The development of environmental monitoring would not be possible without continuous technological progress, public pressure and targeted environmental education. To meet the expectations of users, measuring instruments must not only be ever more accurate, but also practical and straightforward to use and economical to operate. Environmental analytics has begun to strongly overlap and interpenetrate with broadly defined modern digital technology and informatisation [24, 25]. Nowadays, creating new measurement solutions is an interdisciplinary challenge for representatives of both natural and technical sciences, including computer scientists and programmers. In the implementation of largescale measurements of spatially distributed phenomena, fully mobile devices become indispensable, as they transmit the collected data to a server where they are analysed, shared, and often visualised. This will also allow the collected measurement data from ever longer observation sessions to be archived and utilised.
The development of a fully mobile, and thus highly functional recording device anticipated by the target market is accomplished through the use of wireless data transmission technology. Depending on the needs, such technologies can be divided according to i.a. the range of data transmission and the transfer size. Each of these technologies is characterised by a specific segment of users, as well as parameters and technical requirements. The most popular long-range data transmission technologies include the widespread GSM network, while Wi-Fi or Bluetooth networks are characterised by a much shorter range of up to several dozen metres [26, 27]. In terms of data packet transmission rate, on the other hand, GSM and Wi-Fi networks can transmit significantly more data than Bluetooth. When it comes to environmental measurements implemented by a distributed sensor network, the most important operational parameter, which determines the choice of a given solution, is the power consumption used when sending messages. The raw measurement data will usually contain relatively small-sized information packets, but their deployment in areas with difficult access to power supplies makes it necessary to use a solution based on its own energy source, usually a battery with a long or very long life without the need for frequent replacement or charging. The abovementioned wireless data transmission technologies are too energy-intensive for such tasks, as they consume a significant amount of energy during data transmission, which prevents long-term monitoring of environmental data on a larger spatial scale and in uninhabited areas or areas with limited technical infrastructure. LPWAN (Low Power Wide Area Network) networks have been designed with such applications and peripheral locations in mind [28, 29]. Due to its extensive applicability and parameters, LPWAN is one of the most modern technologies increasingly used for the communication between devices [29–32]. As one of the many elements of Industry 4.0, it fits into the idea of Internet of Things (IoT), supporting Smart City solutions. Of the available types of LPWAN networks, three are most extensively used: Sigfox, NB-IoT and LoRaWAN. Each of these types of solutions has its own parameters and is intended for different applications [29, 32].
The LoRaWAN standard was selected for the implementation of this project involving the monitoring of night sky pollution by artificial light. It has the most optimal parameters in relation to the prepared design objectives and applications of the designed device. The LoRaWAN standard is one of the MAC (Medium Access Control) radio communication protocols [27, 33, 34] and is characterised by a long range allowing network connectivity with low power consumption. LoRa technology is used for communication in the LoRaWAN standard and is, for such applications and with the input limitations indicated, an alternative to other technologies such as LTE, Wi-Fi or Bluetooth (Fig. 1).
LoRa is a type of modulation that uses the CSS (Chirp Spread Spectrum) technique, consisting in spreading the spectrum of the transmitted signal [28, 32–34]. The CSS modulation makes full use of the allocated transmission bandwidth, which increases the robustness of the communication against interference, and eliminates inaccuracies related to the Doppler effect and route propagation. LoRaWAN is developed as an open standard that uses the ISM (Industrial, Scientific, Medical) radio spectrum and requires no licence fees. In Europe, LoRa operates at the 868 MHz frequency band. The great advantage of the selected technology is its range, which in the field conditions varies, depending on the type of housing development, from several hundred metres to several kilometres [27, 32, 36]. In the professional literature, one can find examples of measurements and data transmission performed under specific conditions, over a distance of up to 702 km [27]. An additional key function of LoRaWAN is the possibility of bidirectional communication, allowing not only to send but also to receive information. In the process of planning a wireless network, the advantage of LoRaWAN is the use of an unlicensed radio band, thanks to which there are no restrictions and additional requirements, or costs associated with the activation and operation of an already established network. In practice, the LoRaWAN architecture consists of four main components, such as end devices (data loggers), communication gateway(s) and a network and application server.
Due to its universal parameters, LoRaWAN technology is used in many fields of application. Such solutions can be found, among others, in defining the objectives of Smart City, where they form the basis for the transmission of traffic, environmental and logistic information, in the construction industry in monitoring the status of operation and quality of structures, and in modern medicine when monitoring the health of patients staying outside medical facilities [24, 31, 34, 35].