Performance of interleaved trellis codes in the presence of impulse noise

Interleaved trellis coded modulation is described. It utilizes multiple encoder/decoder pairs as a means of mitigating the effects of impulse noise in the high-rate digital subscriber line (HDSL) and related applications such as the asymmetric digital subscriber line (ADSL). The component code for the interleaved scheme is a trellis code coupled with 32-quadrature amplitude modulation (QAM) which has the same spectral efficiency as uncoded 16-QAM. It is found that the interleaved trellis coded modulation scheme is more robust against impulsive noise than the conventional trellis coded modulation. Two trellis codes are considered for the component code for the interleaved scheme: an eight-state code and a simple four-state code. The interleaved scheme using the four-state code performs better than the interleaved scheme using the eight-state code in an impulsive noise environment, even though the asymptotic coding gain for the four-state code in additive white Gaussian noise is less than that of the eight-state code. Computer simulation results are presented for the interleaved and conventional schemes using the two trellis codes for actual impulses with variable durations