Key Performance Indicators For radio network optimization it is necessary to have key performance indicators. These KPIs are parameters that are to be observed closely when the network monitoring process is going on. Mainly, the term KPI is used for parameters related to voice and data channels, but network performance can be broadly characterized into coverage, capacity and quality criteria also that cover the speech and data aspects. The performance of the radio network is measured in terms of KPIs related to voice quality, based on statistics generated from the radio network. Drive tests and network management systems are the best methods for generating these performance statistics. The most important of these from the operator's perspective are the BER (bit error rate), the FER (frame error rate) and the DCR (dropped call rate). The BER is based on measurement of the received signal bits before decoding takes place, while the FER is an indicator after the incoming signal has been decoded. Correlation between BER and FER is dependent on various factors such as the channel coding schemes or the frequency hopping techniques used. As speech quality variation with the FER is quite uniform, FER is generally used as the quality performance indicator for speech. The FER can be measured by using statistics obtained by performing a drive test. Drive testing can generate both the uplink and the downlink FER. The dropped call rate, as the name suggests, is a measure of the calls dropped in the network. A dropped call can be defined as one that gets terminated on its own after being established. As the DCR gives a quick overview of network quality and revenues lost, this easily makes it one of the most important parameters in network optimization. Both the drive test results and the NMS statistics are used to evaluate this parameter. At the frame level, the DCR is measured against the SACCH frame. If the SACCH frame is not received, then it is considered to be dropped call. There is some relation between the number of dropped calls and voice quality. If the voice quality were not a limiting factor, perhaps the dropped call rate would be very low in the network. Calls can drop in the network due to quality degradation, which may be due to many factors such as capacity limitations, interference, unfavorable propagation conditions, blocking, etc. The DCR is related to the call success rate (CSR) and the handover success rate. The CSR indicates the proportion of calls that were completed after being generated, while the handover rate indicates the quality of the mobility management/RRM in the radio network.
.
KPIs can be subdivided according to the areas of functioning, such as area level, cell level
(including the adjacent level), and TRX level. Area-level KPIs can include SDCCH requests, the dropped SDCCH total, dropped SDCCH A-bis failures, outgoing MSC control handover (HO) attempts, outgoing BSC control HO attempts, intra-cell HO attempts, etc. Cell-level KPIs may include SDCCH traffic BH (av.), SDCCH blocking BH (av.), dropped SDCCH total and distribution per cause, UL quality level distribution, DL quality/level distribution etc. The TRX level includes the likes of UL and DL quality distribution.
5.5 NETWORK PERFORMANCE AND MONITORING The whole process of network performance monitoring consists of two steps: Monitoring the performance of the key parameters, Assessment of the performance of these parameters with respect to capacity and coverage. First the radio planners assimilate the information/parameters that they need to monitor. The KPIs are collected along with field measurements such as drive tests. For the field measurements, the tools used are ones that can analyze the traffic, capacity, and quality of the calls, and the network as a whole. For drive testing, a test mobile is used. This test mobile keeps on making calls in a moving vehicle that goes around in the various parts of the network. Based on the DCR, CSR, HO, etc., parameters, the quality of the network can then be analyzed. Apart from drive testing, the measurements can also be generated by the network management system. And finally, when 'faulty' parameters have been identified and correct values are determined, the radio planner puts them in his network planning tool to analyze the change before these parameters are actually changed or implemented in the field.
5.6 DRIVE TESTING The quality of the network is ultimately determined by the satisfaction of the users of the network, the subscribers. Drive tests give the 'feel' of the designed network as it is experienced in the field. The testing process starts with selection of the 'live' region of the network where the tests need to be performed, and the drive testing path. Before starting the tests the engineer should have the appropriate kits that include mobile equipment (usually three mobiles), drive testing software (on a laptop), and a GPS (global positioning system) unit. When the drive testing starts, two mobiles are used to generate calls with a gap of few seconds (usually 15-20 s). The third mobile is usually used for testing the coverage. It makes one continuous call, and if this call drops it will attempt another call. The purpose of this testing to
collect enough samples at a reasonable speed and in a reasonable time. If there are lots of dropped calls, the problem is analyzed to find a solution for it and to propose changes.
5.7 NETWORK PERFORMANCE ASSESSMENT The performance indicators are listed below: Amount of traffic and blocking Resource availability and access Handovers (same cell/adjacent cell, success and failure) Receiver level and quality. Power control.
5.7.1 COVERAGE Drive test results will give the penetration level of signals in different regions of the network. These results can then be compared with the plans made before the network launch. In urban areas, coverage is generally found to be less at the farthest parts of the network, in the areas behind high buildings and inside buildings. These issues become serious when important areas and buildings are not having the desired level of signal even when care has been taken during the network-planning phase. This leads to an immediate scrutiny of the antenna locations, heights and tilt. The problems are usually sorted out by moving the antenna locations and altering the tilting of the antennas. If optimization is being done after a long time, new sites can also be added.
Coverage also becomes critical in rural areas, where the capacity of the cell sites is already low. Populated areas and highways usually constitute the regions that should have the desired level of coverage. A factor that may lower the signal level could be propagation conditions, so study of link budget calculations along with the terrain profile becomes a critical part of the rural optimization. For highway coverage, additions of new sites may be one of the solutions.
5.7.2 CAPACITY Data collected from the network management system is usually used to assess the capacity of the network. As coverage and capacity are interrelated, data collected from drive tests is also used for capacity assessment. The two aspects of this assessment are dropped calls and congestion. Generally, capacity-related problems arise when the network optimization is taking place after a long period of time. Radio network optimization also includes providing new capacity to new hot-
spots, or enhancing indoor coverage. Once the regional/area coverage is planned and executed in the normal planning phase, optimization should take into consideration the provision of as much coverage as possible to the places that would expect high traffic, such as inside office buildings, inside shopping malls, tunnels, etc.
5.7.3 QUALITY The quality of the radio network is dependent on its coverage, capacity and frequency allocation. Most of the severe problems in a radio network can be attributed to signal interference. For uplink quality, BER statistics are used, and for downlink FER statistics are used. When interference exists in the
network; the source has to be found out. The entire frequency plan is checked again to determine whether the source is internal or external. The problems may be caused by flaws in the frequency plan, in the configuration plans (e.g. antenna tilts), inaccurate correction factors used in propagation models, etc.
5.8 PARAMETER TUNING The ending of the assessment process sees the beginning of the complex process of fine-tuning of parameters. The main parameters that are fine-tuned are signaling parameters, radio resource parameters, handover parameters and power control parameters. Network planning will have used standard propagation models and correction factors based on some trial and error methods that may be valid for some parts of the network and invalid for other parts. Then, during network deployment, some more measurements are made and the parameters are fine-tuned again. Once the network goes 'live', the drive test and NMS statistics help in further finetuning of the parameters, and it is at this point that a set of default parameters is created for the whole network. However, as the network is inhomogeneous, these default parameters may not be sufficiently accurate in all regions, thereby bringing down the overall network quality and leading to a reduction in revenue for the network operator. Radio network optimization must be a continuous process that begins during the pre-launch phase and continues throughout the existence of the network.
KPI Assessment and QOS Estimation 6.1. INTRODUCTION
GSM network usually called as „cellular network‟ (as the whole coverage area is divided into different cells and sectors) is comprised of a mobile Station (MS) which is connected to the Base Transceiver Station (BTS) via air interface. In addition to other hardware, BTS contains the equipment called Transceiver (TRX), which is responsible for the transmission and reception of several radio frequency(RF) signals to/from the end user.BTS is then connected to the base station controller(BSC) via abis interface. BSC usually handles radioresource management and handovers of the calls from oneBTS (or cell/sector) to the other BTS (or cell/sector)equipped in it. BSC is then connected to Mobile SwitchingCentre (MSC).Before GSM network installation, RF network planning(RNP) teams plan the BTS sites to cover a certain specificarea keeping in view the terrain and population. Moreover,marketing teams also help RNP teams to predict population and user traffic estimation in the days to come. RNP teams visit the areas to be covered and prepare technical site survey reports (TSSR). RNP teams use specific enterprisetools such as MapInfo, ASSETT etc to plan the sites havingdifferent frequency and miscellaneous parameter allocations.Once the sites are planned, the next phase is to acquire the required land called site acquisition phase. After siteacquisition, engineering teams install BTS sites. RNP teams also testify the planned sites with some test parameters andfrequencies to verify their planned parameters and linkbudgets etc such as signal level, signal quality, speechquality, path balance, path loss, call connectivity and so on.To cater the subscriber demand, RF optimization teamsensure minimum blocking/congestion over air interface inorder to provide better QoS to guarantee significant networkperformance.RF Optimization teams used to analyze erformance statsand evaluate QoS offered by the existing network. Since the deployment of GSM network, it has been observedpractically that there are many phenomena and issues which have been neglected in literature/available text but theyseverely influence the network performance.
6.2. EVALUATION CRITERIA GSM network performance and QoS evaluation are themost important steps for the mobile operators as the revenueand customer satisfaction is directly related to networkperformance and quality. Radio frequency network optimization (RNO) teams play a very significant and vital role in optimizing an operational network to meet the everincreasingdemands from the end users.
Usually the following tasks are assigned to RNO teams:
1) To improve the existing network coverage and capacity.
2) To improve the offered service quality for fulfillment ofcustomer demands. 3) To maintain the KPIs under pre-defined threshold. 4) To sustain the QoS criteria being imposed by country‟sregulatory authority. 5) To standardize and benchmark the network performance with that of competitor‟s network to attract more customers; keeping a balance between cost and quality. 6) To effectively reuse the available bandwidth andfrequency carriers in order to avoid internal interferenceand service degradation.
6.3. PERFORMANCE EVALUATION
GSM Network service providers analyze the network performance and evaluate service quality indicators. These indicators can be used for the following mentioned purposes: 1) To identify and locate BSS (hardware) occasional faults to ensure physical resource availability. 2) To help RF tuning teams to analyze the radio situation,detect radio network problems in one or more BTS andfinally devise a way to optimize the network and adoptcorrective actions like new frequency allocations,antenna tilt adjustment, and parameter modification inOMCR database etc. 3) To monitor system behavior and variance in terms oftraffic load, congestion, successful attempts etc. 4) To predict the upcoming traffic evolution and networkexpansions as per increasing number of mobile users. 5) To benchmark network with another competitor‟snetwork to attract more users at the cost of betterquality.
6.4.PERFORMANCE EVALUATION FLOW
Usually the network performance and indicators are badlyaffected due to wrong site integrations especially in terms ofdefinition and parameter point of view. Following are therequirements of optimization team in terms of networkoperation:
1) Frequency allocation Plan 2) Broadcast control channel (BCCH) Plan 3) Neighboring cells Plan 4) Interference (C/I, C/A) values 5) Best Server Plots
6) Site Audit Reports In order to be capable to measure the networkperformance, the patterns of a normal day should beconsidered, while for performance evaluation congestion situations should also be analyzed. Following KPIs aremore important for GSM radio network optimization & benchmarking to achieve remarkable QoS:
1) CSSR (Call Set up Success Rate). 2) CDR (Call Drop Rate). 3) HSR (Handover Success Rate). 4) TCH (Traffic Channel) Congestion Rate. 5) RX Level. 6) RX Quality.
6.5. CALL ORIGINATION PROCEDURE
Call origination process has been briefly mentioned here from counters perspective.
Step1: Channel Request or demand sent to BTS by MS inorder to set up a call. BTS then forwards the request to BSC.A counter activates in BSC upon receiving channel request from MS in a cell/BTS.
Step2: BSC sends the channel activation command to MSthrough BTS. Another counter activates here in order tocount the channel allocation in a cell/BTS.
Step3: After the channel allocation, call initiates afternecessary authentication from core/MSC end. Once the callconnected, another counter starts in order to count theabnormal call drop or failures (due to BSS or radio link problems).
6.6.KPI ASSESSMENT & QOS ESTIMATION
In order to understand how the behavior of traffic channels(TCH) and control channels (SDCCH) affects the network‟sperformance; one has to analyze TCH and SDCCH blocking when congestion in the network increases . The above mentioned KPIs are frequently used in performancejudgment and QoS estimation of the network.
1.CALL SET-UP SUCCESS RATE (CSSR)
Indicator CSSR Definition Rate of call attempts until TCH successfulassignment. Formula Number of successful seizure of SD channel by Total number of requests for seizure of SD channel. Result =[(CT01+CT02)/CT03]*100 ConditionApplied Where counter CT01 counts SD channels successfully seized for Call termination &CT02 counts SD channels successfully seizedfor Call origination.CT03 counts SD seizure requests.Where SD (usually called SDCCH stands for Stand-alonededicated control channel) and TCH stands for Traffic channel. A number of issues are related for its degradation as addressed below. a) Issues Observed: CSSR might be affected and degraded due to followingissues: 1) Due to radio interface congestion. 2) Due to lack of radio resources allocation (for instance:SDCCH). 3) Increase in radio traffic in inbound network. 4) Faulty BSS Hardware. 5) Access network Transmission limitations (For instance:abis expansion restrictions) b) Analysis & Findings: Following methods are used to diagnose CSSRdegradations as well as improvements: 1) Radio link Congestion statistics monitored using radiocounter measurement. 2) Drive Test Reports. 3) Customer complaints related to block calls have beenreviewed. c)Improvement Methodologies: Following measures significantly improve the CSSR inlive network: 1) Radio Resources enhancement (Parametermodification/changes in BSS/OMCR) such as half rate,traffic load sharing and direct retry parametersimplementation. 2) Transmission media Expansion to enhance hardwareadditions (such as TRX). 3) Faulty Hardware Replacement (such as TRX) in orderto ensure the resources availability in live network
2.CALL DROP RATE (CDR)
Indicator CDR Definition Rate of calls not completed successfully. Formula Number of TCH drops after assignment by Total number of TCH assignments. Result =[(CT04+CT05)/CT06]*100 Condition Applied Where CT04 counts TCH drops due to radiointerface problems & CT05 counts TCH drops due to BSS problems. CT06 countsnumbers of TCH successfullyseized/assigned.A number of issues are associated to its degradation asdemonstrated below. a)Issues Observed: CDR might be affected due to following issues: 1) Interference (either external or internal) being observedover air interface. Internal interference corresponds toin-band (900/1800 MHz) while external interferencecorresponds to other wireless (usually military)networks. 2) Coverage limitation is also one of the factors, whichincrease CDR values. 3) Hardware faults (such as BTS transceiver) can also beincorporated in an increasing CDR, which is a part ofBSS failures. 4) Missing adjacencies (definition in BSS/OMCR) is alsoan important factor in CDR values increment. b)Analysis & Findings: Following methods are used to diagnose the rise in CDRvalues: 1) Radio uplink statistics monitored using radio countermeasurement in order to confirm any uplinkinterference. 2) Path Balance stats which depict average of „ERP-RXPower‟ (where „ERP‟ stands for effective radiatedpower over downlink and „RX‟ stands for receivepower over uplink) also divert attention towards faultyTransceivers hardware. 3) Customer complaints related to block calls would havebeen reviewed. 4) Interference band / Spectrum scanners are also useful infinding and tracing the contaminated frequency carriersresulting in increasing CDR. 5) Drive Test Reports. c)Improvement Methodologies: Following are some methods in order to improve theCDR value up to certain pre-Defined baseline: 1) Faulty Hardware Replacement in order to ensure theresources availability in live network.
2) Frequency plans review and model tuning in order toensure the clean band carriers for serving cells. Forinstance; band conversion is done from 900 to 1800MHZ in order to cater uplink interference. Some timesconcentric cells (multi band cell having GSM & DCStransceivers) solution is also devised. 3) New site integration is also suggested in order toimprove indoor and outdoor coverage, which is usuallytermed as “Grid Enhancement”. 4) Sometimes RF repeaters are also used in order toamplify the radio signal to extend coverage area. 5) Existing coverage optimization might be done usingphysical optimization techniques. 6) Parameter tuning can also be done to improve callsustainability. This is done using OMCR terminal. ForInstance Power control parameters. Decrease emittedpower when signal receive level and quality (measuredby peer entity) are better than a given value and viceversa. 7) Frequency hopping technique is also incorporated tominimize the effect of interference. 8) Change of antenna orientation (azimuth/tilt) i.e.,increase the down tilt of interferer cell antenna.
3.HANDOVER SUCCESS RATE (HSR)
Indicator HSR Definition Rate of successful handovers (intracell +intracell). Formula No of successful [intercell + intracell] HA1 by Total number of handover requests. Result =[(CT07+CT08)/(CT09+CT10)] *100 Condition Applied Where CT07 counts no. of incomingsuccessful handovers & CT08 counts no. ofoutgoing successful handovers. CT09 countsno. of outgoing HO requests while CT10counts no. of incoming HO requests.A number of issues are related for its degradation asillustrated below: a)Issues Observed: HSR might be affected and degraded due to following issues: 1) Interference (either external or internal) being observedover air interface, which might affect on going callswitching in case of handover. 1) HA stands for Handover Attempts 2) Missing adjacencies can also result in HSR degradation. 3) Hardware faults (such as BTS transceiver) can also beincorporated as a decreasing HSR, which is a part ofBSS failures. 4) Location area code (LAC) boundaries wrongly plannedand/or defined (where Location area represents a clusterof cells).
5) Coverage limitation is also one of the factors, which decrease HSR values. b)Analysis & Findings: Following methods are used to diagnose HSRdegradations as well as improvements: 1) Radio Congestion statistics monitored using radiocounter measurement in order to confirm congestionoccurrence in a particular cell or area. 2) Neighboring plans reviewed and adjacencies auditsbeing done. 3) Drive Test reports reviewed. c)Improvement Methodologies: Following methods are employed in order to improve the HSR in live network: 1) Interference free band i.e., Spectrum analysis might be done to ensure it. 2) Adjacencies audits must be done in order to improve HSR. 3) Coverage improvement is also a vital factor of HSR enhancement. 4) BSS Resources addition (such as TRX) is also a factor for HSR improvement. 5) Parameter modification in OMCR such as Handover margin, traffic handover, power budget parameters to assist better cell handovers.
4.TCH CONGESTION RATE (TCHCR)
Indicator TCH Congestion Definition Rate of blocked calls due to resource unavailability Formula Number of calls blocked due to resource unavailable by Total number of requests. Result =(CT11 / CT12)*100 Condition Applied Where CT11 counts number of assignmentfailures when no TCH available while CT12 counts number of normal assignment requestsfor TCH establishment.A number of issues are related for its degradation, whichwould be addressed here.
a)Issues Observed: TCH (traffic channel) congestion might arise due tofollowing issues: 1) TRX Hardware faults can also be incorporated as an increasing factor in TCH congestion. 2) Increasing number of subscribers and/or traffic in a certain area also causes congestion. 3) Lesser capacity sites (mainly due to the media issue or hardware resource unavailability) also cause congestion problems.
b)Analysis & Findings:
Following methods are used to diagnose TCH congestion as well as improvements: 1) Radio Congestion statistics monitored using radio counter measurement in order to confirm congestion occurrence in a particular cell or area. 2) Customer complaints can also reveal the issue. 3) Drive Test reports reviewed. 4) WCR (Worst Cell Ratio) and CSSR (Call Set up Success Rate) KPIs also depict the TCH congestion problem. 5) Future subscriber density and growth is also a factor for the judgment of upcoming congestion.
c)Improvement Methodologies: Following measures are used to minimize the TCHcongestion in live network: 1) BSS Resources addition and expansion (including transceivers and transmission media) are important factors for TCH congestion improvement. 2) Faulty hardware maintenance or replacement can also minimize TCH congestion. 3) Deployment of moving/portable BTS (commonly called COW BTS) can be used as a better solution to improve congestion in case of foreseeable special events such as sports events, important meetings, festivals and exhibitions etc.
5. RX LEVEL: a)Issues Observed: Low RX level might arise due tofollowing issues: 1)Antenna orientation and tilt 2)High VSWR value 3)Tx power
b)Improvement Methodologies: Following measures are used to minimize the RX Level problems in live network: 1)Physical check of orientation and tilt 2)Check RF connectors and RF cables 3)Check the DRX power and connector
6.RX QUALITY: a)Issues Observed: Low RX Quality might arise due tofollowing issues: 1)Interference 2)Low Rx level 3)H/O failure 4)Assignment failure ratio 5)Hardware problem b)Improvement Methodologies:
Following measures are used to minimize the RX Quality problems in live network: 1)Define proper neighbors 2)Check DRX power and connectors 3)Check BCCH and MAIO frequency 4)Reduction of antenna height, orientation and tilt 5)Check the neighbor list and definition 6)Check the neighbor parameters 7)Check DRX and check VSWR and RF cable connectivity 8)Check DRX hardware
DRIVE TEST 7.1 Introduction The Indian telecommunication industry, with about 650 million mobile phone connections as of May 2010, is the second largest telecommunication network in the world. The Indian telecom industry is the fastest growing one in the world and it is projected that India will have a 'billion plus' mobile users by Jan 2012. The Indian telephone lines have increased from a meager 40 million (approx.) in the year 2000 to an astounding figure now. The main drivers for this extraordinary growth are because of Government‟s Telecom reforms and the stupendous success of GSM standard, which is the most popular standard for mobile telephony systems in the world. GSM differs from its predecessor technologies in that both signaling and speech channels are digital, and thus GSM is considered a second generation (2G) mobile phone system. RF Network Planning & Optimization is an ongoing activity for all wireless networks because of its highly growing market demand. By gathering, analyzing network data and revising network parameters using proper RF Planning and Optimization, efficient and effective cellular communication is achieved. RF performance parameters such as the received signal strength, receive voice quality,
carrier to interference ratio, etc., are defined for the efficient and effective functioning of the RF network. The Drive Testing (DT) is performed in GSM network to ensure the availability, integrity, & reliability of the network. How to optimize the BTS coverage area successfully is the real challenge. As we move further ahead, the need for better technologies and reliability of services, integration and cost effective solutions have become a necessity for service providers. If the optimization is successfully performed, then the QoS, reliability and availability of RF Coverage area will be highly improved resulting in more customers and more profits to the mobile telecom service providers.
Figure 6. Integrated drive-test solution consisting of a digital receiver and phone. A GPS receiver provides location information.
7.2 PARAMETERS CONSIDERED FOR THE DRIVE TEST The following parameters are primarily considered while doing the drive test: Call success ratio (CSR):
CSR is the number of successful attempts to make a call. Ideally, a network should be capable of accepting all the calls attempted to be made. The ideal value of CSR is 1 i.e. the network should be capable of accepting 100 % of the calls made. CSR is found out through a long call.
CSR = succeeded attempts/ total number of attempts
Rx level:
It is the received signal strength i.e. it is the strength of the signal received by the receiver cell phone. It can be found out through a long call as well as a short call. The acceptable value of Rx level is at least -95 dbm. Rx quality :
Rx quality is also known as speech quality. It is the quality of the speech received by the receiver cell phone. It is indicated by the Bit Error Rate or the BER. For a network to have good performance, the Rx quality should lie between 0-5. If the Rx quality exceeds 6, then the network‟s performance is not acceptable. It can be found out through a long call as well as a short call. C/I ratio:
The C/I ratio or the Carrier to Interference ratio is an important parameter in analyzing the quality of a network. The C/I ratio gives a relationship between the carrier of the network and the interference it is facing. Theoretically the C/I ratio should be at least 18 db but in practical cases 12 db is also acceptable. Handover success rate (HO Rate):
HO rate is the number of successful handovers made by a cell phone. It is the ratio of the number of successful handovers made to the total number of attempts to make a handover. To find out the HO rate, the mobile should be in dedicated mode i.e. the mobile should be on call.
HO rate = number of successful handover attempts/ total number of handover attempts.
Apart from these parameters the following parameters are also considered:
Frame Error Rate; Cell Site Database- Site Configuration, Latitude & Longitude of the site location, BSIC, LAC, Hopping Frequencies, Non-Hopping Frequencies; MAIO, Antenna Parameters like Tilt, Pattern, Gain, and Azimuth/Orientation.
7.3 DRIVE TEST TOOL: JDSU E6474A v15.2 Agilent technologies have introduced the industry‟s first integrated test solution that in a single protocol analysis tool, seamlessly combines mobile device data captured from a RF interface and from a mobile terrestrial network. Troubleshooting and optimizing today‟s networks requires a broad understanding of the network performance over multiple interfaces. Rapid growth in the number of subscribers and in-data network usage has challenged the radio access network in both RF capacity and data throughput performance measuring across the last hop from the base station to the mobile device is essential for troubleshooting and optimization and without visibility to the air interface, network operators must manually correlate data from independent drive test and protocol analysis tools. Agilent‟s E6474A drive test tool has revolutionized and simplified end to end troubleshooting. The software allows users to correlate signaling procedures from the air interface and radio access network interfaces in a single view to detect and troubleshoot problems from the mobile phone to the network.
The benefits of using this drive test tool are: Automatic correlation of data collected from both the radio and network interfaces to find endto-end performance issues more easily. Mobile device and network combined protocol decoding as well as call trace groupings to enable a complete understanding of mobile access network behaviors. Detection of lost and delayed messages from the air interface. Isolation of base station with RF performance, capacity and interference problems to perform root cause analysis. Evaluation of overall RF performance.
7.4 DRIVE TEST PRE REQUIREMENTS Before starting the drive test, the following data is to be collected from the BTS: Height of Antenna Antenna Azimuth – Orientation Antenna tilt Checking of RF connectorization Verification of serving area by existing Antenna orientations VSWR & TX Power of DRX Also, the following data from the OMC-R is to be collected: BCCH frequency Hopping Frequency MAIO & HSN Neighbor List
7.5 DRIVE TEST PROCEDURE After collecting the required information form the BTS and the OMC-R, the drive test is started. The equipment is set up in a vehicle and long calls as well as short calls are generated. A long call is a call which is generated as well as terminated by the user himself. A short call is a pre programmed call generated by the system for a very small duration, say 10 seconds or more. A long call is used to measure the handover success rate as well as the Rx quality, while CSR and Rx level are measured on a short call. The drive test is done over a distance of 3 km or more from the starting point. Various parameters are observed and recorded during the drive test. The drive test procedure is as follows: Tool may be setup for two mobiles – One for Long call and another for short calls (2 minutes). In the route map following are to be enabled for Analysis. Rx Level RX Quality Survey Markers (like H/O, DCR & H/O symbols) Cell site Database. Call statistics for the Calls in the Point -1 to be enabled. Conduct the Drive Test – covering all sectors by observing the following Parameters:
Rx Level Rx Quality Interference on BCCH & Hopping Frequencies. Handovers & Drop Calls Observe whether the nearest sector is serving or not.
The data, as per the requirements are observed and recorded. The data is analyzed for performance. The following shots have been taken while conducting the drive test:
