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Co-BCCH Optimization for PMCL
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HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential
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www.huawei.com
Co-BCCH Optimization
PMCL 12-May-2009
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Page 2
Co-BCCH Introduction
Co-BCCH Parameter Settings and Optimization
Counter and KPI for Concentric Cell Monitoring
Contents
3.
1.
2.
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Page 3
Co-BCCH Introduction
What is Co-BCCH?
Co-BCCH: Common BCCH Cell, also called GSM900&DCS1800, Multi-band
cell;
Based on Enhanced Concentric Cell Algorithm;
Two layers in a cell: UL (900M) and OL (1800M);
The UL covers the whole cell area, The OL may not match the UL coverage
area;
UL manages BCCH, SDCCH,PDCH and TCH channels, while OL only manages
the TCH channels
UL(GSM 900) carries BCCH, SDCCH, PDCH & TCH, For Coverage
OL(DCS 1800) contains only TCH, For Traffic Load
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Co-BCCH Introduction
Why Co-BCCH?
Improve capability:
UL and OL share the BCCH, SDCCH, PDCH, and the TCH channels will
be increased accordingly
Frequency restrict:
The frequency resource doesn’t support high configuration.
Simplify network structure:
Reduce number of cells in the network
Reduce number of Location Area Codes
Reduce number of neighboring cells
Simplify multi-layer network into one layer network
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Page 5
Co-BCCH Introduction
Co-BCCH Coverage
GSM900 BCCH
SDCCH/TCH
GSM1800 BCCH
SDCCH/TCH
Co-Site Co-BCCH
DCS1800 cell
SDCCH TCH
DCS1800 cell
SDCCH TCHGSM900 sub cell
DCS1800 sub cell
SDCCH
TCH
Accept by GSM900 sub-cell
GSM900 BCCH
SDCCH/TCH
DCS1800 TCH
Radius regulated enable
TA, RX_LEV , RX_QUAL
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Page 6
Co-BCCH Introduction
Co-BCCH TCH Assignment
The TCH Assignment mechanism in Co-
BCCH cell is the same to normal UO cell
Basically base on: Rxlev 、 Rxqual 、 TA
Specially: Classmark 3 which has higher
priority than TA\Lev\Qual
If did not know classmark 3, only assign the BCCH
frequency band TRX
Handover request (classmark 3)
GSM900 BCCH
SDCCH/TCH
DCS1800 TCH
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Co-BCCH Introduction
Co-BCCH Handover
GSM900 cell
(underlay)
DCS1800 cell
(overlay)
Adjacent GSM900 cell
DCS1800 cellDCS1800 cell
B : Load (Capacity), RXLEV (Coverage)
A : RXLEV (Coverage), RXQUAL C : RXLEV (Coverage), RXQUAL
Adjacent GSM900 cell
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Page 8
Risk in Co-BCCH
Distance from
cell antenna
Sig
nal S
tren
gth
(d
Bm
)
-95
-75
0.5 km 1 km
Underlay
GSM900
Overlay
DCS1800
MS REPORTED RXLEV
GSM900
GSM1800 BCCH
MS Can't Measure RXLEV
Different path loss
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Risk in Co-BCCH
GSM900 sub-cell
DCS1800 sub-cell
TA, RX_LEV , RX_QUAL, May
be as good as GSM900
?
?
?
Handover command
Blind Handover from UL to OL
1. Since DCS1800 cells do not have BCCH
channel,
forced handover to DCS1800 cells is blind (no
RXLEV
measurements of adjacent DCS1800 cells).
Risk of dropping calls on DCS1800.
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Risk in Co-BCCH
2. Have to constantly adjust handover parameters to minimize inter-layer
handovers (different cells have different RF environment, morphology
and traffic load).
Solution : For a period Operation & Maintain of COBCCH network, we
can provide formula base on traffic and Key counters.
3. When GSM900 cell experience outage (faulty BCCH TRX, faulty circuit
packs), DCS1800 cell cannot absorb the traffic (lost revenue).
Solution : Configure more than one 900M TRX in the underlay sub-cell,
if BCCH TRX fault, another 900M TRX will replace it.
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Page 11
Restriction of Co-BCCH
• Don’t support different band frequency in one frequency hopping sequence
• Support GPRS in each band, but PDCH must be allocated on TRX whose
frequency band is same to BCCH
• Co-BCCH cell can’t be a Dual Time Slot Extended cell
• Flexibility is not so good as 900-1800 co-site cell
Co-BCCH Co-Site
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Page 12
Co-BCCH Introduction
Co-BCCH Parameter Settings and Optimization
Counter and KPI for Concentric Cell Monitoring
Contents
3.
1.
2.
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Co-BCCH Cell Parameter Settings5 steps to activate Co-BCCH Cell
Cell Type
Co-Cell Property
Avoid blind assignment failure arose by single band MSSet Enhanced
Co-cell Allowed
Be adjacent to itself automatically
Enable BSC getting MRs of UL when MS is occupying TCH on OL.
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Co-BCCH Cell Parameter Settings
Parameters involved- Assignment Assign Optimum Layer
“System optimization” is recommended in Co-BCCH Cell, which indicates the
system selects the optimum layer for TCH assignment as according to uplink
signal strength in MRs provided through the UL's SDCCH
Assign-Optimum-Level Thrsh. Range: 0~63, (-110dBm~-47dBm). 28-35 is recommended
TA Thrsh. of Assignment Pref. Range: 0~255. 63 is recommended
UL Rx-Lev > Assign-Optimum-Level Thrsh. &
TA < TA Thrsh. Of Assignment Pref.
UL Re-Lev < Assign-Optimum-Level Thrsh. Or
TA > TA Thrsh. Of Assignment Pref.
OL ULSystem optimization Mode
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Co-BCCH Cell Parameter Settings
Parameters involved-Concentric handover
Parameters Value
UL to OL HO Allowed Yes
OL to UL HO Allowed Yes
Rx_Lev for Concentric Cell HO Allowed Yes
OL to UL HO received level Thrsh. 20
UL to OL HO received level Thrsh. 30
Rx_Qual for Concentric Cell HO Allowed No
Receiving Quality Thrsh. 60
TA Concentric Cell HO Allowed No
TA Thrsh. 63
TA hysteresis 0
UL to OL Traffic HO Allowed No
Traffic Thrsh. of underlaid 70
Underlaid HO Step period 5
Underlaid HO Step level 5
OL subcell
UL subcell
DL Rx-Lev >= U to O HO received level Thrsh. &
DL RxQual < Receiving Quality Thrsh. &
TA < (TA Thrsh. - TA Hysteresis) &
Traffic in Underlay > Traffic Thrsh. of underlay
DL Rx-Lev < O to U HO received level Thrsh. or
DL Rx-Qual >= Receiving Quality Thrsh. or
TA > (TA Thrsh. + TA Hysteresis)
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Co-BCCH Cell Parameter SettingsParameters involved-Handover
Pref. subcell in HO of intra-BSC
Range: System Optimization, OL, UL
Recommended: UL. UL is preferred during the intra-BSC HO.
Incoming-to-BSC HO optimum layer
Range: UL, OL
Recommended: UL. UL is preferred during the incoming-to-BSC HO.
ULOL
UL configured for incoming handover
Setp1: Handover into UL is preferred
Setp2: If UL is busy enough, handover into OL is performed
Setp3:DLRx-Lev of OL is weak, return to source
cell
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Co-BCCH Cell Parameter Settings Parameters involved-Protection against Ping Pong HO
Properly setting OL to UL HO received level Thrsh and UL to OL HO received level Thrsh.
Penalty Time of UL to OL HO (s): When handed over from UL to OL, If "Penalty allowed" set to "Yes",
system will forbidden MS to handover back to the UL during the "Penalty Time of UL to OL HO (S)".
Range:0~255(s)
Disable intra-cell handover
OL
ULUL to OL HO received level Thrsh.
OL to UL HO received level Thrsh.
Hysteresis1800M users
900M & 1800M users
900M users RX_LEV_ACCESS_MIN
Hysteresis (typical value is 8-12dB) = UL to OL received level Thrsh. - OL to UL received level Thrsh.
The higher the hysteresis, the fewer the ping-pong HO between UL and OL, also traffic distribution will be changed.
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Co-BCCH Parameters Optimization Parameters for Assignment Control
ParametersRecommended Value
Details
Assign optimum layer
System optimization
1.system optimization : traffic distribution can be changed to adapt real traffic model by tuning Assign-Optimum-Level Thrsh, which can preventing congestion on UL, while make good use of OL.
2.UL: calls will be assigned to UL.3.OL: calls will assigned out of OL coverage
Assign-Optimum-Level Thrsh.
23-281.Valid if Assign optimum layer is set System optimization.
2. The lower the parameter, the more calls assigned in OL. However, TCH Assignment success rate may decrease.
TA Thrsh. of Assignment Pref.
63 Valid if Assign optimum layer is set System optimization.
Optimization for Assignment
Traffic Optimization Strategy
Optimization ResultsUL OL
Assign optimum layer
Assign-Optimum-Level Thrsh.
congested idle System optimization ↓ Congestion ↓ HSR ↑ Ass-Succ may ↓
normalSlightly congested
System optimization ↑ Congestion ↓ HSR ↑ Ass-Succ ↑
idle congested Underlaid subcell - Congestion ↓ HSR ↑ Ass-Succ ↑
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Co-BCCH Parameters Optimization Parameters for Handover Control
ParametersRecommended Value
Details
Pref. subcell in HO of intra-BSCsystem optimization
UL: keep good handover performance
system optimization: balance UL and OL traffic
Incoming-to-BSC HO optimum layer ULUL: keep good handover performance
OL: maybe out of OL coverage, risk exists.
Rx_Lev for Concentric Cell HO Allowed
YesDetermine whether the receiving level or quality of downlink, or TA is taken as the judgment condition in the Concentric Cell handover judgment. Rx_Lev is absolutely necessarily. Quality and TA is optional.
Rx_Qual for Concentric Cell HO Allowed
Yes
TA Concentric Cell HO Allowed No
UL to OL Traffic HO Allowed NoDetermines whether the traffic in UL is one of conditions for OL to overlaid handover.
Optimization for handover
Issues of Co-BCCH CellPref. subcell in HO of intra-BSC Optimization Results
UL OL
congested idle System optimization Congestion ↓ Ass-Succ ↑
idle congested UL Congestion ↓ Ass-Succ ↑ HSR ↑
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Co-BCCH Parameters Optimization
Parameters for Concentric Handover
ParametersRecommended Value
Details
OL to UL HO received level Thrsh.
20~30
1.The parameter is DL RxLev.
2.Keep at least 10dB difference between OL to UL HO received level Thrsh and UL to OL HO received level Thrsh in order to avoid Ping Pong HO.
UL to OL HO received level Thrsh.
30~401.The parameter is DL RxLev.
2.The value should be greater than Assign-Optimum-Level Thrsh. ,because the difference between uplink RxLev and downlink RxLev.
Optimization of concentric handover
Issues of Co-BCCH Cell
Optimization Strategy
Optimization ResultsUL to OL HO received level Thrsh.
OL to UL HO received level Thrsh
UL is congested, OL is idle ↓ ↓ Congestion ↓ HSR ↓ DCR ↑
UL is idle, OL is congested ↑ ↑ Congestion ↓ HSR ↑ DCR ↓
UL -> OL HSR is low ↑ - HSR ↑ DCR ↓
OL -> UL HO times is low, DCR is high - ↑ Congestion ↑ HSR ↑ DCR ↓
OL < -> UL HSRs are low. ↑ ↑ Congestion ↑ HSR ↑ DCR ↓
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Co-BCCH Introduction
Co-BCCH Parameter Settings and Optimization
Counter and KPI for Co-BCCH Cell Monitoring
Contents
3.
1.
2.
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KPI for Concentric Cell Monitoring
Key factors affecting KPIs of Co-BCCH Cell Whether TRXs of UL are congested is the key factor that affects KPI of Co-BCCH Cell, which
include: HSR, DCR and assignment success rate.
The Rx_Lev of OL is estimated. Once UL is congested, the incoming HO and assignment will
use channels on OL, which causes HSR, DCR and assignment success rate getting worse
Adjusting parameters based on traffic statistics Cell Measurement Monitoring KPIs of concentric cells, such as congestion rate, call drop
rate, handover success rate, CSSR, and so on
OL/UL Measurement Monitoring assignment procedure, inter-cell handover, handover
between UL and OL and traffic distribution on UL and UL. Especially can get which layer has
higher congestion, lower CSSR, higher CDR. UL to OL HSR, OL to UL HSR also can get
Channel Allocation Measurement Monitoring TRX level performance, can get Successful
TCH seizure rate after allocation, call drop rate and so on, help to find out OL&UL problem.
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KPI for Concentric Cell Monitoring
Traffic statistics items for monitoring
Items Formula
BSC Level
TCH call drop rate (%) TCH call drop / Successful TCH seizures
HO succ. Rate from UL to OL (%)
Successful handovers from UL to OL / Attempted handovers from UL to OL
HO succ. Rate from OL to UL (%)
Successful handovers from OL to UL / Attempted handovers from OL to UL
TCH Level
TCH Assignment Success Rate(%)
successful TCH seizures for call [2106] / attempted TCH seizures for call [2090]
TCH call drop rate(%) TCH call drop [2142] / (successful TCH seizures (all) [2105]- Successful intracell handovers[2265])
TCH Congestion Rate (excluding handover)(%)
(TCH seizure failures for call (no radio resource) [2120] + TCH seizure failures for very early assignment [2127]) / (Attempted TCH seizures for call [2090] + Attempted TCH seizures for very early assignment [2091])
HSR(%)([2239] + [2240] + [2243] + [2244]) / ( [2200] + [2205] + [2290] + [2291]) *100%.
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KPI for Concentric Cell Monitoring
Items Remark
Attempted TCH seizures in UL/OL meeting TCH overflow
Indicating the channel allocation of concentric cell, which can be used to adjust Co-BCCH parameters for assignment and handover.
Handover requests incoming intra-BSC (UL/ OL in preference)
Overflows for incoming intra-BSC handover (UL/OL in preference)
Handover requests incoming inter-BSC (UL/OL in preference)
Overflows for incoming inter-BSC handover (UL/OL in preference)
Assignment requests (UL/OL in preference)
Assignment overflows (UL/OL in preference)
TCH traffic volume in UL / Overlaid (ERL)
Attempted handovers from UL to OL(OL to UL)
Indicating the congestion contributing to HSR.
Successful handovers from UL to OL(OL to UL)
Failed handovers from UL to OL (OL to UL) due to congestion
Average downlink level of handovers from UL to OL (OL to UL) Indicating UL/DL Rx_lev
and TA when handover happened between UL an OL.
Average uplink level of handovers from UL to OL (OL to UL)
Average timing advance (TA) of handovers from OL to UL(UL to OL)
TCH call drop in UL/OLIndicating DCR in UL/OL
TCH call drop rate in UL /OL(%)
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