1. A method comprising:receiving, by a first wireless user device from a base station, configuration information associated with direct data transmission between the first wireless user device and one or more wireless user devices, wherein the configuration information comprises information of a resource selection mode for direct data transmission, and wherein the information of a resource selection mode indicates a resource pool from which the first wireless user device selects a resource for direct data transmission to one or more wireless user devices;
mapping a first target identity to a first group identity, and mapping a second target identity to a second group identity, wherein the first target identity is associated with at least one target wireless user device of a first group of target wireless user devices, and wherein the second target identity is associated with at least one target wireless user device of a second group of target wireless user devices;
transmitting, to the base station, a radio resource control (RRC) message comprising information of the first target identity and information of the second target identity; and
transmitting, to the base station, a signal associated with a MAC-layer message, wherein the MAC-layer message comprises:
a first field that indicates the first target identity and indicates the first group identity; and
a second field that indicates the second target identity and indicates the second group identity.