Hi Timothée, hi Haaris, is it OK if I paste the answer to the question on StackOverflow? http://stackoverflow.com/questions/34096116/gnu-radio-dqpsk-bit-error-rate
Best regards, Marcus On 05.12.2015 22:38, Timothée COCAULT wrote: > Le sam. 5 déc. 2015 à 20:42, Haaris <[email protected]> a écrit : >> Hello >> Almost a month ago i started working on a digital communications project >> which involves GNUradio. >> And I am severely struggling to get past some errors or mismatches I am >> encountering in GNUradio. >> I am desperately in need of some expert help. >> I made a DQPSK modulator and demodulator using GRC. ( screenshots >> provided ) >> Gave a vector source with bits 0,1,0,1 and repeat on, on the input of >> psk modulator. >> I also used an error rate block to calculate bit error rate. >> Now almost everything that is appearing on the scopes is completely >> wrong. >> >> The bit error rate is 0.5, provided that i have added no noise.(which is >> max considering that we will recover 50 percent bits correctly just by >> chance). >> The scope at the psk modulator output shows four constellation points >> even though i am transmitting only one symbol i.e (0,1). >> >> What am i doing wrong? >> Can someone please be kind enough to go through the screenshots and tell >> me the mistake(s). >> Any help will be greatly appreciated. >> Thanks in advance. > > Hi Haaris, > > The documentation of the PSK Mod says : "The input is a byte stream > (unsigned char), treated as a series of packed symbols. Symbols are > grouped from MSB to LSB." > You should add an "Unpacked to Packed block" with 2 bits per chunk and > MSB endianness before. > Likewise, you should add a "Pack K bits" block with K=2 after the PSK > Demod. > > Also, your assumption that you should have one point in the > constellation sink is wrong. > You're using DQPSK so the (0, 1) symbol will add 90 degrees to the > phase, and you will cycle through the 4 points of your constellation. > > And last, keep in mind that each block has a delay, and you can't > compare the input and output bits directly. > Try to use a "Scope plot" with 2 inputs, and add a delay block before > the input bits to synchronise the two. > > > Timothée. > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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