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How advanced mobile networks could power themselves

Mon, 03/24/2014 - 12:11am
MIT Technology Review

A dirty secret of mobile communications is that it uses lots of electricity. It’s also sometimes powered by giant tanks of diesel fuel, especially in poor countries. But new research shows that it’s possible to build complex networks that run on renewable or other local power sources, with no need for backup from the electricity grid or diesel fuel.

Small transmitters, called small cells, will provide much of the capacity for future networks. These small cells might be tethered to small windmills or solar panels and batteries, or even include their own built-in power sources and batteries, as in this prototype. But fluctuations in the electricity generated at each cell could make the networks they serve less reliable.

To address this—and to prevent the need for such networks to use dirty backup power—researchers at the University of Southern California and Samsung developed a model that accounts for how fast each small cell or other wireless device can collect and store energy (including estimates for local sun and wind exposure). The model also takes into account the amount of power each cell uses when active, and the expected user demand. The researchers determined that such networks could often flourish with only a few more small cells than would otherwise be needed, in order to compensate for cells that have run out of power.

The model, led by USC postdoc Harpreet Dhillon, has been accepted for publication in IEEE Transactions on Wireless Communications. It’s still theoretical and requires a practical demonstration, but the work is “very important,” says Jeff Reed, director of the wireless research center at Virginia Tech. “One of the chief obstacles of setting up modern communications in emerging countries is finding a steady source of power. He has shown theoretically the mechanism that allows renewable energy harvesting alone to power the network.”

Some estimates hold that telecommunications accounts for 1 percent of human carbon emissions and that energy consumption related to telecommunications will triple in the next several years. In some markets, energy-related costs already account for as much as half of a mobile network operator’s expenses. “We need to continue to pursue improvements in energy harvesting technologies and energy storage and battery technologies; however the bigger impact will come from reduced energy consumption of the network equipment itself,” says Thierry Klein, network energy research program leader at Alcatel-Lucent’s Bell Labs.

Some simple networks are already powered entirely by renewable energy and batteries, such as one in a Zambian village that uses a single low-power base station (see “A Tiny Cell Phone Transmitter Takes Root in Rural Africa”). “We take the approach of trying to ramp down the power requirements of the network so that with solar and battery we can make it through the night and a couple days of a rainstorm,” says Vanu Bose, whose company, Vanu, deployed that network. “There is no diesel there, but we did it by really reducing the power consumption of the base station overall.”

The concept should gain traction as more kinds of small base stations, called pico cells and femto cells, get physically closer to users and need only a few watts of power, making renewable technologies more feasible as the main energy source.

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