Pilot interference cancellation

• US 8,630,602 B2
• Filed: 06/15/2009
• Issued: 01/14/2014
• Est. Priority Date: 08/22/2005
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Attar, Rashid Ahmed A., Jou, Yu-Cheun, Black, Peter J., Ma, Jun
• Primary Examiner(s): Afshar, Kamran
• Assistant Examiner(s): Iqbal, Khawar
• Application Number:
  US12/484,572
• Publication Number:
  US 20090252201A1
• Time in Patent Office: 1,674 Days
• Field of Search: 455/442, 455/296, 455/63.1, 455/114.2, 455/1, 375/147, 375/148, 375/144, 375/346
• US Class Current: 455/296
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 1/71075 Parallel interference cancellation
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04L 25/0224 using sounding signals
• CPC Class Codes: H04W 52/12 Outer and inner loops

Abstract

Techniques for generalized pilot interference cancellation in a communications receiver. In an exemplary embodiment, a residual pilot is cancelled from a post-traffic cancellation signal following initial first-pass pilot cancellation. Residual pilot cancellation is achieved by adding the first-pass cancelled pilot as earlier stored in memory back to the post-traffic cancellation signal, and pilot filtering the resulting signal to generate an improved pilot interference estimate. In an alternative exemplary embodiment, an arbitrary number of iterations may be applied to generate the pilot interference estimate by successively storing each generated pilot interference estimate in memory.

Claims

1. A method for processing a composite receive signal, the composite receive signal comprising a first channel and a second channel, the method comprising:

estimating the first channel to generate a first estimate;

cancelling the first estimate from the composite receive signal;

decoding at least a portion of the second channel to generate decoded symbols;

re-estimating the first channel based at least in part on the decoded symbols to generate a second estimate, wherein re-estimating the first channel is further based at least in part on additional symbols of the second channel received after decoding the portion of the second channel; and

cancelling a residual estimate from the composite receive signal, the residual estimate comprising the difference between the first and second channel estimates.

2. The method of claim 1, the first channel comprising a pilot, the second channel comprising data, the estimating of the first channel comprising:

correlating the composite signal with the pilot; and

spreading the result of the correlating with the pilot.

3. The method of claim 1, the first channel comprising a pilot, the second channel comprising data, the re-estimating of the first channel comprising:

correlating the composite signal with the pilot and the decoded symbols; and

spreading the result of the correlating with the pilot.

4. The method of claim 3, the method further comprising storing the first estimate in a pilot memory, the re-estimating the first channel further comprising:

adding the first estimate to the composite signal prior to the correlating.

5. The method of claim 1, further comprising weighting the residual estimate with a function of the signal-to-noise ratio associated with the second estimate prior to cancelling the residual estimate from the composite receive signal.

6. The method of claim 1, the composite receive signal further comprising a third channel, the method further comprising:

reconstructing the second channel based on the decoded symbols to generate a reconstructed second channel;

cancelling the reconstructed second channel from the composite receive signal; and

decoding the third channel to further generate decoded symbols.

7. The method of claim 6, the first channel comprising a pilot of a first user, the second channel comprising traffic data of a first user, the third channel comprising traffic data of a second user.

8. The method of claim 6, comprising re-estimating the first channel prior to cancelling the reconstructed second channel from the composite receive signal.

9. A method for processing a composite receive signal, the composite receive signal comprising a first channel and a second channel, the method comprising:

decoding the second channel to generate decoded symbols;

estimating the first channel to generate a first estimate;

cancelling the first estimate from the composite receive signal prior to decoding the second channel;

estimating the first channel based at least in part on the decoded symbols after decoding the second channel to generate a second estimate; and

cancelling the second estimate from a portion of the composite receive signal, the portion received after decoding the second channel.

10. The method of claim 9, the estimating the first channel to generate the second estimate further comprising:

estimating the first channel based on symbols of the second channel received after the decoding of the second channel.

11. The method of claim 9, the estimating the first channel based at least in part on the decoded symbols comprising:

generating an expected transmit pattern for the second channel received after the decoding of the second channel, the generating the expected transmit pattern comprising re-encoding the decoded symbols; and

estimating the first channel by comparing the expected transmit pattern for the second channel with the composite receive signal.

12. The method of claim 11, the estimating the first channel based at least in part on the decoded symbols further comprising comparing the expected transmit pattern for the first channel with the composite receive signal.

13. The method of claim 9, the first channel comprising a pilot, the second channel comprising data, the estimating of the first channel based at least in part on the decoded symbols comprising:

correlating the composite signal with the pilot and the decoded symbols to generate a result, and

spreading the result with the pilot.

14. The method of claim 9, the second channel formatted as a plurality of frames, the decoding of the second channel comprising decoding a frame of the second channel, the estimating of the first channel based at least in part on the decoded symbols comprising:

generating an expected transmit pattern for the remainder of the decoded frame; and

comparing the expected transmit pattern with the composite receive signal.

15. A method for processing a composite receive signal, the composite receive signal comprising a first channel and a second channel, the method comprising:

estimating the first channel to generate a first estimate;

cancelling the first estimate from the composite receive signal;

decoding the second channel to generate decoded symbols;

reconstructing the second channel based on the decoded symbols to generate a reconstructed second channel;

cancelling the reconstructed second channel from the composite receive signal;

re-estimating the first channel after the cancelling the reconstructed second channel to generate a second estimate; and

cancelling a residual estimate from the composite receive signal, the residual estimate comprising the difference between the first and second channel estimates,

wherein the second channel is formatted as a plurality of frames, wherein decoding the second channel comprises decoding a first frame of the plurality of frames, and wherein re-estimating the first channel comprises;

generating an expected transmit pattern for a remainder of the first frame; and

comparing the expected transmit pattern with the composite receive signal.

16. The method of claim 15, the first channel comprising a pilot pattern, the re-estimating of the first channel comprising correlating the composite receive signal with the pilot pattern.

17. A method for processing a composite receive signal, the composite receive signal comprising a first channel and a second channel, the method comprising:

estimating the first channel to generate a first estimate;

cancelling the first estimate from the composite receive signal;

decoding the second channel to generate decoded symbols;

reconstructing the second channel based on the decoded symbols to generate a reconstructed second channel;

cancelling the reconstructed second channel from the composite receive signal;

re-estimating the first channel after the cancelling the reconstructed second channel to generate a second estimate, the re-estimating based at least in part on the decoded symbols; and

cancelling a residual estimate from the composite receive signal, the residual estimate comprising the difference between the first and second channel estimates,

wherein the first channel comprises a pilot, wherein the second channel comprises data, and wherein re-estimating the first channel is further based at least in part on;

correlating the composite receive signal with the pilot and the decoded symbols to generate a result; and

spreading the result with the pilot.

18. An apparatus for processing a composite receive signal, the composite receive signal comprising a first channel and a second channel, the apparatus comprising:

a decoder configured to early decode at least a portion of the second channel to generate decoded symbols;

a channel estimator configured to estimate the first channel based on the first channel to generate a first estimate, the channel estimator further configured to estimate the first channel based at least in part on decoded symbols of the second channel to generate a second estimate; and

a canceller configured to cancel the first estimate from the composite receive signal prior to decoding the second channel, and to cancel the second estimate from the composite receive signal after decoding at least the portion of the second channel,

wherein the channel estimator is further configured to generate an expected transmit pattern for a remainder of the second channel received after decoding the portion of the second channel by re-encoding the decoded symbols and is further configured to estimate the first channel by comparing the expected transmit pattern with the composite receive signal.

19. An apparatus for processing a composite receive signal, the composite receive signal comprising a first channel and a second channel, the apparatus comprising:

means for early decoding at least portion of the second channel to generate decoded symbols;

means for estimating the first channel based on decoded symbols of the second channel to generate a first channel estimate; and

means for cancelling the first channel estimate from the composite receive signal after decoding the second channel,

wherein the means for estimating comprises;

means for generating an expected transmit pattern for a remainder of the second channel received after decoding the portion of the second channel by re-encoding the decoded symbols; and

means for estimating the first channel by comparing the expected transmit pattern with the composite receive signal.

20. A computer-readable tangible storage medium storing instructions executable by a computer to process a composite receive signal, wherein the composite receive signal comprises a first channel and a second channel, the instructions including:

instructions executable by the computer to decode at least a portion of the second channel to generate decoded symbols;

instructions executable by the computer to estimate the first channel to generate a first estimate;

instructions executable by the computer to cancel the first estimate from the composite receive signal prior to decoding the portion of the second channel;

instructions executable by the computer to estimate the first channel based at least in part on the decoded symbols after decoding the portion of the second channel to generate a second estimate;

instructions executable by the computer to generate an expected transmit pattern for a remainder of the second channel received after decoding the portion of the second channel by re-encoding the decoded symbols;

instructions executable by the computer to estimate the first channel by comparing the expected transmit pattern with the composite receive signal; and

instructions executable by the computer to cancel the second estimate from the composite receive signal.