"Spectrum Crunch" Solutions — Who's On The Right Track?

By Ed Biller

The past few months have been exciting for those with an ear to the ground regarding the “spectrum crunch.” Whether you believe we’re nearing a breaking point for usable bandwidth, or you think the fuss is much ado about nothing, you can’t ignore the myriad solutions being presented as a fix. 

In July, the U.S. Department of Defense’s Defense Advanced Research Projects Agency (DARPA) initiated a three-year contest — with almost $4 million in prizes up for grabs — challenging entrants to develop smart systems that “collaboratively and autonomously adapt in real time” to the congested spectrum environment, allocating bandwidth where it’s needed by borrowing where it’s not.

In August, a team of researchers at the University of Southern California, Los Angeles (UCLA), described how a light phenomenon known as orbital angular momentum (OAM) could be applied to ease the spectrum crunch.

Then, earlier this month, the National Science Foundation (NSF) awarded $12 million in grants, spread across 11 principal investigators and projects, bringing the NSF's total investment in this area past $60 million for 140 projects over the past five years. However, NSF’s announcement, while naming the most recent grant recipients, did not describe their technologies in much detail. Let’s remedy that here. Note that spectrum-sharing and development of heterogeneous wireless technologies are just part of the program’s stated goals, so only the applicable recipients are listed:

Automated Enforcement in Spectrum Sharing: Technical Challenges and Policy Considerations — Martin Weiss, University of Pittsburgh; Jung-Min Park, Virginia Tech — Per the researchers’ abstract, “This research examines approaches to improving [preventative] protections, detecting interference events, identifying the interfering parties, and determining how these events are best enforced and adjudicated using techniques that can be readily automated.”

Overcoming Propagation Challenges at Millimeter-Wave Frequencies via Reconfigurable Antennas — Hani Mehrpouyan, Boise State University; Hamid Jafarkhani, University of California, Irvine; Vida Vakilian, California State University, Bakersfield; Nader Behdad, University of Wisconsin-Madison — Boise State University’s Kathleen Tuck reports that this project aims “to create reconfigurable antennas with various states, each with varying and predefined radiation patterns. The antennas will support simultaneous transmission of multiple radiation patterns, each with large directional gain. The former provides beam diversity to overcome mm-wave frequency shadowing, while the latter reduces power amplifier design constraints.”

Real-time Control of Dense, Mobile, Millimeter Wave Networks Using a Programmable Architecture — Nicolo Michelusi, Purdue University; Alexander Sprintson, Texas A&M University; Christopher Anderson, United States Naval Academy — This research will explore the theoretical and experimental issues impeding deployment of mm-wave wireless broadband systems. According to the researchers’ abstract, the project will “focus on the interplay between network-level optimization and physical layer communication, channel sounding, and control.”

Toward Harmonious Coexistence of Heterogeneous Wireless Services — Jeffrey Reed, Virginia Tech — Reed’s team will study coexistence between Wi-Fi and cellular wireless services on unlicensed bands; specifically, the mostly untapped radar spectrum that the U.S. government is mulling for coexistence.

Energy- and Cost-Efficient Spectrum Utilization with Full-Duplex mm-wave Massive MIMO — Borivoje Nikolic, University of California, Berkeley — This project seeks to apply theoretical progress made in the realm of mm-wave massive MIMO systems  to system design and networking techniques. Per the researchers’ abstract, their work will address “key challenges in the development of signal processing algorithms, network protocols, and a prototype hardware design to enable scalable low-latency mm-wave MIMO networks with high degrees of spatial multiplexing.”

Terabit-per-second Scale Networking: Design to Field Trials, Lab to Tower — Edward Knightly, Rice University — Rice University researchers’ goal is to break the terabit/second networking barrier, using “fundamental research, prototype designs, and proof-of-concept field trials,” according to their abstract.  The researchers told Innovation Toronto that they plan to use pulse-based radio technology to break the terabit/second ceiling, rather than today’s commonly used carrier-wave modulation technology.

Blind Source Separation with Integrated Photonics — Paul Prucnal, Princeton University; Shuangqing Wei, Louisiana State University — “The objective of the proposed research is to develop a blind source separation [BSS] technique by using an integrated photonics approach, thereby realizing radio-frequency interference cancellation while preserving user privacy,” states the researchers’ abstract. As more and more wireless signals clog the airwaves, BSS looks to be increasingly important as a means of untangling those signals.

Cloud-based Oblivious Spectrum Mapping and Allocation — John Shea, University of Florida — This project seeks to protect the privacy of users involved in dynamic spectrum access (DSA). While anonymity techniques do exist for DSA, they require high computational complexity, a requirement the researchers hope to eliminate (i.e., so it can be used in devices like cell phones). Note that complete privacy is impossible to achieve in a spectrum-sensing system, at least with current technology, since locations and characteristics of sensing radios may be revealed to other radios and whoever is collecting/combining the information.

SpecSense: Bringing Spectrum Sensing to the Masses — Samir Das, Stony Brook University — This project aims right at the heart of DARPA’s Spectrum Collaboration Challenge, seeking to build an inexpensive, effective spectrum-sharing system. According to the researchers, “SpecSense (i) crowdsources spectrum monitoring using low-cost, low-power custom-designed hardware, and (ii) provides necessary library and interface support for spectrum-aware apps via a central spectrum server/database platform.”

Enabling Opportunistic Environmental Monitoring with Non-Uniform Sampling and Processing Circuits — Mike Shuo-Wei Chen, University of Southern California — This project ultimately is intended to aid global climate change research, transitioning environmental monitoring from complex equipment operating in dedicated RF bands to cheaper equipment unencumbered by dedicated transmitters or bandwidth. That said, the research outcomes surely could impact the consumer wireless market, and any discoveries will be made available for academic dissemination at all education levels.

This is just a small sampling of the numerous ideas bouncing around academia, and the commercial sector isn’t sitting idly by, either. For example, South Africa’s Internet Solutions is working to create an inexpensive spectrum-sensing device, and Japan’s NEC Corporation has developed a radio-sensing system that can visualize radio spectrum usage in real time. The true challenge, though, will be ensuring acceptance of — and accessibility to — viable DSA technologies as they appear.

Do you think the spectrum crunch solution will be found among this most recent batch of academic hopefuls? Perhaps you or your company is working on a technology vital to the solution’s efficacy or cost-effectiveness. Let us know in the Comments section below.

All NSF abstracts cited in this column can be found here.