# An Overview of Emergency Communication Networks
## 5 Sea Ad Hoc Network (SANET)
### Case Study: Broadband-Narrowband Emergency Communication Command System  
At present, the narrowband trunking communication system represented by PDT mainly provides voice services. Its path loss is small and it has a wide coverage, but its transmission band is narrow, and it cannot meet the demand of complex scenarios scheduling command. The broadband cluster system represented by LTE supports different multimedia services and has the advantages of high speed, large bandwidth, and resource sharing, but its coverage is limited. Therefore, the combination of high speed and large bandwidth of the broadband cluster and narrowband voice can realize resource sharing, helping users to realize multimedia command and scheduling, integrating voice, data, and video. Aiming at the problems of the short transmission distance of existing emergency communication equipment and complex system deployment, a portable broadband-narrowband integrated emergency communication command system applied to the emergency rescue scene is proposed. The system adopts a PDT + LTE solution, and soft switch technology based on SIP realizes the unified management of broadband-narrowband cluster users, mixed calls, multimedia cluster scheduling, and other integrated services. The system topology is shown in Figure 10. The portable broadband-narrowband integration emergency command system is deployed in the forward headquarters. Adoption of the multi-link aggregation mode of the public network and LTE private network enables multimedia cluster services such as voice, video, and data. The core equipment of the portable broadband-narrowband emergency communication command system is the switching control platform and the narrowband relay base station. The switching control platform uses a unified switching center to control the broadband and narrowband cluster access system, and provide data and signaling channels, and is responsible for the exchange, control, and transmission of data, with mobility management functions. The narrowband relay base station covers narrowband terminal signals to realize the return of voice signals and transmit the signals to the switching control platform for the next step of broadband and narrowband service integration. In view of potential network disconnection and power failure in the emergency rescue scene, the system adopts a portable LTE base station to realize the network coverage of the rescue scene and build a visual integrated command and dispatch system. The portable LTE base station integrates the base station, the core network, and the scheduling system, and has the characteristics of integration, piggyback, and rapid deployment. In practical application, considering the networking cost and the demand for fast network layout, a more reasonable network coverage scheme can be designed by calculating the coverage scope of the LTE private network. The high-frequency propagation curve was analyzed using the cost-231 hata model. The link parameters of the base station were set, the maximum path loss allowed for the uplink and downlink was calculated, and the uplink and downlink coverage radius was obtained. The link maximum path loss (MAPL) is shown in the following:  
\[\mathrm{MAPL}=\mathrm{EIRP}+\mathrm{G_{tal}}-\mathrm{L_{tal}}-\mathrm{M_{tal}}- \mathrm{Rs} \tag{1}\]  
where EIRP is the effective omnidirectional radiation power at the transmitting end; \(\mathrm{G_{tal}}\) is the sum of the transmitting antenna gain and receiving antenna gain; \(\mathrm{L_{tal}}\) is the sum of human body loss, feeder loss, and penetration loss; \(\mathrm{M_{tal}}\) is the sum of interference margin and shadow margin; \(\mathrm{Rs}\) is the minimum receiving sensitivity.