# An Overview of Emergency Communication Networks
## 3 Review of Emergency Communication Networks
### Network Classification
#### 3.1.2 Ad Hoc Networks  
In 1991, IEEE formally put forward the term \"ad hoc network\" [64]. Ad hoc network technology adopts a \"peer-to-peer structure\" mobile communication mode without a base station. Compared with other network forms, an ad hoc network is a special mobile communication network that can be quickly networked without the prerequisite of relevant infrastructure presetting. Ad hoc networks are characterized by high destructibility, self-healing, and self-organization, and are especially suitable for communication during temporary or sudden emergency events. On an ad hoc basis, a variety of networks have been extended: Wireless Mesh Network (WMN) [65; 66], Wireless Ad Hoc Network (MANET) [54], Vehicular Ad Hoc Network (VANET) [67], Fly Ad Hoc Network (FANET) [68; 69], and Sea Ad Hoc Network (SANET). Each network is described below. 1. Wireless Mesh Network (WMN) WMN [70] is a new network product based on the development of wireless networks and the extension of the ad hoc network. Its network architecture is shown in Figure 2. The main advantages of WMN are: * WMN is a multi-hop network that automatically selects the best path to avoid communication failure due to obstacles, so as to provide service transmission capability for users who are not within line-of-sight range. * WMN has flexible and diverse networking modes, supports dynamic topology networking, provides effective networking capabilities for application scenarios with high mobility requirements, ensures the quality of connectivity among users, and expands network coverage. * WMN is capable of self-organizing, self-healing, and self-balancing, with strong network reliability. WMN is basically similar to MANET in terms of connectivity and operation, except for the design and application scenarios of routing protocols. [PERSON] et al. [71] proposed SKYMESH, a Wi-Fi-based mesh network that can provide Internet to disaster-affected areas. [PERSON] et al. [72] used MANET, WMN, and World Interoperability for Microwave Access (WiMAX) to form a mesh network and expand the service area through satellite communication links. [PERSON] et al. [73] adopted the WMN solution in post-disaster communication to reduce losses. At present, most WMN networking technologies use Coded Orthogonal Frequency Division Multiplexing (COFDM) modulation and characteristic beam technology, which can solve the problem of channel selective fading and channel flatness fading in a multi-path environment. After adopting a Multiple-Input Multiple-Output (MIMO) antenna, high-order modulation, and other technologies, the transmission rate can reach nearly 100 Mbps. Figure 2: Structure diagram of WMN. As a new form of wireless self-organizing network, WMN can not only effectively combine with emergency communication modes such as satellites and short-wave, but also be used as the extension of mobile communication networks such as 4G and metropolitan area networks such as Wireless Personal Area Networks (WPANs) to provide more extensive wireless access coverage and comprehensively improve the quality of emergency communication. WMN is mainly used in mine emergency rescue. In recent years, it has also been more widely used in terms of fire protection [74; 75] and earthquake and other disasters. 2. Mobile Ad Hoc Network (MANET)  
MANET is a new type of broadband WMN based on ad hoc networking mode. Its structure is shown in Figure 3. MANET makes use of the routing and forwarding function of mobile terminals to communicate without infrastructure, thus compensating for the lack of network communication infrastructure available. The features of MANET are:  
* MANET is a distributed, multi-hop relay wireless broadband system without a center, and provides dynamic routing, strong damage resistance, and good scalability. Its network topology changes dynamically, and it internally uses its own routing protocol to complete wireless communication among nodes through wireless multi-hop forwarding.