A New Approach for OSTBC and QOSTBC

Abstract

ABSTRACT A new approach for Quasi-Orthogonal space time block coding (QO-STBC) is proposed, with simple linear decoding via maximum likelihood detection. The conventional QO-STBC can achieve the full communication rate, but at the expense of the decoding complexity and the diversity gain due to the interference terms in the detection matrix. In this paper we propose a QO-STBC scheme that will eliminate the interference from the detection matrix. The proposed code improves the diversity gain compared with the conventional QO-STBC scheme; it also reduces the decoding complexity. A full rate full diversity order DiagonalizedHadamard Space Time code (DHSTBC) is presented Keywords Quasi-Orthogonal space time block coding (QO-STBC), full rate, full diversity order,DiagonalizedHadamard Space Time code (DHSTBC). 1. INTRODUCTION In traditional communication systems there is only one antenna at both the transmitter and the receiver. This antenna system is known as Single Input Single Output (SISO). SISO systems have a major drawback in terms of the capacity, as stated by the well-known Shannon-Nyquist criterion. In order to increase the capacity of SISO systems to meet the high bit rate transmission demanded by modern communications, the bandwidth and the power have to increase significantly. Fortunately, using the Multiple-Input Multiple-Output (MIMO) system could increase the capacity of the wireless system without the need to increase the transmission power or the bandwidth. Transmit diversity is a well-known technique to mitigate fading effects over a communication link. Alamouti [1] proposed a transmit diversity scheme that offers maximum diversity gain using two antennas at the transmitter. The pioneering work of Alamouti has been the basis to create Orthogonal space time block coding systems (OSTBCs) for more than two transmit antennas. First of all, Tarokh studied the error performance associated with unitary signal matrices [2]. Sometime later, Ganesan streamlined the derivations of many of the results associated with OSTBC and established an important link to the theory of the orthogonal and ‘amicable orthogonal’ designs [3]. It has been proved that a complex orthogonal design of STBCs that provides full diversity and full transmission rate is not possible for more than two transmit antennas [1]. To achieve full-rate transmission while maintaining much of the orthogonality benefits of OSTBC, Quasi Orthogonal Space Time BlockCode(QO-STBC) has been proposed [4-6]. A QO-STBC can achieve full rate but interference terms will appear from the neighboring signals during the signal detection which will increase the detection complexity and decrease the gain performance.