Waveform equalization for EDTV systems using QAM

A modified waveform equalizer for a terrestrial QAM (quadrature amplitude modulation) transmission system that is tolerant against ghosts is described. In order to improve the performance of ghost and crosstalk reduction in the QAM subchannel, eight-field sequence reference signals, which are compatible with the GCR (ghost cancel reference) signal proposed by the BTA (Broadcasting Technology Association), and automatic gain control by a CPU are employed. Moreover, modified synchronous demodulation with automatic carrier phase control by a CPU is useful to upgrade (by about 5 dB under a heavy ghost condition) the equalization performance and to reduce the quadrature distortion of the subsignal. The crosstalk in the subchannel can be reduced to a level of 36-40 dB D/U. The QAM technology can be fully applied for terrestrial broadcasting even under significant ghost conditions.<
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