Low-Complexity Diversity Enhanced OFDM for Wireless Communications

We propose a low complexity frequency diversity technique for OFDM to improve its error performance in a frequency-selective wireless channel. Recently, linear precoding has been proposed to achieve frequency diversity (multipath diversity) in OFDM, which overcomes the problem of channel nulls (deep fades in frequency-domain). However, currently reported precoding techniques for OFDM have high computational complexity due to associated maximum-likelihood (ML) decoding or pseudo-inverse of large matrices (linear decoding). In the proposed diversity enhanced-OFDM (DE-OFDM), the decoding complexity is minimal as maximum ratio combining (MRC) is incorporated at the receiver to generate a decision variable for each repeatedly transmitted symbol over multiple subcarriers. Moreover, we show that DE-OFDM does not cause any effective data rate (throughput) loss as DE-OFDM using a higher-order modulation scheme (thus the same data rate as conventional OFDM) can provide a better error performance. Both analytical and simulation results are provided to demonstrate the efficiency of DE-OFDM in achieving frequency diversity benefit with low receiver complexity in multipath (frequency-selective) channels. DE-OFDM also outperforms the previously proposed ICI self-cancellation schemes in a frequency-selective fading channel with small frequency offset error.