2g rf network optimization cases

8/12/2019 2G RF Network Optimization Cases

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2G RF Optim izat ion

2G RF Network

Optim izat ion Cases

Lampiran 5


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Outline

Problems Sysmtoms

Coverage Analysis

Drop Call Analysis

Call Setup Analysis

Handover Analysis

Speech Quality Analysis

Interference Reduction

Parameter Optim

[email protected] 2


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Alternatives

Network

Snapshot

Quick

Check

Analyzing

Programs

Status of the

Network

Decide further

Analysis Program

Coverage

Dropped Calls

Call Setup Success

Handover Perf.

Speech Quality

General Check

Concept for Optimisation

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No service

No covera e

No S stem Availabilit

Network Element Failures

Transmission Network Failures

Low call setu success rateRF Network

No covera e

Interference

Blockin

Fixed Network BSS, SSS

BlockinOverload

Other

High call drop rateRF Network

No coverageInterferenceHandover failure

Fixed Network BSS, SSSNetwork Element FailureTransmission FailuresOther networks

Mobile terminal

Poor speech qualityRF Network

No coverageInterferencePoor handover performance

Fixed Network BSS, SSS

Network element failureTransmission network failureOther networks

Mobile Phone

Problem Symptoms

[email protected]


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Coverage Analys is


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Page - 6

Shadowed Antenna

Antenna Direction

Antenna Height / down tilt

Output Power

Missing Neighbor Relation

Site Location

Faulty Hardware e.g. antenna

Cell is down

Signal Strength Case

Possible Reasons

[email protected]


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Shadowed Antenna Faulty Hardware

Height/down Tilt

Output Power

Visit site

Check antenna installation

Is there a better antenna

position at same site?

Add reduce down tilt?

Can antenna be placed

lower or higher to give

better coverage?

Check output power

Parameters

BSPWRT - NON BCCH FREQ

BSPWRB - BCCH FREQ

Site Location

Possible to move site?

New antenna location at

same site? Is it necessary

to expand and build a new

site?

Check alarm & BTS Error

log

Visit site

Analysis

Missing Neighbor

Is the call dragged?

Is low SS due to missing

neighbor relations


[email protected]


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Change parameter BSPWR , BSPWRT.

Add neighbor relation.

Physical changes:

Antenna direction

Antenna height, tilt or position

New site as last option.


Possible Solutions

[email protected]


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Shadowed Antenna

Antenna Direction

Antenna Height / down tilt

Output Power

Missing Neighbor Relation

Site Location

Faulty Hardware e.g. antenna

Cell is down


Possible Reasons

[email protected]


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Shadowed Antenna Faulty Hardware

Height/down Tilt

Output Power

Visit site

Check antenna installation

Is there a better antenna

position at same site?

Add reduce down tilt?

Can antenna be placed

lower or higher to give

better coverage?

Check output power

Parameters

BSPWRT - NON BCCH FREQ

BSPWRB - BCCH FREQ

Site Location

Possible to move site?

New antenna location at

same site? Is it necessary

to expand and build a new

site?

Check alarm & BTS Error

log

Visit site

Analysis

Missing Neighbor

Is the call dragged?

Is low SS due to missing

neighbor relations


[email protected]


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Change parameter BSPWR , BSPWRT.

Add neighbor relation.

Physical changes:

Antenna direction

Antenna height, tilt or position

New site as last option.


Possible Solutions

[email protected]


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Drop Cal l Analysis


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Dropped Call Analysis

How to measure

drive tests

repeated call setups (preferred)

continuous calls

OMC measurements Reasons for dropped calls

lack of coverage

interference problems

handover problems

lack of synchronisation in network

problems with other parts of the network

[email protected]


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Overview cont.

TCH Drop Excessive Timing Advance

Low Signal Strength

Bad Quality

Sudden Loss

Other reason

TxNDROP(x=F for full rate, x=H for half rate) total number of dropped TCH connections

incremented when theres abnormally terminated

connections [email protected]


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Dropped Call - Low Signal Strength

Dropped calls due to low signal strength can occur in

downlink (DL), uplink (UL) or bothlink (BL)

Reasons :

Isolated site

Antenna/Feederstoo much downtilt, incorrectorientation, hidden antenna, faulty antenna/feeders

Output powerincorrect power settings

BSC Exchange propertyimproper LOWSSUL/DL

settings

Unforseen subscriber behaviouruse MS in lifts, car park

Missing NREL

Obstaclesbuilding, hills, tunnel [email protected]


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Low SS troubleshooting

Check power settings (BSPWRB, BSPWRT),

power balance Check neighbour relations

i. use site position on map and manually determine

neighbour

ii. find suitable neighbour

iii. consistency check to find missing relations

BTS error logcheck for any hardware faults

indicating high VSWR Perform drivetest

Check for missing neighbours, swapped feeders,

probable obstacles

[email protected]


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Low SS troubleshooting cont.

LOWSSUL & LOWSSDL settings

The settings of LOWSSUL/DL influences thecounter step

If LOWSSDL & LOWSSUL have same value, than

STS would probably indicate most of the low SS

drop is on the UL.

Recommend to have LOWSSDL > LOWSSUL

because MS&BTS sensitivity different and SS on

UL&DL are different

[email protected]


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Dropped Call Bad Quality

Dropped calls due to bad quality can occur in

downlink (DL), uplink (UL) or bothlink (BL)

Reasons :

Frequency planadjacent and co-channel interference No dominant serverlow SS

Missing NRELMS is not able to connect to strongest

server

Hardware problemsantennas, feeders, connectors Environmentnear open water

Externalother networks, microwave links, illegal

transmitters

[email protected]


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Bad Quality troubleshooting cont.

Perform drivetest

can locate interferer by halting the effected cell &performing freq. scanning to locate the interfering cell.

can also use spectrum analyser

check for missing NREL

QLIMUL & QLIMDLensure correct settings.Recommended QLIMUL/DL = 55 for hopping and

QLIMUL/DL = 45 for non-hopping

Reduce interferenceif cant change freq, thenconsider downtilt/power down interferer

Use featuresIHO,DTX, Frequency hopping,

MS/BTS Power Control

[email protected]


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Dropped Call Sudden Loss

Valid when none of the first 3 types of

droppped calls (i.e. excessive TA, low SS,BQ) are indicated and locating procedure

indicates missing measurement results from

MS

[email protected]


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Sudden Loss Probable Reason

Environmentsudden drop in SS, such as whensubscribers enter into building, lift, tunnel etc.

BatteryMS battery finishes during

conversation, or battery being pulled out

BTS/MS hardware fault

Transmission faultsynchronization/ABIS link

fault

Interferencevery sudden and severeoccurrence of interference or bad quality

[email protected]


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Sudden Loss troubleshooting

RLINKT & RLINKUPcheck is correct

settings. Consider increasing for certain

scenarios

Check synchronization and link faults

Check BTS error log

Check if its related to human behaviour

[email protected]


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Dropped Call Other reasons

TCH drops due to other reason than low SS,

bad quality, excessive TA and sudden loss.

Reasons :

No specific countersreasons for it occuring are

subjective Hardware faultsBTS or MS

Transmission/link problems

Maintainence workaffecting network service

Interferencesevere interference problems

[email protected]


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Other reasons - troubleshooting

Check BTS error logany HW faults

Check with O&Mtransmission problems,maintainence work during the effected time

period

Check if indicating uplink interference in cell

Check object typehelp find faulty devices

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Cal l Setup Analys is


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BTS

MS E.g: MAXRETR = 2

MAXRETR

Slotted ALOHA mechanism: Several users

may attempt to access channelsimultaneously

in case of collision new attempts are made

MAXRETR: Maximum no. of retries allowed

[email protected]


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Page - 27

Call Setup Failure Analysis

- Possib le reasons w i th rank ing

Low Signal Strength

Interference

High Congestion on SDCCH

High Congestion on TCH

Transmission Fault

Faulty TRU/Hardware

Central Processor Overload

Software File Congestion

Cell is not defined in [email protected]


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Call Setup Failure Analysis

- Possib le so lut ions

Low signal strengthSignal strengthanalysis.

InterferenceInterference analysis.

High Congestion on SDCCH:Define more SDCCHs.

Activate adaptive configuration of logical channel

feature and immediate assignment to TCH.

High Congestion on TCH:

Add capacity/Tune coverage array.

Activate assignment to worse cell.

[email protected]


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Failed Call Setup (Blocked Call)

Example

Multiple Channel Requests.

Successful Random Access after the

third try.

Congestion in SDCCH.

[email protected]


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Handover Analys is


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H d P t


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Handover Parameters

Objectives:

mobile should be connectedto the bestcell

avoid unnecessary

handovers

Consequence

good speech quality

less dropped calls

[email protected]


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Consequence of Missing Neighbours

Missing neighbour cells

Cell dragging

Poor RxLev Interference Exceeded distancePoor RxQual Poor PBGT

Dropped Calls

Congestion

f1

f1

Defined neighbours

Server

Missing neighbour

Interferer

Cell dragging

[email protected]


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H d P t


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Handover Parameters

Fine-tuning of handover parameters

Moving cell boundaries in order to

Enhance success rate for critical handovers

Minimise local interference at the cell edge

Traffic load sharing between cells

Compared to other opimisation measures

improvement potential is limited

Affected by

Measurement averaging Power control parameters

Neighboursshould in general

be mutual

[email protected]

H d C it i


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Rx_Qual

Rx_Lev

L_Rx_Qual_XX_H

L_Rx_Lev_XX_IH

L_Rx_Lev_XX_H0 63

7Intracell HO

due to Quality

No handover

action due to

quality or level

Intercell HO

due to quality

Intercell HO

due to level

Handover Criteria

Handover Region (due to quality and level)

[email protected]


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Handover Types Decision Criteria

Intercell HO 1. RXQUAL_XX > L_RXQUAL_XX_H

due to Quality 2. RXLEV_XX < L_RXLEV_XX_IH

3. XX_TXPWR = Min (XX_TXPWR_Max,P)

HO due to Level 1. RXLEV_XX > L_RXLEV_XX_H

2. XX_TXPWR = Min(XX_TXPWR_Max,P)

HO due to Distance 1. MS_BS_DIST > MS_Range_Max

HO due to 1. RXLEV_NCELL(n) > RXLEV_MIN(n)

Power Budget + Max (0,MS_TXPWR_MAX(n)-P)

2. PBGT(n) > HO_MARGIN(n)

Intracell HO 1. RXQUAL_XX > L_RXQUAL_XX_H

due to Quality 2. RXLEV_XX > L_RXLEV_XX_IH

Handover Decision

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Rx_Qual

Rx_Lev

L_Rx_Qual_XX_H

L_Rx_Lev_XX_IH

L_Rx_Lev_XX_H

Intracell HO

due to Quality

Intracell Handover

Check for simultaneous occurrence of:

Poor quality (high Rx_Qual) Sufficient signal level

L_Rx_Lev_XX_IH

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L l H d


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Rx_

Lev

Driven route

HO_Threshold_Lev

Server

neighbour

HOMARGIN

MinHOReqInt

Level Handovers

Adjacent cell not stronger than current cell +

HO margin Serving cell has insufficient coverage

emergency handover to cell with better coverage

[email protected]

H d C


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Page - 40

INPUT

Large area DT

Specific area DT

Post-Processing

Analysis

Look for:

Repeated handover (Ping Pong)

Repeated Intra-cell handover

Handover failure,

Unrealistic handover

Handover Case

[email protected]


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Repeated Handover (Ping Pong)

- Examp les

[email protected]


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R t d H d (Pi P )


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Page - 43


- Poss ible Reason 2

Offset only in one direction e.g A-B for Inter

BSC relation

CELL A CELL B

A -> B OFFSET = -5dB

BSC 2BSC 1

No B -> A OFFSET

[email protected]

R t d H d (Pi P )


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Page - 44

No dominant Server


Other Possib le Reasons

No dominant server Locating penalty settings

Too small hysterisis setting

[email protected]

R t d H d (Pi P )


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Page - 45

Antenna direction

Antenna Tilts

Plan for new site

Change Locating Parameter e.g.

KHYST or LHYST


Poss ib le Solut ions

[email protected]

R t d H d (Pi P )


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Page - 46

Change Parameter, KHYST or LHYST

HysterisisCELL A CELL B

HandoverFrom A to B


Poss ib le Solut ion

[email protected]

H d C


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Page - 47

Check layer 3 message

Handover command BSC correct?

Check reason for handover SS, RXQUAL

Target cell?

Handover Case

Handover Reversion

[email protected]

H d R i


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Page - 48

Duplicates of BSIC BCCH combinations in neighboring list

610_31610_31

610_12

606_33

608_32

608_32

Serving cellNeighbor cell 1

Road

Neighbor cell 2

Handover command?

Handover Reversion

Common Reason

[email protected]

H d R i


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Page - 49

Uplink interference in target cell

Downlink interference at MS

Solutions

Interference Investigation

Statistics

Scanning

Handover Reversion

Other Reasons

[email protected]

H d C


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Page - 50

Possible Reasons

Wrong intra-cell handover settings

External Uplink Interference

Possible Solutions

Consider to change parameters:

SSOFFSETUL, SSOFFSETDL

QOFFSETUL, QOFFSETDL

A wrong setting of parameters will cause unnecessary IHO

Turn off Intra-cell Handover?

Handover Case

Repeated In tra-cel l Handover

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H d C


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Page - 51

Handover Case

Unreal ist ic Handover

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U li ti H d


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Page - 52

Possible Reasons

Wrong locating settings, in Serving or Target cell

Note: Could be on purpose e.g. Dual Band network with HCS

Solution

Fix locating settings e.g. MSRXSUFF, BSRXSUFF

Unrealistic Handover

Reason & Solut ion

[email protected]



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Speech Qual i ty Anal isys



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Parameters

RxQual

Frame Erasure Rate (FER)

Speech Quality Index (SQI)

Measurements

Drive test

preferably continuous call

OMC statistics

Cause for poor quality

low signal strength (coveragerelated

interference

low signal strength and

interference

Causes of interference

co-channel interference

adjacent channel interference

intermodulation

mainly on one link only

multipath interference

Interfering cell of

base station

within GSM -

network

Base stationwithin GSM

Network

Downlink Interference Measurement


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Downlink Interference Measurement

Typical requirement

speech: RxQual 4

data: RxQual 3

BER % RxQual0.0 - 0.2 0

0.2 - 0.4 1

0.4 - 0.8 2

0.8 - 1.6 3

1.6 - 3.2 4

3.2 - 6.4 5

6.4 - 12.8 6

> 12.8 7

With frequency hopping:

RxQual not a valid parameter

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Frequency Changes


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Frequency Changes

Sometimes necessary to minimise interference

As network reaches capacity limit this becomes difficult Other frequencies may be affected by the change

Can be done at either interfering cell or victim cell

Choice: Whichever happens to be easier to change

Existing plan may be entered into planning tool asconstraints

search for optimum frequency allocation for a given cell

At a certain point the whole network e.g. in a city may

have to be re-planned

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Frequency Changes


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BCCH: 794 BCCH: 794TCH:797

before

BCCH: 794 BCCH: 797TCH:794

after

Effectiveness depends on TCH traffic load

BCCH / TCH sub-bands are mixed

Could be used as a temporary measure

while traffic load is low

Frequency Changes

BCCH/TCH swapping

Method sometimes used: Alternate betweenclusters

[email protected]

BSIC O ti i ti


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f9

f9

f9

BSIC Optimisation

Base Station Identity Codes

Used by the MS to distinguish between cells

using the same frequency

Co-Channel cells must have different

BSICs

[email protected]

Location Area Codes


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Location Area Codes

Purpose

identify location area in incoming call is paged to all BTSs within LA

Large location area

advantage: less location updates (reduced SDCCH

load)

disadvantage: more paging traffic

Boundaries should not cross high traffic areas

Cell reselection across LA boundaries Parameter Cell_Reselect_Hysteresis (typ. 4 dB) used

to avoid unnecessary signalling due to ping-pong cell

reselections

[email protected]

Power Control


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RXQUAL

RXLEV

L_RXQUAL_XX_P

L_RXQUAL_XX_P

Power Increase

(bad quality)

Power Increase

(bad level)

Power Decrease

(Good Level)

Power Decrease

(good quality)

L_RXLEV_XX_P U_RXLEV_XX_P

2*POW_RED_STEP_SIZE

Power Control

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Interference Case


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Page - 61

INPUT

Large area DT

Identify areas with Rxqual > 5

Identify source using Map and STS

New drive test around problem area?

Specific area DT

Post-Processing

Analysis

TEMS

Logfiles

Interference Case

[email protected]

Types of Interference


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Page - 62

BCCH 590

BCCH 590

High

siteBCCH 590

BCCH 590

BCCH 595

BCCH 600 CASE 1

CASE 2

Types of Interference

Co - Channel interference

Adjacent Interference

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Interference Case


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Page - 63

Poor frequency planNo dominant cell --> low C/I ---> increased Rxqual

Frequency Hopping is off

External interference e.g. jammer

Example of high Rxqual due

to low Signal Strength

Interference Case

Possib le Reasons

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Interference Case


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Interference Case

Poss ib le so lut ions

Enable Frequency Hopping or add frequencies to Hopping

group.

Enable BTS Power Control, MS power control and make it

less aggressive. Change frequency of interferer or interfered cell:

Possible to find new frequency by using TEMS Scanning.

Down tilt or change antenna of interferer. Redo frequency plan.

Add new site.

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p

Cell Parameter Optim

Cell Parameter Optimisation


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Cell Parameter Optimisation

Default parameter sets:

Standard setting suitable for most cases Starting point for possible optimisation, however

more relevant after other optimisation activities

Different parameter standards may be used for

different area types

BTS types

etc.

Danger many parameters easy to lose overview

inconsistencies

deterioration of quality

2g rf network optimization cases

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