NTSC co-channel interference detectors responsive to received Q-channel signals in digital TV signal receivers

A method for determining whether or not comb filtering to suppress co-channel NTSC interference is to be employed before trellis decoding in a digital television signal receiver, said method comprising steps of:

• performing a complex demodulation of vestigial-sideband amplitude-modulated digital television signals to separate a received I-channel baseband signal and a received Q-channel baseband signal in an orthogonal relationship with said received I-channel baseband signal;
• determining whether or not artifacts of co-channel NTSC interference of significant level accompany said received Q-channel baseband signal;
• if said artifacts of co-channel NTSC interference of significant level are determined not to accompany said received Q-channel baseband signal, symbol decoding responsive to said received I-channel baseband signal without comb filtering thereof to generate decoded symbols for said trellis decoding;
• if said artifacts of co-channel NTSC interference of significant level are determined to accompany said received Q-channel baseband signal, comb filtering said received I-channel baseband signal to generate comb-filtered I-channel baseband signal;
• if said artifacts of co-channel NTSC interference of significant level are determined to accompany said received Q-channel baseband signal, symbol decoding responsive to said comb-filtered I-channel baseband signal;
• and
• if said artifacts of co-channel NTSC interference of significant level are determined to accompany said received Q-channel baseband signal, postcoding the result of symbol decoding responsive to said comb-filtered I-channel baseband signal to generate decoded symbols for said trellis decoding.

A digital television signal receiver comprising:

• amplifier circuitry for supplying an amplified vestigial-sideband amplitude-modulated digital television signal apt to be accompanied by co-channel interfering analog television signal;
• a complex demodulator responsive to said amplified vestigial-sideband amplitude-modulated digital television signal for supplying an I-channel baseband signal containing artifacts of any co-channel interfering analog television signal and a Q-channel baseband signal containing further artifacts of any co-channel interfering analog television signal;
• symbol decoding apparatus for said I-channel baseband signal including a first data slicer for symbol decoding said I-channel baseband signal during first times, errors in first symbol decoding results from said first data slicer being correctable as long as said artifacts of any co-channel interfering analog television signal are generally below a significant level for said I-channel baseband signal;
• and
• an NTSC co-channel interference detector responsive to said Q-channel baseband signal, for detecting the presence of said further artifacts of any co-channel interfering analog television signal that are above a significant level for said Q-channel baseband signal, which said significant level for said Q-channel baseband signal corresponds to said significant level for said I-channel baseband signal.