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Handover issue

Viewing 12 posts - 1 through 12 (of 12 total)
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  • 7th February 2011 at 22:46 #65718
    Fresh Opt
    Guest

    Hi,
    How can I make a call to not handover from one cell to another very frequently. There is a cell (Cell A) near a point where we have many complains (700-800 m) and is a best server about -75 to -80 dBm. Another cell (Cell B) is far from the point (about 3-4 km) at a higher altitude and is also with good level about -80 dBm. HO between them is mandatory, but, at the point of complains there are many pingpongs between them (according to DT measurements) and hence sense of low quality during the speak. RxQual is fine, NPO indicators show no interference. What should I do to maintain the call in cell A longer than in Cell B. I thought to play with HO Margin and CRO. What else? Vendor is ALU.
    Thanks in advance,
    Fresh Opt

    8th February 2011 at 05:41 #65719
    Jason
    Guest

    Hi Fresh;
    I think I would increase the hysteresis for that specific HO. I am not sure if this is what is meant by the HO Margin.

    JG

    8th February 2011 at 09:32 #65720
    Fresh Opt
    Guest

    Thanks Jason,
    both cells are in the same LAC, no need for increasing or decreasing hysteresis. Ho margin is a margin given in the relationship bw them (default is 5 dB).
    Regards,
    Fresh Opt

    8th February 2011 at 11:28 #65721
    Optim
    Guest

    Bro Fresh,

    HO Margin has nothing to do with LAC.

    What Jason said is the perfect way to retain call on your desired cell. Increase the hysteresis on cell A in relation with Cell B.

    This should DO !!

    Br//

    8th February 2011 at 11:43 #65722
    Fresh Opt
    Guest

    Optim,
    do you mean Cell Reselect Offset (CRO, as I proposed in my first post)? Hysteresis (in ALU) is applied only when a cell changes LA (Cell Reselect Hysteresis – CRH. CRO and CRH are used in different situations.
    Regards

    8th February 2011 at 11:48 #65723
    Optim
    Guest

    No my friend, CRO, CRH are for Idle Mode behaviours.

    Your case is Handover (in dedicated mode) You should look for relational parameters of Neighbors, “Handover Hysteris”. Ericsson has HIHYST and LOHYST for this purpose.

    I assume what you mentioned in your previous post that HO margin is kept to 5 dB, a default value, this seems to be that hysteresis. Try increasing it and check performance then.

    Br

    8th February 2011 at 12:10 #65724
    Fresh Opt
    Guest

    Thank you my friend,
    I think now is clear.
    Regards,

    8th February 2011 at 20:07 #65725
    pix
    Guest

    hi all,

    it is always difficult to apply the vocabulary from one vendor to another. In ALU, hysteresis is a term that only appear in idle mode, while it is also a HO parameter in other systems.

    Anyway, specifically for ALU, here is what you should do :
    * from cell A to cell B:
    HO_MARGIN(A,B) = 8dB
    * from cell B to cell A
    HO_MARGIN(B,A) = 5dB (= default)
    * in cell A
    PING_PONG_HCP = 20s
    A_PBGT_HO = 12 SACCH

    are cell B and A in the same frequency band (900MHz both of them ?)

    If above settings don’t work perfectly, try to increase (slowly !)
    1) the ping pong hcp by +20s
    2) the HO_MARGIN(A,B) by +2dB and the A_PBGT_HO by +2SACCH.

    Beware of emergency HO ratio in the cell A, with the solution 2, as it is getting now more difficult to get out of cell A.
    Regards
    pix

    9th February 2011 at 09:27 #65726
    Fresh Opt
    Guest

    Hi Pix,
    Thanks for the detailed answer. I’m thinking to try with HO Margin=10 dB, but, Ok, lets see your proposal.
    Thanks again,
    Regards,

    9th February 2011 at 13:15 #65727
    Jim
    Guest

    Hi,

    If the system is ericsson there are two parameters that you can play with:
    1-OFFSET: by changing this parameter you are moving the border inside one of the cells.
    in your case you want to maintain the call in cell A so you increase the parameter OFFSETP in the cell realation CELLA_CELLB (note that the parameter OFFSETN will be increased automatically by the same value in the oppisite direction CELLB_CELLA).
    2-for the bingbong handover you have three parameter (HIHYST, LOHIST and HYSTSEP)the HYSTSEP parameters indicated where the handover is happenning (in your case its in 70s to 80s dbm) so if HYSTSEP is still in its deafault value which is 90 , the handover is happening in a high Signal Streangh so you change the HIHYST ( increase it to deteriorate the pingpong handover ).

    hope you find this useful,

    9th February 2011 at 13:33 #65728
    pix
    Guest

    fresh opt,

    Increasing the ho margin is an easy choice, but it might raise some issues in the KPIs.

    The ping pong hcp combined with a little higher ho margin + a little longer a_pbgt_ho should allow (i hope !) to maintain good KPIs.

    But I encourage you to try both solutions or to use different settings. Please experiment as much as possible, and share your results here ! 🙂

    regards
    pix

    9th February 2011 at 14:29 #65729
    Fresh Opt
    Guest

    Thanks Pix, thanks Jim. I’ll share results as soon as I get new DT measurements and check KPIs from NPO.
    Thanks again guys for your help.
    Regards,
    Fresh Opt

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