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  • #46118 Reply
    sammi
    Guest

    Hello to all,

    We have a cell site in extended mode,Omni Directional with 4 TRXs. Recently we locked a TRX for testing purposes. Since then dropped calls have been Increased.I checked counters and figured out that dropped calls are due to Intracell handovers. When I unlocked the radio,dropped calls have been reduced. Do u guys know what causes this and what I need to do to keep the TRX locked and reduce dropped calls.

    Thanks in advance and appreciate your help

    #46119 Reply
    Briny
    Guest

    Was the trx that was locked a SDDCH tx? This would cause problems….

    #46120 Reply
    sammi
    Guest

    HI Briny

    Nope its not SDCCH TRX. Any other suggestions

    #46121 Reply
    Sammi
    Guest

    vanderley and Pix, can u guys help me with this

    #46122 Reply
    pix
    Guest

    hi sammi,

    you’ll need to identify which trx you lock (let’s call it TRX 1), and which one you keep on-air (TRX 2).

    maybe your tch traffic goes on TRX 1 by default, leaving the TRX 2 empty most of the time (check TRX traffic distribution).

    When locking TRX 1, all the traffic is forced to TRX 2. Maybe there are interferences on the frequency of TRX 2, leading to intracell HO. Unfortunately, it can’t go on the TRX 1(because it is locked).

    So the call drops, due to poor quality.

    When you unlock the TRX1, all the traffic can now go on TRX1 and be “saved”.

    There are some other possibilities, but you need to detail more your problem (traffic / TRX before and after lock, HO split before and after, call drop cause before and after, tch mean duration, etc…) and the cell configuration (which TRX do you lock ? TRX “BCCH” or the TRX #2 ?)..

    good luck.

    #46123 Reply
    sammi
    Guest

    hi Pix,

    Thanks for your reply. site has 4 TRXs. I locked TRX4 not the BCCH TRX. I checked counters and figured out there are more intracell handovers leading to drops. How do i find this traffic/TRX.

    Thanks in advance

    #46124 Reply
    mirza
    Guest

    hi sammi,
    i have another ossibilitie in my mind.actually call drops is due to signalling.if u r using 4TRX in a cell and TS0 is always reserve for control channels.if u r using 4TRX its mean u should dedicate 1 more traffic slot for SDDCH on any one frquency.and remain resrve all slots for traffic on all frequency.in onteher mean u should give one more slot to SDDCH.it will increase ur call handling capacity.
    regards
    mirza

    #46125 Reply
    pix
    Guest

    mirza,

    call drop on the TCH channels and SDCCH congestion are different issues, therefore adding SDCCH capacity won’t help.

    sammi,

    are you having SDCCH drops or TCH drops ? I guess it is TCH drops (= call drops)

    The last trx of the cell is usually the one that carries the highest amount of traffic. Because you lock the TRX #4, the traffic is now being mostly carried by TRX #3. Therefore, check interferences…

    You says “there are more intracell HO”. Well, maybe it is because the TRX3 is interfered, therefore most of the traffic is interfered. It leads to a higher amount of interference HO than before. For instance, before locking, there was 80% of calls on TRX4, with good quality. And 20% on TRX3, with poor quality due to interference.

    After locking : 0% on trx4, 80% on trx3 and 20% on trx2. Maybe there is interference on trx3, or possibly trx2. You need to check indicators per TRX. I can’t tell you where you can find them in Siemens because i work with a different vendor, but you’re supposed to know ๐Ÿ˜‰

    To conclude, i’d say you really need to investigate more into details your problem : more indicators (tch mean duration, per trx, tch assignment failure, sdcch drops), more drive-tests, and try to lock other TRX instead of TRX4.

    And finally, check your frequencies !! are you using frequency hopping ?

    good luck…

    #46126 Reply
    Vijay
    Guest

    Hi Sammi,
    How come intra cell handovers come in omni site? I think u better check if it’s defined as omni or sectored site..then check for connections at combiner path(better disconnect the path from the locked TRX)..

    #46127 Reply
    mirza
    Guest

    hi pix,
    i just that MR sammi is talking about call drops due ti control channels.ok u r right.but..u r saying about interferance i think it can be prob but it is not exactly like that.when we plan a cell and give frequency to that .adjacent channel interfarence is already removed .it may be co-channel interferance.but i think it is not like that.the prob is there configuration in TRX frequency in BTS card.he should that configaration.i think then he will be right.
    bye

    #46128 Reply
    pix
    Guest

    hi mirza,

    i don’t see where he is saying the call drops are due to control channels..? But maybe you are working together, since it looks like you know how the did their frequency planning.

    no offense, but no frequency planning is perfect. It always worths a shot to check out the frequency usage of the frequency of TRX2 or TRX3.

    But yes, of course, it can be linked to a TRX hardware issue. I always try to clear out the radio problems first before asking someone to go on site and change the TRX cards.

    Vijay,

    An intracell HO is a handover from one TRX to another TRX within the same cell. They are due to interference on the initial TRX, : they move the call to another TRX, trying to get a clearer frequency on this one.

    (other cases for intracell HO are due to AMR – are they using AMR ?)

    Intracell HO occurs within the same cell, whether it is omni or sectorized.

    #46129 Reply
    sk
    Guest

    may i know why sometimes we find one way call in some sectors,in this case one end customer cant heard another one.what may be the reason?

    #46130 Reply
    Hi Pix,Mirza,vijay
    Guest

    Sorry for the late response. Thx for your replies.

    I will further look into this and update you guys.I’m having TCH drops.Pix ,like u said,it might be Hardware issue too.Let me dig into this.

    Vijay

    Intracell Hand over is between one TRX and another TRX within the same cell. The site no need to be a sectored site.

    Thanks to all of you

    #46131 Reply
    Vijay
    Guest

    Hi Pix,
    Thanks for your reply. But I think the the call transfering from one TRX to other due to interference in first TRX is not handover, its just hopping, simply called Baseband hopping. I didnt come across such an Handover from 1 TRX to other within the same sector/cell considering my experience on Motorola and Nortel BTS. The call is simply put on Hop through the installed TRXs or through the designed Hopping sequence to average out the interference..Do u agree?

    #46132 Reply
    pix
    Guest

    hi vijay,

    no i don’t agree that intracell handover due to interference and baseband hopping are the same thing.

    It is extremely different !

    The former is indeed a REAL handover, with all the signalling, the algorithms, etC…

    While the later (Baseband Hopping) is a mechanism that defines which frequencies a timeslot is going to use in the next frame.

    Now it is true that both works on the same idea : exchange the current frequency ๐Ÿ™‚ that is why it is required that if you want to work with BBH, you might want to disable intracell HO (or not ! if you let it enabled, then you can see interesting “secondary” information out of that)

    You worked in Nokia and Motorola ? In Radio engineering ? I can assure intracell handover is a common & basic feature, it is weird you missed it out. Time to open some of the dusty books on your desk ๐Ÿ™‚

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