Femtocell has been considered as a promising technology in wireless communications to extend indoor service coverage and enhance overall network capacity. Two-tier networks, where the current cellular networks, i.e., macrocells, overlapped with a large number of randomly distributed femtocells, can potentially bring significant benefits. If femtocell access points (FAPs) operate within the same frequency band as macrocells, the cross-tier interference (CTI) creates a distinct impact on the system performance. This paper studies the uplink (UL) interference at FAP caused by approaching macrocell users (MUEs). It is noted that the CTI is more significant to the closed subscriber group (CSG) femtocells. We propose an incentive mechanism (IM) for CSG femtocells to alleviate the UL interfference from approaching MUEs, thus preventing the femtocell users performance from degrading and protecting the neighbor FAPs that might also suffer from the UL interference. Meanwhile, the macrocell also benefits from the IM, in terms of energy saving and UL spectral efficiency. Simulation results show that close to the ideal performance when no CTI presents can be achieved with IM, demonstrating that the proposed scheme is very effective in dealing with uplink CTI.
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