LTE Retainability Problem cause & solution a-z step

Definition: Ability of a user to retain the E-RAB once Connected for the desired duration.

 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) :-

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).

Soln: 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).

Soln:1>PCI Collision issue check(PCI Planning should be correct).There should no PCI re-use within near by cell(1tier,2tier neib).

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

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

4> Also Repeater is responsile sometimes for Hi-UL Interference.Might be due to Power Leakage

RetainAbility/SARR(Session abnormal release rate) 

4> H/W issue,Alarm issue.Correct the issue based on Problem u Identify.Take help of Alex if you are not Understanding the Alarm meaning.

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. active).

Soln: 1> Solve the Poor Coverage issue by making Tilt,Azimuth change or Parameter change(Part of Sector Pwr,ENB Power), for uplink Coverage(P0NominalPucch,P0NominalPusch).

2> High Ul Interference issue(As per earlier mentioned.Also make sure Nominal pwr Should not set very high otherwise it will create interference in neib cell).

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). Soln:1. Recently this issue I have faced in “Sprint NV Project”.After analysis it was found that there was issue with LKF file.Once New LKF file uploaded issue get resolved.

2. If LKF is correctly loaded then This counter will Peg only When user have crossed the ENB License limit.

Pls upgrade the License.Once u think that every basic Optimization u have done.

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).

Soln: 1> Raise Ticket to NOC or IM Team to resolved the issue.

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.e. active).

Soln:1>MME might be Locked/ disabled.

2>  MME mismatch b/w Scource & Target cell.

3> Tranport issue suspected.

4> License issue suspected.

5> Site Configuration issue.

6> Hi-Load on Target Cell.

RetainAbility/SARR(Session abnormal release rate) 

› From drive test analysis, it was observed that a large portion of the drop calls were due to poor radio environment.

› Just before HO, 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.

› In this optimization project, 2 parameters were tuned; 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

Retainibility/SARR(Session abnormal release rate) :

With current A3 setting, A3 event handover will be performed when neighbour cell is greater than a3Offset + hysteresis (RSRP) of the current serving cell.

a3Offset = 3 dB, hysteresis = 1dB  Handover will only be performed once Neighbour Cell RSRP > 4dB of Serving Cell RSRP

Thus, it is important to expedite the HO with reduction of a3Offset to 2 dB. After the parameter change, it was observed that the drop calls due to call dragging was reduced in a cluster of 20 sites.

RetainAbility/SARR(Session abnormal release rate) :-