Method and apparatus for efficient handoffs by mobile communication entities

• US 5,594,943 A
• Filed: 04/02/1996
• Issued: 01/14/1997
• Est. Priority Date: 08/09/1994
• Status: Expired due to Term

• Current Assignee: Pacific Communication Sciences , Inc. (Cirrus Logic Incorporated)
• Original Assignee: Pacific Communication Sciences , Inc. (Cirrus Logic Incorporated)
• Inventors: Balachandran, Kumar
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): BANKS HAROLD, MARSHA DENISE
• Application Number:
  US08/627,675
• Time in Patent Office: 287 Days
• Field of Search: 455/33.1, 455/33.2, 455/33.4, 455/34.1, 455/56.1, 455/67.1, 455/161.2, 455/161.3, 455/62, 455/68, 455/161.1, 455/166.6, 455/226.2, 455/89.1, 370/110.21, 379/60
• US Class Current: 455/436
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data
• CPC Class Codes: H04W 72/54 based on quality criteria
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A method and apparatus used in the context of a digital cellular communication network for allowing a remote unit to determine the conditions under which a handoff should occur and the procedure to be followed. The method and apparatus of the present invention controls handoffs in a manner which causes the boundaries of a cell within a digital cellular network to remain relatively well defined and to very closely conform to the boundaries of a cell of an advanced mobile phone system with which the cellular digital packet data system is associated. The present invention also reduces the effort required by a remote unit within a cellular digital packet data communication system when attempting to change channels. Primary and Secondary Thresholds are defined in accordance with the present invention. These Thresholds aid in determining when a link should be handed off (and thus define the boundaries of cells of the system) and which channels are appropriate candidates to attempt to scan to track a hop or determine when to initiate a handoff. The Thresholds represent performance thresholds which can be used to determine whether the airlink can reliably transmit information.

Claims

1. A method for determining when to change receive channels in a first communication trait operating in a wireless communication network, comprising the steps of:

a. monitoring at least one performance parameter of a channel received within the first communication unit to detect the relationship of each performance parameter with respect to at least both a primary and secondary threshold concurrently associated with each performance parameter, the primary threshold representing a higher level of performance than the secondary threshold;

b. scanning for a forward channel having the highest performance as determined by the relative levels of each performance parameter and attempting to receive data on that channel whenever (1) the monitored performance parameter of the last channel being received is below the secondary threshold or (2) the monitored performance parameter of the last channel being received is below the primary threshold for a predetermined amount of time.

2. The method of claim 1, wherein the step of scanning for a forward channel is also performed whenever synchronization is lost on the channel that was last being received.

3. The method of claim 1, wherein the step of scanning for a forward channel is also performed whenever a predetermined period of time has expired during which no scanning has taken place.

4. The method of claim 1, wherein the step of scanning for a forward channel is also performed whenever a command to deactivate a power conservation mode is executed.

5. The method of claim 1, wherein the step of scanning a forward channel is also performed whenever second communication unit responsible for transmitting the last received channel has ceased transmitting relevant data on the last received channel without an indication to the first communication unit.

6. The method of claim 1, wherein at least one of the monitored performance parameters is a received signal strength indication averaged over time at the first communication unit.

7. The method of claim 1, wherein at least one of the performance parameters is a bit error rate averaged over time at the first communication unit.

8. The method of claim 1, wherein at least one of the performance parameters is a block error rate averaged over time at the first communication unit.

9. The method of claim 1, wherein the at least one of performance parameters is a symbol error rate averaged over time at the first communication unit.

10. The method of claim 1, wherein the primary and secondary thresholds are established in the first communication unit by being receiving each threshold in the first communication unit from a second communication unit from which the forward channel is being transmitted.

11. The method of claim 1, wherein at least one of the performance parameters are established locally within the first communication unit.

12. The method of claim 1, wherein a determination as to which channels are to be scanned depends upon the condition that caused the scanning to occur.

13. The method of claim 12, wherein only the channels assigned to either a second communication unit to which the last received channel was assigned, and channels assigned to each neighboring second communication unit are scanned when (1) the performance parameter of the received channel has been below the primary threshold for a predetermined amount of time, or (2) the performance parameter of the received channel is below the secondary threshold or (3) synchronization is lost on the channel.

14. The method of claim 12, wherein only the channels assigned to a second communication unit to which the last received channel was assigned are scanned when the performance parameter does not violate the primary threshold, and synchronization of the first communication unit with the data stream that was being transmitted on the channel is lost without prior indication of a change of channel.

15. The method of claim 12, wherein only the channels assigned to a second communication unit which is adjacent to a second communication unit to which the last received channel was assigned are scanned when (1) the performance parameter of the last received channel is below the secondary threshold, or (2) no channel has been successfully acquired after scanning only the channels assigned to a second communication unit to which the last received channel was assigned.

16. The method of claim 12, wherein channels are assigned to at least a second communication unit from which the first communication unit is receiving a channel, and at least one communication unit neighboring the second communication unit, all channels within the communication network are scanned when no channel was acquired after either (1) scanning only the channels assigned to a second communication unit to which the last received channel was assigned and each channel assigned to-each communication unit neighboring the second communication unit, or (2) scanning only the channels assigned to each neighboring communication unit.

17. The method of claim 1, wherein a determination as to which channels are to be scanned depends upon (1) whether a loss of synchronization has occurred, (2) whether the performance parameter of the received channel has been below the primary threshold for a predetermined amount of time, or (3) whether the performance parameter of the received channel is below the secondary threshold.

18. A communication unit for communicating with other communication units operating in a wireless communication network, comprising:

(a) a means for monitoring at least one performance parameter of a channel received within the communication unit to determine concurrently the relationship of each performance parameter with respect to at least both a primary and secondary threshold associated with each performance parameter, the primary threshold representing a higher level of performance than the secondary threshold;

(b) means for scanning for a forward channel having the highest performance as determined by the relative levels of each performance parameter and attempting to receive data on that channel whenever (1) the monitored performance parameter of the current channel being received is below the secondary threshold or (2) the monitored performance parameter of the current channel being received is below the primary threshold for a predetermined amount of time.

19. The communication unit of claim 18, wherein the scanning means scans for a forward channel whenever synchronization is lost on the channel that was last being received.

20. The communication unit of claim 18, wherein the scanning means scans for a forward channel whenever a predetermined period of time has expired during which no scanning has taken place.

21. The communication unit of claim 18, wherein the scanning means scans for a forward channel whenever a command to deactivate a power conservation mode is executed.

22. The communication unit of claim 18, wherein the scanning means scans for a forward channel whenever second communication unit responsible for transmitting the last received channel has ceased transmitting relevant data on the last received channel without an indication to the communication unit.

23. The communication unit of claim 18, wherein at least one of the monitored performance parameters is a received signal strength indication averaged over time at the communication unit.

24. The communication unit of claim 18, wherein at least one of the performance parameters is a bit error rate averaged over time at the communication unit.

25. The communication unit of claim 18, wherein at least one of the performance parameters is a block error rate averaged over time at the communication unit.

26. The communication unit of claim 18, wherein the at least one of performance parameters is a symbol error rate averaged over time at the communication unit.

27. The communication unit of claim 18, wherein the primary and secondary thresholds are established in the communication unit by being receiving each threshold in the communication unit from a second communication unit from which the forward channel is being transmitted.

28. The communication unit of claim 18, wherein at least one of the performance parameters are established locally within the communication unit.

29. The communication unit of claim 18, wherein a determination as to which channels are to be scanned depends upon the condition that caused the scanning to occur.

30. The communication unit of 18, wherein a determination as to which channels are to be scanned depends upon (1) whether a loss of synchronization has occurred, (2) whether the performance parameter of the received channel has been below the primary threshold for a predetermined amount of time, or (3) whether the performance parameter of the received channel is below the secondary threshold.

31. The communication unit of claim 30, wherein channels are assigned to at least one stationary communication unit, and only the channels assigned to either a stationary communication unit to which the last received channel was assigned, and channels assigned to each neighboring stationary communication unit are scanned when (1) the performance parameter of the received channel has been below the primary threshold for a predetermined amount of time, or (2) the performance parameter of the received channel is below the secondary threshold or (3) synchronization is lost on the channel.

32. The communication unit of claim 30, wherein channels are assigned to at least one stationary communication unit, and only the channels assigned to a second communication unit to which the last received channel was assigned are scanned when the performance parameter does not violate the primary threshold, and synchronization of the communication unit with the data stream that was being transmitted on the channel is lost without prior indication of a change of channel.

33. The communication unit of claim 30, wherein channels are assigned to at least one stationary communication unit, and only the channels assigned to communication units which are adjacent to a second communication unit to which the last received channel was assigned are scanned when (1) the performance parameter of the last received channel is below the secondary threshold, or (2) no channel has been successfully acquired after scanning only the channels assigned to the second communication unit to which the last received channel was assigned.

34. The communication unit of claim 30, wherein channels are assigned to at least one stationary communication unit, and all channels within the communication network are scanned when no channel was acquired after either (1) scanning only the channels assigned to a second communication unit to which the last received channel was assigned and each channel assigned to each communication unit neighboring the second communication unit, or (2) scanning only the channels assigned to each neighboring communication unit.

35. A communication unit for communicating with other communication units operating in a wireless communication network, the communication unit having a radio block for transmitting and receiving radio frequency signals on at least one channel and a radio control block, coupled to the radio block, for processing data to be transmitted and received by the radio block, the communication unit comprising:

(a) a central processor, coupled to the radio control block, for monitoring at least one performance parameter of a channel received within the communication unit to determine concurrently the relationship of each performance parameter with respect to at least both a primary and secondary threshold associated with each performance parameter, the primary threshold representing a higher level of performance than the secondary threshold, and for scanning for a forward channel having the highest performance as determined by the relative levels of each performance parameter and attempting to receive data on that channel whenever (1) the monitored performance parameter of the last channel being received is below the secondary threshold or (2) the monitored performance parameter of the last channel being received is below the primary threshold for a predetermined amount of time.

36. The communication unit of claim 35, wherein the central processor scans for a forward channel whenever synchronization is lost on the channel that was last being received.

37. The communication unit of claim 35, wherein the central processor scans for a forward channel whenever a predetermined period of time has expired during which no scanning has taken place.

38. The communication unit of claim 35, wherein the central processor scans for a forward channel whenever a command to deactivate a power conservation mode is executed.

39. The communication unit of claim 35 wherein the central processor scans for a forward channel whenever second communication unit responsible for transmitting the last received channel has ceased transmitting relevant data on the last received channel without an indication to the communication unit.

40. The communication unit of claim 35, wherein at least one of the monitored performance parameters is a received signal strength indication averaged over time at the communication unit.

41. The communication unit of claim 35, wherein at least one of the performance parameters is a bit error rate averaged over time at the communication unit.

42. The communication unit of claim 35, wherein at least one of the performance parameters is a block error rate averaged over time at the communication unit.

43. The communication unit of claim 35, wherein the at least one of performance parameters is a symbol error rate averaged over time at the communication unit.

44. The communication unit of claim 35, wherein the primary and secondary thresholds are established in the communication unit by being receiving each threshold in the communication unit from a second communication unit from which the forward channel is being transmitted.

45. The communication unit of claim 35, wherein at least one of the performance parameters are established locally within the communication unit.

46. The communication unit of claim 35, wherein the channels to be scanned depends upon the condition that caused the scanning to occur.

48. The communication unit of claim 46, wherein channels are assigned to at least one stationary communication unit, and only the channels assigned to either a stationary communication unit to which the last received channel was assigned, and channels assigned to each neighboring stationary communication unit are scanned when (1) the performance parameter of the received channel has been below the primary threshold for a predetermined amount of time, or (2) the performance parameter of the received channel is below the secondary threshold or (3) synchronization is lost on the channel.

49. The communication unit of claim 46, wherein channels are assigned to at least one stationary communication unit, and only the channels assigned to a second communication unit to which the last received channel was assigned are scanned when the performance parameter does not violate the primary threshold, and synchronization of the communication unit with the data stream that was being transmitted on the channel is lost without prior indication of a change of channel.

50. The communication unit of claim 46, wherein channels are assigned to at least one stationary communication unit, and only the channels assigned to communication units which are adjacent to a second communication unit to which the last received channel was assigned are scanned when (1) the performance parameter of the last received channel is below the secondary threshold, or (2) no channel has been successfully acquired after scanning only the channels assigned to the second communication unit to which the last received channel was assigned.

51. The communication unit of claim 46, wherein channels are assigned to at least one stationary communication unit, and all channels within the communication network are scanned when no channel was acquired after either (1) scanning only the channels assigned to a second communication unit to which the last received channel was assigned and each channel assigned to each communication unit neighboring the second communication unit, or (2) scanning only the channels assigned to each neighboring communication unit.

47. The communication unit of 46, wherein the channels to be scanned depends upon (1) whether a loss of synchronization has occurred, (2) whether the performance parameter of the received channel has been below the primary threshold for a predetermined amount of time, or (3) whether the performance parameter of the received channel is below the secondary threshold.