GB2458445A

GB2458445A - Mobile communication system and a processor, base station and method for use in the system

Info

Publication number: GB2458445A
Application number: GB0804369A
Authority: GB
Inventors: Per Roed; Konstantin Dolgov; Jens Jakobsen
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2008-03-10
Filing date: 2008-03-10
Publication date: 2009-09-23
Anticipated expiration: 2028-03-10
Also published as: GB0804369D0; GB2458445B

Abstract

A mobile communication system (100) has an infrastructure (135) including a plurality of base stations (103, 107) each operable to provide wireless communications to at least one mobile station (119,123) and a processor (101) operable to receive from the base stations resource requests relating to wireless communications in which mobile stations served by the base stations are to participate and to process the requests, the processor including a congestion detector(311) operable to monitor a rate of receiving or processing the communication resource requests to detect when a congestion condition occurs when a threshold rate is reached or exceeded and a controller (303) operable to send to at least one of the base stations (103, 107) a congestion indication message indicating that the at least one base station is to reduce a rate of forwarding resource requests.

Description

TITLE: MOBILE COMMUNICATION SYSTEM AND A PROCESSOR,

BASE STATION AND METHOD FOR USE IN THE SYSTEM

FIELD OF THE INVENTION

The technical field relates to a mobile

communication system and a processor, base station and method for use in the system. In particular, the

technical field relates to avoiding or reducing

signalling congestion in a processor of the system for receiving and processing requests from base stations of the system for communication resources.

BACKGROUND OF THE INVENTION I5

In a mobile communication system mobile user terminals, such as mobile telephones, portable radios, personal digital assistants, wirelessly enabled mobile computers and the like, herein collectively referred to as mobile stations' or NSs', can communicate via a network infrastructure which generally includes various fixed installations such as base stations (BSs'), also known as base transceiver stations (BTSs'). Each BS has one or more transceivers which serve MS5 in a given region or area, known as a cell' or site', by wireless communications. The cells of neighbouring BSs are often overlapping. Signals sent from MS5 to their serving BS are known as uplink' signals. Signals sent from a BS to MSS are known as downlink' signals.

Uplink and downlink signals may be sent on different channels, e.g. with different carrier frequencies and/or different time slots.

When a user of a MS desires to make a call to one or more other MSs of the system, a call set-up signal may be sent by the MS via its serving ES to a resource allocation processor of the infrastructure. The resource allocation processor may for example serve all cells or sites the system or in a zone of the system.

The signal sent to the resource allocation processor includes a channel aLlocation request indicating for example the kind of channel required, e.g. a voice or data communication channel, and the intended recipients of the call, e.g. as defined by an identifier of an MS or a group of MSs operating within the system. The resource allocation processor processes the channel allocation request and normally allocates a channel for the requested call. The details of the channel allocated are notified to the MSs which are to participate in the call as well as to their serving ESs. The form of the channel allocated depends on the way in which the system operates. For example, the system may be a TETRA system operating according to the protocol of the TETRA standard as defined by the European Telecommunications Standards Institute (ETSI) in which the channels are provided by selected time slots in a timing sequence of the protocol on a selected carrier frequency.

The resource allocation processor may receive and process other communication resource requests from ESs.

For example, the requests may be related to mobility management of MS5, authentication of MSs or provision of encryption keys for encrypted communications by MSs.

The resource allocation processor, which may for example comprise a zone controller of a TETRA system, normally has a limited processing capacity. On some occasions, the rate of receiving channel allocation or other resource requests by the processor may reach a level giving a congestion or overload condition. When this condition occurs, the resource allocation processor has to take action to relieve the congestion. The processor may allow certain channel allocation requests to be dropped. These dropped requests may for example be selected randomly.

The requesting MSs may need to repeat the channel allocation requests. As a result, the overall level of service to MS5 requesting calls is reduced. In severe congestion conditions, the stability of the processing operations carried out by the resource allocation processor can be at risk. This can be made worse by MSs repeating call channel requests within too short a period of time.

Thus, there exists a need for a mobile communication system and a processor, base station and method for use in the system, which address at least some of the shortcomings of past and present techniques and/or procedures employed in such systems for dealing with actual or potential congestion of requests for communication resources.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The accompanying drawings, in which like reference numerals refer to identical or functionally similar items throughout the separate views which, together with the detailed description below, are incorporated in and form part of this patent specification and serve to further illustrate various embodiments of concepts that include the claimed invention, and to explain various principles and advantages of those embodiments.

In the accompanying drawings: IS FIG. 1 is a block schematic diagram of an illustrative mobile communication system.

FIG. 2 is a block schematic diagram of an illustrative form of base transceiver station employed in the system of FIG. 1.

FIG. 3 is a block schematic diagram of an illustrative form of a zone controller employed in the system of FIG. 1.

FIG. 4 is a flow chart of a method of operation in the system of FIG. 1.

FIG. 5 is a flow chart of a continuation of the method of operation of FIG. 4.

Skilled artisans will appreciate that items shown in the drawings are illustrated for simplicity and clarity and have not necessarily been drawn to scale.

For example, the dimensions of some of the items may be exaggerated relative to other items to assist understanding of various embodiments. In addition, the description and drawings do not necessarily require the order illustrated. Apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the various embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Thus, it will be appreciated that for simplicity and clarity of illustration, common and well-understood items that are useful or necessary in a IS commercially feasible embodiment may not be depicted in order to facilitate a less obstructed view of these various embodiments.

DETAILED DESCRIPTION

Generally speaking, pursuant to the various embodiments to be described, there is provided a mobile communication system having an infrastructure including a plurality of base stations each operable to provide wireless communications to at least one mobile station and a processor operable to receive from the base stations resource requests relating to wireless communications in which mobile stations served by the base stations are to participate and to process the requests, the processor including a congestion detector operable to monitor a rate of receiving or processing the communication resource requests to detect when a congestion condition occurs when a threshold rate is reached or exceeded and a controller operable to send to at least one of the base stations a congestion indication message indicating that the at least one base station is to reduce a rate of forwarding resource requests.

The resource requests from base stations may comprise requests relating to at least one of: channel allocation, mobility management, authentication and encryption.

In contrast to the prior art referred to in the

Background section earlier, action to alleviate a

detected congestion condition in the resource allocation processor, e.g. a zone controller, is passed to base stations. The rate of receiving communication resource requests by the processor may thereby be maintained at a suitable level below any serious congestion level, so that the processor may maintain normal operation without itself having to carry out substantial processing actions, which unnecessarily consume processing power, to relieve the detected congestion.

Those skilled in the art will appreciate that these recognized benefits and advantages and other advantages described herein are merely illustrative and are not meant to be a complete rendering of all of the benefits and advantages of the various embodiments of the invention.

Referring now to the accompanying drawings, and in particular to FIG. 1, a mobile communication system 100 in accordance with some embodiments of the invention is shown. The system OO will be described as a TETRA system which includes a zone controller 101 serving as a resource allocation processor. Those skilled in the art will, however, recognize and appreciate that the specifics of this example are merely illustrative of some embodiments and that the teachings set forth herein are applicable in a variety of alternative settings. In such other alternative settings, for example, implementations using different types of resource allocation processor in place of the zone controller 101 are contemplated and are within the scope of the various embodiments.

The zone controller 101 is operably coupled by a link 105 to a BTS (base transceiver station) 103, by a link 109 to a BTS 107, by a link 113 to a BTS 111 and by a link 117 to a ETS 115. Each of the links 105, 109, 113 and 117 may be a two-way broadband link established by a wired and/or wireless connection. The zone controller 101 and the BTSs 103, 107, 111 and 115 are included in a system infrastructure indicated by a dashed line 135. The components of the infrastructure may he fixed in position.

Each of the BTSs 103, 107, 111 and 115 provides communication services to MSs (mobile stations) in a cell or site area defined by the position of the BTS, e.g. a cell having the BTS approximately at its centre.

As shown in FIG. 1, the BTS 103 has wireless links with and provides communication services to MSs 119 and 121, the ETS 107 has wireless links with and provides communication services to LYISs 123 and 125, the ETS 111 has wireless links with and provides communications services to MS5 127 and 129, and the BTS 115 has wireless links with and provides communication services to MSs 131 and 133.

Although two MSs are illustratively shown in FIG. 1 linked to each of the ETSs 103, 107, 111 and 115, another number of MSs may be linked for service to each of those BTSs, e.g. up to one hundred or more may be IS linked to each BTS.

Although four ETSs are illustratively shown in FIG. 1, the number of BTSs of the system 100 operably coupled to the zone controller 101 may be any other number, e.g. less than four or up to one hundred or more.

Each of the BTSs 103, 107, 111 and 115 may have direct, e.g. wired or wireless, links between itself and the other BTSs (not shown), so that communications received from served MSs of one BTS may be forwarded via another BTS to NS5 served by the other BTS.

FIG. 2 shows an illustration of more detail of a BTS in a simplified form 200. Each of the BTS5 103, 107, 111 and 115 may have the form 200. The ETS having the form 200 includes a controller 215 which carries out various known intelligent control and management functions of the BTS. The controller 215 is operably connected to a memory 205, which stores data and programs needed in use by the controller 215, and to a timer 203 which provides synchronization of operations of the controller 215 with those of other components of the system 100. The controller 215 carries out intelligent actions when notified of congestion in the zone controller 101 caused by an excessive rate of communication resource requests being received by the zone controller 101. The actions are illustratively described in more detail later, particularly with reference to FIGS. 4 and 5.

The BTS having the form 200 also includes a processor 201 which processes communications to be sent by or received by the BTS having the form 200. The processor 201 is operably connected to the memory 205, which stores data and programs needed in use by the processor 201, and to the timer 203 which provides synchronization of operations of the processor 201 with those of other components of the system 100. The BTS having the form 200 also includes transceivers 207, 209, 211 and 213 operably connected to the processor 201 and the controller 215. The transceivers 207, 209, 211 and 213 provide wireless communication links (uplinks and downlinks) with MS5 served by (attached to') the ETS having the form 201. Thus, the transceivers 207, 209, 211 and 213 in the ETS 103 having the form 200 provide wireless communication I0 links with the MSs 119 and 121 (FIG.1) . Information in a signal received via one of the transceivers 207, 209, 211 and 213 is delivered to and processed by the processor 201 and may be delivered onward. Information in a signal transmitted by one of the transceivers 207, 209, 211 and 213 is delivered from the processor 201.

The zone controller 101 is a processor which controls certain operational functions of the system 100. In particular, the zone controller 101 controls allocation of communication resources to MSs of the system 100. The resources include communication channels for use by MSs of the system 100 for the making of calls. The system 100 when a TETRA system is a trunked system meaning that a finite number of communication channels are available on a finite number of RF carrier frequencies. The communication channels of a TETRA system are provided as defined time slots for each of the defined carrier frequencies.

Operational components within the system use the same timing sequence in which four consecutive time slots having a length (duration) of 14.17 milliseconds make up a frame having a length of 56.7 milliseconds and eighteen frames make up a multiframe.

In this specification the expressions call' and

calls' refer to user initiated communications between terminals, especially MSs of the system 100. The communications are made on a traffic channel (which may include another channel such as a control channel being used temporarily as a traffic channel) . The

II

communications may be made to transfer user speech information or user communicated data such as comprising user picture, video or text information.

Calls to communicate different kinds of information may be made on channels of different kinds. For example, user speech information may be communicated on one of a set of dedicated voice channels. User communicated data may be made communicated on a data channel, which may be a short data channel, e.g. for the transfer of text information, or a packet data channel, e.g. for the transfer of video information.

The zone controller 101 may also control allocation of other communication resources required in the system 100, such as relating to mobility management IS of MSs, authentication of MSs and provision of encryption resources, e.g. encryption keys, for use by MSs in (end-to-end) encrypted communications.

FIG. 3 shows an illustration of some more detail of the zone controller 101 in a simplified form 300.

The zone controller 101 includes a channel allocator 301 which is a processor which controls allocation of communication channels for use by MS5 of the system 100 for the making of calls. The channel allocator 301 when employed in a TETRA system may allocate voice communication channels, data communication channels or both. The channel allocator 301 receives and processes channel allocation requests from the BTSs of the system on behalf of the MSs that the BTSs serve.

The zone controller 101 having the form 300 also includes a congestion detector 311 operably connected to a memory 305 and a timer 307. The memory 305 stores data and programs needed in operation by components of the zone controller 101 having the form 300, including the congestion detector 311. The timer 307 synchronizes operations in the components of the zone controller 101 having the form 300, including the congestion detector 311. The congestion detector 311 monitors a rate of receiving or processing call channel requests in the channel allocator 301 and detects when an actual or potential congestion condition is reached when the monitored rate reaches a particular threshold level.

Further description of the operation of the congestion detector 311 is given later, particularly with reference to FIGS. 4 and 5.

The zone controller 101 having the form 300 also includes a controller 303 which controls various intelligent operations in the zone controller 101 and in the system 100. The controller 303 is operably connected to a database 309 which holds data concerning MSs operating in the system 100 and their mobility.

The controller 303 is also operably connected to the memory 305 and the timer 307. The controller 303 is also operably connected to the congestion detector 311 and carries out intelligent actions associated with the detection of congestion by the congestion detector 311.

For example, the controller 303 determines which BTSs are to take action to reduce the rate of forwarding channel requests to the channel allocator 301 when notified of an actual or potential congestion condition by the congestion detector 311. Further description of operation of the controller 303 upon receiving notification of the congestion condition by the congestion detector 311 is given later, particularly with reference to FIGS. 4 and 5.

The zone controller 101 having the form 300 includes a transceiver unit 313 which operates to send output. signals to other components of the infrastructure 135 including the BTSs 103, 107, 111 and and to receive input signals from such components.

The transceiver unit 313 may include a single transceiver or multiple transceivers. Each such transceiver may be a wireless transceiver or a transceiver for sending and receiving signals by a wired or other link, depending on how the zone controller 101 communicates with the other components of the system 100.

FIG. 4 illustrates a method of operation of the system 100 in which it is assumed that the zone controller 101 has the illustrative form 300 shown in FIG. 3 and the communication resource requests which can cause congestion in the zone controller 101 include channel allocation requests. In a step 401, channel allocation requests for voice or data channels, e.g. short data channels or packet data channels, received by the channel allocator 301 are monitored by the congestion detector 311. For example, the congestion detector 311 may monitor the number of such requests received per unit of time, e.g. per second or per ten seconds. Alternatively, the congestion detector 311 may monitor a number of operations carried out by the channel allocator 301 in response to receiving channel allocation requests. The congestion detector 311 may also monitor a number of channels already in use and thereby know a number of channels available.

In a step 403, the congestion detector 311 detects (actual or potential) congestion of the channel allocator 301. For example the congestion detector 311 may detect that the number of channel allocation requests received, or the number of operations carried out in response to such requests, per unit of time has IS reached a threshold level. The congestion detected may relate to a particular kind of channel, e.g. a voice channel, a short data channel or a packet data channel, or it may relate to all channels allocated by the channel allocator 301.

In response to step 403, the zone controller 101, e.g. by the controller 303, determines in a step 405 which one or more BTSs, if any, are to be allowed to carry on normally without any limitation of their rate of forwarding channel allocation requests from their served MSs. Such BTSs may be considered to be in a Group A of ETSs of the system 100. Group A may for example consist of BTS5 which have a special operational need to maintain normal operation, e.g. because an incident requiring increased communications has occurred in the areas served by such BTSs. Group A may for example comprise the BTSs 105 and 115 shown in FIG. 1.

At the same time as determining the BTSs in Group A, the zone controller 101 also determines in step 405 which selected BTSs of the system 100 must receive a congestion indication message to take action to limit the rate of sending channel access requests to the zone controller 101. Such selected BTSs may be considered to be a Group B of BTSs of the system 100. Group B may for example comprise the BTSs 107 and 111 shown in FIG. 1.

Following step 405, each BTS of the selected Group A is sent no congestion indication message, as represented by a step 407, and therefore takes no IS action to reduce the rate of forwarding channel access requests to the zone controller 101, as represented by a step 409.

Following step 405, each BTS of the selected Group B is sent in a step 411 at least one congestion indication message, e.g. by the controller 303. The same congestion indication message may be repeated several times to ensure that it is received by the BTS5 of Group B. Alternatively, or in addition, different congestion indication messages may be sent by the zone controller 101 to indicate different degrees of severity of congestion detected by the congestion detector 311. The messages sent in step 411 may for example be Protocol Data Unit (PDU) messages having a format understood by BTSs of the system 100 and may for example be sent on a control channel.

Each congestion indication message sent in step 411 may be in a signal sent solely for the purpose of delivering the congestion indication message.

Alternatively, or in addition, in order to reduce communication traffic flow in the system 100, the message may be in a signal sent to the BTSs of Group B for another purpose, e.g. as a control signalling broadcast to all BTSs.

In a step 413, each ETS of the Group B which received a congestion indication message in step 411 determines, e.g. by its controller 215, what action to take to reduce a rate of forwarding channel allocation IS requests to the zone controller 101. The action determined in step 413 to be taken may be selected depending on the severity of the congestion indicated in step 411.

Steps 415, 417, 419 arid 421 which follow step 413 represent various possible actions that may be taken by each BTS of the Group B to reduce the rate of forwarding channel allocation requests to the zone controller 101. Each BTS of the Group B may take one or more of the actions represented by steps 415, 417, 419 and 421. The same or different actions may be taken by the various BTSs of Group B. In the step 415, a BTS of Group B deletes some of the channel requests it has received from some of its served t4Ss. The ETS may determine that the particular requests have a low priority or have an age older than a particular threshold age. In a step 417, a BTS of Group B delays forwarding selected channel requests. The delay applied may be for a selected fixed period of time or it may be for a randomly selected period of time which differs from one call request to another. In a step 419, a BTS of Group B suspends forwarding a channel allocation request from a particular MS or requests from a particular group of MSs. The particular MS or MSs may for example be known to be operated by users having a low priority communication need or by users who have violated or are likely to violate some imposed rule, e.g. related to restrictions on the length of voice or data calls which may be made. In a step 421, a BTS of Group B suspends forwarding all channel allocation requests, e.g. because it has been pre-determined that the cell or site served by that particular BTS is of low priority.

FIG. 5 shows steps illustrating a continuation 450 of the method 400. The zone controller 101, by the congestion detector 311, continues to monitor the rate of receiving or processing channel allocation requests in step 401. Eventually, in a step 451, a condition of relief of the (actual or potential) congestion of the channel allocator 301 is detected. The detector 311 may for example detect that for a given period of time the number of channel allocation requests received by the channel allocator 301, or a number of operations carried out in response to receiving such requests, is below a threshold level which may he one of multiple threshold levels representing different degrees of severity of congestion.

In response, in a step 453, the zone controller 101, e.g. by the controller 303, determines which selected BTS5 are to be allowed to resume normal service. The selected BTSs may be all of the BTS5 of Group B or a selected sub-set of the BTSs of group B, depending on the extent of relief of congestion which has been detected and indicated in step 451.

In a step 455, a message indicating that normal operation may be resumed is sent to the BTSs selected in step 453. The message sent in step 455 may for example be a Protocol Data Unit (PDU) message having a format understood by BTSs of the system 100 and may for example be sent on a control channel.

The message sent in step 455 may be in a signal sent solely for the purpose of delivering the message.

Alternatively, or in addition, in order to reduce communication traffic flow in the system 100, the message may be in a signal sent to the selected BTS5 of Group B for another purpose, e.g. as a control signalling broadcast to all BTS5.

In a step 457, the selected BTSs that received the message sent in step 455 resume normal operation of forwarding channel allocation requests to the zone controller 101.

Where the relief of congestion detected in step 451 takes place in stages, e.g. by the detected level of congestion falling successively below different thresholds, steps 453 to 457 may be re-applied to different selected sub-groups of the Group B of BTSs until total relief of congestion in the channel allocator 301 is detected and all BTS5 of Group B are allowed to resume normal operation.

The method 400 has been described in terms of avoiding or relieving congestion in the channel allocator 301 of the zone controller 101. The zone controller 101 may include one or more other processors (not shown) which receive and process communication resource requests from BTSs on behalf of their served MSs. The other processor(s) may be included in a unit separate from the channel allocator 301 or in a combined unit. The other processor(s) may for example receive from BTSs and process requests relating to one or more of mobility management of MSs, authentication of MSs and encryption of communications of t4Ss. A method may be operated in the zone controller 101, which is similar to the method 400, to avoid or relieve congestion in the relevant other processor(s) of the zone controller 101 for receiving and processing such requests. The congestion detector 311 may detect congestion in such other processor(s) . Alternatively, each other processor may have its own dedicated congestion detector (not shown) . The method operated for each processor of the zone controller 101 to relieve or avoid congestion may be a method dedicated to that processor. Alternatively, the method operated may be a combined method which applies to a plurality of processors.

The system 100 has been illustratively described above as a TETRA system. As will be appreciated by those skilled in the art, the system 100 could however be another mobile communication system in which a resource allocation processor serves various BS5 of the system, e.g. a GSN system or an APCO 25 system.

Claims

CLAIMS1. A mobile communication system having an infrastructure including a plurality of base stations each operable to provide wireless communications to at least one mobile station and a processor operable to receive from the base stations resource requests relating to wireless communications in which mobile stations served by the base stations are to participate and to process the requests, the processor including a congestion detector operable to monitor a rate of receiving or processing the communication resource requests to detect when an actual or potential congestion condition occurs when a threshold rate is IS reached or exceeded and a controller operable to send to at least one of the base stations a congestion indication message indicating that the at least one base station is to reduce a rate of forwarding resource requests.
2. A system according to claim 1 wherein the processor is operable to receive and process resource requests from base stations which comprise requests relating to at least one of: channel allocation, mobility management, authentication and encryption.
3. A system according to claim 1 or claim 2 wherein Lhe controlJer is operable to send the congestion indication message to the at least one base station in a signal which includes data sent for another purpose.
4. A system according to any one of the preceding claims wherein the at least one base station is operable in response to receiving the congestion indication message to reduce a rate of forwarding communication resource requests.
5. A system according to claim 4 wherein the controller is operable to indicate in the congestion indication signal one of a plurality of possible levels of congestion occurring or about to occur.
6. A system according to claim 5 wherein the at least one base station is operable to select at least one action to reduce a rate of forwarding communication resource requests according to a level of congestion indicated by the congestion indication message.
7. A system according to claim 5 or claim 6 wherein the at least one base station receiving the congestion indication signal is operable to reduce the rate of forwarding communication resource requests to an extent which depends on the indicated level of congestion.
8. A system according to any one of claims 4 to 7 wherein the at least one base station is operable to delay forwarding communication resource requests from at least one mobile station served by the at least one base station for a fixed or randomly selected period of time.
9. A system according to any one of claims 4 to 8 wherein the at least one base station is operable to delay or suspend forwarding communication resource requests from at least one selected mobile station.
10. A system according to any one of claims 4 to 9 wherein the at least one base station is operable to delay or delete communication resource requests which it determines to be of low priority.
11. A system according to any one of claims 4 to 10 wherein the at least one base station is operable not to forward communication resource requests which have reached a threshold age.
12. A system according to any one of claims 4 to 11 wherein the at least one base station is operable to suspend forwarding of all channel allocation requests.
13. A system according to any one of the preceding claims wherein the controller is operable not to send the congestion indication signal to at least one selected base station.
14. A system according to any one of the preceding claims wherein the congestion detector is operable to detect that the congestion condition has been relieved when a rate of receiving or processing communication resource requests has fallen below a threshold rate, and the controller is operable is to send to at least one of the base stations a message indicating that the at least one base station is allowed to resume normal forwarding of communication resource requests.
15. A processor adapted for use as the processor of the system according to any one of the preceding claims.
16. A processor according to claim 15 which comprises a zone controller for use in a TETRA system.
17. A base station adapted for use as the at least one base station of the system according to any one of claims 1 to 14, the base station being operable to receive the congestion indication message from the controller and, in response, to reduce a rate of forwarding communication resource requests to the processor.
18. A method of operation in the system according to any one of claims 1 to 14 which includes monitoring by the congestion detector a rate of receiving or processing the communication resource requests to detect when a congestion condition occurs when a threshold rate is reached or exceeded and, when the congestion condition is detected, sending by the controller to at least one of the base stations the congestion indication message indicating that the at least one base station is to reduce a rate of forwarding communication resource requests and the at least one base station selecting at least one action to reduce a rate of forwarding communication resource requests and taking the selected at least one action to reduce the rate of forwarding the requests.
19. A system according to any one of claims 1 to 14 and substantially as herein described with reference to any one or more of the accompanying drawings.
20. A processor according to claim 15 or claim 16 and substantially as herein described with reference to any one or more of the accompanying drawings.
21. A base station according to claim 17 and substantially as herein described with reference to any one or more of the accompanying drawings.
22. A method according to claim 18 and substantially as herein described with reference to any one or more of the accompanying drawings.Amendment to the claims have been filed as followsCLAIMS1. A mobile communication system having an infrastructure including a plurality of base stations each operable to provide wireless communications to at least one mobile station and a processor operable to receive from the base stations resource requests relating to wireless communications in which mobile stations served by the base stations are to participate and to process the requests, the processor including a congestion detector operable to monitor a rate of * ..* receiving or processing the communication resource requests to detect when an actual or potential congestion condition occurs when a threshold rate is reached or exceeded and a controller operable to send to at least one of the base stations a congestion indication message and wherein the at least one base : .. station is operable to select from a plurality of ****** * possible actions at least one action to reduce a rate of forwarding communication resource requests according to a level of congestion indicated by the congestion indication message.2. A system according to claim 1 wherein the processor is operable to receive and process resource requests from base stations which comprise requests relating to at least one of: channel allocation, mobility management, authentication and encryption.3. A system according to claim 1 or claim 2 wherein the controller is operable to send the congestion indication message to the at least one base station in a signal which includes data sent for another purpose.4. A system according to any one of the preceding claims wherein the controller is operable to indicate in the congestion indication signal one of a plurality of possible levels of congestion occurring or about to occur.5. A system according to any one of the preceding claims wherein the at least one base station receiving the congestion indication signal is operable to reduce the rate of forwarding communication resource requests .. : to an extent which depends on the indicated level of S...* . congestion. *..6. A system according to any one of the preceding ::::. 15 claims wherein the at least one base station is operable to delay forwarding communication resource requests from at least one mobile station served by the : .. at least one base station for a fixed or randomly * * selected period of time.7. A system according to any one of the preceding claims wherein the at least one base station is operable to delay or suspend forwarding communication resource requests from at least one selected mobile station.8. A system according to any one of the preceding claims wherein the at least one base station is operable to delay or delete communication resource requests which it determines to be of low priority.-2-f-- 9. A system according to any one of the preceding claims wherein the at least one base station is operable not to forward communication resource requests which have reached a threshold age.10. A system according to any one of the preceding claims wherein the at least one base station is operable to suspend forwarding of all channel allocation requests.11. A system according to any one of the preceding claims wherein the controller is operable not to send the congestion indication signal to at least one * S..selected base station. * .5512. A system according to any one of the preceding * claims wherein the congestion detector is operable to detect that the congestion condition has been relieved when a rate of receiving or processing communication resource requests has fallen below a threshold rate, and the controller is operable is to send to at least 5**SSS * one of the base stations a message indicating that the at least one base station is allowed to resume normal forwarding of communication resource requests.13. A system according to any one of the preceding claims which comprises a TETRA system and the processor comprises a zone controller for use in the TETRA system.14. A base station adapted for use as the at least one base station of the system according to any one of claims 1 to 13, the base station being operable to receive the congestion indication message from the -2-c--controller and, in response, to select from a plurality of possible actions at least one action to reduce a rate of forwarding communication resource requests according to a level of congestion indicated by the congestion indication message.15. A method of operation in the system according to any one of claims 1 to 13 which includes monitoring by the congestion detector a rate of receiving or processing the communication resource requests to detect when a congestion condition occurs when a threshold rate is reached or exceeded and, when the congestion condition is detected, sending by the controller to at least one of the base stations the * *.* congestion indication message indicating that the at ::::. 15 least one base station is to reduce a rate of forwarding communication resource requests and the at least one base station selecting from a plurality of possible actions at least one action to reduce a rate of forwarding communication resource requests and taking the selected at least one action to reduce the rate of forwarding the requests.16. A system according to any one of claims 1 to 13 and substantially as herein described with reference to any one or more of the accompanying drawings.17. A base station according to claim 15 and substantially as herein described with reference to any one or more of the accompanying drawings. 3o-18. A method according to claim 15 and substantially as herein described with reference to any one or more of the accompanying drawings. * *** * S. S. I SI.. * I S... * S. I. S * II I. *S * I IS II I..I