FI98691C - Apparatus and method for achieving frequency flexibility in digital communication systems - Google Patents

Description

98691

The present invention relates to a digital radiotelephone line system having a base station communicating with a exchange and subscriber stations connected by RF channels to a base station, said base station having a plurality of sequentially repetitive time slots and a plurality of frequency slots. channels.

The present invention relates to wireless digital telephone systems comprising a base station communicating with a plurality of subscriber stations when the subscriber stations are connected to the base station on RF channels in a manner that allows simultaneous communication with subscriber stations 15 on a given channel with many consecutive channels. repeated time slots, with certain time slots being assigned to certain subscriber stations. The present invention provides means for automatically changing frequency or slot connections, or both, in the event that more subscriber stations that are out of transmission are involved, or in the event that transmission is degraded due to modulation change, frequency channel interference, hardware failure, or the like. The conversion means comprises a remote switching processing unit and an switching unit, preferably a concentrating device, comprising a switch which operates according to a control signal from the remote switching processing unit and physically connects the selected port of the communication circuit to the selected slot. The control signals are input according to the status messages received by the remote switching processing unit.

The present invention relates to wireless digital telephone type communication systems, and more particularly to means in such systems that automatically adjust the system to adapt to unwanted phenomena occurring during operation, such as frequency interference, fading, degradation of connection quality, and hardware failure.

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The present invention can be used in the system disclosed in U.S. Patent Application Serial No. 713,925, issued March 20, 1985, now Patent No. 4,675,863, issued June 23, 1987. Such a station 5 consists of a base station and a plurality of subscriber stations connected thereto via RF channels. . It can be used to communicate between subscriber stations and an external telecommunication network with a number of ports. The base station includes a communication circuit that allows simultaneous communication between a plurality of ports and subscriber stations on a given communication channel having many consecutive repetitive time slots, with predetermined time slots assigned to predetermined subscriber stations. The system includes a central office terminal (COT) having 15 remote switching radio processing units (RPUs) that control communication between a given time slot and a given port for a given subscriber station, and a switch that connects the communication circuit to the ports. The switch, which is primarily a centering device 20 as described in more detail below, includes a switch that, with a control signal from the RPU, switches the selected port to a selected communication channel time slot assigned to a given subscriber station.

The communication circuit includes a plurality of channel control units (CCUs) that connect a given communication channel time slot to a corresponding subscriber station according to an instruction signal provided by the RPU to the CCU over the baseband control channel (BCC). These command signals come through the BCC to the RPUs, indicating communication channel time slots and status messages indicating the operating status of the subscriber stations. The given communication channel time slot is coupled to the corresponding subscriber station on the radio frequency (RF) channel in the specified time slot. The BCC is on lines that are separately connected from the RPU to each CCU. Control commands 35 and status messages are transmitted between CCUs and subscriber stations on a radio control channel (RCC) assigned to a predetermined time slot of a predetermined RF channel.

It is a primary object of the present invention to provide frequency and intermediate flexibility to overcome difficulties in transmissions between a base station and associated subscriber units. Another object of the present invention is to provide the above-mentioned flexibility in a relatively simple and inexpensive manner. These objects are achieved by a digital radiotelephone system according to the invention, characterized in that time slots and frequency channels can be selectively relocated to subscriber stations during an ongoing connection of a subscriber station by moving said subscriber station from or to the frequency on which the subscriber station is originally located. , for a second time slot or 15 frequency channels according to a predetermined placement table, said system including locating means for selectively relocating slots and frequency channels to any subscriber station in response to degraded communication between the base station and subscriber station 20 or in response to a separate additional at each subscriber station, another subscriber station, which may have been located in a specific time slot and frequency channel and to which there is currently a connection, relocates 25 second time slots and / or frequency channels to allow another subscriber station to use this particular time slot and / or frequency channel.

Other preferred embodiments of the system according to the invention appear from the appended dependent claims 2-6.

Various objects and advantages of the present invention will become apparent from the following detailed description when read in conjunction with the following drawings, in which: Figure 1 is a block diagram of a base station used in the present invention, with subscriber stations generally designated 98691 4.

Figure 2 is a block diagram of a single subscriber unit incorporating an embodiment of the present invention.

Figure 3 is a block diagram of a dual subscriber unit incorporating an embodiment of the present invention.

Figure 4 is a block diagram of a multi-subscriber unit incorporating an embodiment of the present invention.

Figure 5 is a block diagram of a multi-subscriber unit incorporating an embodiment of the present invention.

Figure 6 shows a radio processing unit matrix of an embodiment of the present invention.

Fig. 7 is a block diagram showing details of a channel module used in the present invention.

Fig. 8 is a block diagram of a radio processing unit incorporating the embodiment 5 of the present invention and its switching means.

Figure 9 is a functional representation of the communication layers between a base station and a subscriber station. Abbreviation Glossary 20 BCC baseband control channel BER bit error rate CCT channel control task CCU channel control unit CO center '25 COT central terminal CRC cyclic redundancy check DBM database module LQ link quality MF error function 30, MPM message processing unit, MTU pääajoitusyksikkö MUX multiplexer PCM Pulse Code Modulation RCC radio control channel 35 of RF radio frequency SCU radio processing unit 98 691 5 RRT etäisradiopääte SCT access control function (device) SDLC synchronous data connection control SM timer module 5 VCU audio coding-decoding unit

Referring to drawings in which like reference numerals refer to like parts, Figure 1 shows a base station, generally designated 10, including a central office terminal (COT), generally designated 12, and a remote radio terminal (RRT), generally designated 14. The COT 12 includes a radio processing unit. (RPU) 16 connected to the gear unit 20 of the interface 18. The gear is preferably a hub, such as a "Model 1218C" digital image hub with a switch available from ITT in New York, New York, USA.

The switch 20 is in circuit with the exchange (CO) 22 via a plurality of two-wire lines 24 and is also in circuit, via echo cancellers 26 and a set of interconnectors 28, with a plurality of multiplexers (MUXs) 30, the multiplexers 20 being connected to a master timing unit (MTU) 32 at each a number of multiplexed time slots provided by the corresponding MUX 30 run on the interconnector 28. The baseband control channel (BCC) 34, which allocates one time slot on one link 28, establishes communication between the channel modules 36 of the MUXs 30 and 25.

Each MUX 30 is implemented with a modular card capable of handling 24 simultaneous pulse code modulation (PCM) circuits or 23 simultaneous PCM circuits and a BCC. The MUXs take data from the interconnectors 28 and distribute it 30 to the channel modules 36 that are in circuit with the transceiver network 38 through the power amplifier 40.

The RPU 11a 16 is the final control of the exchange (hub) 20 and the RRT 14 and processes subscriber requests to establish the required transmission path between the subscriber stations, 35 generally designated 42, and the exchange (CO) 22.

6,98691

Each of the subscriber stations 42 may be a single subscriber unit, a dual subscriber unit, or a multi-subscriber unit. Figure 2 shows a two subscriber unit consisting of a transceiver 50 connected between an antenna 52 and a modern 54 with a modern circuit with an encoder-decoder 56 for encoding or decoding signals from or to a subscriber unit 58. Figure 3 shows the same general type unit except that it consists of a unit of two subscribers in which the antenna 10 60, the transceiver 62, the modern 64 and the encoder-decoder 66 are in a circuit through buffers 68 and 70 separating the subscriber devices 72 and 74.

In the two subscriber unit of Figure 3, if two conversations are transmitted and received in the meantime, the transceiver, modern and encoder-decoder may be individual bidirectional elements that only need to perform the same functions at a time, e.g. transmit or receive on each line. Further, since the unit never receives and transmits simultaneously, no doubler is required because the only doubling takes place via buffers 68 and 70 connected to the subscriber equipment interface circuit (not shown).

Figure 4 shows a multi-subscriber system consisting of an integration, distribution, and duplication network, generally designated 80, connected to an antenna 82 and a plurality of single-subscriber units 84a, 84b, 84n. Each subscriber unit is connected to a respective subscriber unit 86a, 86b and 86n.

Fig. 5 shows a multiple system of the same type as in Fig. 4 except that the network 88 is connected to two subscriber units 90, 92, 94, etc., each of the type shown in Fig. 3 and connected to corresponding two subscriber devices such as unit 90 96 and 98, unit 92 for devices 100 and 102, and unit 94 35 for devices 104 and 106.

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During the discussion, some problems may arise due to various factors, which can be classified as follows: a) multi-subscriber switching, b) modulation change, c) avoidance of interference, and d) hardware failure of a single channel 5.

Figure 6 shows an example of an RPU matrix in which different subscribers are denoted by the letters A-G, with horizontal rows representing frequencies and vertical columns representing spaces. The number "1" represents the state "in use" and "0" represents the state "in use-10". It is only necessary to store the transmission intervals (in the figure) in this matrix, because the reception intervals have always shifted by 2 intervals.

During use, it often happens that all four slots of a given frequency are reserved by different subscribers. Suppose, for example, that there is one unit of two subscribers while the others are units of one subscriber. In the case of a two-subscriber unit, it is necessary that the two subscribers concerned be in adjacent spaces. If one of the two subscribers reserves a certain frequency and a slot while the other slots of said frequency 20 are reserved by individual subscribers and if one of the subscribers of the two subscribers calls because he has picked up the handset or the incoming call is routed to him from the exchange, either The 25th subscriber must be moved to another frequency and / or slot to make space for the second two-subscriber unit subscriber, or the first two-subscriber unit subscriber reserving a certain frequency and slot must be moved to the second frequency where the adjacent slot is available. In this case, the RPU sets the valid connections and saves them in its memory and can therefore determine where the transfer can be performed within the matrix.

A transmission such as the one mentioned above is performed as follows: Suppose, for example, that the first subscriber 35 of a unit of two subscribers is currently discussing at frequency D in slot 1 (reception slot 3). When another subscriber from a two-subscriber unit picks up the handset, an alarm signal (one bit) is sent back to the base station as part of the control bits sent in addition to the conversation. The alarm bit is detected in the channel module 36, which then sends the message back to the RPU 16 via the MUX 30, the link 28, the switch 20 and the interface, either along the opposite conversation path or along a separate path. Conversely, the signal from the exchange (CO) 22 is passed through the switch 20 and the interface 18 to the RPU 16.

In the presence of either signal, i.e. coming from the device or coming from the exchange, one of the subscribers of the two subscriber units must be provided with a slot in order to connect to the base station in the slot next to the slot already used by the first two subscriber units. Even if it were possible to transfer the first of the two subscribers from the frequency channel to D G, it would be a less desirable transfer because the same frequency often does not have two free adjacent slots. In each case, it is at least as easy to move an adjacent single subscriber unit from frequency D, interval 2, to a different frequency. In the example shown, the adjacent subscriber can be moved to any of the eight open slots. Since the individual subscriber to be transferred does not require adjacent slots for transmission and reception, if the transmission is performed only in terms of frequency (e.g., from channel D to channel B or G), it can be performed with the slot not used and is thus interference-free. If a change is made in both interval and frequency, then one interval of 30 transmission data is doubled or lost.

An analogous situation occurs in the case of several single subscriber units, as in Figure 4. Since each unit has a complete set of elements, more than one unit can transmit at the same time. In fact, it is better for all transmissions to take place simultaneously and for receipts to be received simultaneously, in order to avoid overloading the front end of the receivers. Thus, in the matrix of Figure 6, if two subscribers reserve slot 1 on frequencies B and D and a third subscriber requires a call to be initiated, the RPU 16 5 must assign a third subscriber to slot 1 on either frequency F or G.

When the system is as shown in Figure 5, i.e. formed by a plurality of two subscriber units, the first subscribers of each pair of two subscribers should be in the same range but at different frequencies while the second subscriber of each pair should be in an adjacent slot at the same frequency as the corresponding first subscriber.

In the above situations, the RPU sets the valid connections for each time slot and stores them in its memory. It can therefore determine at any point in time when the transfer within the matrix can be performed.

In all of the above situations, where the subject is to determine the intervals and frequencies in multi-subscriber situations, the change stimulus originates outside the base station (either from the exchange or the subscriber unit). In the following cases, which involve a change in modulation due to fading, avoidance of interference, or a change due to equipment failure, the stimulus originates or is detected by the base station itself.

At the base station, each channel module 36, Fig. 7, includes a channel control unit (CCU) 110 and a modern 112 each connected to a voice encoder-decoder unit (VCU) 114 via a respective compressed data connection 116 and a control-mode connection 118. The VCU is connected to a MUX 30 pulse code. PCM) data channels 120 when the CCU is connected to the MUX 30 by synchronous data link control (SDLC) 122.

A number of buffers (not shown in Figure 35) are associated with the various organs. In this regard, each channel module includes an AGC buffer 98691 for each slot and a link quality (LQ) buffer that measures the received differential phase error. In addition, the VCU has a bit error rate (BER) buffer. A cyclic redundancy check (CRC) is sent as part of the coded burst of the 5th interrogation, giving a BER reading to the BER buffer.

In the present case, a high AGC level means that a high signal level is received and the gain of the receiver is low. Conversely, a low AGC level 10 indicates a low received signal level and a high receiver gain. This AGC level is used to indicate whether the signal attenuation is due to signal fading or whether there is interference. A higher AGC level indicates interference because the AGC level 15 is based on the sum of the transmitted signals and any interfering signals. In either case, the correction can be performed by a change in modulation. To this end, as described in more detail below, each channel module 36 includes a modem capable of transmitting and receiving in audio slots with either 16 or 4 phase modulation. In 4-phase modulation, the number of bits per symbol is only half the number of bits in 16-phase modulation, but the bit rate is the same. Thus, when 4-phase modulation is used, two adjacent slots, the matrix of Figure 6, are combined into one elongated slot containing the same number of bits per extended slot as would occur in the slot using a 16-phase operation.

For example, when a two-subscriber system is in operation and if either the BER increases above a certain threshold. * (E.g., 0.1%) or the LQ falls below a certain threshold (e.g., 6 degrees), the contents of the corresponding buffers are reported to the RPU on the MUX switch (hub) connection via connection. In this case, the RPU sends the control signal back via the sa-35 ground connection to the missile module to change the 16-phase function to a 4-phase function. At the same time, if two subscribers are currently operating on adjacent slots of the same frequency, one of the subscribers is switched to the other frequency as described above.

5 If, after changing the modulation level as described above, the AGC level is still high for this particular subscriber, it is assumed that the cause of poor BER and LQ is interference rather than transmission fading. The outputs of all AGC buffers are reported to the RPU, which determines which frequencies (if any) have a low AGC level, with the RPU initiating a frequency change from a high Abc level frequency to a low Abc level frequency for this subscriber. This eliminates interference if it occurs.

15 The base station also has fault function (M) buffers with the functional status of each connection in the base station chain, which includes a switch (hub), communication line, OTHER, channel module, power amplifier, transmitter, and receiver. If the Ms buffer detects a malfunction or a device-20 fault, a signal is sent to the RPU indicating the frequency in question. Upon receiving this MF signal, the RPU initiates a frequency (and, if necessary, intermediate) change for each conversation (if any) currently in progress on the failed channel.

The RPU 18 is the main body in controlling the assignment of frequency channels and slots and its general structure is shown in Figure 8. It consists of a message processing module (MPM) 130 connected to a database module (DBM) 132 and a scheduler module (SM) 134. The MPM handles all SM and The interfaces between the DBM 30 and also the interfaces to the channel control unit (CCU) 110 and the subscriber control task device (SCT) 136 outside the RPU. The CCU is located in the channel module 36, Fig. 7, while the SCT is in circuit with the subscriber stations.

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In operation, if, for example, during a call, the connection quality (LQ) falls below a predetermined level, the RPU is initiated to send a message to the SCT 128, which then communicates with the MPM 122. In this case, the MPM a) sends a signal to the DM 124 to identify the available channel and b) checks with the timer module 126 the schedule control and timing (the timer module arranges the received messages in the reception order). If an available channel is found, the MPM sends a message 10 back to the SCT to rearrange the matrix so that the call is switched to the available channel. If no channel is available, the call remains on the same channel.

If, during a call, all four slots are busy due to interference on a particular frequency, it is necessary to move all subscribers to the corresponding slots on the other frequency, the following occurs: when the downlink is initiated, the RPU sends a message to the SCT requesting a frequency change. The SCT forwards the message 20 to the channel control task device (CCT) at the subscriber station for frequency change processing and also communicates with the MPM at the base station to determine the available CCU channel. The MPM sends a message to the DBM to identify the available channel and also checks the timer module's time to receive the paycheck. If an available channel is found, the MPM sends a message back to the SCTs to rearrange the channel location. If there is no available channel, the SCT sends a busy-sig-30 signal to the RPU and no change is made.

Figure 9 shows the RCC protocol. The RPU 16 communicates with the CCU 110 and the modern 112. At the subscriber station SCT 136 communicates with a CCT 138 equipped with a modern 140. The RCC protocol consists of two layers, 35 a communication link layer 142 and a packet layer 144. The communication link layer is a physical connection between parts, and the packet layer consists of messages transmitted over a physical connection. The data link layer is responsible for error detection, word synchronization and grouping, detection and resolution of collision situations 5 (content leading to a conflict between the same time slot and the same RF channel).

Considering Figure 9, for example, the RPU processes two protocol paths: in the first protocol, the RPU

sends a message to the CCU at the base station requesting 10 modulation changes. In the second protocol, the RPU sends a message to the SCT requesting a change in frequency. In the third protocol, the SCT sends a message back to the RPU to indicate that all channel frequencies are busy.

In another example, the RPU sends a message protocol to 15 SCTs requesting a change in channel frequency. This message initiates two operations: first, the message requires the SCT at the subscriber station to search for a route to another RCC frequency. In this case, the SCT communicates with the CCT. The CCT then searches the channels and, finding the available 20 slots and frequency, it switches to them. In the second operation, the message protocol causes the SCT to call the exchange to be ready for connection.

If during the conversation the quality of the connection drops below a predetermined level, the RPU takes this information to • 25 CCUs and requires a change in the modulation level. The CCU acknowledges this message via the SCLC connection via the MUX to the RPU.

Claims (6)

A digital radio telephone system comprising a base station (10) which communicates with a central station (22) and subscriber stations (42) which are connected to the base station (10) by RF channels, the base station (10) having several sequentially repeating time slots and a plurality of frequency channels, characterized in that the time slots and frequency channels can be selectively redistributed to the subscriber stations (42) during a pointing connection by transmitting the subscriber station (42) from the slot or frequency originally assigned to a frequency or frequency a predetermined allocation table, said system comprising allocation means for selectively re-allocating time slots and frequency channels at which he subscribes subscriber station (42) in response to impaired transmission at the connection between the base station (10) and the subscriber station (42) or as a response to a separate station , which comes in at l where, and a second subscriber station (42), optionally assigned to a particular time slot or frequency channel and communicating at the moment, is assigned another time slot and / or frequency channel to allow another subscriber station (42) to utilize this particular time slot and / or frequency channel. A system according to claim 1, characterized in that each of a plurality of dual subscriber stations (42) operates in communication with the allocation means, each subscriber (42) in each pair of dual subscribers (42) being able to separate allocated adjacent slots in a selective frequency channel by means of the allocation means. 3. A system according to claim 1, characterized in that several individual subscriber stations 98691 17 (42) operate in connection with the allocation means. System according to claim 1, characterized in that the allocation means performs the allocation as the transmission is impaired due to a modulation change, interference on the frequency channel and / or failure of the equipment. 5. A system according to claim 1, characterized in that the allocation means places one of the subscribers (42) according to a predetermined allocation table and prevents a simultaneous change in the time slot and frequency channel of the connection. 6. A system according to claim 1, characterized in that the re-assignment is done to effect change of the modulation speed of a subscriber station.