Research On Parameter Estimation And Interference Suppression Of MIMO-OTH Radar

In recent years, MIMO-OTH(Multiple Input Multiple Output over the Horizon) radar became one of the hot topics in sky wave over-the-horizon radar area, which has received extensive attention of domestic and foreign scholars. This paper mainly studies principle and signal processing algorithm of MIMO-OTH radar, joint estimation of target and ionospheric parameter, transient interference suppression, and ionospheric phase contamination correction. In this paper, the main work and contributions are as follows:(1) Principle and signal processing algorithm of MIMO-OTH radarThis paper establishes the signal model of bistatic MIMO-OTH radar. Then, based on the signal model, this paper studies the signal processing steps and methods for MIMO-OTH radar from the engineering applications, including receiving digital beam forming(DBF), transmitting DBF, matched filtering, Doppler processing, constant false alarm rate(CFAR) detection, and parameter measurement. Lastly, based on the radar equation of bistatic MIMO-OTH radar, the performance of bistatic MIMO-OTH radar is discussed.(2) Joint estimation of target and ionospheric parameters in MIMO-OTH radarIn the traditional over-the-horizon radar system, the ionospheric parameters are measured by the ionosonde, and then the ionospheric parameters are exploited to estimate the target parameters. The estimation accuracy of ionospheric parameters seriously affects the estimation accuracy of target parameters. This paper proposes the joint estimation approaches of target and the ionospheric parameter using ionosonde data and received signal, and derives the lower bounds of the joint estimation methods in two scenarios, where the prior distribution of ionospheric parameters is either unknown or known. The joint estimation methods effectively exploit the information of ionospheric parameters contained in the received signal, and improve the estimation accuracy of target and ionospheic parameters. This paper also proposes the selection criteria between the traditional estimation approach and the joint estimation approach in two scenarios.(3)Transient interference suppression based on the completion of low-rank matrix elementThe sky wave over-the-horizon radar operates in a complex electromagnetic environment, where the external interference and noise are serious. The transient interference is a kind of common interferences for the sky wave over-the-horizon radar, which can seriously degrade the performance of radar. The traditional methods of transient interference suppression need to suppress the sea clutter in advance. However, in the practical radar systems, the correlation between azimuth-distance-Doppler cells is poor due to the ionospheric phase contamination. So, the clutter cannot be suppressed completely, which affects the performance of transient interference suppression. This paper proposes a transient interference suppression algorithm based on the completion matrix element, which does not need to suppress sea clutter in advance. The proposed method can also effectively suppress the noise, and improve the signal to noise ratio.(4) Transient interference suppression based on the decomposition of low-rank matrixAlthough the transient interference suppression algorithm based on the completion matrix element is more effective than the traditional methods, it is still needed to detect the location of the transient interference via the threshold. In the scene, where the transient interference is weaker, it is difficult to detect the location of weak interference. This paper proposes the transient interference suppression algorithm based on the decomposition of low-rank matrix, which does not need the interference location detection. Exploiting the sparsity of the transient interference, this proposed method can separate the transient interference via the matrix decomposition algorithm, and effectively suppress the weak transient interference and noise.(5) Compensating ionospheric phase contamination based on multistage Taylor expansionThe ionospheric state changes along with time, which can cause the modulation of the radar signal phase, and result in the Doppler spectrum spread and the coverage of the slow target. Therefore, it is necessary to compensate the phase contamination before the slow target detection. Due to the nonlinearity of the ionospheric phase contamination, the traditional correction algorithms need to slice data into small segments, and then respectively correct the contamination phase of each segment. However, in practical application, it is difficult to determine the data segment strategy. This paper proposes an algorithm for compensating ionospheric phase contamination based on the multistage Taylor expansion. In the proposed algorithm, the ionospheric phase is approximated by the multistage Taylor expansion, and then the interacting multiple model algorithm is exploited to estimate the ionospheric phase contamination. Finally, the ionospheric phase contamination is corrected by the estimate of the phase. The proposed algorithm does not require the data segment and has better correction performance.