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How does a mobile latch to GSM Network?

Viewing 15 posts - 1 through 15 (of 22 total)
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  • #48472 Reply
    Sripathy
    Guest

    Hi,
    Could you please help me to know how a mobile latches on to a GSM Network for the first time when it is powered on?

    Thanks in advance,
    Sripathy

    #48473 Reply
    Pix
    Guest

    the mobile chooses the cell with the highest C1
    C1 = (RXLEV – RXLEV_ACCESS_MIN) – MAX(MS_TXPWR_MAX_CCH – P, 0)

    with P = maximum power of MS

    For more details, it’s all detailed in these 2 3GPP documents :

    43.022-Functions related to Mobile Station (MS) in idle mode and group receive mode.doc
    45.008-Radio subsystem link control.doc

    #48474 Reply
    vineet
    Guest

    hi,
    this is process of location updating,called IMSI attach.
    whenever mobile is on,it tries to response the paging,and compares with network code stored in the sim.

    #48475 Reply
    naveen
    Guest

    Does the mobile scan for the whole of GSM900,1800,1900 frequency band(in case of a triband handset)? If so then it has to scan for more than 125 ARFCN nos in each band, is this the way it works?

    #48476 Reply
    Pix
    Guest

    Naveen,

    In the specs, it is just said :

    The MS is checking cells in descending order of received signal strength. If a suitable cell is found, the MS camps on it and performs any registration necessary.

    The number of channels to be searched are 15 for GSM 450, 15 for GSM 480, 25 for GSM 750, 30 for GSM 850 Band, 30 for GSM 900 and 40 for DCS 1800 and PCS 1900.

    After that, the MS stops looking.

    It is also said that a mobile *might* keep the last BCCH in memory, during the previous swith-off, so when it is started again, it will look for that BCCH again.

    So, yes, the MS will scan the whole band, but just in order to find the strongest channels (this is fast). Then it will decode the strongest channels, and see whether they belong to its PLMN or not.

    #48477 Reply
    naveen
    Guest

    Hi Pix,

    In that case only certain ARFCNs can be used as BCCH, does the specs list the ARFCNs that can be used as BCCH only.

    Thanks,
    Naveen.

    #48478 Reply
    pix
    Guest

    no, it is the operator that defines the BCCH frequencies ! Of course.

    for instance, in a GSM900 monoband network :

    the mobile will listen to the 30 strongest signals in GSM900, and if none of them is a BCCH from its own PLMN, then he stops…

    #48479 Reply
    naveen
    Guest

    Hi,

    Someone actually told me that the Mobile sends a RACH on ARFCN 0 of each band(900,1800,1900) and then if the mobile is permitted in that PLMN, then it will latch on and do a location update. Is this correct?

    Naveen.

    #48480 Reply
    Pix
    Guest

    No !! of course it is not correct !!
    MS is just listening to the network, there is no sending of message from its side, until it found a cell.

    What is ARFCN 0 ? Is it a magical frequency, hidden from us, but used by mobiles to communicate with the CIA ? :))

    #48481 Reply
    Pavel
    Guest

    *ROFL*

    #48482 Reply
    pix
    Guest

    actually ARFCN 0 is a frequency from the extended GSM band :
    frequency DL = 890.0 MHz, frequency UL = 935.0 MHz

    the E-GSM goes from 0-124 + 975-1023
    the P-GSM goes only from 1-124
    amazing !

    anyway, this ARFCN 0 is not used for any stealth RACH towards the Matrix.

    #48483 Reply
    seth
    Guest

    This is an aproaching process:
    #Scan 124 RF channels and measure
    signal strength for 3-5 seconds
    #Tune to the RF channel with the highest
    received average signal strength
    #Determine if it is a BCCH carrier by searching for frequency correction bursts.
    #Is it a BCCH carrier? The MS shall attempt to synchronize to This carrier and read BCCH info
    #Is it the wanted PLMN?
    #Is the cell barred for access?
    #Is C1 > 0?
    #Camp on the cell
    IF THE ONE OF THIS STAGES NOT ACCOMPLISHED THE MOBILE WILL TUNE AGAIN AT ANOTHER STRONGE FREQUENCY.

    suvendu – 16 Dec 2005

    Dear mr Jood,
    my confiusion is regarding the process by which a MS search for network just after switch on..
    so pls tell me those process…
    means when it will scan forBCCH etc

    jood – 15 Dec 2005

    Hi suvendu
    Attempt to access the home PLMN(broadcasted at BCCH) are performed as specified
    bellow:
    1 The periodic attempts are only performed in automatic mode
    when the MS is roaming in its home country.
    2 After power on, a period of at least n minutes and at most T
    minutes is elapsed before the first attempt is made.
    3 The MS makes an attempt if it is on the visiting PLMN at
    time T after the last attempt.
    4 Periodic attempts are only to be performed by the MS while
    in idle mode.
    5 If the home PLMN is not found, the MS remains on the
    visiting PLMN

    #48484 Reply
    veeresh
    Guest

    hi, iam a bsc engineer working in nokia , i woul dlike to know what is the exactly the DAC(Clock) value of BSC in my bsc ho failures are more, what is concept behind this

    #48485 Reply
    turd!
    Guest

    how about in the case where your simcard is roaming?

    How will the mobile camp to the network?

    #48486 Reply
    turd!
    Guest

    Roaming in the sense that you go from one country to another?

Viewing 15 posts - 1 through 15 (of 22 total)
Reply To: How does a mobile latch to GSM Network?
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