1 Lte Eran6.0 Idle Mode

LTE eRAN6.0 Idle Mode

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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 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

where:

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

D:/LTE/eRAN2.2/lte/para/CellResel-QRxLevMin.html

D:/LTE/eRAN2.2/lte/para/CellResel-QQualMin.html

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



This priority will be broadcast in SIB5



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



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



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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.






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Command for trigger Rx quality criteria

Command for threshed (EUTRAN)

Command for threshold (UMTS)

Command for threshold (GSM)





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





Ns PO when i_s=0

PO when i_s=1

PO when i_s=2

PO when i_s=3

1 0 N/A N/A N/A

2 0 5 N/A N/A

4 0 1 5 6

Ns PO when i_s=0

PO when i_s=1

PO when i_s=2

PO when i_s=3

1 9 N/A N/A N/A

2 4 9 N/A N/A

4 0 4 5 9

FDD Subframe Patterns:

TDD Subframe Patterns

For FDD and TDD, the PO subframe patterns are different, because for TDD mode, some of

the subframes are of uplink.

The meaning of parameters is following:

T is the length of a DRX cycle. It is determined by the shortest UE-specific DRX

cycle. The value of T can be either signaled from the NAS or specified by the

DefaultPagingCycle parameter. If the NAS indicates the DRX cycle, the UE

compares the value signaled from the NAS and the value of DefaultPagingCycle

and uses the smaller value between them. If the NAS does not indicate the DRX

cycle, the value of T is determined by the DefaultPagingCycle parameter and sent

to the UE through an SI message.

N is min(T,NB). The NB parameter specifies the number of PO subframes in a DRX

cycle. Based on the actual configuration on the eNodeB, NB can be set to 4T, 2T, T,

T/2, T/4, T/8, T/16, or T/32.

Ns is max(1,NB/T).

UE_ID is IMSI mod 1024. If a UE without IMSI makes an emergency call, the UE

should use the default UE_ID value of 0.

If NB is greater, more subframes are used for paging.

Following are some FDD examples:

Example1:

Example2:

Example3:

Example4:



In each DRX cycle, a UE monitors one P-RNTI transmitted on the PDCCH only in this PO

and reads the paging messages on the PDSCH. Different UEs may have the same PO. If UEs

are paged by the MME in the same PO, the paging records must be combined into the

same paging message in RRC layer . When certain UE-specific paging and group paging

triggered by change of an SI message occur simultaneously, the paging messages must

also be combined in RRC layer .









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1 Lte Eran6.0 Idle Mode