>>> But from my tests I see that >>> 1 bit error in -> 7 bit errors out >>> 2 consecutive bit errors in -> 2 errors in the output >>> 3 consecutive bit errors in -> 7 errors in the output >>> 4 consecutive bit errors in -> 4 errors in the output >>> ... >>> And so forth up to 7 (Length of the lfsr) >>> >>> The reason I ask is that if I want to change the scrambler and/or the >>> modulation, I assume that this "magic number" will change as well. >> >> If you want a good BER measurement, I wouldn't use the method that you >> describe here. > >You are correct. The scrambler introduces three output errors per >input error for single channel errors that are farther apart than the >length of the shift register. This is the case once the shift >register has already achieved self-synchronization and at low channel >error rates. For the purposes of the simple BERT example, this was >sufficient. (The number 3 comes from the number of taps in the >scrambler polynomial.)
I know this thread is a bit old, but is it possible that there is an mistake in the text? I think it should be written, that 1 bit error in the scramber input introduces 4 errors in the output, because 1 error is passed directly through and 3 feedback errors are introduced by the taps in the scrambler polynomial of: self._descrambler = gr.descrambler_bb(0x8A, 0x7F, 7) # CCSDS 7-bit descrambler If I'm wrong, don't hesitate to correct me. Thanks. Daniel _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
