Adaptive rate control for OFDM communication system

• US 20030086371A1
• Filed: 11/02/2001
• Published: 05/08/2003
• Est. Priority Date: 11/02/2001
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Howard, Steven J., Ketchum, John W., Wallace, Mark, Walton, Jay R.
• Granted Patent: US 7,164,649 B2
• Time in Patent Office: Days
• US Class Current: 370/235
• CPC Class Codes: H04L 1/0002 by adapting the transmission rate
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0015 characterised by the adaptation strategy
• CPC Class Codes: H04L 1/0025 Transmission of mode-switching indication
• CPC Class Codes: H04L 1/0026 Transmission of channel quality indication
• CPC Class Codes: Y02D 30/50 in wire-line communication networks, e.g. low power modes or reduced link rate

Abstract

Techniques to adaptively control the rate of a data transmission in a wireless (e.g., OFDM) communication system. In an aspect, various types of metrics may be derived and used to select the proper rate for the data transmission. Some types of metrics relate to different characteristics of the communication channel, such as SNR, frequency selectivity, time selectivity, and so on. One type of metric relates to the performance of the data transmission. In another aspect, the various types of metrics may be used in different manners to adaptively control the rate. Some metrics may be used for open-loop control of the rate, other metrics may be used for closed-loop control, and some may be used for both. For example, the channel metrics may be used to determine or select the rate, and the performance metrics may be used to determine whether or not to adjust the rate.

Claims

1. In a wireless communication system, a method for controlling a rate of a data transmission, comprising:

deriving a plurality of channel metrics of a plurality of types and indicative of a plurality of characteristics of a communication channel used for the data transmission;

determining an initial rate for the data transmission based on the derived channel metrics;

updating the channel metrics during the data transmission; and

adjusting the rate based on the updated channel metrics.

2. The method of claim 1, further comprising:

deriving one or more performance metrics indicative of performance of the data transmission, and

wherein the rate adjusting is performed based on the one or more performance metrics.

3. The method of claim 2, wherein the one or more performance metrics is used to determine whether or not to adjust the rate.

4. The method of claim 1, wherein the rate is indicative of a particular coding and modulation scheme to be used for the data transmission.

5. The method of claim 4, wherein the rate is further indicative of a particular data rate for the data transmission.

6. The method of claim 1, wherein the plurality of channel metrics include at least one channel metric of a first type and related to signal-to-noise-plus-interference ratio (SNR) of the communication channel.

7. The method of claim 6, wherein the least one channel metric of the first type includes an estimated pre-detection SNR.

8. The method of claim 6, wherein the least one channel metric of the first type includes an estimated post-detection SNR.

9. The method of claim 1, wherein the plurality of channel metrics include at least one channel metric of a second type and related to frequency selectivity of the communication channel.

10. The method of claim 9, wherein the least one channel metric of the second type includes an estimated coherence bandwidth.

11. The method of claim 10, wherein the coherence bandwidth is estimated by

estimating a channel transfer function for the communication channel,

estimating a frequency correlation function for the communication channel based on the estimated channel transfer function, and

estimating the coherence bandwidth based on the estimated frequency correlation function.

12. The method of claim 11, wherein the coherence bandwidth is further estimated by

averaging the estimated frequency correlation function over a particular time interval, and

wherein the coherence bandwidth is estimated based on the averaged estimated frequency correlation function.

13. The method of claim 1, wherein the plurality of channel metrics include at least one channel metric of a third type and related to time selectivity of the communication channel.

14. The method of claim 13, wherein the least one channel metric of the third type includes an estimated coherence time.

15. The method of claim 14, wherein the coherence time is estimated by

estimating a channel transfer function for the communication channel for each of a plurality of time instances,

estimating a time correlation function for the communication channel based on the estimated channel transfer functions for the plurality of time instances, and

estimating the coherence time based on the estimated time correlation function.

16. The method of claim 2, wherein the one or more performance metrics includes a frame error rate (FER).

17. The method of claim 16, wherein the rate is maintained if the frame error rate is within a particular range.

18. The method of claim 17, wherein the rate is reduced if the frame error rate is above the particular range.

19. The method of claim 18, wherein the reduced rate is determined based on the updated channel metrics.

20. The method of claim 17, wherein the rate is increased based on the updated channel metrics if the frame error rate is below the particular range.

21. The method of claim 20, wherein the increased rate is determined based on the updated channel metrics.

22. The method of claim 1, wherein the channel metrics are derived based on a pilot included in a received signal.

23. The method of claim 1, wherein at least one channel metric is derived based on FFT coefficient values.

24. The method of claim 1, wherein the wireless communication system is an orthogonal frequency division modulation (OFDM) system.

25. In an OFDM system, a method for controlling a rate of a data transmission, comprising:

deriving a plurality of channel metrics of a plurality of types and indicative of a plurality of characteristics of a communication channel used for the data transmission;

determining an initial rate for the data transmission based on the derived channel metrics;

updating the channel metrics during the data transmission;

deriving one or more performance metrics indicative of performance of the data transmission; and

if the one or more performance metrics indicate a change to the rate, then determining a new rate for the data transmission based on the updated channel metrics.

26. In a wireless communication system, a method for controlling a rate of a data transmission, comprising:

receiving an indication of an initial rate for the data transmission determined based on a plurality of channel metrics of a plurality of types and indicative of a plurality of characteristics of a communication channel used for the data transmission;

transmitting data at the initial rate;

receiving an indication of an updated rate for the data transmission determined based on updated channel metrics for the communication channel; and

transmitting data at the updated rate.

27. The method of claim 26, wherein the rate is indicative of a particular data rate and a particular coding and modulation scheme to be used for the data transmission.

28. The method of claim 26, wherein the rate is updated based on one or more performance metrics indicative of performance of the data transmission.

29. In a wireless communication system, a rate control loop for controlling a rate of a data transmission, comprising:

a first loop operative to determine one or more performance metrics indicative of the performance of a data transmission and to provide an indication to adjust the rate based on the one or more performance metrics; and

a second loop operative to derive a plurality of channel metrics of a plurality of types and indicative of a plurality of characteristics of a communication channel used for the data transmission, to determine an initial rate to be used for the data transmission based on the derived channel metrics, to update the channel metrics during the data transmission, and to adjust the rate during the data transmission based on the indication from the first loop and the updated channel metrics.

30. A receiver unit in a wireless communication system, comprising:

a channel estimator operative to derive a plurality of channel metrics of a plurality of types and indicative of a plurality of characteristics of a communication channel used for a data transmission and to update the channel metrics during the data transmission; and

a rate selector operative to determine an initial rate for the data transmission based on the derived channel metrics and to adjust the rate based on the updated channel metrics.

31. The receiver unit of claim 30, further comprising:

a decoder operative to provide a status of the performance of the data transmission, and

wherein the rate selector is further operative to adjust the rate based on the status from the decoder.

32. The receiver unit of claim 30, wherein the channel estimator is further operative to derive and provide at least one channel metric of a first type and related to signal-to-noise-plus-interference ratio (SNR) of the communication channel.

33. The receiver unit of claim 30, wherein the channel estimator is further operative to derive and provide at least one channel metric of a second type and related to frequency selectivity of the communication channel.

34. The receiver unit of claim 30, wherein the channel estimator is operative to derive and provide at least one channel metric of a third type and related to time selectivity of the communication channel.

35. A receiver apparatus in a wireless communication system, comprising:

means for deriving a plurality of channel metrics of a plurality of types and indicative of a plurality of characteristics of a communication channel used for a data transmission;

means for determining an initial rate for the data transmission based on the derived channel metrics;

means for updating the channel metrics during the data transmission; and

means for adjusting the rate based on the updated channel metrics.

36. A transmitter unit in a wireless communication system, comprising:

a controller operative to receive an indication of an initial rate for a data transmission, determined based on a plurality of channel metrics of a plurality of types and indicative of a plurality of characteristics of a communication channel used for the data transmission, and to receive an indication of an updated rate for the data transmission determined based on updated channel metrics for the communication channel;

an encoder operative to code data in accordance with a coding scheme indicated by the rate from the controller; and

a modulator operative to modulate the coded data in accordance with a modulation scheme indicated by the rate from the controller.

37. A transmitter apparatus in a wireless communication system, comprising:

means for receiving an indication of an initial rate for the data transmission determined based on a plurality of channel metrics of a plurality of types and indicative of a plurality of characteristics of a communication channel used for a data transmission;

means for coding and modulating data in accordance with an initial coding and modulation scheme indicated by the initial rate;

means for receiving an indication of an updated rate for the data transmission determined based on updated channel metrics for the communication channel; and

means for coding and modulating data in accordance with an updated coding and modulation scheme indicated by the updated rate.