## 2 Literature Review
If the optimum position of the relay-vehicle is at the destination, then AV communicates directly to the destination, otherwise AV communicates with the destination through the relay-vehicle. This enhances the overall vehicular system performance, while at the same time decreases the amount of infrastructure needed by adapting the connection through AV2V and AV2X. The proposed method aims to improve the reliability and the efficiency of the connectivity either between AV2X or AV2V. Different scenarios are investigated during simulation to assess and evaluate the performance of the proposed approach in terms of throughput, packet delivery ratio, packet loss rate and average delivery latency. The proposed approach is evaluated by five different benchmark metrics which are not all commonly utilized in one specific research paper. Hence, related researches [12; 22] are considered for comparison with the proposed model. The proposed model shows how to achieve the optimized required vehicular communication performance through choosing the best inter-vehicle position. The position will be determined based on different environmental conditions to satisfy a required QoS. Table 1 shows the novelty of the proposed model compared with other related research articles. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline  & **Adopted Technique** & **Optimization Problem** & **System Evaluation Metric** & **Investigation Scenario** \\ \hline
[12] & Cooperative communications for a combined V2V with V2V approach. & Minimizing the total energy consumed per bit given an outage probability target, or maximizing the end-to-end throughput. & Energy consumption. Throughput. Packet delivery ratio. Packet loss rate. Average end-to-end-delay. & Direct V2I communication. Multihop V2I communication. Cooperative V2I communication. \\ \hline
[13] & Cooperative communication for a combined use of V2I and V2V. & Maximizing average data rate. & Capacity achieved. & Vehicles assist the transmission between V2I. \\ \hline
[15] & Cooperative caching approach with mobility prediction in vehicular named data networking. & N/A & \(\bullet\) Average access delay. Average hit distance. Average request ratio. Average hit ratio & Communication among vehicles using intra-cluster and inter-cluster communication over vehicle clusters. \\ \hline
[16] & Implicit cooperative positioning algorithm exploits the V2V connectivity. & N/A & The vehicle location accuracy. & Direct communication between V2V and between neighbors such as people, traffic light and vehicles. \\ \hline
[17] & Cooperative communication between V2V. & Optimization power allocation strategy. & Outage probability. & Communication among vehicles through cluster heads. \\ \hline
[18] & Cooperative adaptive cruise control (CACC). & N/A & \(\bullet\) Distances between V2V. Velocity. Tracking error. & Direct communication between V2V. \\ \hline
[20] & Clustering algorithms. & Platoon-optimized clustering. & \(\bullet\) Connectivity probability. Average platoon size. Spacing difference. Speed. & Direct communication between V2V. \\ \hline
[21] & Sectorised relay-assisted V2V communications. & N/A & \(\bullet\) PDR. Average PDR. Average packet reception rate. & Direct communication between V2V. Omnidirectional relay-assisted V2V communications. \\ \hline
[22] & Relaxed approximation-based SDP. & N/A & \(\bullet\) PDR. Average delivery latency. Overhead ratio. & Direct communication between V2V and between vehicles to roadsides. \\ \hline
[23] & Massive multiple-input multiple-output (MIMO). & N/A & \(\bullet\) Bit error rate. Processing time. & Direct communication between V2V and between vehicles to roadsides. \\ \hline
[24] & Non-orthogonal multiple access technique. & N/A & \(\bullet\) System power control. Throughput. User fairness. & Communication between V2I using relay-vehicles. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison between different related works and the proposed model.