The Key Technology Research Of VCM Synthetical Demodulator In Satelliate Data Transmission System

In recent years,with the rapid development of payload technology,the precision of detection and data transmission of satellite is increasing,which make the demand of satellite data transmission rates become higher and higher.In this background,in order to improve the efficiency of communication links,VCM(variable coding modulation)technology is proposed.VCM-based system uses different channel coding and modulation methods in different channel conditions.Compared with traditional CCM(constant coding modulation)technique,VCM system can make full use of link resources,and have higher transmission rate under same bandwidth and power supply.In this paper,based on the characteristics of VCM technology,the synthetical demodulator of VCM system is studied by referrring to the physical layer frame structure of DVB-S2.The main research contents are as follows:1.PLS code decoding,the difference-correlation frame header detector and the two frame synchronization schemes are studied.The two frame synchronization schemes are based on the threshold detection and window search respectively.The performance of the two schemes and the complexity of the algorithm are compared.Compared with the threshold-based schemes,the window-based schemes performance is slightly better.But the resource consumption is bigger.2.Based on the simulation and analysis of the maximum likelihood,Kay,Fitz,L&R,M & M and Jiang data aided frequency offset estimation algorithms,the method of accumulating the autocorrelation of modulation-removed signal is used to improve the performance of M&M algorithm.This way can realize very large frequency offset(20% symbol rate)when the signal to noise ratio is-2d B.3.Carrier phase coarse recovery,based on the maximum likelihood algorithm,using the pilot structure,is realized by linear interpolation.The phase jitter after compensation is close to the case which has no frequency offset and no phase compensation.