STBC for uplink single-carrier CDMA with equalization in the frequency domain

Single-carrier code division multiple access (SC-CDMA), also named cyclic-prefix CDMA in the literature, is a promising air interface for the uplink of the 4G cellular wireless communication systems. It enables the high capacity intrinsically offered by CDMA by making the equalization of the multipath channels and the mitigation of the resulting interference possible at a low complexity. This paper proposes a new air interface that combines SC-CDMA with space time block coding (STBC) across multiple transmit antennas in order to robustify the link. Contrary to existing air interfaces that perform the STBC encoding at the chip level, making them only applicable to the downlink, the STBC encoding is performed at the symbol level, making it also applicable to the uplink. In order to optimally detect the antenna and user signals, a joint detector optimized according to the minimum mean square error (MMSE) criterion is designed. By exploiting the cyclo-stationarity of the channels, the complexity of the joint detector is significantly reduced. It is analytically shown that the inter-antenna interference is canceled out at the output of the first stage of the linear MMSE joint detector, consisting of a matched filter. Assuming typical outdoor channels, a gain of 4 dB signal-to-noise-ratio (SNR) is achieved by the use of two transmit antennas over the single antenna system