To lower the demodulation complexity of traditional bit-interleaved coded modulation(BICM) with iterative decoding(ID) system combined with rotation matrix-based signal space diversity (BICM-ID-SSD), the MultiQAM modulation, which could achieve full SSD diversity, was applied to a BICM-ID system with channel coding and a new architecture called BIC-MultiQAM-ID was proposed. MAP demodulation algorithm, together with a MAP soft-input and soft-output decoder, was used to perform the iterative demodulation and decoding of the system. Simulation results showed that a better performance is achieved compared with the original system which used MultiQAM modulation,ML demodulation and soft-decision Viterbi decoding. When the modulation order and diversity dimension are (4,2) and (2,4), the BER performance is improved about 1.8 dB.
