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MS Power Control Algorithm!!

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  • #54771 Reply

    Hi All,

    I have a query. I have gone through the chain of articles on Power Control, but am not able to resolve a query.

    Suppose network (BSC) has a threshold power level of 28dB. And BTS indicates that UL power level of MS is 25dB. So, does the network indicates to MS the absolute value (28dB) or relative value (+3dB) in the SACCH header?

    Also, please let me know where I could find a good PC algorithm.


    #54772 Reply

    PC algorithms are not standard, so each vendor can define its own (AFAIK). The only standard part is the communication with the MS.

    Regarding the indication of power, it is done with absolute values. There is a coding for each power the MS can transmit.

    If you have any other question, let me know,


    #54773 Reply

    Hi Sachin, you can find the response to your question in 3GPP 45.005 Specification.
    BSC/BTS translate the power to be commanded to MS (into the UL SACCH header) in a power level command, ranging from 0 to 31 and having the meaning that you can find into the tables, depending also on the frequency band.

    #54774 Reply

    Hi Pix/Michele,

    My question is this.
    Suppose my RF planning is such that I want a minimum of 28dB power level in U/L from all MSs. However, one MS is transmitting at 25dB. So, shall I indicate to this MS to transmit at 28dB??

    Is this is the case, then I always need to tell all MSs to transmit at 28dB???


    it may be the case that MS is transmitting at 28dB and I am receiving at 25dB, so I should indicate to MS to transmit at 31dB, so that I could receive at 28dB..

    I hope I could clearly stated my question. Otherwise, let me know.


    #54775 Reply


    your question is not clear, i’m sorry…
    it’s not your job to send a message to the MS, it’s the job of the BTS and BSC ๐Ÿ™‚ what you have to do is set the OMC-R parameters so that the minimum TX power of a MS = 28dBm.
    The messages, the coding and all that is taken care of by the BSS.

    Now, I’m surprised that the minimum TX Power should be equal to 28dBm. Aren’t you mistaking ? It should be MAX power = 28dBm, instead of the usual 33dBm.
    The Minimum power should be set as low as possible, in order to give enough room for power control.

    #54776 Reply


    My only concern (as BSC/BTS) is that suppose if MS is not transmitting at the indicated Power Level, or U/L power (measured by BTS) is less than the threshold value (set by OMC-R), then what action shall I take?

    Shall I indicate to MS (in MS Power Control Message->UL SACCH header) to transmit at the threshold value (set by OMC-R) or shall I indicate the difference to it, that Boss you need to change your U/L power by “+x” or “-x” dB?

    Remember, I am the BSS…

    I hope I could clear the query.


    #54777 Reply


    You are the BSS? What do you mean? You are developing a BSC software?

    As we already said, the value send in the PC command indicates the absolute power.

    it’s not possible to send information that means + “x” dB or – “x” dB.

    So yes, you should send the absolute value of the power in the sacch message, and ensure this value is never less than the MIN MS TX POWER.

    The MS will just follow the command from the BTS, no improvisation ๐Ÿ™‚

    #54778 Reply

    Hi Pix,

    Yes I am working on BSC SW.
    Thanks for the information that we would indicate the Absolute Power to MS in Power Command.
    One question still remains.. ๐Ÿ™‚

    If I am expecting power of 28dB from MS and am getting only 25dB (which is 3dB less), so would I indicate MS to transmit at 28dB or 31dB(so that I could receive at 28dB). ??


    #54779 Reply

    the 3GPP 45.005 gives the coding of each power. If you send the coding equivalent for GSM900 29dBm, then the MS shall interpret it as 29dBm in GSM900.

    If it doesn’t then there is a problem somewhere else:
    the coding between DCS1800 and GSM900 is different by few dBs, check that out.
    Check also the classmark of the MS, I remember the power class of the MS is indicated there, perhaps it’s something to investigate as well.

    Your solution (say “31dBm” and hope the MS sends at 29dBm) is bad because you might actually miss the real problem.

    So, check frequency band and classmark, check out 45.005, and it’ll be fixed.

    #54780 Reply

    Hi Pix,

    I have some doubt in MS power control at BSC. We are intended to use the closed loop power algorithm at BSC(mentioned in 3GPP. 45.008 annex B.2 ) for MS power control .according to this algo.
    The output power will than be:
    P = 0 – CH
    In this case, CH is the actual power level (relative to 0 ) commanded by network.

    So our understanding is that if BSC intially set the required power level 0 = 30db, and it receive the power P from MS = 28db. Then n/w should command the power CH = 32db to the MS.

    So please let me know whether we are correct in our understanding or not?

    #54781 Reply
    Nitin Goel


    According to my understanding, for having one to one mapping of the connections with the peer entiry slr/dlr is used but in the primitive of SCCP (BSSAP) with its user (BSSAP) that is N-CONNECT there is no such parameter, rather it is having the called address and calling address. But these will remain same for all the messages passing through BSS. So we can not use these calling and called address for identification of the message, which MS it is meant for.

    please tell us what we can use for this identification or suggest if we have any gap.


    #54782 Reply

    Dear, Nitin Goel!
    1.There are Source local reference number and Called Party Addres mandatory parameters in SCCP Connection Request Message (CR).
    2.There are Source local reference number and Destination local reference number mandatory parameters in SCCP Connection Confirm Message (CC).
    3. After CC receiving the connection is considered as established. And Destination local reference number is mandatory parameter for all other messages inside this connection.
    With regards, Pan.
    To Sachin:
    Dear, Sachin! I heard earlier about Bat-Man and Spider-Man. But about BTS-MAN and BSC-MAN – for the first time ๐Ÿ™‚

    #54783 Reply



    Please have a look to 45.005, chapter 4.1.1.
    The BTS shall send a message “MS POWER CONTROL” that contains those “power control level”.

    The algorithm you decide to use in your BSC is up to you: 3GPP didn’t define anything : forget about annex B.2 ! It’s misleading.
    Invent your own formula, based on UL_RXLEV and some thresholds.


    #54784 Reply

    Hi Pix,

    Thanks for your inputs.
    I have seen the table in 45.005.

    But I think those Power Levels mentioned are from MS perspective.

    From BSC perspective, I feel that BSC places appropriate power level (absolute power in dB, calculated with its PC algorithm) in MS Power Control message and sends to BTS, which places this in L1 SACCH header.

    Now at MS, whatever power it receives, it tries to sends to that level, otherwise it just sends at it own maximum power level, based on this Power Class and frequency band.

    And regarding classmark that you told me to investigate, they are sent in CC/MM messages, which are not to be decoded at BSC, since BSC doesn’t have those layers.

    Please let me know your understanding.
    I urgently need this info.

    Thanks in advance.
    Best Regards,

    #54785 Reply


    I can’t help you… You said
    “absolute power level”.

    And I 100% agree with you : the BSC sends absolute power level.

    I have no idea what is your problem. You send an order at 28dB to the MS, and the MS is setting its power to 25dB ?

    Is that the problem ?

    Perhaps the absolute power “coding” you sent to the MS is misinterpreted because the MS is readng it with a different “coding” table than yours. It could happen if the MS is in DCS1800 band and the BSC is using the GSM900 coding.
    That’s just a possibility, but I don’t really see anything else. The problem can only be one of misunderstanding :
    BSC misunderstands you
    or BTS misunderstands BSC
    or MS misunderstands BTS

    I’m sorry I can’t help more than that.

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