Low complexity and high diversity gain non-linear constellation precoded MIMO-OFDM system with subcarrier grouping

Abstract

The maximum distance separable codes based non-linear signal space diversity technique provides flexibility in the design of diversity channels and diversity orders. Still, in actual practice, these diversity orders can only be truly augmented by increasing the constellation size. In this paper, we enhance the diversity order/gain by introducing multiple-input multiple-output (MIMO) to the existing non-linear constellation precoded orthogonal frequency division multiplexing (NCP-OFDM) system with subcarrier grouping. Though, it still suffers from the complexity of maximum likelihood (ML) decoding, which exponentially increases with the number of antennas. Assuming the channel is quasi-static in nature, we exploit it to reduce the complexity by introducing space-time block-codes (STBC). The ML decoding complexity of a 2×2 system is of O(224) whereas, by using STBC it reduces to O(213). In addition, we propose an algorithm for decoding, called the maximum scaling coefficient selection (MSCS) to further reduce the complexity to O(28). Simulation results show that there was only a marginal performance loss when using the MSCS algorithm based on ML decoding. Furthermore, the simulation results demonstrate how the diversity gain is maximized by adding additional antennas and by introducing STBC.