Channel variation detection of wireless channel for adaptive transmission schemes

• US 8,213,527 B2
• Filed: 03/25/2009
• Issued: 07/03/2012
• Est. Priority Date: 03/25/2009
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Wang, Genyuan, Jin, Hang
• Primary Examiner(s): Williams, Lawrence B
• Application Number:
  US12/410,659
• Publication Number:
  US 20100246720A1
• Time in Patent Office: 1,196 Days
• Field of Search: 375219-220, 375/222, 375/260, 375/278, 375284-285, 375/316, 375/346, 375/259, 375/267, 370/281, 370/295, 370/302, 370/343, 370480-481, 455/456.5, 455/456.6, 455/561, 455/91, 455/101, 455/103, 455/456
• US Class Current: 375/267
• 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 1/0026 Transmission of channel quality indication
• CPC Class Codes: H04L 1/20 using signal quality detector
• CPC Class Codes: H04L 25/0202 Channel estimation
• CPC Class Codes: H04L 25/0222 Estimation of channel variability, e.g. coherence bandwidth, coherence time, fading frequency

Abstract

A first wireless communication device recovers data from a transmission received over a wireless channel from a second wireless communication device and processes the received data with each of multiple channel variation compensations to produce corresponding processed received data subjected to respective ones of the multiple channel variation compensations. For symbols in the received data and in each of the processed received data, distances are computed to their closest symbols in a symbol constellation set used in the wireless transmission. A corresponding distance metric is computed from the distances for symbols in the received data and from the distances for symbols in each of the processed received data resulting in a distance metric for the received data, and a distance metric for each of the processed received data. Channel variation of a wireless channel between the first and second wireless communication devices is estimated based on the distance metrics.

Claims

1. A method comprising:

receiving at a first wireless communication device a wireless transmission sent by a second wireless communication device;

recovering received data from the wireless transmission received at the first wireless communication device;

processing the received data with each of multiple channel variation compensations to produce corresponding processed received data subjected to respective ones of the multiple channel variation compensations;

for symbols in the received data and in each of the processed received data, computing distances to their closest symbols in a symbol constellation set used by the second wireless communication device in the wireless transmission and computing a corresponding distance metric from the distances for symbols in the received data and from the distances for symbols in each of the processed received data; and

determining a channel variation of a wireless channel between the first wireless communication device and the second wireless communication device based on the distance metrics.

2. The method of claim 1, and further comprising adapting at least one of a transmission modulation and transmission data rate used by the first wireless communication device when transmitting to the second wireless communication device based on the channel variation.

3. The method of claim 1, wherein determining comprises generating data describing a curve derived from the distance metric from the distances for symbols in the received data and distance metrics from the distances for symbols in each of the processed received data, computing a minimum of the curve, computing a distance between the minimum to a reference and generating an estimated channel variation value based on the distance between the minimum of the curve to the reference.

4. The method of claim 3, wherein determining further comprises classifying channel variation of the wireless channel as one of a plurality of channel variation types based on the estimated channel variation value.

5. The method of claim 4, wherein classifying comprises classifying the wireless channel as one of stationary, varied and highly varied, based on the estimated channel variation value.

6. The method of claim 1, wherein processing comprises processing the received data with each of multiple Doppler shifts, and wherein computing comprises computing a distance metric for the received data with no imposed Doppler shift and computing a distance metric for each of the processed received data resulting from processing by respective ones of the Doppler shifts.

7. The method of claim 6, wherein processing comprises processing the received data with a first positive Doppler shift and with a second negative Doppler shift, and wherein computing comprises computing a first distance metric for the received data with no imposed Doppler shift, computing a second distance metric for processed received data resulting from the first positive Doppler shift and a third distance metric for processed received data resulting from the second negative Doppler shift.

8. The method of claim 7, wherein determining comprises generating data describing a curve derived from the first, second and third distance metrics according to a predetermined finite order function, computing a minimum of the curve, computing a distance between the minimum to a zero Doppler shift reference, and generating an estimated Doppler shift channel variation value based on the distance between the minimum of the curve to the zero Doppler shift reference.

9. The method of claim 8, wherein determining further comprises classifying channel variation of the wireless channel as one of a plurality of channel variation types based on the estimated Doppler shift channel variation value.

10. The method of claim 1, and further comprising comparing the distance metric for the received data with a threshold, and wherein processing the received data to produce the processed received data for multiple channel variation compensations and computing distance metrics for each of the processed received data are performed only when the distance metric for the received data is less than the threshold.

11. The method of claim 10, wherein when the distance metric for the received data is greater than the threshold, said determining is based solely on the distance metric for the received data.

12. An apparatus comprising:

at least one antenna;

a receiver that is configured to connect to the at least one antenna and to produce a received signal associated with wireless transmissions received from another wireless communication apparatus;

a controller configured to connect to the receiver, wherein the controller is configured to;

recover received data from the received signal;

process the received data with each of multiple channel variation compensations to produce corresponding processed received data subjected to respective ones of the multiple channel variation compensations;

for symbols in the received data and in each of the processed received data, compute distances to their closest symbols in a symbol constellation set used by the second wireless communication in the wireless transmissions and compute a corresponding distance metric from the distances for symbols in the received data and from the distances for symbols in each of the processed received data; and

determine a channel variation of a wireless channel with respect to the other wireless communication apparatus based on the distance metrics.

13. The apparatus of claim 12, wherein the controller is configured to adapt at least one of a transmission modulation scheme and data rate when transmitting to the other wireless communication apparatus based on the channel variation determined for the wireless channel.

14. The apparatus of claim 12, wherein the controller is configured to determine the channel variation by generating data describing a curve derived from the distance metric from the distances for symbols in the received data and distance metrics from the distances for symbols in each of the processed received data, computing a minimum of the curve, computing a distance between the minimum to a reference and generating an estimated channel variation value based on the distance between the minimum of the curve to the reference.

15. The apparatus of claim 14, wherein the controller is configured determine channel variation by classifying channel variation of the wireless channel as one of a plurality of channel variation types based on the estimated channel variation value.

16. The apparatus of claim 12, wherein the controller is configured to process the received data with each of multiple Doppler shifts, and is configured to compute a distance metric for the received data with no imposed Doppler shift and to compute a distance metric for each of the processed received data resulting from respective ones of the Doppler shifts.

17. The apparatus of claim 12, wherein the controller is further configured to compare the distance metric for the received data with a threshold, and wherein the controller is configured to process the received data to produce the processed received data for multiple channel variation compensations and to compute distance metrics for each of the processed received data only when the distance metric for the received data is less than the threshold.

18. The apparatus of claim 17, wherein when the distance metric for the received data is greater than the threshold, the controller is configured to determine the channel variation based solely on the distance metric for the received data.

19. A tangible computer-readable medium comprising logic for execution encoded therein that when executed is operable to:

recover received data from a wireless transmission received at a first wireless communication device from a second wireless communication device;

process the received data with each of multiple channel variation compensations to produce corresponding processed received data subjected to respective ones of the multiple channel variation compensations;

for symbols in the received data and each of the processed received data, compute distances to their closest symbols in a symbol constellation set used by the second wireless communication device in the wireless transmission and compute a corresponding distance metric from the distances for symbols in the received data and from the distances for symbols in each of the processed received data; and

determine a channel variation of a wireless channel between the first wireless communication device and the second wireless communication device based on the distance metrics.

20. The tangible computer-readable medium of claim 19, and further comprising logic that is configured to adapt at least one of a transmission modulation and transmission data rate used by the first wireless communication device when transmitting to the second wireless communication device based on the channel variation determined for the wireless channel.

21. The tangible computer-readable medium of claim 19, wherein the logic that processes is configured to process the received data with each of multiple Doppler shifts, and the logic that computes is configured to compute a distance metric for the received data with no imposed Doppler shift and to compute a distance metric for each of the processed received data resulting from respective ones of the Doppler shifts.

22. The tangible computer-readable medium of claim 21, wherein the logic that determines comprises logic that is configured to generate data describing a curve derived from the distance metric from the distances for symbols in the received data and distance metrics from the distances for symbols in each of the processed received data according to a predetermined finite order function, computing a minimum of the curve, compute a distance between the minimum to a zero Doppler shift reference, and generate an estimated Doppler shift channel variation value based on the distance between the minimum of the curve to the zero Doppler shift reference.

23. The tangible computer-readable medium of claim 22, wherein the logic that determines is configured to classify channel variation of the wireless channel as one of a plurality of channel variation types based on the estimated Doppler shift channel variation value.

24. The tangible computer-readable medium of claim 19, and further comprising logic that is configured to compare the distance metric for the received data with a threshold, and wherein the logic that processes is configured to process the received data to produce the processed received data for multiple channel variation compensations and the logic that computes distance metrics for each of the processed received data are performed only when the distance metric for the received data is less than the threshold.

25. The tangible computer-readable medium of claim 24, wherein the logic that determines is configured to determine the channel variation based solely on the distance metric for the received data when the distance metric for the received data is greater than the threshold.