Method and apparatus for selectively applying interference cancellation in spread spectrum systems

• US 8,218,602 B2
• Filed: 08/30/2010
• Issued: 07/10/2012
• Est. Priority Date: 09/23/2002
• Status: Expired due to Term

• Current Assignee: III Holdings 1, LLC (Intellectual Ventures LLC)
• Original Assignee: Rambus Inc.
• Inventors: Narayan, Anand, Olson, Eric S., Jain, Prashant
• Primary Examiner(s): Tran, Khai
• Application Number:
  US12/871,748
• Publication Number:
  US 20100323624A1
• Time in Patent Office: 680 Days
• Field of Search: 375/144, 375/130, 375/141, 375/148, 375/346, 375/284, 375/285, 375/367, 370/479, 370/343, 370/335, 370/441
• US Class Current: 375/144
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 1/71072 Successive 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 2001/71077 Partial interference cancellation

Abstract

The present invention is directed to the selective provision of interference canceled signal streams to demodulating fingers in a communication receiver. According to the present invention, potential interferer signal paths are identified. Signal streams having one or more potential interferer signals removed or canceled are created, and a correlation is performed to determine whether the strength of a desired signal path increased as a result. If the correlation indicates that the strength of a desired signal path was increased by the signal cancellation, the interference canceled signal stream is provided to the demodulation finger assigned to track the desired signal path. If the correlation determines that the strength of the desired signal path did not increase as a result of performing interference cancellation, the raw or a different interference canceled signal stream is provided to the demodulation finger.

Claims

1. A method for selectively enabling signal interference cancellation, comprising:

identifying a plurality of signal paths;

for a set of said identified signal paths, determining an observed signal strength;

identifying at least one of said signal paths as a potential interferer based at least in part on the observed signal strength;

creating at least a first interference cancelled signal stream;

determining whether providing said at least a first interference cancelled signal stream to at least a first signal processor will improve a signal to noise ratio of at least a first signal path assigned to said at least a first signal processor; and

in response to determining that said at least a first interference cancelled signal stream will not improve a signal to noise ratio of said at least a first signal path assigned to said at least a first signal processor, discontinuing said creating at least a first interference cancelled signal stream.

2. The method of claim 1, further comprising:

providing a non-interference cancelled signal stream to said at least a first signal processor.

7. The method of claim 1, further comprising:

providing a non-interference cancelled signal stream to said at least a first signal processor.

3. A method for selectively enabling signal interference cancellation, comprising:

identifying a plurality of signal paths;

for a set of said identified signal paths, determining an observed signal strength;

identifying at least one of said signal paths as a potential interferer based at least in part on the observed signal strength;

creating at least a first interference cancelled signal stream;

listing said potential interferers in a cancellation candidate list; and

updating a cancellation list by replacing a signal path in said cancellation list having a signal strength that is less than a signal strength of one of said potential interferers in said cancellation candidate list with said one of said potential interferers.

4. A method for selectively enabling signal interference cancellation, comprising:

identifying a plurality of signal paths;

for a set of said identified signal paths, determining an observed signal strength;

identifying at least one of said signal paths as a potential interferer based at least in part on the observed signal strength;

creating at least a first interference cancelled signal stream; and

updating a channel determination list by entering signal paths from a cancellation list in said channel determination list.

5. A method for selectively enabling signal interference cancellation, comprising:

identifying a plurality of signal paths;

for a set of said identified signal paths, determining an observed signal strength;

identifying at least one of said signal paths as a potential interferer based at least in part on the observed signal strength;

creating at least a first interference cancelled signal stream;

storing an identity of said plurality of signal paths in said channel to create a survey path list;

providing an interference canceled signal stream to at least one of a searcher element and a correlator element; and

updating said survey path list.

6. A method for selectively enabling signal interference cancellation, comprising:

identifying a plurality of signal paths in a searcher;

for a set of said identified signal paths, determining an observed signal strength in a finger processor;

identifying at least one of said signal paths as a potential interferer based at least in part on the observed signal strength;

creating in an interference canceller at least a first interference cancelled signal stream, including cancelling the interference from the at least one potential interferer;

determining whether providing said at least a first interference cancelled signal stream to at least a first signal processor will improve a signal to noise ratio of at least a first signal path assigned to said at least a first signal processor; and

in response to determining that said at least a first interference cancelled signal stream will not improve a signal to noise ratio of said at least a first signal path assigned to said at least a first signal processor, discontinuing said creating at least a first interference cancelled signal stream.

8. A method for selectively enabling signal interference cancellation, comprising:

identifying a plurality of signal paths in a searcher;

for a set of said identified signal paths, determining an observed signal strength in a finger processor;

identifying at least one of said signal paths as a potential interferer based at least in part on the observed signal strength;

creating in an interference canceller at least a first interference cancelled signal stream by cancelling the interference from the at least one potential interferer;

listing said potential interferers in a cancellation candidate list; and

updating a cancellation list by replacing a signal path in said cancellation list having a signal strength that is less than a signal strength of one of said potential interferers in said cancellation candidate list with said one of said potential interferers.

9. A method for selectively enabling signal interference cancellation, comprising:

identifying a plurality of signal paths in a searcher;

for a set of said identified signal paths, determining an observed signal strength in a finger processor;

identifying at least one of said signal paths as a potential interferer based at least in part on the observed signal strength;

creating in an interference canceller at least a first interference cancelled signal stream by cancelling the interference from the at least one potential interferer; and

updating a channel determination list by entering signal paths from a cancellation list in said channel determination list.

10. A method for selectively enabling signal interference cancellation, comprising:

identifying a plurality of signal paths in a searcher;

for a set of said identified signal paths, determining an observed signal strength in a finger processor;

identifying at least one of said signal paths as a potential interferer based at least in part on the observed signal strength;

creating in an interference canceller at least a first interference cancelled signal stream by cancelling the interference from the at least one potential interferer;

storing an identity of said plurality of signal paths in said channel to create a survey path list;

providing an interference canceled signal stream to at least one of a searcher element and a correlator element; and

updating said survey path list.

11. A method for selecting a signal interference cancellation scheme, comprising:

populating a cancellation list in a cancellation controller with an identity of at least a first signal path that has been identified as an interfering signal path;

establishing a connection between a demodulating finger and one of a raw signal stream and an interference cancelled signal stream based on an entry in said cancellation list;

populating a cancellation candidate list comprising an identity of a signal path that is a potential interfering signal path;

canceling said potential interfering signal path from at least one other signal stream; and

determining whether a parameter associated with reception of said at least one other signal path improved as a result of said canceling of said potential interfering signal path.

12. The method of claim 11, wherein in response to determining that a parameter associated with reception of said at least one other signal path did not improve as a result of said canceling of potential interfering signal path, said establishing a connection comprises establishing a connection between said demodulating finger and a raw signal stream.

13. The method of claim 11, wherein in response to determining that a parameter associated with reception of said at least one other signal path did improve as a result of said canceling of potential interfering signal path, said establishing a connection comprises establishing a connection between said demodulating finger and an interference cancelled signal stream.

14. The method of claim 11, wherein said populating a cancellation candidate list comprises populating said cancellation candidate list with identities of a number of signals that are potential interfering signals.

15. The method of claim 11, wherein said at least a first potential interfering signal path has a signal strength that is greater than a predetermined threshold.

16. The method of claim 11, wherein said potential at least a first potential interfering signal path has a signal strength greater than another signal by at least a first predetermined amount.

17. A method for selecting a signal interference cancellation scheme, comprising:

populating a cancellation list in a cancellation controller with an identity of at least a first signal path that has been identified as an interfering signal path;

establishing a connection between a demodulating finger and one of a raw signal stream and an interference cancelled signal stream based on an entry in said cancellation list;

providing a raw signal stream to a searcher finger;

creating a survey path list containing at least a first path identified in said raw signal stream by said searcher finger;

providing an interference cancelled signal stream to said searcher finger; and

updating said survey path list to include at least a second path identified in said interference cancelled signal stream by said searcher finger.

18. A method for selecting a signal interference cancellation scheme, comprising:

populating a cancellation list in a cancellation controller with an identity of at least a first signal path that has been identified as an interfering signal path; and

establishing a connection between a demodulating finger and one of a raw signal stream and an interference cancelled signal stream based on an entry in said cancellation list; and

updating a signal feed list, wherein said signal feed list identifies for each demodulating finger a provided signal.

19. A method for selecting a signal interference cancellation scheme, comprising:

populating a cancellation list in a cancellation controller with an identity of at least a first signal path that has been identified as an interfering signal path;

establishing a connection between a demodulating finger and one of a raw signal stream and an interference cancelled signal stream based on an entry in said cancellation list;

producing in said channel determination module an estimate of a signal path associated with a first one of said demodulating fingers; and

creating a first interference cancelled signal stream by combining said estimate of said provided signal path with at least one of said raw signal stream and a second interference cancelled signal stream, wherein said first interference cancelled signal stream is provided to a second of said demodulating fingers.

20. The method of claim 19, wherein said combining of said estimate of said provided signal path with at least one of said raw signal stream and a second interference cancelled signal stream comprises subtracting a replica of said provided signal path from said at least one of said raw signal stream and said second interference cancelled signal stream.

21. The method of claim 19, wherein said combining of said estimate of said provided signal path with at least one of said raw signal stream and a second interference cancelled signal stream comprises projecting said raw signal stream and said second interference cancelled signal stream into subspace orthogonal to said provided signal path.

22. The method of claim 19, wherein said combining of said estimate of said provided signal path with at least one of said raw signal stream and a second interference cancelled signal stream comprises scaling the estimate of said provided signal path by a quantity proportional to its power and scaling the at least one of said raw signal stream and a second interference cancelled signal stream by a quantity proportional to its power.

23. A method for selectively enabling signal interference cancellation, comprising:

identifying in a searcher at least one signal path in a plurality of signal paths;

for the at least one signal path, determining an observed signal strength in a processing finger; and

identifying at least one of said signal paths as a potential interferer based at least in part on the observed signal strength;

producing an interference cancelled signal stream, wherein said at least one signal path identified as a potential interferer is cancelled from said signal producing an interference cancelled stream;

correlating said interference cancelled signal stream with a reference signal; and

in response to a strength of a desired signal path increasing as a result of creating said interference cancelled signal stream, providing said interference cancelled signal stream to a demodulating finger assigned to demodulate said desired signal path.