Study Of Modulation For Orthogonal Frequency Division Multiplexing

Adaptive modulation has become the subject of intensive study in recent years.It can largely enhance the speed of the system . The adaptive OFDM technology can enhance the spectral efficency and can lower the error rate.In this thesis, the properties of the multicarrier techniques and the theory of OFDM are introduced,and the characteristic of the wireless fading channel and the model of the multipath channel are expatiated firstly. Secondly,we studied the MQAM technique ,which has high link spectral efficency and can flexibly alter the speed according the channel.Then we analysed three fixed rated alterable adptive modulations and a variable rated alterable adptive modulation.The feasibility of the schemes are proved through computer simulation. At last , a low calculational complexity algorithm is proposed. The transmitting power can be adaptively allocated to maximize the total transmitted bits number with the total transmitting power constraint. It need less calculation than the existing algorithms,and can alter the speed and the modulation according to the consumers' request. So,it can satisfy the multimedia communication.