E-VSB
Encyclopedia
E-VSB or Enhanced VSB is an optional enhancement to the original ATSC Standards that use the 8VSB
modulation
system used for transmission
of digital television
. It is intended for improving reception
where signals are weaker, including fringe reception areas, and on portable devices such as handheld televisions or mobile phone
s. It does not cause problems to older receivers, but they cannot take advantage of its features. E-VSB was approved by the ATSC committee in 2004. However, it has been implemented by few stations or manufacturers.
For mobile applications, ATSC suffers significant signal degradation caused by the Doppler effect
. Additionally, low-power handheld receivers are usually equipped with smaller antennas
. These have a poor signal-to-noise ratio
, which is disruptive to digital signals. The E-VSB standard provides for Reed-Solomon forward error correction
to alleviate the data corruption
caused by these issues.
Additionally, the standard can use either the MPEG-4 AVC or VC-1
video codec
s. As these codecs have higher video compression than the original MPEG-2
, they require less bandwidth.
As 8VSB lacks both link adaptation
and hierarchical modulation
of DVB, which would allow the SDTV part of an HDTV signal (or the LDTV part of SDTV) to be received even in fringe reception
areas where signal strength
is low, E-VSB yields a similar benefit. However, E-VSB places a significant processing overhead
on the receiver, as well as a significant transmission overhead
on the broadcaster's total bitrate. These are not a problem with DVB-H
.
A-VSB
is a different and, , unapproved addition to ATSC, which is also designed to send programming to mobile devices, and to allow for single-frequency network
s. It is one of several proposals for ATSC-M/H
, the as-yet undecided standard for mobile broadcasting via ATSC.
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...
. It is intended for improving reception
Reception
Reception is a noun form of receiving, or to receive something, such as information, art, experience, or people. It is often used in the following contexts:...
where signals are weaker, including fringe reception areas, and on portable devices such as handheld televisions or mobile phone
Mobile phone
A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...
s. It does not cause problems to older receivers, but they cannot take advantage of its features. E-VSB was approved by the ATSC committee in 2004. However, it has been implemented by few stations or manufacturers.
For mobile applications, ATSC suffers significant signal degradation caused by the Doppler effect
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
. Additionally, low-power handheld receivers are usually equipped with smaller antennas
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
. These have a poor signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
, which is disruptive to digital signals. The E-VSB standard provides for Reed-Solomon forward error correction
Forward error correction
In telecommunication, information theory, and coding theory, forward error correction or channel coding is a technique used for controlling errors in data transmission over unreliable or noisy communication channels....
to alleviate the data corruption
Data corruption
Data corruption refers to errors in computer data that occur during writing, reading, storage, transmission, or processing, which introduce unintended changes to the original data...
caused by these issues.
Additionally, the standard can use either the MPEG-4 AVC or VC-1
VC-1
VC-1 is the informal name of the SMPTE 421M video codec standard, which was initially developed as a proprietary video format by Microsoft before it was released as a formal SMPTE standard video format on April 3, 2006...
video codec
Video codec
A video codec is a device or software that enables video compression and/or decompression for digital video. The compression usually employs lossy data compression. Historically, video was stored as an analog signal on magnetic tape...
s. As these codecs have higher video compression than the original MPEG-2
MPEG-2
MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission...
, they require less bandwidth.
As 8VSB lacks both link adaptation
Link adaptation
Link adaptation, or adaptive coding and modulation , is a term used in wireless communications to denote the matching of the modulation, coding and other signal and protocol parameters to the conditions on the radio link Link adaptation, or adaptive coding and modulation (ACM), is a term used in...
and hierarchical modulation
Hierarchical modulation
Hierarchical modulation, also called layered modulation, is one of the signal processing techniques for multiplexing and modulating multiple data streams into one single symbol stream, where base-layer symbols and enhancement-layer symbols are synchronously overplayed before...
of DVB, which would allow the SDTV part of an HDTV signal (or the LDTV part of SDTV) to be received even in fringe reception
TV-FM DX
TV DX and FM DX is the active search for distant radio or television stations received during unusual atmospheric conditions. The term DX is an old telegraphic term meaning "long distance."...
areas where 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...
is low, E-VSB yields a similar benefit. However, E-VSB places a significant processing overhead
Computational overhead
In computer science, overhead is generally considered any combination of excess or indirect computation time, memory, bandwidth, or other resources that are required to attain a particular goal...
on the receiver, as well as a significant transmission overhead
Protocol overhead
Protocol overhead refers to metadata and network routing information sent by an application, which uses a portion of the available bandwidth of a communications protocol...
on the broadcaster's total bitrate. These are not a problem with DVB-H
DVB-H
DVB-H is one of three prevalent mobile TV formats. It is a technical specification for bringing broadcast services to mobile handsets. DVB-H was formally adopted as ETSI standard EN 302 304 in November 2004. The DVB-H specification can be downloaded from the official DVB-H website...
.
A-VSB
A-VSB
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...
is a different and, , unapproved addition to ATSC, which is also designed to send programming to mobile devices, and to allow for single-frequency network
Single-frequency network
A single-frequency network or SFN is a broadcast network where several transmitters simultaneously send the same signal over the same frequency channel.-Overview:...
s. It is one of several proposals for ATSC-M/H
ATSC-M/H
ATSC-M/H is a standard in the USA for mobile digital TV, that allows TV broadcasts to be received by mobile devices.....
, the as-yet undecided standard for mobile broadcasting via ATSC.