Building Devices for Anytime-Anywhere Wireless Connectivity

A handheld wireless device in development by two University of Arizona engineering professors could answer the question of how we create more wireless connections when so few remain in the spectrum.

A model of an experimental transmitter and receiver with reconfigurable antennas similar to those in development by Krunz and Xin.

Envision a world without lost signals or time-consuming searches for Wi-Fi connections. UA electrical and computer engineering professors Marwan Krunz (right, top) and Hao Xin (right, bottom) are working to shift how we structure wireless systems and eliminate wireless scarcity.

The surge in Wi-Fi enabled devices has been a boon for society but a strain on the wireless spectrum that provides the frequencies they use. Many of the frequencies are fixed, having been allocated exclusively for radio, television, military, mobile and other operators. What remains is limited.

Marwan Krunz (official portrait)

Krunz's solution to frequency scarcity lies in dynamic spectrum access, or DSA.

DSA classifies frequency users as either primary or secondary – those specifically assigned to the frequency, and those hoping to use it opportunistically – and it encourages sharing between the two. Primary users get dibs; however, when they're not using the frequency, secondary users have the opportunity to temporarily access it.

"There are a lot of wireless users, but their traffic fluctuates depending on the time of day and location – for example, at night or in rural areas," said Krunz. "Those frequencies are not well utilized."

Two features of the wireless spectrum make DSA particularly challenging: the varying levels of primary-user activity in different parts and the degree to which primary users tolerate outside interference. Military radar, for example, will not tolerate any amount of external interference.

Harvesting enough unused wireless capacity for several segments of the allocated spectrum requires a single wireless device that can operate seamlessly on multiple frequencies, often simultaneously.

Hao Xin (official portrait)

Krunz is principal investigator with co-PI Xin on a four-year project – funded by the National Science Foundation – to develop a handheld cognitive radio with two antennas capable of working across frequencies from 470 MHz to 4.4 GHz. Designing such a device that is likewise compact would be a first.

"Conventional antennas only work within a set frequency," explained Xin. "If you tried to adapt one for multiple frequencies, it would either be too large for mobile use, or it wouldn’t work at all."

Added Krunz: "The new device will locate and hop on available frequencies without the users ever seeing or noticing it. It will sense an open channel and use it for a short period of time while keeping an eye out for other open channels. When the primary user wants the channel back, it will hop to another open channel."

It's a whole new world of wireless out there.

Top photo: An experimental "box" transmitter and receiver is shown with two reconfigurable antennas similar to those in development by Professors Marwan Krunz and Hao Xin.

University of Arizona College of Engineering