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Wi-Fi VoIP At 80 mph

Posted by timothy on from the 130-km/h-in-mexico dept.

fredo123 writes "Almost faster than a speeding bullet. As reported in Muniwireless minutes ago, RoamAD and WI-VOD have tested mobile VOIP over Wi-Fi at over 130 Km/h over an 8km stretch of Interstate highway somewhere near the Mexican border. Gee... I wonder what this is for?" No need to guess: according to the MuniWireless link, "the network is for public safety personnel (police, fire, ambulance and border patrol) first, with various community agencies, schools, business and local residents being added as the deployment expands beyond its targeted coverage areas."

5 of 142 comments (clear)

  1. In other news... by fireman+sam · · Score: 2, Informative

    Cars have radios.

    In the harbour tunnel in Sydney traffic reports are broadcast to most frequencies in the FM scale so people listening to the radio will here them.

    Mind you it would be cool to have a VoIP broadcaster in the car so you can tell that jerk doing 20 under the speed limit to get the hell out of the overtaking lane.

    --
    it is only after a long journey that you know the strength of the horse.
  2. Re:How Fast? by DustMagnet · · Score: 5, Informative
    Light moves a lot faster than sound, so the amount of frequency shift is very small. A 2.4 GHz carrier would be shifted to 2.40000029 at 80 MPH.

    The frequencies of radios aren't very exact, so the tuners are designed to deal with some variation. Without knowing exactly how the tuners are designed (especially the filters), I can't answer your question, except to say, a whole lot faster than 80 MPH.

    --
    'SBEMAIL!' is better than a goat!!
  3. 80mph in Mexico by Anonymous Coward · · Score: 1, Informative

    VOIP over Wi-Fi at over 130 Km/h over an 8km stretch of Interstate highway somewhere near the Mexican border.

    Gee... I wonder what this is for?

    I could've used that last week... was visiting family in Mexico, and the border is a no-man's-land of U.S. and Mexican cellular zones fighting it out. At times I haven't been able to make cell calls 1 mile inside the U.S. because stupid TelMex signals were overpowering the weak AT&T signal down there.

    Plus the 80mph thing is not so outrageous. My SUV speedometer shows 110mph max. Let's just say that the manufacturer apparently didn't cheat me... (thanks to those nice, long, straight, lightly-policed freeways Mexico has built recently.)

  4. Re:How Fast? by Anonymous Coward · · Score: 1, Informative

    When going over the doppler effect in my second semester of Physics, I asked the prof why our radios don't get distorted by the doppler effect when we are driving. He swiftly made me look like an ass by doing what I should have done instead of thinking out loud: plugged the numbers into the equation. As such, the equation.

  5. Re:How Fast? by cy_a253 · · Score: 2, Informative

    Explanation here:

    http://en.wikipedia.org/wiki/Relativistic_Doppler_ effect