# Emergency Communication System Based on Wireless LPWAN and SD-WAN Technologies: A Hybrid Approach
## 2 Related Work  
LPWAN and SD-WAN technologies have attracted too much attention in the literature. There are many surveys for the evaluation and comparison of nominal performance indices of these network technologies based on their specifications [5]. Apart from this approach, researchers have focused on IoT-enabled ECSs, which sometimes can provide phone or video calls, and may be combined with sensors to gather and analyze sensitive data (e.g., health data), perform monitoring and warning functions, and enable live tracking. In this section, we present these IoT applications and platforms for ECSs, based on these networks. During a disaster, rescue team personnel are exposed to danger. To avoid risking the lives of these personnel, [PERSON] et al. [11] have integrated a Search and Rescue (SAR) robot into rescue operations. The heavily damaged infrastructure of disaster areas presents the biggest obstacle to using robots in rescue operations. A working communication system allows the robot and base station to share real-time information in the rescue environment. They suggest innovative communication architecture for search-and-rescue missions based on LoRaWAN and a SAR robot in situations where there is limited coverage or no communication system in severely damaged catastrophe sites. The SAR robot can operate in worst-case disaster scenarios where the entire communication infrastructure is destroyed since it is monitored and controlled from a remote base station. The functions of this SAR robot have been tested in a Gazebo simulated environment, while an actual test setup inside the lab facilities has shown great promise. The RoboMaC communication device, a unique full-duplex LoRa-based transceiver device capable of transmitting control commands from the base station to the SAR robot while returning the robot's geolocation data to the base station, has been installed on the SAR robot. By using this technique, the rescue team can locate and assist injured patients while reporting their whereabouts to the base station while tracking and controlling the SAR robot from a distance or standoff position. This eliminates the need for the presence of conventional communication networks. The RoboMaC devices were able to attain a signal range of 1.6 miles. To manage the sporadic and rare events linked with emergencies in wireless Internet-of-Things (IoT) scenarios, [PERSON] et al. [12] proposed a method to increase the performance of emergency communication when LPWANs are the backbone of the IoT. They created an innovative message replication technique (LoRa-REP), which is fully compliant with the LoRaWAN requirements to get around several LoRaWAN limitations. A private LoRaWAN network with a local backend and a public LoRaWAN infrastructure with a cloud-based backend were the two operating paradigms that were taken into consideration and tested. They also offered two examples of real-world applications to demonstrate the viability of their suggested strategy. The outcomes of the real-world use cases demonstrated the effectiveness of the suggested approach, which lowered the loss of emergency messages by at least two times. Moreover, the average transaction time was decreased by 200 ms in the worst-case situation. [PERSON] et al. [13] developed a low-power, robust, and decentralized emergency communication network to coordinate emergency response and relief efforts when infrastructure damages have been caused by natural calamities. Based on LoRa technology, they suggested a workable emergency communication device for mesh networks. To enable mesh networking in LoRa, they implemented a modified Ad Hoc On-demand Distance Vector (AODV) routing protocol. This change routes the metric using the Received Signal Strength Indicator (RSSI). This method's effectiveness was assessed using the Packet Delivery Ratio (PDR). As a result, they created a method to send text messages between mobile phones using a mesh LoRa network.