Demodulation And Despreading Of Spread Spectrum Signals In Burst Communications

With the vigorous development of satellites in various countries around the world,the research on related communication technologies has also made great progress.Among them,spread spectrum communication technology has high anti-interference performance and concealment.The burst mode communication has the characteristics of long signal transmission interval and short duration,which makes it has excellent anti-interception and anti-interference characteristics.In practical applications,the combination of these two technologies is often used to further improve the confidentiality and anti-interference performance of the system.Based on this,this paper proposes a scheme that can quickly realize the pseudorandom code capture of the spread spectrum signal and the synchronization of the carrier in the burst mode communication,so as to realize the demodulation and despreading of the spread spectrum signal in the burst mode communication.The first problem that the burst spread spectrum receiver needs to solve when processing the received signal is to capture the pseudorandom code.Based on a large number of related technical literatures,this paper analyzed several commonly used traditional capture algorithms and PMF-FFT capture algorithm in detail.Through simulation and comparison,it is found that PMF-FFT algorithm has advantages over traditional capture algorithms in the situations of burst mode,low signal-to-noise ratio and high Doppler frequency offset.Therefore,the PMF-FFT acquisition algorithm with better performance was finally selected as the acquisition scheme.In addition,this paper improves the PMF-FFT acquisition algorithm in terms of scallop loss,Doppler frequency offset and acquisition time,so that it can achieve high-precision and rapid acquisition of spread-spectrum signals in the burst mode communication,The capture performance simulation of the improved algorithm under low signal-to-noise ratio shows that it meets expectations,so this paper uses this improved algorithm to design and implement the overall capture scheme.After the acquisition is completed,the carrier needs to be synchronized in time to complete the demodulation of the signal.When selecting the carrier synchronization scheme,this paper fully analyzed the effects of various auxiliary methods and parameter compensation methods on carrier synchronization performance in burst mode.Based on this,a data-assisted open-loop feedforward carrier synchronization scheme is selected.And the frequency offset estimation performance of Kay algorithm,Fitz algorithm and L & R algorithm is simulated and analyzed in this scheme.It is found that L & R algorithm has higher estimation accuracy than Kay algorithm under low signal-to-noise ratio,and its estimation range is larger than Fitz algorithm,it has higher bias tolerance.So this paper uses the L & R frequency offset estimation algorithm and the fourth power-based phase offset estimation algorithm to achieve accurate synchronization of carriers,and gives the overall implementation scheme of carrier synchronization.In the last,this paper gives a specific hardware design and implementation scheme,and conducted performance tests on the design indicators of this scheme.Experiments showed that this scheme can demodulate and despread the spread spectrum signal in burst mode communication.