In an earlier post I discussed the FCC’s recent decision to open up 150 MHz of spectrum in the 3550-3700 MHz band for unlicensed “General Authorized Access” usage as the lowest-priority usage category in a new three-tier model that includes protections for incumbent government users and provides for “Priority Access Licenses” assigned via auction.
In this post I’m going to briefly review two other spectrum bands that the FCC has recently moved to make more available for unlicensed use. Together these changes have potential to increase unlicensed spectrum capacity and flexibility in terms of network designs and business models.
In March 2014 the Commission adopted a Report and Order modifying the rules governing the operation of Unlicensed National Information Infrastructure (U-NII) devices operating in the 5 GHz band. The goal of the changes was to “significantly increase the utility of the 100 megahertz of spectrum” in the 5.150-5.250 GHz band and “streamline existing
rules and equipment authorization procedures for devices throughout the 5 GHz band.”
As a FCC’s March 31 press release explained:
Currently U-NII devices operate in 555 megahertz of spectrum in the 5 GHz band, and are used for Wi-Fi and other high-speed wireless connections…The rules adopted today remove the current restriction on indoor-only use and increase the permissible power which will provide more robust access in the 5.150-5.250 GHz band. This in turn will allow U-NII devices to better integrate with other unlicensed portions of the 5 GHz band to offer faster speeds and reduce congestion at crowded Wi-Fi hot spots such as airports and convention centers.
Broadcast White Space
While the 3.5 GHz and 5 GHz bands can provide substantial amounts of spectrum to augment the overcrowded 2.4 GHz and 900 MHz bands used for Wi-Fi and other unlicensed technologies, the propagation characteristics of these higher-frequency bands translate into limited geographic coverage per base station.
This contrasts with the so-called “White Space” spectrum available for unlicensed use in the sub-700 MHz broadcast band. Often referred to as “prime spectrum real estate,” the broadcast band enjoys relatively strong propagation characteristics. But, at the same time (not surprisingly, given its much-coveted status) it has relatively little free spectrum available for unlicensed use, especially in high-demand metro areas, which are served by relatively large numbers of broadcast stations.
The advancement of unlicensed White Space has been a slow process, dating back to 2002. In 2008 the FCC finally issued a set of rules for White Space operation in the broadcast band. This was followed by a series of refinements, including the authorization of “TV bands database systems” to support non-interfering White Space usage, starting with the Commission’s first authorization of a database operated by Spectrum Bridge in late 2011.
In early 2012 the White Space saga took another turn, when Congress passed a law authorizing the FCC to conduct spectrum auctions to reclaim parts of the TV spectrum for wireless users. This was followed in May 2014 by FCC rules for conducting an “incentive auction” designed to motivate broadcasters to voluntarily give up their spectrum in exchange for a portion of auction revenues. Given the complexity and sensitivity of this ambitious auction plan, it’s not too surprising that its scheduled date has been pushed back twice and is now planned for earlier 2016.
The planned incentive auction and related “repacking” of the broadcast band raised the prospect of a reduction in spectrum available for unlicensed White Space devices (WSD). In response to this, the FCC’s incentive auction rules revisited the Commission’s earlier plan for allocating spectrum to unlicensed use. Though less spectrum will now be available for this purpose, the new plan is designed to ensure that at least three or four 6 MHz channels are available on a nationwide basis, with significantly more spectrum likely to be available in some smaller and more rural markets, where existing high-speed connectivity options are particularly scarce.
This focus on providing a minimum amount of bandwidth nationwide reflects the view expressed by multiple commenters (e.g., see Reply Comments from the Open Technology Institute and Public Knowledge) that “the emergence of a mass market for unlicensed chips, devices and services” based on the 802.11af (“White-Fi” or “Super Wi-Fi”) standard will require the nationwide availability of at least three 6 MHz channels.
The May Incentive Auction Report and Order was followed in late September by a Notice of Proposed Rulemaking revising the Commission’s Part 15 rules governing unlicensed use. These rules loosened some restrictions on power levels and guard band requirements, a change welcomed by White Space advocates, but not by licensed users in adjacent spectrum.
Taken together, Commission’s actions to significantly expand the amount of unlicensed spectrum in frequency bands with diverse propagation characteristics should provide important technical capabilities to support the new generations of unlicensed providers and services discussed in this series of blog posts.
While the 3.5 GHz and 5 GHz bands will provide a substantial amount of new capacity for small-cell deployments, the more limited amount of White Space spectrum will support larger cells, reach longer distances, and provide much-improved in-building penetration by outdoor base stations. And, when combined, this mix of spectrum options should enable unlicensed service providers to architect next-generation networks that cost-effectively deliver significantly faster speeds and more extensive and reliable coverage.