Optimum Subcarrier Grouping and Rotation Matrix for Coded OFDM with Modulation Diversity

Abstract

The application of bit-interleaved coded modulation and iterative decoding (BICM-ID) in OFDM systems with modulation diversity over frequency selective Rayleigh fading channels is considered. A tight bound on the asymptotic error performance is first derived for general precoding over all N subcarriers and used to establish the best achievable performance with modulation diversity. It is then shown that precoding over subgroups of at least L subcarriers per group, where L is the number of channel taps, is sufficient to achieve this best performance while keeping the receiver complexity at minimum. The jointly optimum subcarrier grouping and rotation matrix are derived by solving the Vandermonde linear system.