Analysis of Handover Decision with Adaptive Offset and Link Quality Threshold in Next-Generation Hybrid Macro/Femto-cell Networks

Femto base stations are usually installed in the region of macrocells in next-generation hybrid macro/femto-cell networks, and the transmit power of macro base stations is much larger than that of femto base stations. Because the conventional handover decision is only based on the received signal strength (RSS), user equipments near the center of macrocells hardly camp on femtocells, even if the RSS of femtocells satisfies the link quality requirement. In order to offload more users from macro to femto base stations, a cell-specific virtual offset is added to the RSS to artificially expand the cell range of the femto base stations. We analyze handover decision performance with adaptive offset. When the RSS of femtocells satisfies the link quality threshold, the algorithm compensates large differences between RSS measurements of macrocells and femtocells by a priori setting a femtocell boundary, indicating user equipments to stay inside the expected coverage of femtocells. We mathematically assess the algorithm in a log-distance path loss and log-normal shadowing environment, and compare it with the conventional one under two different trajectories, moving forward and perpendicular. The numerical results show that with our adapted offset the algorithm can efficiently raise the utility of femtocells and reduce unnecessary handover numbers.