【正确答案】比特率和符号率的关系如表6.1.1和表6.1.2所示。
表6.1.1 各种转发器带宽及相应的码率 -3dB带宽BW (3dB)/MHz | -1dB带宽BW' (-1dB)/MH0 | 符号率Rs BW/Rs=1.28 /Mbaud | 有用比特率RU QPSK+1/2/(Mb/s) | 有用比特率RU QPSK+2/3/(Mb/s) | 有用比特率RU QPSK+3/4/(Mb/s) | 有用比特率RU QPSK+5/6/(Mb/s) | 有用比特率RU QPSK+6/7/(Mb/s) | 54 | 48.6 | 42.2 | 38.9 | 51.8 | 58.3 | 64.8 | 68.0 | 46 | 41.1 | 35.9 | 33.1 | 44.2 | 49.7 | 55.0 | 58.0 | 40 | 36.0 | 31.2 | 28.8 | 38.4 | 43.2 | 48.0 | 50.4 | 36 | 32.4 | 28.1 | 25.9 | 34.6 | 38.9 | 43.2 | 45.4 | 33 | 29.7 | 25.8 | 23.8 | 31.7 | 35.6 | 39.6 | 41.6 | 30 | 27.0 | 23.4 | 21.6 | 28.8 | 32.4 | 36.0 | 37.6 | 27 | 24.3 | 21.1 | 19.4 | 25.9 | 29.2 | 32.4 | 34.0 | 26 | 23.4 | 20.3 | 18.7 | 25.0 | 28.1 | 31.2 | 32.8 | |
表6.1.2 DVB-C在CATV网中的应用实例 有用比特率RUMPEG-2 TV/(Mb/s) | 总比特率R'U包括R-s/(Mb/s) | 电缆符号率/Mbaud | 占用的带宽/MHz | 调制方式 | 38.1 | 41.34 | 6.89 | 7.92 | 64 QAM | 31.9 | 34.61 | 6.92 | 7.96 | 32 QAM | 25.2 | 27.34 | 6.84 | 7.86 | 16 QAM | 31.672 PDH | 34.367 | 6.87 | 7.90 | 32 QAM | 18.9 | 25.52 | 3.42 | 3.93 | 64 QAM | 16.0 | 17.40 | 3.48 | 4.00 | 32 QAM | 12.8 | 13.92 | 3.48 | 4.00 | 16 QAM | 9.6 | 10.44 | 1.74 | 2.00 | 64 QAM | 8.0 | 8.7 | 1.74 | 2.00 | 32-QAM | 6.4 | 6.96 | 1.74 | 2.00 | 16-QAM | |