Performance bounds for serially-concatenated trellis-coded modulation

Previous advances using iterative (turbo) decoding techniques have resulted in codes that not only approach the Shannon limit for additive white Gaussian noise (AWGN) channels but are also readily implemented in practice. The original turbo codes include a pair of encoders separated by an interleaver and concatenated in parallel. New turbo codes developed by Benedetto et al. (see IEEE Trans. on. Communications, vol.44, no.5, p.591-600, 1996) include a pair of convolutional encoders also separated by an interleaver but concatenated serially. We extend the work of Benedetto et al. to serially-concatenated trellis-coded modulation (SCTCM). We determine the Bhattacharyya bound for maximum-likelihood decoding using the concept of the uniform interleaver. This bound enables us to determine the key parameters that can be used to develop a systematic code design strategy. We discuss both these results and the accuracy of the bound.