On the Feasibility of In-Device Multiplexed Unlicensed D2D Communications

Device-to-device (D2D) communication finds widespread applicability in enabling connectivity for the Internet of Things. Leveraging the unlicensed frequency bands for D2D communication reduces the spectrum licensing costs, and offloads network traffic from the limited licensed spectral resources. Towards achieving a cost-efficient solution, we study the feasibility of integrating such a D2D operation in the unlicensed band (D2D-U) within legacy cellular devices as a secondary radio access technology in a time division multiplexed manner. To this end, we evaluate the constraints faced in incorporating D2D-U in various challenging environments, such as within devices that use a single radio architecture and a half-duplex with frequency division duplexed cellular operation. We propose time instances that can be exploited to multiplex D2D-U without violating regulatory restrictions imposed on using different unlicensed frequency bands. Based on our analyses and simulation results, we suggest guidelines for a prospective D2D-U protocol that can achieve efficient sidelink communications while also ensuring coexistence with legacy cellular operation.