Dynamic offset threshold for diversity handover in telecommunications system

• US 6,907,245 B2
• Filed: 08/17/2001
• Issued: 06/14/2005
• Est. Priority Date: 12/04/2000
• Status: Expired due to Term

• Current Assignee: Unwired Planet LLC (JP Morgan Chase & Co)
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Ohlsson, Jonas, Johansson, Staffan, Jannok, Daniel
• Primary Examiner(s): Trost, William
• Assistant Examiner(s): LE, DANH C
• Application Number:
  US09/931,580
• Publication Number:
  US 20020068571A1
• Time in Patent Office: 1,397 Days
• Field of Search: 455/442, 455/436, 455/437, 455/438, 455/439, 455/522, 370/331, 370/332, 370/333
• US Class Current: 455/442
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 36/185 using make before break

Abstract

A telecommunications system has a source base station (BS_S) and a destination base station (BS_D), and a handover unit (100) having a dynamic offset threshold determination unit (102) which establishes a dynamic offset threshold for starting soft handover. When the dynamic offset threshold for soft handover is exceeded, a preliminary portion of a handover sequence is initiated at the destination base station. The preliminary portion of the handover sequence is initiated so that a time-critical handover sequence activity (such as L1 uplink synchronization) is well underway, if not completed, by the time the soft handover is actually needed. The dynamic offset threshold for starting handover is based on a probability that the mobile station will engage in the handover. The probability is a statistical probability that handover will actually occur based on handover history of other mobile stations previously and similarly traveling and of the same signal strength. Another portion of the soft handover sequence (e.g., a remaining portion of the soft handover sequence) is initiated when the signal strength from the destination base station as received at the specified mobile station has a predetermined relationship to a fixed offset threshold.

Claims

1. For use in a telecommunications system having a source base station and a destination base station where a specified mobile station establishes a connection with the source base station, a method comprising:

determining a dynamic offset threshold for starting at least a portion of a soft handover sequence for the specified mobile station at the destination base station, the dynamic offset threshold being a function of a probability that the specified mobile station will engage in soft handover;

initiating the at least a portion of the soft handover sequence when a signal strength from the destination base station as received at the specified mobile station has a predetermined relationship to the dynamic offset threshold.

2. The method of claim 1, further comprising initiating another portion of the soft handover sequence when the signal strength from the destination base station as received at the specified mobile station has a predetermined relationship to a fixed offset threshold.

3. The method of claim 2, wherein the another portion of the soft handover sequence is a remainder of the soft handover sequence.

4. The method of claim 1, wherein the probability is a function of signal strength of the destination base station as received at the specified mobile station.

5. The method of claim 1, wherein the probability is a function of signal strength of the destination base station as received at the specified mobile station and a function of signal strength of the source base station as received at the specified mobile station.

6. The method of claim 1, wherein the probability is a statistical probability based on handover history of other mobile stations.

7. The method of claim 1, further comprising initiating the at least a portion of the soft handover sequence when a signal strength from the destination base station as received at the specified mobile station is not less than the dynamic offset threshold, the dynamic offset threshold being a difference between the signal strength of the source base station as received at the specified mobile station and a dynamic offset.

8. The method of claim 7, wherein the dynamic offset is a function of a fixed offset and the probability of the specified mobile station fulfilling the handover criteria.

9. The method of claim 1, further comprising determining the dynamic offset threshold at a control node of the code division multiple access communication system.

10. The method of claim 9, further comprising the specified mobile station sending to the control node a measurement report of the signal strength of the destination base station as received at the specified mobile station.

11. A telecommunications system comprising:

a source base station;

a destination base station;

a dynamic offset threshold determination unit which determines a dynamic offset threshold for starting at least a portion of a soft handover sequence for the specified mobile station at the destination base station, the dynamic offset threshold being a function of a probability that the specified mobile station will engage in soft handover;

wherein the dynamic offset threshold determination unit initiates the at least a portion of the soft handover sequence when a signal strength from the destination base station as received at the specified mobile station has a predetermined relationship to the dynamic offset threshold.

12. The apparatus of claim 11, wherein the probability is a function of signal strength of the destination base station as received at the specified mobile station.

13. The apparatus of claim 11, wherein the probability is a function of signal strength of the destination base station as received at the specified mobile station and a function of signal strength of the source base station as received at the specified mobile station.

14. The apparatus of claim 11, wherein the probability is a statistical probability based on handover history of other mobile stations.

15. The apparatus of claim 11, wherein the dynamic offset threshold determination unit is situated at a control node of the code division multiple access communication system.

16. The apparatus of claim 15, wherein control node receives from the specified mobile station a measurement report of the signal strength of the destination base station as received at the specified mobile station.

17. A telecommunications system comprising:

a source base station;

a destination base station;

a dynamic offset threshold determination unit which determines a dynamic offset threshold for starting at least a portion of a soft handover sequence for the specified mobile station at the destination base station, the dynamic offset threshold being a function of a probability that the specified mobile station will engage in soft handover;

a handover unit which initiates another portion of the soft handover sequence when the signal strength from the destination base station as received at the specified mobile station has a predetermined relationship to a fixed offset threshold.

18. The apparatus of claim 17, wherein the another portion of the soft handover sequence is a remainder of the soft handover sequence.

19. The apparatus of claim 17, wherein the probability is a function of signal strength of the destination base station as received at the specified mobile station.

20. The apparatus of claim 17, wherein the probability is a function of signal strength of the destination base station as received at the specified mobile station and a function of signal strength of the source base station as received at the specified mobile station.

21. The apparatus of claim 17, wherein the probability is a statistical probability based on handover history of other mobile stations.

22. The apparatus of claim 17, wherein the dynamic offset threshold determination unit is situated at a control node of the code division multiple access communication system.

23. The apparatus of claim 22, wherein control node receives from the specified mobile station a measurement report of the signal strength of the destination base station as received at the specified mobile station.

24. A telecommunications system comprising:

a source base station;

a destination base station;

a dynamic offset threshold determination unit which determines a dynamic offset threshold for starting at least a portion of a soft handover sequence for the specified mobile station at the destination base station, the dynamic offset threshold being a function of a probability that the specified mobile station will engage in soft handover;

wherein the dynamic offset threshold determination unit initiates the at least a portion of the soft handover sequence when a signal strength from the destination base station as received at the specified mobile station is not less than the dynamic offset threshold, the dynamic offset threshold being a difference between the signal strength of the source base station as received at the specified mobile station and a dynamic offset.

25. The apparatus of claim 24, wherein the dynamic offset is a function of a fixed offset and the probability of the specified mobile station fulfilling the handover criteria.

26. The apparatus of claim 24, wherein the probability is a function of signal strength of the destination base station as received at the specified mobile station.

27. The apparatus of claim 24, wherein the probability is a function of signal strength of the destination base station as received at the specified mobile station and a function of signal strength of the source base station as received at the specified mobile station.

28. The apparatus of claim 24, wherein the probability is a statistical probability based on handover history of other mobile stations.

29. The apparatus of claim 24, wherein the dynamic offset threshold determination unit is situated at a control node of the code division multiple access communication system.

30. The apparatus of claim 29, wherein control node receives from the specified mobile station a measurement report of the signal strength of the destination base station as received at the specified mobile station.