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Re: [Discuss-gnuradio] PSK modulation and demodulation from gnu radio tu

From: Md. Atiqur Rahman
Subject: Re: [Discuss-gnuradio] PSK modulation and demodulation from gnu radio tutorial.
Date: Mon, 8 Jul 2019 13:40:32 +0200


Thank you for your response. I have had some exams so I couldn't reply on time. 

yes; I will follow those tutorials as you suggested. 
Perhaps I want to ask you that If I want to change the samples/symbol then it could be a problem for QPSK task? I am changing it to 4 to 16 or 32 but now it is no longer synchronized. I have to change the delay by changing the gui range but still problem present.

Is there anything I need to take care of? Please have a look. 

Looking forward to hear from you. Thank you.


On Sun, Jun 30, 2019 at 1:23 PM Kyeong Su Shin <address@hidden> wrote:


I recommend the following tutorials:


If you experience problems in following those tutorials, please come to this mailing list.

The "demodulator block" which you originally attempted use, "PSK demod", is an all-in-one block which does synchronization, equalization, and detection (in detection & estimation theory sense) by itself. But that is not what you want: your flowgraph already has synchronizers and an equalizer, which decimates the signals to 1 sample/symbol (which the "PSK demod" block cannot properly handle). That is why it does not work.

Also, that "PSK demod" block is deprecated and is no longer supported. So, you shouldn't be using that anyway. (Real-world communication systems seldomly use blind synchronization & estimation techniques used in the PSK demod block or in the PSK transceiver tutorial that you are following; they use reference signals and correlators for the synchronization and equalization. The blind techniques do have places, however - like SIGINT.)


Kyeong Su Shin

보낸 사람: Md. Atiqur Rahman <address@hidden>
보낸 날짜: 2019년 6월 30일 일요일 오후 7:27:46
받는 사람: Kyeong Su Shin; address@hidden
제목: Re: [Discuss-gnuradio] PSK modulation and demodulation from gnu radio tutorial.
Hello Kyeong,   

Again thank you so much for helping. And yes my idea is generation IQ modulated signal to feed through the SDR board.

However, to sooner or later I may need to build the block by myself. I have worked with but as you know its failed to generate. Can you tell me any following tutorial to generate the block? 

Yes, I think the delay was the case to correct. However, as you used constellation modulator why we cannot do with demodulator block? Is there any reason? Sorry for the late reply. Looking forward to hearing from you.

Thank you so much.


On Sat, Jun 29, 2019 at 12:13 PM Kyeong Su Shin <address@hidden> wrote:

Hello Atiqur:

If all you want is writing a simple DQPSK transceiver, then you can use a Constellation Decoder block, as like in the attached file. I cannot comment much on the problems that you are experiencing, as I have not looked on the source codes that you are trying to build.

Please note that you may have to change numbers in the "delay" block at the end of the flow graph to get a correct plot. This is because the synchronizer and the equalizer blocks in the flow graph may end up adding a few numbers to the stream, and introduce "time differences" between the two streams. 

Also, please add the mailing list ('discuss-gnuradio.gnu.org') as a recipient when replying to the e-mail thread, as this discussion could useful for other people as well. 


Kyeong Su Shin

보낸 사람: Md. Atiqur Rahman <address@hidden>
보낸 날짜: 2019년 6월 29일 토요일 오전 5:23:59
받는 사람: Kyeong Su Shin
제목: Re: [Discuss-gnuradio] PSK modulation and demodulation from gnu radio tutorial.
Hello  Kyeong, 
First of thank you so much for your quick reply.  From the tutorial one, I am following all section. Unfortunately, from gnuradio with python, I am facing problems. I made the multiply block and its working but when I try to make the qpsk_demod_py_cb it is not working. I have tried to do the same tutorial so many times. Then I shifted to do the oot module by c++. Sometime in the tutorial, some file name changed. Like tutorial with c++ I am working now, my lib/ folder files like .h and .cc edited successfully but for making test: in my python/ folder qa_my_qpsk_demod_cd.py is present but in the tutorial it's named is qa_qpsk_demod.py!!!! However, I made the change .xml file and .py as suggested but still not working. When I do the make test it says tutorial passed but qa_qpsk_demod failed! I make the test and it failed again and again. Honestly, I don't know what I am doing wrong!

I do even see the source code from github and yet their file name is also changed!

All I wanted to do the generating the PSK signal (transceiver). I have failed for the last 3 weeks! Please would you give me some solutions here? I will be so grateful. Thank you.


On Fri, Jun 28, 2019 at 4:32 PM Kyeong Su Shin <address@hidden> wrote:

Hello Atiqur,

The "PSK Demod" that you added into your flowgraph is deprecated, and is no longer supported. It is kept there for the backward-compatibility, but it is not guaranteed to work and will be removed in future. Also, that block does the synchronization and the equalization by itself, so you must remove the preceeding synchronization and equalization blocks if you actually want to use that (you shouldn't, though). Try other blocks, like a Constellation Decoder or a custom Python block.

Channel Model is used to "degrade" the signal (for simulation purposes). It will apply a FIR filter to the incoming signals to simulate the multipath environment. The taps are the filter taps used for that purpose. It is just a sequence of a few random non-zero numbers to simulate the multipath effect, and shouldn't really affect the functionality of the synchronizer and the equalizer blocks. A good equalizer will cancel out the effect of those channel taps. 


Kyeong Su Shin

보낸 사람: Md. Atiqur Rahman <address@hidden> 대신 Discuss-gnuradio <discuss-gnuradio-bounces+ksshin=address@hidden>
보낸 날짜: 2019년 6월 28일 금요일 오후 9:32:46
받는 사람: address@hidden
제목: [Discuss-gnuradio] PSK modulation and demodulation from gnu radio tutorial.
Hello Guys,
I am very much new in gnu radio and trying to do the tutorial that gnuradio published for PSK demodulation. I am using constellation modulator to modulate the signal and demodulate it by PSK demodulation block(not my QPSK demodulator). I did put every parameter as they suggested.  Unfortunately, I do not get the same result(synchronized input and output ). I think its may the Channel model or time recovary block is not set correctly. Moreover, I do not understand why they use the channel model taps parameter to [1.0, 0.25-0.25j, 0.50 + 0.10j, -0.3 + 0.2j]? How did the get that? I did already spend a lot of time for searching about these but do not get any specific understandable solution.

I attach my .grc file in this mail. Please have a look. Looking forward to hearing from you guys.


Attachment: qpsk_32.PNG
Description: PNG image

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