Energy efficient wireless networks towards green communications

Wireless networks have become an essential part of the modern life. However, currently, 3% of the world-wide energy is consumed by the ICT infrastructures which causes about 2% of the world-wide CO2 emissions. The transmitted data-volume increases rapidly and wireless communications are used extensively while network design rules have practically ignored the energy efficient network design approach to limit CO2 emissions. This approach is currently named Green Communications. Significant energy savings in mobile networks can be expected by defining and standardizing energy efficiency metrics and combining energy aware flexible radios and networks. This paper discusses several techniques such as cross layer approach, multiple antennas, cell size reduction and cognitive radio, from the system-wide energy efficiency point of view, outlining challenges and open issues.