A SUITABLE COMBINATION OF MODULATION AND FEC SCHEMES FOR SATELLITE DIGITAL VIDEO COMMUNICATION-NETWORKS

This paper proposes a suitable combination of the digital modulation s chemes and the coding-rate of forward error correction (FEC) schemes f or satellite digital video communication networks. The comparative stu dy is carried out by computer simulation considering non-linearly ampl ified, narrow bandwidth satellite channels with adjacent channel inter ference signals. The proposed system employs an offset QPSK modulation scheme supported by the coding-rate of 7/8 convolutional encoding and Viterbi decoding to realize high-quality and compact spectrum charact eristics in non-linear channels. By employing a 32 Mbps DPCM video cod ec, the developed prototype system achieves a post demodulated S/N rat io of higher than 52 dB. Moreover, it achieves high protection ratio a gainst co-channel interference than conventional analog FM systems. Th e optimized digital video transmission system makes it possible to tra nsmit high-quality NTSC video signals over non-linearly amplified narr ow bandwidth satellite channels, for example 27 MHz or 36 MHz bandwidt h transponders, with high-security digital encryption.