Geofenced broadcasts via centralized scheduling of device-to-device communications in LTE-Advanced

Point-to-multipoint device-to-device (P2MP D2D) communications have been standardized in LTE-Advanced (LTE-A) for proximity-based services, such as advertisement and public safety. They can be combined in a multi-hop fashion to achieve geofenced broadcasts in a fast and reliable way, over areas possibly covered by several cells [18]. This allows LTE-A networks to support critical services, like vehicular collision alerts or cyber-physical systems, at a modest cost in terms of consumed resources. In this paper, we argue that previous approaches, which rely on User Equipment (UE) applications to make distributed decisions about message relaying, incur in high per-hop overhead and make crossing cell border difficult. We then propose a novel approach that relies on centralized decisions made at the infrastructure eNodeBs (eNBs) to schedule unsolicited D2D grants to the optimal set of UEs that should forward a message at any time. The eNBs can also leverage inter-cell communications through the X2 interface to parallelize relaying over different cells, thus covering larger areas fast. We show that our infrastructure-based approach is computationally feasible and geographically scalable, and prove via simulation that it is faster, more reliable and efficient than UE-based multihop relaying.