Handover Failure in LTE

Question

1 ->What are all the Handover failure situations in LTE ( apart from mentioned)

HO failure situations :- Like Target fails to
->get security context (mismatch in integrity/ciphering)
->max number of ue's in connected mode reached
->failed to admit atleast on erab n other

and what the message source eNodeB forwards to UE ( to inform a failure in handover) which leads to reestablishment ?

2->How or what are the possibilities that a UE fails to configure with RRC connection reconfiguration sent n does this happen only during Handover.

Answer 1

LTE handover fails: There are parts in LTE handover:
1- Handover Preparation
2- Handover Execution

**1-HO Fails reasons in preparation parts are below:**

if HO preparation fails 100%, MME pool different in source and target
Target cell is overload
Target cell unavailable
TAC not defined on site
License/software issue

2-Handover execution fails

PCI conflict
Target exceeds cell range
Target is sleeping cell
Target having high uplink interference
Poor RF condition
Alarms on Target cell

Comments

please explain CIO as well ???

Answer 2

The UE send **RRCConnectionReestablishmentRequest** message to the source eNB when T311 started and after T311 has expired then source eNB forward RRCConnectionReestablishmentReject message to UE. Then HO Failure occur. Also If the x2 link is not defined between the target and source eNB. This could also lead to HO Failure.