TCMs matched to ISI channels: New results for combined symbol-by-symbol equalization and decoding

E. Baccarelli, S. Galli
Proceedings of ICC'97 - International Conference on Communications  
The design of good TCM schemes matched to ISI channels requires that analytical performance bounds are also available. In this paper, starting from an application of the union-Bhattacharyya bound, upper-bounds for the performance of the theoretically optimum combined Symbol-by-Symbol (SbS) Abend-Fritchman like equalizer and decoder are presented for the first time in literature. The combined detector acts on the distorted version of the TCM signal received at the output of a channel impaired by
more » ... channel impaired by (known) ISI and AWGN. On the basis of these bounds a novel simple criterion for the design of TCMs optimally matched to any assigned ISI-corrupted transmission channel is then derived and its application to some actual testchannels is illustrated. I. MOTIVATION OF THE WORK Although the high bandwidth efficiency of TCMs makes their utilization very attractive for data-transmissions over bandlimited ISI-impaired channels, to date little has been done about analytical evaluation of TCMs performance on ISI channels, as pointed out in [1,Sect.11.1] and more recently in [2], neither general criteria for the good design of TCMs matched to these channels seem available. The set of bounds recently proposed in [3] well represent the state of the art about this topic. However, the interesting results of [3] have been derived under some simplifying assumptions [3,Sect.III-IV],[4] which could make the resulting bounds loose when not perfectly interleaved systems acting over severely ISI degraded environments are considered. Furthermore, as also explicitly pointed out by the same authors in [3,Sect.IX], no criterion for designing TCMs is developed. The results of [3] (as those of [1,Chap.11] and [ 4, 5] ) also assume the presence of Maximum Likelihood Sequence (MLS) receivers with additive decoding metrics implemented via the standard Viterbi Algorithm (VA). However, an attractive alternative to MLS-VA detectors is today constituted by the so called SbS receivers, originally developed by Abend and Fritchman [6,Sect.6.6], and recently reconsidered with renewed interest [7, 8, 9] . The utilization of SbS equalizers and decoders seems indeed very attractive for data-transmission over severely ISI-impaired links; in fact, several simulation results for TCMencoded data systems have proved that the performances obtained by means of SbS detectors can be over two orders of magnitude better than those achievable with conventional MLS-VA receivers [7] . However, despite its practical as theoretical relevance the question concerning analytical results about the key-parameters dominating the performance of TCM-encoded SbS-decoded ISI-impaired data systems appears today
doi:10.1109/icc.1997.610028 dblp:conf/icc/BaccarelliG97 fatcat:7iqdwouvqrafrpnzgnrd4s65xi