WO2004049748A2

WO2004049748A2 - Communication system and method for reducing congestion therein

Info

Publication number: WO2004049748A2
Application number: PCT/EP2003/050687
Authority: WO
Inventors: Jose Gil
Original assignee: Motorola Ltd; Motorola Inc
Current assignee: Motorola Solutions UK Ltd; Motorola Solutions Inc
Priority date: 2002-11-23
Filing date: 2003-10-03
Publication date: 2004-06-10
Anticipated expiration: 2005-05-23
Also published as: GB2395632B; EP1568245A2; WO2004049748A3; GB0227374D0; GB2395632A; AU2003282111A1

Abstract

A wireless communication system (100, 200) supports speech communication, for example circuit-switched calls, and data communication, for example packet-switched calls. Upon receiving a trigger, for example a data communication resource request (305) that is unable to be supported by the communication system (100, 200), the communication system initiates a congestion relief mechanism. The congestion relief mechanism comprises adapting a provision of speech communications to make available sufficient communication resource for the data communication resource request. The proposed technique provides an ability to maintain a QoS of a data communication system such as GPRS system in a congested cell, by handing over or adapting speech calls such as GSM calls.

Description

COMMUNICATION SYSTEM AND METHOD FOR REDUCING CONGESTION

TBEREIN

Field of the Invention

This invention relates to providing a quality of service (QoS) in a communication system that supports two or more modes of operation. The invention is applicable to, but not limited to, providing a packet data QoS of a General Packet Radio System (GPRS) , whilst maintaining a particular Global System for Mobile communication (GSM) grade of service (GoS), when a communication cell supporting both modes of operation is congested.

Background of the Invention

Wireless communication systems, for example cellular telephony or private mobile radio communication systems, typically provide for radio telecommunication links to be arranged between a plurality of base transceiver stations (BTSs) and a plurality of subscriber units, often termed mobile stations (MSs) .

In a wireless communication system, each BTS has associated with it a particular geographical coverage area. Transmitter power levels and receiver sensitivity performance define the coverage area where the BTS can maintain acceptable communications with MSs. Typically, coverage areas are configured as overlapping areas to facilitate continuous communication as MS move between the areas. The coverage areas are generally termed cells, which can combine to produce an extensive coverage area of the communication system, for example to provide countrywide coverage.

Wireless communication systems are distinguished over fixed communication systems, such as the public switched telephone network (PSTN) , principally in that mobile stations move between coverage areas served by different BTS (and/or different service providers) and, in doing so, encounter varying radio propagation environments. Therefore, in a wireless communication system, MSs perform handover operations, when moving between different geographical areas/cells. In this manner, the MSs can be supported in their communications by the nearest BTS, which typically offers the highest quality signal/communication link.

A fixed network interconnects all BTSs. This fixed network comprises communication lines, switches, interfaces to other communication networks and various controllers required for operating the network, A call from a MS is routed through the fixed network to the destination node or communication unit identified by the call. If the call is between two MSs of the same communication system the call will be routed through the fixed network to the BTS of the cell in which the other MS is currently located. A connection is thus established between the two serving cells through the fixed network. Alternatively, if the call is between a MS and a telephone connected to the Public Switched Telephone Network (PSTN) the call is routed from the serving BTS to the interface between the cellular mobile communication system and the PSTN. It is then routed from the interface to the telephone by the PSTN. A cellular mobile communication system is allocated a finite amount of frequency spectrum for radio communication between the MSs and the BTSs. This spectrum must be shared between all MSs that are simultaneously using the system. Thus, techniques for communicating information simultaneously exist where communication resources in a communication network are shared by a number of users. Such techniques are termed multiple access techniques. A number of multiple access techniques exist, whereby the finite communication resource is divided into any number of physical parameters, such as:

(i) Frequency: in a frequency division multiple access (FDMA) system, frequencies used in the communication system are shared,

(ii) Time: in a time division multiple access (TDMA) system, each frequency used in the communication system, is shared amongst users by dividing the communication resource (each frequency) into a number of distinct time periods (time-slots, frames, etc.), and

(iii) Codes: in a code division multiple access (CDMA) system, where communication is performed by using all of the respective frequencies, in all of the time periods, and the resource is shared by allocating each communication a particular code, to differentiate desired signals from undesired signals.

Traditional traffic in mobile cellular communication systems has been circuit-switched speech where a permanent link is set up between the communicating parties. Recently, wireless communication units have been required to also transmit/receive a substantial amount of data. Furthermore, the requirements for mobile communication units are now to transmit substantial amounts of data at irregular intervals and not necessarily continuously. Consequently, it is inefficient to have a continuous link set-up between users. Thus, a significant increase in packet based data traffic has been observed, where the transmitting remote terminal seeks to transmit data in discrete data sub- blocks, termed data packets.

An established harmonised cellular radio communication system providing predominantly speech communication is the Global System for Mobile Communications (GSM) . An enhancement to this cellular technology has been developed, termed the General Packet Radio System (GPRS) . GPRS provides packet switched technology on GSM' s switched-circuit cellular platform. In the context of the present invention, it is understood that a ""packet' is an information unit identified by a label at layer-3 of the well-known OSI reference model (see International Telecommunications Union (ITU)-T 1.113). A packet switching mode of data transfer, also known as packet mode, is a transfer mode in which the transmission and switching functions are achieved by packet-oriented techniques. This enables dynamic sharing of network transmission and switching resources between a multiplicity of connections (ITU-T 1.113).

It is intended that packet data communication provided by GPRS will enable cellular radio communication networks such as GSM to provide enhanced levels of interfacing and compatibility with other types of communications systems and networks, including fixed communications systems such as the Internet. Further details on packet data systems can be found in 'Understanding data communications: from fundamentals to networking, 2^nd ed.', John Wiley publishers, author Gilbert Held, 1997, ISBN 0-471-96820- X.

In a packet data based system, where a high number of mobile stations may require resources for packet transmissions at unknown and irregular intervals, it is important to schedule the order and time for transmission of the individual packets in order to optimally use the limited resource. This becomes even more important when different data packets have different requirements with respect to delay, bit error rate, etc.

GPRS is introduced as a data service within GSM. Thus, GSM circuit-switched speech services and packet data GPRS services have to share the GSM infrastructure. In the contention for resources between circuit-switched speech services and packet data GPRS services, the GSM speech circuit-switched (CS) speech services have priority over the packet data GPRS services. This is because the GSM operators wish to set a higher priority to GSM voice than GPRS data. Notably, the implication of allocating a higher priority to GSM speech communication over packet data GPRS communication is that a timeslot requested simultaneously by a voice user and by a GPRS data user will be allocated to the voice user. Furthermore, in the event of receiving an incoming circuit-switched speech call; in a cell without an idle traffic channel (TCH) , an in-use GPRS switchable timeslot is reconfigured to operate as a GSM TCH to carry the circuit-switched call. In this regard, the GPRS data transfer that is using the switchable timeslot is no longer able to use the timeslot whilst the circuit- switched call is on going. Hence, the priority allocation to GSM voice users has the potential to severely limit the performance of any data transfer session in progress. Consequently, the GPRS bandwidth of the cell is reduced, thereby compromising the GPRS quality of service (QoS) .

In practice, this reduction in GPRS resource is shared amongst several GPRS users, which is achieved by interleaving TBFs (Temporary Block Flow) . Furthermore, in the situation where all cell resources are occupied by circuit-switched services, no GPRS service can be provided to mobile users.

To allow for congestion in a wireless communication cell, scheduling disciplines are typically introduced. The scheduling principles typically employed are designed to divide the bandwidth fairly amongst all the users. However, irrespective of how good the scheduling discipline is, all users effectively suffer from a poorer service. The level of degradation in performance is dependent upon the number of users sharing the timeslot (s) and the scheduling discipline employed. Within the GPRS standard, a GPRS feature termed 'NC2' exists. NC2 may be used as a form of congestion relief in that it supports the commanding of GPRS MSs to move to neighbouring cells. The inventor of the present invention has recognised and appreciated a problem with such a forced handover process in that the GPRS mobiles might be in an active GPRS data transfer state. In such a case, the command to move to a new cell degrades the transfer control protocol (TCP) throughput enormously. In particular, the use of NC2 in the context of congestion relief causes TCP packets to be lost during the cell reselection process. This, in turn, triggers the TCP slow start algorithm, which further degrades the TCP throughput considerably. In addition, it is clearly inadvisable to move a GPRS MS from its serving cell, which has already been identified as the preferred serving cell, to a neighbour cell which will inevitably provide a poorer level of service.

Another implication of such a forced handover mechanism is that it could create further and more serious problems. The GPRS MSs that have been ordered to move to neighbouring cells, due to traffic congestion in the serving cell, will likely need to transmit at higher radio frequency (RF) powers than in the preferred cell. Increasing a MS' s transmit power increases the interference to its neighbour cells, forcing an increase in the transmission power of the MSs in those neighbour cells. This, in turn, will increase the interference in these neighbour cells. The overall result is an increase the level of interference in the whole network. Hence, the more GPRS MSs that are commanded to reselect to cells that are not their preferred server/cell, the greater will be the interference created in the network. This results in a poorer quality of service to all users in the network.

An additional problem with the NC2 method is that it requires the MS to transmit measurement reports (that include neighbour signal strength information) in the uplink to the packet control unit (PCU) . The transmission of this information requires uplink GPRS bandwidth, which reduces the overall GPRS bandwidth usable for transmission of user data in the uplink. The more MSs that are required to send measurement reports in the uplink the more uplink bandwidth is used for this signalling transmission. Therefore, there is less uplink bandwidth available for transmission of useful data. In contrast, in the downlink, the transmission of NC2 cell reselection commands will use part of the downlink GPRS bandwidth, thus reducing the available downlink bandwidth for the transmission of useful.

A mechanism^' to facilitate GSM congestion relief for GSM voice mobiles is currently provided by Motorola™. The congestion relief mechanism performs automatic handover of voice calls to neighbouring cells when there is congestion in the cell and new incoming calls are requesting a timeslot in the cell. However, this feature only triggers congestion relief handovers when new voice calls cannot be allocated a speech channel and is limited to only GSM communications.

Thus, the feature does not address any of the issues relating to the recent introduction of an overlaid GPRS system. Furthermore, it will not address the user requirements of the alternative (GPRS) system with regard to maintaining a QoS in terms of high throughput and low latency whilst the cell is congested.

The inventor of the present invention has therefore recognised and appreciated a need to provide a congestion relief mechanism that supports two air-interfaces and/or two modes of operation, whereby users of both are competing for the same communication resource. In particular, in the context of a GSM/GPRS scenario, the inventor of the present invention has therefore recognised and appreciated a need to:

(i) Maintain a user QoS performance metric of existing GPRS data transfers in a congested cell, i.e. maintain good throughput and low latency;

(ii) The maintenance of the GPRS QoS is not to be at a cost of the GSM Grade of Service (GoS) in a congested cell, i.e. where the GoS indicates the % success rate for MSs accessing the network;

(iϋ) Maintain the GSM drop call rate goal of <2% in a congested cell; and

(iv) Provide a desired GPRS QoS to a new user in a congested cell.

Thus, there exists a need in the field of the present invention to provide a communication system and a method for congestion relief, particularly when a communication system supports two air-interfaces/modes of operation, wherein the aforementioned disadvantages may be alleviated.

Statement of Invention

In accordance with a first aspect of the present invention, there is provided a wireless communication system, as claimed in Claim 1. In accordance with a second aspect of the present invention, there is provided a packet control unit, as claimed in Claim 7.

In accordance with a third aspect of the present invention, there is provided a base station controller, as claimed in Claim 8.

In accordance with a fourth aspect of the present invention, there is provided a method of congestion relief, as claimed in Claim 9.

In accordance with a fifth aspect of the present invention, there is provided a communication system, as claimed in Claim 15.

In accordance with a sixth aspect of the present invention, there is provided a communication unit, as claimed in Claim 16.

In accordance with a seventh aspect of the present invention, there is provided a storage medium, as claimed in Claim 17.

In summary, the inventive concepts of the present invention alleviate the problems associated with prior art GPRS GoS provision by proposing to adapt the provision of speech communication and speech communication resources to make resources available for GPRS data communication. In accordance with the preferred embodiment of the invention, the proposed mechanism maximises the GPRS GoS in terms of high throughput and low latency while a cell that provides for GSM communication is congested. A preferred mechanism to maintain the GPRS GoS is to handover GSM voice calls to neighbouring cells when there is congestion in the cell and/or more GPRS bandwidth is needed.

Advantageously, the mechanism utilises the fact that voice calls that are handed over to a new cell are not broken or dropped, which is in contrast to the current methodology to handover packet data calls, such as GPRS calls, where data transfers are broken.

In particular, the congestion relief mechanism is employed to take into account at least two different air- interfaces or access protocols, instead of the known congestion relief feature offered by Motorola™ that was conceived purely for voice users.

Brief Description of the Drawings

Exemplary embodiments of the present invention will now be described, with reference to the accompanying drawings, in which:

FIG. 1 shows a block diagram of a cellular radio communications system adapted to support the various inventive concepts of a preferred embodiment of the present invention;

FIG. 2 shows a cell-based communication system adapted to support the various inventive concepts of a preferred embodiment of the present invention; FIG. 3 illustrates a flowchart of a congestion relief mechanism following a packet data communication resource request, in accordance with the preferred embodiment of the present invention;

FIG. 4 illustrates a flowchart of a congestion relief mechanism following a packet data communication resource request, in accordance with the preferred embodiment of the present invention; and

FIG. 5 illustrates a flowchart of a congestion relief mechanism following a packet data communication resource request, in accordance with the preferred embodiment of the present invention.

Description of Preferred Embodiments

Referring first to FIG. 1, a cellular telephone communication system 100 is shown, in outline, supporting a Global System for Mobile communication (GSM) air- interface, in accordance with a preferred embodiment of the invention. The European Telecommunications Standards Institute (ETSI) has standardised both the Global System for Mobile communication (GSM) air-interface and the General Packet Radio System (GPRS) air-interface.

Generally, the air-interface protocols are administered from base transceiver sites, within the network architecture 110, which are geographically spaced apart - one base station supporting a cell (or, for example, sectors of a cell) . Similarly, data users supported by co-located base transceiver sites supporting, say, both pico- and micro- cellular communications may also benefit from the inventive concepts described herein.

A plurality of subscriber units hereinafter referred to as mobile stations (MSs) 112-116 communicate over the selected air-interface 118-120 with a plurality of base transceiver stations (BTS) 122-132. A limited number of MSs 112-116 and BTSs 122-132 are shown for clarity purposes only. The BTSs 122-132 may be connected to a conventional public-switched telephone network (PSTN) 134 through base station controllers (BSCs) 136-140 and mobile switching centres (MSCs) 142-144.

Each BTS 122-132 is principally designed to serve its primary cell, with each BTS 122-132 containing one or more transceiver units and communicating 156-166 with the rest of the cellular system infrastructure

Each Base Station Controller (BSC) 136-140 may control one or more BTSs 122-132, with BSCs 136-140 generally interconnected through MSCs 142-144. Processes within the MSCs are provided to account for the situation where a MS passes between two BTS serving areas. For example, MS 112 may move from an area covered by BTS 122 to an area covered by BTS 124, where the two BTSs are controlled by different BSCs (BSC 136 and BSC 138 in this example) .

Similar processes are supported in MSCs to account for the situation where an MS moves between serving BTSs where these BTSs are connected to different MSCs. These mechanisms therefore allow the cellular telephone communication system to support handover of MSs 112-116 between cells for most, if not all, cases encountered.

Each MSC 142-144 provides a gateway to the PSTN 134, with MSCs 142-144 interconnected through an operations and management centre (OMC) 146 that administers general control of the cellular telephone communication system 100, as will be understood by those skilled in the art.

The various system elements, such as BSCs 136-138 and OMC 146, will include control logic 148, 150, 152, with the various system elements usually having an associated memory function 154 (shown only in relation to BSC 138 for the sake of clarity) . A memory function of the OMC 146 typically stores historically compiled operational data as well as in-call data, system information such as neighbouring cell-site lists and control algorithms such as a list of frequencies to be scanned by the respective MSs.

The GSM system has been overlaid with a general packet radio system (GPRS) air-interface, to provide a packet data capability. In this manner, a number of packet data-capable subscriber units such as MS 112 are able to communicate via circuit-switched (CS) calls on the GSM network and packet data calls on the GPRS network. The GPRS network comprises a number of packet control units (PCUs) 170, 180 operably coupled to service GPRS support nodes (SGSNs) 172, 182 to facilitate communication from the MSs to packet data networks such as the Internet 134. The SGSNs 172, 182 (with only two being shown for clarity purposes only) are operably coupled to the GSM BSCs 136- 138. The SGSNs are operably coupled to external packet data networks via GPRS gateway support nodes GGSNs 174, 184.

In accordance with the preferred embodiment of the present invention, the PCUs 170, 180 together with the respective BSCs 136-138 have been adapted in their traffic management organisation functions within their respective sites. In particular, their functions are configured to free up speech resources to allow packet data calls on the GPRS network, as described later with respect to FIG' s 3-5.

More generally, the dynamic adaptation of the BSCs 136- 138 and/or PCUs 170, 180, programmed according to the preferred embodiment of the present invention, may be implemented in a respective communication unit in any suitable manner. For example, new apparatus may be added to a conventional BSC or PCU, or alternatively existing parts of a conventional BSC or PCU may be adapted, for example by reprogramming one or more processors therein. As such the required adaptation may be implemented in the form of processor-imple entable instructions stored on a storage medium, such as a floppy disk, hard disk, PROM, RAM or any combination of these or other storage multimedia.

Thus, when it is determined that congestion of circuit- switched calls exists in a cell, say the BSC 136 enables the option of triggering congestion relief in the cell. Congestion relief may be triggered when a GPRS timeslot request is received and it is determined by the PCU that the GPRS requirements cannot be served by the existing available radio resource that is being used by (at least some) circuit-switched calls. The congestion relief mechanism forces circuit-switched calls already in progress to, say, handover to their best neighbour cell, as shown in FIG. 2.

Referring now to FIG. 2, a cell-based communication system 200 is shown, illustrating a congestion relief mechanism implemented by the present invention. The cell-based communication system 200 includes a number of cells 205, 210, 215, 220, 225, 230, 235 as known in the art. Each cell is supported by respective BTS.

For example, MS 112 is communicating 118 in a circuit- switched call via its serving BTS 124 with MS 114 in cell 205. Upon receipt of a GPRS request 222 from MS 214, and when no switchable timeslots are available, MS 112 is forced into a handover to cell 215. In this regard, MS 112 is now communicating 218 to BTS 122, in order to continue the circuit-switched speech call to MS 114. Once the CS call between MS 112 and MS 114 has handed over, the GPRS packet data call between MS 214 and, say, MS 212 via BTS 124 and BTS 222 is set up.

In this manner, a mechanism has been provided to ensure GPRS service is made available to a GPRS user in a cell, which has all of its resources occupied, where at least some of the resources are taken up by circuit-switched voice calls. Advantageously, as the circuit-switched call is forced to handover, the communication between the two parties is not broken. This is in contrast to the current methodology whereby a packet switched (GPRS) communication is broken and the communication link cannot be re-connected until the circuit-switched (GSM) call is complete and the resource is made available again.

It is also within the contemplation of the invention that other mechanisms for freeing up resource for GPRS communication may be used. For example, it is envisaged that multi-band MSs may switch between the bands supported by the MS, thereby freeing up resource on the congested frequency band in the cell. Furthermore, it is envisaged that MS having adaptive multi-rate codec (AMR) capabilities may be reconfigured to use an alternative codec. In this manner, the use of an alternative codec may be used to maintain the speech call, whilst freeing up resource to be used for the data request. By providing an increased number of options for reconfiguring GSM circuit-switched users, there is an increased probability of being able to serve new GPRS requests in a congested cell as well as accepting new GPRS/packet data calls. The inventor of the present invention envisages at least two scenarios where the inventive concepts can be applied:

(i) When the GPRS system receives a GPRS resource request. In this scenario, the GPRS system triggers as many congestion relief handovers of GSM circuit-switched calls as there are GPRS timeslots needed, before the GPRS system resorts to sharing GPRS timeslots in use. Such a scenario ensures the maintenance of the GPRS QoS in a congested cell, where there is no cost to the GSM Grade of Service (GoS) . Furthermore, the GSM drop call rate goal of <2% in a congested cell may be maintained, as part of the trigger algorithm. In addition, a desired GPRS QoS is provided to a new user in a congested cell. (ii) When the GSM system receives an incoming GSM speech call in a cell with no available TCH, the recognition of busy GPRS switchable timeslots triggers congestion relief handovers of existing speech calls in the cell. This is performed in contrast to releasing the existing GPRS TBFs on the available switchable timeslots. Such a scenario ensures maintenance of a GPRS QoS performance metric in a congested cell, i.e. good throughput and low latency, as well as maintaining the GSM drop call rate goal of <2% in a congested cell.

In accordance with the preferred embodiment of the present invention, a congestion relief algorithm consists of triggering congestion relief handovers of GSM calls, when a GPRS resource is requested. It is envisaged that the triggers for congestion relief handovers are preferably configurable by the operator, say through a BSS database parameter called ^λgprs__cr'. It is further envisaged that the following are possible triggers ( gprs_cr values) :

(i) gprs_cr=n, where n is a number between '0' and ^Λl' (i.e. the number of GPRS timeslots in the cell). For this scenario, GSM congestion relief handovers are triggered when the number of unused switchable timeslots *n' is less than or equal to gprs_cr. This option allows the GPRS system to reserve dynamically GPRS bandwidth that is needed.

(ii) gprs_cr=-l. For this scenario, GSM congestion relief handovers are triggered only when GPRS requests are received for a cell in which the number of required timeslots is greater than the number of available timeslots. If gprs_cr=-l, congestion relief handovers of voice calls will be triggered whenever a new CS voice call (including handover CS calls) cannot be allocated an idle TCH.

(iii) gprs_cr=-2. It is envisaged that such a value would disable the re-configuration feature. In the preferred embodiment of the present invention, it is envisaged that, before any congestion relief handover operation is triggered, all the existing GPRS requests are granted the number of desired timeslots (usually the maximum number of timeslots that the mobile is capable of using) . Alternatively, this is the number of GPRS timeslots that the Operator wishes to be made available in the cell, but that are not currently in use. In this manner, provision is made for extra GPRS bandwidth to be allocated to new GPRS units entering the cell, as soon as the GPRS units request resource. This avoids GPRS units waiting for congestion relief handovers to happen before they can be allocated their desired number of timeslots.

In summary, the known GSM congestion relief and other mechanisms that the inventor has appreciated can be used for congestion relief, such as AMR, have been used for different purposes to those described in the present invention. However such features are used in a novel and inventive manner to facilitate packet data (GPRS) congestion relief, particularly when GPRS users are sharing the available resource with GSM users. In particular, instead of allowing new voice calls (including the handover of calls from neighbouring cells) to take GPRS timeslots from active TBFs, a congestion relief handover of existing CS voice calls is performed to free up timeslots for the new CS voice calls. In this regard, when gprs cr=n, then the congestion relief handovers on existing voice calls are triggered when the number of idle GPRS timeslots is less than or equal to 'n' .

Referring now to FIG. 3, a flowchart illustrates a congestion relief mechanism following a packet data communication resource request, in accordance with the preferred embodiments of the present invention. The process commences with a packet control unit (PCU) obtaining a downlink channel resource and/or the general packet radio system (GPRS) receives an uplink GPRS request for a number (n) of timeslots, as shown in step 305. If 'n' is less than or equal to a number of unused GPRS timeslots in the cell, in step 310, the system assigns timeslots for the GPRS request (s) in the GPRS carrier in step 365. The timeslots that are assigned are preferably the ones with the least amount of interference.

If n' is greater than the number of unused GPRS timeslots in the cell, in step 310, any unused timeslot (s) are allocated to the one or more GPRS request (s) , as shown in step 312. A determination is then made as to whether any on-going speech calls are operating on switchable timeslots, in step 315. If there is no on-going speech call operating on switchable timeslots, in step 315, a scheduler discipline is preferably performed in step 320. The scheduler discipline will determine how the available GPRS timeslots are to be shared (vis-a-vis an order of data transmission) among the different active GPRS MSs in the cell. This sharing can be done according to different criteria. If there is an on-going speech call operating on switchable timeslots, in step 315, the system initiates a congestion relief operation. The congestion relief operation is performed on as many calls in the cell as there are GPRS timeslots that are needed. The congestion relief operation preferably starts with the carrier exhibiting the least interference, in step 325.

If, following the congestion relief operation, there was no congestion relief handover that was triggered in step 330, preferably one or more AMR handover (s) are triggered, as in step 332. If no AMR handover was triggered, in step 334, a scheduler discipline is performed in step 320.

If, following the congestion relief operation, there was at least one congestion relief handover that was triggered in step 330, or one or more AMR handover was triggered in step 334, intra-carrier handovers are triggered if there are no idle contiguous switchable timeslots, as shown in step 335. Contiguous GPRS timeslots maximise the usage of GPRS bandwidth for different GPRS multi-slot class mobiles.

The idle traffic channel (i.e. the idle contiguous switchable timeslot) is then re-configured to function as a packet data traffic channel (PDTCH) , in step 340. Any idle PDTCHs are then allocated to the rest of the GPRS request (s) , in step 345. A determination is then made as to whether still more PDTCHs are needed, in step 350. If more PDTCHs are needed in step 350, a scheduler discipline is performed in step 355. If no more PDTCHs are needed in step 350, the process finishes in step 360. Referring now to FIG. 4, a flowchart 400 illustrates an alternative mechanism for making GPRS timeslots available following a GPRS service request. The process commences with a packet control unit (PCU) obtaining a downlink channel and/or the general packet radio system (GPRS) receives an uplink GPRS request for a number (n) of timeslots, as shown in step 402. If *n' is less than or equal to a number of unused GPRS timeslots in the cell, in step 405, the system assigns timeslots for the GPRS request (s) in the GPRS carrier in step 410. The timeslots that are assigned are the ones with the least amount of interference.

If n' is greater than the number of unused GPRS timeslots in the cell, in step 410, a determination is made as to whether any on-going speech calls are operating on switchable timeslots, in step 415. If there is no on-going speech call operating on a switchable timeslot, in step 415, the scheduler allocates resources to the new request/s. If there is an on-going speech call operating on switchable timeslots, in step 415, the system initiates a GSM congestion relief operation. The congestion relief operation is performed on a number of calls equivalent to the total number of requested GPRS timeslots minus the unused GPRS timeslots, which are allocated immediately to the GPRS requests, in step 420.

If, following the congestion relief operation, there was no congestion relief handover triggered in step 425, AMR handovers are preferably triggered, as shown in step 427. If AMR handovers were not triggered in step 429, then the scheduler will allocate GPRS timeslots form the currently being used by other GPRS users to the new requests in step 440.

If AMR handovers were triggered in step 429, or following one or more congestion relief handover being triggered in step 425, a determination is made as to whether any ongoing GSM call is still in a switchable timeslot, as shown in step 430. If there are no on-going GSM calls in a switchable timeslot, in step 430, the scheduler will allocate the still required GPRS timeslots to the new requests in step 440.

If there is one or more on-going GSM call in switchable timeslots, in step 430, the on-going GSM call(s) is/are moved to idle traffic channels, in step 435.

Referring now to FIG. 5, a third algorithm is illustrated to trigger congestion relief handovers of existing calls in the cell when a new GSM speech request is received in the (GSM) cell. Currently, new voice call requests in the cell will terminate a GPRS transfer, or part of the GPRS' s bandwidth if there are no idle TCHs in the cell. In contrast, FIG. 5 describes a mechanism to trigger congestion relief handovers of voice calls when no idle TCHs are available, rather than 'steal' GPRS bandwidth. In this regard, the flowchart commences when a base station controller (BSC) receives a request for a new circuit-switched call, in step 505.

If there is any idle traffic channel (s) in the cell, in step 510, this/these idle traffic channel (s) are assigned to the circuit-switched call, as shown in step 515. If there are no idle traffic channel (s) in the cell, in step 510, a determination is made as to whether there is one or more unused switchable timeslots in step 520. If there is one or more unused switchable timeslots in step 520, the timeslot (s) are re-configured to traffic channel (s) and assigned to the requesting circuit- switched call.

If there is no unused switchable timeslot in step 520, the system then initiates a GSM congestion relief operation of existing circuit-switched calls, in step 530. If, following the congestion relief operation in step 530, there was a congestion relief handover/s that was triggered in step 535, one or more idle traffic channel (s) (TCH) are allocated to the new CS call/s, in step 538. If, following the congestion relief operation in step 530, there was no congestion relief handover triggered in step 535, the process attempts to trigger AMR handovers in step 540.

If AMR handovers were triggered in step 545, one or more idle traffic channel (s) (TCH) are then allocated to the new CS calls, in step 538. If, AMR handovers were not triggered in step 545, the process triggers a network control cell reselection process. The cell re-selection process includes moving a GPRS unit from a switchable timeslot and re-configuring the switchable timeslot to a traffic channel, in step 550.

The aforementioned inventive concepts are distinguished over the GPRS congestion relief mechanism of NC2, as the congestion relief mechanism adapts the operation of GSM speech calls, for example handing a call over to a neighbouring cell. Such a handover will only happen to cells that meet the power budget criteria, as determined by the Network Operator.

Although the above scenarios are all described with reference to a GSM/GPRS system, following, for example, receiving a request for a GPRS packet data resource, it is within the contemplation of the invention that this 'request' could be either a new originated call in the cell or an incoming handover.

Although the invention has been described with reference to a speech communication air-interface such as GSM, and a data communication air-interface such as GPRS, it is within the contemplation of the invention that the inventive concepts herein described are equally applicable to any communication system supporting both speech and data. Furthermore, it is envisaged that the inventive concepts are equally applicable to modes of operation in a dual mode of operation communication system, where the modes of operation may relate to air- interfaces or access techniques.

It will be understood that the communication system and method for congestion relief in a communication system described above tends to provide (at least) one or more of the following advantages:

(i) Ability to maintain a GPRS QoS metric in a GSM congested cell, by handing over GSM calls that are able to be handed over.

(ii) Failing the above handover option being a viable course of action, it is envisaged that a back-up option of, say, executing AMR changes or multi-band switching is performed on the existing voice calls.

(iii) The triggers for the congestion relief handovers, or AMR changes, or indeed any other mechanism for freeing up resource, include new voice calls in the cell and/or incoming GPRS call handovers and/or new GPRS resource requests.

(iv) Maintaining a GSM GoS in a congested cell without degrading the throughput of active GPRS transfers. This is achieved by allowing congestion relief handovers or AMR changes of voice calls when no idle TCHs exist, thereby avoiding the taking of switchable timeslots used by existing GPRS transfers.

Whilst specific, and preferred, implementations of the present invention are described above, it is clear that one skilled in the art could readily apply variations and modifications of such inventive concepts.

Thus, a communication system, and a method for reducing congestion have been provided wherein the aforementioned disadvantages associated with prior art arrangements have been substantially alleviated.

Claims

1. A wireless communication system (100, 200) provides a number of communication resources for a plurality of mobile stations (112-116) , wherein the number of communication resources support at least two operational modes where a first operational mode supports substantially speech communication, for example circuit- switched calls, and a second operational mode supports substantially data communication, for example packet- switched calls; the wireless communication system characterised in that, upon receiving a trigger, for example a data communication resource request (305) that is unable to be supported by the communication system (100, 200), the communication system initiates a congestion relief mechanism by adapting a provision of speech communications to make available sufficient communication resource for said data communication resource request.

2. The wireless communication system according to Claim 1, wherein said first operational mode is a GSM speech communication resource and said second operational mode is a packet data communication resource, for example one compliant with a GPRS system.

3. The wireless communication system according to Claim 1 or Claim 2, wherein said adaptation of speech communication comprises performing one or more of the following:

(i) Cell handover (525) of a speech communication; (ii) Moving (435) a speech communication to an idle traffic channel if said speech communication is using a switchable resource, for example a switchable timeslot;

(iii) Switching an operational band of a mobile station (112) that supports multi-band communication;

(iv) Changing a mobile station's operational codec (332, 427), where the mobile station (112) supports adaptive multi-rate codec communications.

4. The wireless communication system according to any preceding Claim, wherein said adaptation of speech communication is employed when one or more of the following conditions exist: (i) No idle traffic communication resource exists

(510);

(ii) No unused switchable communication resource (520), for example timeslots, is available.

5. The wireless communication system according to any preceding Claim, wherein said trigger is generated by say, an Operator, based on a level of data communication resource to be supported in a cell.

6. The wireless communication system according to any preceding Claim, wherein said trigger comprises one or more of the following:

(i) A newly requested speech call in a cell; (ii) An incoming handover of a speech call or a data call; and/or

(iii) A new data communication resource request.

7. A packet control unit (170, 180) adapted to facilitate packet data communication in the communication system of any of Claims 1 to 6.

8. A base station controller (136-138) adapted to provide speech communication in accordance with the communication system of any of Claims,, 1 to 6.

9. A method of congestion relief in a wireless communication system (300, 400, 500) that supports at least two operational modes, the method comprising the steps of: providing a first operational mode that supports substantially speech communication, for example circuit- switched calls; providing a second operational mode that supports substantially data communication, for example packet- switched calls; and receiving (305, 505) a request for a data communication resource when sufficient data communication resource is not available, with at least a portion of a communication system resource being used by speech communication; the method characterised by the step of: adapting a provision of speech communications to make available sufficient communication resource for said data communication resource request.

10. The method of congestion relief in a wireless communication system according to Claim 9, the method further characterised by the step of: providing a data communication resource to a communication unit requesting said data communication resource after said resource is made available by adapting said speech communication provision.

11. The method of congestion relief in a wireless communication system according to Claim 9 or Claim 10, wherein said speech communication resource is a GSM communication resource and said data communication resource is a packet data communication resource, for example one compliant with a GPRS system.

12. The method of congestion relief in a wireless communication system according to any of preceding Claims 9 to 11, wherein said step of adapting comprises performing one or more of the following steps: (i) A Cell handover of a speech communication;

(ii) Moving a speech communication to an idle traffic channel if said speech communication is using a switchable resource, for example a switchable timeslot; (iii) Switching an operational band of a mobile station supporting multi-band communication; and/or

(iv) Changing a mobile station's codec operation, where the mobile station supports adaptive multi-rate codec communications.

13. The method of congestion relief in a wireless communication system according to any of preceding Claims 9 to 12, wherein said step of adapting a provision of speech communications is employed when one or more of the following conditions exist: (i) No idle traffic communication resource exists; and/or

(ii) No unused switchable communication resource, for example timeslots, is available.

14. The method of congestion relief in a wireless communication system according to any of preceding Claims 9 to 13, wherein said step of adapting a provision of speech communications is employed following any one or more of the following steps:

(i) Receiving (505) a newly requested speech call in a cell;

(ii) Receiving an incoming handover of a speech call or a data call; and/or (iii) Receiving (305) a new data communication resource request.

15. A communication system adapted to perform any of the method steps of any of Claims 9 to 14.

16. A communication unit adapted to perform any of the method steps of any of Claims 9 to 14.

17. A storage medium storing processor-implementable instructions for controlling a processor to carry out the method steps of any of Claims 9 to 14.