I. INTRODUCTION  
II. UNDERSTANDING MOBILITY IN CELLULAR NETWORKS  
A. IDLE MODE MOBILITY  
B. CONNECTED MODE MOBILITY  
III. MOBILITY CHALLENGES AND RESEARCH PROPOSALS  
A. RELIABILITY GOALS  
B. LATENCY REQUIREMENTS  
C. SIGNALING MINIMIZATION  
D. USER TRACKING  
E. CELL DISCOVERY  
IV. PROACTIVE MOBILITY MANAGEMENT  
A. History Based Prediction  
B. Measurement Based Prediction  
V. MOBILITY ORIENTED NETWORK PLANNING AND OPTIMIZATION  
B. Changing Core Network (CN) to Achieve Latency Goals  
C. C/U Plane Split  
VI. AI-ASSISTED MOBILITY MANAGEMENT  
VII. FUTURE RESEARCH DIRECTIONS AND CONCLUDING REMARKS  
A. HO Delay Based SINR Distribution  
B. HO Delay Based Uplink Interference  
C. Latency Goals  
D. Energy-Efficiency  
E. Smart Intra-Frequency Search  
F. Smart Inter-Frequency Search  
G. Improving Mobility Load Balancing  
H. Mobility in mmWave Networks  
I. Low-Cost Multi-Connectivity