Design And Implementation Of Satellite Burst Communication System For Inter-satellite Networking

With the development of satellite communications and space technology,rapid-response satellites have gradually become an important part of the future Operationally Responsive Space(ORS)system,playing a significant role in satellite communications field.Spread spectrum technology makes the system obtain good concealment and strong anti-noise and anti-interference ability by the way using specific codes to broaden the signal spectrum.Therefore,it is widely used in military and civil communication,especially in the field of satellite remote control and telemetry.In spread spectrum communication systems,synchronization technology is one of the key technologies of spread spectrum receiver,which has always been a research hotspot in the field of communication at home and abroad.Due to the extremely low demodulation Signal-to-Noise Ratio(SNR)in spread spectrum systems,the synchronization process usually consumes a lot of time and hardware resources.Therefore,the research of efficient and reliable synchronization algorithm is of great significance to improve the performance of spread spectrum system.In this thesis,aiming at the satellite burst communication system for inter-satellite networking,combined with its low SNR communication condition and short-time burst communication characteristic,a complete spread spectrum communication system is designed,and a low-complexity synchronization method suitable for extremely low SNR is proposed.In the meantime,the hardware design and implementation of the whole system are completed.The specific work of this thesis is as follows:1.Firstly,according to the characteristics of satellite burst spread spectrum communication system and the given index requirements,the key parameters of the system are determined.By calculation,the demodulation SNR threshold of the spread spectrum system designed in this thesis reaches-27 d B.Then the signal frame format is designed by the system parameters,and the overall design scheme of the spread spectrum system is given.At last,the baseband signal processing flow of transmitter and receiver and the algorithm principle of each module are introduced in detail.2.Aiming at the shortcomings of time-consuming and high complexity of traditional synchronization algorithms,this thesis focuses on the synchronization method with low complexity under extremely low SNR,including capture,bit synchronization,carrier synchronization and timing synchronization.The existing quadratic Fast Fourier Transform(FFT)accumulation algorithm is optimized and improved,then a low complexity synchronization algorithm in frequency domain based on sparse sliding is proposed,namely,the method of accumulation of correlation peak values in frequency domain is adopted,whose FFT window slides sparsely at intervals of no-integer multiples of spread code’s length.This method not only improves capture probability and makes the synchronization performance reach-30 d B when the maximum frequency offset is 10 k Hz,but also greatly reduces the computational complexity and facilitates the hardware implementation.3.Based on the overall design scheme of the system,the construction,algorithm simulation and performance test of the entire spread spectrum system are completed on MATLAB,and according to the MATLAB simulation results and fixed-point simulation program,the hardware design and implementation of the baseband system of spread spectrum communication are completed.Based on Vivado platform,Verilog HDL codes of transceiver’s each module are written with top-down design idea,and the function simulation and joint debug of the whole system are carried out with Modelsim software to verify its function correctness.Finally,the board level verification is carried out on Field Programmable Gate Array(FPGA)development board,and the system has passed the base band and intermediate frequency self-loop tests.The difficulty in the design of satellite burst communication system described in this thesis lies in the design of the synchronization scheme and algorithm,which is mainly reflected in its harsh communication condition,including extremely low SNR,large frequency offset and burst communication.These factors can have a significant impact on synchronization performance.Therefore,a kind of robust synchronous head is designed,and the existing synchronization algorithm is optimized and improved,then a low-complexity efficient and reliable synchronization scheme is proposed,so that the spread spectrum system designed in this thesis can still have good communication performance under above harsh communication conditions.It provides a reference for the study of satellite burst communication system under similar communication conditions.