Device-to-Device Communications Underlaying Cellular Networks in Unlicensed Bands

Device-to-Device (D2D) communication, which enables direct communication between nearby mobile devices, is an attractive technique to improve spectrum efficiency by reusing licensed spectrum. Nowadays, LTE-unlicensed (LTE-U) emerges to extend the cellular network to the unlicensed spectrum to alleviate the spectrum scarcity issue. In this paper, D2D communication is allowed to work in unlicensed spectrum (D2D-U) as an underlay of the cellular network for further booming the network capacity. A sensing-based protocol is designed to support the unlicensed channel access for both LTE and D2D users, based on which we investigate the subchannel allocation problem to maximize the total sum rate while taking into account their interference to the existing Wi-Fi systems. Specifically, we formulate the subchannel allocation as a many-to-many matching problem with externalities, and develop an iterative user-subchannel swap algorithm. Analytical and simulation results show that the proposed D2D-U scheme can significantly improve the network capacity.