BCCH in OL_Cingular

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  • 8/13/2019 BCCH in OL_Cingular

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    GSM Radio Network Features Slide

    03813-LZU 108 3704 Uae Rev C 1

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 1 (25)

    Overlaid and Underlaid

    Subcells

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 2 (25)

    Why OL/UL Subcells?

    The frequencies allocated to the OL subcell cause and

    suffer less from interference. An OL subcell make it

    possible to use forbidden frequencies.

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    Bf1,f2,f4f4

    f4

    f3,f4

    A

    Bf1,f2f4

    f4

    f3,f4

    f4

    f4

    OL UL

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    GSM Radio Network Features Slide

    03813-LZU 108 3704 Uae Rev C 2

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 3 (25)

    Increased Overall Capacity

    A tighter frequency re-use can be applied in the

    OL subcells giving more frequencies per cell.

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    fu

    fo

    fu

    fo

    fu

    fo

    fo

    fo

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 4 (25)

    Subcell Change UL to OL (SubCell Load

    Distribution, SCLD, Inactive)

    A subcell change will be requested when:

    downlink path loss is equal or below

    LOL - LOLHYST

    ANDtiming advance is lower than

    TAOL - TAOLHYST

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    GSM Radio Network Features Slide

    03813-LZU 108 3704 Uae Rev C 3

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 5 (25)

    Subcell Change OL to UL (SCLD Inactive)

    A subcell change will be requested when:

    Downlink path loss exceeds

    LOL + LOLHYST

    OR

    timing advance is equal to or increases

    above

    TAOL + TAOLHYST

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 6 (25)

    OL/UL Subcell Change (SCLD Active)

    UL subcell as first choice so if capacity exist,

    use UL

    If OL cell has lower C/I than UL due to tighterfrequency re-use, this is good

    Every SCLD interval, specified by parameter

    SCLDTIMEINT, the traffic load in the UL subcell

    that are active for SCLD are examined for SCLD.

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    GSM Radio Network Features Slide

    03813-LZU 108 3704 Uae Rev C 4

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 7 (25)

    Subcell Load Distribution

    Percentage of

    active TCHs

    SCLDUL

    SCLDLL

    Subcell change OL to UL(no other condition)

    No subcell change

    Subcell change UL to OL

    (L < LOL, ta < TAOL)

    When the percentage of idle full rate capable TCHs in the UL subcell equals or

    falls below SCLDLLsubcell changes from the UL to the OL subcell are initiated.

    When the same percentage exceeds SCLDULthen subcell changes from the OL

    to the UL are initiated. In between no subcell changes are initiated.

    Percentage

    of idle TCHs

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 8 (25)

    Subcell Load Distribution

    Apart from OL to UL subcell change due to Subcell Load

    Distribution the mobile station can also be requested to

    move to the UL subcell because of excessive timing

    advance and/or path loss. The following condition is used:

    L >LOL+ LOLHYST or

    ta TAOL+ TAOLHYST

    This condition is checked by Locating every SACCH period.

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    GSM Radio Network Features Slide

    03813-LZU 108 3704 Uae Rev C 5

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 9 (25)

    Subcell Load Distribution

    No SDCCHs should be configured in OL subcells which make

    use of Subcell Load Distribution. This is because Subcell Load

    Distribution is limited to traffic channels, i.e. the SDCCH

    channel in the OL subcell can not be accessed.

    Full rate connections as well as half rate connections can be

    moved by Subcell Load Distribution. High Speed Circuit

    Switched Data (HSCSD) connections can not be moved, but will

    remain in the UL subcell.

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 10 (25)

    Handovers

    Subcell Load Distribution inactive

    Possible to make handover from either the OL or the UL subcell in the serving

    cell to either the OL or the UL subcell in the target cell.

    Handover to an OL subcell is only allowed if the the OL subcell is co-sited

    (indicated by the parameter CS).

    Subcell Load Distribution active

    Handovers to another cell are only possible to the UL subcell.

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    GSM Radio Network Features Slide

    03813-LZU 108 3704 Uae Rev C 6

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 11 (25)

    BCCH in Overlaid Subcell

    The BCCH carrier is configured in the OL subcell (usually

    a non hopping carrier)

    The BCCH carrier uses the same output power as the UL

    subcell

    Signaling (SDCCH) is carried out in the OL subcell as first choice

    TCH traffic in OL subcell, restricted by LOL and TAOL, will be

    close to the site making sure that TCH connections on the BCCHcarrier are only used at high SS

    By restricting the traffic close to the site, a tight reuse of

    BCCH frequencies can be applied

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 12 (25)

    BCCH in Overlaid Subcell

    A non-hopping BCCH carrier in a FLP network does not benefit from

    interference or frequency diversity

    The BCCH carrier should not be used at low signal strength

    With the feature BCCH in OL, only MS:s with low path loss will use the

    BCCH frequency

    UL subcell

    OL subcell

    1/1 hopping TCH

    4/12 BCCH

    LOL

    Traffic taking area

    Coverage area

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    GSM Radio Network Features Slide

    03813-LZU 108 3704 Uae Rev C 7

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 13 (25)

    BCCH in Overlaid Subcell and SCLD

    SCLD inactive

    Only LOL and TAOL are used as criteria to load the BCCH

    Requires tuning of the path loss and timing advance values

    Recommendations: put TAOL to 61 (max) and optimize LOL

    SCLD active

    Easier to load up the BCCH without tuning of LOL

    The hopping channels in the UL subcell are used during low traffic

    At high traffic load, SCLD will move the mobiles with the lowest

    path loss to the OL subcell

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 14 (25)

    Capabilities

    A new CHAP is introduced (CHAP 8):

    CHAP 5 as base (OL Subcell as last resort)

    Enables call setup in the overlaid subcell

    Subcell Load Distribution (SCLD) can be active or inactive when used

    together with BCCH in OL (inactive SCLD requires an SDCCH/8 in the

    UL subcell)

    Extended Range should not be used together with BCCH in OL

    With a good BCCH frequency plan the reuse can go down to 10 - 12

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    GSM Radio Network Features Slide

    03813-LZU 108 3704 Uae Rev C 8

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 15 (25)

    Dimensioning Considerations

    The output power and the size of the OL subcell must

    be so small that the OL subcell not causes or suffers

    from interference.

    The OL subcell must not be too small. Then it will not

    serve any traffic and capacity will be wasted.

    It is important to dimension the OL subcell so it will be

    congested before the UL cell since traffic can spill

    over from the OL subcell to the UL subcell.

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 16 (25)

    Subcell Change and Handover Possibilities at

    Co-Siting

    CS = YES

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    GSM Radio Network Features Slide

    03813-LZU 108 3704 Uae Rev C 9

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 17 (25)

    Subcell Change and Handover Possibilities if

    not Co-Sites

    CS= NO

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 18 (25)

    GPRS conciderations

    GPRS channels can only be allocated in the UL subcell.

    The reason being that the GPRS MS performs cell change by itself.Therefore, the system is not controlling the cell change and cannot

    distribute GPRS MS between subcells.

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    GSM Radio Network Features Slide

    03813-LZU 108 3704 Uae Rev C 10

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 19 (25)

    Note

    The immediate assignment is always carried out in the

    UL subcell (unless CHAP 8 is used).

    Assignment to a another cell is not allowed to an OL

    subcell unless the cells are co-sited (if SCLD active

    assignment to another cell is only possible to the UL

    subcell).

    At congestion in the UL subcell it is possible to assign

    a traffic channel in the OL subcell as a last resort.

    Intra-cell handover between subcells is allowed at

    congestion. An intra-cell handover from the OL to the

    UL subcell is also allowed if MAXIHO have been

    reached.

    03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 20 (25)

    Drawbacks with OL/UL Subcells

    In order to improve the interference situation for

    the frequencies in the OL subcell substantially,

    the OL subcell often must be made very small.

    The gain of frequency hoppin