Research of MIMO-OFDM Model

Abstract

OFDM (Orthogonal Frequency Division Multiplex) technique is one of the promising trends of the new generation wireless telecommunication. It can be combined with MIMO (Multiple Input Multiple Output) technique. The MIMO-OFDM system can improve the performance and the capacity of the wireless telecommunication, suppress co-channel interference and multiple access interference, and achieve the diversity gain as resisting multi-path fading. The advantages and models of these two technologies are discussed according to their definitions. The advantage and model of MIMO-OFDM technology is discussed based on the complementary of these two technologies. The block diagram of MIMO-OFDM system is presented in the end. MIMO Model MIMO (Multiple Input Multiple Output) can be defined simply as following: In any wireless communication system, several antennas are employed in the transmitting and receiving terminal of the link. Its core thinking is the spatial and temporal signal processing. In other words, several antennas are employed to add the spatial dimension to the communication system(1). Its aim is to realize multiple dimensions signal processing while the temporal dimension, which is adopted in the traditional communication system, is also used. The principle of MIMO technique is that the serial data are mapped to the parallel data, and are propagated(2). In the receiving terminal, the parallel data are combined to the serial data, and the received signals are distinguished through the non- correlation of the different antennas signal in the wireless channel. In order to assure the non- correlation of the signals, the spacing of different antennas must be large. So the MIMO system is fitting to be used in the environment of multi-paths of serious scattering(3). Even on the condition of Rayleigh fading of no straight path it can work better(4). The MIMO technique can change the multi-paths effect factor of the traditional communication system to the advantaged factor for the communication performance, and it can increase the transmitting rate of the wireless communication system. This change need not increase the added signal bandwidth and the launching power. Furthermore the MIMO technique can resist the random fading effectively, and improve the performance of the wireless communication system greatly. In principle, MIMO offers three different benefits, namely spatial diversity, beamforming gain, and spatial multiplexing. The stunning novelty of MIMO, however, was that channels could support parallel data streams by transmitting and receiving on orthogonal spatial channels (spatial multiplexing). The number of usefully multiplexed streams depends on the rank of the instantaneous channel matrix, which, in turn, depends on the spatial properties of the radio environment. The spatial multiplexing gain may reach in a sufficiently rich scattering environment. Spatial correlation - manifest as channel matrix rank reduction - will reduce this gain, as it will reduce diversity order. The Fig.1 is the block diagram of the MIMO system, which has M transmit antennas and N receive antennas. The signals at the transmit antenna elements is given as