I. Introduction
The use and production of information and communication technologies contributes an increasing share to global green house gas emissions accounting for over 2% already in 2007 [1]. Within the communications sector a trend towards increasing the energy efficiency of key technologies can be observed. Although mobile radio networks are only a minor producer of green house gas emissions today [2], [3], significant challenges can be expected in the future. Over the past years, mobile telecommunication networks have shown exponentially increasing energy consumption figures, doubling almost every 4 years. Moreover, establishing western standards in communication services on a world wide scale would consume about 40% of today's global electrical power generation capabilities [3].