RF Optimisation

s


Main TopicsWhat is network optimisation? 2

Why optimisation? 2

Aim of network optimisation 3

Advantages for the customer 3

Planning vs. optimising 4

Major problem areas 4

Radio optimisation related processes 5

Tuning 5

Test types 6

Measurement analysis 6

Change request and action 7

Acceptance tests 7

Ongoing optimising 8

Pre-analysis: general network check 8

Customer complaints analysis 9

Collect/analyse OMC statistics 9

Collect/analyse drive test measurements 10

Implement changes 11

Test mobile 11

Repeated call setups 12

Continuous call 13

Statistics 14

Concept for optimisation 14

Analysis programs 15

Problem symptoms 15

Coverage analysis 16

Test mobile measurements 16

Possible problem areas 17

Antenna configuration 18

Antenna types - typical beam patterns 18

Antenna fine tuning 19

Omni vs. sectorised 20

Vertical antenna beam 20

Tilting 21

Antennadiversity type 22

Verification of RF network design 23

Site check 23

Antenna isolation 24

Site physical configuration 25

Site-to-site distances and distribution 25

Special features for improving coverage 26

Cell splitting, sectorisation 26

DTM check 27

Propagation model verification 27

Link budget analysis 28

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Main Topics (continued)Dropped call analysis 29

Call setup analysis 30

MAXRETR 30

Handover performance analysis 31

Handover parameters 31

Consequence of missing neighbours 32

Consequence of many neighbour definitions 32

Handover measurements 33

Handover parameters 33

Radio link measurements 34

Handover algorithm 36

Handover criteria - quality 37

Handover decision 37

Intracell handover 38

Level handovers 39

Distance handover 40

Power budget handover 40

Cell reselection 41

Speech quality analysis 43

Downlink interference measurement 43

Frequency changes 44

BSIC optimisation 45

Call setup/handover mechanisms 45

Location area codes 46

Interference reduction 46

Power control 47

Frequency hopping 48

DTX 49

Channel configuration 50

Capacity enhancements 50

Adding TRX 51

Interference reduction features 51

Traffic load distribution 52

Call setup/handover mechanisms 52

Hierarchical cell structures 53

Concentric cells 53

Overlaid micro-and picocells 54

Microcell frequency planning 54

Speed sensitive handovers 55

Half rate coding/dual rate operation 55

Cell parameter optimisation 56

Performance measurements 56

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What is Network Optimisation?

Improving Capacity, Quality and General Performance of the existing Network Infrastructure

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Why Optimisation?

Coverage holes

Performance degradation by interference

Different subscriber distribution compared to that assumed for the network design

Unexpectedly high subscriber growth

Extensive network expansions ongoing

Frequency resources at the limit

Unexpected mobility profile of

subscribers

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Aim of Network Optimisation

Improved Network Quality➨ Speech quality, Call success rate, Call setup time

Improved Network Availability➨ Service area , Radio Coverage

Optimised utilisation of installed equipment➨ Increase in subscriber potential

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Advantages for the Customer

Optimum utilization of the system resources

Minimized costs

Reduced subscriber complaints

Optimised subscriber satisfaction

Increased Profit One step ahead of theCompetitors

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Planning vs. Optimising

Thorough network planning from start can reduce the optimisation effort significantly!

➨ In a poorly planned network, achievable optimisation effects without major re-design are rather marginal

A close link between the two activities is necessary

Be involved

Feedback result

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Major Problem Areas

no coverage

interference

blocking

handover not working

HW/SW failures

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Radio Optimisation Related Processes

The following processes involve optimisation related activities➨ Tuning Process

✲ drive tests

✲ adjustment of network parameters

➨ Acceptance tests

➨ Ongoing Optimisation✲ Repeated quality control and improvement as network grows / matures

Tuning Acceptance Tests

OngoingOptimisation

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Tuning

Objectives :➨ Verify network configuration against current planning status

➨ Identify and eliminate equipment faults (HW/SW) and installationerrors

➨ Ensure that the network is ready for acceptance testing

TestMeasurement

MeasurementAnalyzing

Change RequestAction

Repeat Processuntil

Agreed Quality

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Test Types

Continuous drive test➨ setup a test call and drive over an area for detecting lack of coverage,

missing handovers, interferences etc.

Spot test➨ detail measurement to be taken at dedicated problem spots for detail

analyzing of specific problem

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Measurement Analysis

Antenna Installation check➨ height, orientation and tilt

Basic cell parameters and functions➨ OMC

✲ BCCH, BSIC, CI, LAC

✲ Neighbour List, consistency

✲ HO and power parameters

✲ Call Setup on all timeslots and speech quality check

✲ HO to other sectors or other neighbours

Test measurement (TEMS etc. together with a GPS)➨ Signal Strength

➨ Co-channel and adjacent interference

➨ Handover relations

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Change Request and Action

SBS System Database ➨ Change BCCH to avoid interference

➨ Change HO-Margin

➨ Add neighbour relations (Mutual)

Site Hardware➨ Antenna tilt etc.

System error➨ Software bugs

➨ Transmission sync. (ADPCM)

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Setup TestScenario

PerformingTest

Test Result

Acceptance Tests

Setup Test Scenario➨ Test Purpose

➨ Test Definitions✲ Coverage Criteria

✲ Coverage Area

✲ Successful Call

➨ Test Condition

➨ Test Equipment

➨ Test Methodology

✲ Test Routes

✲ Test Procedure

✲ Test Duration

➨ Test Analysis✲ Acceptance Criteria

➨ Test Results✲ Signal Level

✲ Signal Quality

✲ Handover

✲ Call Success Rate

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Ongoing Optimising

For improvement of the network after it is launched and filled up by subscribers

Collect / analyse

drive testmeasuremts

Collect / analyse

drive testmeasuremts

Collect / analyse

complaints

Collect / analyse

complaints

Collect / analyseOMC

statistics

Collect / analyseOMC

statistics

Propose / implementchanges

Propose / implementchanges

Repeatprocess until

agreed quality

Repeatprocess until

agreed quality

Pre-analysis: Generalnetworkcheck

Pre-analysis: Generalnetworkcheck

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Pre-analysis: General Network Check

Steps to be carried out:➨ Kick-off meeting

➨ Determine original network planning objectives

➨ Collect information about network status

➨ Determine functional network structure, e.g.– - BTS / BSC locations., antenna direction etc.

– - services and features used

– - network structure (macrocell, microcell etc.)

➨ Determine the network element configuration, e.g.– - number of TRX per cell

– - sector / omni config.

➨ Visit selected sites (if necessary)

➨ Database analysis

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Customer Complaints Analysis

Additional source of information, but difficult to handle

Customer service desk must collect all relevant information➨ Caller and Called No. (PSTN->MS, etc.)

➨ What is the problem? (Voice Quality, Can’t make a call, etc.)

➨ MS is moving or fixed while make call

➨ Where did the problem occur?

➨ When?

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Collect / Analyse OMC Statistics

OMC Measurement➨ Handled traffic (congestion on TCH, SDCCH)

➨ dropped calls

➨ Interference

➨ Handover reason (due to UL_QUAL, Powerbudget, distance…)

Advantages over test drives:➨ Less labor intensive and time consuming

➨ More comprehensive, based on large number of users

➨ not limited to time of test drive

➨ Uplink and Downlink analysis possible

➨ Subscriber behavior mix of outdoor, indoor, incar use

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Collect / Analyse OMC Statistics

Disadvantages, limitations:➨ Limited geographical resolution (Where does the problem occur?)

➨ Cannot separate problems due to coverage from other✲ Call attempts in uncovered areas are not counted

✲ Call drop due to lack of coverage

➨ Network must have minimum load for reliable statistics

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✲ Serving signal level

✲ BER (Rxqual)

✲ Channel Number

✲ CI and LAI

✲ Timing Advance

✲ Layer 3 messages

✲ BSICs

✲ Signal and power levels of neighbouring cells

Collect / Analyse Drive Test Measurements

Test types➨ Continuos drive test (Trace mode)

➨ Spot test

➨ Network performance test (Statistical mode)

Test Measurement➨ Collect MS measurement report data (Downlink only!!)

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Implement Changes

Changes related to database parameters

Actions related to site hardware

Problems to be solved by Normal Roll-out activities

Problems to be solved by other system experts

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Test Mobile

Various modes, e.g.➨ Repeated call setups

➨ Continuous call

➨ Scanning mode✲ check for spectrum

occupancy✲ check for BCCH

with no neighbour

relations

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Repeated Call Setups

Method➨ call setup

➨ hold for predefined time period and then release✲ predefined time = mean holding time

✲ call may be dropped earlier

➨ repeat call setup after predefined waiting time (typical 15 s)

Purpose➨ simulate subscriber behavior

➨ wide area quality assessment and trend identification

BaseTransceiver

Station

BaseStation

Controller

MobileSwitching

Center

PSTN-Interface

Um-

Serial MeasuremtSoftware

Abis- A-Interface

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Repeated Call Setups

Typical parameters➨ call setup success rate, setup time, dropped call rate

➨ statistics can be generated in Tornado / Planet, e.g.Call Diagnostics

RxQual Full Threshold: 4

RxQual Full Threshold (%):90

RxLev Full Threshold: 14

RxLev Full Threshold (%): 90

Maximum Setup Time (s): 10

Call Time Setup Clear Down RxQual (%) RxLev (%) Category

1 21:38.8 6.5 OK 100 100 GOOD

2 23:53.1 FAIL FAIL FAIL FAIL NO SETUP

3 26:08.7 5.7 OK 98 85.3 LOW SIGNAL

4 28:23.9 6.4 OK 79.5 100 NOISY

5 30:38.8 5.8 FAIL FAIL FAIL DROPPED

6 32:54.4 12 OK 100 100 DELAYED

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Continuous Call

Method➨ call setup

➨ hold continuously until drive test route complete✲ in case of call drops re-establish

Purpose➨ Wide area quality trace

➨ Locating individual problem areas

➨ Detailed analysis in problem areas

➨ Quality assessment on rural highways etc.

➨ BS Testing and Functional Testing

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Continuous Call

Typical parameters➨ RxLev, RxQual, BCCH, BSIC,

handover, Layer 3 messages etc.

Import into planning tool ➨ Terrain or clutter background

➨ Comparison of measured network performance vs. prediction

Statistics:➨ RxLev, RxQual, handover

success rate

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Statistics

Combine from both modes

Typical measurements also used for acceptance tests

Measurement Test sample unit No. of samples Measured valueRxLev >

-85 dBm Measurement bin (Tornado) 8,432 99.90%RxQual < 4 Measurement bin (Tornado) 8,432 99.20%Handover success rate Handover attempt 61 93.50%Call setup success rate Call attempt 115 90.30%Mean setup time Call successfully setup 106 5.3 sDropped call rate Call successfully setup 106 1.00%

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Performance Measurements

Provide an overview of network performance (statistics)➨ uplink analysis also possible

➨ validity depends on sufficient samples

Examples: ➨ blocking rate

BTS ID

LAC

CI

BSIC

f1

f2

f3

f4

Busy hour

TCH Blocking Rate

6 4

4052

2 4

83

69

16:00:00 66.53%

2 4

4083

2 2

76

67

16:00:00 30.16%

5 4

4051

2 6

79

66

16:00:00 7.91%

22 4

4183

2 0

77

12:00:00 3.96%

1 4

4082

2 1

84

80

13:00:00 3.81%

BTS ID

LAC

CI

BSIC

f1

f2

f3

f4

Busy hour

SDCCH Blocking Rate

25 4

4052

2 4

83

69

15:00:00 32.99%

6 4

4052

2 4

83

69

16:00:00 5.99%

26 4

4171

2 6

63

13:00:00 2.83%

3 4

4041

2 7

87

13:00:00 2.06%

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Performance Measurements➨ Call setup success rate

➨ Dropped call rate

BTS ID

LAC

CI

Busy Hour

Call Set-up Success Rate

25 4 4152 15:00:00 28.4%

29 4 4131 15:00:00 68.0%

15 4 4032 18:00:00 81.3%

5 4 4051 16:00:00 92.1%

26 4 4171 13:00:00 94.1%

11 4 4071 12:00:00 94.7%

BTS ID

LAC

CI

TCHConnections

RF Loss

Inter Cell HOLoss

Intra CellHO Loss

Call Drop

Rate

37 4

4192

19730 1526 23 153 9%

15 4

4032

12740 723 6 58 6%

22 4

4183

10993 485 18 13 5%

25 4

4152

24748 755 12 29 3%

7 4

4011

8849 240 16 23 3%

26 4

4171

15922 219 28 12 2%

29 4

4131

5712 77 8 6 2%

27 4

4172

10421 156 4 4 2%

19 4

4212

9192 130 9 5 2%

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How

to improve the

network?

Alternatives

NetworkSnapshot

QuickCheck

AnalyzingPrograms

• 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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Coverage: Analysis for Fulfilment of Coverage Requirements (Urban, rural ... areas, outdoor, in-car, indoor)

Dropped Call: Analysis for Dropped Calls due to Interference, SW/HW failures, Transmission Network Failures

Call Setup: Analysis for Blocking and CapacityLimitations, Analysis for Resource Allocation Procedures

Handover: Analysis for Efficient HandoverPerformance

Speech Quality: Analysis for Interference

Analysis Programs

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No serviceNo coverageNo System Availability

Network Element FailuresTransmission Network Failures

Low call setup success rateRF Network

No coverageInterferenceBlocking

Fixed Network BSS, SSSBlockingOverloadOther

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, SSSNetwork element failureTransmission network failureOther networks

Mobile Phone

Problem Symptoms

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Coverage Analysis

Test mobile measurements

Antenna configuration check

Verification of RF network design

DTM check

Propagation model verification

Link budget analysis

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Test Mobile Measurements

Collect RxLev measurements together with GPS co-ordinates

Analyse on planning tool

Reasons for poor coverage:➨ serving cell not best server

✲ handover problems

➨ best server signal low✲ check site / network design

Analyse in terms of relevant

thresholds:➨ indoor level

➨ in-car level

➨ outdoor level

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Test Mobile Measurements

Consequences of poor RxLev:

➨ low RxQual➨ vulnerable

to interferenceLimitation with drive tests:

➨ downlink onlyAnother method:

➨ statistical analysis

➨ OMC or drive tests

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Possible Problem AreasDownlink

➨ Output power low

➨ Obstruction of Tx antenna

➨ Antennae not aligned properly

➨ Broken / wrongly connected cables

➨ Database parameters controlling output power

Uplink➨ Receive sensitivity degraded due

to hardware problems

➨ Obstruction of Rx antennae

➨ Antennae not aligned properly

➨ Broken / wrongly connected cables

➨ Lack of diversity gain

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Antenna Configuration

General points to check➨ antenna type, e.g.

✲ omni

✲ directional 60, 90 or 120 degrees

✲ electrical downtilt

✲ cross-polarised

➨ antenna azimuth angle (for directional antennae)✲ coverage targets

➨ antenna tilt angle✲ electrical + mechanical

➨ diversity & isolation✲ e.g. space diversity,

✲ polarisation diversity

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Antenna Types - Typical Beam Patterns

Directional antenna

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Antenna Types - Typical Beam Patterns

Omni antenna with electrical downtilt

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Antenna Fine Tuning

Horizontal Plane:➨ Possible coverage weakness between sectors

➨ Interference reduction

➨ Traffic load distribution

Vertical Plane:➨ Interference reduction

➨ Possible coverage weakness in the short to medium distance range

➨ Traffic load distribution

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Sectorised cell site with differentdowntilt angles

Omni vs. Sectorised

OMNI cells - more difficult to optimise➨ Electrical downtilt possible, however

✲ same for entire cell

➨ Parameters same for entire cell

Directional antennae➨ narrower beam → easier to control interference

➨ tilting less efficient with wider beams

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Solution: Add mechanical downtilt

2° electrical downtilt

0°

3 dB-point: 5.25°

400 m

City

arctan (60/400) = 8.5°

60 m

Ant. Effectiveheight

Vertical Antenna Beam

High gain antennae with sharp vertical lobe➨ shadow under antenna

In practice: For cluttered environments reflections often compensate

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BSh

➨ Maximum: First null angle pointing at cell edge

Tilting

Antenna downtilt often used to minimise interference➨ Minimum: Vertical mail lobe pointing at cell edge

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0 ° 0 °

Electrical Mechanical

➨ Advantages:✲ Better back lobe characteristics

✲ Better lower side lobe characteristics

➨ Disadvantages:✲ Antennas are more expensive

Tilting

Electrical vs. Mechanical downtilt

A combination ofmechanical / electricaldowntilt may be used

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No Tilt Down Tilted 4 degrees

Tilting

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Antenna Diversity TypeSpace diversity

➨ vertical polarisation

➨ in general good performance

➨ requires extra antenna for diversity

Dual polarisation

➨ mobile antenna normally not held vertically

➨ when signals are reflected polarisation change (vertical normally dominates)

➨ cross polarised preferred✲ good performance in urban areas

➨ save one antenna✲ easier installation

Rx

ant.

1

Rx

ant.

2

Typical > 10 Rx

ant.

Horisontal /vertical

Crosspolarised

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Verification of RF Network Design

Site check

Site physical configuration evaluation

Site-to-site distances and distribution

Special features for improving coverage

Site database configuration evaluation➨ Tx power

➨ power control settings

➨ etc.

BTS

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Site Check

Verify that site is implemented according to plan

Check installation e.g.➨ antenna spacing (diversity, isolation)

➨ antennae in one sector are installed in the same plane

➨ antennae alignment

➨ omni antenna installation

➨ cable installation

k

a

Vertical spacing

d

Horisontal spacing

Rx

Tx

Rx Tx

max 15 °

Antennas mounted in different planes

aa=

d d d

Alignment of antennas

Rx Tx Rxd

k1

Rx

Tx

Rxd

k2 k2

Omni

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Antenna Isolation

0102030405060

50

0

75

0

10

00

12

50

15

00

17

50

20

00

22

50

Spacing A/ mm

Isol

atio

n /d

B

Horizontal

Vertical

Isolation by vertical or horizontal separationbetween two antennas K73316..

A

A

Horizontal

VerticalSource: Kathrein

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Antenna Isolation

0

20

40

60

40

0

50

0

65

0

75

0

90

0

10

00

11

50

12

50

Spacing A/mm

Iso

latio

n /d

B

Horizontal

Vertical

A

Horizontal

Vertical

A

Isolation by vertical or horizontal separationbetween two antennas K73416..

Source: Kathrein

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Site Physical Configuration

Antenna height➨ ideally sites within a given area classification should have similar

heights if traffic distribution is uniform

➨ evaluate site height in terms of objective✲ macrocell / minicell / microcell

✲ limitation of interference

✲ clear obstructions

Antenna tilt / directions➨ avoid coverage gaps

➨ target priority areas

➨ limit interference

Appropriate antenna types➨ sectorise omni cells?

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Site-to-Site Distances and Distribution

For an area of uniform structure / terrain / traffic➨ site-to-site distance should be uniform (assuming uniform site design)

Site distribution should reflect➨ coverage characteristics / requirements

➨ capacity requirements

Typical case➨ Downtown: High site density

➨ Suburban area: less dense

➨ Roads: Sites located along a line

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Special Features for Improving CoverageMicrocell

➨ for indoor coverage

➨ outdoor coverage in high capacity areas

Repeaters➨ alternative to microcell where the

traffic needs are low

➨ indoor

➨ outdoor

➨ road coverage

➨ “coverage hole fill solution”

Other indoor coverage solutions➨ distributed anteanne

➨ fibre optic repeater

➨ leaky cable

HCS, e.g.➨ large cells for car-coverage

➨ small cells for pedestrians

Scale = 0.5 Km

Building Outlines

Building Outlines

Building

Outlines

Place

S tr e et

Str ee

t

Micro Micro -- Cell Site Cell Site --LocationLocation

Macro Macro -- Cell Site Cell Site --LocationLocation

Border

Cell

Macro

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Cell splitting, Sectorisation

Change from large cells to small cells

Difficult , Expensive

Mainly driven by capacity requirements

Result: Improved indoor coverage

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DTM Check

DTM resolution➨ horisontal

✲ macrocell (typical 50-100 m for roads, 50 m for small cities, 20 - 40 m for large cities)

✲ microcell (very high resolution, down to building level)

➨ vertical - should be high

Source data➨ heights and clutter derived from paper maps

➨ clutter and / or vector updates by satellite photographs / aerial photos for metropolitan areas

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Propagation Model Verification

Wrong model wrong coverage prediction

In general, standard models have high performance

Highly specialised model may only be valid for a small area

Model performance depends on accuracy of DTM

To tune the model➨ field strength measurements

➨ check existing model against measurements

➨ modify model parameters

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Link Budget Analysis

Check for link budget imbalance

downlink

uplinkMS Peak Power

Rx Sensitivity MS

Rx Sensitivity BS

cable loss uplink

cable loss downlink

antenna diversity gain

combiner loss

PA output power

Balanced Power Budget

Balanced Power Budget

Uplink Power Budget - Downlink Power Budget = 0! Link Power Budget is balanced!

BTS

downlink uplink

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-85,00

-75,00

-65,00

-55,00

0,20 0,40 0,60 0,80Distance from BTS in km

RxLev/dBm

Links balanced

3dB unbalanced

6dB unbalanced

35% Coverage Loss @ 3dB!

55% Coverage Loss @ 6 dB!

RxLev for IndoorCoverage(90%)

Uplink Power Budget - Downlink Power Budget 0! Link Power Budget is unbalanced!

Caused by wrong assumption forReceiver SensitivityDiversity GainPropagation Environment

Link Balancing viaOptimization of DiversityTower mounted amplifierHigh power amplifier

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Downlink

Uplink

40 dBm

37 dBm

-110 dBm

-107 dBm


Increasing BS Output?➨ Unbalanced link budget

Better BS Rx sensitivity or pre-amplifier➨ Must be matched by higher BS TX power for balanced link budget

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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

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Call Setup Analysis

How to measure ➨ drive tests

✲ repeated call setups

➨ OMC measurements

Reasons for failed call setups➨ lack of coverage

➨ database problems✲ database inconsistencies

✲ parameter settings, e.g.– RXLEV_ACCESS_MIN, RACHBT, RACH_MAX_RETRANS

– cell reselection related parameters

➨ network congestion

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BTS

MS

RACH(1)

RACH (2)

RACH

AGCH

✲ E.g: MAXRETR = 2

MAXRETR

Slotted ALOHA mechanism: Several users may attempt to access channel simultaneously

➨ in case of collision new attempts are made

➨ MAXRETR: Maximum no. of retries allowed

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Handover Performance AnalysisWhen moving from one cell to another (neighbour cells) handovers are necessary

SIEMENS AGMON MAR15 15:18:41

SCALE 1:2500

EqualPowerBoundary Mutual Neighbour Non-Mutual Neighbour Missing Neighbour Too many Neighbours

Missing Neighbourdefinition

Handover Failure

Dropped Call

Too many neighbours

Inaccurate handoverdecision

Handover Failure &Dropped Call

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Handover Parameters

Objectives:➨ mobile should be connected to the

“best”cell

➨ avoid unnecessary handovers

Consequence➨ good speech quality

➨ less dropped calls

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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 neighbourInterferer

Cell dragging

s


Consequence of Many Neighbour Definitions

Only about 100 measurement samples are possible during one measurement period for all defined neighbour cells

Number of BCCH carriers Number of samples perIn BCCH Allocation Carrier in SACCH multiframe

32 3-416 6-710 10-118 12-13: :

(Rec. GSM 0508)

Too many neighbour cells

Inaccurate signal level measurement

False handover decisions

Dropped Calls

Problem:Sites with too large coverage area

s


Handover MeasurementsHandover due to a better cell

(RxLev_1 > RxLev_Full)

Handover due to bad quality

Can also be analysed by statistics

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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 parametersPS! Neighbours should in generalbe mutual

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BTSMSNeighbour

BSC

UL

DL

Radio Link Measurements

BTS measurements (Uplink):➨ Signal level

➨ Quality

➨ BS-MS distance

➨ (Interference levels in idle time slots)

s


BTSMSNeighbour

BSC

UL

DL


MS measurements (Downlink)➨ Signal Level

➨ Quality

➨ Signal levels of neighbouring cells (BCCH)✲ Strongest 6 are reported to the Network

s


BTSMSNeighbour

BSC

UL

DL


BSC (In general) ➨ Collects all data

✲ BTS and MS send measurement reports every 480 ms

✲ Makes handover decisions

Siemens Network, BTS makes HO decisions

s


32 27 2923 29 21 19 22 23 21

Average value = 24


Radio link measurements averaging➨ BTS (BSC) receives measurement samples from BTS + MS

✲ every SACCH-Multiframe (480ms,104 TDMA frames)

➨ “Gliding Window”✲ averaging Window size (max.31)

✲ Window is cleared after call setup or handover

s


32 32 2327 27 29 29 29 21 21

Average value = 27

32 27 2923 29 21 19 22 23 21

F F FS S F F S S F

Measurement Values eachSACCH Multiframe (0.48s)

– W_Lev_Full = 2

– W_Lev_SUB = 1

– Gliding Window = 5


s


Inter-cell HOPower Budget

Intra-cell HOdue to Quality

PBGT

IAQUAL

HandoverDecision

HandoverDecision

IRQUAL

LEV

DIST

Inter-cell HOdue to Quality

Inter-cell HOdue to Level

Inter-cell HOdue to Distance

No handoveraction

no

no

no

no

no

yes

yes

yes

yes

yes

Handover Algorithm

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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 handoveraction due to

quality or level

Intercell HOdue to quality

Intercell HOdue to level

Handover Criteria

Handover Region (due to quality and level)

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Handover Types Decision CriteriaIntercell HO 1. RXQUAL_XX > L_RXQUAL_XX_Hdue 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_MaxHO 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_Hdue to Quality 2. RXLEV_XX > L_RXLEV_XX_IH

Handover Decision

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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7Interferer: f1

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

Sever: f10 1 2 3 4 5 6 7

Intracell Handover

Stay within cell, change frequency / time slot situation➨ in general interference different on different timeslots

➨ change to a different cell may be unnecessary

➨ higher traffic load higher likelihood on other timeslots

➨ not effective with frequency hopping✲ parameter settings for intracell handover should be set to reduce such

handovers

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Rx_Qual

Rx_Lev

L_Rx_Qual_XX_H

L_Rx_Lev_XX_IH

L_Rx_Lev_XX_H

Intracell HOdue 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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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

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BTS

Receiver limit sensitivity

L_RXLEV_XX_H (outgoing level HO)

L_RXLEV_XX_IH (inter HO/ intracell quality HO)

RXLEV_MIN (incoming HO)

Level Handovers

RXLEV_MINthreshold for cell to accept incoming handover

L_RXLEV_XX_Hthreshold for initiating outgoing handover due to signal levelrelation with RXLEV_MIN will determine hysteresis

L_RXLEV_XX_IH threshold for initiating inter / intracell quality HO

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➨ Normally used in combination with other criteria, e.g. ✲ cross-water propagation,

✲ elevated bridges etc.

GSM : max 35 km Enhanced by “Extended Cell”

Distance Handover

Maximum allowable BS-MS distance➨ Default: MS_Range_Max=61 (bits Timing Advance,TA)

✲ Maximum value: 63, corresponding to 35 km

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1. RXLEV_NCELL(n) > RXLEV_MIN(n) + Max(0,MS_TXPWR_MAX(n)-P)

2. PBGT(n) = RXLEV_NCELL(n)-(RXLEV_DL+PWR_C_D)+Min(MS_TWPWR_MAX(n),P)-Min(MS_TXPWR_MAX(n),P)

> HO_MARGIN(n)

Power Budget Handover

Select cell with better signal level at given location

HO margin➨ Large enough to avoid “ping-pong HO”

➨ small enough to allow fast HO

Ping-Pong HO

BTS1

BTS2

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C1 = AV_RXLEV - RXLEV_ACCESS_MIN - MAX(0,MS_TXPWR_MAX_CCH-P) > 0C1 = AV_RXLEV - RXLEV_ACCESS_MIN - MAX(0,MS_TXPWR_MAX_CCH-P) > 0

✲ MS takes 5 samples of the received level on each RF carrier which

are averaged

AV_RXLEV = 1/5 * (RXLEV1+RXLEV2+…+RXLEV5)

Cell Reselection

C1-criterion for cell access:

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For example:

Cell Reselection

BTS

MS

DL

MS class 5 (GSM900)AV_RXLEV=-97 dBm

➨ RXLEV_ACCESS_MIN = -100 dBm

➨ MS_TXPWR_MAX_CCH = 29 dBm (0.8W)

C1 = -97 - (-100) - Max(0,33-29)= -1

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Operator BBTS

MS

DLMS class 5 (GSM900)

C1 = -90 - (-110) - Max(0,33-29)

= +16 ✓

Operator ABTS

DL

C1 = -90 - (-100) - Max(0,33-29)

= +6 ✗

✲ RXLEV_ACCESS_MIN = -110 dBm

✲ MS_TXPWR_MAX_CCH = 33 dBm (2W)

✲ RXLEV_ACCESS_MIN = -100 dBm

✲ MS_TXPWR_MAX_CCH = 33 dBm (2W)

•MS receives signal from Operator A and B = -90 dBmOperator A Operator B

Cell Reselection

For example:

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BTS1 BTS2

C1 High power class MS

Low power class MS

Cell_Reselect_Hysteresis

Cell Reselection

C1 criteria➨ Same Location Area

✲ C1 (neighbour cell) > C1 (serving cell)

➨ Different Location Area✲ C1 (neighbour cell) > C1 (serving cell) + Cell_Reselect_Hysteresis

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Speech Quality AnalysisParameters

➨ RxQual

➨ Frame Erasure Rate (FER)

➨ Speech Quality Index (SQI)

Measurements➨ Drive test

✲ preferably continuous call

➨ OMC statistics

Cause for poor quality➨ low signal strength (coverage

related

➨ 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 station within GSM –Network

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Downlink Interference Measurement

Typical requirement➨ speech: RxQual 4

➨ data: RxQual 3

BER % RxQual0.0 - 0.2 00.2 - 0.4 10.4 - 0.8 20.8 - 1.6 31.6 - 3.2 43.2 - 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

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 as “constraints”

➨ 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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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 between clusters

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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

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Call Setup/Handover Mechanisms

20-25 dB street corner loss: Fast handovers required✲ Micro-micro

✲ Micro-macro

➨ Fast measurement averaging

➨ Carefully tuned handover thresholds

➨ Small handover margins

➨ Short penalty timers

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Location Area Codes

Purpose➨ identify location area

➨ in incoming call is paged to all BTS’s 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

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Interference Reduction

Power Control

Frequency Hopping

Discontinuous Transmission DTX

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Power Control

Quality-triggered PC➨ e.g. L_RXQUAL_XX_P = 4

✲ Triggers a power increase at poor quality

➨ e.g. U_RXQUAL_XX_P = 1✲ Triggers a power reduction at good quality

✲ Virtually disabled by setting to “highest” RXQUAL value

✲ Level criterion is more suitable for power reduction

Level-triggered PC➨ e.g. L_RXLEV_XX_P = 25 (-85 dBm)

✲ Triggers a power increase at bad level

➨ e.g. U_RXQUAL_XX_P = 35 (-75 dBm)✲ Triggers a power reduction at good level

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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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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

f1

f2

f3

TDMA frame(8 time slots)

0

0

BCCH

SDCCH

1 Call 1

5 Call 2

Frequency Hopping

Cyclic / Pseudo Random hopping

Baseband / Synthesized hopping

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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

f1

f2

f3


0

0

BCCH

SDCCH

Call 1

Call 2

Frequency Hopping



s


0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

f1

f2,f3,f4,f5,f6,f7

f2,f3,f4,f5,f6,f7


0

0

BCCH

SDCCH

1 Call 1

5 Call 2

f4

f7

f3 f6

Frequency Hopping



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DTX

Goal: Reduce speech data rate from 13 kbps (user speaking) to 500 bps (enough to encode background noise)

➨ reduce MS power consumption

➨ reduce the interference in a cell

SBS parameter for DTX / VAS administration➨ DTXUL -> 0 : MS may use DTX (If possible)

1 : MS shall use DTX

2 : MS shall not use DTX

➨ DTXDL -> FALSE : downlink DTX disabled at BTS

TRUE : downlink DTX enabled at BTS

PS! No gain for data communications

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Channel Type Channel CombinationTCHFULL TCH/F + FACCH/F + SACCH/FMAINBCCH FCCH + SCH + BCCH + CCCH (AGCH+PCH+RACH)MBCCHC FCCH + SCH + BCCH + CCCH + 4 (SDCCH+SACCH)SDCCH 8 (SDCCH + SACCH)TCHF&HLF* TCH/H(0) + FACCH/H (0) + SACCH/H(0) + TCH/H(1)BCBCH* FCCH + SCH + BCCH + CCCH + 3 (SDCCH+SACCH) + CBCHSCBCH* 7 (SDCCH + SACCH) + CBCHCCCH* BCCH + CCCH

Note: * in SBS BR 3.0

Channel Configuration

✲ For example,– 1TRX : TS0 -> BCBCH

TS1-7 -> TCHFULL

– 2 TRXs : TRX0, TS0 -> MAINBCCH

TRX0, TS1 -> SCBCH

TRX0, TS2-7 -> TCHFULL

TRX1, TS0-7 -> TCHFULL

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Capacity Enhancements

Easy approach: Add TRX’s

Problem: No more frequencies:➨ Options

✲ Traffic load distribution

✲ Interference optimisation features: FH, PC, DTX

✲ Sectorisation: Increasing cell density

✲ Cell splitting: Increasing site density

✲ HCS– Dual band operation (e.g. GSM900/DCS1800)

– Dual mode operation (e.g. GSM900/DECT)

– Underlay / Overlay

– Overlaid micro- and picocells

✲ Half rate coding

✲ Migration to 3rd Generation Systems

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Sec TRX GOS 2% Week1 Week2 Week3 Week4 Week5 Week6 Week7BTS1 1 3 14.9 10.53 9.66 10.21 9.88 10.54 9.97 10.37BTS2 2 2 8.2 7.43 7.26 7.59 6.98 7.55 8.02 8.33BTS3 3 3 14.9 11.92 11.4 12.12 11.82 11.75 12.02 12.15

Adding TRX

Congested cells found by OMC measurements

➨ Sector 2 will experience congestion

➨ Sometimes percentage limit, e.g. 80%, of full load defined✲ Sector 3 is near that limit

Possible limitations of TRX extensions:➨ Need for changed hardware configuration costly

✲ e.g. new BTS rack needed

➨ Frequency Spectrum limited

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✓No additional sites or frequencies required

✓Available, stable

✓Implementation causes no disturbance ofnetwork operation

✗ L ittle or no effect if available spectrum is verylimited (BCCH limitations)

✓No additional sites or frequencies required

✓Available, stable

✓Implementation causes no disturbance ofnetwork operation

✗ L ittle or no effect if available spectrum is verylimited (BCCH limitations)

Interference Reduction Features

Frequency Hopping (FH)

Dynamic Power Control (PC)

Discontinuous Transmission (DTX)➨ allow tighter frequency re-us

(already considered for 40-60 Erl./km2 in macrocell layer with 5 to 10 MHz)

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Default HO boundaries

Changed HO boundaries

Traffic Load Distribution

Traffic in a cell related to cell coverage area

If sufficient overlap between cells:➨ reduce traffic by changing cell boundary

✲ antenna downtilt

✲ reduce power (PWRRED)

✲ alter handover boundaries

➨ Usually a temporary solution only

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Call Setup/handover mechanisms

Relieve macrocells from traffic

➨ Umbrella type handover into microcells

➨ “Directed retry”✲ Allows call setup In second-best server, shares traffic resources between

layers

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O Ls

L

E

C

C

I

P Indoor coverageOutdoor Installatio n

Parking lot

Contiguous Microcellular Coverage

Hotspot

Subway Coverage Extension

Hierarchical Cell Structures

Underlay/Overlay

Umbrella cells: Dominant site with large coverage area➨ low traffic - fast mobiles

Macrocells: Antenna above average rooftop level➨ normal traffic

Microcell: Antenna below average rooftop level➨ cover small high traffic areas

Picocell: Antenna

usually indoors➨ coverage to building

or parts thereof - e.g.

Business users

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f3 f1 f2 f3

Signal level Signal levelC/I = 17 dB C/I = 17 dB

C/I = 0 dB

Concentric cells

“Inner cell” can use 1 x 3 reuse pattern

Special handover mechanisms between layers

Limited gains for uniform traffic distribution

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Macrocells

Microcells

Picocells

Overlaid Micro- and Picocells

The smallest cells should absorb most of the traffic in their coverage area

Larger cells for fast moving mobiles / areas not covered by small cells

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ServingBTS

Micro BTS

Microcell Frequency Planning

Different resolutions required for different layers➨ flexibility of planning tool needed

Dedicated frequency bands for different layers➨ Reduce complexity of frequency optimisation task

➨ Guard band may be needed to avoid adjacent channel interference

Call Setup/handover strategy➨ reduce macrocell traffic

➨ determine mobile speed

➨ Fast handovers✲ Loss around street corner: 20 dB!

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Speed Sensitive Handovers

Mechanisms to separate fast from slow mobiles➨ mobile class

✲ today mostly same class is used (e.g. GSM900 class 4)

➨ measurement of the timing advance delta✲ only works for direction away from site

➨ cell type ✲ try to keep handovers within same layer unless speed change

➨ mean time between handovers

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Half Rate Coding / Dual Rate Operation

Has potential to double network capacity➨ Advantages:

✲ No additional sites / frequencies required

✲ Minimum investment for infrastructure upgrade

➨ Disadvantage:✲ Speech quality degradation (reduction of speech bit rate from 13 kb/s to

6.5 kb/s)– Especially mobile-to-mobile calls

➨ Gain depends on ratio full rate users / half rate users / data traffic

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Cell Parameter Optimisation

Default parameter sets:➨ PS! 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

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FH

, PC

, DT

X

Eff

ect

Cost, Effort

Und

erla

y/O

verl

ay

Cel

l par

amet

erse

ttin

g

HR

Dual band

AddingTRX

Fine tuning of antennaorientation and tilt

FrequencyChanges

Dual mode

Sect

oris

atio

n

Pre

amps

Repeaters

Overlaidmicrocells

Cel

l spi

ltti

ng

Possible Network Optimisation Measures

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Increasing Network Capacity

The relationship between quality and capacity ➨ In a congested network, quality can deteriorate very quickly:

– Violation of all 4 basic quality criteria

Congestion

Interference/Noise

Poor speech quality

Droppedcall

Extended callsetup times

Unavailabilityof service

RF Optimisation

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