Research On Transmission Technology Of Low Earth Orbit Satellite Communication System Based On 5G

Compared with the terrestrial mobile communication network,the LEO satellite mobile communication system has the advantages of wide coverage,wide bandwidth and not affected by natural disasters.It is widely used in areas beyond the coverage of the terrestrial network such as sea,desert and sky.In addition,the satellite mobile network can also provide continuous network connection for Internet of Things devices to achieve real global coverage.3GPP has incorporated satellite communication into 5G non-terrestrial(NTN)communication mode.Therefore,the integration of satellite communication system and terrestrial communication system to form a seamless global integrated network of land,sea and air,to meet the needs of various business services everywhere,is an important development direction of future communications.This paper studies the wireless link transmission technology of LEO satellite mobile communication system.Firstly,the channel transmission characteristics of LEO satellite mobile communication system are analyzed,and some basic concepts of wireless channel are introduced,including free space fading,shadow fading,multipath fading and Doppler frequency shift.In view of the difference between satellite wireless channel and ground channel,the influence of atmospheric factors such as atmosphere,rainfall,cloud and fog on electromagnetic wave transmission is emphatically analyzed.Secondly,the channel estimation method based on 5G pilot in the downlink of LEO satellite mobile communication system is studied.5G downlink uses FDM/CDM combined pilot multiplexing mode,so the basic channel estimation can only be carried out after pilot separation at the receiver.The commonly used channel estimation algorithms include least squares(LS)estimation algorithm,minimum mean square error(MMSE)estimation algorithm and transform domain based estimation algorithm.However,in time-frequency selective channels,the pilot of code division multiplexing at the receiving end will no longer be orthogonal,resulting in inter-pilot interference.To solve this problem,a channel estimation method based on grouping interpolation is proposed.Firstly,the LS estimates of mixed channels are grouped by using the repeated use of orthogonal masks in time-frequency domain.Then,each group is interpolated to increase the number of equations.Then,the LS estimates of channels are solved by combining the pre-and post-interpolation equations.Finally,the MMSE filter is used to obtain the MSE estimates of channels.Value.The simulation results show that this method can achieve better channel estimation performance.Finally,the method of signal detection based on SCMA for LEO satellite mobile communication system is studied.Firstly,a multi-antenna SCMA system model is established,and the basic MIMO signal detection methods,such as maximum likelihood(ML)detection method,zero forcing(ZF)detection method and MMSE detection method,are analyzed.Aiming at the performance deficiency of linear detection method,a serial iterative detection receiver is introduced.In addition,MPA detection method is deduced.To solve the problem of high complexity in multi-antenna scenario,QR decomposition is introduced to simplify it.Furthermore,a strategy of dynamically adjusting the update sequence of node messages is proposed to speed up convergence and reduce the number of iterations.Finally,the BER curves of these methods are obtained by simulation.The simulation results show that the proposed method can achieve better detection performance.