Differential Space-Time Block Code Modulation for DS-CDMA Systems
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Differential Space-Time Block Code Modulation for DS-CDMA Systems Jianhua Liu Department of Electrical and Computer Engineering, P.O. Box 116130, University of Florida, Gainesville, FL 32611, USA Email: [email protected]
Jian Li Department of Electrical and Computer Engineering, P.O. Box 116130, University of Florida, Gainesville, FL 32611, USA Email: [email protected]
Erik G. Larsson Department of Electrical and Computer Engineering, P.O. Box 116130, University of Florida, Gainesville, FL 32611, USA Email: [email protected] Received 29 May 2001 and in revised form 27 December 2001 A differential space-time block code (DSTBC) modulation scheme is used to improve the performance of DS-CDMA systems in fast time-dispersive fading channels. The resulting scheme is referred to as the differential space-time block code modulation for DS-CDMA (DSTBC-CDMA) systems. The new modulation and demodulation schemes are especially studied for the down-link transmission of DS-CDMA systems. We present three demodulation schemes, referred to as the differential space-time block code Rake (D-Rake) receiver, differential space-time block code deterministic (D-Det) receiver, and differential space-time block code deterministic de-prefix (D-Det-DP) receiver, respectively. The D-Det receiver exploits the known information of the spreading sequences and their delayed paths deterministically besides the Rake type combination; consequently, it can outperform the D-Rake receiver, which employs the Rake type combination only. The D-Det-DP receiver avoids the effect of intersymbol interference and hence can offer better performance than the D-Det receiver. Keywords and phrases: wireless communications, space-time coding, smart antennas, spread spectrum, DS-CDMA, Rake receiver.
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INTRODUCTION
The performance of wireless communications systems can be increased drastically by exploiting the spatial diversities offered by multiple transmit and receive antennas in fading channels [1]. Traditionally, research work in spatial diversity mainly focused on the receiving diversity. In fact, receive antenna diversity is being used in base stations to improve the reception in current cellular systems, whereas transmit diversity is just beginning to attract attention [1]. Recently, Alamouti [2] proposed a simple and useful transmit diversity scheme to improve the overall performance of wireless communication systems in flat fading channels. This scheme is one of many interesting techniques emerging in the field of space-time coding, a new coding and signal processing technique that is designed for use with multiple transmit antennas (cf. [1] and the references therein). It introduces temporal and spatial correlation into signals transmitted from different antennas to provide transmit
diversity and coding gain over an uncoded system. However, Alamouti’s method as well as many other transmit diversity schemes, such as those in [3, 4], are based on the assumption that perfect channel state information (CSI) is available at the receiver. Although training is a feasib
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