EURASIP Journal on Applied Signal Processing 
Volume 2004 (2004), Issue 5, Pages 740-750
doi:10.1155/S1110865704309297

Space-Time Chip Equalization for Maximum Diversity Space-Time Block Coded DS-CDMA Downlink Transmission

Geert Leus,1 Frederik Petré,2 and Marc Moonen3

 1Faculty of Electrical Engineering, Mathematics, and Computer Science, Delft University of Technology, Mekelweg 4, Delft 2628CD, The Netherlands
2Wireless Research, Interuniversity Micro-Electronics Center (IMEC), Kapeldreef 75, Leuven 3001, Belgium
3Department of Electrical Engineering (ESAT), Katholieke Universiteit Leuven (K.U.Leuven), Kasteelpark Arenberg 10, Leuven 3001, Belgium
Received 24 December 2002; Revised 4 August 2003

Abstract

In the downlink of DS-CDMA, frequency-selectivity destroys the orthogonality of the user signals and introduces multiuser interference (MUI). Space-time chip equalization is an efficient tool to restore the orthogonality of the user signals and suppress the MUI. Furthermore, multiple-input multiple-output (MIMO) communication techniques can result in a significant increase in capacity. This paper focuses on space-time block coding (STBC) techniques, and aims at combining STBC techniques with the original single-antenna DS-CDMA downlink scheme. This results into the so-called space-time block coded DS-CDMA downlink schemes, many of which have been presented in the past. We focus on a new scheme that enables both the maximum multiantenna diversity and the maximum multipath diversity. Although this maximum diversity can only be collected by maximum likelihood (ML) detection, we pursue suboptimal detection by means of space-time chip equalization, which lowers the computational complexity significantly. To design the space-time chip equalizers, we also propose efficient pilot-based methods. Simulation results show improved performance over the space-time RAKE receiver for the space-time block coded DS-CDMA downlink schemes that have been proposed for the UMTS and IS-2000 W-CDMA standards.