Re: delay

[Kyeong Su Shin]

Hello Kyle,

Are you running a simulation, or actually transmitting the data? I am a bit confused, as the USRP blocks are for the actual tx/rx, and Channel Model blocks are for simulation purposes.

On simulation, the timing offset is usually constant, so you can visually detect and correct the offset by looking at the correlation plot (just plot the magnitude of the correlation results, using QT GUI components). You can add a reference plot by adding a correlation plot with the known delay (to make the offset calculation easier). On real-world experiments, this is not feasible, as the timing offset is usually not constant. I usually write my own blocks to solve such issues, but there are probably easier methods (as well as some third-party alternatives). If you are willing to write your own blocks, please see the following tutorials:

-https://wiki.gnuradio.org/index.php/Tutorials

-https://wiki.gnuradio.org/index.php/Embedded_Python_Block 

Also, one thing that you should note is that the synchronizers described in the PSK demodulation tutorial are usually suboptimal. You can often achieve better BER results by exploiting the structure of your transmitted data.

I attached a correlator simulation flowgraph that I wrote before. I recommend using m-sequences or Gold-sequences instead of Barker-sequences, as the known Barker sequences are often a bit too short for the application. 

Regards,

Kyeong Su Shin

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보낸 사람: McClintick, Kyle W. <address@hidden> 대신 Discuss-gnuradio <discuss-gnuradio-bounces+ksshin=address@hidden>
보낸 날짜: 2019년 11월 13일 수요일 오전 7:10
받는 사람: address@hidden <address@hidden>
제목: delay

 

Hello,

I am having issues calculating BER following the guided PSK demodulation tutorial. While the processing delay is 58 samples as shown in the tutorial, if I change out the channel model for USRP sink/sources, or even change the modulation/demodulation objects to QAM, the delay changes. I understand that I could embed a barker code or some other such a prior sequence and correlate for that, but the native blocks im finding as well as online suggestions are very vague and difficult to implement. If anyone has suggestions as to how to estimate this sample delay no matter the application, I would be very grateful.

Best,

Kyle McClintick

mseq_sim.grc
Description: mseq_sim.grc