Public safety networks. Analysis of the TETRA standard: history and evolution

Nowadays, public protection and disaster relief (PPDR) are widely used in all regions (cities and rural areas) because it brings essential characteristics like security and stability in the society and it secures environment to maintain law and order; besides, it is to protect the life and values of citizens. Due to this reason, it is also called public safety. It is used by firefighting systems, Emergency medical services, law enforcement, emergency and surveillance situation on land and air. To make a communication between the team members and among the teams, there should be a communication system with special characteristics that in harsh condition works without interruption. TETRA is one of the technologies that can satisfy public safety requirements. Due to its specific features, it is used widely not only in EU but also in other territories like Asia and south America. TETRA is a well-known TDMA two-way radio technology for digital voice and data. It was created by the European Telecommunications Standards Institute (ETSI). In early 1990s, ETSI started developing to address the limitation of existing analogue trunked services. The aim was to create a unified system to support voice over a digital technology for critical communications. The TETRA standard was completed in mid of 90s and released to the market in 1997. It supports different frequency bands and can make interoperability among them; also, it has no dependency on the vendors. It is used to meet critical communication requirements for public safety organizations such as police, firefighters, medical services and etc. it is known for robust architecture and secure communication through features like end-to-end encryption, group calling and data services based on narrowband PMR communications. An important point about TETRA is that it is similar to other public safety communication systems like project 25. Like other technologies, TETRA has a physical layer which defines how bits are transmitted over the air including aspects like frequency, modulation, bit rate, frame structure, and channel access. Also, the TETRA physical layer is built for efficiency, robustness, and reliability in critical voice and low-rate data communications. Due to robust modulation and error correction, resilient communication even in difficult radio conditions can be operated. One of the most important features of TETRA is the security and encryption mechanism which is one of the unique advantages of this technology. In TETRA, we have different security protocols that according to sensitivity and use case of the solution, they can be used. The encryption key is varied from 32 to 192 bits which makes the security algorithm so robust. Furthermore, each key is used for a specific use which makes this technology more flexible and robust in security terms. TETRA encryption algorithm (TEA) has 7 categories for different purposes in order to encrypt the communications (for voice and video). Moreover, Terminal Authentication Algorithm (TAA) is part of the mutual authentication process in TETRA’s Air Interface Encryption (AIE), which ensures that a TETRA terminal (radio) is legitimate and authorized to use the network; also, the network is verified by the terminal. This feature prevents unauthorized devices from accessing the TETRA network and blocks unauthorized base stations. This technology offers professional and regular call services for public safety use; besides, it can send messages and status updates. During a disaster the landlines and mobile