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LTE Interoperability in Idle Mode(LTE-GU)
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LTE Interoperability in Idle Mode(LTE->G/U)
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LTE Interoperability in Idle Mode(LTE->G/U)
LTE Interoperability in Idle Mode(LTE->G/U)
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LTE Interoperability in Idle Mode(LTE->G/U)
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Contents
IRAT PLMN Selection Procedure
IRAT Cell Selection Criteria
IRAT Cell Reselection Criteria
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LTE Interoperability in Idle Mode(LTE->G/U)
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States of UE at Switch on
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Related to interoperability which will be discussed in this
course
LTE Interoperability in Idle Mode(LTE->G/U)
A UE that is powered on but does not have an RRC connection to the
radio network is considered to be in idle mode. In the case of idle
mode management, the eNodeB sends configurations by broadcasting
system information, and accordingly, UEs select suitable cells to
camp on. Idle mode management can increase the access success rate,
improve the quality of service, and ensure that UEs camp on cells
with good RX signal levels and qualities.
The idle mode management is related with the following
aspects:
PLMN selection
A UE selects a Public Land Mobile Network (PLMN) and registers on
the PLMN.
Cell selection
A UE selects a cell in the chosen PLMN and camps on the cell so
that the UE can monitor system information and paging messages to
obtain service.
Cell reselection
When camped on a cell, a UE reLTEarly searches for a better cell
according to the cell reselection criteria, for the purpose of
correctly receiving system information and successfully initiating
services.
Tracking Area (TA) registration
A UE registers its location with the Evolved Packet Core (EPC)
through a TA registration procedure so that the EPC can page the UE
within the TA and request the UE to initiate services.
Cell reservation and access control
Cell reservation and access control are two mechanisms for
operators to control their networks. In the cell reservation
mechanism, specific cells can be reserved for operators' use only.
In the access control mechanism, the UEs that can initiate calls in
a cell are determined on the basis of the classes of the UEs.
System information broadcast and paging
In system information broadcast, the information such as parameters
related to cell selection and reselection is broadcast to UEs
through system information over the Broadcast Control Channel
(BCCH). In paging, paging messages are used to inform all UEs in a
cell of a change in the system information and to carry
paging-related information.
The main activities of UEs in idle mode are PLMN selection, cell
selection and reselection, and TA registration. The figure in the
slide above shows the relationships between them.
Items with * will be focused on in this course in detail, for they
are related with different RAT.
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PLMN Selection
Idle Mode
States and Relationships in Idle Mode
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LTE Interoperability in Idle Mode(LTE->G/U)
The main activities of UEs in idle mode are PLMN selection, cell
selection and reselection, and TA registration. Figure in the slide
above shows the relationships between them.
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Camp-on Strategies in the Idle Mode
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UMTS
GSM
LTE
PLMN A
PLMN A
PLMN A
The dual-mode UE camps on the network with the highest priority
(usually LTE by default) through cell reselection.
UMTS
GSM
LTE
PLMN A
PLMN B
PLMN C
The dual-mode UE camps on the network with the highest priority
(usually LTE by default) through PLMN selection.
PLMN Selection
Cell Reselection
Cell selection
Power on
LTE Interoperability in Idle Mode(LTE->G/U)
Idle-Mode Camp-On Within the Same PLMN
Assume that the GERAN/UTRAN and the LTE network share the same PLMN
and both of them use system messages to broadcast information about
the cells of other RATs and the cell priorities. By default, the
LTE network is set with the highest priority. The dual-mode UE
camps on the network with the highest priority through cell
reselection. The camp-on principles are described in the following
situations:
The UE in idle mode camps on the LTE network.
The eNodeB is configured with the cell reselection priorities and
the thresholds for channel quality. These configurations are
broadcast by the eNodeB in system messages to ensure that the UE
does not reselect from the LTE network to the GERAN/UTRAN easily.
When the strength of LTE signals is lower than the predefined
threshold, the UE starts to measure GERAN/UTRAN cells and reselects
the GERAN/UTRAN if the conditions are met.
The UE in idle mode camps on the UTRAN.
The system messages broadcast by the RNC include cell reselection
parameters, LTE frequencies, and priority information. To enable
the UE on the UTRAN to reselect to the LTE network, set the
priority of the LTE network to be higher than that of the UTRAN.
The UE periodically searches for and measures all RAT frequencies
that have high priorities. The UE reselects the LTE network if the
conditions are met. If the signal strength in multiple LTE cells is
higher than the predefined threshold within a period, the UE camps
on the LTE cell that has the highest priority.
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Notes
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The UE in idle mode camps on the GERAN.
The system messages broadcast by the BSC include cell reselection
parameters, LTE frequencies, and priority information. To enable
the UE on the GERAN to reselect to the LTE network, set the
priority of the LTE network to be higher than that of the GERAN.
The UE periodically searches for and measures all RAT frequencies
that have high priorities. The UE reselects the LTE network if the
conditions are met. If the signal strength in multiple LTE cells is
higher than the predefined threshold within a period, the UE camps
on the LTE cell that has the highest priority.
Idle-Mode Camp-On Between Different PLMNs
When the GERAN/UTRAN and the LTE network use different PLMNs,
operators can assign a lower priority PLMN to the GERAN/UTRAN, and
a higher priority EPLMN to the LTE network. Over The Air (OTA)
messages are sent to instruct the UE to update the EHPLMN data
files in USIMs so that the LTE network is prior selected over the
GERAN/UTRAN. If the UE is powered on to camp on a network or
initiates idle-mode cell reselection, the UE prior camps on the LTE
network. The camp-on principles are as follows:
If the UE in idle mode camps on the GERAN/UTRAN:
If the RAN of the GERAN/UTRAN is not upgraded, the UE in idle mode
periodically searches for a PLMN with the highest priority. If the
PLMN is found, the UE performs the cell reselection and camps on
the serving cell on the PLMN with the highest priority. The
searching period is specified by data files in a USIM. If the HPLMN
and EHPLMN are equivalent, that is, the priorities are the same,
the GERAN/UTRAN can only be used as the VPLMN and the LTE network
as the HPLMN. The UE returns to the LET network by periodically
searching for HPLMNs.
If the UE in idle mode camps on the LTE network:
The UE reselects the serving GERAN/UTRAN according to the camp-on
principles for the UE in idle mode camping on LTE networks in the
same PLMN.
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LTE Interoperability in Idle Mode(LTE->G/U)
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Comparation of Camp-on Strategies
LTE use the same or different PLMN IDs with GERAN/UTRAN
It is suggested EUTRAN uses the same PLMN ID with GERAN/UTRAN
Page*
EUTRAN use different PLMN ID with GERAN/UTRAN
Remain in LTE network in Idle state
Set the cell reselect priority in eNodeB ENodeB broadcasts system
information UE stay in LTE and not easy reselect to GERAN/UTRAN
cell
Configure high priority PLMN ID for LTE and low priority PLMN ID
for GERAN/UTRAN (notes UE update EHPLMN date in USIM card via SMS
via OTA mode ) UE will select PLMN of LTE at first when attach or
reselect in idle state
Remain in GERAN/UTRAN network in Idle State
RAN broadcasts cell reselection parameter in SIB3/4 RAN broadcasts
inter-RAT cell reselection parameter in SIB3/4 and inter-RAT
frequency priority of LTE UE searches all high priority of RAT
frequency cell
Configure high priority PLMN ID for GERAN/UTRAN and low priority
PLMN ID for LTE (notes UE update EHPLMN data in USIM card via SMS
via OTA mode ) UE will select PLMN of GERAN/UTRAN at first when
attach or reselect in idle state
Advantage
User smoothly upgrade (do not need update EHPLMN data in USIM card)
The time of cell reselection is short UE Returns to LTE on time
Reduce electric power
RAN does not need upgrade
Disadvantage
Need RAN upgrade
UE search and measure LTE cell for long time Consume electric power
Can’t reselect to LTE on time
LTE Interoperability in Idle Mode(LTE->G/U)
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Contents
IRAT PLMN Selection Procedure
IRAT Cell Selection Criteria
IRAT Cell Reselection Criteria
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PLMN Selection Principle
When a dual-mode UE is powered on in an area covered by both the
LTE and the GERAN/UTRAN network, it needs to select a network to
camp on. The principles of network selection are as follows:
After the dual-mode UE is powered on, it first tries the Registered
Public Land Mobile Network (RPLMN) and the cell that it previously
camps on.
If the RPLMN and cell do not meet the camp-on conditions, the UE
selects a proper PLMN and RAT according to the configurations in
the UMTS Subscriber Identity Module (USIM) and then a qualified
cell.
To improve user experience and make full use of the newly deployed
LTE network, the LTE network is usually set with the highest
priority. The public priorities are broadcast through system
messages.
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PLMN Selection Procedure Overview
(If present and not empty
RPLMN
LTE Interoperability in Idle Mode(LTE->G/U)
PLMN,a PLMN identity consists of a Mobile Country Code (MCC) and a
Mobile Network Code (MNC).
RPLMN
The Registered PLMN (RPLMN) is the PLMN on which the UE has
performed a location registration successfully.
EPLMN List
The Equivalent PLMN (EPLMN) list is a list of PLMNs considered as
equivalent to the local network by the UE in terms of service
provisioning. During PLMN selection, the UE preferentially selects
a PLMN from the list. The EPLMN list is sent from the EPC and
stored in the UE.
EHPLMN
An Equivalent Home PLMN (EHPLMN) is an equivalent to the HPLMN, and
takes precedence over the HPLMN.
The EHPLMN list is stored in the UMTS subscriber identity module
(USIM) of the UE. During PLMN selection, the UE takes into account
both the EHPLMNs and the HPLMN that is extracted from the
international mobile subscriber identity (IMSI), and preferentially
selects an EHPLMN.
HPLMN
The Home PLMN (HPLMN) is the PLMN in which the UE is defined. Each
UE belongs to only one HPLMN.
VPLMN
The Visited PLMN (VPLMN) is the PLMN where the UE is located. A
VPLMN can be the HPLMN.
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notes
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PLMN Selection
Left figure shows the PLMN selection procedure. When a UE is
powered on or recovers from lack of coverage, the UE first selects
the last RPLMN and attempts to register on that PLMN. If the
registration on the PLMN is successful, the UE shows the selected
PLMN on the display, and now it can obtain service from an
operator. If the last RPLMN is unavailable or the registration on
the PLMN fails, another PLMN can be automatically or manually
selected according to the priorities of PLMNs stored in the
USIM.
PLMN Selection in Automatic Mode
When a UE fails to register on its last RPLMN, the UE attempts to
select another PLMN. In automatic network selection mode, the UE
selects a PLMN in the following order:
HPLMN or an EHPLMN.
Each PLMN in the "User Controlled PLMN Selector with Access
Technology" data file in the USIM, in order of priority, according
to the UE's support for Radio Access Technologies (RATs).
Each PLMN in the "Operator Controlled PLMN Selector with Access
Technology" data file in the USIM, in order of priority, according
to the UE's support for RATs.
Other PLMNs with signals of high received quality, in a random
order. The high quality of signals is defined as the Reference
Signal Received Power (RSRP) value of a cell in the PLMN being
greater than or equal to -110 dBm.
Other PLMNs in order of decreasing 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 service.
PLMN Selection in Manual Mode
When a UE fails to register on its last RPLMN, the UE attempts to
select another PLMN. In manual network selection mode, the UE
displays a list of PLMNs, in the same order as the PLMNs to be
selected in automatic network selection mode.
In manual mode, the UE can also try forbidden PLMNs. If the UE
succeeds in registering on the selected PLMN, the PLMN is no more a
forbidden PLMN to the UE. The forbidden PLMNs are determined by the
EPC.
Roaming
When in roaming state, a UE obtains service from a VPLMN that is
different from its HPLMN. For example, the UE obtains service from
a PLMN in another country (that is, from an international roaming
area). When the UE with the roaming service moves out of the
coverage area of its HPLMN, the UE can obtain service from another
PLMN according to the PLMN information stored in the USIM. The
operator determines whether roaming is allowed for a UE.
After the UE registers on a VPLMN by roaming, it periodically
searches for its HPLMN and attempts to return to the HPLMN. The
time interval between consecutive searches for the HPLMN is defined
by the operator and stored in the USIM.
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PLMN Selection Procedure in Detail
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Last RPLMN or equivalent PLMN
“HPLMN&EHPLMN Selector with Access Technology ” data file (in
priority order)
“User Controlled PLMN Selector
“Operator Controlled PLMN Selector
The PLMN with Better Wireless Quality in random order
Other PLMN Base On Wireless Quality in order of decreasing signal
quality
PLMN Select When UE Switch On
The Timer of HPLMN Reselection is Saved in USIM Card(6m~8h in 6m
steps or no periodic attempts)
Stored in UE
Set in SIM
Set in SIM
Set in UE
PLMN + E-UTRAN
PLMN + UTRAN
PLMN + GSM
Customized PLMN/Frequency List in SIM card, UE Prefers to Camp on
LTE Network
LTE Interoperability in Idle Mode(LTE->G/U)
Camp-On After Power-on
When the dual-mode UE is powered on, it first selects a Public Land
Mobile Network (PLMN) and then a proper cell. The selection of the
PLMN and RAT is based on the following information stored in the
USIM:
HPLMN (Home PLMN) Selector with Access Technology
Operator controlled PLMN Selector with Access Technology
User Controlled PLMN Selector with Access Technology
Forbidden PLMNs
Equivalent HPLMN
The first three data files control the selection of the PLMN and
RAT. Each file includes multiple entries, such as a PLMN and the
relevant RAT. The entries are arranged in a descending sequence
based on priority.
For an entry that includes only a PLMN, the UE supports all RATs by
default. Different entries may share the same PLMN but different
specified RATs. These entries are also arranged in a descending
sequence based on the priority of the RAT.
There are two PLMN selection modes for the dual-mode UE, namely,
automatic selection and manual selection.
In automatic selection mode, the UE automatically selects the RPLMN
or Equivalent PLMN (EPLMN) after it is powered on. If there is no
RPLMN, the UE selects a PLMN according to the following priority
list:
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The available Equivalent HPLMN (EHPLMN) with the highest priority,
or the HPLMN when the EHPLMN list does not exist or is empty
Entries in the User Controlled PLMN Selector with Access Priority
data file stored in the USIM (the entries are tried one by one
based on priority)
Entries in the Operator Controller PLMN Selector with Access
Technology data file stored in the USIM (the entries are tried one
by one based on priority)
Other PLMNs and RATs with high channel quality
Other PLMNs and RATs (tried one by one based on channel
quality)
In manual selection mode, the UE displays the available PLMNs and
RATs (based on the preceding priority list) for the subscriber, and
the subscriber selects a PLMN and RAT manually.
After the subscriber selects the PLMN and RAT, the dual-mode UE
selects a proper cell. If the cell is not found, the UE
automatically tries the next PLMN and RAT on the priority
list.
Note: The subscriber may select only the PLMN and not specify the
RAT. Data files stored in the USIM is not a must.
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Contents
IRAT PLMN Selection Procedure
IRAT Cell Selection Criteria
IRAT Cell Reselection Criteria
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Location of UE Search and Selection Procedure
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UE
idle
Behavior
phase
UE
access
phase
Decode system information
Power on
Invisible flow
Visible flow
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PLMN Selection
Cell Search
UE Attach
Cell Search
ERFCN: E-UTRA absolute radio frequency channel number
A method of identifying the center carrier frequencies in E-UTRA.
The carrier frequency in the uplink and downlink is designated by
the EARFCN (E-UTRA Absolute Radio Frequency Channel Number) in the
range 0 - 65535. The channel raster is 100KHz for all bands, which
means that the carrier centre frequency must be an integer multiple
of 100KHz. The relation between EARFCN and the carrier frequency in
MHz for the downlink/uplink is given by an equation and associated
table of frequency bands.
PSS: Primary Synchronize Signal
SSS: Secondary Synchronize Signal
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Synchronized Signal
DL SS is used to realize DL synchronization between UE and eNodeB
and also help UE to get PCI of cell
Page*
LTE Interoperability in Idle Mode(LTE->G/U)
The synchronization signals comprise of the PSS (Primary
Synchronization Signal) and SSS (Secondary Synchronization Signal).
Together they enable the UE to become downlink synchronized and
identify the Physical Cell Identity. There are 504 unique physical
cell identities, divided into 168 cell identity groups each
containing three cell identities (sectors).
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Downlink Synchronization Signals
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System Message Receiving
Purpose: From the system message, UE get all necessary parameters
for the further procedure, such as cell camping, random access,
etc.
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AAL Est Ind(CCP)
System Message Overview
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SI Block
Downlink bandwidth of a cell, Physical HARQ Indication Channel
(PHICH) parameters, and System Frame Number (SFN)
SIB1
Parameters related to cell access and cell selection and scheduling
information of SI messages
SIB2
Common radio parameters used by all the UEs in a cell
SIB3
Common cell reselection parameters for all the cells and
intra-frequency cell reselection parameters
SIB4
SIB5
Inter-frequency EARFCN list and reselection parameters of each
EARFCN used for cell reselection Inter-frequency cell list and
reselection parameters of each neighboring cell used for cell
reselection Inter-frequency cell reselection blacklist
SIB6
UMTS Terrestrial Radio Access (UTRA) Frequency Division Duplex
(FDD) neighboring EARFCN list and reselection parameters of each
EARFCN used for cell reselection UTRA Time Division Duplex (TDD)
neighboring EARFCN list and reselection parameters of each EARFCN
used for cell reselection
SIB7
GERAN neighboring EARFCN list and reselection parameters of each
EARFCN used for cell reselection
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System Information
Downlink bandwidth of a cell, Physical HARQ Indication Channel
(PHICH) parameters, and System Frame Number (SFN)
Parameters related to cell access and cell selection and scheduling
information of SI messages
Bears SIB2~SIB13
SIB2
SIB10
SIB11
SIB12
SIB13
SIB3
SIB4
SIB5
SIB6
SIB7
SIB8
SIB9
Common radio parameters used by all the UEs in a cell
Common cell reselection parameters; intra-frequency cell
reselection parameters
Intra-frequency Ncell related parameters
Intre-frequency Ncell related parameters
UTRAN Ncell related parameters
GERAN Ncell related parameters
CDMA2000 Ncell related parameters
NOTES
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LTE Interoperability in Idle Mode(LTE->G/U)
SI Block
CDMA2000 pre-registration information CDMA2000 neighboring
frequency band list and reselection parameters of each band used
for cell reselection CDMA2000 neighboring cell list of neighboring
frequency band
SIB9
SIB10
SIB11
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RRC States
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RRC Connection
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LTE RRC State Interoperability with 2G/3G
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Cell Selection/Reselection Procedures
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After selecting a PLMN, a UE selects a cell in the PLMN to camp on.
When camped on the cell, the UE monitors system information,
performs measurements on the serving cell and neighboring cells,
and selects a better cell to camp on, according to measurement
rules and cell reselection criteria.
UE performs this procedure according to the selection or
reselection related parameters in the system information or in the
RRC Connection Release message.
A UE can use one of the following two cell selection procedures:
Stored Information Cell Selection and Initial Cell Selection. The
Stored Information Cell Selection procedure takes precedence over
the Initial Cell Selection procedure. The UE uses the latter
procedure only when it fails to find a suitable cell by using the
former procedure.
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After receiving all necessary system message, UE start to measure
RS (Reference Signal) for cell selection judgment
RSRP and RSRQ can be evaluated
Cell Selection
Squal = Qqualmeas – (Qqualmin + Qqualminoffset)
LTE Interoperability in Idle Mode(LTE->G/U)
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
Squal = Qqualmeas - (QQualMin + QQualMinOffset)
LTE Interoperability in Idle Mode(LTE->G/U)
Parameter
Description
Qrxlevmeas
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
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
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Cell Selection Configuration
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The parameter “Minimum Required RX quality level offset(dB)” will
appear only when the “Minimum required RX quality level offset
configure indicator” is configured as “CFG(Configure)”.
Criteria for cell selection:
Squal = Qqualmeas – (Qqualmin + Qqualminoffset)
Following are the description of each parameters:
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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).
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Cell Selection Configuration
Pcompensation = max (PMaximum allowed power – PUE MAX Output Power,
0)
PMaximum allowed power
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Parameter ID
Description
PMaxCfgInd
Indicates whether to configure the the maximum TX power of the UE
in the intra-frequency neighboring cell. Recommended value is
NOT_CFG
PMax
Indicates the maximum TX power of the UE in the cell. If this
parameter is not included in the SIB3, the UE uses the maximum TX
power.
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Page*
Contents
IRAT PLMN Selection Procedure
IRAT Cell Selection Criteria
IRAT Cell Reselection Criteria
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Cell Reselection Overview
The signal strength of both the serving cell and neighboring cells
varies with the movement of a UE, so the UE needs to select a
better cell to camp on. This process is called cell
reselection.
Page*
Related to interoperability which will be discussed in this
course
LTE Interoperability in Idle Mode(LTE->G/U)
UE cell reselection include two steps:
Start the measurement for the neighboring cells
Rank the measured cells based on radio signal quality and
priorities.
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Cell Reselection Procedure
Neighboring Cell Measurement
Different-Priority Inter-Frequency or IRAT Cell Reselection
*
*
Cell Reselection Evaluation Criteria
Confirm the target cell in cell reselection
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Blacklisted Cell Identifying
During cell reselection, UEs are not allowed to measure or reselect
blacklisted cells of the serving cell.
UEs identify blacklisted cells by PCIs(Physical Cell
Identifiers).
Page*
Inter-frequency blacklisted cells
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Data Configuration of Blacklisted Cell
For intra-frequency blacklisted cells
For inter-frequency blacklisted cells
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The Neighboring Cell Priority Overview
During implying measurements and the cell reselection, the UE needs
to obtain the priorities of neighboring frequencies.
Note: Frequencies of different RATs must have different priorities.
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.
The priorities of inter frequency and IRAT are classified into two
types:
Absolute priority
Dedicated priority
Assigned by RRC Conncection Release message and is valid for a
specific UE
Page*
LTE Interoperability in Idle Mode(LTE->G/U)
The priorities of E-UTRAN frequencies and IRAT 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.
Dedicated priority: This priority is UE-specific. Dedicated
priorities are generated by the internal dedicated prioritization
algorithm or generated based on a Subscriber Profile ID (SPID) when
a UE releases radio resources. They are sent to the UE through the
RRC Connection Release message. The validity time of dedicated
priorities is defined by the timer T320ForLoadBalance or
T320ForOther, which is sent to the UE through the RRC Connection
Release message.
During cell reselection, when a UE is camped on a suitable cell,
the UE ignores all the absolute priorities provided in system
information if dedicated priorities are assigned through dedicated
signaling. If the UE acquires the priorities of other frequencies
but no priority of the serving frequency, the UE regards the
priority of the serving frequency as the lowest.
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Types of the Neighboring Cell Priority
Page*
The Serving Cell
Mapping to UE‘s SPID: RATFreqPriorityGroup. Priority
180min
Priority associated with the UE‘s SPID, has higher priority than
that configured by CellReselPriority
The priority is delivered to the UE in an RRC Connection Release
message when the UE attempts to release radio resources for "other”
cause.
Valid within RRCCONNSTATETIMER.T320ForOther
The priority is delivered to the UE in an RRC Connection Release
when the UE attempts to release radio resources for “load balancing
TAU required” cause.
Valid within RRCCONNSTATETIMER.T320ForLoadBalance
Neighboring Cell Priority Handling
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 cells. Reselection
to a neighboring cell is allowed if the cell works on an E-UTRAN or
IRAT frequency that has a priority specified in system information,
and reselection to a cell is prohibited if the cell is blacklisted
by the serving cell as indicated in system information. 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.
An E-UTRAN or IRAT frequency may have an absolute priority or a
dedicated priority.
Absolute priority: The absolute priority of an E-UTRAN or IRAT
frequency is specified by the CELLRESEL. CellReselPriority
parameter and broadcast to UEs in system information.
– The absolute priority of the serving frequency is set by
CELLRESEL.CellReselPriority and broadcast in the SIB3.
– The absolute priority of the inter-frequency neighboring E-UTRAN
frequency is set by
EUTRANINTERNFREQ.CellReselPriority and broadcast in the SIB5.
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notes
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LTE Interoperability in Idle Mode(LTE->G/U)
– The absolute priority of the neighboring UTRAN frequency is set
by
UTRANNFREQ.CellReselPriority and broadcast in the SIB6.
– The absolute priority of the neighboring GERAN frequency is set
by
GERANNFREQGROUP.CellReselPriority and broadcast in the SIB7.
– The absolute priority of the neighboring CDMA2000 frequency is
set by
CDMA2000BANDCLASS.Cdma20001XrttCellReselPri and
CDMA2000BANDCLASS.Cdma2000HrpdCellReselPri and broadcast in the
SIB8.
Dedicated priority: The dedicated priority of an E-UTRAN or IRAT
frequency is UE-specific. It can be determined in the following two
ways:
It can be specified by the Priority parameter.
In this situation, the Priority values of frequencies for one RAT
must all be higher than or less than those in another RAT. In
Flexible User Steering Feature Parameter Description, subscriber
profile IDs (SPIDs) (specified by the Spid parameter) are mapped to
dedicated priorities.
The priority is valid for 180 minutes.
It can be generated by the internal algorithm.
In this situation, the priority is delivered to the UE in an RRC
Connection Release message when the UE attempts to release radio
resources.
The priority is valid only during the interval specified by the
timer T320ForLoadBalance or T320ForOther. Either timer is sent in
the RRC Connection Release message: T320ForLoadBalance is sent if
the release cause is "load balancing TAU required", and
T320ForOther is sent if the release cause is "other". If the timer
expires or the UE enters the RRC_CONNECTED mode, the
algorithm-generated dedicated priorities become invalid.
For details about the timers and SPID, see 3GPP TS 36.331 and
Flexible User Steering Feature Parameter Description
respectively.
In eRAN sharing scenarios, the dedicated priority of a UTRAN or
GERAN frequency can be set for different operators. The priority is
specified by the CellReselPriority parameter in a MO UtranRanShare
or GeranRanShare. A UE preferentially uses the dedicated priority
that is associated with the UE‘s SPID. If the UE is not assigned an
SPID or the SPID is not configured on the eNodeB, the UE uses the
dedicated priority set in the UtranRanShare or GeranRanShare MO for
the corresponding operator.
A UE deletes priorities provided by dedicated signaling in any of
the following situations:
The PLMN is manually selected for the UE.
The UE enters the connected mode.
The validity time (T320ForLoadBalance or T320ForOther) of the
dedicated priorities expires.
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The absolute priority of the serving frequency is set by CELLRESEL.
CellReselPriority which is broadcasted in the SIB3.
The Absolute Priority Configuration- the Serving Cell Reselection
Priority (1/4)
Page*
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Parameter ID
Description
CellReselPrio
Indicates the cell reselection priority of the serving frequency. 0
indicates the lowest priority. This parameter is the networking
planning parameter and needs to be planned in all frequency
layers.
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The Absolute Priority Configuration- EUTRAN Target Cell (2/4)
MOD EUTRANINTERNFREQ
Note: if priority indicator is set Not CFG, then UE doesn’t
implement cell reselection to the target frequency.
Page*
This priority will be broadcast in SIB5
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The absolute priority of the neighboring GERAN frequency is set by
GERANNFREQGROUP. CellReselPriority which is broadcasted in the
SIB7.
The absolute priority of the neighboring UTRAN frequency is set by
UTRANNFREQ. CellReselPriority which is broadcasted in the
SIB6.
The Absolute Priority Configuration- the IRAT Neighbor Cell
Reselection Priority(3/4)
Page*
GSM
UMTS
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The Absolute Priority Configuration - the IRAT Neighbor Cell
Reselection Priority(4/4)
The absolute priority of the neighboring CDMA2000 frequency is set
by CDMA2000BANDCLASS. Cdma20001XrttCellReselPri which is
broadcasted in the SIB8.
Page*
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Dedicated Cell Reselection Priority Configuration and Application
Overview
Page*
Dedicated cell reselection priority in RRC Release is received by
UE when UE leave RRC-Connected state.
Dedicated cell reselection priority is configured in eNodeB based
on Operator policy for every SPID.
Step1:Dedicated cell reselection priority configuration in
eNodeB
Step2: setup the mapping between dedicated priority and SPID
Step3: eNodeB send dedicated cell reselection priority to UE
Step4: UE firstly applies dedicated priority before the optional
validity time of dedicated priorities (T320) expires.
By dedicated Priority based on SPID, Operators can make its
subscribers to camp in a suitable RAT (a cell of LTE/UMTS/GSM) or
frequency (a cell of LTE) based on the service characteristics. For
example, for a data centric subscriber, a LTE cell will be the more
suitable selection than an UMTS cell or a GSM cell; for a voice
centric subscriber, a GSM cell or an UMTS cell will be the more
suitable selection than a LTE cell.
UE
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The Dedicated Priority Configuration for the Flexible User
Steering
If flexible user steering feature is activated, we can set the
dedicated priority based on subscriber profile ID, and valid
duration is 180 min.
It is delivered to the UE in an RRC Connection Release message when
the UE's radio resources are released.
Page*
mapping
Dedicated priority
The dedicated priority is set by RATFREQPRIORITYGROUP. Priority .
The dedicated priority of frequencies for one RAT must all be
different from those for another RAT. The flexible user steering
feature maps a subscriber profile ID (SPID) onto dedicated
priorities of a group of frequencies by configuring the SPIDCFG
object.
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A UE deletes priorities provided by dedicated signaling in any of
the following situations:
The NAS signals the AS to perform PLMN selection.
The UE enters the connected mode.
The validity time (specified byT320) of the dedicated priority
expires.
The value of T320 is fixed to 180 minutes for UE’s SPID. Otherwise,
timers configured in the following figure will be used.
Timers Configuration of the Dedicate Priority
Page*
LTE Interoperability in Idle Mode(LTE->G/U)
T320 and the dedicated priority are sent to the UE in the RRC
Connection Release message. The eNodeB determines the value of T320
in the following two ways:
If the dedicated priority is associated with the UE's SPID, the
value of T320 is fixed to 180 minutes.
If the dedicated priority is not associated with the UE's SPID,
T320 is set by RRCCONNSTATETIMER. T320ForLoadBalance when the RRC
connection is released due to load imbalance and by
RRCCONNSTATETIMER. T320ForOther when the RRC connection is released
due to other reasons.
For details about T320, see section 7.3 "Timers (Informative)" in
3GPP TS 36.331 R10, which was released in March 2011.
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Parameter ID
Description
T320ForLoadBalance
Indicates the length of timer T320 that is configured in the case
of load balancing. It refers to the time period during which the
dedicated priorities (used for cell reselection) retain valid. The
time period is contained in the RRCConnectionRelease message that
is received by the UE. After the timer specified in the
RRCConnectionRelease message expires, the dedicated priorities
become invalid.
T320ForOther
Indicates the length of timer T320 that is configured in the case
of load imbalancing. It refers to the time period during which the
dedicated priorities (used for cell reselection) retain valid. The
time period is contained in the RRCConnectionRelease message that
is received by the UE. After the timer specified in the
RRCConnectionRelease message expires, the dedicated priorities
become invalid.
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Before the cell reselection, a UE performs measurements of
neighboring cells based on the RX signal level and quality of the
serving cell and frequency priorities of the neighboring
cells.
The UE only measures the neighboring frequencies broadcasted in the
system information and the neighboring frequencies whose priority
information is carried in the RRC Connection Release message.
The IRAT Neighboring Measurement Overview
Page*
Inter-Frequency or Inter-RAT Measurement
To trigger inter-frequency or inter-RAT measurements, the following
rules apply:
The UE always performs measurements on the inter-frequency or
inter-RAT neighboring cells regardless of the RX signal level or
quality of the serving cell if the priorities of the neighboring
frequencies are higher than the priority of the serving
frequency.
If the priorities of inter-frequency neighboring frequencies are
less than or equal to the priority of the serving frequency, or if
the priorities of inter-RAT neighboring frequencies are less than
the priority of the serving frequency, the UE determines whether to
start the corresponding measurements according to the following
rules:
The UE does not perform inter-frequency or inter-RAT measurements
if the RX signal level and quality of the serving cell are good,
that is, if the Srxlev and Squal values of the serving cell are
greater than SnonIntraSearchP and SnonIntraSearchQ, respectively.
SnonIntraSearchP indicates the threshold for triggering
inter-frequency or inter-RAT measurements, and is set by CELLRESEL.
SNonIntraSearch . SnonIntraSearchQ indicates the threshold for
triggering RSRQ-based inter-frequency or inter-RAT measurements,
and is set by CELLRESEL. SNonIntraSearchQ . Both SnonIntraSearchP
and SnonIntraSearchQ are broadcast in the SIB3.
The UE performs inter-frequency or inter-RAT measurements if the
Srxlev or Squal value of the serving cell is less than or equal to
SnonIntraSearchP or SnonIntraSearchQ, respectively.
The UE performs inter-frequency or inter-RAT measurements on
neighboring cells regardless of the RX signal level or quality of
the serving cell if CELLRESEL. SNonIntraSearchCfgInd is set to
NOT_CFG. The value NOT_CFG indicates that the threshold for
triggering inter-frequency or inter-RAT measurements does not need
to be set. In this situation, SnonIntraSearchP and SnonIntraSearchQ
are not broadcast in the SIB3; the UE uses the default settings of
SnonIntraSearchP (default value: infinite) and SnonIntraSearchQ
(default value: 0).
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Neighboring Cell Measurement Procedure before Cell
Reselection
Page*
From SIB ,UE can get the serving cell and IRAT 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.
Srxlev
Qqual
LTE Interoperability in Idle Mode(LTE->G/U)
Before cell reselection, a UE performs measurements of neighboring
cells based on the RX signal level and quality of the serving cell
and frequency priorities of the neighboring cells.
The UE only measures the neighboring frequencies broadcast in the
system information and the neighboring frequency whose priority
information is carried in the RRC Connection Release message.
Inter-Frequency or Inter-RAT Measurement
To trigger inter-frequency or inter-RAT measurements, the following
rules apply:
The UE always performs measurements on the inter-frequency or
inter-RAT neighboring cells regardless of the RX signal level or
quality of the serving cell if the priorities of the neighboring
frequencies are higher than the priority of the serving
frequency.
If the priorities of inter-frequency neighboring frequencies are
less than or equal to the priority of the serving frequency, or if
the priorities of inter-RAT neighboring frequencies are less than
the priority of the serving frequency, the UE determines whether to
start the corresponding measurements according to the following
rules:
The UE does not perform inter-frequency or inter-RAT measurements
if the RX signal level and quality of the serving cell are good,
that is, if the Srxlev and Squal values of the serving cell are
greater than SnonIntraSearchP and SnonIntraSearchQ, respectively.
SnonIntraSearchP indicates the threshold for triggering
inter-frequency or inter-RAT measurements, and is set by CELLRESEL.
SNonIntraSearch . SnonIntraSearchQ indicates the threshold for
triggering RSRQ-based inter-frequency or inter-RAT measurements,
and is set by CELLRESEL. SNonIntraSearchQ . Both SnonIntraSearchP
and SnonIntraSearchQ are broadcast in the SIB3.
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notes
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The UE performs inter-frequency or inter-RAT measurements if the
Srxlev or Squal value of the serving cell is less than or equal to
SnonIntraSearchP or SnonIntraSearchQ, respectively.
The UE performs inter-frequency or inter-RAT measurements on
neighboring cells regardless of the RX signal level or quality of
the serving cell if CELLRESEL.SNonIntraSearchCfgInd is set to
NOT_CFG. The value NOT_CFG indicates that the threshold for
triggering inter-frequency or inter-RAT measurements does not need
to be set. In this situation, SnonIntraSearchP and SnonIntraSearchQ
are not broadcast in the SIB3; the UE uses the default settings of
SnonIntraSearchP (default value: infinite) and SnonIntraSearchQ
(default value: 0).
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Data Configuration of Neighboring Cell Measurement Threshold
Page*
SNonIntraSearchQ
SNonIntraSearchP
SNonIntraSearchCfgInd
For the neighbor with lower or equal priority
If the threshold is configured :
When Srxlev > SNonIntraSearchP and Squal > SNonIntraSearchQ,
UE does not perform IRAT measurement
When Srxlev ≤ SnonIntraSearchP or Squal ≤ SNonIntraSearchQ UE
perform inter frequency /RAT measurement
If the SNonIntraSearchCfgInd parameter is set to NOT_CFG, the UE
always perform IRAT measurement
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Low Prio.
S-eNB is worse than Thresh_serving.low & T-BTS is better than
Thresh_x.low
T-eNB is better than Thresh_x.high
Cell Reselection
Cell Reselection Principal
High Prio. -> Low Prio.
UEs camp on Cell which providing best service
Page*
Cell Reselection (High -> Low)
Cell Reselection (Low -> High)
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Inter-RAT Cell Selection Criteria
Page*
During reselection to an inter-RAT neighboring cell, the Srxlev and
Squal values of inter-RAT neighboring cells need to be calculated
as follows:
UTRAN Neighboring cell
Squal = Qqualmeas - (Qqualmin + Qqualminoffset)
Srxlev = -FLOOR(-2 x 10 x log10 Ec/Io)
Reselection to an inter-RAT cell can be classified into reselection
to a higher-priority cell and reselection to a lower-priority
cell.
LTE Interoperability in Idle Mode(LTE->G/U)
Inter-RAT Cell Selection Criteria
During reselection to an inter-RAT neighboring cell, the Srxlev and
Squal values of inter-RAT neighboring cells need to be calculated
as follows:
UTRAN Neighboring cell
Squal = Qqualmeas - (Qqualmin + Qqualminoffset)
Pcompensation = max(UE_TXPWR_MAX_RACH - P_MAX, 0)
The variables in the preceding formulas are described as
follows:
Qrxlevmeas is the measured RX signal level of the neighboring UTRAN
cell.
Qqualmeas is the measured RX signal quality of the neighboring
UTRAN cell.
The values of the preceding parameters are broadcast in the SIB6
from the E-UTRAN when the UE implements reselection estimation on a
neighboring UTRAN cell.
Qrxlevmin is set by the UTRANNFREQ. QRxLevMin parameter.
Qqualmin is set by the UTRANNFREQ. Qqualmin parameter.
UE_TXPWR_MAX_RACH is set by the UTRANNFREQ. PmaxUtran
parameter.
P_MAX is the maximum output power that the UE can physically
provide. It is unconfigurable on the network side.
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Page*
notes
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Values of Qrxlevminoffset and Qqualminoffset are obtained from
UTRAN system information. For details, see section 5.2.3.1 "UTRA
case" in 3GPP TS 25.304 R10, which was released in March
2011.
GERAN Neighboring cell
Srxlev = Qrxlevmeas - Qrxlevmin - Pcompensation
Qrxlevmeas is the measured RX signal level of the neighboring GERAN
cell.
Pcompensation = max(MS_TXPWR_MAX_CCH - P, 0)
The values of the preceding parameters are broadcast in the SIB7
from the E-UTRAN when the UE implements reselection estimation on a
neighboring GERAN cell.
Qrxlevmin is set by the GERANNFREQGROUP.QRxLevMin parameter.
MS_TXPWR_MAX_CCH is set by the GERANNFREQGROUP.PmaxGeran
parameter.
P is the maximum output power that the UE can physically provide.
It is unconfigurable on the network side.
For details, see section 3.6 "Radio constraints" in 3GPP TS 43.022
R10, which was released in March 2011.
CDMA2000 Neighboring cell
Srxlev = -FLOOR(-2 x 10 x log10 Ec/Io)
Ec/Io is the measured RX signal quality of the neighboring CDMA2000
cell.
For details, see 3GPP2 C.S0005-A.
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The General Procedure of Reselection to a Higher-priority
Cell
Page*
When ThrshServLowQCfgInd CFG that is to say, SIB3 contains
threshServingLowQ, only for EUTRAN and UTRAN neighbour cells, using
:
Squal>Threshx.highQ.
While for GERAN and CDMA neighbour cells , no matter whether
ThrshServLowQCfgInd CFG, always using:
Srxlev> Threshx.high
Cell Reselection( Low -> High)
Parameter threshServingLowQ is available only when
“ThrshServLowQCfgInd” is configured as CFG(Configure).
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The Data Configuration of Reselection to a Higher-priority
Cell(1/2)
Page*
TReselUtran
TReselGeran
ThreshXHigh
ThreshXHighQ
ThreshXHigh
GERAN
UTRAN
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LTE Interoperability in Idle Mode(LTE->G/U)
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The Data Configuration of Reselection to a Higher-priority
Cell(2/2)
Page*
CDMA2000
TreselectionHrpd
Cdma1XrttTreselection
Cdma2000HrpdThreshXHigh
Cdma20001XrttThreshXHigh
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LTE Interoperability in Idle Mode(LTE->G/U)
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The General Procedure of Reselection to a Lower-priority Cell
Page*
When ThrshServLowQCfgInd CFG that is to say, SIB3 contains
threshServingLowQ,
For serving cell, Squal<threshServingLowQ
For EUTRAN and UTRAN neighbour cells, Squal>threshXLowQ
When ThrshServLowQCfgInd NOT CFG,
For EUTRAN and UTRAN neighbour cells, Srxlev>threshXLow
While for GERAN and CDMA neighbour cells , no matter whether
ThrshServLowQCfgInd CFG,
Srxlev> threshXLow
Cell Reselection (High -> Low)
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LTE Interoperability in Idle Mode(LTE->G/U)
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The Data Configuration of Reselection to a Lower-priority
Cell(1/2)
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UTRAN
GERAN
TReselUtran
TReselGeran
ThreshXLow
ThreshXLowQ
ThreshXLow
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LTE Interoperability in Idle Mode(LTE->G/U)
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The Data Configuration of Reselection to a Lower-priority
Cell(2/2)
Page*
CDMA2000
Cdma20001XrttThreshXLow
TreselectionHrpd
Cdma1XrttTreselection
Cdma2000HrpdThreshXLow
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LTE Interoperability in Idle Mode(LTE->G/U)
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Contents
IRAT PLMN Selection Procedure
IRAT Cell Selection Criteria
IRAT Cell Reselection Criteria
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LTE Interoperability in Idle Mode(LTE->G/U)
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LTE->GU Cell Reselection – GnGp SGSN
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Locate UE identity
MME check P-TMSI signature
MME mapping MM context
MME performs EPS and PDP context mapping include pre-R8 and R8 QoS
mapping
Create PDP context and delete bearer
Other step is just as intra RAU
LTE Interoperability in Idle Mode(LTE->G/U)
When the UE in idle mode leaves the area covered by both the LTE
network and GERAN/UTRAN and enters an area covered solely by the
GERAN/UTRAN, cell reselection occurs. The UE initiates the RAU
procedure to camp on the GERAN/UTRAN cell. Figure in the slide
above shows the signaling procedure of the cell reselection from
the LTE network to the GERAN/UTRAN.
For details on the signaling procedure, see Appendix D.3.5 of
TS23.401. This course focuses on only major parameters and
steps.
0. The UE selects a GERAN/UTRAN cell. The routing area of the cell
is not registered with the network.
The UE sends an RAU request to the new SGSN. This request includes
parameters such as old-TMSI (TMSI stands for temporary mobile
subscriber identifier), old RAI (RAI stands for routing area
identifier), old P-TMSI signature (P-TMSI stands for
packet-temporary mobile subscriber identity), and Update
Type.
The new SGSN obtains SGSN contexts from the MME.
The new SGSN sends an SGSN context request to the MME to obtain
Mobility Management (MM) contexts and PDP contexts.
The MME completes the mapping between EPS bearers and PDP contexts
and the mapping of EPS bearer QoS parameters to pre-Rel-8 QoS
parameters. After the mapping is complete, the MME sends an
acknowledgement to the new SGSN. The response includes MM contexts
and PDP contexts. At the same time, the MME starts a timer, which
controls the subsequent deletion of bearers.
If the PDP contexts sent by the MME do not include any security
parameters, the security procedure is required.
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LTE Interoperability in Idle Mode(LTE->G/U)
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0. UE changes to UTRAN or GERAN
S-GW
13. Delete Session Response
13. Delete Session Request
8. Cancel Location Ack
10. Update Location Ack
2. SGSN Context Request
3. Security Functions
LTE->GU Cell Reselection, GnGp SGSN
Notes
Page*
LTE Interoperability in Idle Mode(LTE->G/U)
The new SGSN receives SGSN contexts from the MME and returns a
confirmation message to the MME. Then, the MME invalidates the
contexts of the P-GW/S-GW and HSS.
The P-GW updates the PDP contexts as follows
The new SGSN sends a PDP context update request to the P-GW.
The P-GW updates the PDP contexts and sends an acknowledgement to
the new SGSN.
The new SGSN instructs the HSS to update location
information.
Before updating location information, the HSS cancels the location
information in the old SGSN.
The HSS instructs the old SGSN to cancel location
information.
After canceling location information, the old SGSN sends an
acknowledgement to the HSS.
Before updating location information, the HSS inserts subscriber
data into the new SGSN.
The HSS inserts subscriber data to the new SGSN.
The new SGSN accepts the subscriber data inserted by the HSS and
sends an acknowledgement to the HSS.
After updating the location information, the HSS sends an
acknowledgement to the new SGSN.
The new SGSN obtains SGSN contexts and subscriber data. After
updating the location information, the new SGSN sends an RAU accept
message to the UE.
After the RAU procedure is complete, the UE sends an
acknowledgement to the new SGSN.
When the timer started in step 2b expires, the MME initiates the
deletion of the original bearers.
The MME sends a bearer deletion request to the S-GW.
The S-GW deletes the original bearers and sends an acknowledgement
to the MME.
If an S1 connection is established on the user plane before the RAU
procedure is initiated, the MME must instruct the eNodeB to release
the S1 connection. After released, the eNodeB sends an
acknowledgement to the MME.
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LTE Interoperability in Idle Mode(LTE->G/U)
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GU->LTE
Locate UE identity
MME check PTMSI signature
MME mapping MM context
MME performs EPS and PDP context mapping include pre-R8 and R8 QoS
mapping
Crete PDP context and delete PDP context
Other is just as the same as intra E-UTRAN TAU
LTE Interoperability in Idle Mode(LTE->G/U)
When the UE in idle mode moves into an area covered by both the LTE
network and GERAN/UTRAN, the UE reselects an LTE cell with a high
priority. The UE initiates the TAU procedure to camp on an LTE
cell. Figure 3-9 shows the signaling procedure of the cell
reselection from the GERAN/UTRAN to the LTE network.
For details on the signaling procedure, see Appendix D.3.6 of
TS23.401.
When the UE moves into an area covered by both the LTE network and
GERAN/UTRAN, the UE selects an LTE cell to camp on. The TAU
procedure is triggered.
The UE sends a TAU request to the eNodeB. The TAU request includes
parameters such as last visited TAI (TAI stands for tracking area
identity), P-TMSI Signature, and old GUTI (GUTI stands for globally
unique temporary identity).
The eNodeB selects a proper MME and forwards the TAU request to the
MME.
The MME obtains contexts from the old SGSN. The MME sends an SGSN
Context Request message to the old SGSN to obtain MM contexts and
PDP contexts.
The old SGSN sends a response to the MME. The response includes MM
contexts and PDP contexts. At the same time, the old SGSN starts a
timer, which controls the subsequent deletion of bearers.
If the PDP contexts sent from the old SGSN do not include any
security parameters, the security procedure is required.
The MME receives the SGSN contexts and returns a confirmation
message to the old SGSN. Then, the old SGSN invalidates the
contexts of the SGSN and HLR.
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LTE Interoperability in Idle Mode(LTE->G/U)
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TAU procedure
HSS
GW
PDN
SGSN
Gn/Gp
MME
eNodeB
UE
19. Iu Release Complete
18. Iu Release Command
6. Security procedures
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NOTES
Page*
LTE Interoperability in Idle Mode(LTE->G/U)
The MME maps the PDP contexts one by one to EPS bearers and maps
the pre-Rel-8 QoS parameters to the QoS parameters of the EPS
bearers. The MME sends a session setup request to the S-GW. The
parameters in the request include IMSI (IMSI stands for
international mobile subscriber identity), MME Address and TEID
(TEID stands for tunnel end point identifier), P-GW Address and
TEID, and EPS Bearer QoS.
The S-GW creates contexts and sends a bearer update request to the
P-GW. The bearer update request is used to inform the P-GW that the
RAT of the UE is changed and the bearer update is required.
If a PCRF is deployed on the network, the P-GW forwards RAT
information to the PCRF. The PCRF then performs IP-CAN session
establishment.
The P-GW can proceed with the following operations before the PCRF
completes IP-CAN session establishment. If the execution result of
the PCRF requires bearer update, the P-GW initiates the bearer
update procedure.
The P-GW updates contexts and sends a bearer update response to the
S-GW.
The S-GW updates contexts and sends a session creation response to
the MME.
The MME instructs the HSS to update location information.
Before the HSS updates location information, it sends a cancel
location message to the old SGSN. After receiving the message, the
old SGSN cancels the location information about the UE.
If Iu connections are established before the TAU request is
initiated, the old SGSN initiates the release of Iu connections on
receiving the cancel location message.
When the data transfer timer expires, the RNC informs the old SGSN
that the Iu connections are released.
The old SGSN sends an acknowledgement to the HSS.
After updating the location information, the HSS sends an
acknowledgement to the MME.
The UE completes the TAU procedure. The MME accepts the TAU request
and sends E-UTRAN's roaming restrictions and access restrictions
for the UE to the eNodeB.
The UE returns a response to the MME after completing the TAU
procedure.
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LTE Interoperability in Idle Mode(LTE->G/U)
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LTE->GU
Cell Seselection–
S3/S4 SGSN
(S-GW Unchanged)
Locate UE identity
MME check PTMSI signature
MME mapping MM context
S4 SGSN performs EPS and PDP context mapping include pre-R8 and R8
QoS mapping
Modify EPS bearer
LTE Interoperability in Idle Mode(LTE->G/U)
For details on the signaling procedure, see section 5.3.3.3 of
TS23.401.
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LTE Interoperability in Idle Mode(LTE->G/U)
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9. PCEF Initiated IP-CAN Session Modification
22b. Modify Bearer Response
22. Modify Bearer Request
connection
10. Modify Bearer Response
8. Modify Bearer Request
3. Context Request
6. Context Acknowledge
5. Authentication
(A)
Page*
Locate UE identity
MME Check PTMSI signature
MME Mapping MM context
S4 SGSN performs EPS and PDP context mapping include pre-R8 and R8
QoS mapping
Modify EPS bearer
LTE Interoperability in Idle Mode(LTE->G/U)
When the UE in idle mode moves into an area covered by both the LTE
network and GERAN/UTRAN, the UE reselects an LTE cell with a high
priority. The UE initiates the TAU procedure to camp on an LTE
cell, and the S-GW remains unchanged. Figure 3-10 show the
signaling procedure of the cell reselection from the GERAN/UTRAN to
the LTE network.
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LTE Interoperability in Idle Mode(LTE->G/U)
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11. PCEF Initiated IP-CAN
MME
eNodeB
UE
ServingGW
HSS
PDN
eNodeB
UE
18. Iu Release Complete
17. Iu Release Command
6. Authentication / Security
5. Context Response
Thank you
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LTE Interoperability in Idle Mode(LTE->G/U)
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Idle Mode
Cell Selection
(PHICH) parameters, and System Frame Number (SFN)
Parameters related to cell access and cell selection and
scheduling
information of SI messages
SIB2
SIB10
SIB11
SIB12
SIB13
SIB3
SIB4
SIB5
SIB6
SIB7
SIB8
SIB9
Common radio parameters used by all the UEs in a cell
Common cell reselection parameters;
intra-frequency cell reselection parameters
Intra-frequency Ncell related parameters
Intre-frequency Ncell related parameters
UTRAN Ncell related parameters
GERAN Ncell related parameters
CDMA2000 Ncell related parameters
2. SGSN Co
7. Update Location
8. Cancel Location
9. Ins
S
13. S1
14. Update Location Request
15. Cancel Location
UE eNodeB MME
21. Update
Location Ack
7. Modify Bearer Request
11. Modify Bearer Response
13. Cancel Location
UE
RNC/
BSS
eNodeB
SGSN
MME
Serving
GW
PDN
GW
HSS
Release E-UTRAN
PCRF
14. Update Location Request
15. Cancel Location
7. Context Acknowledge
4. Context Request
UE eNodeB
19. Update Location Ack
16. Cancel Location Ack
9. Modify Bearer Request
13. Modify Bearer Response
10. Modify Bearer Request
12. Modify Bearer Response
procedure
RRC Connection (SRB)
Send and/or Receive Data to/from UE
Network Controlled Mobility
UE Reports Channel Quality
DRX can be Configured