# A Systematic Survey on 5G and 6G Security Considerations, Challenges, Trends, and Research Areas
## 3 5G Security Architecture: A Systematic Approach
### User Equipment  
#### 3.3.1 PHY Security  
The physical layer (PHY) of any network is the lowest layer of a typical protocol stack and is responsible for generating and interpreting electrical signals to provide a foundation for communication. This layer of the communication scheme needs to be standardized just like the layers above it in order to maintain the expected level of user experience. The 5G physical layer offers the latest technology within 5G modems to bring the best experience to consumers compared to previous cellular generations. As 5G promises higher data rates, lower latency, and more connection density, these devices need to be specialized more than ever. Security is also a top priority when considering the PHY layer. For example, PLS leverages special channel coding and random characteristics of the wireless channel to protect the confidentiality of the information exchanged between two partners [90] over what is inherently a broadcast medium. Coding acts as a form of data protection, rather than encryption, to allow for bit error recovery. In the scenario of an eavesdropper, which represents an illegitimate passive listener observing a communication channel, attempts are made to intercept and record or decode the physical signals. Depending on how close the eavesdropper is to the signal's origin, it may be possible for the eavesdropper to succeed in their efforts, opening the door to potential data exfiltration. Three ways to combat this scenario at the physical layer are listed in [90]: power control, beamforming, and clustering. For each of these methods, the authors assume that the presence of an eavesdropper is known to the communicating parties. Power control comes into play if an eavesdropper is identified in the region near a legitimate communication channel of a UE and the base station. Power control is a proposed method of heightening the confidentiality of 5G communications: when an eavesdropper is identified, the gNB and UE will reduce the power used in the radio link to lower the chances of the attacker being able to observe the signal. As stated in [90], this is a novel approach to solving this concern, and there has not been much development in making it become a reality. Beamforming is another tactic that can be used to circumvent unwanted listeners in a channel. Beamforming uses an antenna array and phase control of each constituent antenna's signal transmission in order to form a composite signal that, through phase alignment, is strong only in a specific and narrow direction while weak in all other directions [91]. Such highly directional transmissions make it very difficult for an eavesdropper to observe signals outside of a very narrow region, thereby protecting the communication and providing higher confidentiality. Beamforming also improves overall communication reliability by providing a better signal-to-noise ratio (SNR) for the legitimate channel. Physical layer security for 5G and beyond is also extensively covered in [92], where three 5G PLS solutions are presented: (1) a constellation rotation-based signal design for enhanced secrecy in D2D communications [93], (2) fine-grained security level characterization and statistical security guarantees for delay-sensitive services [94], and (3) Fountain Coding-aided security enhancements for IoT applications [95]. In the rotation-based scheme, the constellation of symbols is rotated to provide more protection from interference and also, in turn, improve the security of the D2D communications. The authors state that with the optimization of the constellation angle, an error floor can be created for the detection of non-intended messages while further improving transmission secrecy. The authors' proposed second method is meant to mitigate the success probability of eavesdropping in delay-sensitive operations. The authors introduce a new architecture for secure transmissions in 5G with fine-grained QoS requirements and integrated requirements on security, delay, sustainable traffic load, and reliability.