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© SIEMENS Limited 1999ICN PLM CA NP
s
© SIEMENS Limited 1999ICN PLM CA NP
Main TopicsWhat is network optimisation? 2
Why optimisation? 2
Aim of network optimisation 3
Advantages for the customer 3
Planning vs. optimising 4
Major problem areas 4
Radio optimisation related processes 5
Tuning 5
Test types 6
Measurement analysis 6
Change request and action 7
Acceptance tests 7
Ongoing optimising 8
Pre-analysis: general network check 8
Customer complaints analysis 9
Collect/analyse OMC statistics 9
Collect/analyse drive test measurements 10
Implement changes 11
Test mobile 11
Repeated call setups 12
Continuous call 13
Statistics 14
Concept for optimisation 14
Analysis programs 15
Problem symptoms 15
Coverage analysis 16
Test mobile measurements 16
Possible problem areas 17
Antenna configuration 18
Antenna types - typical beam patterns 18
Antenna fine tuning 19
Omni vs. sectorised 20
Vertical antenna beam 20
Tilting 21
Antennadiversity type 22
Verification of RF network design 23
Site check 23
Antenna isolation 24
Site physical configuration 25
Site-to-site distances and distribution 25
Special features for improving coverage 26
Cell splitting, sectorisation 26
DTM check 27
Propagation model verification 27
Link budget analysis 28
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© SIEMENS Limited 1999ICN PLM CA NP
Main Topics (continued)Dropped call analysis 29
Call setup analysis 30
MAXRETR 30
Handover performance analysis 31
Handover parameters 31
Consequence of missing neighbours 32
Consequence of many neighbour definitions 32
Handover measurements 33
Handover parameters 33
Radio link measurements 34
Handover algorithm 36
Handover criteria - quality 37
Handover decision 37
Intracell handover 38
Level handovers 39
Distance handover 40
Power budget handover 40
Cell reselection 41
Speech quality analysis 43
Downlink interference measurement 43
Frequency changes 44
BSIC optimisation 45
Call setup/handover mechanisms 45
Location area codes 46
Interference reduction 46
Power control 47
Frequency hopping 48
DTX 49
Channel configuration 50
Capacity enhancements 50
Adding TRX 51
Interference reduction features 51
Traffic load distribution 52
Call setup/handover mechanisms 52
Hierarchical cell structures 53
Concentric cells 53
Overlaid micro-and picocells 54
Microcell frequency planning 54
Speed sensitive handovers 55
Half rate coding/dual rate operation 55
Cell parameter optimisation 56
Performance measurements 56
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© SIEMENS Limited 1999ICN PLM CA NP
What is Network Optimisation?
Improving Capacity, Quality and General Performance of the existing Network Infrastructure
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© SIEMENS Limited 1999ICN PLM CA NP
Why Optimisation?
Coverage holes
Performance degradation by interference
Different subscriber distribution compared to that assumed for the network design
Unexpectedly high subscriber growth
Extensive network expansions ongoing
Frequency resources at the limit
Unexpected mobility profile of
subscribers
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© SIEMENS Limited 1999ICN PLM CA NP
Aim of Network Optimisation
Improved Network Quality➨ Speech quality, Call success rate, Call setup time
Improved Network Availability➨ Service area , Radio Coverage
Optimised utilisation of installed equipment➨ Increase in subscriber potential
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© SIEMENS Limited 1999ICN PLM CA NP
Advantages for the Customer
Optimum utilization of the system resources
Minimized costs
Reduced subscriber complaints
Optimised subscriber satisfaction
Increased Profit One step ahead of theCompetitors
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© SIEMENS Limited 1999ICN PLM CA NP
Planning vs. Optimising
Thorough network planning from start can reduce the optimisation effort significantly!
➨ In a poorly planned network, achievable optimisation effects without major re-design are rather marginal
A close link between the two activities is necessary
Be involved
Feedback result
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© SIEMENS Limited 1999ICN PLM CA NP
Major Problem Areas
no coverage
interference
blocking
handover not working
HW/SW failures
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© SIEMENS Limited 1999ICN PLM CA NP
Radio Optimisation Related Processes
The following processes involve optimisation related activities➨ Tuning Process
✲ drive tests
✲ adjustment of network parameters
➨ Acceptance tests
➨ Ongoing Optimisation✲ Repeated quality control and improvement as network grows / matures
Tuning Acceptance Tests
OngoingOptimisation
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© SIEMENS Limited 1999ICN PLM CA NP
Tuning
Objectives :➨ Verify network configuration against current planning status
➨ Identify and eliminate equipment faults (HW/SW) and installationerrors
➨ Ensure that the network is ready for acceptance testing
TestMeasurement
MeasurementAnalyzing
Change RequestAction
Repeat Processuntil
Agreed Quality
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© SIEMENS Limited 1999ICN PLM CA NP
Test Types
Continuous drive test➨ setup a test call and drive over an area for detecting lack of coverage,
missing handovers, interferences etc.
Spot test➨ detail measurement to be taken at dedicated problem spots for detail
analyzing of specific problem
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© SIEMENS Limited 1999ICN PLM CA NP
Measurement Analysis
Antenna Installation check➨ height, orientation and tilt
Basic cell parameters and functions➨ OMC
✲ BCCH, BSIC, CI, LAC
✲ Neighbour List, consistency
✲ HO and power parameters
✲ Call Setup on all timeslots and speech quality check
✲ HO to other sectors or other neighbours
Test measurement (TEMS etc. together with a GPS)➨ Signal Strength
➨ Co-channel and adjacent interference
➨ Handover relations
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© SIEMENS Limited 1999ICN PLM CA NP
Change Request and Action
SBS System Database ➨ Change BCCH to avoid interference
➨ Change HO-Margin
➨ Add neighbour relations (Mutual)
Site Hardware➨ Antenna tilt etc.
System error➨ Software bugs
➨ Transmission sync. (ADPCM)
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© SIEMENS Limited 1999ICN PLM CA NP
Setup TestScenario
PerformingTest
Test Result
Acceptance Tests
Setup Test Scenario➨ Test Purpose
➨ Test Definitions✲ Coverage Criteria
✲ Coverage Area
✲ Successful Call
➨ Test Condition
➨ Test Equipment
➨ Test Methodology
✲ Test Routes
✲ Test Procedure
✲ Test Duration
➨ Test Analysis✲ Acceptance Criteria
➨ Test Results✲ Signal Level
✲ Signal Quality
✲ Handover
✲ Call Success Rate
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© SIEMENS Limited 1999ICN PLM CA NP
Ongoing Optimising
For improvement of the network after it is launched and filled up by subscribers
Collect / analyse
drive testmeasuremts
Collect / analyse
drive testmeasuremts
Collect / analyse
complaints
Collect / analyse
complaints
Collect / analyseOMC
statistics
Collect / analyseOMC
statistics
Propose / implementchanges
Propose / implementchanges
Repeatprocess until
agreed quality
Repeatprocess until
agreed quality
Pre-analysis: Generalnetworkcheck
Pre-analysis: Generalnetworkcheck
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© SIEMENS Limited 1999ICN PLM CA NP
Pre-analysis: General Network Check
Steps to be carried out:➨ Kick-off meeting
➨ Determine original network planning objectives
➨ Collect information about network status
➨ Determine functional network structure, e.g.– - BTS / BSC locations., antenna direction etc.
– - services and features used
– - network structure (macrocell, microcell etc.)
➨ Determine the network element configuration, e.g.– - number of TRX per cell
– - sector / omni config.
➨ Visit selected sites (if necessary)
➨ Database analysis
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© SIEMENS Limited 1999ICN PLM CA NP
Customer Complaints Analysis
Additional source of information, but difficult to handle
Customer service desk must collect all relevant information➨ Caller and Called No. (PSTN->MS, etc.)
➨ What is the problem? (Voice Quality, Can’t make a call, etc.)
➨ MS is moving or fixed while make call
➨ Where did the problem occur?
➨ When?
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© SIEMENS Limited 1999ICN PLM CA NP
Collect / Analyse OMC Statistics
OMC Measurement➨ Handled traffic (congestion on TCH, SDCCH)
➨ dropped calls
➨ Interference
➨ Handover reason (due to UL_QUAL, Powerbudget, distance…)
Advantages over test drives:➨ Less labor intensive and time consuming
➨ More comprehensive, based on large number of users
➨ not limited to time of test drive
➨ Uplink and Downlink analysis possible
➨ Subscriber behavior mix of outdoor, indoor, incar use
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© SIEMENS Limited 1999ICN PLM CA NP
Collect / Analyse OMC Statistics
Disadvantages, limitations:➨ Limited geographical resolution (Where does the problem occur?)
➨ Cannot separate problems due to coverage from other✲ Call attempts in uncovered areas are not counted
✲ Call drop due to lack of coverage
➨ Network must have minimum load for reliable statistics
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© SIEMENS Limited 1999ICN PLM CA NP
✲ Serving signal level
✲ BER (Rxqual)
✲ Channel Number
✲ CI and LAI
✲ Timing Advance
✲ Layer 3 messages
✲ BSICs
✲ Signal and power levels of neighbouring cells
Collect / Analyse Drive Test Measurements
Test types➨ Continuos drive test (Trace mode)
➨ Spot test
➨ Network performance test (Statistical mode)
Test Measurement➨ Collect MS measurement report data (Downlink only!!)
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© SIEMENS Limited 1999ICN PLM CA NP
Implement Changes
Changes related to database parameters
Actions related to site hardware
Problems to be solved by Normal Roll-out activities
Problems to be solved by other system experts
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© SIEMENS Limited 1999ICN PLM CA NP
Test Mobile
Various modes, e.g.➨ Repeated call setups
➨ Continuous call
➨ Scanning mode✲ check for spectrum
occupancy✲ check for BCCH
with no neighbour
relations
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© SIEMENS Limited 1999ICN PLM CA NP
Repeated Call Setups
Method➨ call setup
➨ hold for predefined time period and then release✲ predefined time = mean holding time
✲ call may be dropped earlier
➨ repeat call setup after predefined waiting time (typical 15 s)
Purpose➨ simulate subscriber behavior
➨ wide area quality assessment and trend identification
BaseTransceiver
Station
BaseStation
Controller
MobileSwitching
Center
PSTN-Interface
Um-
Serial MeasuremtSoftware
Abis- A-Interface
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© SIEMENS Limited 1999ICN PLM CA NP
Repeated Call Setups
Typical parameters➨ call setup success rate, setup time, dropped call rate
➨ statistics can be generated in Tornado / Planet, e.g.Call Diagnostics
RxQual Full Threshold: 4
RxQual Full Threshold (%):90
RxLev Full Threshold: 14
RxLev Full Threshold (%): 90
Maximum Setup Time (s): 10
Call Time Setup Clear Down RxQual (%) RxLev (%) Category
1 21:38.8 6.5 OK 100 100 GOOD
2 23:53.1 FAIL FAIL FAIL FAIL NO SETUP
3 26:08.7 5.7 OK 98 85.3 LOW SIGNAL
4 28:23.9 6.4 OK 79.5 100 NOISY
5 30:38.8 5.8 FAIL FAIL FAIL DROPPED
6 32:54.4 12 OK 100 100 DELAYED
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© SIEMENS Limited 1999ICN PLM CA NP
Continuous Call
Method➨ call setup
➨ hold continuously until drive test route complete✲ in case of call drops re-establish
Purpose➨ Wide area quality trace
➨ Locating individual problem areas
➨ Detailed analysis in problem areas
➨ Quality assessment on rural highways etc.
➨ BS Testing and Functional Testing
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© SIEMENS Limited 1999ICN PLM CA NP
Continuous Call
Typical parameters➨ RxLev, RxQual, BCCH, BSIC,
handover, Layer 3 messages etc.
Import into planning tool ➨ Terrain or clutter background
➨ Comparison of measured network performance vs. prediction
Statistics:➨ RxLev, RxQual, handover
success rate
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© SIEMENS Limited 1999ICN PLM CA NP
Statistics
Combine from both modes
Typical measurements also used for acceptance tests
Measurement Test sample unit No. of samples Measured valueRxLev >
-85 dBm Measurement bin (Tornado) 8,432 99.90%RxQual < 4 Measurement bin (Tornado) 8,432 99.20%Handover success rate Handover attempt 61 93.50%Call setup success rate Call attempt 115 90.30%Mean setup time Call successfully setup 106 5.3 sDropped call rate Call successfully setup 106 1.00%
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© SIEMENS Limited 1999ICN PLM CA NP
Performance Measurements
Provide an overview of network performance (statistics)➨ uplink analysis also possible
➨ validity depends on sufficient samples
Examples: ➨ blocking rate
BTS ID
LAC
CI
BSIC
f1
f2
f3
f4
Busy hour
TCH Blocking Rate
6 4
4052
2 4
83
69
16:00:00 66.53%
2 4
4083
2 2
76
67
16:00:00 30.16%
5 4
4051
2 6
79
66
16:00:00 7.91%
22 4
4183
2 0
77
12:00:00 3.96%
1 4
4082
2 1
84
80
13:00:00 3.81%
BTS ID
LAC
CI
BSIC
f1
f2
f3
f4
Busy hour
SDCCH Blocking Rate
25 4
4052
2 4
83
69
15:00:00 32.99%
6 4
4052
2 4
83
69
16:00:00 5.99%
26 4
4171
2 6
63
13:00:00 2.83%
3 4
4041
2 7
87
13:00:00 2.06%
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© SIEMENS Limited 1999ICN PLM CA NP
Performance Measurements➨ Call setup success rate
➨ Dropped call rate
BTS ID
LAC
CI
Busy Hour
Call Set-up Success Rate
25 4 4152 15:00:00 28.4%
29 4 4131 15:00:00 68.0%
15 4 4032 18:00:00 81.3%
5 4 4051 16:00:00 92.1%
26 4 4171 13:00:00 94.1%
11 4 4071 12:00:00 94.7%
BTS ID
LAC
CI
TCHConnections
RF Loss
Inter Cell HOLoss
Intra CellHO Loss
Call Drop
Rate
37 4
4192
19730 1526 23 153 9%
15 4
4032
12740 723 6 58 6%
22 4
4183
10993 485 18 13 5%
25 4
4152
24748 755 12 29 3%
7 4
4011
8849 240 16 23 3%
26 4
4171
15922 219 28 12 2%
29 4
4131
5712 77 8 6 2%
27 4
4172
10421 156 4 4 2%
19 4
4212
9192 130 9 5 2%
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© SIEMENS Limited 1999ICN PLM CA NP
How
to improve the
network?
Alternatives
NetworkSnapshot
QuickCheck
AnalyzingPrograms
• Status of the Network
• Decide further Analysis Program
Coverage
Dropped Calls
Call Setup Success
Handover Perf.
Speech Quality
General Check
Concept for Optimisation
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© SIEMENS Limited 1999ICN PLM CA NP
Coverage: Analysis for Fulfilment of Coverage Requirements (Urban, rural ... areas, outdoor, in-car, indoor)
Dropped Call: Analysis for Dropped Calls due to Interference, SW/HW failures, Transmission Network Failures
Call Setup: Analysis for Blocking and CapacityLimitations, Analysis for Resource Allocation Procedures
Handover: Analysis for Efficient HandoverPerformance
Speech Quality: Analysis for Interference
Analysis Programs
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© SIEMENS Limited 1999ICN PLM CA NP
No serviceNo coverageNo System Availability
Network Element FailuresTransmission Network Failures
Low call setup success rateRF Network
No coverageInterferenceBlocking
Fixed Network BSS, SSSBlockingOverloadOther
High call drop rateRF Network
No coverageInterferenceHandover failure
Fixed Network BSS, SSSNetwork Element FailureTransmission FailuresOther networks
Mobile terminal
Poor speech qualityRF Network
No coverageInterferencePoor handover performance
Fixed Network BSS, SSSNetwork element failureTransmission network failureOther networks
Mobile Phone
Problem Symptoms
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© SIEMENS Limited 1999ICN PLM CA NP
Coverage Analysis
Test mobile measurements
Antenna configuration check
Verification of RF network design
DTM check
Propagation model verification
Link budget analysis
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© SIEMENS Limited 1999ICN PLM CA NP
Test Mobile Measurements
Collect RxLev measurements together with GPS co-ordinates
Analyse on planning tool
Reasons for poor coverage:➨ serving cell not best server
✲ handover problems
➨ best server signal low✲ check site / network design
Analyse in terms of relevant
thresholds:➨ indoor level
➨ in-car level
➨ outdoor level
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© SIEMENS Limited 1999ICN PLM CA NP
Test Mobile Measurements
Consequences of poor RxLev:
➨ low RxQual➨ vulnerable
to interferenceLimitation with drive tests:
➨ downlink onlyAnother method:
➨ statistical analysis
➨ OMC or drive tests
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© SIEMENS Limited 1999ICN PLM CA NP
Possible Problem AreasDownlink
➨ Output power low
➨ Obstruction of Tx antenna
➨ Antennae not aligned properly
➨ Broken / wrongly connected cables
➨ Database parameters controlling output power
Uplink➨ Receive sensitivity degraded due
to hardware problems
➨ Obstruction of Rx antennae
➨ Antennae not aligned properly
➨ Broken / wrongly connected cables
➨ Lack of diversity gain
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© SIEMENS Limited 1999ICN PLM CA NP
Antenna Configuration
General points to check➨ antenna type, e.g.
✲ omni
✲ directional 60, 90 or 120 degrees
✲ electrical downtilt
✲ cross-polarised
➨ antenna azimuth angle (for directional antennae)✲ coverage targets
➨ antenna tilt angle✲ electrical + mechanical
➨ diversity & isolation✲ e.g. space diversity,
✲ polarisation diversity
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© SIEMENS Limited 1999ICN PLM CA NP
Antenna Types - Typical Beam Patterns
Directional antenna
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© SIEMENS Limited 1999ICN PLM CA NP
Antenna Types - Typical Beam Patterns
Omni antenna with electrical downtilt
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© SIEMENS Limited 1999ICN PLM CA NP
Antenna Fine Tuning
Horizontal Plane:➨ Possible coverage weakness between sectors
➨ Interference reduction
➨ Traffic load distribution
Vertical Plane:➨ Interference reduction
➨ Possible coverage weakness in the short to medium distance range
➨ Traffic load distribution
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© SIEMENS Limited 1999ICN PLM CA NP
Sectorised cell site with differentdowntilt angles
Omni vs. Sectorised
OMNI cells - more difficult to optimise➨ Electrical downtilt possible, however
✲ same for entire cell
➨ Parameters same for entire cell
Directional antennae➨ narrower beam → easier to control interference
➨ tilting less efficient with wider beams
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© SIEMENS Limited 1999ICN PLM CA NP
Solution: Add mechanical downtilt
2° electrical downtilt
0°
3 dB-point: 5.25°
400 m
City
arctan (60/400) = 8.5°
60 m
Ant. Effectiveheight
Vertical Antenna Beam
High gain antennae with sharp vertical lobe➨ shadow under antenna
In practice: For cluttered environments reflections often compensate
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© SIEMENS Limited 1999ICN PLM CA NP
BSh
➨ Maximum: First null angle pointing at cell edge
Tilting
Antenna downtilt often used to minimise interference➨ Minimum: Vertical mail lobe pointing at cell edge
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© SIEMENS Limited 1999ICN PLM CA NP
0 ° 0 °
Electrical Mechanical
➨ Advantages:✲ Better back lobe characteristics
✲ Better lower side lobe characteristics
➨ Disadvantages:✲ Antennas are more expensive
Tilting
Electrical vs. Mechanical downtilt
A combination ofmechanical / electricaldowntilt may be used
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© SIEMENS Limited 1999ICN PLM CA NP
No Tilt Down Tilted 4 degrees
Tilting
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© SIEMENS Limited 1999ICN PLM CA NP
Antenna Diversity TypeSpace diversity
➨ vertical polarisation
➨ in general good performance
➨ requires extra antenna for diversity
Dual polarisation
➨ mobile antenna normally not held vertically
➨ when signals are reflected polarisation change (vertical normally dominates)
➨ cross polarised preferred✲ good performance in urban areas
➨ save one antenna✲ easier installation
Rx
ant.
1
Rx
ant.
2
Typical > 10 Rx
ant.
Horisontal /vertical
Crosspolarised
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© SIEMENS Limited 1999ICN PLM CA NP
Verification of RF Network Design
Site check
Site physical configuration evaluation
Site-to-site distances and distribution
Special features for improving coverage
Site database configuration evaluation➨ Tx power
➨ power control settings
➨ etc.
BTS
s
© SIEMENS Limited 1999ICN PLM CA NP
Site Check
Verify that site is implemented according to plan
Check installation e.g.➨ antenna spacing (diversity, isolation)
➨ antennae in one sector are installed in the same plane
➨ antennae alignment
➨ omni antenna installation
➨ cable installation
k
a
Vertical spacing
d
Horisontal spacing
Rx
Tx
Rx Tx
max 15 °
Antennas mounted in different planes
aa=
d d d
Alignment of antennas
Rx Tx Rxd
k1
Rx
Tx
Rxd
k2 k2
Omni
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© SIEMENS Limited 1999ICN PLM CA NP
Antenna Isolation
0102030405060
50
0
75
0
10
00
12
50
15
00
17
50
20
00
22
50
Spacing A/ mm
Isol
atio
n /d
B
Horizontal
Vertical
Isolation by vertical or horizontal separationbetween two antennas K73316..
A
A
Horizontal
VerticalSource: Kathrein
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© SIEMENS Limited 1999ICN PLM CA NP
Antenna Isolation
0
20
40
60
40
0
50
0
65
0
75
0
90
0
10
00
11
50
12
50
Spacing A/mm
Iso
latio
n /d
B
Horizontal
Vertical
A
Horizontal
Vertical
A
Isolation by vertical or horizontal separationbetween two antennas K73416..
Source: Kathrein
s
© SIEMENS Limited 1999ICN PLM CA NP
Site Physical Configuration
Antenna height➨ ideally sites within a given area classification should have similar
heights if traffic distribution is uniform
➨ evaluate site height in terms of objective✲ macrocell / minicell / microcell
✲ limitation of interference
✲ clear obstructions
Antenna tilt / directions➨ avoid coverage gaps
➨ target priority areas
➨ limit interference
Appropriate antenna types➨ sectorise omni cells?
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© SIEMENS Limited 1999ICN PLM CA NP
Site-to-Site Distances and Distribution
For an area of uniform structure / terrain / traffic➨ site-to-site distance should be uniform (assuming uniform site design)
Site distribution should reflect➨ coverage characteristics / requirements
➨ capacity requirements
Typical case➨ Downtown: High site density
➨ Suburban area: less dense
➨ Roads: Sites located along a line
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© SIEMENS Limited 1999ICN PLM CA NP
Special Features for Improving CoverageMicrocell
➨ for indoor coverage
➨ outdoor coverage in high capacity areas
Repeaters➨ alternative to microcell where the
traffic needs are low
➨ indoor
➨ outdoor
➨ road coverage
➨ “coverage hole fill solution”
Other indoor coverage solutions➨ distributed anteanne
➨ fibre optic repeater
➨ leaky cable
HCS, e.g.➨ large cells for car-coverage
➨ small cells for pedestrians
Scale = 0.5 Km
Building Outlines
Building Outlines
Building
Outlines
Place
S tr e et
Str ee
t
Micro Micro -- Cell Site Cell Site --LocationLocation
Macro Macro -- Cell Site Cell Site --LocationLocation
Border
Cell
Macro
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© SIEMENS Limited 1999ICN PLM CA NP
Cell splitting, Sectorisation
Change from large cells to small cells
Difficult , Expensive
Mainly driven by capacity requirements
Result: Improved indoor coverage
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© SIEMENS Limited 1999ICN PLM CA NP
DTM Check
DTM resolution➨ horisontal
✲ macrocell (typical 50-100 m for roads, 50 m for small cities, 20 - 40 m for large cities)
✲ microcell (very high resolution, down to building level)
➨ vertical - should be high
Source data➨ heights and clutter derived from paper maps
➨ clutter and / or vector updates by satellite photographs / aerial photos for metropolitan areas
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© SIEMENS Limited 1999ICN PLM CA NP
Propagation Model Verification
Wrong model wrong coverage prediction
In general, standard models have high performance
Highly specialised model may only be valid for a small area
Model performance depends on accuracy of DTM
To tune the model➨ field strength measurements
➨ check existing model against measurements
➨ modify model parameters
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© SIEMENS Limited 1999ICN PLM CA NP
Link Budget Analysis
Check for link budget imbalance
downlink
uplinkMS Peak Power
Rx Sensitivity MS
Rx Sensitivity BS
cable loss uplink
cable loss downlink
antenna diversity gain
combiner loss
PA output power
Balanced Power Budget
Balanced Power Budget
Uplink Power Budget - Downlink Power Budget = 0! Link Power Budget is balanced!
BTS
downlink uplink
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© SIEMENS Limited 1999ICN PLM CA NP
Link Budget Analysis
-85,00
-75,00
-65,00
-55,00
0,20 0,40 0,60 0,80Distance from BTS in km
RxLev/dBm
Links balanced
3dB unbalanced
6dB unbalanced
35% Coverage Loss @ 3dB!
55% Coverage Loss @ 6 dB!
RxLev for IndoorCoverage(90%)
Uplink Power Budget - Downlink Power Budget 0! Link Power Budget is unbalanced!
Caused by wrong assumption forReceiver SensitivityDiversity GainPropagation Environment
Link Balancing viaOptimization of DiversityTower mounted amplifierHigh power amplifier
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© SIEMENS Limited 1999ICN PLM CA NP
Downlink
Uplink
40 dBm
37 dBm
-110 dBm
-107 dBm
Link Budget Analysis
Increasing BS Output?➨ Unbalanced link budget
Better BS Rx sensitivity or pre-amplifier➨ Must be matched by higher BS TX power for balanced link budget
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© SIEMENS Limited 1999ICN PLM CA NP
Dropped Call Analysis
How to measure ➨ drive tests
✲ repeated call setups (preferred)
✲ continuous calls
➨ OMC measurements
Reasons for dropped calls➨ lack of coverage
➨ interference problems
➨ handover problems
➨ lack of synchronisation in network
➨ problems with other parts of the network
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© SIEMENS Limited 1999ICN PLM CA NP
Call Setup Analysis
How to measure ➨ drive tests
✲ repeated call setups
➨ OMC measurements
Reasons for failed call setups➨ lack of coverage
➨ database problems✲ database inconsistencies
✲ parameter settings, e.g.– RXLEV_ACCESS_MIN, RACHBT, RACH_MAX_RETRANS
– cell reselection related parameters
➨ network congestion
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© SIEMENS Limited 1999ICN PLM CA NP
BTS
MS
RACH(1)
RACH (2)
RACH
AGCH
✲ E.g: MAXRETR = 2
MAXRETR
Slotted ALOHA mechanism: Several users may attempt to access channel simultaneously
➨ in case of collision new attempts are made
➨ MAXRETR: Maximum no. of retries allowed
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© SIEMENS Limited 1999ICN PLM CA NP
Handover Performance AnalysisWhen moving from one cell to another (neighbour cells) handovers are necessary
SIEMENS AGMON MAR15 15:18:41
SCALE 1:2500
EqualPowerBoundary Mutual Neighbour Non-Mutual Neighbour Missing Neighbour Too many Neighbours
Missing Neighbourdefinition
Handover Failure
Dropped Call
Too many neighbours
Inaccurate handoverdecision
Handover Failure &Dropped Call
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© SIEMENS Limited 1999ICN PLM CA NP
Handover Parameters
Objectives:➨ mobile should be connected to the
“best”cell
➨ avoid unnecessary handovers
Consequence➨ good speech quality
➨ less dropped calls
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© SIEMENS Limited 1999ICN PLM CA NP
Consequence of Missing Neighbours
Missing neighbour cells
Cell dragging
Poor RxLev Interference Exceeded distancePoor RxQual Poor PBGT
Dropped Calls
Congestion
f1
f1
Defined neighbours
Server
Missing neighbourInterferer
Cell dragging
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Consequence of Many Neighbour Definitions
Only about 100 measurement samples are possible during one measurement period for all defined neighbour cells
Number of BCCH carriers Number of samples perIn BCCH Allocation Carrier in SACCH multiframe
32 3-416 6-710 10-118 12-13: :
(Rec. GSM 0508)
Too many neighbour cells
Inaccurate signal level measurement
False handover decisions
Dropped Calls
Problem:Sites with too large coverage area
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Handover MeasurementsHandover due to a better cell
(RxLev_1 > RxLev_Full)
Handover due to bad quality
Can also be analysed by statistics
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Handover Parameters
Fine-tuning of handover parameters➨ Moving cell boundaries in order to
✲ Enhance success rate for critical handovers
✲ Minimise local interference at the cell edge
✲ Traffic load sharing between cells
➨ Compared to other opimisation measures improvement potential is limited
➨ Affected by✲ Measurement averaging
✲ Power control parametersPS! Neighbours should in generalbe mutual
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BTSMSNeighbour
BSC
UL
DL
Radio Link Measurements
BTS measurements (Uplink):➨ Signal level
➨ Quality
➨ BS-MS distance
➨ (Interference levels in idle time slots)
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BTSMSNeighbour
BSC
UL
DL
Radio Link Measurements
MS measurements (Downlink)➨ Signal Level
➨ Quality
➨ Signal levels of neighbouring cells (BCCH)✲ Strongest 6 are reported to the Network
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BTSMSNeighbour
BSC
UL
DL
Radio Link Measurements
BSC (In general) ➨ Collects all data
✲ BTS and MS send measurement reports every 480 ms
✲ Makes handover decisions
Siemens Network, BTS makes HO decisions
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32 27 2923 29 21 19 22 23 21
Average value = 24
Radio Link Measurements
Radio link measurements averaging➨ BTS (BSC) receives measurement samples from BTS + MS
✲ every SACCH-Multiframe (480ms,104 TDMA frames)
➨ “Gliding Window”✲ averaging Window size (max.31)
✲ Window is cleared after call setup or handover
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32 32 2327 27 29 29 29 21 21
Average value = 27
32 27 2923 29 21 19 22 23 21
F F FS S F F S S F
Measurement Values eachSACCH Multiframe (0.48s)
– W_Lev_Full = 2
– W_Lev_SUB = 1
– Gliding Window = 5
Radio Link Measurements
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Inter-cell HOPower Budget
Intra-cell HOdue to Quality
PBGT
IAQUAL
HandoverDecision
HandoverDecision
IRQUAL
LEV
DIST
Inter-cell HOdue to Quality
Inter-cell HOdue to Level
Inter-cell HOdue to Distance
No handoveraction
no
no
no
no
no
yes
yes
yes
yes
yes
Handover Algorithm
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Rx_Qual
Rx_Lev
L_Rx_Qual_XX_H
L_Rx_Lev_XX_IH
L_Rx_Lev_XX_H0 63
7Intracell HO
due to Quality
No handoveraction due to
quality or level
Intercell HOdue to quality
Intercell HOdue to level
Handover Criteria
Handover Region (due to quality and level)
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Handover Types Decision CriteriaIntercell HO 1. RXQUAL_XX > L_RXQUAL_XX_Hdue to Quality 2. RXLEV_XX < L_RXLEV_XX_IH
3. XX_TXPWR = Min (XX_TXPWR_Max,P)HO due to Level 1. RXLEV_XX > L_RXLEV_XX_H
2. XX_TXPWR = Min(XX_TXPWR_Max,P)HO due to Distance 1. MS_BS_DIST > MS_Range_MaxHO due to 1. RXLEV_NCELL(n) > RXLEV_MIN(n)Power Budget + Max (0,MS_TXPWR_MAX(n)-P)
2. PBGT(n) > HO_MARGIN(n)Intracell HO 1. RXQUAL_XX > L_RXQUAL_XX_Hdue to Quality 2. RXLEV_XX > L_RXLEV_XX_IH
Handover Decision
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7Interferer: f1
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
Sever: f10 1 2 3 4 5 6 7
Intracell Handover
Stay within cell, change frequency / time slot situation➨ in general interference different on different timeslots
➨ change to a different cell may be unnecessary
➨ higher traffic load higher likelihood on other timeslots
➨ not effective with frequency hopping✲ parameter settings for intracell handover should be set to reduce such
handovers
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Rx_Qual
Rx_Lev
L_Rx_Qual_XX_H
L_Rx_Lev_XX_IH
L_Rx_Lev_XX_H
Intracell HOdue to Quality
Intracell Handover
Check for simultaneous occurrence of:➨ Poor quality (high Rx_Qual)
➨ Sufficient signal level ✲ L_Rx_Lev_XX_IH
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Rx_
Lev
Driven route
HO_Threshold_Lev
Server
neighbour
HOMARGIN
MinHOReqInt
Level Handovers
Adjacent cell not stronger than current cell + HO margin
Serving cell has insufficient coverage➨ “emergency handover” to cell with better coverage
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BTS
Receiver limit sensitivity
L_RXLEV_XX_H (outgoing level HO)
L_RXLEV_XX_IH (inter HO/ intracell quality HO)
RXLEV_MIN (incoming HO)
Level Handovers
RXLEV_MINthreshold for cell to accept incoming handover
L_RXLEV_XX_Hthreshold for initiating outgoing handover due to signal levelrelation with RXLEV_MIN will determine hysteresis
L_RXLEV_XX_IH threshold for initiating inter / intracell quality HO
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➨ Normally used in combination with other criteria, e.g. ✲ cross-water propagation,
✲ elevated bridges etc.
GSM : max 35 km Enhanced by “Extended Cell”
Distance Handover
Maximum allowable BS-MS distance➨ Default: MS_Range_Max=61 (bits Timing Advance,TA)
✲ Maximum value: 63, corresponding to 35 km
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1. RXLEV_NCELL(n) > RXLEV_MIN(n) + Max(0,MS_TXPWR_MAX(n)-P)
2. PBGT(n) = RXLEV_NCELL(n)-(RXLEV_DL+PWR_C_D)+Min(MS_TWPWR_MAX(n),P)-Min(MS_TXPWR_MAX(n),P)
> HO_MARGIN(n)
Power Budget Handover
Select cell with better signal level at given location
HO margin➨ Large enough to avoid “ping-pong HO”
➨ small enough to allow fast HO
Ping-Pong HO
BTS1
BTS2
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C1 = AV_RXLEV - RXLEV_ACCESS_MIN - MAX(0,MS_TXPWR_MAX_CCH-P) > 0C1 = AV_RXLEV - RXLEV_ACCESS_MIN - MAX(0,MS_TXPWR_MAX_CCH-P) > 0
✲ MS takes 5 samples of the received level on each RF carrier which
are averaged
AV_RXLEV = 1/5 * (RXLEV1+RXLEV2+…+RXLEV5)
Cell Reselection
C1-criterion for cell access:
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For example:
Cell Reselection
BTS
MS
DL
MS class 5 (GSM900)AV_RXLEV=-97 dBm
➨ RXLEV_ACCESS_MIN = -100 dBm
➨ MS_TXPWR_MAX_CCH = 29 dBm (0.8W)
C1 = -97 - (-100) - Max(0,33-29)= -1
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Operator BBTS
MS
DLMS class 5 (GSM900)
C1 = -90 - (-110) - Max(0,33-29)
= +16 ✓
Operator ABTS
DL
C1 = -90 - (-100) - Max(0,33-29)
= +6 ✗
✲ RXLEV_ACCESS_MIN = -110 dBm
✲ MS_TXPWR_MAX_CCH = 33 dBm (2W)
✲ RXLEV_ACCESS_MIN = -100 dBm
✲ MS_TXPWR_MAX_CCH = 33 dBm (2W)
•MS receives signal from Operator A and B = -90 dBmOperator A Operator B
Cell Reselection
For example:
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BTS1 BTS2
C1 High power class MS
Low power class MS
Cell_Reselect_Hysteresis
Cell Reselection
C1 criteria➨ Same Location Area
✲ C1 (neighbour cell) > C1 (serving cell)
➨ Different Location Area✲ C1 (neighbour cell) > C1 (serving cell) + Cell_Reselect_Hysteresis
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Speech Quality AnalysisParameters
➨ RxQual
➨ Frame Erasure Rate (FER)
➨ Speech Quality Index (SQI)
Measurements➨ Drive test
✲ preferably continuous call
➨ OMC statistics
Cause for poor quality➨ low signal strength (coverage
related
➨ interference
➨ low signal strength and interference
Causes of interference➨ co-channel interference
➨ adjacent channel interference
➨ intermodulation✲ mainly on one link only
➨ multipath interference
Interfering cell of base station within GSM -network
Base station within GSM –Network
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Downlink Interference Measurement
Typical requirement➨ speech: RxQual 4
➨ data: RxQual 3
BER % RxQual0.0 - 0.2 00.2 - 0.4 10.4 - 0.8 20.8 - 1.6 31.6 - 3.2 43.2 - 6.4 5
6.4 - 12.8 6> 12.8 7
With frequency hopping: RxQual not a valid parameter
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Frequency Changes
Sometimes necessary to minimise interference
As network reaches capacity limit this becomes difficult➨ Other frequencies may be affected by the change
Can be done at either interfering cell or victim cell➨ Choice: Whichever happens to be easier to change
Existing plan may be entered into planning tool as “constraints”
➨ search for “optimum” frequency allocation for a given cell
At a certain point the whole network e.g. in a city may have to be re-planned
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BCCH: 794 BCCH: 794TCH:797
before
BCCH: 794 BCCH: 797TCH:794
after
➨ Effectiveness depends on TCH traffic load
➨ BCCH / TCH sub-bands are mixed
➨ Could be used as a temporary measure✲ while traffic load is low
Frequency Changes
BCCH/TCH swapping➨ Method sometimes used: Alternate between clusters
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© SIEMENS Limited 1999ICN PLM CA NP
f9
f9
f9
BSIC Optimisation
Base Station Identity Codes➨ Used by the MS to distinguish between cells
using the same frequency✲ Co-Channel cells must have different
BSICs
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Call Setup/Handover Mechanisms
20-25 dB street corner loss: Fast handovers required✲ Micro-micro
✲ Micro-macro
➨ Fast measurement averaging
➨ Carefully tuned handover thresholds
➨ Small handover margins
➨ Short penalty timers
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Location Area Codes
Purpose➨ identify location area
➨ in incoming call is paged to all BTS’s within LA
Large location area➨ advantage: less location updates (reduced SDCCH load)
➨ disadvantage: more paging traffic
Boundaries should not cross high traffic areas
Cell reselection across LA boundaries➨ Parameter Cell_Reselect_Hysteresis (typ. 4 dB) used to avoid
unnecessary signalling due to ping-pong cell reselections
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Interference Reduction
Power Control
Frequency Hopping
Discontinuous Transmission DTX
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Power Control
Quality-triggered PC➨ e.g. L_RXQUAL_XX_P = 4
✲ Triggers a power increase at poor quality
➨ e.g. U_RXQUAL_XX_P = 1✲ Triggers a power reduction at good quality
✲ Virtually disabled by setting to “highest” RXQUAL value
✲ Level criterion is more suitable for power reduction
Level-triggered PC➨ e.g. L_RXLEV_XX_P = 25 (-85 dBm)
✲ Triggers a power increase at bad level
➨ e.g. U_RXQUAL_XX_P = 35 (-75 dBm)✲ Triggers a power reduction at good level
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RXQUAL
RXLEV
L_RXQUAL_XX_P
L_RXQUAL_XX_P
Power Increase(bad quality)
Power Increase(bad level)
Power Decrease(Good Level)
Power Decrease(good quality)
L_RXLEV_XX_P U_RXLEV_XX_P
2*POW_RED_STEP_SIZE
Power Control
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
f1
f2
f3
TDMA frame(8 time slots)
0
0
BCCH
SDCCH
1 Call 1
5 Call 2
Frequency Hopping
Cyclic / Pseudo Random hopping
Baseband / Synthesized hopping
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
f1
f2
f3
TDMA frame(8 time slots)
0
0
BCCH
SDCCH
Call 1
Call 2
Frequency Hopping
Cyclic / Pseudo Random hopping
Baseband / Synthesized hopping
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
f1
f2,f3,f4,f5,f6,f7
f2,f3,f4,f5,f6,f7
TDMA frame(8 time slots)
0
0
BCCH
SDCCH
1 Call 1
5 Call 2
f4
f7
f3 f6
Frequency Hopping
Cyclic / Pseudo Random hopping
Baseband / Synthesized hopping
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DTX
Goal: Reduce speech data rate from 13 kbps (user speaking) to 500 bps (enough to encode background noise)
➨ reduce MS power consumption
➨ reduce the interference in a cell
SBS parameter for DTX / VAS administration➨ DTXUL -> 0 : MS may use DTX (If possible)
1 : MS shall use DTX
2 : MS shall not use DTX
➨ DTXDL -> FALSE : downlink DTX disabled at BTS
TRUE : downlink DTX enabled at BTS
PS! No gain for data communications
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Channel Type Channel CombinationTCHFULL TCH/F + FACCH/F + SACCH/FMAINBCCH FCCH + SCH + BCCH + CCCH (AGCH+PCH+RACH)MBCCHC FCCH + SCH + BCCH + CCCH + 4 (SDCCH+SACCH)SDCCH 8 (SDCCH + SACCH)TCHF&HLF* TCH/H(0) + FACCH/H (0) + SACCH/H(0) + TCH/H(1)BCBCH* FCCH + SCH + BCCH + CCCH + 3 (SDCCH+SACCH) + CBCHSCBCH* 7 (SDCCH + SACCH) + CBCHCCCH* BCCH + CCCH
Note: * in SBS BR 3.0
Channel Configuration
✲ For example,– 1TRX : TS0 -> BCBCH
TS1-7 -> TCHFULL
– 2 TRXs : TRX0, TS0 -> MAINBCCH
TRX0, TS1 -> SCBCH
TRX0, TS2-7 -> TCHFULL
TRX1, TS0-7 -> TCHFULL
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Capacity Enhancements
Easy approach: Add TRX’s
Problem: No more frequencies:➨ Options
✲ Traffic load distribution
✲ Interference optimisation features: FH, PC, DTX
✲ Sectorisation: Increasing cell density
✲ Cell splitting: Increasing site density
✲ HCS– Dual band operation (e.g. GSM900/DCS1800)
– Dual mode operation (e.g. GSM900/DECT)
– Underlay / Overlay
– Overlaid micro- and picocells
✲ Half rate coding
✲ Migration to 3rd Generation Systems
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Sec TRX GOS 2% Week1 Week2 Week3 Week4 Week5 Week6 Week7BTS1 1 3 14.9 10.53 9.66 10.21 9.88 10.54 9.97 10.37BTS2 2 2 8.2 7.43 7.26 7.59 6.98 7.55 8.02 8.33BTS3 3 3 14.9 11.92 11.4 12.12 11.82 11.75 12.02 12.15
Adding TRX
Congested cells found by OMC measurements
➨ Sector 2 will experience congestion
➨ Sometimes percentage limit, e.g. 80%, of full load defined✲ Sector 3 is near that limit
Possible limitations of TRX extensions:➨ Need for changed hardware configuration costly
✲ e.g. new BTS rack needed
➨ Frequency Spectrum limited
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✓No additional sites or frequencies required
✓Available, stable
✓Implementation causes no disturbance ofnetwork operation
✗ L ittle or no effect if available spectrum is verylimited (BCCH limitations)
✓No additional sites or frequencies required
✓Available, stable
✓Implementation causes no disturbance ofnetwork operation
✗ L ittle or no effect if available spectrum is verylimited (BCCH limitations)
Interference Reduction Features
Frequency Hopping (FH)
Dynamic Power Control (PC)
Discontinuous Transmission (DTX)➨ allow tighter frequency re-us
(already considered for 40-60 Erl./km2 in macrocell layer with 5 to 10 MHz)
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Default HO boundaries
Changed HO boundaries
Traffic Load Distribution
Traffic in a cell related to cell coverage area
If sufficient overlap between cells:➨ reduce traffic by changing cell boundary
✲ antenna downtilt
✲ reduce power (PWRRED)
✲ alter handover boundaries
➨ Usually a temporary solution only
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Call Setup/handover mechanisms
Relieve macrocells from traffic
➨ Umbrella type handover into microcells
➨ “Directed retry”✲ Allows call setup In second-best server, shares traffic resources between
layers
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O Ls
L
E
C
C
I
P Indoor coverageOutdoor Installatio n
Parking lot
Contiguous Microcellular Coverage
Hotspot
Subway Coverage Extension
Hierarchical Cell Structures
Underlay/Overlay
Umbrella cells: Dominant site with large coverage area➨ low traffic - fast mobiles
Macrocells: Antenna above average rooftop level➨ normal traffic
Microcell: Antenna below average rooftop level➨ cover small high traffic areas
Picocell: Antenna
usually indoors➨ coverage to building
or parts thereof - e.g.
Business users
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© SIEMENS Limited 1999ICN PLM CA NP
f3 f1 f2 f3
Signal level Signal levelC/I = 17 dB C/I = 17 dB
C/I = 0 dB
Concentric cells
“Inner cell” can use 1 x 3 reuse pattern
Special handover mechanisms between layers
Limited gains for uniform traffic distribution
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Macrocells
Microcells
Picocells
Overlaid Micro- and Picocells
The smallest cells should absorb most of the traffic in their coverage area
Larger cells for fast moving mobiles / areas not covered by small cells
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© SIEMENS Limited 1999ICN PLM CA NP
ServingBTS
Micro BTS
Microcell Frequency Planning
Different resolutions required for different layers➨ flexibility of planning tool needed
Dedicated frequency bands for different layers➨ Reduce complexity of frequency optimisation task
➨ Guard band may be needed to avoid adjacent channel interference
Call Setup/handover strategy➨ reduce macrocell traffic
➨ determine mobile speed
➨ Fast handovers✲ Loss around street corner: 20 dB!
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© SIEMENS Limited 1999ICN PLM CA NP
Speed Sensitive Handovers
Mechanisms to separate fast from slow mobiles➨ mobile class
✲ today mostly same class is used (e.g. GSM900 class 4)
➨ measurement of the timing advance delta✲ only works for direction away from site
➨ cell type ✲ try to keep handovers within same layer unless speed change
➨ mean time between handovers
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Half Rate Coding / Dual Rate Operation
Has potential to double network capacity➨ Advantages:
✲ No additional sites / frequencies required
✲ Minimum investment for infrastructure upgrade
➨ Disadvantage:✲ Speech quality degradation (reduction of speech bit rate from 13 kb/s to
6.5 kb/s)– Especially mobile-to-mobile calls
➨ Gain depends on ratio full rate users / half rate users / data traffic
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Cell Parameter Optimisation
Default parameter sets:➨ PS! Standard setting suitable for most cases
➨ Starting point for possible optimisation, however✲ more relevant after other optimisation activities
➨ Different parameter standards may be used for ✲ different area types
✲ BTS types
✲ etc.
Danger➨ many parameters easy to lose overview
✲ inconsistencies
✲ deterioration of quality
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FH
, PC
, DT
X
Eff
ect
Cost, Effort
Und
erla
y/O
verl
ay
Cel
l par
amet
erse
ttin
g
HR
Dual band
AddingTRX
Fine tuning of antennaorientation and tilt
FrequencyChanges
Dual mode
Sect
oris
atio
n
Pre
amps
Repeaters
Overlaidmicrocells
Cel
l spi
ltti
ng
Possible Network Optimisation Measures
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Increasing Network Capacity
The relationship between quality and capacity ➨ In a congested network, quality can deteriorate very quickly:
– Violation of all 4 basic quality criteria
Congestion
Interference/Noise
Poor speech quality
Droppedcall
Extended callsetup times
Unavailabilityof service