Embodiments herein relate to a method in a mobile terminal (10) for requesting access to a wireless communication system. The mobile terminal (10) receives broadcasted system information directly indicating first access request preambles for a first contention based channel, and indirectly indicating second access request preambles for a second contention based channel based on the directly indicated first access request preambles. The mobile terminal (10) further derives the second access request preambles from the first access request preambles. Additionally, the mobile terminal requests access using the second access request preambles or the first access request preambles to access the wireless communication system.