Device-to-device communications over unlicensed spectrum

Abstract

Device-to-device (D2D) communication, which enables direct communication between nearby mobile devices, is an attractive add-on component to improve spectrum efficiency and user experience by reusing licensed cellular spectrum. Nowadays, LTE-unlicensed (LTE-U) emerges to extend the cellular network to the unlicensed spectrum to alleviate the spectrum scarcity issue. In this chapter, we propose to enable D2D communication in unlicensed spectrum (D2D-U) as an underlay of the uplink cellular network to further boom 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 sum-rate of LTE and D2D users 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.