Doppler Shift Calculation And Compensation Study In Mobile Satellite Communication System

In mobile satellite communication system, the electromagnetic wave frequency of thereceiver will be offset due to the relative motion between the satellite and the mobile terminal.In another words，the Doppler effects happens. The satellite operating speed is very fast inLEO satellite mobile communication system, which causes a great frequency shift and bringsa lot of difficulties for demodulation. Then system performance reduces quickly. To ensurereliable communication, we must analyze Doppler shift and its variation rules in the visiblerange. Then we can compensate Doppler effects and improve communication quality.We have introduced comprehensive for the research status and development trend in thispaper firstly. And then we make a detailed analysis of communication link and channelcharacteristics for satellite mobile communication system secondly. The influence of Dopplereffects to communication system is carried out thirdly with characteristics of Doppler effects.Based on research above, we study Doppler calculation and compensation in mobile satellitecommunication system.The following is Doppler shift calculation and compensation study aimed at Dopplereffects in mobile satellite communication system:(1) A simple calculation method of Doppler shift is proposed(SDE，Simplified DopplerEstimation). Based on the geometry analysis, this method uses the rate of distance change toget relative speed, and then calculates Doppler frequency shift. In this paper, Estimationalgorithm of Doppler effects is simulated in different frequency bands. Then Doppler shiftand rate of change are obtained within visual range and MPSK modulation/demodulation intolerated range is analyzed and calculated. And then we simulate it between LEO/GEO andmobile terminal based on the calculation. Comparing with the traditional method, SDEmethod can reduce effectively the complexity and improve the computational efficiency. Inaddition, this method is utilized between GEO satellites and mobile terminals, or betweenLEO satellites and mobile terminals. Go a step further, this method is applied to calculateDoppler between GEO satellite and LEO satellites.(2) Validation plan is given and implemented. On the basis of the new Doppler shiftcalculation, the paper analyzes two typical Doppler compensation projects: pilot andDDS+PLL. By comparing these two projects, a actualize framework about DDS+PLL projectis proposed. Then we complete the platform simulation based on FPGA combined with software and hardware. Under the help of signal analyzer and digital signal analyzer andoscillograph, the plan’s validity can be guaranteed.In a word, the study of Doppler shift calculation and compensation provides theoryensure and resolve project for improving communication quality. It really is a theoreticalsignificance and practical value.