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Revelation

Discussion in 'alt.cellular.verizon' started by Karen, Feb 27, 2004.

  1. matt weber

    matt weber Guest

    On Sun, 29 Feb 2004 02:44:13 GMT, "Karen" <kconan@bigfoot.com> wrote:

    >So Matt, you seem to imply (if not state in a very articulate, intelligent
    >manner) that GSM (at least today) is superior to CDMA at least as far as
    >"sound quality" is concerned (quality being a very subjective term).


    No, only that in the wost case of traffic, GSM will always provide
    better voice quality simply because of the available bandwidth to
    drive the codec. CDMA uses a variable bit rate encoder because as the
    CDMA network loads up, the channel capacity per call goes down,
    because unlike GSM, the channel capacity per call is not fixed. The
    overal channel capacity is essentially fixed, but unlike a true TDMA
    envirornment it is not fixed per caller. As the CDMA available
    bandwidth per call goes down, it degrades the input to the CODEC, so
    the voice quality starts to deteriorate. Listen to a real networks
    tranmission at 5kb verus 16kb and you will get the idea.

    When the CDMA network is not very heavily loaded., it is likely to
    offer better voice quality than GSM because of the higher underlaying
    data rate into the CODEC, however the improvement in voice quality as
    you go past about 10,000 bits per seconds isn't all that obvious,
    especially if you talking about male voices. The basic information
    content of speech just isn't all that high, and in male speech is
    concentrated in the lower part of the telephone bandwidth.


    Can you readily tell the difference between a picture sent in 16
    colour mode (65K colours) from 24 bit colour mode (2Million colours)?
    Not really. You increased the bandwidth required by 50%, but you
    didn't increase the useful information content by 50% did you?

    Later versions of TDMA, especially those used on undersea cables use
    demand assigned time slots, and heavily loaded systems start dropping
    parts of words etc as the demand for time slots exceeds those
    available. Quality of the voice doesn't go down, you just start to
    lose parts of words instead!



    IN fact a number of providers, such as Telstra australia provide an
    alternate overseas access code for data calls, these are routed on
    facilities with a different set of assumptions driving load limits.
     



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