A Receiver for Differential Space-Time -Shifted BPSK Modulation Based on Scalar-MSDD and the EM Algorithm
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A Receiver for Differential Space-Time π/2-Shifted BPSK Modulation Based on Scalar-MSDD and the EM Algorithm Michael L. B. Riediger School of Engineering Science, Simon Fraser University, Burnaby, BC, Canada V5A 1S6 Email: [email protected]
Paul K. M. Ho School of Engineering Science, Simon Fraser University, Burnaby, BC, Canada V5A 1S6 Email: [email protected]
Jae H. Kim School of Mechatronics Engineering, Changwon National University, Changwon, Kyungnam 641-773, Korea Email: [email protected] Received 21 April 2004; Revised 10 September 2004 In this paper, we consider the issue of blind detection of Alamouti-type differential space-time (ST) modulation in static Rayleigh fading channels. We focus our attention on a π/2-shifted BPSK constellation, introducing a novel transformation to the received signal such that this binary ST modulation, which has a second-order transmit diversity, is equivalent to QPSK modulation with second-order receive diversity. This equivalent representation allows us to apply a low-complexity detection technique specifically designed for receive diversity, namely, scalar multiple-symbol differential detection (MSDD). To further increase receiver performance, we apply an iterative expectation-maximization (EM) algorithm which performs joint channel estimation and sequence detection. This algorithm uses minimum mean square estimation to obtain channel estimates and the maximum-likelihood principle to detect the transmitted sequence, followed by differential decoding. With receiver complexity proportional to the observation window length, our receiver can achieve the performance of a coherent maximal ratio combining receiver (with differential decoding) in as few as a single EM receiver iteration, provided that the window size of the initial MSDD is sufficiently long. To further demonstrate that the MSDD is a vital part of this receiver setup, we show that an initial ST conventional differential detector would lead to a strange convergence behavior in the EM algorithm. Keywords and phrases: multiple-symbol differential detection, Alamouti modulation, differential space-time codes, EM algorithm.
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INTRODUCTION
Differential detection of a differentially encoded phase-shift keying (DPSK) signal is a technique commonly used to recover the transmitted data in a communication system, when channel information (on both the amplitude and phase) is absent at the receiver. The performance of DPSK in traditional wireless communication systems employing one transmit antenna and one or more receive antennas is well documented in the literature. In recent years, this encodingThis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
detection concept has been extended to cover the scenario where there is more than one transmit antenna. This leads to differential space-time block codes (STBCs), an extension of the STBCs originally proposed in [1]. Like convent
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