# A Robust Timing Synchronization Algorithm Based on PSSS for LTE-V2X
## 6 Conclusions  
In this paper, we proposed a robust symbol timing synchronization algorithm based on the PSSS for the LTE-V2X communication scenario. Initially, we conducted an analysis of the advantages and disadvantages of existing timing synchronization algorithms. Building upon this analysis, we introduced an improved symbol timing synchronization algorithm, comprising three key steps: coarse synchronization, frequency offset estimation and fine synchronization. By integrating algorithms, designing decision thresholds and compensating for frequency offset, the proposed approach effectively enhances the algorithm's robustness in scenarios characterized by high frequency offsets and low SNRs. The simulation results demonstrate the superior performance of the improved algorithm compared to traditional methods such as cross-correlation, block cross-correlation and selective summing, particularly under conditions of high frequency offsets and low SNRs. In an AWGN channel with a normalized frequency offset of 1, the improved algorithm achieves a detection accuracy of 90% at \(-\)14 dB and 100% at \(-\)10 dB, meeting the stringent detection requirements for vehicular networks. This solution presents an effective approach to symbol timing synchronization in LTE-V2X. Furthermore, we constructed a hardware-in-the-loop simulation platform to comprehensively compare and analyze the performance of the improved algorithm and existing algorithms under various vehicle speeds and scenarios. In high-speed moving scenarios, such as Urban-NLOS and Highway-LOS, the improved algorithm exhibits outstanding PSSS detection performance. Even under challenging low SNR conditions, the CDR of the improved algorithm consistently surpasses that of other algorithms. Figure 14: Comparison of improved and traditional algorithms in Urban-NLOS. (a) 0 km/h. (b) 50 km/h. Regarding future work, based on the research outlined in this paper, further investigations can be pursued in the following three aspects:  
1. Refinement of frequency offset estimation algorithms: Although this paper achieved coarse estimation of the frequency offset using a semi-symbol-based frequency offset estimation algorithm, there remains room for improvement. The inherent \(\pm N\) error between the coarse synchronization point and the ideal synchronization point introduces a certain level of error in the frequency offset estimation. Therefore, future efforts should focus on exploring and developing more accurate frequency offset estimation algorithms to obtain precise frequency offset values. 2. Enhancement of the SSSS detection algorithm: This paper primarily focused on researching and improving the primary synchronization signal detection algorithm. However, since the detection performance of the primary synchronization signal significantly influences overall synchronization signal detection, future work could delve into the development of a robust detection algorithm for secondary synchronization signals. Enhancing the algorithm to detect the SSSS can contribute to an overall improvement in synchronization signal detection performance. 3. Symbol timing synchronization algorithm for 5G NR-V2X: NR-V2X has evolved from LTE-V2X, with the time-frequency resource definition for NR-V2X, having a subcarrier spacing of 15 kHz, being essentially similar to LTE-V2X. The difference lies in the fact that, in LTE-V2X, a 1 ms subframe contains two slots, and each time slot comprises 7 symbols. However, in NR-V2X with a subcarrier spacing of 15 kHz, a 1 ms subframe contains one slot, and the time slot consists of 14 symbols. Similar to LTE-V2X, the sidelink D2D link is also utilized in NR-V2X systems. Therefore, existing synchronization algorithms still hold reference value for NR-V2X. However, to support advanced applications (autonomous driving, vehicle platooning, etc. ), NR-V2X introduces some new features, such as a flexible frame structure and the use of m-sequences to generate primary synchronization signals instead of ZC sequences.