cell phones in motion

[dpopiz]

how do cell phones deal with motion during a call?

The signals always travel at the speed of light, so they're not instant -- a signal sent from the phone to the base station takes some small amount of time to get there.
So you would get a doppler effect, and data would arrive at varying rates right?

 

[gsaldivar]

Each packet of data transmitted by your cell phone contains a tiny piece of digitally encoded audio, a time-code and subscriber ID information that allows your network to reconstruct the audio signal accurately and seamlessly in real-time. The audio signal itself is protected from analog distortion, signal reflection, doppler effect using this method.

More info here:

http://electronics.howstuffworks.com/cell-phone5.htm

http://electronics.howstuffworks.com/cell-phone15.htm

 

[gsaldivar]

Extensive info here:

http://www.privateline.com/Cellbasics/nol-ch09.pdf (PDF)

http://www.privateline.com/PCS/GSM0.html

http://www.privateline.com/Switching/packet.html

 

[Bassyhead]

With digital cell phones this problem is no longer an issue, but with older analog cell phones I would think that the speed of light is probably high enough that the parties on both sides of the line wouldn't be able to tell the difference.

 

[Mark R]

This hasn't historically been much of a problem because of the low data rates of current digital phones.

The new 3G phones are a bit more sensitive - longer data packets are more sensitive to Doppler shift. E.g. the UMTS system only specifies at 2Mbps link for mobile-station velocities of less than about 10 km/h, dropping to 144 kbps at 500 km/h.