A novel multi-hop secure LTE-D2D communication protocol for IoT scenarios

The Internet-of-Things (IoT) is promising to inter-connect physical objects and machines in an intelligent network. In this context, scalable and resilient Machine-to-Machine (M2M) communication protocols are required, and the new Device-to-Device (D2D) feature of the 4G system constitutes an appealing solution. Standardization activities are still in progress, but the rapid diffusion of both LTE and IoT devices and applications leads to development of experimental proposals aimed at merging these two technologies. We contribute in this work with a novel D2D communication protocol, which enables user equipments (UEs) to become the hubs of machine-type traffic by means of a suitable radio interface and upload data in the Web via the mobile network, thus opening to new cloud services. The protocol we propose is designed for multi-hop communications between D2D-enabled terminals and it is equipped with a light-weight security mechanism. It is meant to address the communication needs of UEs inside mobile network coverage, and those of UEs that suffer from scarce radio coverage. In terms of performance, we analyse connectivity and security in the multi-hop D2D network, taking into account the interference created by the transmission of beacon signals during the discovery phase of the wide network. We resort to stochastic geometry to model the end-to-end delay and communication resilience of the multi-hop D2D network.