Downlink Interference Mitigation Scheme for Two-tier OFDMA Cellular Networks

In a two-tier cellular network, macrocells and femtocells coexist. Since femtocells use low transmission power and share network resources with macrocells, they are considered as one of the promising solutions to highly congested network environments. However, since femtocells are deployed in a selforganized manner without cell-planning, they cause severe downlink interference to macro users. Therefore, this paper focuses on the interference problem of macro users caused by femtocells, so-called the coverage hole problem. Our scheme enables femtocells to cooperate with macrocell users through using the proposed uplink signaling subchannel (USS) and resource usage detection procedure (RUDP). It controls femtocells to adjust the amount of their resource usage adaptively, thereby clearing the downlink resources for interfered macro users. Through simple analysis and simulations, we confirm that our scheme outperforms the conventional power control scheme in terms of downlink achievable rate.