E-VSB orEnhanced VSB is an optional enhancement[1] to the originalATSC Standards that use the8VSBmodulation system used fortransmission ofdigital television. It is intended for improvingreception where signals are weaker, includingfringe reception areas, and on portable devices such as handheld televisions ormobile phones. It does not cause problems to older receivers, but they cannot take advantage of its features.[2] E-VSB was approved by the ATSC committee in 2004. However, it has been implemented by few stations or manufacturers.[3]
For mobile applications, ATSC suffers significant signal degradation caused by theDoppler effect. Additionally, low-power handheld receivers are usually equipped with smallerantennas. These have a poorsignal-to-noise ratio, which is disruptive to digital signals. The E-VSB standard provides forReed–Solomon error correction to alleviate thedata corruption caused by these issues.
Additionally, the standard can use either theMPEG-4 AVC orVC-1video codecs. As these codecs have highervideo compression than the originalMPEG-2, they require less bandwidth.
As 8VSB lacks bothlink adaptation andhierarchical modulation ofDVB, which would allow theSDTV part of anHDTV signal (or theLDTV part of SDTV) to be received even infringe reception areas wheresignal strength is low, E-VSB yields a similar benefit. However, E-VSB places a significantprocessing overhead on the receiver, as well as a significanttransmission overhead on the broadcaster's total bitrate. These are not a problem withDVB-H.
A-VSB is a different and, as of July 2008[update], unapproved addition to ATSC, which is also designed to send programming to mobile devices, and to allow forsingle-frequency networks. It is one of several proposals forATSC-M/H, the as-yet undecided standard for mobile broadcasting via ATSC.
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