## 2 UAN Use Cases and Requirements  
UANs enable a wide spectrum of Smart City applications [5; 6; 8; 11]. A list of relevant examples, along with their main features, is provided below and is illustrated in Figure 1.  
* **Garbage collection**. Garbage containers can be provided with sensors that measure the containers' occupancy. This information can be used to ensure compliance with recommendations on waste management, and to optimize garbage truck routes.
* **Lighting control**. Street light control can be automated based on measurements carried out by light sensors. Furthermore, street light intensity levels can be tuned based on the presence of people or vehicles, which can be detected by using presence sensors.
* **Green zone management**. Efficient and automated water irrigation systems can be applied in green zones by exploiting humidity sensors placed in the ground.  
* **Environmental control**. Sensors can be used to monitor physical magnitudes relevant to the citizens' and environmental health, such as weather conditions, air composition, acoustic pollution and ultraviolet solar radiation, among others.
* **Parking availability**. Several types of sensors (such as pressure, ultrasound or magnetic field sensors) may be used to identify empty parking spaces, which constitute a scarce resource in cities. The event of a parking space becoming available must be communicated quickly.
* **Street traffic**. Magnetic loops can be used for monitoring road traffic. The collected information can be published, in order to allow the citizens take suitable route decisions, avoid congested areas and minimize their contribution to air pollution. Furthermore, traffic lights may be intelligently controlled based on the current road traffic state.
* **Utility infrastructure**. Large equipment infrastructures from utility companies are deployed in the city, often underground, for providing gas, electricity, water, telecommunications and sewage services. Use of appropriate underground sensors can dramatically decrease failure detection times, help identify the location of breakdowns or leaks, and allow preventive maintenance.
* **Security**. Presence, proximity or even glass-break sensors may be used to detect or prevent intrusion into municipality areas (e.g., buildings, parks, _etc._) during time periods in which access is not allowed.  
Table 1 shows requirements and characteristics of the presented Smart City applications that must be met by the UANs supporting them. Periodic notifications from sensor nodes constitute the main source of data traffic. These notifications, which also serve as implicit network health messages, are not subject to real-time requirements. A subset of the applications tolerate infrequent sensor node connectivity opportunities (e.g., twice per day). Data traffic is asymmetric in UANs since the messages sent by sensor nodes towards the gateway outnumber the messages sent to actuators (or to sensor nodes, e.g., for management tasks). Applications that involve event-based traffic require permanent connectivity and relatively low delay (e.g., up to around ten seconds). Certain applications pose strict requirements on the sensor node location. In such cases, the UAN must be capable of providing adequate coverage in the intended sensor node locations.  
Figure 1: Example Urban Automation Networks (UAN)-enabled applications in a smart city.