# Experiencing LoRa Network Establishment on a Smart Energy Campus Testbed
## 1 Introduction  
The emergence of the Internet of Things (IoT) has necessitated new types of communication alternatives that consist of a massive number of smart devices and sensors. Unlike conventional communication technologies, sensors transmit a small amount of data with a very long period through the air. In addition, since most of these sensors are battery-driven, long-range communication with low power is a prerequisite [1]. To meet these new requirements, Low-Power Wide Area Network (LPWAN) wireless communication technologies, such as Long Range (LoRa), LTE-M, and SigFox, have been recently introduced. Of the three, LTE-M uses a cellular network, implying high costs, and SigFox only supports very low data rates. LoRa, which is known to allow for communication over a distance of up to several kilometers in urban environments with low power consumption in an unlicensed band, is attracting much attention [2]. Since the debut of LoRa communication chips and related development kits, academia has evaluated the performance of the LoRa PHY (Physical) and MAC (Medium Access Control) layers to determine whether LoRa works as well as its specification indicates when applied on a real-world device. Two popular research topics on the PHY layer are (i) the maximum length over which a radio signal can propagate in an outdoor environment and (ii) the extent to which in-building obstacles, such as internal walls and doors, affect the radio signal. Simulation studies on the MAC layer have focused on how well-known network parameters (e.g., number of nodes and size of data transmission) cause collisions and thus influence overall MAC performance. Existing research has successfullyuncovered the fundamental properties of LoRa. However, some challenges remain unexamined and must be resolved when establishing a LoRa network in the real world. The ultimate goal of our research is to build a smart energy testbed on a Korean campus in which the LoRa network enables wireless communications for end devices. This paper tackles three technical challenges that are confronted when installing LoRa gateways and nodes and configuring their operational parameters. First, the communication range of LoRa in a combined indoor and outdoor environment has not yet been examined. Suppose that a LoRa gateway is deployed, and LoRa nodes (energy devices, sensors, and actuators) are installed outside and inside buildings on the campus. It is questionable whether the gateway can successfully communicate with a smart meter installed in a campus building 1 km away. The signal strength may decrease dramatically as it passes through the buildings between the gateway and smart meter, leading to a shrinkage in the communication range. Existing works have examined PHY performance in either an indoor or outdoor environment, but the communication range in a combined indoor and outdoor environment must be determined before deploying the gateways and nodes. Next, LoRa networks must follow Korean regulations for wireless communications. Adopting the regulations influences LoRa MAC performance, but the impacts have never been enumerated and studied. In Korea, the LoRa Alliance enforces the use of the Listen-Before-Talk (LBT) scheme instead of duty cycling, which has been studied actively in Europe. The LBT scheme restricts data transmission in different ways, but its performance has remained unknown. Moreover, previous research has never investigated which of the back-off algorithms used in LBT work better in LoRa. This knowledge must be acquired before configuring the operational parameters in gateways and nodes. Last, the application parameters required in the smart energy scenario influence LoRa performance. For instance, frequent data collection from several nodes can increase the probability of a packet collision. For example, one collision every 10 s from 1000 nodes is considered a high collision rate.