# An Overview of Emergency Communication Networks
## 5 Sea Ad Hoc Network (SANET)
#### 3.1.4 Wireless Private Networks  
In the case of natural disasters and public security and other emergencies, due to the interruption of public communication networks or the inability to use public communication networks because of security reasons, it is often necessary to restore or supplement on-site communication in a short time using private networks. According to the technology used, emergency private wireless networks can be divided into five stages, namely, analogue cluster/conventional, narrowband digital cluster/conventional, 3G cluster, 4G broadband cluster, and 5G evolution. With digital wireless communication technology, digital cluster and conventional digital technology have been developed rapidly. PDT in China, Tetra and Digital Mobile Radio (DMR) in Europe, and P25 technology in the United States represent the narrowband digital cluster. As public network communication is evolving from 4G to 5G, digital cluster private networks are also gradually evolving in the direction of broadband multimedia [96]. 5G applications in the emergency industry will use 5G and artificial intelligence (AI) as the main approach and vigorously develop related applications. Wireless private networks, represented by digital trunking wireless communication systems, have the characteristics of high confidentiality, high reliability, and low service cost. They are mainly used in specific fields such as public security, fire protection, rescue services, and the petrochemical industry. Private network mobile communication systems include interphones, non-central digital systems, and trunking communication systems. An interphone is a two-way communication tool that is suitable for real-time communication, emergency dispatching, and collective cooperation. If natural disasters destroy the public network infrastructure, thereby preventing communication, the role of interphones will be more obvious. A trunked mobile system is a special dispatching communication system that is part of the advanced development stage of the private radio dispatching network. The system can dynamically, automatically, quickly, and optimally distribute the limited channels to all users of the system, so as to make maximum use of the channel frequency resources of the whole system. To date, an 800 MHz wireless trunking mobile communication system has been gradually established in various cities in China. Trunked mobile communication networks can be divided into two types: Public Access Mobile Radio (PAMR) networks and Private Mobile Radio (PMR) networks. To date, the commonly used standards in digital private communication include DMR, Digital Private Mobile Radio (DPMR), and PDT. The DMR standard adopts Time Division Multiple Access (TDMA) technology, supports single call, full call, group call, and selective call modes, and also supports direct mode communication without a base station. DPMA is a narrowband (6.25 KHz) Frequency Division Multiple Access (FDMA) technology that can provide various forms of voice/data applications. The PDT standard adopts TDMA multiple access mode and is based on the Chinese public security market. It not only supports low-cost single base station system communication, but can also achieve efficient regional coverage. While satisfying basic business requirements, it also adds innovative functions such as simulcast and dynamic frequency resource management. In earthquakes, wind disasters, fires, and other emergency events, the private communication network can quickly access the rescue dispatching platform, to realize flexible networking, efficient command and dispatching, high-quality voice and data transmission, and other functions. LTE is a long-term evolution technology based on 3 GPP.