  The total energy efficiency (TEE), defined as the ratio between the total
data rate and the total power consumption, is considered the most meaningful
performance metric in terms of energy efficiency (EE). Nevertheless, it does
not depend directly on the EE of each link and its maximization leads to
unfairness between the links. On the other hand, the maximization of the
minimum EE (MEE), i.e., the minimum of the EEs of all links, guarantees the
fairest power allocation, but it does not contain any explicit information
about the total system performance. The main trend in current research is to
maximize TEE and MEE separately. Unlike previous contributions, this letter
presents a general multi-objective approach for EE optimization that takes into
account both TEE and MEE at the same time, and thus achieves various trade-off
points in the MEE-TEE plane. Due to the nonconvex form of the resulting
problem, we propose a low-complexity algorithm leveraging the theory of
sequential convex optimization (SCO). Last but not least, we provide a novel
theoretical result for the complexity of SCO algorithms.
