The periodic scan and velocity decision handover scheme for next generation femtocell/macrocell overlay networks

Femtocells, that operating in licensed band, are low power base stations installed indoor to provide user access to 4G systems. The deployment of femtocells is a very promising option for mobile operators to improve user´s communications experience in a cost-effective manner. Traditional macrocell only systems using the signal strength as the major criteria for triggering scan and handover are no longer enough for femtocells system. This paper, in addition to the RSSI trigger, we add periodic trigger and consider mobile station speed into our handover algorithm in next generation WiMAX femtocell/macrocell overlay environments. In particular, the proposed handover mechanism consists of all of the handover scenarios, including femtocell-to-femtocell and macrocell-to-femtocell and femtocell-to-macrocell handover. In simulation, we demonstrate that the proposed mechanism forces the macrocell users handover into available femtocells, thus, improves the femtocell usage, offloads the macrocell traffic while avoiding unnecessary handover when user are moving in high speed.