Research On Adaptive Modulation Technique In OFDM System

By combinating adaptive modulation techniques and OFDM techniques, then different modulation methods can be adapted in different subband and the transmitting power can be allocate according to the channel condition, which effectivelly match the channel and improve the system efficiency. Nowadays, the technique of adaptive modulation in OFDM system is one of the active research areas.In this thesis, the development of adaptive modulation and the basic principles are presented firstly. Then Hughes-Hartogs algorithm, Chow algorithm and Fischer algorithm are studyed. What's more, a new algorithm is presented by improving the Fischer algorithm. The new algoritm has same performance with the former in error ratio, but reduce the calculation iterations and the computation algorithm. An optimal adaptive modulation algorithm in MIMO-OFDM system based on SVD is proposed. The simulation results show that the algorithm have optimal perfomance in allocating bit and power. An adaptive modulation algorithm based on group is presented by improving the algorithm. It is conclude from the simulation results that the new algoritm has approximate performance with the former in error ratio, but has small algorithmic complexity and high efficiency, What's more, less feedback information is needed, which can reduce the system complexity.