Switching threshold and coding-rate optimisation for turbo convolutional and turbo bch coded adaptive modulation

Decision feedback equaliser (DFE) aided turbo coded wideband adaptive quadrature amplitude modulation (AQAM) is capable of accommodating the temporal channel quality variation of fading channels. A procedure is suggested for determining the AQAM switching thresholds and the specific turbo coding rates capable of maintaining the target BER, while aiming for achieving a high effective bits per symbol (BPS) throughput. Subsequently, the performances of both turbo convolutional (TC) and turbo BCH (TBCH) coded fixed and adaptive modulation schemes are characterised and compared when communicating over the COST 207 typical urban (TU) wideband fading channel. It was found that at a given throughput the set of TBCH coded fixed modulation schemes considered outperforms the corresponding TC counterparts, when using a high-latency turbo and channel interleaver. However, both schemes have a similar performance, when applied in conjunction with adaptive modulation.