Adaptive Modulation And Demodulation Technique

Adaptive modulation has become the subject of intensive study in recent years.It can largely increase the bits-ratio of the system.The adaptive OFDM technology can enhance the spectral efficency and lower the error rate consumedly.In this thesis,the theory of SISO-OFDM techniques and the MIMO system are introduced,and the characteristic of the wireless fading channel and the model of the multipath channel are expatiated firstly.Secondly, three optimal algorithms of adaptive modulation technique based on different allocation principles are analysed detailedly in OFDM system.What's more,two new algorithms are presented by improving the Fischer algorithms and the Hughes-Hartogs algorithms.The new improvement in Hughes-Hartogs algorithm has similar performance with the former in bits-error ratio,but reduces the calculation iterations.Besides,the new algorithm may be applied in the actual communication system.The new improvement to the Fischer algorithm has the advantages of the better performance and lower bits-error ratio with the old one.An new optimal adaptive modulation algorithm in MIMO-OFDM system based on SVD is proposed.The each channel matrix is decompounded by SVD and the eigenvalues of the matrix are to implement the allocation of bits and power.Then the Fischer algorithm is presented in the MIMO-OFDM system and acquires better bits-error ratio and the system performance, especially when the channel is in the deep fading or the frequency selective fading.