A new spectral notch generator for pilot tone systems

A novel and very general spectrum shaping code, called look ahead block inversion (LABI), for creating spectral notches of arbitrary width, shape, and location is described. It can trade depth against width and, for a given specification, adds minimum overhead. Uses include protection against AC coupling, tones, or other impairments. When used for pilot tone aided modulation (PTAM), it improves performance compared to previous spectrum shaping codes, though self-noise remains a limitation. The authors extend the investigation of block coding and PTAM with two contributions. First, a novel coding algorithm is introduced which can create notches of arbitrary width, depth, and location by combining an unconventional use of the Viterbi algorithm (VA) at the transmitter with a general distortion criterion based on filtering the data signal. The technique minimizes the fraction of redundant symbols. Second, by simulation, the use of spectrum shaping codes is explored for PTAM, including the effect of self-noise