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Απ: Issue with USRP signal reception when stream is produced by a Vector

From: Γιώργος Γιώργος
Subject: Απ: Issue with USRP signal reception when stream is produced by a Vector Source
Date: Wed, 9 Jun 2021 07:17:03 +0000

Hello Marcus,

Thank you very much for the swift answer. You're quite right, I should have noticed that. I will adjust accordingly and report back to update/close the thread.

Best regards,

Από: Discuss-gnuradio <discuss-gnuradio-bounces+zulkir=hotmail.gr@gnu.org> εκ μέρους του Marcus Müller <mmueller@gnuradio.org>
Στάλθηκε: Τρίτη, 8 Ιουνίου 2021 8:07 μμ
Προς: discuss-gnuradio@gnu.org <discuss-gnuradio@gnu.org>
Θέμα: Re: Issue with USRP signal reception when stream is produced by a Vector Source
Just from very quickly over your attached images:

Your receiver is clipping, you can see that: the receive waveform should never even touch "1".

You need to substantially reduce gain, potentially both in your receiver and transmitter.

Best regards,

On 08.06.21 16:32, Γιώργος Γιώργος wrote:
> Hello to everyone on the list,
> To begin with, my overall goal is to build an adaptive modulation scheme using GnuRadio
> and USRPs. Concept-wise, this will be implemented by calculating the BER at the receiver,
> feeding this data to the transmitter, and switching between two different modulation
> schemes based on threshold BER values.
> I am currently working on an 8DPSK modulation format. After succesfully building and
> testing the flowchart in simulation, I split the transmit and receive chain in order to
> actually test the setup using two B210 USRPs.
> After a little bit of experimentation, transmission is great when using a random source at
> the transmitter. The FFT plot and the Constellation appear as expected. However, when
> using a vector source, which is mighty helpful for my purpose since I have a known bit
> sequence to compare at the receiver, my ouputs are unexpected (screenshots attached). This
> is baffling because the only thing that changed is the bit sequence and nothing in the
> actual signal processing chain (to be frank a packed to unpacked, and upacked to packed
> block were used after the vector source, but I'm getting pretty much the same results
> without them). I have experimented with different parameters but to no avail. It is
> important to note, that the simulations were working fine, regardless of the source that
> was used.
> Any thoughts on why this is happening? I have also attached screenshots of the flowcharts.
> Thank you very much for all the effort you are putting into the project.
> Best regards,
> George

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