handover (ericsson)

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  • 1. HANDOVEROverview

2. Types of Handover Handovers are needed to maintain calls when moving between cellsin active/dedicated mode (CELL_DCH Mode). Cell reselection is the procedure used in idle or when connected incommon channels (Cell_FACH mode) when moving between cells Types of handover Soft/Softer Handover (among Different RBS/Same RBS on the sameWCDMA Carrier) IFHO (among Different WCDMA Carriers) IRAT HO (Inter Radio Access Technology Handover - Voice) IRAT Cell Change (Inter Radio Access Technology Handover CellChange Packet) Service Based Handover (IRAT HO (Speech RAB only) to GSM basedon service needs like coverage) CNHHO CS Hard HO to another RNS based on core networkmeasurements (Optional feature) HS-DSCH Cell Change (HSDPA Mobility)Ericsson Confidential Praveen Chandrasekaran 2 2006-04-10 3. Handover EntitiesEricsson Confidential Praveen Chandrasekaran 3 2006-04-10 4. Overall ProcessInitiationUE Measurements / Evaluation Measurements Filtering, Offsetting, Weighting Evaluation ReportingRNC EvaluationExecutionEricsson Confidential Praveen Chandrasekaran 4 2006-04-10 5. Ericsson Confidential Praveen Chandrasekaran 5 2006-04-10Initiation Event Based triggering where UE is involved in thedecision. Evaluation and reporting can be based on CPICHEc/No or CPICH RSCP. SHO , CNHHO : CPICH Ec/No is default HSCC Evaluation : CPICH RSCP is default For IRAT HO and IFHO, Ue Tx (UL) power can also betaken as an input 6. MeasurementsFrom the Ue perspective all the cells are divided into one of thesesubsets according to 3GPP Active Set (AS): The cells involved in soft handover and measured byEricsson Confidential Praveen Chandrasekaran 6 2006-04-10the UE Monitored Set (MN): The monitored set is created from the neighbor cell lists of all thecells in the Active Set The max number of cells in each set is 32. Unmonitored set: cells excluded from MN set because MN set is full.UE is not ordered to measure them. Detected Set (DN) : The intra frequency cells detected by the UE butnot part of Active Set or monitored set. (Can then be an Unmonitored ora Missing neighbor) 7. Event 1a, Primary CPICH enters Reporting Range Reported Cell not in AS Hysterisis and Time totrigger used to prevent pingpong reports If more than 1 cell isreported, best cell in termsof Ec/No is taken intoconsideration If AS is not full, Cell isAdded otherwise worst cellis replaced (event 1c)Both event 1a and 1b are depicted here.Ericsson Confidential Praveen Chandrasekaran 7 2006-04-10 8. Event 1b, Primary CPICH leaves reporting range Reported Cell is in AS Hysterisis and Time totrigger used to preventping pong effect. If more than 1 cell isreported only 1 cell isremoved at a time butthe last cell is neverremovedBoth event 1a and 1b are depicted here.Ericsson Confidential Praveen Chandrasekaran 8 2006-04-10 9. Event 1c, A non-active primary CPICH becomesbetter than an active Primary CPICH Reported cell is notEricsson Confidential Praveen Chandrasekaran 9 2006-04-10in AS AS is full Worst cell isreplaced. Hysterisis andTimeToTrigger usedto prevent ping pong If more than 1 cell isreported only 1 cellwith best Ec/No istaken intoconsideration 10. Event 2d, Estimated Quality of current frequencyis below a threshold Threshold is eitherRSCP or EcNoEricsson Confidential Praveen Chandrasekaran 10 2006-04-10 Will be used totrigger IRAT( orIFHO )measurements Hysterisis and Timeto trigger used toprevent ping pongeffect. The consequentmeasurements forIRAT (or IFHO) willbe based on whether2d was triggered onRSCP or EcNo Note: Only EcNo based threshold is shown inabove figureAction: UE enters Compressed Mode and starts measuring IRAT (or IFHO)neighbors 11. Event 2f, Estimated Quality of current frequency isabove a threshold Both RSCP andEcNo thresholdshave to be triggered. Hysterisis and Timeto trigger used toprevent ping pongeffect.Ericsson Confidential Praveen Chandrasekaran 11 2006-04-10 If Event 2f istriggeredmeasurements forIFHO and IRAT HOare stopped. Note: Only EcNo based threshold is shown inabove figureAction: UE exits Compressed Mode and stops measuring IRAT (or IFHO)neighbors 12. Event 3a, Estimated quality of current used frequency isbelow a certain threshold and estimated quality of the othersystem is above a certain threshold Measurement quantity iseither RSCP or EcNo basedon which triggered event 2d Hysterisis and Time to triggerused to prevent ping pongeffect. SRNC gets resources fromGSM and handover isperformed BSIC has to be decodedbefore handover can beperformed.Note: Only EcNo based threshold is shown in abovefigureAction: UE asks to perform IRAT HO on a selected GSM cellEricsson Confidential Praveen Chandrasekaran 12 2006-04-10 13. EvaluationsBased on the measurement reports received , the RNC willcheck whether cell is valid or not .An invalid cell is one which is not part of any Active,Monitored , or Unmonitored list (ex: missing neighbor)When UE reports an Invalid cell the connection is droppedwhen this cell becomes releaseConnOffset dBs strongerthan the best cell in the AS. This is to prevent the invalid cellto create too much UL interference as it cannot be powercontrolled by the cells in AS.Ericsson Confidential Praveen Chandrasekaran 13 2006-04-10 14. SHO ProcessEnd result of the processis one of the following Radio Link addition Radio Link removal Combined Radio Linkaddition and Radio Linkremoval New proposal rejection,actual Active Set is maintained Connection is releasedMeasurement Control (which containsthe list of cells the UE has to measure)might not be sent in case there is nochange in the Monitored set fromprevious state.Ericsson Confidential Praveen Chandrasekaran 14 2006-04-10 15. IRAT ProcessEnd result of the processis one of the followingHand over the UEconnection to a GSM/GPRScell. That is, the UE is finallyconnected to the GSM/GPRScell and WCDMA RANresources related to the UEconnection are released.The UE connection remainson the WCDMA RAN due to ahandover to GSM/GPRSfailure.Ericsson Confidential Praveen Chandrasekaran 15 2006-04-10 16. IRAT Cell Change ProcessEnd result of the processis one of the followingThe UE, in CELL_DCH state,changes cell and continuesconnected to a Packet-Switchedservice in the new GSM/GPRScell.The UE, in CELL_FACH state,reselects cell and the UE contactsthe new GSM/GPRS system.The UE remains in the WCDMARAN connected to a Packed-Switched service, due to Inter-RAT Cell Change failureEricsson Confidential Praveen Chandrasekaran 16 2006-04-10 17. SUPPORTING SLIDES 18. Event 2b, Estimated Quality of current frequency is below athreshold and estimated quality of non used frequency isabove a threshold1. Event 2b is triggered if 2conditions are satisfieda) Initial trigger for event 2d for IFHONon-used frequencyusedFreqThres4_2bEricsson Confidential Praveen Chandrasekaran 18 2006-04-10evalb) Estimated quality of non usedfrequency is above absolutethresholds (includes both RSCPand EcNo) given by(NonUsedFreqThresh4_2bEcno +Hyst4_2b/2 andNonUsedFreqThresh4_2bRscp +Hyst4_2b/2, during a time at least equal totimeTrigg4_2b )2. SRNC gets resources from theindicated cell using the otherfrequency and handover isperformed.MeasuredQualityTimeCurrent frequencyHysteresis4_2b/2XHystersesis4_2b/2nonUsedFreqThres4_2bXTimeTrigg4_2bXEvent 2b 19. IFHO ProcessAAEnd result of the processis one of the followingHandover the UE connectionto a new WCDMA RANfrequency succeeds.Resources related to the oldActive Set are released.The UE connection remainson the old Active Set on thesource frequency due to ahandover failure.Ericsson Confidential Praveen Chandrasekaran 19 2006-04-10 20. Event 6a, The Ue Tx Powerbecomes larger than an absolutethreshold If the Ue Tx power is higher thana threshold, defined byueTxPowerThresh6a for a time atleast equal to timeTrigg6a , UEsends a measurement report for6a. No hysterisis is used in thisEvent 6b, The Ue Tx Powerbecomes less than an absolutethresholdEricsson Confidential Praveen Chandrasekaran 20 2006-04-10evaluation This is used to trigger IFHO orIRAT HO based on parametersettings. Only RSCP basedmeasurements are triggered. An additional thresholdutranRelThreshRscp is usedwhen IFHO and IRAT HO istriggered based on event 6a When the Ue TX powerbecomes less than anabsolute thresholdueTxPowerThresh6b for atime at least equal totimeTrigg6b , event 6b istriggered. No hysterisis is used in thisevaluation When SRNC receives thismeasurement report,IFHO/IRAT HO evaluationsare stopped. 21. Soft/Softer Handover Mostcommon handover In DL, the UE performs maximum ratio combining InRAKE receiver leading to Protection against fading Power needed by Node B is lower , leading to reduction ofDL interference and better system capacity In the UL , selection combining is performed in case ofSoft handover and maximum ratio combining in case ofsofter handover leading to Less power transmitted by the UE leading to reduced ULinterference and better system capacityEricsson Confidential Praveen Chandrasekaran 21 2006-04-10 22. Soft handover Example of AdvantageEricsson Confidential Praveen Chandrasekaran 22 2006-04-10 23. Ericsson Confidential Praveen Chandrasekaran 23 2006-04-10