Research On Algorithms For MIMO-OFDM Systems

MIMO (multiple-input multiple-output) and OFDM (orthogonal frequency division multiplexing) have attracted the attention of people because they are the key techniques of the B3G mobile communications and broad band wireless LAN. MIMO systems use multiple antennas at both the transmitter and receiver to transmit signal in the same frequency band at the same time, which can significantly increase the channel capacity and improve the efficiency of band-width. OFDM systems distribute the high-rate data stream to many low-rate data steams and transmit them in a parallel way over many sub channels, which can combat ISI (inter symbol interference) efficiently. As a combination of MIMO and OFDM, MIMO-OFDM systems achieve space, time and frequency diversities efficiently, which can not only greatly improved channel capacity and transmission rate of wireless communication systems, but also efficiently combat multi-path fading and interference.This paper mainly discussed and analyzed the MIMO-OFDM joint time-frequency beamforming algorithm and the combination with channel estimation algorithm. The specific contents are as follows:Firstly, based on the introduction of the characteristics of radio fading channel, this paper introduced MIMO-OFDM basic principle.Secondly, this paper does the research on the joint time-frequency beamforming algorithm which uses different number of IFFT or FFT model in different channel environment, and it analyzes the complexity of algorithm, what's more, it compares the performance of joint time-frequency beamforming algorithm with that of time domain beamforming algorithm and frequency domain beamforming algorithm.Thirdly, this paper adopted the Least Square and Minimum Mean Square Error respectively as criterion of channel estimation. By applying the joint time-frequency beamforming algorithm, the system achieved optimal joint time-frequency beamforming weighting coefficients.Lastly, comparing the coding rate of joint time-frequency beamforming algorithm with that of STBC, this paper studies the performance of the joint time-frequency beamforming algorithm and STBC based on channel estimation, the experimental results show that the performances of joint time-frequency beamforming algorithm and STBC are equivalent in simple multi-path.