lte handover fault diagnosis

8/16/2019 LTE Handover Fault Diagnosis

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LTE Handover Fault Diagnosis

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Inter-frequency handover and inter-!" handover can #e coverage-#ased$ load-#ased or


service-#ased handover. "his course focuses on coverage-#ased handover.

!%&!'&!( event can #e used to trigger coverage-#ased inter-frequency handover. eNode)

can configure which event is used.

)*&)+ event can #e used to trigger coverage-#ased inter-!" handover. eNode) can

configure which event is used.




!* leaving condition：,s Hys "hresh


!+ leaving condition：,s / Hys 0 "hresh

!% leaving condition：,n 1fn 1cn Hys ,s 1fs 1cs 1ff

!' leaving condition：,n 1fn 1cn Hys "hresh

!( leaving condition：,s - Hys 0 "hresh* or ,n 1fn 1cn Hys "hresh+

)* leaving condition：,n 1fn Hys "hresh

)+ leaving condition：,s - Hys 0 "hresh* or ,n 1fn 1cn Hys "hresh+

"he varia#les in the formula are defined as follows2

Ms is the measurement result of the serving cell$ not ta3ing into account any

offsets.

Mn is the measurement result of the neigh#ouring cell$ not ta3ing into account any

offsets.

Ofn is the frequency specific offset of the frequency of the neigh#our cell.

Ocn is the cell specific offset of the neigh#our$ and set to 4ero if not configured for

the neigh#our cell.

Ofs is the frequency specific offset of the serving frequency.

Ocs is the cell specific offset of the serving$ and is set to 4ero if not configured for

the serving cell.

Hys is the hysteresis parameter for the events.

Thresh1 and Thresh2 is the threshold parameter for the events.




Currently intra-frequency handover is most popular in networ3s. So intra-frequency


handover parameters are discussed here.




Step *2 56 measures source cell and target cells. If the trigger condition is fulfilled$ 56


reports measurement results.

Step + and step %2 !fter receiving measurement result$ eNode) ma3es decision to trigger

handover. Source eNode) sends Handover Request message to target eNode)$ including

target cell I7 and some parameters for handover preparation. !fter receiving handoverrequest$ target eNode) tries access control and prepares resource for handover$ then

sends Handover Request Acknowledge to source eNode).

Step '2 Source eNode) sends RRC Connection Reconfiguration including handover

parameters for handover.

Step (2 Source eNode) sends S Status Transfer message to target eNode).

Step 82 56 triggers non-contention #ased random access in target cell.

Step 92 !fter successful random access in target cell$ 56 sends RRC Connection

Reconfiguration Co!"lete message to target eNode).

Step : and step ;2 "arget eNode) sends #ath Switch message to ,,6. ,,6 informs S-

<W to switch S* connection to target eNode). !fter successful switch ,,6 sends #ath

Switch Acknowledge message to eNode).

Step *=2 "arget eNode) sends $% Conte&t Release message to source eNode) to release

the resource of the 56.




,easurement control includes measurement I7$ measurement quantity$ measurement


o#>ect$ measurement report configuration and etc.

"he figure in the slide is an e?ample of measurement o#>ect.




,easurement report configuration contains report configuration I7$ measurement quantity$


report mode and etc.




,easurement report contains measurement I7 and measurement result.


,easurement I7 in measurement report is same with the I7 in the corresponding

measurement control.

"he following is SP and S@ measurement report mapping2


Reported value Measured quantity value Unit

RSRP_00 RSRP < -140 dBm

RSRP_01 -140 ≤ RSRP < -139 dBm

RSRP_02 -139 ≤ RSRP < -138 dBm

… … …

RSRP_95 -46 ≤ RSRP < -45 dBm

RSRP_96 -45 ≤ RSRP < -44 dBm

RSRP_97 -44 ≤ RSRP dBm

Reported value Measured quantity value Unit

RSRQ_00 RSRQ < -19.5 dBRSRQ_01 -19.5 ≤ RSRQ < -19 dB

RSRQ_02 -19 ≤ RSRQ < -18.5 dB

… … …

RSRQ_32 -4 ≤ RSRQ < -3.5 dB

RSRQ_33 -3.5 ≤ RSRQ < -3 dB

RSRQ_34 -3 ≤ RSRQ dB

RSRP measurement report mapping

RSRQ measurement report mapping



Handover command contains PCI of target cell and some related configuration information.





If whole-networ3 handover API is not good$ first transmission and equipment alarms


should #e chec3ed$ then cell-level handover API is analy4ed.




B.HH1.IntraeN).Intrareq.6?ecSucc1ut：Num#er of successful intra-eNode) intra-


frequency outgoing handovers in a cell

B.HH1.IntraeN).Interreq.6?ecSucc1ut：Num#er of successful intra-eNode) inter-


B.HH1.IntereN).Intrareq.6?ecSucc1ut：Num#er of successful inter-eNode) intra-


B.HH1.IntereN).Interreq.6?ecSucc1ut：Num#er of successful inter-eNode) inter-


B.HH1.IntraeN).Intrareq.6?ec!tt1ut：Num#er of intra-eNode) intra-frequency outgoing

handover attempts in a cell

B.HH1.IntraeN).Interreq.6?ec!tt1ut：Num#er of intra-eNode) inter-frequency outgoing


B.HH1.IntereN).Intrareq.6?ec!tt1ut：Num#er of inter-eNode) intra-frequency outgoing


B.HH1.IntereN).Interreq.6?ec!tt1ut：Num#er of inter-eNode) inter-frequency outgoing





"he result is from a networ3 with H5!W6I equipments.





Possi#le scenarios for handover triggered too early2


!fter receiving handover command$ 56 fails to handover to the target cell #ecause

of the #ad signal in target cell$ then 56 triggers C connection reesta#lishment in

source cell.

56 handovers to target cell successfully #ut downlin3 synchroni4ation fails in the

target cell$ then 56 triggers C connection reesta#lishment.




Possi#le scenarios for handover triggered too late2


"he source cell signal is #ad$ so 56 can not receive handover command. "hen 56

triggers C connection reesta#lishment in target cell. If the 56 conte?t is setup

successfully in the target cell$ the C reesta#lishment can #e done.

"he source cell signal drops too fast$ 56 has no time to report measurement result.

"hen 56 triggers C connection reesta#lishment in target cell. "he 56 conte?t can

not #e setup successfully in the target cell$ the C reesta#lishment can not #e

done.

"here is something wrong with the D+ transmission$ HA'O(%R R%)$%ST

message can not #e transferred to the target cell.




In real networ3s$ most handover failures are caused #y 5u interface pro#lems$ resulting in


the a#normal signaling over 5u interface.




"hese are >ust possi#le reasons for a#normal 5u signaling. ,ore information and trace


result should #e collected for deep analysis.




SP2 SP is the downlin3 reference signal power received #y 56. SP and SIN roughly


reflect the downlin3 quality. <enerally the SP is more than -:(d)m for 56 near an

eNode)$ equal to -;(d)m for 56 at the middle of eNode) coverage$ and less than -

*=(d)m for 56 at cell edge.

SIN2 SIN is the downlin3 reference signal SIN. If SIN is less than =d)$ the downlin3channel quality is poor. If SIN is less than -%d)$ the downlin3 channel quality is very poor

and close to the demodulation threshold$ which can easily cause loss of handover

messages. "he uplin3 SIN can #e o#tained from the user performance tracing on the B,".

I)B62 <enerally I)B6 should #e near the target value of *=E. If the channel quality is

very good$ I)B6 is close to =E. If I)B6 is very high$ it means the channel quality is poor

and call drop may happens.

5plin3 scheduling grants and downlin3 scheduling assignments over the P7CCHs2 It is the

num#er of P7CCHs correctly demodulated #y a 56 in each ""I. If there is enough uplin3 or

downlin3 data source and the channel quality is very good$ the num#er of the grants orassignments could #e very high$ even close to *===. If the num#er of uplin3 grants is too

low$ it may #e caused #y #ad channel quality.




or e?ample$ poor downlin3 channel quality not only affects demodulation of the downlin3


signaling$ the incorrectly demodulated P7CCH also affects the uplin3 scheduling$ leading

to loss of uplin3 signaling.




!#normal signaling over D+ interface is usually caused #y D+ transmission pro#lem or


internal pro#lem of site. Internal pro#lem of site is not popular. So it is very possi#le that

D+ transmission causes a#normal signaling over D+ interface. It is not easy to analy4e

transmission pro#lem. In this slide transmission pro#lem is not the focus.




Possi#le solutions2


!d>usting the antenna to change the coverage of serving cell or neigh#oring cell

!d>usting CI1 to ma3e handover happen earlier

"o increase neigh#oring cell CI1 or decrease serving cell CI1 could ma3e

handover happen earlier.




!2 and !ccess esponse


In handover area$ SP is good #ut SIN and I)B6 is #ad. So it is very possi#le that the

pro#lem is caused #y downlin3 interference.




"he figures shows that after ad>ustment handover is triggered successfully. SIN and I)B6


are #etter.


lte handover fault diagnosis

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