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

Femto base stations are usually installed in the region of macro cells 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 macro cells hardly camp on femtocells, even if the RSS of femtocells satisfies the link quality requirement. In order to increase offloading of users(UEs) from macro to pico 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 macro cells and femtocells by a priori setting a femtocell boundary, indicating that user equipments 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.