A method for a terminal including a first media access control (MAC) layer and a second MAC layer to create an authorization key includes performing a first network entry process to a base station through the first MAC layer, and performing a second network entry process for a frequency overlay to the base station through the second MAC layer. In this instance, the first network entry process includes acquiring a key for generating an authorization key through an authentication process according to an authentication method negotiated with the base station, and generating a first authorization key through the key for generating the authorization key. The second network entry process includes generating a second authorization key by using the key generated in the first network entry process for generating the authorization key.