System and Method for Handoff Between Base Stations

• US 20080051086A2
• Filed: 08/09/2005
• Published: 02/28/2008
• Est. Priority Date: 08/10/2004
• Status: Active Grant

• Current Assignee: Nextel Communications (Deutsche Telekom AG)
• Original Assignee: Nextel Communications (Deutsche Telekom AG)
• Inventors: Olfat, Masoud, Etemad, Kamran
• Granted Patent: US 7,693,517 B2
• Time in Patent Office: Days
• US Class Current: 455/436
• CPC Class Codes: H04W 36/0072 of resource information of target access point
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection

Abstract

A system and method for handoff are provided. A mobile station performs a make-before-break handoff of a control channel between a serving and target base station and a break-before-make handoff of a traffic channel between the serving and target base stations. The traffic channel handoff is performed after the control channel handoff has completed.

Claims

1. A method for handoff of a mobile station from a serving base station to a target base station, the method comprising the acts of:

receiving data from a serving base station during a first and second time period;

transmitting control information to the target base station during a time period between the first and second time periods;

receiving data from the target base station during a time period subsequent to the second time period, wherein the mobile station receives data from only one base station during any particular time period.

2. The method of claim 1, wherein the control information comprises ranging information.

3. The method of claim 1, further comprising the act of:

providing a base station signal measurement report to the serving base station.

4. The method of claim 3, wherein a signal of the target base station is included in the base station signal measurement report.

5. The method of claim 1, further comprising the act of:

receiving, from the serving base station, a message instructing the mobile station to attempt to handoff to the target base station.

6. The method of claim 5, wherein the message identifies a reserved ranging channel of the target base station and a connection identification to be used for communicating with the target base station.

7. The method of claim 6, wherein the message also identifies the time period between the first and second time periods.

8. The method of claim 1, wherein the mobile station transmits a handoff complete indication to the serving base station during the second time period.

9. The method of claim 1, wherein the mobile station receives a traffic channel allocation from the target base station during the time period subsequent to the second time period.

10. A method for handoff, comprising the acts of:

informing a mobile station of a first set of time periods for communicating with a target base station over a second control channel;

scheduling information for transmission to the mobile station during time periods other than the first set of time periods; and

transmitting the scheduled information to the mobile station over a first traffic channel during periods of time other than the first set of time periods.

11. The method of claim 10, further comprising the act of:

identifying the target base station based on signal measurement reports.

14. The method of claim 10, further comprising the act of:

informing the mobile station of a reserved ranging channel of the target base station and a connection identification to be used for communicating with the target base station.

15. The method of claim 10, further comprising the acts of:

receiving a handoff complete message; and

terminating communications with the mobile station in response to the handoff complete message.

16. The method of claim 10, wherein the information for transmission to the mobile station includes unicast and multicast data.

17. The method of claim 10, wherein the first set of time periods are every other n frames.

18. The method of claim 10, wherein the handoff is an intra-frequency handoff.

19. The method of claim 10, wherein the handoff is an inter-frequency handoff.

12. The method of claim lo, further comprising the act of:

informing the target base station of information related to the mobile station.

13. The method of claim 12, wherein the information related to the mobile station includes context information.

20. A method for a mobile station to handoff from a serving base station to target base station, the method comprising the acts of:

communicating with the serving base station over a first traffic channel and a first control channel during a first time period;

communicating with the target base station over a second control channel during a second time period;

communicating with the serving base station over the first traffic and control channels during a third time period, which is subsequent to the second time period; and

communicating with the target base station of the second control channel and a second traffic channel during a fourth time period.

21. The method of claim 20, wherein the communication with the target base station during the second period of time comprises ranging information.

22. The method of claim 20, further comprising the act of:

providing a base station signal measurement report to the serving base station.

23. The method of claim 22, wherein a signal of the target base station is included in the base station signal measurement report.

24. The method of claim 20, further comprising the act of:

receiving, from the serving base station, a message instructing the mobile station to attempt to handoff to the target base station.

25. The method of claim 24, wherein the message identifies a reserved ranging channel of the target base station and a connection identification to be used for communicating with the target base station.

26. The method of claim 25, wherein the message also identifies the second time period.

27. The method of claim 20, wherein the mobile station transmits a handoff complete indication to the serving base station during the third time period.

28. The method of claim 20, wherein the mobile station receives a traffic channel allocation from the target base station during the fourth time period.

29. The method of claim 20, wherein the handoff is an intra-frequency handoff.

30. The method of claim 20, wherein the handoff is an inter-frequency handoff.

31. A method for a mobile station handoff from a serving base station to a target base station, the method comprising the acts of:

identifying a base station as the target base station;

exchanging control channel messages with the target base station; and

communicating over a traffic channel with the serving base while exchanging the control channel messages with the target base station.

32. The method of claim 31, further comprising the acts of:

receiving a feedback channel allocation from the serving base station; and

transmitting an identification of the target base station to the serving base station over the feedback channel.

33. The method of claim 32, further comprising the act of:

receiving, from the serving base station, a signaling channel allocation for the target base station, wherein at least one of the control channel messages is a ranging message which is transmitted over the allocated signaling channel.

34. The method of claim 31, further comprising the acts of:

receiving a connection identification from the target base station; and

communicating over an allocated traffic channel with the target base station.

35. A method for a serving base station supporting a handoff of a mobile station to a target base station, the method comprising the acts of:

receiving, from the mobile station, an identification of the target base station;

informing the target base station of a handoff attempt by the mobile station;

communicating over a traffic channel with the mobile station, while the mobile station exchanges control channel messages with the mobile station.

36. The method of claim 35, further comprising the act of:

receiving, from the target base station, a control channel allocation for the mobile station; and

transmitting an indication of the control channel allocation to the mobile station.

37. The method of claim 35, further comprising the acts of:

receiving, from the mobile station, an indication of a traffic channel handoff to the target base station; and

transmitting an indication of the traffic channel handoff to the target base station.

38. The method of claim 37, further comprising the act of:

terminating a traffic channel to the mobile station in response to the indication of the traffic channel handoff.

39. A method for a mobile station handoff from a serving base station to a target base station, the method comprising the acts of:

performing a make-before-break handoff of a control channel between the serving and target base stations; and

performing a break-before-make handoff of a traffic channel between the serving and target base stations.

40. The method of claim 39, wherein the mobile station performs the handoff of traffic channels only after the mobile station performs the act of:

indicating completion of the signaling channel handoff.

41. The method of claim 40, wherein the completion of the control channel handoff is performed over a handoff switching channel.