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SD Failure please help

Viewing 15 posts - 1 through 15 (of 37 total)
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  • #46003 Reply
    Man
    Guest

    In the failure submenu we have something called ghost

    What are ghosts .Please see the exact description

    other (fails, ghosts) …………………../sd_1a

    and how can we reduce it

    #46004 Reply
    Pix
    Guest

    Ghost.. it means that the failure occurs on a “ghost” request. It is simply a random radio signal that was received by the BTS, looking like a RACH access. The BTS process it as a “real” RACH request, starting a SDCCH assignment.

    The SDCCH assignment fails because the RACH is actually a “ghost”… there is no answer from the Air interface after the BTS sent its AGCH messages.

    To reduce it, you can increase the RXLEV ACCESS MIN threshold. Frankly, as long as it doesn’t induce RACH congestion, you shouldn’t worry too much. Keep the SDCCH failures due to ghost within reasonnable amount (< 10% for instance).

    #46005 Reply
    yogesh_rf
    Guest

    hi man,
    as the traffic will increase on site phantom RACH pblm. will be solved,this type of problem normally comes on stand alone sites…..

    BR//
    Yogesh_rf

    #46006 Reply
    Suresh
    Guest

    Using .3,.6,1.2,1.8,2.4 metre dia minilink antennas the capacity of E1 same or various to size.. plz explain me… i am lot of confusion..

    #46007 Reply
    Sumit Verma
    Guest

    what is phantom RACH

    #46008 Reply
    akefa
    Guest

    sdcch does not fail due to phantom rach ! unless t3101 expiration is considered one of the sdcch drop reasons. there is no counter counts how many immediate assignment failed due to timer expiration?! if no, then how could an engineer keep it under 10% ?!

    #46009 Reply
    Flo
    Guest

    Hello all,

    What do you think about this KPI to estimate SDCCH assignment failure due to RACH phantom ?

    ((Number of Channel Required) – (Number of Immediate Assignment + Number of Immediate Assignment Failures due to congestion) + (Number of UL access requests on CCCH when the MS is in packet idle mode))* ( 6 / 2 )

    Tx U

    #46010 Reply
    Flo
    Guest

    Up;

    I wonder how to estimate or calculate dummy RACH, any idea ?

    tx

    #46011 Reply
    Jo
    Guest

    Hi

    Phantom RACH’s are also caused by a site spilling and also has a direct influence on the CSSR of the particular BTS.

    #46012 Reply
    pix
    Guest

    akefa, to answer your msg from 24 june,

    a sdcch failure is not a sdcch drop 🙂 those are 2 different things.

    Failure occurs during the attempt to seize the SDCCH channel.

    Drop occurs during the usage of the SDCCH channel.

    #46013 Reply
    optimiser
    Guest

    You can check the Timing Advance of your cell. Sometimes, when you have phantom rachs, you have very big TA which are not justified (but check that this is not a resurgence case.

    Generally, the problemm can be solved by reducing the cell size (rach_ta_filter)

    #46014 Reply
    Azzazi_RFoptimization_eng
    Guest

    MS_REQ_for_location_update suddenly increase, and Immediate_assigne_fail_rate increase, hence the CSSR is affected.
    this case maybe solved by reseting the cell, or changing the BSIC of the cell.
    and some times, it is solved alone without any action.

    #46015 Reply
    TNS
    Guest

    Hi, all.

    When the MS executes a HO command, it sends an Access Burst ( transmitting with full power ) when it seizes its TS in the target cell.
    The energy shape of Access Burst is identical to the Random Access Burst.
    So it’s possible to be decoded as goast RACH from some cell with the same BCCH freq (as the TS freq of the target cell ) far from the HO place…

    BR

    #46016 Reply
    AAK
    Guest

    Dear Optimizer /PIX

    I am also facing the same issue of Ghost / Phantom RACH.
    But after seeing the TA stats, i couldnt find any large TA on those hours where we have Many Location Update attempts, and then Immediate assignment failures.
    So now how can i make sure that is it Phantom RACH.
    And also what is the solution to minimize it. is it.
    1. Optimize BSIC of the cell
    2. Reduce TA (But in my case no excessive TA reported)

    Kindly reply

    Thanks

    AAK

    #46017 Reply
    TNS
    Guest

    Hi, AAK.

    Pix, correct me if I’m wrong.

    The GSM standard say that it’s normal to have SDCCH failure up to 10% per day.
    It’s based to the number of RACH subTSs per day, the probability the noise to be decoded as Channel Request ( Ghost RACH )and the probability to have a valid request reason…
    It’s clear visible during the night ( when the radio interface is “not loaded”).

    1.The BSIC is not involved in the Channel Request. Optimize the BCCH freq.
    2. I’m not a fan of the TA Filtering and I don’t know someone who uses this approach efficient.

    Downtilt could prevent Ghost RACH in my opinion but may be whit other consequenses…

    BR

Viewing 15 posts - 1 through 15 (of 37 total)
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