Idle Mode Behaviour and Connected Mode Behaviour in 3g - CELL_FACH STATE



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Download Idle Mode Behaviour and Connected Mode Behaviour in 3g - CELL_FACH STATE
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IDLE MODE BEHAVIOUR AND CONNECTED MODE BEHAVIOUR IN CELL_FACH STATE IDLE MODE BEHAVIOUR AND CONNECTED MODE BEHAVIOUR IN CELL_FACH STATE Agenda Introduction PLMN selection Cell selection Cell reselection Location area (LA) and Routing area (RA) updating Paging System information broadcast CELL_FACH State Introduction Idle mode No connection to radio network (No RRC connection established) This minimizes resource utilization in UE and the network UE must be able to access the system and be reached by system with reasonable delays CELL_FACH mode User Equipment (UE) in Connected Mode (has an RRC Connection to radio network) UE uses the common transport channels RACH or FACH CELL_DCH mode User Equipment (UE) in Connected Mode (has an RRC Connection to radio network) UE uses dedicated channels for transmitting data and signalling Idle mode Functions performed PLMN Selection Cell Selection and Reselection Location Area (LA) and Routing Area (RA) updating Paging System Information Broadcast PLMN Selection PLMN selection performed upon power on or upon recovery from lack of coverage If there is no last registered PLMN, or if it is unavailable, the UE will try to select another PLMN “AUTOMATICALLY” or “MANUALLY” depending on its operating mode Manual mode UE displays all PLMN’s (allowed and not allowed) by scanning all frequency carriers The user makes a manual selection and the UE attempts registration on the PLMN PLMN Selection (Contd) In automatic mode, if no last registered PLMN exists or is available, the UE selects a PLMN in the following order of priority Each PLMN in the user-controlled PLMN list in the USIM, in order of priority Each PLMN in the operator-controlled PLMN list in the USIM Other PLMN’s according to the high-quality criterion (WCDMA: CPICH RSCP >= -95 dBm; GSM: SS >= -85 dBm) Other PLMN’s, in order of decreasing signal strength PLMN selection (Contd) Roaming is a service through which a UE is able to obtain services from another PLMN The UE in Automatic mode, having selected and registered a Visited PLMN (VPLMN) periodically attempts to return to its Home PLMN (HPLMN) The time interval between consecutive attempts is stored in the USIM and is managed by the network operator using a timer The timer may have a value between 6 minutes and 8 hours with a step size of 6 minutes A default value is 30 minutes Cell Selection UE looks for a suitable cell in the selected PLMN and camps on to it Cell search procedure UE acquires slot synchronization using P-SCH It acquires frame synchronization using S-SCH Primary scrambling code is obtained from CPICH UE then monitors the paging and system information, performs periodical radio measurements and evaluates cell reselection criteria WCDMA is sensitive to intra frequency interference Measurements used in cell selection and cell re-selection not only relate to signal strength but also to quality of CPICH Cell Selection Strategies used for the cell selection process: Initial Cell Selection: UE has no knowledge of the WCDMA radio channels UE scans all WCDMA radio frequency channels to find a suitable cell with the highest signal level and read BCCH The PLMN is determined from the mcc and mnc in the MIB in BCCH Stored Information Cell Selection: UE knows the carrier frequencies that have previously been used Cell Selection Procedure (Contd) Cell selection procedure (Contd) For cell selection criteria the UE calculates Squal = Qqualmeas - qQualMin (for WCDMA cells) Srxlev = Qrxlevmeas - qRxLevMin – Pcompensation (for all cells) Where Pcompensation = max(maxTxPowerUL – P,0) P is output power of UE according to class Cell selection criteria (S criteria) is fulfilled when Squal>0 ( for WCDMA cells only) and Srxlev>0 Recommended values qQualMin= -19dB (Values in BLUE are values of the parameters) qRxLevMin= -115dBm Note: Increase qRxLevMin if primaryCpichPower is increased to make cell size constant (maxTxPowerUL = 24) Cell reselection UE ranks available cells using R criteria R(Serving) = Qmeas(s) + qHyst(s) R(Neighbour) = Qmeas(n) – qOffset(s,n) Qmeas is the quality value of the received signal Derived from the averaged received signal level for GSM cells Derived from CPICH Ec/Io or CPICH RSCP for WCDMA cells depending on the value of qualMeasQuantity (2, Ec/Io) qHyst(s) = qHyst1 when ranking based on CPICH RSCP (4) qHyst(s) = qHyst2 when ranking based on CPICH Ec/Io (4) qOffset(s,n) = qOffset1sn when ranking based on CPICH RSCP qOffset(s,n) = qOffset2sn when ranking based on CPICH Ec/Io The above two values are 0 for WCDMA cells and 7 for GSM cells Cell reselection (Contd) The ranking is first based on RSCP If a GSM cell is the best cell, the UE reselects to that cell If a WCDMA cell is the best cell, the UE again performs ranking on a parameter depending on qualMeasQuantity and then performs cell reselection The UE will reselect a new cell if it is better ranked than the serving cell for a time interval of treSelection (1) Intra frequency measurements If Squal < SIntraSearch, the UE performs Intra-Freq measurements (22) Remember: Squal = Qqualmeas - qQualMin Inter frequency measurements If Squal < SInterSearch, the UE performs Inter-Freq measurements (0) Inter-RAT measurements If Squal < SRatSearch or Srxlev 0 (4) If the parameter interFreqFDDMeasIndicator = 1, the UE will evaluate cell reselection criteria on inter-frequency cells (0) Paging: When a connection exists between the WCDMA RAN and the UE, “Paging Type 2” is sent through dedicated control channels System information change: Ue receives a System Information Change Indication message containing the information element “BCCH modification info”