Research On Waveform Optimization Design And Processing Of MIMO Sky-wave Over-the-horizon Radar In Interference Environment

Multiple-Input Multiple-output over-the-horizon radar(MIMO-OTHR),as a new system of sky-wave over-the-horizon radar,has received extensive attention since it was proposed.Severe radio frequency interference exists in the working frequency band of sky-wave OTH radar.Only relying on frequency selection to avoid the interference frequency band is no longer suitable for more and more complex interference environments.Therefore,this thesis focuses on the problem of RFI suppression of MIMO-OTHR.the main work and contributions of this thesis are as follows:(1)Principle and signal processing algorithm of MIMO-OTHRThis thesis establishes the MIMO-OTHR signal model and all-digital signal processing steps,including receiving beam forming,matched filtering,transmitting beam forming and Doppler processing,etc.Finally,simulation verification was carried out.(2)MIMO-OTHR waveform design based on mutual information in interference environmentThis thesis studies the RFI suppression of MIMO-OTHR from the perspective of waveform design.From the point of view of information theory,this method can make full use of the prior knowledge of the target,and maximize the mutual information as the optimization target.Under the constant modulus constraint and similar constraint,the MM algorithm is used to solve the problem.Simulation results show that the proposed algorithm has better output SINR performance than OFDM-LFM signal,and can control the range sidelobes to a certain extent.The advantage of this method is that it has good interference suppression capability and is suitable for scenes with high interference intensity.(3)MIMO-OTHR waveform design with low sidelobe in interference environmentAiming at the above-mentioned mutual information algorithm's unsatisfactory range sidelobe problem,a low sidelobe waveform design method is proposed in this thesis.This method takes the whitening filter as the receiver,directly optimizes the integrated sidelobe level(ISL)between the waveform and whitening filter,and also takes into account the output SINR performance.The optimization problem is solved by ADMM algorithm and MM algorithm respectively.The simulation results show that the designed waveform can effectively suppress the range sidelobes and is more conducive to target detection.The advantage of this method is that it has good range sidelobe characteristics and is suitable for the scene with low interference intensity.(4)MIMO-OTHR range sidelobes suppression based on filter designThis thesis studies the range sidelobe suppression of MIMO-OTHR in the interference environment from the perspective of receiving filter design.The receiving filter is designed to suppress the range sidelobe of the region of interest and maximize the output SINR.The range sidelobe is measured by PSL and ISL respectively.The optimization problem under the two constraints can be transformed into a quadratic constrained quadratic programming(QCQP)problem.For the ISL constraint,a solution with lower computational complexity is given.The simulation results show that the proposed method can suppress the interference while suppressing the sidelobes in the region of interest,and the range-Doppler processing results are given for the scene where the strong target sidelobe masks the weak target mainlobe.