Apparatus and method for resource allocation are provided. An apparatus includes a controller configured to: utilize a tree structure with more than one branch in the resource allocation of physical resource blocks, each branch including one or more legal starting positions for resource allocation. Each starting position is associated with a cluster of physical resource blocks, the number of starting positions being different on each branch. The size of the resource clusters of each branch is different. The controller is configured to denote each resource cluster with a predefined index, and allocate one or more clusters to user equipment uplink connection.