[OLSR-users] Fast Roaming Nodes

[Andrew Hodel]

I don't know if cell technologies can even handle that speed, I know
wimax can't.  If it was me, I would have a local 802.11 relay routed
through an external antenna on the train to _try_ and get something to
work.

The calculations being made don't seem to incorporate anything more
then radio properties.  There is a lot more too it.


Regards,
Andrew Hodel


On 4/5/06, Tim Schmidt <(spam-protected)> wrote:
> How would the cell network deal with this?  It may be easier / cheaper
> to rig an access point to an EDGE handset and provide internet access
> on a per-train basis that way.
>
> --tim
>
> On 4/5/06, Weber, Michael J. (US SSA) <(spam-protected)> wrote:
> > John,
> >
> > I think you may need a new envelope...
> >
> > I get 816.67Hz of doppler shift for 2450MHz at 100m/s closure using the
> > equation F' = Fo * (1/(1+(v/Co))), where v is closure speed and Co is
> > speed of the wave in the medium in question. For our purposes, v is 100,
> > Co is 3*10^8, and Fo is 2.45*10^9. If you plug common X band radar
> > frequencies in instead, you get the familiar ~10Hz/mph shift at X band
> > that we hear on the audio monitor of traffic radar. This equation is
> > good only for non-relativistic speeds. :-) I got it here:
> >
> > http://imagine.gsfc.nasa.gov/YBA/M31-velocity/Doppler-shift-2.html
> >
> >
> > Still, I expect it will be quite a challenge to route any train-bound
> > traffic when the attachment point changes once per second. I might
> > suggest a pair of yagis on a pole near the track, one pointing up the
> > track, one pointing down the track, to give longer "hold times." An
> > antenna external to the train would also be a requirement. It will
> > probably be easier to get data from the train to the fixed
> > infrastructure via UDP, but TCP sessions will be difficult.
> >
> > Good luck,
> > Mike
> >
> > > -----Original Message-----
> > > From: (spam-protected)
> > > [mailto:(spam-protected)] On Behalf Of John Gorkos
> > > Sent: Wednesday, April 05, 2006 2:26 PM
> > > To: (spam-protected)
> > > Subject: Re: [OLSR-users] Fast Roaming Nodes
> > >
> > >
> > > I'm no expert, but my back-of-the-envelope calculations for
> > > 100 meters/second
> > > give me a doppler shift of 31.81 MHz at 2450Mhz at 0 degrees
> > > offset.  There's
> > > not a chipset in the world that can find a spread spectrum
> > > signal 31MHz off
> > > center frequency in <1 second, especially given that it's
> > > going from 31.81
> > > MHz UP as it approaches to 31.81MHz DOWN as it goes past.
> > > Unless you're ONLY
> > > using channel 6, you're going to be out of band on your
> > > transmitter.  If you
> > > do only use channel 6, you're going to self interfere.
> > > At 900Mhz, doppler is still 11Mhz, and Canopy isn't that
> > > good. Even if you stood the antennas a good 500 meters off
> > > the tracks and used a 60
> > > degree sector antenna, you've still got a delta of 15MHz.
> > > Plus, 802.11 can't
> > > associate and disassociate to the radios that fast.
> > >
> > > Try going and talking to the NASCAR guys or the Indy car guys
> > > about the
> > > techniques they use to get 802.11, and full motion video off
> > > the race cars.
> > > Hint:  if the cars weren't going in a rough circle around the
> > > antenna, it
> > > wouldn't work.
> > >
> > > John Gorkos
> > >
> > > On Wednesday 05 April 2006 11:41, Jaime Vargas wrote:
> > > > Hello,
> > > >
> > > > I am considering using olsr for a commuter trail corridor.
> > > Our plan is
> > > > to placed routers every 500 feet along the tracks. My
> > > question is can
> > > > olsrd handle user moving on the mesh at 230 miles/hour (337
> > > > feet/second).
> > > >
> > > > That means that user will be hopping from router to router every
> > > > second.
> > > >
> > > > Has anyone tried such setup? We also expect about 40
> > > > users doing this roaming at the same time. We plan to
> > > > do some trials, but before that I will like to know any possible
> > > > shortcomings.
> > > >
> > > > Thanks a lot for the help,
> > > >
> > > > Jaime
> > > >
> > > > --
> > > > Jaime E. Vargas
> > > > Why Wire, Inc.
> > > > 601 Birch St. SW
> > > > Vienna, VA 22180
> > > > T. 703-766-0939
> > > >
> > > >
> > > >
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