# Physical Layer Authentication in Wireless Networks-Based Machine Learning Approaches
## 2 Related Works and Motivation
### Related Review Studies on Physical Layer Security and Authentication  
[PERSON] et al. [25] explored security issues related to the physical layer in cognitive radio networks. They also gave an overview of several existing security attacks and surveyed the related countermeasures on how to defend against these attacks. However, the study did not propose an SLR, and the number of papers included in the literary survey was only eight. [PERSON] et al. [4] provided a comprehensive overview of the fundamentals and technologies of PLS. Further, they discussed the challenges and solutions in different PLS technologies, ranging from wiretap coding, secure signal processing, and physical layer key generation to physical layer authentication. In this survey, sources published before 2016 and recently published papers were not mentioned.  
While [PERSON] et al. [2] investigated research subjects on the system designs of physical layer security and reviewed deep insights into performance metrics and fundamental optimization problems, the emerging development of future wireless technologies has brought new security challenges for 5G networks. [PERSON] et al. [3] and [PERSON] et al. [26] provided surveys summarizing the latest research results on physical layer security for several promising 5G technologies, including heterogeneous networks (HetNet), massive multiple-input multiple-output (MIMO), non-orthogonal multiple access, physical layer security coding, millimetre-wave (mm-wave) communications, and full-duplex (FD) technology, and the fundamental concepts of each technology. As the number of IoT devices expands and new industries utilize IoT technologies, the need for IoT security will rise. Thus, [PERSON] et al. [27] explored some IoT communication protocols and recent developments in PLS techniques and solutions that use beamforming, spread spectrum coding, and radio frequency (RF) fingerprinting. However, since the research approach was not systematic, the method of selecting research papers and their time range are unidentified.  
Multiple survey papers point to physical layer authentication as a promising technique in wireless security communications. [PERSON] et al. [28] provided a comprehensive review of the domain of PLA in wireless communication systems, including the concepts and frameworks of key-based/less PLA systems and common attack models. In addition, [PERSON] et al. discussed key techniques applied in PLA systems. [PERSON] et al. [29] provided an exhaustive survey of features and techniques used in PLA, categorizing existing PLA schemes into passive and active and presenting the significant differences between the two categories. The research was recently published, but a systematic approach had not been considered. Recently, machine learning has appeared as a promising tool for reducing the increasing complexity of wireless networks. The integration of ML and PLS has also enticed some research interest. [PERSON] et al. [10] reviewed physical layer authentication, antenna selection, relay node selection, and integration with ML, and [PERSON] [30] presented reviews of PLA schemes using machine learning for the 5G-based IoT. They also compared PLA schemes. Aside from comparisons between PLA schemes, they examined machine learning techniques used in intrusion detection, access control, and anomaly detection to provide other security advantages in the 5G-based IoT. [PERSON] et al. [31] provided a comprehensive review of the security challenges of radio-frequency wireless systems in industrial. [PERSON] et al. also presented physical layer attack families and countermeasures, including a discussion on the effectiveness of the described solutions.