Method and apparatus for single burst equalization of single carrier signals in broadband wireless access systems

Abstract

A receiver implementing a single carrier single burst equalization (SC-SBE) method is capable of achieving near optimal reception of individual single carrier RF bursts by making an accurate estimate of the burst's propagation channel impulse response (CIR). The SC-SBE method uses a CIR based coefficient computation process to obtain filter coefficients for a minimum mean square error decision feedback equalizer (MMSE-DFE). The MMSE-DFE filter computation process computes a sufficiently large number of coefficients for the DFE filters, i.e., the feed forward filter (FFF) and feedback filter (FBF), so that each filter spans the maximum anticipated length of the CIR. In order to implement the filters efficiently, a coefficient selection process eliminates less significant computed FFF and FBF coefficients. The resulting FFF and FBF are sparse filters in that most of the taps in the filter delay lines do not have a filter coefficient.

What is claimed is: 
     
         1 . An method, comprising:
 estimating a channel impulse response;   determining feed forward coefficients and feedback coefficients for at least one time domain filter based on the channel impulse response; and   selecting a subset of the feed forward coefficients and a subset of the feedback coefficients wherein a number of coefficients in each subset is less than a total number of the determined coefficients.   
     
     
         2 . The method of  claim 1 , wherein selecting a subset of feed forward coefficients and a subset of the feedback coefficients comprises: selecting a coefficient having an amplitude being one of a largest coefficient amplitudes of the feed forward coefficients or the feedback coefficients. 
     
     
         3 . The method of  claim 2 , wherein selecting a subset of feed forward coefficients and a subset of the feedback coefficients further comprises:
 selecting a coefficient having an amplitude greater than K*.sigma..sub.F or K*.sigma..sub.B, wherein sigma..sub.F and .sigma..sub.B are standard deviations of a subset of coefficients whose amplitudes are not one of the largest coefficient amplitudes of the feed forward coefficients or the feedback coefficients, wherein K is a threshold parameter that provides protection against coefficient computation noise.   
     
     
         4 . The method of  claim 3 , wherein the selecting a subset of the feed forward coefficients and a subset of the feedback coefficients comprises:
 pre-selecting computed feed forward coefficients and feedback coefficients.   
     
     
         5 . The method of  claim 4 , wherein the pre-selecting the computed feed forward coefficients and feedback coefficients comprises:
 examining the computed feed forward coefficients and feedback coefficients; and   storing each of the computed coefficients having an amplitude being one of a largest coefficient amplitudes in a coefficient buffer that defines a coefficient search space for a minimization process.   
     
     
         6 . The method of  claim 4 , wherein selecting a coefficient having an amplitude greater than K*.sigma..sub.F or K*.sigma..sub.B comprises:
 sorting the computed feed forward coefficients into a number of largest feed forward coefficients and a number of smallest feed forward coefficients;   sorting the computed feedback coefficients into a number of largest feedback coefficients and a number of smallest feedback coefficients; and   calculating sigma..sub.F and sigma..sub.B based on the number of smallest feed forward coefficients and the number of smallest feedback coefficients.   
     
     
         7 . The method of  claim 6 , further comprising:
 selecting a coefficient to include in the subset of feed forward coefficients if the amplitude of the coefficient is one of a largest coefficient amplitudes of the feed forward coefficients and is greater than K*.sigma..sub.F; and   selecting a coefficient to include in the subset of feedback coefficients if the amplitude of the coefficient is one of a largest coefficient amplitudes of the feedback coefficients and is greater than K*.sigma..sub.B.   
     
     
         8 . An apparatus, comprising:
 circuitry for estimating a channel impulse response;   circuitry for determining feed forward coefficients and feedback coefficients; and   circuitry for selecting a subset of the feed forward coefficients and a subset of the feedback coefficients, wherein a number of coefficients in each subset is less than a total number of the determined coefficients.   
     
     
         9 . The apparatus of  claim 8 , wherein the circuitry for selecting a subset of the feed forward coefficients and a subset of the feedback coefficients comprises:
 circuitry for selecting each coefficient in the subsets of the coefficients based on an amplitude of the coefficient satisfying at least one of:
 the amplitude being one of a largest coefficient amplitudes of the feed forward coefficients or the feedback coefficients; and 
 the amplitude being greater than K*.sigma..sub.F or K*.sigma..sub.B, where sigma..sub.F or sigma..sub.B are standard deviations of a subset of coefficients whose amplitudes are not one of the largest coefficient amplitudes of the feed forward coefficients or the feedback coefficients, wherein K is a threshold parameter that provides protection against coefficient computation noise. 
   
     
     
         10 . The apparatus of  claim 8 , wherein the circuitry for selecting a subset of the feed forward coefficients and a subset of the feedback coefficients comprises:
 circuitry for pre-selecting the feed forward coefficients and feedback coefficients.   
     
     
         11 . The apparatus of  claim 10 , wherein the circuitry for pre-selecting the feed forward coefficients and feedback coefficients comprises:
 circuitry for examining the determined feed forward coefficients and feedback coefficients;   circuitry for selecting a coefficient having an amplitude being one of a largest coefficient amplitudes from the determined feed forward coefficients and feedback coefficients; and   circuitry for storing the coefficient having an amplitude being one of a largest coefficient amplitudes in a coefficient buffer that defines a coefficient search space for a minimization process.   
     
     
         12 . The apparatus of  claim 9 , wherein the circuitry for selecting a subset of the feed forward coefficients and a subset of the feedback coefficients comprises:
 circuitry for sorting the determined feed forward coefficients into a number of largest feed forward coefficients and a number of smallest feed forward coefficients; and   circuitry for calculating the sigma..sub.F based on the number of smallest feed forward coefficient.   
     
     
         13 . The apparatus of  claim 9 , wherein the circuitry for selecting a subset of the feed forward coefficients and a subset of the feedback coefficients comprises:
 circuitry for sorting the determined computed feedback coefficients into a number of largest feedback coefficients and a number of smallest feedback coefficients; and   circuitry for calculating the sigma..sub.B based on the number of smallest feedback coefficients.   
     
     
         14 . The apparatus of  claim 12 , wherein the circuitry for selecting a subset of the feed forward coefficients and a subset of the feedback coefficients further comprises:
 circuitry for selecting a coefficient to include in the subset of feed forward coefficients if the amplitude of coefficient is one of a largest coefficient amplitudes of the feed forward coefficients and is greater than K*.sigma..sub.F.   
     
     
         15 . The apparatus of  claim 13 , wherein the circuitry for selecting a subset of the feed forward coefficients and a subset of the feedback coefficients further comprises:
 circuitry for selecting a coefficient to include in the subset of feedback coefficients if the amplitude of the coefficient is one of a largest coefficient amplitudes of the feed forward coefficients and is greater than K*.sigma..sub.B.   
     
     
         16 . An apparatus, comprising:
 circuitry for estimating a channel impulse response;   circuitry for determining feed forward filter coefficients and feedback filter coefficients for a decision feedback equalizer having sufficient length to cover a maximum anticipated channel impulse response; and   circuitry for pre-selecting the feed forward filter coefficients and the feedback filter coefficients.   
     
     
         17 . The apparatus of  claim 16 , wherein the circuitry for pre-selecting the feed forward filter coefficients and feedback filter coefficients comprises:
 circuitry for selecting a number of largest feed forward coefficients and a number of largest feedback coefficients;   a buffer for storing the number of largest feed forward coefficients and largest feedback coefficients; and   circuitry for identifying from the number of largest feed forward coefficients and largest feedback coefficients a subset of coefficients.   
     
     
         18 . An apparatus, comprising:
 circuitry for estimating a channel impulse response;   circuitry for determining feed forward filter coefficients and feedback filter coefficients;   circuitry for sorting the feed forward filter coefficients and the feedback filter coefficients based on amplitudes of the coefficients;   circuitry for computing standard deviations of the coefficients whose amplitudes are not one of the largest coefficient amplitudes of the feed forward filter coefficients or the feedback filter coefficients; and   circuitry for selecting a subset of the feed forward coefficients and a subset of the feedback coefficients based on the standard deviations.   
     
     
         19 . The apparatus of  claim 18 , wherein the circuitry for sorting the feed forward filter coefficients and the feedback filter coefficients based on amplitudes of the coefficients comprises:
 circuitry for sorting circuitry for sorting the determined computed feedback coefficients into a number of largest feed forward coefficients and a number of smallest feed forward coefficients based on the amplitudes.   
     
     
         20 . The apparatus of  claim 19 , wherein the circuitry for computing standard deviations comprises circuitry for computing the standard deviations based on the smallest number of feed forward coefficients and the smallest number of feedback coefficients, and p 1  the circuitry for selecting a subset of the feed forward coefficients and a subset of the feedback coefficients comprises a threshold comparison circuitry for comparing the number of largest feed forward coefficients and the number of smallest feedback coefficients to a product of the standard deviations and a threshold parameter that provides protection against coefficient computation noise.