Method and apparatus for canceling pilot interference in a wireless communication system

• US 7,190,749 B2
• Filed: 10/10/2001
• Issued: 03/13/2007
• Est. Priority Date: 06/06/2001
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Bender, Paul E., Levin, Jeffrey A., Butler, Brian K., Wilborn, Thomas B.
• Primary Examiner(s): Kim; Kevin
• Application Number:
  US09/974,935
• Publication Number:
  US 20030021334A1
• Time in Patent Office: 1,980 Days
• Field of Search: 375/346, 375/349, 375/350
• US Class Current: 375/346
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception

Abstract

Techniques for canceling pilot interference in a wireless (e.g., CDMA) communication system. In one method, a received signal comprised of a number of signal instances, each including a pilot, is initially processed to provide data samples. Each signal instance'"'"'s pilot interference may be estimated by despreading the data samples with a spreading sequence for the signal instance, channelizing the despread data to provide pilot symbols, filtering the pilot symbols to estimate the channel response of the signal instance, and multiplying the estimated channel response with the spreading sequence to provide the estimated pilot interference. The pilot interference estimates due to all interfering multipaths are combined to derive the total pilot interference, which is subtracted from the data samples to provide pilot-canceled data samples. These samples are then processed to derive demodulated data for each of at least one (desired) signal instance in the received signal.

Claims

1. A method for canceling pilot interference at a receiver unit in a wireless communication system, comprising:

receiving a signal comprised of a plurality of signal instances, wherein each signal instance includes a pilot and data;

estimating pilot interference due to each of the plurality of signal instances;

accumulating estimated pilot interference due to the plurality of signal instances in a buffer to provide a total pilot interference;

subtracting the total pilot interference from the received signal to derive a pilot-canceled signal; and

processing the pilot-canceled signal to derive data for each signal instance in the received signal,

wherein the pilot interference due to each of the one or more signal instances is estimated by

processing the signal instance to derive an estimate of a channel response of the signal instance; and

multiplying pilot data for the signal instance with the estimated channel response to provide the estimated pilot interference.

2. The method of claim 1, wherein the pilot data for each of the one or more signal instances is a spreading sequence for the signal instance.

3. The method of claim 2, wherein the spreading sequence for the signal instance has a phase corresponding to an arrival time of the signal instance.

4. The method of claim 1, wherein the estimated channel response for each of the one or more signal instances is derived by

despreading data samples for the received signal with a spreading sequence for the signal instance,

channelizing the despread samples with a pilot channelization code to provide pilot symbols, and

filtering the pilot symbols to provide the estimated channel response.

5. The method of claim 1, wherein the estimated channel response of the signal instance is derived based on a current segment of data samples for the received signal and the estimated pilot interference is for a subsequent segment of data samples.

6. The method of claim 1, wherein the estimated channel response of the signal instance is derived based on a current segment of data samples for the received signal and the estimated pilot interference is for the same segment of data samples.

7. The method of claim 1, wherein the estimated channel response for each of the one or more signal instances is derived based on data samples for the received signal.

8. The method of claim 1, wherein the estimated channel response for each of the one or more signal instances is derived based on data samples having pilot from the signal instance unremoved but pilots from other interfering signal instances removed.

17. The method of claim 1, wherein the deriving the total pilot interference is performed based on segments of data samples for the received signal.

18. The method of claim 17, wherein the each segment includes data samples for one symbol period.

19. The method of claim 1, wherein the processing to derive data is performed based on segments of pilot-canceled data samples for the pilot-canceled signal.

21. The method of claim 1, wherein the deriving the total pilot interference and the processing of the pilot-canceled signal are performed in a pipelined manner.

22. The method of claim 1, wherein the wireless communication system is a CDMA system.

23. The method of claim 22, wherein the CDMA system supports cdma2000 standard.

24. The method of claim 22, wherein the CDMA system supports W-CDMA standard.

25. The method of claim 22, wherein the CDMA system supports IS-95 standard.

26. The method of claim 22, wherein the received signal comprises one or more reverse link modulated signals in the CDMA system.

27. The method of claim 22, wherein the received signal comprises one or more forward link modulated signals in the CDMA system.

9. A method for canceling pilot interference at a receiver unit in a wireless communication system, the method comprising:

receiving a signal comprised of a plurality of signal instances, each signal instance comprising a pilot and data;

deriving total pilot interference due to one or more signal instances;

subtracting the total pilot interference from the received signal to derive a pilot-canceled signal; and

processing the pilot-canceled signal to derive demodulated data for each of at least one signal instance in the received signal,

wherein the processing of the pilot-canceled signal for each of the at least one signal instance includes;

despreading samples for the pilot-canceled signal with a spreading sequence for the signal instance;

channelizing the despread samples with a data channelization code to provide data symbols; and

demodulating the data symbols with pilot estimates to provide the demodulated data for the signal instance.

10. The method of claim 9, wherein the pilot estimates for each of the at least one signal instance are derived based on data samples for the received signal.

11. The method of claim 9, wherein the pilot estimates for each of the at least one signal instance are derived based on data samples having pilot from the signal instance unremoved but pilots from other interfering signal instances removed.

12. A method for canceling pilot interference at a receiver unit in a wireless communication system, the method comprising:

receiving a signal comprised of a plurality of signal instances, each signal instance comprising a pilot and data;

deriving total pilot interference due to one or more signal instances;

subtracting the total pilot interference from the received signal to derive a pilot-canceled signal; and

processing the pilot-canceled signal to derive data for each of at least one signal instance in the received signal, wherein the pilot interference due to the one or more signal instances is estimated in a time-division multiplexed manner.

13. A method for canceling pilot interference at a receiver unit in a wireless communication system, comprising:

receiving a signal comprised of a plurality of signal instances, wherein each signal instance includes a pilot and data;

estimating pilot interference due to each of the plurality of signal instances;

accumulating estimated pilot interference due to the plurality of signal instances in a buffer to provide a total pilot interference;

subtracting the total pilot interference from the received signal to derive a pilot-canceled signal; and

processing the pilot-canceled signal to derive data for each signal instance in the received signal,

wherein the subtracting includes subtracting samples for the total pilot interference from data samples for the received signal, and

wherein the samples for the total pilot interference and data samples are both provided at a particular sample rate.

16. The method of claim 13, wherein the sample rate is multiple times a chip rate.

14. A method for canceling pilot interference at a receiver unit in a wireless communication system, comprising:

receiving a signal comprised of a plurality of signal instances, wherein each signal instance includes a pilot and data;

estimating pilot interference due to each of the plurality of signal instances;

accumulating estimated pilot interference due to the plurality of signal instances in a buffer to provide a total pilot interference;

subtracting the total pilot interference from the received signal to derive a pilot-canceled signal; and

processing the pilot-canceled signal to derive data for each signal instance in the received signal,

wherein the pilot interference due to a signal instance being processed to derive the data is excluded from the total pilot interference.

15. A method for canceling pilot interference at a receiver unit in a wireless communication system, the method comprising:

receiving a signal comprised of a plurality of signal instances, each signal instance comprising a pilot and data;

deriving total pilot interference due to one or more signal instances;

subtracting the total pilot interference from the received signal to derive a pilot-canceled signal;

processing the pilot-canceled signal to derive data for each of at least one signal instance in the received signal; and

processing the pilot-canceled signal to search for new signal instances in the received signal.

20. A method for canceling pilot interference at a receiver unit in a wireless communication system, comprising:

receiving a signal comprised of a plurality of signal instances, wherein each signal instance includes a pilot and data;

estimating pilot interference due to each of the plurality of signal instances;

accumulating estimated pilot interference due to the plurality of signal instances in a buffer to provide a total pilot interference;

subtracting the total pilot interference from the received signal to derive a pilot-canceled signal; and

processing the pilot-canceled signal to derive data for each signal instance in the received signal,

wherein the deriving the total pilot interference and the processing of the pilot-canceled signal are performed in parallel.

28. A method for canceling pilot interference at a receiver unit in a wireless communication system, comprising:

processing a received signal comprised of a plurality of signal instances to provide data samples, wherein each signs) instance includes a pilot;

processing the data samples to derive an estimate of pilot interference due to each of one or more signal instances;

deriving total pilot interference due to the one or more signal instances based on the estimated pilot interference;

subtracting the total pilot interference from the data samples to derive pilot-canceled data samples; and

processing the pilot-canceled data samples to derive data for each of at least one signal instance in the received signal, wherein the processing the data samples to derive the estimated pilot interference due to each of the one or more signal instances includes

despreading the data samples with a spreading sequence for the signal instance,

channelizing the despread samples with a pilot channelization code to provide pilot symbols,

filtering the pilot symbols to provide an estimate or a channel response of the signal instance, and

multiplying the spreading sequence for the signal instance with the estimated channel response to provide the estimated pilot interference due to the signal instance.

29. A method for canceling pilot interference at a receiver unit in a wireless communication system, comprising:

processing a received signal comprised of a plurality of signal instances to provide data samples, wherein each signal instance includes a pilot;

processing the data samples to derive an estimate of pilot interference due to each of one or more signal instances;

deriving total pilot interference due to the one or more signal instances based on the estimated pilot interference;

subtracting the total pilot interference from the data samples to derive pilot-canceled data samples; and

processing the pilot-canceled data samples to derive demodulated data for each of at least one signal instance in the received signal, wherein the processing the pilot-canceled data samples to derive the demodulated data for each of the at least one signal instance includes

despreading the pilot-canceled data samples with a spreading sequence for the signal instance,

channelizing the despread samples with a data channelization code to provide data symbols, and

demodulating the data symbols to provide the demodulated data for the signal instance.

30. The method of claim 29, wherein the subtracting includes

subtracting interference samples for the total pilot interference from the data samples for the received signal, wherein the interference samples and data samples are both provided at a particular sample rare that is multiple times a chip rate.

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

a receiver configured to process a received signal comprised of a plurality of signal instances to provide data samples, wherein each signal instance includes a pilot and data; and

a demodulator including;

a pilot interference estimator configured to process the data samples to derive an estimate of pilot interference due to each of the plurality of signal instances;

a buffer configured to accumulate estimated pilot interference due to the plurality of signal instances to provide a total pilot interference;

a summer configured to subtract the total pilot interference from the data samples to derive pilot-canceled data samples;

a data demodulation unit configured to process the pilot-canceled data samples to derive data for each signal instance in the received signal; and

a channel estimator configured to provide an estimated channel response for each of the one or more signal instances.

32. The receiver unit of claim 31, wherein the pilot interference estimator is further configured to multiply pilot data for each of the one or more signal instances with the estimated channel response for the signal instance to provide the estimated pilot interference due to the signal instance.

40. The receiver unit of claim 31, further comprising an interference accumulator unit configured to accumulate the total pilot interference for the one or more signal instances.

41. The interference accumulator unit of claim 40, further comprising:

a plurality of sections defined by a time offset.

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

a receiver configured to process a received signal comprised of a plurality of signal instances to provide data samples, wherein each signal instance includes a pilot and data; and

a demodulator including;

a pilot interference estimator configured to process the data samples to derive an estimate of pilot interference due to each of one or more signal instances and to derive total pilot interference due to the one or more signal instances based on the estimated pilot interference,

a summer configured to subtract the total pilot interference from the data samples to derive pilot-canceled data samples, and

a data demodulation unit configured to process the pilot-canceled data samples to derive demodulated data for each of at least one signal instance in the received signal, wherein for each of the at least one signal instance the data demodulation unit is configured to despread the pilot-canceled data samples with a spreading sequence for the signal instance, channelize the despread samples with a data channelization code to provide data symbols, and demodulate the data symbols with pilot estimates for the signal instance to provide the demodulated data for the signal instance.

34. A terminal in a CDMA system, the terminal comprising:

a receiver configured to process a received signal comprised of a plurality of signal instances to provide data samples, wherein each signal instance includes a pilot and data; and

a demodulator including

a pilot interference estimator configured to process the data samples to derive an estimate of pilot interference due to each of the plurality of signal instances;

a buffer configured to accumulate estimated pilot interference due to the plurality of signal instances to provide a total pilot interference;

a summer configured to subtract the total pilot interference from the data samples to derive pilot-canceled data samples;

a data demodulation unit configured to process the pilot-canceled data samples to derive data for each signal instance in the received signal; and

a channel estimator configured to provide an estimated channel response for each of the one or more signal instances.

35. The terminal of claim 34, wherein the pilot interference estimator is further configured to multiply pilot data for each of the one or more sign) instances with the estimated channel response for the signal instance to provide the estimated pilot interference due to the signal instance.

36. A terminal in a CDMA system, the terminal comprising

a receiver configured to process a received signal comprised of a plurality of signal instances to provide data samples, wherein each signal instance includes a pilot and data;

and

a demodulator including

a pilot interference estimator configured to process the data samples to derive an estimate of pilot interference due to each of one or more signal instances and to derive total pilot interference due to the one or more signal instances based on the estimated pilot interference;

a summer configured to subtract the total pilot interference from the data samples to derive pilot-canceled data samples; and

a data demodulation unit configured to process the pilot-canceled data samples to derive demodulated data for each of at least one signal instance in the received signal, wherein for each of the at least one signal instance the data demodulation unit is configured to despread the pilot-canceled data samples with a spreading sequence for the signal instance, channelize the despread samples with a data channelization code to provide data symbols, and demodulate the data symbols with pilot estimates for the signal instance to provide the demodulated data for the signal instance.

37. A base station in a CDMA system, the base station comprising:

a receiver configured to process a received signal comprised of a plurality of signal instances to provide data samples, wherein each signal instance includes a pilot and data; and

a demodulator including

a pilot interference estimator configured to process the data samples to derive an estimate of pilot interference due to each of the plurality of signal instances;

a buffer configured to accumulate estimated pilot interference due to the plurality of signal instances to provide a total pilot interference;

a summer configured to subtract the total pilot interference from the data samples to derive pilot-canceled data samples;

a data demodulation unit configured to process the pilot-canceled data samples to derive data for each signal instance in the received signal; and

a channel estimator configured to provide an estimated channel response for each of the one or more signal instances.

38. The base station of claim 37, wherein the pilot interference estimator is further configured to multiply pilot data for each of the one or more signal instances with the estimated channel response for the signal instance to provide the estimated pilot interference due to the signal instance.

39. A base station in a COMA system, the base station comprising:

a receiver configured to process a received signal comprised of a plurality of signal instances to provide data samples, wherein each signal instance includes a pilot and data; and

a demodulator including

a pilot interference estimator configured to process the data samples to derive an estimate of pilot interference due to each of one or more signal instances and to derive total pilot interference due to the one or more signal instances based on the estimated pilot interference;

a summer configured to subtract the total pilot interference from the data samples to derive pilot-canceled data samples; and

a data demodulation unit configured to process the pilot-canceled data samples to derive demodulated data for each of at least one signal instance in the received signal, wherein for each of the at least one signal instance the data demodulation unit is configured to despread the pilot-canceled data samples with a spreading sequence for the signal instance, channelize the despread samples with a data channelization code to provide data symbols, and demodulate the data symbols with pilot estimates for the signal instance to provide the demodulated data for the signal instance.