ATSC standards
The reduced bandwidth requirements of lower-resolution images allow up to six standard-definition "subchannels" to be broadcast on a single 6 MHz TV channel.
[2] The cost of patent licensing, estimated at up to $50 per digital TV receiver,[3] had prompted complaints by manufacturers.
There is also a standard for distributed transmission systems (DTx), a form of single-frequency network which allows for the synchronised operation of multiple on-channel booster stations.
MPEG-2 audio was a contender for the ATSC standard during the DTV "Grand Alliance" shootout, but lost out to Dolby AC-3.
Later, a story emerged that MIT had entered into an agreement with Dolby whereupon the university would be awarded a large sum of money if the MPEG-2 system was rejected.
[10] The ATSC system supports a number of different display resolutions, aspect ratios, and frame rates.
Before decoding of audio and video takes place, the receiver must demodulate and apply error correction to the signal.
This is due to a restriction of the MPEG-2 video format, which requires the height of the picture in luma samples (i.e. pixels) to be divisible by 16.
A terrestrial (over-the-air) transmission carries 19.39 megabits of data per second (a fluctuating bandwidth of about 18.3 Mbit/s left after overhead such as error correction, program guide, closed captioning, etc.
In theory, television stations in the U.S. are free to choose any resolution, aspect ratio, and frame/field rate, within the limits of Main Profile @ High Level.
For example, NBC stations transmit a 1080i60 video sequence, meaning the formal output of the MPEG-2 decoding process is sixty 540-line fields per second.
However, for prime-time television shows, those 60 fields can be coded using 24 progressive frames as a base – actually, an 1080p24 video stream (a sequence of 24 progressive frames per second) is transmitted, and MPEG-2 metadata instructs the decoder to interlace these fields and perform 3:2 pulldown before display, as in soft telecine.
Once the digital video and audio signals have been compressed and multiplexed, the transport stream can be modulated in different ways depending on the method of transmission.
The proposals for modulation schemes for digital television were developed when cable operators carried standard-resolution video as uncompressed analog signals.
The Canadian Radio-television and Telecommunications Commission in Canada does not have similar rules in force with respect to carrying ATSC signals.
However, cable operators have still been slow to add ATSC channels to their lineups for legal, regulatory, and plant & equipment related reasons.
While the ATSC system has been criticized as being complicated and expensive to implement and use,[13] both broadcasting and receiving equipment are now comparable in cost with that of DVB.
While ATSC is also incapable of true single-frequency network (SFN) operation, the distributed transmission mode, using multiple synchronized on-channel transmitters, has been shown to improve reception under similar conditions.
To overcome this, there are several proposed systems that report improved mobile reception: Samsung/Rhode & Schwarz's A-VSB, Harris/LG's MPH, and a recent[when?]
After one year of standardization, the solution merged between Samsung's AVSB and LGE's MPH technology has been adopted and would have been deployed in 2009.
Mobile reception of some stations will still be more difficult, because 18 UHF channels in the U.S. have been removed from TV service, forcing some broadcasters to stay on VHF.
This band requires larger antennas for reception, and is more prone to electromagnetic interference from engines and rapidly changing multipath conditions.
[18] ATSC 3.0 will provide even more services to the viewer and increased bandwidth efficiency and compression performance, which requires breaking backward compatibility with the current version.
On November 17, 2017, the FCC voted 3–2 in favor of authorizing voluntary deployments of ATSC 3.0, and issued a Report and Order to that effect.
With the test considered a success, South Korea announced that ATSC 3.0 broadcasts would start in February 2017.
