LTE RetainabilityProblem cause & solution a-z step Prepared byRajesh Kumar Point:-E-RAB release can be initiated by ENB & MME Definition based on Counter:SARR=[(PmErabRelAbnormalEnbAct+PmErabRelMmeAct)/ (PmErabRelAbnormalEnbAct+PmErabRelNormalEnb+PmErabRelMme)]*100 Enb Initiated E-Rab Release:1> PmErabRelNormalEnb 2> PmErabRelAbnormalEnbAct MME Initiated E-Rab Release:1> PmErabRelMme 2>PmErabRelMmeAct .RetainAbility/SARR(Session abnormal release rate) :Definition: Ability of a user to retain the E-RAB once Connected for the desired duration. Make EDT.There should no PCI re-use within near by cell(1tier.RetainAbility/SARR(Session abnormal release rate) :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. 2> Coverage issue(make Any PCI Dominant which should be based on Clutter as per Common sense).e. Check Connection b/w Antenna Connector & RRU Connector. Soln: Check Outage report or Fluctuation Report. active).Might be due to Power Leakage.e. Soln:1>PCI Collision issue check(PCI Planning should be correct).Change Azimuth 3> High UL Interference issue on Target cell(PmRadiorecInterferencePwr).2tier neib). active). 4> Also Repeater is responsile sometimes for Hi-UL Interference. 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. . .Take help of Alex if you are not Understanding the Alarm meaning.Azimuth change or Parameter change(Part of Sector Pwr. 2> High Ul Interference issue(As per earlier mentioned.e.P0NominalPusch).RetainAbility/SARR(Session abnormal release rate) :4> H/W issue. Soln: 1> Solve the Poor Coverage issue by making Tilt.Correct the issue based on Problem u Identify.ENB Power).Alarm issue.Also make sure Nominal pwr Should not set very high otherwise it will create interference in neib cell). for uplink Coverage(P0NominalPucch. active). 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 precondition 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. Pls upgrade the License.RetainAbility/SARR(Session abnormal release rate) :- 4> pmErabRelAbnormalEnbLic(The total number of abnormal E-RAB Releases initiated by the RBS due to license reject (per cell). active). . If LKF is correctly loaded then This counter will Peg only When user have crossed the ENB License limit. 2. 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.Once u think that every basic Optimization u have done. "X2 interface down" or "Transport Resource Unavailable".Once New LKF file uploaded issue get resolved. Soln:1. 5>pmErabRelAbnormalEnbActTnFail(The total number of abnormal ERAB releases per cell due to S1 interface down.After analysis it was found that there was issue with LKF file. Recently this issue I have faced in “Sprint NV Project”. Soln: 1> Raise Ticket to NOC or IM Team to resolved the issue. 2> MME mismatch b/w Scource & Target cell. Soln:1>MME might be Locked/ disabled. active).e. 5> Site Configuration issue. 4> License issue suspected. 3> Tranport issue suspected. 6> Hi-Load on Target Cell. .RetainAbility/SARR(Session abnormal release rate) :6>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. A3offset and a2TresholdRsrpPrim. – A3offset : change from 3 to 2 db – a2TresholdRsrpPrim : change from -120 to -110 dbm › A trial was also conducted to evaluate the impact of changing the values below for a few sites with high DCR: – DataRadioBearer : dlMaxRetxThreshold / ulMaxRetxThreshold › 8 to 32 – SignalingRadioBearer : dlMaxRetxThreshold / ulMaxRetxThreshold › 8 to 32 . it was observed that a large portion of the drop calls were due to poor radio environment. › In this optimization project. 2 parameters were tuned.RetainAbility/SARR(Session abnormal release rate) :› From drive test analysis. it was observed that the UE SINR was poor and this caused the UE to drag the call in poor radio environment rather than HO faster to a neighbour cell with better RSRP. › Just before HO. . A3 event handover will be performed when neighbour cell is greater than a3Offset + hysteresis (RSRP) of the current serving cell. a3Offset = 3 dB.Retainibility/SARR(Session abnormal release rate) :With current A3 setting. hysteresis = 1dB Handover will only be performed once Neighbour Cell RSRP > 4dB of Serving Cell RSRP Thus. it was observed that the drop calls due to call dragging was reduced in a cluster of 20 sites. After the parameter change. it is important to expedite the HO with reduction of a3Offset to 2 dB. from drive test › DRB: 400ms (8) 1600ms (32) < T310 (2000ms) analysis. 50ms (DRB) – If retransmission limit increases from 8 32. RL failure due to retransmission limit reached: › SRB: 360ms (8) 1440ms (32) Therefore. it is often observed that the drop occur before T310 time out because ReTx hits upper limit first .RetainAbility/SARR(Session abnormal release rate) :- › RL Failure Timing – t-PollRetransmit = 45ms (SRB). e. .g. › Cause: Radio Link problem –Poor RSRP. below -105dB can cause the up link synch be lost. –10 seconds later a new RRC Connection Request is sent.T301 Timer Timer is 1s.LTE Retainability Tuning › RRC Drops . the UE is unable to successfully RACH the serving cell. – .LTE Retainability Tuning › RRC Drops . UE TX Power and missing relation (PCI). tuning of HysterisisA3. troubleshoot with UETR. – If the issue is seen in good RF conditions. › Cause: Handover Failure – Check RF Conditions. The UE is unable to RACH the Target Cell at Handover. TimetoTriggerA3 and filterCoefficientEUtraRsrp parameters.T304 Timer Timer is 1s. Cause: Radio Link (RL) Synchronization .T310 Timer The UE in RRC-CONNECTED mode. Qout is defined as the level at which the downlink radio link cannot be reliably received and Qin is defined as the level at which the downlink radio link can be received with significant reliability. At the expiry of the timer T310. evaluates in the downlink the quality of the radio link of the serving cell.Poor RSRP and SINR . The UE bases its evaluation on the cell-specific reference signal relative to thresholds Qout and Qin.LTE Retainability Tuning › RRC Drops . the UE switches off uplink transmission. LTE Retainability Tuning › RRC Drops .T311 Timer › Cause: Radio Link (RL) Synchronization –UE not able to find suitable cell due to poor coverage. . UE is not able to synch to target eNB. Timing Advance alignment with target cell. –UE can reach max TX power increasing UL noise. –Poor RF. .LTE Retainability Tuning › RRC Drops – Random Access failure at Handover MAC_RA_Problem – Random Access attempt to re-sync. for no response after 10 retransmission (SIB2) › Cause: RA failure. for no response after 10 retransmission (SIB2) › Cause: RA failure. –UE can reach max TX power increasing UL noise.LTE Retainability Tuning › RRC Drops – Random Access failure at Handover MAC_RA_Problem – Random Access attempt to re-sync. . Timing Advance alignment with target cell. –Poor RF. UE is not able to synch to target eNB. LTE Retainability Tuning › RRC Drops – Maximum RLC Retransmissions › Cause: Repeated RLC Retransmissions due to unsuccessful RLC PDU reception (either UL or DL). – UL/DL interference and Poor RF conditions. . – UE will consider RL failed and initiate RRC Connection Re-establishment. – This occurs when maximum retransmission has occurred at RLC level (ARQ). qci 5 Site Level Parameter RESOURCE_FAIR (0) Site Level Parameter RESOURCE_FAIR (0) 8 1 schedulingAlgorithm .DataRadioBearer Site Level Parameter EUtranCellFDD noOfPucchCqiUsers Sector Level Parameter 640 EUtranCellFDD noOfPucchSrUsers Sector Level Parameter 590 EUtranCellFDD pdcchCfiMode Sector Level Parameter CF_Static_3 (3) EUtranCellFDD ulSrsEnable Sector Level Parameter TRUE UlFss EUtranCellFDD featureStateUlFss pZeroNominalPucch Site Level Parameter Sector Level Parameter -120 EUtranCellFDD pZeroNominalPusch Sector Level Parameter -102 QciProfilePredefined schedulingAlgorithm .RetainAbility/SARR(Session abnormal release rate) :MOC Parameter Name Parameter Type Parameter .qci 3 Site Level Parameter RESOURCE_FAIR (0) QciProfilePredefined schedulingAlgorithm .SignallingRadioBearer Site Level Parameter 160 Hidden Parameter tPollRetransmitDl .default Site Level Parameter RESOURCE_FAIR (0) QciProfilePredefined schedulingAlgorithm .qci 9 Site Level Parameter RESOURCE_FAIR (0) .DataRadioBearer Site Level Parameter 160 Hidden Parameter tPollRetransmitUl .qci 2 Site Level Parameter RESOURCE_FAIR (0) QciProfilePredefined schedulingAlgorithm .qci 8 Site Level Parameter RESOURCE_FAIR (0) QciProfilePredefined schedulingAlgorithm .DataRadioBearer Site Level Parameter 160 Hidden Parameter tPollRetransmitDl .qci 6 QciProfilePredefined QciProfilePredefined schedulingAlgorithm .qci 4 Site Level Parameter RESOURCE_FAIR (0) QciProfilePredefined schedulingAlgorithm .qci 1 Site Level Parameter RESOURCE_FAIR (0) QciProfilePredefined schedulingAlgorithm .High Cap Site System Constant ulInterferenceForgettingFactor (system constant 70) Site Level Parameter System Constant deltaPsdRs2Tx (system constant 872) Site Level Parameter 5 0 System Constant SpdcchLaGinrMargin (system constant 220) Site Level Parameter 30 System Constant numInitialAccessAndIncomingHo (system constant 556) Site Level Parameter 10 Hidden Parameter tPollRetransmitUl .SignallingRadioBearer Site Level Parameter 160 Hidden Parameter dlMaxRetxThreshold .DataRadioBearer Site Level Parameter 8 Hidden Parameter ulMaxRetxThreshold .qci 7 Site Level Parameter RESOURCE_FAIR (0) QciProfilePredefined schedulingAlgorithm . RetainAbility/SARR(Session abnormal release rate) :- Note: Any Suggestion/Feedback will be Highly Appreciable to Improve This Presentation. THANK YOU .