Full diversity achieving MMSE frequency-domain equalizer for single-carrier block transmission with DSSS

Single carrier block transmission with frequency domain equalization (SC-FDE) is an effective technique to combat the impact of frequency selective channels. For single antenna systems, direct-sequence spread-spectrum (DSSS) in the time domain leads to repetition and interleaving in the frequency domain, which means frequency diversity. However, neither carrying out frequency domain equalization first nor despreading first can combine each diversity branch and fully exploit the frequency diversity. In this article, a linear minimum mean square error (LMMSE) receiver structure is proposed, by which each diversity branch can be combined with maximum ratio. The diversity gain and bit error rate (BER) performance are analyzed in a theoretical way. Both theoretical analysis and simulation results show that for single carrier block transmission systems with DSSS and the proposed LMMSE frequency domain equalization structure, full diversity gain can be obtained and the BER performance is obviously improved.