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RF carriers separation calculation (gsm)

Discussion in 'Electronic Design' started by Steve Sousa, Sep 24, 2009.

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  1. Steve Sousa

    Steve Sousa Guest

    Hello:

    The problem is what is the necessary channel separation to transmit several
    gsm signals on the same medium (direct intensity modulation on an optic
    fiber).
    I have searched all over books, google, I've read the etsi docs but i can't
    find it. I've even asked teachers and got nowhere!
    I'm looking for some sort of "guard-band" spec i can use, imagine the usual
    BW plot, a rectangle:

    ----------- -----------
    | | | | | |
    --------------------- how close? ---------------------
    -bw/2 fc bw/2 -bw/2 fc bw/2


    Say i have a gsm signal with a BW of 24 MHz and carrier at 890-914. How
    close can i set another carrier? 866-890 seems too close, but i don't want
    to pull a number from the air and say "MHz between them is fine", there has
    to be some sort of calculation/rule/norm that applies, my understanding from
    ITU-R is that from 470 MHz to 2450 MHz transmitter tolerance for mobile
    stations is 500 KHz, but I'm not sure this is it. I know that the first
    channel is not used, so that would give 200 KHz. Or do i have to estimate
    some sort of filter crossing bw/2 at -3db and some maximum attenuation at
    some harmonic beyond that, like radio-amateurs use (something around -50db?)
    What if one is gsm and the other a different modulation?

    Suggestions for a more appropriate group are welcome.

    Thank you.

    I know you'll ask, this is not homework but it is part of my studies, an
    extra-curricular activity that i now see might be way above my head.

    Best Regards

    Steve Sousa
     
  2. JosephKK

    JosephKK Guest

    You might start here:

    http://www.3gpp.org/
     
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