Recursive metric for NTSC interference rejection in the ATSC-HDTV trellis decoder

In the United States Advanced Television Systems Committee (ATSC) standard for high definition television (HDTV), NTSC co-channel interference rejection may be performed by the comb filter, a filter with spectral nulls at or near the NTSC carriers, and only applied when NTSC interference is detected. In this paper, we discuss the influence of the comb filter on the trellis decoder performance. We then derive the closed form expression for the optimum trellis decoder metric when NTSC co-channel interference is detected and propose a recursive formula for its implementation.