[Blogmeister’s Note: This is the last in a series of posts describing the FCC’s Incentive Auction Notice of Proposed Rulemaking. You can find all installments in this series by clicking here. Contributors to this series include Dan Kirkpatrick, Rob Schill, Don Evans and Harry Cole.]

Once the “reverse” and “forward” auctions have both been completed and TV licenses have all been tucked away in their newly-compacted space, the fun will really begin for the Commission.

Once the “reverse” and “forward” auctions have been completed and the broadcast TV industry has been repacked, the FCC will finally be able to reconfigure the vacated UHF spectrum for mobile. But determining, now, precisely how that reconfiguration will ultimately look, then, poses a unique challenge in view of the number of unknowns currently in play.

Until the “reverse” auction is completed, questions will remain regarding the amount of spectrum that will be available for reconfiguration, the particular frequencies comprising that available spectrum, and the geographic locations covered by that spectrum. Therefore, the band plan described in the Incentive Auction Notice of Proposed Rulemaking (NPRM) is more of a “framework” based on the expectation of cleared frequencies. In admirable bureaucratese, the NPRM describes its goal as “a band plan that balances flexibility with certainty.” 

The certainty includes proposing a fixed amount of downlink spectrum nationwide with uplink spectrum possibly varying in different geographic areas. The idea is to best utilize what are expected to be varying amounts of cleared spectrum in different geographic areas. By providing uniform downlink spectrum throughout all geographical areas, the Commission hopes to assure a more interoperable universe at the device level, where each mobile device can use the same receive filters while the carriers’ base stations can be modified to allow for multiple uplink spectrum signals. A level of interoperability at the device level is expected to lead to lower device costs while allowing for greater economies of scale. 

Consistent with the uncertainties surrounding the final reconfiguration process, the Commission advises that its general “focus” is on five “key policy goals”, to wit: utility, certainty, interchangeability, quantity, and interoperability.

  • Utility: The Commission is proposing to auction the newly-available mobile spectrum in 5 MHz “building blocks”, which can support a variety of wireless mobile technologies (including Wideband-Code Division Multiple Access (W-CDMA), High Speed Packet Access (HSPA) and Long Term Evolution (LTE)). To the extent possible, the Commission will seek to pair the blocks, consistent with the prevailing practice in many existing mobile networks.
  • Certainty: The Commission proposes methods to minimize interference between broadcasters and wireless, as well as harmonizing the band plan with international treaty obligations to Canada and Mexico. Notwithstanding the FCC’s best intentions on this front, though, border-related issues will complicate the reconfiguration process, particularly in view of the disparate plans for DTV conversion in Mexico and Canada.
  • Interchangeability: The FCC intends to assure that the reconfigured band will permit “enhanced substitutability” of the spectrum blocks.  The idea there is that, the more interchangeable the blocks are, the less important it will be to bidders that the particular frequencies up for auction can’t be known at the time of the auction – since whatever blocks they may buy will in any event be “interchangeable”. Technical solutions such as effective guard bands should assist in this regard.
  • Quantity: By providing varying amounts of uplink spectrum in different geographic regions, the Commission will ideally be able to take maximum advantage of whatever spectrum becomes available through the “reverse” auction. Different uplink amounts will permit the Commission to vary the total amount of spectrum per geographical area, which should provide greater efficiency than would a nationwide standard. Also, the Commission plans to maximize new unlicensed spectrum both by allowing such use in the guard bands between TV and wireless and by supplementing the guard bands with “remainder” spectrum from the conversion of 6 MHz blocks (i.e., the standard for television stations) to 5 MHz.
  • Interoperability: The Commission’s “proposed band plan would allow for wide band radio operations using common radio components and improvements as technology evolves over time.”

With all the caveats about unknowns and the like, this is what the FCC has in mind for the reconfigured band.

The Primary Proposal. Under the Commission’s primary proposal (see Figure A), the uplink band would begin at channel 51 and extend downward toward channel 37. Exactly how far down the uplink band might extend will be determined by how much spectrum becomes available through the “reverse” auction and consequent repacking.

On the far side of channel 37, the downlink band would begin at channel 36 and, as with the uplink band, extend downward. How far down it goes would, again, depend on how much spectrum is freed up through the broadcast repacking.

The uplink and downlink bands would be placed with an eye towards limiting interference, thereby minimizing the need for guard bands. The new uplink band would be adjacent to the 700 MHz uplink band; these bands are harmonized so there is no anticipated need for a guard band. The downlink band beginning at channel 36 would effectively utilize channel 37 as a guard band – the current services in channel 37 (radio astronomy and wireless medical telemetry) have been operating adjacent to broadcast television bands without interference. But note the Commission indicates a willingness to consider relocation of the current channel 37 services, of which the FCC has historically been highly protective.

The Commission seeks comment on the proposed spectrum block size. The suggested size is 5 MHz, but the Commission would consider maintaining the 6 MHz block structure used for television operation; it might even look at larger units, e.g., 10 MHz blocks. The Commission is interested in a structure that will allow the aggregation of 5 MHz blocks, both at the initial licensing stage and through the secondary market and channel aggregation. The Commission proposes to auction and license paired blocks of spectrum. Where there is spectrum that cannot be paired, the Commission proposes to make such unpaired spectrum available for downlink purposes.

Alternative Band Plan ApproachesWhile the proposal described above is the FCC’s “lead proposal”, the NPRM includes a few alternative visions for the band plan. 

Down from Channel 51(see Figure B)The Commission could attempt to clear broadcast channels from channel 51 downward without regard to the natural separation of the channel 37 services. A downside would be the need to create a duplex gap between the uplink and downlink bands. The wider the duplex gap the better the mobile performance, but in a smaller licensed band.

One concern with this alternative is that if more than 84 MHz is cleared through the “reverse” auction/TV repacking process, channel 37 would be located in the downlink band – which would require the Commission to address, as part of the reconfiguration, what to do with the radio astronomy and medical telemetry services currently operating at channel 37. (See Figure C.) If radio astronomy and wireless medical telemetry were moved from channel 37, the Commission might seek to place the downlink band at channel 32 rather than channel 36 thereby creating symmetry between the total uplink and downlink spectrum.

In from Channels 51 and 21 (see Figure D)Another alternative would be to maintain the 51-down approach for the uplink band, but start the downlink band up from channel 21.  That would avoid any need to move channel 37 services. There would be no need for a duplex gap, since TV broadcasters would operate between the uplink and downlink bands. However, guard bands would have to be created – one on each side of the downlink band and the lower edge of the uplink band (as in the lead proposal). There is also the question of whether the pass band size would require multiple band plans. 

Prioritizing Paired Spectrum. The Commission may consider a plan based around the pairing of spectrum nationwide instead of on a market-by-market basis. Rather than a series of asymmetrical markets where the uplink varies, the spectrum would be equally divided between paired downlink and uplink spectrum. Where there is residual spectrum it would be used for one block of unpaired downlink spectrum. The obvious downside is that it would be limited to the “lowest common denominator” market availability of spectrum.

Another alternative would involve the creation of two families of paired spectrum, one nationwide and another in smaller markets. The goal here would be to try to balance the desire to offer as much paired spectrum as possible with the need to maximize the total amount of spectrum reallocated.

Different Amounts of Spectrum in Different MarketsBy allowing the conversion of different amounts of broadcast spectrum in different geographic areas, the Commission would hope to maximize the total amount of broadband spectrum available. However, the prospect of multiple band plans gives rise to technical complications, since such plans would create a need for different filters and/or duplexers in mobile devices. To address that problem, the Commission is considering a compromise solution involving “families” and “extended families” of related band plans. (See Figure E.) This way, mobile devices could be manufactured with common receive filter components to fit the common nationwide downlink spectrum, while the need for different receive filters could be addressed through operators’ base stations. 

A further complicating factor: if broadcasters relinquish an unexpectedly large amount of spectrum, technical requirements might necessitate two downlink band plans as an initial matter. The Commission seeks comment on these issues, as well as interoperability concerns.

Geographic Area LicensingThe Commission intends to utilize an intermediate geographic area licensing approach, offering mobile spectrum to serve particular Economic Areas (EAs) rather than broader service areas. Auctioning the spectrum based on nationwide, or broad regional, service areas would be less than desirable because, depending on the results of the TV repacking, spectrum would likely not be available in uniform amounts in all markets. The amount of spectrum that could be available for a nationwide license, then, would be limited to the amount available in the market with the least spectrum relinquished. On the other extreme, a more granular licensing approach – based on, for example, Metropolitan Statistical Areas/Rural Statistical Areas (MSAs/RSAs) that are smaller than EAs – would risk complications in auction design and implementation, as well as in the service roll-out. 

The Commission therefore is looking to the mid-sized, “Goldilocks zone” of licensing based on EAs. The Commission seeks comment on this approach, as well as what additional concerns to consider with respect to areas outside the lower 48 states (i.e., Alaska, Hawaii, U.S. territories, Gulf of Mexico).

The Commission also seeks comment on possible early and voluntary resolution of issues related to broadcast protections affecting lower 700 MHz A Block licensees.  The Commission would seek to facilitate channel relocation requests.

Unlicensed use. With all this band reconfiguration rearranging space for licensed operations, the Commission must still identify those areas of the spectrum which will be available for unlicensed use. The NPRM identifies three types of spectrum suitable for unlicensed use: guard bands, TV white spaces, and channel 37.

Guard bands: The Spectrum Act authorizes guard bands “no larger than [are] technically reasonable to prevent harmful interference between licensed services outside the guard bands.” The Commission is proposing 6 MHz guard bands between mobile broadband use and broadcast use. (See Figure F.) Those would be supplemented with the leftover bits from the relinquished broadcast spectrum – 1 to 4 MHz segments which are too small to be licensed as 5 MHz blocks. These guard bands would be available for unlicensed use. 

Of course, Congress’s insistence that guard bands be “no larger than technically reasonable” frames an obvious question: what is “technically reasonable?” Is a 6 MHz guard band enough to provide the necessary interference protections? Also, could the “remainders” from converting 6MHz television channels into 5MHz broadband channels be properly added to this band?

White Spaces:  In its repacking efforts, the Commission is also seeking to maintain a “substantial amount” of TV white space available for unlicensed operations. The Commission seems to think there will be plenty of white space left after the repacking, but that’s not intuitively obvious. After all, with TV broadcast channels being repacked even more tightly than has historically been the case (and with wireless service filling up most of the space freed up by the TV repacking), “white space” could ordinarily be expected to be in shortened, if not short, supply post-reconfiguration.

Channel 37:The Commission proposes unlicensed use in channel 37 “whether or not we relocate the WMTS and the Radio Astronomy Service.”  Every radio astronomy band is related to specific emissions from some cosmological event of interest to scientists. The channel 37 frequencies are particularly important in studies of the stuff between stars, distant pulsars, and our own Sun. The frequencies are protected by international treaty and used by radio-telescopes worldwide, so it will be interesting to see how commenters and the FCC address this issue.

If these services stay in channel 37, won’t they suffer interference from the on-rush of unlicensed operations? The Commission hopes to avoid this problem by establishing protection areas around the limited number of medical telemetry and radio astronomy sites, thus opening up this slice of spectrum for unlicensed use outside those limited areas.  The NPRM specifically solicits comment on the best protection criteria for medical telemetry and radio astronomy. 

Finally, it’s important to recognize that the voluminous NPRM poses many other questions addressing a wide range of critical issues, including pass band size, the possible authorization of TDD service in the band, and technical rules applicable to spectrum use. We strongly suggest that anyone with an interest in any of these areas review the full text of the NPRM carefully.

Again, comments are currently due no later than December 21, 2012 with replies due on February 19, 2013.

[UPDATE: As we have separately reported, on November 29 the Commission extended the comment and reply comment deadlines to January 25, 2013 and March 12, 2013, respectively.]