Tuesday, January 15, 2013

RF Optimization and Log File Analysis in GSM


Optimization and Log File Analysis in GSM

1. INTRODUCTION
Every alive Network needs to be under continues control to maintain/improve the
performance. Optimization is basically the only way to keep track of the network by
looking deep into statistics and collecting/analyzing drive test data. It is keeping an eye
on its growth and modifying it for the future capacity enhancements. It also helps
operation and maintenance for troubleshooting purposes.
Successful Optimization requires:
• Recognition and understanding of common reasons for call failure
• Capture of RF and digital parameters of the call prior to drop
• Analysis of call flow, checking messages on both forward and reverse
links to establish “what happened”, where, and why.
Optimization will be more effective and successful if you are aware of what you are
doing. The point is that you should now where to start, what to do and how to do.
1.1. Purpose and Scope of Optimization
The optimization is to intend providing the best network quality using available
spectrum as efficiently as possible. The scope will consist all below;
• Finding and correcting any existing problems after site implementation and
integration.
• Meeting the network quality criteria agreed in the contract.
• Optimization will be continuous and iterative process of improving overall
network quality.
• Optimization can not reduce the performance of the rest of the network.
• Area of interest is divided in smaller areas called clusters to make optimization
and follow up processes easier to handle.
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1.2. Optimization Process
Optimization process can be explained by below step by step description:
1.2.1. Problem Analysis
Analyzing performance retrieve tool reports and statistics for the worst
performing BSCs and/or Sites
Viewing ARQ Reports for BSC/Site performance trends
Examining Planning tool Coverage predictions
Analyzing previous drive test data
Discussions with local engineers to prioritize problems
Checking Customer Complaints reported to local engineers
1.2.2. Checks Prior to Action
Cluster definitions by investigating BSC borders, main cities, freeways,
major roads
Investigating customer distribution, customer habits (voice/data usage)
Running specific traces on Network to categorize problems
Checking trouble ticket history for previous problems
Checking any fault reports to limit possible hardware problems prior to
test
1.2.3. Drive Testing
Preparing Action Plan
Defining drive test routes
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Collecting RSSI Log files
Scanning frequency spectrum for possible interference sources
Re–driving questionable data
1.2.4. Subjects to Investigate
Non–working sites/sectors or TRXs
In–active Radio network features like frequency hopping
Disabled GPRS
Overshooting sites – coverage overlaps
Coverage holes
C/I, C/A analysis
High Interference Spots
Drop Calls
Capacity Problems
Other Interference Sources
Missing Neighbors
One–way neighbors
Ping–Pong Handovers
Not happening handovers
Accessibility and Retainability of the Network
Equipment Performance
Faulty Installations
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1.2.5. After the Test
Post processing of data
Plotting RX Level and Quality Information for overall picture of the driven
area
Initial Discussions on drive test with Local engineers
Reporting urgent problems for immediate action
Analyzing Network feature performance after new implementations
Transferring comments on parameter implementations after new changes
1.2.6. Recommendations
Defining missing neighbor relations
Proposing new sites or sector additions with Before & After coverage plots
Proposing antenna azimuth changes
Proposing antenna tilt changes
Proposing antenna type changes
BTS Equipment/Filter change
Re–tuning of interfered frequencies
BSIC changes
Adjusting Handover margins (Power Budget, Level, Quality, Umbrella
HOs)
Adjusting accessibility parameters (RX Lev Acc Min, etc..)
Changing power parameters
Attenuation Adds/Removals
MHA/TMA adds
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1.2.7. Tracking
Re–driving areas after implementing recommendations
Create a tracking file to follow–up implementation of recommendations
1.2.8. Other Optimization Topics
Verifying performance of new sites
Verifying handovers
Verifying data after Re–Homes
Investigating GPRS performance
Verifying Sectorizations
Collecting DTI Scan files
Verifying coverage
Verifying propagation model by importing DTI scan files to Planet
Periodic Consistency Checks
Frequency Planning Check
Analyzing cell access parameters
Analyzing Handover parameters
Analyzing Power control parameters
Analyzing Frequency Hopping parameters (HSN, MAIO)
Implementing/analyzing optional features
Keep helping local engineers with emergency cases
Benchmarking
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1.3. Before Starting
This document was prepared with TEMS screen shots from live examples of previous
experiences to guide RF Engineers on how to define/analyze problems or cases and optimize
network. After each case/problem demonstration, specific step to be taken will be defined and
appropriate recommendation will be given.
The document will be focusing on Drive Testing part of the Optimization Process and give
definitions on basic GSM principals, features and parameters when needed.
The readers of this document are considered to have basic knowledge of cell planning and TEMS
Investigation usage. Only little information will be given just to remember TEMS interface.
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2. DRIVE TESTING
Drive testing is the most common and maybe the best way to analyze Network performance by
means of coverage evaluation, system availability, network capacity, network retainibility and
call quality. Although it gives idea only on downlink side of the process, it provides huge
perspective to the service provider about what’s happening with a subscriber point of view.
The drive testing is basically collecting measurement data with a TEMS phone, but the main
concern is the analysis and evaluation part that is done after completition of the test. Remember
that you are always asked to perform a drive test for not only showing the problems, but also
explaining them and providing useful recommendations to correct them. Please note that a
successful analysis should be supported by handling of network statistics from a statistics tool
(Metrica/NetDoc–NMS/SRP–OSS, etc..) and careful evaluation of coverage predictions from a
cell planning tool (Planet, DB–Planner, TEMs Cell Planner, etc..). Please see Figure 1 for a usual
view from TEMS.
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