# An Overview of Emergency Communication Networks
## 4 Discussion  
When natural disasters occur suddenly, the original public communication network facilities can be destroyed. In order to ensure the smooth development of emergency rescue work, it is necessary to quickly establish a temporary emergency communication network. Emergency communication refers to the means and methods of communication required for the comprehensive utilization of various communication resources to guarantee rescue, including emergency rescue, and the necessary communication when natural or man-made emergencies occur. Realizing the emergency rescue function is a basic condition, and its network structure will seriously affect the rescue efficiency. Emergency communication networks are characterized by uncertainty of time and place, unpredictability of communication demand, urgency of business, flexibility of application, rapidity of network construction, and brevity of the process. Emergency communication networks provide timely and effective communication support for all kinds of emergencies, and are an essential part of the comprehensive emergency support system. Emergency communication networks are heterogeneous networks involving multiple communication technologies. According to the time, place, and damage degree of the infrastructure network, the network composition is uncertain, diverse, and dynamic. At present, emergency communication technologies mainly include satellite communication technology, wireless ad hoc network technology, cellular mobile communication technology, and wireless private network communication technology. Table 7 describes the features of various emergency communication technologies in terms of six aspects: characteristics, advantages, disadvantages, existing schemes, application scenarios, and development directions. The satellite communication system has the advantages of large communication capacity, low bit error rate, flexible networking, high communication quality, and wide coverage, and has the disadvantages of high cost, high latency, and communication blind spots. At present, the implemented schemes include VSAT, Inmarsat, Starlink, Tiantong-1, and BeiDou, which are mainly applied in the fields of personal positioning, marine ecological environment protection, and meteorological disaster prediction. In the future, these technologies will mainly develop in the direction of miniaturization, lower cost, and hybrid networks. The wireless ad hoc network has the advantages of flexible networking, wide network coverage, self-organization, self-healing, self-balancing, high network reliability, and high scalability, However, it experiences high delay and has limited bandwidth capacity. Existing technologies include WMN, MANET, VANET, FANET, and SANET, which are mainly used in mine emergency rescue, fire protection, earthquake, military communication, and marine surveillance scenarios. These technologies will move towards miniaturization, low attenuation, low bandwidth, portability, and hybrid networks. Cellular mobile communication has the advantages of unrestricted distance, wide coverage area, and low cost. At the same time, it is insufficient in terms of stability and anti-jamming capability. The technologies currently used include D2D, 5G, and 6G, which can be applied in the military, medical treatment, security, household, transportation, and construction fields. In the future, it will be necessary to improve their coverage and communication capacity through hybrid networks. Wireless private network communication technology has high reliability and high security, but also has a high cost and small communication capacity. The technologies currently used are mainly PDT, DMR, DPMR, P25, PMR, LTE, and TETRA, which are widely used in the public security, fire protection, rescue, petrochemical, and earthquake response fields. In the future, different technologies will need to unify standards and develop in the direction of fixed-mobile integration, broadband-narrowband integration, and public-private completion.