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Viewing 9 posts - 1 through 9 (of 9 total)
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  • #51999

    Hi everybody, i’m working hardly on GSM / UMTS900 coexistence, and i face some problems regarding the caution distance between the two technology.
    does somebody have such info about the distance i need between the 5MHz band UMTS900 sites and the 2G BTS using the same frequencies?

    Thanks a lot?


    Hello yrrah,

    i think this is stated in a 3GPP document, but i forgot the reference. maybe you can find it by yourself ? It should be in the serie 25:
    TR 25.942 Radio Frequency (RF) system scenarios
    TR 25.816 UMTS 900 MHz Work Item technical report
    or somewhere…

    Da Architect

    Dear yrrah,

    you are subject to:
    Intermodulation Interference!!!



    thanks Da Architect.
    ok when you are talking about Intermodulation Interference, but do you have any idea of the distance (in km)between the site in UMTS900 and a 2G site using one af the frequencies i free?

    Thnaks PIX, i check in the 3GPP documents, but they don’t talk about the distance.

    I’ve heard about 30 kms to avoid interference oevr the 3G UE.
    I’v also heard about going over the 2nd neighbours.

    Does anybody have such info?

    Thanks a lot for your replies.


    hello yrrah,

    i thought you were talking about co-location on the same mast ! ok if both sites are using exactly the same frequencies, then you must ensure that the RxLev(GSM900) falls below a certain threshold so it doesn’t affect the quality of the UMTS (Ec/No). What is the Ec/No limit for UMTS ?

    Then there is no perfect answer : you need to limit the coverage of your GSM900 cell, with downtilt, and/or lower height of antenna, and/or power reduction, etc, so that the RxLev(GSM900) is below the threshold at a certain distance.

    It depends on radio coverage, basically.

    In a typical urban area, with good site design, it is quite safe to say that after 3 or 4km, the GSM site doesn’t provide any coverage (rxlev < -110dBm)


    thanks PIX for your answer.
    I have the constraint not to touch my 2G sites.
    For urban areas, i made some calculations, and i achieve the same distance as you suggest, 3-4 km for 2G coverage.For the 3G coverage, it’s about the same. so, i have to use the same frequencies at about 8 kms.
    but for rural, with the propagation models, i face some difficulties, because, the 2G coverage is about 30 km. so i need to use the same frequencies on the 2G network at about 40 kms.
    i just wanted to know if some of you guys have made some studies about it.

    Thanks again



    mmm, ok, now this is clear 🙂 on my side, i don’t have any study… as UMTS 900 is still new, i’m afraid the few engineers that performed this kind of studies have low probability to come on this website and answer you.

    if i were you, i would rely on drive-tests for the rural sites –> The distance between UMTS900 and GSM900 in rural areas (with “xx” km coverage per site) should be more than 2 times “xx” km. You might face some interference at the cell border, but closer to the antennas, the quality should be alright.

    Beware that a GSM900 site can cover much more than 30km under the right conditions. The prediction tools are usually not reliable at such BTS-MS distances. Especially the formulas such as Okumura-Hata & co. That’s why a drive test is recommended.


    thanks PIX.
    that’s exactly what i’m to do.
    I wille let you know the results as soon as i get them.



    if you can share your results, that would be really really great ! thanks 🙂

Viewing 9 posts - 1 through 9 (of 9 total)
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