# An Overview of Emergency Communication Networks
## 5 Conclusions  
In contrast to traditional communication networks, emergency communication networks are characterized by their fast communication speed, non-fixed communication location, and high flexibility; these advantages can effectively make up for the deficiency of the communication network. Establishing an emergency network is a prerequisite for the smooth implementation of rescue and recovery operations after geological disasters. This paper provides a comprehensive survey of emergency communication networks, highlighting their classifications, characteristics, applications, and development directions. The main findings of this review are summarized as follows:  
* The application of communication networks is introduced by citing different examples. Subsequently, the characteristics and importance of emergency communication network are discussed.
* The classification of emergency communication networks under different standards is introduced. The paper then describes the advantages, disadvantages, and applications of different network technologies, such as satellite networks, WMN, MANET, VANET, FANET, SANET, cellular networks, and wireless private networks.
* This paper summarizes a large number of emergency communication schemes currently in use, analyzes the challenges of these schemes, and proposes some possible directions.
* A case study is introduced of a portable broadband-narrowband integrated emergency communication command system. The characteristics, topology structure, and application method of the case are introduced in detail, and the system was tested in the field. The test results show that the communication distance of the system is 15-20 km, which ensures communication for the visual dispatch of emergency rescue services.
* The problems, challenges, and future research directions of the emergency communication network are discussed, and the development trend of space-air-ground-sea networks is clearly introduced.  
Finally, emergency networks mainly consist of satellite networks, narrowband private networks, broadband private networks, and cellular networks, and the integration of various networking technologies. As public network communication progresses from 4G to 5G, digital cluster private networks are gradually evolving in the direction of broadband multimedia. Broadband private networks are driven by the demands of complex emergency communication scenarios, and have become the mainstream trend in communication construction in major countries around the world. In the field of emergency communication, various networks should be combined to form an integrated network with complementary advantages and mutual cooperation, so as to better complete more complex communication tasks. In the future, the emergency network will develop in the direction of intelligence, integration, popularization, low cost, and space-air-ground-sea integration. With the continuous development of economies and societies, the emergency communication network has been further improved and more new network technologies have emerged. This will further promote the rapid implementation of emergency rescue work.  
Conceptualization, Q.W., W.L., T.Z., L.W. and Q.L.; methodology, Z.Y., Q.A., M.I., S.A. and Y.S.; investigation, Q.W.; resources, L.W. and Q.L.; writing--original draft preparation, Q.W.; writing--review and editing, Q.W., W.L., Z.Y., Q.A., M.I., S.A., Y.S. and T.Z. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by Shaanxi Province key industry innovation chain project (Grant No. 2020 ZDLGY15-07) and China Scholarship Fund.  
**Data Availability Statement:** Not applicable.  
**Acknowledgments:** We are grateful to those who participated in the data processing and manuscript revisions.  
**Conflicts of Interest:** The authors declare no conflict of interest.