Pre-DFT Combining for Coded OFDM

Abstract

Multiple receive antennas have been known to improve bit error performance over fading multipath channels by providing spatial diversity. In systems such as orthogonal frequency-division multiplexing (OFDM), this benefit is obtained at the cost of greatly increased system complexity. Pre-discrete Fourier transform (DFT) combining techniques have been proposed by some researchers to obtain multiple antenna gains at a reduced complexity. However, existing works on pre-DFT combining ignore the specific distance properties of the underlying convolutional code, leading to suboptimal solutions. In this paper, we develop a novel technique for pre-DFT combiner design for bit-interleaved coded modulation (BICM)-coded OFDM on Rayleigh block-fading channels. The combiner is designed for the specific code used and outperforms other known pre-DFT combining techniques. Our simulations show about a 2-3-dB improvement in performance over existing techniques.