A Receiver for Differential Space-Time <inline-formula><graphic file="1687-1499-2005-135356-i1.gif"/></inline-formula>-Shifted BPSK Modulation Based on Scalar-MSDD and the EM Algorithm

• Main Authors: Kim Jae H, Riediger Michael LB, Ho Paul KM
• Format: Article
• Language: English
• Published: SpringerOpen 2005-01-01
• Series: EURASIP Journal on Wireless Communications and Networking
• Subjects: multiple-symbol differential detection; Alamouti modulation; differential space-time codes; EM algorithm
• Online Access: http://jwcn.eurasipjournals.com/content/2005/135356

<p/> <p>In this paper, we consider the issue of blind detection of Alamouti-type differential <it>space-time</it> (ST) modulation in static Rayleigh fading channels. We focus our attention on a <inline-formula><graphic file="1687-1499-2005-135356-i2.gif"/></inline-formula>-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 <it>multiple-symbol differential detection</it> (MSDD). To further increase receiver performance, we apply an iterative <it>expectation-maximization</it> (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 strange convergence behavior in the EM algorithm.</p>