Space-Time Coding Technologies For MIMO

MIMO(Multi-Input Multi-Output) refers to any wireless communication systems adopting multi-transmit antennas and multi-receive antennas. It can greatly enhance communication system performance with a little more system complexity, requiring no more frequency band and higher transmit power. Due to these advantages, MIMO is the focus nowadays and also the trend in future of wireless communication.Space-Time Coding, which is the key technique for MIMO, can provide better BER performance and highly improve the data rating of communication systems. BLAST(Bell LAyered Space Time), which is a branch of STC, is a kind of Space-Time multiplexing technique using multi-path fading to highly improve the data rating and is indeed a method to achieve a high frequency spectrum efficiency. Since advanced in 1993, Turbo coding, well known for its near Shannon performance, has always been the focus of channel coding research. Iterative decoding is also widely adopted, using which to achieve better performance, by other channel codes such as LDPC, TPC etc. Due to the fact that high data rating is based on reliable transmission, BLAST systems cascaded with these high performance channel code is deeply studied. Detecting and decoding separated BLAST system is always poor in BER performance for its loss of soft information. So Iterative Joint Detection and Decoding technique is used more and more to recover the original information. In this paper, we discuss varieties of detection techniques for V-BLAST, such as ML, ZF, MMSE, IIC, SD, soft SD, and so on. SD is a kind of sub-optimal detection algorithm based on Trellice theory, which can highly decrease the detection complexity achieving a near-ML performance. Soft-output SD detection computes the soft information of the received vector by reserving some small-weight trellice points in the given sphere to improve system performance. Finally we focus on the IJDD system of Turbo cascaded with V-BLAST, using soft-SD detection and iterative MAP decoding. In addition, we simulate a TPC, V-BLAST cascaded system as a reference.The other branch of Space-Time coding, STTC and STBC, aims at achieving diversity gain. STTC is the combination of TCM and transmission diversity, achieving full diversity gain and high coding gain but with high code searching and decoding complexity. We simply introduce the basic principles of STTC, STBC coding and decoding. Then STTC, STBC and BLAST cascaded systems are studied.