Radio Power
By Niall McKay in Berkeley, California, Mon Jun 09 09:30:00 GMT 2003

The challenge for the last ten years has been to pack more and more functionality into smaller and smaller communications devices - but the challenge for the next decade will be to improve the power consumption dramatically.


Berkeley computer science PhD student Al Molnar has reason to be pleased. He has designed the world's smallest and lowest powered transceiver or communications chip. "It is a bit like taking a standard radio chip and stripping out all the bits that you don't need and squeezing down what is left into a very small space," says Molnar, a former fisherman and GSM chip designer. "When you are operating at such low power there is a lot of functionality that you no longer need."

He is part of the team that is working on what must be Berkeley's best know computer science research project - Smart Dust - tiny networked electronic particles that collectively make up a sensory network. He was tasked with designing a radio chip that uses the same frequency but about 10,000 times less power than a cell phone radio chip. With it smart dust motes or particles can talk to each other and create ad hoc peer-to-peer networks. However, power efficiency is not only important for the smart dust project, Molnar believes, but also for wireless communications and cellular technology in general.

Beat up the Battery


"It's very easy to beat up the battery guys and say that battery technology has not progressed at the same rate as chip technology," he says. "But we are really beginning to reach the upper limit of what chemistry will allow in terms of getting energy out of a given mass. I mean some batteries have the same energy out put as the equivalent amount of dynamite."

While the challenge for the last ten years has been to pack more and more functionality into smaller and smaller communication devices, the challenge for the next decade will be to improve the power consumption dramatically, according to Molnar.

Cooking with Wireless


Now there are a number of ways to achieve this. Currently, cell phone chip designers are moving more and more functionality from the analogue chip to the digital processing. If wireless communications were cooking one would simply throw all the ingredients of a meal into a dish throw it on a stove and worry about rearrange them at the other end when the meal was cooked. In fact, more and more communications products take a low quality signal and clean it up at the other end. 3G will over come some of these inefficiencies. "Because, the specifications for today's cellular standards were drawn up nearly 20 years ago when digital processing was in its infancy."

However, according to Molnar, we need to reduce cellular power consumption by a least a factor of four.

That will enable the creation of new devices. Active badges or RFID tags technology that can store and transmit information for a very long time, clothing that can communicate with the washing machine or even food packaging that can tell the microwave oven how long it needs and at what setting.

Smart Dust


However some of the most interesting applications according to Molnar, include using this technology as a cable replacement automobiles or electrical devices. "Very low powered radios could act as transmitters or receivers in an car or electrical component so that you could get rid of much of the wiring," he says.

Meanwhile the Defense Advanced Research Projects Agency and the National Science Foundation fund the Smart Dust program. It was invented by Prof. Kris Pister with UC Berkeley's Center for Information Technology Research in the Interest of Society (CIRTIS).

Jason Hill developed the network and software implementation while Brett Warneke, Ben Cook, Mike Scott, and Al Molnar worked on the chip level implementation.

Brett Warneke, built a very low powered microprocessor that will be used in the motes. "My radio is pretty primitive in comparison to Brett's processor," says Molnar. "He has managed to really reduce the power consumption."

Soon some of the students will graduate and join a new start-up founded by Pister called Dust Inc., which will commercialize the technology. However, the projects components, tiny microchips, radios and so on are nearly as interesting as the Smart Dust project itself.

Roughly speaking an average GSM radio will uses up about 3 watts of power to communicate with the base station. However, to obtain that 3 watts you need input between 9-10 watts because GSM radios are typically about 30 percent efficient. The rest of the power is dissipated doing other tasks such as ensuring that the device does not interfere with other devices.

"The trick is to drop the it by roughly the same ratios," he says. "So we want to consume one milliwatt which will give a 200 microwatts output." In fact, each mote will run on a 3-volt battery. So Molnar has devised a way to reuse each electron emitted by the battery. "Each electron will travel to the oscillator, then to the antenna, then back to the radio and then back to the antenna before being dispersed," he says.

It's also possible to reduce power consumption because there is a great deal of functionality that can be stripped from the communications chip. For example, there are many circuits on a normal cell phone chip dedicated to ensuring that the chip does not interfere with other devices.

"The efficiencies are much better at a low wattage," he says. "Basically, there is not enough power to enable the "Smart Dust" motes to interfere with anything else. The draw back is that the motes only have a ten-meter range before the signal has to be handed off to another dust mote," says Molnar.

Of course, the trick now is getting the signal back from the Smart Dust to some sort of base station or data collection point. One possibility would be to build some sort of optical system or to get all the motes to pool their radio signal resource and turn many little transceivers into one big one. However, that is not as easy as it sounds so no doubt that will be the subject of another Berkeley Computer Science PhD.

Niall McKay is a San Francisco-based writer who has written for the Financial Times, Wired Magazine, Salon, and the New York Times. He also contributes to National Public Radio's KQED FM radio in San Francisco. He can be reached at www.niall.org.