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Low MCS usage

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  • #67902

    Hi Pix,
    please give me idea what can be the problem ? In one sector , the usage of higher EDGE coding schemes suddenly decreased.What can be the reasons? I know that in the poor radio condition the used MSC are lower but the KPI for data and voice looks OK…Did you have any idea how to resolve this case?


    hi vang,

    first you must rule out that only 1 MS is the cause of the problem. Check that the volume of data is about the same than previous days. My idea is that your cell has a low traffic, usually, but on that day 1 guy is heavily using EGPRS. Therefore just one person modifies the whole QoS stats for that cell.

    then, check if the other cells in the BSC also face the same problem.

    if yes – > probably an Ater congestion

    if not…

    then it starts to be interesting. either you modified how the traffic is allocated on your TRX (pref_mark, frequency hopping, MAX PDCH, etc.), or one TRX is faulty.
    In first case – check all parameters changes that occured lately
    In second case – restart your TRX’s

    Those are the only ideas that comes up, but the solution might not be here. Starting from there, however, I’m sure you’ll find other leads.

    For info, MCS is chosen based on TRX capabilities, radio quality and Ater load.



    Hi Pix,
    the problem with low MCS usage is just for DL in one cell with 2TRXs.In UL there is no problem with MCS9 usage. From the measurements I see that the MCS distribution is 30-40% for MCS3 and MCS4 and just 2-3% for MCS9.The parameter PS_PREF_BCCH_TRX is “Highest priority on BCCH TRX” and the BCCH TRX is TRAGE. The MAX_PDCH are 12 and MIN_PDCH is one. In this cell there is no Hopping activated.



    could you check your retransmission rate in DL ?
    I think it is available per MCS, isn’t it ?
    Basically, you may want to check your DL quality (BER). The voice is not a good indication on BER because it is very resistant (C/I around 9dB is ok). MCS9 on the other is very sensitive and requires a C/I around 30dB !

Viewing 4 posts - 1 through 4 (of 4 total)
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