[Discuss-gnuradio] DPSK mod/demod in 3-node relay with USRP2 not working

[Vinodhini Ravikumar]

Hi,

I have been trying to implement a relay system using DPSK modulation scheme. I'm basically trying to replicate the decode and forward method using three usrp2 nodes. I generate a .dat file DPSK modulation of a random source initially. The graph goes like this:

First time slot:

file sink --> Tx of node 1 --> Rx of node 2 && Rx of node 3

Second time slot:

Rx of node2 remodulate and store in file sink

Third time slot:

file sink --> Tx of node 2 --> Rx of node 3

Simultaneously in the third time slot, node 1 transmission acts as interference.

Now, the issue here is that, during the second time slot, the file sink remains blank even after demodulating and remodulating the received file. It does not store anything.  Am i doing a mistake somewhere ?  I have attached a screenshot of my flowgraphs here.

Please help me out in solving this.

--
Thanks,
Vinny

Source.grc.png
Description: PNG image

USRPphase1.grc.png
Description: PNG image

USRPphaserelay.grc.png
Description: PNG image