# A Low Power IoT Sensor Node Architecture for Waste Management Within Smart Cities Context
## 7 Conclusions and Future Works  
The aim of this paper was to present an energy efficient solution for waste management in the wider context of Smart Cities. In particular, the solution described in this paper focuses on the realization of a system in charge of measuring the filling level of trash bins and transmitting in real time the collected data to a remote data collection centre. While developed by using off-the-shelf devices, the described solution is conceived with a specific focus on the network architecture and on the optimization of power consumption as well. Regarding the network architecture, this is based on the LPWAN LoRa technology, that proved to provide the best trade-off in terms of power consumption and performances. In particular, LoRa radio modules turn out to be energy efficient, with reduced consumption in transmission if compared to similar technologies: LoRa modules current absorption in transmission is around 20 mA while, for example, off-the-shelf ZigBee radio modules, such as XBee Series 2 absorb, according to the datasheet, around 40 mA. They are characterized by wide area transmission ranges that allow to set up urban-area networks by employing a single or few access points. While these networks are based on star topologies, they allow to apply strict duty-cycling policies to the sensor nodes with an additional, notable reduction on power consumption. The data transmission ranges and the effective feasibility of a single gateway, along with a city-scale network were confirmed by the tests carried out: these tests showed that a 1.1 km transmission range is achievable in urban areas even without line-of-sight, while if ensuring line-of-sight, this value could grow up \(\sim\)3 km. Regarding the power optimization, by using low power components as well as by combining duty-cycling policies, the developed IoT node is expected to operate for an ideal span of time up to 502 days according to power consumption analysis and preliminary laboratory tests. This value is  
Figure 9: Map of the area covered by the LoRa network. Blue dots indicate the more distant line-of-sight spots. expected to be confirmed with the actual implementation of the system: direct long run field tests were not carried out though due to the high variability of the environmental conditions of the deployment scenario. Anyway, the system is conceived with a lifetime that, even its half, widely ensures the operation of the whole monitoring infrastructure. Moreover, this value has been compared with the one achievable by developing the same sensor node using an Arduino UNO board: calculations have shown that the achieved lifetime (502 days) is roughly twice than the one obtainable with the Arduino-based node (259 days). Together with the extended lifetime, the proposed sensor node is also characterized by reduced costs. The main components (microcontroller, counter, sensor, voltage regulators), excluding the LoRa module account for around 10 euros. The LoRa module used for this prototype (i.e., the Libelium SX1272) has currently high costs (around 40 euros), but cheaper alternatives can be found and are emerging day-by-day. Future work will be carried out in this direction, in order to identify cheaper alternatives providing a similar performance level. Additional future work is expected to be carried out also to improve the efficiency of the node. In particular, possible directions to be investigated include the use of two different battery sets to power separately Block A and Block B (see Figure 1) and the adoption of additional software-based energy efficient policies. Some examples could be the use of adaptive protocols modifying the sampling rate according to the variation rate of the filling level of the trash bins as well as transmission policies activating the LoRa module only when significant level variations are detected. In conclusion, the described IoT node was developed and tested in laboratory for the validation of the measured data and in field for the data transmission, proving its effectiveness.