Femtocells are attractive candidates for future cellular systems since they can greatly improve coverage and data rates. However, severe interference may occur and hinder the improved system performance due to a large number of femtocells sharing frequency bands with the macrocell. In this paper, we consider the interference problem in two-tier femtocell networks and propose two frequency partitioning methods to mitigate the interference between the macrocell and femtocells. The key idea of the frequency partitioning methods is to partition the whole frequency band into several nonoverlapping parts and allocate different parts to the macrocell and femtocells in different regions. In the proposed methods, the downlink and uplink frequency bands are both divided into four nonoverlapping parts.

The macrocell and femtocell are divided into three or four regions, with one part of the frequency band allocated to one region. With frequency and region partitioning, the users or base stations in one tier and the interfering users or base stations in the other tier are separated by a certain distance, which can greatly mitigate the interference. The main contribution of the proposed methods is that the macrocell and femtocells can assign allocated resources to their own users independently, and the cross-tier interference can be mitigated without complicated resource allocation or cooperation between the macrocell and femtocells. Moreover, we theoretically analyze the existing interference and average per-channel rate performance of different users in different regions. Simulation results show that the theoretical analysis is reasonable and that the proposed methods can successfully mitigate cross-tier interference.

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