A method is disclosed for determining by a UTRAN a persistence value having a value between 0 and 1 for adjusting a number of access preambles from a plurality of UEs requiring assignment of a common packet channel (CPCH). The method includes the steps of counting a number of the access preambles detected in an access preamble period having a predetermined period; and determining the persistence value based on the number of counted access preambles. The persistence value is determined in a unit of transport format (TF), physical common packet channel (PCPCH), or CPCH set.