Performing an idle mode handoff in a wireless communication device

• US 20030103479A1
• Filed: 10/15/2002
• Published: 06/05/2003
• Est. Priority Date: 11/16/2001
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Anderson, Jon J., Gibson, R. Nicholson, Salaman, Glenn, Ngai, Francis
• Granted Patent: US 7,558,226 B2
• Time in Patent Office: Days
• US Class Current: 370/335
• CPC Class Codes: H04W 36/00 Hand-off or reselection arrangements
• CPC Class Codes: H04W 48/08 Access restriction or access information delivery, e.g. discovery data delivery signalling during connection H04W76/00
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information
• CPC Class Codes: H04W 48/20 Selecting an access point
• CPC Class Codes: H04W 52/0216 using a pre-established activity schedule, e.g. traffic indication frame
• 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 84/06 Airborne or Satellite Networks space-based or airborne stations H04B7/185
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A Wireless Communication Device (WCD) inter-operates with a Code Division Multiple Access (CDMA) communication system. The WCD operates in an idle mode wherein the WCD transitions between a sleep state to conserve power and an awake state to receive one or more paging signals. The WCD attempts to reacquire a first pilot signal associated with a first paging signal that was previously being demodulated, and a second pilot signal that was previously being tracked. The WCD performs a handoff from the first paging signal to a second paging signal associated with the second pilot signal when the attempt to reacquire the first pilot signal fails and the attempt to reacquire the second pilot signal is successful.

Claims

1. A method of performing a handoff operation in a Wireless Communication Device (WCD) operating in a communication system, the WCD operating in an idle mode wherein the WCD transitions between a sleep state to conserve power and an awake state to receive one or more paging signals, comprising:

a. attempting to reacquire a first pilot signal associated with a first paging signal that was being demodulated during a previous awake state;

b. attempting to reacquire a second pilot signal that was being tracked during the previous awake state;

c. performing a handoff from the first paging signal to a second paging signal associated with the second pilot signal when the attempt to reacquire the first pilot signal fails and the attempt to reacquire the second pilot signal is successful; and

d. demodulating the second paging signal during a current awake state, as a result of the handoff operation.

2. The method of claim 1, further comprising:

before step (a), transitioning from the previous awake state to a previous sleep state; and

performing steps (a), (b) and (c) while transitioning from the previous sleep state to the current awake state.

3. The method of claim 1, wherein the first and second paging signals are slotted paging signals associated with a predetermined cycle of time slots, and said step of transitioning from the previous sleep state to the current awake state comprises transitioning to the current awake state so that the current awake state overlaps in time with a time slot of the cycle of time slots that is assigned to the WCD.

4. The method of claim 1, wherein the communication system is a Code Division Multiple Access (CDMA) communication system, and wherein the first pilot signal is spread using a first code and the second pilot signal is spread using a second code, the second code being either a different code from the first code or a time shifted version of the first code, and wherein:

step (a) comprises attempting to reacquire the first pilot signal using the first code; and

step (b) comprises attempting to reacquire the second pilot signal using the second code.

5. The method of claim 4, wherein the second paging signal is spread using a third code related to the second code, and wherein step (c) comprises demodulating the second paging signal using the third code.

6. The method of claim 1, wherein the WCD includes a receiver that was configured to demodulate the first paging signal during the previous awake state, and wherein step (c) comprises reconfiguring the WCD to demodulate the second paging signal.

7. A method of performing a handoff operation in a Wireless Communication Device (WCD) operating in a communication system, the WCD operating in an idle mode wherein the WCD transitions between a sleep state to conserve power and an awake state to receive one or more paging signals, comprising:

a. determining during an awake state that a handoff from a first paging signal to a second paging signal is required;

b. determining during the awake state whether to postpone the handoff until a next awake state; and

c. transitioning from the awake state to a sleep state without performing the required handoff when it is determined to postpone the handoff.

8. The method of claim 7, further comprising:

d. performing the required handoff from the first paging signal to the second paging signal after the WCD transitions from the sleep state to the next awake state; and

e. demodulating the second paging signal during the next awake state as a result of step d.

9. The method of claim 7, wherein the communication system is a Code Division Multiple Access (CDMA) communication system and the second paging signal is a spread spectrum signal, and step (e) comprises despreading the second paging signal using a code.

10. The method of claim 7, further comprising:

prior to step (a), monitoring a first power level of a first pilot signal associated with the first paging signal and a second power level of a second pilot signal associated with the second paging signal; and

wherein step (a) comprises determining the handoff is required based on the first and second power levels.

11. The method of claim 10, wherein step (a) further comprises determining the handoff is required when the second power level is greater than the first power level by a predetermined amount.

12. The method of claim 7, wherein the WCD is scheduled to transition from the awake state to the sleep state at a scheduled time, and wherein:

step (a) comprises determining at a first time during the awake state that the handoff is required;

step (b) comprises determining whether the first time precedes the scheduled time by less than a predetermined time period; and

step (c) comprises transitioning from the awake state to the sleep state at the scheduled time without performing the required handoff when it is determined that the first time precedes the scheduled time by less than the predetermined time period.

13. The method of claim 12, wherein the predetermined time period is less than a time period required to perform the required handoff.

14. The method of claim 7, wherein:

step (b) comprises determining whether a paging slot message associated with the paging signal has been demodulated; and

step (c) comprises transitioning from the awake state to the sleep state without performing the required handoff when it is determined that the paging slot message associated with the paging signal has been demodulated.

15. An apparatus for performing a handoff operation in a Wireless Communication Device (WCD) operating in a communication system, the WCD being capable of operating in an idle mode wherein the WCD transitions between a sleep state to conserve power and an awake state to receive one or more paging signals, comprising:

first means for attempting to reacquire a first pilot signal associated with a first paging signal that was being demodulated during a previous awake state;

second means for attempting to reacquire a second pilot signal that was being tracked during the previous awake state;

third means for performing a handoff operation from the first paging signal to a second paging signal associated with the second pilot signal when the attempt to reacquire the first pilot signal fails and the attempt to reacquire the second pilot signal is successful; and

fourth means for demodulating the second paging signal during a current awake state, as a result of the handoff operation.

16. The apparatus of claim 15, wherein the first, second and third means perform their respective functions while the WCD is transitioning from a previous sleep state to the current awake state.

17. The apparatus of claim 16, wherein the first and second paging signals are slotted paging signals associated with a predetermined cycle of time slots, and the WCD transitions from the previous sleep state to the current awake state so that the current awake state overlaps in time with a time slot of the cycle of time slots that is assigned to the WCD.

18. The apparatus of claim 15, wherein the communication system is a Code Division Multiple Access (CDMA) communication system, and wherein the first pilot signal is spread using a first code and the second pilot signal is spread using a second code, the second code being either a different code from the first code or a time shifted version of the first code, and wherein:

the first means includes means for attempting to reacquire the first pilot signal using the first code; and

the second means includes means for attempting to reacquire the second pilot signal using the second code.

19. The apparatus of claim 18, wherein the second paging signal is spread using a third code related to the second code, and wherein the fourth means includes means for demodulating the second paging signal using the third code.

20. An apparatus for performing a handoff operation in a Wireless Communication Device (WCD) operating in a communication system, the WCD operating in an idle mode wherein the WCD transitions between a sleep state to conserve power and an awake state to receive one or more paging signals, comprising:

first means for determining during an awake state that a handoff from a first paging signal to a second paging signal is required;

second means for determining during the awake state whether to postpone the handoff until a next awake state; and

third means for transitioning from the awake state to a sleep state without performing the required handoff when it is determined to postpone the handoff.

21. The apparatus of claim 20, further comprising:

fourth means for performing the required handoff from the first paging signal to the second paging signal after the WCD transitions from the sleep state to a next awake state; and

fifth means for demodulating the second paging signal during the next awake state.

22. The apparatus of claim 20, wherein the communication system is a Code Division Multiple Access (CDMA) communication system and the second paging signal is a spread spectrum signal, the fifth means comprising means for despreading the second paging signal using a code.

23. The apparatus of claim 20, further comprising:

fifth means for monitoring a first power level of a first pilot signal associated with the first paging signal and a second power level of a second pilot signal associated with the second paging signal; and

wherein the first means includes means for determining the handoff is required based on the first and second power levels.

24. The apparatus of claim 23, wherein the first means further includes means for determining the handoff is required when the second power level is greater than the first power level by a predetermined amount.

25. The apparatus of claim 20, wherein the WCD is scheduled to transition from the awake state to the sleep state at a scheduled time, and wherein:

the first means comprises means for determining at a first time during the awake state that the handoff is required;

the second means comprises means for determining whether the first time precedes the scheduled time by less than a predetermined time period; and

the third means comprises means for transitioning from the awake state to the sleep state at the scheduled time without performing the required handoff when it is determined that the first time precedes the scheduled time by less than the predetermined time period.

26. The apparatus of claim 25, wherein the predetermined time period is less than a time period required to perform the required handoff.

27. The apparatus of claim 20, wherein:

the second means comprises means for determining whether a paging slot message associated with the paging signal has been demodulated; and

the third means comprises means for transitioning from the awake state to the sleep state without performing the required handoff when it is determined that the paging slot message associated with the paging signal has been demodulated.

28. An apparatus for performing a handoff operation in a Wireless Communication Device (WCD) operating in a communication system, the WCD being capable of operating in an idle mode wherein the WCD transitions between a sleep state to conserve power and an awake state to receive one or more paging signals, comprising:

a demodulator;

a first finger;

a second finger;

a searcher adapted to

attempt to reacquire a first pilot signal associated with a first paging signal that was being demodulated by the demodulator and tracked using the first finger during a previous awake state of the WCD, and

attempt to reacquire a second pilot signal that was being tracked by the second finger during the previous awake state; and

a controller responsive to the searcher and adapted to reconfigure the demodulator to demodulate the second paging signal, when the searcher indicates the attempt to reacquire the first pilot signal has failed and the attempt to reacquire the second pilot signal has succeeded.