Analytical evaluation of femtocell deployment in cellular networks using fractional frequency reuse

Although deploying femtocells over traditional cellular networks has been considered as an effective way to improve the coverage and the capacity of the wireless networks, the consequent interference arising from an intercell and a crosstier limits the performance. The authors propose a spectrum allocation scheme for the femtocells and the macrocells based on a fractional frequency reuse (FFR) strategy to mitigate the interference. They adopt a hybrid model where the macrocells form a hexagonal grid whereas the femtocell base stations (FBSs) form a spatial Poisson point process (PPP) to model the two-tier network. Instead of relying on the purely numerical simulations, they give an analytical evaluation of the performance of the mobile users according to their spatial locations. The optimal spectrum allocation is required to maximise the long term expected network throughput with the quality of service (QoS) constraints. Simulations are presented to validate the accuracy of the author´s analysis and figure out the relationship between the network throughput and the density of the femtocells and the radius of the interior region of a macrocell, which can be guidelines in practical system design.