Adaptive equalizer for communication channels
View Patent ↗Adaptive equalizers for a communication channel and corresponding methods of equalizing are described. The adaptive equalizer includes: a fixed pre-filter configured to be coupled to a received signal and provide a pre-filter signal; an adaptive filter coupled to and configured to compensate the pre-filter signal for changes in phase and amplitude; and an interference remover coupled to the adaptive filter and configured to reduce interference in the received signal.
1. An adaptive equalizer for a communication channel, the adaptive equalizer comprising:
a fixed pre-filter configured to be coupled to a received signal and provide a pre-filter signal;
an adaptive filter coupled to and configured to compensate the pre-filter signal for changes in phase and amplitude; and
an interference remover coupled to the adaptive filter and configured to reduce interference in the received signal,
wherein the interference remover further comprises a feedback filter using Decision Feedback Equalizer (DFE) coefficients with a first coefficient b 0 set to a constant value.
2. The adaptive equalizer of claim 1 wherein the interference remover uses Maximum Likelihood Sequence Estimation and a Decision Feedback Equalizer.
3. The adaptive equalizer of claim 1 wherein the interference remover uses Reduced State Sequence Estimation (RSSE) and a Decision Feedback Equalizer (DFE) with the first coefficient b 0 set to a constant value.
4. The adaptive equalizer of claim 3 :
wherein the interference remover includes an adaptive interference remover; and
wherein the adaptive equalizer further comprises: a coefficient adaptor configured for adapting a portion of DFE coefficients over a received signal burst with another portion of the DFE coefficients being fixed over the received signal burst.
5. The adaptive equalizer of claim 1
wherein the adaptive filter is further configured for compensating the pre-filter signal for changes in phase and amplitude over a received signal burst and further comprises a multi tap finite impulse response (FIR) filter; and
wherein the adaptive equalizer further comprises a coefficient adaptor configured to determine and dynamically change coefficients for the multi-tap FIR filter over the received signal burst.
6. The adaptive equalizer of claim 5 further comprising a parameter setting function that is configured to provide parameters to the coefficient adaptor, the parameters used by the coefficient adaptor to determine and dynamically change the coefficients.
7. An adaptive equalizer for a communication channel, the adaptive equalizer comprising:
a fixed pre-filter configured to be coupled to a received signal and provide a pre-filter signal;
an adaptive filter coupled to and configured to compensate the pre-filter signal for changes in phase and amplitude; and
an interference remover coupled to the adaptive filter and configured to reduce interference in the received signal,
wherein the adaptive filter is further configured for compensating the pre-filter signal for changes in phase and amplitude over a received signal burst and further comprises a multi tap finite impulse response (FIR) filter; and
wherein the adaptive equalizer further comprises a coefficient adaptor configured to determine and dynamically change coefficients for the multi-tap FIR filter over the received signal burst;
the adaptive equalizer further comprising a parameter setting function that is configured to provide parameters to the coefficient adaptor, the parameters used by the coefficient adaptor to determine and dynamically change the coefficients,
wherein the parameter setting function is configured to provide parameters including one or more of; a first parameter (K 1 , K 2 ) setting a number of coefficients for the multi-tap FIR filter, a second parameter (L b ) setting a number of coefficients to be adapted for the interference remover, and a third parameter (β) setting a tracking speed for the coefficient adaptor.
8. An adaptive equalizer for a communication channel, the adaptive equalizer comprising:
a fixed pre-filter configured to be coupled to a received signal and provide a pre-filter signal;
an adaptive filter coupled to and configured to compensate pre-filter signal for changes in phase and amplitude; and
an interference remover coupled to the adaptive filter and configured to reduce interference in the received signal,
wherein the adaptive filter comprises a finite impulse response (FIR) filter with a single tap and corresponding coefficient, the FIR filter configured to compensate for phase and amplitude changes in the pre-filter signal over a received signal burst on a symbol by symbol basis.
9. The adaptive equalizer of claim 8 wherein the corresponding coefficient of the single tap FIR filter is adapted over the received signal burst, where adaptation of the corresponding coefficient is in accordance with a parameter (β) that corresponds to a tracking speed of the adaptation.
10. The adaptive equalizer of claim 9 wherein the parameter (β) is dependent on an interference level and a rate of change in the pre-filter signal.
11. An adaptive equalizer for a communication channel, the adaptive equalizer comprising:
a fixed pre-filter configured to be coupled to a received signal and provide a pre-filter signal;
an adaptive filter coupled to and configured to compensate the pre-filter signal for changes in phase and amplitude; and
an interference remover coupled to the adaptive filter and configured to reduce interference in the received signal,
wherein the fixed pre-filter includes a plurality of fixed pre-filters each coupled to a received signal corresponding to a unique branch of a diversity receiver and each providing a unique pre-filtered signal;
wherein the adaptive filter includes a plurality of adaptive filters with each coupled to and configured to compensate one of the unique pre-filter signals for changes in phase and amplitude over a received signal burst to provide one of a plurality of compensated signals;
wherein the adaptive equalizer further comprises a combiner coupled to each of the plurality of compensated signals, the combiner configured to combine the plurality of compensated signals and provide a resultant signal; and
wherein the interference remover is coupled to the resultant signal.
12. An adaptive equalizer for a communication channel, the adaptive equalizer comprising:
a fixed pre-filter configured to be coupled to a received signal and provide a pre-filter signal;
an adaptive filter coupled to and configured to compensate the pre-filter signal for changes in phase and amplitude;
an interference remover coupled to the adaptive filter and configured to reduce interference in the received signal; and
a local oscillator (LO) error estimator that provides a frequency error estimate based on a coefficient of the adaptive filter as that coefficient is adapted over a received signal burst.
13. An adaptive equalizer for a communication channel, the adaptive equalizer comprising:
a fixed pre-filter coupled to a receive signal and configured to provide a pre-filter signal, the fixed pre-filter configured in accordance with filter coefficients provided by a decision feedback equalizer (DFE) coefficient calculator, the filter coefficients provided one time for each data field in a burst of the receive signal;
an adaptive filter coupled to the pre-filter signal and configured to compensate the pre-filter signal for changes in phase and amplitude over a span of the burst of the receive signal to provide a compensated signal; and
an interference remover coupled to the compensated signal and configured to reduce interference in the burst of the receive signal and to provide corresponding soft symbols, the interference remover including a feedback filter configured in accordance with near minimum phase coefficients provided by the DFE coefficient calculator, the near minimum phase coefficients provided one time for the each data field in the burst of the receive signal.
14. The adaptive equalizer of claim 13 wherein the adaptive filter is a finite impulse response (FIR) filter configured in accordance with a single coefficient, the single coefficient dynamically changed over the span of the burst of the receive signal.
15. The adaptive equalizer of claim 13 wherein the feedback filter is configured in accordance with the near minimum phase coefficients with a first coefficient set to a constant value, a first portion of the near minimum phase coefficients dynamically changed over the span of the burst of the receive signal, and a second portion of the near minimum phase coefficients fixed over the span of the burst of the receive signal.
16. The adaptive equalizer of claim 13 further comprising a coefficient adaptor configured to dynamically change a coefficient for the adaptive filter over the span of the burst of the receive signal responsive to parameters, the near minimum phase coefficients, and an error signal provided by the interference remover.
17. The adaptive equalizer of claim 16 wherein the parameters are determined for the burst of the receive signal and determined again for another burst of the receive signal.
18. A method of adaptively equalizing signals transmitted over a communication channel, the method comprising:
filtering a burst of a receive signal with a fixed pre-filter to provide a pre-filter signal, the fixed pre-filter configured in accordance with filter coefficients provided one time for each data field in the burst of the receive signal;
adaptively filtering the pre-filter signal with an adaptive filter to provide a compensated signal, which is compensated for changes in phase and amplitude over a span of the burst of the receive signal; and
reducing interference in the burst of the receive signal with an interference remover to provide corresponding soft symbols, the interference remover configured in accordance with near minimum phase coefficients that are initialized one time for the each data field in the burst of the receive signal.
19. The method of claim 18 wherein the adaptively filtering the pre-filter signal with an adaptive filter further comprises configuring the adaptive filter in accordance with one or more coefficients that are dynamically changed over the span of the burst of the receive signal responsive to adaptation parameters and an error provided by the interference remover.
20. The method of claim 18 wherein the adaptively filtering the pre-filter signal with an adaptive filter further comprises adaptively filtering the pre-filter signal with a finite impulse response (FIR) filter with a single tap and corresponding coefficient.
21. The method of claim 20 wherein the adaptively filtering the pre-filter signal with a finite impulse response (FIR) filter with a single tap and corresponding coefficient further comprises adapting the corresponding coefficient over each data field in the burst of the receive signal in accordance with a schedule and in accordance with a parameter (β) that corresponds to a tracking speed of the adaptation.
22. The method of claim 18 wherein the reducing interference in the burst of the receive signal with an interference remover configured in accordance with near minimum phase coefficients further includes configuring the interference remover in accordance with near minimum phase coefficients that include a first coefficient set to a constant value, a first portion of the near minimum phase coefficients that are dynamically changed over the burst of the receive signal, and a second portion of the minimum phase coefficients that are fixed to an initialized value over the each data field in the burst of the receive signal.