LTE Optimization Guidelines

ACCESSIBILITY for the E-UTRAN is a measure of the ability of a user to obtain an E-RAB from the system.

The Initial E-RAB Establishment process can be divided into the following phases:

ØRRC CONNECTION ESTABLISHMENT

ØS1 SIGNALING CONNECTION ESTABLISHMENT

ØINITIAL E-RAB ESTABLISHMENT OR E-RAB ADDITION 

ACCESSIBILITY for the E-UTRAN is a measure of the ability of a user to obtain an E-RAB from the system.

The Initial E-RAB Establishment process can be divided into the following phases:

ØRRC CONNECTION ESTABLISHMENT

ØS1 SIGNALING CONNECTION ESTABLISHMENT

ØINITIAL E-RAB ESTABLISHMENT OR E-RAB ADDITION

Major Reasons for poor accessibility

1.Poor coverage

ØCheck inter site distance with neighbors site.

ØCheck value of pmBadCovEvalReport (if MCPC enabled, need to check pmCriticalBorderEvalReport). If this counter is pegging high in respect to RRC attempts, then we can say that more number of UEs  are falling in bad coverage.

ØCheck  pmRadioTbsPwrRestricted  to see if UE has reached maximum power of UE.

ØCheck if the cell is overshooting and the power of the cell is to high

Ø

2.Alarms

ØThrough OSS commands “alt” (Current / Active site alarms can be checked) & “lga <nd>” (n is an integer value) (Site alarms present for n days can be checked) .

ØSometimes, due to MOs are not synchronized properly, pmRrcConnEstabFailOverload is pegged high. In this case, the ServiceUnavailable (S1 Connection failure) alarm is observed in sites, even though RRC Conn Users remain to be same.

3.High Load (High Traffic)

ØThe command “ue print -admitted” is used to find the no. of UEs currently latched to the site sector-wise ROP-wise & the counters “pmRrcConnMax (max)” & “pmRrcConnMax (sum)” are used to find out ‘max. active users/ day’ and ‘sum of all active users/day’, respectively.

ØConnected User License Congestion

           Check counter “pmRrcConnEstabFailLic” . If this counter is pegging, which means there will be rrc connection request reject

          due to Connected User License limitation.

4.H/W issue (Hard Reset on site)

ØIf RRUs  are disabled, in that case “HW fault” alarm is observed in sites.

ØCommand “st . aux” shows that the operational state of the auxiliary unit/ RRUs is DISABLED.

Major Reasons for poor retainability 

1.Poor coverage*

        Check if the cell is not overshooting and power per sector is not configured too high.

        Check the CRSgain parameter if needed set to zero (default value)

 2.   Alarms*

        Need to check alarm for HW fault and Transport alarm and Mixed Mode Configuration issue.

3.High UL RSSI Issue

ØHigh UL N+I is impacting to all KPIs. UL NI values {-119 …….. -110 dBm} is considered to be good.

ØThe cause may be Internal Sources (Check Tx & Rx antenna ports, fiber cables and connectors. All connection should be proper) and External Sources ( like repeaters, airport, power plant etc. sources resulting in high EMW in the neighborhood).

ØpmRadiorecInterferencePwr is checked for UL N+I values.

4.VSWR over threshold*

           The cabx command provides VSWR status for RL1 & RL2 (for 2T2R). Both, RL1 and RL2 should be difference of less than 5.

5.    HO failure : If a sector is having high HO Execution fail, it results in poor retainability.

Probable Solutions: -

The counter pmErabRelAbnormalEnbActHo is checked. If this counter is pegging high, it implies poor retainability and resolution of sector HOSR is required.

6.Missing Neighbour

As we implement ANR in the network, just need to make sure that Eutranfreqlrelation to 1350 already created on the EnodeB (per Eutrancell)

 Counter-wise problem identification Steps

NOTE: MME drops are also very high during Poor RET. Need to investigate at MME end.

There is a limitation in MME drops analysis, these cannot be analyzed with the help of ENIQ alone, we need MME statistics for this.

If MME drop is high, we need to investigate through the following steps :

üIf BH/Core issue à All sectors will be impacted

üIf MME issue à Multiple sites in the NW will be impacted.

SARR - Issues & Solutions

1.pmErabRelAbnormalEnbActCdt – The total number of abnormal ERAB releases by the eNB per cell due cell down time (manual intervention) with the pre-condition that the Initial Context Establishment procedure must first have been successfully completed and that there was data in either the UL or DL buffer (i.e. active).

Probable Solutions : - Check Outage report or Fluctuation Report.

2.pmErabRelAbnormalEnbActHo – The total number of abnormal ERAB releases per cell by the eNB due to handover execution failure and that there was data in either the UL or DL buffer (i.e. active).

Probable Solutions:-

üCheck PCI Planning is correct or not, to avoid PCI collision issue. There should not be any PCI re-use in nearby cells (Tier 1, Tier 2 neighbours).

üCoverage issue(make Any PCI Dominant which should be based on Clutter as per Common sense). Make EDT, Change Azimuth

üHigh UL Interference issue on Target cell (PmRadiorecInterferencePwr). Check Connection b/w Antenna Connector & RRU Connector.

üAlso Repeater is responsible sometimes for Hi-UL Interference. Might be due to Power Leakage.

3.pmErabRelAbnormalEnbActUeLost – The total number of abnormal ERAB releases by the eNB per cell due that the contact with the UE is lost with the pre-condition that the Initial Context Establishment procedure must first have been successfully completed and that there was data in either the UL or DL buffer (i.e. active).

Probable Solutions:-

üSolve the Poor Coverage issue by changing  tilt / azimuth or appropriate parameter value setting, E.g. : - partOfSectorPower, ENB Power, P0NominalPucch / P0NominalPusch (for uplink Coverage).

üHigh UL NI Issue(As per earlier mentioned. Also make sure Nominal power Should not set very high otherwise it will create interference in neighbour cell).

4.pmErabRelAbnormalEnbLic – The total number of abnormal E-RAB Releases initiated by the RBS due to license reject (per cell).

5.pmErabRelAbnormalEnbActTnFail – The total number of abnormal ERAB releases per cell due to S1 interface down, "X2 interface down" or "Transport Resource Unavailable", with the pre-condition that the Initial Context Establishment procedure must first have been successfully completed and that there was data in either the UL or DL buffer (i.e. active).

Probable Solutions : - Issue can be resolved with the help of NOC / IM Team by raising the required tickets.

4.pmErabRelAbnormalEnbActHpr – The total number of abnormal ERAB releases by the eNB per cell due to handover preparation and that there was data in either the UL or DL buffer (i.e. active).

Probable Solutions:-

üMME missing issue or MME might be disabled.

üTransport issue suspected.

üLicense issue suspected.

üSite Configuration issue.

Mobility  - Intra (Preparation / execution)

When Intra LTE Handover triggered by event A3 , then ue will have 2 phase before HO takes place :

Preparation – The Source eNodeB sends a request to the Target eNodeB, which performs admission control

Execution – After successful preparation, the Source eNodeB sends a handover command to the UE

Major Reasons for poor mobility (Preparation)

Typically, handover preparations fail if there is something wrong with the target cell.

POSSIBLE CAUSES OF HANDOVER PREPARATION FAILURES

üMME pool should be same.

üIf HO-Preparation fail = 100%, it might be due to MME pool different at source and target end.

üThe command get . termpointmme can be used to find out the MME pool IPs. If different, set as per Market MME pool . (In Jabo  area all Enode B should only connect to one MME Pool (CISCO) after  last migration Sept 7, 2016.

üTarget cell is overloaded (High capacity): Target cell is suffered from CUL Congestion

üTarget cell Unavailable or has active alarm  :  The target cell is down / disabled, X2 or S1 alarm or fault HW alarm.

üFeature / License related to IntraFrequency Handover is not active / disabled

üEnodeB id Conflict, between 2 enodeB that connect to same MME Pool.

ü

POSSIBLE CAUSES OF HANDOVER EXECUTION FAILURES

üANR PCI Conflict (Collision & Confusion)*

üTarget exceeds cell range: The target cell is more than 15km from the UE (or the current cell range setting). In that case Ho-Exec fail occur.

üTarget is a sleeping cell – The target cell is sleeping, need fixed sleeping on daily basis.

üTarget has high uplink interference* ,

         If UL N+I is less than -110 dBm, in that case Ho-Exec fail occur.

üPoor RF conditions*

üRACH Failure to target cell

         Based on ‘Zero Correlation Zero Configuration‘ parameter RACH root Sequence index need to be planned. Difference of 10 is

Major Reasons for poor mobility (Preparation)        

  recommended for RACH root Sequence index per cell.

Typically, handover preparations fail if there is something wrong with the target cell.

POSSIBLE CAUSES OF HANDOVER PREPARATION FAILURES

ü

üCheck feature related PSHO in both side  Enode B (source) and Target (RNC)

         For 3G , PSHO feature is per RN C level.

üTarget cell is overloaded (High capacity): 3G Cell is having congestion (Power, Code, CE , SF and HS and EUL user admission.

üTarget cell Unavailable or has active alarm  :  The target cell has active alarm.

üCheck if RNCid, RAC, LAC and SC of target is correctly defined in Source Cell.

         Check if  3G RNCid , RAC , LAC and SC is correctly defined in Enode B (as Source Cell) under MO :  ExternalutrancellFDD  . Miss

          match  of RNCid , RAC , LAC frequently happen after BTS Rehoming Activity. For SC , it might happen when there is SC retune in

         corresponding 3G Cell target. When miss match detected , utrancellrelation deletion  can be done to mitigate this issue.

POSSIBLE CAUSES OF HANDOVER EXECUTION FAILURES

üANR PCI Conflict (Collision)

üCheck if the cell (Source) is overshooting that cause PCI Collision.

üCheck parameter “RelocOverallValue” is set to 10s

           tRelocOverallValue recommended value for EnodeB that  connect to CISCO MME.