There are 2 messages in this thread.
You are currently looking at messages 1 to .
Is this discussion worth a thumbs up?
Hello all, I am reading DVB-S2 standard. There is a sentence about LDPC, "a powerful FEC system based on LDPC (Low-Density Parity Check) codes concatenated with BCH codes, allowing Quasi-Error-Free operation at about 0,7dB to 1 dB from the Shannon limit, depending on the transmission mode (AWGN channel, modulation constrained Shannon limit)". So what's "allow Quasi-Error-Free operation"? Thanks! Regards, Davy______________________________
In the DVB context "quasi error free" (QEF) means a level of errors that is defined as the "threshold" of where the system is working and where it is not. The "threshold of visibility" is another term sometimes used referring to a rate of errors that just becomes noticeable to a TV viewer. Specifically it is less than one uncorrected error event per transport stream hour which corresponds to a coded BER of about 1E-10 to 1E-11. In my experience, the average viewer will not notice errors at a significantly higher BER so the DVB definition is somewhat conservative. Bottom line, QEF is a somewhat arbitrary low BER value that is used for evaluating the performance of the system, i.e. the C/N required to obtain QEF operation is the threshold. Look around in the other ETSI / ETR documents and you can find the formal definition of QEF. Mark______________________________