Advanced signal processors for interference cancellation in baseband receivers

• US 8,654,689 B2
• Filed: 09/28/2010
• Issued: 02/18/2014
• Est. Priority Date: 09/20/2002
• Status: Expired due to Term

• Current Assignee: III Holdings 1, LLC (Intellectual Ventures LLC)
• Original Assignee: Rambus Inc.
• Inventors: McCloud, Michael L., Nagarajan, Vijay
• Primary Examiner(s): Gauthier, Gerald
• Application Number:
  US12/892,874
• Publication Number:
  US 20110019656A1
• Time in Patent Office: 1,239 Days
• Field of Search: 370/286, 370/342, 370/479, 375/148, 375/261, 375/346, 375/144, 375/285
• 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. A method for cancelling interference from a received baseband signal in a CDMA system, comprising:

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

generating a soft-cancellation operator, and

performing a soft cancellation of the received baseband signal to output an interference-cancelled signal,

wherein the estimates are derived from a Rake receiver.

2. The method recited in claim 1, wherein each finger of the Rake receiver is matched to at least one of a time delay and a base station spreading code.

3. The method recited in claim 1, wherein generating at least one CIV comprises generating at least one of soft estimates and hard estimates from the interfering subchannels.

4. The method recited in claim 1, wherein generating at least one CIV comprises generating at least one or more soft estimates corresponding to interfering user subchannels from each base station tracked by a cellular handset.

5. The method recited in claim 1, wherein the at least one of soft estimates and hard estimates is derived from a selected one of a Rake receiver, an equalizer, and a detector matched to the communication protocol and channel conditions of the received baseband signal.

6. The method recited in claim 1, wherein the at least one CIV is generated using at least one of a symbol estimator, a sub channel selector, a fast Walsh transform, and a PN coder.

7. The method recited in claim 6, wherein the at least one CIV is generated using a symbol estimator employing at least one of Rake processing, receive diversity and equalization.

8. The method recited in claim 1, wherein performing a soft cancellation comprises at least one of subtractive and projective interference cancellation.

9. The method recited in claim 1, wherein the soft cancellation operator comprises a soft-projection matrix generator or an interference-cancelling operator configured for selecting a soft weight that increases a post-processing SINR.

10. The method recited in claim 1, wherein the received baseband signal is coupled to a first Rake finger and generating the at least one CIV comprises generating the at least one CIV from at least one Rake finger that does not include the first Rake finger.

11. The method recited in claim 1, wherein generating the at least one CIV comprises deriving 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.

12. The method recited in claim 1, wherein generating the soft-cancellation operator comprises generating 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.

13. The method recited in claim 12, wherein generating the soft-cancellation operator comprises determining the weight λ

by maximizing a post-processing SINR.

14. The method recited in claim 13, wherein generating the soft-cancellation operator comprises determining the weight λ

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

15. The method recited in claim 1, wherein performing the soft cancellation further comprises coupling the interference-cancelled signal to at least one of a combiner and a Rake receiver.

16. The method recited in claim 15, further comprising combining a plurality of interference-cancelled signals.

17. The method recited in claim 1, wherein the CDMA system is configured to implement receive diversity and equalization.