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 (payload) data rates for 1000 kS. Note that DVB-S2 has a smaller header so is more efficient in that it allows for more audio and video in the payload for the same symbol rate. It also needs slightly less SNR to decode, because it is easier for the receiver to lock to the more advanced waveform.

Standard	Modulation	FEC	SNR Required	Payload Bitrate Available
DVB-S	QPSK	1/2	1.7 dB	1000 kS
DVB-S	QPSK	2/3	3.3 dB	1333 kS
DVB-S	QPSK	3/4	4.2 dB	1500 kS
DVB-S	QPSK	5/6	5.1 dB	1666 kS
DVB-S	QPSK	7/8	5.8 dB	1750 kS
DVB-S2	QPSK	1/4	-2.3 dB	500 kS
DVB-S2	QPSK	1/3	-1.2 dB	666 kS
DVB-S2	QPSK	2/5	-0.3 dB	800 kS
DVB-S2	QPSK	1/2	1.0 dB	1000 kS
DVB-S2	QPSK	3/5	2.3 dB	1200 kS
DVB-S2	QPSK	2/3	3.1 dB	1333 kS
DVB-S2	QPSK	3/4	4.1 dB	1500 kS
DVB-S2	QPSK	4/5	4.7 dB	1600 kS
DVB-S2	QPSK	5/6	5.2 dB	1666 kS
DVB-S2	QPSK	8/9	6.2 dB	1778 kS
DVB-S2	QPSK	9/10	6.5 dB	1800 kS
DVB-S2	8PSK	3/5	5.5 dB	1800 kS
DVB-S2	8PSK	2/3	6.6 dB	2000 kS
DVB-S2	8PSK	3/4	7.9 dB	2250 kS
DVB-S2	8PSK	5/6	9.4 dB	2500 kS
DVB-S2	8PSK	8/9	10.7 dB	2667 kS
DVB-S2	8PSK	9/10	11.0 dB	2700 kS
DVB-S2	16APSK	2/3	9.0 dB	2667 kS
DVB-S2	16APSK	3/4	10.2 dB	3000 kS
DVB-S2	16APSK	4/5	11.0 dB	3200 kS
DVB-S2	16APSK	5/6	11.6 dB	3333 kS
DVB-S2	16APSK	8/9	12.9 dB	3556 kS
DVB-S2	16APSK	9/10	13.2 dB	3600 kS
DVB-S2	32APSK	3/4	12.8 dB	3750 kS
DVB-S2	32APSK	4/5	13.7 dB	4000 kS
DVB-S2	32APSK	5/6	14.3 dB	4167 kS
DVB-S2	32APSK	8/9	15.7 dB	4444 kS
DVB-S2	32APSK	9/10	16.1 dB	4500 kS