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

[Marcus Müller]

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,
Marcus

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
> 
>