Dynamic Optimization of Neighbor Cell List for Femtocells

To select appropriate target cell for handover if a user is moving, cells in user´s neighborhood must be scanned and their signal quality must be measured by a User Equipment (UE). The cells intended to be scanned are listed in a Neighbor Cell List (NCL). The NCL is defined for each cell in the network and it is distributed to the users. A size of the NCL can be negatively influenced by dense deployment of cells with small radius, such as femtocells. In this paper, we investigate potential reduction of an amount of cells in the NCL to minimize signaling overhead and time required for scanning in networks with femtocells. Contrary to a conventional management of the NCL, we reduce the NCL for each UE individually. The lower number of cells in the UEs´ NCL is achieved by consideration of mobility patterns of individual user. To avoid situation when a real target cell is missing in the NCL, we propose a dynamic adaptation of the UE´s NCL according to the quality of signal measured by the UE from a serving cell. As the results show, the proposed approach with dynamic threshold significantly reduces amount of scanned cells comparing to competitive algorithms. Simultaneously, the outage probability and call drop rates are still kept at minimum level by our proposal.