The paper presents the studies that have been led toward the integration of device-to-device (D2D) communications within LTE networks in the frame of the project ACCENTS (Advanced Waveforms, MAC Design and Dynamic Radio Resource Allocation for Device-to-Device in SG Wireless Networks) supported by the French National Research Agency. The solutions presented in this paper cover several aspects of D2D communications; they are the result of a close cooperation between four partners: Thales Communications and Security, CNAM, TeamCast and CentraleSupelec. Physical Layer aspects have been investigated, especially concerning waveforms envisioned for D2D communications within SG networks. Also, a new MAC protocol has been designed to address the issues raised by the integration of D2D transmissions within LTE cells. The solution coming out of the study guarantees a minimum QoS for both types of users (D2D users and regular users) and aims at reusing spectrum while offloading the burden on the base station.