# Design, Deployment and Evolution of Heterogeneous Smart Public Lighting Systems
## 5 Network Architectures and Transmission Technologies
### Wireless Networks  
#### 5.2.1 Cellular Networks  
Cellular networks are ubiquitous and widespread, covering around 95% of world inhabitants [87] and almost the totality of populated areas. Given their ubiquitous reach, cellular networks appear the ideal solution to effortlessly connect light fixtures to the Control Center. In principle, under the umbrella of the cellular network coverage, connecting a streetlight to the smart lighting infrastructure is as simple as equipping it with a cellular radio interface and turning it on. It will immediately connect with the cellular network that is already in place. From the perspective of the public lighting holders, this is certainly a good point, as no network installation is required nor its maintenance. Moreover, cellular networks provide data rates that can scale from few kbps to hundreds of Mbps, thus supporting almost every service, from simple telemetering to more bandwidth-demanding applications, like video-surveillance. Focusing the attention on the basic smart lighting service, which generates small amount of data, it could rely on the two emerging cellular-based IoT standards, namely narrowband-IoT (NB-IoT) and long-term evolution (LTE)-Cat-M1, which have been designed to implement Low-Power Wide-Area Networks (LPWANs). Both technologies are deployed as overlays of the LTE 4G cellular networks and provides data rate up to 250 kbps (NB-IoT) and 1 Mbps (LTE-Cat-M1), respectively. Like all LPWAN technologies,  
Figure 2: PLC-based smart lighting architecture. they have been designed to allow long range (several kms) communications at a low bit rate among connected \"things\", such as sensors powered by batteries. Cellular networks, along with their LPWAN developments, certainly appear a convenient solution for providing the smart lighting infrastructure with the required connectivity. There is, however, a number of issues that should be carefully considered. First of all, connectivity is very critical to smart lighting. Street lights that do not experience an adequate level of received power from the cellular base stations are out of the infrastructure-management control. This issue is particularly critical because, although it is true that cellular networks are ubiquitous and widespread, a target coverage of 100% can not be reached in dense urban environments. Buildings or other obstacles can obstruct the signal propagation to an extent that in some locations the communication is impossible or, at least, intermittent. Furthermore, this situation may occur at any time, as new buildings are raised. Fixing such issue could be very difficult, because the cellular network is owned by a third party (the network operator), which could not be willing (owing to cost or technical difficulties) to change the network layout. Secondly, since cellular networks are run by third party providers, lighting infrastructure holders have to pay a cost for their usage, which could be significant because thousands of streetlights have to be connected. Thus, the economic saving achieved thanks to the smart light management is reduced owing to this additional cost. Moreover, network operators might decide to increase over time the cost for the service subscription, according to dynamics not controlled by the lighting infrastructure holders. Thirdly, using the cellular network to provide connectivity to streetlights suggests that the lighting infrastructure holder is unwilling to implement and manage its private communication network. Although this choice is understandable, as it reduces the effort on the public lighting holder's side, it prevents the possibility to use such private network also for additional IoT services that might be of interest. For instance, the lighting infrastructure holder could gain revenues by giving other utilities (waste collectors, smart bike rentals,...) the access to its private network, or simply give them free access in order to foster such services.