Co-BCCH Optimization for PMCL

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


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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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 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 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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Page 7


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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Page 9

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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Page 10

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



Counter and KPI for Concentric Cell Monitoring

Contents

3.

1.

2.





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Page 13

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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Page 14

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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Page 18

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


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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Page 20

Co-BCCH Parameters Optimization

Parameters for Concentric Handover


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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Page 21



Counter and KPI for Co-BCCH Cell Monitoring

Contents

3.

1.

2.





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Page 22

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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Page 23


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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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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