Multi-Path D2D Leads to Satisfaction

Abstract

Device-to-Device (D2D) communications potentially allow users placed in a cell to establish direct connections among them using several connection modes. In this paper, we propose \textsl{Multi-Path D2D (MPD2D)}, a mathematical optimisation framework that accounts for the availability of D2D modes under flow demand requirements. MPD2D selects the combination of cellular and D2D links that fits better for boosting the network benefit. We consider the \textsl{Underlay} and \textsl{Overlay} as \textsl{Inband} D2D modes over cellular technology (LTE) and the \textsl{Outband} D2D mode exploiting WLAN technology (WiFi). Throughput, energy consumption, interference, and flow requirements are managed in order to maximise a network utility function accounting for cell capacity and power efficiency. We also derive a user's satisfaction metric that accounts for the history of users within the cell. Integrating such a metric is lightweight yet very effective to drive towards almost complete fairness for the system over time. Our optimisation scheme is formulated as a Binary Non-Linear Program which results in very high performance in terms of throughput gain in comparison to other benchmarks for the \textsl{D2D mode selection problem}. Finally, we propose two effective heuristics whose performance and complexity we compare with optimal results and that largely outperform state of the art solutions.