A Non-Stationary Online Learning Approach to Mobility Management

Efficient mobility management is an important problem in modern wireless networks with heterogeneous cell sizes and increased nodes densities. We show that optimization- based mobility protocols cannot achieve long-term optimal performance, particularly in a time-varying environment for ultra-dense networks. To address the complex system dynamics, especially the possible change of statistics due to user movement and environment changes, we propose piece-wise stationary online-learning algorithms to track the activities of small base stations and solve frequent handover (FHO) problems. The BASD/BASSW algorithms are proved to achieve sublinear regret performance in finite time horizon and a linear, non-trivial rigorous bound for infinite time horizon. We study the robustness of the BASD/BASSW algorithms under missing feedback. Simulations show that proposed algorithms can outperform 3GPP protocols with the best threshold, and tend to be more robust than 3GPP to various dynamics which are common in practical ultra- dense wireless networks.