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DROP DUE TO LOW SS

Viewing 15 posts - 1 through 15 (of 20 total)
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  • #59739 Reply
    raman
    Guest

    hi,
    we are facing SD drops due to low ss which are major reasons vendor is E/////….. how to imporve drops without decreasing traffic so much ….

    #59740 Reply
    AliAsgher
    Guest

    In case your cell is Multiband, check if drops are high on 1800. Modify tilts accordingly. Sometimes if OL is uptilted too much it drags calls (as its SS is good) but when it HOs to the UL subcell (on which tilts were somewhat aggressive and it had low SS) the call gets dropped.

    Check your LOL settings too. Are these open area cells?

    If the drop reason is Low SS Uplink, then perhaps your path balance is disturbed. You can confirm this via MRR.

    Oh, so much information is needed and so much can be done.

    #59741 Reply
    raman
    Guest

    it’s single band cell…
    secondly, in E/// SD drop is pegged into low ss counter now i don’t know whether it’s uplink or downlink ….

    in mrr major samples in 7 to 11 km
    how to check path imbalance i do have pathlossul(,) & pathloss dl(,) but how to check then plz help….

    #59742 Reply
    safar
    Guest

    Hi,

    here i have also dual band cell in eric vendor. so which one is best lol setting lol= tx power -rx level.

    so if i want to keep trffic on 1800 and less traffic on 900 then lol should be high means more than 130?

    but here in this case i am getting drop?

    so ali plz help require.

    #59743 Reply
    AliAsgher
    Guest

    @Raman

    Very sorry bro, my mistake. I didn;t see you are talking about SD Drops. I thought you are talking about TCH Drops.
    Well if you are having SD Drops due to low SS then it might be the cause of overshooting cell. Verify the tilts of the cell. Also check if your SDCCH are defined on Hopping TRX? If so, try moving the SDCCH on the BCCH trx. This may improve low SS SD Drops (Although you may see Bad Quality drops if your BCCH frequency is not clean).

    @Safar
    Brother, if you are increasing LOL then you should also decrease FBOFFSET by the same amount. Else the border (OL -> UL handover) will be extended and OL will try to keep the call at very low Rxlevel too. This may cause call drops.
    We have tried to increase LOL (and decrease FBOFFSET) for 1800 traffic shifting in our network. But in some cells where drop rate increases, we uptilt the 1800 by 1 degree. This will improve the TCH Drop Rate.

    #59744 Reply
    raman
    Guest

    problem is that if i give more tilt there may be traffic reduction ….so what to do ?

    #59745 Reply
    safar
    Guest

    hi,

    But by incresing lol call will be remain on 1800 not by rx level but remain on by pathloss? Is it ok?

    Or can u give me standard value of lol in dual band cell. We are keeping 130.

    And buddy can u tell me whats function of fboffset exaxtly and if i increase lol to 140 then what should be fboffset?

    #59746 Reply
    safar
    Guest

    hi ali,

    Can u help me regarding trailing messege?

    #59747 Reply
    AliAsgher
    Guest

    Yes Safar, LOL is based on the path loss criteria. Now assuming you are using BSTXPWR=43 (1800), with LOL=140 and LOLHYST=3

    We will get following values.

    1) UL to OL (Handover Border) will be, Rxlevel (DL) >= -[140-3-43].
    Rxlev(DL) >= -94.
    (Now this means your UL will try to handover call to OL even if RXlevel are as low as -93,-94 dbm. This means that rxlev at OL will be even lesser due to higher pathloss of higher frequencies. This will decrease your assignment to OL success rates.

    2) FBOFFS is used to decide when will the OL handover the call to UL. (It can be eliminated if you include the OWN BCCH frequency in the active MF LIST).
    If not using FBOFFS but including own BCCH in active MF List, following formula is used
    Rxlevel(DL) < -(LOL + LOLHYST - BSTXPWR) Rxlevel(DL) < -(140+3-43) Rxlevel(DL) < -(100) 3) Now, as you can see, the borders of UL OL are UL to OL -> -94 dBm
    OL to UL -> -100 dBm.

    Although the OL to UL limit seems somewhat reasonable, UL to OL is far too stretched. This will be degrading KPIs of your cells.
    You should, make the UL to OL limit somewhere near -80->-85dBm and OL to UL limit -99 dBm. This will give you a nice balance between subcell utilization and call drop rates.

    #59748 Reply
    AliAsgher
    Guest

    *Correction.

    I somehow used LOL=140 for my calculations. You specified 130.

    UL to OL = -84dBm (Value seems fine)
    But as you said, by increasing it your drop rate increased. It is due to handing over call to OL even at lower UL levels.

    You should try to uptilt the OL by 1 degree. (in case you are not using Own BCCH in your MF list). This will make OL levels better slightly and OL will retain call longer. (However if you see increased drop rates due to call dragging, you will have to revert the settings. This is very much dependent on terrain profile)

    #59749 Reply
    safar
    Guest

    Hi ali,

    As per my knowledge lol formula is like this lol = tx power – rx level.

    so by keeping lol 140 1800 call will continue upto its lol 140 and after 140 onwards call will continue on 900 . ok.

    here we have dual band cell (900 and 1800) and bcch is on 900.
    tx power = 45

    so by taking above value if my rx level is 94 then as per formula

    lol = tx power (45) – rx level(-94)
    = 139 so here call will remain on 1800

    and when level will reach -95 or onwards then as per lol call will go on 900 is it ok ali?

    so i want to know with htis setting what should be fboffset value here we have its value 6

    and can u explain whats fboffset exactly function ?still not getting? plzzz. and also tell abt tilt u are telling.

    #59750 Reply
    AliAsgher
    Guest

    Dear Safar,

    LOL criteria can be given as below

    UL -> OL
    L < LOL - LOLHYST (Where L is path loss and is equal to BSTXPWR - RXlev) OL -> UL
    L > LOL + LOLHYST (Where L is pathloss and is equal to BSTXPWR – Rxlev).

    In Locating algorithm when measuring basic Rxlevel, FBOFFSP is used to compensate between different frequency bands and hence a FBOFFS of 6 would mean that you are telling Locating that your BCCH is 6 dB better than your 1800 (or the OL band).

    Hence when the call will return from OL to UL, the SS Downlink will be measured on 1800, and then 900 SS will be predicted (by subtracting FBOFFS) and then the criteria will be evaluated.

    In case you dont want to use FBOFFS, then you can include the BCCH frequency of the cell in its own Active MF LIST. In this way cell will be measuring its own 900 strength (as it is in neighbor list) and no FBOFFS (Frequency band compensation) will be needed as you exactly know the BCCH SS.

    In some cases when your antenna allows different tilts for different bands, you can keep your OL uptilted than your UL so that good OL coverage makes it keep traffic longer (increasing its utilization). But this may also increased DCR as it will tend to increased call dragging while on OL.

    I hope it helps.

    #59751 Reply
    safar
    Guest

    hi ali,
    I think the conditions given by u are in actually reverse.u said L< lol - lolhys then traffic will be on ul .but man its reverse.here if i am decreasing lol from 140 to 110 then my ol traffic is increased.so can u clear this one? And can u explain fboffset with some example plz?

    #59752 Reply
    safar
    Guest

    Hi ali,

    share ur knowledge.

    #59753 Reply
    AliAsgher
    Guest

    Dear Safar,

    The conditions given are correct. Currently I am unable to think of any situation of how OL utilization increased if you decreased LOL.

    In Locating algorithm, FBOFFS is used to estimate BCCH SS if your call is on OL subcell. Thus a value of FBOFFS = 12 means that you are telling Locating that UL is 12 dB better than OL.

Viewing 15 posts - 1 through 15 (of 20 total)
Reply To: DROP DUE TO LOW SS
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