# Design, Deployment and Evolution of Heterogeneous Smart Public Lighting Systems
## 3 Smart Public Lighting: Infrastructure Architecture and Main Tasks  
The most general architecture of a smart public lighting infrastructure is shown in Figure 1, which outlines all the main components, namely, the Control Center, the communication network (the core network in Figure 1) and the light controller (LC).  
The Control Center is the infrastructure management office: it commands/configures (e.g., light-on, light-off, dimming) each streetlight and monitors the infrastructure operating conditions for maintenance purposes. The command/information exchange between the Control Center and each streetlight takes place through the communication network, which must provide adequate coverage over the whole area where the light fixtures are deployed. Finally, LCs are the smart components of streetlights, as they actuate the commands received by the Control Center and send back the required information. In a smart city perspective, LCs may also be equipped with IoT sensors (e.g., for vehicular traffic metering or air quality monitoring), whose measurements are transmitted to application specific management centers (depicted in Figure 1 as Other Applications). Even in their basic version, smart LCs are in charge of four main tasks:  
* Task 1: to monitor in real-time the state of the luminaire,
* Task 2: to monitor in real-time the electric parameters of the fixture,
* Task 3: to drive the power supply, so as to dim the light intensity,
* Task 4: to establish a communication link towards the Control Center.  
pilot signal, whose voltage is interpreted by the power supply as the light percentage that must be provided (e.g., 1 V = 10%, 5 V = 50%, 10 V = 100%). In the latter case, a bidirectional digital bus is used. When this solution is adopted, the most common choice is the Digital Addressable Lighting Interface (DALI) bus [67]. In this case, data are exchanged by means of an asynchronous, half-duplex, serial protocol over a two-wire bus, with a fixed data transfer rate of 1200 bit/s. Bidirectional communications allowed by DALI are certainly a major advantage with respect to the unidirectional 0-10 V control. Ultimately, the following functionalities are digitally enabled by DALI [67]:  
* light dimming,
* failure detection,
* ability to send data related to the lamp's status,
* ability to send electric information (e.g., voltage, current and power factor).  
Additionally, DALI is more flexible than the 0-10 V control, as no polarity has to be respected for the two wires, whereas the opposite is true for the 0-10 V control. On the other hand, DALI entails an extra cost due to the added electronics and, in case of troubleshooting of dimming issues, it is more complex in terms of diagnostic. Typically, when the DALI bus is adopted in smart streetlight infrastructures, it is embedded in the LC of each luminaire.  
As for the communication interface (Task 4), several solutions may be adopted, either wired or wireless. This choice is of paramount importance because the \"smartness\" of the lighting infrastructure as well the cost for its deployment and management strictly depend on the adopted communication technology. Given its importance, this issue will be discussed in Section 5, which is completely dedicated to communication aspects. In the following subsections, instead, Tasks 1, 2 and 3 are discussed.