FI98691B - Arrangement and method for producing frequency flexibility in digital telecommunications systems - Google Patents

Description

98691.

The present invention relates to a digital radiotelephone 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 has means for automatically changing frequency or time slot connections, or both, in the event that 20 additional subscriber stations out of transmission are included in the case that the transmission is degraded by the modulation change. due to frequency channel interference, equipment failure or similar • · \ /. si. The conversion means comprises a remote switching processing unit and a switching unit, primarily a concentrator, • · · * • * / 25 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 port. - • ·: .V size. The control signals are input according to the status messages received by the remote switching processing unit.

This invention relates to wireless digital telephone type communication systems and more particularly. it relates to the means in such systems, • t · ’; / · which automatically adjust the system to adapt to undesirable phenomena occurring during the operation of‘ · .. ’, •‘ •., 35 such as frequency interference, fading, connection quality. *. : deterioration and hardware failure.

• «2 98691

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 with 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 direct 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-20 device as described in more detail below, includes a switch that, with a control signal from the RPU, switches the selected port to the selected one. to the communication channel slot assigned to the subscriber station.

v · · • · *

The communication circuit comprises a plurality of channel control units (CCUs) which connect a given communication • channel slot to a corresponding subscriber station to the CCU of the RPU • · a command signal given by the baseband control channel (BCC) »: .V According to Iin. These command signals come through the BCC according to the communication channel time slots transmitted to the RPU and the status messages indicating the operating status of the subscriber stations. The given communication channel time slot is switched back. to a specific subscriber station on a specified • »· radio frequency (RF) channel. The BCC is on lines that are • · separately connected from the RPU to each CCU. Control commands "• ..35 and status messages are transmitted between CCUrtts 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, on the line, and where another subscriber station that may have been located • ·. ·. : for a specific time slot and frequency channel and to which · ·, ·; · [currently connected, relocated * · '.25 to another time slot and / or frequency channel to allow another subscriber station to use this special time slot;' · * interval and / or frequency channel.

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

Various objects of the present invention and to it. ’ The associated advantages will become apparent from the following detailed description when read in conjunction with the following drawings, in which: Fig. 1 is a block diagram of a base station used in the present invention, with subscriber stations in general. · * 98691 4 marked.

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 an embodiment 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 function • ·: CCU channel control unit • · · I .. 'CO center

• «I

*. 25 COT central terminal • · · CRC cyclic redundancy check '· * ·' DBM database module • · LQ connection quality MF error function {'* .. 30 MPM message processing unit: * · *: MTU master timing unit 9. *. MUX multiplexer • · · PCM pulse code modulation • · '·; · * RCC radio control channel {** .. 35 RF radio frequency: * ·. · RPU radio processing unit • · 5 98691 RRT remote radio terminal SCT subscriber control function (device) SDLC synchronous data link control SM driver 5 VCU audio encoding-decoding unit

Referring to the 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 the interconnector 28 has a set of ··, 1, multiplexed time slots provided by the corresponding MUX 30.

• ·] .. 1 · The baseband control channel (BCC) 34, which occupies one time slot * · · *., 1 slot in one connection line 28, forms the communication between the channel modules 36 of the MUXs 30 and • · · ** ^ 5.

• 1 · ...

Each MUX 30 is implemented with a modular board, • · * .V 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 to the channel modules 36 in the transmitter-to-transceiver circuit: 1 · 1; with the receiver network 38 via a power amplifier 40.

.1. The RPU: 11a 16 is the final control of the switch (hub) 20 and the RRT 14 • 1 · and processes subscriber requests * ··· 1 to set up the required transmission path between the subscriber stations, m 1 • .35 commonly indicated as 42, and the exchange (CO ) Between 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, the modern being in 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. Furthermore, since the unit never receives and transmits simultaneously, no duplicate is needed, because the only doubling that takes place takes place via buffers 68 and 70, which are 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 denoted 80, connected to an antenna 82 and a plurality of single subscriber networks. subscriber units • · * .V 84a, 84b, 84n. Each subscriber unit is connected to a respective subscriber unit 86a, 86b and 86n.

Figure 5 shows the same type of multiple system as in Figure 4 except that the network 88 is connected. ie units 90, 92, 94, etc. of two subscribers, each of which • / # is of the type shown in Figure 3 and is connected to the corresponding '* *! dual subscriber devices such as unit 90 for devices • · · * ...: 96 and 98, unit 92 for devices 100 and 102, and unit 94 35 for devices 104 and 106.

• * • · · • · • • 7 98691

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 20 frequencies are reserved by individual subscribers and if one of the subscribers of a unit of two subscribers requires' V. contact because he has picked up the handset to make a call, ·,: or an incoming call is routed to him from the exchange, either • · '' -.S On that frequency, the adjacent individual * .25 subscriber must be transferred to another frequency and / or • · · • ”j to make space for another subscriber of a two-subscriber unit j · · · '· 1 subscriber or the first subscriber of a two-subscriber unit • 1 and who reserves a certain frequency and slot must be transferred to another frequency where the adjacent slot is available-i' \ .30 sec. In this case, the RPU sets the valid connections and stores them in its memory and can therefore specify 9. where within the matrix the transfer can be performed.

A transfer such as the one above is carried out as follows · ··· 1 in the following way: Suppose, for example, that the first: '\ .35 subscriber from a unit of two subscribers is currently being discussed on frequency D in interval 1 (reception interval 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 • · j ·. *; to any of the eight open spaces. Because the transmitting / transmitting individual subscriber 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 interval idle * · V ,: and is therefore trouble-free. If the change is made with respect to both the interval and the frequency, then one interval: \. 30 times the transmission data is doubled or lost.

· * · *; An analogous situation occurs in the case of several single subscribers. *, As in Figure 4. Since each unit has a complete set of organs, more than one | · ··· * the unit transmits at the same time, in fact it is better; * \. 35 that all transmissions take place simultaneously and receive 9 98691 receptions at the same time, 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 between Salom masses but at different frequencies while the second subscriber of each pair should be adjacent on 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 time at which the transfer within the matrix can be performed.

In all of the above situations, where the subject is the determination of slots 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 involving fading ai- • · ’. resulting modulation change, avoidance of interference, or • · · change due to equipment failure, the stimulus originates or it • · t ’·’ Ϊ5 is detected at the Ilse base station.

9 ··· · ..: 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 corresponding compressed data connection 116 and a control channel. \, 30 with a standby mode connection 118. The VCU is connected to the MUX 30 on pulse 9 code modulation (PCM) data channels 120 when the CCU is connected to the MUX 30 by synchronous data link control (SDLC) 122.

»·· * ... * A number of buffers are associated with the different members (not the pattern: *." 35 sa). In this respect, each channel module contains an AGC buffer 9 9 »9 9 9 9 99 9 9 10 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.Cyclic redundancy check (CRC) is sent as part of the mid-5 irrigation coded ?, a refresh, giving the 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, using I .. '4-phase modulation, two adjacent slots, as shown in Figure 6,

• · I

‘•’ ^ 5 matrix, combined into one elongated slot that •• ϊ contains the same number of bits per extended slot * · * .V as would occur in the slot when using 16-phase • · V .; operation.

For example, when a two-subscriber system is in operation and * either the BER increases above a certain threshold (eg 0.1%) or the LQ falls below a certain threshold (eg 6. ·. Degrees), the contents of the corresponding buffers are reported * · ^; For RPU, MUX connection line switch (center) connection via connection, ... ·. In this case, the RPU sends the control signal back via the same connection to the missile module as a 16-phase function to a 4-phase function. * M «· · •« i 9 · 11 98691 tamlseksl 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, at which point the RPU initiates 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 a functional state 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 h.v. In the event of a malfunction or a device-20 fault, a signal is sent to the RPU indicating the frequency in question. When receiving this MF signal * ·. ·. The RPU initiates a frequency (and, if necessary, intermediate) change ». : for each conversation (if any) that is par- * 1 · I .. ’currently running on the failed channel.

• 1 «. 25 RPU 18 is the main body in controlling the frequency channels »f · *; 1! and slot determinations and its general structure is shown in Figure 8. It consists of a message processing module (MPM) • ·; .V 130 connected to a database module (DBM) 132 and a timer module (SM) 134. The MPM handles all SM connections between the DBM and the DBM j1 \ .30 and also the connections to the channel control unit (CCU) 110 and the subscriber control unit outside the RPU · 1 · 1. to the distribution task device (SCT) 136. The CCU is located in channel channel 36, Fig. 7, while the SCT is in circuit with subscriber guns.

35 • · 1 1 • · · »« 12 98691

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 the call all four slots are busy, due to interference on a certain frequency, it is necessary to move all subscribers to the corresponding slots on the other frequency, the following happens: when the reduced connection is initiated, the RPU sends a message to the SC? . The SCT forwards 20 messages to the channel control task device (CCT) at the subscriber station for frequency change processing * V. and also communicates with the MPM at the base station

. ·. : to determine the available CCU. MPM

«« F sends a message to the DBM about the available channel ID. 25 and also checks the time of the timer module • 9 m; * j to get a place from the schedule. If a available channel is found, the MPM sends a message back to the SCT for reordering the channel location. If there is no available channel, the SCT sends a busy-sig-; .. .. 30 ft RPU and no change is made.

#

Figure 9 shows the RCC protocol. RPU 16 is connected. with the CCU 110 and the modern 112. At the subscriber station SCT 136 it is connected to a CCT 138 | · ·· ’. The RCC protocol consists of two layers,. * '•., 35 a data link layer 142 and a packet layer 144. The road * · • * 13 98691 access 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. ground ready for connection.

* · *. *, If during the conversation the connection quality drops below a predetermined level, the RPU takes this information to the * · * ^ 5 CCU and requires a change in the modulation level. The CCU acknowledges ·! Ϊ * this message via the SCLC connection via the MUX to the RPU.

• · • # • · · • f <· »· · • · m 9 ·« • · «· m» · · # · 9 9 9 9 9 9 99 «9 999 *: 999 9 99 9 9 • ·· % • · t «·> 99 9 9

Claims (6)

14 98691 A digital radiotelephone system having a base station (10) communicating with a exchange (22) and 5 subscriber stations (42) connected by RF channels to a base station (10), said base station (10) having a plurality of sequentially repetitive time slots and a plurality of frequency channels, characterized in that the time slots and frequency channels are selectively relocatable to the subscriber stations (42) during the ongoing connection of the subscriber station by moving said subscriber station (42) between or the frequency on which the subscriber station is originally located , for a second time slot or frequency channel according to a predetermined placement table 15, said system including locating means for selectively relocating slots and frequency channels to any subscriber station (42) in response to degraded communication between the base station (10) and the subscriber station (42) -20 le for an additional subscriber to the station coming on the line- ... le, and where another subscriber station (42), which may have been • · *. \ placed in a specific time slot and frequency channel and • · '· to which there is currently a connection, relocated ·.' ‘Placed in another time slot and / or frequency channel.’ • 125 to allow another subscriber station (42) to use this • · specific time slot and / or frequency channel. A system according to claim 1, characterized in that each of the plurality of dual states:. and the station (42) communicates with the locating means, each. "ί1. 30 pairs of dual subscribers (42), each subscriber (42) being m · · separately located in adjacent slots in the selective * · * .2 frequency channel by the locating means. ·» · A system according to claim 1, characterized in that a plurality of individual subscriber stations (42) are connected to the location elements. • · »2 • · 15 98691 A system according to claim 1, characterized in that the placement means perform their placement due to the deterioration of the data transmission caused by the modulation change, the frequency channel interference and / or the occurrence of a device fault. A system according to claim 1, characterized in that the placement means place one of the subscribers (42) according to a predetermined placement table, preventing the simultaneous switching of the connection time slot and the frequency channel. A system according to claim 1, characterized in that the relocation takes place to change the modulation rate to the subscriber station. • · · • · • · · · · · · · · · · · · · · · · · · · · · · · ···· • · · · · · · · · · · · · · • * · • · • · · · · · · · · · · · · · · · · · · mm · · · · · · • · · · • • • • 9 9 0 9 9 16 98691