# An Overview of Emergency Communication Networks
## 3 Review of Emergency Communication Networks
### Network Classification
#### 3.1.2 Ad Hoc Networks
* MANET has the advantages of having a low deployment and maintenance cost, large coverage, high rate, strong network robustness and adaptability, and link self-sensing and self-healing. It can not only exist as an independent wireless self-organizing network, but also serve as an effective supplement and expansion of an existing heterogeneous network system. * MANET can be widely used in military communication private networks, public security private networks, emergency communication private networks, regional broadband private networks, and wireless monitoring private networks. Due to its significant advantages, MANET is widely used in emergency communications in order to provide effective communications during natural disasters. For example, [PERSON] et al. [76] developed a hybrid MANET topology with the advantages of fast deployment, simple configuration, and convenient interoperability. The proposed solution can provide network access for post-earthquake emergency rescue services to meet the communication requirements of rescue work. [PERSON] et al. [77] designed and implemented a system named TeamPhone, which consists of two components, namely, a message system and a self-rescue system. The message system integrates cellular networks, ad hoc networks, and a self-rescue systems group, and locates the smart phones of trapped survivors. The TeamPhone system can send emergency messages and provide their location information to assist rescue operations. [PERSON] et al. [78] designed disaster communication network management software combining MANET and a wireless local area network (WLAN). MANET can be widely used in environments where wired networks cannot be supported or where communication is temporarily required. The problems faced by MANET include:  
* Wireless transmission bandwidth is limited, and signal fading and noise interference exist;
* Poor security and the wireless link makes the network vulnerable to link layer attacks;  
Figure 3: Structure diagram of MANET. Without centralized nodes, it is difficult to connect with external systems;
* Limitations of mobile terminals: mobile terminals in MANET have the advantages of dexterity and good mobility, but are limited by their power supply, small memory, and low CPU performance. * Vehicular Ad Hoc Network (VANET)  
VANET is a new mobile ad hoc network created by applying the principles of MANET to vehicles. VANET is composed of self-organizing vehicles as mobile nodes, and the communication between nodes can be divided into vehicle-to-vehicle (V2V), vehicle-to-roadside (V2R), and vehicle-to-infrastructure (V2I). Its network structure is shown in Figure 4. VANET is a wireless communication technology that can be deployed quickly, which simplifies data exchange between vehicles and provides a variety of data services [79]. VANET is expected to enter the application field of disaster communication due to its features of connecting emergency vehicles and road navigation. VANET has its own unique characteristics compared to other types of networks, which include: predictable mobility; provision of safe driving and enhancement of passenger comfort and traffic efficiency; lack of power limitation; variable network density; rapid changes in network topology; unlimited network size; and high computing power. In recent years, as automotive technology has advanced, VANET has played an important role in saving drivers' lives and property by disseminating critical incident information. The important purpose of VANET architecture is to provide efficient and effective emergency and warning alerts for vehicles, so that vehicles can make appropriate decisions without delay to safeguard passenger safety [80]. [PERSON] et al. [81] proposed a real-time emergency warning model, based on Android applications, which provided efficient and safe driving for vehicles while establishing a reliable VANET. High-speed movement of vehicle nodes and rapid changes in network topology in VANET result in severe challenges to the design of the network architecture and related protocols.