Space-Time-Frequency Code Technology In MIMO-OFDM System

There are two the toughest challenges in wide band wireless communication system: multipath fading channel and bandwidth efficiency. The MIMO technology can develop fully space resource, using multi-antennas to realize Multi-Input and Multi-Output, which can increase transmission rate of system and improve channel capacity several times. The sub-carriers of the OFDM are orthogonal to each other, which can highly improve spectrum efficiency. Moreover, OFDM divides the whole channel into several sub-channels to make frequency selective multipath fading channel as smooth channel in frequency damain, which can effectively resist frequency selective fading. MIMO-OFDM is the combination of MIMO technology and OFDM technology, adopt code technology for transmission of multi-antenna in OFDM system to improve signal quality and data transmission rate.The paper makes a deep research on space-time-frequency code, which is one of the hot topics in research of MIMO-OFDM system.Firstly, this paper presents the principles of MIMO and OFDM technologies respectively, and also points out their advantages and disadvantages to educe the need to combine them together. On the basis of the above, MIMO-OFDM technology is introduced and its features are also analyzed in details. Secondly, some basic methods of space-time code are introduced, for example, layered space-time code (LSTC), space-time trellis code (STTC), space-time block code (STBC), also the research focus in recent years——differential space-time code (DSTC) and unitary space-time code (USTC), are introduced in the paper. Thirdly, differential unitary space-frequency code and differential unitary space-time-frequency code are made a detailed description and performance analysis in the paper. Finally, combining bi-level differential transmit technology, a new based on cyclic delay diversity bi-level differential unitary space-time-frequency code is proposed, which is made a detailed description and performance analysis, also pointed out it's advantages and disadvantages.