A universal radio antenna receives all kinds of signals traveling through the air – some strong, some weak – and all at different frequencies. In order to convert every analog signal to digital form, a chip would require an analog-to-digital converter that burns “several hundred watts” of power, says Abidi – far too much for a portable device.
Therefore, his team used a modified version of SDR that exploits the fact that not all incoming signals need to be converted at once. People are usually interested in only one channel at a time, he says, such as using Wi-Fi or talking via a specific frequency on a cellular network. So the researchers incorporated a type of device – previously used only in obscure applications – into their circuit that’s able to examine the vast range of radio frequencies, pick out the band of interest, and emphasize it, while de-emphasizing the others. In essence, this tool – what engineers call a “wideband anti-aliasing device” – is able to access the spectrum and focus on a single band, so that only small amounts of analog information need to be converted to a digital signal. By building band-choosing into the circuit, the analog-to-digital conversion takes only tens of milliwatts of power, Abidi says.
Their advance, he notes, was recognizing the potential for this previously under-used wideband anti-aliasing device and integrating it with other wide-band circuit components to build a complete receiver. “The concept had been around for a while,” he explains, “but no one saw how powerful it would be for software-defined radio applications.”
A chip that sorts out the incoming signal such as Abidi’s is the type of technology that could help SDR become a reality in cell phones, say Bruce Fette, chief scientist of communication networks at General Dynamics C4 Systems, a company that builds large software-defined radio equipment for military use. And the idea of SDR is becoming more attractive to the mobile device industry, he says, because it provides so much more flexibility in the functions of a single device, ranging from using the same cell phone all over the world, to having a PDA unlock your car door.
Abidi says there’s still more research to be done before the chip is ready for commercial applications. For one thing, his team has only solved the problem of converting incoming analog to digital signals over such a wide range of frequencies. Wireless devices must also transmit an outgoing analog signal. A truly universal chip will need to convert outgoing signals from digital to analog form over a similarly wide range of frequencies.
Still, his team has solved the most difficult part of the problem by addressing the receiver, Abidi says. Incoming signals are much more complicated because, with a receiver, “you’re listening to the whole world,” he says, whereas “with transmitters, you’re not contending with unwanted signals.”
Krenik adds that, while Adibi’s advance “doesn’t solve every problem the industry faces,” it lays a strong foundation for further work toward SRD.
Abidi and his team hope to smooth out the remaining technical issues with their universal chip by late summer. From there, the work of other researchers who design the digital processor and software for SDR will come into play, he says. Abidi estimates that all these pieces will come together for a prototype sometime next year. And, he says, a universal chip could be in handheld wireless gadgets within three to five years.
Home page photo courtesy of Asad Abidi, UCLA. Caption: A prototype for the “receiver” portion of a “universal” wireless chip that can receive radio frequencies ranging from 800 megahertz to 6 gigahertz – which could eliminate the need for multiple chips in mobile devices, extend their battery life, and make them smaller.