The orthogonal time frequency space (OTFS) system with two-dimensional (2-D) modulation technique is an attractive technology to show the better performance than the conventional orthogonal frequency division multiplexing (OFDM) system, particularly in the high-speed vehicle communications and high-level dimensions of multiple-input multiple-output systems. However, the OTFS system has high peak-to-average power ratio (PAPR), like OFDM system. In this paper, we analyze the PAPR characteristics of the OTFS signal and propose a concept of discrete Fourier transform (DFT)-Spread OTFS system to reduce the PAPR efficiently. The key idea of the DFT precoding technique is to spread the energy of a subcarrier throughout the subcarriers. Therefore, the PAPR is decreased. In the practical wireless communication systems, the power efficiency could become worse, or the bit error rate (BER) is seriously degraded by the high peak signal power in a high power amplifier (HPA). So, by reducing the PAPR, the efficiency of the HPA can be significantly improved and the nonlinear distortion caused by HPA can be decreased, too. We evaluate the spectrum characteristics of conventional OFDM and OTFS schemes and the proposed DFT-Spread OTFS scheme according to the different nonlinear conditions of HPA. Simulation results demonstrate that the power spectrums of the proposed system are less sensitive than the conventional schemes in HPA nonlinear environments. In addition, we compare the uncoded BER performance among the different schemes over the AWGN and delay-Doppler channels according to the several HPA nonlinear conditions for the different mobility speeds of user equipment. The BER performance of the conventional OFDM system breaks down completely in high-mobility scenarios for both HPA linear and nonlinear conditions. The proposed scheme improves the BER performance over AWGN and delay-Doppler channels in HPA nonlinear environments, as compared to the conventional OTFS system. In high-mobility scenarios and at BER of \(1 \times 10^{ - 3}\), simulation results verify that the OTFS and our proposed scheme can achieve a gain of 12.8 dB compared to OFDM scheme. Moreover, the proposed DFT-Spread OTFS scheme can be reduced PAPR by 2.2 dB and 1.8 dB compared to OFDM and OTFS schemes, respectively.

具有二维（2-D）调制技术的正交时频空间（OTFS）系统是一种引人注目的技术，与传统的正交频分复用（OFDM）系统相比，它表现出更好的性能，尤其是在高速车辆通信和多输入多输出系统的高级维度。但是，与OFDM系统一样，OTFS系统具有较高的峰均功率比（PAPR）。在本文中，我们分析了OTFS信号的PAPR特性，并提出了一种离散傅里叶变换（DFT）-扩展OTFS系统的概念，以有效地降低PAPR。DFT预编码技术的关键思想是在整个子载波中扩展子载波的能量。因此，降低了PAPR。在实际的无线通信系统中，功率效率可能会变差，或者由于高功率放大器（HPA）中的高峰值信号功率而严重降低了误码率（BER）。因此，通过降低PAPR，可以显着提高HPA的效率，并且还可以减少由HPA引起的非线性失真。我们根据HPA的不同非线性条件，评估了常规OFDM和OTFS方案以及建议的DFT-扩展OTFS方案的频谱特性。仿真结果表明，所提出系统的功率谱在HPA非线性环境中不如常规方案敏感。此外，我们根据用户设备移动速度不同的几种HPA非线性条件，比较了AWGN和延迟多普勒信道上不同方案之间未编码的BER性能。对于HPA线性和非线性条件，在高移动性场景中，常规OFDM系统的BER性能会完全崩溃。与传统的OTFS系统相比，该方案改善了HPA非线性环境中AWGN和延迟多普勒信道上的BER性能。在高移动性场景中，BER为仿真结果验证了（1×10 ^ {-3} \），与OFDM方案相比，OTFS和我们提出的方案可以实现12.8 dB的增益。此外，与OFDM和OTFS方案相比，所提出的DFT-扩展OTFS方案可以将PAPR分别降低2.2 dB和1.8 dB。