I highlight the zone where there is a symbol recover. When I run the acquisition I can see symbol at the places. Here we just see one because there is a limited number of points displayed. However what is the rest? I got a SPS (sample per symbol) of 2. A part of the rest is certainly the transistion, but I am quite sure there is phase noise also. How can I attenuate those points. My flowgraph is just a UHD source feed into the polyphase clock source which is sent to a costa loop and after that there is my QT constellation sink.
The phase recovery was finaly perform in Matlab. Because the signal we are studying (Zigbee) send a preamble before the communication start, we can compensate for the group delay and the channel's distortion with a anti-causal analysis of the expected signal and the received signal.
The GNU-Radio's blocks weren't efficient at recovering O-QPSK's signal. However with fact that we don't real time treatment of the signal, Matlab was finaly most suitable way to resolve the O-QPSK demodulation of the Zigbee signal.