METHOD FOR DEFINING A SEARCH SEQUENCE FOR SOFT-DECISION SPHERE DECODING ALGORITHM

A low complexity method for determining a search sequence of nodes for an efficient soft-decision sphere decoding algorithm for use in receivers for quadrature amplitude modulation (QAM) communication signals is achieved by determining a first member of the search sequence by rounding a received symbol (z) to a first constellation symbol (xc) of the QAM constellation, classifying the remaining constellation symbols (xi) of the QAM constellation into a plurality of sub-sets of constellation symbols having the same distance metric relative to said first constellation point (xc) according to a metric dsequ(n)=2a·n=max{|real(xc−xi)|,|imag(xc−xi)|}, a being a scaling factor of the constellation grid, and ordering said sub-sets of constellation symbols in ascending order of their distance metric relative to the first constellation symbol (xc), and ordering the members of each sub-set of constellation symbols that are defined by the same distance metric according to their Euclidean distances.