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C/I and C/A

Viewing 8 posts - 1 through 8 (of 8 total)
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  • #52337 Reply
    new engineer

    can any body explain for detail expalnation for C/I and C/A and what is the threshold by example in order to see in TEMS it is come from adjacent frequency or co frequency

    #52338 Reply


    i forgot about the details, but i remember the help (F1) of TEMS is very detailed about this. They give the method of calculation of C/A and C/I.

    i remember that the C/I is not the real C/I though, it’s just an approximation.

    C(co)/I > 9dB is needed in order to have good voice quality (above 12dB is even better)

    C(adj)/I > -9dB in order to have god voice quality (> -6dB, even better)

    #52339 Reply
    new engineer

    would you please give more detail about C/A let say I have BCCH 20 and adjacent BCCH is 19 what must be the Rxlevel difference between them it is -9db in this case the sdjacent BCCH some times will be stronger as you make by equation C-A>=-9 is it write?????????

    #52340 Reply

    BCCH(serving) = -70dBm

    the maximum value of an adjacent frequency should be -61dBm (-9dB difference)

    if the adj is -65dBm, then it’s totally fine.
    if the adj is -60dBm, then it’s bad.

    yes, the adjacent frequency is stronger than the serving frequency. it’s a very useful characteristic for frequency planning with multilayer (umbrella / micro)

    #52341 Reply
    new engineer

    thanks alot and just one more Question about the last sentence(it’s a very useful characteristic for frequency planning with multilayer (umbrella / micro)) what do you mean by this would you please give me more information?

    #52342 Reply

    hi all,
    anyone has a detailed doc about C/I, C/A and interference probability ? I’m exactly searching for curves : interference probability = f(C/I) and interference probability = f(C/A)

    thanks for help

    #52343 Reply

    Why C/A is -ve value whereas C/I is positive value?

    #52344 Reply

    C/A = rxlev(serving cell) – rxlev(adjacent channel)
    with adjacent channel = a channel which is adjacent to the serving channel by -1,-2,-3, +1, +2, +3 offset. (depends o your configuration)

    C/I = rxlev(serving cell) – rxlev(cochannel)
    with cochannel = same frequency as serving cell.

    they can all be +ve or -ve ! but it happens that in a gsm network, only the cochannel interference are very dangerous. So frequency planning needs to pay particular attention to C/I, and keep it as high as possible.

    for C/A, it can be negative since it won’t affect voice quality.

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