The Research And Realization Of Demodulation Algorithm For Burst Signal With Multi Symbol Rates

Burst-mode communication has the characters such as strong ability of anti-interference and anti-interception,efficient usage of channel and small consumption of power.It has been widely used in military and civil communication systems.To using the limited channel and power resource efficiently,the transmitter always adjust the signals' symbol rate by the capacity of mission and the channel quality.It makes significant sense to research the demodulation of burst signal under the circumstance of symbol rate varying.The focus of this paper is to research the key technology in burst signal demodulation,which includes non-data-aided estimation of frequency offset,symbol rate and timing error.A scheme of demodulator design is proposed in this paper,which is then implemented and tested on hardware.Firstly,some typical frequency offset estimation methods,such as algorithms based on DFT,self-correlation or differential frame,are researched in this paper.We improve the algorithm based on DFT by interpolating or dichotomous searching.The application of the above algorithms is analyzed and compared.A new frequency offset estimation method based on Particle Swarm Optimizaton is proposed.The new algorithm can estimate a large range of frequency offset accurately under low SNRs when lacking of signal symbols.Then,we study symbol rate and timing error estimation technology of burst signal.The principle of symbol rate estimation based on amplitude of M-power spectrum,cyclic correlation as well as wavelet transform is deducted.Some defections of these algorithms,such as no symbol rate spectral lines or no prominent spectral lines,are corrected by pre-filtering and spectrum filtering.To detect the timing error,we research some algorithms which based on nonlinear transformation or max mean power,as well as some low sampling algorithms.The simulation comparing of these timing error estimation algorithms is given.Based on the analysis of demodulation algorithms,we finish the design and realization of demodulator for burst signal with multi symbol rates.The demodulator can demode burst DPSK and GMSK signals with multi symbol rates that can reach 200 MSps.The testing result shows that the demodulation scheme,of which the BER performance can reach the request of project,is feasible.