WO2013023849A1

WO2013023849A1 - Enabling macro cell to femto cell handover

Info

Publication number: WO2013023849A1
Application number: PCT/EP2012/063705
Authority: WO
Inventors: Luis Lopes; Alexander Vesely
Original assignee: Nokia Siemens Networks Oy
Priority date: 2011-08-12
Filing date: 2012-07-12
Publication date: 2013-02-21

Abstract

A method is provided, which includes connecting to a macro cell of a communications network, sending an enquiry from a control node of the macro cell to a control node of a femto cell under coverage of the macro cell enquiring which femto cells under coverage of the macro cell are allowed to be accessed, and providing information regarding the cells under coverage of the macro cell that are allowed to be accessed.

Description

DESCRIPTION

TITLE ENABLING MACRO CELL TO FEMTO CELL HANDOVER

FIELD OF THE INVENTION

The invention generally relates to a method and apparatus and in particular but not exclusively to a method and apparatus for enabling macro cell to a smaller cell handover in a communications network. By way of example only, the smaller cell may be a femto cell. Some embodiments may relate to enablement of macro cell to smaller cell handover during an active connection for legacy user equipment connected to the network.

BACKGROUND

A mobile network operator may provide femto cells connected to its network, which can be used in the home or in a business and provide the advantage of improved coverage indoors. A femto cell can be part of a closed subscriber group CSG so that only a limited number of users (mobile stations) which are members of the closed subscriber group are allowed to access the network via each femto cell.

Each femto cell is accessible via a home Node B (HNB) and a home Node B gateway

(HNB-GW) may control one or more femto cells.

A macro cell of a communications network controlled by a radio network controller (RNC) may have several femto cells under its radio coverage, which are accessible via HNBs and controlled by one or more HNB-GWs. The several HNBs may be controlled by one or more HNB-GWs. Femto cells under radio coverage of a macro cell include having a neighbour relationship between the cells or include that the radio coverage area of macro and femto cell overlap.

At the moment, there are problems in the handover of a legacy (for example 3GPP Release 7) user equipment (UE) from the macro cell to a femto cell during an active connection, since the macro cell is not aware of the underlying available femto cells within its radio coverage.

It may not be realistic to expect that the macro RNC would have a full neighbour list of every femto cell in the vicinity of every macro cell that it controls. Since the number of potential neighbouring femto cells may exceed the maximal number of entries in the Neighbouring Cell List (NCL), some femto cells may have to be excluded from the list to guarantee enough addressing space for macro cells. The femto cells may be deployed and switched on/off at random, and hence such a list cannot be easily provided or maintained.

There may also be a problem in the number of primary scrambling channels (PSCs), which are needed for unique identification of a neighbour cell in the macro system. Since femto cell deployment should not affect PSC planning in the macro/pico network, a limited number of PSCs may be dedicated to femto cells. This means that femto cells may reuse the same PSCs within a small area and generally within the coverage of a macro cell (this may be because of the small femto cell size, reduced number of PSC choices, and non-centralized PSC selection).

If the femto cells are operating in closed mode, a legacy UE cannot know whether it is a member of the closed subscriber group and may trigger the initiation of a handover which will be rejected by the femto cell system (access control may be performed by a gateway that is placed between the macro and femto systems).

Thus if the macro cell does not have a neighbour list that includes the femto cells, the macro cell will not know which specific femto cell is being reported by the UE, since the reports are based on the PSC only. Further if the femto cell is operating in a closed mode, the macro RNC may have no information on whether the UE is a member or not of that femto cell. This may result in unnecessary and unsuccessful handovers.

SUMMARY

According to an aspect, there is provided a method comprising: receiving information regarding at least one smaller cell that is allowed to be accessed by at least one specific user equipment; and using said information to determine for at least one specific user equipment one of said at least one smaller cells to which said at least one specific user equipment is to be handed over.

The method may comprise sending a request to a control node associated with at least one smaller cell, for information on which of said smaller cells are allowed to be accessed by at least one given communication device.

The at least one smaller cell may be completely overlapping, partially overlapping or adjacent to a larger cell.

The smaller cell may be a femto cell. The larger cell may be a macro cell.

At least one smaller cell may be controlled by the larger cell.

The information may be at least one of received and used by a controller of a larger cell. The information may be received from a controller of said at least one smaller cell.

The information is may be received over a direct interface between the controller of the larger cell and the controller of the at least one smaller cell.

The method may comprise storing said information. The method may comprise providing at least some of said information to a user equipment.

The user equipment may be a legacy user equipment.

The method may comprise receiving information indicative of a handover failure of a user equipment with said information on said smaller cells.

The method may comprise sending a first handover request, said first handover request being such that a handover failure response will be generated, and responsive to said sending of the first handover request receiving said handover failure indication and said information on said smaller cells.

According to another aspect, there is provided a method, comprising: obtaining information regarding at least one smaller cell that is allowed to be accessed by at least one specific user equipment; and causing said information to be sent to an entity making a handover decision for said at least one specific user equipment.

The information may comprise at least a part of a neighbour cell list.

The information may comprise information identifying a respective smaller cell and scrambling code information associated with said respective smaller cell.

The information may comprises access mode information for a respective smaller cell. The information may comprise distinguishing information for distinguishing one smaller cell from another smaller cell.

The distinguishing information may comprise information related to radio conditions of transmission and/or reception at the smaller cell for distinguishing one smaller cell from other smaller cell.

The distinguishing information may comprise one or more of: information one or more neighbouring larger cells, observed time difference between a respective smaller cell and one or more larger cells, and power of one or more larger cell, for example the power with which signals are transmitted into the cell.

According to another aspect, there is provided a computer program product including a program comprising software code portions being arranged , when run on a processor, to perform the any of the above methods.

According to another aspect, there is provided an apparatus comprising: means for receiving information regarding at least one smaller cell that is allowed to be accessed by at least one specific user equipment; and means for using said information to determine for at least one specific user equipment one of said at least one smaller cells to which said at least one specific user equipment is to be handed over.

The apparatus may comprise means for sending a request to a control node associated with at least one smaller cell, for information on which of said smaller cells are allowed to be accessed by at least one given communication device. The at least one smaller cell may be completely overlapping, partially overlapping or adjacent to a larger cell.

The smaller cell may be a femto cell. The larger cell may be a macro cell.

At least one smaller cell may be controlled by the larger cell.

The receiving means may be for receiving said information from a controller of said at least one smaller cell.

The receiving means may be for receiving said information from a direct interface with said controller of the at least one smaller cell.

The apparatus may comprise means for storing said information.

The apparatus may comprise means for providing at least some of said information to a user equipment.

The user equipment may be a legacy user equipment.

The receiving means may be for receiving information indicative of a handover failure of a user equipment with said information on said smaller cells.

The apparatus may comprise means for sending a first handover request, said first handover request being such that a handover failure response will be generated , and responsive to said to sending of the first handover request, said receiving means is for receiving said handover failure indication and said information on said smaller cells.

According to another aspect, there is provided apparatus comprising: means for obtaining information regarding at least one smaller cell that is allowed to be accessed by at least one specific user equipment; and means for causing said information to be sent to an entity making a handover decision for said at least one specific user equipment.

The information may comprise at least a part of a neighbour cell list.

The information may comprise access mode information for a respective smaller cell The information may comprise distinguishing information for distinguishing one smaller cell from another smaller cell.

The distinguishing information may comprise one or more of: information one or more neighbouring larger cells, observed time difference between a respective smaller cell and one or more larger cells, and power of one or more larger cell, for example power with which signals are transmitted into the cell.

According to another aspect, there is provided an apparatus, said apparatus comprising at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to with the at least one processor cause the apparatus at least to: receive information regarding at least one smaller cell that is allowed to be accessed by at least one specific user equipment; and use said information to determine for at least one specific user equipment one of said at least one smaller cells to which said at least one specific user equipment is to be handed over.

The at least one memory and computer program code may be configured to with the at least one processor means to send a request to a control node associated with at least one smaller cell, for information on which of said smaller cells are allowed to be accessed by at least one given communication device.

The at least one smaller cell may be completely overlapping, partially overlapping or adjacent to a larger cell. The smaller cell may be a femto cell. The larger cell may be a macro cell. At least one smaller cell may be controlled by the larger cell.

The at least one memory and computer program code may be configured to with the at least one processor to receive said information from a controller of said at least one smaller cell.

The at least one memory and computer program code may be configured to with the at least one processor to receive said information from a direct interface with said controller of the at least one smaller cell.

The at least one memory may store said information.

The at least one memory and computer program code may be configured to with the at least one processor provide at least some of said information to a user equipment.

The user equipment may be a legacy user equipment.

The at least one memory and computer program code may be configured to with the at least one processor to receive information indicative of a handover failure of a user equipment with said information on said smaller cells.

The at least one memory and computer program code may be configured to with the at least one processor send a first handover request, said first handover request being such that a handover failure response will be generated, and responsive to said to sending of the first handover request, receiving said handover failure indication and said information on said smaller cells.

According to another aspect, there is provided an apparatus, said apparatus comprising at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to with the at least one processor cause the apparatus at least to: obtain information regarding at least one smaller cell that is allowed to be accessed by at least one specific user equipment; and cause said information to be sent to an entity making a handover decision for said at least one specific user equipment.

The information may comprise at least a part of a neighbour cell list. The information may comprise information identifying a respective smaller cell and scrambling code information associated with said respective smaller cell.

The information may comprise access mode information for a respective smaller cell.

The information may comprise distinguishing information for distinguishing one smaller cell from another smaller cell.

According to another aspect, there is provide apparatus comprising: a handover determining unit configured to receive information regarding at least one smaller cell that is allowed to be accessed by at least one specific user equipment and to use said information to determine for at least one specific user equipment one of said at least one smaller cells to which said at least one specific user equipment is to be handed over.

The apparatus may comprise a transmitter configured to send a request to a control node associated with at least one smaller cell, for information on which of said smaller cells are allowed to be accessed by at least one given communication device.

The smaller cell may be a femto cell. The larger cell may be a macro cell.

At least one smaller cell may be controlled by the larger cell.

The handover determining unit may be configured to receive said information from a controller of said at least one smaller cell.

The handover determining unit may be configured to receive said information from a direct interface with said controller of the at least one smaller cell.

The apparatus may comprise at least one memory configured to store said information. The apparatus may comprise a transmitter configured to provide at least some of said information to a user equipment.

The user equipment may be a legacy user equipment.

The handover determining unit may be configured to receive information indicative of a handover failure of a user equipment with said information on said smaller cells.

The handover determining unit may be configured to send a first handover request, said first handover request being such that a handover failure response will be generated, and responsive to said to sending of the first handover request, said handover determining unit is configured to receive said handover failure indication and said information on said smaller cells.

According to another aspect, there is provided apparatus comprising: a handover information collector configured to obtain information regarding at least one smaller cell that is allowed to be accessed by at least one specific user equipment and to cause said information to be sent to an entity making a handover decision for said at least one specific user equipment.

The information may comprise at least a part of a neighbour cell list.

According to another aspect, there is provided a controller for controlling a larger cell, said controller comprising apparatus as discussed above.

The controller may be a radio network controller and/or a base station.

According to another aspect, there is provided a controller for controlling at least one smaller cell, said controller comprising apparatus as discussed above.

The controller may be a gateway. The gateway may be a HNB-GW.

According to another aspect, there is provided a user equipment configured to connect to a larger cell of a communications network and comprising a receiver configured to receive information regarding smaller cells that said user equipment is allowed to access.

According to another aspect, there is provided a method, which includes connecting to a macro cell of a communications network, sending an enquiry from a control node of the macro cell to a control node of a femto cell under coverage of the macro cell enquiring which cells under coverage of the macro cell are allowed to be accessed , and providing information regarding the cells under control of the macro cell that are allowed to be accessed.

In this way, handover of a legacy user equipment can be achieved during an active connection from the macro cell to a cell under its control, since information is available as to which cells are allowed to be accessed. This can be achieved without any involvement of the user equipment or modification of the user equipment. Preferably, sending the enquiry from the control node of the macro cell to the control node of the femto cell under coverage of the macro cell includes enquiring as to which cells controlled by the control node of the cell under control of the macro cell are allowed to be accessed by a specific user equipment connecting to the macro cell.

Then provid ing information may include providing information as to which cells controlled by the control node of the cell under control of the macro cell are allowed to be accessed by the specific user equipment.

Preferably, the information is provided to the control node of the macro cell by the control node of the cell under control of the macro cell. The information may be provided over a direct interface between the control node of the macro cell and the control node of the cell under control of the macro cell. A direct interface can be established between the control nodes so that UE-specific information may be exchanged between them. This means that UE-specific information can be readily provided to the control node controlling the macro cell as to which cells under control of the macro cell a legacy U E is allowed to access, thereby facilitating handover during an active connection of a legacy UE with the macro cell.

In one embodiment, the information is stored by the macro cell.

In one embodiment, the information is further provided by the control node of the macro cell to a user equipment connecting to the macro cell of the communications network.

Advantageously the user equipment is a legacy user equipment.

The cell under control of the macro cell may be a femto cell.

Preferably, the method further includes using the provided information to create a neighbour cell list. The received UE-specific information may also be used to create a tailored neighbour cell list, which can then be sent to a (legacy) user equipment accessing the macro cell so that it knows which cells controlled by the macro cell it is allowed to access.

In this way, legacy user equipment can be provided with a tailored neighbour cell list containing exactly those cells that they can access. There can be an exchange of neighbour cell information between the control nodes (for example H NB-GW and RNC) upon request if there is a closed subscriber group cell of the legacy UE within the current macro cell coverage.

According to another aspect, there is provided a control node for a macro cell of a communications network. The control node includes a transmitter configured to send an enquiry to a control node of a cell under control of the macro cell enquiring which cells under coverage of the macro cell are allowed to be accessed. The control node also includes a receiver, which is configured to receive information regarding the cells under control of the macro cell that are allowed to be accessed.

Preferably, the transmitter is configured to send the enquiry so as to enquire which cells controlled by the control node of the cell under control of the macro cell are allowed to be accessed by a specific user equipment connecting to the macro cell. Then the receiver may be configured to receive information as to which cells controlled by the control node of the cell under control of the macro cell are allowed to be accessed by the specific user equipment.

The control node may further include a memory unit configured to store the information. In one embodiment, the transmitter is further configured to transmit the information to a user equipment accessing the macro cell. The control node may be configured to use the information regarding the cells under control of the macro cell that are allowed to be accessed to create a neighbour cell list, which can be tailored to a specific user equipment and sent to that user equipment so that it knows which cells it is allowed to access.

Preferably, the control node is configured to establish a direct interface with the control node of the femto cell under coverage of the macro cell. This enables exchange of UE-specific information between the control nodes, which allows soft handover during an active connection to be achieved more easily.

Preferably, the control node is a radio network controller (RNC).

According to another aspect, there is provided a control node for controlling a cell under control of a macro cell of a communications network. The control node includes a receiver configured to receive an enquiry enquiring which cells under coverage of the macro cell are allowed to be accessed. A transmitter is provided, which is configured to provide information regarding the cells under control of the macro cell that are allowed to be accessed.

Preferably, the control node is a home Node B gateway (HNB-GW).

According to another aspect, there is provided user equipment (UE), which is configured to connect to a macro cell of a communications network. The UE includes a receiver configured to receive information regarding cells under control of the macro cell that it is allowed to access.

According to another aspect, there is provided a computer program product including a program comprising software code portions being arranged , when run on a processor, to perform connecting to a macro cell of a communications network, sending an enquiry from a control node of the macro cell to a control node of a cell under control of the macro cell enquiring which cells under coverage of the macro cell are allowed to be accessed, and providing information regarding the cells under control of the macro cell that are allowed to be accessed.

Preferably, the computer program product includes a computer-readable medium on which the software code portions are stored, and/or wherein the program is directly loadable into a memory of the processor.

A number of different aspects have been described. Different features from different aspects may be combined.

Embodiments will now be described, by way of example only, with reference to specific examples, and to the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a simplified schematic block diagram of a communications network;

Figure 2 is a simplified schematic block diagram of a radio network controller;

Figure 3 is a simplified schematic block diagram of a home Node B gateway;

Figure 4 is a flow chart illustrating a method according to an embodiment;

Figure 5 is a message flow diagram illustrating a method according to an embodiment; Figure 6 is a message flow diagram illustrating a method according to an embodiment; Figures 7a and b show message flow diagrams of another embodiment;

Figures 8a and b show a message flow diagram of another embodiment; and

Figure 9 shows a message flow of another embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Figure 1 shows a wireless communications network, which includes a macro cell 1 and a femto cell 2, which is under coverage of the macro cell 1 . In Figure 1 , one femto cell is shown under the coverage of the macro cell. In practice more than one femto cell may be provided under the coverage area of the macro cell. Additionally or alternatively, one or more femto cells may partly overlap the coverage of the macro cell. Additionally or alternatively, one or more femto cells may neighbour the coverage area of the macro cell.

The macro cell 1 and femto cell 2 are in the radio access network (RAN) part of the communications network.

A femto cell may be an open cell where any UE may join that cell, a closed cell where only some permitted UEs are allowed to join the cell or a hybrid cell. A hybrid cell is partially an open cell and partially a closed cell.

Although in the following examples, a UMTS network is illustrated, the communications network described could also be any other wireless communications network, for example LTE, WiMax, etc.

A mobile station or user equipment (UE) 7 may access the macro cell 1 via a Node B 3 controlled by an RNC 4 over an lub interface and access to the femto cell 2 is provided via a home Node B (H N B) 5 controlled by a home Node B gateway (H N B-GW) 6 over an l uh interface.

There is a direct interface lur established between the RNC 4 and the HNB-GW 6 over which information can be exchanged between these two control nodes. The RNC 4 and HNB- GW 6 are interfaced with the core network (CN) part of the communications network. In some embodiments, alternatively or additionally communication between the RNC and HNB-GW may be via the core network.

Figures 2 and 3 show the RNC 4 and HNB-GW 5, respectively, in more detail. The RNC 4 includes a transmitter 8, a receiver 9 and at least one memory M1 . The transmitter 8 may comprise one or more processors 12 and the receiver 9 may comprise one or more processors 13. In some embodiments, the transmitter and receiver may alternatively or additionally share one or more processors. Alternatively or additionally one or more processors may be provided outside the transmitter and receiver. The one or more processors may operate in conjunction with one or more memories. The one or more memories may comprise the at least one memory M1 and/or memory provided in the transmitter and or receiver. In some embodiments, the at least one memory M1 may be provided in the transmitter and/or receiver.

I n some embodiments, the RN C may comprise an apparatus having a handover determining unit. This handover determining unit may be provided as part of the receiver and/or part of the transmitter and/or separate from the receiver and transmitter. The handover determining unit may be provided as a discrete unit or may be provided in a distributed fashion. The handover unit may be implemented in hardware and/or software.

The HNB-GW includes a transmitter 10, a receiver 1 1 and at least one memory M2. The transmitter 10 may comprise one or more processors 14 and the receiver 1 1 may comprise one or more processors 15. In some embodiments, the transmitter and receiver may alternatively or additionally share one or more processors. The one or more processors may operate in conjunction with one or more memories. The one or more memories may comprise the at least one memory M2 and/or memory provided in the transmitter and or receiver. I n some embodiments, the at least one memory M2 may alternatively or additionally be provided in the transmitter and/or receiver.

In some embodiments, the H NB-GW may comprise an apparatus having a handover information collector. This handover information collector may be provided as part of the receiver and/or part of the transmitter and/or separate from the receiver and transmitter. The handover information collector may be provided as a discrete unit or may be provided in a distributed fashion. The handover information collector may be implemented in hardware and/or software.

An embodiment will now be described with reference to the flow diagram in Figure 4. In the following examples, the UE 7 is a legacy UE; that is, the specification of the UE is older than that of the current specification of the communications network (for example the UE is 3GPP Release 7, whereas the network is 3GPP Release 1 1 ).

In Step S1 , the legacy UE 7 connects to the macro cell 1 . The UE 7 is a member of a closed subscriber group/hybrid cell located in the coverage area of that macro cell 1.

In Step S2, the RNC 4 sends an enquiry to the HNB-GW 6 over the interface lur as to which femto cells under coverage of the macro cell 1 are allowed to be accessed. The RNC 4 sends the enquiry to the HNB-GW 6 about permitted CSG/hybrid cells under the coverage of th e servi ng macro cel l 1 of the U E 7 based on the I nternationa l Mobi le Su bscriber Identity/International Mobile Equipment Identity (I MSI/I MEI) or any other subscriber-specific identity of the UE 7. Additionally, the RNC 4 provides also the macro cell 1 Cell-ID.

The HNB-GW 6 performs this check based on its database where final Access Control for legacy UEs takes place.

In response to the enq uiry from the RN C 4 , in Step S3 the H N B-GW 6 provides information to the RNC 4 over the interface lur regarding the cells for which the UE 7 is allowed access to under the particular serving macro cell 1 .

The RNC 4 stores this information and/or uses the information to create a neighbour cell list (NCL) tailored to the UE 7 and provides the NCL to the UE 7. This information is received by the receiver R of the UE 7.

The HNB-GW 6 provides UE-specific information to the RNC 4 as to which femto cells controlled by the HNB-GW 6 would be relevant for the UE 7 (that the UE 7 is allowed to access) so that the RNC 4 may produce a UE- specific neighbour cell list on the serving macro cell.

UE-specific information delivery from the HNB-GW 6 to the RNC 4 takes place over the direct interface lur. The received information can then be used by the RNC 4 for NCL content definition.

The direct interface lur between the RNC 4 and the HNB-GW 6 may also be used for exchange of non UE-specific information between these two control nodes, for example general neighbor cell information, such as which of the neighbouring femto cells under coverage of the macro cell 1 are controlled by a particular HNB-GW.

The method described above is illustrated in more detail in the message flow diagram of Figure 5.

The UE 7 establishes a radio connection with the macro cell 1 . The RNC 4 then sends an access request to the H N B-GW 6 over the interface l ur. This request may include the serving macro cell 1 Cell-I D, Global Cell ID (GCI) or any other identity identifying the serving macro cell 1 . Additionally, the request may include the IMSI or IMEI of the UE 7. The HNB-GW 6 checks the access capabilities of the indicated UE 7 to the femto cells in the access request and sends cell parameters and access capabilities to the RNC 4. The HNB-GW 6 can perform the check by matching the provided serving macro N B 3 Cell-I D or GCI with the Cell-IDs provided by the H N B 5 and stored in the H N B-GW 6. The H N B 5 measurements of the overlaying macro cells can be performed during a Network Listening Mode (NLM) procedure performed during the start-up of a H N B 5. The H N B-GW then sends an access response message to the RNC 4, which includes the femto cells that the UE 7 is allowed to access, as well as cell parameters and access capabilities, for example the CSG membership(s) of the UE 7 or the Primary Scrambling Codes values of the underlying HNB 5. The RNC 4 stores the cell parameters related to the UE 7 in the memory M 1 and includes accessible femto cells into a tailored NCL for the UE 7. The RNC 4 then sends or updates the tailored NCL to the UE 7. The information may be stored in the RNC 4 of the macro cell 1 , as well in memory related to the macro cell 1 or related to the UE 7. This may allow the RNC 4 to avoid further enquiries related to the UE 7 towards the H NB-GW 6 of the femto cell 2 under control of the macro cell 1 when the U E 7 moves within the macro cells of the RNC 4 e.g., if UE 7 moves back into this macro cell 1 of the RNC 4.

In an alternative embodiment, illustrated in the message flow diagram in Figure 6, the exchange of information between the RNC 4 and the H NB-GW 6 takes place via the core network CN, rather than over the interface lur.

The UE 7 establishes a radio connection with the macro cell 1 . The RNC 4 then sends an access request to the core network CN, which in turn sends the access request to the HNB- GW 6. The HNB-GW 6 checks the access capabilities of the indicated UE 7 to the femto cells in the access request and sends cell parameters and access capabilities to the core network CN. The core network CN then sends an access response message to the RNC 4, which includes the femto cells that the U E 7 is allowed to access, as well as cell parameters and access capabilities, for example the CSG membership(s) of the UE 7. The RNC 4 stores the cell parameters related to the UE 7 in the memory M1 and includes accessible femto cells into a tailored NCL for the UE 7. The RNC 4 then sends or updates the tailored NCL to the UE 7.

Reference is now made by way of example only to Figures 7 to 9 which show further embodiments. In these further embodiments, the macro RNC is provided with all the information necessary for a HO decision. Additional information is provided to the RNC which allows the macro RNC to decide whether a reported cell is indeed the femto cell that the UE is a member of, or just a closed cell in the same area using the same PSC. Thus some embodiments are able to determine which of two femto cells using the same PSC is the correct femto cell for handover.

In the following embodiments, the lur (deployed as an interface between the RNC and femto gateway HN B-GW) is used for signalling to address some of the issues mentioned earlier. Alternatively or additionally in some embodiments, it may be possible to realize the same functions using signalling via the core network.

Reference is made to Figure 7a and 7b which shows a first signalling flow.

In step S1 , a UE is attached to a macro cell of a RNC via a serving NodeB S-NB.

In step S2, the RNC determines the permanent or unique identifier of the attached UEs. This identifier may be an IMSI or any other suitable identifier. This identifier may be determined from the UE itself or a core network node.

I n step S3, the RNC of the macro cell requests from the H NB gateway over the lur interface, for a UE that is currently served by the RNC (and for which an identifier is provided), the following data • List of cell identities I Ds (this may include open, closed and/or hybrid cells), access mode and PSCs for those cells for which the UE is a member in the HNB- GW and/or the list of cells which are open or hybrid. In other words for a given UE those femto cells to which the UE is permitted to access are provided to the RNC. Optionally a CSG ID may be provided in some embodiments.

• For each cell so called fingerprint information is also requested. This information is information which is used to correctly identify the given femto cell. This information may comprise one or more of the following:

the neighbour macro cell to the cell (there will be at least one macro cell and in some cases there may be more than one neighbour macro cell);

OTD (observed time difference) between the cell and each of the neighbour macro cells above; and

any other fingerprint information e.g. typical power of each neighbour macro cell measured in the femto cell or the like. The typical power may be a pilot power, for example the power with which signals are transmitted into the cell.

It should be noted that the dashed line of step S2 shows an alternative transmission path for the request from the RNC to the HN B-GW. In the alternative transmission path, the request may go from the RNC to the CN node to the HN B-GW. In an alternative, the routing may be via a node of the mobile communication core network e.g., a serving GPRS support node SGSN, a gateway GPRS support node GGSN, a mobile switching center MSC, mobile switching gateway, a serving gateway S-GW, to the HNB-GW. Any other suitable routing may be used in alternative embodiments.

Step S4 schematically represents the determination of the information requested by the RNC. The information may be determined in response to the request from the RNC, may be previously determined by the HNB-GW or a combination of the two.

In step S5, the HNB-GW provides a response to the RNC directly via the lur interface or a s s h o w n i n d o t t e d l i n e s v i a a C N n o d e . T h e r e s p o n s e c o m p r i s e s one or more of femto cell-IDs, access mode (is the cell open, closed or hybrid), PSCs for each cell, and in addition if the access mode is closed or hybrid then UE membership is indicated), and for each reported femto cell one or more of radio fingerprint information for identification e.g., neighbour macro cell(s), OTD between femto and macro cell(s), pilot power of macro cell(s), or the like

From the response from the gateway, the macro RNC knows specifically the subset of PSCs for which a handover should be initiated for that UE in each area. The RNC can modify locally the neighbour list of the UE, and receive measurement reports to indicate the presence of closed or hybrid cells that may be those that the UE is a member of or are accessible to the UE. This is shown in Figure 7b. In step T1 , the RNC stores the reported HNB cells accessible for the UE, and applies information for radio resource control of the UE. The relevant information will be forward to the UE and NodeB(s).

In step T2, the RNC sends the updated neighbour Cell list or measurement request or both to the UE. This request will comprise an adjusted list of neighbour cells including macro cells and the femto cells which are accessible to the UE.

In step T3, the UE performs measurements on the neighbour cells in the neighbour cell list.

I n step T4, the U E sends a measurement report to the RNC. This includes radio measurement results for the neighbour cells in the neighbour cell list. The report will include information identifying the cells for which the measurement results have been provided.

In step T5, the RNC will store and evaluate the reported measurement results. The RNC may trigger appropriate actions such as handover to a femto cell.

In step T6, the RNC sends either directly or via a CN node (shown in dashed lines) a handover request to the HNB-GW. This handover request may have the identifier of the UE to be handed over as well as the identity of the target cell.

In step T7, handover of the target femto cell is prepared. This may involve the HNB-GW as well as the source and target cells.

In step T8 a handover response is sent by the HN B-GW to the RNC either directly or indirectly via a CN node (shown in dashed lines). This will include the UE identifier and an indication about the success of the handover request or handover preparation in the HNB-GW.

Reference is made to Figures 8a and b which shows another signal flow of another embodiment.

The H N B-GW has a database of femto cells with rad io fingerprint information . Accordingly, in step A1 , radio fingerprint information is determined for each femto cell (HNB) within H NB-GW coverage. This may include any of the information discussed in relation to Figure 7 such as neighbour macro cell(s), OTD between HNB and macro cell(s), pilot power of macro cell(s) or the like. This information may be determined during HNB start up or determined during HNB operation. This information may be kept synchronised between the HNB and HNB- GW during operation. In other words the gateway coordinates or concentrates the radio fingerprint information from all the femto cells connected to the HNB-GW.

In this embodiment, the RNC requests in step A2 the femto gateway provides the full database of femto cell/OTDs (or other radio fingerprint information stored therein) including their access mode. The request of A2 may be limited to requesting database information related to the indicated femto cell(s) only. Femto cell indication may comprise femto cell identifier, PSC, and radio fingerprint information. This request is sent directly to the HNB-GW or via a CN node (shown in dashed lines). I n step A3 , the H N B-GW prepares a response including this H N B cell and radio fingerprint information.

In step A4, the HNB-GW sends the response to the RNC (either directly or via the CN node). This response will be an indexed list of HNB cell-Ids with their access mode, PSCs, and radio fingerprint information related to cell identification.

In step A5, the RNC stores this information.

In step A6, an update of a radio fingerprint of a femto cell is determined.

In step A7, the RNC receives (either directly or via the CN node) an unsolicited HNB cell update notification which comprises update information. This information comprises a list of H NB cell-Ids with their access mode, PSCs, and radio fingerprint information related to the identified cells. This may include all the information again or may only include the information which has changed. This may be repeated periodically after a pre-defined time period or upon modification of the exchanged information.

In step A8, the new information is stored by the RNC.

Reference is now made to Figure 8b. Steps B1 , B2 and B3 are the same or similar to previously described steps S1 , S2 and S3 respectively.

In step B4, the HNB-GW determines the HNB cells under the control of HNB-GW which UE has access to (closed, hybrid, open) and reports in step B5 the accessible HNB cells to the RNC. This may be the HNB cell Ids or HNB indexes to the list previously provided.

This is then followed by the steps of Figure 7b.

In this embodiment, for hybrid cells the macro RNC can initiate a HO reliably and with full knowledge of the target. For closed cells, an additional handshake may be required, where the macro RNC would request the HNB-GW to indicate, for a particular UE, which cells the UE is a member of or are accessible to the UE. The HNB-GW would then provide a list of indices to the previously sent list or of cell identifications.

Reference is now made to a further embodiment shown in Figure 9. Again a signal flow is shown. Steps C1 to C3 are the same or similar to steps S1 to S3 respectively.

However, in this embodiment, the macro RNC (assumed with no a-priori knowledge of UE-specific closed cell list or with no a-priori knowledge of femto cells which the UE may obtain access to) would include at least some of the PSCs known to be used by closed cells in the UE's neighbour list. When a HO is triggered to such a cell (the Handover request), the RNC starts a HO preparation procedure towards the target system or starts to collect information on accessible femto cells of the UE.

If RNC does not yet have information of femto cells accessible to the UE, it may send a Handover request to the HNB-GW directly or via a core network node indicating a dedicated, pre-defined target femto cell identification which has a special meaning to the HNB-GW which supports this embodiment. A supporting H NB-GW would determine a list of accessible femto cells for the indicated UE and provide the list of cells back to the RNC including the fingerprint information, access mode, cell identifiers and further information as in similar steps S5, A4.

A non supporting HNB-GW would identify the femto cell and try to prepare a handover for the UE. If the indicated target cell is not present in the HNB-GW, a failure will be reported back and RNC may not adjust the NCL of the UE with femto cells. Preferably, the dedicated, pre-defined femto cell identifier is not used for a deployed or installed HNB in HNB-GW or is a femto cell identifier which has no UE members.

In step C4, a determination is made of HN B cells under the control of the H NB-GW which the UE has access to (closed, hybrid, open) and accessible HNB cells are reported to the RNC. This may apply as well if the indicated target femto cell is not accessible to the indicated UE or if the indicated target cell identifier is a dedicated, pre-defined femto cell identifier with the special meaning according to this embodiment.

A handover response is sent in step C5 from the HNB-GW to the RNC (either directly or indirectly via the CN node). If the UE is a member of the target CSG, the HO will succeed. If on the other hand , the access control fails at the H N B-GW, the target H N B-GW will send a rejection message, and include in this message the list of cells that the UE can access (with additional macro cell and radio fingerprint information as described above). Thereafter the macro RNC has the information to avoid such failed preparations in the future for this UE.

Note that this process may be accelerated if the RNC initiates a handover towards a HNB-GW which it knows has no chance of succeeding (e.g. if a logical cell ID is defined at the HNB-GW which has no U Es as mem bers, and this is known at the RN C th rough e.g . configuration).

Some embodiments may provide (at the source RNC) information on (i) cells that the UE can access (at an ID level), and (ii) for these cells, the associated physical characteristics that allow positive identification of such cells by a legacy UE. This supports the use case where there is a large number of femto cells (of which the UE can access only a few), sharing a small number of PSCs.

In some embodiments, complete information (per UE) may only be initially available in the HNB-GW, and at the end of the process, it is fully available in the source RNC (which can then use it to modify the neighbour list of an active UE).

This is then followed by the steps of Figure 7b.

It should be appreciated that the signal flows are by way of example only and in alternative embodiments, the signalling may include additionally signalling, omit some signalling and/or occur in a different order.

Where the signalling from a HNB-GW to the RNC is via a mobile communication core network CN node, there may in fact be more than one node. The CN node or node may be different nodes depending on the core network structure e.g., one or more of a serving GPRS support node SGSN, a gateway GPRS support node GGSN, a mobile switching center MSC, a mobile switching gateway, a serving gateway S-GW.

The above embodiments have been described in the context of legacy UEs. It should be appreciated that some embodiments may be used with non legacy UEs.

The above embodiments have been described in relation to femto cells. However it should be appreciated that alternative embodiments may be used additionally or alternatively with other types of cell such as pico or micro cells.

The above described embodiments have had a number of the functions relating to handover control being controlled or performed by an RNC. It should be appreciated that in alternative embodiments, at least some of those functions may be performed in the Node B or other access node. At least some of the functions relating to handover may additionally or alternatively be performed in the gateway.

For the purpose of the embodiments as described hereinabove, it should be noted that

- method steps may be implemented as software code portions and run using one or more processors in the relevant entity in conjunction with one or more memories, may be software code independent and can be specified using any known or future developed programming language as long as the functionality defined by the method steps is preserved;

- generally, any method step is suitable to be implemented as software and/or by hardware without changing the idea of the embodiments and its modification in terms of the functionality implemented;

- method steps and/or devices, units or means likely to be implemented as hardware components at the above-defined apparatuses, or any module(s) thereof, (e.g., devices carrying out the functions of the apparatuses according to the embodiments as described above) are hardware independent and can be implemented using any known or future developed hardware technology or any hybrids of these, such as MOS (Metal Oxide Semiconductor), CMOS (Complementary MOS), BiMOS (Bipolar MOS), BiCMOS (Bipolar CMOS), ECL (Emitter Coupled Logic), TTL (Transistor-Transistor Logic), etc., using for example ASIC (Application Specific IC (Integrated Circuit)) components, FPGA (Field-programmable Gate Arrays) components, CPLD (Complex Programmable Logic Device) components or DSP (Digital Signal Processor) components;

- devices, units or means (e.g. the above-defined apparatuses and network devices, or any one of their respective units/means) can be implemented as individual devices, units or means, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device, unit or means is preserved;

- an apparatus may be represented by a semiconductor chip, a chipset, or a

(hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a fu nctionality of an apparatus or mod ule, instead of bei ng hardware implemented, be implemented as software in a (software) module such as a computer program or a com puter prog ra m prod uct com prising executable software code portions for execution/being run on a processor;

- a device may be regarded as an apparatus or as an assembly of more than one apparatus, whether functionally in cooperation with each other or functionally independently of each other but in a same device housing, for example.

In general, it is to be noted that respective functional blocks or elements according to above-described aspects can be implemented by any known means, either in hardware and/or software, respectively, if it is only adapted to perform the described functions of the respective parts. The mentioned method steps can be realized in individual functional blocks or by individual devices, or one or more of the method steps can be realized in a single functional block or by a single device.

Generally, any method step is suitable to be implemented as software or by hardware. Devices and means can be implemented as individual devices, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device is preserved. Such and similar principles are to be considered as known to a skilled person.

The terms "user equipment (UE)" and "mobile station" described herein may refer to any mobile or stationary device including a mobile telephone, smart phone, personal data assistant (PDA), a computer, a mobile broadband adapter, a USB stick for enabling a device to access to a mobile network, etc.

In the above example, Node Bs have been described as the wireless access node, which is one example of a base station. Other examples of access nodes are the evolved Node Bs (eNBs) and base stations of systems that are based on technologies such as wireless local area network (WLAN) and/or WiMax (Worldwide Interoperability for Microwave Access).

The exemplary embodiments of the invention have been described above with reference to a 3GPP UMTS network. However, the above-described examples may be applied to any wireless communications network.

Although the invention has been described hereinabove with reference to specific embodiments, it is not limited to these embodiments and no doubt further alternatives will occur to the skilled person, which lie within the scope of the invention as claimed. LIST OF ABBREVIATIONS

CSG Closed Subscriber Group

CGI Cell Global Identity

GPRS General Packet Radio Service

HNB Home Node B

HNB-GW Home Node B Gateway

IMEI International Mobile Equipment Identity

IMSI International Mobile Subscriber Identity

LTE Long Term Evolution

NCL Neighbour Cell List

NLM Network Listening Mode

RNC Radio Network Controller

UE User Equipment

UMTS Universal Mobile Telecommunications System

3GPP 3^rd Generation Partnership Project

Claims

1 . A method comprising:

receiving information regarding at least one smaller cell that is allowed to be accessed by at least one specific user equipment; and

using said information to determine for at least one specific user equipment one of said at least one smaller cells to which said at least one specific user equipment is to be handed over.

2. A method as claimed in claim 1 , comprising sending a request to a control node associated with at least one smaller cell, for information on which of said smaller cells are allowed to be accessed by at least one given communication device.

3. A method as claimed in claims 1 or 2, wherein the information is at least one of received and used by a controller of a larger cell

4. A method according to any of claims 1 to 3, wherein the information is received from a controller of said at least one smaller cell.

5. The method according to claims 3 and 4, wherein the information is received over a direct interface between the controller of the larger cell and the controller of the at least one smaller cell.

6. A method as claimed in any preceding claim, comprising providing at least some of said information to a user equipment.

7. A method as claimed in any preceding claim, comprising receiving information indicative of a handover failure of a user equipment with said information on said smaller cells.

8. A method as claimed in claim 7, comprising sending a first handover request, said first handover request being such that a handover failure response will be generated, and responsive to said sending of the first handover request receiving said handover failure indication and said information on said smaller cells.

9. A method, comprising:

obtaining information regarding at least one smaller cell that is allowed to be accessed by at least one specific user equipment; and

causing said information to be sent to an entity making a handover decision for said at least one specific user equipment.

10. A method as claimed in any preceding claim, wherein the information comprises at least a part of a neighbour cell list.

1 1 . A method as claimed in any preceding claim, wherein said information comprises information identifying a respective smaller cell and scrambling code information associated with said respective smaller cell.

12. A method as claimed in any preceding claim, wherein said information comprises access mode information for a respective smaller cell

13. A method as claimed in any preceding claim, wherein said information comprises distinguishing information for distinguishing one smaller cell from another smaller cell.

14. A method as clai med in clai m 13, wherein said distinguishing information comprises information related to radio conditions of transmission and/or reception at the smaller cell for distinguishing one smaller cell from other smaller cell.

15. A computer program product including a program comprising software code portions being arranged, when run on a processor, to perform the method of any of claims 1 to 14.

16. Apparatus comprising:

means for receiving information regarding at least one smaller cell that is allowed to be accessed by at least one specific user equipment; and

means for using said information to determine for at least one specific user equipment one of said at least one smaller cells to which said at least one specific user equipment is to be handed over.

17. Apparatus as claimed in claim 16, comprising means for sending a request to a control node associated with at least one smaller cell, for information on which of said smaller cells are allowed to be accessed by at least one given communication device.

18. Apparatus as claimed in claim 1 6 or 1 7, wherein the receiving means is for receiving said information from a controller of said at least one smaller cell.

19. Apparatus as claimed in claim 18, wherein said receiving means is for receiving said information from a direct interface with said controller of the at least one smaller cell.

20. Apparatus as claimed in any of claims 16 to 19, comprising means for providing at least some of said information to a user equipment.

21 . Apparatus as claimed in any of claims 16 to 20, wherein said receiving means is for receiving information indicative of a handover failure of a user equipment with said information on said smaller cells.

22. Apparatus as claimed in claim 21 , comprising means for sending a first handover request, said first handover request being such that a handover failure response will be generated, and responsive to said to sending of the first handover request, said receiving means is for receiving said handover failure indication and said information on said smaller cells.

23. Apparatus comprising:

means for obtaining information regarding at least one smaller cell that is allowed to be accessed by at least one specific user equipment; and means for causing said information to be sent to an entity making a handover decision for said at least one specific user equipment.

24. Apparatus as claimed in any of claims 1 6 to 23, wherein the information comprises at least a part of a neighbour cell list.

25. Apparatus as claimed in any of claims 1 6 to 24, wherein said information comprises information identifying a respective smaller cell and scrambling code information associated with said respective smaller cell.

26. Apparatus as claimed in any of clai ms 1 6 to 25, wherein said information comprises access mode information for a respective smaller cell.

27. Apparatus as claimed in any of claims 1 6 to 26, wherein said information comprises distinguishing information for distinguishing one smaller cell from another smaller cell.

28. Apparatus as claimed in claim 27, wherein said distinguishing information comprises information related to radio conditions of transmission and/or reception at the smaller cell for distinguishing one smaller cell from other smaller cell.

29. A controller for controlling a larger cell, said controller comprising apparatus as claimed in any of claims 16 to 22 or any of claims 24 to 28 when appended to claim 16.

30. A controller for controlling at least one smaller cell, said controller comprising apparatus as claimed in claim 23 or any of claims 24 to 28 when appended to claim 23.

31 . A user equipment configured to connect to a larger cell of a communications network and comprising a receiver configured to receive information regarding smaller cells that said user equipment is allowed to access.