Channel estimation for an OFDM communicaiton system with inactive subbands

• US 8,903,021 B2
• Filed: 03/04/2013
• Issued: 12/02/2014
• Est. Priority Date: 12/19/2003
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Mantravadi, Ashok, Khandekar, Aamod Dinkar, Teague, Edward Harrison, Kadous, Tamer A.
• Primary Examiner(s): Puente, Eva
• Application Number:
  US13/784,531
• Publication Number:
  US 20130177059A1
• Time in Patent Office: 638 Days
• Field of Search: 375/231, 375/316, 375/260, 375/144, 370/208, 370/203, 370/210
• US Class Current: 375/316
• CPC Class Codes: H04L 25/0218 with detection of nulls
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 25/0232 by interpolation between sounding signals

Abstract

For channel estimation in a spectrally shaped wireless communication system, an initial frequency response estimate is obtained for a first set of P uniformly spaced subbands (1) based on pilot symbols received on a second set of subbands used for pilot transmission and (2) using extrapolation and/or interpolation, where P is a power of two. A channel impulse response estimate is obtained by performing a P-point IFFT on the initial frequency response estimate. A final frequency response estimate for N total subbands is derived by (1) setting low quality taps for the channel impulse response estimate to zero, (2) zero-padding the channel impulse response estimate to length N, and (3) performing an N-point FFT on the zero-padded channel impulse response estimate. The channel frequency/impulse response estimate may be filtered to obtain a higher quality channel estimate.

Claims

1. A method of estimating a frequency response of a wireless channel in a wireless communication system, comprising:

obtaining an initial frequency response estimate for a set of P subbands, where P is an integer greater than one;

deriving a time-domain channel impulse response estimate with P taps for the wireless channel based on the initial frequency response estimate;

setting selected ones of the P taps of the channel impulse response estimate to zero; and

deriving a final frequency response estimate for the wireless channel based on the channel impulse response estimate with selected ones of the P taps set to zero.

2. The method of claim 1 further comprising:

determining L, where L is an integer greater than one and less than P, and wherein L is a number of taps which should not be set to zero; and

setting last P-L taps of the channel impulse response estimate to zero.

3. The method of claim 2, wherein the last P-L taps of the channel impulse response estimate are not derived from the initial frequency response estimate.

4. The method of claim 2, wherein L is equal to an expected delay spread for the system.

5. The method of claim 1, further comprising:

determining energy of each of the P taps; and

setting each of the P taps to zero if the energy of the tap is less than a threshold.

6. The method of claim 5, wherein the threshold is derived based on total energy of the P taps for the channel impulse response estimate.

7. The method of claim 5, wherein the threshold is derived based on a coding and modulation scheme selected for use.

8. The method of claim 5, wherein the threshold is derived based on error rate performance requirement.

9. The method of claim 1, further comprising:

determining energy of each of the P taps;

setting each of first L taps to zero if the energy of the tap is less than a first threshold, where L is an integer greater than one and less than P; and

setting each of last P-L taps to zero if the energy of the tap is less than a second threshold that is lower than the first threshold.

10. An apparatus for estimating a frequency response of a wireless channel in a wireless communication system, comprising:

a processor; and

a memory coupled to a processor, the memory storing instructions that, when executed by the processor, cause the processor to;

obtain an initial frequency response estimate for a set of P subbands, where P is an integer greater than one;

derive a time-domain channel impulse response estimate with P taps for the wireless channel based on the initial frequency response estimate;

set selected ones of the P taps of the channel impulse response estimate to zero; and

derive a final frequency response estimate for the wireless channel based on the channel impulse response estimate with selected ones of the P taps set to zero.

11. The apparatus of claim 10, wherein the instructions further cause the processer to:

determine L, where L is an integer greater than one and less than P, and wherein L is a number of taps which should not be set to zero; and

set last P-L taps of the channel impulse response estimate to zero.

12. The apparatus of claim 11, wherein the last P-L taps of the channel impulse response estimate are not derived from the initial frequency response estimate.

13. The apparatus of claim 11, wherein L is equal to an expected delay spread for the system.

14. The apparatus of claim 10, wherein the instructions include instructions that, when executed by the processor, cause the processor to:

determine energy of each of the P taps; and

set each of the P taps to zero if the energy of the tap is less than a threshold.

15. The apparatus of claim 14, wherein the threshold is derived based on total energy of the P taps for the channel impulse response estimate.

16. The apparatus of claim 14, wherein the threshold is derived based on a coding and modulation scheme selected for use.

17. The apparatus of claim 14, wherein the threshold is derived based on error rate performance requirement.

18. The apparatus of claim 10, wherein the instructions include instructions that, when executed by the processor, cause the processor to:

determine energy of each of the P taps;

set each of first L taps to zero if the energy of the tap is less than a first threshold, where L is an integer greater than one and less than P; and

set each of last P-L taps to zero if the energy of the tap is less than a second threshold that is lower than the first threshold.

19. A system of estimating a frequency response of a wireless channel in a wireless communication system, comprising:

means for obtaining an initial frequency response estimate for a set of P subbands, where P is an integer greater than one;

means for deriving a time-domain channel impulse response estimate with P taps for the wireless channel based on the initial frequency response estimate;

means for setting selected ones of the P taps of the channel impulse response estimate to zero; and

means for deriving a final frequency response estimate for the wireless channel based on the channel impulse response estimate with selected ones of the P taps set to zero.

20. The system of claim 19 further comprising:

means for determining L, where L is an integer greater than one and less than P, and wherein L is a number of taps which should not be set to zero; and

means for setting last P-L taps of the channel impulse response estimate to zero.

21. The system of claim 20, wherein the last P-L taps of the channel impulse response estimate are not derived from the initial frequency response estimate.

22. The system of claim 20, wherein L is equal to an expected delay spread for the system.

23. The system of claim 19, further comprising:

a processor operable to determine energy of each of the P taps and to set each of the P taps to zero if the energy of the tap is less than a threshold.

24. The system of claim 23, wherein the threshold is derived based on total energy of the P taps for the channel impulse response estimate.

25. The system of claim 23, wherein the threshold is derived based on a coding and modulation scheme selected for use.

26. The system of claim 23, wherein the threshold is derived based on error rate performance requirement.

27. The system of claim 19, further comprising:

a processor operable to determine energy of each of the P taps,

to set each of first L taps to zero if the energy of the tap is less than a first threshold, where L is an integer greater than one and less than P, and

to set each of last P-L taps to zero if the energy of the tap is less than a second threshold that is lower than the first threshold.

28. A non-transitory processor readable media for storing instructions operable to:

obtain an initial frequency response estimate for a set of P subbands, where P is an integer greater than one;

derive a time-domain channel impulse response estimate with P taps for the wireless channel based on the initial frequency response estimate;

set selected ones of the P taps of the channel impulse response estimate to zero; and

derive a final frequency response estimate for the wireless channel based on the channel impulse response estimate with selected ones of the P taps set to zero.