Inside of a cell tower base communication shelter (via Pepro)
When it comes to energy savings, most tend to look at the gross inefficiencies of cars, homes or businesses. But surprisingly, much of our daily wasted energy comes from our handheld devices, specifically our cell phones - powering the towers that support them. Power amplifiers (PAs) are used to convert electrical currents into radio signals so they are used by our telecommunication devices as well as the base stations with which they communicate, using up 1% of the global energy production. In comparison, smelting aluminum uses 5% of the global energy supply.
When downloading big files or streaming video, I am sure you notice your phone getting warmer than usual. This is because its power amplifiers are working extra hard to continuously transmit information, whether it be uploading files or notifying of reception and missing bits when downloading. In a single device there are usually multiple PAs, handling different data transmission loads, all contributing to about 65% of energy wasted in heat and quickly depleting batteries. In base stations, PAs amount to similar inefficiencies but have the added expense of requiring air conditioning, with about 11% inefficiencies, to keep them at operating temperatures.
These components have not been modified in years, but thanks to a new business venture formed by MIT electrical engineering professors, Joel Dawson and David Perreault, power amplifiers are getting a makeover, which they claim will translate to devices twice as efficient.
In 2009, the professors and their team wrote a paper detailing a new type of power amplifier architecture very different from what is used today. Till now, much of the power wasted is due to their high standby power. To avoid distorted signals, power amps must keep a low variance between their standby power and transmitting power. This standby consumption worsens when high data rate communication is needed.
The new process, called asymmetric multilevel outphasing (AMO), turns the power amplifier in to something analogous to a car transmission, only that instead of switching gears, it switches between voltages (up to 20 times per second) that can be handled by the internal transistor. Their company, Eta Devices, is manufacturing PAs for base stations as well as mobile devices (still in development) that apply AMO.
In their research, they found that the AMO modulation technique increased the efficiency over a wider output range than standard LINC technology while keeping the high linearity needed for data processing by using digital predistortion. They also detailed the optimization procedure for the supply voltages based on the envelope distribution of the modulated signal. After testing a four-level AMO, their results showed an increase of efficiency from 17.7% to 40.7% for HSUPA transfers and from 11.3% to 35.5% for WLAN 802.11g transfers.
Vodafone cell tower and inside the base station (via Vodafone, ZDNet)
Eta Devices will launch its first product in Feb 2013 at the Mobile World Congress in Barcelona, Spain. This PA will be targeted at markets of developing countries where 640,000 diesel-powered generators use $15 billion of fuel per year powering LTE (long term evolution) cellular base stations. These stations waste 78% of energy as we mentioned above. The new powers amps would reduce that waste by half according to Mattias Astrom, Eta CEO. Indirectly, they will also help conservation efforts by reducing size and numbers of power amps and eliminate the need for so much air conditioning.
The team is confident they will develop just one AMO PA for cellular devices that will replace all the individual chips needed to handle different modes and frequencies used by SDMA, GSM, and 4G/LTE standards. This will result in battery life lasting twice as long. Eta Devices says that a millions base stations, mostly LTE, are developed yearly and the demand will not cease any time soon and obviously, neither will the demand for cell phones.
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