1. A method for a UE performing device-to-device (D2D) communication, the method comprising:receiving, by the UE, a group ID identifying a D2D group that comprises a plurality of UEs for D2D communications, the group ID being associated with the plurality of UEs in the D2D group;
receiving, by the UE from a base station, a configuration for D2D communications of the D2D group, the configuration indicating whether a subframe is configured for the D2D communications of the D2D group;
generating, by the UE, a D2D buffer status report (BSR) for D2D communications by the UE in the D2D group triggered by expiry of a D2D BSR timer, the D2D BSR comprising information of an amount of D2D data available for transmission by the UE in the D2D group, the D2D BSR timer being configured for D2D BSR reporting by the UE, the D2D BSR timer different than a periodicBSR-Timer and a retxBSR-Timer that are configured for cellular BSR reporting by the UE, and the D2D BSR comprising the group ID identifying the D2D group and a D2D BSR logical channel identifier (LCID) of the D2D BSR;
transmitting, by the UE, the D2D BSR to the base station on an uplink channel in a control element;
receiving, by the UE from the base station, a resource allocation for D2D communications of the UE in the D2D group in response to transmitting the D2D BSR;
transmitting, by the UE to the D2D group, D2D data over an allocated resource in response to determining that the allocated resource is configured for D2D communications according to the configuration that is received; and
retransmitting, by the UE, the D2D BSR upon receipt of less than a threshold number of Acknowledgement (ACK) messages for the D2D group, an ACK message being for acknowledging receipt of the D2D BSR.