On Wed, Mar 3, 2010 at 03:36, amarnath alapati <[email protected]> wrote:
> I am using the programs of DIGITAL-BERT folder to see the bit error > rate pattern versus the SNR. The given programs are for BPSK scheme. I tried > to change it for QPSK Scheme. But seems that I did not do it right. I am > giving the modified code in the programs . Please help me out......Thanking > in advance.... Two major issues: 1) On the receiver, you are not demapping your received constellation into QPSK dibit symbols. The current script simply discards the Q channel and slices the I channel about zero to recover BPSK symbols; you never changed any of that. 2) Even were you to do this, the phase ambiguity of QPSK demodulation means you can end up in one of four states on the receiver, so I and Q can be swapped or inverted. In real communication systems this is either handled with differential coding or known synchronization words that allow the receiver to detect the rotated phase lock. BPSK has this problem as well, though limited to correct or inverted demodulation. The original BPSK-based BERT scripts use a self-synchronizing differential bit scrambler and descrambler that is okay with inverted demodulation. Johnathan _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
