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Transcript of Network Optimization
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NETWORK NETWORK OPTIMIZATION OPTIMIZATION
MobiNil, The Egyptian Company for Mobile Services
February 2004
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COURSE OUTLINES
OPTIMIZATION CONCEPTS
OPTIMIZATION ACTIVITIES
PARAMETERS OPTIMIZATION
CAPACITY ENHANCING TECHNIQUES
TYPICAL PROBLEMS & SOLUTIONS
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OPTIMIZATION CONCEPTS
INTRODUCTION
OPTIMIZATION PROCESS
KEY INDICATORS
REPORTS & ACTION PLANS
OPTIMIZATION TOOLS
INPUT DATA
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Subscriber Perception
To setup or receive a call everywhere, with a good voice quality
without interruption + Value added services.
Availability (Access, Capacity)
Audibility (Voice quality)
Mobility (Call Drop)
Roaming (Coverage bars display)
Introduction
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Why Network Optimization?
Changes in subscriber distribution
Changes in subscriber traffic behaviour
Changes in subscriber mobility profiles
Changes in subscriber growth
Uneven network expansion in various regions
Limitations in frequency resources
Introduction
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Objectives of Network Optimization Team
Providing the best Quality of Service and voice quality, the
minimum call drop and blocking rates in the covered area
using the available resources.
Manage and track the process of Radio Optimization
Daily monitoring of network performance
Ensure the targeted Quality of Service
Introduction
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Optimization Engineer Tasks
Minimize dropped calls and handover failures.
Reduce TCH/SDCCH blocking rate and congestion time.
Maximize coverage service area.
Support good audio quality.
Minimize transmission power level to reduce interference
and increase MS battery life.
Introduction
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Note
Quality of radio design is the base of efficient optimization.
The terrain constraints may lead, radio designers, not to
respect the grid giving the optimization engineer the
opportunity to express his optimization skills.
Introduction
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System optimization & performance involves applying a set of
techniques :
Identifying objectives
Isolate system components
Test plan
Taking actions
Conduct post analysis
Optimization Process
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The most familiar key indicators for any operator are:
Drop call rate Call setup success rate Call setup blocking rate TCH/SDCCH access failure HO causes HO failures
When operating with multiple vendor system, it is important to cross map the indicators reported from one vendor and find a corollary to it with the other vendor.
Key Indicators
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Setting Thresholds for Key Indicators
The threshold and the objective of the different key indicators must be set in a realistic way.
The objectives should be driven to improve the overall performance of the network factoring into it :
- The growth rate expected- Budget constraints
It is important to set aggressive goals to work for, but it is equally important to involve members of the staff whose job is to ensure that the mission statement is met.
Key Indicators
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Reports
It is very important to produce regular summary reports for various levels of management so that they know how the system is operating.
When delivering a report, take care to whom it is generated and include only the data needed to be seen.
Reports and Action Plans
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Action Plans
An action plan is the right consequence to the reports.
Establishing a quarterly and monthly action plan for improving the network is essential in ensuring its health.
Each quarter (long term plan), you should identify the worst 10% of your system following the KPIs.
Reports and Action Plans
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The quarterly action plan should be used as the deriving force for establishing the monthly plans.
The short-term action plans coupled with the long term action plans will help derive the success or failure of the overall mission.
Reports and Action Plans
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Radio Planning Tool
Coverage prediction Interference calculation Frequency Planning Traffic analysis Network database management
Optimization Tools
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GIS Tools
MapInfo Used for drive test measurement analysis & presentation.
GIMS
Advanced import and analysis tool built upon MapInfo. Its use is based on the output data from TEMS.
Optimization Tools
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OMC Statistics Monitoring
MARSMotorola Analysis & Reporting System
METRICA OMC statistics and KPI’s for Alcatel Network
RNO Parameters check & modifications, OMC statistics, KPI’s for Alcatel.
Optimization Tools
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Actix Analyzer
Drive test analysis
Q-voice measurements analysis
A & Abis traces analysis
Optimization Tools
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Measurement Tools TEMS
Drive test tools and field problems investigation.
TEMS:- drive test tool, check field problems.
TEMS Investigation:- advanced drive test tool, problem investigation and analysis in
field.
TEMS Light :- indoor measurements.
Optimization Tools
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Q-VoiceDrive test tool used for benchmarking & field detection of the voice quality problems. Also it is used to test new features and releases.
Spectrum Analyzer Measurement for external interference.
Optimization Tools
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Data gathering is an important issue that facilitate the work of the optimizer.
Data could be :- Raw data (Coverage maps, frequency plan, sites database ..etc).- Measurements data (Drive test, A-bis /A
captures, call traces, statistics …etc ).
Handling these data in optimum way will lead to better performance and output.
Input Data
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Plots/Maps Coverage (Global region and specific area) Best server map Frequency planning [Site location (X,Y), BCCH,
channels)]
Sites Database Radio parameters Neighbors list Channel configuration
Input Data
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Statistics and Indicators
Identify occasional faults on a subsystem (BSS, BTS) and establish corrective actions.
Detect and identify radio problem on a cell.
Statistics can be used to trace and verify big changes in the network (FP, parameters changes, implementations of problem solutions).
Predict network behavior according to traffic evolution.
Can’t reveal the cause of a problem, additional analysis via traces and/or drive test should be used.
Input Data
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Drive Tests
Present the real network performance experienced by subscribers.
Provide field information which is often very useful to solve specific problems.
Input Data
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Routes of drive tests must be specified to have valuable outputs:
- All sites and sectors should be tested within the route at least once.
- All major roads & highways should be tested.- All cells should be tested for handout and hand-in
within the routes if possible.- The routes should be approximately 2-3 hours in
duration.
Input Data
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Abis Interface Measurements
Drive tests give a snapshot view of the network.
Drive tests provide detailed information on the downlink only.
Not recommended to adjust cell and HO parameters based on a specific drive test.
Abis is the ideal source for level, quality and interference analysis.
Abis provides synchronized information on uplink and downlink.
Input Data
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A-Interface Measurements
This interface is standardized by ETSI and its implementation is mandatory.
Network optimization based on A-interface analysis makes the process objective and independent of vendor infrastructure.
Collecting data is usually easier (because of the reduced number of link connections) than for Abis or Drive Test data.
Analysis can be run at BSC level, then at cell and even at individual call level, with the same unique dataset.
Input Data
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Rules when solving a problem:
Change one thing at a time and test it.
If it does not work change it back before you do anything else.
Change the minimum number of parameters possible.
Go to the field and test it. Problems occur in the real world not on your PC.
Be as familiar as possible with the radio interface processes.
Keep in Mind!!
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INTRODUCTION
STATISTICS MONITORING
FREQUENCY PLANNING
MEASUREMENTS ANALYSIS
TRAFFIC HANDLING
NEW SITES INTEGRATION
SOLVING COMPLAINTS
SITES REDESIGN
EVOLUTION REPORTS
OPTIMIZATION ACTIVITIES
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The radio optimization is built around three main tasks:
Detection of the problems
Analysis of the problems
Solving the problems
Introduction
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Operation & Maintenance Center (OMC)
OMC reports Network Performance through statistics.
Statistics are pegged based on call states detection by the BTS and BSC.
Some Statistics are also based on Signaling Messages.
OMC Vendors use their own terminology's and calculation methods to generate statistics.
Statistics Monitoring
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In general more or less all statistics indicate the same meaning.
It is essential to understand how statistics are pegged to derive conclusion on network performance.
Statistics should be used as a proactive approach to detect problems in the network.
Statistics Monitoring
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OMC - Report Types
Periodic Reports
Per cell basis every measurement period (30/60 minutes)
Indicate the trend in statistical measurement
Daily Averages
Per cell basis
Snapshot of cells performance and problems
Statistics Monitoring
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SDCCH Performance
SDCCH Congestion
No. of times all SDCCH's found busy, and a Channel Request received.
Statistics Monitoring
Channel Request
Immediate Assign Reject
SDCCH CONGESTION
RACH
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Reserves SDCCH
RACH
T3120
Re-transmission
AGCH
T3101
No Response from MS - T3101 Expires
T3120
Channel Request
Immediate Assignment
SDCCH FAILURE
SDCCH Failure
No. of times MS did not respond to Immediate Assignment within T3101 timer period.
Statistics Monitoring
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TCH Performance
TCH Holding Time
- Time (in secs) spent on TCH.
- Reported as Min, Max and Mean during the measurement period and also as daily average on per cell basis.
TCH Attempts
No of Channel Requests with cause as MOC & MTC
+ Channel Activation Requests for Handover.
Statistics Monitoring
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TCH Congestion
RACHChannel Request
Immediate Assignment
MM/CC Signaling on SDCCH
MSCAssign Request
BSC
No TCHAssign Failure
No of Times TCH not available No of Assignment Requests from MSC + Handover Requests
TCH Congestion =
Statistics Monitoring
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RACHChannel Request
Immediate Assignment
MM/CC Signaling on SDCCH
MSCAssign Request
BSC
Assign Failure
Assignment Command
Assignment Failure
No of Assignment Failures from MS Total No of TCH Assignments
TCH Failure =
TCH Failure
Statistics Monitoring
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TCH Drops
– BTS detects RF fink failure in the Uplink on TCH.
– RF link failure generally based on SACCH reports.
– Also Known as TCH_RF_Loss.
– Reported on periodic and daily average basis for each carrier and timeslot configured for TCH.
Statistics Monitoring
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BSS Counters
Combined into significant formulas: indicators
Used to monitor BSS network quality
Over complete network, with breakdown per cell/BSC
Drawbacks: NSS/PSTN/MS/User problems are not seen
Statistics Monitoring
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Call drop
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500
1000
1500
2000
2500
3000
3500
4000
4500
Aug/ 01/ 2020 Aug/ 02/ 2020 Aug/ 03/ 2020 Aug/ 04/ 2020 Aug/ 05/ 2020 Aug/ 06/ 2020 Aug/ 07/ 2020 Aug/ 08/ 2020 Aug/ 09/ 2020 Aug/ 10/ 2020
0
0.2
0.4
0.6
0.8
1
1.2
1.4
Drop - BSS
Drop - HO
Drop - Radio
% RTCH drop
% Call Drop
Call Drop• Radio• Handovers • BSS
Statistics Monitoring
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Call Setup Success• SDCCH Drop• TCH Assignment Failure
Call success
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4000
6000
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12000
14000
16000
Aug/ 01/ 2020 Aug/ 02/ 2020 Aug/ 03/ 2020 Aug/ 04/ 2020 Aug/ 05/ 2020 Aug/ 06/ 2020 Aug/ 07/ 2020 Aug/ 08/ 2020 Aug/ 09/ 2020 Aug/ 10/ 2020
0
20
40
60
80
100
120
Call drop
Assign f ail
SDCCH drop
% Call success
% Call setup
Statistics Monitoring
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Incoming Handovers• Radio• BSS• Congestion
Intra + inter BSC incoming handovers
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50000
100000
150000
200000
250000
Aug/ 01/ 2020 Aug/ 02/ 2020 Aug/ 03/ 2020 Aug/ 04/ 2020 Aug/ 05/ 2020 Aug/ 06/ 2020 Aug/ 07/ 2020 Aug/ 08/ 2020 Aug/ 09/ 2020 Aug/ 10/ 2020
0
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2
3
4
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Fail - BSS
Fail - Radio
Congestion
Success
% Fail
% Cong
Statistics Monitoring
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Intra + inter BSC outgoing handovers
0
50000
100000
150000
200000
250000
Aug/ 01/ 2020 Aug/ 02/ 2020 Aug/ 03/ 2020 Aug/ 04/ 2020 Aug/ 05/ 2020 Aug/ 06/ 2020 Aug/ 07/ 2020 Aug/ 08/ 2020 Aug/ 09/ 2020 Aug/ 10/ 2020
0
0.5
1
1.5
2
2.5
3
Success
ROC
Drop - Radio
Drop - BSS
% Drop
% ROC
Outgoing Handovers• Failure• Drop• Congestion
Statistics Monitoring
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Objective
Optimum use of resources to flow a target traffic
Reduce Interference to reach the required quality
Frequency Planning
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Frequency Reuse
GSM uses concept of cells
One cell covers small part of the network
Network has many cells
Frequency used in one cell can be used in another cells
This is known as Frequency Reuse
Theoretical Frequency Planning
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F=1
F=2F=3
F=4,8
F=5,9
F=6,10
F=7
F=1
F=2F=3
F=4,8
F=5,9
F=6,10
F=7
F=1
F=2F=3
F=4,8
F=5,9
F=6,10
F=7
F= 1,2,3,4,5,6,7,8,9,10
Clusters
Co-Channel (Reuse) Cells
Theoretical Frequency Planning
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The hexagonal model is used to simplify the planning.
Hypothesis Flat earth (No Relief, no obstacle…..) Omni directional antennas Equal powers Uniform traffic (One group per cell)
Theoretical Frequency Planning
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Pattern Choice Targeted traffic (Number of TRx per cell)
Targeted C/I between reused frequencies (QOS)
Number of available frequencies
Number and density of sites (Radius of cells)
Theoretical Frequency Planning
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Adjacent Channel Reuse
Adjacent ARFCN's should not be used in the same cell.
Adjacent ARFCN's can be used in adjacent cells, but as far as possible this should be avoided.
Taking into consideration the propagation effects, a factor of protection of 600 Khz should be used (Practically not possible in most of the networks due to tight reuse).
In the worst case, adjacent ARFCN's can be used in adjacent cells by setting appropriate handover parameters.
Theoretical Frequency Planning
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BTS
BTS
Omnidirectional Cell Low gain antennas Lesser penetration/directivity Receives interference from all
directions Lower implementation cost
Sectorial Cell High gain antennas Higher penetration/directivity Receives interference from
lesser directions Higher implementation cost
Cell Configuration
Theoretical Frequency Planning
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3,6,9A
A
B
C 3,6,9B
3,6,9C
Receives interference from all directions
Interference in Omni Cells
Theoretical Frequency Planning
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A1
A2
A33
69
B1
B2
B3 3
96
C1
C2
C33
69
Receives interference from lesser directions.
Sectored Cells
Theoretical Frequency Planning
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Reuse Patterns
Reuse Patterns ensures the optimum separation between co-channels.
Reuse pattern is a formation of a cluster with a pattern of frequency distribution in each cell of the cluster.
Same cluster pattern is then reused.
Reuse Patterns examples
Omni - Cells : 3 cell, 7 cell, 12 cell, 14 cell, 19 cells etc..
Sector - Cells : 3/9 , 4/12, 7/21.
Theoretical Frequency Planning
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A1
A2A3 B1
B3C1
C2C3
A1
A2A3 B1
B2B3C1
C2C3
A1
A2A3 B1
B2B3C1
C2C3
A1
A2A3 B1
B2B3C1
C2C3
A1
B1
B2B3
A1
A2A3
B2
C1
C2C3
C2C3 C2C3 C2C3
A1
3/9 Reuse Pattern
Theoretical Frequency Planning
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Adjacent channel interference is very difficult to avoid within the cluster itself.
1
4
3
2
85
7
96
3/9 Reuse Pattern Frequency Allocation
Theoretical Frequency Planning
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D1
D2D3 C1
C3B1
B2B3
C1
C2C3 D1
D2D3A1
A2A3
A1
A2A3 B1
B2B3C1
C2C3
B1
B2B3 A1
A2A3C1
C2C3
C1
D1
D2D3
B1
B2B3
C2
D1
D2D3
D2D3
B2B3
B2B3
A1
4/12 Reuse Patterns
Theoretical Frequency Planning
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1
35
24 6
7
9 1112
10 8
4/12 pattern avoids adjacent channels in adjacent cells
4/12 Reuse Pattern Frequency Allocation
Theoretical Frequency Planning
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Conclusion
Larger reuse patterns give reduction in interference.
Reuse patterns become more effective with sectorial cell configurations.
To implement large patterns (like 4/12, 7/21) , more channels are required.
So with less resources, the best way to plan is :
1. Use optimum no. of channels per cell.2. Thus, increase the pattern size.
Theoretical Frequency Planning
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Keep in Mind!!
Make a better frequency planning for BCCH than for TCH channels.
In the same region, to avoid the mobile to confuse two same BCCH frequencies, use different BSICs.
Keep some joker frequencies when possible.
Theoretical Frequency Planning
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Goal
Build a frequency plan fast with the required quality, and even when the grid is not respected.
Tools
AGORA RECSIM
Automatic Frequency Planning
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Advantages
Can be used with or without frequency groups
Better interference rate than with manual planning
Can include existing frequency planning
Time saving
Easy integration of sites
Automatic Frequency Planning
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Process
Computing the reuse matrixThe reuse matrix computes the minimal inter channel protection between two stations.
Frequency allocationDone from the reuse matrix as to have a minimal global interference.
Computing the interferencesto evaluate the quality of the frequency plan
Automatic Frequency Planning
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Drive tests present the real network performance experienced by subscribers.
Processing of drive tests generates statistical analysis of the reported measurements.
Plot of drive tests presents network real coverage.
Network optimization and redesign is highly dependant on drive tests.
Drive Tests
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TEMS is used for new site integration and live network optimization.
TEMS log files need to be analyzed on a map to filter problems such bad quality, handover failures, call drops, etc…
Post processing is done using MapInfo/GIMS and Actix Analyzer.
Drive Tests
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Quality Analysis
Spot poor quality areas
Check neighbor cells levels
Check neighbor frequencies
Determine the interferer
Drive Tests
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Call Drop
Check Radio condition before call drop.
Check for missing neighbor relations.
HO parameters may need to be re-tuned.
Drive Tests
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Statistics
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10000
15000
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25000
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Coun
t
CDF (percent)dBm
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
Histogram - RxQual (count) Histogram - RxQual (CDF)
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Coun
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CDF (percent)
dBm-107.5 -102.5 -97.5 -92.5 -87.5 -82.5 -77.5 -72.5 -67.5 -62.5 -57.5 -52.5 -47.5 -42.5
Histogram - RxLev (count) Histogram - RxLev (CDF)
Rx-Qual Distribution Rx-Lev Distribution
Drive Tests
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Q-Voice
Q-Voice is one of the most advanced measurement tools in evaluating the voice quality in a cellular network as seen by network subscribers.
Data Collection Part:- QVM( Mobile part fixed in the measurement car).- QVS (Stationary part located at office).
Speech Quality
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Operation
Communication is setup between two parties; QVM and QVS, through a play button on the QVM.
A prerecorded speech sample (5 sec duration) is transmitted through the communication between previously mentioned parties .
The speech sample is evaluated in both direction; UL (from the QVM to the QVS) and DL (from the QVS to the QVM) and each sample is given a score called PACE (The speech Quality indicator).
Measurement data are saved on both the QVM and the QVS.
Speech Quality
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Post Processing
Represented in the QVP with access to the measurement data imported on a database server.
Graphical tools are available for analysis and reporting.
Speech Quality
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Speech Quality
Output Report
P2
16 Nov 2003
excellent good fair poor bad total2022 94 67 31 7 22212038 93 71 13 9 22241493 64 63 17 6 16431973 116 112 18 4 2223
UPLINK DOWNLINK GLOBAL TVOC 1 Jun 2003 14 Sep 2003 16 Nov 200395.3% 95.8% 93.2% MOBINIL 93.3% 93.5% 93.2%94.8% 94.0% 91.4% Vodafone 89.1% 91.9% 91.4%
MOBINIL UPLINK
MOBINIL DOWNLINK
Vodafone UPLINK
Voice quality of last campaign
Vodafone
Analysis and results of Measurements
PACE1.1Voice Quality (Mobiles1+2&3+4):
Measured Zone / ObjectiveDate of mesurement / hour
Vodafone DOWNLINK
Voice quality of the last three campaigns
TVOCMOBINIL
TVOC (Voice Quality indicator)
65.0%
70.0%
75.0%
80.0%
85.0%
90.0%
95.0%
100.0%
UPLINK DOWNLINK GLOBAL
MOBINIL
Vodafone
TVOC (Voice Quality indicator)
65.0%
70.0%
75.0%
80.0%
85.0%
90.0%
95.0%
100.0%
1 Jun 2003 14 Sep 2003 16 Nov 2003
MOBINIL
Vodafone
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Abis is the ideal source for level, quality and interference analysis.
Abis provides synchronized information on uplink and downlink.
Measurements must be carried around the network traffic busy hour.
K1205 protocol analyzer is used to record Abis data.
Abis data are carried on the RSL timeslots on the Abis PCM.
Recorded Abis data are further processed using Actix Analyzer.
Abis Interface
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Analysis of Level Distribution Shows the amount of traffic at particular RxLev values Validates proper neighbor declaration and HO settings Validates power control settings
Abis Interface
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Level versus TALevel plotted against TA can help identifying areas with high indoor traffic served by an outdoor cell.
Abis Interface
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92%
2% 2% 2% 1% 1% 1% 0%
88.4%
2.6% 1.9% 2.0% 1.4% 1.2% 1.9%0.5%
0%
5%
10%
15%
20%
25%
0 1 2 3 4 5 6 7
Quality
Co
un
t
Dow nLink Quality Uplink Quality
Quality Analysis Quality distribution can validate frequency planning. Filtering poor quality samples and plotting against Level and
TA identifies whether interference or coverage problems.
Abis Interface
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Quality Analysis
Plotting quality against Rx-Lev identifies interference problems.
Abis Interface
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Space Distribution Provides an indication of geographical location of traffic. Space distribution of Rx-Lev samples is valuable when
adjusting antenna tilts.
Abis Interface
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Handover Analysis More powerful compared to BSS statistics and A-Interface
measurements. Provides details about incoming and outgoing HO attempts
on a TRX level. Incoming HO failures due to TRX problems can be spotted
directly.
Attempt Attempt163 151 92.6% 0 0 0.0%191 163 85.3% 0 0 0.0%354 314 88.7% 0 0 0.0%
SDCCHSuccess Success
TCHTRX
11000031110004
Grand Total
Attempt Attempt138 138 100.0% 0 0 0.0%142 139 97.9% 0 0 0.0%280 277 98.9% 0 0 0.0%
1110004Grand Total
TCH
1100003
SDCCHTRX Success Success
INCOMING HO
OUTGOING HO
Abis Interface
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Handover Analysis HO attempts and success towards neighbor cells are
processed. HO causes per target cell cannot be analyzed. HO failures are further analyzed to identify cause and radio
conditions prior to handover.Cell Summary Stats (HO Matrix - Abis Analysis of Outgoing Handovers)
Target BCCH
Target BSIC #HO %HO
#HO tch-tch
#HO sdcch-sdcch
#HO sdcch-tch
4 11 2 5% 2 0 011 4 2 5% 2 0 014 2 2 5% 2 0 019 17 9 20% 9 0 021 16 3 7% 3 0 022 30 4 9% 4 0 0
Abis Interface
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Collecting data is usually easier (because of the reduced number of link connections) than for Abis or Drive Test data.
Analysis can be run at BSC level, then at cell and even at individual call level, with the same unique dataset.
Measurements must be carried around the network traffic busy hour.
K1205 protocol analyzer is used to record A data.
Recorded A-interface data are further processed using Cigale or Actix Analyzer.
A-Interface
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Busy Hour
1 Hour of the day in which Traffic is maximum. Also referred to as Peak Hour. Busy Hour is not a fixed hour, its timing will vary in different
locations.
Busy Hour may also be different for different resources
SDCCH busy hour: typically morning hours (frequent on/offs and updates)
TCH busy hour:heavy call traffic hour (could be back home hours)
Traffic Handling
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Set Up TimeAverage time spent on a resource before getting response from the called end.
Holding TimeAverage time spent on any dedicated resource.
Blocked CallA call request rejected due to unavailability of resource.
Traffic Handling
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Sites should be designed to support busy hour traffic.
Call Setup Blocking & SDCCH Setup Blocking should satisfy the required Grade of Service.
Special events should have special treatment to handle expected traffic (Mobile Shelters).
Traffic Handling
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Delivering the frequency plan and the neighbor files of the new site.
Site should be integrated before putting it on air.
During integration, each sector must be checked for call setup and handover.
Each TRx must be checked to detect any faulty hardware.
The counters should be closely checked the first few days after the site is on air to detect any problem.
New Sites Integration
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Quality of Service is a measure of Network Quality.
Quality of Service is judged by the customer.
Customer expects same quality as PSTN.
Increase in mobile penetration led to increase the demand for excellent quality.
Solving Complaints
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Customer Complaints
I am getting "No Service“. My handset regularly displays Network Search. I get a 3 beep tone, when I dial a number. My friends call me, but I keep on missing calls. Speech quality is bad. I can never keep up with my call on this street, it DROPS ! My friend has competitor's phone, that works well .
Can you get something out of this ?Can you figure out the technical problems ?
Solving Complaints
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Access Quality
Speech Quality
Retaining Quality
Solving Complaints
Categories of user quality
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Minimizing the bad effect of overlapping and overshooting which have very bad influence on the performance of the network.
Enhancing the coverage of poor covered areas.
Solving customers complaints.
Sites Redesign
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Each optimizer has to deliver a weekly/monthly evolution report showing the evolution of his zone according to the following indicators:
Call drop rate BH call setup TCH blocking rate BH call setup success rate BH TCH traffic carried Uplink quality HO rate Downlink quality HO rate
Evolution Reports
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Regular Consistency Checks
Defined template for BSS parameters.
Inconsistency checks.
One of the most common problems with networks is that database is incorrectly specified on the OMC-R or/and the BSCs.
It is essential to verify that database is correctly specified. It only needs a small error to cause many problems.
Other Activities
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Alarms Monitoring
Failures and faults can not be considered as optimization operations.
However, we can not make any optimization without solving network faults.
Other Activities
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POWER CONTROL OPTIMIZATION HANDOVER OPTIMIZATION CALL DROP OPTIMIZATION TRAFFIC OPTIMIZATION
PARAMETERS OPTIMIZATION
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Power Control Thresholds
Upper and lower limits Power increase step size Power decrease step size
av_rxlev_ul
l_rxlev_ul_p
u_rxlev_ul_p
-110 dBm
-47 dBm
Normal step Size
Normal Power Control
Power Control Optimization
110
110
Power Control Window
Analysis done on the Uplink power control window.
Use Abis measurements to plot quality vs level.
Determine the optimum power control window.
The optimum window will depend on the frequency reuse pattern and noise floor.
Power Control Optimization
111
111
-110
-105
-100
-95
-90
-85
-80
-75
-70
-65
-60
-55
-50
-45
0
1
2
3
4
5
6
70
2000
4000
6000
8000
Nb
of S
ampl
es
UL Level
UL RxQual
UL PC Window [-90,-80] [0,2+1]
Power Control Optimization
-110
-105
-100
-95
-90
-85
-80
-75
-70
-65
-60
-55
-50
-45
0
1
2
3
4
5
6
70
1000
2000
3000
4000
5000
UL Level
UL RxQual
UL PC Window [-96,-86] [0,2+1]
112
112
This feature causes the mobile and BSS to respond more effectively to changing power level and quality conditions.
The range of power steps is modified so that the step size will be changed dynamically based on the average received level.
The target received level is the middle between U_RXLEV_UL_P and L_RXLEV_UL_P.
Fast Power Control
113
113
Adaptivestep size
av_rxlev_ul
-110dBm
-47dBm
l_rxlev_ul_p
u_rxlev_ul_p
Target Received Level
av_rxlev_ul
l_rxlev_ul_p
u_rxlev_ul_p
-110dBm
-47dBm
Normal step Size
Fast Power Control Normal Power Control
Fast Power Control versus Normal Power Control
Fast Power Control
114
114
Adaptive Power Increase
Adaptive Power Inc_Step_Size = min [MS_P_INC, Max_POW_INC, (power max- MS_TXPWR)]
Where:Max_POW_INC : max power increasepower max : max power of the MSMS_TXPWR : actual power of the MSMS_P_INC is evaluated by the following algorithm
Fast Power Control
115
115
Av_RXLEV_UL <L_RXLEV_UL_P
Yes
Av_RXQUAL_UL =<L_RXQUAL_UL_P
+OFFSET_RXQUAL_FH
Yes
NO
NO
Bad level onlyMS_P_INC = roundup [ POW_INC_FACTOR*
( TARGET_RXLEV_UL - AV_RXLEV_UL])
Bad level and qualityMS_P_INC = roundup { MAX [POW_INC_FACTOR*(TARGET_RXLEV_UL - AV_RXLEV_UL), POW_INC_STEP_SIZE]}
Bad Quality onlyMS_P_INC = POW_INC_STEP_SIZE
MS_P_INC
Fast Power Control
116
116
Adaptive Power Reduction
Adaptive Power Red_Step_Size = MIN [MS_P_RED, Max_POW_RED, (MS_TXPWR - power min)]
Where;Max_POW_RED : max power reductionpower min : min power of the MSMS_TXPWR : actual power of the MSMS_P_RED is evaluated by the following algorithm
Fast Power Control
117
117
Av_RXLEV_UL >U_RXLEV_UL_P
Yes
Av_RXQUAL_UL =>U_RXQUAL_UL_P
Yes
NO
NO
Good level onlyMS_P_RED = roundup{MAX
[ POW_RED_FACTOR* (AV_RXLEV_UL -TARGET_RXLEV_UL ), ]2 dB}
Good level and qualityMS_P_RED = roundup { MAX [POW_RED_FACTOR*(AV_RXLEV_UL - TARGET_RXLEV_UL), POW_RED_STEP_SIZE]}
Good Quality onlyMS_P_RED =
POW_RED_STEP_SIZE
MS_P_RED
Fast Power Control
119
119
The average level and quality used are averaged with window size A_QUAL_PC and A_LEV_PC.
To disable fast power control and use the fixed power control step size, set the parameters
max_pow_inc = inc_step_size max_pow_red = red_step_size pow_inc_factor =1 pow_red_factor =1
Fast Power Control
120
120
Parameter Per Definition Stage 1 Stage 2POW_INC_FACTOR Cell Weighting factor for power increase 0.8 0.8POW_RED_FACTOR Cell Weighting factor for power reduction 0.5 0.5MAX_POW_INC Cell Maximum Power increase in one power command 8 16MAX_POW_RED Cell Maximum Power reduction in one power command 6 6POW_RED_STEP_SIZE Cell Power reduction step size in case of power command
triggered on quality criterion2 2
POW_INC_STEP_SIZE Cell Power increase step size in case of power command triggered on quality criterion
4 4
U_RXLEV_UL_P Cell Upper uplink level threshold for power control -86 -86L_RXLEV_UL_P Cell Lower uplink level threshold for power control -96 -96U_RXQUAL_UL_P Cell Upper uplink quality threshold for power control 0 0L_RXQUAL_UL_P Cell Lower uplink quality threshold for power control 2 2
Field TrialThe following parameters were set
Fast Power Control
121
121
El_Khatib_MSTXPWR
0%
10%
20%
30%
40%
50%
60%
70%
High(33dBm-29dBm) Medium(27dBm-21dBm) Low(19dBm-13dBm)
Before
After1
After2
Fast Power Control
To highlight the change in the MS power distribution, the MS_TX_PWR was classified into 3 categories: high, medium, low.
122
122
El_Mounira_MSTXPWR
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
High(33dBm-29dBm) Medium(27dBm-21dBm) Low(19dBm-13dBm)
Before
After1
After2
Fast Power Control
123
123
Conclusion
The MS_TXPWR was decreased obviously, this was noticed from Abis traces and drive tests.
This saves the battery of the mobiles and can decrease the uplink interference in the area.
The effect of dynamic power increase was not noticed in the Abis traces.
No obvious change in the counters or the QVoice.
Fast Power Control
124
124
Quality Handover Average Window Optimization
HO Margin Optimization
Power Budget Limitation
Handover Optimization
125
125
Bad Pace Analysis Factors affecting speech quality Handovers are the major cause for bad pace
Bad PACE Repartition
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
Bad Level(Coverage)
Poor Quality Poor Leveland Quality
HO event HO w ith Level HO w ithquality
HO w ithquality and
Level
DL UL
Handover Optimization
126
126
Quality Handover Average Window Optimization
Determine optimum length for quality HO window
Determine value based on speech quality analysis
Measure HO/Call
Handover Optimization
127
127
Abis measurements show a degradation of average DL quality after changing the window from 4 to 6 SACCHs
Speech quality also degraded in DL
Avg DL Qual before HO (4SACCHs)
0
5
10
15
20
25
30
35
0 1 2 3 4 5 6 7
RxQual DL
Nb
of H
Os
0%
20%
40%
60%
80%
100%
120%
Avg DL Qual before HO (6SACCHs)
0
2
4
6
8
10
12
14
16
18
0 1 2 3 4 5 6 7
Rx Qual DL
Nb o
f HO
s
0%
20%
40%
60%
80%
100%
120%
Handover Optimization
128
128
UL Quality has been slightly impacted .
Avg UL Qual before HO (4SACCHs)
0
5
10
15
20
25
30
0 1 2 3 4 5 6 (blank)
Rx Qual UL
Nb
of H
Os
0%
20%
40%
60%
80%
100%
120%
Avg UL Qual before HO (6SACCHs)
0
5
10
15
20
25
0 1 2 3 4 5 6 (blank)
Rx Qual ULN
b of
HO
s
0%
20%
40%
60%
80%
100%
120%
Handover Optimization
129
129
Measure the qualtiy Handovers decrease on the tested cell(s). Determine the optimum “quality HO decrease” versus “speech
quality”.
Quality handovers
0
1000
2000
3000
4000
5000
6000
0
10
20
30
40
50
60
UL
DL
% Quality
Handover Optimization
130
130
Suez HO Performance
0
20000
40000
60000
80000
100000
120000
20/08/01 27/08/01 03/09/01 10/09/01 17/09/01
UL Level UL Quality DL Level DL Quality
Suez City
0
0.2
0.4
0.6
0.8
1
1.2
1.4
20/08/01 27/08/01 03/09/01 10/09/01 17/09/01
Cal Drop % HO Per Call
Handover Optimization
Results on Suez City
131
131
HO Margin Optimization
HO_margin increase from 5 to 6.
0
2000
4000
6000
8000
10000
12000
14000
16000
8/25/01 9/1/01 9/8/01 9/15/01
DL_LEV
DL_QUAL
UL_LEV
UL_QUAL
PBGT Volume
20000
25000
30000
35000
40000
8/24/01 8/31/01 9/7/01 9/14/01
Handover Optimization
132
132
HO/Call decreased Speech quality improved
Handovers Per Call
0.350.370.390.410.430.450.470.49
TVOC Jul 11 2001 Aug 23 2001 Sep 22 2001
MOBINIL 93.4% 93.4% 95.9%
CLICK 95.0% 95.6% 95.8%
85.0%
90.0%
95.0%
100.0%
Jul 112001
Aug 232001
Sep 222001
TVOC (Voice Quality indicator)
MOBINIL
CLICK
Handover Optimization
133
133
Cause = 12 (Power Budget HO)EN_PBGT_HO = ENABLE
PBGT(n) > HO_MARGIN(0,n)
And AV_RXLEV_PBGT_HO <= RXLEV_LIMIT_PBGT_HO
Power Budget Limitation
The parameter RXLEV_LIMIT_PBGT_HO is a threshold on the downlink received level, above which it is not necessary to trigger a handover on power budget.
This adds limitation to the PBGT HO, which can be used in dense areas to decrease the number of Handovers.
Handover Optimization
134
134
Cell Type Parameter ValueMicro cells -55Macro cells -65
Field Trial
The parameter RXLEV_LIMIT_PBGT_HO was generalized on a dense area.
Handover Optimization
135
135
Handover_Per_Call_on_Area
0.540.560.580.6
0.620.640.660.680.7
TOT_TMHOCO
Ho per Call Decreased
Handover Optimization
136
136
Better_cell_HO_Area
200000250000
300000350000
400000450000
500000
Better cell
Imperative_HO_Area
050000
100000150000200000250000300000350000400000
Level
Quality
Interf
Handover Optimization
137
137
Call drop
02000400060008000
100001200014000160001800020000
0
0.2
0.4
0.6
0.8
1
1.2
1.4
Dr op - BSS
Dr op - HO
Dr op - Radio
% RT CH dr op
% Cal l Dr op
Total RTCH traffic
0
5000
10000
15000
20000
25000
30000
0
5
10
15
20
25
30
35
Erlang total
Duration avg
Handover Optimization
138
138
Oum_Kalthoum_S3
0.40.450.5
0.550.6
0.650.7
0.750.8
0.850.9
TOT_TMHOCO
Detailed RTCH traff ic
0
10
20
30
40
50
60
70
80
90
100
0
1
2
3
4
5
6
7
8
9
Erlang total
Erlang BH
Cell Analysis HO/Call decreased Traffic Increased TCH congestion may result
Handover Optimization
139
139
The parameter RXLEV_LIMIT_PBGT_HO can be used on cell basis for the following objectives:
Decreasing number of unneeded handovers.
Increasing coverage area of serving cell thus keeping the traffic inside for longer time.
Tuning the parameter is based on the required cell radius.
Great care must be taken to avoid any impact.
Handover Optimization
141
141
RxLev_Access_Min Optimization
Measure call drop versus gain in coverage
Determine optimum value for RxLev_Access_Min
Identify poor coverage spots where traffic can be generated
Call Drop Optimization
142
142
RxLevAccessMin - MNasr1 BSC
0
50
100
150
200
250
300
350
20-Aug-01 27-Aug-01 03-Sep-01
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
TCH Traffic Carried (Erlangs) Drop Call Rate (%)
Changing RxLev_Access_Min from -102dBm to -108dBm
Call Drop Optimization
143
143
Radio Link Timeout Optimization
Radio Link Failure is based on SACCH messages
It is controlled by the Radio Link Counter ( S )
The max value of ' S ' is broadcasted on BCCH
If MS is not able to decode SACCH message, ' S ' decreases by 1
If MS is able to decode SACCH message, ' S ' increases by 2
If ' S ' reaches 0, Radio Link failure is declared
Call Drop Optimization
144
144
Radio Link Timeout Optimization
Test different radio link timeout values
Measure Call Drop and Call Duration
Determine optimum value
High values of radio link timeout may result in TCH congestion
Call Drop Optimization
145
145
RLT - Higaz2 BSC
41.5
42
42.5
43
43.5
44
44.5
45
45.5
46
46.5
01/08/01 08/08/01 15/08/01 22/08/01 29/08/01
0
0.2
0.4
0.6
0.8
1
1.2
1.4
TCH Mean Holding Time (s) Drop Call Rate (%)
Changing RLT from 10 to 14 seconds
Call Drop Optimization
146
146
Traffic Handover
This feature provides smooth traffic distribution among the cells according to the traffic situation of each cell.
The parameter EN_TRAFFIC_HO(0,n) when enabled has two effects:
• It adds modifications to the standard PBGT handovers.• It enables a new kind of handovers which is Traffic
Handover (cause 23).
Traffic Optimization
147
147
If EN_TRAFFIC_HO(0,n) = Enable, then
Cause 12: Power Budget HOPBGT(n) > HO_MARGIN(0,N) + max(0,
DELTA_HO_MARGIN(0,n))
Cause 23: Traffic HOIf DELTA_HO_MARGIN(0,n) < 0dBPBGT(n) > HO MARGIN(N)+ DELTA_HO_MARGIN(0,n)
Traffic Optimization
148
148
DELTA_HO_MARGIN(0,n) Evaluation
If Traffic_load(0)= High and Traffic_load(n)=low DELTA_HO_MARGIN(0,n) = - DELTA_DEC_HO_MARGIN
If Traffic_load(0)=Low and Traffic_load(n)=high DELTA_HO_MARGIN(0,n) = DELTA_INC_HO_MARGIN
If Traffic_load(0)= Traffic_load(n)DELTA_HO_MARGIN(0,n) = 0
Where:DELTA_DEC_HO_MARGIN, DELTA_INC_HO_MARGIN are two cell parameters.
Traffic Optimization
149
149
Averaging A_Traffic_Load
Thresholds Comparison with N_Traffic_Load averages
Load Samples
Av_Traffic_Load
Traffic_Load
A_Traffic_Load:Cell parameter that defines the averaging window of load samples.
N_Traffic_Load: Cell parameter that defines the number of averages to be compared with the thresholds.
Thresholds are: High_Traffic_Load, Low_Traffic_Load,
Ind_traffic_Load.
Traffic Load Evaluation Process
Traffic Optimization
151
151
Field Trial
The trial was on Hares_S1 which suffers from congestion 28%.
The best neighbors are chosen from A traces. Their traffic conditions were checked to ensure there will be enough resources to handle incoming traffic.
Traffic Optimization
152
152
Name Per Definition Proposed
Value
A_Traffic_Load Cell Averaging window size for traffic load. 8
N_Traffic_Load Cell Number of consecutive load averages used in traffic load evaluation process.
3
High_Traffic_Load Cell Load threshold used to determine when traffic load is high. 70%
IND_Traffic_Load Cell Load threshold used to determine when traffic load is indefinite. 65%
LOW_Traffic_Load Cell Load threshold used to determine when traffic load is low. 60%
En_Traffic_HO Per neighbour This flag enables/disables the detection of traffic handover cause. Enable
Delta_INC_HO_Margin Cell Correction factor penalizing handover cause “Power Budget” when traffic is low in the serving cell and high in the neighbour cells
5
Delta_DEC_HO_Margin Cell Correction factor favouring handover cause “Traffic HO” when traffic is high in the serving cell and low in the neighbor cells
5
Parameter Settings for Hares_S1
Traffic Optimization
153
153
Name Per Definition Proposed
Value
A_Traffic_Load Cell Averaging window size for traffic load. 8
N_Traffic_Load Cell Number of consecutive load averages used in traffic load evaluation process.
3
High_Traffic_Load Cell Load threshold used to determine when traffic load is high. 90%
IND_Traffic_Load Cell Load threshold used to determine when traffic load is indefinite. 85%
LOW_Traffic_Load Cell Load threshold used to determine when traffic load is low. 80%
En_Traffic_HO Per neighbour This flag enables/disables the detection of traffic handover cause. Enable
Delta_INC_HO_Margin Cell Correction factor favouring handover cause “Power Budget” when traffic is high in the serving cell and low in the neighbour cells
5
Delta_DEC_HO_Margin Cell Correction factor penalizing handover cause “Power Budget” when traffic is high in the serving cell and low in the neighbor cells
5
Parameters Settings for Neighbor Cells
Traffic Optimization
154
154
RTCH congestion
0
5000
10000
15000
20000
25000
30000
35000
40000
0
10
20
30
40
50
60
70
Congestion
Request
% Cong
% Cong max
% Call setup
60.00%65.00%70.00%75.00%80.00%85.00%90.00%95.00%
100.00%
% Call setup
Hares_S1
Traffic Optimization
155
155
Intra + inter BSC incoming handovers
0
10000
20000
30000
40000
50000
60000
70000
0
10
20
30
40
50
60
70
80
90
Fail - BSS
Fail - Radio
Congestion
Success
% Fail
% Cong
Intra + inter BSC outgoing handovers
0
5000
10000
15000
20000
25000
0
5
10
15
20
25
30
Success
ROC
Drop - Radio
Drop - BSS
% Drop
% ROC
Traffic Optimization
156
156
Handover Causes
0100020003000400050006000700080009000
10000Better Cell
Level
Quality
Interf
Traff ic
Traffic Optimization
157
157
Handover Causes
05000
1000015000200002500030000350004000045000
Better Cell
Level
Quality
Interf
Distance
Gen Capt
Traffic
Neighbor Cells
Call drop
0
200
400
600
8001000
1200
1400
1600
1800
2000
0
0.2
0.4
0.6
0.81
1.2
1.4
1.6
1.8
2
Drop - BSS
Drop - HO
Drop - Radio
% RTCH drop
% Call Drop
Traffic Optimization
158
158
Forced Directed Retry Traffic Handover1 FDR is triggered when the cell
resources are unavailableTraffic HO is triggered after High_traffic_load is fulfilled which can be adjusted.
2 FDR is dependent on the target cell DL_RXLEV
Taffic HO depends on difference between serving and neighbors DL_LEV
3 No limitation on incoming PBGT_HO Incoming PBGT_ HO is penalized if the cell load is high
4 FDR is triggered only on call setup Traffic HO is triggered on both call setup & HO
5 FDR can be triggered to external neighbor ( no restrictions on available resources)
Traffic Ho can not be triggered to external neighbor
Difference Between FDR & Traffic HO
Traffic Optimization
160
160
CAPACITY ENHANCING TECHNIQUES
INTRODUCTION FREQUENCY HOPPING CONCENTRIC CELLS MICRO CELLULAR TECHNOLOGY HALF RATE
161
161
Capacity enhancing solutions include:
Macro cellular technology Frequency hopping Micro cellular technology In-building solutions Dual band technology Directed retry Concentric cells Half Rate
Introduction
162
162
Basic considerations in choosing the best solution:
Available frequency spectrum
Capacity requirements
Mobile handset availability
Network environment
Ease of future expansion
Introduction
163
163
A technique adopted in GSM specifications as it is able to overcome two specific problems:
- Multipath Fading
- Interference
This allows a tighter frequency reuse thus carrier upgrading can be performed, resulting in an increased capacity while maintaining network quality.
If no carrier upgrading is performed, frequency hopping allows quality to be improved while maintaining capacity.
Frequency Hopping
164
164
Frequency Hopping
Multipath Fading
Considering urban environments, radio signals reach the receiver due to reflections and diffraction on different paths resulting in fading effects.
The received signal levels are varying dependent on the applied frequency and on the receiver location.
Slow MS may stay in a fading notch for a long period of time and suffer from a severe loss of information.
165
165
Frequency Hopping
Frequency hopping introduces frequency diversity and combats multipath fading.
Fast moving mobiles do not stay in long and deep fading holes, so they do not suffer severely from this type of fading.
The improvement results in an increased receiver sensitivity under fading conditions and therefore in improved quality in uplink and downlink directions compared to a non-hopping configuration.
166
166
Frequency Hopping
Interference
Without hopping, some receivers (MS or BTS) are not interfered, while others, receiving on another frequency, will experience strong interference.
This interference can be permanent such as BCCH frequencies in downlink direction or some fixed interferers incorrectly radiating in the GSM band.
167
167
Frequency Hopping
With frequency hopping, the interfering scenario will change from TS to TS, due to hopping. Thus all receivers (MS and BTS) experience an averaged level of interference.
This will lead to calls having an average quality rather than extreme situations of either good or bad quality (all the calls will suffer from a controlled interference but only for short and distant periods of time, not for all the duration of the call).
168
168
From the BTS point of view one distinguishes: Baseband Hopping (BBH) Synthesizer frequency hopping(SFH)
Baseband Hopping (BBH)
Each transceiver (TRx) is transmitting on one fixed frequency. Hopping is performed by switching the mobiles from burst to burst to different TRXs.
The amount of hopping frequencies N(hop) is determined by the number of TRXs N(TRx): N(hop) <= N(TRx).
Frequency Hopping
169
169
Baseband Hopping
Frequency Hopping
Frame 0 Frame 1 Frame 2
Carrier A
Carrier B
Carrier C
Carrier D
8 TS / 8x577µs
Frame ….
170
170
Synthesizer Frequency Hopping (SFH)
the TRXs do not get fixed frequency assignments, they may change their frequency from TS to TS according to a predefined hopping sequence.
The number of applicable hopping frequencies may be larger than the number of equipped TRxs:
N(hop) >= N(TRx).
Since no hopping on the BCCH frequency is allowed, synthesizer frequency hopping must not be performed on the BCCH TRx.
Frequency Hopping
171
171
Synthesizer Frequency Hopping
Frequency Hopping
Frame 0 Frame 1 Frame 2
Frequency A
Frequency B
Frequency C
Frequency D
8 TS / 8x577µs
Frame ….
Frequency E
Frequency F
Frequency G
Frequency I
TRX 1TRX 2
TRX 3TRX 4
TRX 5
172
172
Hopping Modes
Frequency hopping can be performed in two modes:
Cyclic hopping mode Random hopping mode
While in cyclic hopping mode the same hopping sequence will be used periodically, in random hopping mode a pseudo random sequence will be used in order to achieve uncorrelated hopping sequences.
Frequency Hopping
173
173
Hopping Parameters
Mobile Allocation List (MA List)
List of frequencies to be used in a hopping sequence. MA List is limited by GSM recommendations to 64.
Hopping Sequence Number (HSN)
Parameter determining how the frequencies within the MA List are arranged.
Range: 0...63Cyclic: HSN = 0Random: HSN = 1...63
Frequency Hopping
174
174
Mobile Allocation Index Offset (MAIO)
Hopping sequence starting point in the MA List. If there are N frequencies in the MA List:
then MAIO = {0,1,…,N-1}.
Frequency Hopping
175
175
A concentric cell is made of two concentrically arranged zones within the same cell:
The inner zone and the outer zone.
Concentric Cells
F1
F2
MS1
BS1
MS2
176
176
Concentric Cells
Two ways of using concentric cells :Capacity Oriented By using it on an interfered cell and guaranteeing a high received level in the inner zone. This allows an additional TRX in the inner zone with a reduced reuse cluster size.
F1
F1F2
MS1
BS1MS2
C1
I1
C2
F2
I2
177
177
Concentric Cells
QoS Oriented By using it on an interfering cell to bring down the level of
interference by powering down the inner zone carriers. If a frequency is interfered, it is possible to convert it to an
inner zone frequency.
F1
MS1
BS1 BS2MS2
F1InterferenceF1
178
178
Mounted below roof top level. Radius of 300m or smaller. Propagation is primarily line of sight. Improved propagation properties, experience less severe
fading and require lower transmitter powers than conventional macrocells.
Frequency planning management. Bandwidth division. Handover and access management. New HO power budget types.
Micro Cellular Technology
179
179
Twice the TCH capacity with the same number of TRXs (using 2 TCH/HR on one timeslot).
Equal voice quality in good radio conditions.
Less resistant to errors.
HR impossible for data.
The MS as well as the MSC must support half rate coding.
Half Rate
181
181
COVERAGE INTERFERENCE UNBALANCED POWER BUDGET CONGESTION (TCH & SDCCH) CALL DROP QUALITY CALL SETUP SUCCESS
TYPICAL PROBLEMS & SOLUTIONS
182
182
DefinitionA network facing coverage problems presents bad Rx-Lev and Rx-Qual at the same time in some areas.
Symptoms - High drop call rate - High rate of DL quality and level handovers - Low proportion of better cell handover
Coverage
183
183
1. If actual coverage is not the one predicted by radio network planning tools then:
- Check antenna system.- Check the parameter bs_txpwr_max (max_tx_bts)to be increased if value is different from planned power budget.
2. If actual coverage is the one predicted then:- Indoor traffic.- If black spot close to cell border, ease outgoing HO.
Coverage
184
184
DefinitionInterference is the presence of good RxLev and bad RxQual at the same time in the same area.
Symptoms - SDCCH/TCH Drop - Low proportion of better cell HO - High rate of DL/UL quality HO and interference HO
Interference
185
185
Typical Causes
1. GSM interference - Co-channel - Adjacent
Channel
2. External interference - Other mobile
network - Other RF sources
Interference
186
186
FrequencyF(BTS1)=F(BTS2)
-9dB
Level
serving
neighbor
GSM Interferences
1. Co-channel interference
Interference occurs if the neighbor level is lower than the serving by <= 9dB(C/I<9dB)
Interference
187
187
Level
FrequencyF(BTS1)=F(BTS2)+1
9dBneighbor
serving
2. Adjacent channel interferenceInterference occurs if the neighbor level is higher than the serving by >= 9dB ( C/I <-9dB)
Interference
188
188
Symptoms of GSM Interference– High rate of quality HO (specially downlink quality)– High rate of call drop– High rate of call failure
Solution– Change of frequency– Down-tilt of interferer, or even change of antenna
orientation– Reduction of BS power– Concentric cell implementation
Interference
189
189
Non GSM InterferenceOther RF interferer : Radar, medical device, army communication devices ...
Symptoms of External Interference– High rate of quality HO (specially uplink quality)– High rate of call drop– High rate of call failure– High rate of interference on idle
Solution– Change of interfered frequency
Interference
190
190
DefinitionA cell facing unbalanced power budget problems presents a too high path loss difference between UL and DL. Always try to have delta as small as possible.
Symptoms– High ratio of uplink quality HO– Low incoming HO success rate – High ratio of call drop rate
Typical CausesMainly hardware problems
Unbalanced Power Budget
191
191
DefinitionTCH congestion rate is too high
Symptoms– High TCH congestion rate– High directed retry rate if activated– Low incoming intra/inter BSC HO success rate
Typical Causes– Special events (football match, car crash…..).– Cell not correctly dimensioned to support daily peak hour
traffic.
TCH Congestion
192
192
Solution– Hardware solution: add new TRxs – Software solution : half rate/ forced directed retry/
concentric cells
TCH Congestion
195
195
Is there any site out of service near by?
Is it a border cell?
TCH_RF_LOSS> threshold
Yes
Yes
No
Yes
Contact BSS
Check if thereis a need for a
new site
Handover_Failures> threshold
Yes
Yes
No
No
Go to TCH_RF_LOSS problem
Go to Ho_Failure problem
Drop_Call_Rate>Threshold
High Drop Call Rate
196
196
T C H _assignm ent_fa ilure> threshold
YesC heck R T F sta tus to
know if D R I is notfunction ing
D L_quality>threshold
Proceed w ith C T Pto determ ine thein terfered carrier
( D isable baseband hopping)
C heck frequencyplan and try to
determ ine poss ib lein terferers
U L_quality>threshold
In terference
U se C T P to check ifthere is path-loss in
downlink>uplink
C ontact w ithBSS
N o
PathBalance
U se C T P tocheck if there is
path-loss indownlink>uplink
C ontact w ithBSS
PathBalance
Externa l_ in terference
C ontact BSS todeterm ine the
in terferedfrequency
C hange thein tereferedfrequency
T ry to so lveneighbor T C H
congestionProblem s
YesFor a ll ne ighbors
T C H _C ongestion>threshold
Proceed w ith C T Pto determ ine thein terfered carrier
( D isable baseband hopping)
C heck frequencyplan and try to
determ ine poss ib lein terferers
In terferenceN o
N o
T C H _R F_LO SS> threshold Yes
Radio Dropped Calls
198
198
Dist_HO > threshold
Level_HO >30
Overshoot-Use drive test to determine the overshoot spot
-Change antenna orientation(down tilt)-change MS_max range
Coverage-Investigate for the need of new site
- Up tilt antenna
TRX_Duration<18s
Check for Adjacent or Co channel frequency
Use traces to check path losses in UL??
UL_quality>threshold
Hardware problemContact BSS
yes
yes
yes
No
No
No
yes External interferenceChange the interfered freq
Interference_on_idle(Motorola) or interference_bands(Alcatel) >threshold??
Peaks of interference not proportional to traffic??
yes
GSM interferenceChange one of the interfered freq.
yes
UL Quality HO
199
199
Dist_HO > threshold
Level_HO >30
Overshoot-Use drive test to determine the overshoot spot
-Change antenna orientation(down tilt)-change MS_max range
Coverage-Investigate for the need of new site
-Up tilt antenna
TCH_Duration<18s
InterferenceChange the interfered freq
Use traces to check path losses in DL??
DL_quality>threshold
Hardware problemContact BSS
yes
yes
yes
No
No
No
For any carrier BER >1.12%
yesyesCheck for Adjacent or Co channel frequency
DL Quality HO
200
200
Handover_Success_Rate < threshold or < average of week + margin
BTS_fail_rate>xx Out__BSC_Success_rate< Out_MSC_Success_rate<
Check neighbor parameters
For all neighbors in same BSC Check
In_BSC_Success_rate<XX
For all external neighbors Check
In_MSC_Success_rate<XX
For these neighbors Check:
Check BCCH/BSIC of neighbors and serving
-point neighbors with same BCCH/ BSIC -point neighbors with same BCCH/ BSIC as serving
yes
Change interfered frequency
UL/DL quality handover >xx
Check the parameterEN_INTRA_REPEATED=0
yes
Change interfered freq
HO Failures