The invention relates to a method for performing a random access procedure between a user equipment and a radio base station. The UE is configured with at least one unlicensed cell having an unlicensed cell frequency, via which the UE performs the random access procedure bandwidth. A minimum frequency bandwidth threshold is defined for transmissions via the unlicensed cell. The user equipment selects a random access preamble sequence for the random access procedure. A frequency bandwidth is determined by the UE for transmitting the random access preamble sequence via the unlicensed cell, the determined frequency bandwidth of the random access preamble sequence being at least the minimum frequency bandwidth threshold. The UE then transmits the random access preamble sequence to the radio base station such that at least the determined frequency bandwidth of the unlicensed cell is occupied.