This paper discusses WCDMA mobile terminal receivers that employ dual-antenna LMMSE equalization in high speed downlink packet access (HSDPA) multicode transmission. The effects of fast fading and non-idealities, like branch power difference and correlation between the antennas, are taken into account by using measured impulse responses in the link simulations. The channel data correspond to difficult "bad urban" cellular environments. The simulation model includes the link adaptation features of future HSDPA terminals. The simulation results show that space-time equalization in a terminal handset provides significant performance gains over conventional RAKE. Dual antennas clearly outperform a single antenna both in chip-level equalization and conventional RAKE reception. It was noted that the equalizer length easily becomes a problem in the large delay spread channel. We also show how the measured channel data can be utilized in the link performance analysis.

A new maximum a posteriori (MAP) equalizer is proposed for digital radio links affected by large multipath delays. The "sparse" nature of the channel, where a few nonzero powerful taps are spaced by many negligible taps, is exploited to achieve a complexity proportional to the number of nonzero taps. When the channel is time-varying, an efficient nonlinear Kalman like channel estimator is employed to track only the nonzero taps.