The present document studies energy efficiency aspects of 5G networks, at both network function level and at 3GPP system level. The study covers:

• energy efficiency KPI definitions, including already existing definitions from other 3GPP WGs and other SDOs and potentially new ones for 5G networks;
• measurement methods, including already existing measurement methods from other 3GPP WGs and other SDOs and potentially new ones for 5G networks;
• potential solutions to improve energy efficiency of 5G networks;
• energy efficiency control framework, as a SON-like framework for the control of energy efficiency of 5G networks.

The study also makes conclusions on the preferred solution(s), and provides recommendations for them.