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 Selection Cell Selection and Re-Selection LA and RA updates Paging SIB 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
(defaut: 21 – 24 dBm) - Max. power that UE can transmit
maxTxPowerUL
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-Selection UE
attempts a cell re-selection (Rcriteria) 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 cell qOffset1sn for RSCP and qOffset2sn for Ec/Io treSelection
– time-to-trigger for cell reselection
– cell selection and reselection quality measure. 1 for RSCP and 2 for Ec/Io qualMeasQuantity
– decision on when to start intra-freq neighbor measurements (default:0 range: 0-27 dB) sIntraSearch
sInterSearch
- decision on when to start inter-freq neighbor measurements (default:0 range: 0-27 dB) – decision on when to start GSM neighbor frequency measurements (default:4 range: 0-20 dB) sRatSearch
– 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) sHcsRat
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 Updates LA/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.
Paging Enables
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 frame tPICH = 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 Information System
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‟s MIB 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 area It searches for the strongest cell thru PSCH and gets some initial synchronization S-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.
