Doug Lung / RF Report
12.20.2013 11:36AM
MIT Development Could Ease Spectrum Crunch
Five-fold spectrum efficiency improvement claimed
“Cognitive Coexistence Radio,” a technology developed by researchers at MIT’s Lincoln Lab could help alleviate ever-increasing RF spectrum space shortage problems.

Afarin Bellisario, technology licensing offer at MIT described CCR this past October at the Telecommunications Industry Association conference in Washington D.C.

In the presentation, Bellisario and Dr. Rachel Learned, a researcher at MIT's Lincoln Laboratory referred to CCR as a possible “holy grail” and “silver bullet” for the wireless industry. Bellisario told SNL Kagan that tests of CCR using spectrum in the 700 MHz and 2100 MHz bands made the spectrum five times more efficient and it’s possible the technology could allow even greater efficiency.

The National Association of Broadcasters (NAB) recently circulated a posting from SNL Kagan to the press outlining the new technology, with Dennis Wharton, executive VP of communications for the NAB, expressing optimism over the new development. His comments carried in the SNL Kagan posting.

“Improvements in technology can usually deal with any allegations of a looming spectrum crunch. Things that people never thought were possible [in cellular technology] are not only within the realm of possibility, but are becoming a reality,” said Wharton.

Brian Markwalter, VP of research and standards at the Consumer Electronics Association told SNL Kagan he wasn't familiar with CCR specifically but said his organization is a “strong support of this kind of innovative development that increases use of spectrum,” but added additional spectrum was still needed. “It can't all be served by technological development. There also needs to be additional spectrum allocated.”

Marty Cooper, who led the development team at Motorola that built the first cellular handset, asked rhetorically: “Why is [efficiency-promoting technology] not being widely used?” The answer, he gave SNL Kagan was: “Primarily because the carriers, the people who could ostensibly benefit from this, don't have much motivation to do it.” He observed that the industry is still in the spectrum stockpile stage, prioritizing the acquisition of spectrum so that leading telcos might have an edge once spectrum truly does become scarce.

How does CCR achieve this efficiency?

The SNL Kagan article explains: “The technology works by implementing multiuser detection to dynamically adjust power levels and data rates on the fly, mitigating the effects of possible interference from nearby devices.”

The article also offered: “Bellisario compared CCR to the basic human ability to filter out background noise in a crowded lecture hall or cocktail party in order to listen to one conversation at a time. She said that, as in the cocktail party, there are limits to the amount of ‘background noise’ from competing devices that CCR can handle, but that it is far more efficient than existing technologies.”

See MIT technology that could solve the spectrum crunch by Kyle Daly on the SNL Kagan site.

I found more details on the technology in the TIA presentation from Dr. Rachel Learned and Dr. Afarin Bellisario, Shifting the Communication Paradigm: Alleviating Congestion by Efficient Sharing of Spectrum.

The presentation stated: “Not all interference should be avoided--Multiuser Detection (MUD) receivers can 'see through' interference. Occupied channels are often the most attractive alternative because interference can be intelligently and adaptively manipulated to eliminate harm to the primary and create opportunity for the secondary link. A key point is that coexistence opportunities cannot be pre-determined and overt negotiation is not desirable (or possible).”

The CCR uses algorithms to find occupied bands for coexistence that cause minimal to no impact on the “other user,” while providing high throughput for its own network. The CCR sets data rates and powers dynamically using algorithms that sense the local RF environment (using one or more members of the CCR net) and consider the impact on coexisting links, receiver algorithm limitations and the capabilities of the error correction and modulation schemes being used.

The illustrations in Bellisario’s presentation indicate the greatest use of the technology would be to allow small cells to coexist with macro-cells in dense urban areas where spectrum is most congested. With conventional technology, there’s a problem if a macro-cell user is in the same building as a small cell user and establishes a link to the macro-cell--the small cell link drops.

A common solution to this problem is to force all small cells to have “public access” (similar to the wireless carrier managed extenders), but that can be problematic. Cognitive coexistence technology solves the problem, resulting in no dropped links, no “barred” bands and no affect on the macro links.

The presentation also provided simulation data highlighting the effectiveness of the technology in improving the throughput of small cell base stations while creating negligible interference to macro-cells.

While this technology looks promising, I do see several hurdles that it must overcome. A major one will be convincing owners of the spectrum to allow CCR small cells into their spectrum. Another one will be creating the CCR network necessary to off-load data from the macro-cell networks. This shouldn't be too difficult for public facilities such as shopping malls or sports arenas, which are already deploying DAS to improve wireless coverage, but could be a problem in residential dwellings.

Cable companies have been rolling out wireless service using unlicensed spectrum. As they have distribution throughout their service area, both inside and outside buildings, they may find it easier to deploy a small-cell CCR net than wireless operators but would need access to the wireless operator's spectrum.


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