BCCH in OL_Cingular

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


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


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03813-LZU 108 3704 Uae Rev C 2


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


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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03813-LZU 108 3704 Uae Rev C 3


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


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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03813-LZU 108 3704 Uae Rev C 4


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



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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03813-LZU 108 3704 Uae Rev C 5



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.


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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03813-LZU 108 3704 Uae Rev C 6


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


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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03813-LZU 108 3704 Uae Rev C 7


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


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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03813-LZU 108 3704 Uae Rev C 8


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.


Subcell Change and Handover Possibilities at

Co-Siting

CS = YES


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03813-LZU 108 3704 Uae Rev C 9


Subcell Change and Handover Possibilities if

not Co-Sites

CS= NO


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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03813-LZU 108 3704 Uae Rev C 10


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.


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.


11/13


03813-LZU 108 3704 Uae Rev C 11


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.


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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03813-LZU 108 3704 Uae Rev C 12


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.


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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03813 LZU 108 3704 Uae Rev C 13


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.


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

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