A-VSB or Advanced VSB is a modification of the

8VSB 8VSB is the modulation method used for broadcast in the ATSC digital television standard. ATSC and 8VSB modulation is used primarily in North America; in contrast, the DVB-T standard uses COFDM. A modulation method specifies how the radio sig ...

modulation system used for transmission of

digital television Digital television (DTV) is the transmission of television signals using digital encoding, in contrast to the earlier analog television technology which used analog signals. At the time of its development it was considered an innovative adva ...

using the

ATSC system Advanced Television Systems Committee (ATSC) standards are an American set of standards for digital television transmission over terrestrial, cable and satellite networks. It is largely a replacement for the analog NTSC standard and, like that ...

. One of the constraints of conventional ATSC transmission is that reliable

reception Reception is a noun form of ''receiving'', or ''to receive'' something, such as art, experience, information, people, products, or vehicles. It may refer to: Astrology * Reception (astrology), when a planet is located in a sign ruled by another ...

is difficult or impossible when the receiver is moving at speeds associated with normal vehicular traffic. The technology was jointly developed by

Samsung The Samsung Group (or simply Samsung) ( ko, 삼성 ) is a South Korean multinational manufacturing conglomerate headquartered in Samsung Town, Seoul, South Korea. It comprises numerous affiliated businesses, most of them united under the ...

and

Rohde & Schwarz Rohde & Schwarz GmbH & Co KG (, ) is an international electronics group specializing in the fields of electronic test equipment, broadcast & media, cybersecurity, radiomonitoring and radiolocation, and radiocommunication. The company provides ...

. A-VSB builds on the existing ATSC transmission standard to enhance DTV receivers’ ability to receive the main MPEG transport stream in dynamic environments. The system enables broadcasters to include multiple streams with additional error correction and

time diversity Time diversity is used in digital communication systems to combat that the transmissions channel may suffer from error bursts due to time-varying channel conditions. The error bursts may be caused by fading in combination with a moving receiver, tr ...

encoding for enhanced reception. In addition, A-VSB facilitates synchronization of multiple transmission towers, which should improve coverage with higher uniform signal strength throughout a service area, even in locations that normally would be shielded by obstacles such as hills or buildings. A-VSB incorporates three new elements: a Supplementary Reference Signal (SRS), a Scalable Turbo Stream (STS), and support for Single Frequency Networks (SFN).

Supplementary Reference Signal

A-VSB receivers utilize the SRS in order to remain synchronized with the transmission. This helps maintain reception of the main stream and any

turbo In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pr ...

streams even with rapidly changing

multipath interference In radio communication, multipath is the propagation phenomenon that results in radio signals reaching the receiving antenna by two or more paths. Causes of multipath include atmospheric ducting, ionospheric reflection and refraction, and ref ...

, such as when the signal is reflected from moving objects near the receiver or when the receiver itself is moving. The SRS adds an additional equalizer

training sequence In computer networks, a syncword, sync character, sync sequence or preamble is used to synchronize a data transmission by indicating the end of header information and the start of data. The syncword is a known sequence of data used to identif ...

to the Transport Stream Adaptation Field, which should be ignored by existing transport decoders. The added signal shortens the existing 24ms equalizer update time by a selectable factor, from 120x to 312x. A receiver equipped with this new equalizer can track rapid multipath fading, and thus supports mobile reception. SRS can be used alone, without the STS, offering a slight improvement in portable (stationary—not true mobile) service.

Scalable Turbo Stream

The addition of a new turbo-coded stream enables broadcasters to increase the error-correction capability of a secondary stream transmission. Two options are proposed for the turbo stream: ½ and ¼ rate codes, i.e., the new video stream requires 2x or 4x the video rate in final transport payload. The new Threshold of Visibility (TOV) SNRs are 9.6 and 4.5 dB, respectively; 1.6dB is claimed with diversity reception. Conventional 8VSB has a TOV SNR of 15.1 dB. The turbo codec uses single-input single-output (SISO) iterative decoding and time interleaving.

Single Frequency Networks

The last option—SFN—is made possible by adding a VSB Frame Initialization Packet (VFIP) that synchronizes the transport frame sequences to a GPS reference.

References

* , January 8, 2007. {{DEFAULTSORT:A-Vsb Radio modulation modes ATSC