Ghost cancellation for 625-line systems

Abstract

The removal of ghosting from received television pictures requires that a known ghost cancellation reference (GCR) or training signal be incorporated in the transmitted signal. A range of possibilities for ghost cancellation for 625 line systems has been examined within the European PALplus consortium, although it was subsequently decided that ghost cancellation should not be a standard feature of PALplus, or indeed confined to PALplus. This and further development work has led to the definition of a ghost cancellation reference signal that is believed to be suitable for all 625-line PAL, PALplus and SECAM transmission systems. The GCR is placed on a single line of the vertical blanking interval, line 318. The GCR belongs to the same family of waveforms as the GCR that has been standardized for use in North America for 525-line NTSC. This gives the potential for the development of common ghost cancellation circuit elements. Experimental ghost cancellation circuitry has developed which makes use of the GCR to enable performance to be evaluated with 625-line systems under a variety of reception conditions. The ghost cancellation techniques may be applied to improve the performance of broadcast transmitter chains, and can also be employed in consumer receivers.