Re: [Discuss-gnuradio] Simultaneous transmission on two antennas

[Eric Blossom]

On Mon, Mar 03, 2008 at 07:28:19PM -0800, Wee Shinhan wrote:
> Hi guys,
> 
> I would like to ask if anyone who have experience or
> have attempted to perform simultaneous transmission
> using 2 antennas to provide some advice and guidance.
> 
> For example, i have 2 orthogonal signal s0 and s1 and
> i wanted to transmit s0 from ant0 and s1 from ant1
> simultaneously. So in the receiver (1 antenna) i
> should see a super position of the 2 signals. 
> 
> However as of now, i changed the codes of examples
> benchmark_tx.py and benchmark_rx.py so that i have 2
> payloads to send to the desired RFX2400, in code it
> seems like they are sending simultaneously but however
> at the receive side i'm still receiving s1 and s2
> separate in 2 packets. Please advice.. Thanks in
> advance.
> 
> Regards,
> ShinHan

ShinHan,

With the current firmware in the USRP, to transmit on two channels
simultaneously requires that you configure the USRP for two channels
and then interleave the data for the two channels.

If you look at gnuradio-examples/usrp/fm_tx_2_duaghterboards.py you'll
see an example that does this.

In your case, you'll need to modulate the two packets worth of data,
then interleave the two streams of samples before sending them to the
usrp.

In the future, the "inband signaling" features may allow you to do
something similar by specifying the "time at which to begin
transmission" for each packet.  However, I recommend that at this
time you interleave the output of your two streams.

Eric