Ghost-canceling reference (GCR) is a special sub-signal on atelevisionchannel that receivers can use to compensate for theghosting effect of a television signal distorted bymultipath propagation between transmitter and receiver.
In theUnited States, the GCR signal is achirp infrequency of themodulating signal from 0 Hz to 4.2 MHz, transmitted during thevertical blanking interval over one video line (line 19 in the U.S.), shifted in phase by 180° once per frame, with this pattern inverted every four lines. Television receivers generate their own local versions of this signal and use the comparison between the local and remote signals to tune anadaptive equalizer that removes ghost images on the screen.
GCR was introduced after its recommendation in 1993 by the Advanced Television Systems Committee.[1]
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