Regulatory Wireless

FCC’s Multiple Front Offensive to Solve Wireless Backhaul Demands

Image courtesy of Cisco[Editor's Note:  Bob Primosch is a Partner with the Washington, D.C.-based, communications law firm Wilkinson Barker Knauer, LLP

According to a recent report published by Cisco, online video now accounts for more than 25% of all broadband traffic. In all likelihood that number will only go up, straining the capacity of existing backhaul alternatives. The FCC thus is taking steps to position fixed wireless as a meaningful option for high-capacity backhaul in areas where fiber might not be cost-effective.

In June, for example, the FCC decided to permit users of the upper 6 GHz band to utilize channel bandwidths as wide as 30 MHz. The FCC’s rules require that 6 GHz links have a minimum path length of 17 kilometers, and a 30 MHz channel must have a minimum payload capacity of 134 Mbits/s. Under ordinary circumstances and assuming proper frequency coordination, 6 GHz licenses can be relatively easy to obtain.

More recently, the FCC launched a wide-ranging proceeding to explore other ways of enhancing wireless backhaul. As a “big picture” item, the FCC is investigating the possibility of permitting use of smaller antennas for backhaul links, and lowering its minimum capacity requirements for links in rural areas where broadband traffic may be lighter. In a separate docket, the FCC is slated to consider whether spectrum in the TV white space can and should be available for licensed wireless backhaul.

Also on tap are several possible near-term rule changes to increase the amount and cost-effectiveness of spectrum available for backhaul below the 13 GHz band. First, the Commission has proposed to permit fixed wireless licensees to share 750 MHz of spectrum in the 6875-7125 MHz and 12700-13200 MHz bands with broadcast stations and cable systems that already utilize microwave links on those frequencies. With certain exceptions, backhaul providers would be required to comply with existing FCC frequency coordination and technical rules (power limits, capacity and loading requirements, etc.) that apply to these frequency bands.

As something of a quid pro quo for the broadcasters, the FCC proposes to eliminate its “final link” rule, which prohibits broadcasters from using certain spectrum as the final radio frequency (RF) link in the chain of distribution of program material to broadcast stations.

In addition, the FCC proposes to give fixed wireless licensees more flexibility to temporarily operate below the FCC’s capacity requirements. Presently, the FCC requires licensees in certain Part 101 bands to operate with a minimum payload capacity at all times (the required capacity is expressed in terms of megabits per second, and varies according to channel bandwidth).

Various vendors and service providers have argued that the rule is too draconian. Fixed microwave links (especially those over longer distances) may suffer from atmospheric fading and increased bit errors. One way to combat fading is to reduce the link’s data rate for a short period of time. This, in turn, requires a temporary change in the type of modulation, a process known as “adaptive modulation” or “ACM.” The FCC is considering whether to permit use of ACM where the link operator otherwise maintains the required minimum data rate both during normal operation and on average.

Finally, the FCC is weighing the merits of a proposal that, in theory, would permit greater spatial reuse of backhaul spectrum via use of side lobe transmissions (also called “auxiliary links”). Under Part 101 of its rules, and except in the case of geographically licensed services, the FCC requires each microwave link to be separately licensed and frequency-coordinated. In 2007, the FCC was asked to declare that a Part 101 fixed wireless licensee may simultaneously license and coordinate its main lobe transmission (or “primary link”) and side lobe transmissions so long as all transmissions collectively comply with the FCC’s technical requirements.

The idea here was to permit the licensee to deploy multiple links over the same spectrum in areas more proximate to its transmitter (as opposed to just a single directional link pointed at one distant receive location), without having to license or coordinate each link separately.  After receiving substantial opposition, the FCC tweaked the proposal a bit. Under the FCC’s modified approach, each “auxiliary” link would be coordinated separately, and the licensee of the primary link would file applications to add the auxiliary links to its license. Auxiliary links would have no interference protection except against subsequent auxiliary links deployed by other licensees. Also, auxiliary links would not be subject to antenna standards or the loading or path length requirements that apply to primary links.

It is expected that the FCC will make progress on some or all of these items, perhaps as soon as the first half of 2011. In the interim, those interested in wireless backhaul opportunities should review the FCC’s Part 101 rules to evaluate which spectrum bands might provide the most cost-effective solution.

Author Robert D. Primosch, Esq.

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