Hi Jason thanks for the feedback. Sorry about the code, it was generated mostly via Grc. I've cleaned it up, should make much more sense now: http://users.tpg.com.au/marcinw//qpskTest.py
I've tried using the available DQPSK blocks as you suggested, but i get the same result. i.e with 108 as the input i get either 108, 177, 27 or 198 as the output. The source code for the graph using the available DQPSK block is given here: http://users.tpg.com.au/marcinw//QPSKtest16.py Onto the differential Encoder, i believe it is encoding my data correctly. I have proven this by connecting a vector sink at the output of the encoder and so with: Input [108] = [1 2 3 0] >> Packed2Unpacked [2, MSB] >> Binary2Gray >> Differential Encoder >> Vector Sink the output at the encoder is: y[0] = (x[0] + y[-1]) % M (where M = 4 for QPSK) y[0] = 1 y[1] = 0 y[2] = 2 y[3] = 2 y[4] = 3 y[5] = 2 y[6] = 0 y[7] = 0 y[8] = 1 y[9] = 0 y[10] = 2 y[11] = 2 y[8] = 3 y[9] = 2 y[10] = 0 y[11] = 0 and so on.... If the system is Encoding my data correctly, i am still led to believe the problem lies with the noisy channel? Do you have any more suggestions? Regards, Marcin p.s Your suggested input of [92d] actually produced the correct output Jason Uher wrote: > > 1) To be honest, your code is really hard to read, which is the reason > I didn't originally reply to your question. I started to look through > to make sure your blocks and connections were set up correctly, but > it's just a big mess. > > 2) There is a DQPSK implementation in the gnuradio blks2 source, > search the repository for it, there is a transmitter and a receiver. > > 3) I would guess your problem has to do with incorrectly applying the > differential coding, since you get a unique stream of symbols in each > of your four cases: > 108d - 1h 2h 3h 0h > 177d - 2h 3h 0h 1h > 27d - 0h 1h 2h 3h > 198d - 3h 0h 1h 2h > > Notice that the difference is the same in each of these cases: > (previous+1) % 4. This comes from the phase ambiguities in the costas > loop, it locks on to wherever. That's why the differential coding is > used. You can confirm this by sending something that's not an even > distribution of symbols. For example, send: 92d - (1h 1h 3h 0h) = (+1 > +0 +2 +1) and I bet you'll get back four different values just like > you do now: > (1h 1h 3h 0h) = (+x +0 +2 +1) > (2h 2h 0h 1h) = (+x +0 +2 +1) > (3h 3h 1h 2h) = (+x +0 +2 +1) > (0h 0h 2h 3h) = (+x +0 +2 +1) > > > Jason > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > -- View this message in context: http://old.nabble.com/DQPSK-Modulation-Demodulation-issue-tp28288015p28384967.html Sent from the GnuRadio mailing list archive at Nabble.com. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
