Time domain spreading and frequency domain maximal ratio combining reception for frequency diversity enhancement in single carrier UWB communication systems

Ultra-wideband technology is a promising candidate for short-range broadband communication systems. Ultra-wideband channels are characterized by dense multiple paths that provide multipath diversity, also referred to as frequency diversity. Single carrier systems with frequency domain equalization have attracted much interest for high data rate communications. In this paper, frequency diversity in single carrier ultra-wideband systems is enhanced by employing simple frequency domain maximal ratio combining (FDMRC) reception with time domain complex quadratic spreading (CQS) sequences. Since ultra-wideband channels exhibit dense multiple paths and strong frequency selectivity, the proposed system can attain significant performance improvement over traditional single carrier frequency domain equalization (SC-FDE) systems. Through the comparison of the impact of the cyclic prefix length, the proposed system shows stronger robustness to inter-block interference than the conventional SC-FDE system. Compared with multicarrier systems, like orthogonal frequency-division multiplexing and multi-carrier code division multiple access, the proposed receiver complexity is reduced greatly. To accommodate multiuser communication, block spreading is further introduced to combine with the frequency diversity enhancement technique for single carrier block transmission UWB systems, realizing multiuser interference-free reception.