Coverage determination and switching between overlay communication systems

• US 20060046661A1
• Filed: 09/02/2004
• Published: 03/02/2006
• Est. Priority Date: 09/02/2004
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Ekvetchavit, Thunyachate, Govindarajula, Ravi
• Granted Patent: US 7,684,373 B2
• Time in Patent Office: Days
• US Class Current: 455/67.110
• CPC Class Codes: H04W 36/14 Reselecting a network or an air interface
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data
• CPC Class Codes: H04W 88/06 adapted for operation in multiple networks or having at least two operational modes, e.g. multi-mode terminals

Abstract

For coverage determination and system switching, a terminal obtains pilot strength estimates for base stations in first and second wireless communication systems (e.g., packet data system and voice/data system) and received signal quality estimates for at least one serving base station in the first system. The terminal derives various metrics based on the received signal quality estimates and pilot strength estimates. The terminal may perform handoff to the second system if weak coverage is detected for the first system, a received signal quality metric (Q) for the first system is below a Q_th—dn threshold, and a pilot strength metric (V) for the second system exceeds a V_th—dn threshold. The terminal may perform handoff to the first system if good coverage is detected for this system, metric Q exceeds a Q_th—up threshold, or a maximum pilot strength metric (M) for the first system exceeds a M_th—up threshold.

Claims

1. A method of determining coverage of a wireless communication system, comprising:

obtaining at least one received signal quality estimate for at least one base station selected for data transmission;

deriving a first metric based on the at least one received signal quality estimate for the at least one base station; and

determining whether the coverage of the system is good based on the first metric.

2. The method of claim 1, further comprising:

obtaining a plurality of pilot strength estimates for a plurality of base stations in the system; and

deriving a second metric based on the plurality of pilot strength estimates for the plurality of base stations, and wherein the coverage of the system is determined further based on the second metric.

3. The method of claim 2, further comprising:

deriving a third metric based on the plurality of pilot strength estimates for the plurality of base stations, wherein the second metric is a sum of the plurality of pilot strength estimates and the third metric is a maximum of the plurality of pilot strength estimates, and wherein the coverage of the system is determined further based on the third metric.

4. The method of claim 1, wherein the first metric is computed based on the received signal quality estimate for a single base station selected for data transmission.

5. The method of claim 1, wherein each of the at least one received signal quality estimate is indicative of a signal-to-noise-and-interference ratio achieved for one of the at least one base station.

6. The method of claim 1, wherein the deriving the first metric comprises

determining a rate for data transmission for each time interval based on the at least one received signal quality estimate obtained for the at least one base station for the time interval, and

computing the first metric based on the rate determined for each time interval.

7. The method of claim 1, wherein the deriving the first metric comprises

determining a rate for data transmission for each time interval based on the at least one received signal quality estimate obtained for the at least one base station for the time interval,

ascertaining an average percentage of time non-null rates are determined, and

computing the first metric based on the average percentage of time for non-null rates.

8. The method of claim 7, wherein the ascertaining the average percentage of time for non-null rates comprises

for each of a plurality of time intervals, setting a filter input for the time interval to a first value if the rate obtained for the time interval is a null rate and to a second value if the rate is a non-null rate, and

filtering filter inputs for the plurality of time intervals to obtain the average percentage of time for non-null rates.

9. An apparatus in a wireless communication system, comprising:

a demodulator operative to obtain at least one received signal quality estimate for at least one base station selected for data transmission; and

a controller operative to derive a first metric based on the at least one received signal quality estimate for the at least one base station and to determine whether coverage of the system is good based on the first metric.

10. The apparatus of claim 9, wherein the demodulator is further operativelto obtain a plurality of pilot strength estimates for a plurality of base stations in the system, and wherein the controller is further operative to derive a second metric based on the plurality of pilot strength estimates and to determine the coverage of the system further based on the second metric.

11. The apparatus of claim 9, wherein the controller is further operative to determine a rate for data transmission for each time interval based on the at least one received signal quality estimate obtained for the at least one base station for the time interval, and to compute the first metric based on the rate determined for each time interval.

12. The apparatus of claim 9, wherein the wireless communication system is a packet data system capable of providing packet data service.

13. An apparatus in a wireless communication system, comprising:

means for obtaining at least one received signal quality estimate for at least one base station selected for data transmission;

means for deriving a first metric based on the at least one received signal quality estimate for the at least one base station; and

means for determining whether coverage of the system is good based on the first metric.

14. The apparatus of claim 13, further comprising:

means for obtaining a plurality of pilot strength estimates for a plurality of base stations in the system; and

means for deriving a second metric based on the plurality of pilot strength estimates for the plurality of base stations, and wherein the coverage of the system is determined further based on the second metric.

15. The apparatus of claim 13, further comprising:

means for determining a rate for data transmission for each time interval based on the at least one received signal quality estimate obtained for the at least one base station for the time interval; and

means for computing the first metric based on the rate determined for each time interval.

16. A processor readable media for storing instructions operable in a terminal to:

obtain at least one received signal quality estimate for at least one base station in a wireless communication system and selected for data transmission to the terminal;

derive a metric based on the at least one received signal quality estimate for the at least one base station; and

determine whether coverage of the system is good based on the metric.

17. A method of switching a terminal between first and second wireless communication systems, comprising:

obtaining at least one received signal quality estimate for at least one base station in the first system;

deriving a first metric based on the at least one received signal quality estimate for the at least one base station in the first system; and

determining whether to switch from the first system to the second system, or from the second system to the first system, based on the first metric.

18. The method of claim 17, further comprising:

obtaining a plurality of pilot strength estimates for a plurality of base stations in the first system; and

deriving a second metric based on the plurality of pilot strength estimates for the plurality of base stations in the first system, and wherein the switch from the first system to the second system, or from the second system to the first system, is determined further based on the second metric.

19. The method of claim 18, further comprising:

obtaining at least one pilot strength estimate for at least one base station in the second system; and

deriving a third metric based on the at least one pilot strength estimate for the at least one base station in the second system, and wherein the switch from the first system, to the second system is determined further based on the third metric.

20. The method of claim 18, further comprising:

determining an amount of time the second metric is below a threshold value, and wherein the switch from the first system to the second system is determined further based on the amount of time the second metric is below the threshold value.

21. The method of claim 18, further comprising:

deriving a third metric based on a maximum of the plurality of pilot strength estimates for the plurality of base stations in the first system, and wherein the switch from the second system to the first system is determined further based on the third metric.

22. The method of claim 17, further comprising:

determining reliability of the first metric, and wherein the switch from the second system to the first system is determined based on the first metric if deemed reliable.

23. The method of claim 22, further comprising:

determining an amount of time the at least one base station in the first system was monitored, and wherein the reliability of the first metric is determined based on the amount of time the at least one base station in the first system was monitored.

24. An apparatus comprising:

a demodulator operative to obtain at least one received signal quality estimate for at least one base station in a first wireless communication system; and

a controller operative to derive a first metric based on the at least one received signal quality estimate for the at least one base station in the first system and to determine whether to switch from the first system to a second wireless communication system, or from the second system to the first system, based on the first metric.

25. The apparatus of claim 24, wherein the demodulator is further operative to obtain a plurality of pilot strength estimates for a plurality of base stations in the first system, and wherein the controller is further operative to derive a second metric based on the plurality of pilot strength estimates for the plurality of base stations in the first system and to determine whether to switch from the first system to the second system, or from the second system to the first system, further based on the second metric.

26. The apparatus of claim 25, wherein the demodulator is further operative to obtain at least one pilot strength estimate for at least one base station in the second system, and wherein the controller is further operative to derive a third metric based on the at least one pilot strength estimate for the at least one base station in the second system and to determine whether to switch from the first system to the second system further based on the third metric.

27. The apparatus of claim 25, wherein the controller is further operative to derive a third metric based on a maximum of the plurality of pilot strength estimates for the plurality of base stations in the first system and to determine whether to switch from the second system to the first system further based on the third metric.

28. The apparatus of claim 24, wherein the first system is capable of providing packet data service, and wherein the second system is capable of providing voice and packet data services.

29. An apparatus comprising:

means for obtaining at least one received signal quality estimate for at least one base station in a first wireless communication system;

means for deriving a first metric based on the at least one received signal quality estimate for the at least one base station in the first system; and

means for determining whether to switch from the first system to a second wireless communication system, or from the second system to the first system, based on the first metric.

30. The apparatus of claim 29, further comprising:

means for obtaining a plurality of pilot strength estimates for a plurality of base stations in the first system; and

means for deriving a second metric based on the plurality of pilot strength estimates for the plurality of base stations in the first system, and wherein the switch from the first system to the second system, or from the second system to the first system, is determined further based on the second metric.

31. The apparatus of claim 30, further comprising:

means for obtaining at least one pilot strength estimate for at least one base station in the second system; and

means for deriving a third metric based on the at least one pilot strength estimate for the at least one base station in the second system, and wherein the switch from the first system to the second system is determined further based on the third metric.

32. The apparatus of claim 30, further comprising:

means for deriving a third metric based on a maximum of the plurality of pilot strength estimates for the plurality of base stations in the first system, and wherein the switch from the second system to the first system is determined further based on the third metric.