Radio channel analyzer to determine doppler shifts across multiple frequencies of a wideband signal

• US 8,401,487 B2
• Filed: 12/30/2009
• Issued: 03/19/2013
• Est. Priority Date: 12/30/2009
• Status: Active Grant

• Current Assignee: Optis Cellular Technology LLC (Brevet Capital)
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Dent, Paul W., Krasny, Leonid
• Primary Examiner(s): Lu, Zhiyu
• Assistant Examiner(s): Bilodeau, David
• Application Number:
  US12/650,201
• Publication Number:
  US 20110158361A1
• Time in Patent Office: 1,175 Days
• Field of Search: 455/67.11, 455/446, 375/224, 375/260, 375/347
• US Class Current: 455/67.11
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 25/0222 Estimation of channel variability, e.g. coherence bandwidth, coherence time, fading frequency
• CPC Class Codes: H04L 25/0232 by interpolation between sounding signals

Abstract

A receiver and receive processing method described herein improves the accuracy of channel estimates by correcting for the assumption that the Doppler shift (or rate-of-change-of-delay) stays constant for each frequency within a signal bandwidth of a received signal. To that end, a receiver according to the present invention comprises a channel processor having multiple processing units. A first processing unit processes reference values (e.g., pilot signals) received for each of a plurality of frequencies within a signal bandwidth at a plurality of different signal times (or the complex propagation channel coefficients estimated therefrom) to determine a set of complex wave amplitudes either for each of multiple frequencies in the signal bandwidth or for each of the different signal times. A second processing unit subsequently processes the complex wave amplitudes to determine complex scattering coefficients, where each complex scattering coefficient corresponds to a respective scattering object in the wireless communication channel.

Claims

1. A method implemented in a wireless device of analyzing multi-path signals received over a wireless communication channel to characterize scattering objects in the wireless communication channel, the method comprising:

receiving a reference value for each of a plurality of frequencies within a signal bandwidth at a plurality of different signal times;

processing said reference values or complex propagation channel coefficients estimated therefrom to determine one of;

a set of Doppler shifts of scattered wave energy and a corresponding set of complex wave amplitudes for each of multiple frequencies within the signal bandwidth, each Doppler shift corresponding to a different angle of arrival; and

a set of path delays and a corresponding set of complex wave amplitudes for each of multiple signal times within an analysis interval; and

processing said complex wave amplitudes to determine;

a set of path delays corresponding to each angle of arrival or a set of angles of arrival corresponding to each determined path delay; and

a complex scattering coefficient for each combination of path delay and angle of arrival, wherein each complex scattering coefficient corresponds to a respective scattering object in the wireless communication channel.

2. The method of claim 1 further comprising interpolating the reference values or the complex propagation channel coefficients estimated therefrom to generate interpolated values at a series of re-sampled times within the analysis interval, wherein the re-sampled times have a different time spacing for different ones of said multiple frequencies such that the product of each time spacing and the corresponding frequency is substantially constant across the multiple frequencies, and wherein processing the reference values or complex propagation channel coefficients estimated therefrom comprises processing the interpolated values.

3. The method of claim 2 wherein processing the interpolated values comprises:

processing the interpolated values jointly over a number of said multiple frequencies to determine a set of frequency-scaled Doppler shifts common to said multiple frequencies to thereby determine a set of rate-of-change-of-delay values that each correspond to the same angle of arrival for said multiple frequencies; and

determining the set of complex wave amplitudes for each of said multiple frequencies based on the rate-of-change-of-delay values and the interpolated values.

4. The method of claim 3 wherein processing the interpolated values jointly over a number of the multiple frequencies comprises applying a joint Prony algorithm to the interpolated values over a number of the multiple frequencies.

5. The method of claim 2 wherein processing the interpolated values comprises processing the interpolated values jointly over said series of re-sampled times in the analysis interval to determine the set of path delays common to the re-sampled times and a corresponding set of complex wave amplitudes for each re-sampled time.

6. The method of claim 5 wherein processing said complex wave amplitudes comprises:

processing the complex wave amplitudes to determine a set of frequency-scaled Doppler shifts for each determined path delay to thereby determine a set of rate-of-change-of-delay values that each correspond to the same angle of arrival across said multiple frequencies; and

determining a corresponding complex scattering coefficient for each combination of path delay and frequency-scaled Doppler shift based on the rate-of-change-of-delay values and the corresponding complex wave amplitudes.

7. The method of claim 6 wherein processing said complex wave amplitudes comprises processing the complex wave amplitudes using a Prony algorithm to determine the set of frequency-scaled Doppler shifts for each determined path delay.

8. The method of claim 5 wherein processing the interpolated values comprises processing the interpolated values jointly using a joint inverse Prony algorithm.

9. The method of claim 1 wherein processing the reference values or the complex propagation channel coefficients estimated therefrom comprises applying a Prony algorithm to the reference values or the complex propagation channel coefficients estimated therefrom to determine the set of Doppler shifts and the corresponding complex wave amplitudes.

10. The method of claim 9 wherein processing said complex wave amplitudes comprises applying an inverse Prony algorithm to the complex wave amplitudes to determine the sets of path delays and the corresponding scattering coefficients.

11. The method of claim 1 further comprising processing the received reference values to estimate the complex propagation channel coefficients at each of the multiple frequencies for the plurality of different signal times.

12. The method of claim 1 further comprising predicting channel estimates for one or more transmit frequencies associated with a fixed network station based on the path delays.

13. The method of claim 12 wherein predicting the channel estimates further comprises predicting the channel estimates for said transmit frequencies at future times based on said Doppler shifts and angles of arrival.

14. The method of claim 13 wherein predicting the channel estimates further comprises smoothing the predicted channel estimates for at least one of the transmit frequencies and one of the future times based on the determined combinations of path delays and angles of arrival.

15. The method of claim 14 wherein smoothing the channel estimates comprises de-weighting the scattering coefficients corresponding to the weak scattering objects relative to the scattering coefficients corresponding to the strong scattering objects to determine the smoothed channel estimates for at least one of the transmit frequencies and future times.

16. The method of claim 1 wherein the wireless device is incorporated into a fixed network station, and wherein receiving the plurality of reference values comprises receiving the plurality of reference values from one or more mobile stations.

17. The method of claim 1 further comprising determining a location of at least one of the mobile stations based on the determined combinations of path delays and angles of arrival.

18. The method of claim 1 wherein the plurality of frequencies comprise a plurality of OFDM subcarriers and the plurality of different signal times comprise a plurality of OFDM symbol periods.

19. A wireless device for analyzing multi-path signals received over a wireless communication channel to characterize scattering objects in the wireless communication channel, the device comprising:

a receiver configured to receive a reference value for each of a plurality of frequencies within a signal bandwidth at a plurality of different signal times;

a first processing unit configured to process said reference values or complex propagation channel coefficients estimated therefrom to determine one of;

a set of Doppler shifts of scattered wave energy and a corresponding set of complex wave amplitudes for each of multiple frequencies within the signal bandwidth, each Doppler shift corresponding to a different angle of arrival; and

a set of path delays and a corresponding set of complex wave amplitudes for each of multiple signal times within an analysis interval; and

a second processing unit configured to process said complex wave amplitudes output by the first processing unit to determine;

a set of path delays corresponding to each angle of arrival or a set of angles of arrival corresponding to each determined path delay; and

a complex scattering coefficient for each combination of path delay and angle of arrival, wherein each complex scattering coefficient corresponds to a respective scattering object in the wireless communication channel.

20. The device of claim 19 further comprising an interpolator configured to interpolate the reference values or the complex propagation channel coefficients estimated therefrom to generate interpolated values at a series of re-sampled times within the analysis interval, wherein the re-sampled times have a different time spacing for different ones of said multiple frequencies such that the product of each re-sampled time spacing and the corresponding frequency is substantially constant across the multiple frequencies, and wherein the first processing unit processes the reference values or complex propagation channel coefficients estimated therefrom by processing the interpolated values.

21. The device of claim 20 wherein said first processing unit is configured to process the interpolated values jointly over a number of the multiple frequencies to determine a set of frequency-scaled Doppler shifts common to said multiple frequencies to thereby determine a set of rate-of-change-of-delay values that each correspond to the same angle of arrival for said multiple frequencies.

22. The device of claim 21 wherein said first processing unit is configured to determine the set of complex wave amplitudes for each of said multiple frequencies based on the rate-of-change-of-delay values and the interpolated values.

23. The device of claim 21 wherein said first processing unit processes the interpolated values jointly over the number of the multiple frequencies using a joint Prony algorithm.

24. The method of claim 20 wherein the first processing unit is configured to process the interpolated values jointly over said series of re-sampled times to determine the set of path delays common to the re-sampled times and a corresponding set of complex wave amplitudes for each re-sampled time within the analysis interval.

25. The device of claim 24 wherein said second processing unit is configured to process the complex wave amplitudes output by said first processing unit to determine a set of frequency-scaled Doppler shifts for each path delay determined by said first processing unit to thereby determine a set of rate-of-change-of-delay values that each correspond to the same angle of arrival for said multiple frequencies.

26. The device of claim 25 wherein said second processing unit is configured to determine a complex scattering coefficient for each combination of path delay and frequency-scaled Doppler shift based on the rate-of-change-of-delay values and the corresponding complex wave amplitudes.

27. The device of claim 26 wherein said second processing unit is configured to processes the complex wave amplitudes using a joint inverse Prony algorithm.

28. The device of claim 25 wherein the first processing unit is configured to process the interpolated values jointly using a joint inverse Prony algorithm.

29. The device of claim 19 wherein said first processing unit processes the reference values or the complex propagation channel coefficients estimated therefrom using a Prony algorithm to determine the set of Doppler shifts and the corresponding complex wave amplitudes.

30. The device of claim 29 wherein said second processing unit processes the complex wave amplitudes using an inverse Prony algorithm to determine the sets of path delays and the corresponding scattering coefficients.

31. The device of claim 19 wherein the receiver includes a channel estimator configured to process the received reference values to estimate the complex propagation channel coefficients at each of the multiple frequencies for the plurality of different signal times.

32. The device of claim 19 wherein the second processor is further configured to determine smoothed channel estimates for at least one frequency and time instant based on the determined combinations of path delays and angles of arrival.

33. The device of claim 32 wherein the second processor is further configured to de-weight the scattering coefficients corresponding to the weak scattering objects relative to the scattering coefficients corresponding to the strong scattering objects to determine the smoothed channel estimates for at least one frequency and time instant.

34. The device of claim 19 wherein the device is incorporated into a fixed network station, and wherein the receiver receives the plurality of reference values from one or more mobile stations.

35. The device of claim 34 further comprising a channel predictor configured to predict complex propagation channel coefficients for one or more transmit frequencies associated with said fixed network station based on the path delays.

36. The device of claim 34 wherein the channel predictor is further configured to predict the complex propagation channel coefficients for said transmit frequencies at future times based on said Doppler shifts and angles of arrival.

37. The device of claim 34 further comprising a mobile locator configured to determine a location of at least one of the mobile stations based on the determined combinations of delays and angles of arrival.

38. The device of claim 19 wherein the plurality of frequencies comprise a plurality of OFDM subcarriers and the plurality of different signal times comprise a plurality of OFDM symbol periods.