The FCC released its Notice of Proposed Rulemaking (NPRM) (FCC 12-118) regarding “Expanding the Economic and Innovation Opportunities of Spectrum Through Incentive Auctions.” As this is only an NPRM, it doesn't provide the final rules, but does offer some insight into the range of options the FCC is considering.
With regards to repacking the spectrum of those broadcasters not giving up their channels in incentive auction, the FCC provides a range of methodologies for meeting the Spectrum Act's requirement to make “all reasonable effort” to protect coverage and population served. These range from protecting existing population from any new interference, with total interference not to exceed the current 0.5 percent de-minimis level, to allowing up to two percent new interference after the repacking.
The first approach is likely to be rejected by wireless carriers interested in the spectrum, as it will limit spectrum availability. The other approach mentioned is likely to be rejected by broadcasters, especially those in congested markets that already had service losses exceeding two percent during the DTV transition.
Perhaps the best compromise is one that would retain the maximum 0.5 percent de-minimis interference level, but would allow the FCC to move the interference from one area to another. Allowing two percent additional interference would be bad for broadcasters in that it could result in loss of service to entire communities in the larger markets. Due to the limitations of the Longley-Rice propagation software and the default antenna parameters, as well as the treatment of Longley-Rice cells with “Error Code 3,” the actual interference could be much larger than that predicted by the FCC OET-69 model mandated by the Spectrum Act.
The NPRM proposes that in addition to allowing stations that are willing to give up, share their spectrum, or move to VHF to participate in the incentive auction, it’s considering allowing stations that agree to new interference above a certain level to participate in the auction. However, the NPRM acknowledges that this would greatly complicate both the auction and the repacking.
Until recently, most thought the FCC would start at the former TV Channel 51 and move down the channel band, acquiring as much spectrum as it could through auctioning and repacking. The NPRM proposes setting aside two bands of UHF spectrum for wireless broadband – uplink (device-to-base station) starting at the former Channel 51 and moving down. The downlink (base station-to-device) frequencies would start at Channel 36 and move down. No guard band would be required for Channel 51, and the current Channel 37 could remain as a guard band for Channel 36. However, a guard band would be required at the lowest channel of the downlink and uplink spectrum, so there will be fewer channels available for either wireless broadband or broadcasters than if only a single contiguous block of spectrum were to be reallocated.
The NPRM proposes a nationwide “600 MHz” downlink band. This would indicate that it’s very likely TV Channels 34, 35 and 36 will be lost even if the auction reallocates 36 MHz from broadcast TV. It also proposes a guard band of 6 MHz between TV broadcast and 600 MHz base stations, although the FCC does ask for comments on whether this amount is appropriate The 700 MHz uplink band would vary from location to location, but if a 36 MHz spectrum gain is assumed, it would mean loss of Channels 49, 50 and 51, as well as the 34, 35 and 36. The FCC is proposing 5 MHz channel blocks, which would provide two 5 MHz wireless spectrum blocks per uplink and downlink, plus an 8 MHz guard band. The guard bands would be available for wireless microphones and white space devices.
I performed a quick analysis to see how many stations would have to give up spectrum or move to another channel based on these scenarios. If Channels 34, 35, 36, 49, 50, and 51 were removed, a total of 210 stations would be affected. (This is based on CDBS data as of May 22, 2012,) Adding Channels 33 and 48 to the list of channels being reallocated, the number of stations affected increases to 281. These scenarios would return 36 and 48 MHz of spectrum, respectively.
The number of channels available will vary from location to location. The NPRM proposes setting aside a minimum fixed number of channels for downlink, starting at Channel 37 nationwide while allowing a variable number of channels for uplink starting at channel 51.
The NPRM includes many other allocation scenarios, including a single block of channels starting at 51, but variations of the one I described appears to be getting the most attention.
As seen in the example above, there will be a substantial amount of guard band spectrum available for white space devices. However, the repacking is likely to reduce the number of available channels for wireless microphones. The NPRM asks if the FCC should retain the rules reserving the first available channels above and below Channel 37 for wireless microphones and other low power broadcast auxiliary applications. The NPRM proposes allowing low-power devices (white space or perhaps wireless microphones) to use Channel 37, which is currently reserved for radio astronomy and wireless medical devices. There’s a lengthy discussion of this in the NPRM, including the possibility of setting aside another UHF channel (i.e. Channel 32) for medical devices. It also asks if other spectrum in the 500-700 MHz band could be reserved for radio astronomy. After reviewing the NPRM, I'm not sure it makes sense to move these operations from Channel 37 unless the amount of spectrum available after the repacking is so large that all channels above and immediately below Channel 37 would be reallocated.
I'm still reviewing the NPRM which runs more than 200 pages. I've only presented a few of the many options proposed. Whatever options the FCC selects, it will have an impact on the future of TV broadcasting as well as the other services, such as wireless microphones, and now white space devices, that share this spectrum.
Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.
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