The FCC held its Broadcast Engineering Forum on June 25, 2010.
As background, the National Broadband Plan recommends repurposing 120 MHz of from the TV bands to mobile broadband. On June 14 the FCC released an Omnibus Broadband Team Technical Paper that describes some of the analyses supporting this repurposing. Chairman Genachowski asked the Commission staff to hold the Forum to consider ideas in the Paper.
At this Forum there were four areas discussed:
- Advancements in Compression Technology
- Cellularization of Broadcast Architecture
- Improvements in VHF Reception
- Methodologies for Repacking the TV Band
Each area had been the subject of discussion by groups in workshops earlier in the day. At the Forum each of the four groups reported preliminary findings and recommendations.
After hearing the Forum, which is a preliminary effort, I”d say its gist is that technical changes in the TV industry aren’t going to free up significant TV spectrum for mobile broadband. There are no advancements in compression technology that can be implemented in a timely manner (i.e., less than 13 years). State-of-the-art in compression technology, and market realities, makes channel sharing by different licensees impractical. Cellularization of broadcast architecture is seen as not practical nor economical. There is room for improvement in VHF reception, perhaps through higher transmit power levels and better, smart receive antennas. An examination of methodologies for repacking the TV band shows no scenarios where stations can avoid sharing channels, unless some stations voluntarily go off-the-air. (And, as we heard in the presentation on compression, sharing is seen as impractical.)
The slides used in each of the four sessions are to be made available on the FCC web site. For those interested in more details now, I share my notes below.
Advancements in Compression Technology
The results of this group were presented by Andrew Setos from the Fox group.
MPEG-2 was published in 1994, and no significant improvements are expected.
Compression equipment has improved such that artifacts are less noticeable, but they are still there. For example, where five years ago there might have been an obvious pixilation, now there is more of a blurring effect.
There are more-modern compression technologies such as MPEG 4. Current TVs do not support MPEG-4, and it could take 13 years to migrate that technology to consumer TVs.
The FCC Technical Paper scenario of multiplexing two HD programs for two different licensees in one 6 MHz channel is not viable due to quality degradation that would result when needing to choose a winner and loser when one HD stream exceeds the bandwidth of the other.
Statistical multiplexing efficiencies are lost with two separate licensees. It can work with the same licensee because the licensee knows what is in the different programs.
As far as pairing an HD station and an SD station in one 6 MHz channel, this is not viable as the trend is toward all HD.
The bit allocation for Mobile DTV is a straight carve-out, and statistical multiplexing does not help.
Cellularization of Broadcast Architecture
Bob Seidel of CBS presented the results of the cellularization group.
A Single Frequency Network (SFN) is much easier with OFDM than with the current 8-VSB modulation method.
“Self-jamming,” or interference between two cells in a SFN, was raised as an undesirable artifact of SFNs that would result in lack of coverage between cells.
SFNs will not help improve reception at the edge of coverage areas because of desired/undesired signal ratios that must be maintained there.
The lack of performance requirements for DTV equalizers is an issue.
Practical issues involved in implementing SFNs include feeding programming to multiple sites, and the cost of building and maintaining multiple sites.
It was suggested that, regarding Mobile DTV, wireless broadband providers should work with broadcasters. The point here is, why broadcast, say, the Super Bowl from hundreds of cell sites when Mobile DTV from one broadcast site will suffice.
Little or no UHF TV spectrum can be repurposed from cellularization.
Improvements in VHF Reception
Kerry Kozad from Dielectric Communications reported on the VHF reception panel.
The group was focused on fixed reception; mobile operation on VHF is not contemplated due to the large mobile antennas that would be required.
The low-VHF band (channels 2-6) is a bigger problem than the high VHF band (channels 7-13). Noise is a bigger problem, for one thing.
There are only 39 stations in the low-VHF band.
Noise varies from location-to-location at low-VHF, making it difficult to have consistent performance and use common planning factors. There are also undesirable propagation effects at the low VHF band. It would likely require an impractical 15 to 20 dB power increase to alleviate these problems.
High-band VHF suffers from the same noise problems, but not as much. A 10 dB power increase would be required to help significantly.
Receiver antennas can be improved, but not much. The best candidate for improved antenna performance is indoor reception, perhaps through smart antennas working in conjunction with the TV set. The TV and antenna manufacturers have to work together for this to happen.
The FCC should not set consumer antenna performance standards. There are too many variables for a one-size-fits-all performance standard.
It would help to standardize descriptive terminology and performance measurement standards.
The FCC should increase maximum power limits, but be aware that there can be more interference with higher power.
Methodologies for Repacking the TV Band
The spectrum repacking session was led by Bruce Franca from MSTV.
He summarized the status of new modeling efforts and reviewed Technical Paper study assumptions.
Population loss (loss of people served) is one of the costs in reclaiming spectrum.
The focus is on reclamation in the UHF band, as mobile broadband operators are not interested in VHF spectrum.
The study assumptions included locating all stations in channels 2-30, and adding no new stations to channels 2-6.
The minimum number of stations that must share in this scenario are 248. From 20 to 40 percent of Designated Market Areas (DMAs) are impacted and must share, depending on border protection.
A more careful approach to DTV interference is suggested. In analog television, interference can be increased 8 dB before someone notices, and can increase 20-30 dB before someone stops watching. In DTV, however, most TV sets go from perfect picture to no picture in 1 dB.
Interference performance is governed mostly by DTV receive performance.
Different propagation models are available, but there is no indication any are generally better than the Longley-Rice model.
One question was whether protected service areas should be adjusted to more accurately reflect viewing practices, and if so, how. Nielsen reports 10.9 million over-the-air homes, but it is not clear what that means. For example, a home with both FIOS and over-the-air reception is not considered over-the-air by Nielsen.
Hispanic households have a high percentage of over-the-air reception: 20% in Los Angeles, 35% in Houston, and 28% in Phoenix.
50 million DTV converter boxes were sold.
In discussion, it was noted that this panel’s results refer to sharing being “required.” That assumes no stations voluntarily choose to go off the air. If sufficient stations choose to go off, sharing is not required.