Green wireless communication networks [Editor´s note]

The increasing usage of conventional energy sources such as oil and coal poses a wide variety of environmental issues, including climate changes, air pollution, and acid rain. At the same time, the prices of conventional energy sources are soaring while the world´s energy consumption is ever increasing. In order to provide sufficient, environment-friendly, and lowcost energy to sustain economic growth and raise living standards across the world, innovation and development of alternative energy sources are required. Green energy, which refers to the eco-friendly renewable energy replenished from natural resources such as sunlight, wind, and geothermal heat, is expected to be a promising alternative to conventional energy sources. According to the 2012 Renewables Global Status Report (GSR), the development of green energy techniques has dramatically reduced the cost of green-powered electricity. For instance, the prices of photovoltaic modules and onshore wind turbines have dropped by 50 percent and close to 10 percent, respectively. Both the decreasing cost and the environmental concerns motivate the usage of green energy. In 2011, renewable sources supplied 16.7 percent of global energy consumption, with an increasing share of renewable energy and decreasing utilization of traditional energy. Moreover, investment in renewables has increased by 17 percent to a record of $257 billion in spite of the widening financial crisis in Europe, and 118 countries reached renewable energy targets.