I. INTRODUCTION

II. TYPES OF UAVS

III. UAV POWER SUPPLY AND CHARGING MECHANISMS

IV. THE ROLE OF UAV-BASED STATION IN WIRELESS COMMUNICATIONS

V. TYPES OF UAV DEPLOYMENTS

VI. ENERGY OPTIMIZATION IN UAV-BASED CELLULAR NETWORKS

VII. OVERVIEW OF ALGORITHMS FOR ENERGY OPTIMIZATION IN UAV-BASED CELLULAR NETWORKS

VIII. ENERGY OPTIMIZATION TECHNIQUES IN UAV-BASED CELLULAR NETWORKS

IX. ENABLING TECHNOLOGIES FOR ENERGY EFFICIENCY IN UAV-BASED CELLULAR NETWORKS

X. CHALLENGES AND OPEN RESEARCH PROBLEMS

XI. CONCLUSION