The Effect of FEC

DVB-S and DVB-S2 transmitters allow the selection of different values of Forward Error Correction. Put simply, forward error correction steals data capacity that would otherwise be used for video and audio, and uses it to correct errors to allow weaker signals to be decoded.

The fraction (for example 2/3) defines how much of the data capacity is available for headers, audio and video. The remainder is used for error correction.

The typical signal to noise required for decoding in each mode and FEC are listed below, together with indicative header+audio+video data rates for 1000 kS.

Standard	Modulation	FEC	SNR Required	Bitrate Available
DVB-S	QPSK	1/2	Example	1000 kS
DVB-S	QPSK	2/3	Example	1333 kS
DVB-S	QPSK	3/4	Example	1500 kS
DVB-S	QPSK	5/6	Example	1666 kS
DVB-S	QPSK	7/8	Example	1750 kS
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