While backhaul has traditionally been carried on copper wire or fiber, carriers are increasingly turning to wireless technology for capacity to meet the increased demand created by growing numbers of bandwidth-hungry mobile devices and applications. Wireless backhaul is particularly desirable in rural and remote locations where laying wire or fiber isn’t practical.
Wireless backhaul falls under the FCC’s Fixed Microwave Service (FS) rules in Part 101 of the rules. The Commission is examining a range of regulatory options to increase the “flexibility, capacity, and cost-effectiveness” of the microwave bands located below 13 GHz, while protecting incumbent licensees in these bands.
Not all options, though. Some backhaul-related proposals – for example, proposals advanced by the Fixed Wireless Communications Coalition (FWCC) for combining adjacent channels and shared use of government spectrum – will be considered in separate rulemakings. But now on the table for consideration and comment are the following proposals advanced in the NPRM portion of the proceeding:
Allowing adaptive modulation. Part 101 spectrum is subject to certain minimum payload requirements (in terms of megabits per second per hertz). Those limits are intended to assure the efficient use of the frequencies. However, in some instances, ambient conditions create adverse effects such as atmospheric fading or “rain fade”, which cause an increase in bit errors and, on occasion, complete loss of communications. One technique for dealing with such conditions is to briefly reduce the data rate by temporary change in modulation type, a process called “adaptive modulation”. While adaptive modulation is already permitted by the rules, its use is subject to the minimum payload requirements. The problem is that, in order to maintain communications during some adverse propagation conditions, the payload capacity must sometimes be reduced below the required minimum.
In order to allow users to take advantage of adaptive modulation without unduly undercutting the goal of efficient use of the spectrum, the Commission proposes to maintain its minimum payload requirements “except during anomalous signal fading, when lower capacities may be utilized in order to maintain communications”. Beyond that vague articulation, however, the NPRM lacks any detail. Instead, the FCC solicits suggestions for specifics (such as, e.g., how “anomalous signal fading” might be usefully defined, or how use of adaptive modulation should be (a) reflected in coordination notices and (b) recorded or logged).
Auxiliary FS stations. The NPRM seeks comment on allowing FS operators to deploy “auxiliary” stations. The concept of such “auxiliary” stations was first proposed to the FCC by Wireless Strategies, Inc. (WSI) in 2007. WSI envisages “simultaneously coordinate[d] multiple links whose transmitter elements collectively comply with the Commission’s antenna standards and frequency coordination procedures”. Essentially, the concept contemplates the re-use of a coordinated primary frequency by additional “auxiliary” links operating nearby on the same frequency. A number of opponents have questioned major elements of WSI’s thinking, arguing among other things that it would lead to excessive interference to other users, impair the integrity of existing systems, and generally be incompatible with traditional point-to-point FS operations.
While the Commission expresses interest in the notion of “auxiliary” stations, it offers no specific proposals. Instead, it poses a long laundry list of questions concerning regulatory limits that might be imposed on “auxiliary” stations.
Additional spectrum for FS. The Commission proposes to allow FS operations in two additional bands (6875-7125 MHz and 12.7-13.2 GHz). A variety of channel widths would be made available for FS operations, to provide opportunity for flexibility and increased use of digital technology. Those bands are currently allocated only to Broadcast Auxiliary Service (BAS) and Cable TV Relay Service (CARS). FS operations in the 6875-7125 MHz band would be subject to the same overall technical rules that currently apply to the adjacent Upper 6 GHz band, since common technical rules would allow use of similar equipment across the two contiguous bands. Technical specs for use of 12.7-13.2 GHz would not change, although the proposed rules would impose on that band the minimum payload capacity and loading requirements currently applicable to the 11 GHz band.
FS operations would be subject to existing frequency coordination procedures – that is, new FS users would have to coordinate with existing BAS and CARS users, whose existing licenses would not be modified as a result of the proposed rules.
With respect to coordination, though, the Commission asks whether the identification of BAS TV pickup stationary receive-only sites in the 6875-7125 MHz band should be made mandatory. Such identification is only optional at this point, and frequency coordination in that band is not as formalized. The Commission recognizes that broadcasters use their BAS facilities for electronic news gathering (ENG) operations, and it specifically questions how use of the spectrum for FS might affect the flexibility of ENG. The Commission also asks whether FS use of the 12.7-13.2 GHz band would have any adverse effect on present or future use of that spectrum by cable operators.
Eliminating the “Final Link” rule. The NPRM proposes to eliminate the “final link” rule which prohibits broadcasters from using licenses subject to Part 101 regulation as the final RF link in the distribution chain of broadcast programming. The Commission expects that this will encourage fuller use of Part 101 spectrum.
In addition to the relatively specific points addressed in the NPRM portion of the Commission’s action, a number of more general questions are presented for comment in the NOI portion. They include:
Lower efficiency standards in rural areas. Would lowering efficiency standards (minimum payload capacities) in rural areas lower backhaul costs while maintaining spectrum efficiency? And in connection with this query, the Commission questions how
“rural” should be defined.
Smaller antennas. Should Part 101 be revised to permit smaller antennas – the idea being that such antennas would likely also be cheaper, more flexible, more easily deployed, etc.? Anyone who thinks the answer to that question is “yes” is invited to provide detailed information about the particular FS bands that might be affected, new standards that might be applied, the geographical areas in which the new standards could or should be applied, and so forth.
Other modifications. What other modifications to the Part 101 rules – or any other policies or regulations, for that matter – might be made to promote flexible, efficient and cost-effective provisions of wireless backhaul service?
Comments are due October 25, 2010. Reply comments are due November 22, 2010.