Modulation And Coding Scheme Design Of The Low Orbit Satellite At Ka-Band

The satellite communication demand of users are growing daily with the rapid development of information technology,Ka band has gradually become the current research hotspot for solving the problem of shortage of available band resources.However,Ka band transmission signal is susceptible to the wireless communication environment.In addition,the high-speed mobility of low earth orbit(LEO)satellites aggravates the time-varying of the transmission channel,which enhances the complexity of the propagation environment,thus promoting the attenuation of the transmission signal.Therefore,this thesis designed the modulation and coding scheme of the LEO at Ka band for improving the effectiveness and reliability of LEO satellite communication system.The research works are as follows:An adaptive information transmission scheme for LEO satellite based on Ka band: aiming at the problem of Ka band satellite communication signal transmission is easily affected by rainfall and ground environment,an adaptive information transmission scheme is proposed by considering with the high-speed movement characteristics of LEO satellite.Firstly,a two-state Ka band LEO satellite channel model considering rain attenuation and the degree of ground shadow is established.Secondly,as for each state,the parameters of rain attenuation distribution based on different elevation angles of satellite are calculated according to the LEO satellite trajectory,and the channel state information can be obtained.Finally,according to the confirmed channel state information,the optimal modulation and coding scheme is selected through the adaptive modulation coding selection algorithm to promote the transmission reliability of spatial information.The simulation results show that the proposed Ka band adaptive information transmission scheme can effectively solves the problem of serious attenuation of transmission signal caused by rainfall,ground transmission environment and satellite mobility,and effectively enhance the transmission quality of LEO satellite communication signal based on Ka band.Modulation and coding selection scheme based on dynamic power allocation: aiming at the problem of low throughput of multi-beam LEO satellite communication system cacused by the surge of users,a modulation and coding scheme based on dynamic power allocation which considering high-speed movement characteristics of LEO satellite is proposed.Firstly,a channel model considering rain attenuation and variation of satellite elevation angles is established.Secondly,the objective function of maximizing system throughput is established under the constraints of total transmitting power and target bit error rate of satellite system.Thirdly,particle swarm optimization algorithm is utilized to allocate transmitting power dynamically under different channel states according to the established objective function.Finally,calculating the current channel signal-to-noise ratio and subsequently choosing the optimal modulation and coding scheme to maximize the system throughput based on the allocated transmitting power.The simulation results show that: the lower elevation angles of satellite,the lower throughput of satellite communication system.The proposed modulation coding selection scheme can effectively promote the system throughput on the basis of system reliability compared with the traditional modulation and coding selection scheme.