Re: [Discuss-gnuradio] How Can I support full-duplex using SBX board when running tunnel.py over OFDM?

[Josh Blum]

On 04/30/2012 08:09 AM, Alex Zhang wrote:
> Hi,
> 
> SBX is the daughterboard which supports full-duplex, but when I run the
> tunnel.py to do the Ping experiment over the OFDM communication link, I
> found that the transmitter can receive a lot of packets which are
> transmitted by itself.  This causes failure for ARP query and the Ping
> requests.  I see in the forum, many friends meet the failure of tunnel.py

I am a little surprised to find that there is a networking kind of
issue. I thought that any of these leakage packets would be discarded by
the network layer (because the IP source and destination would be
incorrect, etc...)

So, how do you think ARP is failing? Even if there is this "echo"
packet, a device should not be able to respond to an ARP request for an
IP address which is not its own. Are you setting different IP addresses?

> because they are using the XCVR2450 which is half-duplex.  But why I still
> have this tunnel.py failed even when I am using the full-duplex SBX?
> 
> Should I use different frequencies for the TX and RX in the same USRP? Does
> the SBX support the TDD based full-duplex?
> 

So if the TX and RX frequency are the same, the receiver (which is
always running) will hear the transmission leakage. That makes sense.
What I think is missing from the tunnel.py example is that RX is not
muted during a TX.

Some recommendations:

1) Use different frequencies for each communication channel.

2) Or mute the RX stream when transmitting to avoid decoding leakage.

-Josh