. 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)

1. 1www.TempusTelcosys.com
Telecom Tutorials

2. BSS Parameters S9

3. 1. 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

4. Why are handovers needed?
 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

5. 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
PERIODIC
CHECKS
UMBRELLA
POWER BUDGET
IMPERATIVE
HOCHANNEL ADMINISTRATION
DIRECTED RETRY
THRESHOLD
COMPARISON
RAPID FIELD DROP
MS SPEED
MS Speed AV_MS_SPEED
Others 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 list
is used in determining which process is performed;
1. 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)
e.g if downlink quality & slow
moving mobile criteria were
satisfied simultaneously
 HO with cause downlink
quality performed

7. • Threshold comparison;
• Quality
• Level
• Distance
• Load
• Periodic checks;
• Power budget
• Umbrella
IF
AV_RXQUAL_DL_HO < hoThresholdsQualDL
THEN
 Downlink Quality HO is performed
The Handover process may be triggered by:
IF
EnablePowerBudgetHO = Yes
THEN
PBGT comparison performed
every
hoPeriodPBGT sec
Averaged value obtained from measurement
averaging process using
hoAveragingQualDL
Target Cell Evaluation Process
Threshold level
based on nx &
px

8. AV_RXLEV_NCELL(n) > rxLevMinCell(n) + Max (0, A)
A = msTxPwrMax(n) - P
P = depending on MS Classmark
1.
In all Handover cases
AV_RXLEV_NCELL(n) > hoLevelUmbrella(n)1’.
Except for Umbrella Handover
PBGT > hoMarginLev/Qual(n) where
PBGT = (AV_RXLEV_NCELL(n) - AV_RXLEV_DL_HO)-(btsTxPwrMax - BTS_TXPWR)
(Note: enableHoMarginLevQual must = Yes) - for RxLev & RxQual handovers
2’.
PBGT > hoMarginPBGT(n) where
PBGT = ((msTxPwrMax - msTxPwrMax(n))-(AV_RXLEV_DL_HO -
AV_RXLEV_NCELL(n))
- (btsTxPwrMax - BTS_TXPWR))
2.
The additional condition
For imperative handovers
only Eq. 1 has to be satisfied

9. Best candidates to RR Management:
• intra BSC HO max 16 cells under the same BSC as the source
cell
• inter BSC HO numberOfPreferredCells
Load 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 Cells
of the same BSC
(intra-BSC) analysis

10. Case 1: 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 -83
=> cell list c , a ,b
Case 2 : One cell with higher priority
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

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 layer
hoPeriodPBGT 1 ... 63 (SACCH)
enablePwrBudgetHandover Y / N
Parameter Range
rxLevMinCell(n) -110 … -47 dBm
msTxPwrMax(n) 0 … 36 dBm
hoMarginPBGT(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 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)

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 Considered
hoThresholdLevUL/DL -110 … -47 dBm
px 1 … 32
nx 1 … 32
Parameter Value
rxLevMinCell(n) -110 … -47 dBm
msTxPwrMax(n) 0 … 36 dBm
hoMarginLev(n) -24 … 24 dB

14. Equations 1 and 2’ are used if parameter enableHoMarginLevQual is set “Yes”
hoMarginLev = 4dB
Cell B
 Cell B is not selected as candidate for
HO due to level since 2dB < 4 dB
(RxLev) Threshold
defined by;
hoThresholdLevUL/D
L
= -92 / -95 dBm
2 dB
Trigger for Handover due to Level
Cell 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 Considered
hoThresholdQualUL/DL 0 … 7
px 1 … 32
nx 1 … 32
Parameter Value
rxLevMinCell(n) -110 … -47 dBm
msTxPwrMax(n) 0 … 36 dBm
hoMarginQual(n) -24 … 24 dB

16. 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

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 HO
hoThresholdInterferenceUL/DL -110 … -47 dBm
px 1 … 32
nx 1 … 32
enableIntraHoInterfUL/DL Y / N
Parameter Value
hoPreferenceOrderInterfUL/DL INTER / INTRA

18. Equations 1 and 2’ are used if parameter enableHandoverMarginQual is set “Yes”
hoThresholdQual = 5
hoThresholdInterferenceDL = -85 dBm
hoPreferenceOrderInterfDL = 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 Interference
Cell A
Cell B
Threshold (Interference Lev)
-85 dBm
5
0
RXLEV
RXQUAL

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 Considered
enableUmbrellaHandover Y / N
hoPeriodUmbrella 0 … 63
(SACCH)
hoLevelUmbrella -110 … -47 dBm
Parameter Value
gsmMicrocellThreshold 0 … 36 dBm
gsmMacrocellThreshold 0 … 36 dBm

20. 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 <= gsm MicrocellThreshold
HO allowed only to microcell ( MS_TXPWR_MAX(n) <= gsmMicrocellThreshold )

21. Umbrella
Handover
A
B-90 dBm
Handover due
to Level
-85 dBm
1800 Macro
1800 Micro
Umbrella Handover
down to micro layer
hoLevelUmbrella = -85dBm
RR
Handover
out of
micros
PBGT Handover
between SAME
layer cells
Example - Priority  microcells
hoLevelUmbrella macro  macro = -47 dBm
(prevents Umbrella HOs between adjacent macrocells)
hoLevelUmbrella macro  micro = -85 dBm
hoThresholdLevDL = -90 dBm
GSM MS class 4 (33 dBm)
gsmMacrocellThreshold = 35 dBm
gsmMicrocellThreshold = 33 dBm
msTxPwrMax(n) = 33 dBm

22. macrocells
microcells
UMB,RR
PBGT,RR
PBGT,RR
UMB,RR
UMB umbrella HO
RR radio reason HO
PBGT 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. 900
macro)
SAME layer (serving
layer)
LOWER layer
(micro)
 Three layers visible to serving cell (relative
to 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 budget
N (not in use)
Parameter
AdjCellLayer

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) cells
Two 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 parameters
for each adjacent micro cell:
• fastMovingThreshold 0 .. 255
• RxLevMinCell
• hoLevelUmbrella
Counter for each adjacent micro cell
+2 measurement and over rxLevMinCell
-1 no meas. or bad level
Target cell selection based on adjacent
cell RX_LEVEL and on hoLevelUmbrella
 FMMS used in macrocell layer to 'estimate' the speed of a mobile based on measurement
reports on adjacent microcells
macrocells
microcells
FMMS HO
initiated
time ‘t’
FMT Counter
HO
time ‘t’
hoLevelUmbrella = -85 dBm
FMT Threshold = 40
RxLevMinCell = -85 dBm

26. BTS
BTS
Adjacent cell
measurements
BSC
BTS sends MS speed
measurements to BSC
every SACCH period
(~480ms)
2
BTS 'measures' MS speed based
on zero cross rate algorithm providing
call is on non-hoping TCH
MS_SPEED_DETECTION not suitable
for use with frequency hopping networks
1
BSC averages speed
indications using
msSpeedAveraging
 AV_MS_SPEED
BSC ignores indications if;
• UL DTx used during SACCH
• MS changing power during SACCH
3
4
AV_MS_SPEED is compared with
thresholds;
• LowerSpeedLimit (slow MS)
• UpperSpeedLimit (fast MS)
to direct MS to appropriate layer
(cell priorities used)
Candidate Selection
 Fast-moving to upper /
Slow-moving to lower
layer adjacent cells
 Equation 1' used
 Priority considered

27. msSpeedAveraging (MSA) 1 ... 32 (SACCH frames)
adjCellLayer (ACL) N / Same / Upper / Lower
hoLevelUmbrella (AUCL) -110 ... -47 dBm
lowerSpeedLimit (LSL) 0 … 255 (1 step 
2km/h) upperSpeedLimit (USL) 0 … 255 (1 step 
2km/h)
msSpeedThresholdNx 1 … 32
msSpeedThresholdPx 1 … 32
Parameter Value
adjCellLayer (ACL) N / Same / Upper / Lower
hoLevelUmbrella (AUCL) -110 ... -47 dBm
FastMovingThreshold (FMT) 0 … 255 (SACCH frames) FMMS
MS Speed
Detection
0 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 handover
during that time
• 255 : No release, only imperative Handover attempt
Distance Process
enableMsDistanceProcess Y / N
msDistanceHoThresholdParam 0 … 63
px 1 … 32
nx 1 … 32
Parameter Value
msDistanceBehaviour 0, 1 … 60, 255

30. Chained
Cell
Serving
Cell
 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
hoThresholdLevULforRapidFieldDrop -110 ... -47 dBm
hoThresholdRapidLevUIN 0 ... 32
chainedAdjacentCell Y / N
Parameter Value

31. MS Chained
Cell
Serving
Cell
Rapid Field Drop Handover
.
.
1st
2nd
-93 dBm
Serving
Cell
hoThresholdRapidLevUl = - 93 dBm
hoThresholdRapidLevUIN (px) = 2
chainedAdjacentCell = Yes
Example

32. • In case of DDE (Deep Dropping Edge), the averaging
window sizes and power budget period are reduced
• level downlink window size
• level uplink window size
• adjacent cell averaging window size
• handover period power budget
Parameter Value
erfdEnabled DIS, UL, DL or UDL
ddeThresholdLev 0 … 63 dB
Nx 1 … 32
Px 1 … 32
ddeWindow 1 … 32 SACCH
modifiedAveWinNcell 1 … 32
modifiedNOZ 1 … 32
erfdOver 1 … 64 sec

33. A MS moves away from cell site,
the signal is dropping gradually
A MS turns a corner,
the signal drops rapidly
SignalLevel
Time
Figure 7 Signal Strength of a Fast Moving MS
MS moves away from cell site,
the signal is dropping gradually
MS turns a corner, the
signal drops faster than
moving in straight line
SignalLevel
Time
Figure 8 Signal Strength of a Slow Moving MS

34. Handover
A handover due to Enhanced Rapid Field Drop is defined by the following
parameters;
• ErfdEnabled - Enables ERFD Handovers
• DdeThresholdLev - Defines the drop in
signal level that must be observed before
ERFD detection. Uses voting nx : px
• DdeWindow - Sets the window size over
which ERFD is to be monitored
• ModifiedAveWinNcell - Defines the modified
averaging window size to be used for
Ncells during period ErfdOver
• ModifiedNOZ - Modified # of zero results
used during period ErfdOver
• ErfdOver - Time period over which parameters
,
ModifiedAveWinNcell and ModifiedNOZ are used to monitor Ncells
Serving cell
Ncell #1
25dB > 20dB
DdeThreshold
hoThresholdLevXL
ErfdOver
ERFD HO initiated
to Ncell #1
XL = DL or UL
DdeWindow =
2 n(1):p(1)
ERFD Detection
-83 -87-63-61-60-60 -89 -91 -94 -89 -89
averagingWindowSizeAdjCell = 4
modifiedAveWinNcell = 2
ERFD 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 – (-83
dBm) = 14 dB
Sample 1 2 3 4 5 6 7 8
Signal
level
-71
dBm
-68
dBm
-70
dBm
-71
dBm
-69
dBm
-70
dBm
-75
dBm
-83
dBm

36.  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 sec
minIntBetweenHoReq 0 ... 30 sec
Parameter Value

37.  Reversion to old channel
( 1 + NUMBER_OF_HO_FAIL ) *
MinIntBetweenUnsuccHoAttempt applied to handover
attempts to the same target cell
 No Radio Resource Available
MinIntBetweenUnsuccHoAttempt applied to handover
attempts to the same target cells ( all those in the list )
 Other Failure Cases
MinIntBetweenUnsuccHoAttempt applied to all types of
handover attempts
Handover 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 during
GUARD_TIME = 2 * HoPeriodPBGT
◦ an Umbrella HO back is not allowed during
GUARD_TIME = 2 * HoPeriodUmbrella
 After an inter-cell HO due to MS-BS distance:
◦ a HO back to the source cell is not allowed during
GUARD_TIME = 20sec + MinIntBetweenHOReq
 After a Traffic Reason HO:
◦ Power Budget HO and Umbrella HO back to the source are not allowed during
GUARD_TIME = 20sec + MinIntBetweenHOReq
 Repetitive Intra Cell HO not allower during
GUARD_TIME = 4 * MinIntBetweenUnsuccHoAttempt