Research On Space-Time Coding In MIMO Systems

With the integration of Internet and multimedia applications in next generation wireless communications, the demand for wide-band high data rate communication services is growing. As the available radio spectrum is limited, higher data rates can be achieved only by designing more efficient signaling techniques. Recent research in information theory has shown that large gains in capacity of communication over wireless channels are feasible in multiple input multiple output (MIMO) systems. The MIMO channel is constructed with multiple element array antennas at both ends of the wireless link. The data rate and reliability of communication systems can be greatly improved by spatial multiplexing and diversity gain, respectively provided by MIMO which is already adopted by some standards and protocols. In MIMO systems, space-time coding combines channel coding and antenna diversity technologies so as to effectively utilize spatial multiplexing and diversity. In addition, providing high-quality multimedia service is an important task of the future wireless communication systems.Space-time coding is based on introducing joint correlation in transmitted signals in both the space and time domains. Through this approach, simultaneous diversity and coding gains can be obtained, as well as high spectral efficiency. The fundamentals of space-time coding have been established by Tarokh, Seshadri and Calderbank in 1998. Space-time coding and related MIMO signal processing soon evolved into a most vibrant research area in wireless communications.The most popular space-time codes are: space-time block codes (STBC), space-time trellis codes (STTC) and layered space-time codes (LSTC). And STBC is most attractive as its low complexity and high diversity gain. But when there are more than two antennas at the receiver, the transmit rate of STBC are smaller than 1. To overcome the disadvantage of STBC, quasi-orthogonal space-time block code (QO-STBC) is a simple method. First, the MIMO system will be constructed. Then we will analyze the performance and space-time code design criteria. We show the main space-time block codes and compare their performances. Then according to the code properties of QO-STBC, we propose a decoding scheme. We first separate the signals from different antennas, and use the maximum likelihood (ML) decoding scheme to decode it.We show the relation between OSTBC and the packing on the Grassmann manifold, and how to construct OSTBC from a packing on the Grassmann manifold. We propose a packing on Grassmann manifold, from which high rate OSTBC for MIMO system with four transmit antennas can be designed. And the performances of the new codes and the traditional OSTBC will be compared.At last, the main research results are concluded, and the further research prospect is pointed out.