# Low-Power LoRa Signal-Based Outdoor Positioning Using Fingerprint Algorithm
## 1 Introduction  
In recent years, the number of Internet of Things (IoT) devices has increased exponentially with the decreasing costs of hardware and communication technologies [1]. IoT devices need to communicate with each other to transmit data packets among themselves. Medium- and long-range IoT devices use both cellular- and noncellular-based communication technologies. Low-power wide-area (LPWA) communication, a noncellular-based communication technology, allows long-range communication among IoT devices with low power consumption and cost. Thus, LPWA communication is highly suitable for long-range wireless IoT devices despite its low bandwidth constraint. Figure 1 shows a comparison of common communication technologies including LPWA.  
Positioning is an essential element in most IoT applications. Global Positioning System (GPS) has been widely used for positioning in most IoT applications. However, GPS chips are rather expensive and have high power requirements, making them unsuitable for long-range and low-power IoT devices. For example, [PERSON] et al. found that a device equipped with GPS and Global System for Mobile communication (GSM) chips consumed around 30-40 times the power consumed by a device equipped with only a long-range (LoRa) chip [3]. Furthermore, GPS functions and communication functions need to be provided separately, making it difficult to miniaturize devices and greatly increasing their production costs.  
Alternatively, LPWA signals can be used for both positioning and communication simultaneously. Therefore, in this study, we focused on LoRa, an LPWA communication technology, that uses Semtech Corporation's proprietary CSS (chirp spread spectrum) modulation scheme. It trades off data rate and sensitivity within a fixed channel bandwidth. LoRa is a physical (PHY) layer implementation, and therefore, it is independent of higher-layer implementations. Thus, LoRa is interoperable with existing network architectures [4].  
The LoRa Alliance released a Long-Range Wide Area Network (LoRaWAN) geolocation whitepaper. LoRaWAN uses the LoRa spectrum modulation method. Its system architecture and communication protocol influence battery life, network capacity, quality of service, security, and so on [5]. The whitepaper compared the cost, battery life, and positioning accuracy of GPS/assisted GPS (AGPS), Bluetooth Low Energy (BLE), Wi-Fi, and LoRaWAN. GPS/AGPS, BLE, and Wi-Fi were found to consume more power than LoRaWAN. The whitepaper also compared the LoRaWAN received signal strength indicator (RSSI) proximity and LoRaWAN time difference of arrival (TDoA) methods, as shown in Figure 2.  
Figure 1: Telecommunication methods [2].  
Figure 2: Comparison of positioning technologies [6].  
The LoRaWAN RSSI proximity method determines whether a LoRa gateway is located nearby by examining whether a signal can be received from it. The LoRa signal covers a wide area and complies with the log-distance path loss model [7]. The position can be calculated more precisely by measuring the decrease in signal intensity [6; 7; 8]. However, the LoRaWAN RSSI proximity method has a large error of approximately 1000-2000 m compared to that of the LoRaWAN TDoA method [6]; the error of the LoRaWAN TDoA method is more than 300 m because of the time resolution [9]. According to the LoRa Association's whitepaper, LoRa gateways enable the accuracy of 20-200 m, which supports Semtech Corporation's Geolocation Capability [6].  
In this study, we propose a LoRa-signal-based positioning method that uses a fingerprint algorithm instead of the RSSI proximity or TDoA methods. We evaluate the accuracy and usability of this algorithm for large real-world areas. The remainder of this paper is organized as follows. Section 2 summarizes related works. Section 3 describes the proposed fingerprint algorithm. Section 4 presents an evaluation of the proposed methods using real-world data. Finally, Section 5 presents the conclusions of this study and discusses future works.