Interference cancellation under non-stationary conditions

Abstract

A method for timing and frequency synchronization in a wireless system is provided. The method comprises the steps of receiving a burst of symbols, selecting a subset of the burst of symbols, iteratively adjusting the subset of the burst of symbols by a plurality of timing offsets and calculating, for each timing offset, a first performance metric corresponding to the adjusted subset. The method further comprises the steps of determining one of the plurality of timing offsets to be a preferred timing offset based upon the first performance metric thereof, iteratively rotating the subset of the burst of symbols by a plurality of frequency offsets and calculating, for each frequency offset, a second performance metric corresponding to the rotated subset, and determining one of the plurality of frequency offsets to be a preferred frequency offset based upon the second performance metric thereof.

1 . A method for timing and frequency synchronization in a wireless system, comprising the steps of:
 receiving a burst of symbols;   selecting a subset of the burst of symbols;   iteratively adjusting the subset of the burst of symbols by a plurality of timing offsets;   calculating, for each timing offset, a first performance metric corresponding to the adjusted subset;   determining one of the plurality of timing offsets to be a preferred timing offset based upon the first performance metric thereof;   iteratively rotating the subset of the burst of symbols by a plurality of frequency offsets;   calculating, for each frequency offset, a second performance metric corresponding to the rotated subset; and   determining one of the plurality of frequency offsets to be a preferred frequency offset based upon the second performance metric thereof.   
   
   
       2 . The method according to  claim 1 , wherein the first performance metric is a midamble estimation error. 
   
   
       3 . The method according to  claim 2 , wherein the midamble estimation error is calculated for each timing offset by:
 calculating a plurality of weights for an interference suppression filter based upon the subset of the burst of symbols;   filtering the burst of symbols using the interference suppression filter with the corresponding plurality of weights to obtain an estimated midamble sequence; and   comparing the estimated midamble sequence with a previously-known midamble sequence to determine the midamble estimation error.   
   
   
       4 . The method according to  claim 3 , wherein the plurality of weights are calculated by solving for
   W SAIC ={tilde over (s)} k [X] T {[X][X] T } −1 ,   where {tilde over (s)} k  is a vector corresponding to an estimate of the subset of symbols, [X] is a matrix of spatial temporal samples of the burst of symbols, and [X] T  is a transpose of [X].   
   
   
       5 . The method according to  claim 3 , wherein the interference suppression filter is a single antenna interference cancellation filter. 
   
   
       6 . The method according to  claim 3 , wherein the interference suppression filter is a dual antenna interference cancellation filter. 
   
   
       7 . The method according to  claim 1 , wherein the second performance metric is a midamble estimation error. 
   
   
       8 . The method according to  claim 7 , wherein the midamble estimation error is calculated for each frequency offset by:
 calculating a plurality of weights for an interference suppression filter based upon the subset of the burst of symbols;   filtering the burst of symbols using the interference suppression filter with the corresponding plurality of weights to obtain an estimated midamble sequence; and   comparing the estimated midamble sequence with a previously-known midamble sequence to determine the midamble estimation error.   
   
   
       9 . The method according to  claim 8 , wherein the plurality of weights are calculated by solving for
   W SAIC ={tilde over (s)} k [X] T {[X][X] T } −1 ,   where {tilde over (s)} k  is a vector corresponding to an estimate of the subset of symbols, [X] is a matrix of spatial temporal samples of the burst of symbols, and [X] T  is a transpose of [X].   
   
   
       10 . The method according to  claim 8 , wherein the interference suppression filter is a single antenna interference cancellation filter. 
   
   
       11 . The method according to  claim 1 , wherein the subset of the burst of symbols includes a first midamble symbol. 
   
   
       12 . The method according to  claim 11 , wherein the plurality of timing offsets are determined by estimating a position of the first midamble symbol in the burst of symbols and selecting the subset of the burst of symbols from symbols centered around the estimated position. 
   
   
       13 . A method for timing and frequency synchronization in a wireless system, comprising the steps of:
 receiving a burst of symbols;   selecting a subset of the burst of symbols;   iteratively adjusting the subset of the burst of symbols by a plurality of timing offsets and a plurality of frequency offsets;   calculating, for each combination of timing and frequency offsets, a performance metric corresponding to the adjusted subset; and   determining one of the combination of timing and frequency offsets to be a preferred combination based upon the performance metric thereof.   
   
   
       14 . The method according to  claim 13 , wherein the performance metric is a midamble estimation error. 
   
   
       15 . The method according to  claim 14 , wherein the midamble estimation error is calculated for each combination of timing and frequency offsets by:
 calculating a plurality of weights for an interference suppression filter based upon the subset of the burst of symbols;   filtering the burst of symbols using the interference suppression filter with the corresponding plurality of weights to obtain an estimated midamble sequence; and   comparing the estimated midamble sequence with a previously-known midamble sequence to determine the midamble estimation error.   
   
   
       16 . The method according to  claim 15 , wherein the plurality of weights are calculated by solving for
   W SAIC ={tilde over (s)} k [X] T {[X][X] T } −1 ,   where {tilde over (s)} k  is a vector corresponding to an estimate of the subset of symbols, [X] is a matrix of spatial temporal samples of the burst of symbols, and [X] T  is a transpose of [X].   
   
   
       17 . The method according to  claim 15 , wherein the interference suppression filter is a single antenna interference cancellation filter. 
   
   
       18 . The method according to  claim 15 , wherein the interference suppression filter is a dual antenna interference cancellation filter. 
   
   
       19 . A wireless apparatus, comprising:
 a receiver configured to receive a burst of symbols; and   a processor configured to:
 select a subset of the burst of symbols; 
 iteratively adjust the subset of the burst of symbols by a plurality of timing offsets; 
 calculate, for each timing offset, a first performance metric corresponding to the adjusted subset; 
 determine one of the plurality of timing offsets to be a preferred timing offset based upon the first performance metric thereof; 
 iteratively rotate the subset of the burst of symbols by a plurality of frequency offsets; 
 calculate, for each frequency offset, a second performance metric corresponding to the rotated subset; and 
 determine one of the plurality of frequency offsets to be a preferred frequency offset based upon the second performance metric thereof. 
   
   
   
       20 . The wireless apparatus according to  claim 19 , wherein the first performance metric is a midamble estimation error. 
   
   
       21 . The wireless apparatus according to  claim 20 , wherein the processor is configured to calculate the midamble estimation error for each timing offset by:
 calculating a plurality of weights for an interference suppression filter based upon the subset of the burst of symbols;   filtering the burst of symbols using the interference suppression filter with the corresponding plurality of weights to obtain an estimated midamble sequence; and   comparing the estimated midamble sequence with a previously-known midamble sequence to determine the midamble estimation error.   
   
   
       22 . The wireless apparatus to  claim 21 , wherein the processor is configured to calculate the plurality of weights by solving for
   W SAIC ={tilde over (s)} k [X] T {[X][X] T } −1 ,   where {tilde over (s)} k  is a vector corresponding to an estimate of the subset of symbols, [X] is a matrix of spatial temporal samples of the burst of symbols, and [X] T  is a transpose of [X].   
   
   
       23 . The wireless apparatus according to  claim 21 , wherein the interference suppression filter is a single antenna interference cancellation filter. 
   
   
       24 . The wireless apparatus according to  claim 21 , wherein the interference suppression filter is a dual antenna interference cancellation filter. 
   
   
       25 . The wireless apparatus according to  claim 19 , wherein the second performance metric is a midamble estimation error. 
   
   
       26 . The wireless apparatus according to  claim 25 , wherein the processor is configured to calculate the midamble estimation error for each frequency offset by:
 calculating a plurality of weights for an interference suppression filter based upon the subset of the burst of symbols;   filtering the burst of symbols using the interference suppression filter with the corresponding plurality of weights to obtain an estimated midamble sequence; and   comparing the estimated midamble sequence with a previously-known midamble sequence to determine the midamble estimation error.   
   
   
       27 . The wireless apparatus according to  claim 26 , wherein the processor is configured to calculate the plurality of weights by solving for
   W SAIC ={tilde over (s)} k [X] T {[X][X] T } −1 ,   where {tilde over (s)} k  is a vector corresponding to an estimate of the subset of symbols, [X] is a matrix of spatial temporal samples of the burst of symbols, and [X] T  is a transpose of [X].   
   
   
       28 . The wireless apparatus according to  claim 26 , wherein the interference suppression filter is a single antenna interference cancellation filter. 
   
   
       29 . The wireless apparatus according to  claim 19 , wherein the subset of the burst of symbols includes a first midamble symbol. 
   
   
       30 . The wireless apparatus according to  claim 29 , wherein the processor is configured to determine the plurality of timing offsets by estimating a position of the first midamble symbol in the burst of symbols and selecting the subset of the burst of symbols from symbols centered around the estimated position. 
   
   
       31 . A wireless apparatus, comprising:
 a receiver configured to receive a burst of symbols; and   a processor configured to:
 receive a burst of symbols; 
 select a subset of the burst of symbols; 
 iteratively adjust the subset of the burst of symbols by a plurality of timing offsets and a plurality of frequency offsets; 
 calculate, for each combination of timing and frequency offsets, a performance metric corresponding to the adjusted subset; and 
 determine one of the combination of timing and frequency offsets to be a preferred combination based upon the performance metric thereof. 
   
   
   
       32 . The wireless apparatus according to  claim 31 , wherein the performance metric is a midamble estimation error. 
   
   
       33 . The wireless apparatus according to  claim 32 , wherein the processor is configured to calculate the midamble estimation error for each combination of timing and frequency offsets by:
 calculating a plurality of weights for an interference suppression filter based upon the subset of the burst of symbols;   filtering the burst of symbols using the interference suppression filter with the corresponding plurality of weights to obtain an estimated midamble sequence; and   comparing the estimated midamble sequence with a previously-known midamble sequence to determine the midamble estimation error.   
   
   
       34 . The wireless apparatus according to  claim 33 , wherein the processor is configured to calculate the plurality of weights by solving for
   W SAIC ={tilde over (s)} k [X] T {[X][X] T } −1 ,   where {tilde over (s)} k  is a vector corresponding to an estimate of the subset of symbols, [X] is a matrix of spatial temporal samples of the burst of symbols, and [X] T  is a transpose of [X].   
   
   
       35 . The wireless apparatus according to  claim 33 , wherein the interference suppression filter is a single antenna interference cancellation filter. 
   
   
       36 . The wireless apparatus according to  claim 33 , wherein the interference suppression filter is a dual antenna interference cancellation filter. 
   
   
       37 . A wireless apparatus, comprising:
 means for receiving a burst of symbols;   means for selecting a subset of the burst of symbols;   means for iteratively adjusting the subset of the burst of symbols by a plurality of timing offsets;   means for calculating, for each timing offset, a first performance metric corresponding to the adjusted subset;   means for determining one of the plurality of timing offsets to be a preferred timing offset based upon the first performance metric thereof;   means for iteratively rotating the subset of the burst of symbols by a plurality of frequency offsets and calculating, for each frequency offset, a second performance metric corresponding to the rotated subset; and   means for determining one of the plurality of frequency offsets to be a preferred frequency offset based upon the second performance metric thereof.   
   
   
       38 . The wireless apparatus according to  claim 37 , wherein the first performance metric is a midamble estimation error. 
   
   
       39 . The wireless apparatus according to  claim 38 , wherein the means for calculating the midamble estimation error for each timing offset comprise:
 means for calculating a plurality of weights for an interference suppression filter based upon the subset of the burst of symbols;   means filtering the burst of symbols using the interference suppression filter with the corresponding plurality of weights to obtain an estimated midamble sequence; and   means for comparing the estimated midamble sequence with a previously-known midamble sequence to determine the midamble estimation error.   
   
   
       40 . The wireless apparatus according to  claim 39 , wherein the means for calculating the plurality of weights comprise means for solving for
   W SAIC ={tilde over (s)} k [X] T {[X][X] T } −1 ,   where {tilde over (s)} k  is a vector corresponding to an estimate of the subset of symbols, [X] is a matrix of spatial temporal samples of the burst of symbols, and [X] T  is a transpose of [X].   
   
   
       41 . The wireless apparatus according to  claim 39 , wherein the interference suppression filter is a single antenna interference cancellation filter. 
   
   
       42 . The wireless apparatus according to  claim 39 , wherein the interference suppression filter is a dual antenna interference cancellation filter. 
   
   
       43 . The wireless apparatus according to  claim 37 , wherein the second performance metric is a midamble estimation error. 
   
   
       44 . The wireless apparatus according to  claim 43 , wherein the means for calculating the midamble estimation error for each frequency offset comprise:
 means for calculating a plurality of weights for an interference suppression filter based upon the subset of the burst of symbols;   means for filtering the burst of symbols using the interference suppression filter with the corresponding plurality of weights to obtain an estimated midamble sequence; and   means for comparing the estimated midamble sequence with a previously-known midamble sequence to determine the midamble estimation error.   
   
   
       45 . The wireless apparatus according to  claim 44 , wherein the means for calculating the plurality of weights comprise means for solving for
   W SAIC ={tilde over (s)} k [X] T {[X][X] T } −1 ,   where {tilde over (s)} k  is a vector corresponding to an estimate of the subset of symbols, [X] is a matrix of spatial temporal samples of the burst of symbols, and [X] T  is a transpose of [X].   
   
   
       46 . The wireless apparatus according to  claim 44 , wherein the interference suppression filter is a single antenna interference cancellation filter. 
   
   
       47 . The wireless apparatus according to  claim 37 , wherein the subset of the burst of symbols includes a first midamble symbol. 
   
   
       48 . The wireless apparatus according to  claim 47 , wherein the plurality of timing offsets are determined by estimating a position of the first midamble symbol in the burst of symbols and selecting the subset of the burst of symbols from symbols centered around the estimated position. 
   
   
       49 . A wireless apparatus, comprising:
 means for receiving a burst of symbols;   means for selecting a subset of the burst of symbols;   means for iteratively adjusting the subset of the burst of symbols by a plurality of timing offsets and a plurality of frequency offsets;   means for calculating, for each combination of timing and frequency offsets, a performance metric corresponding to the adjusted subset; and   means for determining one of the combination of timing and frequency offsets to be a preferred combination based upon the performance metric thereof.   
   
   
       50 . The wireless apparatus according to  claim 49 , wherein the performance metric is a midamble estimation error. 
   
   
       51 . The wireless apparatus according to  claim 50 , wherein means for calculating the midamble estimation error for each combination of timing and frequency offsets comprises:
 means for calculating a plurality of weights for an interference suppression filter based upon the subset of the burst of symbols;   means for filtering the burst of symbols using the interference suppression filter with the corresponding plurality of weights to obtain an estimated midamble sequence; and   means for comparing the estimated midamble sequence with a previously-known midamble sequence to determine the midamble estimation error.   
   
   
       52 . The wireless apparatus according to  claim 51 , wherein the means for calculating the plurality of weights comprise means for solving for
   W SAIC ={tilde over (s)} k [X] T {[X][X] T } −1 ,   where {tilde over (s)} k  is a vector corresponding to an estimate of the subset of symbols, [X] is a matrix of spatial temporal samples of the burst of symbols, and [X] T  is a transpose of [X].   
   
   
       53 . The wireless apparatus according to  claim 51 , wherein the interference suppression filter is a single antenna interference cancellation filter. 
   
   
       54 . The method according to  claim 51 , wherein the interference suppression filter is a dual antenna interference cancellation filter. 
   
   
       55 . A computer-program product for use in a wireless communication system comprising a computer readable medium having a set of instructions stored thereon, the set of instructions being executable by one or more processors and the set of instructions comprising:
 instructions for receiving a burst of symbols;   instructions for selecting a subset of the burst of symbols;   instructions for iteratively adjusting the subset of the burst of symbols by a plurality of timing offsets;   instructions for calculating, for each timing offset, a first performance metric corresponding to the adjusted subset;   instructions for determining one of the plurality of timing offsets to be a preferred timing offset based upon the first performance metric thereof;   instructions for iteratively rotating the subset of the burst of symbols by a plurality of frequency offsets and for calculating, for each frequency offset, a second performance metric corresponding to the rotated subset; and   instructions for determining one of the plurality of frequency offsets to be a preferred frequency offset based upon the second performance metric thereof.   
   
   
       56 . The computer-program product according to  claim 55 , wherein the first performance metric is a midamble estimation error. 
   
   
       57 . The computer-program product according to  claim 56 , wherein instructions for calculating the midamble estimation error for each timing offset comprise:
 instructions for calculating a plurality of weights for an interference suppression filter based upon the subset of the burst of symbols;   instructions for filtering the burst of symbols using the interference suppression filter with the corresponding plurality of weights to obtain an estimated midamble sequence; and   instructions for comparing the estimated midamble sequence with a previously-known midamble sequence to determine the midamble estimation error.   
   
   
       58 . The computer-program product according to  claim 57 , wherein the instructions for calculating the plurality of weights comprise instructions for solving for
   W SAIC ={tilde over (s)} k [X] T {[X][X] T } −1 ,   where {tilde over (s)} k  is a vector corresponding to an estimate of the subset of symbols, [X] is a matrix of spatial temporal samples of the burst of symbols, and [X] T  is a transpose of [X].   
   
   
       59 . The computer-program product according to  claim 57 , wherein the interference suppression filter is a single antenna interference cancellation filter. 
   
   
       60 . The computer-program product according to  claim 57 , wherein the interference suppression filter is a dual antenna interference cancellation filter. 
   
   
       61 . The computer-program product according to  claim 55 , wherein the second performance metric is a midamble estimation error. 
   
   
       62 . The computer-program product according to  claim 61 , wherein the instructions for calculating the midamble estimation error for each frequency offset comprise:
 instructions for calculating a plurality of weights for an interference suppression filter based upon the subset of the burst of symbols;   instructions for filtering the burst of symbols using the interference suppression filter with the corresponding plurality of weights to obtain an estimated midamble sequence; and   instructions for comparing the estimated midamble sequence with a previously-known midamble sequence to determine the midamble estimation error.   
   
   
       63 . The computer-program product according to  claim 62 , wherein the instructions for calculating the plurality of weights comprise instructions for solving for
   W SAIC ={tilde over (s)} k [X] T {[X][X] T } −1 ,   where {tilde over (s)} k  is a vector corresponding to an estimate of the subset of symbols, [X] is a matrix of spatial temporal samples of the burst of symbols, and [X] T  is a transpose of [X].   
   
   
       64 . The computer-program product according to  claim 62 , wherein the interference suppression filter is a single antenna interference cancellation filter. 
   
   
       65 . The computer-program product according to  claim 62 , wherein the subset of the burst of symbols includes a first midamble symbol. 
   
   
       66 . The computer-program product according to  claim 65 , wherein the plurality of timing offsets are determined by estimating a position of the first midamble symbol in the burst of symbols and selecting the subset of the burst of symbols from symbols centered around the estimated position. 
   
   
       67 . A computer-program product for use in a wireless communication system comprising a computer readable medium having a set of instructions stored thereon, the set of instructions being executable by one or more processors and the set of instructions comprising:
 instructions for receiving a burst of symbols;   instructions for selecting a subset of the burst of symbols;   instructions for iteratively adjusting the subset of the burst of symbols by a plurality of timing offsets and a plurality of frequency offsets;   instructions for calculating, for each combination of timing and frequency offsets, a performance metric corresponding to the adjusted subset; and   instructions for determining one of the combination of timing and frequency offsets to be a preferred combination based upon the performance metric thereof.   
   
   
       68 . The computer-program product according to  claim 67 , wherein the performance metric is a midamble estimation error. 
   
   
       69 . The computer-program product according to  claim 68 , wherein the instructions for calculating the midamble estimation error for each combination of timing and frequency offsets comprise:
 instructions for calculating a plurality of weights for an interference suppression filter based upon the subset of the burst of symbols;   instructions for filtering the burst of symbols using the interference suppression filter with the corresponding plurality of weights to obtain an estimated midamble sequence; and   instructions for comparing the estimated midamble sequence with a previously-known midamble sequence to determine the midamble estimation error.   
   
   
       70 . The computer-program product according to  claim 69 , wherein the instructions for calculating the plurality of weights comprise instructions for solving for
   W SAIC ={tilde over (s)} k [X] T {[X][X] T } −1 ,   where {tilde over (s)} k  is a vector corresponding to an estimate of the subset of symbols, [X] is a matrix of spatial temporal samples of the burst of symbols, and [X] T  is a transpose of [X].   
   
   
       71 . The computer-program product according to  claim 69 , wherein the interference suppression filter is a single antenna interference cancellation filter. 
   
   
       72 . The computer-program product according to  claim 69 , wherein the interference suppression filter is a dual antenna interference cancellation filter.