Optimizing 3G Network Performance

1 © Nokia Siemens Networks RNO / Wind 17/10/2007 - NMI
Confidential
RNO Wind
Part II

Confidential
Part II - Content
Retainability
Drop cause relevance
Compress Mode
CM Time
IRATHO
Adjg Optimization
Failure analisys

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Retainability

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Retainability
Drop call (from 3G RNC side) can occur when UE is leaving the 3G layer (during inter-
system HO) or in 3g layer.
It is not easy to find clear relationship between drop call in 3g layer and active set size or
SHO success rate.
Considering WCELs with high permanence in “one cell in active state” (greater than 90%
weighted value) no more than 50% suffer drop call value greater than 1% and increasing
to higher value statistical data does not confirm the cause – effect relationship.
Same behaviour is revealed for SHO success rate KPI.
At the same way is not possible to find direct relationships between intersystem mobility
failure procedure and high value of drop call.
The reason for that has to be seek in the masking effect of the counters involved either
SHO or Active Set Size or in the IRATHO success rate KPIs
Drop call analisys have to be performed with a second level analisys taking into count
that an averall improvement should come from ADJS and ADJG optimization

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RAB & RRC Active Failures
RAB and RRC active failure reasons:
• RNC Internal
• BTS
• UE (for user perspective)
• Radio Interface
• Iur
• Iu
RAB and RRC normal release:
• RAB active complete
• Pre-emption
• SRNC Relocation
• Unspecific error in CN (RAS05.1)
UE RNC
RAB Assignment Request (setup)
CORE
Radio Bearer Setup
RAB Assignment Response
Radio BearerSetupComplete
RAB Assignment Request (release)
Iu Release Command
RAB Assignment Response
Iu Release Request

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 
%
CT_FAIL_UE
RRC_CONN_A
C
CT_FAIL_RN
RRC_CONN_A
CHK
CT_FAIL_I_
RRC_CONN_A
PH
CT_FAIL_CI
RRC_CONN_A
R
CT_FAIL_IU
RRC_CONN_A
S
CT_FAIL_BT
RRC_CONN_A
DIO
CT_FAIL_RA
RRC_CONN_A
CT_FAIL_IU
RRC_CONN_A
L
UT_REF_CEL
RRC_CONN_O
N_REF_CELL
RRC_CONN_I
PEC_CN
CT_REL_UNS
RRC_CONN_A
C
CT_REL_SRN
RRC_CONN_A
MP
CT_REL_P_E
RRC_CONN_A
CT_COMP
RRC_CONN_A
S
CT_FAIL_BT
RRC_CONN_A
DIO
CT_FAIL_RA
RRC_CONN_A
100
Ratio
Drop
RRC















By a RNO point of view the drop due to lack of radio resources are the most important.
Iu, Iur and RNC failure causes are neglected because the dimensioning should assure about it and out
of RNO scope
Fail due to congestion has to be intended as caused by shortage of resources or not appropriate air
interface.
In the following two KPIs to evaluate the drop cause that can be optimized:
 
%
E_RNC
IL_CS_VOIC
RAB_ACT_FA
E_I_CHK
IL_CS_VOIC
RAB_ACT_FA
E_IUR
IL_CS_VOIC
RAB_ACT_FA
E_BTS
IL_CS_VOIC
RAB_ACT_FA
E_RADIO
IL_CS_VOIC
RAB_ACT_FA
E_IU
IL_CS_VOIC
RAB_ACT_FA
E_UE
IL_CS_VOIC
RAB_ACT_FA
_CELL
CE_OUT_REF
RAB_CS_VOI
-
CELL
CE_IN_REF_
RAB_CS_VOI
PE_ER_CN
L_CS_V_UNS
RAB_ACT_RE
_SRNC
L_CS_VOICE
RAB_ACT_RE
_P_EMP
L_CS_VOICE
RAB_ACT_RE
E
MP_CS_VOIC
RAB_ACT_CO
E_BTS
IL_CS_VOIC
RAB_ACT_FA
CE_RADIO
AIL_CS_VOI
RRAB_ACT_F
100
Voice
AMR
Ratio,
Drop
RAB














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The retainability KPI does not take into account RRC-connections that move successfully through
the cell, they only count drop ratio of RRCs that were released in the cell. In this way the drop KPI
shows a bit too high values.
Generic Drop Call KPI does not take into count the following scenario:
To overcome this problem, new counters are implemented in RAS05.1 that are updated when the
reference cell changes
In this context term “reference cell change” means the cell that e.g. M1006 RRC counters are
updated and that is used as stop_bts when pmi_ticket
In Cell-FACH state the reference cell is the cell in which the UE is listening to the FACH channel
M1001C443 RRC_CONN_OUT_REF_CELL - The number of RRC Connections that have left
from the old reference cell
M1001C466 RRC_CONN_IN_REF_CELL - The number of RRC connections that enter a new
reference cell
Successful RRC Setup ->
RRC_CONN_ACC_COMP is
updated
RRC Drop here causes
RRC_CONN_ACT_FAIL_xx to be
incremented and not
RRC_CONN_ACT_COMP is
incremented

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Separating the numerator it is possible to
have two separate KPIs for radio and BTS.
This allows to differentiate the action
required:
Radio
coverage plot , dominance must be verified
indication from UL/DL Load KPI (see PartI)
BTS
HW & CE resource must be checked using
KPI for CE and codes
Radio?
BTS?
Yes
RNP data anlisys
Load analisys
Yes
Start
DC due to congestion
CE upgrade
HW check
End

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Compress Mode

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Compressed Mode Selection
CM is used to create idle periods (gaps) in the transmission during which ncell measurements on
another
system can be made
Gaps can be created using single or double frame approach (Nokia supports both)
Because same data amount is sent in a shorter time => affects WCDMA coverage
Fast Power control information might be lost during the gap => higher Eb/No => affects WCDMA capacity
Compressed frames may be lost if power control is not set correctly => affects WCDMA quality
CM methods are Spreading Factor Halving and Higher Layer Scheduling
Normal frame Normal frame
Measurement gap
Power / Data
Rate Compressed
Mode
Normal frame

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Selection of the compressed mode method is performed in the following way:
AMR, RT PS or
CS data service
SF/2 used for both UL and DL
Transmission Gap Pattern:
Single frame: 7 slot gap,
variable # of normal frames
NRT PS data service
Higher layer scheduling is
Used for both UL and DL
Transmission Gap Pattern:
Single frame: 7 slot gap,
# of normal frames
Double frame: 7 slot gap,
# of normal frames
Selection between HLS ½ and
HLS ¾
Compressed Mode Selection

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CM Time
The approaching of the limit GSMMeasRepInterval * GSMMaxMeasPeriod
can be considered as an indication for the tunig of the related parameters
Time for cell search and for CM can be tuned as well
The following counters are available for the CM procedure monitoring
M1002C437 ALLO DURA FOR COM MODE UL USING SF/2 METHOD IN SRNC /
M1002C433 ALLO FOR COM MODE UL USING SF/2 METHOD IN SRNC
M1002C438 ALLO DURA FOR COM MODE DL USING SF/2 METHOD IN SRNC /
M1002C434 ALLO FOR COM MODE DL USING SF/2 METHOD IN SRNC
M1002C440 ALLO DURA FOR COM MODE DL USING HLS METHOD IN SRNC /
M1002C436 ALLO FOR COM MODE DL USING HLS METHOD IN SRNC
M1002C439 ALLO DURA FOR COM MODE UL USING HLS METHOD IN SRNC /
M1002C435 ALLO FOR COM MODE UL USING HLS METHOD IN SRNC
Dividing the duration by the respective allocation is possible to have an estimation of
the CM Time

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CM Time
After HO triggering condition is fulfilled a RRC message ”Measurement Control” is sent to UE
containing details of the measurement that the UE must execute.
RRC: ”Measurement control ” message (GSM RSSI measurements)
RNC
UE
Duration of the cell search period is calculated by:
GSMRepInterval * GSMNcellSearchPeriod
The neighbour cell search is regulated by the GSMNcellSearchPeriod period parameter. ISHO is
not allowed until the are enough measurement reports given by this parameter (O means that only 1
measurement result is enough for decision making)

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CM Time
Upon reception of the measurements reported by the UE, RNC applies a sliding averaging window to
theRXLEV measurements. The averaged levels are used as input to the IS-HO decision algorithm.
RNC
RXLEV measurements are reported through
”Measurement report” messages
UE
RRC: ”Measurement report”
RRC: ”Measurement report”
The first measurement report
has info from the best GSM cell:
BCCH freq & RSSI, no filtering
used in UE
GsmMeasRepInter
val
is the interval between
measurement reports, which
are sent to BTS
GSMMeasAveWindow
is Measurement Averaging
Window size, sliding window
is used

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CM Time
RNC
NBAP: Compressed Mode Command
WBTS
GSMMinMeasInterval
This is Minimum Measurement
Interval, wait time when the
following CM starts.
In case of an unsuccessful IS-HO attempt, the network will deactivate compressed mode for a time
period given by GSMMinMeasInterval
If the RNC is not able to execute an inter-system Handover, it shall stop the inter-system
measurements after the UE has sent the predefined number of measurement reports to the RNC,
given by GSMMaxMeasPeriod
The Maximum allowed duration of the inter-system measurement is calculated:
GSMMeasRepInterval * GSMMaxMeasPeriod [ es:0.5*20 =10s,]

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CM Time
CM Time
approach max?
High # No
Cell Found?
Yes
Verify
# No Cell Found
Yes
Start
System stable
Add ADJG
CM Time
approach min?
Yes
New ADJG
availale?
Yes
1E/1F tuning
CM tuning
The CM time should
never approach the max
limit stated by
GSMMeasRepInterval *
GSMMaxMeasPeriod
The best cndition is to
perform the IS with the
minimum time
GSMRepInterval *
GSMNcellSearchPeriod
without failure.
In the other cases ADJG
optimzation or tunig of
parameters are required

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IRATHO

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IRATHO
As M1013 described in PartI, M1015 return statistic for intesystem HO. The filtering criteria
can be replicated with the exception of ping-pong
Filtering criteria:
Major
- High number of failures for a defined out-going adjg (failure ADJG)
- high number of fail for a defined source (failure WCEL)
Minor
- very low number of attempt with failure (low used adjg)
- zero number of attempt for declared adjs– stabilized value (no adjg)
- high number of attempts for an out-going adjs (unbalanced ADJG)
out-going condition is sufficient
- high number of attempts for a defined source (unbalanced WCEL)
Same procedures can be applied to the case considering that the event related are 1E and 1F

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1E/1F Events for CPICH Ec/No and RSCP
time
Cell 1
Cell 2
Cell 3
e.g.
P-CPICH
Ec/No
HHoEcNo(RSCP)Cancel
Defines the threshold of Ec/No(RSCP)
that must be exceeded by a measurement
of an active set cell to be canceled the
event 1F related
HHoEcNo(RSCP)CancelTime
determines the time period during which the CPICH
RSCP of the active set cell must stay better than the
threshold HHoRscpCancel before the UE can trigger the
reporting event 1E.
HHoEcNo(RSCP)Thres
hold
determines the absolute CPICH
Ec/No threshold which is used by the
UE to trigger the reporting event 1F.
When the measured CPICH Ec/No of
all active set cells has become worse
than or equal to the threshold in
question, the RNC starts inter-
frequency or inter-RAT (GSM)
measurements in compressed mode
for the purpose of hard handover.
HHoEcNo(RSCP)TimeHysteresis
determines the time period during which the CPICH Ec/No of the active
set cell must stay worse than the threshold HHoEcNoThreshold before
the UE can trigger the reporting event 1F.
1E
1F

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IRATHO – Triggering reason
4. DL DPCH approaches its
maximum allowed power
FMCG: GSMcauseTxPwrDL
5. Quality deterioration report
from UL outer loop PC
FMCG: GSMcauseUplinkQuality
3. UE Tx power approaches
its maximum allowed
power, event 6A/6D
FMCG: GSMcauseTxPwrUL
2 . Low measured absolute
CPICH RSCP, events 1E/1F
FMCG: GSMcauseCPICHrscp
1. Low measured absolute
CPICH Ec/No, event 1E/1F
FMCG: GSMcauseCPICHEcNo
GSMcauseX
These parameters indicates whether a handover to GSM caused by low measured absolute CPICH Ec/No of the serving cell is
enabled (1)
6 . Others
- Load and Service based HO
- IMSI based HO
- Emergency ISHO
Triggering reason gives
an indication

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

Allcauses
RT
N
xxx
CMOD
W
HHO
IS
RT
N
xxx
CMOD
W
HHO
IS
perc
Cause
xxx
)
_(
_
_
_
_
)
_(
_
_
_
_
_
_
It’s important to know which is the most frequent triggering reason:
It’s possible to diffentiate between quality and coverage reasons and understand the
network limiting factors:
1. CPICH coverage
2. Pilot pollution
3. UL/DL Service coverage
In actual case is possible to dsciminate between low CPICH coverage triggered by high# RSCP
attempts or probable pilot pollution triggered by high # Ec/No attempts
A KPI that gives reason for that is

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High # Ec/No?
Start
UL level limiting
Yes
High # RSCP?
High # UE
Tx pwr?
High # UL Qual?
New site required or new
Parametrization for IRATHO
UL qual limiting
Yes
Load analisys and UL
interference evaluation
DL Qual limiting
Yes
DL interference/ Pollution
should be evaluated
DL level limiting
Yes
CPICH power analisys/ new
site required
UL
DL
This condition
should be the
dominannt one
without
associated
failure
Enabling all the causes a screaning on the network is returned individuating the limiting factor
and the required action.
High # DL
DPCH?
Service limiting
Yes
New planning for service is
required
End

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IRATHO - Failure
Failure can happen
at different point:
Before decision
- Before CM
- During CM
- Measuring GSM
cell
After decision
- Drop
Utran and ue have to
treated as particular
case
UE Node B RNC
RRC: Measurement Report
RRC: Measurement Control
NBAP: Radio Link Reconfiguration Prepare
NBAP: Radio Link Reconfiguration Ready
NBAP: Radio Link Reconfiguration Commit
RRC: Physical Channel Reconfiguration
RRC: Physical Channel Reconfiguration Complete
GSM RSSI
Measurement
ISHO triggering
(5 reasons are
possible)
Initial
Compressed
Mode
Configuration
CN
RANAP: SRNS Context Request
RANAP: SRNS Context Response
RANAP: IU Release Command
RANAP: IU Release Complete
RRC: Cell Change Order from UTRAN
RANAP: SRNS Data Forward Command

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CM not possible
The following KPI gives an indication of the number of CM
procedure not started
If CM fails one of the following mus be checked:
Not enough resources – AC reject CM.
Evaluate interference
Expand capacity
(see PartI)
RNC
UE
RRC: Measurement Report (3,4,5)
BTS
Admission Control
check for CM
NBAP: Radio Link Reconfiguration Prepare
NBAP: Radio Link Reconfiguration Ready
NBAP: Radio Link Reconfiguration Commit
RRC: Physical Channel Reconfiguration
RRC: Physical Channel Reconfiguration Complete
BSIC verification phase for target cell
RX Level measurement phase for
all ISHO neighbours
AC is responsible for checkiing if CM is possiblle


j
j
MOD
IS_HHO_W_C
OS
_STA_NOT_P
IS_COM_MOD
OS
_STA_NOT_P
IS_COM_MOD
Considering that M1010C2 (INTER SYST COM MOD STA NOT POS FOR RT) is updated if it is
not possible to start inter-system compressed mode measurement due to radio resource
congestion, BTS- or UE-related reasons to have a better insight on radio congestion it could be
better to use, e.g. for UL the M1002C361 REQ FOR COM MODE UL REJECT TO INT SYST HHO
IN SRNC and the M1002C357 REQ FOR COM MODE UL TO INT SYST HHO IN SRNC and use the
following :
M1002C361/M1002C357

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NO Cell Found
Missing ADJG could be the reason or a dedicated parameter tuning for the 1F event.
The KPI can be madified taling care of the WO_CMOD events
The following KPI gives an indication of the number of GSM cell not found
NO Cell Found means:
there is no suitable gsm target cell in terms of RX Level
OR
the target gsm is suitable but its BSIC verification fails
AND
the maximum number of measurement reported are received
AND
maximum measurement interval is not expired
Compressed
Mode start
No Cell Found
Counters
HHO Attempt
Counters
… measurement
fail
… measurement not
fail



Allcauses
Allcauses
RT
N
xxx
CMOD
W
HHO
IS
RT
N
xxx
CELL
NO
HHO
IS
Rate
Fail
Meas
ISHO
)
_(
_
_
_
_
)
_(
_
_
_
_
_
_
_

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NO Cell Found
High #
NO Cell?
ADJG
Addition?
Yes
Verify
ADJG
Yes
Start
Reduce “Cancel”
Increase “Time hysteresis”
Good GSM coverage
in the near field?
Yes
Coverage anlisys
End
End
Good GSM coverage
in the far field?
Reduce
“thershold”
New site
required
GSMCause=Ec/
Nol?
Yes
Pollution evaluation

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DROP & UNSUCCESS IRATHO



Allcauses
Allcauses
RT
N
xxx
ATT
HHO
IS
RT
N
xxx
HHO
IS
DRPS
CON
Rate
Drop
ISHO
)
_(
_
_
_
)
_(
_
_
_
_
_
_
In this case the optimization is required and
pass through the evaluate of GSM and 3G plot
coverage. Optimize If necessary number of
ADJG or NWP parameters otherwise tune
RNW parameters.
Thresholds can be relaxed to favourite an
early exit from 3G layer
RRC Drop
Counters
HHO Attempt
Counters
ISHO Success
Counters
ISHO Unsuccess
Counters
UE Failure
Counter
UTRAN Failure
Counter
Optimization for unsuccess is not possible
because the reason are:
- physical channel failure (the UE is not able to
establish the phy.
- Protocol error
- Inter-Rat protocol error
- Unspecified
Drop are related to drop call occurred
during the procedure

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3G –> 2G Unbalancing
VOICE
CS
COMP
ACC
RAB
RT
xxx
ATT
HHO
IS
ISHO
Call
Voice
Perc Allcauses
_
_
_
_
_
_
_
_
_
_
_


This topic present the inherent problem due to the fact that the 2G layer is not involved in
the analisys.
Few consideration can be performed under some assumption:
The following KPIs used over a cluster for CS voice service gives the percentage of the CM
started over all the RAB, giving an idea of the attempted mobility procedure requested for a
cluster where the 3G coverage should be assured
Once Correlated with voice drop due to radio link failure and rrc drop during ISHO, the KPI can
help operator in understand the ISHO strategy. Similar KPI is possible for PS
Threshold to shrink the HO area or inhibit the procedure has to be setted
Better to use completes: failures, normal & SRNC reloc on denominator and use the KPI inside the
3G cluster or difining a polygon where 3G service is required

Optimizing 3G Network Performance

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