Research On Technologies Of Adaptive Coding And Modulation Based On Satellite Channel

The fixed coding modulation mode adopted by the traditional satellite digital transmission technology can not meet the increasing demand for the payload of the satellite link.Because this mode ensures the transmission at the worst channel conditions and there are many link margins,it will lead to a waste of link resources when the channel conditions are good.As a key technology to solve this problem,adaptive coding and modulation(ACM)is a hot research technology at present.ACM estimates the real-time SNR of channel at the receiving end to obtain the channel conditions,and then feeds back the optimal coding and modulation mode to the transmitting end through the return link to match the changes of satellite channel,reduce the waste of system resources and improve the link data throughput.By analyzing the bit error rate and spectral efficiency of each coding and modulation mode in DVB-S2 standard,this thesis proposes a mode design method of adaptive coding and modulation in order to maximize the link data throughput.Combined with the dynamic rain attenuation characteristics obtained from the rain attenuation prediction of the satellite channel of Sanya station,the coding modulation mode switching algorithm is given,which can not only meet the link availability and anti rain attenuation performance,but also meet the demand of maximizing data throughput.In addition,this thesis studies the signal-to-noise ratio estimation algorithm based on statistics.Considering the large signal-to-noise ratio range of DVB-S2,the simulation experiment shows that the traditional signal-to-noise ratio estimation algorithm can not meet this range,so a joint estimation algorithm to expand the estimation range is proposed,which can effectively estimate the signal-to-noise ratio range of [-10,30]d B.As the dynamic characteristics of the channel,there are timing error,carrier frequency offset and phase offset at the receiver,which brings challenges to the comprehensive demodulation of DVB-S2 system receiver.By simulation,this thesis tests the feasibility of Gardner timing error estimation algorithm as bit synchronization and the feasibility of joint estimation of M?M algorithm and L?R algorithm as carrier frequency offset estimation.In addition,based on the characteristics of M?M algorithm,this thesis proposes a modified M?M algorithm with lower complexity to meet its requirements as a coarse synchronization estimation algorithm and reduce the complexity.