On BICM receivers for TCM transmission

TL;DR

This paper explains why BICM-T, a simplified BICM scheme without interleaving, performs well in nonfading channels, and shows it can match the performance of traditional TCM with asymptotic gains.

Contribution

It provides a formal analysis of BICM-T, introduces a new distance spectrum for convolutional codes, and demonstrates its asymptotic optimality compared to 1D-TCM.

Findings

BICM-T achieves about 2 dB gain asymptotically.

Optimal convolutional codes for BICM-T are tabulated.

BICM-T performs as well as 1D-TCM in nonfading channels.

Abstract

Recent results have shown that the performance of bit-interleaved coded modulation (BICM) using convolutional codes in nonfading channels can be significantly improved when the interleaver takes a trivial form (BICM-T), i.e., when it does not interleave the bits at all. In this paper, we give a formal explanation for these results and show that BICM-T is in fact the combination of a TCM transmitter and a BICM receiver. To predict the performance of BICM-T, a new type of distance spectrum for convolutional codes is introduced, analytical bounds based on this spectrum are developed, and asymptotic approximations are also presented. It is shown that the minimum distance of the code is not the relevant optimization criterion for BICM-T. Optimal convolutional codes for different constrain lengths are tabulated and asymptotic gains of about 2 dB are obtained. These gains are found to be the same as those obtained by Ungerboeck's one-dimensional trellis coded modulation (1D-TCM), and therefore, in nonfading channels, BICM-T is shown to be asymptotically as good as 1D-TCM.