Research On Downlink Of Satellite Mobile Communication System Based On LTE

The application range of satellite mobile communication system is increasingly wide,and there is no constraint on geographical conditions.The signal can cover the complex plateau areas and remote areas,especially the Wenchuan earthquake which broke out in Sichuan in 2008.Most of the base stations on the ground are paralyzed.The trust system has played an important role in ensuring the safety of people's lives and property and providing timely protection and reducing the losses caused by disasters.Therefore,the rapid development of satellite mobile communication is of great strategic significance to the future development of our country.This paper studies the downlink transmission technology of satellite mobile communication system.First,the characteristics of the satellite communication channel are studied,the characteristics of the frequency selective fading channel are discussed,and the influence of the atmospheric absorption loss and rainfall rate on the satellite communication channel is emphatically studied.At the same time,based on the DAH rain attenuation prediction model,the relationship between the working frequency,the communication elevation angle and the regional rainfall rate and the rain attenuation value is studied respectively.Finally,the commonly used probability distribution functions describing the channel characteristics are introduced.Subsequently,the broadband satellite mobile channel probabilistic statistical model is studied.The fading characteristics of broadband satellite mobile channels are analyzed,and a generalized stationary non correlated scattering model for broadband satellite mobile channels is established.Finally,the implementation and Simulation of the broadband satellite mobile channel are completed,and the original sine wave superposition method is improved and supplemented.The randomness is added to the sine wave superposition method,and the accuracy of the model is verified by the time and frequency domain analysis.Then,the downlink pilot design and channel estimation method for broadband satellite mobile communication system are studied,and the optimal pilot sequence design in large-scale MIMO is proposed.The optimal pilot design criterion for large-scale MIMO is based on the LS channel estimation to minimize the worst-case MSE.In large-scale MIMO environment,the guided frequency sequence sets satisfy the best autocorrelation and Welsh bounds.By using the Chu sequence for optimal pilot design,the maximum upper bound value of the set of pilot sequences is derived when the length of the sequence is given and the maximum number of pilot sequences can be used simultaneously.Simulation results show that the proposed pilot sequence can improve MSE performance and system performance.Finally,the channel estimation algorithm based on least squares and least mean square error is compared.On the basis of the traditional DFT channel estimation algorithm,the DFT channel estimation algorithm based on symmetric extension is studied,which improves the edge discontinuity of the traditional DFT channel estimation algorithm and improves the performance of the estimation.Finally,the downlink synchronization estimation method of broadband satellite mobile communication system is studied.Firstly,the synchronization algorithm based on cyclic prefix is introduced.The algorithm uses the special structure of the cyclic prefix in the OFDM system to synchronize,and the complexity is low.Then by using the maximum likelihood criterion,the timing estimation of the MIMO-OFDM system is derived by two methods,which are the unknown variable of the channel model and the random variable that conforms to the Rayleigh fading.On this basis,a kind of general estimation expression is extracted,and a kind of window function based on the same is proposed.Step algorithm is used to illustrate the influence of different window functions on the synchronization performance.The simulation results show that the synchronization algorithm based on multi energy window is better than the synchronization algorithm based on other window functions.In addition,by carefully selecting the window function,the performance of the algorithm near the multipath energy window can be obtained,because it does not need to estimate the autocorrelation matrix of the channel,and has the lower complexity and robustness.