A base station (BS), a user equipment (UE), a transmission control method for the BS and a data transmission method for the UE are provided. Based on user group information, the base station transmits uplink transmission control information to a plurality of the UEs in a group to make each UE contend for a plurality of subframes in the allocated unlicensed band radio resource pool. If a UE successfully contends for a subframe, the UE transmits a reservation signal and transmits an uplink data signal in the contended subframe. If the UE detects another reservation signal when contending for the subframe, the UE determines whether the another reservation signal is associated with the ID of its group. If associated, the UE transmits the uplink data signal in the subframe.