Research On Applications Of Adaptive Beamforming Technology In OFDM Communication Systems

Future wireless communication system requires that the system should have a good performance over multipaths fading channels, a high frequency band efficiency and ability of high data transmission rate. OFDM is a technology of high rate data stream transmission, which can convert the frequency selective fading channels to a number of parallel flat fading channels to reduce the effects of multipaths fading. Adaptive beamforming technology can make the antenna main lobe to the arrival directions of desired signals and make side lobe or null steerings to the arrival directions of interference signals so as to make full use of desired signals and suppress interferences, which can increase frequency band efficiency and system capacity. Therefore the combination of the adaptive beamforming technology and OFDM technology can satisfy the transmission demands of future wireless communication system.This paper mainly focuses on research of applications of the adaptive beamforming technology in OFDM systems. The common reports are mostly about LMS-OFDM systems which apply LMS beamforming algorithm based on MMSE criterion. However LMS-OFDM systems need reference signal that will occupy more frequency bands and the system's working performance will decrease under strong interferences environment. So a new method named MCMV-OFDM is proposed in this paper, which applies MCMV beamforming algorithm based on the desired signals spatial information to OFDM systems. This new method suppresses interferences and makes full use of useful multipath signals by regarding the received multipath signals from antenna arrays as expected signals based on corresponding beamforming algorithm to form the beam. It can get good estimations for expected signals by utilizing received signals not by reference signal, which improves the communication efficiency. At last, some simulations have been done to the new method under multipaths channels environment. And the simulation results show that comparing to LMS-OFDM system, the new method has very good performance under strong interferences environment.