Interoperability issues on heterogeneous wireless communication for smart cities.

Smart cities have become a reality around the world. They rely on wireless communication technologies, and they have provided many benefits to society, such as monitoring road traffic in real-time, giving continuous healthcare assistance to residents and managing the environment. This article revisits key interoperability questions in heterogeneous wireless networks for smart cities, and outlines a simple, modular architecture to deal with these complex issues. The architecture is composed by sensing, access network, Internet/cloud and application layers. Different features provided by the architecture, such as interoperability among technologies, low cost, reliability and security, have been evaluated through experiments and simulations under different scenarios. The QoS support and the seamless connectivity between pairs of heterogeneous technologies are proposed through a policy-based management (PBM) framework and MIH (Media Independent Handover). Moreover, an 802.11 mesh backbone composed of different types of mesh routers has been deployed for interconnecting the sensors and actuators to the Internet. Key results from experiments in the backbone are examined. They compare: (i) the performance of a single-path routing protocol (OLSR) with a multipath one (MP-OLSR); (ii) the monitoring delays from the proposed low cost sunspot/mesh and arduino/mesh gateways; and (iii) the authentication mechanisms employed. Significant results from simulations allow the analysis of the reliability on vehicular/mesh networks under jamming attacks by applying the OLSR and MP-OLSR routing protocols. Finally, this article provides an overview of open research questions.