太赫兹频段OFDM一体化波形的雷达探测性能分析

Radar performance analysis of OFDM-based jointed radar and communication waveforms in the terahertz band

摘要:

传统的正交频分复用(OFDM)信号在太赫兹通信系统中通常会面临峰均功率比(PAPR)过高的问题，严重降低功率放大器的效率，恶化太赫兹链路的非线性效应。恒模雷达-通信一体化波形可以抑制PAPR的影响。本文采用模糊函数作为评价标准，从距离和速度两方面分析和比较了太赫兹频段正交频分复用-16阶正交幅相调制-线调频(OFDM-16QAM-LFM)、正交频分复用-二进制相移键控-线调频(OFDM-BPSK-LFM)、正交频分复用-最小相移键控-线调频(OFDM-MSK-LFM)3种OFDM一体化波形的雷达探测性能。数值仿真结果表明，OFDM-16QAM-LFM波形在太赫兹频段的距离和速度探测性能良好，但PAPR过高；OFDM-BPSK-LFM、OFDM-MSK-LFM波形采用相位调制代替幅度-相位调制，保持恒定包络特性；OFDM-BPSK-LFM一体化波形的距离分辨力不会随着子载波数量增加而恶化，但速度分辨力随着子载波数量的增加而受到很大影响，不适宜用于高速运动状态下多目标的速度检测；OFDM-MSK-LFM波形可承载更多的子载波，适应复杂场景下的多载波雷达探测需求。本文方法为不同应用场景的一体化波形选择提供了参考。

Abstract:

Traditional Orthogonal Frequency Division Multiplexing(OFDM) signals in terahertz communication systems usually bring about high Peak to Average Power Ratio(PAPR) problems that would seriously degrade the power amplifier efficiency and deteriorate the nonlinear effect of terahertz link. The design of constant-envelope OFDM based Integrated Sensing And Communication(ISAC) waveforms can suppress the harmful effects of high PAPR. The Ambiguity Function is used as the criteria for the range and velocity performance evaluation of three OFDM-based ISAC waveforms in the terahertz bands, namely, OFDM-16QAM(16-Quadrature Amplitude Modulation)-LFM(Linear Frequency Modulation), OFDM-BPSK(Binary Phase Shift Keying)-LFM, OFDM-MSK(Minimum Shift Keying)-LFM. The numerical simulation results demonstrate that, OFDM-16QAM-LFM waveform has excellent range-velocity performance but serious PAPR problems. OFDM-BPSK-LFM, OFDM-MSK-LFM waveforms replace the amplitude-phase modulation with phase modulation, thus maintaining constant-envelope characteristics. The range detection capability of OFDM-BPSK-LFM waveform does not degrade with the increase of subcarriers, while the velocity detection capability is seriously affected. Therefore OFDM-BPSK-LFM waveform is not suitable for the velocity detection of fast-moving objects. OFDM-MSK-LFM waveform can tolerate more subcarriers, making it suitable for multi-carrier radar detection under complex circumstances. This work provides references for the choice of ISAC waveforms in different application scenarios.