Variable interference cancellation technology for CDMA systems

• US 20060227730A1
• Filed: 11/10/2005
• Published: 10/12/2006
• Est. Priority Date: 04/07/2005
• Status: Active Grant

• Current Assignee: III Holdings 1, LLC (Intellectual Ventures LLC)
• Original Assignee: Rambus Inc.
• Inventors: McCloud, Michael L., Nagarajan, Vijay
• Granted Patent: US 7,808,937 B2
• Time in Patent Office: Days
• US Class Current: 370/286
• CPC Class Codes: H04B 1/10 Means associated with receiver for limiting or suppressing noise or interference
• CPC Class Codes: H04B 1/7103 the interference being multiple access interference
• CPC Class Codes: H04B 1/7107 Subtractive 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 1/712 Weighting of fingers for combining, e.g. amplitude control or phase rotation using an inner loop
• CPC Class Codes: H04J 11/0023 Interference mitigation or co-ordination direct sequence spread spectrum [DSSS] systems H04B1/7097; frequency hopping H04B1/713; allocation criteria for ingress interference avoidance H04L5/0062; frequency allocation criteria for requirements on out-of-channel emissions H04L5/0066; arrangements for removing intersymbol interference or baseband equalisers H04L25/03006; peak power aspects in multicarrier modulation H04L27/2614; power management H04W52/00; traffic scheduling H04W72/54, H04W72/541
• CPC Class Codes: H04J 13/0003 Code application, i.e. aspects relating to how codes are applied to form multiplexed channels
• CPC Class Codes: H04J 13/20 having an orthogonal variable spreading factor [OVSF]
• CPC Class Codes: H04J 2011/0006 with CDM/CDMA
• CPC Class Codes: H04W 24/06 Testing, supervising or monitoring using simulated traffic

Abstract

An interference canceller comprises a composite interference vector (CIV) generator configured to produce a CIV by combining soft and/or hard estimates of interference, an interference-cancelling operator configured for generating a soft-projection operator, and a soft-projection canceller configured for performing a soft projection of the received baseband signal to output an interference-cancelled signal. Weights used in the soft-projection operator are selected to maximize a post-processing SINR.

Claims

1. An apparatus configured to remove interference from a received baseband signal in a CDMA system, comprising:

a composite interference vector (CIV) generator configured to produce at least one CIV by combining estimates of interference,

an interference-cancelling operator configured for generating a soft-projection operator, and

a soft-projection canceller configured for performing a soft projection of the received baseband signal to output an interference-cancelled signal.

2. The apparatus recited in claim 1, further comprising a Rake receiver.

3. The apparatus recited in claim 2, wherein each finger of the Rake receiver is matched to at least one of a time delay and a base station spreading code.

4. The apparatus recited in claim 1, wherein the apparatus is configured to cancel interference in a first Rake finger and the CIV generator configured to generate the at least one CIV from at least one Rake finger that does not include the first Rake finger.

5. The apparatus recited in claim 1, wherein the CIV generator is configured to derive the estimates from at least one of a Rake receiver, an equalizer, a receiver employing receive diversity, a receiver employing transmit diversity combining, and a receiver employing space-time decoding.

6. The apparatus recited in claim 1, wherein the interference-cancelling operator is configured to generate a soft-projection matrix to operate on a received data vector, the soft-projection matrix having the form F(λ

)=I−

λ

ss*, where I is an identity matrix, λ

is a weight, and s is a CIV.

7. The apparatus recited in claim 6, wherein the interference-cancelling operator is configured for determining the weight λ

by maximizing a post-processing SINR.

8. The apparatus recited in claim 7, wherein the interference-cancelling operator is configured for determining the weight λ

by maximizing a post-processing SINR for a handset operating in a soft-handoff mode.

9. The apparatus recited in claim 1, wherein the interference-cancelled signal output from the soft-projection canceller is coupled to at least one of a combiner and a Rake receiver.

10. The apparatus recited in claim 9, wherein the at least one of the combiner and the Rake receiver is configured to combine a plurality of interference-cancelled signals.

11. A method for cancelling interference from a received baseband signal in a CDMA system, comprising:

providing for generating at least one composite interference vector (CIV) by combining estimates from interfering subchannels,

providing for generating a soft-projection operator, and

providing for performing a soft projection of the received baseband signal to output an interference-cancelled signal.

12. The method recited in claim 11, wherein the estimates are derived from a Rake receiver.

13. The method recited in claim 12, wherein each finger of the Rake receiver is matched to at least one of a time delay and a base station spreading code.

14. The method recited in claim 11, wherein the received baseband signal is coupled from a first Rake finger and providing for generating the at least one CIV is configured to generate the at least one CIV from at least one Rake finger that does not include the first Rake finger.

15. The method recited in claim 11, wherein providing for generating the at least one CIV is configured to derive the estimates from at least one of a Rake receiver, an equalizer, a receiver employing receive diversity, a receiver employing transmit diversity combining, and a receiver employing space-time decoding.

16. The method recited in claim 11, wherein providing for generating the soft-projection operator is configured to generate a soft-projection matrix to operate on a received data vector, the soft-projection matrix having the form F(λ

)=I−

λ

ss*, where I is an identity matrix, λ

is a weight, and s is a CIV.

17. The method recited in claim 16, wherein providing for generating the soft-projection operator is configured for determining the weight λ

by maximizing a post-processing SINR.

18. The method recited in claim 17, wherein providing for generating the soft-projection operator is configured for determining the weight A by maximizing a post-processing SINR for a handset operating in a soft-handoff mode

19. The method recited in claim 11, wherein providing for performing the soft projection further comprises coupling the interference-cancelled signal to at least one of a combiner and a Rake receiver.

20. The method recited in claim 19, wherein providing for performing the soft projection is followed by providing for combining a plurality of interference-cancelled signals.

21. A chipset configured to perform the receiving method recited in claim 11.

22. A digital computer system programmed to perform the method recited in claim 11.

23. A computer-readable medium storing a computer program implementing the method of claim 11.

24. A base station configured to perform the method of claim 11.

25. A handset configured to perform the method of claim 11.

26. An interference-cancellation system configured for removing interference from a received baseband signal in a CDMA system, comprising:

a means for generating at least one composite interference vector (CIV) by combining estimates of interference,

a means for generating a soft-projection operator, and

a means for performing a soft projection of the received baseband signal to output an interference-cancelled signal.

27. The system recited in claim 26, wherein the means for generating the at least one CIV is configured to obtain the estimates from a Rake receiver.

28. The system recited in claim 27, wherein each finger of the Rake receiver is matched to at least one of a time delay and a base station spreading code.

29. The system recited in claim 26, wherein the means for performing a soft projection is configured to couple the received baseband signal from a first Rake finger, and the means for generating the at least one CIV is configured to generate the at least one CIV from at least one Rake finger that does not include the first Rake finger.

30. The system recited in claim 26, wherein the means for generating the at least one CIV is configured to derive the estimates from at least one of a Rake receiver, an equalizer, a receiver employing receive diversity, a receiver employing transmit diversity combining, and a receiver employing space-time decoding.

31. The system recited in claim 26, wherein the means for generating the soft-projection operator is configured to generate a soft-projection matrix to operate on a received data vector, the soft-projection matrix having the form F(λ

)=I−

λ

ss*, where I is an identity matrix, λ

is a weight, and s is a CIV.

32. The system recited in claim 31, wherein the means for generating the soft-projection operator is configured for determining the weight λ

by maximizing a post-processing SINR.

33. The system recited in claim 32, wherein the means for generating the soft-projection operator is configured for determining the weight λ

by maximizing a post-processing SINR for a handset operating in a soft-handoff mode.

34. The system recited in claim 26, wherein the means for performing the soft projection further comprises a means for coupling the interference-cancelled signal to at least one of a combiner and a Rake receiver.

35. The system recited in claim 34, wherein the means for performing the soft projection further comprises a means for combining a plurality of interference-cancelled signals for receive diversity.