Maybe I did my math wrong, but I think that at 40mph a 2.4GHz signal is Doppler-shifted by fewer than 200Hz. If the demodulator will not track carrier shifts, then I guess that the signal strength will fade to zero 400 times a second. I guess that at that rate of fade, the signal strength will scarcely ever be higher than the receive threshold long enough for a whole packet to get through?
If the access points are spaced closely enough, and if one can hand you off to another quickly enough, and if they are distant enough from the roadway, then you can probably drive at highway speeds without being disconnected. But those are an awful lot of ifs. I am fascinated by the question. Will someone explain? Dave On Fri, Dec 06, 2002 at 06:07:15PM -0800, Kevin Lahey wrote: > I'm curious about using 802.11 from my car. > > No less an authority than Jim Thompson explained to me at BAWUG > last night that 802.11 was useless when the two communicating > systems had a greater than 40-mph speed differential. This is > apparently due to the doppler shift. > > As he pointed out, this wouldn't be a big problem with cars driving > past access points, but would make it tough to put a directed > antenna pointing down the road, since the cars would close in > on it at fairly high speeds. I guess an omni way off the side of > the road could provide service for a reasonable distance. > > Could anybody expand on this for me? I have to admit that I've > had visions dancing in my head of in-car access for quite awhile, > and I'd hate to think that it was unlikely to work... > > Thanks, > > Kevin > [EMAIL PROTECTED] > -- > general wireless list, a bawug thing <http://www.bawug.org/> > [un]subscribe: http://lists.bawug.org/mailman/listinfo/wireless -- David Young OJC Technologies [EMAIL PROTECTED] Engineering from the Right Brain Urbana, IL * (217) 278-3933 -- general wireless list, a bawug thing <http://www.bawug.org/> [un]subscribe: http://lists.bawug.org/mailman/listinfo/wireless
