WO2009067297A1

WO2009067297A1 - A base station for a cellular communication system and a method of operation therefor

Info

Publication number: WO2009067297A1
Application number: PCT/US2008/079057
Authority: WO
Inventors: Paul Stephens; Phil Bloomfield
Original assignee: Motorola, Inc.
Priority date: 2007-11-16
Filing date: 2008-10-07
Publication date: 2009-05-28
Also published as: GB2454872A; GB0722500D0; GB2454872B

Abstract

A base station (101) for a cellular communication system comprises a backhaul loading processor (303) which is arranged to determine a backhaul loading indication for the base station (101). A serving cell control processor (305) then performs serving cell management in response to the current backhaul loading indication. The serving cell management can include admission control management and cell handover management and the serving cell control processor (305) can specifically bias communications away from the base station (305) towards neighbour base stations if the backhaul loading of the base station (101) becomes too high. The invention may reduce peak backhaul resource usage thereby reducing the required backhaul capacity for the individual base station (101).

Description

A BASE STATION FOR A CELLULAR COMMUNICATION SYSTEM AND A METHOD OF OPERATION THEREFOR

Field of the invention

The invention relates to a base station for a cellular communication system and a method of operation therefor, and in particular, but not exclusively, to a Global System for Mobile communication (GSM) Long Term Evolution (LTE) cellular communication system.

Background of the Invention

The frequency band allocated for a cellular communication system is typically severely limited and therefore the resource must be effectively divided between remote/mobile stations. A fundamental property of a cellular communication system is that the resource is divided geographically by the division into different cells. An important advantage of a cellular communication system is that due to the radio signal attenuation with distance, the interference caused by communication within one cell is negligible in a cell sufficiently far removed, and therefore the resource can be reused in this cell. In order to optimise the available communication capacity in a cellular communication system, it is advantageous to have the mobile stations distributed over different cells in accordance with the available communication capacity. For example, current 3^rd Generation Partnership Project (3GPP) Standards proposals describe the concept of handing over traffic to suitably qualified neighbours if a cell is heavily loaded such that the available air interface resource is insufficient. Such handover is based on assessment of the current propagation conditions between the mobile station and the neighbours as well as potentially the current loading of the neighbour base stations. Typically, a call may be handed over to a neighbour cell from a congested cell if the radio propagation conditions are considered sufficiently good to support the call.

However, although such conventional congestion relief may substantially alleviate the situation it also tends to have some disadvantages. In particular, such congestion relief tends to be limited to providing improved utilisation of the air interface resource.

In conventional cellular communication systems, the air interface resource is typically considered to be the limiting factor for both the local capacity capability of a base station as well as the total capacity of the system as a whole. As the air interface resource is considered the scarcest and most expensive resource, the typical approach when implementing cellular communication systems has been to ensure that all other provided resources are sufficient for supporting the maximum possible air interface loading. However, such an approach typically leads to an over-provision of non-air interface resources resulting in increased cost and complexity of the individual components as well as of the communication system as a whole. Hence, an improved cellular communication system would be advantageous and in particular a system allowing increased flexibility, improved resource usage, improved congestion relief, improved handover performance and/or improved performance would be advantageous .

Summary of the Invention

Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.

According to an aspect of the invention there is provided a base station for a cellular communication system in accordance with claim 1.

The inventor of the current invention has realised that improved performance and/or reduced complexity and/or reduced cost and/or facilitated operation or implementation can be achieved for a cellular communication system by a base station performing serving cell management taking the backhaul loading for the base station into account.

The base station may for example detect backhaul resource congestion and perform the serving cell management such that the congestion is reduced. The invention may in many embodiments allow a reduced backhaul resource provision for the individual base station thereby reducing cost and complexity for the system as a whole. The invention may allow improved performance and reliability for the individual communication. Specifically, the risk of a communication being dropped due to backhaul resource congestion can be substantially reduced.

The current backhaul loading indication may be any indication or measure reflecting an actual or estimated current backhaul resource usage. The backhaul loading may e.g. be considered to correspond to the current backhaul requirement divided by the provisioned backhaul capability for the base station.

The implementation of the serving cell control operations considering backhaul parameters in a base station may allow a facilitated implementation and operation and may in particular allow a distributed and localised adaptation to current conditions. This may alleviate many of the disadvantages associated with more centralised approaches such as delay and backhaul bandwidth requirement associated with communication between the base stations and a centralised serving cell controller.

The serving cell management comprises at least one of handover management and admission control management.

According to another aspect of the invention there is provided a method of operation for a base station in accordance with claim 12.

According to another aspect of the invention there is provided a cellular communication system in accordance with claim 13. These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiment (s) described hereinafter.

Brief Description of the Drawings

Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

FIG. 1 is an illustration of a cellular communication system in accordance with some embodiments of the invention;

FIG. 2 is an illustration of a cell overlap for the cellular communication system of FIG. 1 ;

FIG. 3 is an illustration of a base station in accordance with some embodiments of the invention;

FIG. 4 is an illustration of a buffer for a base station in accordance with some embodiments of the invention;

FIG. 5 is an illustration of a method of operation for a base station in accordance with some embodiments of the invention; and

FIG. 6 is an illustration of a method of operation for a base station in accordance with some embodiments of the invention .

Detailed Description of Some Embodiments of the Invention

The following description focuses on embodiments of the invention applicable to a base station for a GSM cellular communication system and in particular to a GSM system including additional functionality in accordance with standards for the Long Term Evolution (LTE) of the GSM system. However, it will be appreciated that the invention is not limited to this application but may be applied to many other cellular communication systems.

FIG. 1 illustrates some elements of a cellular communication system in accordance with some embodiments of the invention.

FIG. 1 illustrates a first and a second base station 101, 103 connected to an interconnecting network 105. Each of the base stations 101, 103 support a cell of the cellular communication system and the network 105 represents the infrastructure functionality of the GSM system required or desired for the operation of the system. Thus, as will be well known to the person skilled in the art, the network 105 includes Base Station Controllers (BSCs) , Mobile Switch Centres (MSCs), Operations and Maintenance Centres (OMC) etc.

FIG. 1 also illustrates a user equipment 107 which can communicate with a base station over the GSM air interface. In the specific example, the user equipment 107 is currently located in the cell supported by the first base station 101 and is currently served by this base station 101. The user equipment may dependent on the specific embodiment for example be a remote station, a GSM mobile station, a communication unit, a 3rd Generation User Equipment (UE) , a subscriber unit, a mobile station, a communication terminal, a personal digital assistant, a laptop computer, an embedded communication processor or any physical, functional or logical communication element which is capable of communicating over the air interface of the cellular communication system.

It will be appreciated that although FIG. 1 for brevity and clarity illustrates only a single user equipment 107 and two base stations 101, 103, these are merely illustrated as representatives of typically a large number of user equipments and base stations.

The connection between the base stations 101, 103 and the network 105 provides the backhaul connection allowing user data and control data to be exchanged between the network 105 and the base stations 101, 103. The backhaul connections are in practical systems typically implemented by dedicated connections which may be wired or e.g. microwave links. In practical communication systems, the resource required to provide sufficient backhaul capacity tends to be complex and costly. For example, for a conventional GSM system, backhaul costs typically account for about 20% of the total cost of operations. In an LTE system, the relationship between capacity on the air interface and the capacity on the backhaul is not easy to determine or assess due to the huge variance in the types of traffic carried and the different quality of service requirements for each type of traffic. Furthermore, LTE has the potential to generate a much greater traffic volume than for a traditional GSM system.

In the past, backhaul capacity has typically been dimensioned such that it is sufficient to cope with worst case conditions and such that the limiting capacity factor is the available air interface resource rather than the available backhaul capacity. However, applying such an approach to e.g. LTE will result in a very high operational cost of providing the backhaul capacity.

As will be described later, the system of FIG. 1 performs serving cell management (e.g. admission control and handover control) in response to the backhaul loading of the base station thereby allowing a reduced worst case (peak) backhaul capacity requirement for the individual base station. As a result, a more accurate provision of backhaul capacity can be achieved resulting in a substantial backhaul cost reduction and thus a significant reduction in the operational cost of the system. In a typical cellular communication system, cells are generally designed to be overlapping such that user equipments in the overlap area typically can be served by more than one base station. This ensures improved reliability and substantially reduces the number of dropped calls and may in addition provide additional capacity for the overlap areas. Indeed, the cell overlap between cells may often be quite significant.

FIG. 2 illustrates an example of a possible cell layout for a set of cells of the GSM system of FIG. 1. In the example, a cell X is supported/ formed by the first base station 101 and is overlapped by six neighbour cells A-F (one of which is served by the second base station 103) . As illustrated, the overlap area of the different cells may vary substantially and furthermore some areas may be overlapped by a plurality of neighbour cells.

In the system of FIG. 1, the first base station 101 is arranged to perform serving cell management in response to the current backhaul loading. Specifically, if the loading of the backhaul increases beyond a given level, the base station starts to bias at least one communication service away from the current serving cell X towards one or more of the neighbour cells A-F.

In the system, the first base station 101 measures the backhaul load of the backhaul connection (the Sl interface for a GSM LTE system) . The load is determined as an indication of the current backhaul requirement divided by the provisioned backhaul capability. A loading threshold for the backhaul loading is defined at a safe margin before the delay limits are exceeded for the specific service and when this loading margin is passed, the first base station 101 initiates a backhaul congestion relief mode of operation wherein suitably qualified traffic is handed over to a neighboring cell with available capacity and/or new call admission requests are rejected or redirected to neighbour cells.

FIG. 3 illustrates elements of the first base station 101.

The first base station 101 comprises a transceiver 301 which is capable of communicating with user equipments 107 over the air interface of the cellular communication system. For a given user equipment 107, a number of different communication (services) may simultaneously be supported. The communications may belong to different communication service types having different quality of service requirements. For example one communication service may support a voice communication and therefore have strict delay requirements whereas another communication service may support an Internet browsing application therefore having very lenient delay requirements .

The first base station 101 furthermore comprises a backhaul loading processor 303 which is arranged to determine a current backhaul loading indication for the first base station 101. It will be appreciated that any suitable value or measure that is indicative of the loading of the backhaul connection can be used. The current backhaul loading may for example be determined or extrapolated based on the measurement of a previous backhaul loading or can be a direct measurement of the current loading.

Examples of suitable backhaul loading indications include for example a current amount of data waiting to be communicated, an estimated communication (transmit) delay for the current amount of data, a measure of air interface resource allocated for data needing to be communicated over the backhaul connection etc.

The first base station 101 furthermore comprises a serving cell control processor 305 which is arranged to perform serving cell management in response to the current backhaul loading indication. The serving cell management comprises various procedures, functionality, algorithms, criteria etc which is used to manage which base station serves the individual user equipment 107 or communication .

The serving cell control processor 305 specifically comprises a bias processor 305 which is arranged to bias at least one communication of a user equipment 107 served by the first base station 101 towards a different base station 103.

Thus, the bias processor 307 can influence the serving cell management such that the probability of a least one communication from at least one user equipment being handed over from the first base station 101 to another base station 103 is increased.

In the example, the bias introduced by the bias processor 307 is only introduced if the current backhaul loading indication meets a first criterion. Specifically, the bias away from the first base station 101 is only introduced if the backhaul loading indication is indicative of the backhaul of the first base station 101 being congested. The first criterion may be selected to reflect that the margin between the available backhaul capacity and the current backhaul requirement is less than a desired amount in order to reduce the likelihood of the backhaul connection being overloaded.

For example, the first criterion can comprise a requirement that the backhaul loading indication for a communication service type of a plurality of communication service types having different Quality of Service requirements indicates that the backhaul loading exceeds a threshold.

As previously mentioned, the first base station 101 may support different communication services which have different quality of service requirements and specifically which may have different delay requirements. The backhaul data is buffered in the first base station 101 before it is transmitted over the backhaul connection. If the backhaul connection is overloaded it cannot transmit sufficient amount of data and accordingly the buffer levels increase. This will increase the buffer delay introduced to the data. However, the criticality of this increased delay depends on the requirements of the individual service and in some embodiments the first criterion comprises a comparison of the current loading for a least one communication service to a threshold that has been set to reflect the delay requirement for that communication service. Accordingly, if the loading indication exceeds the threshold, it is likely that this communication service will soon experience a delay that exceeds the available buffer delay to achieve the QoS delay requirement. In order to mitigate this effect, the first base station 101 enters a backhaul congestion relief mode wherein the bias processor 307 introduces a bias away from the first base station 101.

The serving cell control management performed by the serving cell control processor 305 can in some embodiments include call admission control. Thus, when a new user equipment 107 seeks to initiate process for accessing the first base station 101 as a serving base station, the serving cell control processor 305 determines whether to admit or refuse the user equipment 107. The process can for example be initiated for an access request by an idle user equipment 107 or a handover request for the user equipment 107.

In some embodiments, the bias processor 307 can modify the call admission operation when the first base station 101 enters the backhaul congestion mode. Specifically, it can increase the likelihood of a serving cell access request for a communication being refused. As a low complexity example, the bias processor 307 can simply control the operation to refuse all access requests when the first base station 101 is in the backhaul congested mode. As a more flexible example, the bias processor 307 can adjust the criteria used to determine whether to allow or refuse the request such that these are more stringent . The serving cell control management performed by the serving cell control processor 305 can in some embodiments include handover control. Specifically, the serving cell control processor 305 can be involved in the determination of when a user equipment 107 currently served by the first base station 101 should be handed over to a neighbour base station 103. In such a scenario, the bias processor 307 may modify the criteria used when determining whether to perform a handover such that a handover to another cell is more likely. For example, when the first base station 101 enters the backhaul congested mode the bias processor 307 can reduce the power budget margin required for a handover to a neighbour cell.

The first base station 101 comprises a buffer 309 which is coupled to the transceiver 301 and the backhaul loading processor 303 and which is arranged to buffer backhaul data to be communicated over the backhaul connection as previously described.

In the example, the buffer 309 comprises a sub-buffer 401 for each of a number of different communication service types as illustrated in FIG. 4.

For example, one sub-buffer 401 can buffer all data related to best effort data (having relatively lenient delay requirements), another sub-buffer 401 can buffer all data related to multimedia data (having relatively stringent delay requirements) , another sub-buffer 401 can buffer all data related to Voice over Internet Protocol data (having very stringent delay requirements) and a last sub-buffer 401 can buffer all data related to file data transfer (having very lenient delay requirements) .

The buffer 309 comprises means for allocating the data to be transmitted over the backhaul connection to one of the sub-buffers 401 dependent on which communication service type the backhaul data relates to. Thus, all backhaul data for VoIP services are fed to the sub-buffer 401 for VoIP data etc. The individual sub-buffers 401 are then treated as individual and separate buffers. It will be appreciated that any algorithm or criterion for selecting which data to transmit on the backhaul connection may be used without detracting from the invention.

In the example, the backhaul loading processor 303 determines the backhaul loading indication as the current buffer level for the buffer 309. It will be appreciated, that in some embodiments a single backhaul loading indication may be generated for the buffer 309, such as e.g. an average buffer level for the individual sub- buffers 401, the highest buffer level for any of the sub- buffers 401 or the level of the sub-buffer allocated to the most critical traffic.

However, in the example of FIG. 3, the backhaul loading processor 303 generates a (sub) backhaul loading indicator for each of the sub-buffers 401. Furthermore, the serving cell control processor 305 evaluates a criterion for entering the backhaul congestion mode that comprises an alternative requirement for each communication service type. If any of these alternative requirements is met, it is an indication that backhaul congestion is experienced for at least one communication service type and accordingly the first base station 101 enters the congested mode.

As a specific example, the serving cell control processor 305 can simply compare the current buffer level for each sub-buffer 401 to a congestion threshold 403 defined for each individual sub-buffer 401.

In the system, the threshold for a given communication service type is determined to reflect a QoS parameter for the corresponding communication service type and specifically to reflect a latency requirement for the corresponding communication service type.

In the system, backhaul overload occurs when a buffer for one of the service types exceeds a threshold such that the link latency for that communication service type becomes too high to meet the QoS delay requirement. Accordingly, by setting thresholds at a safe margin before this point, it is possible to refuse new calls and handover some existing traffic to suitably qualified neighbors until the backhaul congestion is relieved thereby mitigating the effect of the backhaul congestion and reducing the risk of exceeding the delay requirement for the individual service.

In some embodiments, the operation of the bias processor 307 may be dependent on which communication service type triggered the entry into the backhaul congestion relief mode. Specifically, the bias processor 307 can selectively introduce a bias towards other cells to communications that belong to the specific communication service type that caused the entry into the congestion relief mode. This will allow the congestion relief to be focused on the specific communication service types that are at most risk.

The first base station 101 furthermore comprises a cell selection processor 311 which is arranged to select at least one neighbour base station to which the bias will be introduced. In the specific example, the cell selection processor 311 is arranged to select a set of neighbour base stations (which may include a single base station, a plurality of base stations or all neighbour base stations) which are possible handover candidates for the user equipment 107.

In the example, the selection of the subset depends not only on the radio conditions relative to the neighbour base stations of the user equipment for which the bias is introduced but depends also on the current conditions experienced at the neighbour base stations.

The first base station 101 therefore comprises a neighbour cell communication processor 313 which is capable of communicating with the neighbour base stations 103 in order to exchange information about the conditions experienced by these neighbour base stations 103.

In the example, the neighbour base stations 103 regularly transmit data that indicates their current air interface resource availability and backhaul loading to other base stations (e.g. using the X2 interface for an LTE system) . These messages are received by the neighbour cell communication processor 313 which feeds the relevant information to the cell selection processor 311 to which it is coupled. The cell selection processor 311 then selects the subset of neighbour base stations 103 as the base stations 103 for which the measurement reports reported by the user equipment 107 are indicative of the neighbour base station 103 being able to support the user equipment 107 and for which the received data indicates that there is available air interface resource and backhaul resource to support the user equipment 107.

In the following, a more specific example of the operation of the first base station 101 will be described with reference to FIG. 5 which illustrates a method of operation for the first base station 101.

The method initiates in step 501 wherein the serving cell control processor 305 evaluates whether the first base station 101 is currently backhaul congested. The serving cell control processor 305 can specifically compare the current buffer level of the sub-buffers 401 to predetermined thresholds 403. If the current backhaul loading (buffer level) is below the threshold, the first base station 101 is considered not to be congested and the method remains in step 501.

If the current loading (for any of the sub-buffers 401) however exceeds the threshold, the first base station 101 is considered to be backhaul congested.

In this case, the first base station 101 proceeds to select a subset of neighbour base stations/cells from the plurality of neighbour base stations/cells as candidate handover targets for the user equipment 107. The base stations/cells are selected such that they meet a number of requirements.

Thus, if the cell is backhaul congested, the serving cell control processor 305 seeks to provide congestion relief by biasing user equipments 107 away from the first base station 101 towards one or more neighbour base stations 103. The possible candidate neighbour base stations 103 are selected such that they meet a handover criterion having a number of requirements selected to ensure that there is a high likelihood that the user equipment 107 can be supported by the base stations 103 of the candidate set.

In the specific example, the subset of neighbour base stations 103 is selected in response to both receive signal levels, backhaul capability and radio resource availability. Furthermore, in the example, each of these parameters is considered sequentially and independently. However, it will be appreciated that in other embodiments other parameters may be considered, the order in which the parameters are considered may be different and/or parameters may be considered together and may be combined in different ways.

In the specific example, step 501 is followed by step 503 wherein the cell selection processor 311 evaluates a requirement that a receive signal level indicated in measurement reports from the user equipment 107 meets a suitable criterion. For example, the cell selection processor 311 can for each neighbour base station/cell 103 compare a (time averaged) receive signal level reported from the user equipment 107 to a predetermined threshold and can exclude the neighbour cells for which the predetermined threshold is not exceeded. It will be appreciated that in many embodiments the relative signal level difference between the neighbour cell and the serving cell will be used rather than the absolute measured signal level for the neighbour cell.

Following step 503, the subset accordingly comprises only neighbour cells for which the current propagation conditions and location of the user equipment 101 are such that the user equipment 107 can be supported in the neighbour cell.

Step 503 is followed by step 505 wherein the cell selection processor 311 evaluates a requirement that an available backhaul resource for the neighbour cell base station 103 meets a criterion.

In step 505 the serving cell control processor 305 determines if it is sufficiently likely that the potential handover candidates have sufficient available backhaul capacity to support the user equipment 107 following the handover. For example, the neighbour cell communication processor 313 can via the network 105 receive indications of the currently unused backhaul resource from the neighbouring base stations 103. It can then estimate the backhaul requirement for the user equipment 107 (e.g. simply based on a measurement of the backhaul capacity that is currently used by the first base station 101) . Accordingly, any base station for which the available backhaul capacity does not exceed the required backhaul resource (e.g. with a certain margin) will be removed from the subset. Step 505 is followed by step 507 wherein the serving cell control processor 305 evaluates a requirement that an available radio resource for the neighbour cell base station 103 meets a criterion.

For example, the neighbour cell communication processor 313 can receive indications of the air interface resource which is currently not used by the neighbour base stations 103. These indications may be directly exchanged between the base stations 101, 103 via the network 105. The cell selection processor 311 can then assess the required air interface resource for the first user equipment 107 and proceed to remove any neighbour base stations for which the available air interface resource is insufficient (e.g. with a suitable margin).

Thus, following step 507, the cell selection processor 311 has generated a subset of potential handover candidates which are considered highly likely to be able to continue to support the user equipment 107 following a handover .

Step 507 is followed by step 509 wherein the handover bias processor 307 proceeds to introduce a modification to a handover requirement for at least one communication of the user equipment 107 with respect to the neighbour base station (s) selected in step 509. The modification is introduced such that the communication/user equipment 107 is biased away from the first base station 101 towards the base station (s) 103 from step 509. In the specific example, the modification may simply be a reduction to the required handover margin in order to initiate a handover. For example, during normal non- congested operation, a user equipment may be handed over to a neighbour cell if the handover margin (the difference between the measured receive signal levels for the neighbour cell and the current serving cell) is, say, 9 dB . During backhaul congested operation, this handover margin requirement may be reduced to, say, 3dB for the base station (s) 103 selected in step 509.

Thus, in the method of FIG. 5, a modification to a default handover requirement is introduced when the base station 101 is backhaul congested such that communications an user equipments 107 are biased away from the first base station 101. The neighbour base station 103 towards which the user equipment (s) 107 is (are) biased is selected such that the current conditions in the neighbour cell (s) is (are) sufficient to support the user equipment 107.

Step 509 is followed by step 511 wherein it is evaluated if the first base station 101 is still backhaul congested. Typically, the backhaul congestion of a base station will be temporary and caused by an increased short-term loading of the base station. However, due to the change in the traffic pattern of the user equipments and/or the application of backhaul congestion relief, base stations will typically return to a non-congested state after a given duration.

In step 511 it is detected when the first base station 101 returns to a non-congested state. Step 511 may apply the same basic approach as used in step 501 and indeed the same criterion for determining backhaul congestion may be used. However, typically a modified backhaul congestion criterion is used to ensure that the base station 101 will not immediately return to the backhaul congested state (i.e. to avoid ping-pong' ing between the states). For example the buffer level threshold (s) for considering the first base station 101 to transition from the congested state to the non-congested state is (are) set lower than the buffer level threshold (s) for considering the first base station 101 to transition from the non-congested state to the congested state.

The serving cell control processor 305 remains in step 511 until the base station is no longer backhaul congested and it then proceeds to step 513 wherein the modification introduced in step 509 is removed. Thus, when the base station 101 returns to the non-congested state, the handover performance returns to normal operation (e.g. the handover margin requirement returns to 9dB) .

Thus, the method of FIG. 5 provides a highly efficient and low complexity approach to providing backhaul congestion relief.

FIG. 6 illustrates a method of operation for a base station of a cellular communication system in accordance with some embodiments of the invention.

The method initiates in step 601 wherein a current backhaul loading indication is determined for the base station . Step 601 is followed by step 603 wherein serving cell management is performed in response to the current backhaul loading indication.

It will be appreciated that the above description for clarity has described embodiments of the invention with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units or processors may be used without detracting from the invention. For example, functionality illustrated to be performed by separate processors or controllers may be performed by the same processor or controllers. Hence, references to specific functional units are only to be seen as references to suitable means for providing the described functionality rather than indicative of a strict logical or physical structure or organization.

The invention can be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented at least partly as computer software running on one or more data processors and/or digital signal processors. The elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the invention may be implemented in a single unit or may be physically and functionally distributed between different units and processors . Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term comprising does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also the inclusion of a feature in one category of claims does not imply a limitation to this category but rather indicates that the feature is equally applicable to other claim categories as appropriate. Furthermore, the order of features in the claims does not imply any specific order in which the features must be worked and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order.

Claims

1. A base station for a cellular communication system, the base station comprising: a buffer including a plurality of sub-buffers for buffering backhaul data, wherein each sub-buffer is allocated backhaul data of one communication service type; means for determining backhaul loading congestion for the base station in response to one sub-buffer level exceeding a first threshold for the one communication service type associated with that one sub-buffer; means for receiving backhaul loading indications for the one communication service type from a plurality of other base stations; means for selecting a neighbouring base station as a candidate handover target in response to the backhaul loading indications for the one communication service type; and bias means arranged to bias at least one communication of the communication service type of the one sub-buffer towards a selected neighbouring base station with a backhaul loading indication below a second threshold for the one communication service type of the one sub-buffer.

2. The base station of claim 1 wherein the bias means is arranged to increase a likelihood of a refusal of a serving cell access request for the at least one communication if the current backhaul loading indication exceeds the first threshold.

3. The base station of claim 1 wherein the bias means is arranged to bias a communication currently served by the base station towards a hand over to the different base station if the current backhaul loading indication exceeds the first threshold.

4. The base station of claim 1 wherein the second threshold is determined from an estimate of the backhaul requirement for the user equipment and the currently unused backhaul resource from the neighbouring base stations corresponding to the communication service type.

5. The base station of claim 1 further comprising means for determining the thresholds for the corresponding communication service type in response to a Quality of Service parameter for the corresponding communication service type.

6. The base station of claim 1 further comprising means for selecting the different base station in response to measurement reports for neighbouring base stations by a user equipment served by the base station.

7. The base station of claim 1 further comprising: means for receiving air interface resource availability indications from a plurality of neighbouring base stations; and means for selecting the different base station in response to the air interface resource availability indications.

8. The base station of claim 1 wherein the bias means is arranged to introduce a modification to a handover requirement for the at least one communication and the different base station if the current backhaul loading indication exceeds the first threshold.

9. The base station of claim 1 wherein the bias means is arranged to remove the modification to the handover requirement when the current backhaul loading indication falls below the first threshold.

10. A method of operation for a base station of a cellular communication system, the method comprising: providing a plurality of sub-buffers for buffering backhaul data, wherein each sub-buffer is allocated backhaul data of one communication service type; determining backhaul loading congestion for the base station in response to one sub-buffer level exceeding a first threshold for the one communication service type associated with that one sub-buffer; receiving backhaul loading indications for the one communication service type from a plurality of other base stations; selecting a neighbouring base station as a candidate handover target in response to the backhaul loading indications for the one communication service type; and biasing at least one communication of the communication service type of the one sub-buffer towards a selected neighbouring base station with a backhaul loading indication below a second threshold for the one communication service type of the one sub-buffer.