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unstable signal level – ALU parameter

Viewing 15 posts - 1 through 15 (of 15 total)
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  • #62785 Reply
    Paul
    Guest

    Dear All,

    Many thanks to you at first!

    By the way, i experienced something related to the stability of signal level. The result drive test showed that the signal level of the covered cell was unstable. At first, it detected -79 dBm, then -83 dBm, -84, -85, and back again to -79 dBm.

    I tried to DISABLE EN_MS_PC, then i checked again. The result showed an improvement. The level signal was more stable than before. But, when I faced the same problem in other cell, disabling EN_BS_PC didn’t work at all.

    I was a little bit confused about this.

    Is there anyone who knows :

    1. What does make the signal unstable (regarding to Drive test result)?
    2. Related to ALU Parameters, we know about EN_BS_PC and EN_MS_PC, actually when should we disable it? Is there anyone know the formula of EN_BS_PC & EN_MS_PC? I couldn’t find it in ALU documentation.

    I would be grateful if anyone could help me to give me explanation.

    Thanks Alot!

    Best regards,

    Paul

    #62786 Reply
    Mania
    Guest

    Hi Paul,
    For EN_MS_PC and EN_BS_PC its only to enable power control on MS and BS side. so that their power is reduced just so much that they get the desired quality and do not cause unnecessary interference for other mobile stations.
    I don’t know which release of Alcatel you are working with or weather they have seperate PC parameters for AMR or not but they could also effect.
    Also I have observed in some cases where there is issue with Antenna / Antenna Cabling system the signals tend to die down early and that might be the issue. Check path balance of the TRXs of that cell and DL path of cablinhg.

    #62787 Reply
    paul
    Guest

    Dear Mania,

    Thanks alot for your explanation.

    I was working in B10 ALU.

    Then, what if there is no problem in path balance of TRX and cabling? Is there parameter to control the received signal level more stable in ALU?

    Thank you.

    Paul

    #62788 Reply
    pix
    Guest

    hello paul,

    a signal level is always unstable, because of the multiple reflection of the waves : sometimes the signal is stronger than real (because of phase addition), other times the signal is weaker, due to phase cancellation.
    The variation can be of +/- 10dB in a city, even if the MS is static.

    You will notice that moving out of the city in an open area, the signal becomes a little bit more stable again.

    Cheers
    pix

    #62789 Reply
    Paul
    Guest

    Dear Pix,

    Thank you for your response.

    I also met a problem. WHen in idle, the signal level was stable, but when in Dedicated, the signal level decreased gradually and sometimes it caused drop. Perhaps there was intereference. DO u have any opinions?

    So, based on ur experience in ALU, is there any parameter to stabilize the signal level? Or perhaps, DTX should be ENABLED as this also reduces the interference.

    Best regards,

    Paul

    #62790 Reply
    pix
    Guest

    paul

    when you said “unstable” do you mean the signal is continuously decreasing ?

    or do you mean it is moving up and down, but the average is the same ?

    regarding idle mode : measurement of rxlev is done only once every 5s. Therefore the measurements look more stable.
    For dedicated mode, the refresh rate is much faster, showing all instantaneous variations.

    DTX should not degrade the RxLev. Keep it activated.

    A gradual decrease in dedicated mode is due to wrong power control parameters.
    What are your values for

    EN_BS_PC

    L_RXLEV_DL_P
    U_RXLEV_DL_P

    L_RXQUAL_DL_P
    U_RXQUAL_DL_P

    A LEV PC
    A QUAL PC

    thanks ๐Ÿ™‚
    regards
    pix

    #62791 Reply
    paul
    Guest

    Dear Pix,

    Sorry for my late response.

    Yes, it’s continuously decreasing (Dedicated mode).

    At first, EN_BS_PC was ENABLE.

    And other parameters :

    L_RXLEV_DL_P =-85
    U_RXLEV_DL_P =-75

    L_RXQUAL_DL_P = 30 x0.1
    U_RXQUAL_DL_P = 30 x0.1

    A LEV PC = 4 SACCH
    A QUAL PC = 4 SACCH

    When I disabled EN_BS_PC, then the signal strength was more stable.

    I concluded that in the area where there were only few sites (Suburban Area), it’s okay to disable power control (EN_BS_PC and EN_MS_PC), but not in the crowded sites (Urban Area) coz it will emerge an interference.

    As I know, if Power control is disabled (EN_BS_PC and EN_MS_PC), the MS will transmit with max power. If PC is ENABLED, MS will adjust the power transmitted regarding to the command from BSC. BSC will send command to MS about how strength the MS must transmit the power.

    Thanks,

    Paul

    #62792 Reply
    Pix
    Guest

    Hi paul,

    A piece of very important advice : always activate power control (dl and ul), especially in Urban Areas.
    The problem is that your parameters are wrong. Try this :

    L_RXLEV_DL_P =-80 ***
    U_RXLEV_DL_P =-70 ***

    L_RXQUAL_DL_P = 30 x0.1
    U_RXQUAL_DL_P = 10 x0.1 ***

    A LEV PC = 4 SACCH
    A QUAL PC = 4 SACCH

    The rxlev will decrease, as you are experiencing, but it will remain acceptable. It will strongly help to decrease your network interference.

    regards
    pix

    #62793 Reply
    Samy
    Guest

    Dears;
    I’m working with B9 of Alcatel and realy suffering with that issue; the whole Net. not just 1 cell; within idle mode and very close to the site with constant location of the MS the signal is -65 then > -72 > -78 > -83 > -89 > -93 > -85 > -72 > -68 > -64 >….. and so on, within idle mode; I’m really surprising; I never seen that; the problem I’m with huawei Exp. therefore help will be heighly appreciated friends; may there is something wrong within parameter setting?

    Regards

    #62794 Reply
    Paul
    Guest

    Dear Pix,

    As I know :

    L_RXLEV_DL_P =-85 (threshold) ==> If RXLev is/below -85, then BSC/BTS will send a PC command to increase the RXlev with step size 2 dB (MAX_POW_INC=8). From -85, -83, -81, -79. Please cmiiw.

    U_RXLEV_DL_P =-75 (threshold) ==> If RXLev is/stronger than -75, then BSC/BTS will send a PC command to decrease the RXlev with step size 2 dB (MAX_POW_DEC=8). From -70, -72, -74, -76. Please cmiiw.

    With your setting, then of course the RXLev will decrease (The threshold is more strict)

    By the way, could it help the RXLev in Indoor? Coz, in urban city, with crowded Sites, interference in hopping channels (SFH)often happen. And many sites in my network in Urban Area still have DTX not activated (DTX_FR_INDICATOR, DTX_HR_INDICATOR = SHALL NOT USE).
    I think, by enabling the DTX, it should help reduce the interference in indoor area (building).

    Thanks alot Pix!

    Dear Sammy,

    I’m sorry, I don’t know about B9. But I think it is similar to B10.

    As Pix said, if the problem in Suburban area (fewer sites), you can try to disable PC. But not in Urban. Is there interference in ur case? Hopping channel may be?
    I also experienced as same as yours, then i try to disable the PC (EN_BS_PC) in suburban area, and it worked ๐Ÿ™‚

    By the way, in which country is Alcatel used? Except my country of course ๐Ÿ˜€

    I thought ALU only in certain country like in my country and Vietnam ๐Ÿ˜€

    Br,

    Paul

    #62795 Reply
    Pix
    Guest

    Paul,

    ALU is everywhere in the world… Not the biggest vendor, but since there are several operators per country, there is always one of them choosing ALU.

    your PC settings regarding the QUALITY if totally wrong.

    Regarding the LEVEL, my settin
    gs are safr than yours : the LEVEL will not decrease as much as with your settings. (your settings : target rxlev = -80dBm, my settings : target rxlev = -75dBm)

    DTX also should be enabled
    DTX_UL = SHALL USE
    DTX DL = SHALL USE

    I don’t understand what is your problem with the PC. Of course the LEVEL is going to decrease, that is the purpose of PC. Enable it everywhere : Suburban, Urban, Rural. If your LEVEL settings are not too low, there will never be a problem.

    >>> Samy,

    Experiencing a little RXLEV variation during IDLE MODE is normal. Your variations are a too strong though, especially if you were in LoS of the antenna.

    Can you establish a call on that cell ? Can you try getting a TCH on the TRX1 ? When the TCH is on TRX1, do you still see those variations ?
    To force the BSC to give you a TCH on TRX1, you can simply play around with the TRX PREF MARK. Put TRX PREF MARK = 1 on the TRX1, and 0 on the other TRXs.

    Regards
    pix

    #62796 Reply
    Samy
    Guest

    Thanks pix and Paul,
    Kindly; the TRX Pref mark is 0, 1, 1, …and I can make calls and with fluctuating and is not a cell or a site the whole Net.; dear if I did that test by changing the TRX Pref to give highest priority to the TRX1 and the problem was exist what we reason we get and if didn’t fixed what would be the reason?

    regards

    #62797 Reply
    Mania
    Guest

    Hi,
    Now lets see, I believe that if power control is trigerred based on level then the MS would take up large steps to reach the intended level in the middle of the power control window. the pow_inc_step_size and pow_dec_Step_size only come into play when the issue is with quality.
    So for the fluctuations in the dedicated mode the issue may be wrong settings of power control window causing osscilations. What are the step sizes you are using could you decrease them and observe try having PC_Level_window width > 2*PC_Inc / dec _Step_Size.
    Also try to set desired best quality to 0 so power decreasing based on quality is not trigerred.
    As for Idle mode fluctuations so severe the only issue that is can think of is a multipath area where you are getting reflections from various paths.try in some open area LOS if the issue still persists then probably the best bet is a hardware issue.
    As in idle mode you are measuring BCCH DL power and it is transmitting at max power.
    Also try changing your test phone it can be faulty and giving you this abnormal reading.

    #62798 Reply
    Paul
    Guest

    Dear All,

    Thanks a lot for all explanations and discussion.

    BR,
    Paul

    #62799 Reply
    RLSSP
    Guest

    diff betn rlssp and rlcpp???

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