Clashes of femtocells with limited number of location area codes

Common cellular blackspots such as low lying areas and indoors have recently countered the problem of poor network coverage through the use of femtocells, i.e., low power mobile base stations deployed in an ad-hoc manner offering dedicated mobile coverage for the home, business or hotspot via a broadband Internet connection. Each active femtocell must be assigned a Location Area Code (LAC) which must differ from neighbouring LACs for Mobility Management purposes of connected end user devices such as handsets. When each LAC is randomly assigned, there is always a probability of adjacent active femtocells being allocated the same LAC. To better understand the frequency of potential clashes, a mathematical analysis is provided to determine the expected number of such conflicts. In this paper, real life femtocell distributions are modelled and simulations performed to confirm derived mathematical results. Both theoretical and simulation results show that the number of clashes can be proportionally decreased by increasing the number of LACs available.