# Experiencing LoRa Network Establishment on a Smart Energy Campus Testbed
## 3 Smart Energy Campus  
The fundamental goal of a smart energy campus is to use the \"energy\" resource more efficiently on the campus, as depicted in Figure 4. To this end, a few energy devices are installed on the campus; they include solar panels, smart meters, thermostats, energy storage systems, etc. Conventional IoT data, such as room temperatures, are also collected by sensors. Upon detecting that a classroom is empty, an energy management system (EMS) turns off the lights and air conditioners in the room to improve the energy efficiency on the campus. Several nodes (energy devices, sensors, and actuators) are installed at locations where typical networks such as the Ethernet or Wi-Fi do not reach. For instance, Figure 5 depicts a solar panel and solar irradiance sensors installed on the roof of a building on the campus. A new installation of network cables, Wi-Fi routers, or other short-range wireless networks is often avoided because of high installation costs. LoRa is considered to be a promising alternative that provides wide area communications. To establish a LoRa network for the smart energy campus testbed, we install gateway(s) and nodes (i.e., energy devices, sensors, and actuators) and set up their operational parameters. The first challenging question confronted is, \"how do we deploy the gateway on the campus?\" One may suggest that it is enough to install one gateway in the center of the campus since previous research shows  
Figure 4: The airplane view of the university’s campus, which is around 600 \(\times\) 600 m in size. A yellow dot represents Building #7, where a LoRa gateway is installed. Figure 5: A solar panel and solar irradiance sensors are equipped on the roof of a building on the campus where conventional networks such as Ethernet and Wi-Fi are not connected. A LoRa node (the gray enclosure below the panel) collects and sends related data to a data server via LoRa communication. that LoRa can reach up to several kilometers. However, the gateway may not communicate with a node installed inside a building located at the farthest corner of the campus. Once hundreds of nodes are installed, severe collisions can occur in the gateway. The LoRa network may need more than two gateways. In fact, we must plan to deploy gateway(s) to maximize LoRa performance. Previous studies, unfortunately, have yet to answer the question. To investigate the challenge and to ultimately establish the LoRa network, this paper introduces technical questions on the PHY, MAC, and application layers. First, we ask the question, \"how well does LoRa PHY perform in a combined indoor and outdoor environment?\" LoRa is known to provide communication ranges of 15 km and 6 km in rural and urban areas, respectively. In practice, however, it may not achieve this performance as a result of various environmental factors. Even in a combined environment in which a gateway communicates with nodes that are inside different buildings and/or on the outside across from buildings, the factors become more complicated and unpredictable. The campus is 600 \(\times\) 600 m in size and has around 30 buildings. Nodes are everywhere on the campus; solar panels are on building roofs and/or in the middle of parking spaces, whereas smart meters and sensors are inside buildings. Can a LoRa gateway communicate with all the smart meters on the campus? If not, what is the maximum communication range in a combined environment? How many gateways do we need to reach all of them? The next question that this study raises is, \"how do new regional parameters and regulations affect LoRa MAC performance?\" In the LBT scheme, a back-off algorithm plays an important role. Upon detecting a busy channel, a node waits for a specified time duration (named the back-off time) before retrying to sense the channel. A short delay makes the node sense frequently, resulting in excessive energy consumption, whereas a long delay can increase the data transmission time, degrading performance.