The Study On The Adaptive Techniques In MIMO-OFDM System

High data-rate, high reliable transmission and guarantee end-to-end Qos are required to be provided for the next generation mobile communication. MIMO, OFDM, and adaptive transmission have been comprehensively considered as the major candidate techniques for future radio communication systems. MIMO technology can increase the channel capability notably and enhance reliability of data-transmission with the help of multi-send antenna and multi-receive antenna. OFDM has the ability of transforming the frequency-selective channel into a collection of parallel flat-fading sub channels. Therefore combination of MIMO and OFDM is regarded as the potential architecture for the future communication system.In this paper, wireless channel, the parameters of multi-path effect and Doppler Effect were analyzed firstly, and then mainly focus on introduction and analysis of Beam-Forming, and 3 key technology of adaptive modulation.Based on the Beam-Forming technology, multi-carrier allocation programs was introduced, and it was discussed based on the correct channel information and non-accurate information of channel. Among two different circumstance, in the correct channel information system model, the greatest eigenvalue distribution criteria for the subcarrier allocation program was introduced, and the simulation results show that the distribution program can be effective multi-user access to the diversity effect. Then channel for non-precision actual information systems were discussed and a channel prediction model was proposed, the model balance the channel Delay through multi-users' correlation coefficient, and the simulation result shows that this model effectively reduce the loss caused by channel information Delay.Finally, the basic principles of water-filling method was studied, and then discussed the most commonly used unchanged-bit number and bit error rate when minimize the transmitting power method. Then the power allocation algorithm which is based on the variable step-bit was proposed, the algorithm optimize the choice of step, and compared with the former algorithm, this power allocation algorithm based on the variable step-bit can decrease the complexity of the system while the performance are quite close to each other. Through simulation, the performance of the multi-user will be better, so it can be good for the multi-user MIMO-OFDM system.