UMTS Optimization Guideline
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UMTS Optimization Guideline
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UMTS Optimization Guideline BASIC TUNING.............................................................................................................................................2 KPIS AND SERVICE REQUIREMENTS....................................................................................................................2 IRAT Performance..................................................................................................................................2 CS Performance......................................................................................................................................2 CS Requirements..............................................................................................................................................3
PS Performance......................................................................................................................................4 PS Requirements...............................................................................................................................................5
TOOLS............................................................................................................................................................8 Tools Requirements................................................................................................................................8 RF Measurements...........................................................................................................................................11 Throughput Measurements..............................................................................................................................12 Call Performance............................................................................................................................................13
Tools Currently Available to Capture / Process data..........................................................................15 Drive Test Equipment and Software...............................................................................................................18 Post-Processing Software................................................................................................................................22
PRE-LAUNCH OPTIMIZATION PROCESS...............................................................................................................24 Database Verification...........................................................................................................................25 Drive Test Route Selection....................................................................................................................27 Drive Test Data Collection...................................................................................................................29 Data Post-processing and Root-Cause Analysis..................................................................................30 Root Cause Analysis and Recommendation.........................................................................................31 High Downlink Interference...........................................................................................................................31 Pilot Pollution.................................................................................................................................................33 Out of Pilot Coverage.....................................................................................................................................34 Insufficient received UL DPCH power...........................................................................................................34 High UE TX Transmit Power.........................................................................................................................35 Swapped feeders.............................................................................................................................................36 Low data throughput.......................................................................................................................................38 Handover Event Detection Failure..................................................................................................................40 No Suitable Cell..............................................................................................................................................42
Assessing Success of Recommended Change.......................................................................................42 OMC STATISTICS BASED TUNING.......................................................................................................43 KPIS............................................................................................................................................................43 IRAT - Inter Radio Access Technology (IRAT) performance ..............................................................51 CS Performance additional information..............................................................................................52 PS Performance additional information...............................................................................................52 TOOLS..........................................................................................................................................................53 Tools Requirements..............................................................................................................................53 Tools Currently Available to Capture / Process Data..........................................................................54 POST-LAUNCH OPTIMIZATION PROCESS.............................................................................................................57 Data Post-processing and Root-Cause Analysis..................................................................................58 Optimization Strategy per Root-cause and/or Problem Category/Type/Area......................................68 Assessing Success of Recommended Change.......................................................................................84
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Basic Tuning KPIs and Service Requirements IRAT Performance Handover between WCDMA and GSM allows the GSM technology to be used to give fallback coverage for WCDMA technology. This means subscribers can experience seamless services even with a phased build-out of WCDMA. The IRAT performance is evaluated under the following test cases. •
IDLE mode to GERAN (3G to 2G cell reselection).
•
Cell FACH state to Cell PCH state (3G PS state transition)
•
URA PCH state (3G PS state transition)
•
3G to 2G with PDP context activation (PS test; 3G to 2G cell reselection)
•
2G to 3G with PDP context activation (PS test; 2G to 3G cell reselection)
•
3G to 2G CS Handover (CS-only test)
•
2G to 3G CS Handover (CS-only test)
•
3G to 2G CS Handover with PDP context activation; Multi-RAB handover (CS + PS test)
•
Event 3A measurement activation / deactivation
CS Performance •
Call Event Success Rate
•
Call Block Rate
•
Drop Call Rate
•
SHO Event Success Rate
•
Location Update success rate
•
Channel Utilization
•
Call Completion Success Rate
•
Signaling Load inCode CONFIDENTIAL and PROPIETARY
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•
Inter Cell Handover Success Rate
•
Handover Success Ratio
•
Paging and Routing Area Updates
•
Connection Setup Success and Dropped
•
Call Setup Rate
•
Bad Quality Call Rate %
•
DL Power Outage %
•
SHO Overhead
•
Bs TXP
•
RAB establishment success rate
CS Requirements These two KPI’s RRC setup complete rate and RRC Establishment complete rate combine to give us another key KPI, accessibility, which is a measure of the origination success rate. Accessibility The network operator should target an Accessibility rate greater than 98 % for circuit switched voice conversations and packets switched data sessions.
Retainability Retainability is a measure of the Radio networks ability to maintain an active mobile session until the user terminates. It indicates the percentage of active calls dropped. inCode CONFIDENTIAL and PROPIETARY
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A typical retainability requirement for a network is Drop Call Rate < 1.5% for voice conversations.
PS Performance •
RLC DL throughput: Total RLC downlink throughput.
•
RLC UL throughput: Total RLC uplink throughput.
•
Session App. Mean Throughput DL (kbit/s): Mean throughput,
calculated over the whole of the current session, for data received at the application level (mean downlink throughput). •
Session App. Mean Throughput UL (kbit/s): Mean throughput,
calculated over the whole of the current session, for data sent at the application level (mean uplink throughput). •
Ping Delay (ms): Delay for an individual Ping Response during the
current Ping session. •
Success Rate of internet connections
•
Variable data rate performance
•
End to end packet delay transfers
•
Throughput at the edge of the cell
•
PS and CS Bearers
•
Attach / Context
•
Blocked Error Rate %
•
Packet Bad Quality %
•
PDP Context Activation success ratio
•
Attach success ratio
•
PDP context drop ratio
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•
Data Transfer drop ratio
•
Attach setup time
•
PDP context activation time
•
Service Access time
•
End to end access time
•
Mean user data rate
•
Round trip time
•
Packet loss ratio
•
Initial Service Response
•
Transfer interruption time
•
End to end accessibility success ratio
•
Service Access Success Ratio
PS Requirements •
HSDPA DL Application Layer Throughput > 400 kbps
•
R’99 DL Application Layer Throughput > 133 kbps
•
HSDPA Ping Round trip Latency < 150ms
•
R’99 Ping Round trip Latency < 150ms
•
OCNS with 20% of Minimum Design capacity.
Optimization Insights Optimizing the Network The optimization process should start in the so-called pilot network, an intermediate stage of the network rollout where only the common channels for signaling and synchronization are use. While carrying no traffic itself, this pilot network provides a useful representation of the traffic flow in the future operational WCDMA network. Many aspects of optimization activities can be done in this phase.
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Some other aspects of optimization such as adjusting the Soft Handover ratio must wait until the user equipment (UE) is in operation. Basic Tuning to be done early phase of roll out Coverage Optimization 1. Since each Node Bs continuously transmits CPICH, scanning the CPICH using a Drive test system enables a quick and effective examination of the network RF Coverage, as well as a means to identify the Node Bs. It is important to detect high CPICH levels from too many cells as this causes interference. 2. Lack of RF Coverage - Can cause calls to drop or be blocked due to lack of coverage at the edge of the cell site coverage or coverage hole in the area. Missing Neighbors and Pilot Pollution 1. Missing Neighbor in the neighbor list - Neighbor condition occurs when a high level pilot (i.e
one whose measured value is above T_Add
(Threshold to Add)) that does not appear in the neighbor list is sent to a phone. This condition adds interference, resulting in a low quality connection, and possible causing dropped calls. 2. Pilot Pollution and Interference - Pilot Pollution occurs when there are an excessive number of pilot signals. In such a situation a subscriber could notice interference on an active call. Balancing of Channel Transmission Powers: The relative output powers of various channels in WCDMA can be freely adjusted, and should be since they have different requirements. Signaling channels need less power than the channels that carry user data.
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Particularly important to ensure that Synchronization channels are transmitted strongly enough to be reliably detected. Cells in the vicinity of one another must use different offsets for the synchronization burst in order for the synchronization channel to work properly. Type of test call in drive-test: Short voice call: Each voice call is made to a PSTN number and held for duration of 100 seconds and waited for 10 seconds between calls. Long Voice call: Voice call is made to a PSTN number and held until the end of the cluster drive test, or until the call dropped. Short CS Data Call: CS data call is made to another mobile or to a CS ftp server and held for a duration of 100 seconds then wait for 10 seconds before making the next call. Long CS Data Call: CS data call is made to another mobile or to a CS ftp server and held until the end of the cluster drive test, or the call dropped. Short PS Call: About 100 seconds worth of data transfer DL or DL FTP a 2.5 MB file (approximately). Long PS Call: About 1 hr worth of data transfer DL or multiple DL FTP files of size about 10MB. KPIs: CPICH RSCP: Received signal code power, the received power on one code measured on the primary CPICH. DL RSSI: Received signal strength indicator, the wide-band received power within the relevant channel bandwidth. CPICH Ec/No: The received energy per chip divided by the power density in the band. UE UL TxPwr: The total UE transmitted power on one carrier. Transport CH BLER: Estimation of the transport channel block error rate.
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Call event success rate: Formula: # Call Ends / (# Call Ends + # Blocked Calls + # Dropped Calls) SHO event success rate: Formula: (# add + # remove + # replace) / # all SHO
Tools Tools Requirements Different tools are required to accomplish basic tuning in UMTS network. •
Cell Planning Tools
•
Route Planning Tools
•
Drive Testing Tools
•
Data Processing and Report Generation Tools
•
RF Test Tools
Cell Planning Tools During basic tuning, Cell Planning Tool is used to: •
Plan and design UMTS network,
•
Analyze coverage and interference,
•
Design neighbor cell relationships and define handover margins,
•
Analyze traffic,
•
Review network capacity planning for voice and data services.
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Route Planning Tools Often Mapinfo is used to plan drive routers before drive-tests. Mapinfo is a commercial application working on PC. In route planning process, Mapinfo can be used to plan route, sites and spatial data visualization and printing. A digital map is required with Mapinfo format including raster and vector information of terrain. Besides Mapinfo, maps or map software such as Microsoft Street and Trips, can be used to plan routes.
Driver Testing Tools During the basic tuning for a pre-launch UMTS network, drive-testing is the most important way to collect the network performance data, since there are limited subscribers using the UMTS pre-launch network and accurate network statistics is not available from OSS. Drive testing tools are used to: •
Record UE and scanner measurement data,
•
Visualize UE and scanner measurement data during drive
testing (synchronized maps, tables, graphs and text information). To do the drive test in UMTS network, the following components are required. •
Test UE
With Test UE, drive testing tools can capture RF measurements on the UE side, like UE transmit power, DL CPICH Eb/No, DL RSSI, etc. Further more, to get a full picture (both downlink and uplink information) of the problem, it is possible to use UE trace function during the drive test, if the RAN and OSS can support this function. Since UMTS can support voice, CS data and PS data, usually we need more test UEs during the drive test. To get all RAB performances in UMTS network, the following call type is necessary to do a drive test:
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Short voice call:
Each voice call is made to a PSTN
number and held for duration of 100 seconds and waited for 10 seconds between calls.
Long Voice call: Voice call is made to a PSTN number
and held until the end of the cluster drive test, or until the call dropped.
Short CS Data Call: CS data call is made to another
mobile or to a CS ftp server and held for a duration of 100 seconds then wait for 10 seconds before making the next call.
Long CS Data Call: CS data call is made to another
mobile or to a CS ftp server and held until the end of the cluster drive test, or the call dropped.
Short PS Call: About 100 seconds worth of data transfer
DL or DL FTP a 2.5 MB file (approximately).
Long PS Call: About 1 hr worth of data transfer DL or
multiple DL FTP files of size about 10MB.
•
Pilot Scanner
A pilot scanner is a tool to measure the CPICH Eb/No and CPICH RSCP regardless the neighbor list setting, correlated with GPS positioning data. It is useful to determine a handover relationship and to evaluate radio wave propagation characteristics, pilot channel qualities, soft handover area locations and downlink interference contributions. •
GPS
GPS can provide position information during drive tests. With GPS we can get the result that abnormal RF problem can be connected to geographical information.
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FTP Server
In order to transfer data stably without any unexpected problem from Internet, a dedicated FTP server should be set up before doing drive tests. Different size files on a FTP server should be put so as to perform short PS data calls or long PS data calls. For example: 1MB, 2 MB, 5 MB, 10MB, 100MB, etc. Data Processing and Report Generation Tools To analyze drive test log file, post data processing tools can be used to display a plot, which includes radio measurement results and geographic information on MapInfo. In addition, this post data processing tools can provide the statistics of call events and radio measurement data, often used in our customer reports.
RF Testing Tools A spectrum analyzer is a tool to monitor spectrum characteristics. It is useful to track external interference inside or outside of the operational band. In the initial deployment phase (coverage limited system), it can be used to survey the level of adjacent channel interference from other operators.
RF Measurements The following is the key RF performance indication in UMTS drive tests. Test UE
Scrambling codes of active set cells and monitored set cells
CPICH_Ec/No of active set cells and monitored set cells
(dB)
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CPICH_RSCP of active set cells and monitored set cells
(dBm)
DL RSSI (dBm)
DL transport BLER (%)
DL SIR target and estimated DL SIR (dB)
UE transmitted power (dBm)
All UE sent and received L3 messages
Pilot Scanner
Scrambling codes of all CPICHs
Ec/No of all CPICHs (dB)
RSCP of all CPICHs (dBm)
DL RSSI (dBm)
Throughput Measurements During the drive test in UMTS network, it is important to measure and monitor wireless data service performance, since wireless data service is the significant
characteristic
of
UMTS
technology.
PS
performance
measurements can be obtained as follows:
RLC DL throughput: Total RLC downlink throughput.
RLC UL throughput: Total RLC uplink throughput.
Session
App.
Mean
Throughput
DL
(kbit/s):
Mean
throughput, calculated over the whole of the current session, for data received at the application level (mean downlink throughput).
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Session
App.
Mean
Throughput
UL
(kbit/s):
Mean
throughput, calculated over the whole of the current session, for data sent at the application level (mean uplink throughput). Application Throughput DL(kbit/s): Current throughput for
data received at the application level (current downlink throughput). Application Throughput UL(kbit/s): Current throughput for
data received at the application level (current uplink throughput). Ping Delay (ms): Delay for an individual Ping Response
during the current Ping session.
Call Performance
Often the drive test tools can provide some call events statistics that can be used to evaluate radio network performance. These call performance statistics can be categorized into four groups. Accessibility RRC connection setup successful rate from the UE point of
view
Number of sent RRC connection setup complete ×100 % Number of sent RRC connection request
RB establishment successful rate per RB from the UE point
of view Number of sent radio bearer setup complete ×100 % Number of received radio bearer setup
Retainability
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Average RRC connection drop rate when the UE is in
cell_DCH mode
N um berof abnorm aldropsin w hich
[ ]
he t U Estateis fromC ell_D C Hto idle -1 s T otaltim eof the w holedrivetest
Average RRC connection drop rate when the UE is in
cell_FACH mode
N um berof abnorm aldropsin w hich he t U Estateis fromC ell_FA C Hto idle -1 s T otaltim eof the w holedrivetest
[ ]
Mobility
Soft handover success rate
(# add + # rem + # repl) / # all Where add = Radio Link Addition events rem = Radio Link Removal events repl = Radio Link Replacement events all = all Radio Link events, including failures
IRAT hard handover success rate
From UMTS to GSM: Number of HO from UTRAN Complete ×100 % Number of HO from UTRAN command
From GSM to UMTS: Number of HO to UTRAN Complete ×100 % Number of HO to UTRAN command
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Quality
Downlink transport channel BLER
Best serving cell CPICH Ec/No, i.e. pilot channel quality
Tools Currently Available to Capture / Process data
At present many drive test software and analyze software are available to capture and post-process measurement data. Basically these software can be categorize into two groups based on the provider of these software.
Software developed by Mobile Infrastructure Equipment Vendor An advantage of this kind of software is that vendors can add some additional test functions to let these software work well with their infrastructure network. For example, Ericsson adds SQI measurement function in their drive test tools – Tems Investigation, this function can evaluate voice quality during drive tests. Also in Ericsson infrastructure network, same function is used in performance statistic. Two major drive test and post-process tools listed below are commonly used in different operators.
Nemo Nemo is a Finland company which dedicates to develop drive test and post-process software for mobile networks. The former of this company is a branch of Nokia. Nemo is used commonly by operators who use Nokia system, like T-Mobile.
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Nemo Outdoor™ Nemo Outdoor™ is a portable engineering tool designed for measuring and monitoring the air interface of wireless networks. Fast and accurate measurement data provides detailed information in real time for 2G, 2.5G, 2.75G, and 3G networks. For more detail information about Nemo Outdoor, please read his web site. http://www.nemotechnologies.com/index.php?249
Nemo Analyze™ Nemo Analyze™ is a front-line analysis tool for quick and easy data review. It can be used on the field or in the office for immediate problem solving and report generation. Nemo Analyze is designed to be the analysis tool for measurement files produced with the Nemo measurement tools: Nemo Outdoor and Nemo Handy. For more detail information about Nemo Analyze, please read his web site. http://www.nemotechnologies.com/index.php?267 Tems Tems products are developed by a branch of Ericsson Corporation. Tems products portfolio includes radio network planning, radio network optimization, benchmarking, indoor coverage testing.
Tems Investigation TEMS Investigation is a portable air-interface tool for troubleshooting, verification, optimization, and maintenance of mobile networks. The tool collects all the data needed to keep the network running smoothly and to plan for future improvements. The collected data is presented in real time, and can be used together with site information to improve troubleshooting inCode CONFIDENTIAL and PROPIETARY
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capability. The flexible interface allows the user to filter network data and focus on relevant information for truly in-depth analysis For more detail information about Tems Investigation, please read his web site. http://www.ericsson.com/solutions/tems/realtime_diagnostics/investigation .shtml
Tems DeskCat TEMS DeskCat is advanced post-processing software. It enables users to easily mine drive test data, visualize air interface problems, and drill down into the data for easy analysis and problem resolution. It also provides the unique System Quality Report for comprehensive network comparison. Designed to support experienced RF engineers and network optimization specialists, but able to provide managerial reports as well. For more detail information about Tems DeckCat, please read his web site. http://www.ericsson.com/solutions/tems/realtime_diagnostics/deskcat.sht ml Software developed by Testing and Measurement Company Developed by companies dedicating to develop sophisticated equipments, these drive test tools have a common characteristic on RF testing function. For example: Rohde-Schwarz TS9951+ ESPI+ROMES3 Rohde-Schwarz TS9951 is a drive test hardware used to support up to 4 mobile phones. Rohde-Schwarz ESPI is a test scanner to accomplish the PN scan and CW measurement. These two tools should be run on the drive test software Rohde-Schwarz ROMES3.
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For more detail information about Rohde-Schwarz products, please read their web site. http://www.rohde-schwarz.com
Agilent E6474A The E6474A Agilent Wireless Network Optimization Platform provides true cross technology scalability and allows early verification of network deployments for 2G, 2.5G and 3G wireless networks. Its optimization platform enables wireless service providers and network equipment manufacturers to proactively address challenges with wireless voice and data networks by quickly and accurately identifying problems.
Drive Test Equipment and Software The field measurement equipment usually consists of: •
A laptop, which store the measurements data and run the drive test software.
•
A GPS, to record the exact location of the measured parameters.
•
Mobile phones and scanners to be used as measurement devices.
Scanner
HUB
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Three phones can used to provide a flexible test configuration and test both data and voice calls (short and long calls). Using both mobile and scanner simultaneously in WCDMA measurements enables the measuring of all pilots available in the area and the comparison of the results to the view seen by the user equipment (UE). The UE reports values based on a neighbor list received through signaling and makes cell reselections and handovers based on the planned neighbor list. However, there can be pilots available that are not defined in the neighbor list and these can be spotted with a scanner. In other words, measurements together with scanner and mobile would also identify missing or interfering pilots. Effective UMTS drive test software should be able to measure and perform the following tasks:
•
Evaluate call-processing operations
•
Perform selected call processing functions
•
Measure and report the amplitude of the received base station
signal •
Measure and report the signal quality of the received base station
signal •
Read and report the neighbor cell list from the broadcast messages
•
Report the amplitude of neighbor list base stations
•
View and log protocol messages in decoded form for easy
interpretation •
Quantify wireless data user’s quality of service (with data
measurement options). •
Perform integrated analysis using the phone and receiver at the
same time •
Correlate call drops within the RF environment
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Show current position and the route traveled on a map as data is
collected. The following is a list of some of the parameters measures. Interlayer Messages • UMTS Layer 3 Messages • GSM Layer 3 Messages • GSM Acknowledged Mode Messages Layer 2 • GPRS RLC/MAC Messages • GPRS GMM/SM Messages QoS Indicators • Real-Time Data Throughputs • RLT Counter Radio link timeout • FER • Vocoder State • DTX State • Retransmitted RLC Block Rate • RLC/MAC Real-Time Data Throughputs • RLP Report • Handover Counter UMTS Measurement Information • UL/DL ARFCN • ARFCN RxLev • Each CPICH in the Active List • Ec/No of each CPICH in the Active List • Composite and per finger RSCP
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• Each CPICH in the Candidate List • Ec/No of each CPICH in the Neighbor List • Cell ID of each CPICH in the Active and Neighbor Lists • BSIC • Power Control – UE Tx Power – DPCH SIR HSDPA Measurement Information • CQI • DCH BLER • DCH Retransmissions • DSCH Throughput (kbit/s) • SCCH OVSF Code Info • HS Session GSM/GPRS/EDGE Layer State and Measurement Information • Layer 1 Information • RR Information • MM Information • MAC Information • RLC Information − Downlink Coding Scheme − Uplink Coding Scheme • LLC Information • GMM Information • SM Information • SNDCP Information • Service State Data and service testing
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• Streaming Video • IP Protocol Trace • Data throughput UL/DL • Ftp, http, and ping test applications. • MMS and SMS testing • New Command sequence • Roundtrip delay
Post-Processing Software Post processing forms a key counterpart to data collection in the verification of infrastructure performance, automated calculation of performance metric analyses and troubleshooting. Key features of a data analysis and post processing tool for UMTS is the ability to: •
Support multiple technologies i.e. GSM, GPRS and WCDMA on one platform simultaneously.
•
Provide maps, histograms and cumulative distribution charts and statistical analyses of key packet data and radio link performance metrics.
•
Correlate WCDMA scanner and UMTS UE measurements from independent log files.
•
Support interfaces to a variety of vendors of drive test equipment, protocol analyzers and measurement programs.
•
Access to radio interface messaging, including message counters and cause value breakdown for failure, error and reject messages.
•
Correlate abnormal data performance with radio link parameters.
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Assess Subscriber-perceived performance analysis for IP and data applications (e.g. HTTP, UDP)
•
Provide support for open interfaces, which can typically be used to collect performance data well in advance of proprietary data sources, like test mobile and peg counter data.
•
Reduce data through binning and standard database type querying and filtering capabilities.
•
Synchronize data collected from different network elements and sources to remove timing discrepancies.
•
Provide interfaces into databases for storing collected data statistics and provide web-enabled reporting interfaces for extracting data.
•
Embed engineering expertise into the software to automate the process of analyzing large amounts of data.
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Pre-Launch Optimization Process An overview of the radio network optimization process will be briefly presented.
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Basic Tuning
Database Verification
Performance Monitor
Performanc e Report
Drive Test
Test User Complain
Performance Analysis
Parameters Tuning
Mechanical Tuning
Performance Review
No
Meet Project Target Yes Finish
Database Verification
Purpose inCode CONFIDENTIAL and PROPIETARY
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The purpose of the database verification activity is to verify that the radio network has been properly configured, meaning that the actual system parameter settings correspond to the recommended values, and RF parameter settings correspond to the radio network design results. RAN database verification is the first step of basic tuning. By implementing the verification, unnecessary troubleshooting will be avoided and further investigations can be carried out focusing on problems other than parameter configuration mistakes. Database verification includes two parts of work- RF Parameters Verification and System Parameters Verification.
RF Parameters Verification The RF parameter settings that are implemented in the live network and the original radio network design results are the base to conduct basic tuning. These RF parameter settings contain PN code plan, neighbor list plan, antenna height, antenna direction and tilt. Make sure that the RF parameter settings in the live network are exactly the same with the radio network design results. Meanwhile, conducting drive test for each site can ensure that no antenna swap mistakes exist in the live network. Often missing neighbors and antenna swaps are the most common mistakes in the pre-launch network, resulting in serious radio network performance problems in UMTS networks, e.g. high drop call rate in some cells, bad quality area (with low Ec/No) etc.
System Parameters Verification In order to avoid abnormal system parameter setting in live network, verifying the parameter settings in the live network correspond to the
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recommended values is important.
These recommended values are
based on lots of testing and simulations results, which are optimal values in most networks. The procedure to implement system parameters verification is as below: 1.
Retrieve current parameter settings from systems
2.
Check current versus recommended parameter values
3.
Apply the consistency check rules to current parameter
values 4.
Produce a list of parameters to be changed and generate the
change requests for clients 5.
Get approval from clients and load changes to the systems
A parameter dump should be created from the live network to retrieve current parameter settings, following by a conversion of the system dump file into readable Microsoft Excel file with script developed by Excel Macro or VB. Equipments from different vendors often provide different recommended system parameter setting values, which may require to be modified when new software version is released. Therefore, it is important to get recommended parameter setting values for current software version from clients before implementing system parameter setting verification.
Drive Test Route Selection Drive testing is done to verify the coverage and the service requirement KPI’s i.e. availability, Retentivity etc or for pin pointing and resolution of any network related issue. The Drive route criteria for both the scenarios are different.
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The main purpose of baseline drive testing is to find the problem
areas of the network. Using field measurement, coverage holes, interference areas, and handoff regions. •
The primary drive route consists mainly of freeways,
highways and high traffic areas (like downtown). The high traffics areas are also define in the coverage and capacity objective, part of the Wireless System Design (and Implementation) Report. Both directions of travel need to be considered. If the three primary types of road do not cover problem areas, secondary road should be considered. If time and resource permit, selected secondary streets can be included in the drive routes. •
For baseline drive test, the drive routes need to cover
farther than good coverage areas. For example, route will include roads covered lower than Ec/Io=-16dB. •
The route should cover all the sectors included in the
test. •
Avoid the area with known coverage problem because of
the unavailability or hardware problems of cells covering the area. Problem Resolution Drive route When problem area is identified, a punctual drive route should be design to verify and quantify the extent of the problem. •
The route should be driven both directions to verify if the
problem exists in one direction or both directions. E.g. To verify handovers from any sector from a site we need to check the outgoing
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and incoming handovers for which we need to drive in both directions of the drive route. •
If we do encounter any problem/ issue we should repeat
the route so as to repeat the problem. •
If in the network there are a couple of problem areas, it is
recommended to have separate spot drives for each of the problem areas.
Drive Test Data Collection Before we start data collection we need to make sure that the hardware is connected and configured properly. •
Make sure all the Phones, Scanners, Scanner Antenna’s, GPS, Hubs and Laptop are connected properly.
•
Make sure all the devices are connected to the appropriate COM port, and the COM ports are configured accordingly.
•
Set up the Autocall settings to set up the phones for Long Call and Short call with the appropriate set up times, number to call, Max Idle time and Connect time.
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Make sure the appropriate Mapinfo workspace for the drive test area is configured in the Drive Test tool.
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Import the most current Cell site database which has information on the Sites, their PN’s and the Antenna orientations.
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Set up the FTP server with a suitable file for testing of Data Download and upload speeds.
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Set up the Scanner configurations as a Pilot Scanner with the appropriate Scan lists, Avg Ec/Io and Correlation taps.
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Open at least one window for the Map, The phone data, Scanner Data, and the Summary data for all the devices.
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Connect all the devices, the Data collection software shows the connected devices.
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Run a test call to confirm that the Autocall, Scanners, GPS and the phones working fine.
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If everything is working fine, start logging and save the log files with suitable identifiers like . Save the log files in the appropriate directory.
Data Post-processing and Root-Cause Analysis Data Post-Processing To optimize the pre-launch network, various input data is needed: •
Performance statistics
•
Performance recording
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Fault logs from RNC and Node B
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Parameter data
Performance statistics Performance statistics is generated from the live, and is made up of a number of predefined counters. Combining these counters into formulas, we can get statistical reports which are useful for performance monitoring and optimization. During the basic tuning for a pre-launch network, since there are limited test users in the network, the performance statistics are not so accurate like the performance statistics in live network. Performance recording Performance recording includes two parts, log-file from drive-test tools and UE trace log-file from OSS with UE tracing function. UE tracing function provides UL information received by Node B side and signaling between
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Node B and RNC. Performance recording is the important input when performing a basic tuning in pre-launch network. Fault logs from RNC and Node B Fault logs are useful to identify abnormal system behavior caused by node faults Parameter data Parameter setting reviews are useful to understand the intention of the original radio plan and to determine how the parameter changes should be.
Root Cause Analysis and Recommendation
High Downlink Interference Phenomena During the drive test, following phenomena might be observed through drive testing tools: •
Received Ec/No of the pilot channel is less than –16dB and
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Received RSCP of the pilot channel is high enough to
maintain the connection, e.g. > -100dBm and •
DL RSSI is very high and
•
The connection drops eventually
Reason 1 – Non Dominant Cell
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Many overlapping cells exist in the problematic areas and received signal strengths of the pilots in these overlapping cells are almost the same. Recommendation A direct and effective solution is to increase the pilot channel power – Primary CPICH power of the desired cell.
Reason 2 – Dominant Interferer An undesired cell is identified because of its high signal strength, causing missing neighbor problem. Recommendation 1 The simplest solution is to convert the interferer to a useful radio link by including the overshooting cell into the neighboring cell list. Recommendation 2 The second solution to solve this problem is to decrease the pilot power - Primary CPICH power of the overshooting cell. With the pilot power decreasing, the total downlink power for the common channels of the interferer decreases. At the mean time, the power of all other common channel decreases because their parameter settings are related to the pilot power value. Recommendation 3 The third solution is to change the antenna configuration of the overshooting cell. The possible practices include tilting down the antenna, re-directing the antenna orientation, reducing the antenna height and so on. This solution will not lead to UL/DL coverage imbalance problem in the interferer because UL/DL path-loss is changed simultaneously.
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Reason 3 – Low Best Serving PPilot/PTot The third possible reason is that the pilot power setting is not large enough to fulfill existing downlink load, because low received Ec/No of the best serving pilot channel (near or less than –16dB) can be observed even if there is no other cell Recommendation To add a new site with “good coverage control” in the problematic area is a common practice.
Pilot Pollution Phenomena In cell_DCH mode, pilot pollution refers to the phenomenon that a UE at one location alters its active set cells frequently (e.g. active set update rate is very high) because many received pilot channels have similar quality (or signal strength) such as Ec/No (or RSCP).
Reason – No Dominant Cell Due to poor cell planning, a large number of overlapping cells exist at a particular area Recommendation 1 To change the antenna configurations or reduce the pilot power of the undesired cells is a common practice to remove the cells overlapping. Recommendation 2
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An alternative solution to remove the cell overlapping is to increase the pilot channel power – Primary CPICH power of the desired cells.
Out of Pilot Coverage Phenomena During the drive test, following phenomena might be observed. •
Received Ec/No of the pilot channel is less than –16dB and
• Received RSCP of the pilot channel is very low, e.g.
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