Differential Space-Time Coding Scheme Using Star Quadrature Amplitude Modulation Method
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Differential Space-Time Coding Scheme Using Star Quadrature Amplitude Modulation Method Xiangbin Yu,1 DaZhuan Xu,1, 2 and Guangguo Bi2 1 Information
and Communication Engineering Postdoctoral Research Station, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China 2 National Mobile Communications Research Laboratory, Southeast University, Nanjing 210096, China Received 5 July 2005; Revised 11 January 2006; Accepted 13 January 2006 Recommended for Publication by Richard Barton Differential space-time coding (DSTC) has received much interest as it obviates the requirement of the channel state information at the receiver while maintaining the desired properties of space-time coding techniques. In this paper, by introducing star quadrature amplitude modulation (star QAM) method, two kinds of multiple amplitudes DSTC schemes are proposed. One is based on differential unitary space-time coding (DUSTC) scheme, and the other is based on differential orthogonal space-time coding (DOSTC) scheme. Corresponding bit-error-rate (BER) performance and coding-gain analysis are given, respectively. The proposed schemes can avoid the performance loss of conventional DSTC schemes based on phase-shift keying (PSK) modulation in high spectrum efficiency via multiple amplitudes modulation. Compared with conventional PSK-based DSTC schemes, the developed schemes have higher spectrum efficiency via carrying information not only on phases but also on amplitudes, and have higher coding gain. Moreover, the first scheme can implement low-complexity differential modulation and different code rates and be applied to any number of transmit antennas; while the second scheme has simple decoder and high code rate in the case of 3 and 4 antennas. The simulation results show that our schemes have lower BER when compared with conventional DUSTC and DOSTC schemes. Copyright © 2006 Hindawi Publishing Corporation. All rights reserved.
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INTRODUCTION
With the fast development of modern communication technique, the demand for reliable high data rate transmission in fading channel is increased significantly, which stimulate much interest in multiple antennas communication, especially, space-time coding schemes [1–3]. However, the effectiveness of most space-time coding schemes depends on perfect channel estimation at the receiver, which is difficult to implement in practice due to rapid changes in time-varying channel, or due to the overhead needed to estimate a large number of parameters such as in a MIMO system [4]. Thus, the differential modulation scheme becomes an attractive alternative. With differential detection, channel state information (CSI) is not required either at the transmitter or at the receiver. Hochwald and Marzetta [5] proposed an effective modulation scheme to improve system capacity (i.e., unitary space-time modulation) with noncoherent detection for multiple antennas in fading channel, and then unitary spacetime coding. Subsequently, Hochwald and Sweldens [6] and
Hughes [7] independently came up with differential unitary space-t
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