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8/13/2019 BCCH in OL_Cingular
1/13
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.
A
Bf1,f2,f4f4
f4
f3,f4
A
Bf1,f2f4
f4
f3,f4
f4
f4
OL UL
8/13/2019 BCCH in OL_Cingular
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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
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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 hopping is reduced when
the available frequencies are divided into two
channel groups.
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GSM Radio Network Features Slide
03813-LZU 108 3704 Uae Rev C 11
03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 21 (25)
Parameter Summary
Main controlling parameters
SCTYPEidentifies the subcell type, overlaid or
underlaid, within a cell.
LOLis the path loss threshold for the serving area of
the overlaid subcell within a cell. This parameter is set
per overlaid subcell.
TAOLis the timing advance threshold for the serving
area of the overlaid subcell within a cell. Thisparameter is set per overlaid subcell.
03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 22 (25)
Additional Controlling Parameters
LOLHYSTis the path loss hysteresis for the serving area
of the overlaid subcell within a cell. This parameter is set
per overlaid subcell.
TAOLHYSTis the timing advance hysteresis for the
serving area of the overlaid subcell within a cell. This
parameter is set per overlaid subcell.
BSTXPWRis the base station power at the reference point
for the locating algorithm on the non-BCCH frequencies
within a cell. This parameter is set per subcell.
BSPWRTis the base station output power after the power
on the non BCCH frequency within a cell. This parameter
is set per subcell.
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GSM Radio Network Features Slide
03813-LZU 108 3704 Uae Rev C 12
03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 23 (25)
TSC is the Training Sequence Code for the specified
subcell within a cell. This parameter is set per subcell, but
it is not available for cells without an overlaid/underlaid
subcell structure. Note that it is recommended not to
changeTSC in the underlaid subcells.
CS indicates if a cell shares the same site as its
Neighbour. This parameter is set per neighboring cell
relation and it can take the values: YES, the cell is co-sited with its Neighbour.
NO, the cell is not co-sited with its Neighbour.
03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 24 (25)
Parameter Controlling Dynamic OL/UL Subcells
OL/UL subcells
Parameter Default Value range Unit
SCLD OFF ON, OFFSCLDTIMEINT 100 100 to 1000 ms
SCLDLL 20 0 to 99 %
SCLDUL 30 0 to 100 %
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GSM Radio Network Features Slide
03813 LZU 108 3704 Uae Rev C 13
03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 25 (25)
Value Ranges and Default Values
Parameter
name
Default
value
Rec. value Value
range
Unit
SCTYPE - UL, OL
LOL - 0 to 150 dB
TAOL - 0 to 61 bit
periods
LOLHYST 3 2 0 to 63 dB
TAOLHYST 0 0 0 to 61 bit
periods
BSTXPWR - 0 to 80 dBm
BSPWR - 0 to 80 dBm
TSC BCC (1) 0 to 7
CS NO YES, NO
MAXIHO 3 FH: 2, no FH: 3 0 to 15
PTIMBQ 10 15 0 to 600 dB
TINIT 10 10 0 to 120 SACCH
period
TIHO 10 10 0 to 60 sec
Controlling parameters
(1) Initially, the TSC is defined by the BCC in the BSIC for the cell.
03813-LZU 108 3704 Uae Rev C GSM Radio Network FeaturesSlide 26 (25)
Value Ranges and Default Values, SCLD
SCLD OFF ON, OFF
SCLDTIMEINT 100 100 to 1000 ms
SCLDLL 20 0 to 99 %
SCLDUL 30 0 to 100 %
Parameters controlling Dynamic OL/UL Subcells
Parameter name Defaultvalue
Recommendedvalue
Value range Unit
Recommended