Distributed Ledgers and Security Mechanisms on Radio Access Networks: A Systematic Review

5G is the most recent technology standard for cellular networks, and one of its key elements is the Radio Access Networks (RAN), which furthers the enabling of the 5G basic capabilities: enhanced Mobile Broadband (eMBB), Massive Machine-Type Communication (mMTC), and Ultra-Reliable, Low-Latency Communication (URLLC). To meet the capabilities required by 5G use cases, 5G is distributed, virtualized, and architecturally more complex than previous generations. These capabilities bring benefits but introduce risks and security challenges that must be addressed through controls designed to support and secure 5G services across any operator cloud. Therefore, this paper focuses on studying and evaluating security mechanisms used in RANs. Special attention is given to Distributed Ledger Technologies (DLTs) since they are one of the most studied topics regarding security enhancement. DLTs could bring advantages for improving network security through encryption to protect the information and automate verification and execution of transactions. For this reason, we carried out a systematic review, extracting and analyzing data from 39 papers from 2010 to 2023. Our main results list RAN-related susceptible security dimensions, vulnerabilities, and possible attacks and threats. We also show how DLTs can enhance RANs and present other considered mechanisms to increase RAN security.