On June 11, 2009, I lost a cherished friend: the Sony Watchman TV I'd owned for 20 years. When analog TV broadcasts went dead that day, my Watchman, along with every other portable analog mini-TV, suddenly became useless. A few portable digital TVs have since appeared to fill the gap, but because the ATSC digital-TV standard wasn't designed for mobile use, none of them can deliver the reliable roving reception of my 1980s-vintage Watchman. The minute a portable digital TV is set in motion, its picture distorts into something that looks more like a defaced Picasso painting than the work of ABC or CBS.
Fortunately for those of us who love our TV on the go, portable TV is coming back. A new mobile-optimized addition to the ATSC digital-TV standard will soon begin broadcasting in cities across the country. Engineers call this standard ATSC-M/H (for Mobile/Handheld), but everyone else calls it Mobile DTV (MDTV). By the end of this year, we should see an incredible variety of MDTV-compatible portable receivers, including TVs but also cellphones, portable media players, car video systems, laptop computers, and USB dongles.
Of course, there are other ways to get mobile TV. Cellphone service providers offer TV programming, and devices like the Slingbox let you stream video from your home A/V system to your cellphone or laptop. But those solutions are more complicated and/or costly than my Watchman was. MDTV service is totally free in its standard form, and all you need to do to get it is flip a switch.
There's no legal requirement for broadcasters to add MDTV, as there was with the original DTV standard. However, enthusiasm among broadcasters for the new technology is high, according to Anne Schelle, executive director of the Open Mobile Video Coalition, an alliance of 28 broadcast companies representing more than 800 stations. "We predict more than 70 stations will be broadcasting [MDTV] by the end of the year," she said. "The costs are only $75,000 to $150,000 for the first channel, then $10,000 to $15,000 for each additional channel. Compared to the millions that stations had to spend to convert to digital TV, this is nothing."
MDTV is an extra stream of data added to a conventional DTV broadcast, with error correction designed to overcome the reception problems encountered when a receiver is in motion. It's based on the same IP your computer uses to access Google and Amazon.
Because MDTV is designed for small screens, the resolution is fairly low: 416 x 240 pixels if the station is using the standard Advanced Video Coding (AVC) technology. This can be increased to either 832 x 480 or 624 x 360 pixels if the station upgrades to the newer Scalable Video Coding (SVC) technology. "Ten inches is about as big as you want to go with the screen," said Dave Arland, a spokesman for LG. MDTV supports frame rates from 12 to 60 hertz. The audio system is HE (high efficiency) AAC, an outgrowth of the same audio-coding technology used in iPods. Sound can be stereo or mono. The ultimate quality of the picture and sound depend on the amount of bandwidth the station devotes to each MDTV channel.
A broadcaster can send up to 8 channels of MDTV programming over a single broadcast DTV channel. The programming can be interactive, sending return data through either a cellphone network or a Wi-Fi connection - and potentially allowing viewers to vote for their favorite singer on American Idol; access Yahoo-type Widgets for things like weather and traffic reports; and order downloads and other pay-per-view programming.
Videophiles might be concerned that squeezing more data onto a DTV broadcast channel will affect the quality of existing HDTV signals. Mark Aitken, director of advanced technology for the 58-station Sinclair Broadcast Group, said the impact of adding MDTV depends on how a station formats its broadcasts.
"Even if you're doing an HD feed and an SD feed [for home TV viewing], there's sufficient room to add a couple of mobile channels if you're sending your HD feed in 720p and have invested in the latest generation of video encoders," Aitken explained. He suggested that few viewers would notice if a station changed its main DTV broadcast format from 1080i to 720p to accommodate MDTV: "On the typical household display device, I would challenge most every viewer to tell me they can see the difference between well-done 720p and well-done 1080i."
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