The invention relates to transmitting and receiving data in subframes of a wireless communication system. It includes at the user equipment receiving an uplink grant for transmitting data on predetermined resources of an uplink carrier; detecting by carrier sensing whether or not the predetermined resources are available for transmission; and if the predetermined resources are detected to be available for transmission, transmitting data in the predetermined resources and transmitting a transmission confirmation indication indicating that the data has been transmitted. At the receiving side, the transmission confirmation indication is transmitted and based on, the received data is handled.