Method and apparatus for performing idle mode reacquisition and handoff in an asynchronous communication system

• US 6,625,467 B2
• Filed: 12/29/2000
• Issued: 09/23/2003
• Est. Priority Date: 07/13/2000
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Levin, Mark, New, Wen Jing, Hughes, Robbin D.
• Primary Examiner(s): Vo, Nguyen T.
• Assistant Examiner(s): Nguyen, Simon
• Application Number:
  US09/751,607
• Publication Number:
  US 20020006805A1
• Time in Patent Office: 998 Days
• Field of Search: 455/436, 455/437, 455/438, 455/439, 455/440, 455/441, 455/442, 455/500, 455/502, 455/513, 455/515, 455/517, 455/524, 455/525, 455/574, 370/332
• US Class Current: 455/525
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 36/00 Hand-off or reselection arrangements
• CPC Class Codes: H04W 36/0061 of neighbour cell information
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information
• CPC Class Codes: H04W 52/0216 using a pre-established activity schedule, e.g. traffic indication frame
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: H04W 68/00 User notification, e.g. alerting and paging, for incoming communication, change of service or the like
• CPC Class Codes: H04W 76/28 Discontinuous transmission [DTX]; Discontinuous reception [DRX]
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

Techniques to efficiently process paging channels in an asynchronous wireless communication system. In one aspect, if the base stations are not synchronized with each other and a remote terminal'"'"'s designated page time is different from base station to base station, the remote terminal can wake up based on the earliest base station in a reacquisition search list that includes candidate base stations to which the remote terminal may be handed off. In another aspect, the criteria to select base stations for evaluation as reacquisition targets may be based on the received power of the base stations as well as their timing, both of which may be made relative to that of a preferred base station. In yet another aspect, the remote terminal may wake up multiple times in a particular paging cycle (i.e., a frame cycle or a DRX cycle) if there are one or more candidates base station to which the remote terminal may be handed off.

Claims

1. At a terminal in a wireless communication system, a method for processing a plurality of transmissions from a plurality of transmitters, wherein one transmitter is designated as a preferred transmitter from which messages intended for the terminal may be transmitted, the method comprising:

receiving the plurality of transmissions from the plurality of transmitters;

determining a received power for each of the plurality of transmitters;

determining a timing associated with each of the plurality of transmitters; and

forming a first list of one or more transmitters to evaluate at a subsequent time period based on the determined received power and timing for the plurality of transmitters.

2. The method of claim 1, wherein the plurality of transmissions are asynchronous with respect to the timing of the preferred transmitter.

3. The method of claim 1, wherein the timing for each transmitter is defined based on a start of a system frame for the transmitter.

4. The method of claim 1, wherein the one or more transmitters in the first list include transmitters to which the remote terminal may be handed off at the subsequent time period.

5. The method of claim 1, wherein a transmitter having timing within a particular time window of the preferred transmitter is included in the first list if the transmitter meets a first set of criteria, and wherein a transmitter having timing outside the particular time window of the preferred transmitter is included in the first list if the transmitter meets a second set of criteria.

6. The method of claim 5, wherein a first criteria in the first set is met if the received power exceeds a first threshold power level, and wherein a first criteria in the second set is met if the received power exceeds a second threshold power level that is greater than or equal to the first threshold power level.

7. The method of claim 1, wherein remaining ones of the plurality of transmitters other than the preferred transmitter are designated as neighbor transmitters, the method further comprising:

maintaining a timer for each neighbor transmitter having received power that exceeds a requisite power level, wherein the timer is indicative of an estimated amount of time in which the associated neighbor transmitter is received above the requisite power level.

8. The method of claim 7, wherein the first list of one or more transmitters is further formed based in part on values in timers maintained for neighbor transmitters.

9. The method of claim 8, wherein a neighbor transmitter is considered for inclusion in the first list if its timer exceeds a specified reselection time.

10. The method of claim 7, wherein the maintaining includes

initializing the timer for a particular neighbor transmitter with an initial value if the neighbor transmitter is received above the requisite power level for a first time in a current active time period.

11. The method of claim 7, wherein the maintaining includes

initializing the timer for a particular neighbor transmitter with an initial value if the neighbor transmitter is received, for a first time in a current active time period, above a first power level that is lower than the requisite power level, wherein the initial value is selected as half of a time duration for a next active time period.

12. The method of claim 10, wherein the initial value for a neighbor transmitter having a timing within the particular time window of the preferred transmitter is selected as 1.5 times a time duration since a last active time period.

13. The method of claim 10, wherein the initial value for a neighbor transmitter having a timing outside the particular time window of the preferred transmitter is selected as half of a time duration since a last active time period plus a time difference between the timing of the preferred transmitter and the neighbor transmitter.

14. The method of claim 10, wherein the maintaining includes

updating the timer for each neighbor transmitter with an update value if the neighbor transmitter is received above the requisite power level for a subsequent time in the current active time period.

15. The method of claim 14, wherein the update value is selected as a time duration for a next inactive time period.

16. The method of claim 1, wherein for each of the one or more transmitters in the first list, the terminal is associated with a page indicator corresponding to a time in which a message may be transmitted by the transmitter to the terminal.

17. The method of claim 16, wherein the subsequent time period is selected based on an earliest page indicator for the one or more transmitters in the first list.

18. The method of claim 16, wherein the subsequent time period is selected based on the page indicator for the preferred transmitter if no other transmitter in the list has an earlier page indicator.

19. The method of claim 1, further comprising:

forming a second list of transmitters to evaluate at the subsequent time period based on the determined received power and timing for the plurality of the transmitters, wherein each transmitter in the second is not a candidate to which the remote terminal may be handed off at the subsequent time period.

20. The method of claim 1, further comprising:

entering into an inactive state until the subsequent time period.

21. The method of claim 1, further comprising:

receiving one or more transmissions from the one or more transmitters in the first list at the subsequent time period; and

determining a received power for each of the one or more transmitters in the first list.

22. The method of claim 21, further comprising:

handing off to a particular neighbor transmitter in the first list if the received power for the neighbor transmitter at the subsequent time period exceeds a requisite power level.

25. The receiver processing unit of claim 1, wherein the controller is further operative to maintain a timer for each neighbor transmitter having received power that exceeds a requisite power level, wherein the timer is indicative of an estimated amount of time the associated neighbor transmitter is received above the requisite power level.

23. At a terminal in a wireless communication system, a method for processing a plurality of transmissions from a plurality of base stations, wherein one base station is designated as a preferred base station from which messages intended for the terminal may be transmitted and remaining base stations are designated as neighbor base stations, the method comprising:

receiving the plurality of transmissions from the plurality of base stations;

determining a received power for each base station;

determining a timing associated with each base station based on a start of a system frame for the base station, wherein the timing for the plurality of base stations are asynchronous with respect to the timing of the preferred base station;

maintaining a timer for each neighbor base station having received power that exceeds a requisite power level, wherein the timer is indicative of an estimated amount of time the associated neighbor base station is received above the threshold power level; and

forming a list of one or more base stations to evaluate at a subsequent time period based on the received power, the timing, and the timer for the base stations.

24. A receiver processing unit for use in a wireless communication system, comprising:

a receiver operative to receive and process a plurality of transmissions from a plurality of transmitters to generate a plurality of streams of samples;

a power measurement unit coupled to the receiver and operative to receive the plurality of streams of samples and determine a received power for each of the plurality of transmitters;

a demodulator coupled to the receiver and operative to receive the plurality of streams of samples and determine a timing associated with each of the plurality of transmitters; and

a controller coupled to the power measurement unit and the demodulator, the controller operative to form a list of one or more transmitters to evaluate at a subsequent time period based on the received power and timing for the transmitters.