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Alpha & Gamma_Tnx in Alcatel-

Viewing 12 posts - 1 through 12 (of 12 total)
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  • #61974 Reply
    paul
    Guest

    Dear All,

    I’ve read the discussion about high gprs_ul_Establisment_fail issue which happened in UL only.

    From the discussion, I concluded that the ALPHA and GAMMA_TNx should be dissable (Value = 0 or (0*0.1)).

    I have this problem too in some sites. Then I tried this setting too in the issued site.

    I have some questions about it :
    I read ALPHA parameter description in ALU PArameter documentation that it should be set as same as that in MFS and BSC. Meanwhile, I set it only in a cell, not checking the MFS Alpa parameter. So, is that okay to set ALPHA = 0 without considering its parameter in MFS? We already sent TR to ALU Vendor about this problem, they recommended me to set ALPHA = 1 or (1*0.1). Before executing what they recommended,i tried to set alpha =0 first. I’ve just set the value this evening, I’ll inform you all tomorrow.

    From the discussion,GAMMA_TNX=UL PC for GPRS. IS this has the same function as well as for voice/GSM UL PC?

    Could anyone help me to explain me related to my issue? I couldn’t find any source related to ALPHA & GAMMA_Tnx.

    Thanks Alot,

    Paul

    #61975 Reply
    pix
    Guest

    hello,

    Don’t worry about MFS or BSC in the name of the parameter, it is a technical trick. When you set a value of alpha in one cell it is actually copied in the MFS DB too. It’s automatic.

    So set alpha to 0 means that you deactivate the UL PC in GPRS. But no impact on UL PC in GSM.

    Set GAMMA TNx to the max value. If you set it to zero, it means the MS will emit at minimum power (0dB)
    There also, this is a dedicated GPRS parameter, it will not impact the GSM PC.

    cheers
    pix

    #61976 Reply
    paul
    Guest

    Dear Pix,

    Thanks for your information. but, I’m rather confuse right now.

    In thread : http://www.erlang.com/forum/erlang/thread.htx?thread=3476

    you said that GAMMA_TNx=UL PC in GPRS. And others (Yogesh Singh) said that if we set Gamma_TNx=0. than it will emit at maximum power.
    He said => UL TX POWER = GAMMA – 16 dB.
    And he recommended to set GAMMA_Tnx and Alpha = 0.

    From your last information (related to the thread), UL TX POWER = GAMMA – ALPHA(DLRxLEV+48).
    If I set ALPHA=0, then, UL TX POWER = GAMMA. So actually, which is the best solution, set both ALPA and GAMMA_TNx to 0 (as Yogesh recomendation), or only set ALPHA to 0 but gamma in Max value (in ALU documentation, default gamma_TNx is 30 and Max is 62, by your recommendation)?

    From your equation, GAMMA_Tnx and ALPHA actually are for UL PC in GPRS.

    This morning (Indonesia time :)), I’ve read the statistic. It seems ALU Vendor did change last night where ALPA = 1 (means 1*0.1) and GAMMA_Tnx = 0. And the the UL_Tbf_Establisment_success increase significantly. That is what makes me a little bit confuse. In your equation, that would be ==> UL TX POWER=0-1(DLRXLEV+48)
    Ul TX POWER =-DLRXLEV-48.

    Could you please clarify my confuse Pix?

    Thanks Alot for your response,

    Paul-PCS

    #61977 Reply
    Pix
    Guest

    Sorry Paul, I’m a bit rusty with the UL PC formula.

    Here is the formula:
    PCH = min(GAMMA0 – GAMMA_Tnx – ALPHA*(C+48),Pmax)

    • GAMMA0 = 39 dBm if the BCCH carrier is in the GSM850 or GSM900 frequency band, and or
    36 dBm if the BCCH carrier is in the DCS1800 or DCS1900 frequency band,
    • GAMMA_Tnx is an uplink power control parameter sent in RLC control messages,
    • ALPHA is the alpha power control parameter,
    • C is the normalised received signal level at the MS. It is the mean of the received signal level
    plus the power reduction Pb used by the BTS on PBCCH blocks relatively to the output power
    used on BCCH,
    • Pmax is the maximum transmitted power, and is equal to GPRS_MS_TXPWR_MAX_CCH if
    there is a PBCCH, or to MS_TXPWR_MAX_CCH otherwise.

    Conslusion : to disable UL PC GPRS : ALPHA and GAMMA should be 0 ! So that PCH = GAMMA0.

    Sorry for my mistake.
    🙂

    Pix

    #61978 Reply
    Paul
    Guest

    Dear Pix,

    Thanks you so much for your explanation.

    Today, I’ve seen the performance.
    Yup, since ALPHA &GAMMA_Tnx=0, then the performance increased significantly (Ul_tbf_Suc_rate = 98-100%).
    But it seemed the vendor falled back those setting again last night (I don’t know why) where ALPHA = 10*0.1 and GAMMA_TNx=15*2dB, but the performance till now is still ok 🙂 Is it a kind of magic in ALU? hehehe.

    The way I learned about ALU Parameter was by trying to put other value, or trying to enale/disable some parameters, instead of studying the meaning of the parameter 🙂 Hehehehe..

    By the way, from your equation, If ALPHA=0, and I set GAMMA_TNx=10*2dB = 20dB, then it would be :

    PCH = min(GAMMA0 – GAMMA_Tnx – ALPHA*(C+48),Pmax)
    PCH=min(39dBm – 20dB-0,43 dBm)
    then PCH = 19 dBm.

    This value is less than PCH=GAMMA0 (which mean no UL_PC for GPRS). And if we see the equation, it’s a matter of reduction, so if UL_PC_GPRS is enable, (ALPHA&GAMMA_TNx are not 0), then UL_PC_GPRS is lower than that without UL_PC_GPRS. Am I right?

    From here, I conclude that it’s better to disable UL_PC_GPRS. ALU recommends ALPHA=10*0.1 and GAMMA_TNx=15*2dB. 🙂 Do you know why?

    Thanks Alot Pix for your responses, I really appreciate that! Perhaps you could help me related to my opinions above. :):)

    Best Regards,

    Paul_Cs

    #61979 Reply
    Pix
    Guest

    paul,

    you are mixing the names, so i didn’t really get your statement 🙂

    you said :
    —————————————–
    By the way, from your equation, If ALPHA=0, and I set GAMMA_TNx=10*2dB = 20dB, then it would be :

    PCH = min(GAMMA0 – GAMMA_Tnx – ALPHA*(C+48),Pmax)
    PCH=min(39dBm – 20dB-0,43 dBm)
    then PCH = 19 dBm.
    —————————————–

    It means the MS will transmit at a power of 19dBm instead of 39dBm (well, max MS power is actually Pmax = 33dBm)

    There is an attenuation of 20dB. That is the attenuation due to UL PC GPRS.

    If you set Gamma TNX = 0, you see that the power of MS = min(39dBm,33dBm) = 33dBm.

    With default ALU values, the alpha introduces a variable adjustment depending on the current RXLEV measured. If RxLev is low, the attenuation is less : the MS transmits louder (PCH = stronger).
    If RxLEv is high, the attenuation is more : the MS will reduce its transmission power (Pch = weaker).

    The MS transmission power = Pch.

    The failure of the UL PC GPRS happens randomly. So as long as you keep the UL PC GPRS activated, you run a risk to face a failure. Tomorrow, next week, in 3 months… who knows. Safe choice is to deactivate all the time.

    Cheers,
    pix

    #61980 Reply
    paul
    Guest

    Dear Pix,

    What a great info!Thanks alot, Now I know it. 🙂

    Yes, I was mixing the value of Pmax and an example, I mean, If I set ALPHA=0 and GAMMA_TNX=10*2B, what it would become.
    Sorry 🙂

    May i repeat your explanation?, that would be :

    The value of Pmax I stated before = GPRS_MS_TXPWR_MAX_CCH=43 dbm (ALU recommendation) with PBCCH.
    The GPRS reselection applied is NC0 (which mean following the condition as same as voice service). I was wrong, PMax should be equal to MS_TXPWR_MAX_CCH = 33 dBm (ALU Recommendation). 🙂

    By the way, attenuation 20 dB is due to UL PC GPRS from GAMMA_Tnx = 10*2dB 🙂 and Alpha=0.

    Then you said about default ALU value of GAMMA_Tnx & ALPHA which means ENABLE UL PC GPRS, that would impact on how much power needed for MS to transmit UL Tbf. So, whenever we activate UL PC for GPRS , and also depends on a fluctuation of RXLev received in MS, it has a higher possibility to have a fail UL TBF establishment. It’s better to deactive UL_PC in GPRS (GAMM_TNx&ALPHA=0) because MS will transmit UL Establishment in a stable power (That’s 33 dBm).

    I hope I’s right :).

    well, thanks so much anyway.

    If there were a facility in this forum to attach picture/statistic, that would be better 🙂 Hopefully, someday this forum can provide this facility. :):)

    by the way, where are you working now? May I join you ? hihihihihi 🙂

    Thanks & best regards,

    Paul

    Your answer actually has answered my confuse.

    From your description :

    #61981 Reply
    Rex
    Guest

    Hi,
    recently we swapped a BTS from GSM900 to DCS1800 in a small town. There was an improvement in quality, all cells around the town are GSM900. But few costumers are complaining that inside of their shops they have problems in GPRS. As they said, after they start using GPRS every time at their phones appear ‘No service’ after some seconds, there is no signal till they close GPRS session. Voice communication is perfect when we call them, quality is fine.
    What could be the reason of losing signal during GPRS session? We tried ALPHA=0 and GAMMA=0 but that is for uplink. Still the same. The module is MCTRX. Other params: MS_TXPWR_MAX=30 dBm, MS_TXPWR_MIN=6 dBm. Before, with GSM900 they didn’t have any problem with GPRS nor voice.
    Any idea?
    Best Regards,
    Rex

    #61982 Reply
    Tanuj
    Guest

    Hi Rex

    because of the change from 900 to 1800 band the indoor coverage has been reduced which has led to this low gprs problem, plz get the indoor coverage checked now after the band change

    Regards
    Tanuj

    #61983 Reply
    Rex
    Guest

    Thanks Tanuj,
    But how come that voice is good and in a good level. We are going to measure that and verifiy that. Acording to costumer the problem is only in gprs, the signal vanishes. Immidiately after stoping gprs the signal is comming back.
    Regards,
    Rex

    #61984 Reply
    Tanuj
    Guest

    Hi Rex

    That is indeed strange, but voice is less affected than gprs in such cases, i am sure that customers will face problems in calling when on long call durations. plz check which mcs is the customer getting during pdp.

    Regards
    Tanuj

    #61985 Reply
    pix
    Guest

    hi,

    are you using 8PSK modulations ? (8PSK : MCS5-MCS9)

    When 8PSK is used, there is a further attenuation of 1.5dB compared to GMSK. So that may be triggering the problem.

    However I find it surprising that the problem is so severe. Did you look at GPRS qos stats ? Anything weird ? (GPRS UL TBF Estab Fail %, GPRS UL TBF Drop %)

    You could also have a look at the RMS DL_RXLEV_avg and UL_RXLEV_avg. If those values are low, it indicates a voice coverage problem (which doesn’t mean the voice quality is impacted, but does suggest there could be an even worse EGPRS coverage).

    Regards
    pix

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