Research On OFDM MIMO Radar Waveform Design

OFDM MIMO radar is a kind of new radar combined OFDM technique and MIMO radar,which attracts broad attention since it was proposed.With the help of frequency diversity and waveform diversity,OFDM MIMO radar is able to improve radar performance in complex battlefield situations.A reasonable waveform design is a prerequisite for waveform diversity.Consequently,on the basis of OFDM MIMO radar waveform design,focusing on transmitter waveform single design and the transmitter-to-receiver joint design,the dissertation makes in-depth study at the issues about waveform design method with low peak-to-average power ratio,the waveform design method to suppress range sidelobe for target identification,and the joint design method of transmit waveform and receiving filter under clutter conditions for target detection.The main contributions are as follows:A waveform design method to suppress peak-to-average power ratio(PAPR)for improving transmitter performance is proposed.PAPR and autocorrelation function are jointly considered.First,a bunch of phase-coded-modulated waveform is constructed.On this basis,PAPR is utilized to establish the objective function,which is constrained by Maximum of Sidelobe Level and Coefficient of Variation of Envelope.Furthermore,the Sequential Quadratic Programming algorithm is adopted to solve the optimization problem.Theoretical analysis and simulation show that the proposed method has superior performance in PAPR suppression in the case of ensuring autocorrelation sidelobe,and it is insensitive to sequence length and initial sequence.A novel OFDM MIMO radar waveform design method with low range sidelobe in specified intervals is proposed for adjacent targets identification.Firstly,the Min-max algorithm and Integrated Sidelobe Level are utilized to establish the objective function,and constant modulus is the constraint.Then,the optimization problem is transformed into an unconstrained optimization problem and solved by BFGS/LBFGS algorithm.Simulation shows that the proposed method has remarkable performance in suppressing sidelobe near the mainlobe,fast convergence,low computational complexity.The optimized waveform is of certain value in practical application.In order to obtain better targets identification performance,an efficient waveform design method with high range resolution and low sidelobe level for OFDM MIMO radar is proposed.Firstly,wideband CP-based OFDM signal is transmitted on each antenna to guarantee large bandwidth and high range resolution.Afterwards,sidelobe suppression is expressed as an optimization problem for any of the antennas and can be solved to obtain optimal waveform.Furthermore,complex orthogonal design is utilized to acquire signals on other antennas in order to achieve code domain orthogonality among antennas and the spatial diversity can be obtained.Simulation demonstrates the performance superiority(high resolution,strict orthogonality and low sidelobe level)of the proposed method,and the desired performance can be achieved under different bandwidths and different initial sequences.Jointly optimization method of the transmit waveform and the receive filter is proposed to improve the target detection performance under clutter with the help of OFDM MIMO radar waveform and frequency diversity.First,the optimization model is constructed with the objective function of output signal-to-clutter-noise ratio maximization and the constraints of transmit power and peak-to-average power ratio.Then the optimization problem can be divided into two parts using cyclic iterative,and the optimal transmit waveform and receive filter can be obtained through Lagrange multiplier method,semi-definite relaxation,and randomization methods.Simulation shows that the gap between the output SCNR and ideal waveform is extremely low within 0.3dB,which is better than SQR and methods only design transmitter.Besides,PAPR constraint and sequence length hardly affect the performance.