## 2 Vehicular Networks
### Cellular-Based Networks  
The Third Generation Partnership Project (3 GPP) introduced cellular-V2X (C-V2X) in Release 14 [24]. The use cases of the ITS spectrum in various countries per government standardization is presented in [25; 26]. A simulation model of the Third Generation Partnership Project (3 GPP) Release 14 Cellular Vehicle-to-Everything (C-V2X) sidelink, upon which 5G New Radio mode 2 was based, is presented in [27]. To support V2X communications, C-V2X Mode 4 modifies the PHY and MAC layers of the LTE sidelink [28]. In high mobility situations, LTE's PHY layer is designed to improve performance. The sensing-based semi-persistent scheduling (SB-SPS) mechanism is implemented at the MAC layer to autonomously select vehicle resources. In [29], to support beacon broadcasting over V2V networks, a distributed network coding MAC protocol (NC-MAC) is proposed. By combining re-transmission, network coding, and preamble-based feedback mechanisms, reliability is improved. In various situations, \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Country** & **Standards** & **Frequency Range (GHz)** & **Data Rates (Mbps)** & **Modulation** \\ \hline US & WAVE & 5.80–5.925 & 6–27 & OFDM \\ \hline Europe & ITS/G5 & 5.85–5.905 & 6–12 & 2 ASK/2 PSK \\ \hline China & C-V2X & 5.905–5.925 & 100 & QPSK/16 QAM/64 QAM/256 QAM \\ \hline Japan & STD/T5 & 5.770–5.880 & 1, 4 & 2 ASK/QPSK \\ \hline Korea & DSRC & 5.895–5.905 & 9, 12, 18, 24, 27 & QPSK/BPSK/2 ASK \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Vehicular communication standards. including highway and urban, simulations demonstrate the performance gains obtained from the NC-MAC protocol compared with the 5G cellular vehicle-to-everything (C-V2X) MAC protocol. The DSRC protocol uses a random back-off scheme to propagate data between MAC and PHY, which causes the inter-layer data propagation delay. However, it remains within microseconds. Rate control is therefore directly proportional to end-to-end latency. The C-V2X MAC, however, can introduce a time offset (on average 50 ms) when translating a packet because of semi-persistent scheduling (SPS) operations [30]. As a part of the C-V2X communication, other technologies such as radar, cameras, and in-vehicle sensors support services such as semi-autonomous driving, autonomous driving, and assisted driving in these vehicles. In addition to better coverage and lower deployment costs, V2X services can be run on a dedicated network using the 5G public network, which offers high QoS features with its flexible network design, including ultra-fast data throughput and ultra low latency [31]. Release 14 of C-V2X released in March 2017 included the first version of the tool. The automotive vertical needs were addressed by a specification called LTE-V2X, which was created in conjunction with the development of the 4G LTE system. As a part of the LTE V2X revisions since Release 15, the 3 GPP has begun looking at the 5G specification for 5G-V2X. NR V2X specifications defining the sidelink, which are integrated with the 5G-V2X specifications defined in Release 16, in June 2020. The sidelink 5G-V2X standard will be improved in Release 17, which is still undergoing testing and is scheduled for release in 2022 [32]. The framework of 5G is based on the fourth-generation LTE mobile standard. Unlike 4G signals, 5G signals are transferred over short distances through a plethora of small, low-power base stations that can be located on light holes or rooftops. This is the primary difference between 5G and 4G signals. Since the new 5G mobile generation uses the low-frequency spectrum to transmit signals, the mobile network structure was built via radio operators. With 5G, signal transmission is virtually unaffected by the weather, building obstructions, or distance. The previous generation of wireless communications worked in a low-frequency spectrum band, so millimeter-waves [33] have to deal with interference and distance challenges that were not present during the last era.