Parallel Interference Cancellation Detection with Inner and Outer Iterations for Space-frequency Block Coded OFDM Systems

In order to simplify the decoding algorithm, it is usually assumed in previously reported work on space-frequency block coded orthogonal frequency division multiplexing (SFBC-OFDM) systems utilizing space-time block codes (STBC) that the frequency responses of adjacent subchannels are approximately constant for a STBC block length (K.F. Lee and D.B. Williams, 2000). Under this assumption, the conventional linear decoder proposed for STBC in V. Tarokh et al. (1999) can be equivalently used in SFBC-OFDM systems to achieve the maximum diversity gain with the lowest computational complexity. However, this assumption is not accurate when the number of OFDM sub-carriers is small or the system operates in a severe multipath environment. The conventional decoder will give rise to interference due to the channel frequency response variations in adjacent subchannels. This result in an irreducible error floor in the high signal-to-noise ratio (SNR) region of the bit error rate (BER) curve and decreased diversity gain. In this paper, we propose a parallel interference cancellation (PIC) detection scheme with inner and outer iterations for G₄ (V. Tarokh et al., 1999) coded SFBC-OFDM transmit diversity systems over frequency selective fading channels. Simulation results will show that the proposed scheme can mitigate the interference effect and make the error floor occur at a very low BER, which can be neglected