The present invention relates to methods and apparatuses (radio base station (120, 600) and UE (110, 700) for enabling a UE to perform a random access. According to embodiments of the present invention, an identification number of a dedicated random access preamble is, in a message, transmitted together with information indicating in which channel or channels the preamble is valid for the UE. The UE (110, 700) can then use the received information and based on that information perform a random access.