# Unveiling LoRa's Oceanic Reach: Assessing the Coverage of the Azores LoRaWAN Network from an Island
## 2 LoRa and LoRaWAN  
Long Range (LoRa) low-power networks are becoming increasingly popular [14]. These networks are an effective communication solution owing to their stability and low cost, and because they do not require licensing, they present a low barrier to implementation. LoRa also has low power and low bandwidth. While this would be a limitation for human communications, it is adequate for machine-to-machine communication, particularly sensors, whose usage is growing exponentially. The low power of LoRa is also critical for the use case of sensors, which, due to low power demand, do not need to be tied to the grid, operating from batteries, frequently combined with photovoltaic cells.  
The low entry barriers of LoRa, namely the low cost associated with the freedom for implementation, differentiate LoRa networks. Unlike other communication solutions, the economics of LoRa allows for the distribution of gateways as necessary for adequate coverage, even where there is a lower density of use due to the lower viability (cost-benefit) threshold.  
LoRa is one of the leading Low Power Local Area Networks (LPWAN) communication technologies being adapted worldwide to connect sensors [15], forming the Internet of Things (IoT). In the IoT, resources tend to be scarce. IoT devices need less memory, processing power, and energy requirements, allowing for ubiquitous sensing, which is unfeasible based on other communication technologies such as Wi-Fi or traditional cellular networks [1; 12].  
The LoRaWAN network architecture (illustrated in Figure 1) is based on a star-of-stars topology, with three types of devices: end device (node) (typically one or more sensors with a LoRa communication element), LoRa gateway (LoRa communication device that receives messages from the end devices), and a LoRa network server, which aggregates the data obtained through the gateways.  
The communication between the end devices and the gateways is LoRa-based. LoRa is composed of two layers: one physical and one logical. The physical layer, LoRa, is Semtech's proprietary wireless modulation technique, which uses chirp spread modeling [13]. The logical layer, LoRaWAN, is a Media Access Control (MAC) layer protocol built on top of the LoRa (physical) modeling layer, designed primarily for sensor networks. It defines how devices use the LoRa hardware, e.g., when they transmit and the format of messages [13]. The communication between the gateways and the network server tends to use higher bandwidth backhauls such as 3-4-5G or ethernet. As shown in Figure 1, the LoRaWAN network architecture allows for bidirectional communication. In the case of end devices, communication is performed with a relatively low frequency (e.g., hourly, or daily, not lower than at two-minute intervals). It is the responsibility of the network server to provide the acknowledgements and select the best links to forward the downlink messages [16].  
LoRa is well documented in the literature [12; 18]. While the physics of LoRa transmission seems well suited for communication over the ocean, which is naturally free of permanent obstacles, the truth is that there are not many trials and tests where these characteristics have been tested and validated [19; 20; 21]. And to our knowledge, no trials have been conducted on an archipelago.  
We set up a LoRaWAN network for Terecira Island in the Azores, Portugal. It covers over 90% of the island and all targeted areas. Since, with the current use, we are far from consuming the available duty cycle, we aim at using it for different applications over the ocean. If reliable service could be extended to approximately 100 km from the shore, then the usability of the network would increase by several orders of magnitude.  
Compared to the existing literature, our test results encourage and augment the potential for using the network to easily cover use cases previously unfeasible or complex and expensive to support, such as small fishing vessels or fishing buoys.