## 2 Background and Related Work of LPWAN  
### Background  
In the past, the information collected by various monitoring equipment could be used through different wireless communication methods such as Zigbee, WiFi, 2G, 3G, or 4G. However, they were all limited by the transmission distance, power consumption, and transmission costs and could not be deployed in a large area, especially in a forest area. For long-distance, low-power, high-coverage wireless communication needs, the newly developed wireless network communication technology of an LPWAN in recent years can be roughly divided into two categories: an NB-IoT, which uses licensed frequency bands, and LoRa, Sigfox, and Weightless, which use unlicensed frequency bands. As shown in Figure 1, compared with other communication technologies, an LPWAN has many advantages, such as its long-distance range, high coverage, low power consumption, low cost, and so on. At present, the global Internet of things and communication manufacturers have actively set up various cross-domain or independent LPWAN base stations, combining their advantages of a long-distance range, high coverage, low power consumption, and low cost with related sensors and smart devices to provide related innovative services. In addition to the common characteristics of a long-distance range, low power consumption, and high coverage, this section evaluates and analyzes the advantages and disadvantages of the above-mentioned LPWAN communication technology and its application areas as follows:  
NB-IoT: An NB-IoT is a carrier-grade network supported by the international telecommunications standards development organization, 3 GPP, and built for the IoT. It has a good network transmission quality, high data security, and a low construction cost. Based on the low-rate IoT market in the licensed spectrum, an NB-IoT can be deployed directly on LTE networks, and an NB-IoT can be quickly deployed without drastically changing the current 4G LTE telecommunication network architecture. In addition, an NB-IoT can also be deployed through equipment upgrades based on the current operator's existing 2G, 3G, and 4G networks, which can reduce deployment costs. As a result, an NB-IoT is supported by telecom companies in various countries and is a widely used Internet-of-things technology worldwide. The Global Mobile Suppliers Association announced in March 2019 that more than 100 operators have deployed an NB-IoT. LoRa: LoRa is the basis of the wireless communication technology developed by the American semiconductor manufacturer Semtech through its acquisition of the French company Cycleo, with the specification completed in cooperation with IBM. The LoRa  
Figure 1: Comparison of LPWAN and other communication technologies. Alliance, composed of Semtech, IBM, and Cisco as the core, promotes related development. LoRa, like Wi-Fi, adopts a mode in which anyone can set up a Wi-Fi access point to build a network environment. With more than 500 members, it can be said to be the most industry-supported LPWAN technology. LoRa's communication protocol and network architecture will directly affect the battery life, network capacity, service quality, security, and network applications of the node. LoRa is a technology that modulates data into electromagnetic waves. The transmission method used is called the \"chirp spread spectrum\". LoRa nodes can only be used to transmit data. Supporting two-way communication is one of the main features of LoRa, which allows terminal devices such as sensors to send information such as the location, occupancy, and data to the network, and receive messages from the network. Sigfox: Although Sigfox from France uses an unlicensed spectrum, it needs to rely on base stations built by manufacturers in order to strike a balance between cost and communication quality. Sigfox is the technology with the lowest transfer rate; the speed is only 100 bits/s, each device can only transmit 140 messages a day, and the maximum capacity of each message is 12 bytes.