The field of this invention relates to network elements, a cellular communication system and methods therefor. The invention is applicable to, but not limited to, a network element for supporting communication within at least one cell of a cellular communication system, and a method for preserving billing plans as a wireless communications unit relocates from one cell to another.

Background of the Invention

Wireless communication systems, such as the 3 ^rd 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 (UMTS™), developed by the 3 ^rd Generation Partnership Project (3GPP™) (www.3qpp.org). The 3 ^rd 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 B's of the 3G system) and "mobile units" (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.

Lower power (and therefore smaller coverage area) cells are currently referred to as 'small' cells, with the term femto cells typically reserved to refer to a residential small cell. Small cells are effectively communication coverage areas supported by low power base stations (otherwise referred to as Access Points (APs) with the term Home Node B's (HNBs) or evolved Home Node B's (HeNB) identifying femto cell access points. These small cells are intended to augment the wide area macro network and support communications to UEs in a restricted, for example indoor, environment. An additional benefit of small cells is that they offload of traffic from the macro network to small cells, thereby freeing up valuable macro network resources. Typical applications for such small cells include, by way of example, residential and commercial (e.g. office) locations, communication 'hotspots', etc., whereby AP's 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 at the macro-cell level may be problematic.

. As will be appreciated by the skilled artisan, an access point is a communication element that facilitates access to a communication network via a communication cell, such as a small cell. One application is that an AP may be purchased by a member of the public and installed in their home. The AP may then be connected to an AP controller over the owner's broadband Internet connection.

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 3GPP 3G system may comprise Node-B functionality and some aspects of Radio Network Controller (RNC) functionality as specified in 3GPP TS 25.467. The AP 104 communicates with User Equipments (UE), via a wireless interface.

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 a voice service may be 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 (Radio Access Network, GERAN) or a Universal Mobile Telecommunication System Terrestrial Radio Access Network (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.

Further, some currently available user equipments include the capability of providing to the user several different communications services simultaneously. For example, the user may be able to conduct a voice call and browse the internet at the same time. One radio access bearer can be used for the voice call and a separate radio access bearer can be used for data internet browsing. A radio access bearer can be considered to be a channel to transport a circuit switched data stream or a packet switched data stream between the user equipment and the core network.

User equipments are also capable of relocating from one cell's area of coverage to that of another, neighbouring cell in a process known as handover (or handout). Relocation may be initiated because the user of the user equipment moves out of a source cell area of coverage and into a target, neighbour cell's area. Alternatively, the user equipment may relocate to another cell in order to access a service which is not available in its current cell.

Communications Services attract charges which are set by the Network Operators who may choose to operate various billing plans and charge different tariffs which may depend on the service provided, the time of day that they are used or on other agreements made between an Operator and its customers.

For example, say an operator supplies to a customer a UE which has 3G(UTRAN) and LTE (E-UTRAN) capability. The user has an access point (HNB) installed in his house which provides femto-cell coverage for the UE and can link voice calls into a macro-cellular 3G Network supported by the Operator. Such use attracts a discounted tariff but the UE is configured to prefer LTE for certain data applications. The Operator wishes to maintain the discounted tariff if the UE hands out from the 3G-HNB for the purposes of needing an LTE radio access bearer and to ensure that the UE is directed back to the HNB when that bearer is no longer needed. However, current hand out procedures cannot achieve this.

In another example, the Operator provides, via a 3G-HNB with a local gateway and Selective

Internet Protocol Traffic Offload (SIPTO) capability, direct internet access for the UE without traversing the operators core network at a special tariff (eg. free). This internet protocol stream will be broken when the UE hands out from the 3G-HNB to a macro-cell and the UE may restart it on the new cell. However, the UE user may not know or notice that a handout has taken place and the network will treat this as a new call and the UE user will be billed at normal rates and the special tariff will no longer apply.

Hence, there is a need for maintaining a billing plan when a UE relocates from one cell to another. Summary of the invention

Accordingly, the invention seeks to mitigate, alleviate or eliminate one or more of the above mentioned disadvantages, either singularly or in any combination.

According to a first aspect of the invention, there is provided a method for maintaining a billing plan in a cellular communication system wherein the method comprises the steps of supporting communications to and from a wireless communication unit in a source cell, and transmitting billing information relating to the source cell to a target cell when handing over the wireless communication unit from the source cell to the target cell and wherein the transmitting step comprises transmitting a handover message which includes a billing Service Area Identity (SAI) relating to the source cell.

According to an optional feature, the billing SAI may be included in a last visited cell list.

According to a second aspect of the invention, there is provided a method for maintaining a billing plan in a cellular communication system, the system supporting communications to and from a wireless communication unit, wherein the method comprises receiving, at a target cell, a handover message transmitted by a source cell, wherein the handover message contains billing information which relates to the source cell and comprising the further step of decoding the handover message to extract a billing Service Area Identity relating to the source cell. The extracted billing Service Area Identity may be used in billing information for the wireless communication unit whilst supporting communication therewith while it is in the target cell.

In this manner, the invention allows a particular tariff (or billing plan) for communications services to be maintained when a user equipment moves from one cell in a cellular communication system to another and with the minimum of processing.

The invention can also permit re-direction or handout upon termination of a service using a particular radio access bearer when that bearer is no longer required.

According to a third aspect of the invention, there is provided a network element for supporting communication to and from a wireless communication unit in a source cell of a cellular communication system wherein the network element includes signal processing logic arranged to insert billing information relating to the source cell into a handover message for transmission to a target cell and wherein the billing information comprises a billing service area identity which is associated with a last visited cell identity.

According to a fourth aspect of the invention, there is provided a network element for supporting communication to and from a wireless communication unit in a cellular communication system wherein the network element includes signal processing logic arranged to decode a handover message received from a source cell and to extract billing information relating to the source cell from the handover message and wherein the billing information comprises a billing service area identity which is associated with a last visited cell identity.

Optionally, the signal processing logic may be further arranged to prioritise the source cell as a target cell for a subsequent handout.

According to a fifth aspect of the invention, there is provided a wireless communication system adapted to support the aforementioned network element functions or the aforementioned method steps.

In further optional embodiments, the wireless communication system may be adapted to support handover from one macro-cell to another macro-cell, from one small cell to another small cell and between macro-cells and small cells.

In a further optional embodiment, the wireless communication system may be adapted to support handover between different radio access networks which may employ different radio access technologies.

According to a sixth aspect of the invention there is provided an integrated circuit comprising at least one digital signal processing module adapted to configure a message for transmission in a cellular communication system. The message comprises a handover message which includes billing information, the billing information comprising a billing Service Area Identity, which is associated with a last visited cell identity.

According to a seventh aspect of the invention, there is provided a integrated circuit comprising at least one digital signal processing module adapted to decode a handover message received in a cellular communication system and for extracting a Billing Service area Identity which is associated with a last visited cell identity. According to an eighth aspect of the invention, there is provided a tangible computer program product having executable code stored therein for programming signal processing logic to perform a method for employing handover messages in a cellular communication system. The tangible computer program product further comprises code for configuring a handover message for transmission to include billing information comprising a billing Service Area Identity which is associated with a last visited cell identity.

According to a ninth aspect of the invention, there is provided a tangible computer program product having executable code stored therein for programming signal processing logic to perform a method for employing handover messages in a cellular communication system. The tangible computer program product further comprises code for decoding a received handover message and for extracting a billing Service Area Identity which is associated with a last visited cell identity.

Either of the tangible computer program products in accordance with the eighth and ninth aspects of the invention 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, and Erasable Programmable Read Only Memory (EPROM), 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.1 illustrates a part of a cellular communication system operating in accordance with an example embodiment.

FIG.2 is a call flow diagram of an example method for preserving a billing plan during a handover within a cellular communication system. Detailed Description

The inventive concept finds particular applicability in a cellular communications system but supports a number of overlapping communication coverage areas, a communications system that comprises a combination of small cells and macro-cells and also one where more than one radio access technology is employed, eg 3G, 2G, LTE.

Referring now to FIG.1 , an example of part of a wireless communication system adapted in accordance with embodiments of the invention is illustrated and indicated generally at 100 and comprises a 3G (UTRAN) small cell (cell A), a 3G (UTRAN) macro-cell (cell B) and a LTE (E-UTRAN) small cell (cell C)

A core network of the Wireless Communications System of FIG.1 includes a Gateway General Packet Radio System (GPRS) Support Node (GGSN) 101 and a Serving GPRS Support Node (SGSN) 102. The GGSN 101 or SGSN 102 is responsible for interfacing the wireless communication system 100 with a packet data network, for example a Public Switched Data Network (PSDN), (such as the internet) or a Public Switched Telephone Network (PSTN). The SSGN 102 performs a routing and tunnelling function for traffic to and from the cells A, B and C while the GGSN 101 links with external packet networks. In an Evolved Packet Core, the equivalent node to a GSGN is a Packet Gateway (P-GW) and in this example, they are shown combined.

The small cell A is linked to the SGSN by way of lu-PS and luh links via a 3G Home Node B Gateway 103. The Home Node B Gateway 103 also connects to a Mobile Switching Centre (MSC) 104 via a luCS link. The small cell A is served by an Access Point (AP) 105. The access point 105 is coupled to a signal processing logic module 106 whose function is to be described herebelow. A user equipment UE107 is attached to the small cell A.

The 3G macro-cell B is served by a Node B 108 which is controlled by a Radio Network Controller (RNC) 109. The RNC 109 is linked to the SGSN 102 and to the Mobile Switching Centre 104. The node B 108 is also provided with a signal processing module 1 1 1 whose functionality is similar to the module 106 associated with the access point 105.

LTE small cell C is linked to the SSGN 102 through a Mobility Management Entity (MME) 1 12. Small cell C is also connected with the P-GW 101 through the MME 1 12 and a Service Gateway S- GW1 13. The MME handles signalling control and mobility while the S-GW 1 13 is a local anchor point for user data. In a similar fashion to the 3G small cell A, the LTE small cell C is served by an access point 1 14. The access point 1 14 is also provided with a signal processing module 1 15 whose functionality is similar to the module 106 associated with the access point 105.

The MSC 104, GGSN 101 , SGSN 102 and S-GW 1 13 are all configured to report billing information to an Operator of the Wireless Communication System 100. This functionality is represented schematically in FIG.1 by a "billing domain" module 1 16 and its connections to the MSC 104, GGSN 101 and SGSN 102.

In the example of FIG.1 , the UE 107 is attached to small cell A and communicating over the UTRAN. The services being provided to the UE 107 whilst it is attached to the small cell A attract a particular tariff and the billing information will be gathered by the Network Operator in the billing domain 1 16. The user of the UE 107 now wishes the UE 107 to provide a new service, an internet connection for example. The UE 107 has been configured to preferably access this particular service over an LTE (E-UTRAN) network. In order to do this, the UE 107 has to be handed over from the current (source) cell A to another (target) cell which is within reception range and which operates within a LTE network. In this example, the UE 107 needs to be handed over from cell A to cell C. However, the network operator wants to ensure that the tariff charged to the user of the UE 107 while the UE 107 is attached to cell C is the same as when it is attached to cell A. Therefore, the billing plan which applies in cell A must be made known to cell C.

Conventionally, during the course of a handover between 3G radio access technologies a transparent container is constructed by the source cell's sub systems which has the format of the target radio access technology. The transparent container typically contains details of the radio access bearers that a UE is currently using (in the source cell) along with other profile details of the UE itself. All these details enable the target network elements eg RNC, node B to configure the required resource appropriately.

In the case of an LTE target cell, the relevant transparent container is the source eNB-to- target eNB transparent container as specified in 3GPP TS 36.413.

In the case of a UTRAN target, the transparent container is the source RNC-to-target RNC transparent container as specified in TS 25.413.

For a GERAN target, the transparent container is the old (source) base station subsystem-to- new (target) base station subsystem transparent container as specified in TS 48.008.

Additionally, from 3GPP release 8 onwards, the transparent containers which are constructed in UTRAN and LTE networks have an Information Element (IE) called "UE History Information". This particular IE provides details of the last visited cell that the UE has been served by, in an active state, prior to being handed over to a target cell. Such "last visited cell" details include cell type, cell ID and the PLMN (Public Land Mobile Network) ID. Hence the target cell is able to identify the source cell when it receives the UE History Information.

Conventionally, each cell in a network has a Service Area Identity (SAI) for billing associated with it. It may have other SAI's for emergency calls and broadcasts, for example. A SAI is configured for each cell so it may be localised to an area, possibly a single cell, by the core network. Conventionally, billing information for calls in any particular cell may be tagged to that cell's billing SAI.

In the embodiment of FIG.1 , the signal processing logic 106 attaches cell A's Service Area Identity, tagged with its billing information, as an IE which is associated with the most recently visited cell in the UE History Information. The access point 105 then transmits this modified UE History Information to the target cell C, via the HNB gateway 103. This UE History Information is received by the He node B access point 1 14 in cell C and passed to his associated signal processing logic module 1 15 for decoding.

The signal processing logic module 1 15 subsequently determines that billing SAI details have been provided for the last visited cell in the most recently visited cell list. From this, it infers that the source cell (cell A) supports some preferred tariff mechanism. The target cell can then use this supplied SAI (from the source cell) in billing information for the UE on the target cell (cell C). This information is reported to the billing domain 1 16 and the user of the UE 107 is charged for services in cell C as he would be charged if he had received them in cell A.

The signal processing modules 106 and 1 15 have the same capabilities so that the reverse situation can apply where cell C is the source cell and cell A is the target cell. In this case, the module 1 15 in cell C configures the UE History Information and module 105 in cell A decodes it.

Similarly the processing logic module 1 1 1 associated with the node B 108 of cell B can be provided with the same functionality as signal processing modules 108 and 1 15. Alternatively, the functionality of the signal processing modules 106, 1 1 1 , 1 15 can be incorporated in other network elements such as a radio network controller 109 or the HNB-GW 103.

Signal processing logic in a target cell which receives the SAI of a source cell can further be configured to prioritise the source cell for a subsequent hand out in cases where the new bearer is no longer required or in other cases such as a Circuit Switched Fall Back (CSFB), for example. Referring now to FIG, 2, this illustrates the call flow 200 for a 3G macro-cell to LTE macro-cell handover in a cellular communication network and employing the methods of an embodiment of the invention.

Such methods permit a billing plan used in a source cell to be preserved when the UE is handed over from a source cell to a target cell.

Specifically a UE 201 is initially attached to a source cell controlled by a source RNC 202 which is linked to a serving node "Source SGSN" 203 which in turn can communicate with a PDN Gateway 204.

A target eNodeB 205 is linked to a target MME 206 which is linked to a Serving Gateway 207 which in turn can communicate with the PDN Gateway 204. The MME 206 is also linked to the Source SGSN 203.

At step 210, a decision is made to at the Source RNC 202 to perform an inter-RAT Handover between UTRAN and E-UTRAN, i.e. to hand over the UE 201 from the source cell to the target cell.

Conventionally the process is started by sending a Relocation Required message from the source RNC to its Serving Gateway GPRS Node (SGSN 203) at step 21 1.

In accordance with this exemplary embodiment the SAI (indicating the billing information) of the source cell is added to the transparent container which is contained in the Relocation Required message.

On receiving this modified Relocation Required message the Source SGSN 203 may check the permissions on allowing the handover (e.g. does the UE subscription allow it to access LTE networks) with the HSS 209 and forward the request (including the SAI) to the target MME 206 at step 212.

Depending on how user data forwarding is configured the target MME 206 may set up a link to a Target Serving Gateway (208) during steps 213 and 214.

At step 215 the Target MME 206 sends the Handover Request message to the Target eNodeB 205

Hence the target eNodeB 205 now has details that reference a special billing plan that was used whilst the UE 201 was attached to the source cell.

The target eNodeB may accept the handover if sufficient resources exist with a Handover Request Acknowledge in step 216 containing details of the radio bearers that can be established.

At this point radio access bearers are established (steps 217 and 218) and the target MME forwards the response to the source RNC 202 following the conventional process (step 219) .

Subsequently the UE is released from the source cell, reconfigures its radio and attaches to the Target eNodeB leading to the completion of the handover process.

While the UE 201 remains attached to a cell of the target eNodeB the SAI of the source cell is used to help derive the billing information which is reported into the relevant billing domain of the Operator of the target cell.

Although the above embodiments of the invention describe a method and means to preserve a billing plan when handing over between two small cells or two macro-cells, it is envisaged that the inventive concept is not restricted to such handovers situations and that other cell combinations are possible. The signal processing functionality of the embodiments of the invention, particularly the signal processing logic of the modules 106, 1 1 1 and 1 15 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' 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 signal 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.

Thus, an improved method and apparatus for facilitating maintainance of a billing plan when a user equipment relocates from one cell to another within a cellular communication system have been described, wherein the aforementioned disadvantages with prior art arrangements have been substantially alleviated.