## 3 Proposed Model and Problem Formulation  
### System Model  
The objective of this proposed model is to build an adaptive model to improve the performance of autonomous vehicle communication. Therefore, the proposed model, as shown in Figure 1, through the constrained optimization techniques, is capable to determine the best vehicle position to communicate with others or to relay the information to any destination. The decision of using direct communication or cooperative communication between AV2X will be taken based on the requirement QoS. Therefore, if the system requirement will be fulfilled within the transmission distance between AV2X, then AV will communicate directly to the destination. On the other hand, if the transmission distance between AV2X will affect the required QoS, then AV will communicate with the destination through relay-vehicle. The proposed model will be evaluated in terms of throughput, packet delivery ratio and packet loss rate, average delivery latency via a combined use of direct AV2X communications and cooperative V2V communications. Additionally, through the performance analysis vehicle mobility, vehicle density, vehicle speed and cooperation among vehicles and infrastructure are considered. Based on the proposed model, each autonomous vehicle conditions will decide, based on the environment, which best autonomous vehicle it should communicate with to efficiently obtain specific road information, send information to other autonomous vehicles or to send information to infrastructure with reliable and efficient connection. A vehicular network is considered, in which the infrastructure provides infotainment services to vehicles. The system consists of a road with four lanes and infrastructures located on each side, and the infrastructure is deployed with equal distance \(L\). The width of a lane is typically small compared with the transmission range of vehicles; it may range from 3.0 to 3.5 m for any road [27]. Each lane contains density of vehicles equal to \(\rho\) and the number of vehicles in each lane will be represented as:  
\[G=D.\rho \tag{1}\]  
where \(G\) is the number of vehicle and \(D\) is the road length. Besides, vehicles in each lane travel at the average speed of \(v\). Moreover, for road safety, the distance between any two consecutive vehicles must follow the 1-s or 2-s rule, where the driver should drive at least 1 or 2 s behind the vehicle in front during ideal conditions based on the rules of different countries [28]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Adopted Technique** & **Optimization Problem** & **System Evaluation Metric** & **Investigation Scenario** \\ \hline \multirow{3}{*}{[25]} & Multihop relaying into & & & Probability of Error. \\  & vehicular communication & & & Bit error rate. \\  & in highways. & & & Outage probability. \\ \hline \multirow{3}{*}{Proposed model} & Multihop relaying & Enhancing system QoS by & & Best relay-vehicle position \\  & between V2X, direct V2X & finding the optimum & & between AV2X. \\  & and V2V communications. & & & \(\bullet\) PDR. \\  & & & position to communicate & \\  & & with or to relay information & & \(\bullet\) Packet loss rate. \\  & & to any destination. & & \(\bullet\) Average delivery latency. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._  
the constraint that interference at any destination (\(I_{IX}\)) must be lower than the maximum required interference (\(I_{IXmax}\)). \(I_{IXmax}\) can be obtained from:  
\[SINR_{AVXmax}=\frac{P_{AV}|h_{AVX}|^{2}}{I_{IXmax}+N_{o}B} \tag{3}\]  
\[I_{IXmax}=\frac{P_{AV}|h_{AVX}|^{2}}{SINR_{AVXmax}} \tag{4}\]  
where \(SINR_{AVmax}\) represents the maximum required signal-to-interference-plus-noise for AVX link. \(P_{AV}\) and \(|h_{AVX}|^{2}\) represent the autonomous vehicle transmission power and the channel gain for the information of autonomous vehicle and everything, respectively. \(B\) is the channel bandwidth, and \(N_{o}\) denotes the power spectral density of AWGN.