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According to the characteristics and requirements of emergency communication, this paper presents a scheme of emergency communication network deployment, and illustrates the organization mode of communication network in the network structure. In addition, the key technologies of emergency communication network are discussed, in order to provide reference for the establishment of emergency communication network in China. China is one of the countries with frequent natural disasters. Major natural disasters often lead to public communication network failure. when the existing public communication network cannot satisfy the normal emergency communication requirements, emergency communications will be in great demand to provide communications security for rescue operations [1]. Emergency communication is one of the urgent tasks for responding to natural or man-made urgent emergency with a nonconventional means of communication to ensure the release of disaster relief command, important information transmission and rescue command completion [2]. Emergency communication is not a new communication technology, but an integrated use of all kinds of communication means and methods in case of emergency. Its core is to comprehensively consider all factors of emergency nature, geographical environment and climatic conditions, and then choose the most reasonable communication resources as an emergency measure. Main features of emergency communication network After the occurrence of natural disasters and other unexpected emergency, the emergency procedure usually experiences four main stages supported by emergency communication system, namely, the emergency alarm, emergency processing stage, stage of emergency notification and emergency communication [3]. The network types and key technologies used in each phase are different ones. Emergency communication networks often need to operate in complex and harsh environment, the geographical and climatic conditions are varied, the network size can be different. This network has the following salient features: involving a variety of network system with different abilities and characteristics, such as cable transmission network, wireless sensor network, cellular mobile communication network, the air relay system and satellite networks; contains a large number of mobile speed and the ability to deal with different communication unit and coordinate communication; includes a wide range of business, with asymmetric information transmission characteristics, such as information received by rescue workers at the scene are more often than sent ones. Emergency communications network deployment Emergency communication systems must be effective and comprehensive in the inspection of deployment area, in order to prevent and manage possible risks. A number of vehicle power station and a large number of portable low power radio are typically deployed in the on-site emergency, which is decided by emergency communication needs, such as the incident area, the terrain, the station's processing ability and power transmission and wireless channel quality and other factors. The vehicle platform has a greater power and stronger processing capacity, as the backbone node; 6th International Conference on Machinery, Materials, Environment, Biotechnology and Computer (MMEBC 2016) © 2016. The authors Published by Atlantis Press 425 the power and processing capacity of the portable radio station is weak, which is a common user node. Backbone Network Mobile (MBN) can be interconnected by a plurality of vehicular stations which can be interconnected by a wire or a microwave relay, and a portable radio station can be used to access the mobile trunk network, and can be connected with each other to form a user network. In order to take into account the performance and scalability of the network, the emergency communication network adopts hierarchical clustering network structure [3]. In the heterogeneous emergency communication network, strong function of the backbone nodes generally act as the cluster head, which usually consists of a backbone node and its direct communication with user nodes and user nodes in the cluster is related to the number of user nodes transmit power, a backbone node capacity, terrain, the channel propagation characteristics and user nodes distribution. As a common node, it can be selected as the cluster head, which is closer to the node and the light load. Emergency scene command center CCU should first be deployed in a position to facilitate coordination and command, and then through the backbone network to collect the situation of the incident area, and the CCU should be responsible for coordinating the communication between the rescue units. At the same time, an appropriate number of backbone nodes (CN) are deployed in a number of preferred locations, and the collections between the CNs or the CN and CCU are allowed. ON is connected to the CN by the way of self organization. Wireless ad hoc network topology often changes, so the requirements of the network protocol can quickly respond to the change, according to the changes of nodes and links in a timely manner to adjust. When there is available ON near the CN, the CN can be used as the cluster head; otherwise, ON uses a cluster head election algorithm to select cluster head for networking. Cluster network structure has good scalability, which is easy to maintain and manage [3]. The backbone network made by the backbone nodes is mainly responsible for long-distance business transmission, small ad hoc networks are mainly responsible for the collection, transmission and reception of emergency site information. The on-site emergency communication network has a strong mobility, which means both ordinary nodes and backbone nodes can be moved, but the average speed of the backbone nodes is relatively slow. In order to meet the requirements of network nodes, the backbone nodes make adjustments according to the nodes the number and distribution of subordinate position. Therefore, the distribution of the common nodes determines the location of the backbone nodes and the topology of the main network. When the emergency communication network is large, it is necessary to divide the whole network into a number of emergency response area networks. Each area network coverage of up to several km to dozens of km, protecting a certain number of backbone nodes and providing communication services to ordinary nodes in the area. Communication between the regional network can be completed by the ground link network or air network. In order to improve the quality of communication and facilitate the management, the common nodes in each area network are expected to hop into the trunk network as far as possible. Sufficient number of backbone nodes can improve the robustness and service of the network, but it will increase the cost of network deployment. Therefore, it is necessary to make a reasonable configuration choice according to the communication needs. A feasible strategy: the number of backbone nodes should enable the backbone network to cover all the normal nodes, so that command and control and other important information can be rapidly transported to the ordinary nodes, allowing ordinary nodes to access backbone network in one hop or multi hop, reducing the number of backbone nodes and increase the system flexibility. The emergency communication system using the IP protocol as a link connecting heterogeneous networks, including rear command center in a wired LAN, on-site emergency (wireless) emergency communication network, and rear command post and emergency communication transmission network (Internet, special cluster network and satellite communications network). The deployment of emergency communication network is shown in Figure 1.

Emergency communication network design and key technology research