Method for post detection improvement in mimo

Abstract

A two-stage approach to MIMO detection improves receiver performance in a computationally tractable manner. A whitening joint detector processes a MIMO symbol stream. The whitening joint detector includes a pre-filter operative to suppress a first subset of the received MIMO streams as colored noise. The whitening joint detector further includes a primary joint detector operative to process a second subset of the MIMO streams and to output a preliminary solution obtained by minimizing a whitening joint detection metric. A secondary detector then operates in the vicinity of the primary joint detector preliminary solution. The secondary detector improves the preliminary solution by comparison to a full joint detection metric.

1 . A receiver operative in a multiple input, multiple output (MIMO) wireless communication network in which two or more streams of communication symbols are transmitted, comprising:
 a whitening joint detector comprising   a pre-filter operative to suppress a first subset of the received MIMO streams as colored noise; and   a primary joint detector operative to process a second subset of the MIMO streams and to output a preliminary solution obtained by minimizing a whitening joint detection metric; and   a secondary detector operating in the vicinity of the primary joint detector preliminary solution, and operative to improve the preliminary solution by comparison to a full joint detection metric.   
     
     
         2 . The receiver of  claim 1  wherein the secondary detector operating in the vicinity of the primary joint detector preliminary solution and operative to improve the preliminary solution by comparison to a full joint detection metric is operative to:
 compute the full joint detection metric on the preliminary solution output by the primary joint detector; 
 take the full joint detection metric on the preliminary solution as the tentative secondary solution; 
 iteratively compute the full joint detection metric on a plurality of vectors of nearest neighbors to symbols found in the primary joint detector preliminary solution; and 
 at each iteration, if the full joint detection metric of a vector of nearest neighbors is less than the tentative secondary solution, substitute the metric as the new tentative secondary solution; and 
 repeat iterations until one of no improvement in the metric over the last tentative secondary solution, or an iteration count is reached; and 
 take the last tentative secondary solution as the output of the secondary detector. 
 
     
     
         3 . The receiver of  claim 2  wherein the secondary detector operates on nearest neighbor symbols in the transmit domain. 
     
     
         4 . The receiver of  claim 1  wherein the secondary detector is further operative to output soft bit values. 
     
     
         5 . The receiver of  claim 4  wherein the secondary detector outputs a vector of determined symbols and a full joint detection metric of the vector of determined symbols, and wherein it determines soft values by
 determining a bit nearest neighbor symbol for each bit of each symbol in the vector of determined symbols; 
 for each bit of each symbol, substituting the corresponding bit nearest neighbor symbol for the determined symbol, and computing the full joint detection metric on the vector of determined symbols with the substitute bit nearest neighbor symbol; and 
 taking as the soft value of each bit of each symbol, the absolute value of the difference between the full joint detection metric computed on the vector of determined symbols and the full joint detection metric on the vector of determined symbols with the substitute bit nearest neighbor symbol. 
 
     
     
         6 . A method of detecting communication symbols in a multiple input, multiple output (MIMO) wireless communication network in which two or more streams of symbols are transmitted, comprising:
 suppressing a first subset of the received MIMO streams as colored noise; and   jointly detecting a second subset of the MIMO streams in a first primary detector and outputting a preliminary solution obtained by minimizing a whitening joint detection metric; and   jointly detecting the second subset of the MIMO streams in a secondary detector operating in the vicinity of the primary joint detector preliminary solution, and improving the preliminary solution by comparison to a full joint detection metric.   
     
     
         7 . The method of  claim 6  further comprising jointly detecting the first subset of the MIMO streams in a second primary detector. 
     
     
         8 . The method of  claim 6  further comprising, in the secondary detector:
 computing the full joint detection metric on the preliminary solution output by the primary joint detector; 
 taking the full joint detection metric on the preliminary solution as the tentative secondary solution; 
 iteratively computing the full joint detection metric on a plurality of vectors of nearest neighbors to symbols found in the primary joint detector preliminary solution; and 
 at each iteration, if the full joint detection metric of a vector of nearest neighbors is less than the tentative secondary solution, substituting the metric as the new tentative secondary solution; and 
 repeating iterations until one of no improvement in the metric over the last tentative secondary solution, or an iteration count is reached; and 
 taking the last tentative secondary solution as the output of the secondary detector. 
 
     
     
         9 . The method of  claim 8  wherein the nearest neighbors to symbols found in the primary joint detector preliminary solution comprise symbols that are nearest neighbors in the transmit domain. 
     
     
         10 . The method of  claim 6  further comprising outputting soft bit values from the secondary detector. 
     
     
         11 . The method of  claim 10  further comprising, in the secondary detector:
 determining a bit nearest neighbor symbol for each bit of each symbol in the vector of determined symbols; 
 for each bit of each symbol, substituting the corresponding bit nearest neighbor symbol for the determined symbol, and computing the full joint detection metric on the vector of determined symbols with the substitute bit nearest neighbor symbol; and 
 taking as the soft value of each bit of each symbol, the absolute value of the difference between the full joint detection metric computed on the vector of determined symbols and the full joint detection metric on the vector of determined symbols with the substitute bit nearest neighbor symbol.