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• The Access burst comprises a preamble and a few bits of payload data
– Several preamble formats (lengths) are specified
• Initial message from the mobile use nonsynchronised timing
• The eNodeB supplies the required Timing Advance
• Any subsequent transmissions can use synchronised PRACH

Initially, the time delay between the base station and the mobile is not known accurately, so the PRACH transmissions are not synchronised. Subsequently, the timebase at the mobile is adjusted and the transmissions are synchronised with uplink transmissions from other mobiles in the cell.
There are several preamble sequences defined for a cell, the mobile selects one randomly and this is used to identify the mobile in the response sent from the base station.