172582997-Idle-Mode

Idle Mode

- Saibaba Attelli

What is Idle Mode? When UE is powered on and can access and be reached by the network.

There is no RRC connection established. There are only signaling messages between UE and Core Network.

What happens in Idle Mode?

PLMN SelectionCell Selection and Re-SelectionLA and RA updatesPagingSIB Broadcast

PLMN Selection

Automatic PLMN Selection-Checks for the availability of last

registered PLMN-If not, UE checks for the availability

of PLMN according to the priority list

Priority List-Home PLMN-PLMN’s in USIM-Operator controlled PLMN’s-Other PLMN’s according to RSCP

PLMN Selection – Automatic Mode

PLMN Priority

Home PLMN

PLMN’s in USIM

Operator Controlled PLMN’s

Other PLMN’s according to RSCP

PLMN Selection

Manual PLMN Selection-UE scans for all allowed and barred PLMN’s-UE attempts registration on selected PLMN-If registration fails, UE enters limited service mode

Roaming PLMN Selection-UE can get service from another PLMN depending upon the service agreement between operators.

Cell Selection

UE attempts a cell selection (S-criteria) when - UE is switched on - After several failed RRC connection request - UE returns to Idle mode from Connected state - UE returns to Idle mode from Emergency call on any PLMN

Cell Selection Parameters

qRxLevMin (default: -115 dBm) - Lowest RxLev that UE can measure

qQualMin (default: -18 dB) - Lowest Ec/Io that UE can decode

maxTxPowerUL (defaut: 21 – 24 dBm) - Max. power that UE can transmit

Squal – Signal to Interference ratio on CPICH

Srxlev – Signal level compensation

Cell Selection Criteria

Cell selection is based on the following equations Squal = Qqualmeas –qQualMin (for WCDMA cell)

Srxlev = Qrxleveas – qRxLevmin – Pcompensation (for all cells)

Cell Selection criteria is fulfilled when Squal>0 and Srxlev>0.

Cell Re-SelectionUE attempts a cell re-selection (R-criteria) when - Camped cell is no longer suitable - UE finds a better neighboring cell (Inter and Intra – frequency neighbors) - UE is in “limited service” state - UE is in Cell_FACH state

Cell Selection and Re-Selection takes place based on RSCP or Ec/Io. UE performs periodic measurements and evaluates Selection and Re-Selection criteria

Cell Re-Selection Parameters

qHyst(s) - Hysteresis value of serving cell (default:4, range: 0-40) qHyst1 for RSCP and qHyst2 for Ec/Io

qOffset(s,n) - Offset between Serving & neighbor cellqOffset1sn for RSCP and qOffset2sn for Ec/Io

treSelection – time-to-trigger for cell reselection

qualMeasQuantity – cell selection and reselection quality measure. 1 for RSCP and 2 for Ec/Io

sIntraSearch – decision on when to start intra-freq neighbor measurements (default:0 range: 0-27 dB)

sInterSearch - decision on when to start inter-freq neighbor measurements (default:0 range: 0-27 dB)

sRatSearch – decision on when to start GSM neighbor frequency measurements(default:4 range: 0-20 dB)

sHcsRat – decision on when to start GSM neighbor frequency measurements, if the serving cell belongs to Hierarchical Cell Structure (HCS) (default:3 range: 0-20 dB)

Cell Re-Selection Criteria

When cell re-selection is triggered, cells that fulfill S-criteria are ranked as per R-criteria.

R(serving) = Qmeas(s) + qHyst(s)R(neighbor) = Qmeas(n) - qOffset(s,n)

Qmeas = RSCP or Ec/Io for WCDMA cell = RSSI for GSM cell

If both GSM and WCDMA cells fulfill S-criteria, ranking is made 1st using RSCP and the best candidate is chosen assuming that qualMeasQuantity is set to RSCP.

If qualMeasQuantity is set to Ec/Io, and if WCDMA cell is ranked as best, then UE performs 2nd round of ranking based on Ec/Io.

Cell reselection also depends upon UE’s capability to start GSM measurements based on both Ec/Io and RSCP. Otherwise, only Ec/Io is used.

Cell Re-Selection to Inter/Intra freq Neighbors

UE performs inter and intra frequency measurements when

- sIntraSearch/ sInterSearch = 0 means the parameter is not sent, UE continuously performs measurements on intra/inter-freq neighbors

-Squal > sIntraSearch/ sInterSearch, UE need not perform intra/inter-freq measurements

-Squal <= sIntraSearch/ sInterSearch, UE needs to perform intra/inter-freq measurements

Cell Re-Selection to GSM Neighbors

UE performs GSM measurements when

- Squal>sRatSearch and Srxlev>sHcsRat means the parameter is not sent, UE need not perform measurements on GSM cells

-Squal<=sRatSearch and Srxlev<=sHcsRat means the parameter is not sent, UE needs to perform measurements on GSM cells

LA and RA UpdatesLA/RA updates are controlled by CN

LA is identified by LAI = PLMN+IAC

RA is identified by RAI = PLMN+rAC

There are 3 kinds of Updates- Normal- Periodic- IMSI Attach/Detach

Normal LA/RA update - UE switched-on in a cell belonging to a new LA or RA - UE leaves connected mode in new LA or RA - UE in idle mode moves to a cell belonging to different LA or RA.

Periodic LA and RA updates are to notify network of UE’s availbility using the two timers t3212(LA update) and t3312(RA update) and to minimize paging attempts for UE’s out of coverage.

IMSI Attach/Detach -The IMSI attach procedure is used to indicate the IMSI as active in the network. The last Location Updating procedure was of type ‘IMSI Attach’ which means UE performed a power-up registration

-The IMSI detach procedure is used to indicate that UE performed a power-down registration or USIM was removed.

IMSI Attach/Detach is sent on BCCH. Default is TRUE.

PagingEnables CN to tell UE for a terminating service request or for the RAN to inform all UE’s that System Info has been modified

UE can be paged in - Idle Mode, Page is broadcast in a LA/RA - Cell_FACH State - Cell_DCH State

PICH and SCCPCH are used to page UE in Idle Mode.

Timing relation between PICH frame and associated S-CCPCH frametPICH = 7680 chips (3 slots)

PICH is used to indicate when UE should read SCCPCH. Paging message is transmitted on the PCH in the SCCPCH frame starting tPICH chips after the transmitted PICH frame. PCH carries the RRC message that contains actual paging information.

UE listens to PICH at predefines times indicated by Discontinuous Reception Cycle (DRX=2k*10 ms).

The UE’s are divided into separate groups and each group reads for specific paging indicator that tells UE to read the associated SCCPCH.

Each paging indicator contains IMSI to identify which UE is paged.

System InformationSystem information is sent to UE when - UE powers on - UE changes cell in Idle Mode or Cell_FACH - UE moves from dedicated mode to common mode - Timer expires for SIB

SI is sent to UE on BCCH regularly. It contains parameters related to cell selection and reselection, LA/RA updates, Handover and Power Control.

Master Information Block (MIB)

MIB contains schedulling information for SIB’sMIB is sent every 80 ms on BCH

System Information Blocks

SIB Characteristics

System Information System Information updates can be triggered by

- Reconfiguration of system parameters - Change of repetition rate for a SIB - Change in value of Broadcast System parameter

UE does not always read system information to reduce power consumption. If system information update fails, RNC repeats procedure until positive response or updateCellReattsNo is reached

updateCellReattsNo: Default Value: 0 (Range 0..10)

When UE is Powered on or returning to coverage areaIt searches for the strongest cell thru P-SCH and gets some initial synchronizationS-PCH provides some additional aid and gets it fully synchronized.UE will lock onto PCCPCH and get cell specific scrambling code and decodes the BCH.BCH contains system information that UE needs to identify (PLMN, Cell ID, configuration parameters etc.)

UE lookups if this is the PLMN network to which it is subscribed? If not, it will continue to search for a different system information.

UE in Idle mode will camp on to SCCPCH and listen to the paging channel (PCH) information to see if there is an incoming call.

An RRC connection is setup when voice or data needs to be sent to or from a specific UE.

Thank you!