Equalizer with adaptive pre-filter

• US 6,775,322 B1
• Filed: 08/14/2000
• Issued: 08/10/2004
• Est. Priority Date: 08/14/2000
• Status: Expired due to Term

• Current Assignee: Unwired Planet LLC (JP Morgan Chase & Co)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Toy, Raymond, Zangi, Kambiz C., Hui, Dennis
• Primary Examiner(s): Corrielus, Jean B.
• Assistant Examiner(s): Ghulamali, Qutbuddin
• Application Number:
  US09/638,718
• Time in Patent Office: 1,457 Days
• Field of Search: 375/229, 375/232, 375/233, 375/343, 375/350, 708/300, 708/322, 708/323
• US Class Current: 375/232
• CPC Class Codes: H04L 2025/0342 QAM
• CPC Class Codes: H04L 2025/0349 as a feedback filter
• CPC Class Codes: H04L 2025/03605 Block algorithms
• CPC Class Codes: H04L 25/03057 with a recursive structure H04L25/03031 takes precedence

Abstract

A computationally efficient method for computing the filter coefficients for a prefilter in a decision feedback equalizer solves linear equations using a fast Toeplitz algorithm. Computations performed to compute the filter coefficients for the right half burst may be used to compute the prefilter for the left hand burst, thereby reducing the number of computations. Also, a square root-free algorithm may be used to solve the system of linear equations, further reducing computational complexity.

Claims

1. An equalizer to equalize a signal transmitted over a communication channel with an unknown and varying impulse response, said equalizer comprising:

an equalizing filter having a plurality of adjustable filter coefficients to filter an input signal to obtain an equalized input signal;

a processor to adjust said plurality of filter coefficients for said equalizing filter in response to variations in said impulse response of said communication channel, said processor programmed to;

generate estimated channel coefficients representing an estimated impulse response of said communication channel;

define a channel coefficient matrix B based on said estimated channel coefficients, a filter coefficient vector {overscore (f)}, and a target vector {overscore (c)}, such that;

2. The equalizer of claim 1 wherein said equalizing filter comprises:

a pre-filter to filter said input signal to obtain a filtered input signal, said adjustable filter coefficients being associated with said pre-filter;

a feedback filter to filter said output signal to obtain a filtered output signal; and

a summer to sum said filtered input signal and said filtered output signal to generate said equalized input signal.

3. The equalizer of claim 1 wherein said fast Toeplitz algorithm is a Trench algorithm.

4. The equalizer of claim 1 wherein said processor is further programmed to partition said filter vector {overscore (f)} to obtain subvectors {overscore (v)} and {overscore (m)} of said filter coefficient vector {overscore (f)}, and to partition said target vector {overscore (c)} to obtain subvectors {overscore (y)} and {overscore (a)} of said target vector {overscore (c)}.

5. The equalizer of claim 4 wherein said processor is further programmed to compute said subvector {overscore (m)} according to the following equation:

6. The equalizer of claim 5 wherein said processor is further programmed to compute said subvector {overscore (v)} according to the following equation:

7. The equalizer of claim 1 wherein said submatrix P₃ is the Hermitian of submatrix P₂.

8. The equalizer of claim 1 wherein said filter coefficients of said equalizing filter are subdivided into a first subset of filter coefficients and a second subset of filter coefficients, and wherein said processor is programmed to compute said first subset of filter coefficients and to compute said second subset of filter coefficients.

9. The equalizer of claim 8 wherein said processor is further programmed to use the invert of submatrix P₁ corresponding to said first subset of filter coefficients to compute the invert of the submatrix P₁ corresponding to said second set of filter coefficients.

10. A method to compute filter coefficients of a pre-filter for an equalizer, said method comprising:

estimating an impulse response of a communication channel;

defining a channel coefficient matrix B and a target vector {overscore (c)} based on said estimated impulse response of said communication channel;

defining a filter coefficient vector {overscore (f)} representing said filter coefficients of said pre-filter, such that the filter coefficient vector is the solution of the system of linear equations;

11. The method of claim 10 wherein inverting partition P₁ using a fast Toeplitz algorithm to obtain P₁⁻

1 comprises inverting partition P₁ using the Trench algorithm.

12. The method of claim 10 further comprising partitioning said filter coefficient vector {overscore (f)} to obtain subvectors {overscore (v)} and {overscore (m)} of said filter coefficient vector {overscore (f)}, and partitioning said target vector {overscore (c)} to obtain subvectors {overscore (y)} and {overscore (a)} of said target vector {overscore (c)}.

13. The method of claim 12 solving said system of linear equations using P₁⁻

1, P₂, P₃, and P₄ to obtain said filter coefficient vector {overscore (f)} comprises computing said subvector {overscore (m)} according to the following equation;

14. The method of claim 13 solving said system of linear equations using P₁⁻

1, P₂, P₃, and P₄ to obtain said filter coefficient vector {overscore (f)} comprises computing said subvector {overscore (v)} according to the following equation;

15. The method of claim 10 wherein said submatrix P₃ is the Hermitian of submatrix P₂.

16. The method of claim 10 further comprising subdividing said filter coefficients of said filter into a first subset of filter coefficients and a second subset of filter coefficients and wherein solving said system of linear equations using P₁⁻

1, P₂, P₃, and P₄ to obtain said filter coefficient vector {overscore (f)} comprises computing said first subset of filter coefficients and computing said second subset of filter coefficients.

17. The method of claim 16 wherein solving said system of linear equations using P₁⁻

1, P₂, P₃, and P₄ to obtain said filter coefficient vector {overscore (f)} comprises inverting submatrix P₁ corresponding to said first subset of filter coefficients to compute the invert of submatrix P₁ corresponding to said second set of filter coefficients.

18. A receiver comprising:

a receiver front-end to amplify received signals and convert said received signals to a baseband signal at a baseband frequency;

a sampler to sample said baseband signal to produce a sampled signal;

an equalizer to equalize said sampled signal, said equalizer comprising;

an equalizing filter having a plurality of adjustable filter coefficients to filter an input signal to obtain an equalized input signal;

a processor to adjust said plurality of filter coefficients for said equalizing filter in response to variations in an impulse response of a communication channel, said processor programmed to;

generate estimated channel coefficients representing an estimated impulse response of said communication channel;

define a channel coefficient matrix B based on said estimated channel coefficients, a filter coefficient vector {overscore (f)}, and a target vector {overscore (c)}, such that;

19. The receiver of claim 18 wherein said equalizing filter comprises:

a pre-filter to filter said input signal to obtain a filtered input signal, said adjustable filter coefficients being associated with said pre-filter;

a feedback filter to filter said output signal to obtain a filtered output signal; and

a summer to sum said filtered input signal and said filtered output signal to generate said equalized input signal.

20. The receiver of claim 18 wherein said fast Toeplitz algorithm is a Trench algorithm.

21. The receiver of claim 18 wherein said processor is further programmed to partition said filter vector {overscore (f)} to obtain subvectors {overscore (v)} and {overscore (m)} of said filter coefficient vector {overscore (f)}, and to partition said target vector {overscore (c)} to obtain subvectors {overscore (y)} and {overscore (a)} of said target vector {overscore (c)}.

22. The receiver of claim 18 wherein said filter coefficients of said equalizing filter are subdivided into a first subset of filter coefficients and a second subset of filter coefficients, and wherein said processor is programmed to compute said first subset of filter coefficients and to compute said second subset of filter coefficients.

23. The receiver of claim 22 wherein said processor is further programmed to use the invert of submatrix P₁ corresponding to said first subset of filter coefficients to compute the invert of the submatrix P₁ corresponding to said second set of filter coefficients.

24. A mobile terminal in a mobile communication system, said mobile terminal comprising:

a transmitter;

a receiver comprising;

a receiver front-end to amplify received signals and convert said received signals to a baseband signal at a baseband frequency;

a sampler to sample said baseband signal to produce an sampled signal;

an equalizer to equalize said sampled signal, said equalizer comprising;

an equalizing filter having a plurality of adjustable filter coefficients to filter an input signal to obtain an equalized input signal;

a processor to adjust said plurality of filter coefficients for said equalizing filter in response to variations in an impulse response of a communication channel, said processor programmed to;

generate estimated channel coefficients representing an estimated impulse response of said communication channel;

define a channel coefficient matrix B based on said estimated channel coefficients, a filter coefficient vector {overscore (f)}, and a target vector {overscore (c)}, such that;

25. The mobile terminal of claim 24 wherein said fast Toeplitz algorithm is a Trench algorithm.

26. The mobile terminal of claim 24 wherein said processor is further programmed to partition said filter vector {overscore (f)} to obtain subvectors {overscore (v)} and {overscore (m)} of said filter coefficient vector {overscore (f)}, and to partition said target vector {overscore (c)} to obtain subvectors {overscore (y)} and {overscore (a)} of said target vector {overscore (c)}.

27. The mobile terminal of claim 24 wherein said filter coefficients of said equalizing filter are subdivided into a first subset of filter coefficients and a second subset of filter coefficients, and wherein said processor is programmed to compute said first subset of filter coefficients and to compute said second subset of filter coefficients.

28. The mobile terminal of claim 27 wherein said processor is further programmed to use the invert of submatrix P₁ corresponding to said first subset of filter coefficients to compute the invert of the submatrix P₁ corresponding to said second set of filter coefficients.

29. A base station in a mobile communication system, said base station comprising:

a transmitter;

a receiver comprising;

a receiver front-end to amplify received signals and convert said received signals to a baseband signal at a baseband frequency;

a sampler to sample said baseband signal to produce a sampled signal;

an equalizer to equalize said sampled signal, said equalizer comprising;

an equalizing filter having a plurality of adjustable filter coefficients to filter an input signal to obtain an equalized input signal;

a processor to adjust said plurality of filter coefficients for said equalizing filter in response to variations in an impulse response of a communication channel, said processor programmed to;

generate estimated channel coefficients representing an estimated impulse response of said communication channel;

define a channel coefficient matrix B based on said estimated channel coefficients, a filter coefficient vector {overscore (f)}, and a target vector {overscore (c)}, such that;

30. The base station of claim 29 wherein said fast Toeplitz algorithm is a Trench algorithm.

31. The base station of claim 29 wherein said processor is further programmed to partition said filter vector {overscore (f)} to obtain subvectors {overscore (v)} and {overscore (m)} of said filter coefficient vector {overscore (f)}, and to partition said target vector {overscore (c)} to obtain subvectors {overscore (y)} and {overscore (a)} of said target vector {overscore (c)}.

32. The base station of claim 29 wherein said filter coefficients of said equalizing filter are subdivided into a first subset of filter coefficients and a second subset of filter coefficients, and wherein said processor is programmed to compute said first subset of filter coefficients and to compute said second subset of filter coefficients.

33. The base station of claim 32 wherein said processor is further programmed to use the invert of submatrix P₁ corresponding to said first subset of filter coefficients to compute the invert of the submatrix P₁ corresponding to said second set of filter coefficients.