Adaptive interference cancellation and equalization using equalizer decision error as a common corrective factor

• US 5,349,609 A
• Filed: 08/03/1993
• Issued: 09/20/1994
• Est. Priority Date: 08/05/1992
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Tsujimoto, Ichiro
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): TSE, YOUNG TOI
• Application Number:
  US08/100,982
• Time in Patent Office: 413 Days
• Field of Search: 375/100-101, 375/103, 375/14, 375/40, 375/58, 375/96, 455/137-138, 455/273, 455/278.1, 455/303
• US Class Current: 375/347
• CPC Class Codes: H04B 7/005 Control of transmission; Equalising
• CPC Class Codes: H04B 7/0845 per branch equalization, e.g. by an FIR-filter or RAKE receiver per antenna branch rake receivers as such H04B1/7115
• CPC Class Codes: H04B 7/0851 using training sequences or error signal minimizing error signal H04B7/0854

Abstract

An interference canceler comprises an adaptive equalizer, first and second diversity branches, and an auxiliary branch. A first correlator detects a correlation between the output of the equalizer and the output of the first diversity branch, and a second correlator detects a correlation between the equalizer output and the output of the second diversity branch. The first and second diversity branch signals are multiplied with the detected first and second correlations, respectively, and diversity combined. A phase variation component of one of the first and second correlations is detected and multiplied with the output of the auxiliary branch to produce a signal whose phase rotation is the same as that of the diversity combined signal. A weight control signal is derived by detecting a correlation between a decision error of the adaptive equalizer and the multiplied auxiliary branch signal. The latter is further multiplied with the weight control signal to cancel the interference component of the diversity combined signal by a subtractor, whose output is coupled to the adaptive equalizer.

Claims

1. An interference canceler comprising:

an adaptive equalizer for equalizing multipath distortions and producing an equalized output signal and a decision error signal;

first and second diversity branches for receiving a transmitted signal and producing first and second diversity branch signals, respectively;

a first correlator associated with said first diversity branch for producing a first correlation output representative of a correlation between the equalized output signal from said adaptive equalizer and said first diversity branch signal, and a second correlator associated with said second diversity branch for producing a second correlation output representative of a correlation between said equalized output signal and said second diversity branch signal;

a first multiplier for multiplying the first diversity branch signal with said first correlation output, and a second multiplier for multiplying the second diversity branch signal with said second correlation output;

a diversity combiner for combining the outputs of said first and second multipliers and producing a diversity combined signal;

an auxiliary branch for receiving an interference signal and producing an auxiliary signal;

means for detecting a phase variation component of one of said first and second correlation outputs;

a third multiplier for multiplying said auxiliary signal with said phase variation component and producing an output signal whose phase rotation is the same as a phase rotation of the diversity combined signal;

weight control means responsive to said decision error signal from said adaptive equalizer and the output signal of said third multiplier for producing a weight control signal;

a fourth multiplier for multiplying the output signal of said third multiplier with said weight control signal;

means for subtracting an output signal of said fourth multiplier from said diversity combined signal to produce an interference-canceled signal and applying the interference-canceled signal to said adaptive equalizer.

2. An interference canceler as claimed in claim 1, wherein said means for detecting a phase variation component comprises a limiter.

3. An interference canceler as claimed in claim 1, wherein said weight control means comprises means for detecting a correlation between said decision error signal and the output of said third multiplier as a representative of said weight control signal.

4. In a diversity receiver comprising an adaptive equalizer for equalizing multipath distortions and producing an equalized output signal and a decision error signal, first and second diversity branches for receiving a transmitted signal and producing first and second diversity branch signals, respectively, and an auxiliary diversity branch for receiving an interference signal and producing an auxiliary signal, an interference canceling method comprising the steps of:

a) producing a first correlation output representative of a correlation between the equalized output signal from said adaptive equalizer and said first diversity branch signal, and producing a second correlation output representative of a correlation between said equalized output signal and said second diversity branch signal;

b) multiplying the first diversity branch signal with said first correlation output and multiplying the second diversity branch signal with said second correlation output;

c) combining the first and second diversity branch signals multiplied by the step (b) and producing a diversity combined signal;

d) detecting a phase variation component of one of said first and second correlation outputs;

e) multiplying said auxiliary signal with said phase variation component and producing an output signal whose phase rotation is the same as a phase rotation of the diversity combined signal;

f) producing a weight control signal in response to said decision error signal from said adaptive equalizer and the auxiliary signal multiplied by the step (e);

g) multiplying the auxiliary signal multiplied by the step (e) with said weight control signal; and

h) subtracting the auxiliary signal multiplied by the step (g) from said diversity combined signal to produce an interference-canceled signal and applying the interference-canceled signal to said adaptive equalizer.

5. A method as claimed in claim 4, wherein the step (d) comprises limiting the amplitude of one of said first and second correlation outputs and producing a constant amplitude signal as representative of said phase variation component.

6. A method as claimed in claim 4, wherein the step (f) comprises detecting a correlation between said decision error signal and said auxiliary signal multiplied by the step (e) to produce said weight control signal.