Optimum pre-DFT combining with cyclic delay diversity for OFDM based WLAN systems

Cyclic delay diversity is applied in an OFDM receiver to increase the frequency-selectivity of the channel seen at the receiver for flat (or less frequency-selective) channels. Diversity combining is performed prior to the discrete Fourier transform (DFT) operation. A new method has been studied to optimize the pre-DFT diversity combining by selecting cyclic shifts and weight factors based on known channel state information. The optimum signal-to-noise ratio for maximum cyclic delay and optimum weight factors for multiple antenna receiver diversity is analyzed. Performance results in terms of bit error probability are presented. Finally, it is found that the proposed scheme drastically reduces computational complexity compared to traditional receiver diversity schemes.