full-duplex 802.11?

[Bruce Janson]

    ...
    To: Samba/Wavelan mailing list <wireless at lists.samba.org>
    ...
    From: Jean Tourrilhes <jt at bougret.hpl.hp.com>
    ...
    Date: Mon, 15 Jul 2002 09:47:46 -0700
    
    Bruce Janson wrote :
    > Now that sub-frequency selectable wireless devices are common, has anyone
    > tried to set up full-duplex point-to-point links?  I would imagine that
    > this could be done using two wireless cards at each end (i.e. four cards
    > in total).  At each end, both cards would be attached to the same antenna
    > (via some sort of "splitter/combiner" Y-shaped junction).  Each card would
    > be tuned to a separate sub-frequency (and of course, that sub-frequency would
    > match that of the corresponding card at the remote end).  Then traffic in
    > one direction would be sent through one network interface (sub-frequency)
    > and that in the other direction confined to the other channel.
    
    	Have you ever seen the shape of a transmitted radio signal
    (versus frequency) ? It looks more or less like a gaussian
    curve. Which mean that even if you don't transmit a full power in the
    adjacent channel, you will transmit enough to "blind" you.
    ...

Jean,
    That was my understanding but I did not (and still do not) know
whether the current wireless devices allow selection of two channels
sufficiently far apart to avoid that overlap.  Moreover, given that the
pairs of colocated cards would be only "bus-slots" apart within the PC
there might be other shielding-related problems.

    	Using the same antenna is "no way". I even suspect that
    electrically you can damage your cards.
    ...

Oh well...

    Using two different pair of
    antennas might be possible but you will need to position the Rx
    antenna properly with respect to the Tx antenna (check your angular
    response).
    ...

(Obviously, I was hoping that the separation in frequency space would be
sufficient.)

Again, has anyone tried this, perhaps, as Jean suggests, using separate
antennas for each card?

Regards,
bruce.