# Review of Communication Technologies for Electric Vehicle Charging Management and Coordination
## 5 5G Technology Integration  
In order to satisfy the different requirements of vehicular networks, a multi-tier heterogeneous network that integrates different vehicular communication technologies is recommended by [50; 83; 84; 85] such that it integrates different network technologies including mmWaves, D2D [86], massive MIMO [87; 88], and software-defined networks (SDN) [89] to meet the communication requirements of different use cases. In these hybrid networks, the architecture can be arranged in a hierarchical or flat manner. In hierarchical architectures, each entity in the network belongs to a hierarchical level, and a specific technology is used for communication between the entities in different levels and a group of entities at the same level [90; 91]. Alternatively, in flat architectures, the communication between the nodes is selected based on the type of data being transmitted or other performance metrics [92; 93]. Accordingly, a multi-tier 5G network is proposed in [94] to support vehicular communication, and the proposed network model is a HetNet that incorporates D2D communication, mmWaves, and a cloud platform. mmWave frequencies provide gigabits-per-second (Gbps) data rates for vehicular communication links and allow efficient spectrum utilization for both V2V and V2I communications [95]. The small wavelengths at mmWave frequencies enable a large number of antennas to be packed in a small form factor, forming a massive MIMO communication network [96]. This generates multiple highly directional beams that compensate for the severe propagation losses at mmWave frequencies while offering the Gbps data rates. In addition, SDNs offer new network architectures with flexible programming and powerful network control capabilities. Due to these characteristics, some researchers suggested integrating SDNs into vehicular ad hoc networks (VANET) such that the SDN controller can optimize \begin{table}
\begin{tabular}{l l l} \hline \hline
**Parameters** & **Rel.14 C-V2X** & **Rel.16 NR-V2X** \\ \hline Frequency bands & LTE bands & sub-6 GHz and mmWave \\ Subcarrier spacing & 15 kHz & sub-6 GHz: 15, 30, and 60 kHz \\  & & mmWave: 60, 120 kHz \\ Retransmissions & Blind & HARQ \\ Waveform & SC-FDMA & OFDM \\ Modulation scheme & QPSK, 16-QAM, 64-QAM \\ Communication types & Broadcast & Broadcast, multicast, and unicast \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison between specifications of LTE C-V2X and 5G NR-V2X [56]. \begin{table}
\begin{tabular}{l l l} \hline \hline
**Parameters** & **IEEE 802.11p DSRC** & **IEEE 802.11 bd DSRC** [56]. \\ \hline Frequency bands & 5.9 GHz & 5.9 GHz \& 60 GHz \\ Subcarrier spacing & 156.25 kHz & 78.125 kHz, 156.25 kHz \& 312.5 kHz \\ Retransmissions & None & Congestion dependent \\ Waveform & OFDM with BCC & OFDM with LDPC \\ Modulation scheme & QPSK & QPSK, 16-QAM \\ Communication types & Broadcast & Broadcast \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison between specifications of IEEE 802.11p and IEEE 802.11 bd DSRC [56]. vehicle routing decisions, spectrum management, and network research management [97]. Furthermore, other researchers propose a vehicular-SDN (SDN-V) architecture [98] that provides better performance compared to conventional routing protocols of VANET in terms of PDR, delay, and network throughput. With the massive data exchange expected in an IoEV with different charging modes and requirements, quasi- and non- orthogonal multiple access (NOMA) techniques are proposed to meet the demand of spectrally efficient 5G vehicular communications in high density networks [99; 100]. This is because NOMA allows each resource block to be simultaneously utilized by multiple users, thereby enabling more vehicular connectivity. The authors in [101] propose a cooperative, relay-assisted NOMA to mitigate traffic congestion and reduce latency in C-V2X communications, particularly for broadcast and multicast messages.