Method and apparatus for combining power control commands received in a wireless communication system

• US 20030045318A1
• Filed: 08/22/2001
• Published: 03/06/2003
• Est. Priority Date: 08/22/2001
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Subrahmanya, Parvathanathan
• Granted Patent: US 6,807,429 B2
• Time in Patent Office: Days
• US Class Current: 455/522
• CPC Class Codes: H04W 52/40 during macro-diversity or soft handoff

Abstract

Techniques to combine soft-decision power control symbols received for multiple active base stations. In one method, a received signal is initially processed to derive soft-decision (multi-bit valued) symbols for power control commands transmitted from a number of base stations. Each soft-decision symbol for each base station is then scaled based on a scaling factor associated with the base station and which is related to the received signal quality for the power control symbols for the base station. The scaling allows power control symbols for more reliably received base stations to be given greater weights. The scaled soft-decision symbols for each power control period are then combined to provide a decision metric for the period. Each decision metric is then compared against a particular threshold, and a power control decision is derived for each decision metric based on the result of the comparison.

Claims

1. In a wireless communication system, a method for deriving power control decisions, comprising:

processing a received signal to derive soft-decision symbols for power control commands transmitted from a plurality of transmission sources;

combining the soft-decision symbols for each power control period based on a particular combination scheme to provide a metric for the power control period; and

deriving a power control decision from each metric.

2. The method of claim 1, wherein the combining includes

scaling each soft-decision symbol for each transmission source based on a scaling factor associated with the transmission source, and

combining the scaled soft-decision symbols for each power control period to provide the metric for the power control period.

3. The method of claim 1, wherein the soft-decision symbols for each power control period are combined in a manner to approximate an a posteriori probability that the plurality of transmission sources transmitted UP commands given the soft-decision symbols derived for the power control period.

4. The method of claim 1, further comprising:

comparing each metric against a particular threshold, and

wherein the power control decision is derived based on a result of the comparing.

5. The method of claim 4, wherein the threshold is a function of a particular number of transmission sources for which the soft-decision symbols are combined for the power control period.

6. The method of claim 2, further comprising:

deriving a log domain representation for each scaled soft-decision symbol, and

wherein log domain representations for each power control period are combined to derive the metric for the power control period.

7. The method of claim 6, wherein the log domain representation for each scaled soft-decision symbol is a log-likelihood ratio (LLR).

8. The method of claim 2, wherein the scaling factor for each transmission source is related to a quality of the soft-decision symbols for the transmission source.

9. The method of claim 8, wherein the quality of the soft-decision symbols for each transmission source is estimated based on a pilot received from the transmission source.

10. The method of claim 1, further comprising:

adjusting transmit power for a data transmission to the plurality of transmission sources based on the power control decision.

11. The method of claim 1, wherein the transmission sources are base stations in a CDMA system.

12. The method of claim 11, wherein the base stations are in an active set of a terminal operating in soft-handoff.

13. The method of claim 1, wherein the wireless communication system is a CDMA system that supports IS-95, cdma2000, or W-CDMA standard.

14. In a CDMA communication system, a method for deriving power control decisions for a reverse link transmission, comprising:

processing a received signal to derive soft-decision symbols for power control commands transmitted from a plurality of base stations;

scaling each soft-decision symbol for each base station based on a scaling factor associated with the base station;

combining the scaled soft-decision symbols for each power control period to provide a metric for the power control period;

comparing each metric against a particular threshold; and

deriving a power control decision for each metric based on a result of the comparing.

15. The method of claim 14, wherein the soft-decision symbols for each power control period are combined in a manner to approximate an a posteriori probability that the plurality of base stations transmitted UP commands given the soft-decision symbols derived for the power control period.

16. The method of claim 14, further comprising:

deriving a log domain representation for each scaled soft-decision symbol, and

wherein log domain representations for each power control period are combined to derive the metric for the power control period.

17. The method of claim 14, wherein the plurality of base stations are in an active set of a terminal operating in soft-handoff.

18. A power control unit for use in a wireless communication system, comprising:

a receiver unit configured to process a received signal to provide samples;

a demodulator coupled to the receiver unit and configured to process the samples to provide soft-decision symbols for power control commands transmitted from a plurality of transmission sources; and

a power control processor coupled to the demodulator and configured to combine soft-decision symbols for each power control period based on a particular combination scheme to provide a metric for the power control period and to derive a power control decision from each metric.

19. The power control unit of claim 18, wherein the power control processor is further configured to scale each soft-decision symbol for each transmission source based on a scaling factor associated with the transmission source.

20. The power control unit of claim 18, wherein the power control processor is configured to combine the soft-decision symbols for each power control period in a manner to approximate an a posteriori probability that the plurality of transmission sources transmitted UP commands given the soft-decision symbols derived for the power control period.

21. The power control unit of claim 19, further comprising:

a signal quality measurement unit configured to estimate a quality of the soft-decision symbols for each transmission source, and

wherein the scaling factor associated with each transmission source is related to the estimated quality of the soft-decision symbols for the transmission source.

22. The power control unit of claim 18, and operative on a reverse link of a CDMA system.

23. A terminal in a wireless communication system, comprising:

a receiver unit configured to process a received signal to provide samples;

a demodulator coupled to the receiver unit and configured to process the samples to provide soft-decision symbols for power control commands transmitted from a plurality of base stations;

a power control processor coupled to the demodulator and configured to combine soft-decision symbols for each power control period based on a particular combination scheme to provide a metric for the power control period and to derive a power control decision from each metric; and

a transmitter unit configured to receive power control decisions from the power control processor and to adjust transmit power for a data transmission to the plurality of base stations based on the power control decisions.