On cross-tier interference in co-channel deployed two-tier macro and femto networks

In this paper, a novel parameter named cross-tier interference to signal ratio (CISR) is defined to characterize cross-tier interference in the co-channel deployed two-tier macro and femto networks. Cross-tier interference to signal budget (CISB) is derived to characterize the tolerance of cross-tier interference for given per-tier downlink signal to interference ratio (SIR) targets and outage probability constraints. Network load is defined to show how the two-tier network is affected by parameters of the femto tier. Based on the analysis of CISRs and network load, the maximum density of simultaneously transmitting co-channel femtocells, tight upper and lower bounds of transmission power of femtocells for guaranteeing reliable macro and femto coverage in the two-tier network are obtained. A decentralized FAP regulation strategy which aims to maximize the number of co-channel transmitting femtocells under consideration of guaranteeing reliable macro and femto coverage is proposed. Simulation results verify our theoretical claims and demonstrate the effectiveness of the proposed femto regulation scheme in terms of spatial reuse efficiency.