Let's get one thing straight: Digital TV is not synonymous with high-definition digital TV (HDTV). It's much more than that. Digital TV encompasses not only HD, but satellite TV, cable TV, Internet Protocol TV (IPTV), and mobile TV as well.
So, is it the next big thing? Believe it or not, you likely have digital TV already, possibly several of them. And you may not even realize it. In fact, the number of digital TV sources continues to climb, as does the number of products that display it. And expectations are that all of these products will find some kind of consumer success.
ATSC HDTV The Advanced Television Standards Committee (ATSC) set the standard for the U.S. version of digital TV, which includes HDTV, back in the 1990s. HDTV is digital TV with a resolution far greater than current analog TV, which is based on the over-50-year-old National Television Standards Committee (NTSC) format.
NTSC television uses 525 interlaced scan lines (with only about 480 effective lines) to present a picture with an aspect ratio (width to height) of 4:3. HDTV provides up to 720 or 1080 lines with an aspect ratio of 16:9, which better matches the movie screen format. Progressive scan is available as well as interlaced scan. Interlaced scan usually is preferred to minimize flicker at low frame rates. Yet progressive scan lines tend to work best with video compression techniques.
The ATSC system compresses the digitized video using the MPEG-2 standard, treats it to a Reed-Solomon forward-error-correction (FEC) scheme and Trellis coding, and then forms it into 188-bit packets. These packets are transmitted over the air via a modulation scheme known as 8VSB, or eight-level vestigial sideband. With 8VSB, the carrier is suppressed, leaving only a weak pilot carrier. Also, it transmits all of the upper sideband and only a portion (vestige) of the lower sideband.
The signal is designed to fit in a standard, 6-MHz bandwidth TV channel. With eight-level coding, every three bits are translated into one of the eight amplitude symbols. This provides a symbol rate of 10,800 symbols/s. The composite data rate is 32.4 Mbits/s, but without the coding, the raw video (plus audio) rate is 19.3 Mbits/s. When delivered by cable, the HDTV signal is modified by dropping the Trellis coding and going to a 16VSB scheme code with 4 bits per symbol and a data rate of 38.6 Mbits/s.
While HDTV was designed for over-the-air delivery, most of it is delivered by cable. More than 60% of the U.S. population gets TV via cable, including HDTV. Less than 15% still receive TV through the old-fashioned, terrestrial-radio method. The remaining 20% or so get their TV by satellite.
HDTV has stumbled through a slow and painful conversion. The greatly improved picture quality over standard NTSC analog TV hasn't pushed droves of consumers to make the switch. Lack of good HD content is part of the problem. More prevailing, though, is that most consumers seem satisfied with the current TV quality.
But with rapid declines in price for large plasma, LCD, and projection sets, momentum is picking up. Also, the FCC mandated the end of analog TV transmissions by February 17, 2009, meaning it's time to buy a digital or HD set... or read a book. But not all is lost. Analog holdouts will be able to get converter boxes to translate the digital signals into an analog equivalent, though with a degraded image.
The FCC's mandate has to do with attempting to reclaim huge portions of the UHF spectrum previously assigned to TV stations. By pushing TV stations to the lower frequencies, the FCC can reallocate that poorly utilized part of the spectrum to cellular and other wireless services.
Virtually all HDTV content these days is 720-line progressive. There's little in the way of 1080i HDTV content. The average consumer can see a definite improvement in picture quality with 720i, but a large screen is really needed to appreciate it. Also, the 720i format degrades on screens that are more than 42 in. Screens of 42 in. and more are needed to see the full potential of 1080i HD. And don't forget, viewing distance is critical in seeing and appreciating the HD content.
SATELLITE TV Many of you have satellite TV because it is one of the greatest broadband TV delivery bargains around. Also known as Direct Broadcast Satellite (DBS), its major vendors are DirecTV and DISHnetwork (EchoStar). For years, each has stolen many customers from cable. Satellite TV has likely reached its peak potential, since the receive-only (RO) format limits its usefulness. Dial-up modems can provide a two-way connection back to the provider, but that's unsuitable with most two-way applications, such as Internet access.
Correction
The author of this story wishes to clarify two issues:
1. I mentioned that virtually all HDTV is 720p. It turns out that in reality most HDTV really is 1080i.
2. I said that the FCC mandated the shutoff of analog TV. It really was Congress who make the decision for the FCC to implement.
Thanks to reader J. Patrick Waddell the chair of the Advanced Television Standards Committee TSG/S6.
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