Linear Equalization Combined with Multiple Symbol Decision Feedback Detection for Differential Space-Time Modulation
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Linear Equalization Combined with Multiple Symbol Decision Feedback Detection for Differential Space-Time Modulation Genyuan Wang Department of Electrical and Computer Engineering, University of Delaware, Newark, DE 19716, USA Email: [email protected]
Aijun Song Department of Electrical and Computer Engineering, University of Delaware, Newark, DE 19716, USA Email: [email protected]
Xiang-Gen Xia Department of Electrical and Computer Engineering, University of Delaware, Newark, DE 19716, USA Email: [email protected] Received 30 May 2001 and in revised form 19 February 2002 Differential space-time modulation (DSTM) for multiple antenna communication systems has been recently proposed for frequency-nonselective fading channels. In broadband multirate systems, frequency-selective fading may occur. In this paper, the DSTM in frequency-selective fading channels is considered. A linear equalizer for the DSTM is proposed over frequency-selective fading channels. Furthermore, the multiple symbol decision feedback detection is used to improve the performance of the linear equalizer. Keywords and phrases: differential space-time modulation, transmit diversity, decision feedback detection, MIMO, linear equalization, RLS.
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INTRODUCTION
Differential space-time modulation (DSTM) has been recently proposed by Hochwald and Sweldens [1], Hughes [2], and Tarokh and Jafarkhani [3] for multiple antenna communication systems, where the channel information is not known to the transmitters or receivers. Several unitary spacetime codes for the DSTM have been proposed in [1, 2] of group codes, in [2, 4] of quaternion codes, and in [5] of fixedpoint free group codes, and in [6] of parametric codes. The 2 × 2 parametric codes obtained in [6] for two transmit antennas have the largest possible diversity product of size five and the largest known diversity product of size sixteen, which will be used in the simulations in this paper later. Space-time coded multiple antenna systems can be casted as multiple input and multiple output (MIMO) systems. The recent studies of DSTM in [1, 2, 3] are on frequencynonselective fading channels where MIMO channel matrices do not have memory. However, in broadband multirate systems, frequency-selective fading and frequency-nonselective fading may co-exist. In this paper, we are interested in the
DSTM system when frequency-selective fading occurs. An equalizer combined with the differential detection is proposed by exploiting the structure of the DSTM and its differential detection. The equalizer is to minimize the detection errors. In such an equalizer, not only the channels are of matrix form but also the input signals and the output signals are of matrix form too. Similar to the existing MIMO equalization techniques in the literature, see for example [7, 8], the least squares (LS) solution and an adaptive RLS algorithm are derived. As a remark, equalizations of space-time trellis coded multi-antenna systems over frequency-selective fading channels have been considered in [9, 10]. The DSTM can be treated as a
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