# A Testbed for GNSS-Based Positioning and Navigation Technologies in Smart Cities:
## 7 Conclusions  
A Smart City requires an intelligent infrastructure to serve its urban area with heterogeneous services and applications. Today, such an infrastructure is essentially composed of three main layers. The _perception layer_, implemented by means of IoT, senses and interacts with the environment and collects and consumes data and information and data flows back and forth through smart gateways to the network layer. This latter interconnects the IoT with the back-end processing technologies. The _network layer_ today is augmented with edge computing capabilities to pre-processing, cross-reference, and fuse data, to create a preliminary distributed intelligence able to interact with the perception layers and with high performance computing elements in the cloud. The _application layer_ is finally responsible to analyse massive data and preliminary information by means of intelligent technologies [64]. Several elements of this infrastructure and the end-users (very often IoT themselves such as smartphones, vehicles, etc.) require precise location and timing information. GNSS is the natural enabler to satisfy these needs, through its global coverage and free of charge provision of location data but it is not the sole ingredient. The HANSEL project, while developing a _testbed_ for diverse positioning and navigation technologies presented in this manuscript, has designed, developed, and tested an architecture (for positioning and timing services) that easily fit in the aforementioned Smart City infrastructure by adding relevant value. Indeed, the HANSEL architecture, once integrated in a Smart City, can be augmented with new services in a scalable fashion. The architecture is made of interoperable micro-services with standard interfaces and format. The proposed approach deviates from a monolithic philosophy and adopts a scalable attitude that allows Smart City architects to split it over the three layers of infrastructure. Microservices constitutes an architectural style structuring services and applications as a collection of (smaller) services that are highly maintainable, testable, and traceable. These microservices can be deployed independently, which reverts to greater flexibility, thus allowing better organisation around different business capabilities and use cases. The HANSEL _testbed_ provides a framework to gather navigation data retrieved from heterogeneous and asynchronous devices (i.e., IoT Sensors, Smartphones, and general purpose GNSS receivers). In parallel it leverages a scientific tool to investigate and support research and development of GNSS state-of-the-art and innovative technologies through a uniform multi-services system. The framework is conceived as a centralised entity that collects data from different services by covering in turn different applications and case studies. All HANSEL services are designed to be interoperable and the service APIs can be exploited through mobile applications running on smart devices or more sophisticated tools. Currently, the service interoperability is foreseen for the CAC and CPA only. The mobile application supporting the DGNSS-CP paradigm is indeed capable of interacting with the CAC to be monitored and retrieve navigation tips (e.g., turn left, turn right, out of path) based on the hybrid PVT solution computed through cooperation with other agents. Interoperability deserves to be ensured for all the service to support future hybridisations of the available technologies. The development and first validation of such an architecture is an important result, no less important than having built the _testbed_ itself because it represents a concrete and viable solution that could overcome limitations of many technologically-advanced solutions on the market today, namely the verticality, the impossibility of reuse, and their vendor lock-in nature, which allows only the manufacturers to pursue upgrades and plan technologies or products evolution.