[Discuss-gnuradio] benchmark_xx.py not consistent output

[usrp n210]

I am using 3 USRPs (USRP N210 ).

I run example program "benchmark_rx.py " and "benchmark_tx.py " in /gr-digital/examples/narrowband/.

I performed experiment on 2 USRP's(A,B) at a time.

so A-B and B-A 2 channels for 2 USRP.

when I send packets from A-B "psk" modulation scheme gives best(171/171)* performance while same is not true for B-A(171/0)*.

while "gfsk" scheme gives good performance from B-A(171/171)*.

Can anybody knows why different modulation scheme gives different result

on different channel ?

Is it related to USRP synchronization ?

Can we perform packet level debugging in USRP ?

How can we find the cause of this problem ?

Or is it implementation related bug in GNU-radio?

* : (n_rcvd/n_right) n_rcvd => received packet,n_right => correct received  packet