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

The invention relates to a digital telephone system in which a plurality of simultaneously received via telephone lines information signals are processed, which are then transmitted via one or more radio frequency (RF) channels.

Increasing demands on the effectiveness of mobile data transmission systems and the better utilization of existing transmission bandwidths have led to the development of some radio telecommunications equipment which transmit data in a time division multiplexed manner.

From US-PS 35 46 684 a communication system is known, which establishes connections in time division multiplex mode (TDM) between a base station and subscriber station. The US patent further describes the use of a memory for selectively switching from one data source to another for transmission of data; such switching occurs, for example, when data from a particular source becomes unimportant or unusable, for example because of an error function. However, the device of the US patent is limited to one-way transmission of the data or voice signals and thus achieves a relatively low transfer speed.

DE-OS 28 38 757 also describes a TDM system using multiplexer circuits. This known device provides a double-directional message transmission by means of a duplex circuit, wherein both a transmitting section and a receiving section are provided. The known TDM system, however, does not allow flexible allocation of the time slots in the TDM, so that a time slot may be operated unidirectionally (ie only transmit or receive only).

DE-OS 28 12 009 describes a message transmission system in which the mobile stations each (as part of a TDM system) is assigned a time slot. Although there are so-called free time slots, these can not be used for bidirectional transmission.

The present invention has for its object to further develop a system and to provide a system in which several bidirectional transmissions take place on the same channel. This object is achieved by the digital telephone system according to claim 1. In effect, therefore, in the present invention, a so-called TDMA (time division multiple access mode) takes place.

Furthermore, the present invention is also based on assigning a predetermined RF channel (of a plurality of available channels) to the TDMA transmission. This object is achieved by the digital telephone system according to claim 7.

The invention provides a system for wireless transmission of multiple information signals using digital time division circuits between a base station and a plurality of subscriber stations. The subscriber stations can be fixed or mobile. The number of time division circuits is determined by the transmission quality of the signals. The base station is connected to an external information network, which may be analog and / or digital. The information signals are selected from the group consisting of voice, data, facsimile, video, computer and equipment signals.

The mobile subscriber stations can optionally move relatively quickly and relatively slowly.

The modulation level of the signals and the power supplied to the system are adjusted according to the signal error perception in the system.

The system is equipped with space diversity using a plurality of antennas, which are selectively removed from each other to provide relatively high signal reception despite signal fading.

The base station operates over a plurality of RF channel pairs. Each channel pair operation is achieved by the combination of a transmit channel circuit for processing a predetermined number of information signals, which are simultaneously received via telephone telephone lines for simultaneous transmission to different subscriber stations over a predetermined radio frequency (RF) channel, and a receiving channel circuit for processing a plurality of signals, which are simultaneously received over a given RF channel from different subscriber stations, to output information signals for transmission over the telephone lines, executed.

Separate conversion devices are each connected to each telephone line for converting the information signals received over the telephone lines into digital signal samples.

The transmit channel circuit includes a predetermined plurality of separate signal compression devices for concurrently compressing the digital signal samples, each derived from separate conversion devices, to provide the predetermined number of separate compressed signals, a channel control unit, which is connected to the compression devices for sequentially combining the compressed signals into a single transmit channel bit stream, wherein each of the respective compressed signals occupies a recurring sequential slot position in the transmit channel bit stream, which belongs to a predetermined compression device, and a unit for outputting a transmission channel signal for transmission over the predetermined RF channel in response to the transmission channel bit stream.

A switch connects the respective separate conversion devices to specified separate compression devices.

A remote central unit is connected to the telephone lines and responds to an incoming connection request signal, which is received over one of the telephone lines, by, that it outputs a slot allocation signal, that indicates which of the separate compression devices the switching device with the one separate conversion device, which is connected to the one telephone line, should connect and thereby assigning the one telephone line the slot in the transmit channel bit stream, belonging to the one separate conversion device, which is so connected by the switch. The remote central unit stores which slots are so allocated and, upon receipt of an incoming connection request, polls the memory and then provides a slot assignment signal which causes the connection to a compression device belonging to one of the slots not associated with another telephone line ,

A call processor is connected to the remote central unit and responds to the slot assignment signal by causing the switch to terminate the connection indicated by the slot allocation signal.

The receive channel circuit includes a receive unit for receiving a receive channel signal and processing the receive channel signal to provide a receive channel bitstream containing separate compressed signals in different respective repeating sequential slot positions. A given variety of separate signal synthesis devices, each of which belongs to a different slot position in the receive channel bit stream, digital signal samples from separate compressed signals, which are included in the respective respective slot positions of the receiving channel bit stream, and a controller for retiring the separated compressed signals from the receive channel bitstream and distributing the retired signals to separate synthesizers, which belong to the respective time slots, from which the signals were eliminated.

Separate reconversion devices are each connected to each telephone line for reconverting the digital signal samples into information signals for transmission over the respective telephone lines. Each separate reconversion device belongs to one of the separate conversion devices and is connected to a common telephone line with the associated separate conversion devices.

The switch connects the respective separate re-conversion devices to specified separate synthesis devices.

The remote central unit responds to the incoming connection request signal, that was received over one of the telephone lines, by, that it provides a slot assignment signal, to indicate which of the separate synthesizers should connect the switch to the one of the separate reconversion devices, which is connected to the one telephone line, and thereby assigning the one telephone line the slot in the receive channel bit stream, which belongs to the one separate synthesizer, which is so connected by the switch. The remote central unit stores which slots are allocated in the receive channel bit stream, polls the memory upon receipt of the incoming connection request, and then issues the slot allocation signal to the call processor to effect connection to a synthesizer belonging to one of the slots which is not assigned to another telephone line.

The system of the invention makes use of advanced digital and widely integrated electronic techniques to provide cheap, reliable high quality communications to various market parts. In a preferred embodiment, a fixed base station device is used which is centrally located to communicate with a large number of subscriber stations located nearby. The central base station may be connected to a central office of a public telephone network via a private branch exchange (PBX) connected to incoming telephone lines. The subscriber stations in the system can be either portable or mobile and can either work relatively slowly or quickly. The subscriber stations are connected to the base station via UHF radio channels and to the user via a standard two-wire DTMF touch-tone telephone or via an RS-232C or via a non-standard telephone (e.g. B. 4-wire). The system can be used to replace existing on-site loops with hard wires or to provide quality telephone service for areas where wire connections are not possible or economical.

A feature of the system according to the invention is its ability to employ Time Division Multiple Access (TDMA) and digital speech coding to allow the simultaneous multiple use of frequencies within a given network. Any number of high-quality voice circuits can operate at once on a given frequency channel (with 25 kHz channel spacing). Four such circuits are used for illustrative purposes. This results in both a spectral and economic advantage over existing analog radio telephone systems that allow only one call at a time on a given frequency channel.

The features that provide a lower cost, fixed, mobile, and portable device are the use of low speed digital voice coding (less than 16 Kbps) coupled with spectrally-effective digital 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 carried by a single pair of 20kHz Bw channels, the 25th kHz in the entire spectrum and in particular in the 400 to 500 MHz and 800 to 950 MHz segments are separated. This combination allows a good quality voice connection over a distance of at least 20 km.

To be competitive with a wired service, a much larger number of subscribers must be accommodated than can be carried simultaneously on a given pair of 25 kHz channels. For example, a 12-channel pair system that has 47 concurrent connections may have a total of 500 subscribed and launched subscribers, the particular number being limited by the desired peak-rate lockout probability. Thus, a subscriber connection request control plan that provides reasonable connection delays is also an important feature of the invention.

Further features of the invention will become apparent from the following description of the preferred embodiments and the drawings. It shows

1 is a block diagram generally showing the high-frequency subscriber telephone system according to the invention;

FIG. 2 is a block diagram of a representative preferred embodiment of the base station in the system of FIG. 1; FIG.

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

4 shows the sequence of messages generated by the subscriber stations and the base station in order to establish a connection between two subscriber stations,

Fig. 5 shows various data processing modules executed in the remote control unit (RPU) in the base station of Fig. 2;

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

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

FIG. 8 shows the processing of protocol messages by the RPU in the base station of FIG. 2. FIG.

FIG. 9 is a memory image of the RPU in the base station of FIG. 2; FIG.

FIG. 10 shows the processing of messages related to the RCC state by the message processing module (MPM) shown in FIG. 5; FIG.

FIG. 11 shows the processing of channel state related messages by the message processing MPM shown in FIG. 5. FIG.

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

FIG. 13 shows the signal interface between the PBX and the VCU in the base station of FIG. 2. FIG.

Fig. 14 (on sheet 1) the signal interface between the STU and the VCU in the subscriber station of Fig. 2,

FIG. 15 shows the temporal relationships of the PBX-VCU interface signals shown in FIG. 13 and the STU VCU interface signals shown in FIG.

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

FIG. 17 shows the temporal relationship of the transmission channel signals of the VCU-CCU signal interface shown in FIG. 16. FIG.

FIG. 18 shows the temporal relationship of the receive channel signals of the VCU CCU signal interface shown in FIG. 16. FIG.

Figures 19A and 19B respectively show the timing of the transmit and receive speech blocks passed between the VCU and the CCU for 16-level PSK modulation.

FIG. 20A illustrates the input and output data timing and content for the receive channel between the VCU and the PBX (or STU) for 16-level PSK modulation. FIG.

FIG. 20B illustrates the input and output data timing and content for the transmit channel between the VCU and the PBX (or STU) for 16-level PSK modulation. FIG.

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

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

Fig. 23 is a timing chart for reading the RCC and 16-level PSK voice data on the transmission bus of the CCU of Fig. 22;

FIG. 24 is a timing diagram for passing RCC and 16-level PSK speech data on the receive bus of the CCU of FIG. 23; FIG.

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

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

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

FIG. 28 is a block diagram of the antenna interface line for the subscriber station of FIG. 3; and FIG

FIG. 29 is a block diagram of the antenna interface line for the base station of FIG. 2. FIG. <tables><table><title>Directory of acronyms Directory of acronyms used in the description</title><tgroup cols="2"><thead><row><entry align="left">ACRONYM</entry><entry align="left">DEFINITION</entry></row></thead><tbody><row><entry align="left">A / D</entry><entry align="left">Analog to digital converter</entry></row><row><entry align="left">ADPCM</entry><entry align="left">Adaptive differential pulse code modulation</entry></row><row><entry align="left">AGC</entry><entry align="left">(Automatic gain control) Automatic gain control</entry></row><row><entry align="left">AT THE</entry><entry align="left">amplitude modulation</entry></row><row><entry align="left">BCC</entry><entry align="left">(Baseband Control Channel) baseband control channel</entry></row><row><entry align="left">BPSK</entry><entry align="left">(Binary Phase Shift Keying Modulation) Binary phase shift keying</entry></row><row><entry align="left">BW</entry><entry align="left">(Bandwidth) bandwidth</entry></row><row><entry align="left">CCU</entry><entry align="left">(Channel Control Unit) Channel control unit</entry></row><row><entry align="left">CODEC</entry><entry align="left">(Combined Coder and Decoder) Combined coder and decoder</entry></row><row><entry align="left">DEMOD</entry><entry align="left">Demodulator (receiver part of the modem)</entry></row><row><entry align="left">THERE</entry><entry align="left">Digital to analog converter</entry></row><row><entry align="left">dB</entry><entry align="left">decibel</entry></row><row><entry align="left">DID</entry><entry align="left">(Direct Inward Dial) Extension</entry></row><row><entry align="left">DMA</entry><entry align="left">(Direct Memory Access) Direct memory access</entry></row><row><entry align="left">DPSK</entry><entry align="left">(Differential Phase Shift Keying Modulation) Differential phase shift keying</entry></row><row><entry align="left">DTMF</entry><entry align="left">(Dual tone multi-frequency signaling scheme) Two-tone multi-frequency signal image</entry></row><row><entry align="left">ECL</entry><entry align="left">(Emitter-coupled logic) emitter-coupled logic</entry></row><row><entry align="left">FCC</entry><entry align="left">(United States Federal Communications Commission) American Federal Communications Commission</entry></row><row><entry align="left">FIFO</entry><entry align="left">(First-in first-out memory) shift memory</entry></row><row><entry align="left">FIR</entry><entry align="left">(Finite-Duration Impulse-Response filter) Filter for finite duration pulses</entry></row><row><entry align="left">Hz</entry><entry align="left">Hertz (oscillations per second)</entry></row><row><entry align="left">I</entry><entry align="left">(In-phase) In-phase</entry></row><row><entry align="left">IF</entry><entry align="left">(Intermediate Frequency) Intermediate frequency</entry></row><row><entry align="left">kbps</entry><entry align="left">Kilobits per second</entry></row><row><entry align="left">kHz</entry><entry align="left">kilohertz</entry></row><row><entry align="left">km</entry><entry align="left">kilometre</entry></row><row><entry align="left">LSB</entry><entry align="left">(Least significant bit) least significant bit</entry></row><row><entry align="left">MDPSK</entry><entry align="left">(Multiphase differential phase shift keying modulation) multiphase differential phase shift keying</entry></row><row><entry align="left">MHz</entry><entry align="left">megahertz</entry></row><row><entry align="left">MODEM</entry><entry align="left">Combined Modulator and Demodulator combined modulator and demodulator</entry></row><row><entry align="left">MPM</entry><entry align="left">(Message Processing Module) Message processing module</entry></row><row><entry align="left">ms</entry><entry align="left">millisecond</entry></row><row><entry align="left">OCXO</entry><entry align="left">(Oven Controlled Crystal Oscillator) thermostated crystal oscillator</entry></row><row><entry align="left">PBX</entry><entry align="left">(Private Branch Exchange or Automatic Switch) PABX or dialer</entry></row><row><entry align="left">PCM</entry><entry align="left">(Pulsed Coded Modulation) Pulse Code Modulation</entry></row><row><entry align="left">PSN</entry><entry align="left">(Public Switched Network) Public switched telephone network</entry></row><row><entry align="left">PSTN</entry><entry align="left">(Public Switched Telephone Network) public telephone network or other connection carriers (typically Telco)</entry></row><row><entry align="left">Q</entry><entry align="left">(Quadrature) 90 ° shift</entry></row><row><entry align="left">QPSK</entry><entry align="left">(Quadrature Phase Shift Keying Modulation) Phase shift keying with 90 ° shift</entry></row><row><entry align="left">RBTG</entry><entry align="left">(Ringback Tone Generator) Ringback tone generator</entry></row><row><entry align="left">R.A.M.</entry><entry align="left">(Random Access Memory) Memory with direct access</entry></row><row><entry align="left">RCC</entry><entry align="left">(Radio Control Channel) Radio control channel</entry></row><row><entry align="left">RELP</entry><entry align="left">(Residual Excited Linear Prediction) residual excited linear prediction</entry></row><row><entry align="left">RF</entry><entry align="left">(Radio frequency) high frequency</entry></row><row><entry align="left">RFU</entry><entry align="left">(Radio Frequency Unit) Radio Frequency Unit</entry></row><row><entry align="left">RPU</entry><entry align="left">Remote Connection Processor Unit Remote Connected Central Unit</entry></row><row><entry align="left">ROME</entry><entry align="left">(Read-only Memory) Read Only Memory</entry></row><row><entry align="left">RX</entry><entry align="left">Receive</entry></row><row><entry align="left">SHF</entry><entry align="left">(Super High Frequency) super high frequency (3000 to 30 000 MHz)</entry></row><row><entry align="left">SIN</entry><entry align="left">(Subscriber Identification Number) Subscriber identification number</entry></row><row><entry align="left">SLIC</entry><entry align="left">(Subscriber Loop Interface Circuit) Matching circuit for digital subscriber line</entry></row><row><entry align="left">STIMU</entry><entry align="left">(System Timing Unit) System time clock unit</entry></row><row><entry align="left">STU</entry><entry align="left">(Subscriber Station Telephone Interface Unit) Subscriber station telephone interface unit</entry></row><row><entry align="left">SUBTU</entry><entry align="left">(Subscriber timing unit) Subscriber time clock unit</entry></row><row><entry align="left">TDM</entry><entry align="left">(Time Division Multiplexing) Time Parts</entry></row><row><entry align="left">TDMA</entry><entry align="left">(Time Division Multiple Access) Time Division Multiple Access</entry></row><row><entry align="left">Telco</entry><entry align="left">(Telephone Company) Telephone company</entry></row><row><entry align="left">TX</entry><entry align="left">(Transmit) Send</entry></row><row><entry align="left">UHF</entry><entry align="left">Utrahochfrequenz</entry></row><row><entry align="left">UTX-250</entry><entry align="left">A switch that includes processing and interfacing and that may or may not be a PBX</entry></row><row><entry align="left">UW</entry><entry align="left">(Unique Word) unique word</entry></row><row><entry align="left">VCU</entry><entry align="left">(Voice Codec Unit) Voice coding and decoding unit</entry></row><row><entry align="left">VCXO</entry><entry align="left">(Voltage Controller Crystal Oscillator) Voltage controlled crystal oscillator</entry></row><row><entry align="left">VHF</entry><entry align="left">(Very High Frequencies (30 to 350 MHz))</entry></row></tbody></tgroup></table></tables>

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

Reference is made to FIG. 1. The system according to the invention provides subscriber loop telephone service with UHF radio between subscriber stations (S) 10 and a base station 11. The base station 11 provides call connections directly between the radio-based subscriber stations 10 and is connected to the central office 12 of a telephone company (Telco) for calls to and from outside the system.

For example, the illustrated system operates on common carrier frequency channel pairs in the 454 MHz to 460 MHz band. This group of frequencies contains 26 specific channels. The channels are spaced 25 kHz apart and have an allowable bandwidth of 20 kHz. The distance between the transmitting and the receiving channel is 5 MHz, wherein the center frequency of the lower of the two frequencies is assigned to the base station broadcasts. As indicated previously, 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 divided (TDM). The transmission from the subscriber station to the base station (the receiving channel) is a time division multiple access (TDMA).

All systems are compatible with 47 CFR FCC parts 21, 22 and 90 as well as other relevant regulations.

The transmission between the base station 11 and the subscriber stations 10 is performed digitally by filtered multiphase differential phase shift keying (MDPSK) on 25 kHz spaced full-duplex channels in the 454 to 460 MHz band, thereby satisfying the demands for a 20 kHz bandwidth, as stated in the FCC Rules Parts 21, 22 and 90 (e.g. B. 21.105, 22.105 and 90.209). The system can also be used for other bandwidths and distances within any one possible portion of the VHF, UHF and SHF spectrum.

The symbol rate on each 25 kHz FCC channel is 16 kilo symbols / second in each direction. Speech transmission is performed using 16-level PSK modulation and speech digitization at a coding speed of 14.6 Kbps. The modulation can also be a two-level modulation (BPSK) or a four-level modulation (QPSK). A mix of different modulation levels can be used simultaneously on the same channel. With time sharing, the system allows a call for any multiple of two phases at the speed of 14.6 Kbps (4 phases make two calls, 16 phases allow four calls, etc.) or more at correspondingly slower speeds. Of course, this is just one example because, as shown in the following table, many different combinations of modem bits / symbols or phases and codec speeds can be used: <heading>table</heading><heading>2-way calls or duplex lines with codec speeds of</heading>

The base station may transmit and receive on any or all of the available FCC 25 kHz spaced frequency channels in the 454 to 460 MHz band, with the channels being selectable. The channel frequency selection for each voice channel is always performed automatically by the base station only for one, but may be overridden at an operator console interface provided in the base station.

The base station may have a transmission power of typically 100 watts for each frequency channel.

The base station provides modulation control and time slot and frequency channel assignments to the subscriber stations. Additionally, the base station may apply matching power control over the subscriber stations to reduce consecutive time slot differences and adjacent channel channel interference.

The switching between telephony lines of the telco (telephone company) and the TDM slots on the selected channel is preferably performed by the base station using a digital switch, although it is possible to use an analog switch for this purpose.

The base station allows triple spatial diversity on the receive channels.

The subscriber station can work with a triple-branch diversity. The transmitter power is typically adjustable between 0.1 and 25 watts, but can be adjusted for other power ranges. While voice communications over the subscriber station are perceived as real-time full duplex operation, the radio frequency system operates in half duplex mode through the use of appropriate time division clocking techniques.

The subscriber station is associated with any telephone set for voice communications, or the telephone may be built into the system. In addition, a data port such as an RS-232C, standard 25-pin port can be provided for 9600 tape speed data transmission between the subscribers. The base station and the subscriber station may receive the operating power from any one possible source, either internal or external.

Fig. 2 shows a block diagram of an embodiment of the base station which maintains 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. There are several timeslots in each channel.

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

Connections between the PSTN and the subscriber stations are made and maintained in the Private Branch Exchange (PBX) 15, which is located in the base station. The PBX 15 is a model UTX-250 system, a commercially available finished product of the United Technologies Building Systems Group. Many of the existing features of the general PBX system are used in the telco interface control required by the system of the present invention. The PBX 15 also converts voice information to or from the PSTN into 64 Kbps μ-law companded Pulse Code Modulated (PCM) digital sampling pulses. From this point on, the voice information is processed in digital form by the base station and subscriber stations up to the interface circuit connected to the subscriber telephone or as permitted by the subscriber's transmitter and receiver.

Digital voice information from the PBX 15 is first processed by a voice compression system known as codec 16, which reduces the voice information rate from 64 Kbps to about 14.6 Kbps or less. The codec 16 uses either a residual excited linear predictive (RELP) algorithm or an SBC encoder-decoder to perform the speech velocity compression. Typically, four codecs 16 are present in a speech coding and decoding unit (VCU) 17 for performing speech compression for the four or more time slots in each frequency channel. Each base station VCU 17 can process four or more full-duplex voice connections for both the transmit and receive channels of each channel pair. Switching connections of the PBX 15 determine which voice call is being processed by which VCU 17 and by which codec 16 in the selected VCU 17. The circuits of each VCU 17 are hardware-designed so that a voice call on a particular frequency and slot assignment in the base station is always processed by the same VCU codec 16.

Each VCU 17 is connected to a channel control unit (VCU) 18. The CCU 18 controls the TDMA function and also functions as a link level protocol processor. Each CCU 18 receives the transmit channel output signals of the codecs 16 in the corresponding VCU 17 and forwards the data to a modem unit 19 in the correct time slot and format. Each CCU 18 determines the modulation levels to be used for broadcasting (such as 2-, 4- or 16-level PSK modulation) under the direction of a remote-control CPU RPU 20. Each CCU 18 also processes control information for transmission to the subscriber stations through the Radio Control Channel (RCC) slot and during additional control bits in the voice channels. Each channel pair includes a series combination of a VCU 17, a CCU 18, and a modem 19.

Properly formatted transmit data from each CCU 18 is forwarded to the modem 19 at a rate of 16K symbol / second. Each modem 19 receives these synchronous symbols and converts them to a gray-coded multi-level phase-sampled (PSK) format. The transmit channel output signal of the modem 19 is a modulated IF signal. This signal is introduced into the RF / IF processing 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 operating under the overall control of the RPU 20. The UHF signal is amplified by power amplifiers in the RFU 21 and forwarded via an antenna interface unit 22 to a transmitting antenna 23 for outdoor broadcasting.

The reception mode of the base station is essentially the inverse of the transmission mode. Each RFU 21, each modem 19, each CCU 18, each VCU 17 and the PBX 15 are designed for full-duplex operation.

The Remote Control Unit (RPU) 20 is the central control processor that forwards connection data and control messages to the CCU. The RPU 20 includes a general-purpose computer based on a Model 6800 microprocessor that performs the advanced system management functions and control mechanisms for establishing, canceling, and maintaining the connection. The RPU 20 also communicates with a call processor 24 in the PBX 15 to control the connections between the codecs 16 and the telephone company telephone lines made by a switch matrix 25 of the PBX 15.

Each subscriber station is a relatively small unit located at each user location in the system. The subscriber station connects the standard telephone set and / or the data terminal or the user's integrated acoustic transmitter and receiver to the base station via the UHF radio channel. The mode of operation of the subscriber station is very similar to that of the base station. However, while the base station can operate on one or more frequency channels simultaneously, each of which has the capacity to maintain multiple voice circuits, the subscriber station only operates on one frequency at a time.

FIG. 3 shows a block diagram of a subscriber station. The functional distribution is that of the base station (Fig. 2) very similar. The user interface function is performed by the subscriber telephone interface unit (STU) in the subscriber station. The corresponding function in the base station is executed by the PBX module. The STU in the subscriber station also performs all control functions of the subscriber station, as does the RPU in the base station. The subscriber stations act as helpers of the main base station in the overall system control architecture. The STU can be linked to an external device or send and receive acoustically.

By following the data stream through the subscriber station, it will be noted that the user's voice or data information is first processed by a subscriber line unit (STU) 27. The voice signal inputs from the user's telephone are received in the VCU 28 and digitized. The format of the digitized speech signals is identical to the format used by the PBX 15 in the base station. The subscriber station includes a VCU 28, CCU 29, a modem 30 a and an RFU 31 a, which have the same functions as the corresponding units, in the in Figs. 2 described description part of the base station architecture have been described. A difference in subscriber station operation is usually that it is limited to only one voice channel at a time. The subscriber station operates in essentially half-duplex mode, transmitting in one part of the TDMA frame and receiving in another part of the TDM frame. At a frame size of 45 ms, the subscriber's half-duplex signature is transparent to the user listening to ongoing speech input from the subscriber at the other end of the call connection. The STU 27 and VCU 28 as well as the modem 30 a can be doubled to allow more than one subscriber call.

The half-duplex operation of the subscriber station provides the opportunity to make more efficient use of the existing subscriber station hardware. The VCU and CCU of the subscriber station operate in substantially the same manner as in the base station, at least as far as voice data handling is concerned. However, the modem 30a operates in half-duplex mode, so that either the receiving or transmitting part of the modem is used, but not at the same time. The main saving is that the RFU 31a only has to operate in half-duplex mode. This saves energy because the RF power amplifier is effective for no more than half the time. Also, the RF transmitting antenna 32a may be switched to operate as a second receiving antenna during the receiving portions of the frame using an RF antenna switching function. In addition, no duplexer is required.

Each subscriber station also has a diversity network, with three modems and a diversity combining circuit 33. The diversity combining circuit 33 collects demodulated receive information from each of the demodulators of the three modems 30 a, 30 b, 30 c and merges the three streams to form a single, "best guess" symbol stream which is then sent to the CCU 29 for processing is resent. The demodulation circuits or demodulators in the three modems 30 a, 30 b, 30 c separate the RX RFUs 31 a, 31 b, 31 c and thus the antennas 32 a, 32 b, 32 c.

In the base station, three receive antennas 34 a, 34 b and 34 c are arranged at an appropriate distance from each other to provide non-interrelated spatially distinct signals which are processed by a diversity network. The operation of the diversity network is clear to the operation of the CCU and therefore can be replaced at any time by a single modem effect if the diversity effect is not needed.

The base station also has a space diversity network for each transmit and receive channel pair. Although the diversity network is not shown, the base station diagram of FIG. 2 the same as that of the subscriber station of FIG. 3 which shows the diversity network switching for a single transmit and receive channel pair. Thus, each transmit and receive channel pair in the base station actually includes three demodulators and a modem connected to a diversity combining circuit as shown in FIG. 3 is shown connected.

Accurate clock synchronization between the base station and the subscriber stations is crucial in the overall system. The master time clock basis for the entire system is created by the base station. All subscriber units in a given system must be synchronized on this time base in terms of frequency, temporal symbol scheduling, and temporal framing.

The base station has a System Timing Unit (STIMU) 35 which provides a high accuracy timing allocation reference clock signal at 80,000 MHz. This reference 80 MHz clock signal is divided to produce a 16 kHz clock signal and a 22.222 Hz (45 ms continuous) frame marker signal. The total transmission timing of the base station is generated by these three main synchronous reference signals. The 80 MHz clock signal is used by the modems 19 and the RFUs 21 for accurate IF and RF frequency bases. The 16 kHz clock signal provides the symbol speed timing for transmissions on all base station frequencies. The 45 ms mark signal is used to designate the first symbol in a new frame. This marker is effective for one symbol time duration (62.5 microseconds equals 1/16000 Hz). All frequency channels in the base station use the same time reference for transmission. The three timing signals (80 MHz, 16 kHz and the beginning of frame (SOF) marker) are fed 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 transmit and receive channel pairs. The 16 kHz and SOF markers are used by the CCU 18 to time the transmission of the speech and control symbols according to the current frame structure on that frequency.

The temporal reception division in the base station is ideally identical to the time transmission schedule of the base station. D. that is, the SOF marker and symbol clock signals should be exactly lined up between the transmit and receive signals. However, since perfect timing synchronization from the subscriber station transmission can not be expected, the timing reception of the base station modem 19 must match the incoming symbols from the subscriber station. This is required so that the sample period in the receive operation of the base station modem 19 provides the best estimate of the symbol received by the subscriber station. A small elastic buffer in the CCU 18 associated with the receiving part of the modem 19 offsets this slight timing distortion.

The subscriber stations in the overall system synchronize their time reference signals with the main time base in the base station. The synchronization is achieved by a multi-step method wherein the subscriber station initially acquires the time reference of the base station through the use of RCC messages from the base station. This procedure is described below.

When the subscriber station has initially acquired the time reference from the base station, a spurious algorithm in the demodulators of the subscriber station modems 30a, 30b, 30c keeps the reception timing accurate. The subscriber station advances its own transmissions back to the base station a small amount of time to compensate for the delay in transmission round-trip due to the subscriber station's removal. This method results in the transmission of all subscriber stations being received by the base station in the correct phase with respect to each other.

The system timing unit (STIMU) 35 provides the time base for all transmissions in the base station. The STIMU 35 incorporates a highly accurate (3 × 10 -9) thermostated crystal oscillator operating at a fixed frequency of 80 MHz. This basic clock frequency is divided by 5000 in the STIMU 35 to form the 16 kHz symbol clock signal and divided again by 720 to form a frame start (SOF) marker signal. These three timing reference signals are latched and supplied to each base station modem.

The Subscriber Time Division (SUBTU) (not shown in FIG. 3 shown) provides an 80 MHz clock signal, a 16 kHz symbol timing signal and a frame mark signal of 45 ms duration for the subscriber stations. These signals are identical to those of the base station STIMU except that the 16 kHz clock signal is used as the receive symbol timing in the subscriber station. The 16 kHz clock signal is used for transmission timing in the base station. The transmission timing in the subscriber station is provided by a delayed version of the subscriber station reception time schedule. The delay is a variable amount determined by the range calculation performed between the base station and the subscriber station.

The time division 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 adjusted by the subscriber station modem to be picked up by the base station time scheduling signal as received at the input of the subscriber's RF unit.

logs

The following logs detail the procedures for system control, collision avoidance, and call signaling in the system, as well as the transmitted frame structure. With reference to the components of the system, reference will be made to the components of the base station described above with respect to Fig. 2, unless otherwise specified.

The system uses 20 kHz BW full duplex channels in the 450 MHz spectral range on 25 kHz centerings and accommodates multiple simultaneous calls per channel. Each full-duplex channel consists of a receive and a transmit frequency separated by 5 MHz. The lower frequency of each channel is assigned to the base station for transmission and is referred to as the forward frequency. The higher frequency of each channel, referred to as the reverse frequency, is assigned to the subscriber stations for transmission. Thus, the base station transmits at the forward frequency and receives at the reverse frequency. The reverse applies to the subscriber stations.

The ability of the system, a spectrally effective method of transmitting up to multiple voice channels on a single frequency, is mainly dependent on modem operation. The modem 19 must operate in such a way that it has an efficiency of 3.2 bits / Hz when operating in 16-phase DPSK operation at a speed of 16 K symbols / second.

The modem 19 is strictly a means for converting the 1, 2, 4 or more bit symbols from the CCU 18 into a phase-modulated IF carrier for transmitting and reversing the process on the receiving side. All control for the frame timing and mode selection is performed by the CCU 18. An interface between the CCU 18 and the modem 19 may consist of two four-bit unidirectional synchronous (16 K symbols / second) data buses (Tx and Rx). Additionally, an eight-bit state / control bus may provide control information to the modem and report the state from the modem to the CCU 18. The modem 19 also supplies the CCU 18 with the main 16 kHz symbol clock signal. In the base station, this clock signal is received by the master oscillator in the system time division unit 35, to which the entire base station (and therefore the entire system) is synchronized. In the subscriber station, this clock is derived from the incoming symbols received by the base station. Therefore, all transmissions are based on the time base in the base station. A major function of the subscriber modem operation is to synchronize the local subscriber clock signal to the base station time reference signal by decoding the timing of the received symbols.

The modem demodulator part uses an 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 to an IF transmission frequency of 20.2 MHz. The signal is then sent to the RFU for filtering, further conversion to RF, and pre-broadcast gain.

The modem reception demodulator part receives the IF reception signal from the RFU 21 at the reception IF frequency of 20 MHz. This signal is converted down to the baseband, then digitized with an A / D converter section. The resulting digital samples are processed by a microprocessor-based signal processing unit. This operation part performs filter equalization and synchronization algorithms on the input samples and then demodulates the PSK signal to provide the symbol stream of 16 K symbols / second. This signal processing unit also has a self-training operation which is used to teach the processing unit the inaccuracies of the analog filters used in the receiving stream. When the signal processing unit is formed, the demodulator digital equalization process offsets the input samples by these inaccuracies in the analog filter components. This technique allows the use of less expensive analog components of low tolerance and increases overall system capability to demodulate weak or noisy signals.

The symbols demodulated by the modem are output at the symbol rate to the CCU 18 during receive operation. The modem 19 provides the timing associated with this symbol stream. Both the base station and the subscriber stations derive the receive function timing from the incoming receive signal.

A more detailed description of modem functions and features is set forth below with respect to FIG.

The basic TDM / TDMA channel per subscriber provides a total of 16 Kbps in each direction dedicated to each conversation. Of this channel capacity, 1.43 Kbps are needed in each direction for organization control and demodulation introductions. The VCU therefore operates at a fixed data rate of 14.57 Kbps. This is equivalent to 328 bits per codec frame duration, defined as half the modem frame duration or 22.5 ms.

To accommodate multiple calls per channel, each channel is divided into "slots" via a Time Division Schedule (TDM). These slots specify the system frame format. The length of the system frame consists of a predetermined constant number of symbols. The system frame duration was optimized taking into account the speech encoding speed and the number of sense symbols needed by the modem 19 at the beginning of each burst. The number of slots in the system frame depends on the modulation level of the channel. If z. B. is the modulation level of the channel QPSK, then the system frame consists of two slots per frame. Increasing the modulation level of the channel increases the number of information bits encoded per symbol and therefore increases the data rate of the channel. In a 16-level DPSK, the system frame is divided into four slots, each handling the speech data rate for a call. It is important to know that even at higher modulation levels, the number of symbol times required for modem synchronization remains constant.

The format of the system frame ensures that the modem 19 in the subscriber station will never have to operate in full duplex mode (ie transmit and receive at the same time). Consequently, the slots at the reverse and forward frequencies are time delayed by at least one slot time.

The system frame for the system is set at 45 ms duration. The symbol transfer rate is set at 16K symbols / second. Each symbol is transmitted during a same unit of time, which is equal to 1/16000th of a second (62.5 microseconds). This gives a fixed 720 symbols per frame, numbered from 0 to 719 from the beginning of the system frame. These 720 symbols can consist of 1, 2 or 4 information bits, each of which corresponds to step speeds of 2.4 or 16 phases.

The system frame time (45 ms) is further divided into two or four time division slots depending on the modulation format for the slots composing the frame. Each slot may correspond to one of three types of slots: 1. Radio Control Channel (RCC), 2. 4-ary voice channel, and 3. 16-ary voice channel.

The RCC is always transmitted in a binary (2-phase) modulation mode. The RCC and the 16-ary voice channel slots each require 180 symbols for transmission, ie one-fourth of a system frame duration. Since the 16-ary voice channel 4 information bits per symbol (which is 2⁴ = 16 phases), the 16-ary 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 organization and control purposes, resulting in a voice bit rate of 14.57 Kbps. The 4-ary voice channel slot requires 360 symbols to transmit, equal to one half of the system frame duration. Each symbol in this type of slot consists of one of four differential phases, so that 2 bits per symbol (2 = 4 phases) are transmitted. The resulting bit rate is 16 Kbps, the same as for the 16-ary speech channel. The same number of bits (not symbols) are reserved for the modem and for control purposes so that the speech information rate is 14.57 Kbps as in the 16-ary voice channel slot type.

The system frame on any given frequency channel may be composed of any combination of these three types of slots within the following five limits: 1. A maximum of (720) symbols are transmitted in each system frame. Combinations of the three types of slots may be combined at a given frequency to accomplish this. In the event that not all the channel capacity with the base station frame transmission (i.e. H. less than 720 symbols are transmitted in one frame), null symbols are introduced to fill the 720 symbol frame capacity. A zero symbol is a symbol that has no transmission energy. Second Only one frequency in a multi-frequency base station contains an RCC slot type. Only one RCC is effective at any given time throughout the system. The frequency at which the RCC operates is set by a system initiation parameter and is changed only if that frequency becomes unavailable for some reason. The RCC slot is always associated with the first 180 symbols of the system frame (referred to as slot 0). Third A base station frequency can operate in a constant transmit mode. The subscriber station transmits during not more than half of the total frame time. The subscriber station transmits only 25% of the frame when carrying a call when operating in RCC or 16-ary voice channel mode. The subscriber station transmits during 50% of the frame when operating in 4-ary voice channel mode. A subscriber station can only transmit in one slot during any given frame when carrying a call. 4th All 4-ary voice channels must start transmitting at the symbol number 0 or 360. D. that is, the first half or the second half of a frame may contain a 4-ary speech channel. 5th Transmissions between the forward and reverse frequencies are allocated so that the reverse message of a given slot begins transmitting 180 symbols after transmission of the forward frequency message. This precludes the subscriber station from requiring to transmit at the reverse frequency while simultaneously receiving at the forward frequency.

Under these constraints, up to four voice connections can be processed on a single frequency if all four connections consist of the 16-ary voice channel format when operating in 14.4-Kbps codecs. The slots in the system frame are numbered by the position in the frame structure. The numbering system does not have to be contiguous. If one or more of the slots in the frame are of a 4-ary voice channel slot type, the numbering system "skips" over the second slot duration contained in the longer 4-ary slot. The slot numbering system for the reverse frequency (i.e. H. Subscriber) transmissions is offset from the numbering of the base station (forward frequency) transmission. Therefore, a subscriber receiving information on slot 2 of the forward frequency transmits on slot 2 at the reverse frequency offset by one-half frame in time. Tables 1 to 5 represent possible frame formats and the numbering associated with each slot. <heading>Table 1</heading><heading>Radio control channel structure</heading><heading>Table 2</heading><heading>4-way voice channel frame construction</heading><heading>Table 3</heading><heading>16-ary voice channel frame structure</heading><heading>Table 4</heading><heading>Mixed modulation framework: 2/16-PSK and 4-PSK</heading>

For each slot symbol description, reference should be made to Figs. 2-1 to 6-3. <heading>Table 1</heading><heading>Mixed modulation: 4-PSK and 16-PSK</heading>

With reference to Table 3, the construction of the 16-ary speech channel slot style having 180 symbols will be described. The first 8 symbols of this type of slit are called filter start. The filter start time period present at the beginning of each slot type is a time in which no power is transmitted, thereby giving the receiving portion of the modem 19 time to clean its filters in preparation for the new slot.

The beginning of the filter is followed by a bit synchronization period. During this time, a degenerate 16-ary pattern is simulated which simulates an alternating BPSK signal. The receiving part of the modem 19 uses this field to set the phase reference of the transmitting part of the modem 19.

Next, a 12-bit codeword is used to determine the synchronization between the subscriber and base stations and to exchange control and status information. Codewords are used to exchange the current state of the connection, the connection quality, and performance and timing settings. Each control word is encrypted using ten-bit Hamming code which allows single-error correction and double-error correction. The CCU 18 determines the gain and loss of synchronization by tracking the number of consecutive codewords that are received correctly or incorrectly, and the CCU 18 forwards synchronization changes to the RPU 20 in the base station. In the subscriber station, the CCU 29 forwards synchronization changes to the STU 27.

The Hamming code adds five bits of information to five parity bits to produce a ten-bit code. Each parity bit is calculated by executing a modulo-two stage of all bits in positions in the codeword that contains the bit represented by the parity bit. Although the codeword is sent with all data bits aligned and followed by all parity bits by placing the parity bits in the word with only one bit in the position represented by the bit and in that the data bits in other positions can be brought to the code as follows:

When a codeword is received, parity bits are calculated from the received data bits and compared to the received parity bits. If the calculated total parity bit is different than the received total bit, then the calculated parity bit is exclusive or moderate-linked to the received bits to indicate the address of the error bit. If the calculated and received total bits are the same and the other four bits are not, two errors were detected. If all parity bits are the same, the data was received correctly.

The rest of the slot contains two voice codec packets containing 328 information bits each.

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

The Radio Control Channel (RCC) serves the dual purpose of providing a base for the subscriber stations to initially accept the system timing from the base station and to provide out-of-band signaling between the base station and the subscriber stations.

The format of the radio control channel slot is the same for the forward and reverse channels except the following areas. The first eight symbols of a control slot transmitted by the base station (forward channel) contains an amplitude modulation gap ("AM hole"), which is a period of time in which no energy is transmitted. This gap is used by the subscriber stations to uniquely identify the control channel. At the beginning and end of the reverse channel control slot are some extra symbols to take into account the fact that the subscriber stations are offset in their time division by a few symbols.

All slots contain eight symbols of "zero" transmission, the Filter Start field, which enables the modem to clean its receive filters to prepare for the next slot. The next field of the slot is a fixed bit sync pattern. The transmitted pattern is an alternating BPSK signal. The receive modem uses this field to establish a phase reference and a frequency lock on the sending modem.

The CCU 18 continually searches for a unique word (UW) which is an eight-symbol sequence to identify an incoming RCC message. The base station CCU 18 must exhaustively search for a valid RCC message in each RCC slot. It accomplishes this task by querying for the unique word in a window of ± 3 symbols around the nominal UW location based on the main system timing. The search algorithm begins with the nominal UW position and shifts a symbol to the right and to the left until it (1) finds the UW pattern and (2) verifies a correct RCC checksum. The search ends as soon as (1) and (2) are fulfilled or all possibilities are exhausted. The shift information, the RCC message, and the performance message are sent to the RPU 20 after a successful search.

The subscriber station CCU 29 may be in one of two modes when receiving RCC data: frame search or monitoring. The frame search mode is used to acquire the receive frame timing from the incoming RCC data and is automatically enforced when the RCC synchronization is lost. Monitor mode is entered as often as receive frame synchronization is acquired.

In the frame search mode, the CCU 29 must exhaustively search the subscriber station for a valid RCC message immediately after receiving an RCC slot in the subscriber station. Like the CCU 18 of the base station, it accomplishes this task by following the unique word in a window of ± 3 symbols around the nominal UW location based on the timing derived from the modem's AM hole detection. queried. The search algorithm begins with the nominal UW position and shifts a symbol to the right and to the left until it (1) finds the UW pattern and (2) verifies a correct RCC checksum. The search ends as soon as (1) and (2) are fulfilled or all possibilities are exhausted. The shift information from a successful search is used to set the receive frame flags generated by the CCU. The detection ends when (1) and (2) above are satisfied for three consecutive frames, with the UW in its nominal position. The STU 27 is informed of the frame detection when it occurs. RCC messages are not sent to the STU 27 during frame search mode.

When the frame detection is completed, the CCU 29 of the subscriber station enters the monitoring mode. Only the nominal UW position is checked to eliminate the possibility of false UW acquisitions. If no UW is detected on five consecutive frames, the channel is declared non-in-sync and entered the frame search mode. (This transition should be very unlikely or the performance of the system is unacceptable.) The STU 27 is informed of this out-of-synchronization condition. During the monitoring mode, RC messages having a correct checksum and subscriber ID number (SIN) are forwarded to the STU 27.

The remainder of the slot is used to exchange information between the base station and the subscriber stations. The data part consists of twelve bytes. The first eight bits of data contain a binding field that forwards information regarding the state of the system, collision, discovery and reservation information.

The purpose of the binding level protocol is to detect erroneous messages on the radio control channel. The binding protocol also dissolves competitors on the RCC slot.

The binding field includes "empty transfer", "system busy", "collision", "transfer detected" and "slot reservation" bits. These bits are set by the CCU 18 of the base station and read by the CCU 29 of the subscriber station.

The idle 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 bit setting, it performs the usual synchronization and error checks, but does not forward the message to the respective RPU 20 or STU 27 if the message was received without error.

The system busy bit indicates that all voice channels are assigned and no new connection requests (for a fixed amount of time) should be attempted.

The collision bit resolves contention situations where two or more subscriber stations attempt to transmit in the same control slot.

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

The slot reservation bit reserves the next slot on the reverse control channel.

The remainder of the data portion is used to address and exchange information during call setup and teardown operations. The data part is followed by a 16 bit cyclic redundancy check (CRC) over the slot's unique word and data parts. The CRC is used to detect errors that occur during transmission of the RCC messages. The CRC algorithm involves the division of a block of data by a predetermined bit sequence and the transmission of the remainder of that partition as a part of the data block. The polynomial for generating the CRC has the following form: P (x) = 1 + x⁵ + x¹² + x¹⁶ (Equation 1)

When the CRC verifies the verification of a received message, the message is not forwarded from the CCU 18 to the RPU 21 in the base station or from the CCU 29 to the STU 27 in the subscriber station.

When a subscriber station goes into service and is connected, the subscriber station must detect the system timing and synchronization related to the base station. This detection is achieved by transmission exchanges on the radio control channel (RCC) and refining on the voice channel. The events that lead to system capture are the following: 1. When power is applied at the beginning of the subscriber station, the system starts and the subscriber station CCU 29 gives a sequence of commands to the demodulators of the subscriber station modems 30a, 30b, 30c which result in the RCC acquisition. Second The demodulator of each modem 30 a, 30 b, 30 c is first set in its teaching mode. During this time, the modem teaches its receive digital filters the characteristics of the receive analog filters. The analog filters may degrade due to time and temperature variations. Each modem adjusts its digital filter coefficients during the teaching mode to compensate for these degradations. After the CCU 29 receives the state from the demodulators of the modems 30 a, 30 b, 30 c that the teaching sequence is complete, the CCU sets the receive frequency to the standard RCC frequency. The CCU then commands the modem to accept the RCC frequency and look for the characteristic amplitude modulation "gap" of the RCC, referred to as the AM hole. The AM hole 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 transmitted slot types include only eight-symbol "zero" transmission. The extra eight symbols of the zero information uniquely identify this burst as the RCC at the beginning of a slot burst. Third The first action of the demodulators of the modems 30 a, 30 b, 30 c is to perform a coarse frequency detection. The received signal is processed in a digital phase locked loop, and the subscriber VCXO is set to the transmission frequency of the base station. After acquiring the frequency, the modem begins searching for the AM hole. The modem looks for a sequence of small or no amplitude symbols. If this sequence has been detected for a number of frames, the modem asserts a "strobe AM" signal to initiate the CCU frame timing circuit. If no AM hole sequence was detected, the modem returns the state to the CCU that the RCC acquisition was unsuccessful. The CCU then starts to pick alternative RCC frequencies in the same way. 4th After AM punch detection, the demodulators of the modems 30a, 30b, 30c perform refined frequency detection and initial bit synchronization adjustments. The first 60 symbols of the RCC control slot are a fixed bit sync pattern that is used by the modem to switch to the phase of the base station (bit timing). At this point, the RX clock in the subscriber station is useful as a symbol clock. 5th The subscriber station CCU 29 has received a rough symbol timing adjustment via the AM enable signal from the modem. After the frequency detection and the bit synchronization, the CCU checks the data received from the modem and searches for a unique word of the RCC. This unique word gives the frame the absolute symbol count reference. The CCU then sets its symbol counter so that the counters are aligned with this reference. The subscriber station is now aligned with the transmission system timing of the base station (both frequency and symbol timing) and switched on it. 6th The remaining portion of the system time slot detection determines the distance delay between the base and the subscriber station. This delay can be in a range of 0 to 1.2 symbol times (one way) in the system. During a call setup, the subscriber station sends a message to the base station via the RCC. 7th The base station modem 19 is always looking for new subscribers. These burst pulses may be delayed from 0 to 3 symbol times from the base reference frame start of the base station. During each slot, the demodulators of the base station modems 30a, 30b, 30c look for a transmission on the reverse RCC slot. All timing and phase information must be derived during the first part of the slot (initiation), otherwise the slot and its information will be lost. There is no second way when incoming control slots are received. The incoming control slots are received on the RCC according to the Aloha wait scheme, described below, following this individual indication of the events leading to system capture. 8th. During each slot, the base station modem 19 performs a fast AGC adjustment and bit timing allocation estimation during the first 60 symbols of the slot. The receive split clock signals are adjusted to compensate for the distance delay of the subscriber station. The received data is then supplied to the CCU 18 of the base station. The CCU 18 determines the location of the unique word in the stream and determines the integer distance delay between the base station and the subscriber station. The modem 19 provides AGC information to the CCU 18 for determining the subscriber station TX power settings. The modem 19 also provides the CCU 18 with connection quality and part-time information. The connection quality is used to determine if a collosion has occurred. A poor level of link quality indicates that the signal was most likely not of good quality due to simultaneous transmission by more than one subscriber on the RCC slot. The part-time estimate is the value of the partial range delay between the base station and the subscriber station calculated by the modem 19. 9th This power and distance delay information is processed by the CCU 18 and sent to the RPU 20. The RPU 20 formats this information into the RCC format and transmits this information to the subscriber station via the RCC control slot. The subscriber station CCU 18 decrypts 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 updates its own integer TX symbol frame counter and updates the modem's TX clock sub delay counters. 10th During the call connection for a subscriber station, the base station RPU 20 assigns the frequency and slot assignment to the voice call. This information is communicated over the RCC, and the subscriber station CCU 29 sets the RX frequency and commands the modem to begin determining the voice slot. AGC timing and frequency information is carried forward from the RCC operation to the voice channel operation. This is possible because all frequencies in the system are synchronized to the same frame timing reference in the base station. 11th To accurately set the timing of the subscriber station, a refinement process is performed at the beginning of each voice call. During this refinement phase, the connection over the voice channel is similar to that of the control channel, the modulation level is BPSK, and the message is in RCC format, but no "AM" hole is generated in the base station; these new RCC messages are exchanged only between the CCUs 18 and 19. The modem 19 is set in the refinement mode in the base station and in the output control mode in the base station. During the refinement, the CCU 29 of the subscriber station generates a message containing, for the most part, a fixed bit pattern along with a variable portion indicating the acceptance or rejection of the previous message received from the base station. The base station modem 19 forwards timing and power settings to the CCU 18 of each slot being received. Performance settings are sent continuously to the subscriber station. Timing settings and control information indicating continuation or termination of the refinement mode are sent out after a period of calculations. The base station CCU 18 gathers the timing settings from the modem 30 for 30 frames, calculates an average, and then sends the setting to the CCU 29 of the subscriber station. Then another 30-frame refinement operation is performed by the base station CCD 18, the results being sent back to the CCU 29 of the subscriber station. The refinement phase is terminated by the CCU 18 of the base station and the voice call is initiated when the deviations of the settings received from the modem 19 are within an acceptable range such as 1% or the refinement has taken a maximum amount of time.

During call setup and teardown, the subscriber stations communicate with the base station by transmitting messages via the reverse RCC slot. The traffic attributes of the subscriber stations attempting to gain access to the RCC may, in essence, be marked as stochastic. If a subscriber station wishes to send a message to the base station, some form of control mechanism must be able to mediate which subscriber station is allowed to transmit since several subscriber stations might try to transmit on the same slot. The slot aloha scheme is well suited to the context of a large number of subscribers who relatively rarely request direct accesses to the RCC channel.

The slot aloha scheme allows the subscriber stations to send messages in the particular RCC slot, regardless of whether other subscriber stations are also trying to transmit on the same control slot. The natural consequence of this independence of operation is that messages from different subscriber stations can be sent simultaneously and therefore collide. In order to handle collisions, this scheme requires that a positive acknowledgment (ACK) be sent by the base station upon proper receipt of the message from the subscriber station. If the ACK becomes necessary within the allocated maximum time required for the transmission and processing of delays in each direction (approximately 1 to 2 frame times), the subscriber station must retransmit the message. Repeated transmissions may be caused by an error in receiving the ACK in the subscriber station. In general, the subscriber stations can not determine the cause of the problem. Thus, a random delay is selected by the subscriber stations prior to retransmission of the message to avoid repeated collisions with other transmitters that might be present in a previous collision.

A complication arising from the Aloha scheme is the fact that the channel may become unstable if random retransmission delays are not long enough. When this happens, the channel is blocked by retransmissions and the throughput drops to zero. An adjunct technique mitigates this problem by increasing each average random retransmission delay of the subscriber station with subsequent retransmissions.

The difficulties associated with collision repeat transmissions and access delay stability control are that the delays are typically geometrically distributed. To avoid large deviations in the delay, it is therefore necessary to operate the channel at a utilization of considerably less than 36%.

In particular, a usage of 20% or less makes it unlikely that more than one retransmission due to collisions is necessary. Using a random delay of, for example, 8 frame pages for 45 ms frames, the total average delay with a retransmission is then 450 ms (i.e. H. on average, the delay includes: a frame delay for the original transmission, plus a frame delay for the feedback, plus the eight-frame random delay).

To ensure that the utilization is not greater than 20%, we must take into account the average time T between connection 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 is given. For F = 45 ms, N = 1000 participants and T = 30 minutes, the utilization is 1.5%.

Thus, at the maximum usage of 20%, a number of 1000 subscribers making an average call every half minute may have a frame time of 45 ms with access latencies of approximately 45 ms when a retransmission is required and an average access time of about 70 to 80 ms are maintained. The price paid for the much lower average delay is an increased lag variation, which is rarely two retransmission times for the 20 or less percent utilization; H. 1 s, should exceed.

The Aloha scheme seems to be well suited for a system that has a large number of subscribers requiring relatively infrequent direct access to the control channel, and should allow the design goal of build delays of less than 1 second for the expected ones Subscriber parameter is achieved. In contrast, polling and fixed TDMA techniques result in unacceptable delays.

All phases of call processing involving call origination, call disconnection and slot connection require information exchange over the control channel and / or voice slot control section. The various phases of call processing relating to both subscriber station processing and base station processing will now be described.

The subscriber identity number (SIN) of the subscriber station and the dialed numbers are two call control items which must be supplied to the base station in a call request message at each call made by a subscriber station. For subscriber-to-subscriber calls, the user selects the number in a register in the subscriber's memory. The user initiates the connection with the base station by pressing the send key or by time-out. Only when the number is fully assembled and stored in the subscriber station, the radio channel is used. Thus, the customer can dial at a slow speed without using valuable bandwidth or radio control channel (RCC) time.

The sequence of messages generated by the subscriber stations and the base station to establish a connection between two subscriber stations is shown in FIG. 4 shown. The control channel connection level protocol is used to check the various error conditions that occur as a result of channel errors. In addition, messages received by the base station at the reverse control frequency are automatically acknowledged in the next control slot at the forward control frequency. The following sections give a brief description of a message exchange for connecting between two subscriber stations.

When the base station receives a connection request message on the control channel from a subscriber station A, it first checks the received SIN for errors. Without a valid SIN, the base station does not know who sent the message. If the dialed digits are incorrect or incomplete, the base station transmits an indication clear message on the prewarming control channel frequency to the calling subscriber station A with status information indicating the problem.

If the original attempt is correct or legal (i.e. H. the destination unit is not busy), the voice channel is assigned to the originating subscriber station A and the base station transmits a call in the form of an incoming call message at the forward control frequency to the destination subscriber station B. If the destination subscriber station B does not answer the call with a call accepted message after two attempts or returns a busy state indication via a challenge clear message, then the base station sends a display clear message to the original subscriber station A. busy state information (i.e. H. Determining unit is removed) or that the destination subscriber station does not answer the call.

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 voice channel synchronization is achieved, the destination subscriber station B generates an audible tone heard in the destination subscriber station B and also generates the callback tone over the voice channel to the original subscriber station A.

When the destination subscriber station B is picked up, the voice slot control part changes from a sync call display to a sync pickup display, and call continuation messages are output via the voice channel via the base station between the two subscriber stations. The destination subscriber station B terminates the audible ringing tone and disconnects the ringback tone from the voice channel at this point. The circuit is now complete and the exchange of voice and / or data signals can begin.

The registration of a call with an external telephone is carried out in the same way as the call with another subscriber station. The subscriber station dials only the desired digits and presses the send button or waits for the timeout. This generates a radio request message to the base station. The base station decides whether to call another subscriber station or to take an outside telephone line. In this case, an external telephone line is taken and the dialed digits are output on the telephone line in a pulse shape. While the digits are output in pulse form, the voice frequency is assigned to the originating subscriber station. When a subscriber station receives the call connection message, it changes the frequency and synchronizes on the assigned voice channel. When the voice channel is ready, the subscriber station handset is disconnected from local silence and connected to the external telephone line. From this point, the destination telephone office generates all call continuation tones.

An incoming external call takes a telephone line to the base station. The originating telephone office transmits between two to five digits, identifying the unique words of the destination subscriber station SIN, to the base station via an extension (DID) telephone line. If the selected subscriber station is not busy, the base station sends a call message via the RCC to the appropriate subscriber station. Three possible situations can arise. First, the subscriber station accepts the incoming call and processing proceeds as described below. Second, no response is received. In this case, the base station will try the call twice more. If the base station has exhausted the retry count without a response from the subscriber unit, then a ringback tone is generated in the original unit. The third state is when the subscriber station dials busy (i.e. H. is removed) and returns a call-clear message to the control channel. In this case, a busy character is returned to the original subscriber station.

In the case of a successful call request, the voice channel is allocated and an outside tone is generated on the handset of the destination subscriber station while an audible ring back tone is sent from the subscriber station back to the originating subscriber. If the destination subscriber station answers the call (i.e. H. the base station detects a transition from on-hook to off-hook), both the outer ringer and the channel back panel message are removed. At this point, the voice channel is ready for a call.

A normal call termination is triggered by the subscriber who is hanging up. The base station determines the transition from the detached to the suspended state via the control part of the voice channel. Upon detection of this transition, the base station removes the assignment of the voice channel. The channel must not be reused until the base station sees the subscriber station lose synchronization on that channel. When the call that is being interrupted goes to another subscriber station, an end message is sent to the second subscriber station in the control part of the voice channel. The subscriber stations re-synchronize themselves to the transmissions of the RCC and send request clear messages to the base station.

The termination of a call also takes place 5 seconds after the base station loses radio contact with a subscriber station.

A voice connection may be "lost" due to fading or channel interference at the destination receiver. The following conditions are checked in the subscriber stations and the base station to determine if the call is in trouble: the call quality value returned by the subscriber or base station receiver is below a predetermined threshold at successive receipts; a loss of word synchronization was detected on several consecutive transmissions.

Messages originating from the base station are transmitted to all active subscriber stations. These messages are transmitted by the base station over the radio control channel. The purpose of the broadcast message is to inform all active subscriber stations of changes in the operation of the system (i.e. H. Changing the frequency of the RCC, or sending a command to the modems to go into the auto-test mode, etc.). These messages are not confirmed by the subscriber stations.

Remote Control Unit (RPU)

The RPU operates as a control computer in the base station architecture, it is linked to the CCUs 18 associated with the radio equipment and the PBX 15 as shown in FIG.

The RPU 20 coordinates the necessary measures for radio call processing. The RPU 20 exchanges messages with the subscriber stations, the PBX 15 and the CCUs 18 to make connections and disconnections. The call processing functions include allocation and release of the radio channels. The RPU 20 also maintains a database that reflects the current state of the system; the database contains information about the condition of the equipment, subscriber stations, connections and the radio channels in the system.

Call origination begins when the RPU receives a message from either the PBX call processor 24 for a call from an external line or from a subscriber for a call intended for an external telephone or other party. A connection from a subscriber comes in via the radio control channel (RCC) via the CCU 18 of the base station. The RPU 20 allocates a voice channel and exchanges messages with the subscriber station, the PBX 15, and the CCU 18 to make the connection.

Disconnection begins with a message received from the PBX 15 or a subscriber indicating that a telephone has been hung or is being received by the CCU 18 indicating that synchronization over the radio channel has been lost. The RPU informs the CCU 18 and the PBX 15 of the disconnection and the RCC is released.

The RPU software performs the following functions: 1. It processes subscriber, CCU, and PBX messages that control call setup, call drop, and channel assignment; Second she initiates and maintains a read / write system database; Third it supports a system console that allows system queries and manual system control; 4th it handles the BCC links by maintaining baseband control channel (BCC) conversation protocol over a 9600 baud asynchronous serial interface; 5th it handles the PBX interface by maintaining the PBX message protocol; and 6. she keeps a transactional note that provides diagnostic and raw cost data.

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

The RPU hardware includes a General Purpose Computer based on the Motorola Model 68000. This machine is designed with 1Mbyte Random Access Memory (RAM) and 10Mbytes nonvolatile hard disk storage. The input / output consists of a system control point and a unit that supports eight asynchronous serial data interfaces.

As shown in FIG. 5, the RPU software package simulates a system including a scheduler module 40, a BCC interface module or modules 41 a, 41 b,. , , 41 n, a PBX interface module 42, a console module 43, a registration module 44, a message processing module (MPM) 45, and a database module 46.

Except for the database module 46, all modules are called by the control program module 40 to run. The modules communicate with each other through a system of mailboxes. The database module 46 is based on a collection of subroutines for accessing information in the database.

The control program module 40 provides the power line code for the RPU software. She is responsible for programming and activating all other modules. She is also responsible for maintaining event scheduling and mailboxes that allow in-process communication and inter-process communication.

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

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

The console module 43 provides a system operational interface that allows system state issues and modifications and message exchange between the RPU 20 and the rest of the system.

The registration module 44 provides raw transaction information for diagnostic and system analysis purposes.

Message processing module 46 processes all received RCC, BCC and PBX messages. It performs all subscriber call origination and teardown operations that are not performed by the PBX 15 and assigns the radio channels. It also includes a background task that monitors the state of the CCUs 18.

The database module 46 provides a consistent interface to all data structures necessary for call processing. It also contains a frequency assignment task which allocates the radio channels.

The RPU database contains a structure that describes the system configuration, including information about all participants and the state of all radio channels. These structures can be 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 a sorted list of all valid subscribers. The list is sorted to facilitate participant participation. The SIN table has one input for each participant in the system.

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

Initiate a telephone call from a subscriber station.

This section briefly describes the normal call setup process for a subscriber initiated telephone call. A subscriber (the "originating subscriber") picks up, dials a valid telephone number (the telephone number of the "destination") and presses the send button or waits for a period of time. The originating subscriber station sends a call request message over the control channel to the base station. The RPU BCC modules 41 receive the radio request message and forward it to the MPM 45. The MPM 45 performs a simple dial digit validation and sends a radio request message to the PBX module 42, which forwards the message to the PBX call processor 24. The PBX call processor 24 validates the dialed digits and returns a call log message to the RPU 20. The MPM 45 allocates a voice slot to the originating user station. The MPM 45 issues a channel change command to the CCU 18 containing the voice slot associated with the originating user station. The MPM 45 issues a call connection command to the originating subscriber station, which command assigns the voice frequency and the voice slot to the originating user station. The MPM 45 issues an assignment message to the PBX call processor 24, which commands the PBX call processor 24 to allocate a message channel. At this point, the originating subscriber station is completely established. It is now waiting for a connection via the PBX switch matrix 25 to the "destination". The "destination" may be either another subscriber station or a telephone to which access is to be provided over a telephone line 14, this does not make any difference.

Receiving a call in a subscriber station

This section briefly explains how to handle an incoming call to a subscriber station. The PBX call processor 24 determines that a telephone call is destined for a subscriber station. The PBX call processor 24 generates an incoming call message. This message contains information about the nature of the incoming call, in particular whether the call comes from an outside telephone line 14 or from another subscriber station. The RPU PBX module 42 receives the PBX message from the PBX call processor 24 and sends it to the MPM 45. When the call comes from another subscriber station, the MPM 45 sets the subscriber-to-subscriber index from both the originating and destination subscriber stations and commands the respective CCUs 18 to enter the indoor mode. The MPM 45 issues a paging message to the subscriber station specified by the incoming call message. The correct subscriber station answers with a call acceptance message. The MPM 45 responds to the call acceptance message by issuing a channel change message to the corresponding CDU and a call connection message to the corresponding subscriber station. The MPM 45 then issues an assignment message to the PBX call processor 24, which causes the PBX switch matrix 25 to make the termination call for the incoming call.

Failure recovery

This section briefly describes the response of the RPU 20 to channel fading during a call. The CCU 18, which handles the voice channel that is dwindling, notices that the channel is losing synchronization. The CCU 18 generates a non-synchronization event message. The BCC module 41 receives the event message and forwards it to the MPM 45. The MPM 45 sends an on-hook message to the PBX call processor 24 and places the subscriber in hibernation and in the on-hook state.

Processing an incoming BCC message

A BCC message is routed from CCU 18 to RPU 208 via a 9600 baud asynchronous interface. The BCC module 41, which handles the particular CCU interface, reads the message and checks the link level information bits to verify the integrity of the incoming message. If the BCC module 41 determines that the message is acceptable, an appropriate acknowledgment is returned to the sending CCU 18. Otherwise, a retry or a negative acknowledgment will be returned. The BCC module 41 then sends the message to the MPM 45. The message is then placed in the message processing mailbox 48 using the mailboxes provided by the scheduler module 40. (See Fig. 6).

If there is no input signal from the CCU 18 and the BCC mailbox 49 containing output messages to the CCU is empty, the BCC module 41 "blocks" and the control goes to the scheduler model 40.

The scheduler module 40 makes the next module in the round trip schedule effective, and this module then runs until it blocks. The scheduler module then makes another effect, and so on. Later, the scheduler module makes the MPM 45 effective.

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

Generate an outgoing BCC message

FIG. 6 also explains the data path of an outgoing BCC message. An outgoing BCC message is generated by the MPM 45 in response to any particular event. The message is constructed in the MPM 45 and sent 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 returns control to the scheduler module.

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

Processing RCC messages

An outbound RCC message is treated the same as an incoming BCC message because an RCC message is a type of BCC message. Also, an outgoing RCC message is generated and forwarded in the same way as an outgoing BCC message.

Processing an incoming PBX message

A PBX message is received by the PBX call processor 24. This message is forwarded to the RPU 20 via a 9600 baud asynchronous interface. As shown in FIG. 7 The RPU PBX module 42 reads in the PBX message and sends it to the MPM mailbox 48. If there are no more incoming characters and the PBX mailbox 50 containing the outgoing PBX messages is empty, the RPU PBX module 42 "blocks" and control returns to the scheduler module 40.

The MPM 45 reads the PBX message along with any other messages queued in its mailbox 48. The PBX message is processed based on 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 subscriber, and the generation of new messages. Fig. 7 illustrates the data path of the incoming PBX message.

Generate an outgoing PBX message

Referring again to FIG. An outgoing PBX message is generated by the MPM 45 in response to an event. The message is constructed in the MPM 45 and sent to the PBX module 42. After this message and any other necessary messages have been sent and if there are no more messages in the MPM mailbox 48, the MPM 45 "blocks" and control returns to the scheduler module 40.

The scheduler module 40 continues to make other modules in the wrap-around schedule effective until the RPU PBX module 42 is made active.

The RPU PBX module 42 reads the PBX message from its mailbox 50 and forwards the message to the PBX call processor 24 via the serial data output.

Generating registration messages

At significant locations in each of the modules in the RPU software package, an important information-containing message is sent to the registration module 44. This information is dated and output to a file. Fig. 8 explains the registration data paths.

Console input and output module

The input portion of the console module 43 executes command purpose and recognition along with command validation. Valid console commands have the ability 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 to the console port.

Scheduler module

The scheduler module 40 is considered a special system module and is responsible for the scheduled control of all other RPU modules. The main responsibilities of the scheduler module 40 are to select the next module to execute and to provide intermediate and inner module communication.

Although the various RPU modules can be considered as separate modules, in reality all modules are an application method of a control operating system. It is the scheduler model 40 that performs the orbital handling of the other RPU modules. The scheduler model 40 handles the stack for each of the pseudo RPU modules by assigning a fixed portion of the stack space to each pseudo module at the beginning. Just before then each module is to run, the stack pointer is changed by the scheduler module 40 to point to the appropriate stack address for the correct module. A memory map of the RPU 20 is shown in FIG. 9 shown.

Each RPU module runs until it blocks. When a module blocks, control returns to the scheduler, which allows another module to be scheduled and run. A module can block in different ways:

Bringing EVENT EVENT () that forces the module to stall until an event occurs, or by calling WAIT () blocking for a certain number of seconds, or by calling BLOCK () for a round of the orbit loop blocked.

Another major task that the scheduler module 40 performs is inter-module communication between the modules. Mailboxes are used as means for sending or receiving messages to other modules or used by other modules. Each module can search for its mail in its mailbox by using the mail read request. Likewise, a module may send mail to another module by using the mailing call. The scheduler module maintains a separate mailbox for each of the modules that are in the schedule loop. When a module sends a message to another module, the message is copied to the destination mailbox. Later, when the destination point is about to run, the scheduler module checks its mailbox to determine if there is a message in the mailbox. If so, the scheduler module 40 generates an event of the type POST that forces the module not to be blocked. If it is blocked by a HOLEREIGNIS () and scheduled to run.

An event list is also held by the scheduler module for each module in the plan loop. Events can consist of post or timing events. Post events are always generated when the scheduler module determines that messages are dependent on the currently running module. A module can put a timing event on the event list by calling EVENT (), with the number of seconds to wait before an event is generated. The scheduler module 40 checks the event list of the module each time it passes through the run-flat loop, looking for timer runs. When a timer expiration is detected, the corresponding module is instructed to run and the event is returned to the module through the HOLEREIGNIS () call.

The scheduler model 40 includes routines that are used to initiate the RS-232 interfaces between the CCU 18 and the RPU 20 and between the PBX 15 and the RPU 20. These routines, which provide exclusive software control over the RS-232 interfaces, disable the usual processing of the control sequences by the rule operating system. Other routines are used to flush the I / O memories and to read and write the I / O input and output. Scheduler module 40 also keeps track of system time for all RPU modules.

BCC interface module

Each BCC module 41 provides an interface between a CCU 18 and the other software modules in the RPU 20. The messages exchanged between the CCU 18 and the RPU 20 consist of binary data of different lengths transmitted over an asynchronous communication link. The BCC module 41 is responsible for providing message integrity over the communications link, including error detection, sequential ordering, and message acknowledgment.

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

The inputs to this module 41 include messages received from the CCU or other RPU software modules. Messages are output from this module either to the CCU via the RS-232 ports or to other RPU software modules through the correct mailbox.

The purpose of this module 41 is to process the message traffic between the RPU 20 and the CCU 18. Module 41 continually searches for messages received from CCU 18 and forwards them to the correct RPU software module. Likewise, this module is constantly searching for messages from other RPU software modules destined for a CCU 18. An alternate bit protocol is used to open outstanding messages (i.e. H. not confirmed) to one in each direction. Sequence and acknowledgment bits serve as necessary final control to accomplish this function. The protocol is described in more detail in the following paragraphs.

In the following description, an object that can process messages is referred to as "we" or "us", and the other is referred to as "you" or "you". The protocol can be explained by specifying the actions when a message is received. There are only four basic measures that depend on two conditions. These conditions are determined by comparing the sequence and acknowledgment bits of the received message with the expected one.

For an incoming message, the ACK bit is as expected if it is the same as the SEQ bit of our last sent message. Accordingly, the SEQ bit is as expected if different 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 arrival to be a new message.

The action taken when receiving a message is now grouped under four combinations generated by the above conditions: 1. ACK as expected; SEQ as expected. Mark our last transmitted message as confirmed (which allows us to send a new message). Process the newly arrived message (confirm it in the next message we send). Second ACK as expected; SEQ not as expected. Mark our last submitted message as confirmed (allowing us to send a new message). Put down the newly arrived message (do not confirm it). Third ACK not as expected; SEQ as expected. If we have sent a message that has not yet been confirmed, send it again. If we do not have such a message, then something went wrong at the destination and we should reset it as described below. Process the newly arrived message. 4th ACK not as expected; SEQ not as expected. Our last message was not received at the destination point. Submit it again. Put down the newly arrived message.

The reset bit is used to reset the SEQ and ACK bits. If we receive a message with the reset bit on it, it should be accepted as a new message, regardless of its SEQ bit, and it should be acknowledged. In addition, the ACK bit on the received message reflects the SEQ bit of the last message we have received. We should gag this bit before the next message is sent. For example, if we receive a message whose ACK / SEQ digit is "4" (reset equal to 1, ACK equals 0, SEQ equals 0), then the ACK / SEQ digit in response "1" (reset equal to zero, ACK is zero, SEQ is I). Each side should reset, if it believes that the protocol is out of action.

If we receive a message from them and have no new message pending and a standard reply is not coming soon, we will confirm the message by sending a special ACK message. The ACK bit will acknowledge the received message, but the SEQ bit will not change due to the last message that is being sent. This will cause them to process the confirmation and deposit the newly arrived message. The content of this message is a null message. Since this message is stored anyway, the content of this message is insignificant.

PBX interface module

The PBX module 42 provides the interface between the UTX-250 PBX call processor 24 and the other software modules of the RPU 20. The messages exchanged between the two machines consist of an ASCII message exchange. ASCII characters are defined here as 7 or 8-bit ASCII. Both the PBX call processor 24 and the RPU 20 must be able to accept odd, equal, or small parity characters. The text of the messages consists of chains with different lengths or printable characters.

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

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

The purpose of the PBX module 42 is to process the message traffic between the RPU 20 and the PBX call processor 24. This module continually searches for messages received from the PBX call processor 24 and forwards them to the correct RPU software module. Likewise, this module is constantly searching for 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 sign indicating the beginning of a message or carriage return indicating the end of a message. This module is capable of handling full-duplex message traffic.

console module

The console module 43 is the window of the operator in the current state of the RPU 20. The console provides the ability to display information concerning the current state of the subscribers and the radio channels, to change connections and channel conditions, and to send messages to the PBX 15 and the CCUs 18. The console processes the input stream from the port and executes the desired command.

The console module 43 provides the interface to the operator's attachment to the base station. The console module 43 processes the input from the port and executes the command. Data is retrieved from the database and written into it, messages are output to the terminal screen and messages are sent to other modules. The interfaces of this module include: 1. Characters are entered from the control panel. Second Characters are output to the operation screen. Third Data is extracted from the database and written into it. 4th Messages are sent to the PBX, BCC and message processing modules.

A group of parser routine input characters come from the control panel. Immediate data entry is displayed at the beginning of each command line. The data is buffered, the editing characters are processed, the input is reported back to the display and the data is limited to bars. By providing the parser with a group of data structures describing all possible commands and valid bars in each command, the parser performs recognition on the entered data, responds to question marks, and displays lead words for data entry. Each bar is checked to be the type of expected data. Keywords are matched with the list of acceptable wholes, and numbers are converted to integers. When the command line entry is complete, further verification takes place. Numbers are checked to see if they are within the range, and some commands check the state of the system before the command is executed.

Commands fall into three categories: 1. Commands that display information from the database, 2. Commands that modify the database, and 3. Commands that send messages.

Information can be displayed about the subscriber, the connection the CCU and channel status. All display commands require that information be retrieved from the database and formatted data be output to the operator display. The modification commands include the ability to force a subscriber connection to a particular channel and the ability to turn channels on and off. The modification instructions are used in testing the frequency allocation algorithm. All modification commands are written into the database.

PBX, BCC and RCC messages can be sent from the console module 43 to various other modules in the system. A message send command requests the operator all the information needed for the message, the message is then formatted and sent to the specified module. PBX messages are sent to the RPU PBX module 42, which sends the message to the PBX call processor 24. BCC and RCC messages may be sent from the RPU 20 to the CCUs 18 via the BCC modules 41, which add the link level protocol bits to the outgoing messages. Inputs from the CCUs 18 are simulated and messages including both BCC and RCC messages are sent to the MPM 46.

Registration module

The logger module 44 is responsible for registering RPU events or messages. The registration module 44 maintains the following three disk files: a transaction log with information that is similar to billing information, an error log that consists of error messages, and a message log that consists of system alert messages.

The registration module 44 consists of a group of subroutines retrieved from the other RPU modules. Each subroutine is responsible for timestamping the message and writing the message to the correct disk file. Each subroutine has an overall flag that determines which messages should be registered and which should not. The totals are set and reset by using console commands.

Message Processing Module (MPM)

The MPM 45 performs the high level call processing functions between the PBX 15 and the subscriber stations. It is responsible for call processing functions such as starting pages, assigning voice channels, and controlling call continuation tones, as well as subscriber and external telephones. The MPM 45 also processes state messages received from the CCUs 18. For example, channel state information consisting of link quality or subscriber port status is processed by the MPM 45.

The MPM 45 is organized as a state machine, with PBX and BCC messages being bars for the message processing state machine. The MPM 45 processes the bars (tokens) by updating the database, issuing the necessary responses, and then transitioning to the next state.

The MPM 45 uses system mailboxes maintained by the scheduling module 40 to receive messages from other RPU modules and send messages to other RPU modules. Also, the MPM uses 45 subroutines in the database module to retrieve state information from the database or to bring it up to date.

As previously described, the MPM 45 is organized as a state machine. Bars that force processing to occur consist of messages or timeouts. The MPM 45 determines the type of bar (ie, timer, RCC message, PBX message, etc.) and the subscriber station or channel touched by the bar. The MPM 45 processes the bar by generating the correct responses to the messages and moving to the next state.

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 a subscriber station. The channel state machine shown in FIG. 11 is used to process messages received from a CCU 18.

Initially, all participants are in RCC hibernation and all channels are in channel hibernation, indicating that no connections are established or ongoing.

The state changes for a typical outside call to a subscriber are the following. An external call message is received by the PBX call processor 24, which includes the telephone number and the destination subscriber station of the call. A call message is sent to the subscriber station and the state of the subscriber station is set to RUF. When a call acceptance message is received from the subscriber station, the state of the subscriber station is set to ACTIVE. At this point, the channel is allocated and the PBX call processor 24, the CCU 18 and the subscriber station are informed of the channel assignment. The channel is then placed in the call sync wait state (Fig. 11). When the CCU 18 indicates that the synchronization has been accepted, the channel state is set to synchronization call. Finally, when the CCU 18 indicates that the subscriber has picked up, the channel is set to the synchronization decrease state. The synchronization decrease state indicates that a voice connection is established.

A subscriber-to-subscriber call begins with a call request message received from the original subscriber station. The original subscriber station is set to the dialed state and a radio request message is sent to the PBX call processor 24. PBX call processor 24 then returns a CALL CALL message to the original subscriber station and an incoming call message to the destination subscriber station. In response to the CALL message, a channel is assigned and the PBX call processor 24, the CCU 18, and the original subscriber station are informed of the association. The channel of the original subscriber is set to the state HEADED REMOTE SYNCHRONIZATION WAITING until the channel goes into synchronization. When the CCU 18 of the base station perceives the transmission from the original subscriber, it generates a channel event message SYNCHRONIZATION HEADER TAKEN. The RPU 20 processes the channel event message by changing the state of the channel to the status SYNCHRONIZATION LISTENED AMOUNT. An incoming call message for the destination subscriber station is processed in the same manner as an external call message as described above. In addition, the channels that are switched into the connection are switched to internal operation if both participants are in synchronization.

A breakup begins when one of the parties to the call hangs up. When a phone that is outside the system is hung, a message is received by the PBX call processor 24 through the MPM 45. When a subscriber hangs up, the CCU 18 sends a message indicating that the subscriber station has hung up. In any case, the other party is informed of the disconnection, the channel is switched to the disconnected state, and the subscriber station is put into the aborted state. When the CCU 18 indicates that the synchronization is lost, the channel and the subscriber station are returned to the idle state.

Background tasks

A background task routine is used by the MPM 45. The background task is initially associated with the CCUs 18 after a cold or warm restart. When the system is in operation, the background task also monitors the CCUs 18 to keep the database on-the-fly and associated with an RCC.

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.

Data is written to the database and retrieved from it.

Initially, 18 baseband survey messages are sent to all CCUs for the RPU 20 to determine the current state of the system. All information received by the baseband event or response messages is stored in the RPU database. When the RPU 20 receives a baseband event message indicating that a CCU 18 is ready but not deferred (i.e. H. the CCU 18 has not yet started), the frequency assigned to the CCU 20 is marked as assigned. The CCU 18 is then sent channel interrogation messages to bring the database up to the current state of the system. The initiation of the CCU is completed when each CCU 18 has either responded to all open poll messages or when it is determined that the CCU 18 is down. At this time, each CCU 18 that has indicated that it is ready and deferred (i.e. H. the CCU has just started), assigned a frequency. If a CCU 18 has not been assigned a control channel, then the RPU 20 attempts to allocate the control channel. The first choice is to assign the control channel on the first frequency to the CCU 18, because this is where the subscriber first searches for the RCC. The next choice is any CCU 18 with slot 0 not in use, and the last choice is a CCU 18 with a connection on slot 0. If all the effective CCUs 18 already have a connection on slot 0, then one of the connections and the control channel is assigned to this slot.

When the RPU 20 was in communication with all the CCU 18, the status of the CCUs 18 is monitored via status 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 a baseband event message is received indicating that the CCU 18 is not ready. At this time, the CCU 18 is marked as not ready in the database. In addition, all connections are aborted, all channels are returned to the fault state, and the frequency assigned to the CCU 18 is released. If the CCU 18 contained the control channel, then a new control channel is assigned.

If a baseband event message is received indicating that a CCU 18 is ready and reset, then the CCU 18 is assigned a frequency. If no control channel of a CCU 18 is currently assigned, then slot 0 of the deferred CCU is assigned the control channel.

If a baseband event message is received indicating that a CCU 18 has lost a connection with the RPU 20, then channel polling messages (i.e. H. one for each of the four channels) to the CCU 18 to bring the RPU database up to date with the current state of each CCU channel. When a response to each channel interrogation message is received, the current channel status and connection information in the database is updated. If a channel is in the state SYNCHRONIZATION WAIT, then it is assumed that the subscriber is no longer in the connection and the connection is terminated.

Initially, the CCUs 18 are polled by the RPU 20 for their initial state. The CCUs 18 also send in event messages as they start up 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 routines necessary for database access. They provide a tight thread association with the database for each module requesting access to the information therein. Most of the access routines affect the SIN table and the BCC table. Access to all fields within these tables is provided by the access routines.

The database module is also responsible for starting the database at the beginning. All significant fields are initiated by the introductory part of the database module to appropriate values.

The database module also provides the following: 1. Routines to support TTY initiation; 2. a binary search routine for subscriber searches in the SIN table; 3. Routines and tables to support frequency-to-CCU planning; 4. control of diagnostic indication information; and 5. Frequency assignment.

The database module 46 is a collection of routines that allow controlled access to the database by other modules. By routing all accesses through the database routines, the database is essentially hidden from outside modules. This allows the database to change without requiring modifications to any of the other modules. If the database changes, only the interface routine to the changed part of the database needs to be changed.

Frequency allocation task

The frequency assignment task performed by the RPU 20 selects an appropriate frequency and contactor for a subscriber station that requires a voice channel. The dialing algorithm pulls the call type (i.e. H. internal or external) and the modulation level (i.e. H. 16-year-old or 4-year-old). Although the frequency assignment task is functionally independent of the database module 46, it is closely linked to the data structures in the database. Due to this fact, this function is described separately from the database module, although technically it is a routine in the database module 46.

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

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

The inputs to the frequency assignment task consists of an index in the subscriber station's SIN table that requires a channel and the index in the SIN table of the original subscriber station. The index of the original subscriber station is only valid if the channel is set up for a call to an internal destination. At all other times, the originator index is a predetermined illegal index defined as DB NULL. These indexes provide access to all the information needed to allocate an appropriate channel (i.e. H. Frequency and slot).

The frequency assignment routine returns to a truth value when a frequency-slot combination has been successfully assigned. In the other case, it goes back to FALSE. When assigned, the frequency and the selected slot are placed in the SIN table for the subscriber station which needs the frequency assignment.

Each frequency is divided into four TDM slots. The RPU database maintains a count of how many slots are available in each location. When an assignment request falls in the external source category, a slot is selected from the slot position with the largest empty count. When a slot position is selected, the first frequency available at that slot is selected. In fact, it does not matter which slot is selected when a request falls into this category. However, this technique tends to distribute the system load evenly across all slots and, more importantly, increases the likelihood of optimal slot allocations for both parties of an internal call. This is true because system time scheduling computations have shown that the optimal slot assignment for a subscriber-to-subscriber call is that the base-station transmit slot for each subscriber is in the same slot at different frequencies. By assigning the trigger of a call from subscriber to subscriber to the most available slot position, the probability is greater than when the time comes for the destination subscriber station to be able to assign the same slot position to a different frequency. For example, if position no. 2 is the most available position, it is selected. When processing the assignment request of the destination subscriber station, it is more likely that another slot in position no. 2 is available for selection, whereby the optimal slot-to-slot allocation can take place.

When an assignment request falls within the internal destination category, the slot to be allocated is selected from a dial table. A dial table contains lists ordered from the most desired slot position assignments to the least desired slot position assignments for the destination party. This order is based on the slot assignment of the original subscriber. Up to this point the modulation type was not mentioned. The reason for this is that the basic assignment rules do not change for 4-ary and 16-ary slot options except for one important exception. This is that only slot 0 or slot 2 is assigned for a 4-ary connection. Because of this exception, and the fact that two subscribers can be tuned to different modulation types, a total of four unique dialing tables are required to cover all possible call combinations. These are the following: <heading>Table 6</heading>

Selection table for preferred slot for internal call type 16-ary (destination) of 16-ary (origin).

Each column of each table has a rating assigned to it. This rating indicates the degree of desire for a particular slot. The most requested slot has a rating of 1 and fewer slots requested have ratings of 2, 3 and so on. If two or more columns of a selection table have the same degree of desire, they have the same rating number followed by an alphabetic character. If z. B. of three columns with 2a, 2b and 2c respectively, all three columns have the same degree of desire and their order (a, b, c) is arbitrary. <heading>Table 7</heading>

Preferred slot selection table for type 16-ary internal call (destination) from 4-ary (origin) <heading>Table 8</heading>

Table for preferred slot on internal call of type 4-ary (destination) of 16-ary (origin) <heading>Table 9</heading>

Preferred slot selection table for 4-ary type (destination) internal call from 4-ary (origin).

The frequency assignment task has two inputs. These inputs provide access to crucial information needed for proper frequency and slot selection.

The first entry is the index in the SIN table for the subscriber station that needs a channel. With this index, the frequency assignment can determine the default modulation type of the calling party. It also indicates the routine where the results of its selection algorithms (ie frequency and slot numbers) are to be classified.

The second input to the frequency allocation task indicates the category of the frequency slot arrangement. The value of the second input is either an index in the SIN table or the previously defined illegal value DB NULL. When a valid index is received, the frequency allocation request is identified as the destination page of a subscriber-to-subscriber call and the selection tables should be used. When DB NULL is received, the request falls into the external source category and the "most available slot position" algorithm is used.

The frequency assignment task returns to TRUE if a frequency-slot combination has been successfully assigned, otherwise returns to FALSE. It also causes a desirable side effect. If the assignment is successful, the baseband index and slot fields of the SIN table are filled in for the requesting agent.

The frequency allocation algorithm can be divided into two stages. The first level, called the classification level, determines the category of the assignment request. The second stage, called a selection stage, finds and assigns a frequency-slot combination using the appropriate algorithm as determined by the allocation request category.

The classification level first determines if an automatic frequency selection should occur. When the requesting agent is set to manual mode, the specific values ​​of the manual modulation level, the manual frequency and the manual slot specify the frequency-slot modulation to be assigned. If the specified frequency slot is available, it will be assigned to the requesting party. If the specified frequency slot is not available, the routine returns to an FALSE value. If the requesting agent has been placed in automatic mode, further classification is required.

Having determined that automatic selection must occur, the frequency allocation algorithm determines the requirement category. These request categories are as follows: "External-in" applies when a destination subscriber station is called from an external telephone; "External Out" applies when an originating subscriber station calls an external telephone; "Internal-Out" is when an originating subscriber station calls another subscriber's station; "Internal-in" applies if a destination subscriber station is called by another subscriber station.

If the request is an external-in, external-out or internal-out request, a slot position is selected by searching for the most available position. When the position is selected, all frequencies are scanned sequentially until a vacant slot (or adjacent slot pair in the case of a 4-ary request) of the desired location is found. At this point, the routine places the corresponding values ​​in the SIN table and exits, returning to a true value. If the request falls into the last category (internal-in), further information is required.

If an internal-type request is made, two more bits of information are required. The slot assignment and the modulation type (4-ary or 16-ary) of the originating subscriber must be extracted. When this is done, the corresponding selection table is determined based on the modulation type of the originating entity and the destination participant. After the table has been selected, the originator's slot assignment is used to determine the appropriate row of the selection table to be used. Each follower of the selected row contains equal or less desirable slot assignment. This list is iterated until an available slot is found starting with the most requested position and continuing until all slot positions have been used up. For each slot position (or slot pair of 4-ary links), each frequency is scanned sequentially until the actual slot (or slot pair) is found. The derived frequency slot values ​​are not entered in the corresponding SIN table and the routine exits, returning to a TRUE value.

A "slot counter" arrangement keeps track of the number of available slots for each slot position. These counters are maintained by the database module and the frequency assignment task points to them.

The SIN table contains significant information about each participant that is recognized by the system. The following accesses to the SIN table are made. Modulation Level (Read): The subscriber's modulation level requesting a frequency is extracted from this table along with the originator's modulation level during an internal call setup. Slot Number (Read): The slot assignment of the originating party in an internal call setup must be selected. Slot Number (Write): The slot assignment of the subscriber requesting a channel is entered here. Baseband Index (Write): The frequency assignment of the subscriber requesting a channel is entered here.

The BCC table is used by the frequency allocation routine search for an available frequency slot combination. The following accesses to the BCC table are made: Channel State (Read): The state of a channel is checked to determine availability. Channel State (Read): The channel state is checked to verify that the specified channel is a voice channel. Channel State (Write): The channel state is changed when the specified channel is selected for assignment. Channel Control (Write): The modulation type of the requesting subscriber is written to the channel control byte. SIN Index (Write): Establishes a connection from the selected channel to the requesting party.

The frequency assignment routines go directly into the database. Due to speed and efficiency considerations, this is necessary. Whenever possible, the database routines are used to enter the database from the frequency allocation routines.

Subscriber Telephone Interface Unit (STU)

The STU, in its basic mode, acts as an interface unit to convert the 2-wire analog signal fed from a standard telephone set into 64-Kbps PCM encoded digital sample signals. It is on Fig. 12 Referenced. The STU includes a Digital Subscriber Line Matching Circuit (SLIC) 53 which is directly connected to a Type 500 touch-tone telephone over lines 37. The SLIC 53 provides the correct voltage and impedance characteristics for telephone operation. In addition, the SLIC 53 allows a "RUF" stream to be fed to the telephone set and also performs a "SAVE / DROP" -take. The signal outputs of SLIC 53 on line 54 are analog voice frequency (VF) transmit and receive signals. These are then converted into PCM strobe signals by a PCM codec 55. PCM Codex 55 uses the μ-255 companding algorithm to digitize the speech signals into 8-bit strobe signals at 8 kHz rate. The PCM Codex 55 is essentially full-duplex. The digitized speech samples are then passed via line 56 to a "mode select" multiplexer (MUX) 57. The mode of operation of the MUX is determined by the subscriber control unit SCU 58 which is linked to the MUX 57 by a transmit and receive FIFO 59. The SCU 58 essentially includes a Model 803 microcontroller. The SCU is connected to the CCU 29 via an RS-232 interface circuit 60 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 mode is the voice mode. In this mode, voice samples are forwarded from the PCM codec 55 via the mode select MUX 57 and a VCU driver / receiver circuit 61 to the VCU 28 where they are further processed to increase the bit rate from 64 Kbps to 14.6 Kbps and where they are then forwarded for transmission to the base station.

The second mode is the data mode. In this mode, the 64 Kbps stream to or from the VCU 28 does not include voice information, but the information transmitted to the base station includes an unformatted stream of data from an external data source at a rate up to the 14.6 Kbps channel data transfer rate. The STU also includes an RS-232 data port 62 for connection to a data device (e.g. B. Terminal) via a line 63 using a standard asynchronous 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 port 62. The VCU 28 will packetize the synchronized data so that they pass through the 14.6 Kbps boundary of the channel. Full duplex data transmission is maintained in this mode.

The third STU mode is the call setup mode. In this mode, no data is transferred from the STU 27 to the VCU 28 via the mode select MUX 57. However, a ringing tone generating circuit 65 is connected to the mode selecting MUX 57. This circuit digitally synthesizes the tones used in call log-in procedures such as busy and error tones. During the call log-in, DTMF digits dialed by the subscriber are sensed by a DTMF detector circuit 66 and processed by the SCU 58 to register the call. The ringing tone generating circuit 65 returns the corresponding tones to the subscriber's head harness. A pager 67 is connected to the SLIC 53. A timing generator 68 provides timing signals to the PCM codec 55, the VCU driver receiving circuit 61, and the ringing tone generator 65. When the call log is completed, the STU switches to either the voice mode or the data mode for communication with the base station.

An additional requirement for the STU is to delete unwanted echo signals from remote connections. The delay of the roundtrip for the speech signals between the base station and the subscriber station is well over 100 ms. Any signal reflected due to impedance mismatch at each end will result in annoying echo return. This problem is handled in the base station by an echo canceling system in the PBX function. The STU must provide the echo cancellation in the subscriber station. An echo attenuation of at least 40 dB is expected from this deletion. However, the delay of the echo to be canceled is very small because the reflection of interest is between the SLIC 53 in the STU and the local telephone set itself. The distance is typically only a few tens of feet and the delay is essentially zero.

The 8031 ​​microcontroller 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 base station RPU 20 via messages sent over the radio control channel (RCC) and controls all the individual functions of the STU 27. The SCTU also communicates with the subscriber station's CCU 29 via the baseband control channel (BCC). The RES-232 interface to the CCU 29 operates at 9600 baud and is used to transmit control information between the CCU 29 and the STU 27 in the subscriber station.

Voice Coding and Decoding Unit (VCU)

The Voice Coding and Decoding Unit (VCU) employs four full-duplex RELP voice compression systems. The VCU execution is identical for the base station and the subscriber stations. In the subscriber station, only a quarter of the total functionality is used (i.e. H. only one of the four channels). The interface to the STU 27 in the subscriber station is identical to the interface used by each of the four PBX channels in the interface of the VCU 17 in the base station. The VCU 17, 28 uses a fully digital scheme to apply the RELP speech algorithm described in co-pending U.S. patent application no. 667 446, which has the name "RELP vocoder application in digital signal processors" and on 2. November 1984 by Philip J. Wilson has been filed, and the content of which is incorporated herein. As an alternative, a subband codec may be used. The processed data is supplied to the CCU 18, 29 on a common parallel bus interface controlled by CCU software. The CCU 18, 29 sends the control signals of the VCU 17, 28 to determine the mode and configuration in the VCU 18, 29. The operation modes, the functional description, and the application considerations associated with the VCU 17, 28 are described below.

The interfaces between the PBX 15 and the VCU 17 are shown in FIG. 13 shown. The interfaces between the STU 27 and the VCU 28 are shown in FIG. 14 shown. The interfaces of the STU 27 are a subset of the interfaces of the PBX 15 in which the STU 27 provides only full duplex voice channel operation. The timing relationships for the PBX and STU interfaces are identical and are shown in FIG. 15 shown. Table 10 describes the features that are characterized by the features shown in FIG. 15 used symbols are shown. <heading>Table 10</heading>

It is on Fig. 13 Referenced. The PBX SDAT0, 1, 2 and 3 lines 70, 71, 72, 73 transmit data signals from the PBX 15 to the VCU 17 in the base station. In the subscriber station, the data signal from the STU-SDAT0 line 74 from the STU 27 to the VCU 28 (Fig. 14). 8-bit μ-255 companded serial data is generated during the active part of the PBX / STU gate 0 or PBX gate 1 ... 3 sent to the voice codec at a clock rate of 256kHz. Data is clocked into the VCU 17, 28 on the rising edge of the 256 kHz clock.

The VCU SDAT0, 1, 2 and 3 lines 75, 76, 77, 78 transmit data signals from the VCU to the PBX 15 in the base station. The VCU SDAT0 line 29 transfers data from the VCU 28 to the STU 27 in the subscriber station. 8-bit μ-255 companded serial data is transferred from the language codex to the PBX 15 or the STU 27 during the active high part of the PBX / STU gate 0 or PBX gate 1 ... 3 sent with a 256 kHz clock rate. Data is clocked out of the VCU 17, 28 on the rising edge of the 256 kHz clock.

The PBX gates 0, 1, 2 and 3 lines 80, 81, 82, 83 transmit gate signals from the PBX 15 to the VCU 17 in the base station. The STU gate 0 line 84 transmits a gate signal 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 transmission of PBX / STU SDAT0, PBX SDAT1 ... 3 and VCU SDAT0 ... 3. This gate signal is active every 125 ms for eight consecutive clock periods.

The PBX CLK 0, 1, 2 and 3 lines 85, 86, 87, 88 transmit 256 kHz clock signals from the PBX 15 to the VCU 17 in the base station. The STU CLK 0 line 89 transmits 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 connect the PBX / STU SDAT0 and PBX SDAT1 ... 3 To clock signals in the VCU 17, 28 and the VCU SDAT0 ... 3 Signal to PBX 15 or STU 27 clock. However, the clocks are not synchronized with any clocks generated in the VCU 17, 18, CCU 18, 29 or the modem 19, 30.

In the base station, the PBX-VCU interface converts four channels of synchronous 64 Kbps serial data into 8-bit parallel data, which is then applied to the four transmit voice codecs 16 at 8 kHz sampling rate. In the subscriber station, only one channel (channel 0) is converted by the STU VCU interface. The necessary clocks and gates are provided by the PBX 15 and the STU 27.

The PBX VCU and STU VCU interfaces also perform the complementary function for the receive voice codecs. In the base station, 8-bit parallel data received from the four code channels is converted to four 64 Kbps synchronous serial channels for return 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. The timing relationships for the transmit and receive channels between the VCU and the CCU are shown in Figs. 17 and 18, respectively. Tables 11 and 12 describe the features represented by the symbols used in Figs. 17 and 18, respectively.

Figures 17 and 18 detail the events that occur during the VCBTP shown in Figures 19A and 19B. The individual interface signal definitions are given in the following paragraphs.<heading>Table 11</heading><heading>Table 12</heading>

FIG. 19A and 19B show 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 keying (PSK). At the upper end of Fig. 19A is the system frame timing to which all transfers are referred. This frame timing is also shown in Figs. 19B applicable. A modem frame is 45 ms in length and contains four voice slots (or channels). Each voice slot consists of two system voice block periods (SVBP) of voice data, each containing 82 symbols (requiring 5.125 ms) and an additional 16 organizational data symbols requiring 1.0 ms of frame time.

For the broadcast channels, a block of 328 bits (41 bytes) of processed speech is transferred from the VCU 17, 28 to the CCU 18, 29 prior to the beginning of each SVBP during a speech codec block transmission period (VCBTP). The 64 Kbps input data stream of the VCU associated with a processed speech block is divided into speech coded block periods (VCBPs) having a length of 22.5 milliseconds. With reference to transmission channel 0 in FIG. 19A, unprocessed VC input data in the VCB periods OA1 and OB1 are assigned to the processed data in the VCBT periods OA1 and OBi. Also, the VCB periods for channels 0 and 2 are one half of a VCBP (i.e. H. 11.25 ms) from the VCB periods for channels 1 and 3.

For the receiving channels (as shown in FIG. 19B), a block of 328 bits (41 bytes) of processed speech is transferred from the CCU 18, 29 to the VCU 17, 28 at the end of each SVBP during a VCBTP. As with the transmit channels, the time shift of the VCBP to the VCBTP is application dependent and a (maximum) shift of a VCBP is shown in FIG. 19B. To understand the relationship of the input and output data of the speech codec, reference is made to FIG. 19A and 19B. For Receive Channel 0, compressed voice data transferred to the VCBP during OA10 and OB10 is associated with the processed expanded data stream in VCBPS OS10 and OB10.

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

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

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

The TCDACK line 93 transmits a transmission channel data acknowledge signal from the CCU 18, 29 to the VCU 17, 28. The TCDACK / signal transfers the data to the TCDATA / Bus and returns the TCDAV /.

The TCSCWR line 94 transmits a transmit channel state / control write signal from the CCU 18, 29 to the VCU 17, 28. The TCSCWR signal writes the speech codec control word into the corresponding transmit channel control register which is designated by the TCADDR lines. The data is latched into the register on the rising edge of the TCSCWR signal.

The TCSCRD line 95 transmits a transmit channel state / control read signal from the CCU 18, 29 to the VCU 17, 28. The TCSCRD signal passes the state byte to the TCDATA bus from the language code state register determined by the TCADDR lines.

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

The TCVCST line 97 transmits a transmission channel voice code reset signal from the CCU 18, 29 to the VCU 17, 28. The transmit voice codec determined by the TCADDR lines is reset.

The RCADDR lines 98 transmit receive channel address signals from the CCU 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 transmits receive channel data signals between the CCU 18, 29 and the VCU 17, 28.

The RCDAV line 100 transmits a free receive channel data signal from the CCU 18, 29 to the VCU 17, 28. The RCDAV signal indicates to the speech codec designated by the RCADDR lines that a byte of data is available in the RCDATA register. The RCDAV signal routes the data to the RCDATA bus and into the RCDATA register and resets the RCDACK line.

The RCDACK line 101 transmits a receive channel data acknowledge signal from the VCU 17, 28 to the CCU 18, 29. The RCDACK signal indicates to the CCU 18, 29 that data has been read from the RCDATA register and that another byte may be transferred from the CCU 18, 29.

The RCSCWR line 102 transmits a receive channel state / control write signal from the CCU 18, 29 to the VCU 17, 28. The RCSCWR signal writes the control word into the corresponding voice codec control register designated by the RCADDR lines. Data is latched into the register on the rising edge of the RCSCWR signal.

The RCSCRD line 103 transmits a channel state / control read signal from the VCU 17, 28 to the CCU 18, 29. The RCSCRD signal directs the voice codec state word onto the RCDATA bus from the state register designated by the RCADDR lines.

The BLOCKRDY line 104 transmits a block ready signal from the CCU 18, 29 to the VCU 17, 28. The BLOCKRDY signal is used to initiate a 41 byte block transfer of data from the CCU 18, 29 to the speech codec designated by the RCADDR lines.

The BLOCKRDY signal is used by the speech codec to start the VCBP timing. The CCU 18, 29 must have a data byte available in the RCDATA register before the rising edge of the BLOCKRDY signal.

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

The receive channel VCU hardware receives 41 byte blocks of input data from the CCU 18, 28 during a VCBTP as shown in FIG. 20A. After the data has been processed in accordance with the current mode, the 8-bit μ-law companded data is transmitted at an 8 kHz rate to the PBX (STU) interface module. Latching of data is performed in the VCU 17, 28 to simplify the input / output requirements of the CCU 18, 29. Control information is passed between the VCU 17, 28 and the CCU 18, 29 via a set of control and status ports for each receive channel at the beginning of a VCBTP, as shown in FIG. 18 by optionally. The following operating modes are supported by the receiving codecs:

In the external mode, the voice bandwidth expansion is performed at an input data rate of 14.6 Kbps (328 bits every 22.5 ms) and a data output rate of 64 Kbps. Voice data may also include DTMF tones.

In the internal mode, previously compressed 14.6 KBps of voice signals are routed from the CCU 18, 29 via the VCU 17, 28 to the PBX 15 or STU 27. Since the PBX 15 or STU 27 expects 64 Kbps of data, there must be padding of the data stream. Output (64 Kbps) data consists of one byte of silence (FF hex) pattern until voice data from the CCU 18, 29 becomes available. A sync byte (55 hex) is then output which is followed by the 41 previously processed data bytes, after which the idle byte pattern is continued. FIG. Figure 20A shows an example of the input and output data timing and content for 16 PSK modulation.

In the idle mode, input blocks of speech data from the CCU 18, 29 are consumed but not used. A free output byte pattern (FF hex) to the PBX 15 or the STU 27 is maintained to ensure line silence.

In the wait mode, ongoing hardware diagnostic routines are executed and the resulting status is stored in the status register. Block transmissions to the CCU 18, 29 do not occur 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 forwarded to the CCUs 18, 29.

The transmit channel VCU hardware receives an 8-bit μ-law companded PCM (at 8 kHz sample rate) from the PBX / STU interface. After processing the data corresponding to the current mode, the output data to the CCU 18, 29 in blocks of 41 bytes during a Sprachcodecblockübertragungsperiode (VCBTP) as shown in FIG. 19A. The caching of data is performed in the VCU 17, 28 to simplify the input / output requirements of the CCU 18, 29. Control information is passed between the VCU 17, 28 and the CCU 18, 29 via a set of control and status ports for each transmit channel at the beginning of a VCBTP, as shown in FIG. 17 shown, passed. The following modes are supported by the send codecs:

In the external mode, voice bandwidth compression is performed at an output data rate of 14.6 Kbps. (328 bits every 22.5 ms). Processed voice data is then forwarded in 41 byte blocks to the CCU 18, 29. The voice data may also include two tone multi-frequency (DTMF) tones.

In the internal mode, previously processed speech data is passed from the PBX 15 or the STU 27 via the VCU 17, 28 into the CCU 18, 29. The 64 Kpbs input data stream consists of a free byte pattern (FF hex), a sync byte (55 hex), 41 previously processed compressed speech data bytes, and additional free bytes until the next sync byte occurs. The speech codec monitors the sync byte input data occurring at a byte boundary, and then caches the 41 bytes of speech data. The speech block is then forwarded to the CCU 18, 29 during the next VCBTP as described above. FIG. Figure 20B shows an example of the input and output data timing and content for 16-PSK modulation. Segment 1 on the output channel is a synchronization byte; and segment 2 is a processed voice byte. The hatched segment represents a free byte pattern. It should be noted that the synchronization and speech data bytes do not occur across the VCBP boundaries.

In the idle mode, input speech data from the PBX 15 or the STU 27 is consumed but not used. The 41 bytes of output speech data to the CCU contain a silent speech pattern.

In the wait mode, ongoing hardware digression routines are executed and the resulting state is stored in the state register. Block transmissions to the CCU 18, 29 will not occur until the mode is changed by a block request according to the 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 execution requirements of the RELP algorithm, but the frame must be an integer sub-multiple of the speech coded block period (VCBP), which is 22.5 ms.

Due to the fact that the PBC 15 and the STU 27 operate asynchronously from the internal system timing, a means must be incorporated for detecting, reporting, and compensating data overflows and underflows of the VCUs 17, 28. This condition occurs about once every 5,000 VCBPs. While the perception of over / underflows is application dependent, these errors are reported in the state word. Data underflows can be compensated by repeating the last speech sample as required, and overflows can be handled by disregarding speech samples as needed.

After a reset of any (or all) codecs, the VCBTPA is the first block transmitted by the CCU 18, 29, as shown in Fig. 19A as an example.

Control channel unit (CCU)

The control channel unit (CCU) performs similar functions in both the subscriber stations and the base station. The hardware used in the two station types for the CCU function is actually identical. The software in the subscriber station differs slightly from that in the base station. The CCU performs functions related to information information and timing ways associated with operation on the time division transmission channels. The basic inputs to the CCU come from four sources. First, the actual digitized samples to be transmitted. These are transmitted to the CCU 18, 29 from the VCU 17, 29 (Fig. 2 and 3). These data may be encrypted voice samples or data samples from the RS-232 data port 10 in the STU (Fig. 12). In any case, the digital channels work at 16 Kbps. Four channels can be simultaneously processed by the CCU 18 when operating in the base station, with all four operating 16-level PSK transmission channels. The subscriber station CCU 29 operates on only one stream, but this stream may be located in any of the four slot locations associated with the TDMA framing scheme. The second input to the CCU comes via the base control channel (BCC) from the STU 27 (in the subscriber station) or the RPU 20 (in the base station). The second input provides control messages pertaining to the modes, status and control information. Many of the BCC messages from the CCU 18, 29 are Radio Control Channel (RCC) messages received by the CCU 18, 29. The CCU 18, 29 sends control information from the RCC messages to the STU 27 or the RPU 20, and receives control messages from the RPU 20 or the STU 27 in response. This determines what the CCU 18, 29 should 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 CCU modem string. In addition, the modem 19, 30a provides the state of accuracy of its bit-tracking synchronization, RF AGC level adjustments, and other "goodness" indicators used by the CCU 18, 29 to determine whether sufficient interference-free communications over the Channel occur. The CCU 18, 29 attempts to control the "fine-tuning" of the current operation of the modem 19, 30a via commands to vary transmit power levels, AGC levels, and timing / range calculation. Quality level measurements of the modem transmissions are reported to the RPU 20 or the STU 27. The fourth input source is the actual modem data received as symbols of up to four bits each (depending on the modulation levels). These symbols are latched, demultiplexed and output to the receive circuits of the VCU 17, 28 for decoding.

FIG. 21 shows a block diagram of the CCU. The architecture of the CCU consists essentially of two one-way direct memory access (DMA) data channels with a smart microprocessor. The function of the DMA channels is to transfer data from the VCU to the modem and vice versa. The CCU interface to the VCU includes two parallel DMA buses, 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). The data processed by the transmit circuits in the VCU are latched in the VCU memory until the CCU requests a DMA transfer. 41 Bytes are transferred to the CCU during each block transfer period. Two of these blocks are transmitted per active voice channel (up to four voice channels in the base station) per TDMA frame. The CCU receives these transmit bytes via a transmit language codec interface module (TVCIM) 109 and caches them in a transmit memory module (TMM) 110. Depending on the particular mode of operation for the given channel, a CCU processor included in the microcontroller module (MCM) 111 appends a control / synch header to the coded voice bytes, thereby providing a complete voice packet for forwarding to the modem via a transmit modem interface module 112 is formatted. The MCM 111 maintains frame timing information and transmits data to the modem at the correct time. Before the transmit data is forwarded to the modem, they are sent from the MCM 111 of the 8-bit byte format used by the CCU to a symbol format containing 1, 2 or 4 bits per symbol, depending on the modulation levels for this slot, converted.

The reverse procedure is performed for the receive data from the modem. Data from the modem is received by a receive modem interface module (RMIM) 114 and latched into a receive memory module (RMM) 115. This data is then converted from the 1, 2 or 4-bit per symbol format used by this modem to the 8-bit byte format used internally by the CCU and all other baseband processing , The organization and control bits are subtracted from the incoming data stream on the RX bus 108 by the MCM 111 in accordance with its knowledge of the frame timing provided by the modem to a Frame Timing Module (FTM) 116 and its own recognition of various codewords in the symbol stream , The converted data is supplied to the VCU via a receiving voice codec interface module (RVCIM) 117.

The CCU also provides the link level control of the Radio Control Channel (RCC) transmissions in both the base and subscriber stations. In the base station, only one CCU is configured by the RPU to process the RCC channel. The CCU controls the receipt and formatting of messages from the RPU in the base station to the STU control in the subscriber stations. This control function of the CCU includes sensing and error control in the RCC messages as well as formatting and packetizing the RCC information for transmission over the radio link. The CCU also determines collisions on the incoming RCC in the base station. The CCU controls power and range calculations for subscriber stations, taking initial acceptance actions. The protocol for acceptance and other RCC functions has been described above.

FIG. 22 shows the software-applied functional architecture of the CCU. The CCU has three separate data paths: the transmit bus TX 107, the receive bus RX 108, and the local microcontroller bus 119. The microcontroller 111 shares the TX bus 107 with a memory access (DMA) controller 120 and displays the RX bus 108 with a director DMA controller 121. Microcontroller 111 uses these remote buses to control the DMA control terminals, the control / status registers, and to intervene in transmit buffer 110 and receive buffer 115. The control and status registers 122 remote from the local microcontroller bus 119 provide interfaces to the RFU, the modem, and the CCU hardware. An RS-232C connection 123 between the RPU and the CCU is supported by a UART on the microcontroller chip 111. In the subscriber station, the RPU is replaced by the STU, but the interface remains 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 be further divided into on-chip RAM and off-chip RAM. In the transmit buffer and the receive buffer, the microcontroller can intervene only when the respective DMA controller is at rest.

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 prefix and the unique word (RCC only) are constants that are initiated by the microcontroller 111 after the CCU is reset. The code word (voice only), the voice data and the RCC data are written into the transient latch 110 by the microcontroller just before the DMA transfer to the modem 19, 30a. Since the RCC "Zero ACK" is a fixed message sent at a high frequency, it is stored as a separate whole in the temporary memory 110.

The receive memory 115 is divided into a number of different segments. A segment is for storing voice data cached and transmitted on a VCU block basis. RCC data is buffered separately from voice data to enable it to be received over a longer period of time. If necessary, the microcontroller 111 may maintain a two-frame RCC history in the receive buffer 115, making the RCC copy task (from the cache to the local RAM) a less time-critical event.

The local RAM contains the working variables used by the microcontroller 111. An important data structure stored there supports the baseband control channel (BCC) between the CCU and the RPU. A register row of the local RAM is allocated to supply basic wait information to the RS-232C interrupt handler. A hint and length field in this row defines the active transmit data block (TXDB) from which data is read and sent. The TXDB contains length and indication information for the next TXDB in the queue and thus forms a connection list. On the receive side, a circular buffer is used to store incoming data bytes. When a complete message is received, the interrupt handler identifies the serial code to interpret it.

The microcontroller 111 uses its local bus 119 to intervene in the modem, the RFU and CCU control / status registers 122. The bus also provides access via isolation logic circuits 124 and 125 to the TX bus 107 and RX bus 108, respectively. In order to avoid a contention operation, the buses 107, 108 are intervened only by the microcontroller 111 when the respective DMA controller 120 or 121 is at rest.

The CCU and RPU make averaging over connection 123 through a full-duplex RS-232C interface, referred to as baseband control channel (BCC). Asynchronous characters are 8-bit binary and are transmitted at 9600 baud. A start bit and an end bit are used for the data byte frame. Messages are terminated by a unique byte using byte-stuffing to avoid the unique byte occurring in the middle of a message. An alternate bit protocol and 8-bit checksum are used to ensure link integrity.

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

The BCC interface is controlled by an internal interrupt. The software is interrupted when receiving or transmitting a byte.

In the base station, the CCU microcontroller 111 is responsible for controlling and monitoring the entire four-channel data path associated here with which the VCU 17, 28, the CCU 18, 29, the modem 19, 30 a and the RFU 20, 31 a includes. In the subscriber station, the microcontroller 111 controls and monitors the same hardware, but supports only one data path. The CCU in turn is controlled by the RPU (in the base station) or the STU (in the subscriber station).

The CCU provides the VCU mode information. Mode changes only occur at system slot boundaries. During the voice compression process, the CCU also provides the VCU with information about the position of the VCU block in the system slot (there are two VCU blocks per system slot). The addressing VCU is executed by the CCU prior to a data transfer that performs the MUX / DEMUX task. The VCU state is read by the CCU after each block transfer, and corresponding statistics are maintained by the CCU. The CCU may also trigger a VCU hard reset and / or a VCU.

The microcontroller 111 supplies the current modulation level to a symbol-to-byte converter 126 on the RX bus 108 and to a byte-to-symbol converter 127 on the TX bus 107.

The modem is provided with information concerning the type of data received, the RCC or the voice due to the various acceptance procedures used in its reception. The modem provides the CCU with a fractional clock offset, the AGC level, and a link quality value for each slot. The CCU frequency assignment is performed by the RPU or STU. The CCU controls the initiation of a modem hard reset, auto check, or receive page training mode.

The CCU handles the full duplex data flow over the transmit and receive buses 107, 108. During a given slot time, transmit voice data originating from the VCU is forwarded in block form to the transmit buffer 110 via the transmit DMA controller 121. Each block is a VCU block in length, so two such transmissions are required for each voice channel. The CCU gives the VCU the corresponding channel address before transmission, causing a multiplexing operation.

An introductory and codeword stored in the transmit buffer 110 is sent out before the VCU data at the beginning of each slot. The transmit DMA transfers data from the transmit buffer to the repeating FIFO queue 128 while the modem receives from the FIFO queue 128 as needed. The byte-to-symbol conversion is performed by the byte-to-symbol converter 127 during transmission. The control of the transmit DMA terminal is performed by the microcontroller along with the generation and introduction of the voice packet / codeword.

The receive data flow is pretty much the mirror image of the send side. Data is written to the repeating FIFO stack 129 as it appears from the modem 19, 30a. The receive DMA controller 121 dumps the FIFO stack 129 into the receive buffer 115 as needed. The symbol-to-byte conversion is performed by the symbol-to-byte converter 126, and the frame timing is executed by the clock circuit 130. The byte boundary alignment occurs automatically as soon as the channel is in synchronization. When a complete VCU block is received, it is forwarded to the corresponding VCU in the form of a DMA block. The control of the receive DMA control is performed by the microcontroller 111.

Codeword detection is performed for each slot. The microcontroller 111 performs this task by copying the codeword byte into the local RAM and comparing it to a list of valid codewords. During each slot, modem 19, 30a provides a partial symbol offset and an AGC value. These are read by the microcontroller 111 and interpreted accordingly. If there are performance or range problems, the subscriber station is informed thereof by a transmit codeword.

The transmit RCC data is synthesized in the transmit buffer 110 by the CCU in accordance with the contents of the RCC message queue. If the RPU has sent an RCC message to the CCU, that message is formatted in the transmit buffer 110. Otherwise, the NULL KNOW message, which is permanently stored in the cache 110, is used. Once the RCC packet is ready, the RCC initiation, the unique word, and the RCC data are DMA-transmitted to the modem 19, 30a as needed. The CCU performs the collision detection and sets the outgoing RCC collision detection bit accordingly.

The receive RCC data handler has two modes: "frame search" and "monitor". In the frame search mode, the RCC channel is assumed to be out of synchronization. Each incoming RCC message must be synchronized using a unique word-perceptual algorithm. In the monitoring mode, the RCC channel is in synchronization and the unique word search algorithm is not set up. The base station is always in the frame search mode because subscribers can burst in at any time with a bad time schedule. In the subscriber station, the RCC data handler is in the monitor mode, unless the station has not accepted the RCC synchronization.

In the frame search mode, the recognition of the unique word (UW) is performed after each RCD slot. The microcontroller 111 performs this task by clicking on the unique word in a window around the "nominal" location of the unique word. Successful recognition of the unique word gives the CCU symbol timing information.

Receive RCC data is forwarded from the modem 19, 30 a to the receive buffer 115 DMA. When the transfer is complete, the RCC data is copied to the local microcontroller RAM for processing. Receive RCC packets are filtered by the CCU. An RCC packet is forwarded to the RPU only if the unique word is determined and the CRC is correct.

During RCC operation, the corresponding VCU channel is on hold. No data transfers occur between the VCU and the CCU during this channel duration on both the transmit and receive data paths 107, 108.

The software runs on an Intel 8031 ​​microcontroller 111. Program storage is provided by an external EPROM on the local microcontroller bus. The software is required to respond to DMA service requests in real time, maintaining a data rate of up to 64 Kbps in both directions without data loss. FIFO latches through the stacks 128 and 129 on the modem interfaces provide the required fill time for the microcontroller 111 to perform the DMA block transfers and system control functions.

The software is divided into five separate modules: Monitoring, Data Transfer, BCC Transceiver, BMM Control and Utility. Each module has only one input and output location, except for the interrupts and error conditions. Another exception is the utility module, which contains a selection of utilities that are directly accessible from the other modules. In general, inter-module communication occurs through the use of global variables defined in a separate data segment.

The monitoring module includes an initiation function, maintains overall program control, and performs basic self-checking functions.

The data transfer module supports the control of data transfer over the TX bus 107 and the RX bus 108 for voice and RCC and performs synchronization word awareness on all voice and RCC data for all modulation levels and supports the CCU-RPU RS-232 communication link 123.

The BCC transceiver module performs BCC transmit-receive tasks, handles the BCC queues, formats send BCC messages, processes receive BCC data, and moves RCC data to and from the CCU via the CCU.

The BBM control module controls the RFU, modem, VCU, and CCU hardware via registers, reads and interprets state information from these devices (eg, modem AGC, link quality, and symbol ambiguity), decodes embedded codewords in the receive voice channel, formats them Codeword for the transmit speech channel, and obtains a true-time software / hardware timer and performs all ongoing self-checks.

The utility module runs various utilities that other modules have access to.

The CCU software is divided into four separate operations, which are essentially simultaneous. Three of these are the BCC data, TX-DMA and RX-DMA operations, which are intermittently controlled and only put into effect when a particular event demands attention. All three of these event-driven processes are arranged in data transfer modules. The rest of the process, which is distributed across all modules, is a background operation that triggers, controls, and monitors the other three operations.

When BCC messages arrive from the RPU (or STU in the subscriber station), they are received and buffered by the BCC data process. When a complete message has been received, the BCC data process notifies the background process via a mailbox. The background process polls this mailbox during its main loop, thus detecting any new messages. The messages are interpreted by the background and the appropriate action is taken.

Each response is written into the transmit BCC message queue by the background process and the BCC data process is informed.

The BCC messages may trigger a redesign of the CCU data channels. The necessary control information is assigned to the modem 19, 30 a and the VCU 17, 28 at the appropriate times. The modem responds to a new control word at the slot boundaries. The VCU expects mode changes to occur on the first VCU block transfer of a slot boundary. The background process is responsible for maintaining the correct timing.

The collection of state information is performed by the background TX-DMA method and the RX-DMA method. The latter two collect state words from the TX resp. RX side of the VCU. This is necessary because these status registers are accessible only via TX bus 107 and RX bus 108, which are idle for limited periods of time. The background method collects state information directly from the modem 19, 30 a via the status registers 122 on the local bus 119. When all state information is collected, it is sorted by the background process and stored in special state variables. State requests received from the RPU are handled by the background method based on this state flow.

Some state information, such as the AGC value and the partial bit offset, may necessitate a CCU action. In addition to being stored as state history, these data are used to correct subscriber performance and range problems. In the case of RCC messages, performance and range information is sent directly to the RPU as part of the RCC. The background method performs this function by formatting a BCC message containing RCC, AGC and range data. When the packet is ready, it is placed in the transmit BCC queue and the BCC data process is notified. For voice channels, this state information is used to format codewords embedded in outgoing speech packets. The background method performs this formatting function and controls the transmission of the codeword over the voice channel. All codewords must be transmitted through five frames in a row, resulting in a 5: 1 redundancy coding. The TX-DMA method automatically sends the codeword selected by the background method.

The background method also maintains a software / hardware clock. This is done by polling one of the 8031 ​​timers and counting overflows. The timing clock function provides a time base for software timeouts and other time-dependent events. The background method provides that system timing is maintained by polling the CCU hardware error indicators cyclically and by verifying that data transfer events occur should they occur in the system frame. System frame information is provided over the beginning of the system frame state line and a timer associated with the 16 kHz clock 130 is connected. The data synchronization is performed by the background method.

The BCC data method responds to RS-232 interrupts that can occur in both the send and receive directions of the port. The method simply outputs another byte on the sending side or takes another byte on the input side. A message end limiter on the receive side causes the BCC data routine to notify the background process.

The TX-DMA method and the RX-DMA method handle the transmit and receive DMA channels.

A step-by-step description of the data transfer function controlled by the software is given below. Events in the data transfer process are marked by DMA control interrupts. The interrupt occurs after the DMA controller completes the associated block transfer. Each pass begins at the beginning of a slot data transfer. It may be helpful, the Fig. 23 and 24 as you go through this section. FIG. 23 Fig. 11 is a timing diagram for transmitting RCC and 16-PSK voice data on the transmission bus of the CCIJ. FIG. 24 Fig. 10 is a timing diagram for transmitting RCC and 16-PSK data on the receive bus of the CCU. Tables 13 and 14 describe the characteristics of the time symbols shown in FIG. 23 or. 24 are shown. <heading>Table 13</heading><heading>Table 14</heading>

Send Function-RCC

1. Receive "end-of-TX DMA transfer" interruption

This signals that the processing of the previous slot is complete and that the processing of the next slot can begin. The TX-DMA procedure is called. a) Write out control channel and modulation switching information. This information is needed by the modem 19, 30 and the byte to symbol converter 127. b) Formatted any pending RPU RCC message in the transmit buffer 110. Otherwise, prepare the null confirmation message and send it. c) Initiate the DMA transfer from the transmit buffer 110 to the modem 19, 30a allowing it to point to the RCC initiation, the unique word and the RCC data block. d) Return from the break and continue with background processing.

Sending function language

1. Receive "end-of-TX DMA transfer" interruption

This signals that the processing of the previous slot is complete and that the processing of the next slot can begin. The TX-DMA procedure is called. a) Write out speech channel and modulation switching information for next slot. This information is needed by the modem 19, 30 a and the byte-to-symbol converter 127. b) Select the VCU port address and allow DMA transfer from VCU to transmit buffer 110. c) Write VCU control word. d) Interrupt VCU to start transmission. e) Return from interruption and continue with background processing.

Second Receive "end-of-TX DMA transfer" interruption

This signals that the VCU to latch transfer is complete. The TX-DMA procedure is called. a) Read VCU status word. b) Write codeword to transmit buffer 110. c) Initiate and allow DMA transfer from the transmit buffer 110 to the modem 19, 30 a, pointing to the voice initiation, the codeword, and the speech data block. d) Return from interruption and continue with background processing.

Third Receive "end-of-TX DMA transfer" interruption

This signals that the first half-slot transmission from the transmit buffer 110 to the modem 19, 30 a is ready. The TX-DMA procedure is called. a) Select VCU port address and enable DMA transfer from VCU to transmit buffer. b) Write VCU control word. c) Interrupt VCU to begin transmission. d) Return from interruption and continue with background processing.

4th Receive "end-of-TX DMA transfer" interruption

This signals that the VCU-to-cache transfer is complete. The TX-DMA procedure is called. a) Read VCU status word. b) Trigger and enable DMA controller 120 for transmit memory to modem transmission. c) Return from interruption and continue with background processing.

Listener-RCC

1. Receive "end-of-RX-DMA transfer" interruption

This signals that the processing of the previous slot is complete and that the processing of the next slot can begin. The RX DMA procedure is called. a) Setup for BPSK modulation. This information is needed by the symbol-to-byte converter 126. The modem 19, 30 a has already received this information at this time. b) Initiate DMA transfer from the modem 19, 30 a to the receive buffer 115 for the RCC message and release it. c) Return from interruptions and continue with background processing. AGC calculation and bit synchronization error processing should take place at this time.

Second Receive "end-of-RX-DMA transfer" interruption

This signals that the RCC transmission from the modem 19, 30a to the receive buffer 115 is complete. The RX DMA procedure is called. a) Copy RCDC in local RAM. b) Return from interruption and continue with background processing. Prepare to pass the received RCC to the RPU if a clear word is heard and the checksum is correct.

Reception function - language

1. Receive "end-of-RX-DMA transfer" interruption

This signals that the processing of the previous slot is complete and that the processing of the next slot can begin. The RX DMA procedure is called. a) Structure for voice data with correct modulation. This information is needed by the symbol-to-byte converter 126. The modem has already received this information at this time. b) Initiate DMA transfer from modem 19, 30 a to the receive buffer for the first half-slot of voice data and release it. c) Return from interruption and continue with background processing. AGC calculation, bit synchronization error and codeword processing should take place at this time.

Second Receive "end-of-RX-DMA transfer" interruption

This signals that the first half-slot transmission from the modem 19, 30 a to the reception buffer 115 is ready. The RX DMA procedure is called. a) Select VCU port address and enable DMA transfer from receive buffer 115 to the VCU. Interrupt VCU to start transmission. b) Return from interruption and continue with background processing.

Third Receive "end-of-RX-DMA transfer" interruption

This signals that the first half slot transfer from receive buffer 115 to the VCU is complete. The RX DMA procedure is called. a) Initiate and enable DMA controller 121 for second-slot modem-to-receive buffer transmission 121. b) Return from interruption and continue with background processing.

4th Receive "end-of-RX-DMA transfer" interruption

This signals that the second half-slot transmission from the modem 19, 30 a to the reception buffer 115 is ready. The TX-DMA procedure is called. a) Select VCU port address and enable DMA transfer from receive buffer 115 to VCU. Interrupt VCU to start transmission. b) Return from interruption and continue with background processing.

CCU software version

The software program execution begins as a result of a hardware reset and the flow begins in the monitor module. The monitoring module undertakes any hardware and software initiation before entering a main service loop. The monitoring module performs some basic self-checking functions after a hardware reset and upon request from the RPU. The main service loop makes the other modules accessible in sequence. The monitor module training is such that tasks are subdivided into manageable time slices, whereby it is guaranteed that the main service loop has a reasonable periodicity of the worst case. Tasks that require a true-time response are handled via interrupt service routines.

Each interrupt service routine performs a minimum of processing to satisfy the service request. This is done in order to maximize the serial nature of the program execution and to keep the interrupt service to a minimum. Typically, an interrupt service routine transfers data to or from an interface and sets a boolean to indicate that the action has been taken. A serially executed code accessible from the main service loop then continues to process this information as needed.

The CCU microcontroller 111 is a data flow machine in that software events are controlled by the arrival and departure of data. A precise system time schedule provides the framework for this data flow. However, software events are derived directly from the data flow and not from system framing markers. This approach allows the software to respond to "true" events (such as data input / output requests) rather than "artificial" events (such as system timing marks). The software relies on the hardware to convert its asynchronous actions into events that are synchronous with the system frame timing. For this work, it is necessary for the software to guarantee that things are initiated and ready before the system frame event occurs.

It can therefore be seen that although the CCU software is not heavily loaded, it is called to respond to events and complete certain tasks within a limited amount of time.

The time-of-day processing is intermittently advanced and thus requires considerable attention in its construction. There are four potentially conflicting true time events required by the microcontroller: transmit DMA operator, receive DMA operator, transmit RS-232 operator, and receive RS-232 operator. The RS-232 interrupts have the lowest priority because they occur at a maximum rate of one per ms. The software is designed so that the one ms time limit is not exceeded. Response times for voice and RCC data handling are more critical and a discussion follows.

The relative timing for the data transmissions on the transmit bus and the receive bus are shown in FIGS. 23 and 24. The graphs are drawn approximately to scale and show worst case timing. The time division multiplexing characteristic of the transmit and receive buses is clearly represented by the diagrams. The dark cross lines on the transmit and receive threads correspond to the microcontroller activity on the respective bus (t_S, t_RCC). During this time, the respective DMA controller 120, 121 is at rest. The short periods of time between the DMA Control Statements (t_VCB) correspond to the VCU block transfers. During this time, DMA control is dedicated to each VCU. For the rest of the time (t_M0, t_M1, t_M2, t_M3) serves the DMA controller 120, 121 of the modem interface.

The repeating FIFO stacks 128, 129 on the modem interface create the primary timing limit implicit in the timing diagrams. The FIF stacks hold 16 symbols, giving 1 ms of buffer time before underflow (TX) or overflow (RX). During this ms, the CCU may use the transmit or receive bus 107, 108 to complete the block transfers to and from the VCU or to copy RCC data into the local RAM.

After powering up, the CCU software performs an internal self-check and puts the VCU, the modem, and the RFU in the default state. The microcontroller 111 monitors the system frame timing and begins performing block transfers to allow the VCU to get synchronization. When the data transfers are initiated, the microcontroller 111 uses the DMA block end interrupt to obtain the system time schedule. This interruption is directly connected to the data throughput of the CCU and thus to the 16 kHz symbol clock 130. The VCU retains the system timing via DMA transfer requests generated by the microcontroller 111 as a result of the end-of-block interrupt. The microcontroller 111 continues to monitor the frame timing to ensure that proper system operation is maintained.

In the subscriber station brings a system start synonymous with radio synchronization. This is done by locating the RCC and deriving the system timing from it. When the reception timing is established, the microcontroller 111 establishes the transmission timing with the base station.

The communication module supports the timing and background data transmission events in the CCU. Data transfers are serviced for the transmit data path, receive data path, transmit BCC and receive BCC. All of these tasks are intermittent events that require a true-time response. The module also performs synchronization acceptance and monitoring as a background task.

The transmit data path handler is called when the transmit DMA controller 120 requires service. This typically occurs after a DMA block transfer, at which time the DMA peripheral unit invokes a block end transfer interrupt. The interruption is received on one of the two external interrupt lines of the microcontroller 111 Model 8031. The operation required by the interruption depends on the type of data transmission, RCC or speech and the time of occurrence in the slot.

The transmit data path interruption occurs at predictable times during each slot period. The interruption times and duration are shown in FIGS. 23 and 24. At each occurrence, the microcontroller 111 must initiate the DMA peripheral unit for the next block transfer. This process should be performed within 150 μs from the interrupt completion interrupt request. In the case of RCC data, the first service request from the microcontroller 111 requires that it format the RCC message in the transmit buffer 110 before the DMA transfer. This process must be completed within 900 μs. Since the processes on the transmit path are usually short and require a fast response, the interrupt is given the highest priority.

The only output from the transmit data path interrupt handler is the VCU state word that was collected after the VCU block transfer. This status word is analyzed by the software in the BBM control module.

The receive data path scheduler is called when the receive DMA controller 121 needs service. This typically occurs after a DMA block transfer, at which time the DMA peripheral unit invokes a block end transfer interrupt. The interrupt is received on one of the two external interrupt lines of the 8031 ​​microcontroller 111. The operation required by the interruption depends on the type of data transmission, RCC or speech and the time of occurrence in the slot.

The receive data path interrupt occurs at predictable times during each slot period. These interruption times and duration are shown in FIG. 23 and 24. At each occurrence, the microcontroller 111 must initiate the DMA controller 121 for the next block transfer. This process should be performed within 150 ms from the interrupt request to the interrupt completion if DMA triggering is the only task to be performed. In the case of RCC data, the last service request from the microcontroller 111 requires that it copy the RCC message from the receive buffer 115 to the local RAM after the DMA transfer. This process must be completed within 900 ms. Since the transmission path operation may occur during this time, the reception path interruptions have a lower priority than that of the transmission path. The receive data path interrupt handler makes the VCU state word available after each VCU block transfer. This status word is analyzed by the software in the BBM control module. The dispatcher also reads new RCC messages from the channel, which are then interpreted in the BCC transceiver module.

The BCC receive module is applied to the chip via the RS-232 UART. The UART can generate an internal interrupt which is triggered whenever a byte is received or sent. The BCC handler calls a status bit to determine which of the two cases caused the interrupt and then proceeds to service the port accordingly.

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

The BBC communications handler uses pointers to pause or pause data as received and sent. Only a connection level processing occurs here, including a byte plug and the insertion of the end of the message. These actions are described in the system interface description.

Very little data processing occurs in the BCC transceiver module. Its main task is to put data on hold and on hold while it handles the transmit-receive and BCC data paths. The data synchronization acceptance and monitoring described below includes the main processing functions of the BCC transceiver module.

The synchronization word perception means a synchronization operation on the symbol level. The term "synchronization word" applies generally and refers to both the unique word in the RCC and the codeword in the voice channels. The unique word (UW) is a fixed 8-bit pattern set at the beginning of an RCC message. A codeword (CW) is currently any one of eight possible 8-bit patterns set at the beginning of a voice channel. In addition to their synchronization role, codewords are used to display the connection state, power settings, and range settings.

The basic CCU must exhaustively search for a valid RCC message in each slot. It performs this task by pressing the unique word in a window ± 3 symbols around the nominal UW location based on the main system time schedule. The search algorithm begins at the nominal UW position and shifts a symbol to the right and left until it (1) finds the UW pattern and (2) asserts a proper RCC checksum. The search ends as soon as (1) and (2) are satisfied or all possibilities are exhausted. The shift information, the RCC message and the performance information are sent to the RPU after a successful search.

During each voice slot, the CCU of the base station searches the received voice data for a valid codeword. Only the nominal codeword position is checked since no active symbol synchronization is performed during the speech process. If no codeword is detected on 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 any appropriate action at this point. The synchronization is considered recovered after three out of five consecutive frames have successful codeword awareness.

The subscriber station CCU may be in one of two modes when receiving RCC data: "frame search" or "monitor". The frame search mode is used to acquire the receive frame timing from the incoming RCC data and is called automatically when receive RCC synchronization is lost. The monitor mode is entered whenever the receive frame synchronization is accepted.

If the subscriber CCU is in frame search mode, it must exhaustively search for a valid RCC message after each RCC slot. Like the basic CCU, it performs this task by keys after the unique word in a window ± 3 symbols around the nominal UW location based on timing derived from the modem AM hole perception. The search algorithm begins with the nominal UW position and moves a symbol to the right and to the left until (1) it finds the UW pattern and (2) confirms a correct RCC checksum. The search ends as soon as (1) and (2) are satisfied or all possibilities are exhausted. The shift information from a successful search is used to set the receive frame flags generated by the CCU. The assumption ends when (1) and (2) are satisfied in three nominal successive frames with the UW in its nominal position. The STU is notified of the frame acceptance when it occurs. RCC messages are not sent to the STU during the frame search mode.

When the frame acceptance is completed, the CCU of the subscriber station enters the monitoring mode. Only the nominal UW position is checked to eliminate the possibility of false UW assumptions. If no UW is detected at five consecutive frames, then the channel is declared out of synchronization and the frame search mode is entered. The STU is informed of this external synchronization state. During watchdog mode, RCC messages have a proper checksum and SIN numbers are forwarded to the STU.

During each voice slot, the CCU of the subscriber station searches the received voice data for a correct code word. Only the nominal codeword position is checked since no active symbol synchronization is performed during the speech process. All possible codewords are searched in this direction of the channel. The codewords may cause incremental changes in the subscriber station's power and range values. Incremental range changes can actually result in a symbol change as well as partial range values. If no codeword is detected on five consecutive frames, then the channel is declared out of synchronization and the STU is informed of this condition. The synchronization is considered recovered after three out of five consecutive frames have successful codeword awareness.

Additional CCU considerations

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

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

The CCU control software provides the gate for DMA transfers, but external control must provide handshaking to initiate and sustain the block transfer. This is especially important for the modem interface, where 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 exercised or the DMA peripheral unit is at rest.

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

Frame timing information must be available to the microcontroller 111. This could take the form of a symbol clock input to an internal timer of the microcontroller.

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

modem

The modem operates in one of three modes. In the base station, the modem forwards on a full duplex send and receive function. When operating in the subscriber station, the modem operates in half-duplex mode, sending only during part of the TDMA frame and receiving during another part of the TDMA frame. The third mode is a self-adaptive teaching mode. A modem version has all these functions. The modem performs the corresponding function in response to probe signals coming in from the controlling CCU.

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

The modem transmission parts include a TX symbol filter 132, a digital / analog (D / A) converter 133, a 200 kHz band filter 134, a mixer 135, and a TX (transmit) time division control circuit 136. The receiving portion of the modem includes a mixer 138, an analog-to-digital (A / D) converter 139, a FIFO stack 140, and a Model TMS 320 microprocessor 141.

The modem sending part sends the information supplied to it from the CCU with a 16-level PSK modulation. It is the task of the CCU on the receiving side to interpret the data as DPSK, QPSK or 16 PSK. The modem sends without knowledge of the modulation level.

The modem transmission part is fully hardware and does not require any settings. Symbols received by the CCU are encrypted and their respective waves are shaped to provide good interference characteristics and to tolerate amplitude or group delay distortion. The justification of this concept is made on the assumption that in the frequency band adjacent to the band used (within 50 to 100 kHz) there are no strong spurious signals (power densities of 30 to 40 dB above the signal). The modem sending part uses a relative wide IF filter (100 kHz) so that the transmitted signal does not suffer from amplitude or group delay distortion and filters out any harmonics produced by the digital filtering made in the baseband.

The TX symbol filter 132 is a fixed-coefficient digital FIR (finite duration impulse response) filter. The filter 132 simulates a six-pole filter at a sampling rate of 50 samples per symbol per six-symbol stay in the FIR filter.

The modem receives symbols from its respective CCU at a rate of 16 K symbols / second. These symbols are then converted into a DPSK code for input to line 143 to FIR filter 132. The FIR algorithm requires every other symbol to be inverted before it enters the FIR filter. The Gray code is used for DPSK coding. This ensures that if one symbol is received incorrectly, there is a high probability that the two symbols will be erroneous by only one bit to the receiver codec.

The impulse response of the FIR filter 132 is checked off with 6T (T = 1/16 kHz). The FIR filter over-clips the symbols at a frequency of 800 kHz so that each symbol is sampled 50 times during its 5T stay in the filter. This corresponds to a sampling rate of 3T / 25, where the sampling time is T / 25, so that the samples are output every 3T / 25 duration. The output signals are distorted such that only every first and fourth, second and fifth or third and sixth pair of samples overlap each other. Each of these T / 25 long samples is actually divided into two parts. During the first half of the sampling period, the I-part of the output signal is calculated, and during the second half of the duration, the Q-part of the output signal is calculated. Thus, the actual frequency at which the FIR filter 132 outputs data is 50 × 16 kHz = 800 kHz. The I and O samples are staggered by half a sample period, but this is corrected by the FIR filter 132.

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

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

The desired signal from the D / A converter 134 is centered at 200 kHz with a bandwidth of approximately 32 kHz. By multiplying the 200 kHz wave at 20 MHz, the output wave mixes the I and Q samples with the SIN and COS components of the IF frequency. Thus, the 20 MHz signal can directly multiply the output wave and the exact component multiplies are handled automatically. Therefore, there is no need for a single SIN (IF) / COS (IF) generating circuit to multiply the I / Q samples from the D / A converter as in the receiver. This also removes the separation passage in the mixer from the baseband to the output of the mixer.

The output data stored in the transmit FIR filter 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. Also, the IF filter in the RFU (Figures 28 and 29) adds the two values ​​to form the correct transmitted wave since its bandwidth is relatively small compared to the IF frequency.

In the modem receiving part, the mixer 138 mixes an analog waveform received from the RFU on the line 150 via a 20-MHz band filter (not shown) with a 20-MHz IF signal on the line 151 to apply the analog signal to the baseband on the Line 152 down to convert. The analog signal is then converted by the A / D converter 139 into a digital signal on the line 153 which is latched in the FIFO stack 140 for processing by the microprocessor 141. The microprocessor 141 performs the frequency and bit tracking of the received digital signal as well as the FIR filtering and the demodulation of the signal into a binary symbol stream which is passed on 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 to the modem by the CCU. The modem also sends control signals to the RFU to control functions such as transmit power level, frequency, AGC, and antenna diversity switching.

The modem interfaces are shown in FIGS. 26 and 27. The modem receives most of its inputs from the CCU. Other inputs are from the RFU and the time division units. The modem inputs are the following:

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

The TX data lines 156 transmit a 4-bit symbol to be transmitted by the modem (2 bits for QPSK, 1 bit for BPSK). The MOD bus 157 is a bi-directional microprocessor bus that provides control / status information to / from the modem. MOD-WR line 158 feeds a control signal to the lock MOD bus into the modem. The MOD RD line 159 carries a control signal to set modem state and other information on 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 address lines 161 carry address signals to various locations to capture values ​​within the modem. The TX-SOS line 162 carries a signal to begin the transmission of a TX slot. The RX SOS line 163 carries a signal to begin receiving an RX slot.

The IF receive line 165 carries an IF receive frequency input signal to the modem 19, 30 a from the RFU 21, 31 a.

The following lines carry the described signals to the modem 19 from the STIMU 35. The 80 MHz line 167 carries an 80 MHz ECL clock signal. A similar signal is supplied to the modem 30a from a timing unit (not shown) in the subscriber station. The 16 kHz line 168 carries a main TX CLK signal which is used in the base station. The SOMF line carries a main frame start signal in the base station from the STIMU. 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, 30 a to the CCU 18, 20. The TX-CLK line 171 carries a 16 kHz clock signal which gives the CCU the symbol transmission timing. Symbols are clocked into the modem with the rising edge of that clock. In the base station, all slots have the same master TX clock. Thus, all signals are sent from the base station at the same time. In the subscriber station, the TX clock is offset by the partial range delay by the modem due to information provided by the CCU. The RX clock line 172 carries the 16 kHz clock signal derived from the received signal. This signal is always provided in the subscriber station, but only during the control slot acceptance in the base station. This clock signal clocks the received symbol to the CCU and gives the CCU the symbol timing. The RX data lines 173 carry the 4-bit receive symbol which is clocked by the RX clock signal. The MOD bus 157 carries state and data information from the modem. The MOD-SOMF line 175 sends the SOMF signal from the STIMU to the CCU in the base station. The AM strobe line 176 carries a high-to-low transition to give the CCU a coarse frame marker during RCC acceptance in the subscriber station. This is a monostable line that is pulsed when the microprocessor 141 detects the approximate location of the AM hole.

The following lines carry the described signals from the modem 19, 30 a to each RFU 21, 31 a. The RF-RX bus 178 is an 8-bit bus between the modem and the RFU part. This bus conveys AGC and frequency selection information to the RF-RX part. The modem controls the AGC values ​​to be sent and sends CCU frequency selection information. The frequency selection information is supplied to the modem through the CCU via the MOD bus 157. During teaching, the modem controls RF-RX frequency selection. The RF TX bus 179 is an 8 bit bus between the modem and the RFU TX part. This bus transmits TX power level and frequency selection information to the RFU TX part. The modem has nothing to do with these, so the information is only sent to the TF-TX part. The RX 80 MHz REF line 180 carries an ECL 80 MHz reference clock signal to the RFU RX part. The TX-EN line 182 to the RFU TX part carries a signal to turn on the RF transmission. The RX-EN line 183 to the RFU RX part carries a signal to turn on RF reception. The AGC WR line 184 carries a write strobe to capture the AGC data in the RFU RX part. The RXFREQ WR line 185 carries a write strobe for frequency writing to the RFU TX part. The PWR WR line 186 carries a write strobe to capture the line information in the RFU TX section. The PWR RD line 187 carries a read strobe to read back power information from the RFU TX part. The TXFREQ RD line 188 carries a read strobe to read back the transmit frequency from the RFU TX part. The TXFREQ WR line 189 carries write strobe frequency write data to the RFU TX part. The IF transmission line 190 feeds the transmitted IF frequency signal 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 frequency tracking control information. The VCXO WR line carries a write pulse to the VCXO circuit for snapping the VCXO bus 192 into the VCXO. Similar signals are fed from the modem 30a to a timing unit (not shown) in the subscriber station.

The base station modem operation is associated with a fixed RF frequency. Communication in the base station is full-duplex, so the modem receiver and transmitter work simultaneously. A modem is also assigned the task of the control frequency channel modem so that it only transmits and receives information with the radio control channel (RCC) format during the assigned control slot period. All transmissions from the base station modems are clocked to the master TX clock signal at 16kHz on line 171. Unlike the subscriber modems, the base station modems 19 output to the CCU 18 the fraction of the symbol time between the main TX clock signal on the line 171 and the derived RX clock signal on the line 172 in the modem 19. This information is then sent to the subscriber station in the RCC so that the subscriber station delays its transmission so that its signal is received in the base station in synchronism with all other slots.

The base station modem 19 also sends a zero power signal in the control slot to provide the RCC AM hole (which establishes a frame reference) when the RFU transmits a zero power signal. This non-bearer portion of the RCC transmission is used for the initial RX acceptance in the subscriber station.

The modem 19 is unaware of the fact that four of the CCU 18 multiglexed voice codecs in the base station are for four 16-PSK subscriber slot assignments. The modem 19 accepts the bitstream 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 clock signal on the line 172 which is fetched from the received transmission. This serves as the main clock of the subscriber station. The TX clock signal on line 171 to the CCU 29 is not a master clock as in the base station. It is derived from the RX clock signal on line 172 and delayed by the fractional time selected by the CCU 29. The CCU 29 determines the delay from the RCC. The delay is determined by the distance between the base and subscriber layers. The subscriber station CCU 29 supplies this part-time information to the modem 30 a via the MOD bus 157. The modem 30 a itself takes into account the partial delay. The CCU 29 takes into account the integer symbol delay by introducing the TX-SOS signal onto the line 162 which is delayed by the correct number of symbols. This process balances the signals arriving from the base station from changes in the range of all subscriber stations.

The communication in the subscriber station is half-duplex. Thus, if the transmitter is at rest, it is locked. The modem 30a, when not actively transmitting, is switched to its receive mode and thus can monitor the gain levels of the receive signal being prepared when a burst from the base station arrives.

The subscriber station modem 30a does not send an AM guard band for the RXX slot. It is not necessary because the base station determines the frame. Unlike the fixed frequency base station modems 19, the subscriber station modems 30 a may also transmit or receive data over any of the 26 frequencies selected by the CCU 29 in the RFU.

There are many sources of delay in the modem that have a pronounced effect on system timing. These include analog filter delays, propagation delays, FIR filter processing delays, etc. These delays shift the TX and RX frames together, and these shifts must be carefully considered.

The delay between the TX-SOS signal on line 162 in the base station and the first analog-symbol "peak" received in the base station is +7.4 symbols. Therefore, there is a distortion between the TX and RX slots. To properly decrypt the incoming phase, the modem must start sampling about 3.5 symbols before the "tip" arrives. After that, the distortion 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 starts approximately 4T after the start of the TX slot. The RX slot start is determined as the time in which the first analog sample is taken to determine the first "peak" that is being received.

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

While receiving a slot, modem 19, 30a performs frequency synchronization by accepting and then resumes tracking. In the subscriber station, the VCXO is under the direct line of the microprocessor 141 via a D / A converter. The microprocessor frequency assumption and the tracking algorithms compute the changes in the VCXO necessary to maintain synchronization.

In the base station, an OCXO located in the STIMU 35 is fixed and acts as the master clock of the system. Therefore, no frequency deviations will occur during reception.

During the reception of any slot, the modem 19, 30a also performs bit synchronization on the bit synchronization scrambling of the received data stream. An algorithm performs a bit-tracking loop in the receiver. The microprocessor 141 has the line through a variable frequency divider of the 80 MHz VCXO or OCXO (only during the control slot demodulation). Within the bit tracking loop, the microprocessor 141 converts the frequency division to obtain the bit synchronization. While receiving a voice channel, the division values ​​have step sizes of 0.1% of 16 kHz, but during a control slot, the values ​​can change more drastically by up to ± 50%.

The frame synchronization is handled in completely different ways in the base station and the subscriber stations. In the base station, the main SOMF (Start of Modem Frame) signal is sent to the CCU 18 on the line 175 from the time division unit on the line 169 via the modem 19. 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 all slot and frame time divisions.

In the subscriber station, the frame synchronization is performed by the CCU 29 with the recognition of the unique word in the received RCC data stream. After initial assumption, modem 30a provides a single approximate frame marker (AM scan pulse) on line 176. During acceptance, modem 30 searches for the AM hole in the RCC. When the AM hole is detected, it counts the modem 30 a for a few frames and then sends the AM strobe mark on line 176 to the CCU 29 at the frame location of the AM hole. The CCU 29 uses the strobe marker to set up initial frame mark counters (windows) that can be modified by the CCU software for accurate frame synchronization. This also means that the AM hole was detected and the RCC was accepted.

The slot synchronization is under the direction of the CCU 18, 29. The signals TX-SOS on line 162 and RX-SOS on line 163 are commands to the modem 19, 30 a to start transmitting or receiving a slot. These signals are synchronized to the TX clock signal on line 171 and the RX clock signal on line 172, respectively.

The auto-adjust mode is a looped-back state into which the modem enters to teach the digital FIR filter coefficients to correct any receive analog filter degradations that may occur with time or temperature. This analysis is performed by returning the loop of transmit data through the RF unit and receiving a known pattern in the receiver. The coefficients are optimized using a five-limit LaGrangesches system. These limit conditions are (1) the received data stream, (2) the 0.05T delayed data stream, (3) the 0.05T advanced data stream, (4) the data stream from the adjacent upper channel, and (5) the data stream from the adjacent lower channel.

During teaching, the microprocessor 141 supplies to the TX-FIR filter 131 on the line 143 a sequence of 32 symbol-length teaching patterns. This is done via a FIFO stack (not shown) that is turned on during the teaching mode. Lead times / delays are performed by the receive bit tracking circuit, which distorts the two currents by 0.05T.

The CCU 18, 29 places the modem 19, 30a in the teaching mode to allow the modem transmitting section to read the particular teaching data from the FIFO stack in the modem. The receiver is advanced / retarded for some of the tests. When the process is finished, the modem sends a status message to the CCU 18, 29 that the coefficients are calculated. At this point, the CCU 18, 29 tests the modem by putting it into normal operation and reading out a fixed pattern that instructs the RFU 21, 31a to loop back and read and validate the returned data ,

The modem is described in more detail in our co-pending patent application entitled "Subscriber Radio Frequency Telephone System Modem" filed by us on the same day, the disclosure of which is incorporated herein by reference.

RF / IF unit (RFU) and antenna interface

The RFU subsystem provides the communication channel connection between the modem and the antennas in both the base station and the subscriber station. The RFU operates as a linear amplitude and frequency translator and is substantially transparent to the channel data and modulation characteristics.

The antenna interface circuit for the subscriber station is shown in FIG. An RFU control logic circuit 192 is connected to the transmitting antenna 32 and the three receiving antennas 32 a, 326 and 32 c through the antenna interface circuit. The RFU control logic circuit 192 is also linked to the transmitting part of the modem 30 a and the receiving parts of the modems 30 a, 30 b and 30 c. In fact, 32 and 32 a are the same antennas.

The transmitting part of the antenna interface includes an up-converter and amplifier circuit 193, a frequency synthesized TX frequency synthesizer, 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, a frequency synthesized RX frequency synthesizer 199, a preamplifier 200 connected to the switch 197. Each additional dimming receiver TXn (n = 2, 3) includes a down converter and amplifier 202, an RX normal frequency synthesizer 203, and a preamplifier 204.

The RFU control logic circuit 192 supplies the following signals to the transmitting section of the antenna interface circuit in response to signals received from the transmitting section of the modem 30a. (1) A TX enable signal on line 206, to make the TX / RX switch 197 to release the transmission by the transmitting antennas 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 normal frequency generator 194, and (5) a channel select signal on line 210, also to the TX normal frequency generator 194. The TX normal frequency synthesizer 194 responds to the channel select signal on line 210 by supplying a TX frequency select signal on line 211 to the up converter and amplifier 193 equal to the difference between the desired transmit frequency and the modem IF frequency. Frequency is.

The RFU control logic circuit 192 supplies the following signals to each receiving section of the antenna interface circuit in response to signals, that of the respective receiving parts of the modems 30 a, 30 b and 30c are received: (1) A TX enable signal on line 213 around down-converter and amplifier circuits 198, 202 bring to, to work in two reception modes, (2) an automatic gain control (AGC) signal on lines 214 to the down converter and amplifier circuits 198, 202 . (3) a clock reference signal on lines 215 to the RX normal frequency generators (synthesizers) 199, 203 and (4) a channel select signal on lines 216 also to the RX normal frequency generators 199, 203 . which responds to the channel selection signal on lines 216 thereby that there is an RX frequency selection signal on lines 217 to scan converter and amplifier circuits 198, 202 supplies, which is equal to the difference between the desired receive frequency and the modem IF frequency. The down converter and amplifier circuits 198, 202 provide IF output signals on the line 218 to the RFU control logic circuit 192 for delivery to the receiving portions of the respective modems 30 a, 30 b and 30 c.

The up-converter and amplifier circuit 193 in the transmitter section receives the modulated IF signal on line 207, amplifies it and translates it into 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 correct output level and suppress unwanted signals at the mirror and harmonic frequencies. The transmitter output frequency is the sum of the modem IF frequency and a conversion frequency composed in 25 kHz stops from the reference frequency supplied by the modem.

The subscriber station RFU operates as a half-duplex transceiver, with the receivers being inactive during transmission intervals. The transmit burst rate is high enough to simulate full duplex operation for the user. The assigned frequency channel is the frequency channel selected by the base station kPU.

The antenna interface circuit for the base station is shown in FIG. An RFU control logic circuit 219 is connected to the transmitting antenna 23 and the three receiving antennas 34 a, 34 b and 34 c through the antenna interface circuit. The RFU control logic circuit 219 is also linked to the transmitting part of the modem 19 and the receiving parts of the modems 19, 19b and 19c. (Modems 196 and 19c are diversity modems, not shown in Fig. 2.)

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

The RFU control logic circuit 219 supplies the following signals to the transmitting section of the antenna interface circuit in response to signals, received by 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 up-converter and amplifier 220, (3) a clock reference signal on line 24 to TX normal frequency generator 221, and (4) a channel select signal on line 242 also to TX normal frequency generator 221. TX normal frequency generator 221 responds to the channel select signal on line 242 by supplying an RX frequency select signal on line 243 to the upconverter and amplifier 220 which is equal to the difference between the desired transmit frequency and the modem IF frequency. A level control signal is supplied on line 244 from the power detector 224 to the up converter and amplifier 220.

The RFU control logic circuit 219 supplies the following signals to each receiving section of the antenna interface circuit in response to signals, that of the respective receiving parts of the modems 19, 19 b 19 c) (1) An automatic gain control (AGC) signal on lines 245 to the down-converter and amplifier circuits 230, 234 . (2) a clock reference signal on lines 246 to the RX normal frequency generators 231, 235 . and (3) a channel select signal on lines 247 also to the RX normal frequency generators 231, 235 , RX normal frequency generators 231, 235 respond to the channel select signal on lines 247 by supplying an RX frequency select signal on lines 248 to downconverter and amplifier circuits 230, 234 equal to the difference between the desired receive frequency and the modem frequency. IF frequency is. The down-converter and amplifier circuits 230, 231 supply IF output signals on the line 249 to the RFU control logic circuit 219 for delivery to the receiving sections of the respective modems 19, 19b, 19c.

The RFUs in the base station and the subscriber stations are similar except for the additional high power amplifier 223, which is used to increase the transmission power of the base station RF outputs. The basic function of the RFUs in each station is to convert the modulated IF (20.2 MHz) signal from the modem transmission part to the desired RF transmission frequency in the 450 MHz UHF range. The receiving side of the RF unit performs the opposite action of down-converting the receive 450 MHz UHF signals into an IF signal at 20 MHz. The transmission and reception frequencies are offset by 5 MHz from each other. The RF units are programmed by the CCU control function to operate on different frequencies used throughout the system. Typically, each base station RFU is set to operate on a given frequency allocation at system launch and does not change. The number of RFUs in the base station corresponds to the number of transmit and receive frequency channel pairs supported in the base station. The subscriber station RFUs typically change the operating frequency with each new telephone connection.

The RFU's include variable AGC and transmit line level settings. The AGC gain coefficient is provided by the modem based on a calculation in the receive-part processor 141 in the modem. The subscriber station transmit power level is calculated by the CCU based on messages received from the base station on the RCC channel and other control parameters.

If all slots in a frequency channel are not used, the RFU will send a sleep pattern set by the CCU. If a full frequency channel is not used, the transmitter for that frequency can be turned off by the CCU software via the modem.

The switching time for the diversity circuits is less than 50 ms.

Three antennas and three separate RF / IF units are provided. (Single send, three receive.)

Many parts of the base station RFU and the antenna interface are identical to the parts described above for the subscriber station. This subsection highlights the differences.

The base station RFU's and antenna interface circuits operate on a full duplex basis. All transmitters and receivers normally operate in the 100% duty cycle. In addition, it is economically attractive for the base station to operate at a higher transmit power and to use low noise diversity receivers. The transmitter is designed to operate at the highest permissible power level without dynamic control. Receive diversity is provided by multiple receive antennas and multiple modems.

The base station usually does not change the operating frequency and the transmit power level during normal operation. The transmitting and receiving parts are fully adjustable on each of the 26 channels.

The transmitter portion of the base station antenna interface receives the modulated IF input signal on line 239 from the modem and processes it as in the subscriber transmit part described above. It is further amplified to the required power level and filtered through a cavity preselected bandpass filter 225 to reduce noise at the operating frequencies of equally located receivers and to reduce the undesirable emission level.

The base station receiving portion of the antenna interface is similar to the receiving portion described for the subscriber station, except that the front end is preceded by cavity preselected bandpass filters 233, 237, which help to eliminate end sensitization caused by similarly located or near transmitters , Low noise preamplifiers are also used to reduce the usable threshold signal level. All antennas 23, 34 a, 346, 34 c have a 30 dB separation from any other antenna. Additional isolation is provided in the transmitter and receiver sections to ensure a separation of approximately 80 dB between the transmitted signals and the received signals. The bandpass filter, the preamplifiers and amplifiers are arranged adjacent to the respective transmit and receive antennas.

Diversity reception processing

Diversity reception is used to reduce the likelihood of channel fading below the assumed threshold. The diversity system is able to provide three-way diversity over the path from the subscriber to the base and the path from the base to the subscriber. The diversity hardware in both the base station and the subscriber stations includes a dedicated diversity combining 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 FIG. 2 If so, it is present in the base station and connected to the modems and the CCU in the base station in the same manner as in the subscriber station.

When operating in diversity reception, the base station or subscriber station uses three receive antennas separated by a sufficient distance to ensure that fading features of the received signals are not related. These three antennas feed through the three identical receive sections to the RFU control logic circuit whose IF output signals go into separate modems for demodulation. A TMS-320 microprocessor in the diversity combiner 33 (diversity processor) receives the output signals from the modems and provides a more reliable data stream to the rest of the system in a manner that emulsifies a single modem. The two tasks of performing the diversity combining and appearing as a single modem for the CCU are the responsibility of the diversity processor hardware and software.

The diversity processor reads from the three modems their data symbols, AGC values, signal + noise, magnitude and phase error (deviation of the perceived phase from the ideal 22.5 ° reference vectors). The algorithm used to determine the demodulated symbol involves the use of decision logic and signal-to-noise ratio calculations for each modem to identify the most likely correct answer modem.

The registers of the diversity processor CCU interface are nearly identical to the registers of the modems, except that the additional registers used to pass information used in the diversity processing function are not needed, so that only three address bits are necessary ,

Since the input / output capabilities of the TMS320 microprocessor are small and most of the processing with an input / output register type operates at one time, a special register that holds the register address that is needed at the time is used , For example, the AGC value must be read by each modem, the maximum value selected and the result read into the input / output registers of the diversity processor where they can be read by the CCU. The addressing of these registers is made most effective when the address of the AGC register is first read to a port where it is set on the modem address lines. Thereafter, the processor only needs to address the correct modem or microprocessor register row, thereby speeding up input / output operations.

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

An important function of the diversity processor is to maintain the communications between the CCU and the three modems. This communication must be performed fast enough to meet all the requirements of the CCUs, but not so fast that the diversity processor becomes overloaded.