[OLSR-users] Fast Roaming Nodes

John Gorkos (spam-protected)
Wed Apr 5 20:26:08 CEST 2006

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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