## 2 Distributed Control and IoT Architectures in Smart Environments
### Low Power Wide Area Networks  
The communication for IoT applied to smart environments can be carried out in several ways. Backend servers use traditional Internet infrastructures. Connectivity of IoT smart objects is mainly  
Figure 2: Multiple views of the IoT architecture (The rightmost model is defined in [36]).  
wireless: the most popular choices are technologies like Bluetooth, ZigBee, Z-Wave, and Wi-Fi, if the distances are up to 100 m. Beyond that range, there is the new field of the LPWAN technologies, where LoRaWAN and SigFox are the most widespread ones. Everything started considering that, in order to be effective, large coverage, network scalability, low-cost and low-power consumption are all fundamental requirements. Hence, LPWAN approach has been suggested as a viable answer to these requests. In particular, the LPWAN technologies trade off radio coverage, node density and power consumption with relatively long update rate. Generally speaking, LPWAN is an umbrella for covering those technologies that typically:  
* Operate in the sub-GHz unlicensed bands (avoiding the over-crowded and shorter range 2.4 GHz band); regional limitations may arise, which are usually accomplished by using \"listen-before-talk\" and duty-cycle based strategies;
* Leverage on narrowband modulation, resulting in a limited raw throughput on one side, but providing very good receiver sensitivity (allowing a link budget on the order of 150 dB) on the other one;
* Implement simple and low demanding protocol stacks complemented by simple communication infrastructure (thus minimizing both the power consumption and the cost); thus, end nodes are kept simple and the complexity is moved into the backend servers.  
In particular, referring to the latter aspect, the network topology is a star (i.e., single-hop network), mimicking the approach typically pursued by mobile communications (in which mobile devices connect to a base station controlled by a base station manager). It has to highlight that mobile communications, despite partially overlap with LPWAN target scenarios, are an ideal complement and, especially when 5G systems will be available, could be used for implementing the backbone of a wireless multi-tier approach. In some papers, such possible integration has been discussed [42; 43].  
Considering the heterogeneous requirements of the Smart Campus application the most suitable LPWAN solution is LoRaWAN, whose main features are flexibility, scalability, wide diffusion, and module availability from many manufacturers. Moreover, the technical properties of LoRa (e.g., the virtual channels for implementing adaptive datarate) and the possibility to build proprietary infrastructure make LoRaWAN unique. On the other hand, SigFox is not suitable for smart campus since it operates on a third-party service provider, and it suffers from low datarate and fixed number of message per day. For sake of completeness, in Appendix A is reported an overview of LoRaWAN technology with a discussion of its features. An experimental validation of its suitability for the scope of this paper (in terms of coverage and latency) is also included.