Transmission Issues Between Two LimeSDRs

Hi,

I’m currently using GNU Radio to transmit a signal from a file source between two LimeSDR-Mini v2.4 devices, connected via a wired link at 30 MHz. On the transmitter side, I’m utilizing a constellation modulator, and on the receiver side, I have a polyphase clock sync, Costas loop, and an equalizer in place.

The issue I’m encountering is that when I connect the Tx and Rx of the same LimeSDR, the data is decoded correctly. However, when I transmit between two separate LimeSDRs, the signal is not decoded properly.

Is there any special consideration or configuration required for transmission between two different LimeSDRs?

Thanks for your help.

Best regards.

There are some standard things you can check:

  1. Can your receiver deal with a frequency error? 2 different units may have a frequency error, while 1 unit receiving itself will cancel out any error in the TCXO.
  2. Are you sure your polyphase timing correction works? I’ve seen people fool themselves by doing a loopback like this, and because the timing was already correct, a non-working sync section had no impact.
    Can you try running your transmission in software loopback, but with a programmable impairment block to add timing error, frequency error etc. and see what breaks the recovery?

I tried with frequency offset without the channel and it can adjust upto 20 KHz with a sampling frequency of 1 MHz. I also tried the timing error and it was recovered. Although a higher frequency offset definitely breaks the recovery.

Is there any example grc file of using gnuradio with two different LimeSDR without using any external clock or synchronization?