Cost-Efficient Mobility Management in 5G

Signal quality fluctuates significantly due to blockages of Line of Sight, shadowing, and user mobility. This renders mobility management in 5G quite challenging. To improve it, 3GPP introduced Conditional Handover (CHO), which reduces handover failures by preparing target Base Stations in advance. This algorithm adapts to the varying channel conditions and constantly prepares/releases cells, which leads to an increased exchange of control messages between the user, serving and target BSs. Connecting to the BS with the strongest signal is not always beneficial because available resources and other users' channels should be considered for a successful network operation. Hence, the need to carefully decide when to hand over, and when that happens, to select the best target BSs. In this paper, we formulate an optimization problem that minimizes the network signaling by reducing the number of unprepared handovers and wasted cell preparations, while providing a minimum rate to everyone. As the problem is NP-hard, we proceed with two approaches. Firstly, we relax it and obtain a lower bound. Secondly, we propose a Cost-Efficient CHO (CECHO) algorithm with performance guarantees. Using 5G trace data, we compare CECHO with two baselines and show that it outperforms them by at least 54% while being near-optimal.