Digital Television

Television

Digital Television was introduced in the late 1990s. As DTV offer new business opportunity and that is why many television broadcasters and electronics industries attracted towards this new technologies.

With a higher quality image & sound, choice of more no. of channels, no doubt that DTV is more efficient than the standard analog television broadcasting.

Following are the countries switched over or turning to DTV:

  • Netherland is the first country who adopted DTV in 2006.
  • Finland switch to Digital Television broadcasting in 2007.
  • USA is planning to switch over to DTV in 2009.
  • Canada has planned to adopt digital television technology in August 31, 2011.
  • United Kingdom will switch to DTV in phases and targeted to finish this by 2012.
  • China scheduled to launch DTV in 2015

Advantages of DTV
Following are the advantages of DTV over analog TV:

  • In DTV, there is no ghosting or noise as is in analog Tv broadcasting. The reason is that DTV Tuners and converter boxes receive numeric information by the antenna. The decoder only needs enough information to put the picture together.
  • Digital channels require less bandwidth and the bandwidth varies depending on the level of compression.
  • Due to less bandwidth requirement, broadcasters can broadcast more digital channels in the same space, TV Service can also be launched.
  • Broadcasters can provide value added services such as multimedia or interactivity.

Multiplexing: This technology can be very useful tool for generating additional revenue to broadcasters because DTV allows multiplexing i.e. more than one program on the same channel. So broadcaster can have electronic program guides, additional languages and subtitled.

Disadvantages to conversion
Analog switch-off technology: The entire consumer as well as the manufacturers needs to render all non-digital televisions obsolete on the switch-off date or an external converter box needs to be attached to the analog television.

With a converter, some of the analog equipments will be less functional like remote control will not work for changing the channels as this function will be handled by converter box, recording of analog signal by VCRs or DVR will not be possible and can record only downloaded programmes. Converter box is not portable so portable analog television will not work with this new technology.

Compression and allocated bandwidth: Images in DTV broadcasting have some defects due to limited bandwidth and the compression of the signal like:

  • Quantization noise.
  • Incorrect color.
  • Blockiness.
  • A blurred, shimmering haze.

The above are not present in analog television broadcasting.

Delay in Channel Search and preload time: In DTV, there is a delay, when we change the channel so some time channel surfing feels difficult. This is not present in Analog Television.
There is an audio echo effect when two televisions in adjacent rooms of a house are tuned to the same channel because different devices need different amounts of preload the digital broadcast signal.

Cliff Effects: Signal strength Changes due to degrading antenna connections or changing weather conditions. In that case the digital TV results in a perfect picture initially, until the television (receiver) starts picking up noise or losing signal. Some receiving equipment initially show a picture even with damage and some may go from perfect to no picture at all.

As compare to the analog TV, DTV signal is much affected by multi-path interference. It cause a spotty loss of audio or picture freezing. In extreme cases the signal is lost completely. The solution to avoid this signal lose is to install a directional outdoor antenna, aligned with the transmitting location.

Technical information – Formats
Digital television supports many different picture formats.

  • In India, PAL format of Standard definition TV (SDTV) is in use ,which have 720 × 576 (rescaled to 768 × 576) for 4:3 aspect ratio and 720 × 576 (rescaled to 1024 × 576) for 16:9 aspect ratio.
  • Other countries who are using NTSE systems have 640 × 480 format for 4:3 aspect ratio and 704 × 480 (rescaled to 848 × 480) format for 16:9 aspect ratio.

Bandwidth:
However, television broadcasters may choose to reduce these resolutions to save bandwidth like in United Kingdom, many DVB-T channels use a horizontal resolution of 544 or 704 pixels per line.

In North America, terrestrial DTV channels are allowed to broadcast at a data rate up to 19 megabits per second, or 2.375 megabytes per second which generally not required for a single channel so the bandwidth can be divided across several subchannels (video) of different quality and compression rates, non-video data casting services that allow one-way high-bandwidth streaming of data to computers.

Reception
There are following different ways of receiving the DTV:

  • Antenna System: DTT (Digital Terrestrial Television) signal can be received by using a antenna but with compromising the no. of channels and the quality of the signal.
  • Digital Cable/ Digital Satellite: most familiar method of receiving DTV signal.
  • MMDS: is for those countries where transmission of TV signal is by using microwave.
  • DMB and DVB-H: permit handheld devices like Mobile phones to receive TV signal.
  • IP TV: you can receive DTV signal via Internet protocol.
  • Computer: DTV signal can be received via open internet by using P2P internet television software.