# An Overview of Emergency Communication Networks
## 1 Introduction
In the case of damage to public communication network facilities, and a sudden decrease in performance and increase in traffic volume, it is necessary to use a combination of unconventional and multi-communication means to restore communication capability. The important characteristics of emergency communication networks [11] are shown below:  
* Ability to work during both a disaster situation and at times of normality;
* Dynamic expansion of the network to provide more coverage;
* Accurately transmit disaster information and provide comprehensive services;
* Have high reliability, high redundancy, high safety, and high anti-interference capabilities. An emergency communication system comprises the integration and application of various communication technologies and approaches in an emergency. Therefore, the emergency communication system should make full use of mature communication technologies and network equipment, and integrate them into an extensible and reliable secure communication network. Generally, the emergency communication network uses the existing fixed wire network, the mobile cellular network [12], the Internet, and other public communication networks. Private communication networks, such as trunking communication networks [13], satellite communication networks [14; 15], and short-wave communication networks [16; 17; 18; 19], will also be used. In addition, public media networks are also used, such as radio, television, and newspapers, as well as on-site monitoring and rescue networks, such as sensor networks [20] and ad hoc networks [21; 22; 23; 24]. An emergency communication network is a heterogeneous network involving a variety of communication technologies, and its composition is diverse and dynamic. In recent years, through the study of public events and natural disasters, it has been found that the emergency communication platform needs to use the existing public networks or private networks to communicate [25; 26; 27], and the communication between rescue units at all levels needs to be interconnected. In order to solve the intercommunication problem of various emergency communication platforms, China proposed an integrated communication system based on the Internet protocol for the construction of a post-disaster emergency rescue communication platform [28; 29; 30]. Some researchers have proposed an interconnected communication solution that integrates satellite communication, 4G, and mesh technologies [31; 32]. At present, the emergency wireless private network is also evolving into the Professional Digital Trunking (PDT) narrowband digital cluster and B-TrunC broadband cluster private network. In addition, multi-system converged communication technologies such as fixed-mobile integration, narrowband convergence, and public-private network complementarity have also been proposed. In view of the characteristics of the 5G communication network, such as high rate, high reliability, low delay, and low power consumption, as well as the rapid development of networking technology [33], the integration of wireless ad hoc networking technology and 5G communication technology has gradually entered the field of emergency communication [34; 35]. The future emergency network will develop in the direction of integration, popularization, lower cost, mobile Internet integration, and space-air-ground-sea integrated networks [36; 37]. The new generation of emergency communication systems should integrate a variety of communication technologies, and ensure timely, efficient, and safe emergency communication services for rescue and disaster relief, major activities, and other work. Several survey articles in the literature consider issues related to the emergency communication network. [PERSON] et al. [38] investigated the existing emergency communication networks and big data analysis from the perspective of content and space. [PERSON] et al. [39] conducted a detailed investigation of wireless emergency response systems. [PERSON] et al.