LTE Retainability

8/20/2019 LTE Retainability

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LTE Retainability

Problem cause &solution a-z step

Prepared by- Rajesh Kumar


2/18

RetainAbility/SARR(Session abnormal release rate) :-

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=[(PErabRelAbnoralEnbAct!PErabRelMeAct"#

(PErabRelAbnoralEnbAct!PErabRelNoralEnb!PErabRelMe"$%''

Enb nitiated E-Rab Release:-

1> PmErabRelNormalEnb

> PmErabRelAbnormalEnbAct

MME nitiated E-Rab Release:-

> PmErabRel!me

>PmErabRel!meAct


3/18


1> )ErabRelAbnoralEnbActCdt"#he total number of abnormal ERAB

releases by the eNB $er cell due cell do%n time "manual inter&ention' %ith the

$re-condition that the (nitial Conte)t Establishment $rocedure must first ha&e

been successfully com$leted and that there %as data in either the *+ or ,+ buffer

"i.e. acti&e'.

Soln: Chec uta/e re$ort or 0luctuation Re$ort.

>)ErabRelAbnoralEnbAct*o"#he total number of abnormal ERABreleases $er cell by the eNB due to hando&er e)ecution failure and that there %as

data in either the *+ or ,+ buffer "i.e. acti&e'.

Soln:1>PC( Collision issue chec"PC( Plannin/ should be correct'.#here should

no PC( re-use %ithin near by cell"1tiertier neib'.

> Co&era/e issue"mae Any PC( ,ominant %hich should be based on Clutter as

$er Common sense'.!ae E,#Chan/e A2imuth3> 4i/h *+ (nterference issue on #ar/et cell"PmRadiorec(nterferenceP%r'. Chec

Connection b5% Antenna Connector 6 RR* Connector.

7> Also Re$eater is res$onsile sometimes for 4i-*+ (nterference.!i/ht be due to

Po%er +eaa/e.


4/18


7> 458 issueAlarm issue.Correct the issue based on Problem u (dentify.#ae hel$

of Ale) if you are not *nderstandin/ the Alarm meanin/.

3> )ErabRelAbnoralEnbAct+e,ost"#he total number of abnormal ERAB

releases by the eNB $er cell due that the contact %ith the *E is lost %ith the $re-

condition that the (nitial Conte)t Establishment $rocedure must first ha&e been

successfully com$leted and that there %as data in either the *+ or ,+ buffer "i.e.

acti&e'.Soln: 1> Sol&e the Poor Co&era/e issue by main/ #iltA2imuth chan/e or

Parameter chan/e"Part of Sector P%rENB Po%er' for u$lin

Co&era/e"P9NominalPucchP9NominalPusch'.

> 4i/h *l (nterference issue"As $er earlier mentioned.Also mae sure Nominal

$%r Should not set &ery hi/h other%ise it %ill create interference in neib cell'.

.


5/18


7 )ErabRelAbnoralEnb,ic"#he total number of abnormal E-RAB

Releases initiated by the RBS due to license reect "$er cell'.Soln:1. Recently this issue ( ha&e faced in ;S$rint N< Proect=.After

analysis it %as found that there %as issue %ith +0 file.nce Ne% +0 file

u$loaded issue /et resol&ed.

. (f +0 is correctly loaded then #his counter %ill Pe/ only 8hen user

ha&e crossed the ENB +icense limit.

Pls u$/rade the +icense.nce u thin that e&ery basic $timi2ation u ha&e

done.

?>)ErabRelAbnoralEnbAct.n/ail"#he total number of abnormal

ERAB releases $er cell due to S1 interface do%n @ interface do%n@ or

@#rans$ort Resource *na&ailable@ %ith the $re-condition that the (nitial

Conte)t Establishment $rocedure must first ha&e been successfullycom$leted and that there %as data in either the *+ or ,+ buffer "i.e.

acti&e'.

Soln: 1> Raise #icet to NC or (! #eam to resol&ed the issue.


6/18


>)ErabRelAbnoralEnbAct*)r "#he total number of abnormal ERAB

releases by the eNB $er cell due to hando&er $re$aration and that there%as data in either the *+ or ,+ buffer "i.e. acti&e'.

Soln:1>!!E mi/ht be +oced5 disabled.

> !!E mismatch b5% Scource 6 #ar/et cell.

3> #ran$ort issue sus$ected.7> +icense issue sus$ected.

?> Site Confi/uration issue.

> 4i-+oad on #ar/et Cell.


7/18


0rom dri&e test analysis it %as obser&ed that a lar/e $ortion of the

dro$ calls %ere due to $oor radio en&ironment. Dust before 4 it %as obser&ed that the *E S(NR %as $oor and this

caused the *E to dra/ the call in $oor radio en&ironment rather than

4 faster to a nei/hbour cell %ith better RSRP.

(n this o$timi2ation $roect $arameters %ere tuned A3offset and

a#resholdRsr$Prim.– A3offset : chan/e from 3 to db

– a#resholdRsr$Prim : chan/e from -19 to -119 dbm

A trial %as also conducted to e&aluate the im$act of chan/in/ the

&alues belo% for a fe% sites %ith hi/h ,CR:

– ,ataRadioBearer : dl!a)Ret)#hreshold 5 ul!a)Ret)#hreshold› F to 3

– Si/nalin/RadioBearer : dl!a)Ret)#hreshold 5 ul!a)Ret)#hreshold› F to 3


8/18

Retainibility/SARR(Session abnormal release rate) :-

8ith current A3 settin/ A3 e&ent hando&er %ill be $erformed %hen

nei/hbour cell is /reater than a3ffset G hysteresis "RSRP' of the currentser&in/ cell.

a3ffset H 3 dB hysteresis H 1dB 4ando&er %ill only be $erformed once

Nei/hbour Cell RSRP > 7dB of Ser&in/ Cell RSRP

#hus it is im$ortant to e)$edite the 4 %ith reduction of a3ffset to dB.

After the $arameter chan/e it %as obser&ed that the dro$ calls due to call

dra//in/ %as reduced in a cluster of 9 sites.


9/18


R+ 0ailure #imin/– t-PollRetransmit = 7?ms "SRB' ?9ms ",RB'

– (f retransmission limit increases from F 3 R+ failure due toretransmission limit reached:

› SRB: 39ms "F' 1779ms "3'

› ,RB: 799ms "F'

199ms "3'#herefore from dri&e test

analysis it is often obser&edthat the dro$ occur before

#319 time out because Re#)

hits u$$er limit first

I #319 "999ms'


10/18

LTE Retainability Tuning

Timer is s! the "E is unable tosuccess#ully R$% the ser'ing cell(

RR% )rops - T*+ Timer

%ause, Radio Lin problem–Poor R.RP! e(g( belo/ -+0d1 can cause the up linsynch be lost(

–+ seconds later a ne/ RR% %onnection Re2uest is sent(


11/18


RR% )rops - T*+3 Timer

%ause, ando'er 4ailure

– %hec R4 %onditions! "E T5 Po/er and missing relation 6P%78(

– 7# the issue is seen in good R4 conditions! troubleshoot /ith "ETR! tuning o#ysterisis$*! TimetoTrigger$* and 9lter%oe:cientE"traRsrp parameters(

J

Timer is s! The "E isunable to R$% the Target %ell atando'er(


12/18


RR% )rops - T*+ Timer

The "E in RR%-%;


13/18


RR% )rops - T* Timer

%ause, Radio Lin 6RL8 .ynchronization–"E not able to 9nd suitable cell due to poorco'erage(


14/18


RR% )rops – Random $ccess #ailure at ando'er

%ause, R$ #ailure! "E is not able to synch to target e


15/18


@$%AR$AProblem – Random$ccess attempt to re-sync! #orno response a#ter +retransmission 6.71B8

RR% )rops – Random $ccess #ailure at ando'er

%ause, R$ #ailure! "E is not able to synch to target e


16/18


RR% )rops – @a>imum RL% Retransmissions

%ause, Repeated RL% Retransmissions due to unsuccess#ul RL% P)" reception6either "L or )L8(

– This occurs /hen ma>imum retransmission has occurred at RL% le'el 6$R=8(

– "LC)L inter#erence and Poor R4 conditions(

– "E /ill consider RL #ailed and initiate RR% %onnection Re-establishment(


17/18

@;% Parameter Ret>Threshold - )ataRadio1earer .ite Le'el Parameter

E"tran%ell4)) no;#Pucch%2i"sers .ector Le'el Parameter G3+

E"tran%ell4)) no;#Pucch.r"sers .ector Le'el Parameter 0H+

E"tran%ell4)) pdcch%9@ode .ector Le'el Parameter %4A.taticA* 6*8

E"tran%ell4)) ul.rsEnable .ector Le'el Parameter TR"E

"l4ss #eature.tate"l4ss .ite Le'el Parameter

E"tran%ell4)) pIero


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Note: Any Su//estion50eedbac %ill be 4i/hly A$$reciable to (m$ro&e #hisPresentation.

T$

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LTE Retainability