System and method for assigning communications resources in a wireless communications system. A method for operating a base station comprises receiving a resource request for radio resources for a mobile station, in response to a determining that the base station will service the resource request, assigning radio resources based on the resource request and transmitting an indicator of the assigned radio resources to the mobile station, and in response to a determining that the base station will not service the resource request, returning to a normal mode of operations. The assigning of radio requests makes use of a channel tree comprised of two non-orthogonal sets of mappings between nodes of the channel tree and radio resources, with each node corresponding to at least one radio resource.