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SDCCH Drop very high

Viewing 9 posts - 1 through 9 (of 9 total)
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  • #46880 Reply
    CHAI
    Guest

    Hi need help here, regarding one cell with high sdcch drop. There are 3 cells with 4 configured each , the tre health of the other 2 cells are ok, they have good hosr, low cdr (sdcch and tch) but i noticed that cell 1 is different compared to other cells.

    I divide the total counts of successful sdcch seizure and sdcch attempts seizure. I found out that the successful sdcch rate is low that results high sdcch drop.

    I checked per tre, and the best tre with the best stats was the mbcch tre, but the other tre’s drop rate is higher compared to the mbcch tre.

    I checked the frequency channel of this cell if there’s any interference but no interfered channel.

    No hardware faults on the boards of the tre.

    Have you experience this kind of problem? hope you can share your ideas on how to solve this problem.

    Thanks.

    #46881 Reply
    Pix
    Guest

    hello chai,

    To sum up your post:
    Cell 1, TRE 1 = OK
    Cell 1, TRE 2 = SDCCH DROP
    Cell 1, TRE 3 = SDCCH DROP
    Cell 1, TRE 4 = SDCCH DROP
    Cell 2, OK
    Cell 3, OK

    1) on cell 1, all your TREs are carrying a SDCCH timeslot ? That is surprising ! If there is no SDCCH ts defined on a TRX, you can’t observe SDCCH drop on this TRX.

    2) Are those standard “static” SDCCH ts or dynamic SDCCH ts ?

    3) What about the tch mean duration on each TRX of cell 1 ? Do you see traffic on those TRX 2, 3 and 4 ? TCH DROP RATE is OK ?

    What you can try to do :
    1. perform drive-tests, perform call setups, and check for crossed sectors. Lock some TRX in order to force call setups on all different TRX.
    2. unlock all TRX and put all the sdcch timeslots on the m-BCCH TRX (and follow up QOS)

    And that’s it.. i hope it’s gonna help you.

    Regards,
    Pix

    #46882 Reply
    Gito Prastomo
    Guest

    1. If the problem is interference, kindly check DL interference per TRX (perform drivetest),check UL interference (on idle TCH per interference band on statistic counters), check handover attempt distribution (if high attempt due to quality -> interference)
    2. If the problem is DL/UL power, kindly check HO attempt distribution (HO due to UL/DL Level should high)->check the feeder connection,maybe cross feeder,check combiner connection and check TRX
    3. Kindly test with this, swap all TRX in to other cells, if the problem change to other cell->the problem is on the Module

    Goodluck

    #46883 Reply
    Gito Prastomo
    Guest

    1. it must be ensured that there is no SDCCH Blocking and AGCH Loss

    #46884 Reply
    CHAI
    Guest

    Hi PIX,

    Thanks for your response.

    Here’s my reply on your question:
    1) on cell 1, all your TREs are carrying a SDCCH timeslot ? That is surprising ! If there is no SDCCH ts defined on a TRX, you can’t observe SDCCH drop on this TRX.

    =Yes, all TREs on Cell 1 have configured SDCCH TS.

    2) Are those standard “static” SDCCH ts or dynamic SDCCH ts ?

    = The configured SD TS are all static. We have dynamic ts too but we have a recovery time for this, TCH min recovery time for SDCCH to revert back to TCH channel.

    3) What about the tch mean duration on each TRX of cell 1 ? Do you see traffic on those TRX 2, 3 and 4 ? TCH DROP RATE is OK ?

    = Regarding the TCH DROP on TRE 2, 3, and 4. All is Ok but if you check on the immediate assignment success, it was quite low because of the high sd drop rate for the said TREs.

    My solution to that problem was to swapped all SD Channel TS to TCH channel TS (for all TREs except the MBCCH TRE). Then I put the 3 SD Channels to MBCCH TRX and swapped the TCH TRE. Then after one day, I checked the stats and the SD Drop
    rate of Cell 1 improved.

    My concern was how come the other TREs did not produce good SDCCH drop rate. What could be the possible problem? is it the TREs but if i checked the board no alarms/faults seen.

    Thank you,

    Br,

    CHAI

    #46885 Reply
    CHAI
    Guest

    Hi Gito,

    Thanks for your response.

    When you say SDCCH Blocking, it’s same with congestion or overflow right? If yes, cell1 has 0 SDCCH blocking.

    even if you swapped the TREs, I think it would be the same result. Since the 4 TREs are connected to one combiner unit.. i was thinking maybe the backplane has a problem..

    br,

    CHAI

    #46886 Reply
    Pix
    Guest

    Chai,

    It seems to me you totally isolated the problem from a possible “radio issue”. According to you, if there is a problem, it’s not due to the radio or TRE. (unless 3 TRX are faulty..? not probable)
    All other BTS elements than the TRE are common, so the problem should also happened on BCCH.

    So (in my opinion) it leaves three possibilities..

    1. RSL issue (SUM card, Abis nibbles allocation)
    Are those 3 TRE located on same RSL than the BCCH TRE ? Can find a problem on the signalling link on the Abis ? Can the dynamic Abis allocation provok some disturbance ?

    2. TCU issue (BSC)
    Are those 3 TRE located on same TCU than the BCCH TRE ? If it’s a different TCU, maybe there’s something going on there.

    3. N7 signalling (MSC)
    I’m not very familiar with this part .. i leave it to you 🙂

    Thanks for sharing this problem here and its solution (when you’ll find it !), sorry i can’t help much.

    let us know how it goes,
    pix

    #46887 Reply
    CHAI
    Guest

    Hi Pix,

    Actually here’s the configuration of the 4 TREs..

    4 TREs

    TRE0 TRE1 TRE2 TRE4
    |
    |
    |
    Simple Combining Unit (SCU)
    |
    |
    Combiner Distribution Unit (CDU)
    |
    |
    TX/RX of Antenna

    Anyways, thanks for the info.. once i solve the problem i will post it asap!

    thanks

    br,

    CHAI

    #46888 Reply
    Gito Prastomo
    Guest

    Hi,

    Is it synthesized hopp ?
    I have ever meet this problem on the network, and my solution is move sdcch channel into BCCH TRX.
    And I have recorded with K12 traces, and it was found that certain TS has problem,but I have swapped the TRX, still not solved.
    Then I try to Change the COBA,because the certain TRX belongs to the same COBA (The COBA was flicker), but the result is the same..
    Then summarize to customer that the backplane has problem….
    If your problem like above, I recommend to try change the backplane, but ensure that all database is correct including hopping type and setting

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