## 1 Introduction  
As a critical component of future wireless communication networks, vehicle to everything (V2X) communication strives to meet stringent standards concerning the volume of connected devices, data rate, latency, and dependability [1; 2]. In 2018, the Third Generation Partnership Project (3 GPP) released the R15 standard [3], which mentioned the enhancement of long-term evolution-V2X (LTE-V2X), that is, under the premise of compatibility with R14 LTE-V2X, the delay performance, reliability performance, and transmission rate of LTE-V2X are further improved by reducing the resource selection window and adding transmission diversity and carrier aggregation. In 2020, 3 GPP officially froze the R16 standard [4], which defined the new ratio-V2X (NR-V2X) based on 5G. NR-V2X supports higher frequency shifts and bandwidth. Meanwhile, ultra-reliable low-latency communication (URLLC) can be achieved with the help of 5G, thus meeting the more advanced business requirements of vehicle formation, advanced driving, and remote driving. However, V2X channels differ significantly from traditional cellular channels [5]. Because of the relative speed, there may be a higher Doppler shift when communicating between users with high mobility. As a representative of multicarrier modulation techniques, orthogonal frequency division multiplexing (OFDM) [6] is widely employed in 4G/5 Gmobile communications due to its benefits of high data transmission rates, high bandwidth efficiency, and significant resistance to multipath fading [7]. In high-speed mobile scenarios, however, the Doppler effect caused by terminal and scatterer movement can seriously damage the orthogonality of subcarriers in OFDM, resulting in intercarrier interference (ICI) [8], which poses a significant challenge for channel estimation and equalization. As a result, creating new modulation waveforms and high-mobility communication techniques for next-generation wireless networks will be a major research area in the future. In recent years, orthogonal time frequency space (OTFS) has progressively become a hot research issue in academia due to its capacity to successfully offset the channel's Doppler effect and has been discovered to significantly outperform OFDM in doubly-selective channels [9; 10]. Furthermore, it inherits the same multipath resistance as OFDM and as a unique modulation scheme based on delay-Doppler (DD) domain, allows each symbol to experience the same channel gain even under high Doppler conditions. Simultaneously, OTFS can be implemented as a pre-processing and post-processing module of a filtered OFDM system, which not only allows for dense and flexible encapsulation of the reference signals to support the critical requirements in large antenna arrays in massive multiple-input multiple-output (MIMO), but also achieves compatibility with 4G and 5G system architecture [11]. Currently, there has been a lot of work to apply OTFS to complex scenarios, such as high-speed mobility. Ref. [12] employs OTFS modulation to construct a 5G-NR transmitting and receiving scheme that can be applied on unmanned aerial vehicles (UAVs) to perform accurate measurements of arrival time even in high-mobility scenarios. In addition, to address the challenges of high mobility in V2X systems, ref. [13] designs a new OTFS-based multi-antenna receiver. Due to the high resolution provided by multi-antennas, the channel sparsity in the delay-Doppler domain can be guaranteed. On this basis, a combined maximum proportion combination (MRC) OTFS iterative detection method is proposed, and the simulation results show the superiority of this scheme. All these prove that OTFS has the characteristics of anti-high Doppler. Despite the benefits of OTFS listed above, the DD-domain spreading of OTFS symbols generated by 2D channel convolution during transmission provides a significant barrier to channel estimate.