## 1 Introduction
### Related Work  
An early investigation [5] focuses on the co-channel interference in the presence of periodic or non-periodic traffic generation; the former applies, for example, when the Society of Automotive Engineers (SAE)'s basic safety messages (BSMs) or the ETSI cooperative awareness messages (CAMs) under specific conditions are assumed, whereas the latter applies, for example, when CAMs are considered in more general cases where the vehicle movements (specifically variations of direction, speed, and acceleration) cause the packet generation interval to vary between 100 ms and 1 s [6; 7]. The results show that without any mitigation methods applied in the co-channel coexistence scenario, periodic packet generation is preferable to non-periodic traffic in terms of the packet reception ratio (PRR) performance for both technologies. This is because, with periodic traffic, the LTE-V2X could predict more accurately which resources would be accessible in the near future and mitigate the packet collision between these two technologies. The possible benefit of co-channel coexistence mitigation methods for reducing performance loss is then suggested through early simulations in [8].  
Later, as required by the CEPT, the feasibility of co-channel coexistence between ITS-G5 and LTE-V2X was investigated by the ETSI [4] and several solutions (Method A\(\sim\)F as mentioned above and briefly described in the following) were introduced, which are all based on the superframe structure to separate the two technologies into different time domains. The simulation results together with the sub-work in [9] suggest that \"Method A and Method C are the two most promising approaches for co-channel coexistence between ITS-G5 and LTE-V2X\". Following this report, a white paper [10] scrutinizes in detail those proposed methods. After confirming that without any mitigation methods, the performance of both technologies degrades significantly due to mutual interference, the white paper confirms the results conducted in [4] that some variants of A and C are preferable to other methods, considering the performance or the implementation complexity. A simplified version of Method C was also proposed later in [11], showing similar or better performance to the original solution, but with a simpler implementation that does not require the use of what are called superframes (see Section 3).  
A comparison of selected methods was also provided in the white paper [12], varying the packet size, packet generation period, and vehicle density. The simulation results show that the large packet size (1000 bytes) and the high-density scenario would degrade the performance, especially for Method A. It also concludes that the simplified version of Method C presented in [11] is \"the best all-rounder\" solution for co-channel coexistence compared with the others.  
Apart from the mentioned papers, a few others discuss coexistence scenarios in which two ITS technologies are allocated in different channels, e.g., with vehicles that use both technologies to transfer and relay packets from one technology to the other [13], or assuming that every vehicle uses two technologies simultaneously [14]. These works assume separate bands for the two technologies and vehicles equipped with both of them, which are assumptions not considered in this paper. In particular, in this paper we assume the following:  
* Each vehicle is equipped with one of the two technologies, which are IEEE 802.11p and NR-V2X;
* All stations share the same channel and therefore potentially interfere with each other;
* Without loss of generality, we focus on vehicles only (and not road side units).