Research On Anti-impulsive-interference Algorithms For Over-the-horizon Radar

The signal processing of Over-the-horizon radar (OTHR) is always one of the research hot-spots, and faces many technical difficulties. Among those interferences in OTHR, the impulsive interference (IMI) has the great impact. The IMI mainly include the radio frequency interference, the lightning in the air, and the meteor echo in the universe. Although the adaptive digital beamforming (ADBF) can suppress these IMIs to a certain extent, but there is still some remained interference impact, lifting up the noise bases and depressing the detection performance of target peak, even submerging the target into the noise background .Based on the fruits of other previous researchers, this dissertation makes some research on algorithms for OTHR temporal signal anti-impulsive-interference after digital beamforming. The main works and the innovation points include:1. Inherited and improved the existing algorithmsBased on the existing fruits of other researchers, it firstly follows the classical"clutter suppression"-"temporal detection"-"restoration"routine, and construct the framework for the anti-impulsive-interference tasks. It realizes wavelet detection for IMI detection. It changes the existing algorithms for the wavelet coefficient in the previous papers into the fast algorithm based on CZT, and discusses its details.2. Proposed two new detection algorithmThe first one is based on the fractal method, and realizes the interference detection in the clutter background. The second one relies on the time-varying characteristics of short-time signal subspace to detection the position of interference, without clutter suppression before detection.3. Propose the concept and model of the general frequency domainThe impulsive interference is modeled as an ideal Dirac function, whose Doppler spectrum is modeled as a general sinusoid signal. The frequency of this general sinusoid signal is just corresponding to the IMI temporal position. Thus, it leads to a batch of detection algorithms. This dissertation utilizes MUSIC algorithm and AR model algorithm to detect IMI sucessifully, only depending on the simplest ideal high-pass filter to suppress the clutter.Based on the above general sinusoid signal model and applying the subspace projection processing, this dissertation prososes a joint detection and suppression algorithm: after the ideal high-pass filtering, the principal component analysis (PCA) is processed on the genral sinusoid signal to determine the eigenvalues and eigen-vectors corresponding to the general sinusoid signal. These eigen-vectors can reconstruct the subspace of general sinusoid signal (referred to as signal subspace). The raw Doppler spectrum signal without clutter-suppression is projected into the orthogonal complement subspace of signal subspace (referred to as noise subspace), which can reaches the goal of filtering impulsive interference.4. Construct the software and hardware simulation platformTo solve the lack problem of echo signal in the research, it constructs the simulation platform to supply plenty of exeriamental data for algorithm verification. It constructs the software simulation platform based on MATLAB and hardware simulation platform based on GPU general computation, which greatly improves the efficiency of MATLAB compuatation instead of code transplantation into DSP.