Many broadcasting stations are already using part of the HDTV 6 MHz channel (19.4 Mbps) to transmit several simultaneous multi-cast SD channels, and those are already degrading considerably the quality of the once alone HD channel, reducing its available bandwidth to close to half of the 19.4 Mbps, a bandwidth it requires to show acceptable quality.

Points of Reference

One particular example I sadly watched deteriorate over the past 8 years is the WETA PBS HDTV channel in the area of Washington D.C. The once excellent PBS broadcaster gradually added several SD sub-channels into the 6MHz channel allocation, it started doing the mix only during the day, and switching to HD at night, however, in parallel to the HD channel an SD banner kept transmitting for each SD channel while not sending content.

Then, over the past few years WETA PBS has been transmitting them all in parallel during the whole day, 1HD and 3SD, and the HD channel quality has suffered to the point of being now a poor representation of HD even when no fast motion is present on the image.

PBS's approach has motivated me to skip the HD channel due to its poor quality. I cannot appreciate its content when is transmitted in such degraded quality.

Ironically, I started viewing the HD channel content in 1998 because I was attracted by its unique image quality, a pioneer station in the early adoption of HDTV. In other words, the quality of the image made me view a program that I might not have viewed otherwise, the power of HDTV quality produced the effect I expected, even when I am not a TV viewer.

WETA was first in HDTV in 1998; it was an example of early adoption of quality HD when only a few others in the nation did the effort to transmit HD, now their dedication to HD quality is sacrificed for multi-casting, and others are following the same path or quality degradation.

The Mbps Challenge

I can anticipate how the mobile A-VSB bandwidth requirements could become an invitation to further deteriorate main HDTV terrestrial channels if using the sharing approach within the 6MHz slot, especially on those channels that are already multi-casting several SD feeds together with their parallel HD channel.

Samsung's assessment that subtracting 7Mbps from a HD channel for A-VSB would only be "a bit of challenge" for the quality of an HDTV channel, is short by more than a bit, we have currently many cases with terrestrial broadcast, satellite, and cable services that are doing such bit starvation and the quality degradation is very noticeable, and very unacceptable.

Since Mr. Godfrey indicated that some broadcasters would probably use alternative channels or independent channels to distribute mobile services, while the HD channel is broadcast untouched separately, there is a chance that the AVSB implementation would not affect HDTV quality.

However, if such situation of alternative channels would not be available in certain areas, the possibility of quality reduction of the HD feed is quite possible.

How the Tool is Used Could be the Problem

Samsung is supplying the technology and the tool, broadcasters could take that tool and transform quality into a quantity revenue model, and we know the effect of that scenario already from the experiences with cable and satellite when using their over-compression to fit more channels and services within a limited pipe.

It is very important to note that although the DTV implementation does not mandate HDTV resolution, it is the main reason why consumers are investing in expensive sets, to view a quality image, not just a digital image. Digitizing HD to inferior quality would not motivate consumers embrace the DTV transition and buy new sets, and would certainly upset consumers that would see HDTV quality disappear after they invested on new sets.

Ideally, there should be a system to monitor quality across all video services offered in the nation, satellite, cable, and broadcast. Because that is not in place, consumers are left with the option to accept or switch services in a constant basis. Although that promotes competition it also causes unnecessary inconvenience and extra switching costs to consumers. We will have to wait to witness if the AVSB tools are actually used to benefit the consumers without degrading HD quality.

A Competitor - LG's MPH (Mobile-Pedestrian-Handheld)

In April 2007 at NAB, LG introduced a system developed by Zenith Electronics and Harris to broadcast ATSC DTV broadcasts to mobile devices. It was not disclosed if the system was submitted to consideration as a standard, to compete with the A-VSB system from Samsung and Sinclair, mentioned above.

The system uses a multiple-stream approach, the main stream for legacy DTV devices tuning to 8-VSB and the MPH stream for mobile devices even operating at high speed.

The Efforts for a Mobile Standard

Since I first wrote these articles, several other solutions were submitted for acceptance to the ATSC from other industry competitors.

In June 2007, the ATSC disclosed that a total of 10 proposals were submitted for consideration responding to a request for proposals issued by the ATSC in May, and due in July. Several conditions were established, which include but are not limited to, protecting legacy receivers and existing services, be compatible with the current ATSC DTV system, and operate in the same RF channel without penalizing legacy equipment.

The mobile standard was named ATSC-M/H, and the work was assigned to the ATSC Specialist Group on ATSC-M/H (TSG/S4), led by Mark Aitken of Sinclair Broadcast Group.

In other parts of the world, the European Union initiated the implementation of DVB-H (Digital Video Broadcasting to Handhelds) as the mobile devices standard for TV broadcasting in Europe.

This concludes this series of articles regarding A-VSB as a DTV Mobile Broadcasting solution.