Downlink frequency-domain chip equalization for single-carrier block transmission DS-CDMA with known symbol padding

Single-carrier block transmission (SCBT) DS-CDMA, also known as chip-interleaved block-spread (CIBS) CDMA, is an interesting transmission technique for future broadband cellular systems because it inherits the benign properties of both SCBT and CDMA. By zero padding (ZP) each chip block, the orthogonality of the spreading codes is retained regardless of the underlying multipath channel which allows for deterministic maximum likelihood (ML) user separation employing low-complexity code-matched filtering. In this paper, we focus on downlink single-carrier block transmissions with known symbol padding (KSP) (as opposed to ZP) which pad each chip block with a postfix of known symbols that can be used for training purposes at the receiver. Specifically, we propose three methods for direct equalizer estimation that all exploit the presence of the known symbol postfix but differ in the amount of additional a-priori information they assume to determine the equalizer coefficients. Simulation results demonstrate the outstanding performance of the semi-blind joint CDMP/KSP-trained method, that additionally assumes knowledge of a code division multiplexed pilot (CDMP) and the multiuser code correlation matrix.