September 23, 2013

Grant to explore benefits of sharing radio spectrum

by Andrea Hahn

CARBONDALE, Ill. -- Here’s an experiment. Get up from where you are, take a five-minute stroll, and during that time, count all the instances you see of wireless technology in use.  Computers, sure.  Televisions and radios.  Cell phones.  Bluetooth. GPS units.  Garage door openers.  Key fob door locks.

All those wireless devices are using the radio spectrum -- and the spectrum is becoming crowded.  The Federal Communications Commission (FCC) has warned that the radio spectrum is not unlimited -- and that we could in fact run out of it.  It’s a serious enough issue that, in 2010, President Barack Obama directed the federal government to identify 500 MHz of spectrum for wireless broadband use, and called on the National Science Foundation (NSF) to work with the Department of Commerce and other agencies to explore and research innovative spectrum-sharing technologies.

This week, the National Science Foundation awarded a Southern Illinois University Carbondale research team nearly $900,000 to research more efficient and flexible access to the radio spectrum.

Their idea?  Share.  At a profit.

Xiangwei Zhou, assistant professor of electrical and computer engineering, and Alison Watts, professor of economics, received $896,629 for their proposal, “Efficient Temporal-Spatial Spectrum Sharing through Voluntary Exchange.”

Think again about the many wireless devices using the radio spectrum band.  What keeps all of this from descending into radio spectrum band chaos is FCC regulation.  The FCC determines which entities use what frequencies and for what purpose. 

Primary users of the spectrum are FCC licensed, and include commercial users (major broadcast television and radio networks, for example) and non-commercial (the government, for example).  Behind them, jostling for a place at the spectrum band table, are secondary users – wireless transmitters and receivers seeking opportunities to access licensed spectrum.  The FCC has not approved this secondary uses in most cases.

Those entities designated as primary users do not use the spectrum all the time.  Secondary users access the spectrum opportunistically, meaning by accessing whatever band is available.  The secondary user senses the spectrum it wants to access, determining the presence, if any, of primary users.  If the spectrum is not in use, the secondary user accesses it in a way that limits the interference on the spectrum perceived by the primary user. 

Problems arise from this catch-as-catch-can spectrum use.  Secondary users can interfere with primary users’ access if both connections use the same channel.  This, as Zhou and Watts explain, is part of the reason primary users are reluctant to allow secondary users onto their section of the spectrum – even if they aren’t using it continually.

As the researchers said in a project summary, “Primary users have little motivation to permit this type of secondary use as there is no benefit to them and only risk.”

But what if there was benefit to the primary user?  And a way for the secondary user to claim part of the spectrum without having to rely on opportunity?

A solution may lie in the marketplace.  Zhou and Watts suggest voluntary exchange – monetary or barter – between primary and secondary users.  In other words, a primary user who has unused spectrum availability could sell or trade part of their spectrum band to a secondary user.

The advantages are easy to see.  The primary user is compensated for giving up part of the spectrum band assigned to it, and has increased opportunities to find willing secondary user customers.  The secondary user has increasingly reliable spectrum access. Consumers ultimately would pay less for spectrum access through primary and secondary users, and will benefit from the innovative uses of the spectrum expected to result from new and competitive users.  Also, less wasted spectrum, less “white noise,” reduces the crowding and makes an increasingly scarce resource more efficient.

As with so many things, it’s a solution more easily said than done.  The bulk of the SIU Carbondale research will focus on how to make it happen.

“To encourage spectrum sharing and enhance spectrum efficiency, it is important to have a mechanism or solution concept that creates the correct incentives for both primary and secondary user,” Zhou and Watts wrote in their project summary.  “However, there are significant communication costs as well as limitations involved in the sale or exchange of spectrum bands.”

Some form of sharing mechanism must be in place for this to happen efficiently.  Zhou and Watts will study these sharing mechanisms, spectrum management tools, and the online spectrum marketplace in order to find a system that benefits primary users, secondary users, and society. 

Zhou and Watts want to take the project a step further.  They want to find ways to maximize the number of users on each spectrum frequency band -- to maximize without causing interference among them.

That’s where the “efficient temporal-spatial sharing” part of the research comes in.  “Spectrum sharing is at least a three-dimensional problem dealing with time, frequency, and space,” Zhou said.  “We need to have the right time-frequency-space cube for each user.”

Zhou and Watts will use this research project and the funding from it as a learning and student research opportunity.  They plan to introduce topics from the research into classes they already teach, including game theory (economics), digital communications, and wireless and personal communication systems.

Graduate students can also join the research, using individual components of it in support of master’s and doctoral degrees.  Zhou and Watts will encourage students to publish and to present their findings in academic journals and at academic conferences.  As the students promote their own research, they also participate in the dissemination of knowledge and technological understanding, and they also promote SIU Carbondale. 

The researchers also see opportunities for interdisciplinary study crossing the fields of economics, computer science, engineering, and sociology.

Finally, they note that the benefit to society generally -- to average, non-expert wireless device users -- are considerable, from cost reduction, leading to greater accessibility, to access to improved and innovative technologies.