Space-time-frequency Coding In MIMO-OFDM Systems

With the rapid development of wireless communication technology, the commercialization of3G services has been popular around the world. To meet people’s growing demand for datacommunications and multimedia services,4G services are gradually developing. As a coretechnology for4G mobile communication system, MIMO technology has the ability to improve thecapacity of the communication system. And OFDM technology can transform non-stationarychannel into stable flat fading channel. Therefore, the combination of MIMO technology andOFDM technology, can not only have a high spectral efficiency, but also in terms of anti-multipathshow a huge advantage. MIMO-OFDM technology takes advantage of time, frequency and spatialdiversity that enables wireless systems has a great increase in the tolerance to noise. TheSpace-Time-Frequency coding technology is one of coding technology which has a jointconsideration of the spatial domain, time domain and frequency domain that enables multi-antennasystem could obtain maximum diversity gain in frequency selective fading channel. In this paper,we discusse the MIMO-OFDM systems coding technology in detail, and focuse on thespace-time-frequency coding techniques. The main work is as follows:(1) This paper does a research in background and significance of MIMO-OFDM systems andspace-time-frequency coding. The basic model of MIMO-OFDM systems and related technologiesare briefly analyzed.(2) A detailed study of the space-time coding, space-frequency coding is analysised on the basis ofMIMO fading channel, Focuses on the coding structure and design criteria of orthogonal space-timecodes and quasi-orthogonal space-time codes, and through the introduction of cyclic delay diversityincreases the frequency diversity gain of space-frequency coding.(3) Based on space-time-frequency block coding design methods, we make use of the technologyof subcarrier clustering and unitary constellation precoding to study a layered blockspace-time-frequency block coding scheme. Out of a reasonable compromise in diversity gain andmultiplexing gain, we focus on the structure and properties of linear dispersion coding, and for thelinear dispersion code can not get a good frequency diversity gain, we propose a linear dispersespace-time-frequency coding based on orthogonal precoding, this encoding method can obtain goodfrequency diversity gain and at the same time get a full space-time diversity gain.(4)We introduce several commonly used multi-user co-channel interference cancellation algorithms,including zero forcing algorithm, the minimum mean square error (MMSE) algorithm,and atwo-step interference cancellation algorithm based on two transmit antennas. At the same time, based on beamforming technology, we propose a simple multi-user interference cancellationspace-time-frequency coding method, which construct a set of orthogonal matrix to make datasymbols spread in space, time and frequency domain. Only simple linear processing in Receive endcan effectively eliminate multi-user interference.(5) Made a comprehensive summary of the full text, and point out some directions for futureresearch.