Avoidance of Cross-Tier Interference from Open Access Femtocells to Macrocell Users

Cross-tier interference can have severe impacts on the overall macrocell capacity. Avoiding such interference is very important for the co-existence of femtocells within a macrocell. In this paper, we use simple handover strategy between the macrocell and the femtocell to alleviate the problem of cross-tier interference from open access femtocells. The handover to an interfering femtocell is performed only when the femtocell contains unutilised resources having very little or no level of downlink interference to serve the macrocell user. In order to deal with the problem of increased number of handovers associated with the open access femtocells, a timer with a minimum and a maximum value is proposed in every macrocell user. The macrocell user measures the RSS (received signal strength) from the nearby interfering femtocells, and starts the timer from 0 to the minimum value as soon as the RSS from the femtocells become greater than the RSS from the macrocell. Once the timer expires, the macrocell user checks the RSS from the interfering femtocells. If the RSS from the interfering femtocells is still high, the macrocell user again starts the timer from 0 to the maximum value. After the timer expires, the macrocell user again checks the RSS from the interfering femtocells. If the RSS is high, the macrocell user requests a handover. However, if the RSS from the interfering femtocells is low, no handover request is made. The efficiency of the proposed timer can be seen from the simulation results