The effect of interleaver depth and QAM channel frequency offset on the performance of multichannel AM-VSB/256-QAM video lightwave transmission systems

The effect of a convolutional interleaver with variable depth in a quadrature amplitude modulator (QAM) modem to combat burst-errors generated by bursty composite second-order (CSO) distortions in multichannel AM-VSB/256-QAM video lightwave transmission systems has been analyzed. It is shown that by offsetting the QAM channel frequency relative to the dominant CSO distortions with I=204, J=1 interleaver, the 256-QAM coded bit-error rate was reduced by more than 500 times even in the presence of large CSO distortion levels (>-60 dBc) compared with the no interleaver and QAM frequency offset case. These results should help in the selection of the proper interleaver depth as well as the QAM channel frequency plan, depending on the magnitude of the CSO/CTB distortions in the CATV network.