Research Of Uplink Transmission Technology In Broadband Satellite Mobile Communication Systems

The satellite communication technology has the advantages of wide coverage,long communication distance,wide band,high capacity,excellent channel quality and stable performance.As the key technology to achieving the goal of ensuring people to communicate with anyone at any time,any place,equipment costs of satellite communication systems do not increase with the communication distance.This thesis focuses on the research and implementation of the uplink of satellite mobile communication systems,and devotes to designing an uplink transmission scheme for satellite mobile communication systems which is compatible with terrestrial mobile communication systems.First of all,multi-beam antenna array,digital beamforming technology and channel characteristics of satellite mobile communication systems are presented.The satellite transmission link has the characteristics of long time delay,high path loss and large Doppler frequency shift,due to the influence of transmission distance,large-scale fading,small-scale fading and Doppler Effect.These characteristics result in incompatibility between the terrestrial mobile communication technologies and the satellite mobile communication technologies.Secondly,the random access channel of the satellite mobile communication systems is researched.Based on the study of terrestrial mobile communication systems and extension methods,a new random access scheme is proposed.In this scheme,a polar-extension based random access sequence is designed to avoid range blurring,and the DFT pruning based hybrid time frequency transmitter and down-sampling based frequency domain receiver is exhibited.Simulation results present that the extended sequence,whose autocorrelation maintains the characteristic of single peak,can satisfy the long delay of satellite communication systems and ensure the effectiveness of Random Access.After that,this thesis proposes a two-dimension transform domain filtering method,which utilizes the spatial domain correlation feature of Multibeam Array Antenna in satellite systems.The method can filter out noise of the spatial domain and enhance the performance of channel estimation.Simulation results indicate that the method has significant gain compared to the traditional MMSE filtering method of transform domain,especially in the low snr regime.Finally,the implemention of transmitter and receiver of the random access channel designed before are discussed.The fix-point processing of the transmitting and receiving program of the polarity extended random access is presented,and the fixed-point simulation link is established.Simulation results verify that the performance still maintains in a high level compared to floating point link.After that,we implement the transmitter and receiver by Verilog on the Xilinx Kintex-7 series 410T FPGA,and test results are consistent with the simulation results of fixed-point program.