Systematic Design of Space-Time Trellis Codes for Diversity and Coding Advantages
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Systematic Design of Space-Time Trellis Codes for Diversity and Coding Advantages Zoltan Safar Department of Electrical and Computer Engineering, University of Maryland, College Park, MD 20742, USA Email: [email protected]
K. J. Ray Liu Department of Electrical and Computer Engineering, University of Maryland, College Park, MD 20742, USA Email: [email protected] Received 15 June 2001 and in revised form 17 January 2002 The emerging need for high data rate wireless services has raised considerable interest in space-time coding. In this work, we propose a systematic code construction method that jointly considers diversity advantage and coding advantage for an arbitrary number of transmit antennas and any memoryless constellation. Our approach is to directly assign channel symbols to transmit antennas at different states by exploiting the properties of the state transitions in the trellis. The code construction problem is reduced to a combinatorial optimization problem and a computationally efficient suboptimal solution is proposed. The flexibility of the method is demonstrated by designing space-time trellis codes for QPSK, 8PSK, 16PSK, asymmetric QPSK and 4ASK constellations. Space-time code construction for a large number of transmit antennas (6, 8, and 10) is also considered. The simulations show that our design procedure results in codes that outperform the ones constructed by previously existing methods. The achievable performance gain is governed by the distance structure of the chosen constellation. Keywords and phrases: space-time codes, trellis codes, transmit diversity, wireless communications.
1.
INTRODUCTION
In wireless communications, the transmitted signal undergoes severe distortion due to multipath fading and interference from other users. The design of communication systems that offer reliable transmission at high data rates is a challenging task in such circumstances. To combat the adverse effects of the radio signal propagation environment, several diversity techniques have been developed [1]. These techniques offer increased protection against the channel-induced distortion by providing multiple versions of the transmitted signal to the receiver. Time diversity, for example, represents redundancy in the time domain. A form of time diversity, channel coding combined with interleaving, adds redundancy with a certain algebraic structure that can be exploited to detect and correct transmission errors [2]. Another widely used diversity technique is spatial diversity, which adds redundancy in the spatial domain. By building a system with multiple transmit and/or receive antennas and making use of the larger number of signal propagation paths between the transmitter and the receiver, the quality of the wireless link can also be improved [1].
Information-theoretic works [3, 4, 5, 6, 7] have shown that the capacity of fading channels is substantially increased when using multiple transmit and/or receive antennas. The results of [6] for the quasi-static, flat Rayleigh fading channel model can be summarized
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