Target Parameter Estimation Of Radar Based On Time Reversal In Multipath Environment

The multipath effect causes the amplitude of the echo signal received by the radar to be greatly attenuated,which seriously affects the performance of the radar's parameter estimation of the target.The effect of multipath effect can be mitigated by suppressing or separating multipath signals.However,this type of algorithm has poor applicability under low signal to noise ratio(SNR)conditions,and multipath signals also contain target parameter information.Therefore,from the perspective of using multipath signals,this article discusses how to improve the performance of radar parameter estimation in a multipath environment.Time Reversal(TR)technology has the characteristic of adaptive space-time focusing,which can effectively use multipath signals.By inverting the echo and retransmitting it,the transmitted signal will be adaptively matched with the transmission channel and refocused at the target.Through time reversal,both the SNR of the echo and the performance of parameter estimation in a multipath environment can be effectively improved.This paper studies the application of time reversal to target parameter estimation under different radar systems.The main contents of this paper are organized are as follows: 1.The mechanism of multipath reflection is introduced in detail,including the geometric relationship between the multipath signal and the direct wave signal and the influencing factors of the reflection coefficient.By deriving the time symmetry of the wave equation and the reciprocity of the Green function,the basis and premise of the time reversal focusing theory are derived.Moreover,the space-time focusing characteristic of time reversal is explained in detail.The above contents lay the foundation for the study of the application of time reversal in radar parameter estimation of targets.2.Aiming at the problem of parameter estimation in phased array radar with a multipath environment,combined with time reversal,methods of wideband distance estimation and DOA estimation based on time reversal are proposed.Considering the multi-target and multireflection point scene,a wideband echo model of the array in complex multipath scenarios is established,and the SNR gain from time reversal is derived.By reversing the echo and retransmitting it,the time reversal echo is obtained which is used to estimate the distance and the angle of the target.Through the combination of time reversal technology and wideband signal,the methods proposed in this paper can obtain higher distance and angular resolution and lower root mean square error(RMSE)of ranging and angle measurement.In general,the proposed methods improve the performance of parameter estimation of radar.3.As for the problem of angle estimation of monostatic multiple input multiple output(MIMO)radar in a multipath environment,combined with time reversal,a DOA estimation method of a monostatic MIMO radar based on time reversal is proposed.In addition,a multipath echo model of monostatic MIMO radar is established,and the influencing factors of the SNR gain brought by time reversal are analyzed from the perspective of time domain.Retransmit the echo after time reversal.Then,the time reversal echo is matched and filtered,and a spatial smoothing algorithm is used to estimate the angle of the target.The angular resolution and the accuracy of the method proposed in this paper are significantly better than the traditional algorithms.4.Aiming at the problem of angle estimation of bistatic MIMO radar in multipath environment,combined with time reversal,a method for The direction of departure(DOD)-DOA jointly estimating of bistatic MIMO radar based on time reversal is proposed.Furthermore,a multipath echo model of a bistatic MIMO radar is established.In the method,firstly,the first received signal is orthogonalized,and then it is time reversed and retransmitted.Then,the time reversal echo is matched filtered,and the spatial difference smoothing algorithm is used for decoherence.Finally,the unitary estimating signal parameters viarotational invariance techniques(ESPRIT)algorithm is used to achieve the automatic pairing estimation of the DOD and DOA of the target.Through time reversal,the signal achieves adaptive energy focusing at the target,thereby improving the SNR of the echo,which can significantly improve the performance of angle measurement.