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BCCH Failure

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Viewing 9 posts - 76 through 84 (of 84 total)
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  • #36688 Reply
    Kuldeep
    Guest

    Hi,
    Can you please highlight on why we need BCCH with CCCH (BCCH/CCCH) in case we need more than one ccch in a cell. Whereas in case of PCCCH only one timeslot contain PBCCH not all PCCCH channels needs to carry it when there are more than one pccch in a cell.
    I mean why can’t we have standalone CCCH as we already have BCCH/CCCH/SCH/FCCH in a cell for transmitting SIs.

    #36689 Reply
    pix
    Guest

    kuldeep, i’m not sure i understand your question.
    BCCH + CCCH = CBCH (combined BCCH), it is a mix of BCCH and SDCCH/4 signalling.
    It is not mandatory to have CBCH in a cell.
    It can be a possiblity to set a CBCH in a cell in order to replace one ts BCCH and one ts SDCCH. (explanation : If the cell has TCH congestion, you might want to remove the SDCCH/8 and replace it by a TCH timeslot, therefore you need to compact the BCCH and the SDCCH in one timeslot : the CBCH)

    Another case : you have a cell with 1 TS BCCH + 1 TS SDCCH, but you notice SDCCH congestion. You don’t want to loose TCH capacity, so you might decide to keep the existing SDCCH and replace the BCCH by a CBCH. So in the end, you have the same TCH capacity but +50% of SDCCH capacity.

    #36690 Reply
    Kuldeep
    Guest

    Hi, Thanks for reply.
    Actually my concern was regarding the configuration of BCCH and CCCH.
    According to 3GPP TS45.002 the only permitted channel combination for CCCH are:
    1)BCCH + CCCH + SCH +FCCH /SDCCH4
    2)BCCH + CCCH + SCH +FCCH
    3)BCCH + CCCH
    Also we can have more than one CCCH in a cell. The Ist or 2nd combinations are mandatory for (Basic) Ist CCCH and its timeslot should be 0 and this combination cannot be repeated.
    If we need to have additional CCCHs due to any reason then they should be configured on timeslot 2,4,6 with channel configuration BCCH + CCCH.
    My question is why we need to have BCCH alongwith additional CCCH as we already have BCCH for SI broadcasting on timeslot 0.
    Can U pls highlight on it.

    Best Regards,
    Kuldeep

    #36691 Reply
    Vanderley
    Guest

    Hi,

    This is because the MS cannot listen to the two timeslots simultaneosly (CCCH = PCH + RACH + AGCH). It is the same if you have PBCCH the GPRS attached MS listens to the PBCCH not to normal BCCH.
    Actually it’s like this:
    “Creation of additional BCCH+CCCH is possible but only on the timeslots 2,4 and 6 of C0. The info about the used control channel configuration is sent in the Parameter ‘CCCH_CONF’, which is part of the IE ‘Control Channel description’ sent in the SYS_INFO3 on the BCCH. If more than one BCCH is created for a cell the MSs observe the BCCH on timeslot 0 first and – having detected that there are more than one (from the CCCH_CONF) – select one BCCH/CCCH timeslot for all their CCCH activities on the basis of their CCCH_GROUP. The CCCH_GROUP is calculated from the last three digits of the IMSI and the CCCH configuration”

    #36692 Reply
    kuldeep
    Guest

    Hi,
    Thanks for reply.
    I have some doubt regarding PCCCH configuration that there are two permitted combination according to TS45.002:
    PBCCH+PCCCH+PDTCH/F+PACCH/F+PTCCH/F
    and
    PCCCH+PDTCH/F+PACCH/F+PTCCH/F
    Here additinal PCCCH can be configured without PBCCH. I mean PBCCH transmits PSI only at one timeslot (not on every timeslot where PCCCH is comfigured), how MS manages to listen on both ts for PCCCH and PBCCH here.
    Can u pls elaborate it.

    Best Regards,
    Kuldeep

    #36693 Reply
    Vanderley
    Guest

    Hi,

    MS also listens to PDTCH and BCCH simultaneosly but this is because of the GPRS/EDGE standards which are quite new in respect to traditional GSM ones. As PCCCH also contains PDTCH I guess it works the same way. Note that you must have PBCCH in order to configure PCCCH.

    #36694 Reply
    kuldeep
    Guest

    Hi Vanderley,
    Thanks.It helps me a lot.
    Can u please highlight on how can i visualize the different FDMA/TDMA as a continues frames one after another. Actually am confused how Frame Numbers are mapped on different channels.
    I mean how do MS know that this FN is of some particular channel.

    Best Regards,
    Kuldeep

    #36695 Reply
    pix
    Guest

    oooh… we don’t have multiple CCCH configurations in Alcatel systems, that’s something new to learn 😀

    #36696 Reply
    kuldeep
    Guest

    Hi,
    I have some doubts regarding Frame structure of GPRS:
    Please correct me where i am wrong
    I understood why we can’t have standalone CCCH(i mean channel CCCH without BCCH). This is becoz all CCCH(max 4 in a cell) should be configure on same frequency(C0).
    And according to CCCH-Group MS will listen to CCCH it can be on time slot 0, 2 , 4 or 6.
    Now MS without multislot capabilities can’t listen to 2 slots on same TDMA frame, that why we need to provide BCCH on the same slot with CCCH.
    TDMA frame for all CCCHs is same but timeslots are different like this .

    Now in case of PBCCH and PCCCH, we configure more than one PCCCH on diferent frequency (RFLs are different), now there TDMA frames will like this:
    for RFL1:
    for RFL2:
    now on RFL1 we also have PBCCH(PBCCH+PCCCH+PTCCH+PACCH+PDTCH)
    and on RFL2 we do not have PBCCH(PCCCH+PTCCH+PACCH+PDTCH) as these are the only permitted channel configurations.
    Now MS with PCCCH-Group 1 will listen to PCCCH on RFL2. My question is how will it listen to both PBCCH on TS0 on RFL1 and PCCCH on TS2 on RFL2 as both TRXs are different and they are transmiting contimuesly on different RFLs. Will MS not miss one of them.
    pls clarify it.

    BEST REGARDS,
    KULDEEP

Viewing 9 posts - 76 through 84 (of 84 total)
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