5.1 Introduction
| It is anticipated that transmit and receive antenna arrays together with adaptive space-time processing techniques will be used in future high-capacity cellular communication systems, to combat interference, time dispersion and multipath fading. There has been a significant amount of recent interest in developing adaptive array techniques for wireless communications (e.g., [48, 154, 356, 570, 571]). These studies have shown that substantial performance gains and capacity increases can be achieved by employing antenna arrays and space-time signal processing to suppress multiple-access interference, co-channel interference, and intersymbol interference, and at the same time to provide spatial diversity to combat multipath fading. In this chapter we discuss a number of signal processing techniques for space-time processing in wireless communication systems. We first discuss adaptive antenna array processing technques for TDMA systems. We then discuss space-time multiuser detection for CDMA systems. Due to multipath propagation effects and the movement of mobile units, the array steering vector in a multiple-antenna system changes with time, and it is of interest to estimate and track it during communication sessions. One attractive approach to steering vector estimation is to exploit a known portion of the data stream (e.g., the synchronization data stream). For instance, the TDMA mobile radio systems IS-54/136 use 14 known synchronization symbols in each time slot of 162 symbols. These known symbols are very useful for estimating the steering vector and computing the optimal array combining weights. We discuss a number of approaches to adaptive array processing in such systems. Many advanced signal processing techniques have been proposed for combating interference and multipath channel distortion in CDMA systems, and these techniques fall largely into two categories: multiuser detection (cf. Chapters 1 “4) and space-time processing [370]. Recall that multiuser detection techniques exploit the underlying structure induced by the spreading waveforms of the DS-CDMA user signals for interference suppression. In antenna array processing, on the other hand, the signal structure induced by multiple receiving antennas (i.e., the spatial signatures) is exploited for interference suppression [34, 231, 273, 348, 467, 505, 574]. Combined multiuser detection and array processing has also been addressed in a number of works [90, 121, 142, 202, 347, 504, 505]. In this chapter we provide a comprehensive treatment of space-time multiuser detection in multipath CDMA channels with both transmitter and receiver antenna arrays. We derive several space-time multiuser detection structures, including the maximum likelihood multiuser sequence detector, linear space-time multiuser detectors, and adaptive space-time multiuser detectors. The rest of this chapter is organized as follows . In Section 5.2 we discuss adaptive antenna array techniques for interference suppression in TDMA systems. In Section 5.3 we treat the problem of optimal space-time processing in CDMA systems employing multiple receive antennas. In Section 5.4 we discuss linear space-time receiver techniques for CDMA systems with multiple receive antennas. In Section 5.5 we discuss space-time processing methods in synchronous CDMA systems that employ multiple transmit and receive antennas, and their adaptive implementations . Finally, in Section 5.6 we present adaptive space-time receiver structures in multipath CDMA channels with multiple transmit and receive antennas. The following is a list of the algorithms appearing in this chapter.
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EAN: 2147483647
Pages: 91