63077585 idle-mode-parameter-optimization

1 © Nokia Siemens Networks Presentation / Author / Date
For internal use
Slowing Down the Inter RAT Cell Reselections;
Parameter Tuning & Monitoring Guide
Version 1.0
23.09.2007 Reunanen Jussi

For internal use
Agenda
• Treselection
• Hysteresis between 3G->2G and 2G->3G cell reselections
• PRACHRequiredReceivedCI and
PowerRampStepPRACHpreamble
• PrxAlpha
• PrxTarget

For internal use
Treselection – Introduction
Treselection: how long the reselection conditions must be fulfilled
before reselection is triggered
• Impacts all cell reselections : Inter RAT, intra frequency and inter
frequency
• The UE reselects the new cell, if the cell reselection criteria (R-
criteria, see next slide) are fulfilled during a time interval
Treselection

For internal use
Treselection – Introduction
First ranking of all the cells based on
CPICH RSCP WCDMA and RSSI GSM( ) ( )
Rs = CPICH RSCP + Qhyst1
Rn= Rxlev n( ) - Qoffset1
Rn GSM Rs WCDMA( ) > ( )
And
Rxlev GSM( ) >QrxlevMin
Rn GSM Rs WCDMA( ) > ( )
And
Rxlev GSM( ) >QrxlevMin
YesNo
Cell re-selection
to GSM
Cell re-selection
to GSM
Neighbour WCDMA or GS
cell calculation with offse
parameter
Serving WCDMA cell
calculation, with
hysteresis parameter
UE starts GSM measurements if
CPICH Ec No/ < qQualMin + sSearchRAT
UE starts GSM measurements if
CPICH Ec No/ < qQualMin + sSearchRAT
SintraSearch
SinterSearch
SsearchRAT
CPICH EcNo
qQualMin
econd ranking only for WCDMA
cells based on CPICH Ec No/
Rs CPICH Ec No Qhyst2= / +
Rn CPICH Ec No n -Qoffset2= _ / ( )
econd ranking only for WCDMA
cells based on CPICH Ec No/
Rs CPICH Ec No Qhyst2= / +
Rn CPICH Ec No n -Qoffset2= _ / ( ) Cell re-selection to
WCDMA cell of highest
R value
Cell re-selection to
WCDMA cell of highest
R value

For internal use
Treselection – Recommended Values
As this parameter impacts on all the cell reselections too long Treselection timer
might cause problems in high mobility areas but too short timer causes too fast cell
reselections and eventually causes also cell reselection ping pong
Recommended value 1s should work in every conditions i.e. enough averaging to
make sure that correct cell is selected
However careful testing is needed to check the performance of different areas
• (Dense) Urban area, slow moving UEs with occasional need for fast and
accurate (to correct cell) reselections e.g. outdoor to indoor scenarios or city
highways – in some cases cell by cell parameter tuning is performed to find most
optimal value between 0s and 2s but typically 1s is optimal value when workload
is considered as well
• Highways, fast moving UEs must reselect correct cell – typically 1s works the
best (however occasionally also 0s might be needed in fast speed outdoor to
indoor cell reselections e.g. tunnels)
• Rural areas, slow or fast moving UEs need very often reselect between different
RATs and make proper cell reselections even when the coverage is poor –
typically 1s works the best
• Location Area Borders, usually the coverage is fairly poor – typically 1s works
the best but sometimes to reduce location area reselection ping pong 1s is used
when going from LA1 to LA2 and 2s from LA2 to LA1

For internal use
Treselection – KPIs and Analysis
RRC connection request amount for inter RAT cell reselection ratio to all RRC
Connection request causes
• When Treselection is increased this KPI should decrease
RRC connection request amount for registrations ratio to all RRC Connection
request causes
• When Treselection is increased this KPI should decrease
TP_ATTRRC_CONN_SM1001C0
_ATTSELL_RE_SELINTR_RAT_CM1001C42
ON_ATTSREGISTRATIM1001C46

For internal use
At the same time the CSSR and especially the RRC Connection Setup and
Access Complete must be monitored
• The KPIs below should remain the same despite the Treselection
modification or even get better
• If the CSSRs or RRC Connection Setup and Access Complete decrease the
Treselection value should be decreased
• RNC_94d: RRC Setup and Access Complete Ratio from network point of
view
• RNC_565e: CSSR CS Voice (RAS05.1) or RNC_565d : CSSR CS Voice
(RAS05)
• The RRC Connection Setup attempts should decrease
– M1001C0 RRC_CONN_STP_ATT

For internal use
• Following RRC Connection Setup failure causes should decrease as the
amount of RRC Connection setup attempts is decreasing
– M1001C3 RRC_CONN_STP_FAIL_AC
– M1001C4 RRC_CONN_STP_FAIL_BTS
– M1001C5 RRC_CONN_STP_FAIL_TRANS
– M1001C530 RRC_CONN_STP_FAIL_IUB_AAL2
• Above indicate saved resources and more detailed analysis can be done
based on counters below
– BTS CE : RAS05.1
– Iub : AAL2 Path Average Reserved Bandwidth % : RAS05
E_DLMAX_USED_CM5001C3
CE_ULMAX_USED_M5001C4
E_DLMIN_USED_CM5001C5CE_ULMIN_USED_M5001C6
E_DLAVG_USED_CM5001C7
E_ULAVG_USED_CM5001C8
RATEGUAR_CELL_AAL2_PATH_M550C0
SNBR_SAMPLEM550C7
ATEVED_CELL_RSUM_RESERM550C1
100%×

For internal use
Hysteresis Between 3G->2G and 2G->3G Cell
Reselections – Introduction & Recommended Values
Parameters for cell reselections
• Qqualmin = -18dB Ssearch_RAT =2dB -> the 3G->2G cell reselection starts
when Ec/No hits -16dB
• FDDQmin/GPRSfddQmin = -14dB (6) and QsearchP/Qsearch = always
The cell reselection paramters 3G -> 2G and 2G -> 3G provide only 2dB hysteresis
which is not enough and can been noticed from the RNC statistics as high amount
of INTR_RAT_CELL_RE_SEL_ATTS from all the RRC Connection Setup Attempts
• Recommendation is to adjust the GFDM/FDM from -14dB to -10dB (or even up to
-8dB) to provide 6 to 8 dB hysteresis between 3G to 2G cell reselection and 2G
to 3G cell reselection
On top of Treselection the above parameters will slow down further the 2G to 3G
and 3G to 2G cell reselections

For internal use
Reselections – Introduction & Recommended Values
However careful testing is needed to check the performance of different areas
• UEs must reselect correct cell in case of 3G outdoor to certain 2G – in these
cases adjacency based parameter Adjqoffset1 can be used to prioritize certain
2G neighbor
– Impacts the R-criteria as shown below

For internal use
Reselections – KPIs and Analysis
RRC connection request amount for inter RAT cell reselection ratio to all RRC
Connection request causes
• When hysteresis is increased this KPI should decrease
RRC connection request amount for registrations ratio to all RRC Connection
request causes
• When hysteresis is increased this KPI should decrease
_ATTSELL_RE_SELINTR_RAT_CM1001C42
ON_ATTSREGISTRATIM1001C46

For internal use
At the same time the CSSR and especially the RRC Connection Setup and
Access Complete must be monitored
• The KPIs below should remain the same despite the hysteresis modification
or even get better
• If the CSSRs or RRC Connection Setup and Access Complete decrease the
hysteresis value should be decreased
• RNC_94d: RRC Setup and Access Complete Ratio from network point of
view
(RAS05)
• The RRC Connection Setup attempts should decrease
– M1001C0 RRC_CONN_STP_ATT

For internal use
• Following RRC Connection Setup failure causes should decrease as the
amount of RRC Connection setup attempts is decreasing
– M1001C3 RRC_CONN_STP_FAIL_AC
– M1001C4 RRC_CONN_STP_FAIL_BTS
– M1001C5 RRC_CONN_STP_FAIL_TRANS
– M1001C530 RRC_CONN_STP_FAIL_IUB_AAL2
• Above indicate saved resources and more detailed analysis can be done
based on counters below
– BTS CE : RAS05.1
– Iub : AAL2 Path Average Reserved Bandwidth % : RAS05
E_DLMAX_USED_CM5001C3
CE_ULMAX_USED_M5001C4
E_DLMIN_USED_CM5001C5CE_ULMIN_USED_M5001C6
E_DLAVG_USED_CM5001C7
E_ULAVG_USED_CM5001C8
RATEGUAR_CELL_AAL2_PATH_M550C0
SNBR_SAMPLEM550C7
ATEVED_CELL_RSUM_RESERM550C1
100%×

For internal use
CLUSTER JBK09
0%
20%
40%
60%
80%
100%
< 50% 50-70% 70-85% 85-100%
85-100% 1 1
70-85% 3 7 1 1
50-70% 12 10 9 7 6 8
< 50% 41 39 47 50 51 48
6/ 19/ 2007 6/ 20/ 2007 6/ 21/ 2007 7/ 10/ 2007 7/ 11/ 2007 7/ 12/ 2007
BEFORE AFTER
Cluster JBK09
Count of % I NTR_RAT_CELL_RESEL
Comparison Date
Grouping1
Cluster JBK09 Percentage Distribution after implementation:
☺Decreasing black and red colour as high percentage of Inter Rat Cell Reselection
☺Increasing green colour as low percentage of Inter Rat Cell Reselection
Decreasing
☺Before  25% of Cells having >50% of all
RRC setups for inter RAT cell reselection
☺After  12% of cells having >50% of all
RRC setups for Inter RAT cell reselection
Reselections – KPI Analysis Example
Hysteresis from 2dB -> 6dB

For internal use
PRACHRequiredReceivedCI and
PowerRampStepPRACHpreamble – Introduction
• During drive testing it is usually noted that there are call setup failures where the
network does not seem to respond to RRC Connection Requests with RRC
Connection Setup –message
• These are problems due to the spiky UL noise and due to that the power
ramping is not aggressive enough to provide high enough Tx power for the
terminal during open loop PC
MAJOR ROADS INNER & OUTER BLOCKED COUNT
BREAKDOWN
No Immediat e
Assignment , 1
No Radio
Bearer Set up
Complet e, 2
No Alert ing or
Connect , 1
N-300 and T-
300 expiry, 4
No Set up, 1
RRC Connect ion
Reject , 3

For internal use
PowerRampStepPRACHpreamble – Introduction
The parameters affecting to open loop power control are, in brackets are the recommended
values:
• PRACH_preamble_retrans (7)
• RACH_tx_Max (16)
• PowerOffsetLastPreamblePRACHmessage (2 dB)
• PowerRampStepPRACHpreamble (2dB)
Downlink
BS
L1 ACK / AICH
Uplink
MS Preamble
1
Not detected
Message partPreamble
2
Preamble
PRACH_preamble_retrans
# PRACH preambles transmitted during one
PRACH cycle without receiving AICH response
UEtxPowerMaxPRACH
… … … …
RACH_tx_Max
# preamble power ramping cycles that can be
done before RACH transmission failure is
PowerRampStepPRACHpreamble
PowerOffsetLastPreamblePRACHmessage
Ptx = CPICHtransmissionPower-
RSCP(CPICH) +RSSI(BS) +
PRACHRequiredReceivedCI (-20dB)
Ptx = CPICHtransmissionPower-
RSCP(CPICH) +RSSI(BS) +
PRACHRequiredReceivedCI (-20dB)

For internal use
PowerRampStepPRACHpreamble – Recommended Values
• Typically the parameter PRACHRequiredReceivedCI is set to -18…-20dB
instead of the default -25dB (typically -20dB is enough)
• Also the parameter PowerRampStepPRACHpreamble is adjusted in case the
problem of missed MT calls or call setup failures due to missing RRC
Connection Setup still persists (default 2dB usually works the best but in some
networks also 3dB is used)
• Check also the values for RACH_tx_Max and PRACH_preamble_retrans
– They should be set accordingly as:
– PRACH_preamble_retrans (7)
– RACH_tx_Max (16)
• Also the parameters should all be set in line as below:
– PowerOffsetLastPreamblePRACHmessage (2 dB)
– PowerRampStepPRACHpreamble (2dB)
– PRACHRequiredReceivedCI (-20dB)
– PRACH_preamble_retrans (7)
– RACH_tx_Max (16)

For internal use
PowerRampStepPRACHpreamble – Recommended Values
• If for example PowerRampStepPRACHpreamble is set to 3dB then other
parameters should be adjusted with extra care to avoid unnecessary UL noise
spikes
• Current defaults are tested to work properly without excessive increase in UL
noise

For internal use
PowerRampStepPRACHpreamble – KPIs and Analysis
• The impact of this parameter has to be tested with drive testing (as in case the
PRACH preambles are not heard and therefore the RRC Connection Request is
not heard by the BTS/RNC no RRC connection setup attempt counter is
incremented)
• From the network statistics following should be monitored
– RNC_177b Noise Floor of the System
– RNC_101b Average Uplink load
▪ Related to above the M1001C3 RRC_CONN_STP_FAIL_AC should not increase (if do then load
level reduction actions are needed, explained in PrxAlpha tuning section)
– Secondary KPIs to follow
▪ If the CSSRs or RRC Connection Setup and Access Complete decrease the hysteresis
value should be decreased
▪ RNC_94d: RRC Setup and Access Complete Ratio from network point of view
▪ RNC_565e: CSSR CS Voice (RAS05.1) or RNC_565d : CSSR CS Voice (RAS05)
▪ The RRC Connection Setup attempts should increase but the failures should not increase
(especially AC rejections which are related to UL noise increase / Average UL load)
• M1001C0 RRC_CONN_STP_ATT
• M1001C4 RRC_CONN_STP_FAIL_BTS
• M1001C5 RRC_CONN_STP_FAIL_TRANS
• M1001C530 RRC_CONN_STP_FAIL_IUB_AAL2

For internal use
PowerRampStepPRACHpreamble – KPI Analysis Example
Two values for PRACHRequiredReceivedCI tested (drive testing)
100%
0% 0% 0%
88%
2% 5% 6%
0%
20%
40%
60%
80%
100%
1 2 3 4
# RRC Connection Request Messages per call setup
%
PRACH req. C/I = -20dB PRACH req. C/I = -25dB
Clear improvement in number of
needed RRC Connection Request
messages per call. For 20dB 100%–
of established calls are setup
with only 1 RRC Connection
Request message
Clear improvement number of
sent preambles per RRC
Connection Request for 20dB–
case. For 20dB 50% of cases–
the needed number of preambles
is <=4 where as for 25dB it is–
~6.5
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1 2 3 4 5 6 7 8
PRACH req. C/I = -25dB PRACH req. C/I = -20dB
There should be significant
improvement also for call setup
delay
• -20dB & -25dB : UL interference conditions are at the same level (reported
in SIB 7 for both cases)

For internal use
Clear improvement in call setup
delay for 20dB case. ~65% of–
the established calls are through
with only 3.5 3.7s delay and the–
>5.5s delay tail disappears (in this“ ”
Two values for PRACHRequiredReceivedCI tested (drive testing)
• -20dB
• -25dB
• UL interference conditions are at the same level
(reported in SIB 7 for both cases)
96.2%
100.0%
94%
95%
96%
97%
98%
99%
100%
-25dB -20dB
Call Setup Success Rate
0.0%
20.0%
40.0%
60.0%
80.0%
100.0%
120.0%
<3.5s
3.5s-3.7s
3.7s-3.9s
3.9s-4.1s
4.1s-4.3s
4.3s-4.5s
4.5s-4.7s
4.7s-4.9s
4.9s-5.1s
5.1s-5.3s
5.3s-5.5s
>5.5s
Call Setup Delay (seconds) RRC Conn. Req. to Alerting
PRACH req. C/I = -25 PRACH req. C/I = -20

For internal use
AMR Voice Before 1st
drive 2nd
drive
Average Preamble
Counts 2.40 2.01 1.617
Average
RACH_TX_Pwr -9.11 -7.09 -6.581
average UL
interference -102.42 -102.07 -101.53
Video Before 1st
drive 2nd
drive
Average preamble
count 2.84 1.77 1.933
Average
RACH_TX_Pwr -6.95 -6.45 -6.888
average UL
interference -102.46 -102.15 -101.33
1. The number of resend for PRACH (Preamble Count) has reduced
after the parameters changing, that mean shorter time to build
the radio link. 1st
drive is after PRACHRequiredReceivedCI been
changed (-25dB -> -20dB), while 2nd
drive is after RACH_tx_max been
changed (8 -> 16)
2. Meanwhile the RACH_TX_Pwr for both AMR and Video services is
increased, which mean more power is consumed by the UE .
3. The slighlty increased UL interference can be tried to be reduced
by taking the alpha trimmed mean filter into use to filter the
Prx measurements in BTS

For internal use
AMR (MOC) Before 1st
drive
2nd
drive
Average CS call setup time (MOC) 2.36s 2.44s 2.38s
Call Setup Success Rate 97.87% 99.30% 100.00%

For internal use
PrxAlpha – Introduction
In case the indicators below have increased due to the open loop PC parameter
modifications
• RNC_177b Noise Floor of the System
• RNC_101b Average Uplink load
Or in generally if there are high amount of rejections due to following rasons
• M1001C3 RRC_CONN_STP_FAIL_AC
• M1001C80 RAB_STP_FAIL_CS_VOICE_AC
• M1001C85 RAB_STP_FAIL_CS_CONV_AC
The BTS PrxTotal filtering parameters can be modified i.e. how the BTS averages
the PrxTotal measurements before sending the results to the RNC in Radio
Resource Indication messages

For internal use
Frame mean of Prx_total is pre-calculated using arithmetic mean of
the slot values (15 slots)
Averaged frames are sorted based on PrxMeasAveWindow frames
Filtered values are calculated by taking arithmetic frame mean
values which are between ALPHA and (1-APLHA) defined by
PrxAlpha
• N x α lowest and highest measurements removed
• N x (1- 2α) measurements remain
Av. Frame measurements
Prx• PrxMeasAveWindow = 10 & PrxAlpha = 0.2
• Frame averages are calculated for 10 frames
• 2 max. & 2 min. values excluded : 6 values
remaining
• Final average Prx_total is calculated on the 6
values

For internal use
RADIO RESOURCE INDICATION (RRI)
message
Prx Total is reported to the RNC for LC, AC and
PS usage, on every RRIindicationperiod (200
ms)
The BTS
is
measuring
:
Prx Total
BTS sends the LASTEST
averaged measurement
result to RNC every RRI
period
RNC is calculating
a sliding window
averaged value
over the values
given by RRI
messages
Frame measurements
Prx
…
RRIxRRIx+1RRIx+2 RRIx+n
Sliding window average
result on every RRI
period
WinAcRabSetupUI
∑=
+⋅=
m
j
jntotalrx Totalx
m
P
1
_ _Pr
1
BTS uses ALPHA TRIMMED MEAN
FILTER
PrxAlpha
PrxMeasAvWindow

For internal use
PrxAlpha – Recommended Values & Example
PrxAlpha=0.1
PrxMeasAveWindo
w=10
RRIPeriod=200ms
PrxAlpha=0
PrxMeasAveWindo
w=10
RRIPeriod=200ms
Clearly some impact when changing
the PrxAlpha -> suggests that the
interference conditions are
somewhat spiky and the PrxTotal
values could be further reduced
adjusting the PrxAlpha
The PrxAlpha parameter value
should be adjusted in 0.1 step
intervals and KPIs monitored for
each parameter value

For internal use
PrxAlpha – KPIs and Analysis
Following indicators should be monitored for each PrxAlpha value

For internal use
PrxTarget – Introduction
If the received Non-controllable power (RT) + the estimated power
increase caused by the to be established RAB is above the
PrxTarget, the RT RAB setup is rejected
If the received Non-controllable power (RT) is above the PrxTarget
limit then the RRC Connection Setup is rejected
• However note that for the following RRC Connection Request
cause values the AC limits are not used (in UL nor in DL)
– Emergency call
– Registration
– Detach
– Originating High Priority Signaling
– Terminating High Priority Signalling
– Inter-RAT cell re-selection
– Inter-RAT cell change order

For internal use
PrxTarget – Recommended Values & Example
TOTAL NUMBER OF RRC CONN STP FAIL AC
0
1000
2000
3000
4000
5000
6000
6/1/2007
6/2/2007
6/3/2007
6/4/2007
6/5/2007
6/6/2007
6/7/2007
6/8/2007
6/9/2007
6/10/2007
6/11/2007
6/12/2007
6/13/2007
6/14/2007
6/15/2007
6/16/2007
6/17/2007
6/18/2007
6/19/2007
6/20/2007
6/21/2007
6/22/2007
6/23/2007
6/26/2007
6/27/2007
6/28/2007
6/29/2007
6/30/2007
7/1/2007
Total Moving Avg
WCELL Name (All) Batch 4th Batch
Sum of RRC_CONN_STP_FAIL_AC
Date
In case the PrxAlpha tuning does not reduce the AC rejections then
the PrxTarget can be increased to reduce the AC rejections
Typically just 2dB increase provides significant reduction on the AC
rejections
Starting 16 June 2007  PtxTarget
modified 4dB -> 6dB
Starting 16 June 2007  PtxTarget
modified 4dB -> 6dB

For internal use
PrxTarget – Recommended Values
First the following counters should be checked
– The above should be compared with the parameter value PrxNoise (WCEL)
– Max(RNC_177b, PrxNoise) = A
• M1000C0 AVE_PRXTOT_CLASS_0, M1000C1 PRXTOT_DENOM_0

For internal use
PrxTarget – Recommended Values
First the following counters should be checked
• The PrxTotal distribution should be calculated from above and the needed
PrxTarget distribution and average
– Average needed PrxTarget; A – RNC101b
– Distribution can be calculated the same way A-AVE_PRXTOT_CLASS_X and the %
of samples for each class PRXTOT_DENOM_X/(PRXTOT_DENOM_1+
PRXTOT_DENOM_2+ PRXTOT_DENOM_3+ PRXTOT_DENOM_4+
PRXTOT_DENOM_5)
• Then the PrxTarget parameter tuning should be performed in steps of 2dB
towards the highest calculated PrxTotal value
• Max PrxTarget value should not exceed 10dB (in normal conditions without any
special interferer)

For internal use
PrxTarget – KPIs and Analysis
When the PrxTarget is modified following KPIs should be monitored
• RNC_94d: RRC Setup and Access Complete Ratio from network point of view
(RAS05)

63077585 idle-mode-parameter-optimization

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