# GNUradio DQPSK bit error rate

**URL:** <https://www.ruby-forum.com/t/gnuradio-dqpsk-bit-error-rate/243565>\
**Category:** GNU Radio\
**Created:** [December 4, 2015, 8:04pm UTC](https://www.ruby-forum.com/t/gnuradio-dqpsk-bit-error-rate/243565 "2015-12-04T20:04:59Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![Rafa\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/958977/32.png) [@Rafa\_F](https://www.ruby-forum.com/u/Rafa_F)\
**Post date:** [December 4, 2015, 8:04pm UTC](https://www.ruby-forum.com/t/gnuradio-dqpsk-bit-error-rate/243565/1 "2015-12-04T20:04:59Z")

</div>

Hello all  
Almost a month ago i started working on a digital communications project  
which involves GNUradio.  
I am now 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.