3.5 GHz spectrum sharing effort could take years to produce results

The FCC's plan to open up frequencies in the 3.5 GHz band is all about small cells and spectrum sharing, the latter being a concept that does not excite many operators, and it could take years before carriers are able to use any of the targeted frequencies.

FCC Chairman Julius Genachowski said the commission will initiate formal steps by year's end to implement key recommendations from the President's Council of Advisors on Science and Technology (PCAST), which released a report two months ago advocating wider deployment of small cells and shared, rather than exclusive, use of spectrum.

Genachowski specifically said the commission would work to free up 100 MHz in the 3.5 GHz band but did not actually mention sharing in the brief announcement. However, ARS Technica confirmed with an FCC spokesperson that the commission plans to explore ways to open up for sharing with wireless carriers the 3550-3650 MHz spectrum currently being used in government radar operations. Genachowski, who in the past advocated use of this band for small cells, also did not specify what type of sharing he had in mind--geographic sharing or temporal sharing.

PCAST recommended taking the TV white space approach in opening up the 3.5 GHz band to "general authorized access" devices. White-space spectrum sits between TV channels, and unlicensed TV Band Devices (TVBDs) using TV white space spectrum must be able to communicate with a spectrum database to identify which channels are available at a given location, and they also need to employ cognitive radio operation, including spectrum sensing and management.

The TVWS industry is still quite embryonic and relies upon passive end-user devices rather than the more active, intelligent devices PCAST expects to come down the pike in coming years, which some industry players, such as CTIA, say could take years to develop and use commercially. Yet moves in Europe might boost development of savvier cognitive radio technologies. The European Commission is working to gain support from both the European Parliament and the Council of the European Union for a broad shared-spectrum regulatory environment.

Further, TVWS has been built for fixed or nomadic uses rather than highly mobile ones. However, that could match up quite well with actual small cell usage, which is envisioned for dense urban areas where people are consuming massive amounts of wireless data, such as streaming video.

GigaOM contends the 3.5 GHz band "would be ideal for small cell deployments," because operators would be assured that their small cell deployments in that band would not create interference with their primary macro networks. Further, the higher 3.5 GHz frequencies, which do not propagate as far as lower ones, would be well suited to the diminutive coverage areas needed to be served by small cells.

However, critics have said that for small cell networks to offers the most spectral efficiencies, they need to be tightly integrated with an operator's macrocell networks, which may not be possible under a shared-spectrum scenario, particularly if the frequencies are unlicensed.

Many operators, AT&T (NYSE:T) in particular, are dubious about the opportunities for spectrum sharing, preferring to have exclusive use to frequencies, particularly those that they pay the FCC to use. Further, they would prefer to use spectrum below 3 GHz.

However, mobile operators' growing need for spectrum could eventually force their hands. For example, spectrum-strapped T-Mobile USA is already part of a joint industry-government effort to test spectrum sharing in the 1755-1780 MHz band, which the operator hopes will open up the AWS-3 band for eventual auction long before all government entities are cleared from the spectrum.

Given the technological hurdles and the question of how quickly mobile operators will get on board with the idea of spectrum sharing, it will likely take years before the 3.5 GHz is actually shared between the government and wireless operators that use the frequencies for commercial services.

For more:
- see this FCC release
- see this ARS Technica article
- see this GigaOm article
- see this ComputerWorld article

Related articles:
Europe pushes carriers to share their spectrum with 'innovators'
T-Mobile: We'll prove shared 1755-1780 MHz band can be auctioned
Europe's first TV white space licensee to use Fairspectrum's database
AT&T shreds PCAST's shared spectrum vision
AT&T raises red flag over shared spectrum plan
Spectrum sharing: Easier said than done
CTIA embraces spectrum sharing, but sees it as second-best option