Space-time chip equalizer receivers for WCDMA downlink with code-multiplexed pilot and soft handover

In the downlink of WCDMA systems, multipath propagation destroys the orthogonality of the user signals and causes multi-user interference (MUI). Chip-level 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 downlink of WCDMA systems employing long spreading codes and a code-multiplexed pilot. The proposed receivers exploit the presence of common pilot symbols in the so-called Common Pilot Channel (CPICH) of the Universal Terrestrial Radio Access (UTRA) for 3G systems. Moreover, they can simultaneously track multiple base-station signals, whenever the mobile station enters soft handover mode. For both receivers, we derive a Least Squares algorithm for block processing and a Recursive Least Squares algorithm for adaptive processing. The proposed receivers are compared in terms of performance with the conventional space-time RAKE receiver and the ideal fully-trained space-time chip equalizer receiver