  This paper focuses on energy-efficient coordinated multi-point (CoMP)
downlink in multi-antenna multi-cell wireless communications systems. We
provide an overview of transmit beamforming designs for various energy
efficiency (EE) metrics including maximizing the overall network EE, sum
weighted EE and fairness EE. Generally, an EE optimization problem is a
nonconvex program for which finding the globally optimal solutions requires
high computational effort. Consequently, several low-complexity suboptimal
approaches have been proposed. Here we sum up the main concepts of the recently
proposed algorithms based on the state-of-the-art successive convex
approximation (SCA) framework. Moreover, we discuss the application to the
newly posted EE problems including new EE metrics and power consumption models.
Furthermore, distributed implementation developed based on alternating
direction method of multipliers (ADMM) for the provided solutions is also
discussed. For the sake of completeness, we provide numerical comparison of the
SCA based approaches and the conventional solutions developed based on
parametric transformations (PTs). We also demonstrate the differences and roles
of different EE objectives and power consumption models.
