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what could be the raeson?

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  • #51763 Reply

    you are at a distance of say 50m from a BTS, say BTS-A. BCCH is 78 and the Rxlevel is -49dbm. Neighbour list has another BCCH 71 with Rxlevel=88dBm, say BTS-B.

    You initiate a call from BTS-A. But immediately it is snatched by BTS-B. And you have a very poor Rxqual 6 or 7. But the call will continues on this BCCH(71) only.You end the call and TEMS will get back to the serving cell-A(BCCH=78).

    I mean what could be the reason for this snatching.?

    I lock the cell-B(BCCH=71). Again i tried the call and this time the TCH allocated to me was of the same cell which i suppose to ie cell-A(BCCH=78).

    After that i went to cell-B(BCCH=71). And i initiated a call. The call was latched to the same cell ie cell-B. And i started moving towards the cell-A. But to my surprise even after reaching the distance of 20m from cell-A my call was not handed over by the cell-B(BCCH=71).

    And this is happening with other cells also.

    i want to know what could be the reason for this.

    1) Problem with the hardware with cell-B?

    2) Problem with the parameter of cell-B

    or anything else?

    Pl note all the adjacent cell definitions have been checked and found correct.



    #51764 Reply

    Your SDCCH Might be interfered…try the following

    Try adding a SDCCH to the TRX other than the BCCH carrier for BTSA(BCCH78)

    #51765 Reply

    i would suspect:
    1- handover parameters : the cell B is the preferred cell, and cell A will “push” MS towards it. I don’t which vendor you’re using (i forgot), but it usually has to do with different layers (overlaid, underlaid) or different frequencies (1800 is preferred)

    2- is that a “directed retry” ? the call setup is performed on cell A : is the TCH allocated on cell A for a while SDCCH(cell A) -> TCH(cell A) -> TCH(cell B), or is there actually a SDCCH(cell A) –> TCH(cell B) directly ? You can check this by looking at the Layer 3 messages.

    your experiment is very good : it shows that cell A can indeed carry the call if needed –> it means that the cell A is not interfered (unless cell B is the interferer ???) and cell A is not congested.

    so IMO, check your directed retry and handovers parameters, along with the cells band and cell types.


    #51766 Reply

    Problem is solved.
    This is a hardware problem with the BOIA card(Nokia Ultrasite family BTS. The card is replaced and every thing is working fine now from Rxlevel to handovers both with neigbours as well as sectors of own.

    One thing more i want to say is that before the replacement of BOIA card i have obesrved on starnge thing with TEMS pocket.

    In IDLE mode the Rxlevel shown for the serving BCCH are around -4X or -5X. But the moment i initiate a call the Rxlevel goes to -88, -91dBM range. This happens right from the SDCCH allotment to TCH allotment.
    I end the call and the Rxlevels returns back to normal. ie -49 to -55 range.

    After changing the BOIA card(BASE OPERATION INTERFACE) this problem was solved.

    It is my simple perception that there is no reason for a MS to measure and show a wide difference in the Rxlevel of a BCCH carrier in IDLE vs DEDICATED mode…. if there is no movement of MS.

    Though the problem is solved but it is still under the category of HIT and trial…

    Wonders what equation exits between a control card of a BTS and the RADIO behavior.



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