Space-time chip equalizer receivers for WCDMA forward link with time-multiplexed pilot

In the forward link of WCDMA systems, multipath propagation destroys the orthogonality of the user signals and causes multi-user interference (MUI). Channel equalization can restore the orthogonality and suppress the MUI. However, adaptive implementations of the chip equalizer receiver that can track time-varying multipath channels are hard to realize in practice. In this paper, we propose new training-based and semi-blind space-time chip equalizer receivers for the forward link of WCDMA systems employing long spreading codes and a time-multiplexed pilot. The proposed receivers exploit the presence of user specific pilot symbols in the so-called dedicated physical control channel (DPCCH) of the Universal Terrestrial Radio Access (UTRA). Whereas the DPCCH-trained receiver only assumes knowledge of the desired user´s pilot symbols and code sequence in a training-based cost function, the enhanced DPCCH-trained receiver assumes knowledge of each active user´s pilot symbols and code sequence in a semi-blind cost function. For both receivers, we derive a least squares algorithm for block processing and a recursive least squares algorithm for adaptive processing. Both receivers can track time-varying multipath channels and outperform the conventional RAKE receiver with perfect channel knowledge. The enhanced DPCCH-trained chip equalizer receiver outperforms the regular DPCCH-trained chip equalizer receiver and comes close to the performance of the ideal fully-trained chip equalizer receiver