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RACCH REJECTION DUE TO DISTANCE

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  • #63200 Reply
    agz
    Guest

    Hi all,

    Cn any1 tell me how does BTS rejects RACCH request if MS is beyond the defined maximum distance for RACCH..Neither does the BTS knows about the TA of the MS (as it is accessing N/W for the first time) nor there is no Training sequence bits in access burst(RACCH) for the BTS to calculate TA..

    #63201 Reply
    Pix
    Guest

    There is indeed a 41-bit training sequence in the access burst. .. and the TA is computed by the BTS thanks to the UL Access Burst “channel request”.

    Training Sequence Code in the Normal Bursts is used for “very” fine tuning of the timing advance.

    regards
    pix

    #63202 Reply
    agz
    Guest

    Pix,
    U mean the 41 bits synchronization bits are actually Training sequence bits..then what does this 36 bits of access information in access burst do???
    and one more thing..if by computing BTS asks MS to send the data in advance by say 3 bits(i.e 3*3.69micro second)is MS advancing the data 3slots(the diff bn rx and tx of MS)-(3*3.69)microsecond..

    #63203 Reply
    Pix
    Guest

    1/ well, this is not the “training sequence code”, but it is called a synchronization sequence. Check 3GPP if you want the details… The Access Information part contains : the cause of the Channel Request and a Random ID.

    2/ yes. BTW, 3.69 microseconds is the duration of one symbol ? I didn’t know that.

    regards
    pix

    #63204 Reply
    agz
    Guest

    Pix,
    Then what happens during Handovers..what TA shall MS use during the handover phase.,
    Like what difference does it mske between synchronized(TA info not used)and non-sync handovers(TA info used)??

    #63205 Reply
    pix
    Guest

    hi,

    excellent question 🙂 I checked in the books…

    as far as I can understand, in the ALU system, the sync HO and the async HO are exactly the same. (suprising !)
    I don’t know if they changed it in B10 or something, but right now, both procedures are absolutely identical.

    The target BTS will calculate the Timing Advance of the MS thanks to the HO ACCESS messages. Those works like the “CHANNEL REQUEST” : they are sent over “access bursts”. So here you go : TA computation for incoming HO is the same as for channel requests.

    Regards
    pix

    #63206 Reply
    agz
    Guest

    Pix,

    This is what written in ETSI 05.10 for initial TA estimation..
    “When the BTS detects an access burst transmission on RACH it shall measure the delay of this signal relative to the expected signal from an MS at zero distance under static channel conditions. This delay, called the timing
    advance, shall be rounded to the nearest symbol period and included in a response from the BTS when applicable.”

    k.k..and Now in case of handover,by HO access message target BTS calculates TA and then sends its info to MS via physical msg…

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