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IEEE BTS Talks Mobile DTV

The 60th Annual IEEE Broadcast Symposium opened Wednesday with tutorials on HD Radio, which included a presentation by John Kean from NPR Labs on "The Design and Use of the HD Radio Coverage Model." Many of the lesson's John Kean learned in researching HD Radio coverage could apply to mobile DTV as well.

Wednesday's keynote luncheon speaker, Lt. Col. Douglas A. Williams, from the U.S. Air Force Special Operations Command, gave a very interesting presentation on broadcasting from an aircraft. Even though he began the presentation by stating that he wouldn't be talking about the engineering involved, attendees heard about the antennas, frequency bands and power levels used as well as the unique challenges of operating high power transmitters from a large aircraft. Yes, large air cooling systems are needed to keep the transmitters cool and yes, they do stop broadcasting during aerial refueling.

The afternoon session provided background technical and practical data on ATSC mobile DTV. Rich Chernock from Triveni Digital provided an extended tutorial on all aspects of ATSC Mobile DTV. One of many tips discussed during the tutorial included the requirement that, unlike conventional ATSC, the data coming out of the studio transmitter link at the transmitter site has to match the data going into the link at the studio, bit for bit.

Tim Laud from Zenith Electronics presented data on tests he conducted in the Chicago area using the assorted coding options available in ATSC mobile DTV. So far, most mobile DTV broadcasts are using all quarter-rate coding or mixed rate (1/2, 1/4, 1/4, 1/4) coding. It turns out that other combinations could offer a better trade-off between robustness and efficiency. Some suggestions: use one-half rate coding on segments A and B only, ignoring the less robust C and D segments. Also, changing the Reed Solomon coding on all quarter-rate coding from 48 parity bits to 24 party bits has a small impact on robustness while allowing more data. I'll have more on this in a future column.

Finally, anyone who's had an opportunity to listen to mobile DTV on a small portable device knows that audio can be a problem Down-mixing 5.1 audio from the main channel into stereo audio for mobile isn't good enough. The dynamic range is too large for the small speakers and the noisy environments in which many of these devices operate. Conventional audio processing won't work. Tim Carroll from Linear Acoustic cautioned the audience not to use one of his conventional audio processors for Mobile DTV. Although, Carroll didn't mention it, I suspect we'll see a customized Mobile DTV audio processor from Linear Acoustic soon.

Sessions continue Thursday through Friday, ending with a panel discussion, including Bob Weller from the FCC, on spectrum issues related to the FCC's Broadband Plan.

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.