Method and network element for controlling handover

• US 20040121777A1
• Filed: 10/24/2003
• Published: 06/24/2004
• Est. Priority Date: 04/26/2001
• Status: Active Grant

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Nokia Corporation
• Inventors: Holma, Harri, Schwarz, Uwe, Heikkinen, Kai, Artamo, Atte, Tigerstedt, Karl, Wacker, Achim
• Granted Patent: US 7,197,318 B2
• Time in Patent Office: Days
• US Class Current: 455/452.1
• CPC Class Codes: H04W 36/22 for handling the traffic

Abstract

The present invention relates to a method and apparatus for controlling a connection transfer in a cellular network having at least two systems, such as a GSM system and a WCDMA system. Based on a load determination, a service-based inter-system or inter-frequency handover of the connection to another system or to another carrier of the same system is initiated if the determined is below a threshold and service priorities are indicating it. If it exceeds the threshold, an additional load-based inter-system or inter-frequency handover can be initiated. If the load of the target cell is not known, a load estimation based on a learning process can be used to derive a probability of success of an interfrequency or inter-system handover, which may be used for deciding on the initiation of the inter-system handover. The learning process may be performed by evaluating preceding interfrequency or inter-system handovers to the target cell or preceding interfrequency or inter-system handovers from the target cell. Thereby, users can be shared between different radio access technologies or systems or between different carriers of one system to thereby improve network capacity and quality of service for both systems and carriers. Furthermore, unnecessary inter-system handovers can be prevented in case the load of the target cell of the other system is not known.

Claims

1. A method for controlling a connection transfer in a cellular network having at least two carriers or at least two systems, said method comprising the steps of:

a) determining the load of one of said at least two carriers or one of said at least two systems, used by a connection;

b) initiating a service-based inter-system or inter-frequency handover of said connection to another one of said at least two systems or another one of said at least two carriers, respectively, based on a service priority, if said determined load is below a predetermined threshold; and

c) initiating a load-based inter-system or inter-frequency handover of said connection to another one of said at least two systems or another one of said at least two carriers, respectively, if said determined load exceeds said predetermined threshold.

2. A method according to claim 1, further comprising the step of allowing said service-based-inter-system or inter-frequency handover if the load of a target cell does not exceed said predetermined threshold.

3. A method according to claim 1 or 2, wherein said at least two carriers are WCDMA carriers.

4. A method according to any one of the preceding claims, further comprising the step of using different thresholds for said inter-system and inter-frequency handovers.

5. A method according to any one of the preceding claims, wherein said at least two systems comprise a GSM system and a WCDMA system.

6. A method according to any one of the preceding claims, further comprising the steps of performing said initiation steps only after the expiry of predetermined time periods.

7. A method according to any one of the preceding claims, wherein said predetermined threshold corresponds to a load of 80% of the maximum load.

8. A network element for controlling a connection transfer in a cellular network having at least two carriers or at least two systems, said network element comprising:

a) determining means (10) for determining the load situation of one of said at least two carriers or one of said at least two systems, used by said connection; and

b) handover control means (20) for initiating a service-based inter-system or inter-frequency handover of said connection to another one of said at least two systems or another one of said at least two carriers, respectively, based on a service priority, if said determined load is below a predetermined threshold, and for initiating a load-based inter-system or inter-frequency handover of said connection to another one of said at least systems or another one of said at least two carriers, respectively, if said determined load exceeds said predetermined threshold.

9. A network element according to claim 8, further comprising timer means (15) for counting a time period which must have expired before said load-based or service-based inter-system or inter-frequency handovers are initiated.

10. A network element according to claim 8 or 9, wherein said at least two carriers are WCDMA carriers.

11. A network-element according to any one of claims 8 to 10, wherein said at least two systems comprise a GSM system and a WCDMA system.

12. A network element according to any one of claims 8 to 11, wherein said network element is a base station controller.

13. A network element according to any one of claims 8 to 11, wherein said network element is a radio network controller.

14. A method for controlling a connection transfer in a cellular network having at least two systems, said method comprising the steps of:

a) determining the load situation of one of said at least two systems, used by a connection;

b) estimating a probability of success of an inter-system handover of said connection to another one of said at least two systems, based on a learning process; and

c) deciding on said inter-system handover based on said estimated probability of success.

15. A method according to claim 14, wherein said learning process comprises evaluating the history of successful and/or unsuccessful inter-system handovers to a target cell.

16. A method according to claim 15, wherein said learning process comprises evaluating an incoming inter-system handover message from a target cell.

17. A method according to claim 16, wherein said evaluation is based on a reason message in said incoming inter-system handover message.

18. A method according to claim 16, wherein said evaluation is based on a service priority setting in said target cell.

19. A method according to any one of claims 14 to 18, wherein said decision step leads to one of the results of initiating said inter-system handover, postponing said inter-system handover, and canceling said inter-system handover.

20. A network element for controlling a connection transfer in a cellular network having at least two systems, said network element comprising:

a) determining means (10) for determining the load of one of said at least two systems, used by a connection; and

b) handover control means (20) for estimating a probability of success of an inter-system handover of said connection to another one of said at least two systems, based on a learning process, and for deciding on said inter-system handover based on said estimated probability of success.

21. A network element according to claim 20, further comprising timer means (15) for counting a delay time set by said handover control means based on the decision result.

22. A network element according to claim 20 or 21, wherein said network element is a base station controller.

23. A network element according to claim 20 or 21, wherein said network element is a radio network controller.