LTE DT Analysis Guidelines_v1 0

LTE DT ANALYSIS GUIDELINES Document Name

LTE DT Analysis Guidelines

Date Created

11 March, 2016

Version

V 001

Approved By

ISAT NPS Manager

Document Number

INDOSAT OPTI – 001

Owner

NPO

Prepared By

Wang Zilong/Sim Chee Hwa

Designed For

NPO

Reviewed By

Nicanor Adriano

Project

Indosat Optimization 2016

1. VERSION HISTORY Version 001

2.

Modified By

Date Modified

Description of Changes

Wang Zilong / Sim Chee Hwa

March 11, 2016

Version 1.0

OBJECTIVE

The purpose of this document is to give general guidelines on the process and strategy in analyzing cluster DT for the purpose of optimizing the radio network of Indosat and fulfilling the reporting requirements of the project. This document is particularly for the consumption of regional team engineers who are doing the actual analysis and reporting. It lays out the process that the regional teams should follow and strategies on how they will analyze the problems and the expectations on their output. The target is for the regional engineers to produce a good quality report and reliable analysis & recommendations. This guideline is particularly focused on analysis for the cluster DT, VIP route and City route reporting required by Indosat. After reading this document analysis engineer is still required to read the 2 mentioned original guidelines to get full details of the requirement for this project. 3.

PROCESS

Step 1: Level 1 and Level 2 engineers are doing cluster DT analysis and reporting.

LTE DT ANALYSIS GUIDELINES Step 2: Once report is done it is submitted to senior engineers for layer 1 checking before it goes to DT Lead (Samsul). If the one who made the report is the senior engineer the layer 1 check is the regional TL. Step 3: Once report is reviewed and confirmed by the senior engineer it will be submitted to regional team lead for final review. During the strategic and central DT team visit to the regions the layer 2 check was done by the strategic engineers. Reports are being presented in a conference room with projector so all the engineers can scrutinize the analysis and report and at the same time give valuable inputs. If the senior engineer is the one making the report the layer 2 check is the DT Lead. Step 4: After confirmation by Layer 2 check the report is submitted to DT Lead for submission to ISAT. The DT Lead makes final sanity check before submission to ISAT to ensure correct format is followed and major parts of the analysis and recommendations are good and reliable. Once DT Lead confirms the readiness of the report it is then submitted to ISAT for checking. Step 5: Once report is submitted to ISAT and confirmed by ISAT changes are implemented through NCR and PCR. Step 6: Once all PCRs and NCRs are implemented a next drive will be triggered. This drive is a verification drive to confirm if all the changes have improved the cluster or DT route. Step 7: After DT2 or Verification DT is finished the analysis engineer checks the improvement, degradation and persistent bad spots of the clusters. If all KPIs are passed or all the bad spots are improved (if not improved it should be justified) a second report will be submitted to ISAT for the closure of the cluster. If KPIs are not passed or the bad spots were not improved the process goes back to Step 1. Step 8: This Final step is for the submission of the final report for the closure of the subject cluster. Since deadlines are tight at this time and priority is to finish optimization of all the clusters Final report is waived at the moment and instead an improvement report is submitted. The improvement report will be the substitute for the Final report for now just to confirm the following: a. Bad spots were improved b. Identify which spots improved, degraded or persisting c. The degraded spots will be rectified and a revision to the improvement report will be done d. The persisting bad spots will also be rectified

LTE DT ANALYSIS GUIDELINES 4.

Identification of UE State (Idle or Connected Mode) 4.1 Idle Mode If the UE is in Idle Mode, the RRC State will result in “Idle”.

4.2 Connected Mode If the UE is in Connected Mode, the


COVERAGE ANALYSIS Below as the guidance for coverage analysis

Flow 5.1 Coverage Analysis Flow

In general, RSRP and SINR analysis can be grouped into four different sections as below whereby other details are explained at clause 5.1 onwards.

Figure 5.1 RSRP vs SINR

Section 1 2

3

4

Scenario

Action

Normal No Action -weak coverage Improve dominant coverage - overshooting coverage - lack of dominant cell - weak coverage - overshooting coverage Improve dominant coverage and optimize signal - lack of dominant cell quality - PCI MOD conflict - Interference - lack of dominant cell - overshooting coverage Optimize signal quality - PCI MOD conflict - Interference Table 5.1 Summary of action for RSRP vs SINR issue

LTE DT ANALYSIS GUIDELINES 5.1 Poor RSRP Analysis 5.1.1 Why Poor RSRP? RSRP is the linear average of reference signal power (Watts) across the specified bandwidth (RBs).During cluster drive for LTE, coverage problem in general can be summarized to below few category Weak Coverage: - Whereby the coverage area’s RSRP stay less than -110dBm. (details refer clause 5.1.2.1) Overshooting Coverage: - The coverage area of an eNodeB goes beyond the planned scope, and generates discontinuous dominant areas in other eNodeBs’ coverage areas. (details refer clause 5.1.2.2) Lack of a dominant cell: - Area where there is no dominant cell or the dominant cell change frequently. There are several overlapping cells, and the signal strength is similar. (details refer clause 5.1.2.3) 5.1.2

Identification & Analysis DT result with RSRP < -110dBm are consider poor coverage spot and required to be highlighted for coverage analysis. 4G Signal Strength RSRP [-116, -110) [-120, -116) < -120 Table 5.2: Poor RSRP Filtering Criteria

All the areas with signal levels that falls into Poor Coverage Criteria in Table 5.1should be identified by circle or rectangle or triangle which ever suites the report best. These areas will be called bad spots. Each of these bad spots should be analyzed in detail on the succeeding pages of the report.

Figure 5.2: Poor RSRP Filtering and Analysis samples from Cluster DT

LTE DT ANALYSIS GUIDELINES 5.1.3

Weak Coverage Analysis & Action Area with signal strength < -110dBm will be consider as weak coverage area. Key point for weak coverage analysis and action as below:-

Flow 5.2: Weak Coverage Analysis

a.

b.

c.

d.

Dominant Cell Checking – Cross check for any plan cell dominant the area, if no proceed to best effort optimization; if yes, cross check on the status of the plan cell over next action. Cell status checking – Cross check is the plan cell On Aired? If yes, proceed to next step; If no, take note of the cell and proceed with best effort optimization; re-optimize the area after cell on air. Dominant Optimization – Serving cell and neighbor cell should have a delta of 10dBm different in order to dominant an area. Neighbor cell should be down tilt once the different found to be < 10dBm causing poor dominant coverage over the area with lots’ of ping pong handover issue. Best effort Optimization – Since the area already well know is coverage holes area, RNO should beware not to over-tilt neighbor cell to serve the area. Shall there be any proposal implement, RNO should always cross check from TA value after up-tilt proposal to prevent overshooting coverage issue on neighbor cell Case:Area circled as red below found to have poor coverage. Further verification found there’s a plan site that yet to integrate and On-Air. Best effort optimization performed with note, re-optimization of the area to be trigger after site On-Air.


Identification of Overshooting Coverage Analysis Overshooting coverage has to be avoided to ensure good network quality. Always ensure the serving cell is the nearest cell. When a signal strength is worst than 110dBm and overlapped with another nearer serving cell signal, the said signal are consider to be overshooting.

Flow 5.3 Overshooting Analysis

a.

PCI Plotting Check RNO can cross check from PCI plotting in Genex Assistant tools to verify for any overshooting cell via PCI color grouping. (by plotting the “Serving PCI” into active map, and select the “Synchronize Cell Color” symbol) PCI plotting of picture on below Figure 5.3 show a good example whereby PCI 62 and 63 had been spotted easily having overshooting issue.

Figure 5.3 PCI Plotting Check

b. TA Check Double confirmation from TA.UE index value from OSS KPI may be referred for overshooting cell. Each “TA.UE.Index” value symbolic a range of distance of UE performing Random Access. During optimization, RNO have to minimize the overlapping of cell coverage between source and target cell base on TA.UE.Index range.

Figure 5.4 L.RA.TA.UE Index Table

LTE DT ANALYSIS GUIDELINES Case:Analysis below showing the serving cell have coverage concentrated at radius of 2 ~ 10km while the nearest site (approximately 800m) is not serving. Solution was proposal on down-tilting the far serving so the nearer cell can dominant* the coverage, following with a Drive Test rectification. * Study the TSSR of the nearby site to cross check is there any blocking.

Serving Cell Timing Advance

Timing Advance of Target Cell

5.1.5

Lack of Dominant Cell Identification and Analysis Lack of dominant coverage may be another common issue contributing on poor coverage. Lack of dominant coverage can be caused by following two conditions and the solution is similar with clause 5.1.2.1 a. Coverage hole area Similar with weak coverage, RNO have to cross check is there any dominant cell over the said area or not. Details please refer clause 5.1.3 on weak coverage analysis. b.

Poor Optimization Common case in lack of dominant cell, whereby there are too many dominant signals over a single spot. Due to LTE doesn’t practise SHO but HHO, each overlapping signal will be consider as a noise towards the dominant cell. RNO have to ensure each area has only ONE dominant cell with minimum 10dBm delta different between the serving and neighbour cell’s signal strength over cell centre, whereby overlapping coverage limited to cell edge only for Handover purpose.*RNO may refer clause 5.3 for antenna optimization guidance for poor optimization issue. *Indosat’s practise cell re-selection / intra-frequency handover triggering threshold of 3dBm delta between serving and target cell.

LTE DT ANALYSIS GUIDELINES 5.2 Poor SINR Analysis 5.2.1 Why Poor SINR? SINR (Signal to Interference-plus-Noise Ratio) is a measurement of signal quality which is not defined in the 3GPP specifications but defined by the UE vendor. There are few common scenarios contributing towards poor SINR as below:Lack of a dominant cell: - Area where there is no dominant cell or the dominant cell change frequently. There are several overlapping cells, and the signal strength is similar. (details refer clause 5.1.5) PCI Mod Conflict - Due to PCI MOD 3, 6 and 30 theories; PCI MOD conflict will contribute towards poor SINR quality. UL Interference Checking UL Interference cross checking from OSS counter.

Flow 5.4 Reference flow for Poor SINR

5.2.2

Identification of Bad Spot DT result with SINR < 7dB are consider poor quality spot and required to be highlighted for quality analysis. Signal Quality SINR

[0, 7) <0 Table 5.3: Poor SINR Filtering Criteria

Once bad spot had been filtered, RNO could proceed on checking is there any dominant cell serving the area. Shall there be any case whereby there’s no dominant cell coverage and neighbor cells is more than 3 with RSRP within 10dBm different, RNO may proceed to perform antenna down-tilt proposal on neighbor cell.


PCI MOD Conflict In LTE system, the physical cell identifier (PCI) is used to differentiate radio signals of different cells. PCI can be reused in the whole network, but should be unique in one coverage area to ensure UE can distinguish different cells. PCI cross checking on cluster is a must action. PCI= 3 * SSS+ PSS SSS = 168 groups PSS = 0,1,2,3 cells / group UE captures ID within PCI Group through demodulating PSS (Primary Synch Channel), and captures PCI Group ID through demodulating SSS (Secondary Synch Channel). Thus, it is the main requirement to avoid PCI collision and confusion under the same group of PCI within nearby area (MOD 3 for MIMO 2, 4 antenna system while MOD 6 for SISO antenna system). Due to DL PCI conflict is reflected on Reference Signal and PSS/SSS, while UL signal is DMRS and SRS, thus UL PCI conflict can be in the different up to 30 groups (MOD 30) with the same concept applied. When a PCI MOD conflict is found, RNO may refer to below action flow as reference.

Flow 5.5 PCI MOD Conflict Checking

Case 1 (PCI MOD 3 Conflicts):Shown as below picture, the PCI of serving cell is 7, the PCI of the first neighbouring cell is 13, which have the same mod3. And the SINR is low. By exchange the PCI of the first neighbouring cell with that of the other cell on the same site. That is, exchange PCI 13 with PCI 14. After the exchange, the average SINR increases by 7dB.

LTE DT ANALYSIS GUIDELINES

Case 2 (PCI MOD 30 Conflicts):Shown as below picture, cell L_AREA_PSR_KLIWONKP_SEWU_KN3 and cell L_PASARKLIWON3 have overlapping coverage and have the same PCI MOD 30, which will effect with poor UL signal. From analysis, we found coverage of PCI 122 is overlapping with coverage of site PASAR_KLIWON_TIMUR. Cross verification from Google Map also show the area has a flat terrain. Thus, re-azimuth of L_PASARKLIWON3 from azimuth 330d to 210d and AREA_PSR_KLIWONKP from azimuth 210d to 240d will improve the issue.


UL Interference Checking Always cross check the “L.UL.Interference.Avg” counter from OSS KPI for UL interference checking. a. If the value of L.UL.Interference.Avg is greater than -105dBm**, the interference is considered high. b. If the value of L.UL.Interference.Avg is greater than -105dBm** for the entire day, the cell post risk on abnormal interference.

Flow 5.5 Interference checking flow

LTE DT ANALYSIS GUIDELINES 5.3 Antenna Optimization RNO may propose antenna optimization when poor RSRP, poor SINR or other related issue encounter. Below is the guideline for Antenna Optimization Proposal.

Flow 5.6 Antenna Optimization

5.3.1

Terrain / Contour Analysis If there is any suspect poor coverage are due to terrain/contour issue, it can be cross check using Google terrain/contour snapshot of the serving site/cell to bad spot: To use Elevation Profile, user may use the “Ruler” option in Google Earth to draw a line > Save the path > Right click on the path saved and proceed with the option of “Show Elevation Profile”

Figure 5.5 Show Elevation Profile at Google Earth

In addition, Google Earth now enhanced with a street view setting at the corner right where you may cross check the street view setting. (Depending on the city and option)

Figure 5.6 Street View Option in Google Earth


TSSR Checking Cross checking of TSSR data may assist RNO on the decision making when comes to Antenna Re-Engineering. Panoramic view from TSSR may provide the information to RNO either the antenna is suitable for up-tilting or re-azimuth. Example from the view of PCI 353 at the left, the coverage of cell had been blocked by the building. Thus, further up-tilt this cell will not assist in dominant the coverage of the main road over the other of the building. RNO have to perform data collection before proposing antenna re-engineering.

5.3.3

TA Checking It is important to cross check and analyze the TA index before and after antenna reengineering on the source and neighbor cell. Details may refer clause 5.1.4.

5.3.4

Tilt Analysis (Kathrein) Tools Kathrein scale division tools can be use to cross check and simulate antenna beam coverage before performing uptilt / downtilt of antenna. With the result being referred, risk of over-tilt can be prevented.

Figure 5.7 Kathrein Scale Division

When a sector is proposed to be down-tilted to eliminate/reduce its overshooting or limit its coverage to specific area the engineer needs to ensure that the area affected will still have good signal level from another potential best server. The engineer needs to check and ensure that the next nearest neighbour will serve the area well. Below are some reminders to be take note when performing antenna re-engineering. a. RNO only allow to perform Mechanical tilt adjustment if Eletrical tilt adjustment had reach the maximum limit (10degrees) b. RNO should always perform Tilt-Analysis before proposing antenna tilt-adjustment.

LTE DT ANALYSIS GUIDELINES c. RNO should always ensure or crosscheck from TSSR that such tilt adjustment proposal will not cause blocking / shadowing effect.

Tilt Reminder

Engineer is reminded always analyze carefully when doing physical changes: - Always check the map to ensure action is logical in terms of site-to-site distance, distance to served area, coverage on target area, etc. - Ensure that there will be other cell/site that will cover the degraded area when downtilt/azimuth change is done - Always consider neighboring cells when doing analysis - Ensure that the lost traffic will be absorbed by neighboring cells - Ensure that there will still be enough overlap of coverage with neighboring cell for proper handover. - Always check and consider terrain conditions – google earth elevation profile will be good reference. - Consider the tilt of all technologies – GSM, DCS, U21, U9 – in the analysis. - Always use Kathrein Touchdown Points or any other tool to have good estimation of tilts vs coverage. - After doing physical change verify statistics if no KPI was compromised (example is traffic reduction). - Always do a follow-up check after physical change (check from time to time if improvement is stable). - After tilts are executed check if effect is correct a. ET change in DCS – DCS cell should have changes in TA behavior b. ET change in U21 – U21 cell should have changes in TP behavior c. ET change in GSM – GSM cell should have changes in TA behavior - HARD RULE / RULE of THUMB a. U21 should ALWAYS have less or equal tilt than U9; NEVER U21 more than U9 b. DCS should ALWAYS have less or equal tilt than GSM; NEVER DCS more than GSM


Tilt Analysis – For Down-tilt & Up-tilt


Low Throughput Analysis 6.1 Bad Spots Identification Good RSRP and good SINR should result with good throughput. However, coverage hole are have to be identify and separated. Optimization shall be done on best effort for such area and propose for new site. Throughput for such area should be re-check and re-optimize after the new site had been integrated. 6.2 Bad Coverage Analysis Other than LTE resource, LTE signal quality and signal strength is the main factor effecting how the scheduling and modulation works. Thus, we need to ensure in good coverage and good SINR before expecting good throughput. 6.3 ALARM checking Check whether there are active alarms or faults that affect the service rate and clear them first. Particular attention to the following alarms: - RF Unit Hardware Fault - RF Unit PA Over current - RF Unit Clock Problem - RF Unit TX Channel Gain Out of Range - RF Unit RX Channel RTWP/RSSI Too Low - RF Unit RX Channel RTWP/RSSI Unbalanced - RF Unit VSWR Threshold Crossed 6.4 Low DL Throughput Analysis and Troubleshooting Initial analysis on DL throughput that is < 10Mbps; further analysis on Ideal KPI threshold for DL throughput to be < 20Mbps.

Figure 6.1 Lagend of LTE RLC DL Throughput.

Flow below may be reference when encounter low DL throughput performance issue.


Flow 6.1 Low DL Throughput Analysis Flow

6.4.1

AMBR Checking AMBR profiling check will able to determine what will be the maximum allocated performance the USIM could reach according the profile. Thus, AMBR check is crucial as the first step checking when encounter low throughput reading.

AMBR rate can be easily found over the “S1AP_INITIAL_CONTEXT_SETUP_REQ” message from S1 trace as show in Figure 6.2.

Figure 6.2 S1 Trace

Alternately, AMBR can be check in “Attach Accept” message as in Figure 6.3 below.


Figure 6.3 Attach Accept L3 Message

6.4.2

DL Grant and RB Utilization To obtain good peak throughput, grant count and RB utilization plays an important roles. UE should fully utilize the resources and have good MCS scheduling under good radio environment with MIMO and Rank 2 (TM3) connectivity during test. Below table show the modulation and TBS index samples according to 3GPP 36.213. With good SINR and scheduling, grant count sample will be able to modulate at higher MCS. For DL services, maximum MCS should be up to 28, range 24~28 are the higher modulation range that we would preferred. If grant samples can’t be modulated at the below said MCS, RNO are advise to cross check on the signal quality (refer to SINR optimization)


Table 6.1 Modulation and TBS Index Table of PDSCH as in 3GPP 36.213

Due to Indosat FDD network is operating at 10MHz, thus there will be a maximum of 50RBs allocated on the bandwidth. If RBs utilization can’t reach maximum, RNO are advised to cross check for any sharing of network loading by other user. Grant count sample is direct proportional with the samples of services. For FDD network, DL grant count can reach maximum up to 1000 samples. RNO may check for any active PDSCH alarm over serving cell if unable to obtain maximum grant count samples even after performing multithread services.

Figure 6.4 DL MCS capture from Genex Probe

* For FDD, Maximum DL Grant Count to be 1000. * For TDD, SA:2 SSP:7 Max DL GC = 800 ; SA:2 SSP:5 Max DL GC= 600

6.4.3

MIMO and UE Checking In order to obtain peak performance, UE transmission mode plays an important role. Outdoor Macro Site : TM3 IBC Site : TM1


Table 6.2 Details about UE Transmission Mode

RNO could proceed to check eNB MIMO configuration via “LST MIMOADAPTIVEPARACFG”, whereby recommended configured is OL_ADAPTIVE. For UE device cross checking, RNO may refer to below few steps whereby the information can be obtain via Genex Probe > Radio Parameter window. Shall any of the condition is not met, RNO are advice to rectify the UE used. Reference signal received power (RSRP) difference between the RX antenna and the RX antenna is not more than 5dB. TX and RX correlation is not more than 0.5.

Figure 6.5 Radio Parameter Window from Genex Probe

6.4.4

HO Analysis Frequent Handover or Ping-Pong Handover, Delayed handover, Handover Failure will decrease the throughput performance as LTE practice hard handover. Each handover will result to a new calculation of scheduling, thus directly impacting the performance. RNO should ensure handover only trigger at cell edge. Any ping pong handover issue over good RSRP or SINR area should perform coverage and SINR Optimization (clause 5.1 and 5.2). Cross check on the CIO value too if there are too many A3 event occurring. * Handover related case may refer to clause 7.0 and 8.0 in Handover and ERAB Drop topic

Case 1: Poor DL throughput due to Ping Pong Handover Over one of the case study over a 20MHz LTE FDD network, we found there are a lot of A3 event triggered under area with good RSRP and SINR. D Verification also found serving site azimuths were not well planned causing overlapping signal over the poor DL throughput area.


A re-optimization of azimuth of the cell improvised the dominant coverage and uplifted the performance by 17%.

6.5 Low UL Throughput Analysis and Troubleshooting Initial analysis on UL throughput that is < 5Mbps; further analysis on Ideal KPI threshold for UL throughput to be < 10Mbps.

Figure 6.6 Lagend of LTE RLC UL Throughput.

Flow below may be reference when encounter low DL throughput performance issue.


Flow 6.2 Low UL Throughput Analysis Flow

6.5.1

AMBR Checking Similar with clause 6.4.1, AMBR check is crucial as the first step checking when encounter low throughput reading. (Details may refer clause 6.4.1)

6.5.2

UL Grant & RB Utilization As explained in 6.4.2, grant and RB utilization during UL services are equally important for user to obtain good throughput. Similar with topic over 6.3.2, the only different will only be the MCS modulation for UL. If the UE close to the cell center, the count number in the UL MCS pane on the Probe should be reaching MCS 28 for category 5 UE and 900 @ MCS 24 + 100 @ MCS 23 for category 4 UE. If the sum is less than 1000, always cross check the data source is sufficient. Below table show the modulation and TBS index samples according to 3GPP 36.213. With good SINR and scheduling, grant count sample will be able to modulate at higher MCS. If grant samples can’t be modulated at the below said MCS, RNO are advise to cross check on the signal quality (refer to SINR optimization)


Table 6.3 Modulation and TBS Index Table of PUSCH as in 3GPP 36.213

Figure 6.7 DL MCS capture from Genex Probe

* For FDD, Maximum UL Grant Count to be 1000. * For TDD, SA:2 SSP:7 Max GC = 200 / SA:2 SSP:5 Max GC= 200


IBLER Checking Adaptive modulation and coding (AMC) module must be selected based on the channel quality to adapt the link change. The basic AMC module selection is an IBLER of 10% at the MCS order. Figure below show how to query IBLER of Huawei UE.

Figure 6.8 HARQ Window from Genex Probe

If the IBLER diverged, RNO should proceed to check whether the radio link is low quality and does the UE use maximum TX power. If UE doesn’t use maximum TX power, it might be UE problem. RNO should also proceed to check is the SINR adjusting switch is turned off. When the SINR adjusting switch is turned off, the SINR before MCS order selection cannot be adjusted according to IBLER, thus the IBLER cannot be converged. Run the LST CELLULSCHALGO command to query the setting of SINR adjusting switch. As show figure below, the default SINR target value in UL scheduling algorithm is 10%.

Figure 6.9 LST CELLULSCHALGO

6.5.4

HO Analysis Similar with clause 6.3.4, RNO should ensure handover only trigger at cell edge. Any ping pong handover issue over good RSRP or SINR area should perform coverage and SINR Optimization (clause 5.1 and 5.2) * Handover related case may refer to clause 7.0 and 8.0 in Handover and ERAB Drop topic


Handover Analysis/ Neighbor Relation Checking 7.1 Neighbour Relation and Configuration Checking 7.1.1 Intra-Frequency Neighbor Checking Cross check all cell have co-locate neighbour cells defined as intra-freq neighbour. Each cell required to have minimum 10 intra-frequency neighbour relations defined. LST EUTRANEXTERNALCELL; LST EUTRANINTRAFREQNCELL; 7.1.2

Inter-Frequency Neighbor Checking Cross check all cell with co-locate Inter-Frequency cell have co-locate inter-Frequency neighbour cells defined as inter-freq neighbour. LST EUTRANINTERNFREQ; LST EUTRANEXTERNALCELL; LST EUTRANINTRAFREQNCELL;

7.1.3

Inter-RAT Neighbor Checking Similar with above cases, cross checking on the Inter-RAT neighbor cells will be required. LST UTRANNFREQ; LST UTRANEXTERNALCELL; LST UTRANNCELL; There are 3 different WCDMA layering strategy depending, which are F1 – 10713; F2 – 10688 as U2100 and U900 – 3011.

7.2 ANR Switch Check Cross check all ANR switch over eNodeB algo switch are turned on. IntraRatEventAnrSwitch @ AnrSwitch IntraRatAnrAutoDelSwitch @ AnrSwitch 7.3 Handover Configuration Check Cross check all threshold and parameter are correctly defined LST INTRARATHOCOMM LST INTERRATHOCOMM LST INTRAFREQHOGROUP LST INTERFREQHOGROUP LST INTERRATHOUTRANGROUP * Parameter threshold may refer to parameter audit guideline. * Handover related case may refer to clause 9.0 in ERAB Drop.


ERAB Drop Analysis 8.1 Identification Method There are several scenarios in LTE Cluster DT that may lead to drop of service, usually (but not limited) to below: Cross coverage caused call drop  Missing neighbor cell relationship caused call drop  UE inter-signaling procedures caused call drop * examples included @ case sharing below

Formula: eRAB AbnormRel/eRAB Setup Success * 100 From Genex Probe, the observation windows related call drop in Probe are shown in Figure 8.1& 8.2:

Figure 8.1 KPI Statistics and Event List Window at Genex Probe.

Figure 8.2 Event Statistics Window at Genex Probe.

Each call drop event can be unique, thus separate analysis needed to be done. Analysis can be start with below guidance:-

Coverage Checking

Ensuring there are dominant coverage

Signaling Checking

Identify actual issue from signaling flow

Flow 8.1 Analysis Flow of E-RAB Drop

Neighbor Relation Checking

Parameter and neighbor relation checking

LTE DT ANALYSIS GUIDELINES 8.2 Coverage Check If the signalling analysis result shows that the call drops are related to poor signal quality (RSRP < 116dBm, SINR < 0dB), you are advised to perform network coverage optimization in the corresponding area. Details may refer to clause 5.1

Figure 8.3 Example of UE at Poor SINR environment

LTE DT ANALYSIS GUIDELINES 8.3 Signaling Analysis 60% of call drop in drive test are due to handover issue. Thus understanding the handover signalling flow is mandatory in order to indentify the root cause. Figure 8.4 and 8.5 below show the basic signalling flow of Handover.

Figure 8.5 Signaling Flow of S1 and X2 Handover

LTE DT ANALYSIS GUIDELINES Case 1: After UE sending a Measurement Report to eNB, enB will proceed and send a “S1AP_Handover_Required” to MME and awaiting a confirmation of “S1AP_Handover_Request” and so on. However, eNB doesn’t receive such message from MME, whereby eNB will then release of the UE connection. Understanding the signalling flow is crucial to identify this drop.

8.4 Neighbor Relation Check Neighbour relations are the bridges for handover. Missing or configuration error of neighbour relations will lead to handover failure. Thus, neighbour relations and related switch checking is mandatory. Details of neighbour relation check were initial introduced over clause 7.1. System

Intra-Frequency

Defining the frequency

N/A

Defining the external Cell Defining the neighbor relation

Inter-Frequency

IRAT

ADD EUTRANINTERNFREQ; ADD UTRANNFREQ; ADD EUTRANEXTERNALCELL; ADD UTRANEXTERNALCELL;

ADD ADD EUTRANINTRAFREQNCELL; EUTRANINTERFREQNCELL; Table 8.1 MML Command for Neighbor Relation Check

ADD UTRANFREQNCELL;

Besides that, IntraRAT event ANR switch needed to be turn ON too. (Please refer to clause 7.2) Figure 8.5 show an example of missing neighbor configuration. By clicking the measurement report, RNO may know what the PCI has reported. Cross check the PCI reported with the neighbor relation defined to confirm is there any missing neighbor definition over the serving cell.

Figure 8.6 Example of Missing Neighbor Measurement Report over L3 Message.

LTE DT ANALYSIS GUIDELINES Case1: Poor Coverage UE trigger handover during poor coverage radio environment is the common contribution on call drop even. Radio optimization will be required to improvise such issue.

Case 2: Cross Coverage After UE received HO CMD (RRCCconnectionReconfiguration), UE failed to make a Random Access in target cell, at last UE had a call drop. In the same time, we notice that UE is 10km from target cell, which seems quite far ENB’s parameter shows the cell radius is 4km: MOD CELL:LocalCellId=2, CellName=93575-2, SectorId=2, CellRadius=4000.

UE is 10km from target cell, but the cellRadius is 4km, that is why UE failed to random access in target cell. So this call drop is due to a cross coverage of the target cell.

LTE DT ANALYSIS GUIDELINES Case3: Missing neighbour relations

Review the signalling flow: The signalling shows that UE send many A3 Measurement Reports to eNB, but UE didn’t get the Handover command (Figure 3). At last UE had a very bad signal quality, a call drop happened. Check eNB HO parameter (The configuration file is collected on 28th May): a. Check “LST EUTRANEXTERNALCELL” and “LST EUTRANINTRAFREQNCELL”, site have a normal neighboring relation with all the target cells. b. Check handover switch and ANR switch:NoHoFlag=PERMIT_HO_ENUM,MOD ENODEBALGOSWITCH:HoAlgoSwitch=IntraFreqCoverHoSwitch-1. The parameter is OK. Since the site have well defined neighbour relation, what could go wrong? A further cross check on the operational logs and OSS result, we found the neighbour relations was added by ANR after the switch was enabled

LTE DT ANALYSIS GUIDELINES Case4: UE inter-signalling procedure Signalling review skill will be required for this analysis. Cross checking UE signalling and look for the missing / error signalling in normal radio environment. Re-confirmation of analysis with S1/Uu trace for confirmation will be required. Example of event below due to missing “RRCConnectionReconfiguration Message”; with the flow in clause 9.3 being referred, the UE should receive such message after feedback measurement report to eNB. A further checking found the site have VSWR issue.


CSFB Analysis 9.1 Identification Method Check whether the CSFB success rate does not meet the standard. Formula: Number of times the alerting message is received or sent / Number of times the UE sends Extended Service Request message. 9.2 Signaling Analysis Perform comparison and analysis based on the standard process to identify the abnormal points of the signalling. Complete CSFB: Extended Service Request (4G) RRC Connection Release (4G) Alerting (3G) If the procedure failed on 4G side, for example, there is no RRC Connection Release message, make the CSFB related parameter check on 4G side. If the procedure failed on 3G side, check the 3G radio quality/traffic/load. 9.3 CSFB Signaling Flow During CSFB based on PS Re-direction, the UE is transferred from the E-UTRAN to the UTRAN by performing Blind Redirection. It then initiates a CS service in the UTRAN.

Figure 9.1 Signaling Flow of CSFB

9.4 Parameter Check If the fail setup happened on LTE side, please check the following parameters on the corresponding eNodeB. LST ENODEBALGOSWITCH HoModeSwitch UtranRedirectSwitch-1& BlindHoSwitch-1 LST CELLHOPARACFG HoModeSwitch BlindHoSwitch-1 LST CSFALLBACKPOLICYCFG CsfbHoPolicyCfg=REDIRECTION-1, IdleModeCsfbHoPolicyCfg=REDIRECTION-1 LST UTRANNFREQ; LST UTRANEXTERNALCELL; LST UTRANNCELL; Check if configure BlindHoPriority=32 for the co-sector UMTS sector.

LTE DT ANALYSIS GUIDELINES Case1: CSFB MOT stochastic fail

1. Further checking on CSFB switch

2. Further checking on Alarm - Clear 3. Further checking on Neighbour relation and found no BlindHo priority was set for the neighbour relation. Thus, CSFB will become stochastic fail. 4. A re-configuration the neighbour relation with related BHO priority had solved the issue.

LTE DT ANALYSIS GUIDELINES 10.0 PARAMETER OPTIMIZATION 10.1 LTE Parameter Optimization – Idle and Reselection Parameter CIO Offset is the most recommended parameter to adjust if an engineer wants to advance or delay a HO since it is neighbor relation specific parameter and HO to other neighbors’ are not affected. However, cluster analyzer is advised to discuss with the senior RNO on the change and effect of this parameter before implementation. Reminder:- All Engineer are reminded to discuss with senior RNO / TL before implementing any parameter optimization change. All parameter change must gain documented approval from NPO / ISAT.

10.2 LTE Parameter Optimization – Handover Parameter There are other handover related offset and hysteresis parameter which can be optimized for handover event triggering. However, cluster analyzer is not advised to propose for this parameter. Further details may refer to senior RNO. Be careful in adjusting the HO parameters below as they affect HO to all neighbors. If an engineer wants to advance or delay HO with a particular cell/neighbor then a neighbor related parameter should be adjusted such as CIO and CIO offset. Reminder:- All Engineer are reminded to discuss with senior RNO / TL before implementing any parameter optimization change. All parameter change must gain documented approval from NPO / ISAT.

Table 10.3 LTE Handover Event

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