# A Low Power IoT Sensor Node Architecture for Waste Management Within Smart Cities Context
## 6 Operation Tests
### Tests on Data Transmission through LoRa Channel  
The effectiveness of the LoRa technology for the deployment of a city-scale monitoring infrastructure was analyzed by testing the actual data transmission ranges in a real scenario. For this purpose, a prototype network infrastructure was set up in the historic centre of Siena, Italy, with the aim of demonstrating the feasibility of the realization of a single star network covering a whole urban area. The prototype infrastructure was constituted by a gateway node composed by a Libelium SX1272 LoRa module (Libelium, Zaragoza, Spain) connected to a laptop through a Waspmote USB Gateway and by one sensor node that will be described in a while. The three key parameters to be set for the LoRa communication modules, i.e., the Spreading Factor (\(SF\), the number of symbols sent per bit of information), the Bandwidth (\(BW\)) and the Coding Rate (\(CR\)), were set according to the datasheet to obtain the highest sensitivity: in particular, setting \(SF=12\), \(BW=125\,\mathrm{kHz}\), and \(CR=4/5\) the sensitivity value grows up to \(-136\,\mathrm{dBm}\).  
Following the network setup, the transmission ranges were tested by placing the gateway in a fixed position, and checking that the actual packet was correctly received as the sensor node was moved in different spots around the city. In particular, since the historic centre of Siena is still surrounded by its medieval city walls, the received packet was tested in a set of spots along the walls track and along the main roads of the centre, as well as in a couple of more distant sites from the centre but in line of sight with the gateway location. The gateway was placed on the top of the tower of the University Rectorate, which is exactly placed in the centre of the city and almost equidistant from the city walls. These tests proved the feasibility of the system since the maximum achieved transmission range in the city centre (i.e., within the medieval walls) was \(1.1\,\mathrm{km}\). Moreover, also some peripheral spots (i.e., outside the medieval walls) were tested achieving a maximum transmission rage of \(2.7\,\mathrm{km}\) in line-of-sight, hence strengthening the practicability of the system. Concerning the spots within the city walls, the line-of-sight was not always ensured due to the morphology of the city centre. Indeed, the centre of Siena is built atop three hills: this means that the valley bottoms are not visible from the top of the Rectorate tower. Such an issue did not affect the peripheral spots though.  
In order to check the presence of packet losses, the data transmissions were performed exploiting a prototype composed by the HC-SR04 sensor and the Arduino UNO board provided with the Libelium SX1272 module connected through the ad-hoc Multiprotocol Radio Shield (i.e., the same prototype as the one set up in Section 6.1 equipped with LoRa connectivity). None of the packets were missed during the transmissions from all of the testing sites (i.e., at each of the city gates and every \(500\,\mathrm{m}\) along the city walls track as well as along the main roads of the centre). Albeit packet losses were observed whenever the prototype was moved amid a testing site and the following one, this is not a matter of concern since the nodes are expected to be still on the deployed trash bins in the city centre. Thus, the LoRa technology proved to cover the system deployment area (i.e., the city centre), as it can be seen in Figure 9, without the necessity to enable the boost mode on the transmission module.  
In addition, it was also empirically proved that no more than \(10\,\mathrm{s}\) are requested to accomplish the transmission. No analysis on the received signal strength indication (RSSI) values was carried out because the main purpose of the test was only to prove the effectiveness of the data receiving and not the signal sensitivity.