Detection of block-spread OFDM in fast fading

The block-spreading technique allows OFDM-based communications systems to exploit frequency diversity. Previous detection algorithms for block-spread OFDM (BSOFDM) are not robust to fast fading, when the communications channel state changes significantly during an OFDM symbol period. It is demonstrated through the use of a new matched filter bound that the performance degradation under fast fading of these algorithms is caused by limitations of the decoding algorithms, and is not an inherent limitation of BSOFDM. An iterative algorithm is introduced with intrinsic data-level parallelism for detecting BSOFDM in the presence of fast fading. Detection is first performed independently on sub-blocks of the received symbol vector. Information is exchanged between these parallel detectors in an iterative manner by estimating the interference between the blocks and removing it from the signal vector. It is shown that the computational complexity of this algorithm is not significantly higher than the detection algorithms for BSOFDM over stationary channels, and achieves excellent BER for fast fading with fixed-point arithmetic, making it suitable for use on embedded systems.