Research On The Key Technologies Of Synchronization For Signals With Low Probability Of Intercept

As electronic warfare plays an increasingly important role in modern warfare,how to ensure that transmission signals can be transmitted safely and effectively without being intercepted by the enemy is a key factor for the victory of electronic warfare.Therefore,it is of great significance to study the low probability of interception of communication signals.Therefore,this paper proposes a Low probability of Interception(LPI)communication system based on variable symbol rate.Compared with the traditional LPI communication system,this system does not have periodicity in receiving and sending sequences and can effectively reduce the probability of interception.When the system is implemented,the inter-symbol interference(ISI)is caused on the transmission side.In order to eliminate the effect of ISI,the symbol detection process of the received signal is modeled as a Hidden Markov Process(HMP),which is detected by the Viterbi Algorithm(VA).Simulations verify that the BER detection rate for the low probability of variable symbol rate communication system is basically the same as that of the signal error rate curve without ISI and the fixed symbol rate.Secondly,this dissertation studies the symbol synchronization algorithm for communication signals with low symbol probability and high probability of interception.Due to the influence of inter symbol interference in the signal,the traditional synchronization method based on the symmetry principle of the two sampling points with respect to the best sampling point is not suitable,such as early late gate,digital interpolation,etc.Therefore,in addition to studying the traditional symbol synchronization algorithm based on pilot sequence correlation,this paper also proposes a blind symbol synchronization algorithm for LPI communication system with variable symbol rate.The simulation verifies that when the signal to noise ratio reaches a certain threshold,both of these algorithms can achieve 100% synchronization probability.Finally,this paper studies the carrier synchronization algorithm for low probability of interception of communication signals with variable symbol rate.It mainly includes frequency offset estimation based on Fast Fourier Transform(FFT),data assisted autocorrelation and cross correlation algorithms,and Costas ring method.These methods are suitable for different scenarios.The FFT algorithm is suitable for coarse frequency offset estimation,the data assisted method is suitable for frequency offset fine estimation,and the Costas method is suitable for carrier tracking.For the data assisted method,since the symbol sequence does not have periodicity,the performance of the frequency offset algorithm using autocorrelation estimation is poor.When the local pilot sequence is known,the algorithm for estimating the frequency offset using the local pilot sequence for cross correlation performs better.It is further demonstrated that the system has a lower probability of interception.