UMTS Pre-Launch Optimization

8/12/2019 UMTS Pre-Launch Optimization

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UMTS Pre-Launch OptimisationO046


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Course Objectives

Understand the Pre-Launch Optimisation framework

Look at potential initial Radio Network issues

Understand Neighbour and Scrambling Code planning issues

Understand and implement UTRAN Parameters

Understand the process of drive testing and its analysis

Have an introduction to Performance Management


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Course Structure

Day 1 (AM)

Revision of P025

Optimisation Overview

Pilot Pollution

Probability of Noise Rise Failure

Day 1 (PM)

Coverage Issues

Capacity Issues

Neighbour Issues

Scrambling Codes


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What is Ec/Io and Eb/No?

W/Hz W/Hz W/Hz

W/Hz W/Hz dBW/HzEb

No

Ec

Io

Eb

No

Eb/No

EbNo

Eb/NoEb

No

W/Hz dBW/Hz

Signal

Intra-cell Noise

Inter-cell Noise

Before

SpreadingAfter

Spreading With Noise

AfterDespreading

/Correlation

PostFiltering

Orthog = 0

Post

FilteringOrthog > 0

f f f

f f f

f f


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What is Processing Gain ?

Processing Gain (dBs) in UMTS= 10 log (3840000/User Rate (bps))


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Course Structure

Day 2 (AM)

Drive Test Analysis

Pre-Launch Optimisation

Procedure

Day 2 (PM)

Functional Testing

Summarising Case Study


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2- Optimisation Overview

O ti i t i O i


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What is Optimisation ?

Strictly speaking, it should be only minor improvements

Fine tuning of Radio Interface and Network Parameters

Major performance assessment should be a part of the Planningprocess

Key issues

Coverage

Functionality

Interference Capacity



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QuestionWhat defines capacity in the UP link?

iN

E

W

b

1

CapacityPole

0

QuestionHow can you increase capacity on theuplink?


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QuestionFor Eb/No of 4.7dB with interference of 0.5. What is

the uplink capacity?

iN

E

W

b

1

CapacityPole

0

kbps853

5.013

3840000CapacityPole

0.53Eb/No3840000W

i

4.7 = 10 log Ratio

0.47 Antilog = ratio

=3


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QuestionWhat defines capacity in the DOWN link?

The Downlink benefits from orthogonality between channelisation codes.

is orthogonality factor and has a value between zero and 1.

iN

E

W

b -

1

CapacityPole

0


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Orthogonal Variable Spreading Factor Codes can be defined by a code tree:

SF = Spreading Factor of code (maximum 512 for UMTS)

SF = 1 SF = 2 SF = 4

Cch,1,0 = (1)

Cch,2,0 = (1,1)

Cch,2,1 = (1,-1)

Cch,4,0 =(1,1,1,1)

Cch,4,1 = (1,1,-1,-1)

Cch,4,2 = (1,-1,1,-1)

Cch,4,3 = (1,-1,-1,1)

OVSF codes


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Capacity

UPLINK

kbps853

5.013

3840000CapacityPole

0.53Eb/No3840000W

i

4.7 = 10 log Ratio

0.47 Antilog = ratio

=3

iNE

W

b -

1

CapacityPole

0

DOWNLINK- Orthogonal =0.5

= 3840000/3

=1280000



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Why is Optimising different for UMTS ?

Single Frequency

Cannot frequency plan around problems caused by rogue sites.

Need to optimise clusters of sites rather than single cells.

Level of loading affects performance

Cell activity affects coverage and throughput. Interpretation of measurements required.

Flexible structure sensitive to small changes in performance

Air interface performance directly affects capacity and coverage.

Mixed Services

p



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When is the Network ready for PreL-Opt?

Network dimensioned and nominal plan produced

KPIs identified

Network performance simulated using a software tool

KPIs are within specs on the tool

Network has been built

Need to verify on the field before acceptance



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Pre-launch Optimisation

Plan (using a planning tool)

Assess and Improve (optimise the plan)

Build

Test

Diagnose Problems

Rectify

Pre-launch optimisation phase



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Quality

Definition

Quality

TargetsMonitor

Quality

Configuration

Analysis

Quality

Reporting

Improvement

Plan

Corrective

Actions

SpecificQuality

issues

Specific

Corrections

Network Quality Cycle



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Post-launch Optimisation (1)

Performance Management

Performance Counters

Increasing network capacity

Adding more sites

Further sectorisation of existing sites

Utilising more than one carrier

Providing indoor solutions



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Post-launch Optimisation (2)

Increasing coverage for higher data rate services

Benchmarking

Parameter Optimisation


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3- Initial Radio Network Planning issues

In i t ial Radio Network Planning Issues


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What the Network was designed for

Network dimensioned for certain services

Voice

64kbps VT, 128kbps DL web browsing

Network dimensioned for certain loading expectations

Network designed on top of existing 2G network


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Basic Terms

RSCP = Received Signal Code Power (W)

RSSI = Received Signal Strength Indicator (W) ISCP = Interference Signal Code Power (W) (non-orthogonal part of RSSI)

Ec = chip energy (J/chip), N0 = noise density (W/Hz)

RSSI = N0*bandwidth = N0*3.84*106

Io = noise density (W/Hz)

ISCP = Io*bandwidth = I0* 3.84*106

Ec/N0 = RSCP/RSSI, Ec/I0 = RSCP/ISCP

SIR = Signal-to-Interference Ratio (measurements done on the DPCCH)

SIR = (RSCP/ISCP)*SF/2 (DL) (3GPP)

SIR = (RSCP/ISCP)*SF (UL) (3GPP)



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GSM Sites legacy



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GSM Sites legacy

Most 3G networks built co-sited with GSM sites

Co-siting often done on a one to one basis

Many times this means same antenna heights, same

azimuths

This can bring a list of pre-launch optimisation issues



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GSM Legacy Issues

Different coverage, depending on used frequencies

GSM 1800 - UMTS 2100

GSM 900UMTS 2100

GSM 1900UMTS 1900

GSM 850UMTS 850

Potential boomer sites

Possible higher Interference



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Planning Tool Examples

UMTS Network co-sited with the GSM Network

Coverage footprints

GSM 900 GSM 1800 WCDMA 12.2 WCDMA 144 WCDMA 384


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GSM 900 GSM 1800 WCDMA 12.2 WCDMA 144 WCDMA 384

Mobile TX 33dBm 30dBm Mobile TX 21dBm 24dbm 24dBm

Thermal Noise -121 -121 Thermal Noise -107 -107 -107

Diversity

Gain

8dB 8dB Processor Gain

Require SNR 14dB 14db Required Eb/No 5dB 2dB 1dB

Receiversensitivity

-111 -111 Receiversensitivity

Rx antenna gain +16dBi +18dbi Rx antenna gain 18dBi 18dBi 18dBi

Body loss -3dB -3dB Body loss

Tx antenna gain 0dBi 2dBi 2dBi

Max Path Loss 151dB 152dB

Frequencyadjustment

11dB 1dB

Max Path Loss 162dB 153dB Max Path Loss


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What about Downlink path loss?

If you allocate 3dbm of power for one service what is the path loss?

If you want 10 of these services. Do you require 30dbm?

How much power is available?

How much power is allocated to pilot?

Things planners MUST understand

Are there any other channels we allocate power to?

How does NR affect path loss?

ALL THE ABOVE IS COVER IN DETAIL ON THE PO25 Course

Li k F il


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Link Failures

Give a list of possible failures inDL?

Give a list of possible failures in UP Link?

Power

Pilot pollution

Hand over

Path Loss

Interference own cell

Interference from other cells

Power of UE

Path loss

GSM L S l ti



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GSM Legacy- Solutions

Down-tilt

Pilot Power management

If necessary, reduce High Sites coverage and introduce low-

height gap-filler sites

Pil t P M t (1)


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Minimum Ec/Io requirement for measurement is20 dB Minimum Ec/Io requirement for demodulation is18 dB

Minimum Ec/Io requirement for proper channel estimation is16 dB

However, the UEs and Scanners actually measure

CPICH_RSCP/RSSI, or Ec/No This difference may be tolerated during the initial Drive Tests, but

needs to be accounted for before Launch

Pilot Power Management (1)

Pil t P M t (2)



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Pilot Power Management (2)

Pilot Power = 5-10% of Total Power (30-35 dBm)

Control Channel Powers = 3-5 dB below Pilot (27-33 dBm)

CCPCHs

Other signalling Channels = 3-5 dB below Pilot (27-33 dBm)

PICH, AICH, SCHs

Summary: Total Non-Traffic Channels = 20-25% of total power


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Pilot Pollution

Active Set and Pilot Pollution



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Active Set and Pilot Pollution

The Cells with which the UE is communicating form the UEs

Active Set

This Active Set is made typically of 3 cells/pilot signals

Any Pilot which is not a member of a UEs Active Set andexceeds a certain threshold (typ. Ec/Io>-15dB) is considered aPolluter

Pilot Pollution is a common WCDMA issue that needs to be

sorted immediately

Why does Pilot Pollution happen?



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Why does Pilot Pollution happen?

No dominant server on an area

Too many strong pilots received

High sites, low down-tilt values

Propagation modeled incorrectly

Cells too close together, product of 1 to 1 co-siting




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UMTS Network co-sited with the GSM Network

Cells too close together

Low or no down-tilts

Pilot Pollution- Solutions



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Pilot Pollution- Solutions

Down-tilt

Pilot Power management

Azimuth management, if possible

If necessary, reduce High Sites coverage and introduce low-

height gap-filler sites



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Probability of Noise Rise Failure

Noise RiseIn i t ial Radio Network Planning Issues


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Noise Rise

The effective noise floor of the receiver increases as thenumber of active mobile terminals increases.

This rise in the noise level appears in the link budget and limitsmaximum path loss and coverage range.

Three Users

Background NoiseOne User

Two Users

Noise Rise and Loading FactorIn i t ial Radio Network Planning Issues


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Noise Rise and Loading Factor

Noise Rise Loading Factor 1 dB 20%

3 dB 50%

6 dB 75%10 dB 90%

UL

-- 1log10RiseNoise 10

Why does Probability of NR failure increase?



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Why does Probability of NR failure increase?

Too many users on a cell

High sites can attract too many users to them

Low NR limit parameter value

Planning Tool ExamplesIn i t ial Radio Network Planning Issues


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High loading on the network

Traffic poorly distributed

Low NR limit parameter values on cells

Some high sites

Prob. of NR failure- SolutionsIn i t ial Radio Network Planning Issues


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Prob. of NR failure Solutions

After dealing with high sites, and Pilot Pollution

Set NR limit parameter to a value of about 6dB

If possible, try to even loading using Azimuth management

If no other option, introduce more cells, consider microcells or

adding an additional carrier



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Coverage Issues

Eb/NoIn i t ial Radio Network Planning Issues


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Eb/No is the Bit Energy we obtain after despreading in thepresence of the Noise generated by all other users and the

Noise from NodeB equipment

Theres a different Eb/No requirement for UL and DL:

Typical requirement 1 to 10 dB

Requirement varies by Bearer, Service, Multipath Profile, MobileSpeed, and Type of Receiver.

Target Eb/No



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Target Eb/No

UMTS Link Budgets are made for Bearers

A UMTS service may use one or more Bearers, with each

Bearer having a QoS Eb/No requirement

A typical Voice Bearer requires an Eb/No of 5dB

A typical 128 kbps Bearer requires and Eb/No of about 2dB

Why do Coverage problems arise? (1)In i t ial Radio Network Planning Issues


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y g p ( )

Failure to meet Eb/No requirements on UL or DL

Simple propagation issues

Low pilot values, High Noise on the network

No diversity

Not enough multipath

Why do Coverage problems arise? (2)In i t ial Radio Network Planning Issues


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y g p ( )

High mobility of users

Low use of soft handovers

Uneven Ec/Io conditions throughout the network

Planning Tool ExamplesIn i t ial Radio Network Planning Issues


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Propagation issues

Low pilot values, High Noise on the network

No diversity

UL Eb/No Failures

Coverage problems- SolutionsIn i t ial Radio Network Planning Issues


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Acknowledge different propagation situation than GSM

Pilot power management

Minimise Noise on the network through down-tilts

Use Rx diversity

Use Mast Head Amplifiers

Optimise soft handover parameters

Downtilting (1)In i t ial Radio Network Planning Issues


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Downtilt antennas.

Consider mounting antennas on the

side of buildings.

Downtilting (2)



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Controlling the backlobe can produce a small but significant

improvement in capacity.

0

0Elec 6Mech

00

6

6

6

6Elec 0Mech

0

6

60

6Elec -6Mech

0

-6

12

0

Mast Head Amplifiers (TMAs)



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Used to lower the Noise Figure of the receiver

Can offset feeder losses

MHA used to increase coverage range

Typ. 1.6 dB Noise Figure (NF)

Typ. Gain of 12dB (adjustable)

Increase uplink capacity Adds Insertion loss on DL (~ 1.3 dB)

AntBias-T

DC

TMA

by pass

Uplink Rx Space Diversity



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Common to have two receive antennas per sector at the base station.

Even if highly correlated, coherent combination should yield ~3 dBimprovement.

In practice a gain of 4 dB or more is expected from antennas spaced 2-3 m

apart.

Receive

antenna 1

Receive

antenna 2

Uplink Rx Space Diversity



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This is not conventional space diversity.

Each antenna is connected to a separate finger of the Rake

receiver.

This is possible due to the synchronisation and channel estimation

derived from the Pilot channel.

Thus Eb/No is improved, rather than simply an effective power

gain.

Very low individual Eb/No will probably mean a very low pilot level

which will lead to poor coherence and little gain - process becomesself-defeating.



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Capacity Issues

Capacity Objectives



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Manage effectively predicted Load on Service Area

Capacity dependant on:

Number of users

Position of users relative to the cell

Services demanded

UE Power Control

KPIs

Cell UL Load Factor

Cell DL Power

Factors affecting Capacity



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Number of Users: The more users the more noise

Position of Users: The farther away, the more noise

Services demanded: The more high-bitrate users on the cell, theless overall number of users possible

UE Power Control: Imperfect power control will account for morenoise in the network

Why do Capacity problems occur?



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Failure to meet Power requirements on DL

Too many users being taken on the UL

Too many users on a given Bearer

Max Power per Bearer parameter

Excessive soft handover situations

Low Resource failures




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Too many users being taken on the UL

Too many users on a given Bearer

Capacity problems- Solutions



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Reduce number of users admitted into cells

Reduce NR limit parameter

Down-tilt

Re-distribute traffic to other cells

Re-assign users to lower power Bearers (parameters)

Optimise Max Power per Bearer (parameters)

Reduce soft handover cases (parameters)

Soft and Softer Handover



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In UMTS it is possible to have a UE connected to more than 1NodeB. This is called Soft Handover

When in Soft Handover, the RNC can combine the best signalsfrom the NodeBs, hence providing a Soft Handover Gain

Softer Handover applies when the mobile is being served by twocells on the same site. A Softer Handover gain also occurs.

However, too many mobiles in Soft or Softer Handover couldimpose a significant Overhead on the system

Soft Handover- Summary (1)



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A SHP gain is obtained

Allowing soft handoverincreases the air interfacecapacity

Extra channels required.Typical cell usage: 25 primarychannels; 10 soft handoverchannels

Probability of Soft Handover

Soft Handover- Summary (2)



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Use of extra channels can

cause extra load on basestation transmitter

As SHO terminals tend tobe near the cell edge,

power requirement forthese terminals will be high

Soft and Hard Capacity



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Hard Capacity: Hard limit imposed by actual channel elements

Typ. 16 Kbps Channel elements. Also called Resources orCards

Soft Capacity: Variable, depending on Network loading


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3- Dimensioning the network

Coverage Planning

Link Budget based

i.e. simple numerical calculation

Coverage Planning


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Firstly a link budget is created

The maximum path loss is used to calculate the cellrange using a propagation model

The cell range is used to calculate the site area

Site Numbers = (Total Area)/(Site Area)

Create Link Budget

Calculate Range

Calculate Site Area

Calculate Number of

Sites in a given Area

Max PL

Max Range

Max Area

UL Link Budget - voice

The UMTS Link Bud ge


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If the UE can transmit at powers up to +21 dBm, the maximum link loss is: 21 -(-120) = 141 dB.

The maximum air interface path loss can be calculated by considering antennagains and miscellaneous losses (e.g. feeder loss, body loss)

If antenna gain = 17 dBi and losses = 4 dB, then maximum path loss = 141 +17 - 4 = 154 dB

Note: margins not considered (e.g. shadow fading, building penetration loss).These could total 25 dB.


The UMTS Link Bud geThe UMTS Link Bud ge


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Noise Floor -104 dBm

Noise Rise Limit 4 dBProcessing Gain 25 dB

Target Eb/No 5 dB

Receiver Sensitivity -120 dBm

UE Tx Power +21 dBm

Maximum Link Loss 141 dB

Antenna Gain 17 dBi

Feeder loss 3 dB

Body loss 1 dB

Maximum path loss 154 dB

Margins 24 dB

Target path loss 130 dB

-104 -25+4+5 =-120



N i Fl 104 dB


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QuestionIf the noise rise was increased to 8dB. What would the

path loss be and receiver sensitivity?

Noise Floor - 104 dBm

Noise Rise Limit 4 dB

Processing Gain 25 dB

Target Eb/No 5 dB

Receiver Sensitivity - 120 dBm

UE Tx Power +21 dBm


Antenna Gain 17 dBi

Feeder loss 3 dBBody loss 1 dB


Margins 2 4 dBTarget path loss 130 dB



Noise Floor 104 dBm


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QuestionIf the noise rise was increased to 8dB. What would the

path loss be and receiver sensitivity?

Noise Floor - 104 dBm

Noise Rise Limit 8 dB

Processing Gain 25 dB

Target Eb/No 5 dB

Receiver Sensitivity -116 dBm

UE Tx Power +21 dBm


Antenna Gain 17 dBi

Feeder loss 3 dBBody loss 1 dB


Margins 2 4 dBTarget path loss 126 dB

-104 -25+8+5 =-116

Propagation model

Th th l t i t d d b f f t


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The path loss at any point depends on a number of factors:

Clutter

Distance from transmitter Frequency

Antenna height

Much less extent mobile antenna height

Propagation model

This dependence is comple that it is er diffic lt to describe it ith e act


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This dependence is complex that it is very difficult to describe it with exactmathematical expression.

However, a number of propagation models are available that can estimatethe path loss and hence coverage.

Using the results we can determine cell size and number of base stations.

Propagation model

Path Loss(r) = PL (ro) + 10nlog (r)


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PL(ro)=path loss= ro is 1km away from the transmitter antenna n=Path loss exponent

r= Kilometers

Propagation model



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PL(ro)=path loss= ro is 1km away from the transmitter antenna

n=Path loss exponent

r= Kilometers

Slope =10n

n=Path loss exponent

Transmitter antenna

PL(ro)

Path

Loss r

r

1m

referencepoint

Propagation modelHata model


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The path loss at any point is given by:

Path loss = A + B logr

r= distance of the point in kilometers

A and B = constants depend on terrain characteristics, carrier frequencies and antenna heights.

Propagation model


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Example 1

Base station height = 50mMobile height = 1.5m

Frequency = 900Mhz

PL = 123.3 + 33.77 log r

note: Path loss at 1m is 123.3 at

900 Mhz

Example 2

Base station height = 50m

Mobile height = 1.5m

Frequency = 1.900Mhz

PL = 131.82+ 33.77 log r

note: Path loss at 1m is 131.82 at

1.9900 Mhz

Propagation model


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Example 1- Translating path loss to range

For a base station antenna height of 15m and operating frequency of 2000Mhz.

Path loss melropolitan area = 144.95 + 37.2 log r

Path loss urban area = 141.95 + 37.2 log r

Path loss suburban area = 129.68 + 37.2 log r

Path loss open area = 109.44 + 37.2 log r

Propagation modelExample 1- Translating path loss to range

For a base station antenna height of 15m and operating frequency of 2000Mhz.


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g p g q y

Path loss metropolitan area = 144.95 + 37.2 log r


Path loss suburban area = 129.68 + 37.2 log r

Path loss open area = 109.44 + 37.2 log r

Path loss metropolitan area=144.95 + 37.2 log r

140.9 =144.95 + 37.2 log r

-37.2logr=144.95 -140.9

=4.05/37.2

=Antilog -0.1088

=0.778m

Propagation model


For a base station antenna height of 15m and operating frequency of


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For a base station antenna height of 15m and operating frequency of2000Mhz.



Path loss suburban area = 129.68 + 37.2 log rPath loss open area = 109.44 + 37.2 log r

Open Area Suburban Area Urban

area

Metropolitan area

12.2 KbpsService

780m

Complete the table

Propagation model


For a base station antenna height of 15m and operating frequency of


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For a base station antenna height of 15m and operating frequency of2000Mhz.



Path loss suburban area = 129.68 + 37.2 log rPath loss open area = 109.44 + 37.2 log r

Open Area Suburban Area Urban

area

Metropolitan area

12.2 KbpsService

7km 2Km 940Km 780m

Complete the table

Area Calculation

C ll l h


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Cells are complex shapes

We assume in dimensioning that cells conform to aregular shape

Hexagons are commonly used because of their closepacking properties

K factors used to represent the difference between acircle of radius r and the site area

The K factor will depend upon the number of sectors

K = 0.827

K = 0.62

r

r

2rkArea

Coverage-based Dimensioning: Example


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Area to be covered: 80 km2.

Link Budget for NR of 3dB suggests maximum pathloss of 151 dB can be tolerated, assuming sectoredantennas are used.

In building margin and shadow fading margin reducethis to 131 dB

Path loss model

K = 0.62

R

dBlog35137 RL

km674.01010

35635137 --LR

Coverage-based Dimensioning: Example


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K = 0.62

R km674.01010 35635137 --LR

22 km88.062.0 R

9088.080

Area covered by 3-sectored site

Number of sites required =

90 sites required (270 cells)


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4- Neighbours and Scrambling Codes

Neighbours and Scrambl ing Code


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UMTS FDD Neighbour types

UMTS FDD Neighbour types

Intra-Frequency: UMTS to UMTS- Same Carrier



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Inter-Frequency: UMTS to UMTS- Between Carriers

Inter-Mode: UMTS to UMTS- Between FDD and TDD Modes

IRAT: UMTS to GSM

IRAT: GSM to UMTS

Neighbour list/ Monitored set (1)



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The Monitored set is the list of cells that the UE continuously

measures, but whose pilot Ec/Io are not strong enough to beadded to the active set

Defines list of potential additions to the active set

Maximum of 32

Neighbour list/ Monitored set (2)



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Cells on the neighbour list will be examined to see if they

meet criteria to enter soft or softer hand over with the primaryserver

Neighbour lists of active set merged

If a Neighbours Pilot has an Ec/Io level greater than thecurrent Best Pilot minus the Window add value, then theNeighbour is added to the active set

Identifying Suitable Neighbours (1)



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Planning tools,such as Asset3G can plan neighbours

automatically using proprietary algorithms

Based on mutual interference of cells

If a cell with a strong pilot does not join the active set it willbecome a strong interferer

Neighbours can be inward, outward or mutual.




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Neighbours should be prioritised on the basis of the amount

of interference they could cause and the probability of themforming the necessary primary server for an exiting UE

Tools are viewed as a way of generating a first passneighbour list. Manually adjusted




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Planning tool criteria:

Pilot RSCP (Ec): minimum value required

Pilot Ec/Io: minimum value required

Soft HO margin: compares pilot strength of potential neighbour withthat of best server.

Minimum area for which above criteria are met.

Varying the above parameters will alter the length of the Ncelllist.

List will be prioritised on the basis of the area for which eachcell meets the criteria.

IRAT Handover (1)



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Inter Radio Access Technology Handover

Customers transferring to 3g should:

gain access to video telephony services

benefit from higher data rates for GPRS

experience a service at least as good as GSM for voice services

Satisfying this last requirement will necessitate successfulIRAT handovers occurring.

IRAT Handover (2)

Active UE will handover to GSM when Ec/No thresholds are met



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Active UE will handover to GSM when Ec/No thresholds are met

Ec/No should be logged

Ec/No

time

Enter compressed mode

Perform Hand Over

2d

3a

IRAT Handover (3)

Normally, the UE receives the GSM Synch Channel duringcompressed frames in UTRA FDD to allow measurements



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compressed frames in UTRA FDD to allow measurements

from other frequencies

The UMTS terminal needs to enter compressed mode, alsoknown as slotted mode, to enable it to make measurementsfrom another frequency without a full dual receiver

Compressed mode means halting transmission andreception for a short time

IRAT Handover (4)

Eb/No performance degrades in compressed mode byabout 2dB



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about 2dB

Secondary issues: compressed mode requires higherpower (or reduced throughput)

Fast power control loop is interrupted.

IRAT Neighbour Lists: Planning



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Likely strategy:

Make co-sited GSM cell a neighbour

Make neighbours of this cell a neighbour

Manually adjust as appropriate.

Again, drive test data will be used to tune the list.



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Neighbour issues

Missing Neighbours



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Refers to SCs that are measured with good pilot quality (> -

15dB) and are not on the Neighbour list

Detected through drive testing and Post-Processing

Too Many Neighbours



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It may be that Neighbours on a list are not strong enough to

be actual handover candidates

List must be kept to probably less than 18 to account for softhandover neighbours


Incorrect Neighbours


Si il T N i hb h h h i


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Similar case to Too many Neighbours, though here its not

the quantity but the quality of the Neighbours thats a problem

Some Neighbours may not be strong candidates, and somestrong pilots may be left out.

There may be a SC from a distant boomer site that need to beremoved


Scrambl ing Code Planning Issues


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Scrambling Code Planning Issues

Scrambling Codes in UMTS (2)

Each cell must have a primary scrambling code.


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UMTS uses 512 primary scrambling codes, divided into 64

groups of 8

The P-SCH and S-SCH are decoded by the UE to find the P-

CPICH

The P-SCH also contains the SC group, which then leaves the

UE to find by trial and error the right code


Once connected into the network P-CCPCH broadcasts

neighbour lists so helping the UE to find suitable handover


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neighbour lists, so helping the UE to find suitable handover

partners

UMTS does not allow for handover to pilots who are not on the

neighbour list.

If fewer codes per group are used, the mobile will find its best

server more rapidly


Also, less processing that has to be done by the mobile in

general This increases the UE battery life and decreases


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general. This increases the UE battery life and decreases

signalling on the network

Handover, is made faster and more reliable by limiting the

number of codes.

The challenge is to avoid interference whilst limiting the

number of codes and the number of groups.

Scrambling Codes Issues

High sites can interfere with other cells using the same

Scrambling code


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Scrambling code

Bays and water bodies can represent a challenge to SC

planning

New sites integration: must have a strategy in place to

prepare for future SC requirements

SC Planning Strategies (1)

Probably most widely used strategy is that of Coloured

Clusters or 64x1


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Clusters or 64x1

Consists of creating clusters where only 1 code number

(colour) is used from all 64 Code Groups

Each cluster would have a different colour. 8 colours are

possible, though its advisable to use only 6. The 7thcolour

may be used for special cases, and the 8thcolour for

expansion.

SC Planning Strategies (2)

Look for geographical features to identify clusters or obvious

grouping of sites


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grouping of sites

Clusters should be planned of around 19 sites: this would

use 19x3= 57 groups out of 64 available, leaving room for

expansion

This limit can be relaxed for rural areas where sites are

further apart and code reuse due to distance becomes

possible.

SC Colour Coding example


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High Sites (Boomer) SC Planning

Where clusters have obvious boomers, assigning the offendingcell/cells the 7thcode (for example). This will allow for this site to beid tifi d f h t it i h d i t ti


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identified for what it is when drive testing

Plus boomers may well be turned off as time goes on and this willthen not affect the particular cluster colour code plan.

Planners may also use the 7thcolour code for temporary sites, likeexperimental areas where new services are being tested.


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5- UTRAN Parameters

UTRAN Parameters

Many parameters required for the configuration of UTRAN


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Current practice tends to load default values

Parameter optimisation is often left for the Post-Launch stage

However, we can take a look at the effect of optimising SoftHandover parameters

Playing with SHO parameters (1)

To reduce DL interference


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A significant interferer can be added to the Neighbour list so that itcan become a member of the active set. In this way, it wouldnt bean interferer anymore.

Some considerations before doing this include:

Check that the interferer cell actually makes a good neighbour

Check that no unnecessary handovers are generated

Check that that the handover overall process is not too slow

Playing with SHO parameters (2)

To attract traffic on the DL


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By setting the offset parameter to positive a cell can take more trafficfrom Neighbouring cells. This can bring its own issues

To dump traffic on the DL

By setting the offset parameter to negative a cell can take more trafficfrom Neighbouring cells. This can create some problems as well.


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Handover Events

IF Handover Events- Radio Link Addition

Event 1a: A primary CPICH enters the reporting range (FDD only)


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Event 1a:A primary CPICH enters the reporting range (FDD only)

If Active Set is not full and CPICH_Ec/Io > Best_CPICH

Reporting range + Hysteresis_1a for more than the Time To Trigger

period (TTT) then the SC is added to Active Set

Reporting Range: the Soft Handover threshold

Reporting Range - Hysteresis Event 1a = Window Add

Reporting Range + Hysteresis Event 1b = Window Drop

IF Handover Events- Radio Link Removal

Event 1b: A primary CPICH leaves the reporting range (FDD only)


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Event 1b:A primary CPICH leaves the reporting range (FDD only)

If CPICH_Ec/Io < Best_CPICHReporting rangeHysteresis_1b

for more than the Time To Trigger (TTT) period then the SC is

removed from the Active Set

IF Handover Events- Radio Link Replace

Event 1c: A non-active primary CPICH becomes better than an


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Event 1c:A non active primary CPICH becomes better than an

active primary CPICH (FDD only)

If Active Set is full and Best_Candidate_CPICH_Ec/Io >

Worst_CPICH_in_AS + Hysteresis_1c for more than the Time To

Trigger (TTT) period then the old SC is replaced with new SC.

TTT TTT

TTT

WCDMA IF Soft Handover Algorithm


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Pilot Ec / N0 of cell 1



Reporting_range

- Hysteresis_event1AHysteresis_event1C

Reporting_range

+ Hysteresis_event1B

Connected to cell 1

Event 1A=add cell2

Event 1C=replace cell 1

with cell 3

Event 1B=remove cell

3

Note:Maximum number of SC in AS is 2

Connected to cell 1 and 2

Compressed Mode Events

Event 1e:A primary CPICH becomes better than an absolute threshold

(FDD only)


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If CPICH_EcIo > Threshold_1e + Hysteresis_1e for more than Time To Triggerthen compressed mode stops.

Event 1f:A primary CPICH becomes worse than an absolute threshold

(FDD only)

If CPICH_EcIo < Threshold_1fHysteresis_1f for more than Time To Trigger

then compressed mode begins.

Absolute

hreshold

Reporting

event 1E

Measurement

quantity

Time

P CPICH 1

P CPICH 2

P CPICH 3

Absolute

hreshold

Reporting

event 1F

Measurement

quantity

Time

P CPICH 1

P CPICH 2

P CPICH 3

GSM/GPRS Measurement Events


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Event 2d: The estimated quality of the currently used frequencyis below a certain threshold

If Quality < Threshold_2dHysterisis_2d for more than Time To

Trigger then GSM/GPRS measurements begin.

Event 2f: The estimated quality of the currently used frequencyis above a certain threshold

If Quality < Threshold_2f + Hysterisis_2f for more than Time To

Trigger then GSM/GPRS measurements stop.

IRAT Handover Events


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Event 3a: The estimated quality of the currently usedUTRAN frequency is below a certain threshold and the

estimated quality of the other system is above a certain

threshold.

If UTRAN_Quality < Threshold_UTRAN_3aHysteresis_3a

and Other_System_Quality > Threshold_other_3a +Hysteresis_3a for more than Time To Trigger then IRAT HO

begins.

UE internal measurements Events


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Event 6a: The UE Tx power becomes larger than anabsolute threshold

If UE_Tx_power > Threshold_6a + Hysteresis_6a for more than

Time To Trigger then RNC decides what to do.

Event 6b: The UE Tx power becomes less than an absolutethreshold

If UE_Tx_power < Threshold_6b - Hysteresis_6b for more than

Time To Trigger then RNC decides what to do.


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6- Drive Testing and Optimisation Teams

Optimisation Team Structure

Pre-launch Optim isatio


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Each RNC area has: Drive Test Team

Systems Analysis Team (SAT)

Configuration Engineer

The Structure - Drive Test Team



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Drive representative routes gathering: Scanner data (rooftop mounted calibrated antenna)

Mobile (UE) data (test mobile on rear seat connected to laptop)

Scanner provides accurate measurements of pilot strength etc.

UE data provides evidence of call success and uplink Tx power.

Drive test data is passed to the SAT team.

The Structure - The SAT team

In addition to defining the drive test routes:



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The SAT team process the data to provide

summative results (CCSR, c.d.f of pilot strength etc.)

diagnoses of problems.

Problems are resolved through close liaison withthe configuration engineer.

The Structure - The configuration engineer

The Configuration engineer



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g g

monitors the state of the network

requests changes to network configuration (antennaorientation etc.)

tracks changes through the system

The Structure - example



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Drive test reveals calls dropped in an area where best pilotis very low.

SAT team checks with configuration engineer regardingcell status

Check made with planning tool to see whether problem is

predictable

If no obvious reason, SAT directs drive test team toinvestigate.

The Structure - example (continued)



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Drive test team report that an obstacle/terrain featureexists that is not on map data.

SAT team recommend solution (antennaheight/orientation)

Effect checked on planning tool

Configuration Engineer actions change and reports whenimplemented.

SAT instructs drive test team to re-examine

Drive Test Data: the need for consistency

Optimisation of physical aspects, in summary:

Measure the performance



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Implement configuration changes

Measure again to show improvement.

Clearly there is a need for consistency


Potential for inconsistency:

Different (uncalibrated) antenna/feeder



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Different drive test route

Different UE speed over the route (hold ups at trafficlights etc.)

Different analyser being used.

Different level of network loading (affects Ec/Io).


Ideally:

Use the same analyser, feeder and antenna for the



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before and after measurements. Ensure that you keep to the same route.

Be consistent regarding UE speed. Sample data on adistance, rather than time, basis. If this is not realistic,try and pause sampling when held up in heavy traffic.

Check to see if load testing is going on in this area.Make measurements at the same time of day to getnear-equal loading conditions.

Drive Testing: Optimisation of Site Clusters

Procedure

Identify size and location of clusters

Drive Testin


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Define Cluster characteristics Coverage, Interference, Handover region size and

location

Neighbour list assessment

Access, handover and call failures

Take Measurements

Drive tests

Ec/Io, pilot power, UE TX Power, Neighbours, call

success drops and Handover stats.

Service allocation, FER/BLER, Throughput, Max and Av.

BER, Delay

An engineer will have responsibility for a particularcluster.

Cluster Defining

Identify Clusters of sites

Based on

Terrain

Drive Testin


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Traffic distribution

Network is to be optimised in clusters

This method provides for

Work delegation

Progress tracking

Minimises tool processing time

Cluster Defining

Network

A D t fill

Eg Scrambling

Codes; Node B

P t

Drive Testin


137/208

Network of clusters Cluster of sites Site

Site Approval

Cluster Approval

Acceptance Datafill Parameters

Drive Test Routes

Drive Testin

Drive testing should be performed on

radial and circumferential routes


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Radial routes show variation

in signal quality with distance

from base station

Circumferential routes providepredictions for signal quality in

different directions from the base

station

Typically, three routes should be

defined per cluster: consistency is vital.

Drive Tests: measuring Ec/Io

Requirement is for pilot SIRto be

greater than -15 dBin 95% of locations

where coverage is acceptable, under

Drive Testin


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conditions of heavy loading.

Ec/Ioshould be greater than -16 dB

when network is heavily loaded.

For quiet network Ec/Ioshould be

greater than -10 dBfor 95%of the

area.

Higher values of Ec/Io will be needed

where high data rates on DL are

required.

Drive Tests: effect of loading on Ec/Io

Ec/Io can vary by 7 dB with loading

conditions.

It i it l th t diti t th ti f

Drive test

Drive Testin


140/208

It is vital that conditions at the time ofmeasuring are known (you will not get

Ec/Io>-10 dB on a heavily loaded

network).

For pre-launch optimisation it is

common to assume the network is

quiet.

But, if someone else is doing a load

test while the drive test is taking

place.

Load test

Sampling and Vehicle Speeds

Drive Testin

Drive testing should measure the local mean. That is:

Multi-path variation should be ignored.

Shadow fading should be included.


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Signal variation due to more than onemulti-path reflection with near-constant

mean level.

Sampling and Vehicle Speeds: Lee Criteria

Drive Testin

William Lee identified ideal measurement process:

Average 36 samples over a distance of 40 to get a data point


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Average 36 samples over a distance of 40 to get a data point. Samples to be taken at least 0.8 apart

This corresponds to:

An averaging window of 5.6 metres.

36 samples taken at least 11 cm apart.

Using the Scanner

Drive Testin

Scanners have a fixed sampling rate.

However it is per reading: if you are sampling 6 channels


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However, it is per reading : if you are sampling 6 channelsthe rate is one sixth.

You either define an averaging period or post-process.

E.g. Anritsu scanner:

Sampling period 10 ms per channel

Typical number of channels: 6 (each channel now 60 ms)

Averaging period can be set. 1 s typical.

Using the Scanner

Drive Testin

E.g. Anritsu scanner:

In order to get the averaging distance down to 5.6 metres, the speed

would have to be 20 kph


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would have to be 20 kph.

Speed (kph)

inter-sample distance

(cm)

Samples per

period

Averaging distance

(m)

20 33 16.7 5.6

40 67 16.7 11.1

60 100 16.7 16.7

80 133 16.7 22.2

100 167 16.7 27.8

120 200 16.7 33.3

Consequences of violating Lee Criteria

Drive Testin

Inter-sample distance too large:

Not in itself a problem (Lee specifies minimum distance), but you

have to fit in a large number of samples into the averaging distance


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have to fit in a large number of samples into the averaging distance.

Too few samples:

36 samples predicted to give s.d. of 1 dB.

17 samples would give s.d of (36/17) = 1.45 dB

Note pilot power measurement accuracy quoted as 2 dB.

Averaging window too large:

Miss sharp peaks and troughs

Most appropriate value depends on environment.


Drive Testin

Varying the averaging window:

28 m averaging


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-95

-90

-85

-80

-75

0 10 20 30 40

distance (m*28)

pilotstrengthdBm

pilot s trength

5.6 m averaging

-95

-90

-85

-80

-75

0 50 100 150 200

distance (m*5.6)

levelindBm

Pilot strength

28 metre averaging

5.6 metre averaging


Drive Testin

Effect is to miss the extremes

Affects the cumulative distribution:


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Cumulative distributions

-100

-95

-90

-85

-80

-75

-70

0 20 40 60 80 100

percentile

level

5.6 m averaging

28 m averaging

Lee Criteria: Conclusions

Drive Testin

Do not issue a global recommendation for 20 kph drive test

speeds However:


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speeds. However:

If the coverage in certain areas causes concern, and requires a

detailed investigation, there are ways of maximising accuracy and

confidence in measurements.

There is no point in correcting a measured value of -68 dBm pilot(very good) to, say, -72 dBm (still very good).

Drive Test measurements: the need foraveraging

Drive Testin

If you simply take spot measurements, you will include

multipath variations.


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best server

-120

-100

-80

-60

-40

-20

0

0 5000 10000

best server

best svr moving average (20)

-100

-80

-60

-40

-20

0

0 5000 10000

best svr

moving

average (20)

Unsmoothed data Smoothed data

-7

Ec/Io

Server 1


150/208

-16

0 100%Samples

Cumulative Distribution

Server 2

The need for averaging

Drive Testin

C.d.f. reveals differences.

Only 0 5 dB difference atcrucial 5% (95% better


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Only 0.5 dB difference atcrucial 5% (95% better

than) level.

Averaging can make file sizes

more manageable (they canbe enormous) and speed

analysis as a result.


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Drive Test Equipment

Some equipment suppliers

Anritsu

http://www.eu.anritsu.com

Drive Test Measurement


153/208

Portability and ease of setup prove to be the strongest

points of the Anritsu scanner.

The Anritsu scanner was very simple to set up

The information collected, although limited to RSCP,

Ec/Io and SIR measurements for up to 32 received

scrambling codes.

The receiver sensitivity was found to be better than

that of the Agilent scanner- measuring RSCP signal

levels as low as -122dBm.

Drive Test Equipment

Some equipment suppliers

Agilent

http://we.home.agilent.com/



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The extensive amount of output information

Although more complicated in terms of setup

Agilent scanner provides the user with more

measured information and additional graphicalfunctionality.

A strong solution but has limited sensitivity and is

not hand portable.

Drive Test Planning

Pre-planning of drive test routes

Knowledge of network

Site location

Site configuration



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Site configuration

Knowledge of location

Towns

Terrain

Operator known issues

GSM problem areas

Test-mobile Measurements

A known CPICH transmit power inconjunction with the CPICH RSCP andUTRA carrier RSSI would allow thecalculation of pathloss to the cell and allow

an estimation of cell dominance in idlemode



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mode.

Estimate of the orthogonality of the downlinkis still problematic

Drive test data is essential to validatepropagation models.

7- Drive Test Analysis


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7 Drive Test Analysis

Drive Test Measurements

Prediction Assessment

Test Site Comparison

Comparison of model against drive test measurements of site notused in the calibration process



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used in the calibration process

Drives vs. Predicted Best Server

Comparison between predicted and measured best servers

Drives vs. Predicted Pilot Pollution

Comparison between predicted and measured pilot pollution

Test Site Comparison

Drive Test data compared with 3g calibration tool

Analysis should provide both mean and standard deviation agreement

For example


Drive Test Measurements Analysis


159/208

p

Mean error of 1.8dB

S.D of 7.9

Is a good practical fit

Drives vs. Predicted Best Server

Exposes discrepancies with map data and local features Mud banks, rocks,

Exposes limitations in antenna models and propagation model

Drives vs. Predicted Pilot Pollution

Will highlight regions of multipath interference, difficult to calculate

Test-mobile Measurements The commonly identified KPIs are not in themselves appropriate for pre-

launch optimisation and acceptance

Test-mobile measurements, depending on the availability of engineering

mobiles, should allow measurement of:



160/208

CPICH and P-CCPCH availability

DCH - Dedicated channel DL performance

Cell dominance

Active set size

Required UL Tx Power

These measurements would be possible under both loaded and unloadedconditions

Interpretation of Measurements It is not sufficient to know what measurements can be made.

The optimisation engineer needs to be able to interpret measurements

This will often entail taking a number of KPIs in conjunction.

For example, lets imagine a drive test



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The test route is 100 metres in length along a route such that the distance to the nearest

cell remains approximately constant.

The following KPIs are extracted from the measured data.

+39.6 dBmAverage Downlink Total TrafficChannel Power

+21.4 dBmAverage Uplink Channel Power

-22 dBEc/No Neighbour 2

-20 dBEc/No Neighbour 1-11 dBEc/No Serving Cell

maximum uplink channel power is 23 dBmmaximum total downlink channel power is 42 dBm.

Interpretation of Measurements

The cell is under stress

Uplink power is close to maximum

There is only one dominant serving cell.



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Pilot levels of other cells are much lower than main cell

We are near the edge of the cell from the uplink coverage viewpoint

Uplink power is close to maximum

Let us assume that the reason for carrying out the drive test was because coverage

levels were reported as poor on this particular road.

What methods would you recommend for improving this coverage?

Possible Actions Mast head Amplifier

Only reduces feeder loss and can introduce DL problems

due to insertion loss - may already be fitted as standard.

Transmit Diversity



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Will increase load on DL and with fast moving traffic has little

effect.

Additional Site

Very expensive option and should be last on list

Reduce Noise Rise Limit

Reduction of noise rise limit will increase coverage but will

reduce total capacity.

Coverage and Interference Goals

Typical Criteria: 95% of area delivers pilot strength of > 89 dBm



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yp 95% of area delivers pilot strength of >-89 dBm

(dense urban) or -94 dBm (urban).

95% of area covered should register Ec/No

better than -10 dB.

Improving Coverage: Procedure

From drive-test data: Identify coverage holes



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y g

Assess the most serious of those and rank inorder of priority

Rectify problems in priority order until criterionis met.

Improving Interference

Within covered area (i.e. pilot better than requiredthreshold) attaining a Ec/No better than -10 dB is

easy (perhaps -9 or -8 would be a better target) ifthe network is lightly loaded



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the network is lightly loaded.

If pilot strength is -95 dBm, noise plus interferencemust be -85 dBm (thermal noise)

Even in an area where there are three equal pilotsand common channel power equals pilot power,pilot Ec/No should be 1/6 or -8 dB.


Scanner Data.

Area wherethere are three

l l l l



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equal low-levelpilots revealsEc/Io of -8 dB.


Scanner Data.

Area where thereare seven low-level

il t ( t l



168/208

pilots (not equalstrength).

Best Ec/Io =-10 dB


Typical drive test result from well-optimised cluster.


Ec/Io >-12 dB 99.91%Ec/Io >-11 dB 99.44%


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Ec/Io >-10 dB 98.14%

Ec/Io >-9 dB 94.97%

Ec/Io >-8 dB 89.44%

Ec/Io >-7 dB 81.22%

Ec/Io >-6 dB 68.83%

Ec/Io >-5 dB 53.66%

Ec/Io >-4 dB 34.94%

Ec/Io >-3 dB 13.46%

-9 dB seems to be more appropriate threshold.

Improving Interference: Procedure

Identify areas of low Ec/Io

Examine pilot levels (there will probably be

more than three). Identify any unwanted pilots (from cells that



170/208

Identify any unwanted pilots (from cells thatare not intended to provide coverage in thatarea).

Reduce level of these pilots (usually bydown-tilting)be aware of the effect on coverage in servicearea of cell: use planning tool.

Inter Radio Access Technology (IRAT) HandOver

IRA

The neighbour list of UMTS cells should include GSM cells.

The neighbour list includes:


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The co-located GSM cell

Neighbours of this cell

Testing IRAT in a network

IRA

Different testing strategiesneed to be adopteddepending on whether theUE is:

t th d f UMTS


172/208

at the edge of UMTScoverage

at the centre of the network

at a hotspot

Testing at a cell edge

IRA

In active mode: drive will beuni-directional

In idle mode: drive should be

bi-directional

Active mode: make a


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Active mode: make acontinuous call

monitor for IRAT hand over (or calldrop)

monitor rapid GSM hand oversafter IRAT (10 seconds)

check GSM network sustainsconnection (30 seconds)

Route should initially berestricted to Motorways, Aroads and B roads.

Testing at a network centre

IRA

IRAT can be required due tocoverage holes (especiallyindoors) or excessive

interference. Not inevitable that IRAT will


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occur.

Mobile can be encouraged toenter IRAT mode (placed on

floor of vehicle?)

Conclusions

IRA

Urgent requirement exists forthe IRAT success rate to beassessed.

Drive tests must be undertakenaccordingl


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accordingly.

Initial selection of routesinfluenced by characterisation

feedback.

8- Functional Drive Testing


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Functional Testing

Functional Testin

Whilst drive testing and measuring pilot strengths, it is usualto monitor call success.

Calls are usually one of three types;

voice (AMR)

video telephony (VT)


177/208

p y ( )

packet traffic (http or ftp)

AMR or VT testing can be one of two types

drive till drop cyclic call attempts (e.g. 2 minute cycle)

packet traffic involves downloading data of varying sizes.

Functional Testing - measurements

Functional Testin

When carrying out cyclic testing with AMR or VT the CallCompletion Success Rate (CCSR) is the most significantparameter.

When testing packet traffic, the Context Activation SuccessRate (CASR) and the throughput/time to download are ofgreat interest


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great interest.

Agreement must be made on suitable timeouts: e.g. how longshould the UE attempt to establish a call (20 seconds?)

before a failure is registered. Likewise for context activation. Driving till drop checks for continuous coverage

requirements, neighbour planning and hand over procedures.

Functional Testing - using results

Functional Testin

In the period before the physical environment has besatisfactorily optimised, functional tests are of interest toindicate that the network is functioning properly and willindicate events such as sleeping cells.

However, not every call drop will be investigated as it isknown that there are gaps in coverage and/or areas of high


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known that there are gaps in coverage and/or areas of highinterference.

Once the physical environment has been optimised, the

functional test results become very significant and provide thefinal verdict on the whole optimisation process.

Functional Testing - approach

Functional Testin

It must be accepted and anticipated that the functional testingwill not reveal perfect results. Calls will still drop or fail to setup.

Failures can fall into one of several categories Coverage or interference problems


180/208

Hand over failure

Network problem

Handset issue

Coverage/Interference Problems

Functional Testin

Remember we would to thresholds at 95% probability - not100%.

Hope is that the 5% of problem areas will not be critical.

A call drop due to coverage and/or interference problemindicates that air interface is of poor quality in an important


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p q y parea. This should be addressed.

Note that all RF measurements have been performed on thedownlink. An uplink problem should be investigated if thedownlink looks OK. E.g. is the cell receiver and mast headamplifier functioning satisfactorily. It is possible to monitor theUE Tx power (e.g. >11 dBm indicates potential problem).

Hand over problems

Functional Testin

Perhaps neighbour list is not properly optimised.

Remember that hand over requires a number of sophisticatedoperations to be successfully carried out.

Hand over is time dynamic. Not only do conditions have to beright for HO, they have to be right for a sufficient time for


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active set updates to occur.

E.g. if there is only one cell in the active set, if this levelsuddenly drops before update can occur, the call might drop.UE speed may affect success rate.

Truly optimising HO region extremely time-consuming: pre-launch best to concentrate on problem areas.

Corrections can include parameters such as HO margin in

addition to physical changes.

Network Problems

Functional Testin

Call can drop due to spurious messages going between theUE and the Network.

Additionally, some cells may be inactive (sleeping).

Instances must be recorded and reported.


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Handset issues

Functional Testin

On some occasions failure may be specific to a handset.

Perhaps the handset does not respond to a paging commandor other message.

Perhaps the handset drops a call in an environment whereother handsets do not drop calls.


184/208

UMTS technology is still improving.

Identifying the Cause

Functional Testin

In order to gain an insight into the likely cause of call drop, it isimportant to examine the communication between the UE andthe network.

These are generally known as layer 3 messages.

Two call drop examples are explained


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Two call drop examples are explained.

Example 1: measurement reports

Functional Testin

Measurements reported by the UE show:

Pilot dropping to -115 dBm

Ec/Io dropping to -20 dB

BLER rising to very high levels

Diagnosis is a straightforward poor coverage situation


186/208

Diagnosis is a straightforward poor coverage situation.

Detailed investigation reveals that an additional site is likely tobe required.

Further questions:

does scanner agree with poor coverage diagnosis?

What differences should be expected between scanner and UEmeasurements?

Example 1: measurement reports

Functional Testin

Difference between scanner and UE measurements can be aslarge as 20 dB for certain vehicle configurations.

UE antenna is in the vehicle, scanner antenna is roof-

mounted.

You must be comfortable that the difference is appropriate


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You must be comfortable that the difference is appropriatefor the test you are making:

Should interior of vehicle simulate significant (comparable to in-building) penetration losses?

Is the UE measurement reliable - e.g. is it measuring the same pilot asthe scanner?

Example 2: AS update reports

Functional Testin

Another call drop occurred where the coverage in the form ofpilot strength was good.

AS update reports reveal an interesting sequence of events.

Cell 3: Ncell to cell 1


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Cell 1: expected primary server Cell 2: Ncell to cell 1

Location of call drop


Functional Testin

Due to shadowing effects, the following sequence took place.

Cell 3: Ncell to cell 1 Cell 2 became bestserver.


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Cell 1: expected primary server Cell 2:

Location of call drop

Cell 1 drops fromactive set.

Signal from Cell 3rises (not on Ncell listfor cell 2) causingpoor Ec/Io.

Call drops due to low

Ec/Io.


Functional Testin

Solutions:

Quick fix:

add Cell 3 to Ncell list for Cell 2.

Longer term:

investigate radiation from Cell 3. It is a distant cell and is not


190/208

expected to become a member of the active set in the area inquestion.

Radiation from Cell 3 should be controlled, probably by down-

tilting but giving due regard to its required coverage area.

Example 3: Sudden Change in Signal

Strength

Functional Testin

Drive test reportsEc/Io for best server.

Transition regionsbetween coverageareas can be small,

ti l l i b

Cell 2

Cell 2 is 15 dBstronger thanCell 1


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particularly in urbanenvironments.

If UE moves rapidlythrough such an area,call can drop.

Cell 1

Cell 1 is 15 dBstronger thanCell 2


Strength

Functional Testin

For a successful handover, the signalsreceived by the UE

should rise and fall ata rate so that the UEcan execute the

Signalstrength transition

Successful HO


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necessary active setupdates.

time

time

transition

Call drop


Strength

Functional Testin

Transition region mustbe large enough toallow active set

update to occurbefore UE isoverwhelmed by

Cell 2

TransitionRegion


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overwhelmed byinterference.

Cell 1


Strength

Functional Testin

This can be alleviatedby:

providing a separate

cell at the intersection Cell 2


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Cell 1


Strength

Functional Testin

This can be alleviatedby:

providing a separate

cell at the intersection

placing cells abovestreet level to achieve

Cell 2


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street level to achievegreater penetration


Strength

Functional Testin

Detecting the problem:

The Analysis Engineer will notice call drops

Investigation reveals that the UE reports very poor Ec/Io immediatelybefore it drops

Once in idle mode the UE re-connects onto the new cell.


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The Ec/Io reported will be very good.

This large difference in Ec/Io indicates that the problem falls into this

category Scanner data showing pilot levels from the two cells will support the

reasoning.

MIB

RNC NBAP:BCCH Information

IDLE MODE

SIB

BCH PCHCPCHRACH FACH DSCH DCH

PICH

Spreading/Modulation

SIBs

Most of the system informationparameters are determined by the RNC.

The NodeB is informed about theparameters via the NBAP message BCC

information.

System information Blocks (SIBs) isgrouped into SIB1 to SIB 18. Each SIB isresponsible to carry a specify content


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DPDCH

DPCCH

PDSCH

S-CCPCH

P-CCPCH

PCPCH

PRACH

S-SCH

CPICH

AICH

AP-AICH

CD/CA-ICH

P-SCH

Physical Channels

TransportChannels

responsible to carry a specify content.Depending on the UE state it reads

specific SIBs and uses the transmittedparameters

Master information Block (MIB)mib-ValueTag 2,

plmn-Type gsm-MAP : {

plmn-Identity {

mcc {

2,3,4

mnc {

2, 0

sibSb-ReferenceList {

There is a large number of SIBs, which haveto be read by the UE. This requires a lot of

battery power. Therefore, a Master informationBlock (MIB) was introduced, which gives

references and scheduling information about

the SIBs.


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{

sibSb-Type sysInfoType1 :12,

scheduling {

segCount 1,

sib-Pos rep128 : 6


scheduling {

segCount 1, sib-Pos rep128 : 7

The MIB is transmitted in every 8th radioframe on the P-CCPCH (on position

SFN mod =8 =0 and TTI of 20mS

Master information Block (MIB)mib-ValueTag 2,

plmn-Type gsm-MAP : {

plmn-Identity {

mcc {

2,3,4

mnc {

2, 0

sibSb-ReferenceList {

A UE must find out the schedule of variousSIBs so that it can wake up and receive only

those blocks it needs and skip others.

The network may indicate that someinformation in a SIB has changed by setting the

update flag (value tag). Once the tag haschanged the mobile knows that it should

recover the corresponding system informationagain.


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{


scheduling {

segCount 1,

sib-Pos rep128 : 6


scheduling {

segCount 1, sib-Pos rep128 : 7

g

If any SIB changes, then MIB also changes.

System Information Blocks SIBs

18 SIBs defined by ETSI TS 25.331 Release 4

Type 1

NAS system information as well as UE Timers and counters

Type 2

URA identity Type 3

Parameters for cell selection and re-selection

System Info and Message Flows


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Type 4

Same as Type 3 but in connected mode

Type 5

Parameters for configuration of common physical channels

Type 6




Type 7

Fast changing parameters for UL interference

Type 8

Only for FDDstatic CPCH information to be used in the cell Type 9

Only for FDD -- CPCH information to be used in the cell

T 10



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Type 10

Only FDDUsed by UEs having their DCH controlled by a DRAC.

DRAC

Type 11

Contains measurement control information to be used in the cell

Type 12




Type 13

Used for ANSI-41

Type 14

Only TDD Type 15

UE positioning method for example GPS

T 16



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Type 16

Radio bearer, transport channel and physical channel parameters to bestored by UE for use during Handover HO

Type 17

Only TDD

Type 18

Contains PLMN identities of neighbouring cells


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Example 3g Message Flow

RRCU 10:36:28.320 CCCH RRC_CONNECTION_REQUEST

RRCD 10:36:28.660 CCCH RRC_CONNECTION_SETUP

RRCU 10:36:29.461 DCCH DCCH_RRC_CONNECTION_SETUP_COMPLETE

L3U 10:36:29.531 DCCH CM_SERVICE_REQUEST

RRCU 10:36:29.531 DCCH INITIAL_DIRECT_TRANSFER

L3D 10:36:29.842 DCCH CM_SERVICE_ACCEPT

RRCD 10:36:29.842 DCCH DOWNLINK_DIRECT_TRANSFER

L3U 10:36:29.862 DCCH SETUP

RRCU 10:36:29.862 DCCH UPLINK DIRECT TRANSFER



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In this segment a call is established

Check the SIBs with the descriptions in the ETSI TS 25.331 document

RRCU 10:36:29.862 DCCH UPLINK_DIRECT_TRANSFER

L3D 10:36:30.162 DCCH CALL_PROCEEDING

RRCD 10:36:30.162 DCCH DOWNLINK_DIRECT_TRANSFER

RRCD 10:36:30.733 DCCH RADIO_BEARER_SETUP

RRCU 10:36:31.444 DCCH RADIO_BEARER_SETUP_COMPLETE

Example 3g Message Flow

During Call is message flow is repeated over and over

RRCU 10:38:48.651 DCCH MEASUREMENT_REPORT

RRCD 10:38:48.922 DCCH ACTIVE_SET_UPDATE

RRCU 10:38:48.932 DCCH ACTIVE_SET_UPDATE_COMPLETE

RRCD 10:38:49.403 DCCH MEASUREMENT_CONTROL

L3U 10:44:23.433 DCCH IMSI_DETACH_INDICATION

RRCU 10 44 23 433 DCCH UPLINK DIRECT TRANSFER



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RRCU 10:44:23.433 DCCH UPLINK_DIRECT_TRANSFER

RRCD 10:44:23.713 DCCH RRC_CONNECTION_RELEASE

RRCU 10:44:23.753 DCCH RRC_CONNECTION_RELEASE_COMPLETE



Call detach sequence

8- Site Integration


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Site Integration (1)

Visit the site and check it physically

Verify antennas type, azimuths and tilts

Check for feeders for type, length and crossed feeders

Check site is according to design

No hardware problems



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Load default parameters- Data fill

Check Pilot Power and offsets for other channels

Check Neighbour lists

Site Integration (2)

Check coverage next to site

Drive test for Coverage, Ec/Io, Handovers

Check clockwise and anti-clockwise ABC- CBA

Verify Neighbours are working

Integrate Clusters, not individual sites



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UMTS Pre-Launch Optimization

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