Methods for estimation and interference cancellation for signal processing

• US 8,391,338 B2
• Filed: 10/29/2010
• Issued: 03/05/2013
• Est. Priority Date: 09/23/2002
• Status: Active Grant

• Current Assignee: III Holdings 1, LLC
• Original Assignee: Rambus Inc.
• Inventors: Lamba, Gagandeep Singh, Guess, Tommy, McCloud, Michael, Narayan, Anand P., Jain, Prashant
• Primary Examiner(s): Tran, Khai
• Application Number:
  US12/916,439
• Publication Number:
  US 20110064066A1
• Time in Patent Office: 858 Days
• Field of Search: 375/148, 375/130, 375/147, 375/149, 375/316, 375/326, 375/340, 375/346, 375/347, 375/349, 370/337, 370/342, 370/335
• US Class Current: 375/148
• CPC Class Codes: H04B 1/7097 Interference-related aspects
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 1/71072 Successive interference cancellation
• CPC Class Codes: H04B 1/71075 Parallel interference cancellation
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• CPC Class Codes: H04B 1/7117 Selection, re-selection, allocation or re-allocation of paths to fingers, e.g. timing offset control of allocated fingers
• CPC Class Codes: H04B 15/00 Suppression or limitation of noise or interference by means associated with receiver H04B1/10
• CPC Class Codes: H04B 2001/71077 Partial interference cancellation
• CPC Class Codes: H04B 2201/709718 Determine interference
• CPC Class Codes: H04J 13/00 Code division multiplex systems for frequency hopping H04B1/713
• CPC Class Codes: H04J 13/0048 Walsh
• CPC Class Codes: H04L 43/08 Monitoring or testing based on specific metrics, e.g. QoS, energy consumption or environmental parameters
• CPC Class Codes: H04W 24/08 Testing, supervising or monitoring using real traffic

Abstract

A receiver in a CDMA system comprises a front end processor that generates a combined signal per source. A symbol estimator processes the combined signal to produce symbol estimates. An S-Matrix Generation module refines these symbol estimates based on the sub channel symbol estimates. An interference canceller is configured for cancelling interference from at least one of the plurality of received signals for producing at least one interference-cancelled signal.

Claims

1. A method for signal processing comprising:

receiving a signal in a receiver, the signal comprising a plurality of channels;

performing a first fast Walsh transform on the signal to determine a magnitude for each of the plurality of channels;

weighting each of the magnitudes to obtain a first modified result;

performing at least a second fast Walsh transform on the first modified result to obtain a second modified result; and

generating a first interference vector from the second modified result.

2. The method of claim 1, further comprising:

performing at least a third fast Walsh transform on the second modified result to obtain a third modified result; and

generating a second interference vector from the third modified result.

3. The method of claim 2, further comprising:

generating a composite interference vector from the first interference vector and the second interference vector.

4. The method of claim 1, wherein weighting comprises:

comparing each of the one or more corresponding magnitudes to a threshold value; and

applying a weight of zero to each of the one or more corresponding magnitudes that is greater than the threshold value to obtain a first modified result.

5. The method of claim 1, wherein the first fast Walsh transform corresponds to a Walsh code set for symbols of at least a minimum valid length.

6. The method of claim 1, wherein the second fast Walsh transform corresponds to a Walsh code set for symbols of a maximum valid length.

7. The method of claim 3, further comprising:

applying the composite interference vector to the received signal to create an interference canceled signal.

8. The method of claim 7, wherein applying the composite interference vector comprises subtracting the composite interference vector from the received signal to create an interference canceled signal.

9. A computer-readable medium having stored thereon instructions that when executed by a processor implement a method comprising:

performing a first fast Walsh transform on a received signal to obtain a result, the received signal comprising a plurality of channels, each channel having a magnitude;

weighting each of the magnitudes to obtain a first modified result;

performing at least a second fast Walsh transform on the first modified result to obtain a second modified result; and

generating a first interference vector from the second modified result.

10. The computer readable medium of claim 9, further comprising instructions that when executed by a processor implement the step of:

performing at least a third fast Walsh transform on the second modified result to obtain a third modified result; and

generating a second interference vector from the third modified result.

11. The computer readable medium of claim 9, further comprising instructions that when executed by a processor implement the step of:

generating a composite interference vector from the first interference vector and the second interference vector.

12. The computer readable medium of claim 9, wherein weighting comprises:

comparing each of the one or more magnitudes to a threshold value; and

applying a weight of zero to each magnitude that is greater than the threshold value to obtain a first modified result.

13. The computer readable medium of claim 9, wherein the one or more magnitudes contains a number of magnitudes that is equal to the number of chips in a longest valid symbol.

14. The computer readable medium of claim 9, wherein the first fast Walsh transform corresponds to a Walsh code set for symbols of at least a minimum valid length.

15. The computer readable medium of claim 9, wherein the second fast Walsh transform corresponds to a Walsh code set for symbols of a maximum valid length.

16. The computer readable medium of claim 9, further comprising instructions that when executed by a processor implement the step of:

applying the composite interference vector to a received signal stream to create an interference canceled signal stream.

17. The computer readable medium of claim 16, wherein applying the composite interference vector comprises subtracting the composite interference vector from the received signal stream to create an interference canceled signal stream.

18. A method implemented in a logic circuit of a receiver, comprising:

receiving a signal stream in a logic circuit, the signal stream comprising a plurality of channels;

obtaining a first number of chip values from the signal stream;

performing a fast Walsh transform on the first number of chip values to obtain a first set of transformed values, wherein the first set of transformed values includes a first number of elements equal to the first number of chip values;

weighting each of the first set of transformed values to create a first modified set of values; and

performing at least a second fast Walsh transform on the first modified set of values to create a second modified set of values.

19. The method of claim 18, wherein weighting each of the first set of transformed values comprises:

comparing a value of each of the first number of elements to a threshold; and

applying a weight of zero to each of the first number of elements that exceeds the threshold.

20. The method of claim 18, wherein obtaining a first number of chip values comprises:

despreading the signal stream by applying a despreading code;

performing carrier phase recovery on the despread signal stream to produce a carrier phase recovered signal stream; and

obtaining a first number of chip values from the carrier phase recovered signal stream.

21. The method of claim 18, further comprising:

performing an (n-1)^th fast Walsh transform on an (n-2)^th modified set of values to create an (n-1)^th transformed set of values;

weighting each of the (n-1)^th set of transformed values to create an (n-1)^th modified set of values; and

creating a first interference vector component from the (n-1)^th modified set of values.

22. The method of claim 21, further comprising:

performing an n^th fast Walsh transform on an (n-1)^th modified set of values to create an n^th modified set of values;

weighting each of the n^th set of transformed values to create an n^th modified set of values; and

creating a second interference vector component from the n^th modified set of values.

23. The method of claim 22, further comprising:

combining the first interference vector component and the second composite interference vector component to create a composite interference vector.

24. The method of claim 22, further comprising:

scaling the second composite interference vector component to obtain a scaled second composite interference vector component; and

adding the first composite interference vector component to the scaled second composite interference vector component to obtain a composite interference vector.

25. The method of claim 24, further comprising:

applying the composite interference vector to a received signal stream to create an interference canceled signal stream.

26. The method of claim 25, wherein applying the composite interference vector comprises subtracting the composite interference vector from the received signal stream to create an interference canceled signal stream.

27. The method of claim 18, wherein the first number of chip values is equal to a number of chips included in a longest valid symbol.

28. The method of claim 21, wherein the (n-1)^th fast Walsh transform corresponds to a Walsh code set for symbols of at least a minimum valid length.

29. The method of claim 22, wherein the n^th fast Walsh transform corresponds to a Walsh code set for symbols of a maximum valid length.

30. A receiver, comprising:

a despreader operable to despread a received signal to produce a despread signal;

a carrier phase recovery module coupled to the despreader;

a fast Walsh transform module operable to perform a fast Walsh transform stage on an output of the carrier phase recovery module;

a weighting module configured to weight each output from the fast Walsh transform module to produce corresponding first modified values; and

a multiplexer configured to provide the corresponding first modified values to the fast Walsh transform module to perform at least a second fast Walsh transform on each corresponding first modified value to obtain a first interference vector.

31. The receiver of claim 30, further comprising:

a scaler operable to multiply the first interference vector by a value to produce a first scaled interference vector.

32. The receiver of claim 31, further comprising:

a summer operable to add a plurality of scaled interference vectors to obtain a composite interference vector.