LTE Radio Network Optimization

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LTE Radio Optimization 28-10-2021


Temas Recomendables LTE Air Interface The Air interface LTE Air Interface General Principles Dynamic Resource Allocation Intra LTE Mobility

LTE Counters and KPIs Standard Definitions KPI Overview KPI Definitions Template E-UTRAN KPI Definitions

LTE Counters and KPI OSS aspects principles Performance measurements within OSS hierarchy Performance measurement activation and architecture

LTE Functionalities and Features Overview LTE/EPC Network Elements LTE Radio Interface and the X2 Interface Physical Layer Technologies LTE UE Categories RRM Framework

LTE Counters and KPI (KPI architecture) Field measurement KPIs RAN KPIs E-UTRAN measurement architecture LTE Performance Measurements

Channel Configuration and Random Access Overview DL Channels and Signals UL Channels and Signals Random Access RA Procedure Preamble Generation


Temas Recomendables Admission Control Task of Radio Admission Control Admission Control Algorithms and Thresholds Smart Admission Control Power Control Overview UL-PC: PUSCH UL-PC: PUCCH DL-PC Adaptive Modulation and Coding Outer Loop Quality Control DL Adaptive Modulation and Coding (AMC) UL Adaptive Modulation and Coding (AMC) Inner Loop Link Adaptation (ILLA) Outer Loop Link Adaptation (OLLA) Adaptive Transmission Bandwidth (ATB) Extended UL Link Adaptation (E-ULA) Fast Uplink Adaptation (F-ULA)

Idle Mode Mobility Measurements in LTE Cell Selection Cell Reselection Mobility States Intra LTE Mobility Connected Mode Mobility Overview Measurements Management Intra Frequency HO o Intra Cell HO o Better Cell HO o Coverage HO HO over S1 CSG Cell Support / S1 based handover towards CSG cells Inter Frequency HO Mobility Offsets. UL & DL Scheduler DL Scheduler UL Scheduler


Field Measurement KPI Classification W-CDMA BS Firewall

GGSN GPRS Backbone

Field Measurement KPI can be classified into the following categories Field • Coverage Measurement KPI • Accessibility • Retainability BS LT • Service Quality E • Mobility

RNC

CS data Modem server

3G MSC PSTN

S-GW

S1 Field Measurement KPI

PS data server

3G SGSN

FMT

P-GW

Internet

Internet


Field Measurement KPI LTE Accessibility: RRC Setup Success Rate E-RAB Setup Success Rate S1 Setup Success Call Setup Success Rate

eNodeB 1

UE

Usage: Cell Availability Resource Block Usage PDCP/RLC Layer Throughput

X2

X Retainability: RRC Drop Rate E-RAB Drop Rate KPIs are categorized to distinguish different performance aspects. The names indicate the respective category according to 3GPP32.410 and 3GPP32.450.

Mobility: Intra eNodeB HO Success Rate Inter eNodeB HO Success Rate

Integrity: Average CQI Average Latency RLC PDU Retransmission eNodeB2

Inter RAT X redirection


Top Level KPIs FDD FL15a/ TL15a Category Accessibility

Retainability

Integrity/Quality

Key Performance Indicator Initial E-RAB Accessibility Total E-UTRAN RRC Connection Setup Success Ratio Initial E-RAB Setup Success Ratio E-RAB Drop Ratio, RAN View (pre-emptions excluded) E-RAB Retainability Rate, RAN View, RNL Failure with UE Lost IP Scheduled Throughput in DL

Usage

LTE_5112c LTE_5025e LTE_5581b

PDCP SDU Delay in DL Average Latency Uplink Total HO Success Ratio, intra eNB

LTE_5350a – 5358a LTE_5359a – 5367a LTE_5471a-5479a LTE_5137a LTE_5043a

Total HO Success Ratio, inter eNB X2 based

LTE_5058b

Total HO Success Ratio, inter eNB S1 based

LTE_5084a

Average PDCP Layer Active Cell Throughput DL Average PDCP Layer Active Cell Throughput UL Average Active UEs with data in the buffer DL Average Active UEs with data in the buffer UL Cell Availability Ratio

LTE_5292d LTE_5289d LTE_5800d LTE_5801d LTE_5750a

IP Scheduled Throughput in UL

Mobility

KP ID LTE_5060i LTE_5218e


KPI Architecture and Counters New KPIs for FL15a/ TL15a KPI Id

Name E-RAB Setup Failure Ratio per Cause

LTE_5761a - LTE_5763a

Release FL15a/TL15a

LTE_5703a-LTE_5705a

E-RAB Drop Ratio per Cause

FL15a/TL15a

LTE_5693a – LTE_5696a

E-RAB Modification Success Rate per QCI Characteristic

FL15a/TL15a

LTE_5697a LTE_5698a

E-RAB Modification Failure Ratio per Cause

FL15a/TL15a

LTE_5690a-LTE_5692a

Enhanced Cell ID Location Service Related Key Performance Indicators

FL15a/TL15a

LTE_5707a

RRC Connection Setup Failure Ratio per Cause

FL15a/TL15a

LTE_5741a-LTE_5745a

CS Fallback related Key Performance Indicators

FL15a/TL15a

LTE_5713a-LTE_5724a

Inter RAT HO with SRVCC related Key Performance Indicators

FL15a/TL15a

LTE_5711a

E-UTRAN Inter-Frequency QCI1 HO KPIs

FL15a/TL15a

LTE_5731a

Successful SCell Swap to Successful SCell Configuration Ratio

FL15a/TL15a

LTE_5728a-LTE_5730

LB HOs Related Key Performance Indicators

FL15a/TL15a

Average CQI

FL15a/TL15a

Cell in Power Saving Mode Ratio

FL15a/TL15a

SCell Scheduling Blocking Rate

FL15a/TL15a

LTE_5749a

Percentage of UEs using CoMP in the cell

FL15a/TL15a

LTE_5708a

Percentage of Time the Cell was in the C-Plane Overload State

FL15a/TL15a

LTE_5709a

Percentage of Time the Cell was in the U-Plane Overload State

FL15a/TL15a

LTE_5725a-LTE_5727a

CRAN receptions related Key Performance Indicators

FL15a/TL15a

LTE_5732a-LTE_5737a

MBMS related Key Performance Indicators

LTE_5706a

LTE_5712a

LTE_5740a

LTE_5702a LTE_5700a

LTE_5701a

LTE_5738a

LTE_5739a

LTE_5747a

FL15a/TL15a Percentage of Automatic Access Class Barring due to Overload Duration FL15a/TL15a DL Spectral efficiency FL15a/TL15a

LTE_5748a

UL Spectral efficiency

LTE_5699a

FL15a/TL15a


KPI Architecture and Counters KPI ID LTE_5060i LTE_5574e LTE_5086b-LTE_5089b LTE_5023e LTE_5209b LTE_5024e LTE_5025e LTE_5572b LTE_5090c-LTE_5092d LTE_5237c-LTE_5571c LTE_5119d LTE_5812b LTE_5587c LTE_5610a – LTE5618a LTE_5625b

LTE_5626b LTE_5004b LTE_5117b LTE_5228c LTE_5218f LTE_5227c LTE_5229e LTE_5230e LTE_5392c LTE_5562a-LTE_5564a LTE_5658a – LTE_5661a LTE_5371a LTE_5751a LTE_5752a LTE_5403b

LTE_5627b

LTE_5590c

Name E-RAB Accessibility E-RAB Setup Failure Ratio per Cause E-RAB Normal Release Ratio User Perspective QCI1 Normal Release Ratio, User perspective E-RAB Normal Release Ratio RAN View E-RAB Drop Ratio, RAN View E-RAB QCI1 Drop Ratio, RAN View E-RAB Drop Ratio per Cause E-RAB Drop Ratio, User Perspective E-RAB Drops per PDCP SDU volume, User Perspective E-RAB Release ratio due to Radio resources not available Maximum Number of Simultaneous E-RABs per QCI Characteristic the formula with counter names without any KPI ID change E-RAB Modification Failure Ratio per Cause

Modified KPIs for TL15a/FL15a

– typo correction in

Radio Bearer Drop Ratio Radio Bearer Success Ratio RRC Connection Setup Attempts Total E-UTRAN RRC Connection Setup Success Ratio RRC Connection Setup Success Ratio per Establishment Cause RRC Connection Setup Failure Ratio per Cause RRC Connection Setup Rejection Ratio per Establishment Cause Inter RAT HO with SRVCC related Key Performance Indicators – description updated Incoming HO Related Key Performance Indicators - typo correction in the formula with counter names without any KPI ID change Average SINR per Cell for PUSCH – typo in KPI ID corrected Planned Cell Unavailability Ratio – a note added without the KPI ID change Unplanned Cell Unavailability Ratio - a note added without the KPI ID change Average number of UEs utilizing UL intra-eNB CoMP


Performance Management Architecture Overview • •

• •

Groups of counters activated/deactivated within Flexi Multiradio BTS with tools. The measurement interval is configurable to 15, 30 or 60 minutes or 6, 12, or 24 hours. The upload interval is configurable (15, 30 or 60 min) When the reporting interval expires a notification is sent to OSS indicating that on or more PM files are ready for transfer

OSS Reporting Suite (RS)

BTS Site manager Administration of Measurements

PM

Network Performance Manager (NPM)

iOMS

Configuration file (Measurement activation)

Flexi Multiradio BTS

Upload notification

Measurement collection

Upload PM-report file

storage

PM


Performance management counter data flow parametrization Also optimizer, cell outage detection, SON, etc. iOMS Southbound IF

/tmp

OSS

collected xml

multiple xml eNB

Northbound IF

DB (parsing: kpireporter)

PostgreSQL – DB (cross-platform)

Kpireporter (Custom SQL queries)

OR 3rd party sw (data warehouse + analysis) through “measurement data export” interface

Reporting Suite Network Performance Manager → KPI reports


Aggregation levels and reporting – example Reporting output Export to excel

Aggregation levels and reporting – exemplary Reporting Suite output

Report name

Content of the report grouped into functional areas

Period of the measurement report

Filtered and aggregated report for the selected object


Ejemplos KPI de Radio en LTE


Uso de KPI para Troubleshooting • Los KPI se utilizan, usualmente, en conjunto para determinar la causa y posible solución de problemas en la red, así como para troubleshooting inmediatos. • Un solo KPI no ofrece suficiente información para analizar y es necesario comprender como se vinculan unos con otros junto a los conceptos de red de LTE y el conocimiento de sus interfaces y eventos principales. RRC Connection Setup Failure

Falla en Interfaz Aire

Causa

No hay mensaje de RRC CONNECTION SETUP COMPLETE de los UE

Sintoma

L.RRC.SetupFa il. NoReply > 0

Acción de Mejora Optimizar cobertura de RF en la celda y ajustar parámetro QRxLevMin


Case 1: Priority Based Cell reselection example

This example, taken from a live network, shows values set for parameters related to priority based cell reselection process. With the current settings, a subscriber would reselect higher priority ‘AWS band’ 1700 MHz frequency cell (i.e. Advanced Wireless Services. 1710 to 1755 MHz UL, and from 2110 to 2155 MHz DL band) over a low priority 700 MHz frequency cell. If some of the values are changed, reselection process would be impacted.


Case 1: Priority Based Cell reselection example NOTE : Considering Qrxlevminoffset =0 & Pcompensation =0 hence Srxlev = Qrxlevmeas – Qrxlevmin


Idle Mode Nokia Parameters for Cell Reselection MOC

Parameter

Value

Comments

LNCEL

sIntraSearch

62

Relative to LNCEL: qRxLevMin (-122 dBm)

LNCEL

sNonIntrSearch

4

Relative to LNCEL: qRxLevMin (-122 dBm)

LNCEL

qrxLevMin

-122 dBm

LNCEL

Qhyst

3 dB

LNCEL

threshSrvLow

2

LNCEL

tReselEutr

1s

LNCEL

cellReSelPrio

7

IAFIM

qOffCell

0 dB

IRFIM

interFrqThrL

2

IRFIM

qRxLevMinInterF

-122 dBm

IRFIM

interTResEutr

1s

IRFIM

eutCellResPrio

6

LTE1900 layer

UFFIM

utraFrqThrL

0

Relative to UFFIM:qRxLevMinUtra (-115 dBm)

UFFIM

tResUtra

1s

UFFIM

ucelResPrio

4

UFFIM

qRxLevMinUtra

-115 dBm

Relative to qRxLevMin (-122 dBm)

LTE2600 layer

Relative to IFFIM:qRxLevMinInterF (-122 dBm)

WCDMA layer


Case 2: 3CC CA example In this example the operator has deployed three carriers. When a network has more than one carrier, layering is important to optimize cell reselection and frequency prioritization. In this case the operator is using 2.6 GHz, 1.8 GHz, and 900 MHz LTE carriers and one WCDMA carrier. The frequency bands of 3 carriers are B3, B7 and B8.


Case 2: 3CC CA example Different cell reselection criteria for a subscriber is required when moving from high to low priority and from low to high priority frequencies. The reselection thresholds change accordingly.


Case 3: Initial Traffic Balancing This case is from a customer network where a second carrier was launched, but the traffic on 2nd carrier was very low. The operator wanted to put equal traffic on the two carriers.


Case 3: Initial Traffic Balancing There was low/negligible traffic on the second carrier until April 21st. Faulty hardware was suspected, health check was done – but everything looked normal. On April 21st, ‘CellreselectionPriority’ parameter was optimized to influence the cell reselection process for the subscribers to achieve traffic balancing. After setting correct priorities, the second carrier started taking traffic and the two carriers shared the load- as shown in the figure above. The values for the parameter ‘cellReselectionPrio’ for the first and the second carriers were set to 4 and 5 respectively to achieve the traffic balance.


Case 4: Reselection parameter Example This case is another example how the idle mode mobility parameters ‘qRxLevMin’, ‘sIntraSearch’, ‘sNonIntraSearch’ could be optimized for intra and inter frequency cell reselection. A customer network is using parameter setting as shown in the table below. The impacts of using the (current) settings are described in the same table. These parameters impact cell edge coverage and intra and inter frequency search process.


LTE Event Review Connected mode mobility is based on measurements sent by the UE. The measurement reporting by UE can be done on an event triggered and/or on a periodic basis.


LTE Event Review When a UE in RRC_CONNECTED mode measures poor coverage in the current LTE frequency, it informs the network by a measurement report for event A2 (serving cell becomes worse than threshold). Depending on the active features and the network configuration, the UE can be ordered to start new measurements before a handover, or a Release with Redirect (session continuity) is triggered. In case the serving cell is fully covered by another cell, the eNodeB can order the UE to perform a blind handover. The important basic features need to be activated and optimized and which are associated with the described mobility functionality are: • Coverage-Triggered Inter-Frequency Session Continuity • Coverage-Triggered GERAN Session Continuity • Coverage-Triggered WCDMA Session Continuity • Coverage-Triggered CDMA-eHRPD Session Continuity • Coverage-Triggered TD-SCDMA Session Continuity • Coverage-Triggered Inter-Frequency Handover • Coverage-Triggered WCDMA IRAT Handover Intra-LTE Inter-Mode Handover • Coverage-Triggered TD-SCDMA IRAT Handover


LTE Event Review A summary of coverage triggered mobility (IRAT, inter-frequency and inter-mode) is reviewed & illustrated below, if MCPC feature is not activated.


LTE Event Review Mobility with “Mobility Control at Poor Coverage” feature The “flow diagram” for the ‘Mobility Control at Poor Coverage’ (MCPC) triggered functionality is shown below. Assuming that the license is installed and the feature is activated (with the parameter ‘featureStateMobCtrlAtPoorCov’)


LTE Event Review

UEs in a cell will only make inter-frequency or IRAT measurements if the ‘ueMeasurementsActive’ parameter is set to ‘true’. The UE is allowed to make these measurements before the timer specified by the parameter ‘a5B2MobilityTimer’ expires. If the default setting of 0 msec is used, measurements are not made. The decision on whether to use event A3 or A5 for other LTE frequencies depends on the setting of the ‘interFreqMeasType’ parameter.


Dropped Call Performance Improvement 1 Parameter Name Timer T300

Abbreviated name T300

Set1 200ms

Set2 400ms

Maximum number of out-of-sync indications

n310

n10

n6

Timer T310

t310

2000ms

500ms

Timer T311

t311

3000ms

5000ms

• Making the UE deciding the out of sync status faster – Reduce n310 from n10 to n6 • Making UE to decide RL failure status earlier and start looking for candidate for re-establishment – Reduce t310 from 2s to 500ms • Allow UE to search for RRCre-estab candidate longer time – Increase the t311 from 3s to 5s


Dropped Call Performance Improvement 2 Parameter Name Timer T300

Abbreviated name T300

Set1 200ms

Set2 400ms

Set3 400ms

Maximum number of out-of-sync indications

n310

n10

n6

n6

Timer T310

t310

2000ms

500ms

1000ms

Timer T311

t311

3000ms

5000ms

5000ms

Timer T301

t301

200ms

200ms

400ms

• Set 3 has best performance due to – More time for RL failure detection in UE and therefore for startingT311 – Longer time for UE to send RRC Reestablishment Request i.e. T300 should be equal to T301

Value [%] STDEV Before

216 28/10/2015 © Nokia 2014 For internal use

Gap

0.016568947 0.17611639

RL40 Upgrade

0.160462035

0.015654355

T301,310 Change

0.146949134

0.029167255


Dropped Call Performance Improvement 3

Some site related problems Average level prior to parameter changes

=> Main improvement => Minor improvement => Minor improvement


Dropped Call Performance Improvement 4 •

Dropped calls decreased especially due to the first signaling messages which are using the selected Power Control strategy -

2nd RRCConnection Reconfiguration Complete to the target cell right after the HO

-

Clear impact visible due to the wrongly selected power control parameters

After RL40 DCR improved

After Changing P0 and Alpha, from - 90, 1 to 100,1 DR improvement once again.


DroppedCallPerformanceImprovement5


DroppedCallPerformanceImprovement5


DroppedCallPerformanceImprovement5


Dropped Call RateImprovement • Radio problem indication based on CQI DTX can be used to improve Drop Rate: This parameter “nCqiDtx tells the Number of cons ecutive CQI DTX detections required for RL failure. • The parameter defines the number of consecutive CQI DTX detections causing radio link failure indication. Special value 0 means that the feature is disabled. - nCqiDtx was tested for 2 different eNBs with different new values (0 i.e. disable and 100)

Value

ERAB drop rate

QCI1 drop rate

nCqiDtx=50

0.15

1.26

nCqiDtx=0

0.04

0.00

74% improvement

100% improvement

Value

ERAB drop rate

QCI1 drop rate

nCqiDtx=50

0.28

0.58

nCqiDtx=100

0.16

0.12

43% improvement

79% improvement


Dropped CallRateImprovement • Very big improvement from both nCqiDtx = 0 and 100 due to the fact that 55.7% of all dropped calls are caused by CQI failure


Dropped CallRateImprovement


Case: Improvement in the RACH Access Success Rate

Solution and Configuratio: The statistics about the RACH success rate and the L.RA.GrpA.Att counter on the live network indicate that the more times of the RACH access had, the poorer the success rate was.


Case: Improvement in the RACH Access Success Rate Solution and Configuration: In addition, values of interference-related counters were normal. Therefore, the issue might be caused by the access of non-false-alarm. Survey of the live network found that the two cells were beside sea. UEs in them were possibly out of cell radius.

Enable Extended Cell Range. Set its parameters as follows: MOD CELL: PreambleFmt = 1, CellRadius = 29000


Case: Improvement in the RRC Connection Setup Success Rate Background: Cell 1 on a site of project XX suffered a continual low setup success rate of approximately 40% on average, failing to meet demands.

Solution and Configuration Check results showed that the value of the L.UL.Interference.Avg counter was greater than -105 dBm, which meant that the fault was caused by uplink interference. By means of cell trace, the fault was that the RRC CONN CMP message from UEs could not be received due to uplink intermodulation interference.


Case: Improvement in the RRC Connection Setup Success Rate


Case: Improvement in the RRC Connection Setup Success Rate

Effect: The intermodulation interference was eliminated after the customer performed site engineering rectification. The RRC Connection Setup Success Rate recovers to the normal state.


Case: Improvement in the E-RAB Setup Success Rate Background: After DRX (with both entry and exit thresholds being 1000) was enabled in a certain network in country A, the E-RAB setup success rate of top problematic cells decreased by 0.08%. It was detected that UEs in these cells occasionally did not send SR, and eNodeBs did not send uplink scheduling indications to the UEs.

Solution and Configuration: Select the SmartPreAllocationSwitch option. The MML command is as follows: MOD CELLALGOSWITCH: LocalCellId = x, UlSchSwitch = SmartPreAllocationSwitch-1;

Effect: After the SmartPreAllocationSwitch option was selected, the E-RAB setup success rate became normal


Case: Improvement in the E-RAB Setup Success Rate


Case : Improvement in the Service Drop Rate Background: Network K in country L was found to suffer a high service drop rate. Since June 9, 2012, the average service drop rate of the live network had deteriorated to 20% as field engineers checked traffic statistics.


Case : Improvement in the Service Drop Rate After reviewing the operation log, it was found that the UeInactiveTimer parameter value was changed from 10s to 1800s,

The setting of the UeInactiveTimer parameter value has a direct impact on UE status. If the UE is constantly in connected mode, normal releases will significantly reduce so that service drop rate will increase.

Solution and Configuration: Set the UeInactiveTimer parameter to 10s. The MML command is as follows: MOD RRCCONNSTATETIMER: UeInactiveTimer = 10;


Case : Improvement in the Service Drop Rate Effect: The service drop rate recovers to the normal state


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