# Performance Analysis of Existing ITS Technologies: Evaluation and Coexistence
## 2 Fundamentals and Related Work
### Previous Evaluation Work  
The assessment of ITS technologies (ITS-G5 and LTE-V2X) has been addressed in previous studies to enable vehicular networks. The approaches were mainly oriented as follows:  
* We have found several research studies on vehicular networks that address and evaluate the actual performance of vehicular communications technologies. These studies are related to analysis and compare the suitability of ITS technologies to  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Numerology**} & \multirow{2}{*}{**SCS**} & **Slots per** & \multirow{2}{*}{**Slots per Frame**} & **TTI** \\  & & **Subframe** & & \\ \hline
0 & 15 KHz & 1 & 10 & 1 ms \\ \hline
1 & 30 KHz & 2 & 20 & 0.5 ms \\ \hline
2 & 60 KHz & 4 & 40 & 0.25 ms \\ \hline
3 & 120 KHz & 8 & 80 & 0.125 ms \\ \hline
4 & 240 KHz & 61 & 160 & 0.0625 ms \\ \hline \hline \end{tabular}
\end{table}
Table 2: Supported numerologies in NR-V2X.  
Figure 2: NR-V2X time–frequency structure.  
support different performance keys [7; 8; 9; 10; 11; 12; 13], such as congestion situation, data rate, reception ratio, latency, etc.
* In addition, mechanisms and protocols used by each technology have been studied separately to propose the most appropriate configuration. In this context, the studies [14; 15; 16; 17; 18; 19] focus on the performance analysis of resource allocation parameters (at the PHY/MAC layers) considered by the SPS procedure in LTE-V2X technology. These studies were conducted under different scenarios to evaluate the effect of various parameters, such as selection and sensing window, transmit power, probability and reselection counter, etc. In addition, other works [20; 21; 22; 23; 24] propose performance evaluation of the direct communications using IEEE 802.11p (dedicated short-range communications (DSRC) or ITS-G5) to support application requirements under diverse situations such as communications range, data rate, congestion, etc.  
Therefore, the literature does not present a complete study that evaluates these ITS technologies' boundaries and capabilities. We consider that the assessment study remains open for the following reasons:  
* The diversification of use cases and their requirements;
* The variability of vehicular density with road capacity;
* The amount and kind of data exchanged according to the road environment perception;
* The limitation on simulation tools.  
However, this work intends to provide a comprehensive and complementary study to previous research. The objective is to establish a general evaluation model that simulates each technology's performance boundaries according to several constraints, such as density, range, PRR and delay. This approach identifies suitable configurations and the most appropriate technology for a given use case. The operating constraints of these use cases depend and vary based on the road infrastructure capacity and data exchanged. The aim is to assess ITS technologies according to their suitability to use case requirements. In addition, based on this model, we propose a co-existence solution between ITS technologies based on density-sharing for the required use case. Although this paper assumes that both technologies operate simultaneously in different frequency bands, their PHY/MAC layers parameters are not modified. Therefore, the channel selection mechanism is out of the scope of this present work.