For nearly a decade, Anant Sahai has been toying with radios smart enough to know how to skip from one channel to another while leaving occupied frequencies undisturbed. The work people conducted on these smart, or cognitive, radios sparked the beginning of the wireless revolution. But for the years prior to 2008, Anant, an Electrical Engineering and Computer Sciences professor at the University of California, Berkeley, and others who studied cognitive radios did so strictly as an academic pursuit. Any other use of the systems was illegal.
Finally, in 2008, the Federal Communications Commission (FCC) opened the radio frequencies that had previously been the sole domain of television broadcasters to other device manufacturers. The freed up frequencies gave cell phone and Internet providers the opportunity to blast tens of megabits per second of data over tens of kilometers. It also allowed them to establish Internet signals and enable faster Web browsing on mobile devices and in trains, planes and automobiles across the country. It moved what was purely academic research on smart radios to the realm of being legal and made it possible for the wireless technology to eventually blanket the country, Anant says.
Anant first became interested in network connections and information flow while working with LIDS professor Sanjoy Mitter as a graduate student from 1994-2000. For his dissertation, Anant explored the ways signals are transmitted and distorted when traveling through noisy environments, and how those distortions need to be corrected if the signals are going to be used for controlling systems. While his thesis was largely theoretical, Anant says the most important thing he learned at LIDS was the fundamental value of toys and cultivating a playful aesthetic.
Anant spent the year after graduating from LIDS at the startup Enuvis, Inc. (cofounded by LIDS professor John Tsitsiklis and LIDS alum Ben Van Roy), where he got a taste of the practical world while developing algorithms that would make GPS services available inside buildings and cities. At the time, smart phones and on-demand, location-based services were just beginning to emerge in the electronics market. But the location-calculating algorithms of the early 2000s were not sensitive enough to transfer signals from GPS satellites through the maze-like infrastructure of a city, through walls and windows and into tiny, hand-held receivers. At Enuvis, Anant and his colleagues developed new techniques to pick up GPS signals through the clatter of the cityscape. The work ultimately fed into today's iPhone and Android capabilities: the ability to pinpoint a user's location on a map and to offer suggestions for nearby restaurants, gas stations and grocery stores.
But what Anant knew from his work at LIDS and Enuvis was that lower-frequency signals, like those used in analog TV broadcasts, penetrated buildings more effectively than what currently existed in terms of Wi-Fi, Bluetooth, or cell-phone connections. So after Anant accepted a position at Berkeley, his undergraduate alma mater, in 2002, he quickly formed a research group where he and his students began to investigate nearly every aspect of cognitive radios and signal transmission. He also became the faculty adviser for the Berkeley chapter of Eta Kappa Nu, the national electrical and computer engineering honor society.
In 2008, Anant's group was among the first to test the effects of the FCC's decision to make unoccupied analog channels, called white space, available across the country. Specifically, Anant and his group wanted to see if the resulting increase in bandwidth, or spectrum, actually translated into better wireless capability. They found that connections were up across the board, and that rural area residents gained more spectrum compared to city residents, which was expected, since they started off with fewer occupied channels. However, the FCC's rules did not always allow the rural residents enough flexibility in managing and powering their connections to overcome the comparatively larger distances the wireless signal needed to travel to reach a cell tower or even a neighbor. "To us, this meant that the FCC's one-size-fits-all rules were ill-matched to the diversity of the American experience," Anant says. Consequently, while he and his students favored opening up white spaces to improve Internet connectivity, they were concerned with how the FCC would regulate the current and future growth of the available radio spectrum. By September 2010, the FCC revised its requirements for white space devices operating in TV frequencies, but the agency did not stipulate exactly the way the rules would be enforced and how devices would be certified. The standard regulatory framework was also clunky and slowed innovation, preventing smart radio-frequency devices from adapting. As a result, Anant and his team began to think about a way to build an efficient, "light-handed" regulation system.
The team's goal is to prevent harmful interference, or cheating, which could happen if a cognitive radio switches to a frequency being used by a digital television channel. To regulate the system, Anant's group began playing with what Anant calls "the toy extreme of spectrum jails". The thought is to parallel wireless regulation to the human laws of driving. In this parallel there would be a universal, flexible and simple-to-certify protocol to get devices up and operating, a design similar to the way cars are inspected and have license plates. Individual drivers also use a standard set of laws, like driving on the right, and are monitored by police and issued citations. Similarly, in the team's plan for transmitters, each one would be licensed and monitored. If cheating happens, the transmitter is "jailed," meaning it has its data transfer rate slowed (think dial-up versus broadband) and has to "sing" gibberish in a "garbage" frequency, which wastes energy. Instead of mandating one way of doing things, the goal is to simply make it irrational to cheat. This approach also leaves open the possibility of "innovating within the spirit of the rules," Anant says, an important feature if regulation is to accommodate the many different contexts in which wireless communication needs to be effective.
Understanding exactly what happens when a device gets thrown in the wireless slammer, however, requires that engineers know better how systems use power to both transmit and decode information. Anant says that by drawing on the fresh ideas his students bring to signal processing and tapping into his LIDS work and colleagues, researchers are developing a better sense of the fundamental tradeoffs between the power it takes to send a signal and what it takes to read one. The work being done by Anant and his group has many important and interesting implications. However, Anant is quick to say that doing the sort of research that asks new questions and connects disparate fields together, is also simply fun. It is precisely this kind of cross-cutting research that will -- one day -- factor into wireless service that is more widely available, secure and faster.