Fundamental Trade-Offs on the design of green radio networks

Introduction There is currently a global concern about the rise in the emission of pollutants and energy consumption. The carbon dioxide (CO2) footprint of the information and communications technologies (ICT) industry, as pointed out by [1], is 25% of the 2007 carbon footprint for cars worldwide, which is similar to that of the whole aviation industry. Within the ICT industry, the mobile network is recognized as being among the biggest energy users. The exponentially growing data traffic in mobile networks has made the issue an even grander challenge in the future. In a data forecast report provided by Cisco [2], it has been pointed out that the global mobile data traffic will increase 26-fold between 2010 and 2015. In particular, unexpectedly strong growth in 2010 has been observed mainly due to the accelerated adoption of smartphones. For instance, China Unicom's 3G traffic increased 62% in a single quarter from Q1 to Q2 of 2010, while AT&T reported a 30-fold traffic growth from Q3 2009 to Q3 2010. The unprecedented expansion of wireless networks will result in a tremendous increase in energy consumption, which will further leave a significant environmental footprint. Therefore, it is now a practical issue and demanding challenge for mobile operators to maintain sustainable capacity growth and, at the same time, to limit the electricity bill. For instance, Vodafone Group has announced the goal of reducing its CO2 emissions by 50% against its 2007 baseline of 1.23 million tonnes, by the year of 2020 [3].