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HANDOVER PROCESSHANDOVER PROCESS
Nokia Networks Thailand
Radio Network Planning
Prepared By
Aumpika Viaun
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HANDOVER PROCESSHANDOVER PROCESSContentsContents
1. Overview
2. Handover Decision
3. Target Cell Evaluation
4. Handover Algorithms
5. Level & Quality & Interference
Handover
6. Power Budget Handover
7. Umbrella Handover
•Combined Umbrella & Power Budget
•MS Speed
8. Imperative Handover
9. Timers for Handovers
10. Direct Access to Desired Layer/Band
11. Related Parameters
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HANDOVER PROCESSHANDOVER PROCESSCausesCauses
Timing Advance
Adjacent Cells
Downlink Quality
Uplink Quality AV_RXQUAL_UL_HO
AV_RXQUAL_DL_HO
Downlink Level
Uplink Level AV_RXLEV_UL_HO
AV_RXLEV_DL_HO
AV_RANGE_HO
AV_RXLEV_NCELL(n)
QUALITY
&INTERFERENCE
LEVEL
DISTANCE
PERIODICCHECKS
UMBRELLA
POWER BUDGET
IMPERATIVEHOCHANNEL ADMINISTRATION
DIRECTED RETRY
THRESHOLDCOMPARISON
RAPID FIELD DROP
Others:
Intelligent Underlay Overlay
Traffic Reason
……….
MS SPEED
MS Speed AV_MS_SPEED
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HANDOVER PROCESSHANDOVER PROCESSIntraIntra--BSC HOBSC HO
CH Actvn
CH Actvn Ack
MS BTS (NEW)BTS BSC MSC
HANDO CMDHANDO CMD
HANDO ACC
HANDO Detec
Phys Info
HANDO COM
HANDO COMCH RELEASE
CH RELEASE ACK
HO PERFORMED
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HANDOVER PROCESSHANDOVER PROCESSInter Inter --BSC HOBSC HO
MS BSC (NEW)BSC(OLD) MSC
HANDO REQD ACK
HANDO CMD
HANDO ACC
HANDO COM
HANDO COM
HANDO REQD
HANDO REQD
HANDO CMD
HANDO DET
CLEAR CMD
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HANDOVER PROCESSHANDOVER PROCESSHandover PriorityHandover Priority
• Handover priority
1. Uplink and downlink Interference
2. Uplink quality
3. Downlink quality
4. Uplink level5. Downlink level
6. Distance
7. Rapid Field Drop
8. Slow moving MS
9. Better cell i.e. Periodic check (Power Budget HO or Umbrella HO)
10. PC: Lower quality/level thresholds (UL/DL)
11. PC: Upper quality/level thresholds (UL/DL)
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HANDOVER PROCESSHANDOVER PROCESSHandover AlgorithmsHandover Algorithms
AV_RXLEV_NCELL(n) > hoLevelUmbrella(n)
PBGT > hoMarginPBGT(n) where
PBGT = ((msTxPwrMax - msTxPwrMaxCell(n))-(AV_RXLEV_DL_HO - AV_RXLEV_NCE
- (btsTxPwrMax - BTS_TXPWR))
AV_RXLEV_NCELL(n) > rxLevMinCell(n) + Max (0, A)
A = msTxPwrMax(n) - P P = depending on MS Classmark
PBGT > hoMarginLev/Qual(n) where
PBGT = (AV_RXLEV_NCELL(n) - AV_RXLEV_DL_HO)-(btsTxPwrMax - BTS_TXPWR)
1.
2.
1’.
In all Handover cases (in imperative HO only requirement)
Except for Umbrella Handover
2’.
The additional condition
If enableHoMarginLevQual = Y
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HANDOVER PROCESSHANDOVER PROCESSTarget Cell Selection (1)Target Cell Selection (1)
The evaluation on the preferred list of the target cells is based on:
4. The load of the neighbouring cells which belong to the sam
1. The radio link measurements
2. Threshold comparison3. The priority levels of the neighbouring cells
as the serving cell.
5. Rx level comparison – if it is needed
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HANDOVER PROCESSHANDOVER PROCESSTarget Cell Selection (2)Target Cell Selection (2)
If two or more Adjacent cells with equal priorities
-> Ranking based on radio properties
Load check of Candidates by btsLoadThreshold (0..100%)
If overloaded priority decreased by hoLoadFactor (0...7)
Best candidates to RR Management:intra BSC HO max 16 cells under the same BSC as the source cell
inter BSC HO numberOfPreferredCells
Comparison of priorities of Candidates (hoLevelPriority
(0..7))
1.
2.
3.
Only for AdjacentCell of thesame BSC
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HANDOVER PROCESSHANDOVER PROCESSTarget Cell Selection (3)Target Cell Selection (3)
All cells have equal priority
cell a b c
Rx_Level -75 -80 -83
1. Load overl. overl. n.overl.hoLoadFactor 1 1 1
2. Priority 3 3 3
New Priority 2 2 3
3. Rx_Level -75 -80
=> cell list c , a ,b
One cell has higher priority because of some r
cell a b c
Rx_Level -75 -80 -83
1. Load n./overl. n.overl. n.overl.hoLoadFactor 2 1 1
2. Priority 4 3 3
New Priority 4/2 3 3
3. Rx_Level -75 -80/-80 -83
=> cell list a,b,c (if cell a is not overload)
=> cell list b,c,a
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HANDOVER PROCESSHANDOVER PROCESSHandover due to Level (1/2)Handover due to Level (1/2)
• Trigger
• Threshold Comparison ( hoThresholdsLevUL/DL (px - nx) )
• Candidate Selection
• Equation 1 used
• Equation 2 used if enableHoMarginLevQual = N
• Equation 2' with hoMarginLev used if enableHoMarginLevQual = Y• Priority and Load Considered
hoThresholdLevUL/DL -110 … -47
px 1 … 32
nx 1 … 32
Parameter Value
rxLevMinCell(n) -110 … -47 dBmmsTxPwrMax(n) 5 … 43 dBmhoMarginLev(n) -24 … 24 dB
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HANDOVER PROCESSHANDOVER PROCESSHandover due to Level (2/2)Handover due to Level (2/2)
Equations 1 and 2’ are used if parameter enableHoMarginLevQual is set “Yes”
2 dB
hoMarginLev = 4 dB
Trigger for Handover due to Level
A
B
=> Cell B is not selected as candidate for
HO due to level since 2dB < 4 dB
hoThresholdsLevUL/DL
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HANDOVER PROCESSHANDOVER PROCESSHandover due to Quality (1/2)Handover due to Quality (1/2)
• Trigger
• Threshold Comparison ( hoThresholdsQualUL/DL (px - nx) )
• Candidate Selection
• Equation 1 used
• Equation 2 used if enableHoMarginLevQual = N
• Equation 2' with hoMarginQual used if enableHoMarginLevQual = Y• Priority and Load Considered
hoThresholdQualUL/DL 0 … 7
px 1 … 32
nx 1 … 32
Parameter Value
rxLevMinCell(n) -110 … -47 dBmmsTxPwrMax(n) 5 … 43 dBmhoMarginQual(n) -24 … 24 dB
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HANDOVER PROCESSHANDOVER PROCESSHandover due to Quality (2/2)Handover due to Quality (2/2)
Equations 1 and 2’ are used if parameter enableHoMarginLevQual is set “Yes”
2 dB
hoMarginQual = 0 dB
Trigger for Handover HO due to Quality
A
B
=> Cell B is selected as potential candidate for HO due to Quality since 2 dB > 0 dB
hoThresholdsQualUL/DL
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HANDOVER PROCESSHANDOVER PROCESSHandover due to Interference (1/2)Handover due to Interference (1/2)
• Trigger : Threshold Comparison
• Threshold Comparison for Quality ( hoThresholdsQualUL/DL (px - nx) )
• Threshold Comparison for Level ( hoThresholdsInterferenceUL/DL (px - nx) )
• Candidate Selection
• Priority InterCell / Intracell selected at BSC independently UL / DL
• Priority Inter
Quality HO if Any Target
Otherwise Intra Cell HO
enableIntraHoInterfUL/DL Y / N
hoThresholdInterferenceUL/DL -110 … -47
px 1 … 32
nx 1 … 32
Parameter Value
hoPreferenceOrderInterfUL/DL INTER / INTRA
BSC
• Priority Intra
Intra Cell HO
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HANDOVER PROCESSHANDOVER PROCESSHandover due to Interference (2/2)Handover due to Interference (2/2)
Equations 1 and 2’ are used if parameter enableHandoverMarginQual is set “Yes”
hoThresholdQual = 4
hoThresholdInterferenceDL = -85 dBm
hoPreferenceOrderInterfDL = intra Trigger for Handover due to Interference
A
B
- Field strength higher than threshold
- Bad quality
=> interference=> intra cell handover !!
Threshold (Interference Lev)
-85 dBm
5
0
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PBGT = ((msTxPwrMax- msTxPwrMax(n)) - (AV_RXLEV_DL_HO-AV_RXLEV_NCELL(n))- (btsTxPwrMax - BTS_TXPWR)
PBGT = ((33dBm-33dBm)-(-90 - -80)-(42dBm-42dBm)
= 10 dB
10 dB > 6 dB OK !!!!
AV_RXLEV_NCELL(n) > rxLevMinCell(n) + Max (0, msTxPwrMax(n) - msTxPwrMax)
-80 dBm > -99 dBm + (33 dBm - 33 dBm) = -99 dBm
1.
2.
Equations 1 and 2 are used
AV_RXLEV_DL_HO = -90 dBm
msTxPwrMax = 33 dBm (= 2W)
btsTxPwrMax = 42 dBm (= 16 W)
BTS_TX_PWR = 42 dBm = (16 W)hoMarginPBGT(n) = 6 dB
Serving Cell: Best Adjacent Cell:
AV_RXLEV_NCELL(n) = -80 dBm
rxLevMinCell(n) = -99 dBm
msTxPwrMax(n) = 33 dBm (= 2W)
btsTxPwrMax = 42 dBm (= 16 W)
HANDOVER PROCESSHANDOVER PROCESSPower Budget Handover (1)Power Budget Handover (1)
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HANDOVER PROCESSHANDOVER PROCESSPower Budget Handover (2)Power Budget Handover (2)
• Trigger
• Periodic Check ( hoPeriodPBGT )
• Candidate Selection
• Equation 1 & 2 used
• Priority and Load Considered
•Typically used between cells of the same "Layer"
hoPeriodPBGT 1 ... 63 (SACCH Period)
enablePwrBudgetHandover Y / N
Parameter Value
rxLevMinCell(n) -110 … -47 dBmmsTxPwrMax(n) 5 … 43 dBmhoMarginPBGT(n) -24 … 24 dB
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HANDOVER PROCESSHANDOVER PROCESSPower Budget Handover (3)Power Budget Handover (3)
time
cell 1
cell 2
RX_lev
HoMarginPBGT
“ “ Power Budg et HO” Power Budg et HO”
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6 dB
Umbrella
Handover
A
B-90 dBm
Handover due
to Level
Macro cell
Micro cellExample
GSM MS class 4 (33 dBm)
gsmMacrocellThreshold = 35 dBm
gsmMicrocellThreshold = 33 dBmmsTxPwrMax(n) = 33 dBm
hoLevUmbrella = -85 dBm
hoThresholdLevDL = -90 dBm
-85 dBm
Umbrella
Handover
Handover due
to Level
HANDOVER PROCESSHANDOVER PROCESSUmbrella Handover (1)Umbrella Handover (1)
• Trigger
• Periodic Check ( hoPeriodUmbrella )
• Candidate Selection
• Equation 1' used
• Consistency between mobile classmark and target cell power constraints
• Priority and Load Considered
• Multi-Layered Network
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HANDOVER PROCESSHANDOVER PROCESSUmbrella Handover (2)Umbrella Handover (2)
Max power capability of MS >= gsmMacrocellThreshold
HO allowed only to a macrocell ( MS_TXPWR_MAX(n) >= gsmMacrocellThreshold )
gsmMicrocellThreshold < Max power capability of MS < gsmMacrocellThreshold
HO only to middle size cell ( gsmMicrocellThreshold < MS_TXPWR_MAX(n) <gsmMacrocellThreshold )
Max power capability of MS <=
HO allowed only to microcell ( MS_TXPWR_MAX(n) <= gsmMicrocellThreshold )
enableUmbrellaHandover Y / NhoPeriodUmbrella 0 … 63 (SACCH)
hoLevelUmbrella -110 … -47
Parameter Value
gsmMicrocellThreshold 5 … 43
gsmMacrocellThreshold 5 … 43 BSC
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HANDOVER PROCESSHANDOVER PROCESSUmbrella Handover (3)Umbrella Handover (3)
Cell 1 (GSM 900)
Cell 2 (DCS 1800)
RX_lev (dBm)
time
“ “ Umb rel la HO” Umb rel la HO”
HoLevelUmbrella
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macrocells
microcells
UMB,RR
PBGT,RR
PBGT,RR
UMB,RR
UMB umbrella HORR radio reason HO
PBGT power budget HO
HANDOVER PROCESSHANDOVER PROCESSCombined Umbrella & Power BudgetCombined Umbrella & Power Budget
• 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, msTxPwrMaxCell(n)
• MS classmark
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HANDOVER PROCESSHANDOVER PROCESSMS SpeedMS Speed
• Multi-Layer Network
• Slow Moving MS in Microcells
• Problem :
• Determine the MS speed
•Direct MS to correct Layer
• Fast Moving MS in Macrocells
• Methods (Nokia specific)
• Fast moving MS handling (S5)
•MS speed detection (S6)
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HANDOVER PROCESSHANDOVER PROCESSImperative Handover Imperative Handover
• Handover considered to be imperative:
• Handover due to Distance
• Order to empty a cell ( from O&M )
• Directed Retry and IDR
• Rapid Field Drop
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HANDOVER PROCESSHANDOVER PROCESS
Imperative Handover: DistanceImperative Handover: Distance
Distance Process ---> msDistanceBehaviour (0,1..60,255) in BSC
• 0 : Release immediately
• 1 - 60 : Release after certain time 1 - 60 s, try handover during th
• 255 : No release, only imperative Handover attempt
Distance Process
enableMsDistanceProcess Y / N
msDistanceHoThresholdParam 0 … 63px 1 … 32
nx 1 … 32
Parameter Value
msDistanceBehaviour 0, 1 … 60, 255 BSC
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MS
hoThresholdLevULforRapidFieldDrop -110 ... -47 dBm
hoThresholdRapidLevU1N 0 ... 32
chainedAdjacentCell Y / N
Chained
CellServing
Cell
HANDOVER PROCESSHANDOVER PROCESSImperative Handover :Rapid Field Drop (1/2)Imperative Handover :Rapid Field Drop (1/2)
• 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 Network
Parameter Value
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MS
Rapid Field Drop Handover ..1st
2nd
hoThresholdRapidLevUl = - 93 dBm
hoThresholdRapidLevUlN (px) = 2
chainedAdjacentCell = Yes
ChainedCellServingCell
-93 dBm
Serving
Cell
HANDOVER PROCESSHANDOVER PROCESSImperative Handover :Rapid Field Drop (2/2)Imperative Handover :Rapid Field Drop (2/2)
Example
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HANDOVER PROCESSHANDOVER PROCESSTimersTimers
• Minimum time between consecutive handovers related to the same connections
• 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
• Interference
minIntBetweenUnsuccHoAttempt 0 ... 30 (seconds)
minIntBetweenHoReq 0 ... 30 (seconds)
Parameter Value
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Direct Access to Desired Layer/Band (1/2)Direct Access to Desired Layer/Band (1/2)
• DADL/B is DR like procedure, triggered due to exceded TCH load in accessed cell
• Target cells are selected according to MS properties, radio environment and adjacent cellindications and priorities
• Allows also the support for Phase 1 MSs
• BENEFIT: By directing the calls to proper layer / band as early as possible the network canabsorb more traffic and thus provide more capacity
E-GSM 900 cell
GSM 1800 cell
P-GSM 900
micro cell
accessed P-GSM
900 macro cell
2nd
1st3rd
TCH
TCH
TCH
SDCCH
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• DADL/B is applied in call setup phase if
• DADL/B feature is enabled with BSC level optionality management parameter • TCH load of accessed cell exceeds the BTSLoadThreshold
• There are adjacent cells defined with the d adlbTargetCel l parameter (cells verifiedaccording to MS capabilities), which are to be used as target cells for DADL/B handover.
• The signal level of the DADL/B target cell exceeds the HOLevelUmbrella(n)
• BSC will evaluate the target cells for DADL/B handover during the time indicated with theMinTimeLimitDR parameter
• Adjacent cell priorities HOPriori tyL evel(n) and load factors HOLoadFactor(n) are used intarget cell sorting for DADL/B handover
• DR will be applied if there is real TCH congestion in accessed cell
• If the DADL/B handover fails (no TCHs available in target cells, no DADL/B target cells, MSreturns to old channel) the TCH is tried to allocate attempted from the accessed cell
• Pre-emption has higher priority than DADL/B handover
DADL/B functionality (2/2)DADL/B functionality (2/2)
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DEFAULTDEFAULT PARAMETERsPARAMETERs SETTING FOR AIS’s PROJECTSETTING FOR AIS’s PROJECT
&&
RELATED ISSUED DISCUSSIONRELATED ISSUED DISCUSSION
(REFERENCE DOCUMENTS)(REFERENCE DOCUMENTS)
HANDOVER PROCESSHANDOVER PROCESSRELATED PARAMETERSRELATED PARAMETERS