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Inteference

  • This topic has 12 replies, 1 voice, and was last updated 13 years ago by Usman.
Viewing 13 posts - 1 through 13 (of 13 total)
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  • #51833 Reply
    taqi
    Guest

    HI all

    can any one tell me the worst UL and DL power in Dbm.(when we calculate interference in Air interference)

    #51834 Reply
    pix
    Guest

    interference is measured in dB, a level is measured in dBm… a bad level is -110dBm, an interference cochannel is considered at c/i < 9dB

    #51835 Reply
    SHARKIE
    Guest

    Thank you for your response to my previous question.
    However, i have a case were am having a high SD drop on a number of sites. this i have observed for a few days now. i did define some missing neighbors on a few sites, what could be the reason for this high SD drop?

    #51836 Reply
    pix
    Guest

    bad coverage
    high interference
    hardware problems (TRX, BSC boards, path loss unbalance)

    #51837 Reply
    ZHT
    Guest

    Hi,
    Does anyone know how would the MS select which uplink frequency to communicate with the BS?

    If there are “alot” of MS making a call simultanuously at one BS, would there be a very bad uplink interference?

    #51838 Reply
    pix
    Guest

    zht,

    each mobile is assigned a particular frequency during the call setup. up to 8 MS can share one frequency in uplink.
    Each MS is also a particular timeslot on this frequency : a frequency is divided in 8 slots, one slot is a certain schedule of usage. So each MS will transmit UL signal at a certain time, at a certain frequency. This is GSM 🙂

    #51839 Reply
    ZHT
    Guest

    Thanks Pix for your prompt reply. Can the BS select which UL freq to assign to the MS? If there is a band pass filter installed in the system, would it be possible to programme the BS to select which UL freq to assign?

    #51840 Reply
    pix
    Guest

    GSM is based on FDMA : the frequency band is divided into channels of 200kHz each, with channels in downlink and channels in uplink.

    A pair of channels UL+DL is represented by a number “ARFCN”. In GSM900 there are 124 channels, from ARFCN=1 to ARFCN=124.

    ARFCN=1 correponds to UL=890.2 MHz and DL=935.2 MHz.

    When a MS setups a call, it is allocated on one timeslot of one ARFCN (in case of NO HOPPING). The allocation is usually decided by the BSC, which chooses which ARFCN and which timeslot.

    #51841 Reply
    ZHT
    Guest

    Hi Pix,
    How does the BSC select the UL frequency and timeslot for the MS to us?

    #51842 Reply
    pix
    Guest

    “for the ms to us” ??

    i’m not sure i understand…

    the BSC provides a timeslot to the MS, based on different criteria, such as voice/packet, hopping/not hopping, preference/no preference, dualrate/fullrate, etc etc

    you got to find the document that talks about that in your vendor…

    #51843 Reply
    navin
    Guest

    hi all. can any body hep me solve my network problem
    during conversation speech getting disturb and again gets normal within the same cell. (no handover case.)

    #51844 Reply
    pix
    Guest

    you should look for anything that could generate interference in the area (alarm system, anti theft mechanism, army radar, DECT office phones, etc..)

    #51845 Reply
    Usman
    Guest

    regarding the query that your voice/speech gets bad and that it again becomes normal you have to check few things:
    1. you should check the BER/RxQual and FER value.
    2. you should the C/I value because the voice quality usually gets worse due to interference.
    3. you need to check that if the hopping is enabled or not because then you need to check the MAIO and HSN to identify the faulty DRI

    these all reasons usually contribute to bad speech quality. even sometimes your mobile gets faulty and it is actually disrupting the voice quality.
    thnx and i hope you may find the good reason of bad quality.

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