WO2013023845A1 - Enabling macro cell to femto cell handover - Google Patents

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 enabling macro cell to femto cell handover in a communications network. More particularly, the invention relates to enablement of macro cell to femto cell handover during an active connection for a legacy user equipment connected to the network.

BACKGROUND OF THE INVENTION

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 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 H NBs and controlled by one or more H NB-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, handover of a legacy (for example 3GPP Release 7) user equipment (UE) from the macro cell to a femto cell during an active connection is impossible to achieve, since the macro cell is not aware of the underlying available femto cells within its radio coverage. Since the number of potential neighbouring femto cells exceeds the maximal number of entries in the

Neighbouring Cell List (NCL) they have to be excluded from the list to guarantee enough addressing space for macro cells. On the other hand UE(s) belonging to closed subscriber groups should be provided femto cells configured with the relevant closed subscriber group(s) to which the UE belongs.

The invention has been devised with the foregoing in mind.

SUMMARY OF THE INVENTION

Accordingly, the invention provides 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 informa- tion 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 providing 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 in- formation 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 UE 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 U E-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 contol nodes (for example HNB-GW and RNC) upon request if there is a closed subscriber group cell of the legacy UE within the current macro cell coverage.

The invention further provides 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).

The invention also provides 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).

The invention also provides a user equipment (U E), which is configured to connect to a macro cell of a communications network. The UE includes a re- ceiver configured to receive information regarding cells under control of the macro cell that it is allowed to access.

The invention also provides 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.

The invention will now be described, by way of example only, with reference to specific embodiments, 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 of the invention;

- Figure 5 is a message flow diagram illustrating a method according to an embodiment of the invention; and

- Figure 6 is a message flow diagram illustrating a method according to an embodiment of the invention.

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

Although in the following examples, a UMTS network is illustrated, the communications network described could also be any other wireless communica- tions 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 (HN B) 5 controlled by a home Node B gateway (HNB-GW) 6 over an luh 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.

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 a memory M 1 . The HNB-GW includes a transmitter 10 and a receiver 1 1 .

An embodiment of the invention 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 U E 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 the serving macro cell 1 of the UE 7 based on the International Mobile Subscriber Identity/International Mobile Equipment Identity (IMSI/IMEI) 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 enquiry from the RNC 4, in Step S3 the HN 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 H NB-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 NB-GW 6 over the interface lur. This request may include the serving macro cell 1 Cell-ID, 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 NB 3 Cell-ID or GCI with the Cell-IDs provided by the HNB 5 and stored in the HNB-GW 6. The HN B 5 measurements of the overlaying macro cells can be performed during a Network Listening Mode (NLM) procedure performed during the startup of a HNB 5. The HNB-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^) 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 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.

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 HNB-GW 6 of the femto cell 2 under control of the macro cell 1 when the UE 7 moves within the macro cells of the RNC 4 eg., if UE 7 moves back into this macro cell 1 of the RNC 4.

In an alternative embodiment of the invention, illustrated in the message flow diagram in Figure 6, the exchange of information between the RNC 4 and the HNB-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 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 UE 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 tai- lored NCL for the UE 7. The RNC 4 then sends or updates the tailored NCL to the

UE 7.

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

- method steps likely to be implemented as software code portions and being run using a processor at a network control element or terminal (as examples of devices, apparatuses and/or modules thereof, or as examples of entities including apparatuses and/or modules therefore), are 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 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 functionality of an apparatus or module, instead of being hardware implemented, be implemented as software in a (software) module such as a computer program or a computer program product comprising 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 without changing the idea of the present invention. 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, a computer, a mobile broadband adapter, a USB stick for enabling a device to access to a mobile network, etc.

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

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: 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 coverage of the macro cell enquiring which cells under coverage of the macro cell are allowed to be accessed; providing information regarding the cells under coverage of the macro cell that are allowed to be accessed.

2. The method according to claim 1 , wherein the step of sending an enquiry comprises enquiring as to which cells controlled by the control node of the cell under coverage of the macro cell are allowed to be accessed by a specific user equipment connecting to the macro cell.

3. The method according to claim 2, wherein the step of providing information comprises providing information as to which cells controlled by the control node of the femto cell under coverage of the macro cell are allowed to be accessed by said specific user equipment.

4. The method according to any of claims 1 to 3, wherein the information is provided to the control node of the macro cell by the control node of the femto cell under coverage of the macro cell

5. The method according to claim 4, wherein the information is provided over a direct interface between the control node of the macro cell and the control node of the femto cell under coverage of the macro cell.

6. The method according to claim 4 or claim 5, wherein the information is stored by the macro cell.

7. The method according to any of claims 4 to 6, wherein 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.

8. The method according to claim 7, wherein the user equipment is a legacy user equipment.

9. The method according to any of claims 1 to 8, wherein the femto cell under coverage of the macro cell is a femto cell.

10. The method according to any of claims 1 to 9, wherein the information is provided in the form of a neighbour cell list

1 1 . A control node for a macro cell of a communications network, the control node comprising: a transmitter configured to send an enquiry 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 a receiver configured to receive information regarding the cells under coverage of the macro cell that are allowed to be accessed.

12. The control node according to claim 1 1 , wherein the transmitter is configured to send the enquiry so as to enquire which cells controlled by the control node of the femto cell under coverage of the macro cell are allowed to be accessed by a specific user equipment connecting to the macro cell.

13. The control node according to claim 12, wherein the receiver is configured to receive information as to which cells controlled by the control node of the femto cell under coverage of the macro cell are allowed to be accessed by said specific user equipment.

14. The control node according to any of claims 1 1 to 13, wherein the control node further comprises a memory unit configured to store said information.

15. The control node according to any of claims 1 1 to 14, wherein the transmitter is further configured to transmit said information to a user equipment accessing the macro cell.

16. The control node according to any of claims 1 1 to 15, wherein the control node is configured to establish a direct interface with the control node of the cell under control of the macro cell.

17. The control node according to any of claims 1 1 to 16, wherein the control node is an RNC.

18. A control node for controlling a femto cell under coverage of a macro cell of a communications network, the control node comprising: a receiver configured to receive an enquiry enquiring which cells under coverage of the macro cell are allowed to be accessed; and a transmitter configured to provide information regarding the cells under coverage of the macro cell that are allowed to be accessed.

19. The control node according to claim 18, wherein the control node is a HNB-GW.

20. A user equipment configured to connect to a macro cell of a communications network and comprising a receiver configured to receive information regarding cells under coverage of the macro cell that it is allowed to access.

21 . 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; providing information regarding the cells under coverage of the macro cell that are allowed to be accessed.

22. The computer program product according to claim 21 , comprising 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.