Migration to Digital Television

What is Digital TV?

Digital Television is a new broadcasting technology that allows signals to be delivered virtually free of interference. By transmitting the information used to make a TV picture and sound as “data bits” (as a computer does) will allow for transmission of pictures with a higher resolution and dramatically better picture and sound quality than is currently available.

Why are we switching to Digital TV?

Digital Television (DTV) is more efficient than the current analog system. In the same bandwidth a broadcaster can provide one analog channel of programming, a broadcaster can provide a super sharp “high definition” (HDTV) program or multiple “standard definition” (SDTV) programs simultaneously. Providing multiple program streams is called “multicasting.” The number of programs a broadcaster can send depends on the level of picture detail, or resolution.

Going digital has additional benefits including:

  • Increased channel capacity such that more channels can be offered within a fixed amount of broadcast bandwidth.
  • Increased programming options including interactivity and Video-on-Demand (VoD).
  • Improved picture quality even with a standard-definition signal.
  • Improved security to prevent unauthorized persons from receiving services.

What is HDTV?

HDTV is a DTV service that provides high resolution programming in a wide screen format. The current analog TV picture is made up of 480 horizontal lines. HDTV can have up to 1080 lines, allowing for incredible picture detail.

What is required to watch an HDTV program?

An HDTV decoder (set-top) or television with an integrated HDTV tuner is required in order watch broadcasts in HDTV format.

What is the FCC Transition Plan?

As of May 2003, more than 1,000 stations were on the air with DTV signals, and every major TV market was served by at least one DTV station. The Target date set by Congress for the completion of the transition to DTV is December 31, 2006. That date however, may be extended until 85% of homes in an area are able to watch the DTV programming. At that point, broadcasting on the analog channels will end and that spectrum will be put to other uses. Until the transition is completed, TV stations are required to broadcast both their digital and analog signals.

What is the basically technology that makes this possible?

Compression is a crucial step to making digital TV a practical and profitable service. Compression enables the shift to digital television by drastically reducing the amount of data bandwidth required to retransmit a digitized program. As a compression and transmission medium for digitized audio and video, today’s digital broadcast industry relies mainly on MPEG-2, the standard developed by the Motion Picture Experts Group.

MPEG-2 based protocols have become the standard for carrying broadcast-quality compressed digital video, audio and data over terrestrial, satellite and cable broadband networks. In short, MPEG-2 has become to digital what IP is to the Internet.

The MPEG standards define the syntax, or structure and semantics of a compressed bit stream and the procedure for decoding the stream back in the original video and audio content. Since neither specific algorithms nor encoding methods are defined by MPEG, these can improve over time without any risk of violating the standards. This flexibility affords manufacturers the opportunity to gain a proprietary advantage from new technical developments.

How can this DTV technology be delivered by Small Cable System operators?

The easiest way to deliver DTV signals to subscribers is to retransmit the available off-air digital television signals.

With this approach, an operator uses an off-air antenna to receive the digital & high definition programming from local broadcast sources. These signals, currently found in the UHF band are transmitted in 8VSB (vestigial side band) format. The 8VSB signal is received by a digital high definition processor and converted to any available channel, including on-channel if desired, for distribution on the existing cable system. The signal can then be viewed at the customer’s home with any HDTV capable television with an integrated tuner or an external HDTV receiver (ATSC/8VSB).

The DHDP Series from Blonder Tongue is the ideal choice for delivery of high definition signals utilizing this method.

What other potential delivery methods exist or will be available?

Currently large Cable Operators are delivering DTV & HDTV signals on their system through the use of QAM based transmission and HD capable QAM set top decoders in the home. This approach offers a lot of flexibility and control but is costly since an operator would need to receive a digital broadcast signal and ‘mux’ it into a system and remodulate it for transmission on the system. A consumer would then require the set top decoder to be supplied by the cable operator.

Satellite Operators are also starting to offer HDTV signals in addition to their standard definition digital line up. Currently, there is no clear-cut method for delivering these signals. The potential methods could be to deliver them in 2 ways. The first of which is a L-Band transport methodology. This is not the most desired method as it requires a large amount of bandwidth for each transponder (approx. 30 MHz) and operates at high frequencies (1450-2150 MHz). The second approach would be to transcode the satellite delivered QPSK signal to QAM making it more bandwidth efficient and frequency friendly, thusly allowing for transmission over an existing cable system and reception in a consumers home. Both of these methods would require dedicated HD decoders in the home, the first a QPSK type and the later a QAM type. Currently, EchoStar is working toward making approach 2 a reality by developing a HD capable QAM decoder and HD capable transcoder equipment from Blonder Tongue.