1. A method of processing communications signals, comprising: receiving, at a receiver, a constellation which has unused constellation points; using a plurality of lookup tables for indicating whether a particular constellation point is used and the corresponding codeword for the used constellation points; indexing the lookup tables using the two integers u and v; finding the initial estimate of u and v: ū and v ; computing a modified Euclidean distance to the immediate constellation point neighbors that correspond to the upper and lower integers of ū and v ; and from the distance to the nearest neighbor, computing the log-likelihood ratio value.