LTE Idle Mode – Cell Reselection
After cell selection UE performs measurement and
carry out cell reselection of new candidate cell. This is based on certain
criterion. Reselection process involves 2 steps
1. Measurements
Condition: Specifies when
to start measuring neighboring cells. Once condition is met UE measures the
RSRP level of the E-UTRA cells on the current frequency and any inter-frequency
and inter-RAT frequency carriers.
2.
Reselection Condition: Specifies
reselection criteria for candidate cell. There are two
different mechanisms for cell reselection:
Legacy Based
Priority Based
Cell reselection can be either Legacy or Priority
based.
Legacy Based
This is classical Ranking based
system and is applied to intra-frequency reselection.
• It is also applied to inter
frequencies which are equally prioritized.
•
UE applies cell ranking R criterion on serving cell and neighboring cell.
Priority
Based
Priority values in the range [0..7] are used,
where 0 indicates lowest priority and 7 indicates highest priority.
Priorities
can be set for:
Inter
Frequencies: Lower,
Equal or Higher Priority
Inter-Rat
Frequencies: Higher
or Lower Priority
Equal
priorities between different RATs are not supported
Idle Mode – Cell Reselection: Priority
Based
CellReselectionPriority :
Absolute reselection priority for E-UTRA or IRAT frequency
sNonIntraSearch : Threshold for inter
and IRAT frequency
threshXLow : Threshold for Srx value of serving cell below which UE
performs cell
reselection
towards a lower priority cell.
threshXLow : Threshold for
Srx value of target cell for cell reselection towards a
lower priority Inter or IRAT frequency.
tReselectionEutra :
Cell reselection timer value for EUTRAN
tReselectionUtra :
Cell reselection timer value for UTRAN
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