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The document discusses drive test analysis for mobile networks. It describes the key elements of an effective drive test program including understanding network performance using call and data metrics. The drive test process involves defining test routes and clusters, collecting data, analyzing key performance indicators (KPIs) like call setup success rate and throughput, and troubleshooting issues. Defining test cases, KPIs, and categorizing failures is important for understanding genuine network problems versus measurement errors.

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Drive Test Analysis Objectives After this module the delegate shall be able to:- • Understand the different elements required for an effective drive test program • Understand how all aspects of drive data can be used to obtain a view of network performance • Differentiate between genuine (RF) and non-genuine (system) failures • Understand the KPIs that can be obtained
Drive Test Process Cluster Preparation •Define Cluster •Define Drive Route Data Analysis •Levels of Reporting •Failure Type Breakdown •Post Processing functionality •KPI Gap Analysis Data Preparation and Collection •Services to test •KPI definitions •Equipment •Exclusions •Call Patterns •OSS Alarms •Network Stats Trouble Shooting •Root Cause Analysis •Corrective Action •Further data logging (maybe) • New Site Integration • RF Tuning • Network Optimisation • Network Benchmarking (Golden Routes) Why Drive the network?
Drive Test Analysis – Test Equipment • Ne o Outdoo Multi ith UE s, “ a e a d GP“ Land Unit NQMP FTP Server • Important to drive with Call logging equipment and 3G and 2G scanner in the same vehicle
Drive Test Analysis – Test Equipment, Scanner • The purpose of using the RF scanner is to be able to scan and measure all used carriers/cells and their corresponding DL scrambling codes. – For low coverage areas – For antenna installation problems – For missing neighbours – For coverage optimisation – With the scanner you can get the following info from the surrounding cells: • Different Scrambling codes • CPCIH RSCP value (dBm) • CPICH EcNo value (dB)
Drive Test Analysis – Test Equipment, UE • The Scanner measures all SCs, whereas the UE only measures SC signals from the cells that the system has informed/ordered the UE through the BCH (neighbour list) or via the easu e e t o t ol essage. – RSCP Active/Monitored Set – Carrier RSSI – Ec/No Active/Monitored Set – UL/DL Data Throughput – The BLER downlink – Pilot BER – Random Access Initial Tx Power – Random Access Preamble Count – Random Access Preamble Step – Random Access Tx Power – SIR target (UE dependent) – UE Tx Power – Call Statistic: AMR, CS and PS data calls
Drive Test Analysis – Call Patterns AMR Call Mobile Originated Calls (MOC) • 2 min calls • 30 sec idle • UE in Dual mode (2G/3G) Mobile Terminated Calls (MTC) • 2 min calls • 30 sec idle • UE in dual mode (2G/3G) • Enough call samples have to be made to make the measurement statistically valid. • In a 50 call sample one dropped call will cause a change in performance of -2% • In a 500 call sample one dropped call will cause a change in performance of -0.2% • Call length should be defined at the beginning • We can use different call testing patterns for different optimisation techniques • Short Calls (for Calls setup performance and delay) • Long calls (for Drop call performance and SHO performance) PS Call • GPRS Attach, • PDP Context Activation • FTP Download (1MB file)/FTP Upload (500 KB file) • PDP Context Deactivation • GPRS Detach • Alternate download and upload with 30 sec idle time • Session is upload or download • UE in Dual mode (2G/3G)
Drive Test Analysis – Defining KPIs AMR Statistics Threshold KPIs MOC Setup time 5 sec MOC CCR 99 % RAW END USER Event Count Ratio Count Ratio Call Attempts 132 122 Call Setup Success Rate 108 81.8% 108 88.5% Call Setup Failure Rate 24 18.2% 14 11.5% Failures due to Tool (TSF) 10 41.7% Failures due to Core Problem 10 41.7% 10 71.4% Failure ASU (Sync) Problem 2 8.3% 2 14.3% Failure due to Low Coverage Levels 2 8.3% 2 14.3% Call Setup Success and Setup Time > 5s 7 6.5% 7 6.5% Long Setup due to slow cell reselection 0.0% 0 0.0% Long Setup due to clash with InterRAT reselection 0.0% 0 0.0% Long Setup due to Unknown (suspect UE) 0.0% 0 0.0% Long Setup due to Unknown 0.0% 0 0.0% Average Call Setup Time 3.66 3.66 Call Completetion Rate 105 97.2% 105 97.2% Call Drop Rate 3 2.8% 3 2.8% Call Drop Poor 3G Coverage 1 33.3% 1 33.3% Call Drop on GSM due to Interference 2 66.7% 2 66.7% Overall Call Completion Rate 105 79.5% 105 86.1% ISHO Attempt 14 14 ISHO Success 14 100.0% 14 100.0% ISHO Failed 0 0.0% 0 0.0% ISHO Failed cause physical channel failure 0 N/A 0 N/A PS Data KPI Report KPI Thresholds Value Unit Attach Time 4 sec PDP Activation Time 2 sec FTP Download Throughput 110 kbit/s FTP Upload Throughput 55 kbits Signalling Statistics Count Success rate Attach Attempt 155 Attach Success 140 90.32% Attach Time more than threshold 5 3.57% Attach Time less than threshold 135 96.43% Attach Failed 15 9.68% Average Attach Setup Time 1.36 Activate PDP Context Attempt 124 Activate PDP Context Success 124 100.00% Activation Time more than threshold 2 1.60% Activation Time less than threshold 123 98.40% Activate PDP Context Failed 0 0.00% Average PDP Context Activation Time 0.96 FTP Download Attempts 51 FTP Download Success 48 94.12% FTP Download throughput more than threshold 25 52.08% FTP Download throughput less than threshold 23 47.92% Average FTP Download Throughput 107.02 FTP Upload Attempts 32 FTP Upload Success 30 93.75% FTP Upload throughput more than threshold 20 66.67% FTP Upload throughput less than threshold 10 33.33% Average FTP Upload Throughput 55.53 Data Transfer Cut-off Ratio 6.02% PDP Context Dropped 4 3.23% Deactivate PDP Context Request 121 Deactivate PDP Context Accept 121 100.00% Deactivate PDP Context Failure 0 0.00% Detach Request 281 Detach Accept 129 45.91% Overall Data Session Completion Rate 78 62.90% RAU Statistics Count Success rate RAU Attempt 22 RAU Success 13 59.09% RAU Failed 9 40.91% Cell Reselection Statistics Count Success rate Cell Reselection from UMTS to GSM Attempts 2 Cell Reselection from UMTS to GSM Success 1 50.00% Cell Reselection from UMTS to GSM Delay E2E 15.27 Cell Reselection from UMTS to GSM Delay Signalling N/A Cell Reselection from GSM to UMTS Attempts 1 Cell Reselection from GSM to UMTS Success 0 0.00% Cell Reselection from GSM to UMTS Delay E2E N/A Time in System Seconds Ratio GSM 171 1.02% UMTS 16559 98.98% • Need to agree •What a figu es ill o tai •What E d Use ill o tai •Other cuts of Data
KPI-08 PS PDP context activation •Same as 10 •350 occurrences •PS PDP activation trigger point: •UE not PS attached •UE sends 1st ‘RRC Connection Request’ •PS PDP activation completion trigger point: •UE receives ‘RRC: Downlink Direct Transfer (SM: Activate PDP Context Accept)’ •Successful completion if: •UE receives ‘RRC: Downlink Direct Transfer (SM: Activate PDP Context Accept)’ •Cluster_PDP_Context_Activation_SR_% = PDP Context Activation Completion / PDP Context Activation Attempts *100 98% KPI-09 PS throughput downlink •Repeated FTP calls, 1 Mbyte file download, 1 Ue •384 kbps •Average throughput •350 calls •Data Session Set-up trigger point: •UE receives 1st DL packet •Data Session Completion trigger point: •UE receives last packet •Session output: •Average downlink throughput •Cluster_PS_DL_Throughput = Average Throughput Over Data Sessions 200 Kbps KPI ID Criteria Test Description Trigger Statistics Success Rate KPI-01 Voice 12.2 kbps AMR CCSR •1 MOC+ 1 MTC in the same van, 2 Ues •1 call (party A to party B, party A terminates the call): 15 seconds call + 15 seconds idle. Party A to be logged •350 calls •Call set-up trigger point: •Party A’s UE sends 1st ‘RRC Connection Request’ •Call completion trigger point: •Party A’s UE receives ‘RRC Connection Release (cause normal)’ •Successful completion if: •15 sec call duration (from RRC Conn. Request to RRC Conn. Release) •Party A’s UE receives ‘RRC Connection Release (cause normal)’ •Cluster_AMR_Overall_CCSR_% = Call Completion / Call Attempts *100 98% KPI-02 Voice DCR •1 MOC to PSTN, 1 Ue •1 call: 90 seconds call + 15 seconds idle •350 calls •Call Set-up trigger point: •3G UE receives ‘RRC: Downlink Direct Transfer (Alerting for NZ, Connect Acknowledge for AU)’ •Call completion trigger point: •3G UE receives ‘RRC Connection Release (cause normal)’ •Successful completion if: •90 sec call duration (from RRC Conn. Request to RRC Conn. Release) •3G UE receives ‘RRC Connection Release (cause normal)’ •Cluster_AMR_Overall_DCR_% = 1 - Call Completion / Set up Calls *100 < 2% KPI-03 Voice 3G- 2G Handover (inter- & intra-MSC) •1 MOC to PSTN, 1 Ue in dual mode •1 call: continuous call until 3G2G coverage border is passed •50 occurrences as a minimum •3G to 2G HO start point: •UE receives ‘RRC: Handover From UTRAN Command’ •3G to 2G HO completion trigger point: •UE sends ‘Handover Complete’ to 2G BSS •Successful completion if: •UE sends ‘Handover Complete’ to 2G BSS •Cluster_Voice_3Gto2G_HO_Overall_SR_% = HO Completion / HO Attempts *100 98% Drive Test Analysis – Test Case definition Examples … Short calls to test Call Setup Success Long calls to test Drop call ratio
Need to Define the KPI measurement (from Drive test) • Call Setup Success - CSSR (voice, circuit switched data) – Successful all setup ea s that DL/UL Di e t T a sfe CC: Ale ti g essage is e ei ed UE. • Call Setup Time (voice, circuit switched) – Call setup dela is easu ed f o L3 essages, sta ti g f o ‘‘C Co e tio “etup essage to DL Di e t T a sfe CC: Ale ti g essage. • Call Drop (voice, circuit switched) – A dropped call occurs. The call will be dropped in case RRC connection release (not normal release) message has been send from RNC to UE. • Session Setup Success (packet switched) – This is related to PDP context activation. Successfully activated PDP context means that activate PDP context accept message has been sent from RNC to UE (RRC: downlink direct transfer (SM:activate PDP context Accept)). • Session Setup Time (packet switched) – The sessio setup ti e is the dela et ee the ti e the UE se ds the data sessio a ti atio request until GPRS attach and PDP context activation has been successfully completed. • Session Drop (packet switched) – Session drop rate can be defined as the number of successful PDP deactivations against number of successful PDP activations.
Definition of Call Set-Up Success Rate (CSSR) UE RRC: Connection Request RRC Connection Setup phase Resource Reservation in RNC, BTS, Transmission RRC: RRC Connection Request Setup RRC Connection Access phase RNC waits reply from UE RRC: RRC Connection Completed RRC: Initial Direct Transfer cm service request RANAP: Initial UE Message DIRECT TRANSFER (Call Proceeding) RANAP: RAB Assignment Request RRC: Radio Bearer Set-up RRC: Radio Bearer Setup Complete RAB Connection Setup phase Resource Reservation in RNC, BTS, Transmission RANAP: RAB Assignment ResponseDIRECT TRANSFER (Alerting) BTS RNC CN DIRECT TRANSFER (Connect) DIRECT TRANSFER (Connect Acknowledge) RAB Connection Access phase RNC waits reply from UE Call Set-up Success Rate Call Set-up Time Successful call setup means that DL/UL Di e t T a sfe CC: Ale ti g essage is received by UE
Definition of the Call Completion Rate (CCR)UE RNC MGWNode B Call Established Iu Release Command Iu Release Complete RRC Connection Release RRC Connection Release Complete RRC Connection Release Complete RRC Connection Release Complete Radio Link Deletion Request Radio Link Deletion Response ALCAP: Release Request ALCAP: Release Response ALCAP: Release Request ALCAP: Release Response Call Released Direct Transfer (Disconnect) Direct Transfer (Release) Direct Transfer (Release Complete) DIRECT TRANSFER (Alerting) DIRECT TRANSFER (Connect) DIRECT TRANSFER (Connect Acknowledge) Call Drop Rate Call Duration
Definition of Session Setup Time - PSUE CN RNCWBTS INITIAL DIRECT TRANSFER (Attach Request) Downlink Direct Transfer (Authentication & Ciphering Request) UE already has an RRC connection SCCP: Connection Request SCCP: Connection Confirm RANAP: Authentication & Ciphering Request Security Mode Command Uplink Direct Transfer (Authentication & Ciphering Response) RANAP: Authentication & Ciphering Response RANAP: Security Mode Command Security Mode Command RANAP: Security Mode Command RANAP: Common ID Downlink Direct Transfer: Identity Request RANAP: Identity Request Uplink Direct Transfer: Identity Response RANAP: Identity Response Downlink Direct Transfer: Attach Accept Direct Transfer: Attach Accept Uplink Direct Transfer: Attach Complete Direct Transfer: Attach Complete INITIAL DIRECT TRANSFER (Active PDP Context Request) DIRECT TRANSFER (Active PDP Context Request) DIRECT TRANSFER (Active PDP context Accept) RANAP: RAB ASSIGNMENT REQUESTRRC: Radio Bearer Set-up RRC: Radio Bearer Set-up Complete RANAP: RAB ASSIGNMENT RESPONSERRC: Measurement Control INITIAL UE MESSAGE (GPRS Attach) Session Set-up Time
• Non-genuine failures – Measurement system fault (Collection Tool or Analysis) • Genuine failures – RF issue (Coverage / Interference / Poor dominance) – Missing neighbour – System issue WBTS – System issue RNC – Core network issue – System – (Unknown ) WBTS RNC Core NW UE Iub Iu It is beneficial to categorise call failures during the analysis and reporting Failure Breakdown
• The KPI measurement conditions should be used to define exclusion areas during drive test for acceptance of a cluster. • All failures happening in those area, that do not respect the coverage requirements should be discarded. Signal above RSCP threshold Signal below RSCP threshold Signal above Ec/No threshold Signal below Ec/No threshold-110dBm - -95dBm -80dBm Time RSCP Call OK Call OK Call OK Call NOK Call NOK -12dB -5dB -20dB Ec/No Threshold Exampleof Call SuccessCriteria Discard sample   Call-(A) Call-(B) -110dBm - -80dBm Time RSCP Call OK Call OK Call OK Call NOK Call NOK - -5dB -20dB Ec/No Threshold Exampleof Call SuccessCriteria Discard sample   Call-(A) -110dBm - -80dBm Time RSCP Call OK Call OK Call OK Call NOK Call NOK - -5dB -20dB Ec/No Threshold Exampleof Call SuccessCriteria Discard sample  -110dBm - -80dBm Time RSCP Call OK Call OK Call OK Call NOK Call NOK - -5dB -20dB Ec/No Threshold Exampleof Call SuccessCriteria Discard sample   Call-(A) Call-(B) Failure Breakdown
Failure Breakdown Call Set-up Failures Breakdown - Benchmark Drive 5% 20% 0% 5% 0% 0% 10% 5% 35% 15% 0% 5% Equipment Registration Clash Core Network Fail in 2G RAN (fixed in next release) Site maintenance (TMUK) RAN (Other) Missing neighbours 3G RF slow cell Reselection site configuration & maintenance (Nokia) Other Call Set-up Failures Failure Type total % Equipment 0 0.0 Registration Clash 0 0.0 Core Network 0 0.0 Fail in 2G 6 19.4 RAN (fixed in next release) 0 0.0 Site maintenance (TMUK) 16 51.6 RAN (Other) 0 0.0 Missing neighbours 0 0.0 3G RF 3 9.7 Slow cell reselection 0 0.0 site configuration & maintenance (Nokia) 0 0.0 Other 6 19.4 Call Setup Failure Breakdown - Final Drive 0% 0% 0% 19% 0% 0% 0% 10% 0% 0% 19% 52% Equipment Registration Clash Core Network Fail in 2G RAN (fixed in next release) Site maintenance (TMUK) RAN (Other) Missing neighbours 3G RF Slow cell reselection site configuration & maintenance (Nokia) Other Call Set-up Failures Failure Type total % Equipment 1 5.0 Registration Clash 4 20.0 Core Network 0 0.0 Fail in 2G 1 5.0 RAN (fixed in next release) 0 0.0 Site maintenance (TMUK) 0 0.0 RAN (Other) 2 10.0 Missing neighbours 1 5.0 3G RF 7 35.0 slow cell Reselection 3 15.0 site configuration & maintenance (Nokia) 0 0.0 Other 1 5.0 AMR Call Setup Failures
Drive Survey Analysis Process Summary Diagram
Non Genuine Call Setup Failure Scenarios • Measurement systems are often not perfect and may introduce errors in data collection or analysis • Examples of non-genuine failures seen: – Uplink: CM Service Abort within milliseconds from CM Service Request – Call atte pt du i g Lo atio A ea update LA lash – Use i itiated UL CC Dis o e t – Location Area update interpreted as call setup failure – Cell reselection back to 3G from 2G interpreted as call setup failure
Non Genuine Call Setup Failures • Measurement system failures by drive test tool – CM “e i e A o t ithi illise o ds f o CM “e i e ‘e uest – No time for response from NW
Non Genuine Call Setup Failures • Measurement system failures by drive test tool • Call attempt during Location Area update (LA update clash) LA Update Request Call attempt RRC Release
Non Genuine Call Setup Failures Measurement system failures by Actix workbook – Successful or failed Location Area update interpreted as call setup failure RRC Connection for Inter-RAT cell reselection LA Update Request
Non Genuine Drop Call Scenarios Measurement system failure examples: – Drive test tool • Use i itiated UL CC Dis o e t – Analysis Workbook • Inter-Rat cell reselection from 2G to 3G interpreted as drop call • Complete (e.g 90 seconds) call on either 3G or 2G • No drop in the log file / same drop listed twice
Genuine Call Setup Failure Scenarios – RF issue • Interference / Dominance / Coverage • Missing neighbour – System Issue - BTS • No espo se to ‘‘C Co e tio ‘e uest • ‘‘C Co e tio ‘eje t to ‘‘C Co e tio ‘e uest – System issue - RNC • CC Dis o e t afte Call P o eedi g due to DL ‘‘C Co e tio ‘elease – Core NW • CM “e i e A o t afte CM “e i e ‘e uest – System issue (test number) • CC Dis o e t afte CC P og ess
Genuine Drop Call scenarios • RF issue – Interference / Dominance / Coverage – Missing Neighbours • System issue BTS – “udde CC Dis o e t due to DL ‘‘C Co e tio ‘elease – Sudden drop to idle, no disconnect messaging • System issue RNC – “udde CC Dis o e t due to DL ‘‘C Co e tio ‘elease
Failure Location • Analyse the signalling flow to find the location of failure and potential cause • UE log may only capture some of the messages
DRNCUE CNSRNCWBTS 2. RRC connection set-up 6. Service Established 7. Branch addition/deletion & Active set update 1. Cell search, BCCH decoding & RACH access 3. UE <--> CS-CN signalling 4. RAB set-up 8. Service Released 5. UE <--> CS-CN Signalling AMR CS Call Phases
Start Best se e s RSCP > -102dBm Best se e s Ec/No > -12dB Coverage Optimization Dominance Optimization AICH(ACK) received? Yes Missing Neighbour ? Neighbour list Optimization No No No Yes UL coverage & RACH parameter. Optimization (changing serving cell) ‘‘C Co e tio “etup e ei ed? (DCH ‘‘C Co e tio setup Co pleted se t f o UE? “Radio Bearer setup failu e ‘e ei ed? Report & Finish Check failure cause (Not radio problem/cell update) Report & Finish (Check failure cause) AC optimization (check PrxNoise & interferer around BTS) Report & Finish ‘‘C “etup ‘eje t e ei ed? Yes No Yes Yes Yes Report & Finish (Reason of problem: L1 sync fail) Report & Finish (Check failure cause) Call Setup Failure Analysis Process A B C D E Yes Yes No No No No
Call setup failures – RF issue • RF issue? Coverage / Interference / Dominance A See the example in Module 3 – RF Optimisation
Call setup failures – Missing Neighbour A • Missing neighbour analysis over the whole route (3G-3G, 3G-2G) • Search for failures due to missing 3G-3G neighbours • Search for failures due to missing 3G –2G neighbours – It is suggested to place 2G scanner to the test vehicle
Call Setup Failure Analysis- Block B - • The purpose of this activity is to check the Random Access Process is working adequately by investigating whether AI (Acquisition Indicator) has been received through DL AICH • If AICH was not received by UE, the cause of the problem can be classified into: – Inadequate RAN parameter related to Random Access: RAN parameter settings for pre-amble transmission or open loop power control information is not correct. – UL Coverage limit: UL coverage of UE is smaller compared to serving cells DL o e age so that UE s T po e a ot ea h se i g ell. B
Call Setup Failure Analysis- Block B -UE WBTS RNC Preamble/RACH Acquisition Indicator/AICH RRC: RRC Connection Request/PRACH NBAP: RADIO LINK SETUP REQUEST RRC: RRC CONNECTION SETUP/FACH L1 Synchronisation NBAP: SYNCHRONISATION INDICATOR RRC: RRC CONNECTION SETUP COMPLETE/DCH UE in CELL_DCH state NBAP: RADIO LINK SETUP RESPONSE B
RACH Process Downlink BS L1 ACK / AICH Uplink MS Preamble 1 Not detected Message partPreamble 2 PRACH_preamble_retrans # PRACH preambles transmitted during one PRACH cycle without receiving AICH response UEtxPowerMaxPRACH … … … … RACH_tx_Max # preamble power ramping cycles that can be done before RACH transmission failure is reported PowerRampStepPRACHpreamble PowerOffsetLastPreamblePRACHmessage Initial preample power: •Ptx = CPICHtransmissionPower-RSCP(CPICH) +RSSI(BS) + PRACHRequiredReceivedCI B
Call Setup Failure Analysis- Block B- • Solutions for RACH optimisationMax UE Tx power hit the UE_P_MAX(24dBm)? To increase PRACH_Preamble_retrans Or PowerRampStepPRACHPreamble No Yes Is UL Interference abnormally HIGH? Yes No Report there might be an interfering source Nearby the serving cell Change the Serving cell to cover the problem Area => UE is too far to reach the serving cell B
Call Setup Failure Analysis- Block BB Open loop Power Control parameters from RACH Info message
Call setup failures – System issue BTS• No espo se to ‘‘C Co e tio ‘e uest – Good RF conditions – W o g MHA setti gs o a le loss setti gs a ause the site ot to hea the UE – PrxNoise statistics, receive link parameters and HW units to be checked (faulty MHA, wrong MHA parameters, wrong cable / feeder loss parameters, faulty units) C
Call setup failures – System issue BTS• ‘‘C Co e tio ‘eje t afte ‘‘C Co e tio ‘e uest – Good RF conditions – Admission Control can reject too many (or admit too many) connection requests due to wrong PrxNoise measurements. – PrxNoise statistics, receive link parameters and HW units to be checked C
Call Setup Failure Analysis • UE has the appropriate DL/UL coverage but if RNC does not allow to set up the RRC connection of the requested RAB (Radio Access Bearer), Call setup will fail. • Admission Control (AC) is involved in RRC connection setup. AC can reject RRC reject RRC connection Setup due the DL Load, UL load or DL Spreading codes – Marginal Load Area: • If measured UL (PrxTotal) or DL (PtxTotal) load exceeds target thresholds (PrxTarget and PtxTarget) AC can still admit new RAB to the cell if a new non-controllable load keeps below target thresholds (in practice this means that AC can admit only new controllable load RABs i.e. NRT RABs) – Overload Area: • If measured UL (PrxTotal) or DL (PtxTotal) load exceeds overload thresholds (PrxTarget + PrxOffset and PtxTarget + PtxOffset) then AC can't admit more RABs to the cell C
Call Setup Failure Analysis • During the pre-optimization phase it is unlikely that AC will stop an RRC connection setup during the drive testing because there are normally very few UEs in the network. (Traffic loading is trivial) • However, it should be checked that measured PtxTotal and PrxTotal are less than PtxTarget (e.g. 40dBm) and PrxTarget (e.g. 4dB, 60% loading) respectively. • If DL AC does not allow RRC setup check the Tx power of WBTS, # of channels transmitted, Signaling messages. • If UL AC does not allow RRC setup: Check out if there is an interfering source nearby the serving cell. C
Call Setup Failure Analysis To check if Layer 1 Synchronization (slot/frame sync) has failed • If ‘‘C Co e tio “etup as e ei ed UE ut UE does ot se d ‘‘C Co e tio “etup Co pleted , e ill epo t L s h o izatio failu e a d have to check L1 system messages. D
• CC Dis o e t afte Call P o eedi g • Good RF conditions • Failures in RAB setup occur et ee the ‘AB Assig e t ‘e uest ei g received from Core Network and the RAN sending out Radio Bearer Setup. Therefore the failure is between BTS and Core Network. ECall setup failures – System issue RNC
• CC Dis o e t afte Call P o eedi g o t. • An example (site shows high values on counter ‘AB_“TP_FAIL_C“_VOICE_BT “ du i g the d i e test • In the recent check the counter showed no failures. ECall setup failures – System issue RNC
Call setup failures – Core NW Security Mode Command Common ID UE RNC MGWNode B RRC Connection Establishment Initial Direct Transfer (CM Service Request) SCCP: Connection Request SCCP: Connection Confirm Location Reporting Control • RRC: Initial Direct Transfer message is sent using acknowledged mode RLC to the CS core domain. Routing is to be based upon the local P-TMSI • The NAS message is not read by the RNC but is forwarded to the multimedia gateway. The NAS message includes the IMSI as a UE identity • The SCCP: Connection Request message establishes the connection orientated signalling link in the same way as it was for the RRC connection phase.This does not reserve any resources for the AMR call itself. • The Connection Confirm message identifies the RNC with a destination local reference which is the same as the source reference within the Connection Request message • The Connection Confirm message identifies the CS core with a source local reference • The CS core sends a RANAP: Location Reporting Control message to the RNC requesting information regarding the location of a particular UE • The RANAP: Common ID message specifies the IMSI belonging to the UE • The Security Mode Command message triggers the start or stop of ciphering and integrity protection. • CM “e i e A o t afte CM “e i e ‘e uest • Good RF conditions • “e u it Mode Co a d -message not received by UE, thus the failure is believed to be at Core Network. E
Call setup failures – System Issue (test number)• CC Dis o e t afte CC P og ess • Cause: recovery on timer expiry • The call goes via IN SCP to a recording. • A static test was done by Nokia Customer Care and in few instances the call dropped after 30 seconds of recording passed. Hence the problem is associated with the test number not the RAN 30 sec Cause: recovery on timer expiry E
Start Best server’s RSCP > -102dBm Best server’s Ec/No > -12dB Coverage Optimization Dominance Optimization Yes Yes Neighbour list Optimization Missing Neighbour Yes Call Drop Failure Analysis Process SHO Failed Investigate possible BTS or RNC problem No ISHO Failed No ISHO Failure Analysis B YesSHO Failure Analysis A No No No
Call Drop Failure Analysis Process (SHO Analysis) DL ASU received Yes SC Clash UE Tx Power Max Fix SC Clash CPICH Optimisation Uplink Interference Load Optimisation/ External Interferer Link Unbalanced Yes Yes Yes Yes No No No Yes Inter RNC HOCheck Iur Yes Congestion on target cell Load Optimisation No Yes No Check neighbour definition parameters Check RF Levels NoDL Tx Power Max Yes Start D C
Drop call failures – RF issue • RF drops mostly due to poor dominance or interference • Poor coverage could lead to ISHO, although poor dominance or interference can cause ISHO to fail. • Rapid field drop can cause drop due to coverage • Poor dominance or interference can cause Compressed Mode (CM) to start even if RSCP is still good. • In CM UE transmits with higher power (more interference) and spends less time on 3G (less accurate measurement reporting) • Poor dominance or interference can lead to Active Set update failures and eventually to drop call. Poor dominance causes Active Set update failures A
Drop call failures – RF issue DL synchronisation is lost -> UE has stopped transmitting TrChAgg and DL DPCCH BER high A
Drop call failures – RF issue Transport Channel BER. Btw UE<->RNC (MAC layer) Sometimes DPCCH BER (btw UE<->WBTS) can be a better indicator of what's happening to the dedicated channel than the CPICH EcNo, in particular in the case that power control may not be tracking well Fairly good CPICH Pilot EcNo A
Drop call failures – System issue BTS Drop to IDLE B • Sudden drop to idle, no disconnect messaging – Site malfunctions to be checked – In the example below site had faulty unit (WTR)
Drop call failures – System issue RNC “udde ‘‘C Co e tio ‘elease DPCCH BER • CC Dis o e t due to DL ‘‘C Co e tio ‘elease • No response to UL Measurement Reports • In the example site had no alarms, good RF & BER • Not able to add SC265 to Active Set, next call on the same cell => no failure. • Difficult to troubleshoot if the failure does not happen systematically => follow up in the next weeks drive / do a separate drive test in the area B
Drop call failures (SC conflict) • Sudden drop to idle mode (no disconnect messaging) • Cause of the failure: overshooting site and SC reuse • Short term solution to add overshooting neighbour in ADJS definitions Cell ABC, SC258 Transport channel BLER 100% C
Drop Call - Uplink Interference UL interference from the SIB7 message D
Drop Call – Link Balance• UL & DL Power Control commands can help indicating problems in link balance. • PC frequency is 1500 Hz, thus ideally the sum of PC commands to increase or decrease power is 1500 • E.g. if the sum of UL PC commands is < 1500, this would indicate UE is starting to loose synchronization • in Compressed Mode there is less PC commands, UE spends time on 2G UE RX power control message: DL reception weak -> UE is ordering WBTS to increase power. Sum of UL PC commands < 1500, UE not receiving all the PC commands. D
Drop call failures – System issue RNC or BTS ? • CC Dis o e t due to DL ‘‘C Co e tio ‘elease is just a consequence of failure which can be due to different reasons – From UE point of view L3-messaging does not identify the point of failure distinctly – BTS or RNC failure? => Suspect BTS first, then RNC • Rule out BTS failures – Check the site performance from Counters (Iub, Service level, cell resources SHO, etc) and that site is carrying traffic – PrxNoise, receive link parameters, alarms – SC–reuse – UE performance ? • Identified causes for Active Set Update failure – Deaf sites P Noise – Faulty HW – SC-reuse
Drive Test Analysis – Reporting Levels Optimiser • Very High Level KPIs that give a users perception of the network (Network KPI) • KPIs that provide an Engineering view of network performance e.g CSSR, CDR, OCSR, SHO performance. (KPIs required for each optimisers area) • Highly detailed KPIs that give a detailed picture of network performance at an Engineering level and allow root cause analysis Regional Optimisation Manager Senior Management • Processing Drive Data to provide the information required at the bottom level means that the higher level information can be easily extracted • The different reporting levels may want to see KPIs based on different cuts of the data (e.g. raw or end user)
KPI reporting • Non-ge ui e failu es to e e o ed f o the a KPI s Call Completion Call SetUp Success Rate 97.5% 97.9% Call Drop Rate 1.3% 0.3% Overall Call Success Rate 96.2% 97.6% Call Connection time <= 8s 97.6% 97.6% No of Call Attempts (within coverage) 634 625 No of Call Setup Failures 16 13 No of Successful Call Setups 618 612 No of Call Drops 8 2 No of Completed Calls 610 610 Call Completion Call SetUp Success Rate 97.5% 97.9% Call Drop Rate 3.1% 2.1% Overall Call Success Rate 94.5% 95.9% Call Connection time <= 8s 97.6% 97.6% Call Completion Call SetUp Success Rate 98.1% 98.6% Call Drop Rate 1.3% 0.3% Overall Call Success Rate 96.8% 98.2% Call Connection time <= 8s 97.6% 97.6% No of Call Attempts (within coverage) 630 621 No of Call Setup Failures 12 9 No of Successful Call Setups 618 612 No of Call Drops 8 2 No of Completed Calls 610 610 Non-genuine call setup failures removed Non-genuine drops removed Fi al KPI s Fi al KPI s
KPI reporting • Weekly KPI trends (non-genuine failures should be excluded) All Routes 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% w k41 w k42 w k43 w k44 w k45 w k46 w k47 w k48 w k49 w k50 w k51 w k52 w k02 0 100 200 300 400 500 600 700 800 Call SetUp Success Rate Call Drop Rate Overall Call Success Rate Time on 3G Time on 2G Call Attempts
KPI reporting BTS failure chart (call setup failure & drops) • Cumulative number of failures that occurred per site over time • If the UE is spending only a small percentage of time on 3G problems may not be identified. CELL_C Cell_A Cell_D CELL_B
BTS failure examples: CELL_A • Long history of failures (over weeks 46, 47, 02) • Call Setup failure scenarios: – CC Dis o e t afte CC Call P o eedi g – CM “e i e A o t afte CM se i e ‘e uest • 3rd sector showing low average PrxNoise –108 dBm Commissioning data (feeder loss) was found incorrect. • After this site was still failing, not carrying traffic. – Ala 775 – failu e i WCDMA BT“ O&M Co e tio – COCO rebuilt (27.1.05)
BTS failure examples: CELL_B • Failures only on week 49 • No espo se to ‘‘C Co e tio ‘e uest • No alarms • At WBTS: MHA parameters ok • At RNC: MHA=0, cable loss = 3 dB (DPCCH init pwr) • PrxNoise checked OK, OMC statistics showed the site carried traffic during the drive. • No failures in the following weeks drives
BTS failure examples: CELL_C • Failures over weeks 44, 45, 49, 50 • No espo se to ‘‘C Co e tio ‘e uest ost frequent failure, also one case of sudden drop to idle. • Test calls were made, the counters were not incremented during the test. Protocol analyser proved no activity in Iub. The counters were incremented only after site reset. • Ala W“MA ‘‘- us e o • The site had faulty WTR, incorrect feeder loss in
BTS failure examples: CELL_D • Failures on weeks 47 and 48 • No espo se to ‘‘C Co e tio ‘e uest • Incorrect feeder loss in commissioning data.

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wcdma-drive-test-analysis-ppt-libre

  • 1.
    Drive Test Analysis Objectives Afterthis module the delegate shall be able to:- • Understand the different elements required for an effective drive test program • Understand how all aspects of drive data can be used to obtain a view of network performance • Differentiate between genuine (RF) and non-genuine (system) failures • Understand the KPIs that can be obtained
  • 2.
    Drive Test Process Cluster Preparation •DefineCluster •Define Drive Route Data Analysis •Levels of Reporting •Failure Type Breakdown •Post Processing functionality •KPI Gap Analysis Data Preparation and Collection •Services to test •KPI definitions •Equipment •Exclusions •Call Patterns •OSS Alarms •Network Stats Trouble Shooting •Root Cause Analysis •Corrective Action •Further data logging (maybe) • New Site Integration • RF Tuning • Network Optimisation • Network Benchmarking (Golden Routes) Why Drive the network?
  • 3.
    Drive Test Analysis– Test Equipment • Ne o Outdoo Multi ith UE s, “ a e a d GP“ Land Unit NQMP FTP Server • Important to drive with Call logging equipment and 3G and 2G scanner in the same vehicle
  • 4.
    Drive Test Analysis– Test Equipment, Scanner • The purpose of using the RF scanner is to be able to scan and measure all used carriers/cells and their corresponding DL scrambling codes. – For low coverage areas – For antenna installation problems – For missing neighbours – For coverage optimisation – With the scanner you can get the following info from the surrounding cells: • Different Scrambling codes • CPCIH RSCP value (dBm) • CPICH EcNo value (dB)
  • 5.
    Drive Test Analysis– Test Equipment, UE • The Scanner measures all SCs, whereas the UE only measures SC signals from the cells that the system has informed/ordered the UE through the BCH (neighbour list) or via the easu e e t o t ol essage. – RSCP Active/Monitored Set – Carrier RSSI – Ec/No Active/Monitored Set – UL/DL Data Throughput – The BLER downlink – Pilot BER – Random Access Initial Tx Power – Random Access Preamble Count – Random Access Preamble Step – Random Access Tx Power – SIR target (UE dependent) – UE Tx Power – Call Statistic: AMR, CS and PS data calls
  • 6.
    Drive Test Analysis– Call Patterns AMR Call Mobile Originated Calls (MOC) • 2 min calls • 30 sec idle • UE in Dual mode (2G/3G) Mobile Terminated Calls (MTC) • 2 min calls • 30 sec idle • UE in dual mode (2G/3G) • Enough call samples have to be made to make the measurement statistically valid. • In a 50 call sample one dropped call will cause a change in performance of -2% • In a 500 call sample one dropped call will cause a change in performance of -0.2% • Call length should be defined at the beginning • We can use different call testing patterns for different optimisation techniques • Short Calls (for Calls setup performance and delay) • Long calls (for Drop call performance and SHO performance) PS Call • GPRS Attach, • PDP Context Activation • FTP Download (1MB file)/FTP Upload (500 KB file) • PDP Context Deactivation • GPRS Detach • Alternate download and upload with 30 sec idle time • Session is upload or download • UE in Dual mode (2G/3G)
  • 7.
    Drive Test Analysis– Defining KPIs AMR Statistics Threshold KPIs MOC Setup time 5 sec MOC CCR 99 % RAW END USER Event Count Ratio Count Ratio Call Attempts 132 122 Call Setup Success Rate 108 81.8% 108 88.5% Call Setup Failure Rate 24 18.2% 14 11.5% Failures due to Tool (TSF) 10 41.7% Failures due to Core Problem 10 41.7% 10 71.4% Failure ASU (Sync) Problem 2 8.3% 2 14.3% Failure due to Low Coverage Levels 2 8.3% 2 14.3% Call Setup Success and Setup Time > 5s 7 6.5% 7 6.5% Long Setup due to slow cell reselection 0.0% 0 0.0% Long Setup due to clash with InterRAT reselection 0.0% 0 0.0% Long Setup due to Unknown (suspect UE) 0.0% 0 0.0% Long Setup due to Unknown 0.0% 0 0.0% Average Call Setup Time 3.66 3.66 Call Completetion Rate 105 97.2% 105 97.2% Call Drop Rate 3 2.8% 3 2.8% Call Drop Poor 3G Coverage 1 33.3% 1 33.3% Call Drop on GSM due to Interference 2 66.7% 2 66.7% Overall Call Completion Rate 105 79.5% 105 86.1% ISHO Attempt 14 14 ISHO Success 14 100.0% 14 100.0% ISHO Failed 0 0.0% 0 0.0% ISHO Failed cause physical channel failure 0 N/A 0 N/A PS Data KPI Report KPI Thresholds Value Unit Attach Time 4 sec PDP Activation Time 2 sec FTP Download Throughput 110 kbit/s FTP Upload Throughput 55 kbits Signalling Statistics Count Success rate Attach Attempt 155 Attach Success 140 90.32% Attach Time more than threshold 5 3.57% Attach Time less than threshold 135 96.43% Attach Failed 15 9.68% Average Attach Setup Time 1.36 Activate PDP Context Attempt 124 Activate PDP Context Success 124 100.00% Activation Time more than threshold 2 1.60% Activation Time less than threshold 123 98.40% Activate PDP Context Failed 0 0.00% Average PDP Context Activation Time 0.96 FTP Download Attempts 51 FTP Download Success 48 94.12% FTP Download throughput more than threshold 25 52.08% FTP Download throughput less than threshold 23 47.92% Average FTP Download Throughput 107.02 FTP Upload Attempts 32 FTP Upload Success 30 93.75% FTP Upload throughput more than threshold 20 66.67% FTP Upload throughput less than threshold 10 33.33% Average FTP Upload Throughput 55.53 Data Transfer Cut-off Ratio 6.02% PDP Context Dropped 4 3.23% Deactivate PDP Context Request 121 Deactivate PDP Context Accept 121 100.00% Deactivate PDP Context Failure 0 0.00% Detach Request 281 Detach Accept 129 45.91% Overall Data Session Completion Rate 78 62.90% RAU Statistics Count Success rate RAU Attempt 22 RAU Success 13 59.09% RAU Failed 9 40.91% Cell Reselection Statistics Count Success rate Cell Reselection from UMTS to GSM Attempts 2 Cell Reselection from UMTS to GSM Success 1 50.00% Cell Reselection from UMTS to GSM Delay E2E 15.27 Cell Reselection from UMTS to GSM Delay Signalling N/A Cell Reselection from GSM to UMTS Attempts 1 Cell Reselection from GSM to UMTS Success 0 0.00% Cell Reselection from GSM to UMTS Delay E2E N/A Time in System Seconds Ratio GSM 171 1.02% UMTS 16559 98.98% • Need to agree •What a figu es ill o tai •What E d Use ill o tai •Other cuts of Data
  • 8.
    KPI-08 PS PDP context activation •Sameas 10 •350 occurrences •PS PDP activation trigger point: •UE not PS attached •UE sends 1st ‘RRC Connection Request’ •PS PDP activation completion trigger point: •UE receives ‘RRC: Downlink Direct Transfer (SM: Activate PDP Context Accept)’ •Successful completion if: •UE receives ‘RRC: Downlink Direct Transfer (SM: Activate PDP Context Accept)’ •Cluster_PDP_Context_Activation_SR_% = PDP Context Activation Completion / PDP Context Activation Attempts *100 98% KPI-09 PS throughput downlink •Repeated FTP calls, 1 Mbyte file download, 1 Ue •384 kbps •Average throughput •350 calls •Data Session Set-up trigger point: •UE receives 1st DL packet •Data Session Completion trigger point: •UE receives last packet •Session output: •Average downlink throughput •Cluster_PS_DL_Throughput = Average Throughput Over Data Sessions 200 Kbps KPI ID Criteria Test Description Trigger Statistics Success Rate KPI-01 Voice 12.2 kbps AMR CCSR •1 MOC+ 1 MTC in the same van, 2 Ues •1 call (party A to party B, party A terminates the call): 15 seconds call + 15 seconds idle. Party A to be logged •350 calls •Call set-up trigger point: •Party A’s UE sends 1st ‘RRC Connection Request’ •Call completion trigger point: •Party A’s UE receives ‘RRC Connection Release (cause normal)’ •Successful completion if: •15 sec call duration (from RRC Conn. Request to RRC Conn. Release) •Party A’s UE receives ‘RRC Connection Release (cause normal)’ •Cluster_AMR_Overall_CCSR_% = Call Completion / Call Attempts *100 98% KPI-02 Voice DCR •1 MOC to PSTN, 1 Ue •1 call: 90 seconds call + 15 seconds idle •350 calls •Call Set-up trigger point: •3G UE receives ‘RRC: Downlink Direct Transfer (Alerting for NZ, Connect Acknowledge for AU)’ •Call completion trigger point: •3G UE receives ‘RRC Connection Release (cause normal)’ •Successful completion if: •90 sec call duration (from RRC Conn. Request to RRC Conn. Release) •3G UE receives ‘RRC Connection Release (cause normal)’ •Cluster_AMR_Overall_DCR_% = 1 - Call Completion / Set up Calls *100 < 2% KPI-03 Voice 3G- 2G Handover (inter- & intra-MSC) •1 MOC to PSTN, 1 Ue in dual mode •1 call: continuous call until 3G2G coverage border is passed •50 occurrences as a minimum •3G to 2G HO start point: •UE receives ‘RRC: Handover From UTRAN Command’ •3G to 2G HO completion trigger point: •UE sends ‘Handover Complete’ to 2G BSS •Successful completion if: •UE sends ‘Handover Complete’ to 2G BSS •Cluster_Voice_3Gto2G_HO_Overall_SR_% = HO Completion / HO Attempts *100 98% Drive Test Analysis – Test Case definition Examples … Short calls to test Call Setup Success Long calls to test Drop call ratio
  • 9.
    Need to Definethe KPI measurement (from Drive test) • Call Setup Success - CSSR (voice, circuit switched data) – Successful all setup ea s that DL/UL Di e t T a sfe CC: Ale ti g essage is e ei ed UE. • Call Setup Time (voice, circuit switched) – Call setup dela is easu ed f o L3 essages, sta ti g f o ‘‘C Co e tio “etup essage to DL Di e t T a sfe CC: Ale ti g essage. • Call Drop (voice, circuit switched) – A dropped call occurs. The call will be dropped in case RRC connection release (not normal release) message has been send from RNC to UE. • Session Setup Success (packet switched) – This is related to PDP context activation. Successfully activated PDP context means that activate PDP context accept message has been sent from RNC to UE (RRC: downlink direct transfer (SM:activate PDP context Accept)). • Session Setup Time (packet switched) – The sessio setup ti e is the dela et ee the ti e the UE se ds the data sessio a ti atio request until GPRS attach and PDP context activation has been successfully completed. • Session Drop (packet switched) – Session drop rate can be defined as the number of successful PDP deactivations against number of successful PDP activations.
  • 10.
    Definition of CallSet-Up Success Rate (CSSR) UE RRC: Connection Request RRC Connection Setup phase Resource Reservation in RNC, BTS, Transmission RRC: RRC Connection Request Setup RRC Connection Access phase RNC waits reply from UE RRC: RRC Connection Completed RRC: Initial Direct Transfer cm service request RANAP: Initial UE Message DIRECT TRANSFER (Call Proceeding) RANAP: RAB Assignment Request RRC: Radio Bearer Set-up RRC: Radio Bearer Setup Complete RAB Connection Setup phase Resource Reservation in RNC, BTS, Transmission RANAP: RAB Assignment ResponseDIRECT TRANSFER (Alerting) BTS RNC CN DIRECT TRANSFER (Connect) DIRECT TRANSFER (Connect Acknowledge) RAB Connection Access phase RNC waits reply from UE Call Set-up Success Rate Call Set-up Time Successful call setup means that DL/UL Di e t T a sfe CC: Ale ti g essage is received by UE
  • 11.
    Definition of theCall Completion Rate (CCR)UE RNC MGWNode B Call Established Iu Release Command Iu Release Complete RRC Connection Release RRC Connection Release Complete RRC Connection Release Complete RRC Connection Release Complete Radio Link Deletion Request Radio Link Deletion Response ALCAP: Release Request ALCAP: Release Response ALCAP: Release Request ALCAP: Release Response Call Released Direct Transfer (Disconnect) Direct Transfer (Release) Direct Transfer (Release Complete) DIRECT TRANSFER (Alerting) DIRECT TRANSFER (Connect) DIRECT TRANSFER (Connect Acknowledge) Call Drop Rate Call Duration
  • 12.
    Definition of SessionSetup Time - PSUE CN RNCWBTS INITIAL DIRECT TRANSFER (Attach Request) Downlink Direct Transfer (Authentication & Ciphering Request) UE already has an RRC connection SCCP: Connection Request SCCP: Connection Confirm RANAP: Authentication & Ciphering Request Security Mode Command Uplink Direct Transfer (Authentication & Ciphering Response) RANAP: Authentication & Ciphering Response RANAP: Security Mode Command Security Mode Command RANAP: Security Mode Command RANAP: Common ID Downlink Direct Transfer: Identity Request RANAP: Identity Request Uplink Direct Transfer: Identity Response RANAP: Identity Response Downlink Direct Transfer: Attach Accept Direct Transfer: Attach Accept Uplink Direct Transfer: Attach Complete Direct Transfer: Attach Complete INITIAL DIRECT TRANSFER (Active PDP Context Request) DIRECT TRANSFER (Active PDP Context Request) DIRECT TRANSFER (Active PDP context Accept) RANAP: RAB ASSIGNMENT REQUESTRRC: Radio Bearer Set-up RRC: Radio Bearer Set-up Complete RANAP: RAB ASSIGNMENT RESPONSERRC: Measurement Control INITIAL UE MESSAGE (GPRS Attach) Session Set-up Time
  • 13.
    • Non-genuine failures –Measurement system fault (Collection Tool or Analysis) • Genuine failures – RF issue (Coverage / Interference / Poor dominance) – Missing neighbour – System issue WBTS – System issue RNC – Core network issue – System – (Unknown ) WBTS RNC Core NW UE Iub Iu It is beneficial to categorise call failures during the analysis and reporting Failure Breakdown
  • 14.
    • The KPImeasurement conditions should be used to define exclusion areas during drive test for acceptance of a cluster. • All failures happening in those area, that do not respect the coverage requirements should be discarded. Signal above RSCP threshold Signal below RSCP threshold Signal above Ec/No threshold Signal below Ec/No threshold-110dBm - -95dBm -80dBm Time RSCP Call OK Call OK Call OK Call NOK Call NOK -12dB -5dB -20dB Ec/No Threshold Exampleof Call SuccessCriteria Discard sample   Call-(A) Call-(B) -110dBm - -80dBm Time RSCP Call OK Call OK Call OK Call NOK Call NOK - -5dB -20dB Ec/No Threshold Exampleof Call SuccessCriteria Discard sample   Call-(A) -110dBm - -80dBm Time RSCP Call OK Call OK Call OK Call NOK Call NOK - -5dB -20dB Ec/No Threshold Exampleof Call SuccessCriteria Discard sample  -110dBm - -80dBm Time RSCP Call OK Call OK Call OK Call NOK Call NOK - -5dB -20dB Ec/No Threshold Exampleof Call SuccessCriteria Discard sample   Call-(A) Call-(B) Failure Breakdown
  • 15.
    Failure Breakdown Call Set-upFailures Breakdown - Benchmark Drive 5% 20% 0% 5% 0% 0% 10% 5% 35% 15% 0% 5% Equipment Registration Clash Core Network Fail in 2G RAN (fixed in next release) Site maintenance (TMUK) RAN (Other) Missing neighbours 3G RF slow cell Reselection site configuration & maintenance (Nokia) Other Call Set-up Failures Failure Type total % Equipment 0 0.0 Registration Clash 0 0.0 Core Network 0 0.0 Fail in 2G 6 19.4 RAN (fixed in next release) 0 0.0 Site maintenance (TMUK) 16 51.6 RAN (Other) 0 0.0 Missing neighbours 0 0.0 3G RF 3 9.7 Slow cell reselection 0 0.0 site configuration & maintenance (Nokia) 0 0.0 Other 6 19.4 Call Setup Failure Breakdown - Final Drive 0% 0% 0% 19% 0% 0% 0% 10% 0% 0% 19% 52% Equipment Registration Clash Core Network Fail in 2G RAN (fixed in next release) Site maintenance (TMUK) RAN (Other) Missing neighbours 3G RF Slow cell reselection site configuration & maintenance (Nokia) Other Call Set-up Failures Failure Type total % Equipment 1 5.0 Registration Clash 4 20.0 Core Network 0 0.0 Fail in 2G 1 5.0 RAN (fixed in next release) 0 0.0 Site maintenance (TMUK) 0 0.0 RAN (Other) 2 10.0 Missing neighbours 1 5.0 3G RF 7 35.0 slow cell Reselection 3 15.0 site configuration & maintenance (Nokia) 0 0.0 Other 1 5.0 AMR Call Setup Failures
  • 16.
    Drive Survey AnalysisProcess Summary Diagram
  • 17.
    Non Genuine CallSetup Failure Scenarios • Measurement systems are often not perfect and may introduce errors in data collection or analysis • Examples of non-genuine failures seen: – Uplink: CM Service Abort within milliseconds from CM Service Request – Call atte pt du i g Lo atio A ea update LA lash – Use i itiated UL CC Dis o e t – Location Area update interpreted as call setup failure – Cell reselection back to 3G from 2G interpreted as call setup failure
  • 18.
    Non Genuine CallSetup Failures • Measurement system failures by drive test tool – CM “e i e A o t ithi illise o ds f o CM “e i e ‘e uest – No time for response from NW
  • 19.
    Non Genuine CallSetup Failures • Measurement system failures by drive test tool • Call attempt during Location Area update (LA update clash) LA Update Request Call attempt RRC Release
  • 20.
    Non Genuine CallSetup Failures Measurement system failures by Actix workbook – Successful or failed Location Area update interpreted as call setup failure RRC Connection for Inter-RAT cell reselection LA Update Request
  • 21.
    Non Genuine DropCall Scenarios Measurement system failure examples: – Drive test tool • Use i itiated UL CC Dis o e t – Analysis Workbook • Inter-Rat cell reselection from 2G to 3G interpreted as drop call • Complete (e.g 90 seconds) call on either 3G or 2G • No drop in the log file / same drop listed twice
  • 22.
    Genuine Call SetupFailure Scenarios – RF issue • Interference / Dominance / Coverage • Missing neighbour – System Issue - BTS • No espo se to ‘‘C Co e tio ‘e uest • ‘‘C Co e tio ‘eje t to ‘‘C Co e tio ‘e uest – System issue - RNC • CC Dis o e t afte Call P o eedi g due to DL ‘‘C Co e tio ‘elease – Core NW • CM “e i e A o t afte CM “e i e ‘e uest – System issue (test number) • CC Dis o e t afte CC P og ess
  • 23.
    Genuine Drop Callscenarios • RF issue – Interference / Dominance / Coverage – Missing Neighbours • System issue BTS – “udde CC Dis o e t due to DL ‘‘C Co e tio ‘elease – Sudden drop to idle, no disconnect messaging • System issue RNC – “udde CC Dis o e t due to DL ‘‘C Co e tio ‘elease
  • 24.
    Failure Location • Analysethe signalling flow to find the location of failure and potential cause • UE log may only capture some of the messages
  • 25.
    DRNCUE CNSRNCWBTS 2. RRCconnection set-up 6. Service Established 7. Branch addition/deletion & Active set update 1. Cell search, BCCH decoding & RACH access 3. UE <--> CS-CN signalling 4. RAB set-up 8. Service Released 5. UE <--> CS-CN Signalling AMR CS Call Phases
  • 26.
    Start Best se es RSCP > -102dBm Best se e s Ec/No > -12dB Coverage Optimization Dominance Optimization AICH(ACK) received? Yes Missing Neighbour ? Neighbour list Optimization No No No Yes UL coverage & RACH parameter. Optimization (changing serving cell) ‘‘C Co e tio “etup e ei ed? (DCH ‘‘C Co e tio setup Co pleted se t f o UE? “Radio Bearer setup failu e ‘e ei ed? Report & Finish Check failure cause (Not radio problem/cell update) Report & Finish (Check failure cause) AC optimization (check PrxNoise & interferer around BTS) Report & Finish ‘‘C “etup ‘eje t e ei ed? Yes No Yes Yes Yes Report & Finish (Reason of problem: L1 sync fail) Report & Finish (Check failure cause) Call Setup Failure Analysis Process A B C D E Yes Yes No No No No
  • 27.
    Call setup failures– RF issue • RF issue? Coverage / Interference / Dominance A See the example in Module 3 – RF Optimisation
  • 28.
    Call setup failures– Missing Neighbour A • Missing neighbour analysis over the whole route (3G-3G, 3G-2G) • Search for failures due to missing 3G-3G neighbours • Search for failures due to missing 3G –2G neighbours – It is suggested to place 2G scanner to the test vehicle
  • 29.
    Call Setup FailureAnalysis- Block B - • The purpose of this activity is to check the Random Access Process is working adequately by investigating whether AI (Acquisition Indicator) has been received through DL AICH • If AICH was not received by UE, the cause of the problem can be classified into: – Inadequate RAN parameter related to Random Access: RAN parameter settings for pre-amble transmission or open loop power control information is not correct. – UL Coverage limit: UL coverage of UE is smaller compared to serving cells DL o e age so that UE s T po e a ot ea h se i g ell. B
  • 30.
    Call Setup FailureAnalysis- Block B -UE WBTS RNC Preamble/RACH Acquisition Indicator/AICH RRC: RRC Connection Request/PRACH NBAP: RADIO LINK SETUP REQUEST RRC: RRC CONNECTION SETUP/FACH L1 Synchronisation NBAP: SYNCHRONISATION INDICATOR RRC: RRC CONNECTION SETUP COMPLETE/DCH UE in CELL_DCH state NBAP: RADIO LINK SETUP RESPONSE B
  • 31.
    RACH Process Downlink BS L1 ACK/ AICH Uplink MS Preamble 1 Not detected Message partPreamble 2 PRACH_preamble_retrans # PRACH preambles transmitted during one PRACH cycle without receiving AICH response UEtxPowerMaxPRACH … … … … RACH_tx_Max # preamble power ramping cycles that can be done before RACH transmission failure is reported PowerRampStepPRACHpreamble PowerOffsetLastPreamblePRACHmessage Initial preample power: •Ptx = CPICHtransmissionPower-RSCP(CPICH) +RSSI(BS) + PRACHRequiredReceivedCI B
  • 32.
    Call Setup FailureAnalysis- Block B- • Solutions for RACH optimisationMax UE Tx power hit the UE_P_MAX(24dBm)? To increase PRACH_Preamble_retrans Or PowerRampStepPRACHPreamble No Yes Is UL Interference abnormally HIGH? Yes No Report there might be an interfering source Nearby the serving cell Change the Serving cell to cover the problem Area => UE is too far to reach the serving cell B
  • 33.
    Call Setup FailureAnalysis- Block BB Open loop Power Control parameters from RACH Info message
  • 34.
    Call setup failures– System issue BTS• No espo se to ‘‘C Co e tio ‘e uest – Good RF conditions – W o g MHA setti gs o a le loss setti gs a ause the site ot to hea the UE – PrxNoise statistics, receive link parameters and HW units to be checked (faulty MHA, wrong MHA parameters, wrong cable / feeder loss parameters, faulty units) C
  • 35.
    Call setup failures– System issue BTS• ‘‘C Co e tio ‘eje t afte ‘‘C Co e tio ‘e uest – Good RF conditions – Admission Control can reject too many (or admit too many) connection requests due to wrong PrxNoise measurements. – PrxNoise statistics, receive link parameters and HW units to be checked C
  • 36.
    Call Setup FailureAnalysis • UE has the appropriate DL/UL coverage but if RNC does not allow to set up the RRC connection of the requested RAB (Radio Access Bearer), Call setup will fail. • Admission Control (AC) is involved in RRC connection setup. AC can reject RRC reject RRC connection Setup due the DL Load, UL load or DL Spreading codes – Marginal Load Area: • If measured UL (PrxTotal) or DL (PtxTotal) load exceeds target thresholds (PrxTarget and PtxTarget) AC can still admit new RAB to the cell if a new non-controllable load keeps below target thresholds (in practice this means that AC can admit only new controllable load RABs i.e. NRT RABs) – Overload Area: • If measured UL (PrxTotal) or DL (PtxTotal) load exceeds overload thresholds (PrxTarget + PrxOffset and PtxTarget + PtxOffset) then AC can't admit more RABs to the cell C
  • 37.
    Call Setup FailureAnalysis • During the pre-optimization phase it is unlikely that AC will stop an RRC connection setup during the drive testing because there are normally very few UEs in the network. (Traffic loading is trivial) • However, it should be checked that measured PtxTotal and PrxTotal are less than PtxTarget (e.g. 40dBm) and PrxTarget (e.g. 4dB, 60% loading) respectively. • If DL AC does not allow RRC setup check the Tx power of WBTS, # of channels transmitted, Signaling messages. • If UL AC does not allow RRC setup: Check out if there is an interfering source nearby the serving cell. C
  • 38.
    Call Setup FailureAnalysis To check if Layer 1 Synchronization (slot/frame sync) has failed • If ‘‘C Co e tio “etup as e ei ed UE ut UE does ot se d ‘‘C Co e tio “etup Co pleted , e ill epo t L s h o izatio failu e a d have to check L1 system messages. D
  • 39.
    • CC Diso e t afte Call P o eedi g • Good RF conditions • Failures in RAB setup occur et ee the ‘AB Assig e t ‘e uest ei g received from Core Network and the RAN sending out Radio Bearer Setup. Therefore the failure is between BTS and Core Network. ECall setup failures – System issue RNC
  • 40.
    • CC Diso e t afte Call P o eedi g o t. • An example (site shows high values on counter ‘AB_“TP_FAIL_C“_VOICE_BT “ du i g the d i e test • In the recent check the counter showed no failures. ECall setup failures – System issue RNC
  • 41.
    Call setup failures– Core NW Security Mode Command Common ID UE RNC MGWNode B RRC Connection Establishment Initial Direct Transfer (CM Service Request) SCCP: Connection Request SCCP: Connection Confirm Location Reporting Control • RRC: Initial Direct Transfer message is sent using acknowledged mode RLC to the CS core domain. Routing is to be based upon the local P-TMSI • The NAS message is not read by the RNC but is forwarded to the multimedia gateway. The NAS message includes the IMSI as a UE identity • The SCCP: Connection Request message establishes the connection orientated signalling link in the same way as it was for the RRC connection phase.This does not reserve any resources for the AMR call itself. • The Connection Confirm message identifies the RNC with a destination local reference which is the same as the source reference within the Connection Request message • The Connection Confirm message identifies the CS core with a source local reference • The CS core sends a RANAP: Location Reporting Control message to the RNC requesting information regarding the location of a particular UE • The RANAP: Common ID message specifies the IMSI belonging to the UE • The Security Mode Command message triggers the start or stop of ciphering and integrity protection. • CM “e i e A o t afte CM “e i e ‘e uest • Good RF conditions • “e u it Mode Co a d -message not received by UE, thus the failure is believed to be at Core Network. E
  • 42.
    Call setup failures– System Issue (test number)• CC Dis o e t afte CC P og ess • Cause: recovery on timer expiry • The call goes via IN SCP to a recording. • A static test was done by Nokia Customer Care and in few instances the call dropped after 30 seconds of recording passed. Hence the problem is associated with the test number not the RAN 30 sec Cause: recovery on timer expiry E
  • 43.
    Start Best server’s RSCP >-102dBm Best server’s Ec/No > -12dB Coverage Optimization Dominance Optimization Yes Yes Neighbour list Optimization Missing Neighbour Yes Call Drop Failure Analysis Process SHO Failed Investigate possible BTS or RNC problem No ISHO Failed No ISHO Failure Analysis B YesSHO Failure Analysis A No No No
  • 44.
    Call Drop FailureAnalysis Process (SHO Analysis) DL ASU received Yes SC Clash UE Tx Power Max Fix SC Clash CPICH Optimisation Uplink Interference Load Optimisation/ External Interferer Link Unbalanced Yes Yes Yes Yes No No No Yes Inter RNC HOCheck Iur Yes Congestion on target cell Load Optimisation No Yes No Check neighbour definition parameters Check RF Levels NoDL Tx Power Max Yes Start D C
  • 45.
    Drop call failures– RF issue • RF drops mostly due to poor dominance or interference • Poor coverage could lead to ISHO, although poor dominance or interference can cause ISHO to fail. • Rapid field drop can cause drop due to coverage • Poor dominance or interference can cause Compressed Mode (CM) to start even if RSCP is still good. • In CM UE transmits with higher power (more interference) and spends less time on 3G (less accurate measurement reporting) • Poor dominance or interference can lead to Active Set update failures and eventually to drop call. Poor dominance causes Active Set update failures A
  • 46.
    Drop call failures– RF issue DL synchronisation is lost -> UE has stopped transmitting TrChAgg and DL DPCCH BER high A
  • 47.
    Drop call failures– RF issue Transport Channel BER. Btw UE<->RNC (MAC layer) Sometimes DPCCH BER (btw UE<->WBTS) can be a better indicator of what's happening to the dedicated channel than the CPICH EcNo, in particular in the case that power control may not be tracking well Fairly good CPICH Pilot EcNo A
  • 48.
    Drop call failures– System issue BTS Drop to IDLE B • Sudden drop to idle, no disconnect messaging – Site malfunctions to be checked – In the example below site had faulty unit (WTR)
  • 49.
    Drop call failures– System issue RNC “udde ‘‘C Co e tio ‘elease DPCCH BER • CC Dis o e t due to DL ‘‘C Co e tio ‘elease • No response to UL Measurement Reports • In the example site had no alarms, good RF & BER • Not able to add SC265 to Active Set, next call on the same cell => no failure. • Difficult to troubleshoot if the failure does not happen systematically => follow up in the next weeks drive / do a separate drive test in the area B
  • 50.
    Drop call failures(SC conflict) • Sudden drop to idle mode (no disconnect messaging) • Cause of the failure: overshooting site and SC reuse • Short term solution to add overshooting neighbour in ADJS definitions Cell ABC, SC258 Transport channel BLER 100% C
  • 51.
    Drop Call -Uplink Interference UL interference from the SIB7 message D
  • 52.
    Drop Call –Link Balance• UL & DL Power Control commands can help indicating problems in link balance. • PC frequency is 1500 Hz, thus ideally the sum of PC commands to increase or decrease power is 1500 • E.g. if the sum of UL PC commands is < 1500, this would indicate UE is starting to loose synchronization • in Compressed Mode there is less PC commands, UE spends time on 2G UE RX power control message: DL reception weak -> UE is ordering WBTS to increase power. Sum of UL PC commands < 1500, UE not receiving all the PC commands. D
  • 53.
    Drop call failures– System issue RNC or BTS ? • CC Dis o e t due to DL ‘‘C Co e tio ‘elease is just a consequence of failure which can be due to different reasons – From UE point of view L3-messaging does not identify the point of failure distinctly – BTS or RNC failure? => Suspect BTS first, then RNC • Rule out BTS failures – Check the site performance from Counters (Iub, Service level, cell resources SHO, etc) and that site is carrying traffic – PrxNoise, receive link parameters, alarms – SC–reuse – UE performance ? • Identified causes for Active Set Update failure – Deaf sites P Noise – Faulty HW – SC-reuse
  • 54.
    Drive Test Analysis– Reporting Levels Optimiser • Very High Level KPIs that give a users perception of the network (Network KPI) • KPIs that provide an Engineering view of network performance e.g CSSR, CDR, OCSR, SHO performance. (KPIs required for each optimisers area) • Highly detailed KPIs that give a detailed picture of network performance at an Engineering level and allow root cause analysis Regional Optimisation Manager Senior Management • Processing Drive Data to provide the information required at the bottom level means that the higher level information can be easily extracted • The different reporting levels may want to see KPIs based on different cuts of the data (e.g. raw or end user)
  • 55.
    KPI reporting • Non-geui e failu es to e e o ed f o the a KPI s Call Completion Call SetUp Success Rate 97.5% 97.9% Call Drop Rate 1.3% 0.3% Overall Call Success Rate 96.2% 97.6% Call Connection time <= 8s 97.6% 97.6% No of Call Attempts (within coverage) 634 625 No of Call Setup Failures 16 13 No of Successful Call Setups 618 612 No of Call Drops 8 2 No of Completed Calls 610 610 Call Completion Call SetUp Success Rate 97.5% 97.9% Call Drop Rate 3.1% 2.1% Overall Call Success Rate 94.5% 95.9% Call Connection time <= 8s 97.6% 97.6% Call Completion Call SetUp Success Rate 98.1% 98.6% Call Drop Rate 1.3% 0.3% Overall Call Success Rate 96.8% 98.2% Call Connection time <= 8s 97.6% 97.6% No of Call Attempts (within coverage) 630 621 No of Call Setup Failures 12 9 No of Successful Call Setups 618 612 No of Call Drops 8 2 No of Completed Calls 610 610 Non-genuine call setup failures removed Non-genuine drops removed Fi al KPI s Fi al KPI s
  • 56.
    KPI reporting • WeeklyKPI trends (non-genuine failures should be excluded) All Routes 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% w k41 w k42 w k43 w k44 w k45 w k46 w k47 w k48 w k49 w k50 w k51 w k52 w k02 0 100 200 300 400 500 600 700 800 Call SetUp Success Rate Call Drop Rate Overall Call Success Rate Time on 3G Time on 2G Call Attempts
  • 57.
    KPI reporting BTS failurechart (call setup failure & drops) • Cumulative number of failures that occurred per site over time • If the UE is spending only a small percentage of time on 3G problems may not be identified. CELL_C Cell_A Cell_D CELL_B
  • 58.
    BTS failure examples:CELL_A • Long history of failures (over weeks 46, 47, 02) • Call Setup failure scenarios: – CC Dis o e t afte CC Call P o eedi g – CM “e i e A o t afte CM se i e ‘e uest • 3rd sector showing low average PrxNoise –108 dBm Commissioning data (feeder loss) was found incorrect. • After this site was still failing, not carrying traffic. – Ala 775 – failu e i WCDMA BT“ O&M Co e tio – COCO rebuilt (27.1.05)
  • 59.
    BTS failure examples:CELL_B • Failures only on week 49 • No espo se to ‘‘C Co e tio ‘e uest • No alarms • At WBTS: MHA parameters ok • At RNC: MHA=0, cable loss = 3 dB (DPCCH init pwr) • PrxNoise checked OK, OMC statistics showed the site carried traffic during the drive. • No failures in the following weeks drives
  • 60.
    BTS failure examples:CELL_C • Failures over weeks 44, 45, 49, 50 • No espo se to ‘‘C Co e tio ‘e uest ost frequent failure, also one case of sudden drop to idle. • Test calls were made, the counters were not incremented during the test. Protocol analyser proved no activity in Iub. The counters were incremented only after site reset. • Ala W“MA ‘‘- us e o • The site had faulty WTR, incorrect feeder loss in
  • 61.
    BTS failure examples:CELL_D • Failures on weeks 47 and 48 • No espo se to ‘‘C Co e tio ‘e uest • Incorrect feeder loss in commissioning data.