OFDM wavefroms designed with piecewise nonlinear frequency modulation pulse for MIMO radar

Multiple-input multiple-output (MIMO) synthetic aperture radar (SAR) waveform diversity design has drawn extensive attention since it has a great potential in remote sensing. The orthogonal frequency-division multiplexing (OFDM) waveform designing becomes one of the most significant tasks in MIMO SAR system. In this article, a novel piecewise nonlinear frequency modulation (NLFM) waveform is proposed. The OFDM waveform is composed of the piecewise NLFM waveforms as its subpulses, and each subpulse has a different subcarrier beginning frequency. The subpulse is centre symmetrical and can be divided into three segments. The first and third segments of the subpulse are linear frequency modulation waveforms, and the second segment of the subpulse is an NLFM waveform. A few parameters are used to control the duration and bandwidth of each segment in the subpulse. Genetic algorithm is used for the OFDM waveforms to optimize the sidelobes of autocorrelation and cross-correlation function. Compared with other OFDM waveform design methods, the proposed method is more flexible and has higher degrees of freedom and thus can yield waveforms with a better autocorrelation and cross-correlation properties. The performances of ambiguity function and cross ambiguity function are analysed to have low time delay and Doppler correlation peaks. Simulation results demonstrate the validity of the proposed method.