New Strategies for Coded Modulation Diversity over Rayleigh Fading Channels

We consider the joint exploitation of coding and diversity techniques to achieve efficient, reliable wireless transmission. The system of interest comprises a powerful non-binary low-density parity-check (LDPC) code that will be soft-decoded to supply strong error protection, a quadratic amplitude modulator (QAM) that directly takes in the non-binary LDPC symbols and will be soft-demodulated, and a modulation diversity (or signal space diversity, SSD) operator that will provide power- and bandwidth-efficient diversity gain. By relaxing the rate of the SSD rotation matrices to below 1, we show that a better rate allocation can be arranged between the LDPC codes and the SSD, which brings significant performance gain over previous systems. To facilitate the design and evaluation of the relaxed SSD rotation matrices, three types of efficient constructions are demonstrated and a set of four criteria are developed. Through analysis and simulations, we show that our strategies are very effective in combating random fading and strong noise on Rayleigh fading channels.