On Mobility Parameter Configurations That Can Lead to Chained Handovers

Optimization of mobile networks is a crucial task for operators aiming to offer a high quality of service. In this paper, we focus on the handover (HO) problem. An HO is the procedure through which a user changes its serving cell, ensuring service continuity for mobile users. The HO procedure is typically governed by several variables: the received signals powers and the HO parameters (offsets and hysteresis) corresponding to the different cells. HO parameters allow to modify the cell borders in order to balance loads, and prevent radio link failures and HO ping-pongs. There are two approaches for defining HO parameters: one is to use per-cell parameters and the other is to use per-cell-pair parameters. Per-cell-pair parameters provide more degrees of freedom in HO parameter optimization as we benefit from independent parameters for each neighbour. However, we show that it can lead to instabilities in the form of continuous chained HO, i.e., several HOs that follow one shortly after another, among three or more cells. Then, we show that using the same HO parameters toward all neighbouring cells, i.e., per-cell parameters, is risk free of such problems. We provide numerical results outlining the tendencies of this risk.