UMTS To LTE Reselection
LTE 2 reselection mechanisms are used in UMTS
Legacy Based:
This is ranking based system and it applies to
intra-frequency, inter-frequency as well as for GSM reselection.
Priority Based:
This
mechanism applies for cell reselection from WCDMA to LTE
Priority based method results into 2 different scenarios:
High Priority UMTS to Low Priority LTE
Low Priority UMTS to High Priority LTE
Both legacy based and
priority based cell reselection can be active at the same time.
Reselection from Low Priority UMTS to
High Priority LTE
If LTE frequency is of higher priority than the
current frequency, measurements are always performed.
Measurement Condition:
The
UE searches every layer of higher priority at every Thigher_priority_search = (60*Nlayers)
seconds.
Nlayers is the total number of configured higher
priority E-UTRA frequencies
Reselection Condition:
Cell reselection occurs if UE finds a cell with an
Srxlev value greater than ThreshHigh.
Srxlev (target) > ThreshHigh
Reselection from High Priority UMTS to
Low Priority LTE
Measurement Condition:
The
UE only starts measurement for candidate LTE when following threshold is met.
Srxlev
(serving) < SPrioritySearch1
Squal (serving) < SPrioritySearch2
Reselection Condition:
If Srx value of the serving cell falls below the
threshServingLow value, UE attempts to reselect a cell on LTE. Cell reselection
occurs if UE finds a cell with an Srxlev value greater than threshLow value for
that frequency.
Srxlev (source) < ThreshServing
Low Srxlev (target) > ThreshLow
Comments