Method and system for triggering handoff of a call between networks

• US 20050059400A1
• Filed: 09/12/2003
• Published: 03/17/2005
• Est. Priority Date: 09/12/2003
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Nguyen, Bich Tu, Jagadeesan, Ramanathan T.
• Granted Patent: US 7,082,301 B2
• Time in Patent Office: Days
• US Class Current: 455/436
• CPC Class Codes: H04W 36/144 over a different radio air interface technology
• CPC Class Codes: H04W 36/302 due to low signal strength
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]
• CPC Class Codes: H04W 88/06 adapted for operation in multiple networks or having at least two operational modes, e.g. multi-mode terminals
• CPC Class Codes: H04W 92/02 Inter-networking arrangements

Abstract

A method for handing off a call between networks includes monitoring a quality of a first link between a mobile station and a wireless local area network (WLAN) when the mobile station is actively connected with the WLAN on a call and monitoring a quality of a second link between the mobile station and a cellular network when the mobile station is actively connected with the WLAN on the call. The method also includes handing off the call from the WLAN to the cellular network when the quality of the first link is less than a handoff trigger threshold for a drop count duration and when the quality of the second link is greater than a minimum cellular link quality threshold.

Claims

1. A method for handing off a call between networks, comprising:

monitoring a quality of a first link between a mobile station and a wireless local area network (WLAN) when the mobile station is actively connected with the WLAN on a call;

monitoring a quality of a second link between the mobile station and a cellular network when the mobile station is actively connected with the WLAN on the call; and

handing off the call from the WLAN to the cellular network when the quality of the first link is less than a handoff trigger threshold for a drop count duration and when the quality of the second link is greater than a minimum cellular link quality threshold.

2. The method of claim 1, further comprising preventing a handoff of the call from the cellular network to the WLAN until expiration of a dwell timer as long as the quality of the second link remains above the minimum cellular link quality threshold.

3. The method of claim 2, further comprising:

monitoring the quality of the first link between the mobile station and the WLAN when the mobile station is actively connected with the cellular network on the call; and

handing off the call from the cellular network to the WLAN when the quality of the first link is greater than the handoff trigger threshold plus a hysteresis margin for a pick-up count duration.

4. The method of claim 3, further comprising tuning a control to change a value of the hysteresis margin.

5. The method of claim 3, further comprising tuning a control to change a value of the drop count duration.

6. The method of claim 3, further comprising tuning a control to change a value of the dwell timer.

7. The method of claim 1, wherein the WLAN communicates using IEEE 802.11 protocol.

8. The method of claim 1, wherein monitoring a quality of a first link between a mobile station and a WLAN comprises monitoring a WLAN metric.

9. The method of claim 8, wherein the WLAN metric comprises one of a group of metrics consisting of a received signal strength, a signal to noise ration, a signal quality, an error vector magnitude, a bit error rate and a packet error rate.

10. The method of claim 8, wherein the WLAN metric comprises a quality of service parameter.

11. The method of claim 10, wherein the quality of service parameter comprises packet jitter, delay or WLAN collision error rate.

12. The method of claim 1, wherein monitoring a quality of a first link between a mobile station and a WLAN comprises monitoring a plurality of WLAN metrics.

13. The method of claim 12, wherein monitoring a plurality of WLAN metrics comprises determining a vector comprising a plurality of WLAN metrics.

14. The method of claim 12, wherein monitoring a plurality of WLAN metrics comprises determining a scalar value comprising a function of a plurality of WLAN metrics.

15. The method of claim 1, wherein monitoring a quality of a second link between the mobile station and a cellular network comprises monitoring a cellular metric.

16. The method of claim 15, wherein the cellular metric comprises one of a group of metrics consisting of a received signal strength, a bit error rate and a frame error rate.

17. The method of claim 1, wherein the drop count duration comprises a first number of samples out of a second number of samples taken at a sample interval.

18. The method of claim 17, wherein the sample interval comprises 250 milliseconds.

19. A system for handing off a call between networks, comprising a mobile station comprising a controller operable to:

monitor a quality of a first link between the mobile station and a wireless local area network (WLAN) when the mobile station is actively connected with the WLAN on a call;

monitor a quality of a second link between the mobile station and a cellular network when the mobile station is actively connected with the WLAN on the call; and

hand off the call from the WLAN to the cellular network when the quality of the first link is less than a handoff trigger threshold for a drop count duration and when the quality of the second link is greater than a minimum cellular link quality threshold.

20. The system of claim 19, wherein the controller is further operable to prevent a handoff of the call from the cellular network to the WLAN until expiration of a dwell timer as long as the quality of the second link remains above the minimum cellular link quality threshold.

21. The system of claim 20, wherein the controller is further operable to:

monitor the quality of the first link between the mobile station and the WLAN when the mobile station is actively connected with the cellular network on the call; and

hand off the call from the cellular network to the WLAN when the quality of the first link is greater than the handoff trigger threshold plus a hysteresis margin for a pick-up count duration.

22. The system of claim 21, wherein the mobile station further comprises a tuning knob operable to tune the hysteresis margin to change its value.

23. The system of claim 19, wherein the WLAN communicates using IEEE 802.11 protocol.

24. The system of claim 19, wherein a controller operable to monitor a quality of a first link between a mobile station and a WLAN comprises a controller operable to monitor a WLAN metric.

25. The system of claim 24, wherein the WLAN metric comprises one of a group of metrics consisting of a received signal strength, a signal to noise ration, a signal quality, an error vector magnitude, a bit error rate and a packet error rate.

26. The system of claim 24, wherein the WLAN metric comprises a quality of service parameter.

27. The system of claim 26, wherein the quality of service parameter comprises packet jitter, delay or WLAN collision error rate.

28. The system of claim 19, wherein a controller operable to monitor a quality of a first link between a mobile station and a WLAN comprises a controller operable to monitor a plurality of WLAN metrics.

29. The system of claim 28, wherein a controller operable to monitor a plurality of WLAN metrics comprises a controller operable to determine a vector comprising a plurality of WLAN metrics.

30. The system of claim 28, wherein a controller operable to monitor a plurality of WLAN metrics comprises a controller operable to determine a scalar value comprising a function of a plurality of WLAN metrics.

31. The system of claim 19, wherein a controller operable to monitor a quality of a second link between the mobile station and a cellular network comprises a controller operable to monitor a cellular metric.

32. The system of claim 31, wherein the cellular metric comprises one of a group of metrics consisting of a received signal strength, a bit error rate and a frame error rate.

33. The system of claim 19, wherein the drop count duration comprises a first number of samples out of a second number of samples taken at a sample interval.

34. The system of claim 33, wherein the sample interval comprises 250 milliseconds.

35. A system for handing off a call between networks, comprising:

means for monitoring a quality of a first link between a mobile station and a wireless local area network (WLAN) when the mobile station is actively connected with the WLAN on a call;

means for monitoring a quality of a second link between the mobile station and a cellular network when the mobile station is actively connected with the WLAN on the call; and

means for handing off the call from the WLAN to the cellular network when the quality of the first link is less than a handoff trigger threshold for a drop count duration and when the quality of the second link is greater than a minimum cellular link quality threshold.

36. The system of claim 35, further comprising means for preventing a handoff of the call from the cellular network to the WLAN until expiration of a dwell timer as long as the quality of the second link remains above the minimum cellular link quality threshold.

37. The system of claim 36, further comprising:

means for monitoring the quality of the first link between the mobile station and the WLAN when the mobile station is actively connected with the cellular network on the call; and

means for handing off the call from the cellular network to the WLAN when the quality of the first link is greater than the handoff trigger threshold plus a hysteresis margin for a pick-up count duration.

38. The system of claim 35, wherein the WLAN communicates using IEEE 802.11 protocol.

39. The system of claim 35, wherein means for monitoring a quality of a first link between a mobile station and a WLAN comprises means for monitoring a WLAN metric.

40. The system of claim 39, wherein the WLAN metric comprises one of a group of metrics consisting of a received signal strength, a signal to noise ration, a signal quality, an error vector magnitude, a bit error rate and a packet error rate.

41. The system of claim 35, wherein means for monitoring a quality of a second link between the mobile station and a cellular network comprises means for monitoring a cellular metric.

42. The system of claim 41, wherein the cellular metric comprises one of a group of metrics consisting of a received signal strength, a bit error rate and a frame error rate.

43. Software embedded in a computer readable medium comprising code operable to:

monitor a quality of a first link between a mobile station and a wireless local area network (WLAN) when the mobile station is actively connected with the WLAN on a call;

monitor a quality of a second link between the mobile station and a cellular network when the mobile station is actively connected with the WLAN on the call; and

hand off the call from the WLAN to the cellular network when the quality of the first link is less than a handoff trigger threshold for a drop count duration and when the quality of the second link is greater than a minimum cellular link quality threshold.

44. The medium of claim 43, wherein the code is further operable to prevent a handoff of the call from the cellular network to the WLAN until expiration of a dwell timer as long as the quality of the second link remains above the minimum cellular link quality threshold.

45. The medium of claim 44, wherein the code is further operable to:

monitor the quality of the first link between the mobile station and the WLAN when the mobile station is actively connected with the cellular network on the call; and

hand off the call from the cellular network to the WLAN when the quality of the first link is greater than the handoff trigger threshold plus a hysteresis margin for a pick-up count duration.

46. The medium of claim 43, wherein the WLAN communicates using IEEE 802.11 protocol.

47. The medium of claim 43, wherein code operable to monitor a quality of a first link between a mobile station and a WLAN comprises code operable to monitor a WLAN metric.

48. The medium of claim 47, wherein the WLAN metric comprises one of a group of metrics consisting of a received signal strength, a signal to noise ration, a signal quality, an error vector magnitude, a bit error rate and a packet error rate.

49. The medium of claim 43, wherein code operable to monitor a quality of a second link between the mobile station and a cellular network comprises code operable to monitor a cellular metric.

50. The medium of claim 49, wherein the cellular metric comprises one of a group of metrics consisting of a received signal strength, a bit error rate and a frame error rate.

51. A method for handing off a call between networks, comprising:

monitoring a quality of a first link between a mobile station and a cellular network when the mobile station is actively connected with the cellular network on a call;

monitoring a quality of a second link between the mobile station and a wireless local area network (WLAN) when the mobile station is actively connected with the cellular network on the call; and

handing off the call from the cellular network to the WLAN when the quality of the first link is less than a handoff trigger threshold for a drop count duration and when the quality of the second link is greater than a minimum WLAN link quality threshold.

52. The method of claim 51, further comprising preventing a handoff of the call from the WLAN to the cellular network until expiration of a dwell timer as long as the quality of the second link remains above the minimum WLAN link quality threshold.

53. The method of claim 52, further comprising:

monitoring the quality of the first link between the mobile station and the cellular network when the mobile station is actively connected with the WLAN on the call; and

handing off the call from the WLAN to the cellular network when the quality of the first link is greater than the handoff trigger threshold plus a hysteresis margin for a pick-up count duration.

54. The method of claim 53, further comprising tuning a control to change a value of the hysteresis margin.

55. The method of claim 53, further comprising tuning a control to change a value of the drop count duration.

56. The method of claim 53, further comprising tuning a control to change a value of the dwell timer.

57. The method of claim 51, wherein the WLAN communicates using IEEE 802.11 protocol.

58. The method of claim 51, wherein monitoring a quality of a first link between a mobile station and a cellular network comprises monitoring a cellular metric.

59. The method of claim 51, wherein monitoring a quality of a second link between the mobile station and a WLAN comprises monitoring a WLAN metric.