Space-Time Chip Equalization for Maximum Diversity Space-Time Block Coded DS-CDMA Downlink Transmission
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Space-Time Chip Equalization for Maximum Diversity Space-Time Block Coded DS-CDMA Downlink Transmission Geert Leus Faculty of Electrical Engineering, Mathematics, and Computer Science, Delft University of Technology, Mekelweg 4, 2628CD Delft, The Netherlands Email: [email protected]
Frederik Petre´ Wireless Research, Interuniversity Micro-Electronics Center (IMEC), Kapeldreef 75, 3001 Leuven, Belgium Email: [email protected]
Marc Moonen Department of Electrical Engineering (ESAT), Katholieke Universiteit Leuven (K.U.Leuven), Kasteelpark Arenberg 10, 3001 Leuven, Belgium Email: [email protected] Received 24 December 2002; Revised 4 August 2003 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. Keywords and phrases: downlink CDMA, space-time block coding, space-time chip equalization.
1.
INTRODUCTION
Direct sequence code division multiple access (DS-CDMA) has emerged as the predominant multiple access technique for 3G cellular systems. In the downlink of DS-CDMA, orthogonal user signals are transmitted from the base station. All these signals are distorted by the same channel when propagating to the desired mobile station. Hence, when this channel is frequency-selective, the orthogonality of the user signals is destroyed and severe multiuser interference (MUI) is introduced. Space-time chip equalization can then restore the orthogonality of the user signals and suppress the MUI [1, 2, 3, 4]. Multiple-input multiple-output (MIMO) systems, on the other hand, have recently been shown to realize a significant
increase in capacity for rich scattering environments [5, 6, 7]. Both space division multiplexing (SDM) [8, 9] and spacetime coding (STC) [10, 11, 12] are popular MIMO communication techniques. SDM techniques mainly aim at an increase in throughput by transmitting different da
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