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Thread: How to solve Rxqual = 7 ( Call drop in GSM)

  1. #1
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    Unhappy How to solve Rxqual = 7 ( Call drop in GSM)

    Dear everyone

    DO you know how to solve drop call cause by bad Rxqual

    i have a IBC site and call drop happend most popular in 2 in total of 3 cells
    When i walk between those cell, rxlev down to -100dBm and Rxqual down to 7
    then call drop.

    Do you know how to solve it?
    Thanks
    Attached Images Attached Images
    Last edited by muctimonline; 2017-01-06 at 05:18 PM

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  3. #2
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    1 out of 1 members found this post helpful.

    Default Re: How to solve Rxqual = 7 ( Call drop in GSM)

    For this case, RxLevel and RxQuality are bad. So you need check low RxLevel first

    • Check power settings, power balance.
    • Check neighbor relations.
    • Check for any hardware faults, indicating high VSWR,....
    • Check the site position, antenna direction, position
    • Check if the cell has indoor coverage problem. If yes, add Indoor Site instead

    Then check Frequency Plan.

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  5. #3
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    Default Re: How to solve Rxqual = 7 ( Call drop in GSM)

    Quote Originally Posted by sohappy View Post
    For this case, RxLevel and RxQuality are bad. So you need check low RxLevel first

    • Check power settings, power balance.
    • Check neighbor relations.
    • Check for any hardware faults, indicating high VSWR,....
    • Check the site position, antenna direction, position
    • Check if the cell has indoor coverage problem. If yes, add Indoor Site instead

    Then check Frequency Plan.
    thank you for yr answer

    Check neighbor relations. -> Almost are same on 3 cells
    Check for any hardware faults, indicating high VSWR,.... -> No HW alarm fault, no VSWR
    Check the site position, antenna direction, position -> you can see on my attachment in #1? and give me your suggestion
    check Frequency Plan. -> could you guide me how to check Freq plan ?

    For power settings, power balance., i am asking the vendor to increase the power.

    Thank in advance

  6. #4
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    Default Re: How to solve Rxqual = 7 ( Call drop in GSM)

    Hi,

    First, check if when you have good rxlev so the Rxqual keeps bad value and ocurrs drop call. then its probably interference issue (check frecuencies used on BCCH, TCH)
    Second, if when you have good rxlev and rxqual so your problem is related to coverage (check power set on TRX, timing advanced, tilt) the idea is improve rxlev in this area.

    cheers!

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  8. #5
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    Default Re: How to solve Rxqual = 7 ( Call drop in GSM)

    Quote Originally Posted by jenriqp View Post
    Hi,

    First, check if when you have good rxlev so the Rxqual keeps bad value and ocurrs drop call. then its probably interference issue (check frecuencies used on BCCH, TCH)
    Second, if when you have good rxlev and rxqual so your problem is related to coverage (check power set on TRX, timing advanced, tilt) the idea is improve rxlev in this area.

    cheers!


    Hi

    In my case, when TCH and BCCH are different , the Rxlev and Rxqual gone to bad together.
    Does TCH freq is must be same as BCCH freq?
    And how to check TCH and BCCH freq plan are correct ?
    Please guide me!

    Please refer below image for more details
    Screenshot_2017-01-05-18-14-39.jpg
    Screenshot_2017-01-05-18-37-58.jpg

  9. #6
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    Default Re: How to solve Rxqual = 7 ( Call drop in GSM)

    BCCH and TCH are required to be diffrent, and you should have a differance of >= 3 channels on same sector ( ex.g. Arfcn BCCH: 1 - Arfcn TCH: 4).
    As we can see you may not only have a Quality Issue, but rather have a coverage issue, RxLev of -109dBm is not enough to have a proper working voice service.

    You can confirm your coverage issue by doing an idle mode measurment or even better, doing a scan in-order to find out if you got missing neighbors that are stronger on that area.

    In case of a IBS with a DAS, try to add an additional antenna in-order to improve your RxLev.

    In case of bad RxQual (4-7) with levels of RxLev (>= 90dBm) do following.
    - Disable DL Power Control, check for improvement
    - Change BCCH/TCH Arfcn, check for improvement
    - Change RF Unit
    ...
    thanks, for reading.

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  11. #7
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    Default Re: How to solve Rxqual = 7 ( Call drop in GSM)

    Hi, do you have drops on TCH frequency only, i.e. ARFCN 694? What is the rxlev in idle mode at the same spot? if it much higher than rxlev you see in connected mode, most likely cause is that IBS is only allowing ARFCN 701 to go through antenna system, but it is not amplifying or attenuating 694. In that case you'll have to check IBS config. It could be that you have RF unit with 2 TX ports, and configuration is that BCCH is on 1 port, and TCH is on another. If only 1 port of RF unit is connected to IBS, then you could have similar situation.

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  13. #8
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    Default Re: How to solve Rxqual = 7 ( Call drop in GSM)

    Quote Originally Posted by pathloss View Post
    BCCH and TCH are required to be diffrent, and you should have a differance of >= 3 channels on same sector ( ex.g. Arfcn BCCH: 1 - Arfcn TCH: 4).
    As we can see you may not only have a Quality Issue, but rather have a coverage issue, RxLev of -109dBm is not enough to have a proper working voice service.

    You can confirm your coverage issue by doing an idle mode measurment or even better, doing a scan in-order to find out if you got missing neighbors that are stronger on that area.

    In case of a IBS with a DAS, try to add an additional antenna in-order to improve your RxLev.

    In case of bad RxQual (4-7) with levels of RxLev (>= 90dBm) do following.
    - Disable DL Power Control, check for improvement
    - Change BCCH/TCH Arfcn, check for improvement
    - Change RF Unit
    ...
    My case is DAS system, i requested to add more antenna to improve Rxlev. Now they are making new design for this IBC
    my building has 3 cells and CDR occurred only on 1 cell

    Could you make clear for me about "doing a scan in-order to find out if you got missing neighbors that are stronger on that area." ???
    I checked and found that 3 cells have same neighbors and same threshold.
    Our system is Huawei it is the best if you share me the guide.
    I am appriated for that
    thanks

  14. #9
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    Default Re: How to solve Rxqual = 7 ( Call drop in GSM)

    Quote Originally Posted by giegala View Post
    Hi, do you have drops on TCH frequency only, i.e. ARFCN 694? What is the rxlev in idle mode at the same spot? if it much higher than rxlev you see in connected mode, most likely cause is that IBS is only allowing ARFCN 701 to go through antenna system, but it is not amplifying or attenuating 694. In that case you'll have to check IBS config. It could be that you have RF unit with 2 TX ports, and configuration is that BCCH is on 1 port, and TCH is on another. If only 1 port of RF unit is connected to IBS, then you could have similar situation.
    you mean there is a problem wiht DAS configuration?

  15. #10
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    Default Re: How to solve Rxqual = 7 ( Call drop in GSM)

    Quote Originally Posted by muctimonline View Post
    My case is DAS system, i requested to add more antenna to improve Rxlev. Now they are making new design for this IBC
    my building has 3 cells and CDR occurred only on 1 cell

    Could you make clear for me about "doing a scan in-order to find out if you got missing neighbors that are stronger on that area." ???
    I checked and found that 3 cells have same neighbors and same threshold.
    Our system is Huawei it is the best if you share me the guide.
    I am appriated for that
    thanks
    Hi,

    As the drops affect only one cell, it's good to focus one that one.

    1) You did provide feedback to your planning team, that there is a no coverage/ weak coverage zone.
    Did you clearly identify the area of no coverage? (Often it's in the basement, parking area)
    2) In order to do a scan, you will need a handset (or dedicated scanner) that is capable of it, for example TEMS (That is what you seem to use) or Nemo Phones (W995, K800i etc). Than you need to go back and do a Walk-Test.
    - Do you know the channels (ARFCN's) that the MNO has licenced? You will need to scan them.
    - Some older TEMS Phones had a licence for on device scanning (W995), new TEMS Phones do not have that feature, but as alternative can be connected to a Laptop with TEMS Investigation. In Investigation you define the channels that need to be scanned, and you can use it for post analysis.

    I do not really have a "How to guide" for such a task. It's one of the basic tasks when doing RNP & RNO.

    3) It is as well possible that your cell provides coverage outside of the building and that you catch fast moving devices, that can't handover to another cell. This can lead to a higher CDR.

    Unfortunatly I'm not familiar with Huawei and I dont know a method to perform scan via OSS.

    By the way OSS can confirm Interference via ICM (Idle Channel Measurments), if your cell has high interferance you will see it there to (IB3 to IB5).

    BR,
    thanks, for reading.

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