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NSN BTS TCH AND SDCCH DROP ISSUE

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  • #65807 Reply
    taupaji
    Guest

    I have a problem with a certain area consisting of 30 bts which has high TCH, SDCCH and HO drop. Most of the drop reasons are being noted by the counter TC_RADIO_FAIL and TC_RADIO_FAIL_OLD(HO FAIL). Avg. LINK BALANCE is varying in the range +/-20 for these sites. My query is can calls picked up from far away cause link imbalance?? And what should be the average MS power value picked by a BTS be?? these range from 0 to around 66..

    And there is another set of BTS which are being noted by the counter TC_LAPD_FAIL. Can you

    #65808 Reply
    taupaji
    Guest

    contd…

    And there is another set of BTS which are being noted by the counter TC_LAPD_FAIL. Can someone help me with the reasons causing these failures..

    #65809 Reply
    pix
    Guest

    hi,

    Link balance in NSN… What should be the “right” value ? LB = 0dB ?
    If you see such variations, it is very strange, but in any case it means that your BTS or feeders or antenna hardware is faulty. Probably some BTS baords, such as TRX or Combiners.

    Link Unbalance will cause MS to loose coverage, even though they are located within the serving cell area. It will not cause faraway MS to be connected. That’s quite the opposite : nearby MS can’t get a good signal anymore.

    The link could be unbalanced in DL : MS can’t hear BTS,
    or it could be unbalanced in UL : BTS can’t hear the MS.
    Results are the same : connection is poor.

    MS power ? I think you mean “UL RXLEV” measured by the BTS ?
    0 = -110dBm
    1= – 109dBm
    2= -108dBm

    63= -47dBm
    66 = -44dBm (but that’s weird : the range should stop at 63)

    TC LAPD FAIL : probabaly an ABIS failure or ATER failure.

    cheers
    pix

    #65810 Reply
    taupaji
    Guest

    thanks…
    also the counter TC_RADIO_FAIL amounts to around 50% of all TCH faliures in my network. I am checking
    1) ADJACENCIES WITH HIGH HO FALIURE RATIO
    2) CELLS BY DL AND UL LEVEL BALANCE (CELL LEVEL) the values I quoted are from these. they are cell level. I think I need to go TRX level here.
    3) DISTANCE RANGE DISTRIBUTION PER CELL (TA SHEET)
    Some people say there’s some issue in the Sync. Will BSC oscillator control word monitoring help??
    What else can I do to resolve these?? Any advice(as absurd as it may be) is welcome…

    #65811 Reply
    taupaji
    Guest

    And overall TCH drop and SD drop is noticed to be directly proportional to traffic in all hierarchies ie from cell to network. Congestion not noticed much.

    #65812 Reply
    pix
    Guest

    hi,

    if there is SYC issue, then the incoming HO failure for that specific BTS must be very high ! Whereas the HO outgoing is ok.

    I told you already : if you have link unbalance, then your hw is faulty.
    check your hw…
    yes, please, check link unbalance per trx, in order to detect faulty trx and faulty combiners.

    what else do you need to know ?

    regards
    pix

    #65813 Reply
    taupaji
    Guest

    thanks…
    yup, HO is comparatively OK in these cells.. so no sync issue..

    And I wanted to know the tolerable limit of Link balance and MS power??

    Thanks again.. New in town… so very desperate… 🙂

    #65814 Reply
    taupaji
    Guest

    And tolerable ul/dl interference..??

    #65815 Reply
    pix
    Guest

    link balance is ok between -5dB and +8dB (= around 0)
    If outside of these boundaries = hardware problem in your BTS.

    MS power is acceptable between -47dBm and -90dBm

    It’s not so happy between -90dBm and -100dBm

    It’s bad below -100dBm.

    interference : what’s your measurement unit ?
    C/I ?
    C/I > 9dB
    or what ? HO_cause_interference ?
    should be less than 5%.

    regards
    pix

    #65816 Reply
    taupaji
    Guest

    thanks pix… problem solved in some cases…

    My work asks me to target network wise so I still have a few queries?

    Here we have noticed that the days traffic is more we have more tch drops but congestion remains same…
    Can the link imbalance also cause tch drop to be proportional to traffic increase?? Or can TA overshoot be the expected problem??
    or is it subjective??

    Thanks again.. 🙂

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