A-VSB
Encyclopedia
A-VSB or Advanced VSB is a modification of the 8VSB
modulation
system used for transmission
of digital television
using the ATSC system. One of the constraints of conventional ATSC transmission is that reliable reception
is difficult or impossible when the receiver
is moving at speeds associated with normal vehicular traffic. The technology was jointly developed by Samsung
and Rohde & Schwarz
.
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
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).
, 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 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.
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....
modulation
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
system used for transmission
Transmission (telecommunications)
Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
of digital television
Digital television
Digital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
using the ATSC system. One of the constraints of conventional ATSC transmission is that reliable reception
Television antenna
A television antenna, or TV aerial, is an antenna specifically designed for the reception of over the air broadcast television signals, which are transmitted at frequencies from about 41 to 250 MHz in the VHF band, and 470 to 960 MHz in the UHF band in different countries...
is difficult or impossible when the receiver
Digital media receiver
A digital media receiver , also commonly referred to as a media extender, media streamer, digital media hub, or digital media adapter , is a home entertainment device that can connect to a home network to retrieve digital media files from a personal computer or other networked media server and...
is moving at speeds associated with normal vehicular traffic. The technology was jointly developed by Samsung
Samsung
The Samsung Group is a South Korean multinational conglomerate corporation headquartered in Samsung Town, Seoul, South Korea...
and Rohde & Schwarz
Rohde & Schwarz
Rohde & Schwarz is an independent group of companies specializing in electronics. Well known as a manufacturer of electronic test equipment, they also manufacture equipment used for broadcasting, radiolocation, and radio communications...
.
A-VSB builds on the existing ATSC transmission standard to enhance DTV
Digital television
Digital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
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
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...
encoding for enhanced reception. In addition, A-VSB facilitates synchronization of multiple transmission towers, which should improve coverage with higher uniform signal strength
Signal strength
In telecommunications, particularly in radio, signal strength refers to the magnitude of the electric field at a reference point that is a significant distance from the transmitting antenna. It may also be referred to as received signal level or field strength. Typically, it is expressed in...
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 streams even with rapidly changing multipath interferenceMultipath interference
Multipath interference is a phenomenon in the physics of waves whereby a wave from a source travels to a detector via two or more paths and, under the right condition, the two components of the wave interfere...
, 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
Blind equalization
Blind equalization is a digital signal processing technique in which the transmitted signal is inferred from the received signal, while making use only of the transmitted signal statistics. Hence, the use of the word blind in the name....
training sequence 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
Fading
In wireless communications, fading is deviation of the attenuation that a carrier-modulated telecommunication signal experiences over certain propagation media. The fading may vary with time, geographical position and/or radio frequency, and is often modelled as a random process. A fading channel...
, and thus supports mobile reception. SRS can be used alone, without the STS, offering a slight improvement in portable (stationary—not true mobile) service.