# Review of Communication Technologies for Electric Vehicle Charging Management and Coordination
## 6 Physical Layer Security  
Due to the broadcast nature of wireless vehicular communication networks, particularly those utilized for enabling EV charging services, several security and privacy concerns are raised due to network vulnerability to various types of threats. These include eavesdropping, jamming, and spoofing attacks, as illustrated in Figure 5.  
As shown in Figure 5, eavesdropping occurs when an illegitimate entity, i.e., an eavesdropper, listens to the messages exchanged over the communication link between two legitimate nodes, typically between the vehicle and the infra  
Figure 5: Overview of the different physical layer security threats in a vehicular communication network. the other hand, not only listens to the wirelessly exchanged messages but also controls the communication channel between the legitimate users. Jamming attacks at the physical layer are analogous to denial-of-service (DoS) attacks at the application layer, where a jammer generates an intentional interference to disrupt and overload the communication channel between the vehicles, leading to throughput degradation and possibly broken connectivity. One of the most crucial requirements in vehicular communication is the security and privacy of the information shared between EVs and other network entities, to ensure protection against these different types of attacks. In wireless communications, security techniques can be categorized into: cryptographic methods and physical layer security (PLS) methods. Cryptographic methods are key-based methods that are typically applied at higher network layers to encrypt messages before transmitting them onto the wireless channel [104; 105; 106]. Nevertheless, with the high density and high mobility of vehicular networks and the heterogeneous network deployments discussed earlier, the management of different cryptographic keys becomes a challenging task [42; 107]. Accordingly, physical layer security (PLS) is gaining increasing interest, as it utilizes the inherent properties of the wireless channels, namely channel fading, noise, and interference to hide the content of messages exchanged over the wireless communication channel, thereby providing security to the users [43]. PLS techniques are also more suitable for delay-sensitive applications such as DWC systems, since they are typically implemented by simple, lightweight signal processing algorithms. In order to counteract eavesdropping attacks at the physical layer, channel-based adaptation techniques are adopted, in which the transmission parameters are adjusted to the channel characteristics of the receiver. These include beamforming, adaptive modulation, and adaptive power allocation [43]. mmWave beamforming is particularly useful to protect the channel against eavesdroppers, as it allocates narrow mmWave beams to the different legitimate users to degrade eavesdropping channels [108]. Furthermore, the integration of PLS with NOMA is considered in [107] as an approach to achieve secure spectrum sharing and protection against eavesdroppers. In addition, to avoid spoofing attacks, reciprocal channel properties such as channel state information (CSI) and received signal strength (RSS) can be utilized to authenticate the communication nodes [109]. Nevertheless, the high mobility of vehicular communications introduces rapid temporal variations to the communication channels, which increases the signalling overhead required to exchange CSI and other channel properties [96]. More effective resource allocation designs are hence required to acknowledge rapid channel variations while ensuring reliable information exchange over V2V communication links and providing protection against eavesdroppers and spoofing attacks. MIMO and spectral spreading techniques are the most commonly adopted PLS strategies to overcome jamming [88; 110].