Generalized BICM-T transceivers: Constellation and multiplexer design

Recently, it has been shown that the performance of bit-interleaved coded modulation (BICM) using convolutional codes in nonfading channels can be significantly improved if the coded bits are not interleaved at all. This particular BICM design is referred to as BICM trivial (BICM-T) and is shown to be asymptotically as good as Ungerboeck´s one dimensional (1D) trellis coded modulation (TCM). This BICM-T design and analysis considered a simple case of rate 1/2 channel encoder with equally spaced 16-ary quadrature amplitude modulation (QAM) constellation where the code rate matches with the modulation order as required in TCM transmission. In this paper, we consider and analyze a new BICM-T design that uses a non equally spaced signal constellation in conjunction with a bit level multiplexer. With this design and analysis, one can not only exploit the full benefit of BICM-T design by jointly optimizing different transceiver´s modules but also enjoys the same design flexibility as the traditional BICM to independently choose the code rate and the modulation order. The presented numerical results for 64-ary QAM with rate 1/3 code shows that the considered design can offer gains up to 2.5 dB over the traditional optimal BICM design for a target bit error rate (BER) of 10⁻⁶.