CDMA receiver employing successive cancellation of training-signal interference

• US 6,172,969 B1
• Filed: 01/28/1998
• Issued: 01/09/2001
• Est. Priority Date: 01/31/1997
• Status: Expired due to Term

• Current Assignee: Inphi Corporation
• Original Assignee: OKI Electric Industry Company Limited
• Inventors: Kawakami, Eiichiro, Shimizu, Satoru
• Primary Examiner(s): Horabik, Michael
• Assistant Examiner(s): JONES, PRENELL P
• Application Number:
  US09/014,709
• Time in Patent Office: 1,077 Days
• Field of Search: 370/342, 370/335, 370/333, 370/479, 375/346, 375/208, 375/206, 375/207, 455/296
• US Class Current: 370/342
• CPC Class Codes: H04B 1/71075 Parallel interference cancellation

Abstract

A code division multiple access receiver, which receives a signal combining both information signals and training signals, has an interference canceler that successively estimates and cancels interference caused by the training signals. The interference canceler also successively estimates and cancels interference caused by the information signals. The estimating and canceling process is preferably repeated, for each training signal and each information signal, in two or more stages.

Claims

1. A method of canceling interference in a code division multiple access communication system in which training signals having known values and information signals having unknown values are combined into a single received signal, comprising

(a) in a first stage of a series of stages, the steps of:

making successive estimates of said training signals and interference caused by said training signals;

successively removing the interference estimated to be caused by said training signals from said received signal;

making successive estimates of said information signals and interference caused by said information signals;

successively removing the interference estimated to be caused by said information signals from said received signal; and

outputting the estimated training signals, the estimated information signals, and a residual signal from which the interference estimated to be caused by said training signals and the interference estimated to be caused by said information signals has been removed;

(b) in each stage after said first stage of said series of stages, the steps of;

receiving the residual signal and estimated training signals output from a preceding stage in said series;

using the estimated training signals and the residual signal received from said preceding stage to re-estimate said training signals;

successively estimating residual interference caused by said training signals;

successively removing the estimated residual interference from the received residual signal;

making successive re-estimates of said information signals and estimates of residual interference caused by said information signals;

successively removing the residual interference estimated to be caused by said information signals from the received residual signal; and

outputting the re-estimated training signals, the re-estimated information signals,

and a residual signal from which the residual interference estimated to be caused by said training signals and the residual interference estimated to be caused by said information signals has been removed; and

(c) the step of extracting information signals from said received signal after the interference estimated to be caused by said training signals and said information signals in said steps (a) and (b) has been removed.

2. The method of claim 1, wherein said step (a) further comprises, for each training signal, the steps of:

correlating at least a residual part of said received signal with a spreading code used with said training signal, to obtain a despread training signal;

estimating a channel parameter according to said despread training signal and a known value of said training signal;

applying said channel parameter to said known value of said training signal to obtain an estimated training signal; and

spreading said estimated training signal by said spreading code, thereby estimating the interference caused by said training signal.

3. The method of claim 1, wherein said step (a) is carried out serially, on one training signal and one information signal at a time.

4. The method of claim 1, wherein said step (a) is carried out in parallel on all training signals and all information signals, reducing said received signal to a residual signal, and are then repeated in parallel on said residual signal.

5. A method of canceling interference in a code division multiple access communication system in which training signals having known values and information signals having unknown values are combined into a single received signal, comprising:

(a) in a first stage of a series of stages, the steps of;

making successive estimates of said training signals and interference caused by said training signals;

successively removing the interference estimated to be caused by said training signals from said received signal;

making successive estimates of said information signals and interference caused by said information signals;

successively removing the interference estimated to be caused by said information signals from said received signal; and

outputting the estimated training signals, the estimated information signals, and a residual signal from which the interference estimated to be caused by said training signals and the interference estimated to be caused by said information signals has been removed;

(b) in each stage after said first stage of said series of stages, the steps of;

receiving the residual signal and the estimated information signals output from a preceding stage in said series;

making successive re-estimates of said training signals and estimates of residual interference caused by said training signals;

successively removing the residual interference estimated to be caused by said training signals from the received residual signal;

using the estimated information signals and the residual signal received from said preceding stage to re-estimate said information signals;

successively estimating residual interference caused by said information signals; and

successively removing the estimated residual interference caused by said information signals from said residual signal; and

outputting the re-estimated training signals, the re-estimated information signals, and a residual signal from which the residual interference estimated to be caused by said training signals and the residual interference estimated to be caused by said information signals has been removed; and

(c) the step of extracting information signals from said received signal after the interference estimated to be caused by said training signals and said information signals in said steps (a) and (b) has been removed.

6. The method of claim 5, wherein said step (a) further comprises, for each training signal, the steps of:

correlating at least a residual part of said received signal with a spreading code used with said training signal, to obtain a despread training signal;

estimating a channel parameter according to said despread training signal and a known value of said training signal;

applying said channel parameter to said known value of said training signal to obtain an estimated training signal; and

spreading said estimated training signal by said spreading code, thereby estimating the interference caused by said training signal.

7. The method of claim 5, wherein said steps (a) are carried out serially, on one training signal and one information signal at a time.

8. The method of claim 5, wherein said steps (a) are carried out in parallel on all training signals and all information signals, reducing said received signal to a residual signal, and are then repeated in parallel on said residual signal.

9. A receiver for receiving a signal in which training signals having known values are combined with information signals having unknown values by code division multiple access spectrum spreading, comprising:

an interference canceler that makes successive estimates of interference caused by the training signals, successively removes the interference estimated to be caused by the training signals from the received signal, makes successive estimates of interference caused by the information signals, successively removes the interference estimated to be caused by the information signals from the received signal, and extracts the information signals from the received signal after the interference estimated to be caused by the training signals and the interference estimated to be caused by the information signals have been removed, said interference canceler comprising;

a plurality of training signal estimators that use respective training signals to estimate respective channel parameters, and use said channel parameters to estimate the interference caused by respective training signals; and

a plurality of information signal estimators that use the channel parameters estimated by respective training signal estimators to estimate the interference caused by said information signals, said interference canceler being organized into a series of stages, from a first stage, to which said received signal is supplied, to a last stage, in which said information signals are extracted, each stage having a plurality of said training signal estimators and a plurality of said information signal estimators;

each said stage, except said last stage, finishes a next stage in said series with a residual signal from which the interference estimated so far by the training signal estimators and information signal estimators has been removed;

in each stage, except said last stage, the training signal estimators estimate respective training signals and the information signal estimators estimate respective information signals, these estimated training signals and estimated information signals being supplied to the next stage in said series; and

in each stage, except said first stage, the training signal estimators use said residual signal and the estimated training signals received from a preceding stage in said series to re-estimate said training signals, and the information signal estimators use said residual signal and the estimated information signals received from the preceding stage to re-estimate said information signals.

10. The receiver of claim 9, wherein said information signal estimators estimate said information signals by making a hard decision.

11. The receiver of claim 9, wherein said information signal estimators estimate said information signals by making a soft decision.

12. The receiver of claim 9, wherein the training signal estimators in said first stage operate in parallel on said received signal, and the training signal estimators in each stage after said first stage operate in parallel on the residual signal received by said other stage after said first stage.

13. The receiver of claim 9, wherein the training signal estimators in each said stage operate serially.

14. The receiver of claim 9, wherein said receiver receives signals from n transmitting stations, n being a positive integer, and each said stage has n training signal estimators and n information signal estimators.

15. The receiver of claim 9, wherein said receiver receives signals from n transmitting stations, n being a positive integer, and each said stage has n×

L training signal estimators and n×

L information signal estimators, L being a path diversity factor.

16. The receiver of claim 9, wherein for each training signal, said interference canceler has at least one training signal estimator comprising:

a spreading-code generator for generating a spreading code;

a training signal generator for generating a known training signal;

a correlator for correlating an input signal with said spreading code to obtain a despread training signal;

a channel estimator for estimating a channel parameter according to said known training signal and said despread training signal;

a first multiplier for applying said channel parameter to said known value of said training signal to obtain an estimated training signal; and

a second multiplier for spreading said estimated training signal by said spreading code, thereby estimating the interference caused by said training signal.

17. The receiver of claim 16 wherein said input signal is said received signal in at least one of said training signal estimators, and is a residual signal, from which some interference has already been removed, in at least another one of said training signal estimators.