## 4 Numerical Results and Discussion  
In this section, the performance of the proposed model is evaluated through Matlab and NS-2 software simulation package in terms of best inter-vehicle position, and optimum transmission distance between V2X and V2V, to enhance the system reliability and efficiency which is presented by throughput, packet delivery ratio and packet loss rate. The proposed approach is also examined in terms of average delivery latency. In the simulation model, all vehicles keep the same distance between each other. Additionally, the 2-s rule is followed [28] for road safety and for stopping in time to avoid collision and reducing the rate of accidents. This rule does not always come with specific distances that must be observed, but the general rule is that each driver must keep sufficient distance between his/her vehicle and the vehicle in front. This required minimum distance or time between the vehicles should be two seconds in order to avoid an accident if the car in front stops suddenly or reduces speed. For example, if a driver is driving a car with a speed of 40 km/h, then the minimum safety distance between his/her vehicle and the front vehicles must be approximately 23 m.  
For the mobility generation, mobility-files in NS-2 have been built. In addition, to evaluate the system performance, some information is required to be extracted from the simulations. Hence, an AWK script was implemented to extract these metrics from the trace files generated during the simulation using NS-2. Moreover, in the suggested scenarios, all vehicles are running at an average speed which is 60 km/h, the lane width in the road is 3.5 m, and the distance between two consecutive vehicles is approximately 34 m based on the 2-s rule. The network parameters used for simulation are listed in Table 2.  
Figure 3 depicts the best position of the relay-vehicle versus the distance between AV2X at various QoS requirements. As can be observed, when the transmission power increases, especially with high \(SINR_{th}\), the distance between the relay-vehicle and the destination must decrease to fulfill the system requirements. In addition, it can be noticed that when the transmission distance between AV and X is less than or equal to 50 m (\(d_{AVX}\leq\) 50 m) \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Value** \\ \hline _No_ & \(-\)174 dBm \\ \hline \(B\) & 10 MHz [26] \\ \hline _Rs_ & 1 bit/s/Hz \\ \hline _PVmax_ & 23 dBm [26] \\ \hline _Packet size_ & 512 bytes \\ \hline _fc_ & 5.9 GHz \\ \hline \(a\) & 3 \\ \hline _Simulation time_ & 1000 s \\ \hline _Node_ & 5-100 \\ \hline _Speed_ & 20–70 km/h [22] \\ \hline _Traffic agent_ & TCP \\ \hline _Queue_ & PriQueue with size of 50 packets \\ \hline _Propagation mode_ & Two Ray Model \\ \hline _Antema_ & Omni-directional with height of 1 m \\ \hline _Routing Protocol_ & DSRC \\ \hline _Number of seed_ & 3 \\ \hline _Noise_ & AWGN \\ \hline _\(\rho_{max}\)_ & 100 vehicle/km \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation parameters. there is no need for a cooperative link with different required QoS. It also means that, at this transmission distance, the best relay-vehicle position from the destination is zero or less than 1 m, which means that the relay-vehicle position will be at the destination. Thus, in that case, the direct communication will be the efficient way for communication between AV2X. Additionally, it can be shown that increasing the transmission distance between AV and X increases the need for cooperative communication.