BANDWIDTH-EFFICIENT CODED MODULATION WITH OPTIMIZED LINEAR PARTIAL-RESPONSE SIGNALS

We study the design of optimal signals for bandwidth-efficient linear coded modulation, Recent results show that for linear channels with in tersymbol interference (ISI), reduced-search decoding algorithms have near-maximum-likelihood error performance, but with much smaller compl exity than the Viterbi decoder. Consequently, the controlled ISI intro duced by a lowpass filter can be practically used for bandwidth reduct ion, Such spectrum shaping filters comprise an explicit coded modulati on, for which we seek the optimal design, We simultaneously constrain the bandwidth and maximize the minimum Euclidean distance between sign als, We show that under quite general assumptions the problem can be f ormulated as a linear program, and solved with well-known efficient op timization techniques, Numerical results are presented, and the perfor mance of the optimal signals, measured by their combined bandwidth and noise immunity, is analyzed, The new codes are comparable to set-part ition (TCM) trellis codes, Tests of an M-algorithm decoder confirm thi s and show that the performance occurs at small detection complexity.