Closed subscriber group cell handover

• US 20090047960A1
• Filed: 05/23/2008
• Published: 02/19/2009
• Est. Priority Date: 08/13/2007
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Gunnarsson, Fredrik, Frenger, Pal, Moe, Johan
• Granted Patent: US 8,265,033 B2
• Time in Patent Office: Days
• US Class Current: 455/436
• CPC Class Codes: H04J 11/0093 Neighbour cell search
• CPC Class Codes: H04W 36/0058 Transmission of hand-off measurement information, e.g. measurement reports
• CPC Class Codes: H04W 36/00835 Determination of neighbour cell lists
• CPC Class Codes: H04W 36/0085 Hand-off measurements
• CPC Class Codes: H04W 84/045 using private Base Stations, e.g. femto Base Stations, home Node B

Abstract

A radio terminal connection may be handed over from a serving base station associated with a serving cell to a closed subscriber group (CSG) cell served by a CSG base station in which only radio terminals belonging to the CSG are permitted to access and receive service from the CSG cell. Radio terminals in the serving cell are generally informed not to report to the serving base station signal quality measurements of signals transmitted by CSG base stations. But if a radio terminal in the serving cell is authorized to access and receive service from the CSG cell, then that radio terminal is instructed to report to the serving base station signal quality measurements of signals transmitted by the CSG base station. Based on that report, the connection may be handed over to the CSG base station. A central node provides a CSG authorization list identifying CSG authorized radio terminals to the serving base station when a listed CSG cell is a neighboring cell which the radio terminal is authorized to access.

Claims

1. A method relating to handover of a radio terminal connection from a serving base station associated with a serving cell to a closed subscriber group (CSG) cell served by a CSG base station, where only a radio terminal belonging to the CSG is permitted to access and receive service from the CSG cell, and where information is provided to radio terminals in the serving cell that identifies radio terminals that are not to report to the serving base station signal quality measurements of signals transmitted by the CSG base station, the method implemented in the serving base station comprising:

determining that one of the radio terminals in the serving cell is authorized to access and receive service from the CSG cell;

sending a message to the one radio terminal indicating that the CSG cell may be considered as a handover candidate for the radio terminal;

based on a signal quality measurement report corresponding to the CSG base station, determining that a connection with the one radio terminal may be handed over to the CSG base station; and

facilitating handover of the connection to the CSG base station.

2. The method in claim 1, wherein the information not to report to the serving base station signal quality measurements of signals transmitted by the CSG base station is broadcast in the serving cell and includes a list identifying cells for which the information is not to be reported or a list of cells identifying only those cells for which the information is to be reported.

3. The method in claim 2, further comprising:

broadcasting a modified cell list in the serving cell to modify those cells for which the information is not to be reported.

4. The method in claim 1, wherein radio terminals are informed not to report to the serving base station signal quality measurements of signals transmitted by the CSG base station using a first message that indicates that the CSG cell is a forbidden cell, and

wherein the sending step includes sending a second subsequent message to the radio terminal indicating that the radio terminal should report signal quality measurements of signals transmitted by the CSG base station.

5. The method in claim 4, wherein the first message that indicates that the CSG cell is a forbidden cell contains the information that the cell is barred, restricted, or a CSG cell.

6. The method in claim 4, wherein the first message is transmitted by the serving base station or by the CSG base station.

7. The method in claim 1, wherein the determining includes receiving an authorization list of CSG cells from a central node coupled to the serving base station indicating that the radio terminal is authorized to access and obtain service from the CSG cell.

8. The method in claim 7, wherein the authorization list is filtered in the central node to only include the CSG cells that are possible handover candidates for the radio terminal considering the location of the radio terminal.

9. The method in claim 1, wherein:

the CSG cell is part of a CSG network of CSG cells to which the radio terminal is authorized to access and request service, each of the CSG network cells having an associated cell identifier, and

the determining includes receiving a CSG cell identifier range from a central node coupled to the serving base station.

10. The method in claim 9, further comprising:

signaling the radio terminal to report measurement information for one or more handover candidate CSG cells that broadcast a cell identifier in the CSG cell identifier range.

11. A serving base station for assisting in handover of a radio terminal connection from the serving base station associated with a serving cell to a closed subscriber group (CSG) cell served by a CSG base station, where only a radio terminal belonging to the CSG is permitted to access and receive service from the CSG cell, and where information is provided to radio terminals in the serving cell that identify radio terminals that are not to report to the serving base station signal quality measurements of signals transmitted by the CSG base station, the serving base station comprising:

radio transceiving circuitry, and

a data processing system including electronic circuitry configured to;

determine that one of the radio terminals in the serving cell is authorized to access and receive service from the CSG cell;

send a message to the one radio terminal indicating that the CSG cell may be considered as a handover candidate for the radio terminal;

based on a signal quality measurement report for the CSG base station, determine that a connection with the one radio terminal may be handed over to the CSG base station; and

facilitate handover of the connection to the CSG base station.

12. The serving base station in claim 11, wherein the radio transceiving circuitry broadcasts information not to report to the serving base station signal quality measurements of signals transmitted by the CSG base station in the serving cell and includes a list identifying cells for which the information is not to be reported or a list of cells identifying only those cells for which the information is to be reported.

13. The serving base station in claim 12, wherein the radio transceiving circuitry broadcasts a modified cell list in the serving cell to modify those cells for which the information is not to be reported.

14. The serving base station in claim 11, wherein radio terminals have been informed not to report to the serving base station signal quality measurements of signals transmitted by the CSG base station using a first message that indicates that the CSG cell is forbidden for general access, and

wherein the electronic circuitry is configured to generate a second subsequent message to be transmitted via the radio transceiving circuitry to the radio terminal indicating that the radio terminal should report signal quality measurements of signals transmitted by the CSG base station.

15. The serving base station in claim 14, where the message indicating that the CSG cell is forbidden includes that the cell is a barred cell, a restricted cell, or a CSG cell.

16. The serving base station in claim 11, wherein the electronic circuitry is configured to receive an authorization list of CSG cells from a central node coupled to the serving base station indicating that the radio terminal is authorized to access and obtain service from the CSG cell.

17. The serving base station in claim 16, wherein the electronic circuitry is configured to compare the authorization list of CSG cells to the neighbor cell relation list of the serving cell and to compile a new authorization list of CSG cells in the serving cell'"'"'s neighbor cell relation list.

18. The serving base station in claim 17, wherein the electronic circuitry is configured to send the serving cell'"'"'s neighbor cell relation list to the central node prior to receiving the authorization list of CSG cells.

19. The serving base station in claim 11, wherein:

the CSG cell is part of a CSG network of CSG cells to which the radio terminal is authorized to access and request service, each of the CSG network cells having an associated cell identifier, and

the electronic circuitry is configured to receive a CSG cell identifier range from a central node coupled to the serving base station and to check whether the radio terminal'"'"'s cell identifier is in the received CSG cell identifier range, and if so, to authorize the radio terminal to access and receive service from any of the CSG cells in the CSG network.

20. The serving base station in claim 19, wherein the radio transceiving circuitry signals the radio terminal to report measurement information for one or more CSG cells that broadcast a cell identifier in the CSG cell identifier range.

21. The serving base station in claim 11, wherein the electronic circuitry is configured to receive an authorization list of CSG cells during handover from a previous serving base station for the radio terminal, and wherein the authorization list of CSG cells indicates that the radio terminal is authorized to access and obtain service from the CSG cell.

22c. c. The serving base station in claim 11, wherein the electronic circuitry is configured to receive an authorization list of CSG cells from a central node when the radio terminal accesses the radio network at the serving base station, and wherein the authorization list of CSG cells indicates that the radio terminal is authorized to access and obtain service from the CSG cell.

23. A radio terminal for communicating with a serving base station associated with a serving cell, where the radio terminal belongs to a closed subscriber group (CSG) cell served by a CSG base station, and where only a radio terminal belonging to the CSG is permitted to access and receive service from the CSG cell, comprising:

radio transceiving circuitry, and

a data processing system coupled to the radio transceiving circuitry including electronic circuitry configured to;

receive first information informing the radio terminal not to report to the serving base station signal quality measurements of signals transmitted by CSG base stations;

obtain a measure of quality of signals transmitted by neighboring base stations other than CSG base stations and report those signal quality measurements to the serving base station for a possible handover operation;

receive second information overriding the first information and informing the radio terminal to report to the serving base station signal quality measurements of signals transmitted by the CSG base station; and

measure a signal quality of a signal transmitted by the CSG base station and report the CSG base station signal quality measurement to the serving base station.

24. The radio terminal in claim 23, wherein when the radio terminal receives instructions to handover to the CSG base station, the electronic circuitry is configured to instruct the radio transceiving circuitry to establish communications with the CSG base station.

25. The radio terminal in claim 23, wherein the second information includes a range of CSG cell identifiers, the electronic circuitry is configured to measure a signal quality of a signal received by any CSG base station having a cell identifier in the range and report those CSG base station signal quality measurements to the serving base station.

26. The radio terminal in claim 23, wherein if the radio terminal is unable to obtain or maintain service from a serving base station, the electronic circuitry is configured to scan a signal quality of a signal received by any nearby CSG base station and to select a nearby CSG base station to provide service, wherein an authorized CSG base station has a higher selection priority than an unauthorized CSG base station.

27. A central node, comprising:

an interface for communicating with a serving base station serving a serving cell and with a closed subscriber group (CSG) base station serving a CSG cell in which only a radio terminal belonging to the CSG is permitted to access and receive service from the CSG cell;

a memory for storing a CSG authorization list which for each of multiple radio terminals identifies all CSG cells that the radio terminal is authorized to access and receive service from; and

a controller configured to provide a CSG authorization list to the serving base station serving a one radio terminal in the serving cell when the CSG authorization list includes CSG cells which the radio terminal is authorized to access, and to otherwise not provide the CSG authorization list to the serving base station.

28. The central node in claim 27, wherein the controller is configured to only include CSG cells in the CSG authorization list that are neighbors to the serving cell and that the radio terminal is authorized to access.

29. The central node in claim 28, wherein the memory stores a neighbor cell relations (NCR) list for the serving cell and the controller uses the NCR list to determine whether a CSG cell is a neighboring cell.

30. The central node in claim 28, wherein the central node is configured to receive a neighbor cell relations (NCR) list for the serving cell from the serving base station, and the controller is configured to use the NCR list to determine whether a CSG cell is a neighboring cell to a serving cell.

31. The central node in claim 27, wherein the controller is configured to permit modifications to the CSG authorization list.

32. The central node in claim 27, wherein the CSG cell is part of a CSG network of CSG cells to which the radio terminal is authorized to access and request service, each of the CSG network cells having an associated cell identifier, and wherein the controller is configured to determine a CSG cell identifier range for the CSG network and provide the CSG cell identifier range to the serving base station.

33. The central node in claim 27, wherein the controller is configured to determine a CSG tracking area associated with one or more CSG cells that the radio terminal is authorize to access, and when the central node is notified that the radio terminal has accessed the serving cell, to check whether the CSG tracking area corresponds to a tracking area of the serving cell, and if so, to inform the serving base station about the one or more CSG cells.

34. The central node in claim 27, wherein the controller is configured to determine a CSG PLMN identity associated with one or more CSG cells that the radio terminal is authorize to access, and when the central node is notified that the radio terminal has accessed the serving cell, to check whether the CSG PLMN identity corresponds to a compatible PLMN identity associated with the serving cell, and if so, to inform the serving base station about the one or more CSG cells.