Liu Tianqu, Sun Jinping, Li Qing, Hao Zhimei, Wang Guohua
School of Electronics & Information Engineering, Beihang University, Beijing 100191, China.
Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, UK.
Sensors (Basel). 2021 Nov 19;21(22):7704. doi: 10.3390/s21227704.
The OFDM chirp signal is suitable for MIMO radar applications due to its large time-bandwidth product, constant time-domain, and almost constant frequency-domain modulus. Particularly, by introducing the time-frequency structure of the non-linear frequency modulation (NLFM) signal into the design of an OFDM chirp waveform, a new OFDM-NLFM waveform with low peak auto-correlation sidelobe ratio (PASR) and peak cross-correlation ratio (PCCR) is obtained. IN-OFDM is the OFDM-NLFM waveform set currently with the lowest PASR and PCCR. Here we construct the optimization model of the OFDM-NLFM waveform set with the objective function being the maximum of the PASR and PCCR. Further, this paper proposes an OFDM-NLFM waveform set design algorithm inspired by alternating optimization. We implement the proposed algorithm by the alternate execution of two sub-algorithms. First, we keep both the sub-chirp sequence code matrix and sub-chirp rate plus and minus (PM) code matrix unchanged and use the particle swarm optimization (PSO) algorithm to obtain the optimal parameters of the NLFM signal's time-frequency structure (NLFM parameters). Next, we keep current optimal NLFM parameters unchanged, and optimize the sub-chirp sequence code matrix and sub-chirp rate PM code matrix using the block coordinate descent (BCD) algorithm. The above two sub-algorithms are alternately executed until the objective function converges to the optimal solution. The results show that the PASR and PCCR of the obtained OFDM-NLFM waveform set are about 5 dB lower than that of the IN-OFDM.
由于其较大的时间带宽积、恒定的时域以及几乎恒定的频域模量，OFDM线性调频信号适用于MIMO雷达应用。特别是，通过将非线性调频（NLFM）信号的时频结构引入OFDM线性调频波形的设计中，得到了一种具有低峰值自相关旁瓣比（PASR）和峰值互相关比（PCCR）的新型OFDM-NLFM波形。IN-OFDM是目前具有最低PASR和PCCR的OFDM-NLFM波形集。在此，我们构建了以PASR和PCCR的最大值为目标函数的OFDM-NLFM波形集优化模型。此外，本文提出了一种受交替优化启发的OFDM-NLFM波形集设计算法。我们通过交替执行两个子算法来实现所提出的算法。首先，我们保持子线性调频序列码矩阵和子线性调频速率加减（PM）码矩阵不变，并使用粒子群优化（PSO）算法来获得NLFM信号时频结构的最优参数（NLFM参数）。接下来，我们保持当前最优的NLFM参数不变，并使用块坐标下降（BCD）算法优化子线性调频序列码矩阵和子线性调频速率PM码矩阵。上述两个子算法交替执行，直到目标函数收敛到最优解。结果表明，所获得的OFDM-NLFM波形集的PASR和PCCR比IN-OFDM低约5dB。
