Ch 04 HANDOVER_gvl
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Ch 04 HANDOVER_gvl

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. Overview ...

. Overview
2. Handover Causes & Priorities
3. Threshold Comparison Process
4. Target Cell Evaluation Process
5. Handover Algorithms
Power Budget (PBGT)
Level & Quality (RXLEV & RXQUAL)
Umbrella (& Combined Umbrella/PBGT)
MS Speed (FMMS & MS_SPEED_DETECTION)
6. Imperative Handovers
Distance
Rapid Field Drop (RFD) & Enhanced Rapid Field Drop (ERFD)
7. Handover Timers
Call continuity - to ensure a call can be maintained as a MS moves geographical location from the coverage area of one cell to another
Call quality - to ensure that if an MS moves into a poor quality/coverage area the call can be moved from the serving cell to a neighbouring cell (with better quality) without dropping the call
Traffic Reasons - to ensure that the traffic within the network is optimally
distributed between the different layers/bands of a network
If 2 or more handover (PC) criteria are satisfied simultaneously the following priority list
is used in determining which process is performed;
. Uplink and downlink Interference
2. Uplink quality
3. Downlink quality
4. Uplink level
5. Downlink level
6. Distance
7. Enhanced (RFD)
8. Rapid Field Drop (RFD)
9. Slow moving MS
10. Better cell i.e. Periodic check (Power Budget HO or Umbrella HO)

11. PC: Lower quality/level thresholds (UL/DL)
12. PC: Upper quality/level thresholds (UL/DL)

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Ch 04 HANDOVER_gvl Presentation Transcript

  • 1. 1www.TempusTelcosys.comTelecom Tutorials
  • 2. BSS Parameters S9
  • 3. 1. Overview2. Handover Causes & Priorities3. Threshold Comparison Process4. Target Cell Evaluation Process5. Handover Algorithms• Power Budget (PBGT)• Level & Quality (RXLEV & RXQUAL)• Umbrella (& Combined Umbrella/PBGT)• MS Speed (FMMS & MS_SPEED_DETECTION)6. Imperative Handovers• Distance• Rapid Field Drop (RFD) & Enhanced RapidField Drop (ERFD)7. Handover Timers
  • 4. Why are handovers needed? Call continuity - to ensure a call can be maintained as a MSmoves geographical location from thecoverage area of one cell to another Call quality - to ensure that if an MS moves into a poorquality/coverage area the call can be movedfrom the serving cell to a neighbouring cell (withbetter quality) without dropping the call Traffic Reasons - to ensure that the traffic within the networkis optimallydistributed between the differentlayers/bands of a network
  • 5. Timing AdvanceAdjacent CellsDownlink QualityUplink Quality AV_RXQUAL_UL_HOAV_RXQUAL_DL_HODownlink LevelUplink Level AV_RXLEV_UL_HOAV_RXLEV_DL_HOAV_RANGE_HOAV_RXLEV_NCELL(n)QUALITY&INTERFERENCELEVELDISTANCEPERIODICCHECKSUMBRELLAPOWER BUDGETIMPERATIVEHOCHANNEL ADMINISTRATIONDIRECTED RETRYTHRESHOLDCOMPARISONRAPID FIELD DROPMS SPEEDMS Speed AV_MS_SPEEDOthers causes;- Intelligent Underlay/Overlay (IUO)- Traffic Reason Handover (TrHO)- Direct Access to Desired Layer/Band (DADL/B)
  • 6. If 2 or more handover (PC) criteria are satisfied simultaneously the following priority listis used in determining which process is performed;1. Uplink and downlink Interference2. Uplink quality3. Downlink quality4. Uplink level5. Downlink level6. Distance7. Enhanced (RFD)8. Rapid Field Drop (RFD)9. Slow moving MS10. Better cell i.e. Periodic check (Power Budget HO or Umbrella HO)11. PC: Lower quality/level thresholds (UL/DL)12. PC: Upper quality/level thresholds (UL/DL)e.g if downlink quality & slowmoving mobile criteria weresatisfied simultaneously HO with cause downlinkquality performed
  • 7. • Threshold comparison;• Quality• Level• Distance• Load• Periodic checks;• Power budget• UmbrellaIFAV_RXQUAL_DL_HO < hoThresholdsQualDLTHEN Downlink Quality HO is performedThe Handover process may be triggered by:IFEnablePowerBudgetHO = YesTHENPBGT comparison performedeveryhoPeriodPBGT secAveraged value obtained from measurementaveraging process usinghoAveragingQualDLTarget Cell Evaluation ProcessThreshold levelbased on nx &px
  • 8. AV_RXLEV_NCELL(n) > rxLevMinCell(n) + Max (0, A)A = msTxPwrMax(n) - PP = depending on MS Classmark1.In all Handover casesAV_RXLEV_NCELL(n) > hoLevelUmbrella(n)1’.Except for Umbrella HandoverPBGT > hoMarginLev/Qual(n) wherePBGT = (AV_RXLEV_NCELL(n) - AV_RXLEV_DL_HO)-(btsTxPwrMax - BTS_TXPWR)(Note: enableHoMarginLevQual must = Yes) - for RxLev & RxQual handovers2’.PBGT > hoMarginPBGT(n) wherePBGT = ((msTxPwrMax - msTxPwrMax(n))-(AV_RXLEV_DL_HO -AV_RXLEV_NCELL(n))- (btsTxPwrMax - BTS_TXPWR))2.The additional conditionFor imperative handoversonly Eq. 1 has to be satisfied
  • 9. Best candidates to RR Management:• intra BSC HO max 16 cells under the same BSC as the sourcecell• inter BSC HO numberOfPreferredCellsLoad check of Candidates by btsLoadThreshold (0..100%)If overloaded priority decreased by hoLoadFactor (0...7)1.Comparison of priorities of Candidates (hoLevelPriority (0..7))2.If two or more Adjacent cells with equal priorities-> Ranking based on radio properties (RxLev)3.Only for Adjacent Cellsof the same BSC(intra-BSC) analysis
  • 10. Case 1: All cells have equal priorityCell a b cRx_Level -75 -80 -831. Load overl. overl. n.overl.hoLoadFactor 1 1 12. Priority 3 3 3New Priority 2 2 33. Rx_Level -75 -80 -83=> cell list c , a ,bCase 2 : One cell with higher prioritycell a b cRx_Level -75 -80 -831. Load n./overl. n.overl. n.overl.hoLoadFactor 2 1 12. Priority 4 3 3New Priority 4/2 3 33. Rx_Level -75 -80/-80 -83=> cell list a,b,c (if cell a is not overload)=> cell list b,c,a
  • 11.  Trigger◦ Periodic Check ( hoPeriodPBGT ) Candidate Selection◦ Equation 1 & 2 used◦ Priority and Load Considered When used in association with Umbrella HO (& AdjCellLayer)PBGT handovers are only between cells of the SAME layerhoPeriodPBGT 1 ... 63 (SACCH)enablePwrBudgetHandover Y / NParameter RangerxLevMinCell(n) -110 … -47 dBmmsTxPwrMax(n) 0 … 36 dBmhoMarginPBGT(n) -24 … 63 dB
  • 12. PBGT = ((msTxPwrMax- msTxPwrMax(n)) - (AV_RXLEV_DL_HO-AV_RXLEV_NCELL(n))- (btsTxPwrMax - BTS_TXPWR)PBGT = ((33dBm-33dBm)-(-90 - -80)-(42dBm-42dBm)= 10 dB10 dB > 6 dB OK !!!!AV_RXLEV_NCELL(n) > rxLevMinCell(n) + Max (0, msTxPwrMax(n) - msTxPwrMax)-80 dBm > -99 dBm + (33 dBm - 33 dBm) = -99 dBm1.2.Equations 1 and 2 are usedAV_RXLEV_DL_HO = -90 dBmmsTxPwrMax = 33 dBm (= 2W)btsTxPwrMax = 42 dBm (= 16 W)BTS_TX_PWR = 42 dBm = (16 W)hoMarginPBGT(n) = 6 dBServing Cell: Best Adjacent Cell:AV_RXLEV_NCELL(n) = -80 dBmrxLevMinCell(n) = -99 dBmmsTxPwrMax(n) = 33 dBm (= 2W)btsTxPwrMax = 42 dBm (= 16 W)
  • 13.  Trigger◦ Threshold Comparison (hoThresholdsLevUL/DL with px / nx ) Candidate Selection◦ Equation 1 used◦ Equation 2 used if enableHoMarginLevQual = N◦ Equation 2 used if enableHoMarginLevQual = Y◦ Priority and Load ConsideredhoThresholdLevUL/DL -110 … -47 dBmpx 1 … 32nx 1 … 32Parameter ValuerxLevMinCell(n) -110 … -47 dBmmsTxPwrMax(n) 0 … 36 dBmhoMarginLev(n) -24 … 24 dB
  • 14. Equations 1 and 2’ are used if parameter enableHoMarginLevQual is set “Yes”hoMarginLev = 4dBCell B Cell B is not selected as candidate forHO due to level since 2dB < 4 dB(RxLev) Thresholddefined by;hoThresholdLevUL/DL= -92 / -95 dBm2 dBTrigger for Handover due to LevelCell A
  • 15.  Trigger◦ Threshold Comparison (hoThresholdsQualUL/DL with px / nx) Candidate Selection◦ Equation 1 used◦ Equation 2 used if enableHoMarginLevQual = N◦ Equation 2 used if enableHoMarginLevQual = Y◦ Priority and Load ConsideredhoThresholdQualUL/DL 0 … 7px 1 … 32nx 1 … 32Parameter ValuerxLevMinCell(n) -110 … -47 dBmmsTxPwrMax(n) 0 … 36 dBmhoMarginQual(n) -24 … 24 dB
  • 16. Equations 1 and 2’ are used if parameter enableHoMarginLevQual is set “Yes”2 dBhoMarginQual = 0 dBTrigger for Handover HO due to QualityAB Cell B is selected as potential candidate forHO due to Quality since 2 dB > 0 dB
  • 17.  Trigger:◦ Threshold Comparison for Quality (hoThresholdsQualUL/DL with px / nx)◦ Threshold Comparison for Level (hoThresholdsInterferenceUL/DL with px / nx) Candidate Selection◦ Priority for InterCell / Intracell HO selected at BSC independently for UL / DL◦ Priority InterCell HO◦ Quality HO if any candidate◦ If not IntraCell HO◦ Priority IntraCell HOhoThresholdInterferenceUL/DL -110 … -47 dBmpx 1 … 32nx 1 … 32enableIntraHoInterfUL/DL Y / NParameter ValuehoPreferenceOrderInterfUL/DL INTER / INTRA
  • 18. Equations 1 and 2’ are used if parameter enableHandoverMarginQual is set “Yes”hoThresholdQual = 5hoThresholdInterferenceDL = -85 dBmhoPreferenceOrderInterfDL = intra• Field strength higher than threshold(AV_RXLEV_DL_HO >hoThresholdsInterferenceDL• Bad quality(AV_RXQUAL_DL hoThresholdsQualDL Handover due to DL interference intra cell handover !!Trigger for Handover due to InterferenceCell ACell BThreshold (Interference Lev)-85 dBm50RXLEVRXQUAL
  • 19.  Used in multi-layer/band networks (better for bands - no speed criterion) Typically used in association with PBGT (Combined PBGT/Umbrella feature) Trigger◦ Periodic Check (hoPeriodUmbrella) Candidate Selection◦ Equation 1 used◦ Consistency between MS classmark and target cell power constraints◦ Priority and Load ConsideredenableUmbrellaHandover Y / NhoPeriodUmbrella 0 … 63(SACCH)hoLevelUmbrella -110 … -47 dBmParameter ValuegsmMicrocellThreshold 0 … 36 dBmgsmMacrocellThreshold 0 … 36 dBm
  • 20. Max power capability of MS >= gsmMacrocellThresholdHO allowed only to a macrocell ( MS_TXPWR_MAX(n) >= gsmMacrocellThreshold )gsmMicrocellThreshold < Max power capability of MS < gsmMacrocellThresholdHO only to middle size cell ( gsmMicrocellThreshold < MS_TXPWR_MAX(n) < gsmMacrocellThreshold )Max power capability of MS <= gsm MicrocellThresholdHO allowed only to microcell ( MS_TXPWR_MAX(n) <= gsmMicrocellThreshold )
  • 21. UmbrellaHandoverAB-90 dBmHandover dueto Level-85 dBm1800 Macro1800 MicroUmbrella Handoverdown to micro layerhoLevelUmbrella = -85dBmRRHandoverout ofmicrosPBGT Handoverbetween SAMElayer cellsExample - Priority  microcellshoLevelUmbrella macro  macro = -47 dBm(prevents Umbrella HOs between adjacent macrocells)hoLevelUmbrella macro  micro = -85 dBmhoThresholdLevDL = -90 dBmGSM MS class 4 (33 dBm)gsmMacrocellThreshold = 35 dBmgsmMicrocellThreshold = 33 dBmmsTxPwrMax(n) = 33 dBm
  • 22. macrocellsmicrocellsUMB,RRPBGT,RRPBGT,RRUMB,RRUMB umbrella HORR radio reason HOPBGT power budget HO When enablePowerBudgetHo = Yes & enableUmbrellaHo = Yes◦ Power Budget Handover to cells of the same layer◦ Umbrella Handover to cells of different layer Based on◦ gsmMacrocellThreshold, gsmMicrocellThreshold◦ msTxPwrMax, msTxPwrMax(n)◦ MS classmark
  • 23. UPPER layer (e.g. 900macro)SAME layer (servinglayer)LOWER layer(micro) Three layers visible to serving cell (relativeto serving cell) Used in target cell evaluation for;◦ Fast moving MS handling in macro cell◦ HOs based on MS speed (BSS6)◦ Combined umbrella and power budgetN (not in use)ParameterAdjCellLayer
  • 24. Mobile distribution in multi-layer networks based on speed of mobile• Slow moving MS  lower layer (micro) cells• Fast moving MS  upper layer (macro) cellsTwo proprietary Nokia features;• Fast Moving Mobile Support (FMMS)• Estimation of MS speed based on duration of stay in target cell• used to move MSs from UPPER (macro) to LOWER (micro) cells• MS_SPEED_DETECTION• Measurement of MS speed based on zero crossing detection process• Used to move slow MS from macro  micro & fast MS from micro  macro
  • 25. Macro cell’s parametersfor each adjacent micro cell:• fastMovingThreshold 0 .. 255• RxLevMinCell• hoLevelUmbrellaCounter for each adjacent micro cell+2 measurement and over rxLevMinCell-1 no meas. or bad levelTarget cell selection based on adjacentcell RX_LEVEL and on hoLevelUmbrella FMMS used in macrocell layer to estimate the speed of a mobile based on measurementreports on adjacent microcellsmacrocellsmicrocellsFMMS HOinitiatedtime ‘t’FMT CounterHOtime ‘t’hoLevelUmbrella = -85 dBmFMT Threshold = 40RxLevMinCell = -85 dBm
  • 26. BTSBTSAdjacent cellmeasurementsBSCBTS sends MS speedmeasurements to BSCevery SACCH period(~480ms)2BTS measures MS speed basedon zero cross rate algorithm providingcall is on non-hoping TCHMS_SPEED_DETECTION not suitablefor use with frequency hopping networks1BSC averages speedindications usingmsSpeedAveraging AV_MS_SPEEDBSC ignores indications if;• UL DTx used during SACCH• MS changing power during SACCH34AV_MS_SPEED is compared withthresholds;• LowerSpeedLimit (slow MS)• UpperSpeedLimit (fast MS)to direct MS to appropriate layer(cell priorities used)Candidate Selection Fast-moving to upper /Slow-moving to lowerlayer adjacent cells Equation 1 used Priority considered
  • 27. msSpeedAveraging (MSA) 1 ... 32 (SACCH frames)adjCellLayer (ACL) N / Same / Upper / LowerhoLevelUmbrella (AUCL) -110 ... -47 dBmlowerSpeedLimit (LSL) 0 … 255 (1 step 2km/h) upperSpeedLimit (USL) 0 … 255 (1 step 2km/h)msSpeedThresholdNx 1 … 32msSpeedThresholdPx 1 … 32Parameter ValueadjCellLayer (ACL) N / Same / Upper / LowerhoLevelUmbrella (AUCL) -110 ... -47 dBmFastMovingThreshold (FMT) 0 … 255 (SACCH frames) FMMSMS SpeedDetection0 means "Not Used"
  • 28.  Handover considered to be imperative:◦ Handover due to Distance◦ Order to empty a cell ( from O&M )◦ Directed Retry and IDR◦ Rapid Field Drop (RFD)◦ Enhanced Rapid Field Drop (ERFD)
  • 29. Distance Process ---> msDistanceBehaviour (0,1..60,255) in BSC• 0 : Release immediately• 1 - 60 : Release after certain time 1 - 60 s, try handoverduring that time• 255 : No release, only imperative Handover attemptDistance ProcessenableMsDistanceProcess Y / NmsDistanceHoThresholdParam 0 … 63px 1 … 32nx 1 … 32Parameter ValuemsDistanceBehaviour 0, 1 … 60, 255
  • 30. ChainedCellServingCell Trigger◦ Threshold Comparison ( HoThresholdRapidLevUl(px) Rx_Lev_UL (Not averaged / Only UL) Candidate Selection◦ Only Chained adjacent cell◦ Equation 1 only / no priority Multi-Layered NetworkhoThresholdLevULforRapidFieldDrop -110 ... -47 dBmhoThresholdRapidLevUIN 0 ... 32chainedAdjacentCell Y / NParameter Value
  • 31. MS ChainedCellServingCellRapid Field Drop Handover..1st2nd-93 dBmServingCellhoThresholdRapidLevUl = - 93 dBmhoThresholdRapidLevUIN (px) = 2chainedAdjacentCell = YesExample
  • 32. • In case of DDE (Deep Dropping Edge), the averagingwindow sizes and power budget period are reduced• level downlink window size• level uplink window size• adjacent cell averaging window size• handover period power budgetParameter ValueerfdEnabled DIS, UL, DL or UDLddeThresholdLev 0 … 63 dBNx 1 … 32Px 1 … 32ddeWindow 1 … 32 SACCHmodifiedAveWinNcell 1 … 32modifiedNOZ 1 … 32erfdOver 1 … 64 sec
  • 33. A MS moves away from cell site,the signal is dropping graduallyA MS turns a corner,the signal drops rapidlySignalLevelTimeFigure 7 Signal Strength of a Fast Moving MSMS moves away from cell site,the signal is dropping graduallyMS turns a corner, thesignal drops faster thanmoving in straight lineSignalLevelTimeFigure 8 Signal Strength of a Slow Moving MS
  • 34. HandoverA handover due to Enhanced Rapid Field Drop is defined by the followingparameters;• ErfdEnabled - Enables ERFD Handovers• DdeThresholdLev - Defines the drop insignal level that must be observed beforeERFD detection. Uses voting nx : px• DdeWindow - Sets the window size overwhich ERFD is to be monitored• ModifiedAveWinNcell - Defines the modifiedaveraging window size to be used forNcells during period ErfdOver• ModifiedNOZ - Modified # of zero resultsused during period ErfdOver• ErfdOver - Time period over which parameters,ModifiedAveWinNcell and ModifiedNOZ are used to monitor NcellsServing cellNcell #125dB > 20dBDdeThresholdhoThresholdLevXLErfdOverERFD HO initiatedto Ncell #1XL = DL or ULDdeWindow =2 n(1):p(1)ERFD Detection-83 -87-63-61-60-60 -89 -91 -94 -89 -89averagingWindowSizeAdjCell = 4modifiedAveWinNcell = 2ERFD HO
  • 35. ddeWindow = 3 SACCH (n = 3)ddeThresholdLev = 10, px = 2 and nx =3 the BSC compares the most recent measurement sample 8(multiframe k) with the measurement sample 5 (multiframe k-n). DDE_LEVEL = RXLEV(k- ddeWindow) – RXLEV(k) = -69 dBm – (-83dBm) = 14 dBSample 1 2 3 4 5 6 7 8Signallevel-71dBm-68dBm-70dBm-71dBm-69dBm-70dBm-75dBm-83dBm
  • 36.  Minimum time between consecutive handovers related to the sameconnections◦ MinIntBetweenHoReq Minimum time between handover attempts after a failure◦ MinIntBetweenUnsuccHoAttempt◦ Applied differently in Intercell / Intracell handovers Additional Guard Periods are used for Back-handovers◦ Quality◦ Distance◦ Traffic reason◦ InterferenceminIntBetweenUnsuccHoAttempt 0 ... 30 secminIntBetweenHoReq 0 ... 30 secParameter Value
  • 37.  Reversion to old channel( 1 + NUMBER_OF_HO_FAIL ) *MinIntBetweenUnsuccHoAttempt applied to handoverattempts to the same target cell No Radio Resource AvailableMinIntBetweenUnsuccHoAttempt applied to handoverattempts to the same target cells ( all those in the list ) Other Failure CasesMinIntBetweenUnsuccHoAttempt applied to all types ofhandover attemptsHandover Timers (2/3)After a HO Failure
  • 38.  After a HO due to quality (UL/DL) and interference (UL/DL):◦ a Power Budget HO back is not allowed duringGUARD_TIME = 2 * HoPeriodPBGT◦ an Umbrella HO back is not allowed duringGUARD_TIME = 2 * HoPeriodUmbrella After an inter-cell HO due to MS-BS distance:◦ a HO back to the source cell is not allowed duringGUARD_TIME = 20sec + MinIntBetweenHOReq After a Traffic Reason HO:◦ Power Budget HO and Umbrella HO back to the source are not allowed duringGUARD_TIME = 20sec + MinIntBetweenHOReq Repetitive Intra Cell HO not allower duringGUARD_TIME = 4 * MinIntBetweenUnsuccHoAttempt