00- LTE eRAN8.1 Idle Mode ISSUE 1.01.pdf

LTE eRAN8.1 Idle Mode
Confidential Information of Huawei. No Spreading Without Permission

 PLMN Selection in Automatic Mode
 When a UE fails to register on its last RPLMN or EPLMN, the UE attempts to select another
PLMN. In automatic network selection mode, the UE selects a PLMN in the following order:
 The EHPLMN with the highest priority if the EHPLMN list is available and contains
at least one EHPLMN, or the HPLMN if the EHPLMN list is blank or unavailable.
 Each combination of PLMN with radio access technology (RAT) in the "User
Controlled PLMN Selector with Access Technology" data file in the USIM, in order
of priority.
 Each combination of PLMN with RAT in the "Operator Controlled PLMN Selector
with Access Technology" data file in the USIM, in order of priority.
 Other combinations of PLMNs with RATs providing high-quality signals, in a
random order. A high-quality signal is defined as the Reference Signal Received
Power (RSRP) value of a cell in the combination of PLMN with RAT being greater
than or equal to -110 dBm.
 Other combinations of PLMNs with RATs in order of descending RX signal quality.
 When the UE finds a suitable cell in a PLMN during the preceding procedure, the UE attempts to
register on the PLMN. If the registration is successful, the UE camps on the suitable cell; otherwise,
the UE tries the next PLMN.
 If the registration on none of the PLMNs is successful, the UE enters the Limited service state. If no
PLMN is available, the UE cannot obtain any services.

 Cell search is a procedure in which a UE achieves time and frequency synchronization with
a cell, obtains the physical cell identifier (PCI), and learns the RX signal quality and other
information about the cell based on the PCI.
 The detailed cell search procedure is as following:
 The UE monitors the P-SCH to achieve clock synchronization with a maximum
synchronization error of 5 ms. The UE determines the cell identity in a cell identity
group based on the mapping between cell identities and primary synchronization
signals.
 The UE monitors the S-SCH to achieve frame synchronization, that is, time
synchronization with the cell. Cell identity groups have a one-to-one relationship
with secondary synchronization signals. Therefore, the UE acquires the number of
the cell identity group to which the cell identity belongs by monitoring the S-SCH.
 The UE monitors the Broadcast Channel (BCH) to acquire other information about
the cell
 The UE determines the PCI based on the cell identity and the cell identity group
number.
 The UE monitors the downlink reference signal to acquire the RX signal quality in
the cell

 The stored information cell search: It requires stored information on carrier frequencies and
information on cell parameters. The information is obtained from previously received
measurement control information elements or from previously detected SI messages of
cells.
 Initial cell search: If there is no prior knowledge of frequency information, the UE scans all
RF channels in the E-UTRAN bands according to its capabilities in order to find a suitable
cell. On each carrier frequency, the UE searches for the strongest cell only.

 Period of MIB: 40ms

 The scheduling period of the SIB1 is fixed to 80 ms. The first transmission of the SIB1 is
scheduled in subframe 5 of radio frames for which the SFN mod 8 = 0, and repetitions are
scheduled in subframe 5 of the later radio frames for which SFN mod 2 = 0 in each period.

 The modification period of the SI message is N radio frames, and the period starts from
radio frames for which SFN mod n = 0. During the n modification period, the eNodeB
transmits the paging message to inform UEs in RRC_IDLE mode and UEs in
RRC_CONNECTED mode about the SI message change when a paging cycle arrives. When
the n+1 modification period arrives, the eNodeB transmits the updated SI message.
 The length of the SI modification period n = ModifyPeriodCoeff x DefaultPagingCycle
 ModifyPeriodCoeff is the coefficient of the modification period, indicating the
minimum number of interceptions on the paging messages for the UE in the SI
message modification period.
 DefaultPagingCycle is the default paging cycle in the unit of radio frames.
 ModifyPeriodCoeff and DefaultPagingCycle are broadcast in the SIB2.

 A UE considers an E-UTRAN cell as a suitable cell only when the measured RSRP and
reference signal received quality (RSRQ) values of the cell are greater than the receive (RX)
level threshold (Qrxlevmin) and the RX signal quality threshold (QQualMin) for the cell,
respectively.
 An E-UTRAN cell becomes a suitable cell when both the following conditions are met:
 Srxlev > 0 Squal > 0
 Srxlev = Qrxlevmeas - (Qrxlevmin + Qrxlevminoffset) – Pcompensation
 Squal = Qqualmeas - (QQualMin + QQualMinOffset)
Parameter Description
Qrxlevmeas Measured RSRP value
Qrxlevmin Minimal Required Rx level (dBm) in SIB1
Qrxlevminoffset Offset to Srxlev, relative with PLMN priority ,.QrxlevminOffset is only applied when a
cell is evaluated for cell selection as a result of a periodic search for a higher priority
PLMN while camped normally in a VPLMN in SIB1
Pcompensation max (PMaximum allowed power – PUE MAX Output Power, 0), where PMaximum allowed power is sent in
SIB1
Qqualmeas measured RX signal quality (RSRQ value) of the cell, expressed in units of dB.
Qqualmin Minimal required signal quality
QQualMinOffset Offset to Qqualmin, relative with PLMN priority ,.QrxlevminOffset is only applied when
a cell is evaluated for cell selection as a result of a periodic search for a higher priority
PLMN while camped normally in a VPLMN in SIB1

 Following are the description of each parameters:
Parameter ID Description
Qrxlevmin
Indicates the minimum required RX level. This parameter is
used in the formula of the cell selection criterion S.
Qrxlevminoffset
Indicates the offset to the minimum required RX level. This
value is included in criteria S and used in the evaluation of
cell selection. This parameter is valid only when the cell
selection is triggered by periodic searches for higher-priority
PLMNs and the UE is served by a Visited Public Land Mobile
Network (VPLMN).
Qqualmin
Indicates the minimum RX level of the cell. It is included in
criteria S and used in the evaluation of cell selection.
QQualMinOffsetCfgInd Indicates whether to set the offset to the minimum required
RX qulity for the cell. If this parameter is set to CFG, the
offset is required. If this parameter is set to NOT_CFG, the
offset does not need to be set.
QQualMinOffset Indicates the offset to the minimum required RX quality for
the cell. It is included in criteria S and used in the evaluation
of cell selection. This parameter is required only when the
cell selection is triggered by periodic searches for higher-
priority PLMNs and the UE is served by a Visited Public Land
Mobile Network (VPLMN).

 UE cell reselection include two steps:
 Start the measurement for the neighboring cells
 Rank the measured cells based on radio signal quality and priorities.

 After having camped on a cell, a UE may decide to camp on another cell by performing cell
reselection. Before cell reselection, the UE is required to measure the signal strength of
certain neighboring cells and evaluate each of them by using the criteria that are suitable
according to the priority of the neighboring cell, that is, the priority of the frequency on
which the neighboring cell operates.
 During the measurements and implementation of cell reselection, the UE needs to obtain
the priorities of neighboring frequencies. Note that any two RATs must have non-
overlapping priorities of frequencies. During the evaluation for reselection to an intra-
frequency neighboring cell, the UE ignores the priority of the target frequency because
cells that work on the same frequency have the same priority.

 Frequencies of different RATs must have different priorities.
 The priorities of E-UTRAN frequencies and inter-RAT frequencies are classified into the
following types:
 Absolute priority: This priority is specified by the CellReselPriority parameter and
is sent to UEs through broadcast of system information. Serving cell frequency
priority will be delivered in SIB3, inter-frequency priority will be delivered in SIB5,
3G frequency priority will be delivered in SIB6 and 2G frequency priority will be
delivered in SIB7.
 Dedicated priority: The dedicated priority of an E-UTRAN or inter-RAT frequency is UE-
specific. It is delivered to the UE in an RRC Connection Release message when the UE's
radio resources are released.

 This priority will be broadcast in SIB3.
 A larger value of this parameter indicates a higher probability of a UE camping on the cells
assigned with the same frequency as the serving one, and a smaller value indicates a lower
probability.

 This priority will be broadcast in SIB5.

 3G frequency will be broadcast in SIB6 and 2G frequency will be broadcast in SIB7.

 Note: The dedicated priority of frequencies for one RAT must all be different from those
for another RAT.

 If the threshold is set to “CFG”, these two thresholds will be delivered in SIB3.

 From SIB ,UE can get the serving cell and inter frequency/RAT neighbors’ priorities.
 For the high priority cells, UE measure them always, for the low priority cells, UE measure
them in case of the serving cell signal is lower than the threshold.
 The intra frequency cells have the same frequency priority, frequencies of different RATs
must have different priorities.

 Following are description of parameters:
Threshold for non-intra
freq measurements
configure indicator
Indicates whether to set the measurement triggering
threshold for reselection to inter-frequency or inter-RAT cells.
QRxLevMin
Indicates the minimum required RX level used in intra-
frequency E-UTRAN cell reselection, which corresponds to
the IE q-RxLevMin in SIB3. This value is included in criteria R
and used in the evaluation of cell
SIntraSearchCfgInd
Indicates the minimum RX level of the cell. It is included in
criteria S and used in the evaluation of cell selection.

SIntraSearchQ
Indicates the RSRQ threshold for starting intra-frequency
measurements. It determines the probability of triggering cell
reselection to an intra-frequency neighboring cell.
SNonIntraSearchQ
Indicates the RSRQ threshold for starting inter-frequency or
inter-RAT measurements. It determines the probability of
triggering cell reselection to an inter-frequency or inter-RAT
neighboring cell.
QQualMin
Indicates the minimum required RX signal quality used in
intra-frequency E-UTRAN cell reselection, which corresponds
to the IE q-QualMin in SIB3. This value is included in criteria
R and used in the evaluation of cell reselection.

 A UE makes a cell reselection decision according to cell reselection criteria. When making a
decision on reselection to an intra frequency or equal-priority inter frequency cell, the UE
checks whether the signal quality of a neighboring cell is higher than that of the serving
cell.
 The cell-ranking criteria R_s for the serving cell and R_n for neighboring cells are defined as
follows:
 R_s = Qmeas,s + Qhyst
 R_n = Qmeas,n - CellQoffset
Where:
 Qmeas_s is the measured RSRP of the serving cell, expressed in units of dBm
 Qhyst is the hysteresis for the serving cell used in the ranking criteria, expressed in
units of dB.
 Qmeas_n is the measured RSRP of the neighboring cell, expressed in units of dBm
 CellQoffset is the offset for the neighboring cell used in the ranking criteria,
expressed in units of dB
 According to the cell reselection criteria, the UE should reselect the new cell only if both
the following conditions are met:
 The new cell is ranked higher than the serving cell during the cell reselection time.
 More than one second has elapsed since the UE camped on the serving cell.

 Following are description of parameters
Qhyst
Indicates the hysteresis for cell reselection when RSRP values
are used in the evaluation. This parameter must be set based
on the slow fading characteristic of the area covered by the
cell. The greater the slow fading variance is, the larger the
value of this parameter must be set to. A larger value of the
hysteresis results in a larger boundary of the serving cell and
a higher probability of cell reselection to neighboring cells
TReselEutran
Indicates the cell reselection duration of the E-UTRAN. When
the signal quality of the new cell is better than the serving
cell all the time and the UE stays in the current serving cell
for more than 1s, the UE is initiating cell reselection request
to the new cell.

CellQoffset
Indicates the offset for the intra-frequency neighboring cell,
which is used in evaluation for cell reselections. A larger
value of this parameter results in a lower probability of cell
reselections. If this parameter is not set to dB0, it is delivered
in SIB4 or SIB5.

 For EUTRAN and UTRAN, either Srxlev or Squal could be used for cell reselection, depends on the
following parameter:
 If ThrshServLowQCfgInd is set “CFG”,then it use Squal
 Otherwise, it use Srxlev
 For GERAN, it only uses Srxlev
 Srxlev and Squal evaluation is the same as cell selection algorithm.
 If SIB3 contains the value of ThrshServLowQ, a UE performs reselection to a higher-priority inter-
frequency or inter-RAT neighboring cell when both the following conditions are met:
 The neighboring cell has one of the following measurement results:
 The Squal value of the evaluated neighboring E-UTRAN or UTRAN cell is always
greater than the RX signal quality threshold used in reselection to higher-priority
cells (ThreshXHighQ) during the cell reselection time specified by the
TReselEutran or TReselUtran parameter.
 The Srxlev value of the evaluated neighboring GERAN or CDMA2000 cell is always
greater than the RX signal level threshold used in reselection to higher-priority cells
(ThreshXHigh) during the cell reselection time specified by the TReselGeran or
Cdma1XrttTreselection parameter
 The UE has camped on the serving cell for more than 1 second.
 If SIB3 does not contain the value of ThrshServLowQ, a UE performs reselection to a higher-
priority inter-frequency or inter-RAT neighboring cell when the following conditions are both met:
 The Srxlev value of the evaluated neighboring cell is always greater than the ThreshXHigh
value during the predefined cell reselection time
 The UE has camped on the serving cell for more than 1 second

 If SIB3 contains the value of ThrshServLowQ, a UE performs reselection to a lower-priority inter-
frequency or inter-RAT neighboring cell when all the following conditions are met:
 No cell meets the criteria for reselection to higher-priority cells
 The Squal value of the serving cell is always less than the RX signal quality threshold for the
serving cell used in reselection to lower-priority cells (ThrshServLowQ) during the
predefined cell reselection time.
 The neighboring cell has one of the following measurement results:
 The Squal value of the evaluated neighboring E-UTRAN or UTRAN cell is always
greater than the RX signal quality threshold used in reselection to lower-priority
cells (ThreshXLowQ) during the predefined cell reselection time.
 The Srxlev value of the evaluated neighboring GERAN or CDMA2000 cell is always
greater than the RX signal level threshold used in reselection to lower-priority cells
(ThreshXLowQ) during the predefined cell reselection time.
 If SIB3 does not contain the value of ThrshServLowQ, a UE performs reselection to a lower-priority
inter-frequency or inter-RAT cell when all the following conditions are met:
 No cell meets the criteria for reselection to higher-priority cells
 The Srxlev value of the serving cell is always less than the RX signal level threshold for the
serving frequency used in reselection to lower-priority cells (ThrshServLow) during the
predefined
 The Srxlev value of the evaluated neighboring cell is always greater than the threshold used
in reselection to lower-priority cells (ThreshXLow) during the predefined cell reselection
time cell reselection time.

 The TA is a concept introduced to the LTE/SAE system for location management of UEs.
The EPC sends paging messages to all eNodeBs in the TA. A TA is identified by a Tracking
Area Identity (TAI), which consists of the MCC, MNC, and Tracking Area Code (TAC).
 eNodeB broadcast the tracking area code by SIB1.
 A UE informs the EPC of its Tracking Area (TA) by TA registration. There are two ways for
the UE TA registration:
 Attach/Detach
 TA update
 When a UE needs to obtain service from a network but is not registered to the network,
the UE performs an Attach procedure for TA registration.
 After a successful Attach procedure, the UE is allocated an IP address. The Mobile
Equipment Identity (MEI) of the UE will be sent to the Mobility Management Entity (MME)
for authentication.
 When the UE fails to access the EPC or the EPC does not allow the access of the UE, a
Detach procedure is initiated. After the Detach procedure, the EPC no longer pages the UE.

 UEs are notified of cell status by the following information in the SIB1:
 cellBarred (set by CELLACCESS.CellBarred): cell barring status. If a cell belongs to
multiple PLMNs, this information is common for all PLMNs.
 cellReservedForOperatorUse (set by CELLOP.CellReservedForOp): whether a cell
is reserved for an operator. This information is PLMN-specific.

 Access classes are applicable to access of UEs on the radio interface. There are 16 access
classes, numbered from 0 to 15. The information about access classes 0 to 9 and 11 to 15
is stored in USIMs, and the information about access class 10 is signaled to UEs through
system information broadcast to indicate whether cells allow emergency calls.
 Access classes 0 to 9 are ordinary classes. Each UE is randomly allocated one out of
the ten classes. UEs of these classes can obtain service in their HPLMN, EPLMN, and
VPLMNs.
 Access classes 11 to 15 are special classes. They are allocated to specific high-priority users.
Each UE may be allocated one or more out of the five classes. These special access classes
are described as follows:
 Class 11: for PLMN use
 Class 15: for PLMN staff
 Class 12: for security services
 Class 13: for public utilities
 Class 14: for emergency services

 UEs in RRC_IDLE mode use DRX to receive paging messages in order to reduce power consumption.
The eNodeB may have to buffer the paging message until a UE’s paging occasion occurs.
 The time positions of paging messages are fixed on the Uu interface, which are indicated by the
Paging Frames (PFs) and Paging Occasion (PO) subframes. One PF is one radio frame, which may
contain one or multiple Pos. One PO is a subframe where the Paging Radio Network Temporary
Identifier (P-RNTI) is contained. The PO is transmitted over the PDCCH. UEs read paging messages
over the Physical Downlink Shared Channel (PDSCH) according to the P-RNTI.
 The PF number and PO subframe number can be calculated according to the IMSI of the UE, DRX
cycle, and number of PO subframes in a DRX cycle. Frame numbers are stored in the SI related to
the DRX parameters of the UE. When the DRX parameters change, PF number and PO subframe
number change accordingly.
 The SFN of a PF is derived from the following formula:
 SFN mod T = (T div N) x (UE_ID mod N)
 The subframe number i_s of a PO is derived from the following formula:
 i_s =Floor (UE_ID/N) mod Ns

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