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CAPITAL CURRENTS: The new ATSC digital mobile video service

Fri, 07/31/2009 - 8:10pm
Jeffrey Krauss, President of Telecommunications and Technology Policy

Retrans negotiations may get very interesting.

The next big thing in the television business might be mobile video – delivering digital TV programs to portable handheld devices. Or maybe not.

Jeffrey KraussBoth Verizon Wireless and AT&T Wireless are using a technology developed by Qualcomm, called MediaFlo, to deliver mobile entertainment and information services to their subscribers. And now the Advanced Television Systems Committee, the TV industry standards body, has jumped on the bandwagon, developing a standard for TV broadcasters to use. Hardware was developed to support live demonstrations at the NAB Show in April. Some broadcasters are enthusiastically promoting mobile TV; others are less excited.

There are a couple of aspects in the ATSC’s plans that might affect cable operators. But first, a description of the ATSC mobile system. The ATSC has assigned it document A/153 and has awarded it Candidate Standard status. An ATSC Candidate Standard is a document that has received significant review by experts and is then made available to a broader audience for implementation and technical feedback.

While A/153 uses a number of standards already developed for mobile video distribution, the significant invention is the ability to carry mobile video within a digital stream that was designed for delivery of TV programs to fixed TV receivers. Broadcasters use a modulation called 8-VSB with a particular type of forward error correction (FEC) that was never intended for mobile reception. A/153 defines a way to partition the transmitted data so that ordinary broadcast signals continue to be delivered to fixed receivers and increased error protection is applied to the mobile data. In addition, long and regularly spaced training sequences are inserted into the mobile data.

The broadcast signal is partitioned on a bursty time-slice basis so that mobile receivers need only receive the mobile data portion of the signal. This allows the mobile receiver to cycle power in its tuner and demodulator to save energy.

The A/153 signals are designed so that they do not interfere with the legacy digital TV signals defined in ATSC standard A/53. Existing digital TV receivers will ignore the A/153 data and will continue to receive the TV broadcast signals that conform to the A/53 standard.

A/153 uses specifications such as OMA BCAST, developed by the Open Mobile Alliance, and FLUTE (File Delivery over Unidirectional Transport), developed as RFC 3926 by the Internet Engineering Task Force. The video coding is Advanced Video Coding, also called H.264 or MPEG-4 Part 10, constrained to a picture size of 240 x 418. For full details, you can download the relevant documents here.

Recall that a digital broadcast TV channel runs at the data rate of about 19.4 Mbps. The mobile signal defined in A/153 can use up to about 14.7 Mbps, and the remaining 4.7 Mbps is reserved for legacy signals that conform to A/53 and can be received by existing digital TV receivers. Using legacy MPEG-2 video coding, which is the only video coding that existing DTV receivers support, that 4.7 Mbps is sufficient for a standard-definition TV signal, but it’s not sufficient for HD.

So how does all of this affect cable operators? After all, cable subscribers have big-screen digital TVs that are connected to a cable and fixed in place. They don’t want to display a 240 x 418 picture on a 1080 x 1920 screen. They don’t expect to be walking around the house receiving cable signals on a portable device. And that’s exactly the point. A cable operator that receives broadcast signals off-air will want to strip out any mobile signals, rather than delivering them to home subscribers. Maybe existing headend equipment is able to do that already, or maybe some new hardware is needed. It’s worth investigating.

But suppose the cable operator receives a separate feed from a broadcaster, over fiber or microwave facilities. And suppose the broadcaster uses 14.7 Mbps of his off-air signal for mobile video and the remaining 4.7 Mbps for SD broadcasting to off-air receivers. And suppose the broadcaster wants to deliver an HD signal to the cable headend. Can a broadcaster deliver an SD signal to off-air viewers and an HD signal to cable subscribers? You betcha. There are no FCC rules to prohibit this – at least not yet.

I doubt that a cable operator would be required to carry the HD feed under FCC must-carry rules. But this is where the retransmission negotiations will get interesting. According to trade press reports, cable operators have increasingly been getting the short end of the stick in retransmission deals and have been forced to pay broadcasters increasing sums. This could turn the tables. I wonder how much broadcasters would be willing to pay cable operators to carry an HD feed, when only SD is delivered off-air.

Of course, this is all very speculative. While free mobile video service has taken off in some other countries, nobody knows whether U.S. viewers will be willing to pay to receive TV programs on a handheld device. But it’s not too early to start considering the implications.

 jkrauss@krauss.ws

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