Efficient detection schemes for STBC over time-varying channels

Abstract

Among the diversity enhancing schemes, space-time block code (STBC) by Alamouti have been investigated by many researchers as a technique combating impairments in wireless fading channels. STBC provides full spatial diversity without channel state information (CSI) at the trans-mitter. This is caused by the fact that STBC is orthogonal block code. For the same reason, in hardware implementation aspects, it has very simple decoding structure. Actually, the encoding complexity for STBC is essentially of the same order as that for single-input and single-output (SISO) system. The decoding complexity is an important issue for practical employment of multiple-input and multiple-output (MIMO) system. Therefore, STBC is widely adopted in industrial standards such as WiMAX and LTE. However, above features are available only under one assumption: quasi-static channel responses over two symbol periods. In practical environments, this assumption is not always true. For example, both WiMAX and LTE should work with high mobility communication system. In this case, time-varying fading channels are formed as a result of Doppler effect. As a results, the previous assumption that the channel is invariant during two symbol interval is not reasonable for some applications. Unfortunately, in this condition, the simple decoding structure does not work well due to inter-transmit-antenna-interference (ITAI). In other words, STBC is no more orthogonal block code. To overcome this ITAI effect, several detection methods were proposed such as linear zero-forcing (ZF), decision-feedback (DF) and maximumlikelihood (ML) detection, which are well-known and generally used as MIMO detection algorithms. Among them, only the ML detection achieves the second order diversity. Nonetheless, it has exponential decoding complexity especially high-order modulation is considered. In addition, the ML complexity can not meet the original advantage of STBC which is to have simple decoding structure. In...