Research On A Passive Radar For Detecting Targets Based On The OFDM Communication Signal

An overall low-altitude opening has been a worldwide trend with the increasing development of modern aviation.Aiming at study the methods of echos processing,we create a passive radar based on the OFDM communication signal from the base stations for low-altitude target detecting to realize better accuracy and lower cost.In this paper,a series of research will be done as following:First of all,according to the MQAM-OFDM signal model,the ideal anti-interference performance,high spectral efficiency and extremely low bit-error rate can be proved.The OFDM communication signal has thumb-shaped ambiguity function which means both high range and Doppler frequency resolution.However,it is sensitive to the Doppler frequency shift and what is worse,its self-correlation function may be troubled by “Sidelobe Peaks” which result in false-alarm.By employing LMS\NLMS or RLS algorithms,the DPI and MPI could be counteracted,the remained noise of which can be eliminated through the improved smoothing filter to weaken the “Sidelobe Peaks”.Secondly,a uniform circular array is picked as the reception antennas to get 3-d angular information through signal processing.,The target angles could be calculated by searching spatial spectrum peaks from the DOA simulation results.A two-step pulse compression and the improved method based on CP which may obtain the high-resolution 1-d range profile are considered in condition of value in use classical pulse compression.Two algorithms are required for the estimation and conpensation of the Doppler frequency offset,the mean frequency method is better to meet MSE,calculation and low-SNR environment than the other.Then an improved AM-CFAR operator could detect the weak target echo signals effectively.Finally,we pick up the candidates such as velocity,accelerated speed and moving trace from the motion features to determine whether the system should alarm or not.MQAM-OFDM signals have ideal Doppler resolution so that it could be employed to distinguish low-velocity targets below 1 Mach.Both the velocity and the Doppler frequency are relative with the range between the target and the center of antenna array through deducing the expressions in a spherical coordinate frame.Discussing in condition of uniformly accelerated motions,the estimation method based on maximum likelihood principle could catch the minimum variance unbiased estimation of accelerated speeds.Simulating the Extended Kalman Filter,a extremely-few-error pursuit path can be achieved by building CV or CA\CAI model.As expected,a systematic detecting method is proposed consequently.