umts pre-launch optimization
TRANSCRIPT
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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
Optimisation Overview
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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
Optimisation Overview
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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
Optimisation Overview
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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
Optimisation Overview
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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
Optimisation Overview
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Quality
Definition
Quality
TargetsMonitor
Quality
Configuration
Analysis
Quality
Reporting
Improvement
Plan
Corrective
Actions
SpecificQuality
issues
Specific
Corrections
Network Quality Cycle
Optimisation Overview
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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
Optimisation Overview
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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)
In i t ial Radio Network Planning Issues
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GSM Sites legacy
In i t ial Radio Network Planning Issues
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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
In i t ial Radio Network Planning 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
In i t ial Radio Network Planning Issues
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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
In i t ial Radio Network Planning Issues
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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)
In i t ial Radio Network Planning Issues
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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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In i t ial Radio Network Planning Issues
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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?
In i t ial Radio Network Planning Issues
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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
Planning Tool Examples
In i t ial Radio Network Planning Issues
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Planning Tool Examples
UMTS Network co-sited with the GSM Network
Cells too close together
Low or no down-tilts
Pilot Pollution- Solutions
In i t ial Radio Network Planning Issues
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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
In i t ial Radio Network Planning Issues
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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?
In i t ial Radio Network Planning Issues
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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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Planning Tool Examples
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
In i t ial Radio Network Planning Issues
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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)
In i t ial Radio Network Planning Issues
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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)
In i t ial Radio Network Planning Issues
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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
In i t ial Radio Network Planning Issues
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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
In i t ial Radio Network Planning Issues
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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.
In i t ial Radio Network Planning Issues
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Capacity Issues
Capacity Objectives
In i t ial Radio Network Planning Issues
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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
In i t ial Radio Network Planning Issues
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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?
In i t ial Radio Network Planning Issues
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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
Planning Tool Examples
In i t ial Radio Network Planning Issues
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Too many users being taken on the UL
Too many users on a given Bearer
Capacity problems- Solutions
In i t ial Radio Network Planning Issues
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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
In i t ial Radio Network Planning Issues
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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)
In i t ial Radio Network Planning Issues
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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)
In i t ial Radio Network Planning Issues
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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.
UL Link Budget - voice
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
UL Link Budget - voice
The UMTS Link Bud geThe UMTS Link Bud ge
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
Maximum Link Loss 141 dB
Antenna Gain 17 dBi
Feeder loss 3 dBBody loss 1 dB
Maximum path loss 154 dB
Margins 2 4 dBTarget path loss 130 dB
UL Link Budget - voice
The UMTS Link Bud geThe UMTS Link Bud ge
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
Maximum Link Loss 137 dB
Antenna Gain 17 dBi
Feeder loss 3 dBBody loss 1 dB
Maximum path loss 150 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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Path Loss(r) = PL (ro) + 10nlog (r)
PL(ro)=path loss= ro is 1km away from the transmitter antenna n=Path loss exponent
r= Kilometers
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
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 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
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
Example 1- Translating path loss to range
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 metropolitan 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 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
Example 1- Translating path loss to range
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 metropolitan 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 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.
Identifying Suitable Neighbours (2)
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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
Identifying Suitable Neighbours (3)
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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)
Neighbours and Scrambl ing Code
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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
Neighbours and Scrambl ing Code
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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
Neighbours and Scrambl ing Code
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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
Neighbours and Scrambl ing Code
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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.
Neighbours and Scrambl ing Code
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Neighbour issues
Missing Neighbours
Neighbours and Scrambl ing Code
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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
Detected through drive testing and Post-Processing
Incorrect Neighbours
Neighbours and Scrambl ing Code
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
Detected through drive testing and Post-Processing
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
Scrambling Codes in UMTS (3)
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
Scrambling Codes in UMTS (4)
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
Pilot Ec / N0 of cell 2
Pilot Ec / N0 of cell 3
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
Pre-launch Optim isatio
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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:
Pre-launch Optim isatio
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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
Pre-launch Optim isatio
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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
Pre-launch Optim isatio
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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)
Pre-launch Optim isatio
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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
Pre-launch Optim isatio
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Implement configuration changes
Measure again to show improvement.
Clearly there is a need for consistency
Drive Test Data: the need for consistency
Potential for inconsistency:
Different (uncalibrated) antenna/feeder
Pre-launch Optim isatio
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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).
Drive Test Data: the need for consistency
Ideally:
Use the same analyser, feeder and antenna for the
Pre-launch Optim isatio
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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
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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
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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.
Consequences of violating Lee Criteria
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
Consequences of violating Lee Criteria
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
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-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
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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/
Drive Test Measurement
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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
Drive Test Measurement
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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
Drive Test Measurement
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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 Measurement
Drive Test Measurements Analysis
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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:
Drive Test Measurement
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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
Drive Test Measurement
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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.
Drive Test Measurement
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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
Drive Test Measurement
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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.
Improving Interference
Scanner Data.
Area wherethere are three
l l l l
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equal low-levelpilots revealsEc/Io of -8 dB.
Improving Interference
Scanner Data.
Area where thereare seven low-level
il t ( t l
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pilots (not equalstrength).
Best Ec/Io =-10 dB
Improving Interference
Typical drive test result from well-optimised cluster.
Pre-launch Optim isatio
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
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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
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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)
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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
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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.
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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
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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
Example 2: AS update reports
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.
Example 2: AS update reports
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
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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
Example 3: Sudden Change in Signal
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
Example 3: Sudden Change in Signal
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
Example 3: Sudden Change in Signal
Strength
Functional Testin
This can be alleviatedby:
providing a separate
cell at the intersection Cell 2
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Cell 1
Example 3: Sudden Change in Signal
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
Example 3: Sudden Change in Signal
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
sibSb-Type sysInfoType2 :2,
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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{
sibSb-Type sysInfoType1 :12,
scheduling {
segCount 1,
sib-Pos rep128 : 6
sibSb-Type sysInfoType2 :2,
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
Same as Type 5 but in connected mode
System Information Blocks SIBs
18 SIBs defined by ETSI TS 25.331 Release 4
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
System Info and Message Flows
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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
Same as Type 11 but in connected mode
System Information Blocks SIBs
18 SIBs defined by ETSI TS 25.331 Release 4
Type 13
Used for ANSI-41
Type 14
Only TDD Type 15
UE positioning method for example GPS
T 16
System Info and Message Flows
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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
System Info and Message Flows
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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
System Info and Message Flows
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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
RRCU 10:44:23.884 DCCH RRC_CONNECTION_RELEASE_COMPLETE
RRCU 10:44:24.034 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
Pre-launch Optim isatio
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