GSM Network Optimization Express-PS Service OptimizationV1.0

Suitable for staff with P&O skill certificate IV or lowerIssued by GSM Network P&O Dept.PS Service OptimizationGSM Network Optimization Express

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Version Introduction

VersionDateWriterAssessorTranslatorAmendment recordsV1.02009-04-09Jiang YiZheng HaoFeng Xiao YingFirst edition

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Brief IntroductionMain content of PS service optimizationIntroduction to PS service performance evaluationRelation between PS service optimization and CS service optimizationMain influencing factors of PS service performanceMain methods for improving PS service KPI

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Main content of PS service optimizationDevelopment of PS serviceFeatures of PS serviceNetwork structure of PS service Main content of PS service optimizationMain flow of PS service optimizationKPIs in PS serviceRecommended risk values of the KPIs

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1. Development of PS serviceDevelopment of packet switched PS service (PS service) falls into two phases:GPRS General Packet Radio serviceEDGE Enhanced Data Rate for GSM EvolutionGPRS was first introduced in R97 and was regarded as the extension of GSM CS system. It is applied to meet the need of accessing to network or other PS networks. Because the transmission speed of GPRS is far not up to the requirement of 3G network, 3GPP has developed Enhanced Data Rate for GSM Evolution EDGE (used in R99 and subsequent ones) as the evolution direction towards 3G.

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2. Features of PS serviceHigher requirement on radio environmentRadio transmission speed of PS service is high, so it has higher demand for radio environment. This feature is more evident with EDGE.Greater need of resourcePS service supports single subscriber to occupy more than one channels, therefore it requires more channel resource than CS service does.Complex packet transmission mechanismCell-reselection influence on PS serviceCell-reselection may cause breakup in PS service, which has obvious impact on PS service performance.Greater influence on radio side due to changes of CN and external network environmentThe nature of PS service is to connect MS to network or other networks (WAP) through GSM network, so problems with CN or external networks may bring great impact on the radio performance.

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3. Network structure of PS servicePCU in BSC supports PS serviceCN of PS service consists of SGSN, GGSN, which are connected with external networks.No obvious changes in network structure at BSS side; simply upgrade of software/hardware

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4. Main content of PS service optimizationAdjustment of PS network resourceAdjustment of each network elements resource and parameters; adjustment of resource configuration at interfaces, such as Gb or Gs, etc.Adjustment of PS radio networkOptimization of radio resource management and radio signal quality; optimization of coverage and mobile performance in different coding modeChecking of PS network configurationChecking of network parameters/ timers/alarms/configuration principlesAnalysis of PS network KPIsAnalysis of data transmission speed of GPRS, GPRS data packet retransmission rate, traffic flow at each interface, statistics of data packet mistake/loss at each interface, system histeresis, GPRS network attachment success rate, PDP context activation success rate, WAP access success rate, success rate of handover between CS and PS, bandwidth utilization rate at each interface, etc.PS data test & handling user complaints

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5. Main flow of PS service optimizationData analysisNetwork evaluationAdjust related parameters according to adjustment plan drawn from data analysis:Adjustment of parametersOptimization of radio environmentBasing on OMCR statistics and on-site test data, make analysis in details:Analysis of KPIs & adjustment suggestionsLocation of network problemsAnalysis of test indicatorsIt is a comprehensive evaluation of network operation performance and service quality; tasks to be fulfilled are:Alarm checkingData & configuration checkingNetwork load evaluationOn-site tests

System optimizationVerification & fine tuning

Observe improvement of indicators after the optimization, make fine-tuning accordingly to achieve the best situation.

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6. KPIs in PS service Traffic statisticsKPIUL/DL TBF establishment success rateRetransmission rateUL/DL TBF signaling establishment failure rateUL/DL TBF data establishment failure rateReference KPIPDCH utilization rate utilization rate of different coding modes of RLC data blocksAverage quantity of TBF on PDCHUL TBF establishment reject times

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6. KPIs in PS service Tests statisticsDT indicatorsCoverage rateCall drop rateWAP homepage login success rateFTP download/upload speedCQT indicatorsAttachment success rateAverage attachment time length PDP activation success ratePDP activation time lengthPing success ratePing time lengthAverage FTP download/upload speed

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7. Recommended values of the KPIs

KPIMeaning Reference valueUL/DL TBF establishment success rateNo. of UL/DL TBF establishment success times / No. of UL/DL TBF establishment requests *100%>90% represents that the cell is in normal condition;10% represents the cell is a bad cell (GPRS)UL/DL TBF signaling establishment failure rateNo. of abnormal released TBF / No. of UL/DL TBF signaling establishment success*100%>20% represents the cell is a bad cellUL/DL TBF data establishment failure rateNo. of abnormal released TBF / No. of UL/DL TBF data establishment success*100%>20% represents the cell is a bad cell

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7. Reference values of the KPIs**coverage rate and call drop rate depend on network situation

Item Indicator Reference valueGPRSEDGEAttach testAttach time average (s)33Attach success rate(%)90.00%90.00%PDP activation testPDP activation time (s)1.51.5PDP activation success rate(%)90.00%90.00%Ping testAverage time delay (s)22Success rate90.00%90.00%FTP testFile download speed average(KB/S)210DT WAP testWAP website login success rate90.00%90.00%WAP homepage display time(s)1212WAP webpage refresh success rate90.00%90.00%WAP webpage refresh time(s)88WAP picture/ring download success rate90.00%90.00%Coverage rate95.00%92.00%Call drop rate3.00%2.00%Average application layer throughput(KB/s)1.55

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II. Introduction to PS service performance evaluationMain content of PS service performance evaluationGeneral cares in setting up service modelsSetting of related parametersSpecial features of PS service load evaluationContent of test evaluationCommon testing tools of PS service

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Main content of PS service performance evaluationAlarm checkingservice modal setupRatio of GPRS traffic to EDGE traffic; definition of busy hourData configuration checkingCheck the correctness and reasonability of data configurationLoad evaluationGet to know radio channel resource, Abis interface resource and load situation of BSC PS processing part (PCU) through performance reports.Evaluation of PS/CS assessment criteria Comparison and evaluation of PS/CS KPIsOn-site tests & evaluation

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2. General cares in setting up service modalsservice model setupDefine busy hour of trafficDefine areas of dense trafficObserve trend of traffic volumeDefine EDGE permeation rateNormally there are two busy periods: busy hour of TBF establishment and busy hour of data flowAssessment of access KPIs is uses the busy hour statistics of TBF establishmentAdopt operators standards, if they have specific requirement for assessment time.Distribution of PS service is usually unbalanced in different areas.Areas with dense PS traffic: schools, office buildings, hotels, airports, ect..Permeation rate plays an important role in EDGE optimization. Adjust parameters according to this rate.Proportion of mobile phones supporting EDGE differentiates in different areas, and it is changing as the market changes.PS service increases rapidly, so data flow may be doubled or tripled.Be well familiar with history data, which helps estimate optimization target in a more precise way.

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3. Setting of related parametersWhether PS service is enabled?Reporting mode of MS measurementWhether CS subscriber migration is disabled?At lease 1 static channel is configured in each cell;PS channels should be configured consecutive;TSC of PDCH must be the same as BCCCheck if auxiliary timeslots are configured under V2.Whether flow-control model is set correct?Setting of parameters under flow-control model

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4. Special features of PS service load evaluationWhether configuration of Abis resource meets channel configurationPS service evaluation mainly consists of:Evaluation of radio channelsEvaluation of PCU/DSP loadConfiguration of ABIS resourceWhether channel configuration of PS service is reasonableWhether configuration of cells on DSP of PCU is reasonable

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5. Content of test evaluation GPRS Attach delay, GPRS attach success rate Test of GPRS PDP activation delay, and success rate Test of Ping delay, and success rate FTP download/upload speed WAP login/refresh delay, and success rate WAP download (picture/ring) speed, and success rate Test of Kjava download success rate Test of SMS point-to-point delay, and success rate Test of MMS PUSH delay, PUSH success rate, end-to end success rateFTP download/upload speed Test of WAP login/refresh delay, and success rate WAP download (picture/ring) speed, and success rateCQT DT

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6. Common testing tools of PS service

Common DT toolsFunctions Test phoneUtilization frequencyCDSA test tool developed by China Mobile. It can carry out tests of Attach, PDP activation, WAPMMSPING, FTP download, etc. and collect performance statistics. Besides, it supports signaling analysis on LC/MAC, LLC layer.SagemTEMSA PS service testing tool commonly used in China and other countries. It can carry out most of the testing items in PS service tests and collect statistics. Besides, it displays data flow on RLC,LLC,SNDCP, and application layer, and supports signaling analysis on layer3.Sony-Ericsson/NOKIAWanHeIts testing tool is commonly used in China, which can carry out tests of common PS service under GPRS/EDGE, and complete collection of performance statistics.SagemDingLiIts testing tool is commonly used in China, which can carry out tests of common PS service under GPRS/EDGE, and complete collection of performance statistics.Sagem

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III Relation between PS service optimization and CS service optimizationWhat do PS service and CS service optimization have in common?Compared with PS service, what does CS service focus on?In which aspects do PS service and CS service may conflict with each other?How to solve conflict in channel resource between PS service and CS service?Whats the difference between the coverage of PS service and CS service?

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1. What do PS service and CS service optimization have in common?PS service quality depends on GSM network quality. PS service has higher requirement for radio environment than CS service, so it also needs to carry out the following items:Optimization of coverage;Optimization of frequency (Frequency Hopping and BCCH have low reusability;Optimization of adjacent cells;Checking of equipment operating status

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2. Compared with PS service, what does CS service focus on? PS service has higher requirement for radio environment It emphasizes more on the reasonability of radio frequency planning It has higher requirement for coverage strength Appropriate control over cell reselection is needed. PS service requires more channel resource more precise traffic model more reasonable channel configuration reasonable configuration of PCU resource

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3. In which aspects do PS service and CS service may conflict with each other?PS serviceCS serviceOne PS service subscriber can occupy several radio channels simultaneously. Therefore it requires further expansion and improvement of system resource to achieve high speed PS service.As PS service is increasing, competition for radio channels is now the major conflict between PS service and CS service.

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4. How to solve conflict in channel resource between PS service and CS service?Preferentially satisfy resource needs of CS serviceFor cells whose CS service and PS service are both very busy, satisfy CS service needs first. At least one static PDCH should be guaranteed, so that PS service is usable.Reasonably configure dynamic PS channels, improve usability of channel resourceTraffic models of PS service and CS service are usually different, especially in busy hours. We can establish accurate traffic model of PS service, reasonably configure the static/dynamic PS channels, and make them convert to TCHs when CS service is busy, PS channels when PS service is busy, so that the utilization rate of channels will be improved.Reasonably set TRX occupation priorityPS service channels are usually configured on TRX of BCCH, some of which are configured as dynamic channels, so the BCCH TRX should have lower priority, so as to prevent dynamic PS channels from being occupied by voice channels.

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5. Whats the difference between the coverage of PS service and CS service?CS service and PS service use the same network, while the coverage of PS service is much smaller than that of CS service.GSM protocol stipulates that sensitivity of receiver under different coding modes should not be the same. Normally, MS sensitivity under coding modes MCS5MCS6 or MCS7 is -101dBm-99dBm or -96dBm, while that of CS service is -104dBm.8PSK modulation mode (coding mode MCS5-MCS9) is introduced in EDGE system. Compared with that of GMSK coding mode of CS service, its output power is lower by 4dB.

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IV. Main influencing factors in PS service performanceHow to check load condition of system resource?Why PS service has higher requirement for C/I?How much does frequency planning influence PS service?How to choose the appropriate coding mode?Why cell reselection shall be avoided in PS service?How will MS capability impact PS service performance?Why CN and external networks often influence PS service?What are the common factors influencing test results?What is flow control? Why there is flow control?How to configure flow control parameters?

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1. How to check load condition of system resource? Assessment of radio channelAssessment of PCU loadChecking configuration of Abis resourceMake assessment from the aspects of time, number of channels and number of subscribers on each channel.Plan and configure dynamic/static channels according to traffic of busy hour and idle hour.Adjust channels according to the standard that max no. of TBF on each PDCH shall not exceed 2.For cells with busy CS service, balance the traffic before PS channel planning.

PCU is the core module for processing PS service at BSC. Heavy PCU load may lead to access problems at radio side.If performance report displays too many times of DSP channel overflow, it means PCU congestion.Its usually appropriate to configure 10~15 cells on each DSP. (in iBSC)Try to balance the number of cells and traffic flow processed on all the DSPs.Sufficient auxiliary timeslots should be configured in V2 equipment.Different coding modes have different demands for Abis resource. CS1 and CS2 need only one channel of 16K, CS3 and CS4 need 2 channels of 16K.MCS35 coding modes need 2 channels, MCS6 needs 3, MCS 79 need 4 (5 is needed under V2BSC)Insufficient Abis resource may lead to slow download speed.

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2. Why PS service has higher requirement for C/I?PS services utilization efficiency of TRX is much higher than that of CS service, so it has higher requirement for radio C/I. Advanced coding mode and fast moving speed require better C/I. *The above table shows coding modes requirement for C/I, when BLER=10%;**TU3=moving speed-3Km/hTU50=moving speed-50Km/h

Channel typeCoding modeTU3(Non-FH) dBTU3 (FH) dBTU50(Non-FH) dBPDTCH/CS113910PDTCH/CS2151314PDTCH/CS3161516PDTCH/CS4212324PDTCH/MCS1139.510.5PDTCH/MCS2151212.5PDTCH/MCS316.516.517PDTCH/MCS41921.522PDTCH/MCS51814.515.5PDTCH/MCS6201718PDTCH/MCS723.523.524PDTCH/MCS828.52930PDTCH/MCS9303233

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3. What should be noticed in PS service frequency planning?At the early stage of PS service development, PDCH was configured on BCCH TRX.Its not suggested to enable power control or DTX for PDCH timeslots. PDCH on BCCH TRX (doesnt support dynamic power control or DTX) wont bring interference to the network.In frequency planning, BCCH frequency is not often reused, so it doesnt bring much interference, therefore it can provide better C/I.BCCH TRX doesnt support radio FH, which helps avoid influence of FH.

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4. How to choose the initial coding mode?Advanced coding mode has higher requirement for radio environment, we should choose appropriate coding mode according to radio environment.The recommended initial coding speed for DL is CS2/MCS6. When radio environment is poor, the initial coding speed can be appropriately reduced.EDGE provides two methods for link quality control:LA link adaptation: to retransmit with low-speed coding modes of the same coding family. IR incremental redundancy: to retransmit with the same coding mode and different perforation mode, and make joint decoding.

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5. Why cell reselection shall be avoided in PS service?Cell-reselection during PS service will cause breakup of the current service. The service has to be re-established after the reselection. Data download and upload will be ceased during cell reselection, which obviously affects the performance of PS service.Because there is no Handover in PS service, the service performance in the moving course will be affected (reselection takes 5~6 seconds, while handover only takes hundreds of milliseconds).

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6. How will MS capability impact PS service performance?The download speed of MS supporting EDGE is 3 times as much as that of MS only supporting GPRS

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7. Why CN and external networks often influence PS service?

Compared with CS service, network structure of PS service is more complex. The essence of data network is to connect MS to network or other networks (WAP) with GSM network. Once there is problem with external network or CN, the service at radio side will be greatly impacted.

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8. What are the common factors influencing test results?

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9. What is flow control? Why there is flow control?When the flow at Gb interface, which is between SGSN and BSS, is too large, a control of flow will be performed, which is regarded as flow control. Flow control is executed (only on down link) by SGSN with the control parameters provided by BSS.To avoid abandoning some of the LLC data (Data stored in the cache over a certain time will be discarded) because packet channels are too busy within a BVC on BSS (too many buffered LLC frames);To avoid abandonment of the new DL LLC data because of memory constraints (LLC buffer overflows).Aim of flow control

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10. How to configure flow control parameters?Currently two flow control modes (mode 1 and 2) are supported in our systems. Its parameters shall be carefully checked when connected with SGSN provided by other suppliers.Flow control mode must be set 2, when SGSN are provided by HW or Motorola. As for SGSN from other suppliers, there is no specific restriction on flow control mode, but usually mode 2 is recommended.

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V. Common methods of improving PS service KPIs

How to improve UL/DL TBF establishment success rate?How to reduce UL/DL TBF signaling establishment failure rate?What are the possible reasons of high retransmission rate?How to check (KPIs) when there is no access to network?What are the possible reasons of slow network speed?How to control and reduce reselection in PS service?How to improve radio environment?What is Campell algorithm? How to use it to optimize PS channels in cells?

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How to improve UL/DL TBF establishment success rate? (1)Influencing factorsBad radio environmentCorrectness of parameters settingStability of equipment & transmissionUsability of PS serviceCorresponding actions Check coverage or interferenceCheck the setting of T3168Check the setting of max No. of UL/DL TBFCheck transmission/equipment alarms (error rate)Check single board

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How to improve UL/DL TBF establishment success rate? (2)Checking alarms & noticesLocate corresponding EBRP/UPPB single board or DSP unitFrequent resource request failure means congestion problemOptimization of DSP resource distribution, expansion of channels and boardsChecking frequencyReset/change single boardCollect/print signaling; report problemsProblem range: cell/BSCBSCCellCongestion/radio problem?Checking external interferenceWeak coverageChecking antenna systemsignaling trace/printingAvoid TCH congestion during PDCH expansionXOn-site testsOptimization flow of UL/DL TBF establishment success rateHigh UL/DL data block retransmission rate means poor radio environment

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2. How to reduce UL/DL TBF signaling establishment failure rate?Influencing factorsInterference in radio environmentWrong setting of parametersStability of equipment and transmissionUsability of PS service

Corresponding actionsCheck and eliminate interference in radio environmentSetting of N3101/N3103/N3105Setting of T3191Check and eliminate transmission/equipment alarms (error rate)Check operation of single board

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3. What are the possible reasons of high retransmission rate?Retransmission rate is one important KPI to show the quality of radio environment. Normally high retransmission rate means bad radio environment.Retransmission rate is also closely related to the coding mode employed. In the same radio environment, higher coding rate brings higher retransmission rate, but the network speed isnt necessarily slow.In practical application, its recommended to observe retransmission rate under different coding mode. Under the same coding mode, higher retransmission rate means poorer radio environment.

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4. How to check the problem when there is no access to network? (1)When there is no access to network, the checking flow is as follows:Observe UL/DL TBF establishment success rateNormal?Observe PDP activation success rateObserve MS attaching to networkOptimize radio environmentEliminate hardware faults and setting mistakesCarry out on-site testsOptimize UL/DL TBF establishment success rateTest connection with external networkYesNoIts requested that the average of UL/DL TBF establishment success rate of the whole network >90%cells with UL/DL TBF establishment success rateC2serving cell+CRHProper increase in CRH value may effectively reduce reselection and improve DT down load speed.Adjust antenna down-tilt, control coverage, eliminate frequent reselectiondue to lack of main coverage cell.Enable C2 algorithm, set parameters like CRO,PT, etc., to reduce reselection.Common methods as in CS:Methods different from CS:

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7. How to improve radio environment?Radio environment is the generic term for coverage, interference situations. Improvement in radio environment is quite helpful in improving indicators of PS service.

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8. What is Campell algorithm? How to use it to optimize PS channels in cells? (1)Basing on the comprehensive consideration of all the services, Campell algorithm constructs an equivalent service (which is also regarded as intermediary service or virtual service). Computer system provides channel number of the service and the total equivalent traffic, then outputs the capacity estimation of the mixed services.PS service contains different services, whose bearing rate and traffic are also different.Comprehensively consider resource needed by each service (no. of channels-supposing bandwidth of each channel is 10Kbps), and equivalent traffic (expected time to be occupied)Campell algorithm integrates all the services and convert them to one equivalent service (virtual service), then outputs its traffic Ex and service weight Ax.Equivalent service traffic Ex obtains the number of equivalent channels through ErlB, then multiplies it with comprehensive service weight and gets the actual number of channels.1234

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8. What is Campell algorithm? How to use it to optimize PS channels in cells? (2)In actual optimization, fill out the configuration information in the following EGPRS template.Log on http://tools.cmdi.chinamobile.com/campell, register and enter EGPRS radio channel configuration, choose EGPRS radio channel calculation, fill it out step by step, then export the result of PS channel planning.

CellIDRLC throughput of GPRS busy hours(kbytes)RLC throughput of EGPRS busy hours(kbytes)cell traffic of busy hours(erl)total cell TCHsCS1 usage scale01CS1 retransmission rate01CS2 usage scale01CS2 retransmission rate01CS3 usage scale01CS3 retransmission rate01CS4 usage scale01CS4 retransmission rate01MCS1 usage scale01MCS1 retransmission rate01MCS2 usage scale01MCS2 retransmission rate01MCS3 usage scale01MCS3 retransmission rate01MCS4 usage scale01MCS4 retransmission rate01MCS5 usage scale01MCS5 retransmission rate01MCS6 usage scale01MCS6 retransmission rate01MCS7 usage scale01MCS7 retransmission rate01MCS8 usage scale01MCS8 retransmission rate01MCS9 usage scale01MCS9 retransmission rate01

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