Performing an unscheduled uplink transmission by a user equipment, UE, in an unlicensed portion of a radio spectrum, the method comprising: performing (1002), by the UE, a listen before talk, LBT, operation in the unlicensed portion of the radio spectrum, wherein the LBT operation includes sensing the portion of the radio spectrum for a pre-determined minimum amount of time for traffic; and performing (1004), if no traffic was sensed, the unscheduled uplink transmission, by the UE, of data in an unscheduled mode of operation for at least one transmission burst. Receiving (10110) by the UE an uplink transmission grant. In response to receiving the grant, transmitting, by the UE, an uplink transmission burst of new data, and sending (1012), by the UE, an unscheduled retransmission for the data if a new uplink grant or HARQ ACK/NACK is not received from an eNB within a pre-specified time window.