# On the Evaluation of the NB-IoT Random Access Procedure in Monitoring Infrastructures
## 2 State of the Art
### NB-IoT in Smart Monitoring Infrastructures  
NB-IoT appeared as a key technology for offering wireless connectivity to constrained smart devices, while supporting a massive deployment of sensors. By dynamically adapting its features, NB-IoT is able to satisfy most of the requirements of application scenarios distinguished by a high density of terminals, e.g., Smart City, Industry 4.0, and Precision Agriculture. As a matter of fact, several applications based on smart NB-IoT monitoring infrastructures have already been conceived. [PERSON] et al. [32] proposed a general information monitoring approach combining NB-IoT and LoRa communication and a solar power supply system. In particular, the LoRa subnode collects sensor information and conducts point-to-point communications with the main node. Then, it processes the received data and sends information to the server through the NB-IoT communication module. Furthermore, the authors suggested applying their system for grassland and lake information monitoring infrastructures. The Smart City is the main theme in [33; 34; 35; 36; 37; 38; 39]. Specifically, the study in [33] considers some of the key challenges related to smart cities to study the energy consumption, the latency, and scalability for NB-IoT and eMTC technologies. In addition, it formulates the data transmission delay and the maximum number of devices per cell based on different network configurations, by introducing a network simulator tool based on NS-3. [PERSON] et al. [34] placed a grid of ultrasonic or infrared sensors at different harbor spots in order to monitor their occupancy. Collected sensor data are then sent to the administration, becoming able to smartly manage spot reservation and release. Based on the measurements taken in a Danish harbor, the authors indeed demonstrated the suitability of the NB-IoT technology as a signal carrier for maritime applications as well, even though water and boat masts partially affect the transmission. A smart parking system is proposed in [35] in order to reduce the deployment cost and improve the user payment experience. In the proposed system, data of sensor  
Figure 4: Random access procedure sequence diagram. Figure 5: Coverage class hopping of three distinct users during random access procedure with \(\alpha=4\). nodes installed in parking spaces is transmitted by NB-IoT, whereas charge management, sensor node surveillance, task management, and business intelligence modules are implemented on a cloud server. The system was then actually deployed in two Chinese cities for improving the utilization of existing parking facilities effectively. [PERSON] et al. (2019) presented an indoor environment-temperature monitoring system based on NB-IoT sensors and then validated it by means of real experimental results. [PERSON] et al. (2019) addressed the issue of urban garbage management by designing a smart garbage bin based on NB-IoT technology. In particular, they employed infrared and odor sensors to provide garbage detection and classification. As a result, the proposed system changes the existing urban sanitation work mode and improves the efficiency of sanitation workers, at the same time promoting the reuse of recyclable resources. Instead, (2019) designs an intelligent LED street light control system aiming at saving energy and reducing the maintenance cost and difficulty of the urban street lighting. It consists of a cloud server, a remote monitoring interface, and street light control terminals communicating through NB-IoT. This solution realizes local intelligent control and remote supervision of street lights and, thanks to an energy-saving algorithm, the energy consumption of the street lighting is greatly reduced. Finally, in (2019), the authors tried to address the problem of air pollution in a Smart City context. In particular, they developed five types of air pollution detection sensors based on the NB-IoT network in Thailand. Experimental results demonstrate the feasibility of inspecting real-time air quality as a service.