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Re: [Discuss-gnuradio] Distorted QPSK Constellation
From: |
Salman Dinani |
Subject: |
Re: [Discuss-gnuradio] Distorted QPSK Constellation |
Date: |
Thu, 15 Jan 2015 10:41:14 -0800 |
Hi
to all,
Thanks
very much to all of you for your valuable suggestions.In accordance with your suggestions,
I experimented with my designed DQPSK system and got few problems which I am
listing down.All the referenced figures are attached.
- I
reduced the symbol per sample to 4 (previously it was 8) and added a RRC filter
before constellation plot (figure RRC_const) but constellation remains the same
L
- I
successfully demodulated the distorted constellation output by using Cosine
signal source as input (figure DQPSK_demod_S_2). As someone previously suggested
reducing the samples per symbol, I set it to 2 and ran the simulation. The
demodulated output was out of phase w.r.t input (figure S_2_P_1).As I varied the
frequency, the phase difference also varied as shown in figures S_2_P_2 and
S_2_P_3. When I set this parameter to 4 (figure DQPSK_demod_S_4). The output
got corrected (In-Phase) for all frequencies (figure Plot_DQPSK_S_4).
Why
the signal is out of phase and phase shift is varying with frequency??Why
this problem got corrected when Samples per symbol changed to 4?
- In
order to send my desired bit stream, I made a file in Libre office with bits
11110000 and saved it with txt extension. (i.e. data.txt). Before applying to
the system, I tried to check the output of file source on scope. But when I ran
the program (figure File_source), the output was zero.
After several trials, I put the bit streams in inverted commas “11110000” (figure
file_dat ) some data appeared at the output (figure output_dat). But this is
not the data which I wrote in the file.
Is
there a special format for sending data via File Source??
I
am very sorry if my questions appear to be childish but I am not able to figure them
out. Eagerly waiting for your expert opinions.
Regards
Salman
Dinani
RRC_const.PNG
Description: PNG image
DQPSK_demod_S_2.PNG
Description: PNG image
S_2_P_1.PNG
Description: PNG image
S_2_P_2.PNG
Description: PNG image
S_2_P_3.PNG
Description: PNG image
DQPSK_demod_S_4.PNG
Description: PNG image
File_source.PNG
Description: PNG image
file_dat.PNG
Description: PNG image
output_data.PNG
Description: PNG image