The other day, I was doing 60mph at between 11 and 12 miles from our mountain POP (moving directly away from it), using a 5.5dBi omni on my car. Signal strength was good, not one ping packet was lost. I also did a speedtest and had over 500kbps while moving (reasonable based on the limited gain of the omni and the distance from the POP, etc, etc). Same day I did another test, moving E to W at 55mph at about 8 miles from the same POP, same setup, throughput was great, around 1Mbit sustained, even though some buildings were in the way on occation (some packet loss, but intermittant, just as I drove past them).
The speed of light moves at 186,000 Miles per Second. Relative to your speed, there is very little difference generated by your speed differential. The problem comes down to timing of the radios, not the speed at which the signal travels. I've heard of other people testing as fast as 90mph or faster and we've done tests in the past on the freeway from a nearby POP at upwards of 80Mph with no problems. This is all basically stock 802.11b gear (Orinoco AP's and Lucent Silver or Gold cards). If you have trouble getting good connections while moving, check your LoS and if LoS is perfect, try different radios. Judd David Young wrote: > 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 -- general wireless list, a bawug thing <http://www.bawug.org/> [un]subscribe: http://lists.bawug.org/mailman/listinfo/wireless
