Handoff decision making in 3-tier heterogeneous cellular networks

This paper studies the problem of handoff decision making in 3-tier heterogeneous networks which consist of one macrocell and numerous small cells and femtocells. This study shows that the decision making of whether a user equipment (UE) switches to a small cell or femtocell is highly related to the UE velocity when it approaches the boundary between the macrocell and small cell or between the macrocell and femtocell. To avoid a UE with high speed switches to a small cell or femtocell for getting better signal strength but will be enforced to switch back to the macrocell soon caused by his/her high moving speed, this paper investigates a ratio of handoff processing time to a cell to the expected resident time in a cell as the criterion for the UE handoff among these cells (e.g., small cells, and femtocells). Numerical results show that the inappropriate handoff probability of the proposed scheme is lower than that of without considering the UE velocity when the moving speed is high (e.g., the speed is higher than 100 km/hr).