Design And Implementation Of Spread Spectrum Signal Detection And Tracking

With the advantages of hidden information,anti-interference and so on,Spread Spectrum Communication(SSC)technology has been developed rapidly and achieved lots of remarkable achievements in the military and civil fields.In general,pseudo code cycle is very long,the bandwidth of the spread spectrum signal is much larger than that of the information code,and the power spectrum density is lower.These superiorities can not only reduce the probability of mutual interference between various wireless signals,but also better hide information.In the receiver,by using the same signal as transmitted pseudo code for dispreading,the original information code signal is restored.Among different kinds of SSC technology,the Direct Sequence Spread Spectrum(DS-SS)communication technology is more widely used.This paper studies the DS-SS signal receiving technology,mainly including acquisition and tracking of pseudo code,acquisition and tracking of carrier wave.Firstly,the basic theory of SSC technology is introduced,and then the DS-SS signal receiving algorithm is presented.Finally,the simulation and implementation are carried out on Matlab/Simulink platform and FPGA respectively.This paper realizes the pseudo code acquisition based on partial matching filter-fast Fourier transform(PMF-FFT)method,which is a two-dimensional space searching process and can acquire pseudo code offset and Doppler frequency offset simultaneously.Pseudo code acquisition methods can be generally categorized as moving pseudo-code and moving data.The role of the delayed phase-locked loop is to copy the synchronization of pseudo code with the spread spectrum signal according to the offset of the acquired pseudo code,which can achieve the dynamic tracking of pseudo code.The acquisition and tracking of the carrier wave can move on after pseudo code synchronization.For large frequency offset signal,we can use FFT to estimate the approximate range of the spread spectrum frequency,namely carrier wave acquisition.After succeeding in carrier wave acquisition,the carrier wave tracking will be started,in which the accurate tracking of the input signal can be realized by the Costas phase-locked loop.The Costas phase-locked loop is a dynamic tracking processing,which can keep the synchronization of the receiving system to the input signal when the frequency or phase of the input signal changes.Finally,the transmitted signal from the spread spectrum signal source is used to verify the effectiveness of the proposed algorithm,and the performance of the spread spectrum signal receiver is analyzed in this paper.The acquisition method of the carrier wave was improved.Through the simulation and hardware verification,the spread spectrum detection and tracking algorithm studied in this paper can realize fast dispreading and demodulation of DS-SS signal.