Performance of high-speed downlink packet access with double space-time transmit diversity

Abstract

In this work, we investigate the performance of High-Speed Downlink Packet Access (HSDPA) for WCDMA when used in combination with Double Space-Time Transmit Diversity (DSTTD) over temporally and spatially correlated Multi-Input Multi-Output (MIMO) channels with narrow Laplacian angle spread. We first investigate various fading channel models, their statistical properties and generation methods before introducing the ray-based spatial channel model (SCM) as formalized by the 3GPP/3GPP2 SCM Ad-Hoc Group (AHG). We investigate two generation methods to emulate power azimuth spectra with a Laplacian distribution and show that the equal sub-ray power method suggested by the SCM-AHG is less effective in accurately reproducing the theoretical spatial correlation properties of a channel with Laplacian angle spread than the more straight-forward sampled Laplacian approach. In order to assess the performance of the combined HSDPA-DSTTD system over the SCM channel we first determine the effect of temporal and spatial correlations on each of their constituent parts. DSTTD is shown to effectively combine receive diversity, transinit diversity and spatial multiplexing and we analyze the behavior of each of these subsystems individually. Receive diversity can be obtained with a maximum ratio combiner(MRC) and we show flow MRC can still extract significant diversity gain in channels with high levels of spatial correlation. Transmit diversity can by provided by means of space-time block codes (STBCs) and we show the very detrimental effect of large Doppler spreads on the performance of STBCs. Very high spectral throughputs can be realized by the Vertical Bell Layered Space-Time (V-BLAST) spatial multiplexing scheme for which we investigate and compare various detection schemes such as zero-forcing (ZF) and minimum mean squared error (MMSE) equalization techniques with optimum successive interference cancellation (OSIC). We investigate efficient algorithms to reduce the decod...