system timing and synchronization based on the base station. This recording is carried out by transmission exchange via the radio control channel (RCC) and a separation to the voice channel. The events that lead to system uptake are as follows:

1. When power is first turned on in the subscriber station, the system will respond and the subscriber station CCU 29 will issue a series of commands to the demods of the modems 30a, 30b, 30c, resulting in the reception of the RCC.

Second The demod of each of the modems 30a, 30b, 30c is next put into the training database. During this time, the modem teaches its receiving digital filters the characteristics of the analog receive filters. The analog filters may be detuned due to time and temperature. Each modem adjusts its digital filter coefficients during the shuffle operation to compensate for these detuning. After the CCU 29 has received the state of the demods 30a, 30b, 30c that the

AT 404 202 B

Training sequence is complete, the CCU resets the receive frequency to the RCC frequency that was assumed. The CCU then commands the modem to pick up the RCC frequency and look for the characteristic amplitude modulation gap, referred to as the AM gap. The AM gap is a period of 16 symbols in duration if no power is transmitted from the base station during the beginning of the RCC transmission. All other sent slot types include only a zero transmission of eight symbols. The eight extra symbols of the null information at the start of a slot burst uniquely identify the burst as an RCC burst.

Third The first act of the demods of the modems 30a, 30b, 30c is to make a rough frequency recording. The received signal is processed in a digital phase locked loop and the subscriber VCXO is set to the base station transmit frequency. After the frequency recording, the modem begins to search for an AM gap. The modem searches for a sequence of symbols with little or no amplitude.

If this sequence is found after a number of frames, the modem will assert an AM call signal to start the CCU frame timing circuit. If no AM column sequence is found, the modem returns the status to the CCU that the RCC acquisition was unsuccessful. The CCU begins to pick alternative RCC frequencies in the same way.

4th Upon detection of an AM slot, the modems of the modems 30a, 30b, 30c perform a refined frequency acquisition and initiate the bit synchronization control. The first 60 symbols of the RCC control slot are fixed bit synchronization patterns that are used by the modem for interlocking with the phase of the base station (bit timing). At this point, the RX clock at the subscriber station is usable as a symbol clock.

5th The CCU 29 of the subscriber station has received via AM-Auftastsignai from the modem a rough symbol timing adjustment. After receiving the frequency and bit synchronization, the CCU examines the data received by the modem and searches for the single RCC word. This single word gives the absolute symbol count reference for the frame. The CCU then adjusts its symbol counters to match that reference. The subscriber station is now concurrently with the system timing of the transmission (frequency and symbol timing) in the base station and locked to it.

6th The remaining part of the system timing acquisition determines the delay range between the base and the subscriber station. This delay can be shifted in the system (one way) between 0 and 1.2 symbol times. While a call is being placed, the subscriber station sends a message to the base station via the RCC.

7th The modem 19 of the base station is constantly looking for new input bursts from the subscribers. These bursts may be delayed by 0 to 3 symbol times from the reference start of the frame in the base station. During each slot, the demods of the base station modems 30a, 30b, 30c look for a transmission in the returning RCC slot. All timing and phase information must be derived during the first part of the slot (message header), otherwise the slot and its information will be lost. There is no second opportunity when incoming control slots are received. The incoming control slots are received at the RCC according to the Aloha wait scheme described below, following this series of events resulting in system detection.

8th. During each slot, the base station modem performs a fast AGC adjustment and a bit timing estimate during the first 60 symbols of the slot. The timing signals of the receiving part are adjusted to compensate for the range delay of the subscriber. The received data is then delivered to the CCU 18 of the base station. The CCU 18 determines the location of the single word in the stream and determines the total delay range between the base station and the subscriber station. The modem 19 provides the AGC information to the CCU 18 to determine the TX power setting at the subscriber station. The modem 19 also provides the connection quality and part-time information to the CCU. Link quality is used to determine if a collision has occurred. A poor link quality measurement result indicates that the signal did not have high quality, most likely due to a simultaneous transmission of more than one subscriber in the RCC slot. The estimated part-time is the value of the sub-range delay between the base and the subscriber stations calculated by the modem 19.

9th This power and range delay information is processed by the CCU 18 and forwarded to the RPU. The RPU 20 places this information in the RCC format and sends this information to the subscriber station via the RCC control slot. The subscriber station CCU 18 decodes this information and makes the necessary adjustments to the transmit power and range delay counters in both the modem 19 and the CCU 18. The CCU 18 brings

AT 404 202 Β updates its entire own TX symbol frame counter and also carries the modem in the modem

Clock of the counter for the partial delay to the last state.

10th During the call connection for a subscriber station, the RPU 20 assigns the frequency and

Slot assignment for the speech call too. This information is passed through the RCC and the subscriber station's CCU adjusts the RX frequency and commands the modem to detect the RX frequency

To start speech slot. AGC, timing and frequency information is transferred out of the RCC procedure into the voice channel procedure. This is possible because all frequencies in the system are synchronized by the same frame time reference in the base station.

11th To fine tune the timing of the subscriber station, a refinement procedure on the

Beginning of each speech connection introduced. During the refinement phase, the connection over the voice channel is similar to that over the control channel, the modulation is BPSK and the messages are in RCC format, but no AM gap is generated in the base station: these new RCC messages are between the CCUs 18 and 29 exchanged. The modem 19 is arranged in the refinement mode in the base station, and in external control operation in the subscriber station. During the refinement, the CCU 29 generates a message to the subscriber station which contains, for the most part, a fixed bit pattern, together with a variable portion indicating the acceptance or rejection of the previous message received from the base station. The base station modem 19 passes timing and power adjustments to each received slot to the CCU 18. Performance adjustments are sent continuously to the subscriber station. Time adjustments and control information indicating the continuation or termination of the refinement operation are sent out after a calculation period. The CCU 18 of the base station collects the time adjustments from the modem 19 for 30 frames, calculates a means and sends the adjustment to the CCU 29 of the subscriber station. Then, another 30 frames in the CCU 18 of the base station are subjected to a refinement process which, with the result, are sent back to CCU 29 of the subscriber station. The refinement phase is terminated by the CCU 18 of the base station and the speech connection begins when the deviations of the adjustments received by the modem 19 are within an acceptable range, such as 1%, or the refinement period has exceeded a maximum time value.

During call setup and disconnection, the subscriber station services the base station by sending messages over the returning RCC slot. The traffic characteristics of a subscriber station attempting access to the RCC may be characteristically stochastic. When a subscriber station desires to send a message to the base station, some forms of control mechanisms must decide which subscriber station access is allowed because several subscriber stations might try to transmit in the same slot. The slotted Aloha scheme is well suited for linking a large total number of subscribers requiring relatively rare access to the RCC channel.

The slotted aloha scheme allows the subscriber stations to send messages in the designated RCC slot completely regardless of whether other subscriber stations are also trying to send in the same control slot. The natural consequence of this freedom of action is that messages from different subscriber stations can be sent and therefore collide. To handle these collisions, this scheme requires that a positive acknowledgment (ACK) be sent from the base station following the correct receipt of the subscriber station message. If the ACK is not received within the maximum grant time required for the transmission and processing of the delays in each direction (approximately 1 - 2 frame times), the subscriber station must retransmit the message. Return transmissions may be caused by an error in receiving the ACK in the subscriber station. In general, the subscriber station can not determine the cause of the problem. Thus, the subscriber station chooses any delay before re-transmitting the message to avoid repeated collisions with other transmitters, which may have been the case in a previous collision.

One complication that may appear in an aloha scheme is the fact that the channel becomes unstable when random retransmission delays are not long enough. When this happens, the channel is clogged by retransmissions and the throughput drops to zero. A freelancing technique minimizes this problem by increasing the average random retransmission delay at each subscriber station by successive retransmissions.

The entanglements of retransmission collisions and the stability control for the delay access is that the delays are typically geometrically distributed. In order to avoid large deviations of the delay, it is therefore necessary to drive the channel with a load of substantially less than 36%.

AT 404 202 Β

In particular, a load of 20% or less makes it unlikely that more than one retransmission due to collisions becomes necessary. Using a random delay of, for example, eight frame times for 45 ms frames, the total average delay in a retransmission is 450 ms (eg on average, the delay includes: a frame delay of the original override, plus a frame delay for the acknowledgment, plus the eight frame random delay):

To ensure that the utilization does not become greater than 20%, we must consider the average time T between the call requests per subscriber, the total number N of subscribers, and the frame time F for values ​​less than 36%, where the utilization by NF / T given is. For F = 45 ms, N = 1000 participants, and T = 30 minutes, the utilization is 1.5%.

Thus, for a maximum utilization value of 20% for a total of 1000 subscribers, each of which can make a call on average every half a minute, based on a 45 ms frame time, an access delay of about 45 ms can be achieved when retransmission is required , and an average access time of approximately 70-80 ms. The price paid for the much lower average delay is an increased delay margin which, for 20% or less utilization, occasionally has two retransmission times, ie a second, would exceed.

The Aloha approximation scheme appears to be well-suited for a system with a large population of subscribers who relatively rarely request direct access to the control channel, and would allow the planned goal of building delays of less than one second, which would be expected Population parameter is sought. In contrast, voter and fixed TDM technology provide unacceptable delays.

All phases of call processing including call setup, call disconnection and slot connection require information exchange over the control channel and / or the control section of the talk slot. The following describes the various phases of call processing, both in terms of processing in the subscriber station and processing in the base station.

The Subscriber Station Identification Number (SIN) and digits dialed are two call control terms that must be introduced into a Call Requests message for each call made by a subscriber station. In the case of calls from subscriber station to subscriber station, the user selects the number in a register in the memory of the subscriber station. The user initiates the connection to the base station by pressing a transmit button or by waiting for a timeout. Only when the number is completely assembled and stored in the subscriber station, the radio channel is used. Therefore, the subscriber can dial at a low speed without involving valuable bandwidth of the radio control channel (RCC) or time.

The message sequence generated by the subscriber stations and the base station to establish a connection between two subscribers is shown in FIG. The control channel connection level protocol is used to check the various error conditions that occur due to channel errors. Furthermore, messages received by the base station on the returning control frequency are automatically acknowledged in the next control slot on the going control frequency. The following paragraphs provide a brief description of a message exchange for establishing a conversation between two subscriber stations.

When the base station receives a CALL REQUEST message over the control channel from a subscriber station A, it first checks the received SIN for errors. If the SIN has an error, the message is dropped. Without a valid SIN, the base station does not know who sent the message. If the selected digits are incorrect or incomplete, the base station sends a CLEAR INDICATION message on the going control channel frequency to the requesting subscriber station A, with state information explaining the problem.

If the request attempt is correct and allowed (ie the destination unit is not busy), the voice channel is assigned to the requesting subscriber station A and the base station transmits a PAGE in the form of an incoming call message on the forward control frequency to the destination subscriber station B. If the destination subscriber station B does not answer the PAGE with a CALL ACCEPTED message after two attempts or returns a busy status indication with a CLEAR REQUEST message, then the base station sends a CLEAR INDICATION message to the requesting subscriber station A with the busy status information (ie Destination unit is off-hook) or that the destination subscriber station does not answer the PAGE.

If the destination subscriber station B accepts the incoming call, then a CALL-ACCEPTED message is sent back to the base station and the voice channel is assigned. When the synchronization of the speech channel is completed, the destination subscriber station B generates an audible ring heard at the destination subscriber station B and also generates the RINBACK tone over the speech channel to

AT 404 202 Β requesting subscriber station A.

When the destination subscriber station B picks up, the voice slot control section changes from a synchronous ringing indication to a synchronous off-hook indication and CALL PROGRESS messages are handled via the speech channel via the base station between the two subscriber stations. The destination subscriber station B stops the audible ringing and separates the RINGBACK tone from the speech channel at this time. The circuit is now complete and the voice / data exchange can begin.

The assignment of a call to an external telephone is made in the same way as the call to another subscriber station. The subscriber station simply selects the desired digits and presses the send button or waits for the lock time. This generates a radio request message to the base station. The base station decides whether to look for another subscriber station or to detect an external trunk. In this case, an external trunk is detected and the selected digits are pulsed on the trunk. As the digits are delivered pulsed, the speech frequency is allocated for the requesting subscriber station. When a subscriber station receives the CALLCONNECT message, it alters the frequency and synchronizes itself to the assigned voice channel. Simultaneously, when the voice channel is ready, the subscriber station's handset is disconnected from the local mute and connected to the external trunk. From this point on Telco's destination office will generate all other ringing tones.

An incoming external call occupies a trunk in the base station. The requesting office sends 2 to 5 digits, which identify the individual digits of the destination subscriber station SIN, to the base station via the direct dialing trunk (D / D). If the selected subscriber station is not busy, the base station transmits a PAGE MESSAGE to the associated subscriber station. Three possible situations can occur. First, the subscriber station will accept the incoming call and processing will proceed as described later. Second, no response is received. In this case, the base station repeats the call process twice. If the base station has exhausted the repeating pulse sequence without a response from the subscriber unit, then a RINGBACK tone is generated in the requesting unit. The third state is a result of the busy dialing subscriber station (ie lifted) and the return of a CLEAR REQUEST message to the control channel. In this case, a busy tone is returned to the requesting subscriber station.

In the case of a successful PAGE request, the voice channel is assigned, an external call is generated at the handset of the destination subscriber station, while an audible RINBACK tone is generated backwards to the requesting part by the subscriber station. When the destination subscriber station answers the call (ie the base station detects the transition from hang-up to take-off), the external ringing and the RINGBACK message is suppressed. At this point the voice channel is ready for a call.

A normal call termination is initiated by the calling subscriber. The base station determines the transition from pickup to hang up via the control section of the talk channel. After determining the transition, the base station triggers the assignment of the speech channel. The channel can be used again until the base station sees that the subscriber station has lost synchronization with that channel. If the disconnected call is destined for another subscriber station, an on-hook indication is sent to the second subscriber station in the control section of the speech channel. The subscriber station resynchronizes itself to the transmissions of the RCC and sends CLEAR REQUEST messages to the base station.

The termination of a call thus takes place five seconds after the base station has lost contact with a subscriber station.

A voice connection may be lost due to fading or channel interference at the targeted receiver. If the connection has failure problems, the following conditions are checked at the subscriber station and the base station: The value for the connection quality returned by the subscriber or the base station is below a predetermined threshold for successive recordings; for some consecutive transfers, a word synchronization loss was detected.

Base station originated messages are broadcast to all active subscriber stations. These messages are transmitted by the base station via the radio control channel. The purpose of the sent messages is to make all active subscriber stations aware of changes in the operation of the system (ie Change the frequency of the RCC or a command to the modems to go into the self-test mode, etc). These messages are not confirmed by the subscriber stations. Remote Control Processing Unit (RPU)

The RPU functions as a control computer within the architecture of the base station; it is linked to the CCUs 18 associated with the radio equipment and, as shown in Figure 2, to the PBX

AT 404 202 Β

15th

The RPU coordinates the necessary actions for the processing of radio calls. The RPU exchanges messages with the subscriber stations, the PBX 15, and the CCUs 18 to make connections or disconnections. Included in the call processing functions is the allocation and delegation of radio channels. The RPU 20 operates a database that reflects information about the current state of the system; the database contains information about the state of the devices, the subscriber stations, the connections and the radio channels within the system.

Call setup begins when the RPU receives a message either from the PBX call processor 24, that a call has been received from an external line, or from a subscriber wishing to place a call to an external telephone or other party. The traffic from a subscriber comes in via the Radio Control Channel (RCC) via a CCU 18 of a base station. The RPU 20 allocates a voice channel and exchanges messages with the subscriber station, the PBX 15 and the CCU 18 to establish the connection.

A disconnect begins with a message received from the PBX or a participant's announcement that he has hung up. or from the CCU 18 indicating that the synchronization over the radio channel has been lost. The RPU informs the CCU 18 and the PBX 15 of the interruption and the RCC is disconnected.

The RPU software performs the following functions:

1. Processes party, CCU and PBX messages that control call setup, call interruption and channel allocation;

Second Initiates and maintains a read / write database system;

Third Maintains an operating system that allows for system examinations and a manual control system;

4th Treats the BCC interface by supporting the baseband control channel (BCC) communication protocol over a 9600 baud asynchronous serial interface;

5th Treats the PBX interface by supporting the PBX message protocol; and

6th Contains implementation logic that provides diagnostic and billing data.

The RPU software transmits a serial interface to the PBX call processor 24. It also transmits serial interfaces to each of the CCUs in the base station configuration.

The RPU hardware includes a Motorola Model 68000, which is designed as a general-purpose computer. This machine is equipped with a Mbyte random access memory (RAM) and 10 Mbytes non-volatile hard disk storage. I / O consists of a system console and a unit that has eight asynchronous serial data interfaces.

As shown in Figure 5, the RPU software package simulates a system that includes: a scheduler module 40, a BCC interface module (s) 41a, 41b ..... 41n, a PBX interface module 42, a console module 43, a tachograph module 44, a message processing module (MPM) 45 and a database module 46.

All modules, except the database module 46, are called by the scheduler module 40 to expire. The modules communicate with each other via a mailbox system. The database module 46 is based on a collection of access information subroutines in the database.

The scheduler module 40 provides a main line code for the RPU software. It is responsible for the pre-planning and activation of all other modules. It is also responsible for maintaining event timers and mailboxes that allow for internal and intermediate information exchange processing.

The BCC interface modules 41a, ... 41n have an asynchronous serial interface and a connection level protocol. They also monitor the connection state with the CCUs 18.

The PBX interface module 42 brings an asynchronous serial interface to the call processor 24 of the PBX.

The operations console module 43 provides a system service interface that allows system state queries and allows message exchange between the RPU 20 and the rest of the system.

Co-write module 44 provides raw implementation information for diagnostic and system analysis purposes.

Message processing module 46 processes all RCC, BCC and PBX messages. It performs the setup and disconnection of all subscriber calls that are not being performed by the PBX 15 and allocates the radio channels. It also includes a background program that monitors the state of the CCUs 18.

The database module 46 provides a solid interface to anything that requires data structures for call processing. It includes a frequency allocation program which includes the radio channels

AT 404 202 Β allocates.

The RPU database contains structures that describe the system structure, including the information to all participants and the status of all radio channels. These structures are described as follows:

The RPU database contains a baseband control channel (BCC) data structure for each CCU 18 in the system.

A subscriber identification table (SIN table) contains an ordered list of all valid subscribers. The list is organized to facilitate the accuracy of the participants. The SIN table has one input for each participant in the system.

The RPU software performs part of the subscriber unit's call processing. This processing takes place in the message processing module. The call processing is performed by message exchange between the MPM 45, the PBX module 42 and all BCC modules 41.

Initiation of a telephone call from a subscriber station

This paragraph briefly describes the normal process of establishing a call for a telephone call initiated by a subscriber. A subscriber (the requesting subscriber ") picks up, dials a valid telephone number (the telephone number of the destination station) and presses the send button or waits for the lock time. The requesting subscriber station sends a CALL REQUEST message to the base station via the control channel. The RPU BCC modules 41 receive the RADIO REQUEST message and forward it to the MPM 45. The MPM 45 performs some simple correctness checks of the selected digits and sends a RADIO REQUEST message to the PBX module 45, which forwards the message to the PBX control processor 24. The PBX call processor 24 evaluates the selected digits and issues a PLACE CALL message to the RPU 20. The MPM 45 allocates a speaking slot to the requesting subscriber station. The MPM 45 generates a CHANGE CHANNEL command to the CCU 18 containing the talk slot allocated to the requesting subscriber station. The MPM 45 generates a CALL CONNECT command to the requesting subscriber station, which command assigns the voice frequency and slot to the requesting subscriber station. The MPM 45 generates an ALLOCATE message to the PBX call processor 24, which tells the PBX call processor 24 to allocate a message channel. At this point, the requesting subscriber station is fully on. It now waits for a connection via the PBX switching matrix 25 to the destination. The destination "can either be another subscriber station or a telephone which must be accessible via a Telco transmission line, it makes no difference.

Receiving a call from a subscriber station

This section briefly discusses how to handle an incoming call at the subscriber station. The PBX call processor 24 determines that the telephone call is for a subscriber station. The PBX call processor 24 generates an INCOMING CALL message. This message contains information about the nature of the call, in particular whether the call comes from an external trunk 14 or from another subscriber station. The RPU PBX module 42 receives the message from the PBX call processor 24 and delivers it to the MPM 45. When the call comes from another subscriber station, the MPM 45 sets the subscriber-to-subscriber index to both the calling and called subscriber stations and commands the involved CCUs 18 to go into internal operation. The MPM 45 generates a PAGE message to the subscriber station prescribed in the INCOMING CALL message. The associated subscriber station responds with a CALL ACCEPT message. The MPM 45 responds to the CALL ACCEPT message by generating a CHANGE CHANNEL message to the associated CCU 18 and a CALL CONNECT message to the associated subscriber station. The MPM then generates an ALLOCATE message to the PBX call processor 24 which causes the PBX selector matrix 25 to establish the end call for the incoming call.

Interception of a signal failure

This section briefly describes the behavior of the RPU 20 in the event of channel fading during the course of a call. The CCU 18 handling the dwindling speech channel sees that the channel is losing synchronization. The CCU 18 generates a NO-SYNC message. The BBC module 41 receives the event message and conveys it to the MPM 45. The MPM 45 sends an ONHOOK message to the call processor 24 of the PBX and sets the subscriber to the idle state and the channel to the on-hook state.

AT 404 202 B

Processing an incoming BCC message

A BCC message is passed through a 9600 baud asynchronous interface from the CCU 18 to the RPU 20. The BCC module handling this particular CCU reads in the message and checks the bits of the link level information to check the correctness of the incoming message. If the module 41 determines that the message is acceptable, an appropriate acknowledgment is returned to the sending CCU 18. Otherwise, a retry run or a negative acknowledgment will be returned. The BCC module 41 now sends the message to the MPM 45. This message is placed in the message processing mailbox 48 using the mailboxes provided at the scheduler module 40 (see Figure 6).

If there is no other input from the CCU 18, and the mailbox 49 containing output messages to the CCU is empty, the module 41 blocks and the controller transfers to the scheduler module 40.

The scheduler module 40 activates the next module in the scheduler round and that module runs until it blocks. The scheduler module then activates another, and so on. At some later point, the scheduler module activates the MPM 45.

The MPM 45 then reads in the BCC message, along with any other messages queued for it in its 48 mailbox. The BCC message is identified and processed. Such processing may include changes to the database and the generation of new messages. FIG. 6 illustrates the data path of an incoming message.

Generation of an outgoing BCC message

Figure 6 also illustrates the data path of an outgoing BCC message. An outgoing BCC message is generated by the MPM 45 in response to any particular events. The message is established within the MPM and submitted to the BCC module 41, which handles the destination CCU 18. After this message and any other necessary messages have been sent and if there are no more messages in the mailbox 48 of the MPM, the MPM blocks and control is returned to the scheduler modem.

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

Processing of RCC messages

An incoming RCC message is treated exactly like an incoming BCC message, since an RCC message is a kind of BCC message. An outgoing RCC message is thus generated and transmitted in the same way as an outgoing BCC message.

Processing an incoming PBX message

A PBX message is received from the PBX call processor 24. This message goes through a 9600 baud asynchronous interface to the RPU 20. Referring to Figure 7, the RPU reads PBX module 42 in the PBX message and sends it to the MPM mailbox 48. If there are no more incoming characters and the mailbox 50, the the outbound PBX message is empty blocks the RPU PBX module 42 and the controller is transferred to the scheduler module 40.

The MPM 45 reads in the PBX message, along with any other messages that have lined up in its mailbox 48. The PBX message is processed according to the type of message and the current state of the subscriber specified in the message. The processing may include changes in the database, changes in the state of the participants and the generation of new messages. FIG. 7 illustrates the data path of the incoming PBX message.

Generation of an outgoing PBX message

Referring to Figure 7, an outgoing PBX message is generated by the MPM 45 in response to an event. The message is established within the MPM 45 and sent to the PBX module 42. After this message and other required messages have been sent and no further

AT 404 202 Β

Messages in the mailbox 48 of the MPM blocks the MPM and control is returned to the scheduler module 40.

The scheduler module 40 continues to activate further modules in the scheduler round until the RPU PBX module 42 is activated.

The RPU PBX module reads the PBX message from its mailbox 50 and then transmits the message past the serial data output to the PBX call processor 24.

Generation of penscript messages

At key points in each of the modules, the RPU software package contains a factual message that is sent to the tachograph module 44. This information is marked in time and output to the file. FIG. 8 illustrates the data paths of the co-writer.

Input / output modules of the control panel

The front end of the service module 43 provides command input and identification along with the instruction integrity check. Valid operation console commands have the authority to query and update the RPU database and send messages to the RPU modules. The output resulting from the console display commands is output directly at the console output.

Scheduler module

The scheduler module 40 is considered a special module system and is responsible for scheduling all other RPU modules. The main tasks of the scheduler module 40 are to enable selection of the next module to be executed and intermediate and internal module connections.

Although all the different RPU modules can be thought of as separate modules, in reality all modules are an application process of a Regulus workstation. It is the scheduler module 40 that performs all-round monitoring of the other RPU modules. The scheduler module 40 manages the wait stack for each of the dummy modules by allocating a fixed portion of the stack volume to each of the dummy modules at the startup time. Then, just before each module begins to run on schedule, the stack pointer is changed by the scheduler module 40 to show the corresponding stack address to the associated module. Figure 9 shows a memory map of the RPU.

Each RPU module runs until it blocks. When a module blocks, it returns the control to the scheduler, which allows another module to file and start up. A module can block in several ways: a GETEVENT call that forces the module to block until an event is pending, or a WAIT call that blocks for a certain number of seconds, or a BLOCK call that blocks the loop of the scheduler round for a run.

Another important function that the scheduler module performs is the inter-module traffic. As a means, mailboxes are used to send or receive messages to or from other modules. Each module can check whether mail is in its mailbox by using an MAIL READ call. Likewise, a module can send mail to another module using the MAILSEND call. The scheduler module operates its own mailbox for each of the modules that reside in the scheduler loop. When a module sends a message to another module, the message is copied to the destination mailbox. Later, when the goal is to run, the scheduler checks its mailbox to see if there is a message in the mailbox. If so, the scheduler module generates an event of type MAIL which forces the module to become unblocked if it was blocked by a GETEVENT () and thus begins to run as scheduled.

An event list is also maintained by the scheduler module for each module in the scheduler loop. Events can consist of post or clock events. Post events are generated whenever the scheduler module determines that messages are present for the currently baptized module. A module can put a clock event on the event list by making a PUTEVENT () call with the number of seconds to wait before an event should occur. The scheduler module 40 checks the event list of the schedulers on each loop over the loop of the scheduler loop, looking for clock expiration times. When a clock expiration is encountered, the associated module is initiated and the event is returned to the module by the GETEVENT () call.

AT 404 202 Β

The scheduler module 40 includes subroutines that are used to initiate RS-232 links between the CCU 18 and the RPU 20 and between the PBX 15 and the RPU 20. These subprograms, which take over the software control exclusively via the RS-232 interface, switch off the usual processing of control sequences by the Regulus operating system. Additional subroutines are used to buffer the I / O buffers and to read and write in the input and output of the terminal.

BCC interface module

Each BCC module 41 provides a link between a CCU 18 and other software modules in the RPU 20. The messages exchanged between the CCU 18 and the RPU 20 are binary data of various lengths transmitted over an asynchronous traffic link. The BCC module 41 is responsible for the correctness of the traffic connection messages, including error detection, message ordering and message acknowledgments.

The hardware interface between the CCU 18 and the RPU 20 consists of an asynchronous 9600 baud RS-232 interface.

The inputs to this module 41 include messages received from the CCU or other RPO software modules. Messages are output from this module either to the CCU via the RS-232 interface or to other software modules via the associated mailbox.

The purpose of the module 41 is to process the message traffic between the RPU 20 and the CCU 18. The module 41 continuously checks the messages received from the CCU and forwards them to the associated software module. Likewise, this module continuously checks the messages from other RPU software modules destined for a CCU 18. An alternate bit protocol is used to store pending (ie unconfirmed) messages to limit one in each direction. Stringing and acknowledgment bits provide the necessary flow control to accomplish these functions. The protocol is described in more detail in the following paragraphs.

In the following discussion, a size that can handle messages is referred to as us or us, and the other is referred to as 'you' or 'us'. The protocol can be explained by showing the actions that are taken when a message is received. There are only four basis actions that depend on two conditions. These conditions are determined by comparing the ranking and acknowledgment bits of the received message with the expected one.

For an incoming message, the ACK bit is considered as expected if it is the same as the SEQ bit of our last transmitted message. Similarly, the SEQ bit is considered as expected if it differs from the SEQ bit of the last received message. In other words, the expected conditions are that an incoming message confirms our last message and we also expect each new entry as a new message.

The actions taken on the basis of a received message are now grouped under four combinations, which result from the above conditions:

1. ACK as expected; SEQ as expected. Marks our last sent message as confirmed (allows us to send a new message). Processing the most recent message received (confirms it in the next message sent by us).

Second ACK as expected; SEQ not as expected. Marks our last message sent as not confirmed (allows us to send a new message). Elimination of the recent message received (does not confirm it).

Third ACK not as expected; SEQ as expected. If we sent a message that has not yet been confirmed, send it back. If we have no such message, then something went wrong at the destination and we need to reset as described below. Process the latest arrived message.

4th ACK not as expected; SEQ not as expected. Our last message was not received at the destination. Send it back. Dispose of the recently arrived message.

The reset bit is used to reset the SEQ and ACK bits. If we receive a broadcast with a reset bit on it, it must be accepted and acknowledged as a new message without regard to its SEQ bits. Further, the ACK bit on the received message reflects the SEQ bit of the last message that we have received from it. We need to translate this bit before sending the next message. For example, if we receive a message whose ACK / SEQ bit is 4 "(Reset = 1, ACK = 0, SEQ = 0), then the ACK / SEQ bit must be 1 for the answer (Reset = 0, ACK = 0, SEQ = 1). Each page can reset if it thinks the log is out of order.

AT 404 202 B

When we receive a message from them and we have no new message in limbo and a standard message is not imminent, we will acknowledge the message by sending a special ACK message. The ACK bit will acknowledge the received message, but the SEQ bit of the last message we sent will not change. This will cause them to complete the confirmation and cancel the most recent message. The content of this message is a null message. However, since this message was somehow eliminated, their content should be irrelevant.

PBX interface module

The PBX module 42 provides the link between the UTX-250 PBX call processor 24 and the other software modules of the RPU 20. The messages exchanged between the two machines must consist of an ASCII character oriented message exchange. Both the PBX call processor 24 and the RPU 20 must be capable of accepting even or odd or no parity characters. The test of the messages consists of strings of different lengths or printable characters.

The hardware interface between the PBX call processor 24 and the RPU 20 consists of an asynchronous 9600 baud RS-232 interface.

Inputs to the PBX module 42 include messages received from the PBX call processor 24 or from other RPU software modules. The messages of this module are output either to the call processor 24 or to other RPU software modules via the corresponding mailbox.

It is the purpose of the PBX module 42 to process the message traffic between the RPU 20 and the PBX call processor 24. This module constantly checks the messages received from the PBX call processor 24 and transfers them to the corresponding RPU software module. Likewise, this module continuously checks the messages from other RPU software modules destined for the PBX call processor 24. *** "

Each character received by the PBX call processor 24 is checked for equality with the greater than character&gt; indicating the beginning of a message or a carriage return indicating the end of a message. This module is capable of handling full-duplex message traffic.

Control panel module

The control panel module 43 is the window of the operator in the current state of the RPU 20. The control panel provides the ability to display information regarding the current state of the participants and the radio channels. Change connections and channel states and send messages to the PBX 15 and the CCUs 18. The control panel processes the input power from the field office and executes the desired commands.

The operator putty module 43 provides the link to the terminal of the operator in the base station. The control panel module 43 processes the input from the terminal and executes the command. Data is extracted from the database and written in, displays are displayed on the screen of the terminal, and messages are sent to other modules. The interfaces for this module include:

(1) Characters are input from the keypad of the operator.

(2) Characters are issued to the screen of the operator.

(3) Data is taken from the databench and written.

(4) Messages are sent to the PBX, BCC, and message processing module.

A set of parser programs inputs characters from the keypad of the operator. A data entry message is displayed at the beginning of each command line, the data is buffered, the characters to be output are processed, the input is returned to the display panel, and the data is decomposed into characters. By providing the parser with a set of data structures describing all possible commands and valid characters within each instruction, the parser performs identification of the input data, answers questions, tags, and displays keywords for data entry. Each character is checked to see if it is of the expected data type; Keywords are matched with the list of acceptable sizes and numbers are converted to integers. Once the command line entry is complete, further checks are performed; Numbers are checked to see if they are within the range and some commands are used to check the state of the system before the command is executed.

AT 404 202 Β

The commands fall into three categories: (1) commands representing information from the database, (2) commands modifying the database, and (3) commands sending messages. Information can be presented by the subscriber, the link, the state of the CCU and the channel. All presentation commands require information to be extracted from the database and submitted data to the operator for display. The modification commands include the ability to place a subscriber connection on a particular channel and the ability to free and disable channels. The modification commands are used in testing the frequency allocation algorithm. All modification commands are written in the database.

PBX, BCC and RCC messages can be sent from the control panel module 43 to various other modules of the system. A SENDMSG command tells the operator all information necessary for the message, the message is formatted and directed to the display module. PBX messages are sent to the RPU PBX module 42, which sends the message to the PBX call processor 42. BCC and RCC messages may be sent from the RPU 20 to the CCU 18 via the BCC module 41, which adds the bits of the link level protocol to the outgoing message. The input from the CCUs 18 is simulated and messages including both BCC and RCC messages are conveyed to the MPM 46.

Logger module

The tachograph module 44 is responsible for writing RPU events or messages. The co-write module 44 operates the following three disk files: an unwind block with information similar to the charge information, an error block consisting of error messages, and a message block consisting of system alert messages.

The tachograph module 44 consists of a set of subroutines retrieved from the other RPU modules. Each subroutine is responsible for timestamping the message and writing the message to the appropriate disk file. Each subroutine has a global flag that determines whether or not to write messages. The global flags are set and reset using console commands.

The message processing module (MPM)

The MPM 45 performs the high-level call processing function between the PBX 15 and the subscriber stations. It is responsible for call processing functions such as the initiation of calls, the assignment of speech channels and the control of tones for subscribers and external telephones. The MPM 45 also processes state messages that it receives from the CCUs 18. For example, the channel state information, consisting of the connection quality or the fork state at the subscriber, is processed by the MPM 45.

The MPM 45 is set up as a state machine, wherein PBX and BCC messages are characters for the message processing state machine. The MPM 45 processes the characters by updating the database, issuing the required responses, and then transitioning to the next state.

The MPM 45 uses the mailbox system operated by the scheduler module 40 to send and receive messages from and to the other RPU modules. The MPM 45 also uses subroutines in the database module to extract or update status information from the database.

As described above, the MPM 45 is set up as a state machine. Characters that force any processing to be performed consist of messages or timeouts. The MPM 45 determines the type of character (ie, clock, RCC message, PBX message, etc.) and the subscriber station or channel seized by the character. The MPM 45 processes the characters by generating the actual message path and the transition to the next stage.

The MPM 45 actually consists of two state tables. The RCC state machine shown in Figure 10 is used to process messages from the PBX call processor 24 or RCC messages from the subscriber station. The channel state machine shown in FIG. 11 is used to process messages from the CCU 18.

Initially, all subscribers are in the idle RCC state and all channels are in idle channel state, indicating that there is no connection or is under construction.

AT 404 202 Β

The state changes for a typical field call to a subscriber are as follows. An external call message is received by the PBX call processor 24, which message contains the telephone number of the subscriber station targeted with the call. A PAGE message is sent to the subscriber station and the state of the subscriber station is set to PAGE. When a CALL ACEPT message is received from the subscriber station, the state of the subscriber station is set to ACTIVE. In this point, a channel is allocated and the PBX call processor 24, the CCU 18 and the subscriber station are informed of the channel allocation. The channel is placed in the RING SYNC-WAIT state (Figure 11). When the CCU 18 indicates that synchronization has been achieved, the channel state is changed to SYNC RING. Finally, when the CCU 18 indicates that the subscriber has picked up, the channel is placed in the SYNC OFFHOOK state. The SYNC OFFHOOK status indicates that a voice connection has been established.

A subscriber-to-subscriber call begins with a CALL REQUEST message received from the calling party. The calling subscriber station is placed in the DIAL state and a RADIO REQUEST message is sent to the PBX call processor 24. The PBX call processor 24 then returns a PLACE CALL message to the calling subscriber station and sends an INCOMING CALL message to the called station. In response to the PLACE CALL message, a channel is assigned and the PBX call processor 24, the CCU 18 and the calling party station are informed of the arbitration. The state of the calling party channel is set to OFFHOOK SYNC WAIT until the channel enters synchronization. When the CCU 18 of the base station detects the transmission from the calling party, it generates a SYNC OFFHOOK channel event message. The RPU 20 processes the channel event message by changing the state of the channel to the SYNC OFFHOOK state. A message about the incoming call for the called party is, as described above, processed in the same way as an external call notification. In addition, the channels included in the connection are put into the internal operating state as soon as both devices are synchronized.

Separation begins when one of the two parts involved in the connection goes to ONHOOK, ie hangs up. When a phone located outside the system puts in, the MPM 45 will receive an ONHOOK message from the PBX call processor 24. When a subscriber hangs up, the CCU 18 sends a message indicating that the subscriber station is now ONHOOK. In any case, the other part is informed of the disconnection, the channel is placed in the DISCONNECT state and the subscriber station is in the TEARDOWN state. When the CCU 18 indicates that the synchronization has been lost, the channel and the subscriber station are returned to the idle state.

Background Processes

A background processor program is executed by the MPM 45. The background process first inverts after a cold or warm restart with the CCUs 18. Once the system is up and running, the background process also monitors the CCUs 18 to keep the database and an allocated RCC running.

BCC messages generated by both the CCUs 18 and the BCC modules 41 are received by the BCC modules 41. Messages are sent to the CCUs 18 via the BCC modules 41.

Writing data into and extracting data from the database

First, all CCUs send 18 BASEBAND QUERY messages to have the RPU 20 detect the current state of the system. All baseband event or behavioral message information is stored in the RPU database. When the RPU 20 receives a baseband event message indicating that a CCU 18 is ready and not resetting (ie the CCU 18 has not just turned on), the frequency assigned to the CCU 18 is noted as being allocated. The CCU 18 then sends CHANNEL QUERY messages to update the database regarding the current state of the system. The CCU processing is completed as soon as each CCU 18 has either met all pending query messages or it is clear that the CCU 18 has failed. At the time that each CCU 18 that has indicated that it is ready and reset (ie the CCU 18 has just turned on), a frequency is allocated. If no control channel has been assigned to a CCU 18, then the RPU will try to allocate the control channel. The first choice is to allocate the control channel to the CCU 18 on the first frequency, since there the subscriber will first search for an RCC. The next choice is any CCU 18 with slot 0 that is not in use, and the last choice is a CCU 18 with a connection on slot 0. If all working CCUs 18 already one

AT 404 202 Β

Connection on slot 0, then one of the connections over the slot 0 is terminated and the control channel is assigned to this slot.

Once the RPU 20 has contacted all CCUs 18, the state of the CCUs 18 is monitored via state messages received from the CCUs 18 or the BCC modules 41. The BCC modules 41 continuously monitor the connection path to each CCU 18. A CCU 18 is considered out of service when receiving a message about a baseband event indicating that the CCU 18 is not operational. At this time, the CCU 18 is marked as inoperative in the database. Further, all connections are broken, all channels are returned to the initial state, and frequency allocation to the CCU 18 is canceled. If the CCU 18 contained the control channel, then a new control channel is allocated.

When a message is received with a baseband event indicating that the CCU 18 is operational and reset, the CCU 18 is assigned a frequency. If a CCU 18 is not currently allocated a control channel, then slot 0 is assigned to the reset CCU of the control channel.

If a message is received with a baseband event indicating that a CCU 18 has lost connection with the RPU 20, then CHANNEL QUERY messages (ie one for each of the four channels) is sent to the CCU 18 to update the database regarding the current state of each channel of the CCUs. As soon as a response to each CHANNEL QUERY message is received, the current channel state and connection information is included in the database. If a channel is in the SYNC WAIT state, then it is assumed that the subscriber is no longer involved in the connection and the connection is disconnected.

Initially, the CCUs 18 are polled by the RPU 20 about their initial state. Finally, the CCUs 18 also send messages whenever they turn on or change state. The exchange of messages keeps the RPU database up to date with the current state of the system.

Database module

The database module 46 contains the database interface programs necessary to access the database. They provide a limited single thread interface to the database for any module requesting access to the information contained therein. The majority of the access programs are interested in the SIN table and in the BCC table. Access to all fields within these tables is provided by access programs.

The database module is also responsible for starting the database at power up. All important fields are prepared by the initialization part of the database module to allocate sizes.

The database module also provides the following:

(1) programs for carrying the TTY initialization;

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

(3) Programs and tables to support frequency-to-CCU mapping.

(4) controlling diagnostic display information; and (5) frequency allocation.

The database module 46 is a collection of programs that allow controlled access to the database by other modules. By channeling all accesses through the database programs, the database is hidden from external modules. This allows the database to change without modification requirements from any of the other modules. If the database changes, only the interface program of the changed part of the database needs to be changed.

Frequency allocation process

The frequency allocation process is performed by the RPU 20 and selects an appropriate frequency and slot for a subscriber station requesting a voice channel. The dial algorithm detects the type of call (ie internal or external) and the modulation level (ie 16's or 4's). Although the frequency allocation process is functionally independent of the database module 46, it is closely related to the data structures within the database. Because of this fact, this function is described separately from the database module, although technically it is a program within the database module.

The frequency allocation process is used by the MPM during the call setup. It makes extensive use of the data structures within the database module.

AT 404 202 Β

All frequency allocation requirements fall into one of two categories. The first is the external source category and the second is the internal target category. The internal destination category covers the incoming part (ie the destination) of an internal call. The external source category covers all other cases involving an external call, whether they are incoming or outgoing, or whether an internal call is the cause.

The input to the frequency allocation process consists of an index within the SIN table of the subscriber station requesting a channel and the index in the SIN table of the calling subscriber station. The calling subscriber station index is only valid if the channel is set up for an internal destination call. At all other times, the caller's index is a predefined illegal index defined as DB NULL. These indices provide access to all the information required to use a suitable channel (ie Frequency and slot).

The frequency allocator returns a value of TRUE if a frequency-slot combination is successfully assigned. Otherwise FALSE will be returned. If assigned, the frequency and the selected slot are entered in the SIN table at the subscriber station that requested the frequency assignment.

Each frequency is distributed over four TDM slots. The RPU database keeps track of the number of slots available in each location. When an allocation request falls in the external source category, a slot is selected from the slot position that has the least occupancy. Once a slot position is selected, the first frequency is selected with that available slot. In fact, it does not matter which slot is selected when a request falls into this category. This technique tends to distribute the system load evenly across all slots and, more importantly, increases the likelihood of optimal slot allocation for both parts of an internal call. This is true because system timing calculations have shown that the optimal slot allocation for a subscriber to subscriber call is that when the base-station transmit slot is in the same slot for each different-frequency subscriber. By allocating the most available slot position to the caller of a subscriber to subscriber call, the probability is greater than at the time when the targeted subscriber station will be able to allocate the same slot position on a different frequency. For example, if position no. 2 the most available position is then chosen. When processing the allocation request of the targeted subscriber station, it is much more likely that another slot in position no. 2 is available for selection, and thus the optimal slot-to-slot assignment occurs.

When an assignment request falls within the internal target category, the slot to be allocated is selected from a selection table. A selection table contains lists of the destination subscribers, ordered from the highest to the lowest desired slot position allocation. This ordering is based on the slot allocation for the calling party. Up to this point the modulation types have not been mentioned yet. This is because the basic mapping rules do not change for the 4 and 16 slot choices, except for one important exception. This is that only slot 0 or slot 2 can be assigned for a 4-way connection type. Due to this exception and due to the fact that the two subscribers can be set to different types of modulation, a total of four selection tables is needed to cover all possible combinations of calls. These are the following:

Table 6

<td>Introductory slot</td><td>1st Choice</td><td>2nd choice</td><td>3rd choice</td><td>4th choice</td>

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

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

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

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

<td>Rating -"</td><td>(1)</td><td>(2a)</td><td>(2 B)</td><td>(3)</td>

<td colspan="5">The 16-point (origin) intercom preferred slot selection table</td>

Note that each column of each table has a rating assigned to it. This review shows the desirability of a particular slot. The most desirable slot has rating 1, and less desirable slots have ratings 2, 3, etc. If two or more columns of a selection table have the same desirability, they have the same rating number followed by a letter of the alphabet. For example, if three columns are labeled 2a, 2b, and 2c, all have

AT 404 202 Β three of these columns have the same desirability, and their order (a, b, c) is arbitrary.

Table 7

<td>Introductory slot</td><td>1st Choice</td><td>2nd choice</td><td>3rd choice</td><td>4.Wahl</td>

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

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

<td>Rating--</td><td>(1a)</td><td>(1b)</td><td>(2a)</td><td>(2 B)</td>

<td colspan="5">Internal 16s (target) of 4s (calls r talk preferred slot selection table</td>

Table 8

<td>Introductory slot</td><td>1st Choice</td><td>2nd choice</td>

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

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

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

<td>Slot 3</td><td>2</td><td>0</td>

<td>Rating -</td><td>(1)</td><td>(2)</td>

<td colspan="3">Internal 4-digit (target) 16-bit call preferred slot selection table</td>

Table 9

<td>Introductory slot</td><td>1st Choice</td><td>2nd choice</td>

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

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

<td>Rating---</td><td>(1)</td><td>(2)</td>

<td colspan="3">Internal 4-way (target) 4-way call preferred slot selection table</td>

The frequency allocation process has two inputs. These inputs provide access to critical information needed to select the frequency and slot.

The first entry in the SIN table is the subscriber station index requesting a channel. With this index, frequency allocation can determine the default modulation type of the requesting subscriber. It also tells the program where to put the results of its dialing algorithm (ie the frequency and slot numbers).

The second input to the frequency allocation process indicates the frequency slot request category. The size of the second input is either an index in the SIN table, or it is the previously defined illegal value DB NULL. When a valid index is received, the frequency allocation request is identified as the destination side of a subscriber-to-subscriber call and the selection tables must be used. When DB NULL is received, the request is considered to fall in the extem source category and the algorithm for the most available slot position is used.

The frequency allocation process returns TRUE if a frequency-slot combination is successfully assigned, otherwise FALSE is returned. It also causes a desirable side effect. If the assignment is successful, the base band index and the slot fields of the SIN table of the requesting subscriber are entered.

AT 404 202 Β

The frequency allocation algorithm can be decomposed in two stages. The first level, called the classification level, determines the category of the requested allocation. The second stage, called a selection stage, finds a frequency-slot combination and also allocates it, using the appropriate algorithm as in determining the allocation request category.

The classification stage first determines if an automatic frequency selection has taken place. When the requesting agent is set to manual, the prescribed values ​​of the hand modulation level, the hand frequency, and the hand slot determine the frequency slot modulation to be allocated. If frequency slots are available as prescribed, they will be assigned to the requesting subscriber. If frequency slots are not available as prescribed, the program will die by returning a FALSE value. If the requesting agent has been set to automatic, another classification is requested.

Upon determining that an automatic choice is to be made, the frequency allocation algorithm determines the required category. The requested categories are as follows: External-In "is used when the destination subscriber station is called from an external telephone; External out is used when a calling subscriber station calls an external telephone; Internal-out is used when a calling subscriber station calls another subscriber station; Internal-in "is used when a particular subscriber station is called by another subscriber station. If the request is external-in, external-out, or internal-out, a slot location is selected by searching for the most accessible location. Once the position is selected, all frequencies are scanned sequentially until a vacant slot (or an adjacent slot pair in the case of a 4-way request) is found in the desired position. At this point, the program inserts the appropriate values ​​into the SIN table and ends by returning a value of TRUE. If the request falls into the last category (internal-in), further information is requested.

When a request is made from the internal-in type, two more bits of information are requested. The slot allocation and the modulation type (4 or 16) of the calling subscriber must be selected. Once this is done, the appropriate selection table is determined based on the modulation type of the calling party and the called party. After the table has been selected, the caller's slot allocation is used to determine the correct line from the selection table used. Each successor element of the selected line contains an equivalent or less desirable slot allocation. This list is run through until an available slot is found, starting with the most desired position, and continuing until all slot positions have been exhausted. For each slot position (or pair of slots for 4 links), each frequency is visited consecutively until the current slot (or slot pair) is found. The derived frequency and slot values ​​are not entered in the inputs of the associated SIN table, and the program ends by sending back a value of TRUE.

A slot count area holds the track of the number of available slots for each slot position. These counts are preserved by the database module and are related to the frequency allocation process.

The SIN table contains important information from every system-approved participant. The following accesses are executed for the SIN table:

Modulation Level (Read): The subscriber's modulation level requesting a frequency is extracted along with the calling subscriber's modulation level during internal call setup.

Slot number (read): The slot allocation of the calling subscriber with an internal one

Call establishment must be sought.

Slot Number (Registered): The slot allocation of the subscriber requesting a channel is inserted here.

Baseband Index (Registered): The frequency allocation of the subscriber requesting a channel is used here.

The BCC table is used in the frequency allocation search program for an available frequency-slot combination. The following accesses are made to the BCC table:

Channel state (read): The state of a channel is checked to determine its availability.

Channel State (Read): The channel state is checked to see if the specified channel is on

Speech channel is.

Channel State (Register): The channel state is changed when the specified channel is to

AT 404 202 Β

Assignment is selected.

Channel control (write in): The modulation type of the requesting subscriber is written into the channel control byte.

SIN Index: Establishes a connection from the selected channel to the requesting one

Member.

The frequency allocation programs access directly into the database. This is necessary in terms of speed and efficiency considerations. Whenever possible, database access subroutines are used to access the database by the frequency allocation program.

Interface unit for subscriber telephone (STU)

In its basic mode of operation, the STU operates as an interface unit to translate the two-wire analog signals associated with a standard telephony set into 64 kbps encoded digital samples. Referring to Figure 12, the STU includes a subscriber line interface circuit (SLIC) 53 which is directly interconnected to a Type 500 key telephone over line 37. The SLIC 53 provides the appropriate voltage and impedance characteristics for telephone operation. In addition, the SLIC 53 provides a ringing power to be supplied to the telephone and also performs on / off detection. The signal outputs of the SLIC 53 on line 54 are analog, voice-frequency (VF) transmit and receive signals. These are subsequently converted to PCM samples by a PCM encoder / decoder 55. The PCM Codec 55 uses the u-255 compander algorithm to digitize the speech signals into 8-bit samples at an 8 kHz rate. Of course, the PCM Codec 55 works in full duplex mode. The digitized speech samples are then supplied via line 56 to a mode select multiplexer (MUX) 57. The operating mode of the MUX is determined by the subscriber control unit SCU 58, which is connected to the MUX 57 by a transmission and

Receive FIFO 59 is linked. The SCU essentially includes a model 8031 ​​microcontroller. The SCU 58 is coupled to the CCU 29 via an RS-232 interface circuit 60 to the CCU 29 and also controls the operation of the SLIC 53.

The STU can operate essentially in one of three different modes. The first and most basic is the speech operation. In this mode, voice samples are transferred from the PCM codec 55 via the mode selector MUX 57 and a VCU driver / receiver circuit 6t to the VCU 28 where they are further processed to reduce the bit rate from 64 kbps to 14.6 kbps and then to transmission come to the base station.

The second mode is data operation. In this mode of operation, the 64 kBpS stream to and from the VCU 28 does not include voice information, but the information sent to the base station is a reformatted data stream from an external data source at a speed of up to 14.6 kBpS data rate of the channel. The STU also includes a data register 62 for connection to data devices (eg a terminal) via a line 63 using an asynchronous standard RS-232 interface operating at up to 9600 baud. The STU includes a UART and timing circuit 64 to synchronize the data from the RS-232 data register 62. The VCU packages the synchronized data so that they pass below the 14.6 kbps boundary of the channel. This mode uses full duplex data transmission.

The third STU mode is the call setup. In this mode, no data is sent from the STU 27 to the VCU 28 via the mode selector MUX 57. However, a ringback tone generator circuit 65 is connected to the mode selector MUX 57. This circuit digitally forms the tones used in paging procedures. During call cancellation, user selected DTMF digits are detected by a DTMF detector circuit 66 and processed by the SCU 58 to clear the call. The ringback tone generator circuit 56 returns corresponding tones to the user's headset. A ringing generator 67 is connected to the SLIC 53. A clock generator 68 provides clock signals to the codec 55 of the PCM, to the VCU driver-receiver circuit 61 and to the ring-back tone generator 65. Once the call cancellation is complete, the STU will switch to either voice mode or data mode for connection to the base station.

An additional requirement for the STU is the suppression of unwanted echo signals in remote connections. The delay of the to and fro path for the speech signals between the base station and the Telfnehmerstation may well be over 100 ms. Any signal reflected as a result of impedance mismatch results in an unpleasant echo cancellation. This problem is handled in the base station by an echo cancellation system in the PBX function. The STU must bring about echo cancellation in the subscriber station. At least 40 dB of echo cancellation is expected for

AT 404 202 Β this suppression required. The delay of the echo to be suppressed is very small because the reflection of interest occurs between the SLIC 53 in the STU and the local telephone itself. This distance will typically be a few tenths of a foot and the delay will be essentially zero.

The 8031 ​​microprocessor controller in the SCU 58 performs the functions of the RPU 20 and the PBX call processor 24 in the base station. It communicates with the RPU 20 of the base station by means of the messages sent to the radio control channel (RCC) and controls all the individual functions of the STU 27. The SCTU also services the subscriber station CCU 29 via the baseband control channel (BCC). The RS-232 interface to the CCU 29 operates at 9600 baud and is used to carry control information between the CCU 29 and the STU 27 in the subscriber station.

The speech coding / decoding (codec) unit

The Voice Code Unit (VCU) embodies four full-duplex RELP voice compression systems. The structure of the VCU is identical in the base station and in the subscriber station. In the subscriber station, only a quarter of the functionality is utilized (ie only one of the four channels). The interface to the STU 27 in the subscriber station is identical to the interface VCU 17 in the base station. The VCUs 17, 28 use only a digital SChema to embody the RELP speech algorithm as described in pending US patent application no. 667446 under the title RELP Vocoder Implemented in Digital Signal Processors, filed on 2. November 1984 by Philip J. Wilson, is described. This disclosure is hereby incorporated by reference. Alternatively, a sub-band codec can be used. The processed data is delivered to the CCUs 18, 19 to a common parallel bus interface controlled by the CCU software. The CCUs 18, 19 send control signals to the VCU 17, 28 to determine the type of operation and configuration in the VCUs 18, 29. The modes, functional description, and realization considerations associated with the VCU 17, 28 are described below.

The interfaces between the PBX 15 and the VCU 17 are shown in FIG. The interfaces between the STU 27 and the VCU 28 are shown in FIG. The STU 27 interfaces are a subset of the PBU interfaces of the PBX 15, in which the STU 27 delivers only a full duplex voice channel operation. The timing relationships for the PBX and the STU interfaces are identical and shown in FIG.

Table 10

<td>symbol</td><td>parameter</td><td>min</td><td>Type</td><td>Max</td><td>unit</td>

<td>twO</td><td>PBX frame duration</td><td>-</td><td>125</td><td>-</td><td>US</td>

<td>tw1</td><td>Clock pulse duration</td><td>1.8</td><td>2.0</td><td>2.2</td><td>US</td>

<td>tw2</td><td>Gate 0 inactive duration</td><td>-</td><td>93.75</td><td>-</td><td>US</td>

<td>tw3</td><td>Gate 0 inactive Gate 1 Duration</td><td>-5.9</td><td>7.8</td><td>9.7</td><td>US</td>

<td>tw4</td><td>Gate 1 inactive Gate 0 Duration</td><td>-52.8</td><td>54.7</td><td>56.6</td><td>US</td>

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

<td>td1</td><td>Start pulse clock 1 delay</td><td>0</td><td>250</td><td>-800</td><td>ns</td>

<td>td2</td><td>Clock 0 - Gate 0 edge delay</td><td>100</td><td>1000</td><td>2000</td><td>ns</td>

<td>tD3</td><td>Clock 1 - Gate 1 edge delay</td><td>100</td><td>1000</td><td>2000</td><td>ns</td>

<td>Tso</td><td>Input data setup time</td><td>20</td><td>1500</td><td>-</td><td>ns</td>

<td>ts1</td><td>Output data Autbauzeit</td><td>500</td><td>1800</td><td>-</td><td>ns</td>

<td>Tho</td><td>Hold time of the output data</td><td>500</td><td>2200</td><td>-</td><td>ns</td>

Referring to Fig. 13, the PBX SDAT0 1, 2 and 3, the lines 70, 71, 72, 73 bring data signals from the PBX 15 to the VCU 17 in the base station. In the subscriber station, the data signal is brought to the STU SDAT0 line 74 from the STU 27 to the VCU 28 (Figure 14). 8-bit u-225 companded data is brought to the speech codec during the active section of the PBX / STU GATEO or PBX GATE 1 ..... 3 with a clock rate of 256 kHz. The data will be in the VCU 17, 28 at the rising

AT 404 202 Β

Flank of the 256 kHZ clock clocked.

The VCU SDATO 1, 2 and 3 lines 75, 76, 77, 78 bring data signals from the VCU to the PBX 15 in the base station. The VCU SDATO line 29 brings data from the VCU 28 to the STU 27 in the subscriber station. 8-bit ix-225 companded serial data is sent to the PBX 15 or the STU 27 from the voice codec during the active high section of the PBX / STU GATEO or PBX GATE1 ... 3 at a clock rate of 256 kHz. The data is clocked out by the VCU 17, 18 at the rising edge of the 256 kHz clock.

The PBX GATEO, 1, 2 and 3, lines 80, 81, 82, 83, bring gate signals from the PBX 15 to the VCU 17 in the base station. The STU GATEO, line 84, brings gate signals from the STU 27 to the VCU 28 in the subscriber station. The gate signal is an active high signal which is used to enable the handover of the PBX / STU SDATO, PBX SDAT1 .... 3 and VCU SDATO .... 3. This gate signal is active every 125 microseconds for eight consecutive clock periods.

The PBXs CLKO, 1, 2 and 3, lines 85, 86, 87, 88, provide the 256 kHz clock signal from the PBX 15 to the VCU 17 in the base station. The STU CLKO line 89 brings a 256 kHz clock signal from the STU 27 to the VCU 28 in the subscriber station. A 256 kHz clock signal is used to send the PBX / STU SDATO and

PBX SDAT1 ... 3 signals into the VCU 17, 28 and also the VCU SDATO ....... 3 signals in the PBX or in the STU 27. However, the clocks are not with any of the clocks that are within the VCU 17, 18, CCU 18, 29, or in the modem 19, 30 are synchronized.

In the base station, the PBX-VCU converts four channels of synchronous 64 kBpS serial data into 8 bit parallel data, which thus becomes available for the four transmitting speech codecs 16 with a sampling rate of 8 KHz. In the subscriber station, only one channel (channel 0) is converted by the STU VCU interface. The required clocks and gates are supplied by the PBX 15 and the STU 27.

The PBX-VCU and STU-VCU interfaces also perform the complementary function for the receive codecs. In the base station, the 8-bit parallel data received from the four code channels is converted into four 64 kbps synchronous serial channels for retransmission to the PBX 15. In the subscriber station, a voice channel is converted and sent back to the STU 27.

The hardware interfaces between the VCU 17, 28 and the CCU 18, 29 are shown in FIG. Timing relationships for the transmit and receive channels between the VCU and the CCU are shown in full in FIGS. 17 and 18, respectively. Tables 11 and 12 describe the characterizing features represented by the symbols used in Figs. 17 and 18, respectively.

It should be noted that FIGS. 17 and 18 illustrate in detail the events that occur during the VCBTB shown in FIGS. 19A and 19B. The definitions of the individual interface signals are given in the following paragraphs.

AT 404 202 Β

Table 11

<td>symbol</td><td>characteristics</td><td>min</td><td>Max</td><td>unit</td>

<td>tdi</td><td>Speech codec block transfer period</td><td>-</td><td>750</td><td>usec</td>

<td>td2</td><td>TCVC response time</td><td>1.25</td><td>15</td><td>usec</td>

<td>tD3</td><td>CCU DMA response time</td><td></td><td>1.25</td><td>usec</td>

<td>td4</td><td>Exchange delay</td><td></td><td>15</td><td>nsec</td>

<td>td5</td><td>VC block period delay</td><td></td><td>150</td><td>usec</td>

<td>thi</td><td>Holding the control data</td><td></td><td></td><td>nsec</td>

<td>th2</td><td>Holding the status data</td><td></td><td></td><td>nsec</td>

<td>th3</td><td>Hold the TC data</td><td></td><td></td><td>nsec</td>

<td>ts1</td><td>Structure of the control data</td><td></td><td></td><td>nsec</td>

<td>ts2</td><td>Structure of the status data</td><td></td><td></td><td>nsec</td>

<td>ts3</td><td>Structure of the TC data</td><td></td><td></td><td>nsec</td>

<td>tw1</td><td>write time</td><td></td><td></td><td>nsec</td>

<td>tw2</td><td>reading time</td><td></td><td></td><td>nsec</td>

<td>tw3</td><td>Block Request Duration</td><td>1.5</td><td></td><td>usec</td>

Table 12

<td>symbol</td><td>Charaksterik</td><td>min</td><td>Max</td><td>unit</td>

<td>td6</td><td>Block transfer period</td><td></td><td>750</td><td>usec</td>

<td>td7</td><td>CCU data response time</td><td></td><td>1.25</td><td>usec</td>

<td>td8</td><td>VC response time</td><td>1.25</td><td>15</td><td>usec</td>

<td>td9</td><td>exchange delay</td><td></td><td>15</td><td>nsec</td>

<td>tdIO</td><td>VC Block Period Delay</td><td></td><td>150</td><td>usec</td>

<td>th4</td><td>Holding the control data</td><td></td><td></td><td>nsec</td>

<td>th5</td><td>Holding the status data</td><td></td><td></td><td>nsec</td>

<td>th6</td><td>Hold the RC data</td><td></td><td></td><td>nsec</td>

<td>ts 4</td><td>Control data structure</td><td></td><td></td><td>nsec</td>

<td>ts5</td><td>State data structure</td><td></td><td></td><td>nsec</td>

<td>ts6</td><td>Structure of the TC data</td><td></td><td></td><td>nsec</td>

<td>tw4</td><td>write time</td><td></td><td></td><td>nsec</td>

<td>tw4</td><td>reading time</td><td></td><td></td><td>nsec</td>

<td>TW6</td><td>Block Request Duration</td><td>1.5</td><td></td><td>usec</td>

Figures 19A and 19B show the timing relationships between the various transmit and receive speech blocks transmitted between the VCU 17, 18 and the CCU 18, 19 for 16-level phase shift (PSK) modulation. At the top of Figure 19A is the frame timing of the system to which all transmissions are referenced. This frame timing is also applicable to Figure 19B. A modem frame is 45 ms long and includes four speech slots (or channels).

AT 404 202 Β

Each talk slot consists of two system speech block (SVBP) periods of speech data, each containing 82 symbols (requiring 5.125 ms) and an additional 16 superimposed data symbol requiring 1.0 ms of frame time.

For the broadcast channels, a block of 328 bits (42 bytes) of processed speech is transferred from the VCU 17, 28 to the CCUs 18, 29, prior to the beginning of each SVBP during a speech codec block transfer period (VCBTP). The 64 kBpS input data stream of the VCUs associated with a processed speech block is considered to be split into speech codec block periods (VCBPs) which are 22.5 ms long. Referring to the transmission channel 0 in Fig. 19A, unprocessed VC input data in VCBP's 0A1 and OBI are combined with processed data in VCBTPs 0A1 and 0B1. It should be noted that the VCBPs for channels 0 and 2 are one half of a VCBP (ie 11.25 ms) are offset from the VCBPs of channels 1 and 3.

For the receive channel (as shown in Figure 19B), a block of 328 bits (41 bytes) of processed speech is transferred from the CCUs 18, 29 to the VCUs 17, 28 to the VCUs 18, 28 at the end of each SVBP during a VCBZP. As in the transmit channels, the time offset of the VCBP versus the VCBTP is execution dependent and a (maximum) deviation of a VCBP is shown in FIG. To understand the relationships between the input and output data of the speech codec, reference is made to Figs. 19A and 19B. For receive channel 0, compressed voice data transmitted during VCBTPs 0A10 and 0B10 are merged with the processed expanded data stream into VCBPS 0A10 and 0B10.

The TCADDR lines 90 bring channel address signals from the CCUs 18, 29 to the VCUs 17, 28. These three address lines are used to select the current transmit channel address.

The TCDATA bus provides transmit channel data signals between the VCU 17, 28 and the CCU 18, 29.

The TCDAV line 92 brings a transmit channel / data available signal from the VCU 17, 28 to the CCU 18, 29. The TCDAV / signal indicates to the CCU 18, 29 that a data byte is available in the TCDATA register. The TCDAV signal remains low until a TCDACK signal is activated.

The TCDACK line 93 brings a transmit channel / data acknowledge signal from the CCU 18, 29 to the VCU 17, 28. The TCDACK signal controls the data on the TCDATA bus and resets TCDAV.

The TCSCWR line 94 brings a transmit channel state / control write signal from the CCU 18, 29 2u to the VCU 17, 28. The TCSCWR signal writes the speech codec control word into the associated transmit channel control register designated by the TCADDR line. The data is stored in the register with the rising edge of the TCSCWR signal.

The TCSCRD line 95 brings a transmit channel state control read signal from the CCU 18, 29 to the VCU 17, 28. The TCSCRD signal controls the status byte designated by the TCADDR line from the speech codec state register on the TCDATA bus.

The BLOCKRQ line 96 brings a block request signal from the CCU 18, 29 to the VCU 17, 28. The BLOCKRQ signal is used to perform a 41 byte block transfer of data from the speech codec (specified by the TCADDR lines) to the CCU 18 , 29 via the TCDATA bus. BLOCKRQ is used by the speech codec to start VCBP timing.

The TCVCRST line 97 brings a transmit channel voice codec reset signal from the CCU 18, 29 to the VCU 17, 28. The transmit voice codec, specified by the TCADDR lines, is reset.

The RCADDR lines 98 bring receive channel address signals from the CCUs 18, 29 to the VCU

17, 28. These address lines are used to select the current receive channel address as follows:

The RCDATA bus 98 brings receive channel data signals between the CCUs 18, 29 and the VCUs 17, 28.

The RCDAV line 100 brings a receive channel data available signal from the CCU 18, 29 to the VCU 17, 28. The RCDAV signal indicates to the voice codec, specified by the RCADDR lines, that a data byte is available in the RCDATA register. The RCDAV signal controls the access of the data to the RCDATA bus and into the RCDATA register and resets the RCDACK lines.

The RCDACK line 101 brings a receive channel data acknowledge signal from the VCU 17, 28 to the CCUs 18, 29. The RCDACK signal indicates to the CCU 18, 29 that the data has been read from the RCDATA register and that further bytes have been read from the CCU 18 , 29 can be transferred.

The RCSCWR line 102 brings a receive channel state / control write signal from the CCU 18, 29 to the VCU 17, 28. The RCSCWR signal writes the control word determined by the RCADDR lines into the associated voice codec control register. The data is stored in the register with the rising edge of the RCSCWR signal.

The RCSCRD line 103 brings a channel state / control read signal from the VCU 17, 28 to the CCU

18, 29. The RCSCRD signal controls the speech codec / status word determined by the RCADDR lines from the status register to the RCDATA bus.

AT 404 202 B

The BLOCKRDY line 104 brings a block ready signal from the CCU 18, 29 to the VCU 17, 28. The BLOCKRDY signal is used to provide a 41 byte block transfer of data from the CCU 18, 29 to the voice codec specified by the RCADDR lines, initiate. The BLOCKRDY signal is used by the speech codec to start VCBP timing. The CCUs 18, 29 are needed to have an available data byte in the RCDATA register before the rising edge of the BLOCKRDY signal.

The RCVCRST line 105 brings a receive channel speech codec reset signal from the CCU 18, 29 to the VCU 17, 28. The speech codec specified by the RCADDR lines is reset by the RCADDRS signals.

The VCU hardware of the receive channel receives 41 byte blocks as input data from the CCU 18, 29 during a VCBTP, as shown in FIG. 20A. After processing the data in accordance with the current mode, the 8-bit μ.-law companded data is transferred at a rate of 8 kHz to the BPX (STU) interface module. Data buffering is made in the VCU 17, 28 to simplify the input / output conditions of the CCU 18, 29. As shown in Figure 18, control information is passed between the VCU 17, 28 and the CCU 18, 29 via a set of control and status registers for each receive channel at the beginning of a VCBTP. The following modes are supported by the receiving codecs:

In external operation, bandwidth expansion is performed at an input data rate of 14.6 kbps (392 bits every 22.5 ms) and a data output speed of 64 kbps. Speech data can also include DTMF tones.

In internal operation, previously compressed 14.6 kBpS voice is sent from the CCU 18, 29 via the VCU

17, 28 to the PBX 15 or the STU 27. Since the PBX 15 or the STU 27 expects 64 kBpS, a shortening of the data stream must be made. Output (64 kbpS) data consists of an empty byte pattern (FF hex) until voice data from the CCUs 18, 29 becomes available. Then, a synchronous byte (55 hex) is output, followed by 41 previously processed data bytes, after which the empty byte pattern is continued. Figure 20A provides an example of input-output data timing and content for 16 PSK modulation.

In idle mode, input blocks of voice data are consumed by the CCUs 18, 29 but not used. An empty output byte pattern (FF hex) to the PBX 15 or the STU 27 is maintained to ensure the silence of the line.

In standby mode, diagnostic programs are executed continuously and the resulting state is stored in the status register. Block transfers to the CCUs 18, 29 are not made until the mode is changed by a block request according to the VCBTPA. The new control word (and mode) is read by the speech codec and the diagnostic status information is read to the CCU

18, 29 given.

The VCU Hartware transmit channel receives companded PCM (8 kHz sample rate) from the PBX / STU interface according to 8-bit u-law. After processing the data according to the current mode, output data is transferred to CCUs 18, 29 in blocks of 41 bytes during a Blkok transfer period (VCBTP) as shown in FIG. Within the VCU 17, 28, the data is buffered to simplify the input / output conditions of the CCU 18, 29. Control information is exchanged at the beginning of a VCBTP via a set of control and status registers for each transmit channel between the VCU 17, 28 and the CCU 18, 29, as shown in FIG. The following modes are supported by the send codecs:

In external operation, the bandwidth compression for speech is done at a 14.6 kbps output speed (328 bits every 22.5 ms). Processed voice data is passed in 41 byte blocks to the CCU 18, 29. The voice data may also include dual-tone multiple frequency DTMF (dual-tone-multi-frequency) tones.

In internal operation, previously processed voice data has passed from the PBX 15 or the STU 27 via the VCU 17, 28 and into the CCU 18, 29. The 64 kbps input data stream consists of an empty byte pattern (FF hex), a sync byte (55 hex), 41 previously processed compressed speech data bytes, and additional empty bytes until the next sync byte occurs. The speech codec monitors the input data for the sync byte occurring in one byte area, and then stores the 41 bytes of the speech data. During the next VCBTP, as described, the speech block is then transferred to the CCUs 18, 29. Figure 20B provides an example of the timing of the input and output data and the contents for 16-PSK modulation. Segment 1 on the output channel is a synchronous byte, and segment 2 is a processed voice byte. The obliquely shaded segments represent an empty byte pattern. Note that the sync and voice data does not occur over the VCBP areas.

In idle mode, the voice data is consumed by the PBX 15 or the STU 27, but not used. The 42 bytes of voice data for the CCU contain a silent voice pattern.

AT 404 202 B

In standby mode, diagnostic hardware programs are continually executed and the resulting state is stored in the state register. Block transmissions to the CCU 18, 29 are not performed until the mode is changed by a block request corresponding VCBTPA. The new control word (and mode) is read by the VCU 17, 28 and the diagnostic status information is passed to the CCU 18, 29.

A codec frame is defined according to the performance requirements of the RELP algorithm, the frame must be an integer divisor of the speech codec block period (VCBP), which is 22.5 ms.

Due to the fact that PBX 15 and STU 27 operate asynchronously with internal system timing, resources must be incorporated into VCU 17, 28 that detect, report, and compensate for data overflow and data shortage. This condition is estimated to occur once every 5000. VCBP before. Since the detection of excess or deficiency is due to the structure, the notification of such errors in the status word is provided. If necessary, data shortage can be compensated by repeating the last speech sample, and surpluses can be treated if necessary by ignoring the speech sample (s).

After resetting any (or all) codecs, as shown for example in Figure 19A, VCBTPA will be the first transferred block from the CCU 18, 29.

Channel control unit (CCU)

The channel control unit (CCU) performs similar functions in both the subscriber station and the base station. The hardware used in the two station types for the CCU function is indeed identical. The software in the subscriber station differs slightly from that of the base station. The CCU performs some functions concerning the formatting of the information and the timing related to the operation in the time division transmission channels. Key inputs to the CCU come from four sources. First, there are the current digitized samples to be transferred. These are transferred from the VCU 17, 28 to the CCUs 18, 29 (Figures 2 and 3). These data may be encoded voice samples or data samples from the RS-232 data register 10 in the STU (Figure 12). In any case, the digital channels work with 16 kBpS. From the CCU 18 four channels can be processed simultaneously when working in the base station with all four 16-level PSK transmission channels. The subscriber station's CCU 29 operates only on one stream. However, this stream can be specified in any of the four slot locations associated with the TDMA framing scheme. The second input to the CCU comes through the baseband control channel (BCC) from the STU 27 (in the subscriber station) or from the RPU 20 (in the base station). This second input provides control messages regarding the modes, status and control information. Many of the BCC messages from the CCUs 18, 29 are Radio Control Channel (RCC) messages received from the CCUs 18, 29. The CCUs 18, 29 feed the control information from the RCC messages to the STU 27 or the RPU 20 and in response receive control messages from the RPU 20 or the STU 27. This determines what the CCU 18, 29 has to do with the data from the VCU 17, 28. The third input source provides timing and status information from the modem 19, 30a. The modem 19 provides the master clock signal used in the VCU VCU modem string. In addition, the modem 19, 30a provides the status about the accuracy of its bit sync synchronization, the RF AGC level inputs, and other goodness indications used by the CCU's 18, 29 to determine if sufficiently reliable connections are made over the channel , The CCU 18, 29 attempts to control the fine tuning of the instantaneous operation of the modem 19, 30a through commands, the transmitter power level, the AGC levels, and the calculation of the timing / distance calculation. Measurements of the level quality of the modem transmissions are reported to the RPU 20 or the STU 27. The fourth input source is the current modem data received as symbols, each of which can have up to four bits (depending on the modulation levels). These symbols are buffered, demultiplexed, and supplied to the VCU 17, 28 receive circuits for decoding.

Figure 21 is a block diagram of the CCU. The architecture of the CCU is essentially that of two single-use direct memory access (DMA) data channels with intelligent microprocessor control. The task of the DMA channels is to transfer data from the VCU to the modem and vice versa. The CCU interface to the VCU comprises two parallel DMA multiplexers, one TX bus 107 for the transmit channel (VCU to CCU to modem) and one RX bus 108 for the receive channel (modem to CCU to VCU). Data processed by the transmit circuits in the VCU are buffered in the VCU memory until the CCU requests a DMA transfer. During each block transfer period, one-and-one-byte bytes are transferred to the CCU. Two of these blocks are transmitted per channel (up to four speech channels in the base station) per TDMA frame. The CCU receives these send bytes via a transmit speech codec interface 44

AT 404 202 Β dul (TVCIM) 109 and buffers it in a transmit memory module (TMM) 110. Depending on the particular drive mode for the given channel, a CCU processor attached to a microcontroller module (MCM) hangs.

111 incorporated a control / synchronization header to the coded voice bytes, in which way a complete voice packet for transmission to the modem via a transmit modem interface module

112 is brought into the format. The MCM 111 retains information about the frame timing and transmits the data to the modem at the appropriate time. Before being transferred to the modem, the transmit data is converted by the eight byte format MCM 111 used by the CCU to a symbol format containing 1, 2, or 4 bits per symbol, depending on the modulation levels for that slot.

The reverse process is done for the receive data from the modem. The data from the modem is received by a receive modem interface module 114 and popped in a receive memory module (RMM) 115 . This data is then converted from the 1, 2, or 4-bit per symbol format used by the modem to the 8-bit format used internally by the CCU and all other baseband processing. The additional bits and control bits are separated from the data stream arriving on the RK bus 108 by the MCM 111 according to the frame timing known to it from the modem to a Frame Timing Module (FTM) 116 and its own identification of various codewords in the symbol stream. The converted data is passed to the VCU via a Voice Mail Codec Interface Module (RVCIM) 117.

The CCU also provides the link level control for the transmissions over the Radio Control Channel (RCC) at both the base and the subscriber stations. In the base station, only one CCU is represented by the RPU as processing the RCC channel. The CCU controls the receipt and formatting of messages from the RPU in the base station to the STU controller in the subscriber stations. This control function of the CCU includes the detection and error control in the RCC messages as well as the formatting and packaging of the information for transmission over the radio link. The CCU also detects collisions on the incoming RCC in the base station. The CCU controls the performance and range calculations for the subscriber stations by performing the initial coverage services. The detection protocol and other RCC functions have been described above.

FIG. 22 shows the functional architecture of the CCU built for the software. The CCU has three separate data paths: the transmit bus TX 107, the receive bus RX 108, and the local bus 119 for the microcontroller. The microcontroller 111 shares the TX bus 107 with a memory access (DMA) controller 120 and displays the RX bus with a director DMA controller 121. The microcontroller 111 uses these remote multiplex lines to control the peripherals of the DMA controller, the control / status registers 122, and access to the transmit buffer 110 and the receiver buffer 115. The control and status registers 122 provide, off the microcontroller's local bus 119, interfaces to the RFU, modem, and CCU hardware. An RS-232C connection 123 between the RPU and the CCU is carried on the microcontroller chip 111 by a UART. In the participant's station, the RPU is replaced by the STU, but the interfaces remain the same.

The microcontroller 111 has access to three physically separate RAM areas: the local RAM, the transmit buffer, and the receive buffer. The local RAM may still be broken into one on the CHIP RAM and one away from the CHIP RAM. Transmit buffer and receive buffer only have access to the microcontroller if the respective DMA control unit is free.

The transmit buffer 110 is divided into a number of different segments. Each segment contains the skeleton of a voice or RCC packet ready for transmission over the channel. The preamble and the single word (RCC only) are constants that are initiated by the microcontroller 111 after resetting a CCU. The codeword (voice only), voice data and RCC data are written into the transit buffer 119 by the microcontroller just prior to the DMA transfer to the modem 19, 30a. Once RCC zero ACK is a high frequency sent fixed message, it is stored as a separate unit in the transmit buffer 110.

The receive buffer 115 is divided into a number of different segments. A segment is for storing voice data that is buffered and passed to a VCU block base. RCC data is buffered separately from the voice data to allow for retention over a longer period of time. If required, the microcontroller 111 may store in the receive buffer 115 a two frame RCC history by making the RC Copy task (from the buffer to the local RAM) of a time critical event shorter.

The local RAM contains the working variables used by the microcontroller 111. An important data structure stored there carries the baseband control channel (BCC) between the CCU and the RPU. A register bank of the local RAM is dedicated to providing basic queue information to the RS-232C interrupt handler. Define a pointer and length field in this bank

AT 404 202 Β the active send data block (TXDB) from which the data is read out and sent. The TXDB contains lengths and pointer information for the next TXDB in the queue; From this a closed list is formed. On the receive side a circular memory is used to store incoming data bytes. When a complete message is received, the interrupt handler takes over the serial code and interprets it.

The microcontroller 111 uses its local bus 119 as access to the modem and the CCU control / status registers 122. The bus also provides access to the bus 107 and the bus 108 via the isolating logic circuits 124 and 125, respectively, to receive transmissions at the same time avoid, the Fernvielfachleitungen 107, 108 are accessible only via the microcontroller 111, if the respective DMA controller 120 or 121 is free.

The CCU and the RPU communicate over link 123 with a full-duplex RS 232C interface called baseband control channel (BCC). Asynchronous characters are eight-bit binary and are transmitted at 9600 baud. A start bit and a stop bit are used to frame the data bytes. Messages are terminated by a single byte with byte justification, which is used to avoid the occurrence of the single byte within a message. An alternate bit protocol and an eight bit checksum are used to ensure the integrity of the connection.

Two external program interruptions are supported by the microcontroller. One is generated by the transmit DMA controller 120 and the other is generated by the receive DMA controller 121. These interrupts occur when the respective control controller 120, 121 completes its block transfer; then release control of its bus to the microcontroller 111.

The BCC interface is controlled by an internal interrupt. The software is interrupted upon receipt or transmission of a byte.

In the base station, the microcontroller 111 is responsible for controlling and monitoring the entirety of the four channel data paths associated with it, including the VCU 17, 28, the CCU 18, 29, the modem 19, 30a, and the RFU 20, 31a. In the subscriber station, the microcontroller 111 controls and monitors the same hardware, but carries only one data path. The CCU is itself controlled by the RPU (in the base station) or by the RPU (in the subscriber station).

The CCU supplies the VCU with the information about the operating mode. Modifications of the operating mode occur only with system slot limitations. During the speech compression process, the CCU also provides information to the VCU, such as the location of the VCU block within the system slot (there are two VCU blocks per system slot). VCU addressing is established by the CCU prior to a data transfer that executes the MUX / DEMUX process. The state of the VCU is read in by the CCU after each block handover and corresponding statistical terms are retained by the CCU. The CCU may also initiate a hard reset of the VCU and / or VCU.

The microcontroller 111 associates the current modulation level with a symbol / byte converter 126 in the RX bus 108 and a byte / symbol converter 127 in the TX bus 107.

The modem is provided with information concerning the nature of the received RCC or voice data because of the different detection procedures used in its reception. The modem provides the CCU with a fractional clock offset, the AGC level, and the link quality value of each slot. Frequency allocation to the CCU is provided by the RPU or the STU. The CCU controls the initiation of a hard modem reset, a self test or the receive side during training operation.

The CCU handles the full-duplex data flow over the TX and RX lines 107, 108. During a given slot time, transmit voice data originating from the VCU is transmitted as a block to the transmit buffer 110 via the transmit DMA receiver 121. Each block is a VCU block in length; therefore two such handovers are required for each voice channel. Before handover, the CCU supplies the VCU with the corresponding channel addresses, thus performing the multiplex operation.

A preamble and a codeword stored in the transmit buffer 110 are sent out in front of the VCU data at the beginning of each slot. The transmit DMA transfers the data from the transmit buffer to the re-timed FIFO stack 128 while the modem receives data from the FIFO stack as required. The translation of bytes into symbols is performed by the byte-to-symbol converter 127 during the handover. The control of the peripheral transmit DMA is performed by the microcontroller simultaneously with the creation and insertion of the codeword for the speech packet.

The receive data flow is very precisely a mirror image of the transmitter side. The data is written to the re-timed FIFO stack 129 as it appears from the modem 19, 30a. Receive DME controller 121 dumps FIFO stack 129 into receive buffer 115 as needed. The symbol / byte translation is done by a symbol / byte converter 126 and frame timing is performed by clock circuit 130. Alignment of the byte delimiter occurs automatically as soon as the channel

AT 404 202 Β is synchronous. Once a complete VCU block is received, the DMA block is transferred to the corresponding VCU. Control of the receive DMA controller is performed by the microcontroller 111.

The detection of the codeword is carried out for each slot. Microcontroller 111 performs this process by copying the codeword byte in local RAM and comparing it to a list of valid codewords. During each slot, the modem 19, 30a provides a fractional symbol shift and an AGC value. These are read by the microcontroller 111 and interpreted accordingly. If there are performance or distance problems, the subscriber station is informed of this by the transmit codeword.

RCC transmission data is assembled in the transmission buffer 110 by the CCU according to the contents of the RCC message string. When the RPU has sent a message to the CCU, that message is formatted in the transmit buffer 110. Otherwise, the NULL KNOWLEDGE message, which is permanently stored in the transmit buffer 110, is used. Once an RCC packet is ready, the RCC preamble, the single word, and the RCC data are DMA-transferred as needed to the modem 19, 30a. The CCU performs a collision detection and sets the RCC collision limiting bit accordingly.

The Receive RCC Data Handler has two modes: Frame Search and Monitor. In frame search mode, the RCC channel is considered to be out of sync. Each incoming RCC message must be synchronized using a single-word algorithm. In monitor mode, the channel is synchronized and the algorithm invoking the only word is not called. The base station is always in frame search mode because the subscriber can not jump in with the bad timing at any time. At the subscriber station, the RCC data handler is in monitor mode unless the station has reached RCC synchronization.

In the frame search mode, the detection of the single word is performed after each RCC slot. The microcontroller 11 performs this process by scanning in a window around the location of the single word. Successful detection of the single word brings the symbol timing information to the CCU. Received RCC data is transferred from the modem 19, 30a to the receive buffer 115 DMA. Once the transfer is complete, the RCA data is copied for processing in the microcontroller's RAM. Receive RCC packets are filtered by the CCU. An RCC packet only goes to the RPU if the only word is found and the CRC is correct.

During RCC processing, the corresponding VCU channel is kept operational. During this channel period there is no data transmission between VCU and the CCU on either the transmit path 107 or the receive path 108.

The software works on an INTEL 8031 ​​microcontroller 111. For program storage, an external EPROM is provided in the local bus of the microcontroller. The software is used to address real-time DMA service requests, maintaining 64 kbps data flow in both directions without data loss. The FIFO latching through the stacks 129 and 129 at the modem interface provides the necessary short time for the microcontroller 111 to perform the data block transfer and system control functions.

The software is divided into five separate modules: Supervisor, Data Transfer, BCC Transmitter / Receiver, BMM Controller and Services. Each module is characterized by having only one input and output, except for interrupts and error conditions. Another exception is the service module, which contains a range of service programs to which other modules have direct access. In general, traffic flows between the modules by using global variables defined in a separate data segment.

The supervisor module includes a prep function, maintains the entire program control, and performs basic self-test functions.

The data transfer module controls the data transfer via TX bus 107 and RX bus 108, both voice and RCC, performs the detection of the sync word on both voice and RCC data at all modulation levels, and provides the CCU-RPU RS -232 Transport 123.

The BCC transceiver module performs BCC transceiver tasks, handles the BCC queue, formats BCC transmit messages, processes BCC receive data, and moves RCC data into and out of the CCU via the BCC.

The BBM control module controls the RFU, modem, VCU and CCU hardware via registers, reads and interprets state information from these devices (eg the AGC modem, link quality and symbol ambiguity), decodes codewords embedded in the voice channel, formats it Codeword for the voice channel, holds a real-time software / hardware timer in operation and performs on-line self-tests.

AT 404 202 Β

The service module executes various service programs that are accessed by other modules.

The CCU software is divided into four separate processes, which operate essentially simultaneously. Three of these are the BCC data, TX DMA, and RX DMA processes, which are interrupt driven and are only used when a particular event requires attention. All three of the event-driven processes are housed in the data transfer module. The remainder of the process, spread across all of these modules, is a background process that prepares, controls and monitors the other three processes.

When BCC messages arrive from the RPU (or the STU in the subscriber station), they are received and stored by the BCC data process. Once a complete message is received, the BCC data process notifies the background process via a mailbox. The background process questions this mailbox during its main loop; therefore he will gather any new news. The messages are interpreted by the background and a relevant process is picked up. Any response will be inscribed in the BCC broadcast message string from the background and the BCC data process will be displayed correctly.

BCC messages can initiate a preparation of the data channel of the CCU. The required control information is written into the modem 19, 30a and VCU 17, 17 at the allocated time. The modem acts on a new control word at the slot edges. The VCU expects operational state changes in the course of the first VCU block transfer of a slot edge. The background process is responsible for the observation that the correct timing is maintained.

The detection of states is performed by the background, the TX DMA process and the RX DMA process. The last two collect state words from the TX and RX pages of the respective VCU. This is necessary because these status registers are only accessible via TX bus 107 and RX bus 108, which are only free for a limited period of time. The background process collects the state information directly from the modem 19, 30 a via the station registers 122 on the local bus 119. Once collected, all state information from the background process is compared and stored as a specific state variable. State requests received from the RPU are handled by the background process based on the state history.

Some state information, similar to the AGC value and the fractional bit shift, may require CCU activity. Such data, regardless of how it is stored as a state history, is used to correct subscriber performance and distance problems. In the case of RCC messages, performance and range information is routed directly to the RPU as part of the RCC to the RPU. The background process performs this function by formatting a BCC message containing RCC, AGC, and range data. Once the package is ready, it will be put into the send BCC queue and the BCC data process will be reported. For voice channels, this state information is used to format the codewords embedded in outgoing speech packets. The background performs this formatting and controls the transmission of the codeword over the voice channel. All codewords must be transmitted in a five-row in one line, which provides a 5: 1 redundancy coding. The TX DMA process automatically transfers the codeword selected by the background process.

The background process also maintains a software / hardware real-time clock. This is done by choosing one of the 8031 ​​clocks and counting the overflows. The real-time clock function provides a time base for software timeouts and other time-dependent events. The background process checks to see if the system timing is still in place by querying the CCU hardware error indicators and verifying that data transfer events have occurred if they should be in the system frame. The framing information of the system is provided via the system start frame state line and a clock connected to the 16 kHz clock 130. The data synchronization is performed by the background process.

The BCC data process responds to RS-232 interrupts that can occur both in the channel in the transmit direction and in the receive direction. The process simply outputs another byte on the transmit side, or it takes another byte on the input side. An end-of-message boundary icon on the receiving side causes the BCC data program to report the background process.

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

A step-by-step description of the data transfer function controlled by the software will be described below. Events in the data transfer process are marked by interruptions in the DMA controller. The interruption occurs after the DMA controller completes the allocated block transfer. Each pass begins at the beginning of a data slot transfer. It can be a help

AT 404 202 Β, during the discussion of this section, the figures 23 and 24 to consider. Figure 23 is a timing diagram for the transfer of RCC and 16 PSK voice data to the transmission bus of the CCU. Figure 24 is a timing diagram for the transfer of RCC and 16 PSK data to the receive bus of the CCU. Tables 13 and 14 describe the features of the time symbols shown in Figs. 23 and 24, respectively.

Table 13

<td>time symbol</td><td>process</td><td>Max (us)</td><td>Minus)</td><td>Type)</td>

<td>ts</td><td>CCU DMA construction</td><td>150</td><td>...</td><td>100</td>

<td>TVCS</td><td>VCU DMA transfer</td><td>600</td><td>...</td><td>100 '</td>

<td>TRCC</td><td>RCC transfer to the CCU</td><td>...</td><td>...</td><td>900</td>

<td>TMO</td><td>RCC tx modem block</td><td>...</td><td>10350</td><td>10350</td>

<td>t | U2</td><td>1. Rx modem block</td><td>...</td><td>4300</td><td>4300 '</td>

<td>TM3</td><td>2. Rx modem block</td><td>...</td><td>4225</td><td>4825 '</td>

* Based on RELP VCU

Table 14

<td>time symbol</td><td>process</td><td>Max (us)</td><td>Minus)</td><td>Type)</td>

<td>ts</td><td>CCU DMA construction</td><td>150</td><td>...</td><td>100</td>

<td>tvCB</td><td>VCU DMA transfer</td><td>600</td><td>...</td><td>100 *</td>

<td>* M0</td><td>1.Tx modem block</td><td>...</td><td>5225</td><td>5825 *</td>

<td>tM1</td><td>2.Tx modem block</td><td>...</td><td>4225</td><td>4825 *</td>

<td>Im2</td><td>RCC Rx modem block</td><td>...</td><td>5600</td><td>5800 *</td>

<td>TRCC</td><td>RCC transfer to the CCU</td><td>...</td><td>...</td><td>900</td>

'Based on RELP VCU

Send function - RCC

1. Receive an end of the TX-DMA transfer interruption. These signals mean that the processing of the preceding contactor has ended and the next slot can begin. The TX DMA process is brought in.

a. Write out the control channel and the modulation circuit information. This information is needed by modem 19, 30a and byte / symbol converter 127.

b. Format any pending RPU RCC message in the transmit buffer 110. Otherwise, prepare and send the nullification message.

c. Initialize and release the DMA transfer from the transmit buffer 110 to the modem 19, 30a, pointing to the RCC preamble, the single word and the RCC data block.

d. Return from the break and continue with background processing.

Send function - language

1. Receive an end of the TX DMA transfer interruption. These signals mean that the processing of the previous slot has ended and that the processing of the next contactor can begin. The TX DMA process is brought in.

AT 404 202 Β

a. Write out the voice channel and the modulation circuit information for the next step. This information is needed by modem 19, 30a and byte / symbol converter 127.

b. Select the VCU channel address and release the DMA transfer from the VCU to the transmit buffer 110.

c. Write the VCU word.

d. Return from the break and continue with background processing.

Second Receive an end of the TX DMA transfer interruption. These signals mean that the transfer from the transmit buffer of the VCU has ended. The TX DMA process is brought in.

a. Read the VCU status word.

b. Write the code word in the transmit buffer 110.

c. Initialize and release the DMA transfer from the transmit buffer 110 to the modem 19, 30a, pointing to the speech preamble, codeword, and speech data block.

d. Return from the break and continue the rounding process.

Third Receive an end of the TX DMA transfer interruption. These signals mean that the first half-slot transfer from the send buffer 110 to the modem 19, 30a has ended. The TX DMA process is brought in.

a. Select the VCU channel address and release the DMA transfer from the VCU to the send buffer.

b. Write the VCU control word.

c. Suspended the VCU transfer start.

d. Return from the break and continue with background processing.

4th Receive an end of the TX DMA transfer interruption. These signals mean that the transfer from the VCU to the send buffer has ended. The TX DMA process is brought in.

a. Read the VCU status word.

b. Initialize and release the DMA controller 120 for send transfer from the send buffer to the modem.

c. Return from the break and continue with background processing.

Reception function - language

1. Receive an end of the TX DMA transfer interruption. These signals mean that the processing of the previous slot has ended and that the processing of the next slot can be started. The RX DMA process is called in.

a. Build the right modulation for the voice data. This information is needed by the symbol / byte converter 126. At this time, the modem has already received the information.

b. Initialize and release the DMA transfer from the modem 19, 30a to the receive buffer for the first half slot for the voice data.

c. Return from the interruption and continue with the background process. The AGC calculation, the bit for the ambiguity of the synchronization and the processing of the codeword must already have taken place at this time.

Second Receive an end of the TX DMA transfer interruption. This signals that the transfer of the first half slot from the modem 19, 30a to the receive buffer 115 has ended. The TRX DMA process is called in.

a. Select the address of the input channel of the VCU and release the transfer from the receiver buffer 115 to the VCU. Interrupt VCU to start the transfer.

b. Return from the interruption and continue with the background process.

Third Receive an end of the RX DMA transfer interruption. This signals that the first half-slot transfer from the receive buffer 115 to the VCU is complete. The RX DMA process is called in.

a. Initialize and release the DMA controller 121 for the modem to receiver buffer transfer for the second slot half.

b. Return from the interruption and continue with the background process.

Third Receive an end of the RX DMA transfer interruption. This signals that the transfer of the second half-slot from the modem 19, 30a to the receive buffer 115 has been completed. The TX DMA process is brought in.

a. Select the VCU input channel address and enable the transfer from the receive buffer 115 to the VCU. Suspended the VCU transfer start.

b. Return from the interruption and continue with the background process.

AT 404 202 Β

Implementation of the CCU software

The execution of the software program begins as a result of a hardware reset and the flow begins to flow into the supervisor module. The supervisor module handles the initialization of any hardware and software prior to entering a main service loop. After resetting hardware and requesting from the RPU, the supervisor module performs some basic self-test functions. The main service loop accesses the other modules in turn. The supervisor module is designed to subdivide processes into convenient time periods so as to guarantee that the main service loop has reasonable worst case periodicity. Processes requiring real-time response are handled by a service interruption.

Each service interrupt performs the minimum processing to satisfy the service request. This is done to preserve the serial nature of the program execution as much as possible and to minimize the timing of interruptions. Typically, a service interrupt will transfer data to or from an interface and set a boolean to indicate that the action has been performed. Serial-executed code, picked up by the main service loop, then continues to process the information as requested.

The CCU microcontroller 111 is a data flow machine into which software events are driven by the arrival and departure of data. Precise system timing provides the framework for this data flow; However, software events are derived directly from the data flow and not from the frame markings of the system. This approach allows the software to address real events (such as data I / O requirements) rather than artificial events (such as system timing marks). The software makes it easier, via the hardware, to translate the asynchronous action of the shaper into events that are synchronous with the system frame timing. For this work, it is necessary for the software to have things initialized and ready before the system frame event occurs.

It is therefore apparent that while the CCU software is not heavily loaded, it is called to respond to events and complete certain processes within a limited time. This real-time processing is interrupt-driven and therefore requires considerable care in its engineering. There are four potential conflicting real-time events required by the microcontroller: send DMA service, receive DMA service, send RS-232 service and receive DMA service. The RS-232 interrupts have the lowest priority because they occur in a maximum ratio of one per millisecond. The software is designed so that the enforced time of one millisecond will not be exceeded. Response times for speech and RCC data handling are much more critical and a discussion of them follows.

The rtive timing for the data transfers to the transmit bus and the receive bus is shown in FIGS. 23 and 24. The diagram is approximately true to scale and shows the worst-case timing scenario. The time division multiplex nature of the transmission and reception lines is clearly represented by the diagrams. The dark transverse lines indicate the transmission and reception path, according to the activity of the microcontroller on the respective bus (t_s, t_Rcc) During this time, the respective DMA controller 120, 121 is free. The short time periods between the DMA inserts (tvca) correspond to the VCU block transfers. During this time, the DMA controller is reserved for the respective VCU. For the remainder of the time (tMo tmi, tM2, fas), the DMA controller 120, 121 is assigned to the modem interface for service.

The re-clocking FIFO stacks 128, 129 provide the modem interface with the first time constraint included in the timing diagrams. The FIFO stacks hold 16 symbols, providing one millisecond buffer time before underflow (TX) or overflow (RX). During this millisecond, the CCU may use the transmit or receive threads 107, 108 to complete the block transfer to and from the CCU or to copy RCC data into the local RAM.

After switching on, the CCU software carries out an internal self-test and puts the VCU, the modem and the RFU in their initial state. The microcontroller 111 monitors the frame timing of the system and begins executing block transfers to allow the VCU to achieve synchronization. Once data transfers are initiated, the microcontroller 111 uses the end of the block interrupt DMA to maintain system timing. This interruption is directly linked to the data flow thr ough the CCU and therefore to the 16 kHz symbol clock 130. The VCU implicitly preserves the system timing over the DMA. The microcontroller 111 continues to monitor the timing of its operation.

AT 404 202 of the In the subscriber station, the startup of the system thus involves radio synchronization. This is done by locating the RCC and deriving the timing system from it. Once the reception is completed, the microprocessor keeps the transmission timing with the base station fixed.

The data transfer module brings the real-time and background data transfer events to the CCU. The data transfers are used for transmit data away, the receive data path, the send BCC and the receive BCC. All of these processes are interrupt-driven events that require real-time response. The module also executes synchronization acquisitiond monitoring as a background process.

The transmit data path handler is invoked when the transmit DMA controller 120 requests services. This typically occurs as a result of a DMA block transfer, at which time the DMA peripheral brings an end to the block transfer interrupt. The interrupt is received on one of the two interrupt lines of microcontroller 111, model 8031. The service requested by the interrupt depends on the type of data transfer, RCC or voice, and on the time of occurrence within the slot.

The transmit data path interrupt occurs at a predictable time during each slot period. The interruption times and durations are shown in FIGS. 23 and 24. At each occurrence, microcontroller 111 is needed to initialize the DMA peripherals for the next block transfer. This operation must be performed within 150 μs from the interrupt request to the completion of the interruption. In the case of RCC data, the first requested service requires the microcontroller 111 to format the RCC message in the transmit buffer 110 prior to the DMA data transfer. This operation must be completed within 900 us. Since the processes on the transmission path are usually short and require a fast response, the interruption is given the highest priority.

The single output from the transmit data path interrupt handler is the VCU status word that is picked up after the VCU block transfer. This status word is analyzed by the software in the BBM control module.

The receive data path handler is called in when the receive DMA controller 121 requests service. This typically occurs as a result of a DMA block transfer, at which time the DMA peripheral causes an end of the block transfer interrupt. The interrupt is received from one of two external interrupt lines of the 8031 ​​microcontroller 111. The service requested by the interruption depends on the type of data transfer, RCC or voice, and the time it takes to get within the slot.

The receive data path interrupt occurs at a predictable time during each slot period. The interruption times and durations are shown in FIGS. 23 and 24. At each occurrence, the microcontroller 111 is required to initialize the DMA controller 121 for the next block transfer. This process must be performed within 150 μs from the interrupt request to the completion of the interrupt if DMA initialization is the only process to be performed. In the case of RCC data, the last requested service requires the microcontroller 111 to copy the RCC message from the receive buffer 115 after the DMA transfer in local RAM.

This process must also be performed within 150 μs from the interrupt request to the completion of the interrupt if DMA initialization is the only process to be performed. In the case of RCC data, the last service request requires the microcontroller 111 to copy the RCC message from the receive buffer 115 in the local RAM after the DMA transfer. This process must also be completed within 900 microseconds. Since the service of the transmission path can take place during this time, the reception path interruptions have a lower priority than those of the transmission path. The receive data path interrupt handler makes the VCU status word available after each VCU block transfer. This status word is analyzed by the software in the BBM control module. The dispatcher also reads out the RCC messages from the channel, which are then interpreted in the BCC transceiver module.

The BCC receiver module is built into the single chip RSS 232 UART. A Uart is capable of generating an internal interrupt which is triggered whenever a byte is received or sent. The BCC handler selects a status bit to determine which of the two cases caused the interrupt and continues to operate the channel accordingly.

The baud rate generator is programmed for a nominal speed of 9600 baud, resulting in a maximum of 1920 breaks per second. Each interruption must be completed within 1 ms in order to avoid data loss. Since the typical interrupt frequency is low and the response time is relatively long, data transfer interrupts have a low priority.

AT 404 202 Β

The data transfer handler uses pointers to queue or untag data as it is being sent or received. Here only the processing of the connection level is done, including byte stuffing and the insertion of the end of message. These actions are described in the description of the system interfaces.

Very little data processing takes place in the BCC transceiver module. Its job is to put data in and out while handling the send, receive, and BCC data paths. The data synchronization detection, described below, includes the most significant processing functions of the BCC transceiver module.

The detection of the sync word includes a synchronization method at the symbol level. The term sync word is a generic name that is applicable to both the single word in the RCC and the codeword in the voice channel. The only word (UW) is a fixed 8-bit pattern used at the beginning of an RCC message. A codeword (CW) is usually one of 8 possible 8-bit patterns used at the beginning of a voice channel. In addition to its synchronization role, codewords are used to indicate the connection state, power adjustment, and range adjustments.

The base CCU must exhaustively check a valid RCC message in each slot, ie, it performs this task by sampling for the single word in a t3 symbol solid above the UW's nominal location, based on the main system timing. The search algorithm starts with the UWNlocation and inserts a symbol to the right and left of it until (1) the UW pattern is found and (2) a correct checksum is present. The search ends as soon as (1) and (2) are fulfilled or all possibilities are exhausted. After a successful search, the move information, the RCC message, and the performance information are sent to the RPU.

During each voice slot, the CCU of the base station checks the received voice data for a valid codeword. Only the desired position of the code word is checked, since no active symbol synchronization is carried out during the speech operation. If no codeword can be found in five consecutive frames, then the channel is declared out of synchronization and the RPU is informed of this condition. It is up to the RPU to take appropriate action on this point. After three out of five consecutive frames with successful codeword detection, the synchronism to be restored is defined.

The subscriber CCU, when receiving RCC data, can be in one of two modes: frame search or monitor. The frame search operation is used to detect the reception frame timing from the incoming RCCData, and it is automatically used when the receive synchronization is lost. Monitor mode is entered once the receive frame sync has been detected.

In frame search mode, the subscriber CCU must exhaustively check for a valid RCC message after each RCC slot. Like the basic CCU, it performs this task by sampling the nominal position of the UW after the single word in a ± 3 symbol window, based on the timing derived from the modem for AM hole detection. The search algorithm begins with the target UW position and inserts a symbol on the right and left until it (1) finds the UW pattern and (2) determines a correct RCC checksum. The search is completed as soon as (1) and (2) are fulfilled or all possibilities have been exhausted. The shift information from a successful search is used to set the receive frame marker generated by the CCU. The detection ends when (1) and (2) are satisfied with the UW in its nominal position for three consecutive frames. The STU is informed of frame detection when it occurs. During frame search operation, RCC messages are not routed to the STU.

When the frame detection is completed, the CCU of the subscriber station enters the monitor mode. Only the UW setpoint is checked to avoid the possibility of detecting a wrong UW. If no UW is detected after five consecutive frames, then the channel is declared out of synchronism and entered frame search mode. The STU is informed of this out-of-sync state. During monitor operation, RCC messages having a correct checksum and SIN number are passed to the STU.

During each voice slot, the CCU of the subscriber station checks the received voice data for a correct code word. Only the reference position of the code word is checked, since during active voice mode no active symbol synchronization is performed. All possible codewords are searched in this direction of the channel. Code words may cause additional changes in the power and range values ​​in the subscriber station. Additional range changes may actually result in the alternation of symbols as well as in fractional range values. If no codeword is detected in five consecutive frames, then the channel is considered out of sync53

AT 404 202 Β mus explains and the STU is informed of this condition. The synchronism to be stored is defined after three-out-of-five consecutive frames with successful codeword detection.

Additional considerations about the CCU

The transmit DMA transfer request between the transmit buffer 110 and the modem 19, 30a must be derived from the full bit of the FIFO stack 128. This implies that the FIFO stack 128 will always be full when a DMA block transfer is completed.

The receive DMA transfer request between the modem 19, 30a and the receive buffer 115 must be derived from the empty bit of the stack 129. This implies that FIFO stack 129 is always empty when a DMA block transfer is completed.

The CCU controller software provides the gate pulse to enable the DMA transfer, but external control must provide the exchange of synchronization pulses to initiate and sustain the block transfer. This is especially significant for the modem interface, where the frame timing is critical.

The microcontroller 111 should have the ability to stop a DMA transfer. The software will not attempt to use the DMA bus during a block transfer unless this control is needed or the DMA peripheral is free.

The re-clocking FIFO stacks 128, 129 should be automatically cleared (reset) periodically.

The frame timing information must be available to the microcontroller 111. This may take the form of a smybolt clock input to an internal timer of the microcontroller.

When an RCC or voice packet is received synchronously by the CCU, no symbol shift is required to bring the packet to a byte boundary. This should be applied regardless of the modulation level.

modem

The modem operates in one of three modes. In the base station, the modem carries a full duplex send and receive function. When operating in the subscriber station, the modem operates in half duplex mode, transmitting during one part of the TDMA frame and receiving it during another part of the TDMA frame. The third operating mode is a self-adapting training operation. In a modem construction, all these functions are housed. The modem performs the appropriate functions in response to probe signals coming in from the controlling CCU.

The subscriber station modem 30a and the modem 19 in the base station are identical. A block diagram of the modem is shown in FIG.

The transmitting portion of the modem includes a TX symbol filter 132, a digital to analogue converter (D / A) 133, a 200kHz bandpass filter 134, a mixer 135, and a TX (transmit) timing circuit 136. The receiving part of the modem comprises a mixer 138, an analog to digital converter (A / D) 139, a FIFO stack 140 and a microprocessor 141, model TMS 320.

The transmitter part of the modem transmits the information supplied to it by the CCU with a 16-level PSK modulation. It is the responsibility of the CCU on the receiver side to interpret this data as DPSK, QSPK or 16 PSK. The modem sends without knowledge of the modulation level.

The transmission part of the modem is fully integrated into the hardware and requires no adjustment. Symbols received by the CCU are encoded and their corresponding waveforms are profiled to provide good interference characteristics and to avoid interference with amplitude or group delay. The justification for this concept is based on the assumption that there are no strong interfering signals (power densities of 30 - 40 dB above the signal) in the frequency band (within 50-100 kHz) which is close to the band used. The transmitter part of the modem uses a relatively wide IF filtering (100 kHz) so that the transmitted signal does not suffer from amplitude or group delay interference and also any harmonics produced by baseband digital filtering are filtered out.

The TX symbol filter 132 is a digital filter FIR with fixed coefficients (filter with a finite-duration impulse response). This filter 132 simulates a six-hole filter at a sampling rate of 50 samples per symbol per 6 symbol stays in the FIR filter.

The modem receives symbols from the respective CCU at a rate of 16K symbols / second. These symbols are then converted to DPSK code and trapped as input via line 143 to FIR filter 132. The FIR algorithm requires that every other symbol be inverted before it enters the FIR filter. For the DPSK coding the Gray code is used. This poses

AT 404 202 Β sure that if a symbol was received in error, there is a high probability that the two symbols to the receiving codec will only have one bit error.

The impulse response of the FIR filter 132 is truncated at 6T (T = 1/16 kHz). The FIR filter samples the symbols at a rate of 800 kHz so that each symbol is sampled 50 times during its 5T stay in the filter. This is equivalent to a sampling rate of 3T / 25, where the sampling period is equal to T / 25, so that the samples are output every 3T / 25 period. The outputs are interlaced so that only the first and fourth, second and fifth or third and sixth pairs of samples overlap at any one time. Each of these T / 25 long samples is currently split into two parts. During the first half of the sampling period, the I part of the output is calculated, and during the second half of the period, the Q part of the output is calculated. Thus, the instantaneous rate at which the filter outputs the data is 50 x 16 kHz = 800 kHz. The I and Q samples are offset by half a period, but this is corrected by the FIR filter 132.

The signals representing the multiplication of symbols and impulse responses in the FIR filter 132 and the addition of two of these multiplications are provided by an 8Kx8 ROM to line 144 in response to the symbols received on line 143.

The FIR filter 132 outputs 10 bit digital samples to the line 144 at a rate of 800 kHz. These values ​​are fed to the D / A converter 133 to produce an analog well shape on the line 145. This waveform is the time-divided I and Q waveforms of the symbol to be transmitted. This split waveform on line 145 is filtered by 200 kHz bandpass filter 134 and then fed to mixer 135 via line 146. The mixer's local oscillator input is an IF signal of 20 MHz on line 147. The I and Q components are ramped up to a 20.2 MHz IF output on line 148. The output signal on line 148 is supplied to the RFU 21, 31a via a 20.2 MHz bandpass filter (not shown).

The desired signal from the D / A converter 134 is tuned to a frequency of 200 kHz with a bandwidth of about 32 kHz bandwidth. By multiplying the 200 kHz waveform to 20 MHz, the output waveform mixes the I and Q samples with the SIN and COS components of the IF frequency. Therefore, the 20 MHz signal can directly multiply the output waveform and the exact component multiplication is done automatically. Therefore, there is no need for a discrete SIN (IF) / COS (IF) generator circuit to multiply the I / Q samples from the D / A as at the receiver. This also eliminates the separate feed via the mixer from the baseband to the output of the mixer.

The output data stored in the transmit filter FIR 132 is calculated to correct for any errors that may occur due to the 1/50 T difference in the I and Q time values. The IF filters in the RFU (Figs. 28 and 29) also add the two values ​​to form the correctly transmitted waveform since the bandwidth is relatively narrow compared to the IF frequency.

In the modem receiving section, the mixer 138 mixes an analog waveform received from the RFU on line 150 via a bandpass filter (not shown) with a 20 MHz IF signal on line 151 to lower the analog signal to baseband on line 152 , The analog signal is then converted by an A / D converter 139 into a digital signal on line 153 which is stored in the FIFO stack 140 for processing in the microprocessor 141. The microprocessor 141 performs the frequency and bit adjustment of the received signal as well as the FIR filtering and demodulation of the signal in a binary symbol stream which is passed over line 154 to the CCU.

In addition to the analog and digital data signals being processed by the modem, a number of control and status signals are sent to and from the modem. These signals are generally sent from the CCU to the modem. The modem also sends control signals to the RFU to control such functions as transmit power level, frequency, AGC, and antenna diversity switching.

The modem interface is shown in FIGS. 26 and 27. The modem receives most inputs from the CCU. Further inputs come from the RFU and the timer units. The modem inputs are the following:

The following lines carry the described signals from the CCU 18, 29 to the modem 19, 30a:

The TX data line 156 carries a 4-bit symbol to be transmitted by the modem (2 bits for QPSK, 1 bit for BPSK). The MOD BUS 157 is a bidirectional microprocessor bus that provides control / status information to / from the modem. The MOD WR line 158 carries a control signal to the memory MOD BUS in the modem. The MOD RD line 159 carries a control signal to set the modem state and other information to the MOD BUS for transmission to the CCU 18, 29. The MOD RESET line 160 carries a control signal to reset the modem. The MOD_ADD line 161 routes address signals to various locations to store quantities within the modem. The TX SOS line 162 carries a signal for the beginning of the transmission of a TX slot. The RX SOS line 163 carries a start signal

AT 404 202 Β receiving a RX slot.

The IF RECEIVE line carries an IF receive frequency input signal from the RFU 21, 31a to the modem 19, 30a.

The following lines carry the described signals from the STIMU 35 to the modem 19. The 80 MHz line 167 carries an 80 MHz ECL clock signal. A similar signal is supplied from a clock unit (not shown) in the subscriber station to the modem 30a. 16kHz line 168 carries a main TX CLK signal used in the base station. The SOMF line carries a main start of the frame signal from the STIMU to the base station. This signal is not used in the modem, but sent to the CCU 18, 29.

The following lines carry the described signals from the modem 19,30a to the CCU 18, 29th The TX CLK line 171 carries a 16 kHz clock signal which supplies the CCU with the symbol transmit timing. The symbols are clocked in the modem with the rising edge of this clock. In the base station all slots have the same main TX CLK. Therefore, all signals are sent out from the base station at the same time. In the subscriber station, the TX CLK is offset by the partial range delay by the modem based on the information provided by the CCU. The RX CLK line 172 carries the 16 kHz clock signal derived from the received signal. This signal is constantly delivered to the subscriber station, but it is delivered to the base station only during the detection of the control slot. This clock signal clocks the received symbol to the CCU and obtains the symbol timing of the CCU. The RX DATA lines 173 carry the received four-bit symbol, which is clocked by the RX CLK signal. The MOD BUS 157 carries state and data information from the modem. The MOD SOMF line 175 conveys the SOMF signal from the STIMU to the CCU in the base station. The AM STROBE line 176 brings a high to low transition to give the CCU a coarse frame marker during RCC acquisition in the subscriber station. This is a single shot line that is pulsed when the microprocessor 141 detects the approximate location of the AM gap.

The following lines carry the described signals from the modem 19, 30a to each RFU 21, 31a. The RF RX BUS 178 is an eight bit bus between the modem and the RFU part. This bus sends AGC and frequency dialing information to the RF RX part. The modem controls the AGC values ​​to be sent and transports the frequency selection information to the CCU. The frequency selection information is fed to the modem from the CCU via the MOD BUS 157. During the training operation, the modem will control the RF RX frequency selection. The RF TX BUS 179 is an eight bit bus between the modem and the RFU TX part. This bus sends the TX power level and frequency selection information to the RFU TX part. The modem has nothing to do with this because the information is only directed to the RF TX part. The RX 80 MHz REF line 180 carries an 80 MHz reference clock signal to the RFU RX part. The TX EN line 182 to the RFU TX part carries a signal which enables the RF transmission. The RX EN line 183 to the RFU RX part carries a signal to enable the RF reception. The AGC WR line 184 carries an SCP test signal to store the AGC data into the RFU RX part. The RXFREQ WR line 185 carries a write-on signal for writing the frequency into the RFU TX part. The PWR WR line 186 carries a write strobe signal to store the power information into the RFU TX part. The PWR RD line 187 carries a read strobe signal to re-read the power information from the RFU TX part. The TXFREQ RD line 188 carries a read strobe signal to re-read the transmit frequency from the RFU TX part. The TXFREQ WR line 189 carries a write-on signal which writes the frequency into the RFU TX part. The IF TRANSMIT line 190 carries the transmitted signal on the IF frequency to the RFU.

The following lines carry the described signals from the modem 19 to the STIMU 35. The VCXO BUS 192 is a 20-bit data bus to a VCXO in the STIMU 35 with the frequency tracking control information. The VCXO WR line carries a write pulse to the VCXO circuit for storing the VCXO BUS 192 in the VCXO. Similar signals are brought from modem 30a to a timing controller (not shown) in the subscriber station.

The operation of the base station modem is tied to a fixed frequency. The base station has full duplex traffic, so the receive and transmit modem work simultaneously. A modem is also designated as a channel frequency control module which transmits and receives information only during the assigned control slot period with the Radio Control Channel (RCC) format. All transmissions from the modems of the base station are clocked via line 171 at 16 kHz from the main TX CLK signal. Unlike the subscriber modems, the modems 19 of the base station to the CCU output the fraction of the symbol time between the main TX CLK signal on line 171 and the modem-derived signal on line 172. This information is then sent via the RCC to the subscriber station so that the subscriber station will delay its transmission to receive its signal in the base station in synchronism with all other slots.

AT 404 202 Β

The base station modem 19 also sends a zero power signal into the control slot to provide the RC AM slot (which establishes a frame reference) when the RFU transmits a zero power signal. This carrierless part of the RCC transmission is used to initialize the RX detection in the subscriber station.

The modem 19 remains unaware that there are four speech codecs in the base station which are multiplexed by the CCU 18 to four 16 PSK subscriber slot allocations. The modem 19 accepts the bitstreams from the CCU 18 and handles the transmission as a single codec subscriber.

All operations in the subscriber station modem 30a are derived from the received RX CLK signal on line 172, which is retrieved from the received transmission. It serves as the main clock in the subscriber station. The TX CLK signal on line 171 to the CCU 29 is not a master clock in the base station. It is derived from the RX CLK signal on line 172 and delayed by the part time as selected by the CCU 29. The CCU 29 determines the delay of the RCC. The delay is determined by the distance between the base station and the subscriber station. The subscriber station's CCU 29 provides this part-time information via the MOD BUS 157 to the modem 30a. The modem 30a itself is responsible for the partial delay. The CCU 29 is responsible for the total symbol delay by inserting the TX SOS signal on line 162, delayed by the correct number of symbols. This process equalizes the signals arriving at the base station from changes in the area of ​​all subscriber stations.

In the subscriber station there is half-duplex operation. Therefore, the transmitter is blocked when it is free. When the modem 30a is not actively transmitting, it is set to its receive mode and so can monitor the gain levels of the receive signal to be prepared when a burst arrives from the base station.

The subscriber station modem 30a does not transmit a monitoring band for the RCC slot. None is needed because the base station defines the frame. Unlike the fixed frequency modems 19 of the base station, the subscriber station modems 30a may transmit or receive data via any of 26 frequencies selected by the CCU 29 in the RFU.

There are many sources of delay in the modem that have a pronounced affect on system timing. Such things include analog filter delays, propagation delays, FIR filter processing delays, etc. These delays offset the TX and RX frames, and this offset must be included in a careful computation.

The delay between the TX SOS signal on line 162 in the base station and the first received symbol peak in the base station is +7.4 symbols. Therefore, there is an offset between the TX and the RX slots. To correctly decode the incoming phase, the modem must begin sampling about 3.5 symbols before the spike arrives. Thus, the offset between the TX SOS signal and the beginning of the RX sample is about 4 symbols in length.

In the base station, the start of the RX slot is about 4T after the start of the TX slot. The start of the RX slot is defined as the time at which the first analog sample is picked up to detect the first peak being received.

The subscriber station clocks are completely derived from an 80 MHz master VCXO in the subscriber unit's timing unit (not shown). The VCXO is controlled via an analog line from the modem 30a. From this all receive and transmit clocks are calculated. The modem 30a then provides the CCU 29 with the 16 kHz RX CLK signal on line 172 derived from the incoming data stream. The CCU 29 itself detects the single word in the control channel and can determine from the single word frame and slot mark and the RX CLK signal on line 172. The AM split signal from the signal demodulated by the modem informs the CCU 29 where to look for the single word.

During the reception of any slot, the modem 19, 30a performs the frequency synchronization by detecting and then continuously tracking it. In the subscriber station, the VCXO is under the direct control of the microprocessor 141 via a D / A converter. The algorithm of the frequency acquisition and tracking microprocessor calculates the changes in the VCXO required to maintain synchronization.

In the base station, an OCXO accommodated in the STIMU is fixed and works as the main clock of the system. Accordingly, there is no frequency deviation during reception.

During receipt of any slot, the modem also performs bit synchronization on the encrypted bit synchronization of the received data stream. An algorithm performs a bit-tracking loop within the receiver. The microprocessor 141 has control over a variable frequency divider of the 80 MHz VCXO or the OCXO (only during the demodulation of the

AT 404 202 Β

Control slot). Within the bit tracking loop, the microprocessor 141 modifies the frequency division to achieve bit synchronization. While receiving a speech channel, the subsets have increments of 0.1% of 16 kHz, but during a control slot, the values ​​can change drastically by more than ± 50%.

The frame synchronization is handled in the base station and in the subscriber station in two completely different ways. At the base station, the main SOMF signal (start of the modem frame) from the time control unit on line 169 is conveyed via modem 19 via line 175 to the CCU 18. This is the main SOMF signal used for all transmissions from the base station. From this and the main system symbol clock signal (16 kHz), the CCU 18 can derive the entire slot and frame timing.

In the subscriber station, frame synchronization is performed by the CCU 29 upon detection of the single word in the received RCC data stream. After initial capture, the modem 30a provides a single pulse to the line 176 as an approximate frame marker (AM STROBE). During acquisition, the modem 30a searches for the AM gap in the RCC. When the AM (AM_HOLE) is found, it counts the modem 30a during a few frames and then supplies the AM_STROBE flag on line 176 to the CCU 29 with the AMHole framing. The CCU 29 uses this scan mark to windowing the first frame mark counters, which can be modified by the software for exact frame synchronization. This also means that the AM HOLE was found and the RCC is detected.

The slot synchronization is under the control of the CCU 18, 29. The signals TX SOS on line 162 and RX SOS on line 163 are commanded by the modem 19 at the beginning of the transmission or reception of a slot. These signals are respectively synchronized with the TX CLK signal on line 171 and the RX CLK signal on line 172.

The self-adapting mode is a reverse-looped condition in which the modem enters to train the coefficients of the receiver's digital FIR filters to correct for detuning of the analog receive filters that may occur over time or due to temperature. The analysis is performed by looping back the transmit data via the RF unit and receiving a known pattern in the receiver. The coefficients are optimized using a LaGrange system with 5 constraints. These constraints are (1) the received data stream; (2) the 0.05T delayed data stream; (3) the data stream leading by 0.05 T; (4) The data stream from the adjacent channel above; (5) the data stream from the adjacent underlying channel.

During training, microprocessor 141 provides to TX FIR filter 131 via line 143 a series of 32 symbol-long training patterns. This is done via a (not shown) FIFO stack, which is released during the training operation. Lead times / delays are made by a receive bit tracking circuit which can offset the two currents by 0.05T.

The CCU 18, 19 puts the modem 19, 30a into the training mode to allow the transmitter part of the modem to read out the specific training data from the FIFO stack in the modem. The receiver part is advanced / delayed for some of these tests. When the process is complete, the modem sends a status message to the CCU 18, 29 that the coefficients have been calculated. At this time, the CCU 18, 29 tests the modem by setting it to normal and issuing a set pattern, which commands the RFU 21 to loop back and read and check the returned data for validity.

The modem is described in further detail in the pending US patent application Modem for RF Telephone System "filed on the same date by Eric Paneth, David N. Critchlow and Moshe Yehushua. The disclosure in the same is hereby incorporated by reference.

RF / IF unit (RFU) and antenna interface

The RFU subsystem provides the post-channel link between the modem and the antenna in both the base station and the subscriber station. The RFU functions as a linear amplitude and frequency translator and is substantially transparent to the channel data and modulation characteristics.

The circuit for the antenna interface in the subscriber station is shown in FIG. An RFU control logic circuit 192 is coupled to the transmit antenna 32 and the three receive antennas 32a, 32b and 32c through the antenna interface circuitry. The control logic circuit 192 is connected to the transmitting part of the modem 30a and the receiving parts 30a, 30b and 30c of the modem. In fact, 32 and 32a are the same antenna.

AT 404 202 B

The transmitting portion of the antenna interface includes an up-converter and amplifier circuit 193, a TX synthesizer 194, a power amplifier 196, and a TX / RX mode switch 197. A first receiving part RX 1 of the antenna interface includes a down converter and amplifier 198, an RX synthesizer 199, and a preamplifier 200 connected to the switch 107. Each additional diversity receiver TXn (n = 2, 3) includes a down converter and amplifier 202, a synthesizer 203, and a preamplifier 204.

The RFU control logic circuit 192 provides the following signals to the transmitting portion of the antenna interface circuit in response to the signals received from the transmitting portion of the modem 30a: (1) a TX enable signal on line 206; to cause the TX / RX switch 197 to to release the broadcast via the broadcast antenna 32; (2) an IF input signal on line 207 to the up-converter and amplifier 193; (3) a power control signal on line 208, also to the up converter and amplifier 193; (4) a clock reference signal on line 209 to TX synthesizer 194; and (5) a channel selection signal on line 210, as well as the TX synthesizer 194. The TX synthesizer 194 responds to the channel select signals on line 210 by providing a TX frequency select signal via line 211 to the up-converter and amplifier 139 which is equal to the difference between the desired transmit frequency and the IF frequency of the modem.

The RFU control logic circuit 192 provides the following signals to each of the receiving sections of the antenna interface circuit in response to the signals, that of the respective receiving part of the modem 30a, 30b and 30c: (1) a TX enable signal on line 213, the down-converter and amplifier circuits 198, 202 to cause to work in the reception business; (2) an automatic gain control (AGC) control signal on line 214 to the down converter and amplifier circuits 198, 202; (3) a clock reference signal on line 215 to the RX synthesizers 199, 203; and (4) a channel select signal on line 216, also to the RX Synthesizers 199, 203 corresponding to the channel select signal on line 216, by providing an RX frequency select signal on line 217 to the downconverter and amplifier circuits 198, 202; this is the difference between the desired receive frequency and the IF frequency of the modem. The down-converter and amplifier circuits 198, 202 provide IF output signals via line 218 to the RFU control logic circuit 192 as a feed to the respective receiving portions of the modem 30a, 30b, and 30c.

The up-converter and amplifier circuit 193 in the transmitter section receives via line 207 the modulated IF signal amplified and translates it to the selected RF channel frequency. A combination of filters (not shown), amplifiers 196, 197, and level control circuits (not shown) is then used to provide the actual output level and suppress unwanted signals by mirror and harmonic frequencies. The output frequency of the transmitter is the sum of the IF frequency of the modem and a conversion frequency, combined in 25 kHz stops from the reference frequency fed to the modem.

The subscriber station RFU functions as a half-duplex transceiver whose receivers are inactive during the transmit interval. The speed of the broadcast burst is high enough to simulate a full duplex operation for the user. The assigned frequency channel is that selected by the RPU of the base station.

The antenna interface circuitry of the base station is shown in FIG. An RFU control logic circuit 219 is coupled to the transmit antenna 23, and the three receive antennas 34a, 34b, and 34c are coupled through the antenna interface circuitry. The RFU control logic circuit 219 is also interconnected to the transmitting portion of the modem 19 and to the receiving portions 19, 19b and 19c. (The modems 19b and 19c are diversity modems and not shown in Figure 2).

The transmitting portion of the antenna interface includes an up-converter and amplifier circuit 220, a TX synthesizer 221, a power amplifier 222, a high-power amplifier 223, a power detector 224 and a band-pass filter 225. A first receiving part RX 1 of the antenna interface comprises a down converter and amplifier 230, an RX synthesizer 231, a preamplifier 232 and a bandpass filter 233. Each additional diversity receiving part RXn comprises a down converter and amplifier 234, an RX synthesizer 235, a preamplifier 236 and a bandpass filter 237.

The RFU control logic circuit 219 provides the following signals to the transmitting part of the antenna interface circuit in response to the signals received from the transmitting part of the modem 19: (1) a TX ON signal on line 239 to the up-converter and amplifier 220 to turn on the transmission part, to release the transmission by the transmitting antenna 23; (2) an IF input signal on line 240, also to the up converter and amplifier 220; (3) a clock reference signal on line 24 to TX synthesizer 221; and (4) a channel selection signal on line 242, also to the TX synthesizer 221. The TX synthesizer 221 responds to the channel select signal on line 242 by providing an RX frequency select signal via line 243 to the up-converter and amplifier 220 which is equal to the difference between the desired one

AT 404 202 Β

Transmission frequency and the IF frequency of the modem. A level control signal is provided via line 224 from the power detector 224 to the up-converter and amplifier 220.

The RFU control logic circuit 219 provides the following signals to each of the receiving portions of the antenna interface circuit in response to those of the respective receiving portions of the modems 19, 19b, 19c received signals: (1) an automatic gain control (AGC) control signal via line 245 to the down converter and amplifier circuits 230, 234; (2) a clock reference signal via lines 246 to the RX synthesizers 231, 235; and (3) a channel select signal via lines 247 also to the RX synthesizers 231, 235th The RX synthesizers 231, 235 respond to the channel select signal on the lines 247 by providing an RX frequency select signal via the line 248 to the downconverter and amplifier circuits 230, 234 which is equal to the difference between the desired receive frequency and the IF frequency of the modem , The down-converter and amplifier circuits 230, 231 provide IF output signals over line 249 to the RFU control logic circuit 219 as feed to the receive portions of the respective modems 19, 19b, 19c.

The RFUs in the base station and in the subscriber stations are similar to each other except for the additional high power amplifier 223 which is used to increase the transmission power of the RF output of the base station. The basic function of the RFUs in each station is to convert the modulated IF (20.2 MHz) signal from the transmitting part of the modem to the desired RF transmitting frequency in the 450 MHz UHF range. The receiving side of the RF unit performs the opposite action, namely the reduction of the 450 MHz UHF signals to an IF signal at 20 MHz. The transmission and reception frequencies are offset from each other by 5 MHz. The RF units are programmed by the CCU control function to operate at the various frequencies used throughout the system. Typically, each RFU of the base station is deployed to operate upon and not change the initialization of the system on a given frequency allocation. The number of RFUs in the base station corresponds to the number of transmit and receive channel pairs maintained in the base station. The subscriber station RFUs will typically change the frequency of operation on each new call.

The RFU's include changeable AGC and transmit power level adjusters. The gain coefficient for the AGC is provided by the modem based on a calculation in the receive part processor 141 in the modem. The subscriber station's power level is calculated by the CCU based on the message and other control parameters arriving from the base station via the RCC channel. If not all slots in a frequency channel are used, the RFU will send an empty computer inserted therein by the CCU. If a complete frequency channel is not used, the transmitter for that frequency can be blocked by the CCU software through the modem.

The switching time for the diversity switches should be less than 50 microseconds.

There are three antennas and three separate RF / IF units (one transmitter, three receiver antennas).

Some parts of the RFU of the base station and the antenna interface are identical to those of the subscriber station described above. These subdivisions highlight the differences.

The base station RFU's and antenna interface circuits operate on a full duplex basis. All transmitters and receivers work in a 100 percent working cycle. Moreover, it is more economically attractive to operate in the base station with a higher transmitter power and to use low noise circuits with diversity in the receivers. The transmitter is designed to work with the highest allowable power level, without dynamic control. Diversity reception is provided by means of multiple antennas and multiple modems.

The base station usually does not change the frequency or the power level during normal operation. The transmitting and receiving sections are fully tunable to each of the 26 channels.

The transmitting portion of the antenna interface of the base station receives the modulated IF INPUT signal via line 239 from the modem and processes it as the transmitting portion of the subscriber station described above. It is further amplified to the required power level and filtered through a cavity precursor bandpass filter 225 to reduce noise at the operating frequencies of accommodated receivers and to reduce the leakage level.

The receiving portion of the antenna interface of the base station is similar to that discussed at the subscriber station except that the input side is preceded by cavity precursors bandpass filters 233, 237 which are intended to eliminate the sensitivity reduction caused by accommodated or nearby transmitters , Likewise, low noise preamplifiers are used to lower the useful threshold signal level. All antennas 23, 34a, 34b, 34c have a 30 dB standoff from any other antennas. Additional isolation is provided in the transmit and receive parts to provide an approximate 80 dB gap between the transmitted and received

AT 404 202 B

Ensure signals. The bandpass filter, preamplifiers and amplifiers are located near the associated transmit or receive antennas.

The diversity reception method

Diversity reception is used to keep the probability of channel fading below an acceptable threshold. The diversity system is able to add three diversity branches on the way from the subscriber to the base and from the base to the subscriber. The diversity hardware at both the base station and the subscriber station includes a special diversity combination circuit, three modems and their associated RF units and antennas. Only a modem RFU antenna combination has transmission capability. Although the diversity combining circuit 33 is shown only in the subscriber system diagram of Figure 2, it is present in the base station and connected to the modems and the CCU in the same manner as in the subscriber station.

When working with diversity reception, the base station or the subscriber station use three receive antennas which are separated from each other far enough to ensure that the fading phenomena of the received signal do not correlate. These three antennas feed into the RFU control logic circuit via three identical receive sections via the antenna interface, whose IF outputs go into separate modems for demodulation. A TMS 320 microprocessor in diversity combining circuit 33 (diversity processor) receives the outputs from the modems and provides a more reliable data stream to the rest of the system in a manner similar to a single modem. The hardware and software of the diversity processor are responsible for the two tasks, the implementation of the diversity combination, and to appear like a single modem to the CCU.

The diversity processor reads its data symbols, AGC values, signal + noise, magnitude and phase error (deviation of the detected phase from the ideal 22.5 degree reference vector) from the three modems. The algorithm used to determine the demodulated symbol involves the use of a majority vote and signal-to-noise ratio calculations for each modem to identify the modem with the most likely correct answer.

The registers of the diversity processor CCU interface are nearly identical to the registers found in the modems, except that the extra registers used to pass information used in the diversity processing function are not needed.

Because the I / O capabilities of the TMS320 microprocessor are low, and most processes operate concurrently with one type of I / O register, a special register containing the register addresses needed at that time is used. For example, the AGC values ​​from each modem must be read out, the highest value selected, and the result written to the I / O registers of the diversity processor where they can be read by the CCU. The addressing of these registers is performed more efficiently if the address of the AGC register is written to a register from where it is set on the modem address line. Thereafter, the processor only needs to address the correct modem or microprocessor register bank, which speeds up the I / O operations.

In the subscriber station diversity system, each modem has its own timing unit, and the timing signals used by the three modems in the diversity system are not necessarily in phase. Because the clock signals of the three modems are not synchronized with each other, latches are required to hold the data symbol output of each modem until the diversity processor reads them out.

An important function of the diversity processor is to maintain traffic between the CCU and the three modems. This link traffic must be executed fast enough to meet all the requirements of the CCU's, but not so fast that the diversity processor is overloaded.