I was reading some info on the GSM specs about a week ago, and it said:

Phase and frequency synchronization must allow for Doppler shift for vehicle
speeds up to 250km/h as well as for frequency standard drift, and timing
advance to compensate for propagation delay due to round trips for paths, in
cells up to 35km radius. 

The carrier frequencies are spaced 200khz apart.  Since it's late, I don't
really want to figure out how much the doppler shift is, but I would assume
that it's enough to where it's possible to get too close to one of the other
frequencies used.  


> -----Original Message-----
> From: Chuck Cole [mailto:cncole at earthlink.net]
> Sent: Tuesday, July 23, 2002 1:05 AM
> To: tcwug-list at tcwug.org
> Subject: [TCWUG] Doppler on what?
> Existence of a voice level doppler shift in a supposedly 
> digital scheme like
> GSM is hard to accept...
> > -----Original Message-----
> > From: tcwug-list-admin at tcwug.org 
> [mailto:tcwug-list-admin at tcwug.org]On
> > Behalf Of Austad, Jay
> > ...    GSM 1800/1900 has
> > special provisions for handling frequency shifts due to the
> > doppler effect,
> > since many people talk on their phones while driving. ...
> Maybe I'm missing a big piece of the picture (and the specs), but this
> doesn't make sense.  GSM supposedly digitizes the voice at 
> the handset, then
> sends and receives digital packets.  The modulation for the 
> digital encoding
> would see doppler, but the voice digitizing and recovery in 
> the handset
> would not.  The modulation only does ones and zeros and 
> probably with some
> compressed error correcting code, so the modulation 
> (subcarrier) doppler is
> irrelevant for bit recovery.  "Channelizing" or some such 
> might be affected
> by the RF carrier frequency having a doppler shift, but PLLs probably
> nullify that up to some speed such as you suggested.  Just 
> what GSM doppler
> are you discussing?
> Just curious..
> Chuck
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