# Design, Deployment and Evolution of Heterogeneous Smart Public Lighting Systems
## 5 Network Architectures and Transmission Technologies
### Wireless Networks
#### 5.2.3 Mesh Networks  
Connectivity issues arising with star networks can be overcome adopting a mesh network architecture. In this case, wireless nodes can connect directly, non-hierarchically and even dynamically, to as many other peer nodes as required, provided that they are in their coverage range, and cooperate with one another to efficiently route data. This lack of dependency on a central node allows for every node to participate in the relay of information, which propagates hop-by-hop. The typical mesh network in a smart lighting scenario is depicted in Figure 4. One observes that streetlights are grouped in clusters, in which hop-by-hop communications are allowed among neighbors. These communications usually take place by means of short range, low cost, communication technologies, such as IEEE802.11.4 and Bluetooth. Within each cluster, one or more streetlights can communicate with a special network node that is also equipped with a long-range communication technology (cellular, optical fiber,...). This enhanced node acts as a gateway, allowing the bidirectional exchange of information/commands between the Control Center and all poles of the cluster. If the cellular network is adopted to connect the gateways to the Control Center a fee is to be paid, which is however scarcely significant as the number of gateways is much lower than the number of streetlights. This architecture is much less prone to coverage issues, because neighboring streetlights are close one to the other, and in most cases they experience line-of-sight propagation conditions. Moreover, inter-pole communications do not require any subscription (nor any fee) to a network provider, because the owner of the public lighting infrastructure is also the owner of the inter-pole communication network. In the following, two of the most important technologies for mesh networking are presented, namely IEEE802.15.4 and Bluetooth. **IEEE 802.15.4**: IEEE 802.15.4 [95] is a short-range wireless technology supporting applications with relaxed throughput in wireless personal area networks (WPANs). The standard specifies the physical and media access control layers for Low Rate-Wireless PANs (LR-WPANs), and is maintained by the IEEE 802.15 working group. It is the basis for the Zigbee, WirelessHART, ISA100.11a, 6 LoWPAN, MiWi, Thread and SNAP specifications,  
Figure 3: LoRaWAN/Sigfox-based smart lighting architecture. each of which further extends the standard by developing the upper layers, which are not defined in IEEE 802.15.4. As far as the physical layer is concerned, several modulations schemes can be used, providing over the-air speeds of up to 250 kbps in specific unlicensed (depending on the geographic region) 800, 900 and 2400 MHz bands. The transmission range goes from tens to hundred meters, depending on the propagation conditions. Figure 4 shows the general architecture of a smart lighting mesh network based on the IEEE802.15.4 technology. At the lowest level, an IEE802.15 equipped LC is mounted in each streetlight, directly controlling the luminaire and providing connectivity with the other light-poles. At the intermediate level, managing a sector of the lighting infrastructure, there is an enhanced IEEE 802.15.4 node that acts as a gateway towards the Control Center, thanks to an additional long-range communication interface, either wireless (e.g., cellular) or wired (e.g., optical fiber). According to the IEEE 802.15.4 terminology, the gateway is termed Coordinator, whereas each sector of the lighting infrastructure controlled by a Coordinator is termed personal area network (PAN). In order to avoid mutual interference, adjacent PANs work on different channels. Lastly, at the upper level there is the Control Center, which manages all sectors of the lighting infrastructure. The information propagates from the center to the peripheral (and backwards) hopping from one luminaire to another.