Monday, October 13, 2008

FCC Digital Must Carry

The FCC Digital Must Carry rule clarifies how cable companies must carry digital over-the-air broadcast signals for its basic tier subscribers. If a TV station returns its analog spectrum and converts to digital operations then it must be carried by local cable systems. Basic tier service costs about $14/month in most areas. The following are excerpts from the FCC document and an analysis of what they mean and how this is good for consumers:

"The Report and Order finds that the signal strength level necessary to provide a good quality digital signal at a cable system’s principal headend is –61 dBm."

This prevents the cable companies from transmitting a digital signal that to too weak to be demodulated error-free by the QAM tuners in HDTVs.

"Primary Video. The Report and Order finds that the “primary video” entitled to mandatory carriage includes a single programming stream and other program-related content. The television station chooses which one of its unrelated multiplexed signals gets carried under the Act. The Further Notice seeks comment on how to define “program-related” in the context of primary video."

The TV station and not the cable company get to decide which two streams (1 primary and 1 multiplex) will be carried. The HD stream will usually be the primary stream, so the TV station gets to decide which of its sub channels also get to be carried. Some stations have multiple SD streams (> 2) instead a larger HD + SD sub channel configuration, so in that case the TV station gets to decide which two will be carried.

"Program-related. A cable operator would be required to carry the following material carried on a digital television signal because it could be considered program-related under the WGN factors: (1) closed captioning, (2) V-chip data, (3) Nielsen ratings data, and (4) channel mapping and tuning protocols (“PSIP”)."

Requiring that the channel mapping PSIP data be carried without damage is important because this allows a method for consumers and HDTVs to be able to find the channels. Many cable companies place the must carry stations at random locations across the dial which makes them difficult for the user to find. Some cable companies routinely move these stations in a further attempt to frustrate consumers who don't use a cable company supplied set-top box. The PSIP data makes the stations easier to find and some HDTVs will map them automatically.

"The Report and Order finds that a cable operator would not necessarily be materially degrading a digital television signal if it carries less than the full 19.4 mbps transmitted by a broadcaster."

This allows the cable company to utilize QAM modulation which is more bandwidth efficient than the over-the-air ATSC VSB modulation.

"The Report and Order finds that a cable operator may not carry a digital television signal in a lesser format or lower resolution than that afforded to a non-broadcast digital programmer carried on the cable system.

This means that a cable company cannot degrade the video resolution, MPEG-2 bitrate, or audio AC3 bitrate to a level that is lower than any of the extended or premiere channels that is also carries. Since almost all cable companies will broadcast a high quality HBO, Showtime, or VOD stream in high bitrate 1080i with 5.1 384kbps AC3, this means they cannot degrade the must carry channels to a level less than this. They are basically prohibited from transcoding the must carry channel to unencrypted standard def (SD) while charging for the encrypted high def (HD) version.

"However, a digital-only television station may demand that a cable operator carry its digital signal in an analog format without the prohibition against material degradation being violated. If a television station chooses to be carried in this manner, it is treated in the same manner as an analog signal."

This gives the TV station the option to also be broadcast in analog NTSC for non digital-ready viewers. I believe this rule expires sometime in 2010. (TBD, find the exact date with a link to the relevant FCC doc)

"Cable operators are permitted to remodulate digital broadcast signals from 8 VSB to 64 or 256 QAM. Cable operators are not required to pass-through 8 VSB."

This allows cable companies to use QAM which is more bandwidth efficient than VSB modulation and will allow more channels to be broadcast on the cable. This also allows cable company set-top boxes to only have QAM tuners which should reduce costs.

"The Report and Order finds that there is no need to implement channel positioning requirements for digital television signals like those that exist for analog signals."

This allows the cable company to place the must carry station at any digital channel location it wants. It is unfortunate that this exception exists because when there are 100+ digital channels this becomes a game of find the needle in the haystack for the consumer. Fortunately PSIP alleviates some of this pain.

"The Report and Order finds that channel mapping protocols contained in the PSIP datastream adequately address a television station’s channel positioning concerns."

See above. Unfortunately the first generation of digital HDTVs don't support PSIP that well.

"The Report and Order finds that a cable operator must notify its subscribers whenever a digital television signal is added to the cable system channel line-up."

This allows a consumer to know when to perform an auto-scan and find the new channels. Unfortunately the cable company is not required to notify subscribers when they randomly move channel numbers around.

"The Report and Order finds that digital television signals must be available to subscribers on a basic service tier. The Further Notice seeks comment on voluntary carriage of digital signals on a tier other than the basic tier."

This just restates the requirement that basic tier subscribers be able to receive digital channels without any extra charge.


The basic tier subscriber cannot be charged extra for the ability to view local HD stations in their original quality. Transmission options are clear-QAM, VSB, or issuing free set-top boxes to all subscribers. For technical and economic reasons the cable companies will choose the clear-QAM option.

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