Improved performance of coded OFDM-MFSK using combined alphabets and extended mapping

OFDM-MFSK is a robust noncoherent transmission scheme that is able to cope with fast fading channels. The disadvantage of OFDM-MFSK is a lower end-to-end bandwidth efficiency in comparison to other transmission schemes, such as quadrature amplitude modulation. In this paper we describe two methods, combined alphabets and extended mapping using combined alphabets, to improve the bandwidth efficiency and/or the bit error rate performance of coded OFDM-MFSK based systems employing iterative demapping and decoding. We provide the suitable log-likelihood metrics for different channel models, and analyze the performance of the system with the help of extrinsic information transfer charts. Finally simulation results are given.