[Discuss-gnuradio] Strange constellation appears on pi/4 dqpsk and dqpsk
From:
加藤義也
Subject:
[Discuss-gnuradio] Strange constellation appears on pi/4 dqpsk and dqpsk thru scope_sink.
Date:
Sun, 24 Jan 2010 21:14:51 +0900
Hello Friends.
Please someone advice me out for my situation. I faced strange constellation at pi/4 dqpsk / dqpsk.
I am now trying to implement pi/4 dqpsk modulator/demodulator on GnuRadio3.2.2 with using USRP2(RFX2400).
And mostly is working now.
In these days, I tried to have BER ratio, by PN9 XORed my original bit pattern.(for spreading frequency) and ratio shows very poor. If I compete with other systems. which ratio is like 6 to 10dB more SNR is needed at same BER.
-Used already impremented dqpsk as a modulator. and it's constellation shows
similar strange plot. which is as http://www.telemann.co.jp/gnuradio-image/dqpsk-scope-sink.png -Not PN9 XORed dqpsk shows sharpen constellation as shown in "dqpsk(notpn9)-scope-sink.png"
-I have read gnuradio-core/src/lib/general/gr_mpsk_receiver_cc.cc:gr_make_mpsk_receiver_cc() and in my guess "phase_error_detector_generic" and "decision_generic" brought this issues.
Is my guess get pointed? or irrelevant?
If it is, I would like to think more how to make "phase_error_detector_pi_4qpsk" and "decision_pi_4qpsk".
I used following parameter for gr_make_mpsk_receiver_cc(). costas alpha = 0.15
gain mu = None def mu = 0.5 omega relative limit = 0.005 fmin = -0.025 fmax= 0.025