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Re: [Discuss-gnuradio] Simultaneous RX/TV with RFX2400

From: Jakub Moskal
Subject: Re: [Discuss-gnuradio] Simultaneous RX/TV with RFX2400
Date: Tue, 14 Apr 2009 00:16:37 -0400

Hi Michael,

my intention is to allow a communication between two USRP's hooked up
to two different computers. Each USRP has one RFX2400 daughterboard
and one antenna connected to the Tx/Rx port.  I have a more of a CS
than ECE background and my focus here is on the application level. I
would like the radios to be able to send and receive messages
asynchronously - which can mean asynchronous communication at the
application layer, but synchronous below - perhaps not even observable
above. In my scenario, radios send messages which are read from some
buffer and at the same time receive messages and put them in a
different buffer for further processing. How do I go about
implementing such scenario? Do I have to implement a protocol which
consists of some time-based switching of rx/tx? Can I achieve it with
only one antenna per USRP, or do I need two of them - one for Tx//Rx
and one for Rx2 port?

I imagine that in the case of only two radios, I could achieve this
behavior by allowing one radio to Rx while the other is Tx-ing and
after short time, switching the direction to the opposite, to allow
the first radio to Tx. However, I don't see how this could be achieved
if 2+ radios are involved - without the prior knowledge of the number
of "neighbors". That is why I thought each radio should be allowed to
Tx and Rx at the same time.

Thank you for help!

On Mon, Apr 13, 2009 at 4:19 PM, Michael Dickens <address@hidden> wrote:
> Hi Jakub - 2 possibilities, depending on how one interprets your question:
> A) If what you mean is "using a single host computer that controls the two
> USRPs such that one transmits while the other receives and vice-versa, but
> never a single USRP both Tx and Rx simultaneously", then yes, that can be
> done; you could probably even use two host computers that sync the Tx/Rx in
> a MAC-like way using the current GNU Radio software, so long as each USRP is
> not trying to do simultaneous Tx and Rx.  If using a single host computer:
> on each USRP, you'd use set_auto_tr(true) and then control both USRPs from
> the same Python script.  My colleague Glenn has done this in a "TDMA
> fashion" to compare properties of actual and theoretical relays; see his MS
> thesis and related paper at UND <
> http://www.nd.edu/~jnl/group/glenn-bradford/ >.
> B) If what you mean is "simultaneous Tx/Rx on each USRP, using a single RFX
> and single antenna", then this problem is (1) possibly not do-able in the
> current state of GNU Radio software and USRP hardware; and (2) even if it is
> do-able, certainly not easily so in GNU Radio software without significant
> hacking to make it work.  The primary issue is in jointly estimating the
> channel parameters (both the Tx -> Rx delay and filter coefficients), which
> might be time-varying or dependent on qualities beyond the direct TX signal.
>  I'm happy to discuss this interpretation further off-list.
> Hope this helps! - MLD

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