## 3 State-of-the-Art  
The main purpose of this research is to develop autonomous base stations leveraging the LoRaWAN protocol for a wide range network, minimizing deployment costs related to Internet usage and also allow isolated communities to get some services even without having Internet access. This work was initially motivated by the desire to offer to citizens of developing countries the possibility of being able to measure the quality of the air and, thus, urge their government agencies to undertake appropriate policies and actions to ensure a healthy and sustainable environment. The review of major relevant publications showed that all of them take Internet connectivity for granted. This is the case in:  
* Reference [6] which proposes a system to monitor external environmental factors such as temperature, humidity, and some gases using a Raspberry Pi as base station and the ESP8266 Wi-Fi Module (at the end devices level) to collect data and storing them on MySQL servers over the Internet. Since the WiFi coverage of the base station is not wide, this solution is not amenable for large-scale coverage. * Reference [7] which proposes an air quality monitoring system in the city of Dhaka (Banglades), using mq-2, mq-3 and mq-7 sensors attached to a micro-controller which is connected to the Internet. [6] seems to be more adoptable than this one. * Reference [8] which presents a participatory urban detection framework for monitoring PM2.5 (Particulate matters up to 2.5 mm). Their framework is based on open hardware, open source software and open data. They were able to develop four Internet-connected PM2.5 monitoring devices with different design considerations based on previous results. The approach adopted here is original, the only drawback is the use of the Internet at every collection points and therefore not optimal in terms of cost for wide deployment and not feasible for isolated communities. * Reference [9] which developed a system for assessing air quality using the BeagleBone equipped with the MQ-7 sensor to measure CO, MQ-11 to measure H2, and a GPS to record position. With this system, if the Internet is interrupted, access to the data is lost. * Reference [10] which measures environmental parameters such as temperature, humidity, light intensity and air quality using a Wio-Link board and Raspberry Pi (access to the Internet), then publishes this data to an MQTT broker. We can see the same difficulties as in [6], except that here their solution is oriented notifications by email or sms. * Reference [11] which presents an autonomous real-time air quality monitoring system that registers PM2.5, carbon monoxide, carbon dioxide, temperature, humidity and atmospheric pressure. They use an Arduino uno connected to a Raspberry Pi (by USB) that routes data to the cloud via the Internet. We can see the same limitations here. Furthermore, authors claim that their solution is real-time. This challenges its usefulness in many African countries due latency issues. * Reference [12] which leverages the MQ7 and MQ135 sensors, the ESP8266 WiFi module and the Nucleo F401 RE microcontroller to measure gases such as CO, CO2, SO2 and NO. An NoSQL Mongo database is housed in a Raspberry Pi 3 that functions as a gateway for the WiFi connected nodes. The base station also functions as a web server for data visualization. This solution is usable both locally and via the Internet, but the coverage of the base stations is still limited, thus, limiting its application in a significant range. In all these references, Internet access is assumed at most data collection points. This cannot be taken for granted in isolated communities or in places with high Internet latency. This suggests that the word \"Internet\" in \"Internet-of-Things\" should not be taken literally. In developing countries, Internet is still a scarce resource and even where it is available, it might not be affordable for a majority of the population [13].