If you haven't done so already, please be sure to read the other articles in this series:

In the first article I covered the subject of how the architecture of the system works. In this article I address the subject of bandwidth requirements and how that plays a role with existing HDTV terrestrial bandwidth requirements for quality HD. Bandwidth Requirements At CES 2007, Mr. Godfrey addressed a subject that I have personally questioned at Samsung press conference regarding what A-VSB does to an HDTV channel in terms of quality when borrowing from its allocated bandwidth. He started by initially saying "if the broadcaster is going to continue broadcasting his HD main program, there isn't enough bandwidth left to transmit an HD Turbo stream to mobile devices at the same time - so the Turbo stream must be SD or lower in resolution. The Turbo-Coded stream uses double- or quadruple-redundant coding to increase signal strength in high-speed applications." If they adopt SRS, broadcasters who transmit a single HDTV program would encounter no tradeoff in the resolution of a signal sent to legacy and future DTV sets, Godfrey contended. At its highest setting, he explained, the SRS signal would use only 2-3Mbps of the 19.4Mbps of bandwidth allocated to DTV stations, "and most HDTV broadcasters are not using the full 19.4Mbps for the main HD program", he contended. "MPEG-2 encoders used by broadcasters are so good now that even for rapidly changing images in sports broadcasts, 17Mbps is fine for a completely high-definition picture without trade-offs," he contended. A few stations might run into trade-offs, however, if they broadcast one HD signal and two to three multicast standard-definition (SD) signals simultaneously. The Turbo Coding option, which uses up much less bandwidth than SRS, is scalable up to 600kbps, which could suffice for improved reception on handheld devices with screens up to 5 inches, he added. For in-car TVs with 7-inch to 10-inch screens, a bit-stream with less than 4Mbps of bandwidth could be enough, he said. If an HD station pushes Turbo Coding to 4Mbps for "big-screen" mobile applications, and sets aside the maximum 3Mbps for the SRS signal, only 12.4Mbps would be available for the station's main HD program. At that data rate, "it's still HD, but a bit of a challenge," Godfrey admitted. As an alternative for smaller independent stations delivering only SD streams, Godfrey cited the potential for a subscription service that the station could offer to stream multiple channels of content to portable devices. Stay tuned for further coverage of the subject in upcoming articles.