Research On TDOA Pairing And Time Synchronization Of Multiple Stations For SSR Reply Signal

The Secondary Surveillance Radar is extensively applied in the military and civil fields including battlefield status identification and airport approach control.And the non-cooperative passive localization based on TDOA(Time Difference of Arrival)of multiple stations for SSR reply signal is one of the efficient method to localize a variety of targets.However,when it is used to the real localization system,there are still some problems such as the detection and recognization of the SSR reply signal,TDOA pairing and time synchronization of multiple stations for SSR Reply Signal.This dissertation focuses on these problems and main research contents are as follows:(1)The detection and recognization of the SSR reply signal under low SNR conditions are studied.To cope with the low detection probability and high false alarm probability of SSR reply signal detection under low SNR conditions,a novel method of detection and recognization of Mode S and Mode A/C reply signal is pointed out.The correlation method is applied to detection of Mode S reply signal.A mathematical model is established and the threshold and detection probability is derived.The detection probability is raised through triple correlations,which include correlation of the whole signal,matched filtering of single pulse and correlation detection using signal preamble with multiple pulses.Mode A/C reply signal is detected through its frame pulses.The false alarm probability is decreased with the combination of TOA(Time of Arrival)and PA(Pulse Amplitude)and the performance of detection is improved.Finally,the algorithm is verified by computer simulation and real data.(2)TDOA pairing and localization of multiple stations for SSR reply signal are studied.Because of the equal frequency and pulse width,and there are more than one pulse within a signal packet,a method of TDOA pairing based on the correlation of signal contents is proposed.According to the regularity of TOA sequence,the same TOA sequence is paired to decrease the pairing ambiguity.Considering the interleaving of different signals,confidence level is applied to the pairing and the code with a low confidence level will not be paired.A TDOA localization algorithm based on SSR reply signal is established and the performance of localization is analyzed by Monte Carlo simulation.(3)Time synchronization of multiple stations based on ADS-B(Automatic Dependent Surveillance-Broadcast)is studied.In view of the effects of system biases,a mathematical time synchronization model with biases is built.Via the analysis of ADS-B position errors,station position surveillance errors and TDOA measurement errors,ADS-B latency which may cause the distinct synchronization error is pointed out.Aim at eliminating the system biases in time synchronization,a joint estimation algorithm of the ADS-B latency and station clock correction is proposed,and the theoretical derivation of the Cramer-Rao lower bound(CRLB)is derived.The geometrical distribution of the synchronization error is given out by simulation to analyse the performance of the method.