TechniSat SkyCable QPSK/DVB-T CI TWIN - Handbuch (Seite 79)

79
EN
5.4 DVB-C data rates
Modulation 16 QAM 32 QAM 64 QAM 128 QAM 256 QAM
Theoretical max.
bandwidth usage
in Bits/s Hz
4 5 6 7 8
Gross data rate in (MBit/s)
at:
Symbol rate 6.90 MBaud
Channel bandwidth
27.6 34.5 41.4 48.3 55.2
Net data rate in (MBit/s) 25.44 31.97 38.15 44.15 50.87
To ascertain the net data rate, the following criteria need to be taken into consideration:
Channel bandwidth B = (7 MHz or 8MHz)
Modulation process (64 QAM or 256 QAM)
Roll-off factor r = 0.15
Frame length in 204 byte transport stream
RS code (204,188)
6 bit per Symbol [with 64 QAM]
8 bit per Symbol [with 256 QAM]
The code conversion for 8-bit (= 1 byte) wide words to 6-bit wide symbols means
changing the frame length from 204 bytes to 272 symbols in the data stream.
Example:
With reference to an 8 MHz channel and 64 QAM this gives:
Therefore a maximum of 6.96 - 10 6 symbols per second can be transferred. As each symbol consists of 6 bits, this gives
a gross bit rate of:
To calculate the net bit rate the external error correction according to Reed Solomon coding needs to be considered as well.