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. I've tried to have constellation of my implementation with using scope_sink. Now, I found the implementation shows strange constellation as I attached file http://www.telemann.co.jp/gnuradio-image/pi_4dqpsk-scope-sink.png The demodulator is using origin as gr_make_mpsk_receiver_cc(). I sought where this strange constellation is come from. Of course, I doubt this is because of my implementation at the first. What I tried following things. -Used rented Agilent VecterSignalAnalyzer 89600/89640 to get constellation. for whether, At least Tx does work fine both pi/4 dqpsk and dqpsk.and shows beautiful constellation. as http://www.telemann.co.jp/gnuradio-image/pi_4dqpsk-89600.png http://www.telemann.co.jp/gnuradio-image/dqpsk-89600.png -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 and configuration of the test is as http://www.telemann.co.jp/gnuradio-image/configuration.png Thank you very much in advance. Yoshiya Kato -- -- 株式会社テレマン・コミュニケーションズ 加藤義也<[email protected]> 121-0012 東京都足立区青井6-8-11 電話:03-5888-7300 FAX:03-5888-7301 Telemann Communications Co., Ltd. TEL:+(81)-3-5888-7300 FAX:+(81)-3-5888-7301 Board Member / Technical Director Yoshiya Kato <[email protected]>
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