GB2510918A - Network elements, wireless communication system and methods therefor - Google Patents

Abstract

A target cell for handover of a User Equipment from a source cell in a Multi-Operator Core network is selected by storing the PLMN IDs of neighbor cells, identifying a best candidate neighbouring cell for handover from measurement reports sent by the User Equipment and comparing the stored PLMNID of the best candidate neighbouring cell with the PLMNID in use in the source cell. If the source and best candidate neighbouring cell PLMN IDs match then handover to the best candidate neighbouring cell is initiated, otherwise a handover to a next best candidate neighbouring cell with the same PLMNID as the source cell is initiated. The invention enables networks with different radio access network sharing arrangements or no sharing at all to co-exist and provide mobility of a User Equipment. The above may be implemented within small (e.g. femto) cells served by Home Node Bs.

Description

NETWORK ELEMENTS, WIRELESS COMMUNICATION SYSTEM AND METHODS THEREFOR

Field of the invention

The field of this invention relates to network elements, a wireless communication system and methods for facilitating a handover process and is particularly applicable to a MOCN-(Multiple Operator Core Network) supporting cell co-existing with neighbouring cells with different PLMN (Public Land Mobile Network) configurations.

Background of the Invention

Wireless communication systems, such as the 3 Generation (3G) of mobile telephone standards and technology, are well known. An example of such 3G standards and technology is the Universal Mobile Telecommunications System (UMTSTM), developed by the 3 Generation Partnership Project (3GPPTM) (www.3crnp.orci). The 3rd generation of wireless communications has generally been developed to support macro-cell mobile phone communications. Such macro cells utilise high power base stations (NodeBs in 3GPP parlance) to communicate with wireless communication units within a relatively large geographical coverage area. Typically, wireless communication units, or User Equipment (UEs) as they are often referred to in 3G parlance, communicate with a Core Network (CN) of the 3G wireless communication system via a Radio Network Subsystem (RNS). A wireless communication system typically comprises a plurality of radio network subsystems, each radio network subsystem comprising one or more cells to which UEs may attach, and thereby connect to the network. Each macro-cellular RNS further comprises a controller, in a form of a Radio Network Controller (RNC), operably coupled to the one or more Node Bs, via a so-called lub interface.

The second generation wireless communication system (2G), also known as GSM, is a well-established cellular, wireless communications technology whereby base transceiver stations" (equivalent to the Node Bs of the 3G system) and "mobile stations" (user equipment) can transmit and receive voice and packet data. Several base transceiver stations are controlled by a Base Station Controller (BSC), equivalent to the RNC of 3G systems.

Communications systems and networks are developing towards a broadband and mobile system. The 3rd Generation Partnership Project has proposed a Long Term Evolution (LTE) solution, namely, an Evolved Universal Mobile Telecommunication System Territorial Radio Access Network, (E-UTRAN), for a mobile access network, and a System Architecture Evolution (SAE) solution, namely, an Evolved Packet Core ( EPC), for a mobile core network. An evolved packet system (EPS) network provides only packet switching (PS) domain data access so voice services are provided by a 2G or 3G Radio Access Network (RAN) and circuit switched (CS) domain network. User Equipment( UE) can access a CS domain core network through a 2G/3GRAN such as the (Enhanced Data Rate for GSM Evolution, EDGE) Radio Access Network (GERAN) or a Universal Mobile Telecommunication System Terrestrial Radio Access Network ( UTRAN), and access the EPC through the E-UTRAN.

Some User Equipments have the capability to communicate with networks of differing radio access technologies. For example, a user equipment may be capable of operating within a UTRAN and within an E-UTRAN.

Lower power (and therefore smaller coverage area) cells are a recent development within the field of wireless cellular communication systems. Such small cells are effectively communication coverage areas supported by low power base stations. The terms "picocell" and "femtocell" are often used to mean a cell with a small coverage area, with the term femtocell being more commonly used with reference to residential small cells. Small cells are often deployed with minimum RF (radio frequency) planning and those operating in consumers' homes are often installed in an ad hoc fashion.

The low power base stations which support small cells are referred to as Access Points (AP) with the term Home Node B (HNB) or Evolved Node Node B (eHNB) identifying femtocell Access Points. Each small-cell is supported by a single Access Point. These small cells are intended to augment the wide area macro network and support communications to multiple User Equipment devices in a restricted, for example, indoor environment. An additional benefit of small cells is that they can offload traffic from the macro network, thereby freeing up valuable macro network resources An HNB is an Access Point that provides a wireless interface for user equipment connectivity. It provides a radio access network connectivity to a user equipment (UE) using the so-called luh interface to a network Access Controller, also known as a Home Node B Gateway (HNB-GW). One Access Controller (AC) can provide network connectivity of several HNBs to a core network.

Typical applications for such Access Points include, by way of example, residential and commercial locations, communication hotspots', etc., whereby Access Points can be connected to a core network via, for example, the Internet using a broadband connection or the like. In this manner, small cells can be provided in a simple, scalable deployment in specific in-building locations where, for example, network congestion or poor coverage at the macro-cell level may be problematic.

Thus, an AP is a scalable, multi-channel, two-way communication device that may be provided within, say, residential and commercial (e.g. office) locations, hotspots' etc, to extend or improve upon network coverage within those locations. Although there are no standard criteria for the functional components of an AP, an example of a typical AP for use within a 3GPF 3G system may comprise Node-B functionality and some aspects of Radio Network Controller (RNC) functionality as specified in 3GPF TS 25.467. These small cells are intended to be able to be deployed alongside the more widely used macro-cellular network and support communications to UEs in a restricted, for example in-building', environment.

Herein, the term "small cell" means any cell having a small coverage area and includes "picocells" and "femtocells." In some applications, an Access Point serving a small cell is provided with a network listen device which detects broadcast signals of neighbouring cells.

In order to use network resources more efficiently, it has been proposed that multiple Core Network Operators share a RAN. In one such network sharing arrangement called Multi-Operator Core Network (MOCN), multiple Core Networks belonging to different Operators share a common RAN.

A Public Land Mobile Network (PLMN) run by an Operator has its own unique identifier (referred to herein as a PLMNID) which is composed of a Mobile Country Code (MCC) and a Mobile Network Code (MNC). A base station (or node B or Access Point, for example) which is either controlled by the Operator or shared with other Operators, broadcasts a Location Area Identity (LAI) which is composed of the PLMNID of the Operators it supports and a Location Area Code (LAO). The LAC may be unique to a particular base station/node B/Access Point. If two Operators have agreed to co-operate ie.to provide communications services to UEs which are subscribed to the other Operator, then their PLMNIDs are said to be equivalent.

A PLMNID which is broadcast in particular cell may be received by neighbouring cells whose Access Points are provided with network listen devices and also by a UE located in that cell.

A handover from a source cell to a target cell may be initiated when the strength or quality of the signal from the serving (source) cell becomes too poor to maintain the communication, for example. A UE measures broadcast signals from neighbouring cells and reports the measurements to its serving cell which may identify a best candidate cell (generally the closest) to handover to. In the small cell example, UE measurements are reported to the Home Node B supporting the cell.

A neighbour cell list contains: inter a/ia, cell ID, frequency and scrambling code information for all of the cells whose coverage area overlaps with the UE's current serving cell, An Access Point may be provisioned with a neighbour cell list prior to deployment In other arrangements, an Access Point may not be provisioned with a neighbour cell list but instead, it may configure the list itself based on measurements of signals (broadcast by neighbouring cells) detected by its network listen module.

The 3GPP 23.252 MOCN specification permits relocating to a MOCN configured neighbour.

Regarding mobility, 3GPP Radio Resource Control Specification 25.331 provides a method to enable cell reselection, enhancing the SIB 18 (System Information Block) with multiple PLMN lists of the neighbours. However 3GPP specifications do not address relocation/handover from a MOCN -supporting HNB/RNC.to a MOCN-supporting HNB/RNC with different MOCN configuration or to a non-MOON-supporting HNB/RNC. 3GPP TS 23. 251 specifies that in the case of relocation, the selected target core network operator should be the same as the one in use. This is accomplished by not changing the serving PLMN if the PLMN in use is supported n the target cell. If the PLMN in use is not supported in the target cell the RNC selects the target PLMN based on either (i) pre-configured information in the RNC or BSC, or (ii) the SNA (Shared Network Area) Access Information IE (see TS 25.413 [13]) provided by the SGSN. This has the drawback of requiring the configuring and coordinating of data in both core network and radio access network.

Summary of the invention

Accordingly, the invention seeks to mitigate, alleviate or eliminate the above-mentioned disadvantage.

Aspects of the invention provide network elements, a wireless communication system and methods therefor as described in the appended claims.

According to a first aspect of the invention there is provided a method for identifying a target cell for handover of a wireless communication unit from a source cell in a wireless communication system comprising a plurality of cells, each cell having one or more PLMNIDs associated therewith, the method including; at a network element supporting the source cell, storing the PLMNIDs of neighbouring cells, receiving from the wireless communication unit, measurement reports containing identities of neighbouring cells which are candidate sells for handover, comparing the stored PLMNIDs of a best candidate neighbouring cell with the PLMNID in use in the source cell and if there is a match, handing over to the best candidate neighbouring cell, otherwise initiating a handover to a next best candidate neighbouring cell with the same FLMNID as is in use in the source cell.

If there are no candidate cells having the same PLMNID as the source cell, then the method may be extended by including the further step of initiating handover to a candidate neighnouring cell which has an equivalent PLMMID.

If there is no candidate cell with an equivalent PLMNID then a target cell may be selected based on some pre-configured information as is provided for in 3GBP TS 23.251.

A best candidate cell and a next best candidate cell for handover may have properties as defined by the 3GPP standards and can be generally understood to be those neighbouring cells whose broadcast signals, as received by the wireless communication unit, are of sufficient strength or quality to enable communications to be established.

The cells comprising the plurality of cells in the wireless communication system may be macrocells or small cells or a mixture of the two.

The invention enables core networks with different radio access network (RAN) sharing arrangements or no sharing at all to co-exist and provide mobility of a User Equipment (UE) therebetween. The invention further ensures that no handover is attempted to a cell that does not support a UE's choice of FLMNID if there is a potential cell with the UE's choice (or an equivalent PLMNID) and therefore ensures continuity of sessions in a MOGN configuration. The invention provides the flexibility for cells to co-exist with neighbours having different PLMN configurations. For example a Home Node B can hand over to a non-shared network or to a network that has a different RAN sharing and so a different FLMN arrangement. A further advantage of the invention is that the handover messaging as specified in the MOCN specifications of 3 GPF 23.251 and 3 GFP 25.413 is not changed in any way.

According to a second aspect of the invention, there is provided an apparatus for identifying a target cell for handover of a wireless communication unit from a source cell in a wireless communication system comprising a plurality of cells, each cell having one or more PLMNIDs associated therewith, the apparatus including; a memory for storing the PLMNIDs of neighbouring cells, and a signal processor arranged to receive from the wireless communication unit, measurement reports containing identities of neighbouring cells which are candidate sells for handover and arranged to compare the PLMNIDs of the best candidate neighbouring cell with the PLMNID in use in the source cell and if there is a match, initiate a handover to the best candidate neighbouring cell, otherwise initiate a handover to a next best candidate neighbouring cell with the same PLMNID as is in use in the source cell.

The apparatus may be included in a radio network controller (RNC) which may receive the measurement reports via a base station or node B, for example. The memory in the RNC may be pre- provisioned with a list of cell IDs and the associated PLMNIDs that they support and may be also pre-provisioned with PLMNID equivalents.

Alternatively, the apparatus may be included in a Home Node B. The memory in the Home Node B may be pre-provisioned with a list of cell IDs and the associated PLMNIDs that they support and may be also pre-provisioned with PLMNID equivalents. As an alternative to pre-provisioning the memory in the Home Node B, the Home Node B may be provided with a network listen device which listens to signals broadcast by neighbouring cells. The signal processor may then be arranged to extract the cell ID and associated PLMNIDs from the broadcast signals from neighbouring cells and to store them in the memory.

The memory and for signal processor of the apparatus may be implemented in one or more integrated circuits.

According to a third aspect of the invention there is provided a wireless communication system arranged to support the method and apparatus of the above aspects.

According to a fourth aspect of the invention, there is provided tangible computer program product having an executable computer program code stored thereon for execution by a processor to perform a method in accordance with the first aspect.

The tangible computer program product may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, an Electrically Erasable Programmable Read Only Memory and a Flash memory.

These and other aspects, features and advantages of the invention will be apparent from, and elucidated with reference to, the embodiments described hereinafter.

Brief Description of the Drawings

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Like reference numerals have been included in the respective drawings to ease understanding.

FIG. I illustrates a part of a wireless communication system operating in accordance with an example embodiment. and FIG. 2 is a flow chart of an example of a method for identifying a handover target cell.

Detailed Description

The inventive concept finds particular applicability in a cellular communication system comprising multiple operators sharing a common radio access network.

Those skilled in the art will recognize and appreciate that the specifics of the specific examples described are merely illustrative of some embodiments and that the teachings set forth herein are applicable in a variety of alternative settings. For example, since the inventive concepts do not depend on any particular radio access technology, it is envisaged that the inventive concepts can be applied to 2G, 3G and LTE technologies, for example. As such, other alternative implementations within cellular communication systems conforming to different standards are contemplated and are within the scope of the various teachings described. Furthermore, although the example embodiments illustrate a system comprising small cells connected to one HNB-GW, the invention can be applied to small cells radio network systems with separate HNB-GW, macrocell systems or systems comprising a mixture of small and macrocells.

Referring now to FIG.1, an example of part of a wireless communication system operating in accordance with embodiments of the invention is illustrated and indicated generally at 100 and comprises a multi-operator core network configuration sharing a radio access network.

Three core networks 101, 102 and 103 are operated by three different operators A, B and C. Each core network has a distinct PLMNID. These are PLMNA, PLMNB and PLMNC for each of the core networks 101, 102, 103 respectively. The core networks 101-103 share a single radio access network which includes three small neighbouring cells served by Home Node Bs 104, 105, 106 which are all linked to a HNB-GW 107 which in turn, provides the interface to the core networks as is conventional.

In this example, a first Home Node B (HNB) 104 is a MOON-supporting HNB which supports core networks A, B and C as represented by the dashed lines in FIG. 1 connecting the HNB 104 with the three core networks 101, 102, 103. A second HNB 105 is a non--MOON-supporting HNB and supports core network B only as represented by the dashed line connecting HNB 105 and core network 102. A third HNB 106 is a MOCN-supporting HNB and supports core networks B and C as represented by the dashed lines connecting HNB 106 and core networks 102 and 103.

A first User Equipment (UE) 108 is a subscriber to core network C. A second UE 109 is a subscriber to core network A. The first HNB 104 is provided with a network listen device 110, a memory 111 and a signal processor 112.

Initially, the memory 111 in the first HNB 104 is provisioned with the PLMNIDs of the core networks that it supports, namely PLMNA, PLMNB and FLMNC. Also, the memory 111 is provisioned with the IDs of PLMNs which are equivalent. In this specific example, PLMNA and PLMNB. are designated as being equivalents.

A first example of the operation of the system of FIG. I will now be described with reference to FIG.1 and FIG. 2 which is a flowchart of a method for identifying a target cell for handover.

At 201, the network listen device 110 receives broadcast messages from the second and third Home Node Bs 105, 106. From these broadcasts, the signal processor 112 extracts the cell ID associated with each of the second and third HNBs 105, 106 and the PLMNIDs which are supported by each of the second and third HNBs 102, 103. At 202, this extracted data is stored in the memory 111.

Initially, the UE 108 is registered with the small cell supported by the first HNB 104. Thus the HNB 104 can be considered to be a "source" cell as far as the UE 108 is concerned and the second and third HNBs 105, 106 can be considered to be candidate handover target sells for the UE 108. As is conventional, the exchange of messages between the UE 108 and the first HNB 104 during the registration process permits the HNB 104 to determine which of the core network operators the UE subscribes to. So in this example, as the UE 108 is a subscriber of core network C, the PLMNID in use while the UE 109 is registered with the first HNB 104 is PLMNC.

On deciding that a handover to another cell is required, the first HNB 104 requests the UE 108 to send measurement reports of neighbouring cells. At 203, the measurement reports are received by the HNB 104 and, as is conventional, contain the cell IDs of neighbouring cells which are candidate target sells for a handover from the source cell. A candidate cell with the highest signal strength received by the UE 108 may be defined as the "best" candidate, for example. From the measurement reports, the signal processor 112 identifies the best handover candidate cell and links its cell ID with supported FLMNIDs stored in the memory 111.

At 204, the signal processor 112 compares the FLMNIDs supported by the best candidate target cell with the PLMIID currently in use (in the source cell). If the PLMNID currently in use is supported by the best candidate target cell, then the HNB 104 initiates a handover to the best candidate target cell at 205. The handover process and associated messaging proceeds in accordance with conventional techniques.

In this example, the best candidate cell is that supported by HNB 105. However, HNB 105 does not support PLMNC only PLMNB. Therefore, at 206 the signal processor 112 identifies the next best candidate cell from the measurement reports, determines the PLMNIDs that it supports (from the data in the memory 111) and compares them with the PLMNID in use. In this example, the next best candidate cell is the one supported by HNB 106 which does support PLMNC. Therefore, at 207, the HNB 104 initiates a handover procedure to HNB 106.

In a second example of operation, the UE 109 (which subscribes to core network A) is initially registered with the first HNB 104. The Measurement reports received from the UE 109 at the HNB 104 reveal that the best candidate cell is that served by HNB 105. The result of the comparison stages in the signal processor 112 at 204 and 206 reveal that neither of the candidate cells support PLMNA. So in this case, the signal processor 112 inspects the memory 111 to determine if there is an equivalent PLMNID for PLMNA, that is, a PLMNID that is interchangeably useable for the PLMNID in use in the source cell. In this example, a pre-configured equivalent to PLMNA is PLMNB. The best candidate to support PLMNB is HNB 106. So at 208, the HNB 104 initiates a handover to HNB 106, being the best candidate cell with an equivalent PLMNID. The handover process proceeds in accordance with conventional techniques.

Each of the second and third HNBs 105 and 106 may be equipped with a memory and signal processor having the same functionality as that of the memory 111 and signal processor 112 of the first HNB 104, so that they may perform a similar handover target identification method in situations where either of the second or third HNBs act as a source cell.

The signal processing functionality of the embodiments of the invention, particularly the signal processing module 112 may be achieved using computing systems or architectures known to those who are skilled in the relevant art. Computing systems such as, a desktop, laptop or notebook computer, hand-held computing device (PDA, cell phone, palmtop, etc.), mainframe, server, client, or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment can be used. The computing system can include one or more processors which can be implemented using a general or special-purpose processing engine such as, for example, a microprocessor, microcontroller or other control module.

The computing system can also include a main memory, such as random access memory (RAM) or other dynamic memory, for storing information and instructions to be executed by a processor. Such a main memory also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor. The computing system may likewise include a read only memory (ROM) or other static storage device for storing static information and instructions for a processor.

The computing system may also include an information storage system which may include, for example, a media drive and a removable storage interface. The media drive may include a drive or other mechanism to support fixed or removable storage media, such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a compact disc (CD) or digital video drive (DVD) read or write drive (R or RW), or other removable or fixed media drive. Storage media may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that is read by and written to by media drive. The storage media may include a computer-readable storage medium having particular computer software or data stored therein.

In alternative embodiments, an information storage system may include other similar components for allowing computer programs or other instructions or data to be loaded into the computing system. Such components may include, for example, a removable storage unit and an interface, such as a program cartridge and cartridge interface, a removable memory (for example, a flash memory or other removable memory module) and memory slot, and other removable storage units and interfaces that allow software and data to be transferred from the removable storage unit to computing system.

The computing system can also include a communications interface. Such a communications interface can be used to allow software and data to be transferred between a computing system and external devices. Examples of communications interfaces can include a modem, a network interface (such as an Ethernet or other NIC card), a communications port (such as for example, a universal serial bus (USB) port), a PCMCIA slot and card, etc. Software and data transferred via a communications interface are in the form of signals which can be electronic, electromagnetic, and optical or other signals capable of being received by a communications interface medium.

In this document, the terms computer program product', computer-readable medium' non-transitory computer-readable medium' and the like may be used generally to refer to tangible media such as, for example, a memory, storage device, or storage unit. These and other forms of computer-readable media may store one or more instructions for use by the processor comprising the computer system to cause the processor to perform specified operations. Such instructions, generally referred to as computer program code' (which may be grouped in the form of computer programs or other groupings), when executed, enable the computing system to perform functions of embodiments of the present invention. Note that the code may directly cause a processor to perform specified operations, be compiled to do so, and/or be combined with other software, hardware, and/or firmware elements (e.g., libraries for performing standard functions) to do so.

In an embodiment where the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into computing system using, for example, removable storage drive. A control module (in this example, software instructions or executable computer program code), when executed by the processor in the computer system, causes a processor to perform the functions of the invention as described herein.

Furthermore, the inventive concept can be applied to any circuit for performing signal processing functionality within a network element. It is further envisaged that, for example, a semiconductor manufacturer may employ the inventive concept in a design of a stand-alone device, such as a microcontroller of a digital signal processor (DSP), or application-specific integrated circuit (ASIC) and/or any other sub-system element.

It will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to a single processing logic. However, the inventive concept may equally be implemented by way of a plurality of different functional units and processors to provide the signal processing functionality. Thus, 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 organisation.

Aspects of the invention may 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 or configurable module components such as FPGA devices. Thus, 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.

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, for example, 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 performed 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. In addition, singular references do not exclude a plurality. Thus, references to a', an', first', second', etc. do not preclude a plurality.

Claims (11)

1. Claims 1. A method (200) for identifying a target cell for handover of a wireless communication unit (108) in a wireless communication system (100) comprising a plurality of cells, each cell having one or more PLMNIDs associated therewith, the method including; at a network element (111) supporting the source cell, storing (202) the FLMNIDs of neighbouring cells, receiving (203) from the wireless communication unit, measurement reports containing identities of neighbouring cells which are candidates for handover, comparing (204) the stored F'LMNIDs of a best candidate neighbouring cell with the PLMNID in use in the source cell, and if there is a match, initiating (205) a handover to the best candidate neighbouring cell, otherwise initiating (207) a handover to a next best candidate neighbouring cell with the same PLMNID as is in use in the source cell.
2. 2. The method of claim 1 including, at the network element (111), initiating a handover to a candidate neighbouring cell which has an equivalent PLMNID when no next best candidate neighbouring cell with the same PLMNID as is in use of the source cell is available.
3. 3. The method of either preceding claim wherein the source cell and the neighbouring cells are small cells served by Home Node Bs.
4. 4. An apparatus (111, 112) for identifying a target cell for handover of a wireless communication unit (108) from a source cell in a wireless communication system (100) comprising a plurality of cells, each cell having one or more PLMNIDs associated therewith, the apparatus including; a memory (111) for storing the PLMNIDs of neighbouring cells, and a signal processor (112) arranged to receive from the wireless communication unit, measurement reports containing identities of neighbouring cells which are candidates cells for handover, and arranged to compare the PLMNIDs of the best candidate neighbouring cell with the PLMNID in use in the source cell and if there is a match, initiate a handover to the best candidate neighbouring cell, otherwise initiate a handover to a next best candidate neighbouring cell with the same PLMNID as is in use in the source cell.
5. 5. The apparatus of claim 4 wherein the memory (111) contains a list of cell identities and the associated PLMNIDs that each cell supports.
6. 6. The apparatus of claim 4 claim 5 wherein the memory contains a list of FLMNID equivalents. -12-
7. 7. The apparatus of claim 4 including a network listen device which detects broadcast signals from neighbouring cells and wherein the signal processor (112) is arranged to extract the cell identities and associated PLMNIDs of neighbouring cells from the broadcast signals and store them in the memory (11
8. 8. The apparatus of any of claims 4 to 7 wherein the signal processor (112) and memory (111) are implemented in one or more integrated circuits.
9. 9. A wireless communication system (100) arranged to support a method as claimed in any of claims 1 to 3 or an apparatus as claimed in any of claims 4 to 8.
10. 10. A tangible computer program product having an executable computer program code stored thereon for execution by a processor to perform a method in accordance with claim 1.
11. 11. The tangible computer program product of claim 10 comprising at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, an Electrically Erasable Programmable Read Only Memory and a Flash memory.