The Highly Efficient Satellite Downlink Transmission Technique With OTDM

As an efficient transmission technique,Orthogonal Time Division Multiplexing(OTDM)technique can combine multiple signals into one signal.It can be implemented with low complexity and can improve system power efficiency through pre-distortion.If this technique is applied to the satellite downlink communication system,the user capacity can be increased,the satellite transponder processing can be simplified,and the system power efficiency can be improved.In this thesis,the highly efficient satellite downlink transmission technique with OTDM is studied.The main work and the achievable research results of this thesis are as follows:1.A highly reliable synchronization method for OTDM system is proposed.Firstly,a hybrid synchronization code combining m sequence and ±1 sequence is proposed,which uses the special autocorrelation relationship to improve system communication reliability.Secondly,two synchronization signal addition methods are proposed.One is to add the synchronization signal and the transmission signal,which can save time and frequency resources.And the other is to interleave the synchronization signal and the transmission signal,which can simplify the satellite transponder processing.Lastly,a highly accurate time-frequency synchronization loop based on group delay matched filter and FFT operation is proposed.The synchronization loop can complete frame synchronization and frequency offset compensation at once time,so that the OTDM system can work normally under large frequency offset and time delay.At the same time,the method can also complete the accurate sample synchronization without increasing the signal sampling rate,so that it is easy to implement.2.Several highly efficient transmission techniques of the satellite downlink communication system with OTDM are proposed.Firstly,the theoretical error code formula of 16 APSK in the best constellation form is given,and a general error code derivation method is proposed.Secondly,an optimal sampling OTDM system is proposed.The system reduces the spectral gap of the signal by changing the sampling rate to reduce the occupancy of spectrum.The simulation results show that the spectral efficiency is improved by about 30% compared with the normal OTDM system.Thirdly,a high power efficiency OTDM transmission method based on digital baseband pre-distortion technique is proposed.The method can ensure linear amplification of the signal without power back-off.The simulation results show that it can improve the power efficiency of the system by more than 10 d B compared with the normal transmission system.Lastly,a rain attenuation compensation method by changing the modulation mode is proposed,which can improve communication reliability under bad weather conditions.Through the research and innovation of these techniques,the highly efficient communication of the satellite downlink transmission system with OTDM is realized.3.The FPGA design of highly efficient OTDM communication system is given.The function of each sub-module is verified by comparing with MATLAB simulation.Finally,a design method of ARM+FPGA is proposed,and an OTDM wireless hardware communication system constituted by ZCU102,ZC702 and ad9361 is built based on this method.