Machine Learning-Enabled Traffic Steering in O-RAN: A Case Study on Hierarchical Learning Approach - Habib, Md Arafat; Zhou, Hao; Iturria-Rivera, Pedro Enrique; Ozcan, Yigit; Elsayed, Medhat; Bavand, Majid; Gaigalas, Raimundas; Erol-Kantarci, Melike (IEEE Communications Magazine, Communications Magazine, IEEE, IEEE Commun. Mag., 2025)