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In digital television transmission the symbol rate calculation is:
symbol rate in symbols per second = (Data rate in bits per second * 204) / (188 * bits per symbol)
The 204 is the number of bytes in a packet including the 16 trailing Reed-Solomon error checking and correction bytes. The 188 is the number of data bytes (187 bytes) plus the leading packet sync byte (0x47).
The bits per symbol is the (modulation's power of 2)*(Forward Error Correction). So for example in 64-QAM modulation 64 = 26 so the bits per symbol is 6. The Forward Error Correction (FEC) is usually expressed as a fraction, i.e., 1/2, 3/4, etc. In the case of 3/4 FEC, for every 3 bits of data, you are sending out 4 bits, one of which is for error correction.
Example:
given bit rate = 18096263
Modulation type = 64-QAM
FEC = 3/4
then
symbol rate = 18096263/(6)*(3/4) * 204/188
= 4363638
In digital terrestrial digital television (DVB-T, DVB-H and similar techniques) OFDM modulation is used, i.e. multi-carrier modulation. The above symbol rate should then be divided by the number of OFDM sub-carriers in view to achieve the OFDM symbol rate.
symbol rate in symbols per second = (Data rate in bits per second * 204) / (188 * bits per symbol)
The 204 is the number of bytes in a packet including the 16 trailing Reed-Solomon error checking and correction bytes. The 188 is the number of data bytes (187 bytes) plus the leading packet sync byte (0x47).
The bits per symbol is the (modulation's power of 2)*(Forward Error Correction). So for example in 64-QAM modulation 64 = 26 so the bits per symbol is 6. The Forward Error Correction (FEC) is usually expressed as a fraction, i.e., 1/2, 3/4, etc. In the case of 3/4 FEC, for every 3 bits of data, you are sending out 4 bits, one of which is for error correction.
Example:
given bit rate = 18096263
Modulation type = 64-QAM
FEC = 3/4
then
symbol rate = 18096263/(6)*(3/4) * 204/188
= 4363638
In digital terrestrial digital television (DVB-T, DVB-H and similar techniques) OFDM modulation is used, i.e. multi-carrier modulation. The above symbol rate should then be divided by the number of OFDM sub-carriers in view to achieve the OFDM symbol rate.
