Cell ID extension in femtocell environments

In this paper, we solve a cell identification problem in a femtocell environment. Wireless communication standards specify physical cell identifiers (PCIs) for user entities (UEs) to discriminate data from different cells and for networks to identify cells. However, in the densely deployed area, the number of PCIs for femtocells may not be sufficient. The scarcity of PCIs results in identification ambiguity due to duplicated PCIs in a certain area, which may result in handover failure. Using time synchronization between femtocells and macro-cells, we propose a scheme to efficiently identify cells in a femtocell environment. The proposed scheme defines the virtual cell identifier (vID) of a femtocell as the system frame number offset of the femtocell with respect to a macro-cell and differentiates femtocells with combinations of vIDs and PCIs. Our scheme can increase the number of cell identifiers up to 1024 times using even coarse local time synchronization without changing the existing physical layer specification. The improvement in cell identification resolution reduces redundant message transactions, resulting in network performance enhancement. Since our scheme demands only local time synchronization between adjacent cells, it can be applied to asynchronous as well as synchronous wireless systems. We verify the proposed scheme via simulations in various environments.