3G RANOP 1
Module 5 –Inter System Handover (ISHO) Optimisation
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Presentation / Author / Date
Module 6 – Inter System Handover Optimisation
Objectives
• Review the 3G <> 2G Cell re-selection process and
parameters
• Understand the key areas of optimisation for 3G <> 2G
Cell re-selection process
• Review the Handover Process & Compressed Mode
• Understand 3G ISHO Service Optimisation (AMR and PS
Data)
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ISHO Optimisation - Agenda
• 3G <> 2G Cell Re-selection Process
• 3G <> 2G Cell Re-selection Analysis
• Handover Process & Compressed Mode
• 3G ISHO Analysis
• 3G ISHO Service Optimisation
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Optimisation Process- Goals
• Optimum Cell Re-selection and ISHO performance should satisfy the following
requirements;
• Optimum setting of trigger thresholds to;
• Ensure 3G<>2G transitions are triggered at the correct time to prevent call set
failures and call drops due to 3G coverage/interference
• Avoid unnecessary transitions and minimising associated signalling load
• Satisfy traffic management strategy (i.e maximise ‘Time on 3G’ if required)
• Ensure selection of good 2G GSM target cell in terms of radio conditions (best cell)
• Minimise time delays involved in the 3G<>2G reselection and ISHO processes
• Maximise end user experience
• Achieving optimum performance requires;
• Detailed understanding of the processes and associated parameters
• Field investigation analysis to benchmark current performance
• Trials to investigate potential changes to optimise performance
• Optimum 3G<>2G neighbour plan
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Cell Reselection 3G -> 2G Procedure
• Whilst camping in a 3G cell the UE performs intra-frequency, inter-frequency, and intersystem measurements based on the measured CPICH EcNo of the serving cell according
to the following rules:
• Serving cell parameters Sintrasearch (12dB), Sintersearch (2dB) and SsearchRAT (4dB) are
compared with Squal (CPICH Ec/No – Qqualmin (-18dB)) in S-criteria for cell reselection
• UE will measure neighbour cells depending on how parameters are set (if parameters
are not sent UE shall measure all cells)
• 1 - None (Squal > Sintrasearch )
• 2 - WCDMA intra-frequency (Sintersearch < Squal  Sintrasearch)
• 3 - WCDMA intra- and inter- frequency, no inter-RAT cells (SsearchRAT < Squal
 Sintersearch)
Sintrasearch
SintersearchSsearchRA
•
4
WCDMA
intraand
inter-frequency
and
inter-RAT
cells
(Squal
 SsearchRAT )
In T-Mobile UK network UE starts
T
measuring 2G cells when Ec/Io ≤ 14dB
4
3
2
1
WCDMA
CELL
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Cell Reselection 3G -> 2G Procedure
CPICH EcNo
UE starts GSM measurements if
CPICH Ec/No < qQualMin + sSearchRAT
SintraSearch
First ranking of all the cells based on
CPICH RSCP (WCDMA) and RSSI (GSM)
SinterSearch
Rs = CPICH RSCP + Qhyst1(4dB)
Rn= Rxlev(n) - Qoffset1(14dB)
SsearchRAT
Serving WCDMA cell
calculation, with
hysteresis parameter
Neighbour WCDMA or GSM
cell calculation with offset
parameter
qQualMin
No
Yes
Rn (GSM) > Rs (WCDMA)
And
Rxlev (GSM) >QrxlevMin (-111dBm)
Second ranking (R criteria) only for
WCDMA cells based on CPICH Ec/No
Rs = CPICH Ec/No + Qhyst2
Rn=CPICH_Ec/No(n)-Qoffset2
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Cell re-selection
to GSM
Cell re-selection to
WCDMA cell of highest
R value
Cell Reselection 3G -> 2G
• Optimum setting of 3G>2G cell reselection triggers depends on:
• Designed utilisation targets for the 3G network (Time on 3G)
• Desired Call Set-up Success Rate (CSSR)
• Minimising the possibility of ping – pong
Call Setup status statistics for each Ec/No range
• As long as the Ec/No is >-12…14dB the CSSR is excellent
100%
90%
80%
70%
[%]
60%
qQualMin + sSearchRAT ~ -14dB
50%
40%
30%
20%
10%
0%
> -4
7
-4 to -
-6 to -
-8 to -
6
8
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-10 to
-12 to
-12
-14
Ec/No [dB]
-14 to
-16 to
-18 to
-16
-18
-21
Presentation / Author / Date
<-21
• To define optimum re-selection
thresholds it is important to
understand Ec/Io and RSCP
performance profiles for T-Mobile UK
network
• Bin sizes important
Cell Reselection 3G -> 2G
In urban area the mapping has been
found as:
-14dB Ec/No -> ~-102dBm RSCP
Dense Urban Area
Call Setup status statistics for each RSCP range
100%
90%
80%
70%
[%]
60%
50%
40%
30%
20%
10%
0%
> -60
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-60 to 70
-70 to 80
-80 to - -90 to - -100 to - -112 to 90
100
112
115
Ec/No [dB]
< -115
Cell Reselection 3G -> 2G
• Due to very different fading conditions, it may be necessary to consider different
parameter sets for 3G -> 2G reselection in different scenarios;
• 3G border
• Outdoor, typical outdoor to dedicated indoor (in case of missing 3G indoor)
Ec/No (dB)
RSCP (dBm)
• Special indoor cases without dedicated 3G where the UE speed is high (e.g.
tunnels)
• For example in 3G border
0
-4
-20
coverage environment the
-6
-40
-8
EcNo level can be seen to
-10
-60
-12
drop much faster
-80
-14
-100
compared to RSCP
-16
-120
-18
-20
Time
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Presentation / Author / Date
14:19:28.093
14:18:52.091
14:18:16.090
14:17:41.099
14:17:05.098
14:16:30.097
14:15:55.097
14:15:20.097
14:14:52.867
-140
Cell Reselection 2G -> 3G
Compare levels
of all GSM cells
to WCDMA
neighbour
Check quality
of neighbour
WCDMA cells, no
priorities between
WCDMA
neighbours
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UE starts WCDMA measurements if Rxlev
running average (RLA_C) is below or above
certain threshold:
RLA_C  Qsearch_I and Qsearch_P (GPRS)
UE can select WCDMA cell if the level of the
serving GSM and non-serving GSM cells has been
exceeded by certain offset for a period of 5 s:
CPICH RSCP > RLA_C +
FDD_Cell_Reselect_Offset
UE will re-select WCDMA cell in case it's
quality is acceptable:
CPICH Ec/No  Minimum_FDD_Threshold
Presentation / Author / Date
05.08:This may take up to 30s
Check levels every 5s
from serving GSM cell
and best 6 GSM
neighbour cells
Cell Reselection 2G -> 3G
• Re-selection measurements are controlled by parameter threshold to search WCDMA
RAN cells (QSRI)
• This parameter defines a threshold and also indicates whether these measurements
are performed when RLA_C (a running average of received signal level) of the
serving GSM cell is below or above the threshold
• In GSM the UE is usually set to measure the 3G neighbours all the time i.e. Qsearch_I and
Qsearch_P are both set to 7
UE starts WCDMA measurements if Rxlev
running average (RLA_C) is below or above
certain threshold:
RLA_C  Qsearch_I and Qsearch_P (GPRS)
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Cell Reselection 2G -> 3G
• For the the camping in indoor environment the set-up could be :
• Indoor GSM / Outdoor GSM (serving indoor)-> Indoor WCDMA / Outdoor
WCDMA (serving indoor)
• Mobile station measuring WCDMA neighbor only when it is well inside the
building using parameter Threshold to search WCDMA RAN Cells
• The defined set-up can be also used in outdoor environment to push the UEs to
3G as soon as possible from the 2G cell to the border 3G cell
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How to avoid ping-pong ?
• As a general rule the value for FDD_Qmin parameter can be set to –11…-12 dB
(i.e. for the case where the QqualMin +Ssearch_RAT = -14dB)
CPICH Ec/No
FDD_Qmin >= QqualMin + Ssearch_RAT
UE will re-select WCDMA cell in case it's
quality is acceptable:
CPICH Ec/No  Minimum_FDD_Threshold
FDD_Qmin >=-12
QqualMin + Ssearch_RAT
= -14dB
QqualMin = -18dB
t
Camping in 3G
Camping in 2G
Camping in 3G
• The “rule” to set the FDD_Qmin value
has not been possible to be fulfilled until
the specification change (05.08 v8.18.0,
2003-8) has been implemented to the
UEs – as below
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Fdd_Qmin mapping
Aif parameter
0 1 2 3 4 5 6 7
Fdd_Qmin (old) [dB] -20 -19 -18 -17 -16 -15 -14 -13
Fdd_Qmin (new) [dB] -20 -6 -18 -8 -16 -10 -14 -12
ISHO Optimisation - Agenda
• 3G <> 2G Cell Re-selection
• 3G<>2G Neighbour Plan Design Guidelines
• Handover Process & Compressed Mode
• 3G ISHO Analysis
• 3G ISHO Service Optimisation (AMR and PS Data)
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Inter-System Neighbours – Design Guidelines
• Principles for 3G2G neighbour relations
• Neighbouring plan should be kept as simple as possible
• The best neighbours at each point of the 3G coverage border should be in
the list of adjacencies.
• If a 2G layer has a strong interference situation (tight frequency re-use),
layers with less interference could be preferred
• If a 2G layer has high blocking probability, layers with less traffic could be
preferred
• Avoid 2G neighbour lists containing multiple instances of the same RF carrier
• Ensure 2G neighbour plan maximises reuse between cells on same BCCHBSIC combination
• Principles for 2G3G neighbour relations
• The overlapping 3G cell should be in the list of adjacencies of all underlying
2G cells
• If the list of overlapping cells includes more than 32 GSM cells, it has to be
shortened
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Multiple Instances of same RF Carrier in 2G Neighbour
List
• Dropped in 3G PS ISHO.
• 9 Compressed Mode Activated, but no HO Command.
• During each phase of CM, RNC selects BCCH1 (2 GSM cells in ncell list BCCH1
BSIC29 & BCCH1 BSIC5) and asks UE to verify BSIC, but never receives MR
with the BSIC reported.
1f SC332
EcNo=-13dB,
RSCP=113dBm.
MC to verified the BSIC.
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2G Coverage
3G-2G Adjacencies – Design Guidelines
Co-Azimuthed:
N3G = N2G + Cell2G
3G
2G
Co-Sited, Not Co-Azimuthed:
N3G = N2GCell1 п N2GCell2 + Cell12G + Cell22G
3G
2G
Not Co-Sited, Not Co-Aziluthed:
Manual Design
3G
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2G
Presentation / Author / Date
Inter-System Neighbours – Design Guidelines
• 2G->3G: Max # of IS Neighbours per 2G cell (ADJW):
• Max number of 3G neighbours= 32
• However in Nokia implementation to allow the SI2 message in only one BCCH block
the 3G neighbours list size should be limited to 10 neighbours.
• 3G->2G: Max # of IS Neighbours per 3G cell (ADJG):
• Max number of 2G neighbours= 32
• Minimize the number of 2G neighbours to improve the performances Nokia suggest to
limit the number of 2G neighbours to 16 when possible
• If too many adjacencies are declared the cell will go blocked by system with alarm:
• 7761 RNW O/M SCENARIO FAILURE (BCCH scheduling error) in RN1.5.2ED2
• 7771 WCDMA CELL OUT OF USE (BCCH scheduling error) in RN2.0
• Nokia RNC software Technical Note 46 specifies Restriction on number of cells in
SIB11/12 message for 47 neighboring cells (worst case)
• On one hand the SIB type 11 and 12 messages can contain information on the
maximum of 96 cells (32 intra-frequency cells, 32 inter-frequency cells and 32 GSM
cells), but on the other hand the physical size of SIB data (no more than 3552 bits)
has capacity only for 47 neighboring cells.
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ISHO Optimisation - Agenda
• 3G <> 2G Cell Re-selection
• Neighbour planning
• Handover Process & Compressed Mode
• 3G ISHO Analysis
• 3G ISHO Service Optimisation (AMR and PS Data)
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Inter System Handover 3G -> 2G Procedure
Handover Triggering Thresholds set in
RNC
Event Triggered Coverage/Capacity
based HO fulfilled in RNC
RNC commands the UE to start
IS measurements periodically
Measurements are done in
Compressed Mode (CM)
RSSI measurements and
verification for GSM cells
UE reports best GSM cells having
strongest RSSI results back to RNC
RNC makes HO decision and
commands UE to target cell
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!
• Currently ISHO measurements can be triggered
for 5 different reasons
• To measure GSM frequencies, 3G UE needs
(a) dual receiver or (b) Compressed Mode
capability
• Most UEs currently use CM to ‘create’ gap
during which BCCH frequencies on the 2G
network can be measured
• CM introduces a delay which depends on the
measurement reason and pattern used
• Two types of CM measurements; GSM RSSI &
GSM BSIC verification
• Methods for implementing CM are (i) High
Layer Scheduling (HLS), (ii) Spreading Factor
Halving (SF/2) and (iii) Puncturing
• Handover decision driven by RNC using
measurements made by UE
• Compressed Mode affects 3G coverage,
capacity and quality
Inter System Handover 3G -> 2G Procedure
Configured UE measurements
RAN Internal measurements
Downlink DPCH power
UL Quality
deterioration
UE Tx power
Initiate Compressed Mode
Configure GSM measurements
UE Reports
GSM RSSI measurements
GSM cell
meets HO condition ?
No
Yes
Is BSCI verification
required for PS call ?
No
Yes
Initiate Compressed Mode
Configure GSM measurements
UE Reports
GSM BSIC measurements
Initiate Handover
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CPICH RSCP
CPICH Ec/I0
ISHO 3G -> 2G - AMR Signalling Flow
Node
B
UE
RRC: Measurement Report
RNC
RRC: Measurement
Control
NBAP: Radio Link Reconfiguration
NBAP: Radio Link Reconfiguration Prepare
Ready
RRC: Physical Channel Reconfiguration
Complete
RRC: Measurement Report
RRC: Measurement Report
NBAP: Radio Link Reconfiguration
Commit
RRC: Physical Channel
CN
ISHO triggering (5
reasons are
possible)
Initial Compressed
Mode
Configuration
Reconfiguration
NBAP: Compressed Mode
Command
RRC: Measurement
Control
NBAP: Compressed Mode
Command
RRC: Measurement
Control
GSM RSSI
Measureme
nt
GSM BSIC
Identification
RANAP: Relocation
Required
RRC: Handover from UTRAN
Command
RANAP: Relocation
Command
RANAP: IU Release
Command
RANAP: IU Release
Complete
• BSIC verification always performed for AMR calls – no interrupt in voice call
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ISHO 3G -> 2G - PS Signalling Flow
U
E
Node
B
RRC: Measurement Report
CN
RNC
RRC: Measurement
Control
ISHO triggering (5 reasons are
possible)
NBAP: Radio Link Reconf iguration Prepare
NBAP: Radio Link Reconf iguration Ready
NBAP: Radio Link Reconf iguration Commit
Initial Compressed
Mode Configuration
RRC: Physical Channel Reconf iguration
RRC: Physical Channel Reconf iguration
Complete
NBAP: Compressed Mode Command
RRC: Measurement Control
GSM RSSI Measurement
RRC: Measurement Report
RRC: Cell Change Order f rom UTRAN
RANAP: SRNS Context Request
RANAP: SRNS Context Response
RANAP: SRNS Data Forward Command
RANAP: IU Release
Command
RANAP: IU Release
Complete
• In most cases BSIC verification is not required (data interrupt as UE moves to 2G)
• PS makes use of RRC: CELL CHANGE ORDER FROM UTRAN message
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Compressed Mode
Procedure
RNC commands the selected
UEs to enter compressed mode
and provides compressed mode
parameters and neighbour list
During the DL reception gap UE
can make measurements from 2G
network
UE measures RSSI of GSM
neighbours and reports these to
RNC periodically
RNC commands UE to decode
BSIC of cell with strongest RSSI
• RNC informs UE of CM pattern and 2G neighbour list in RRC:
Measurement Control message
• 3GPP states that the UE must be capable of recording a
minimum number of GSM RSSI measurement samples per
transmission gap
• GSM RSSI measurements are made without acquiring GSM
synchronisation
• UE reports on strongest 6 GSM neighbours at periodic
interval defined by GSMMeasRepInterval
• RNC applies a sliding averaging window to the
measurements provided by the UE
• RNC instructs UE to perform BSIC verification (AMR=always,
PS=as required) using new CM pattern
• BSIC verification needs synchronisation to GSM frame
RNC makes HO decision
IS-HO trigger
RNC sends handover command
to UE
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WCDMA
RSSI
measurements
T RSSI
IS-HO
command
Target Cell found
BSIC verification
T BSIC
!
Compressed Mode Method
• Single frame approach (used in
spreading factor halving and HLS
½ data rate)
• Double frame approach (used in
puncturing and HLS ¾ data rate)
• Compressed mode Methods used in Nokia
CM Method
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AMR Speech
SF/2
Presentation / Author / Date
RT Data
SF/2
NRT Data
½ or ¾ Rate HLS
Other Relevant CM Parameters
• Compressed mode can be enabled/disabled on a per RNC basis using CMmasterSwitch
parameter
• The maximum number of UE allowed to be in compressed mode simultaneously can be
limited using the MaxNumbUECMcoverHO parameter
• PrxTarget, PrxOffset, PtxTarget and PtxOffset are also used when making the decision
whether or not a UE is allowed to apply compressed mode
• If the cell exceeds Prx/txTarget then one more UE may apply compressed mode during
that radio resource indication period
• If the cell exceeds Prx/txTarget + Prx/txOffset then no more UE may apply compressed
mode during that radio resource indication period
Scope
Configurable
Nokia Range
Default/T-Mobile UK
RNC
Yes
0 (false), 1 (true)
1
MaxNumbUECMcoverHO
WCEL
Yes
0 to 255
16
PrxTarget
WCEL
Yes
0 to 30 dB
4 dB
PrxOffset
WCEL
Yes
0 to 6 dB
1 dB
PtxTarget
WCEL
Yes
-10 to 50 dBm
40 dBm
PtxOffset
WCEL
Yes
0 to 6 dB
CMmasterSwitch
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1 dB
ISHO Optimisation - Agenda
• 3G <> 2G Cell Re-selection
• Handover Process & Compressed Mode
• 3G<>2G neighbour Plan Verification
• 3G ISHO Analysis
• 3G ISHO Service Optimisation (AMR and PS Data)
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3G ISHO Analysis Overview
• 3G ISHO performance should be analysed from;
• Drive Test Data
• Network Statistics
to obtain an overall picture of ISHO performance
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ISHO Analysis from Drive Test
Data
• Drive Test Analysis should deliver ISHO performance metrics
such as;
• Number of ISHO attempts
• ISHO & Compressed Mode Success Rate
• Trigger reasons
• Failure Causes
• ISHO Times and Interrupt Delays
• Number of CM cycles needed
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ISHO Analysis from Drive Test
Data
Need to analyse each ISHO
attempt to determine;
• Whether it was a necessary ISHO
• What the trigger mechanism was
(helps determine whether trigger
thresholds are set correctly)
• Whether the ISHO was successful
and if not the failure cause (e.g. No
cell found, UE failed BSIC
verification, UE didn’t receive
HandoverFromUTRANCommand)
• ISHO Success Rates
• Process needs to be automated
within the drive test postprocessing tool(s)
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PS ISHO Failure Analysis - Example
13%
7%
33%
Network does not isse 'Cell Change Order'
UE responds to 'Cell Change Order' with a 'Failure'
UE does not react to the 'Cell Change Order'
7%
UE does not report any GSM RSSI measurements
UE does not receive the CM 'Measurement Control'
7%
UE fails BSIC verification
33%
• Generating an ISHO Failure Breakdown enables areas for further
optimisation to be identified
• May require further troubleshooting with data logging, RNC counters etc. to
determine root cause of failure
• Analysis should be performed for each service (i.e. AMR, PS etc.)
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Example PS ISHO Failure Analysis
• 78 % of the failures occur after the UE has completed a 2G cell re-selection.
100 % of these 2G cell re-selections was onto a 2G cell which was not in the
3G system neighbour list
• The 2G neighbour lists thus appear to have missing neighbours which
subsequently result in a 2G cell re-selection and a slowing down of the intersystem handover procedure
• This failure scenario could be used to refine the 3G system inter-RAT
neighbour lists during the post processing and analysis of any drive test data
0%
22%
22%
UE does not read any 2G sys info
UE reads 2G sys info but does not send RACH (no cell resel)
0%
UE reads 2G sys info and sends RACH but does not est.
connection (no cell re-sel)
UE reads 2G sys info and completes 2G cell re-sel but
does not send RACH
UE reads 2G sys info and completes 2G cell re-sel and
sends RACH but does not est. connection
56%
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ISHO Failure - No Cell Found Failure Example
Compressed Mode started
Tstart = 17:22:41.7
MW = 12 s
Tstop = 17:22:53.7
Compressed Mode stopped
GsmMaxMeasPeriod x GsmMeasRepInterval = 12s
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ISHO Failure - No Cell Found Failure Example
RxLev = -110 + 4 = -106 dBm
AdjgRxLevMinHO = -104 dBm
POOR GSM
COVERAGE
4
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Presentation / Author / Date
No suitable cell
ISHO Failure - UE receives
iuv_relocation_prep_fail
• GSM BSIC verification is achieved and
RNC sends iuv_relocation_required
message with the target CI, LAC but
receives an iuv_relocation_prep_fail
message back from the CN
• Failure due to data build error in 2G MSC
• In this failure case no
HandoverFromUTRANcommand is
observed
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Analysing ISHO Delay
• ISHO delay ultimately impacts overall ISHO performance > longer the delay,
greater chance of ISHO failing
• Performance impact greater on PS calls (throughput reduction)
• ISHO delay is affected by;
• RNC databuild – 2G neighbour lists provided to UE must be optimum.
The longer the list the longer it takes UE to complete RSSI
measurements
• Radio Plan - Areas of excessive interference will hinder UE’s ability to
decode BSIC and registration procedure
• System design - Implementation of Gs interface enables faster
‘combined’ LAU/RAU registration procedure, rate of broadcasting
IS-HO
IS-HO trigger
system information messages,
e.g. SI13 Target Cell found
command
WCDMA
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RSSI
measurements
T RSSI
BSIC verification
T BSIC
ISHO delay, AMR
UE
RNC
ISHO triggered: Event 6A/1F/
RRC: Measurement Control (IE tgmp=GSM
RSSI)
RRC: Measurement Report
Total Delay
Ta
Trssi
RRC: Measurement Control (IE tgmp=GSM
BSIC)
RRC: Measurement report: BSIC no. decoded
.
.
.
RRC: Measurement report : BSIC decoded
Handover from UTRAN
TBSIC
Thandover
• Measurements taken from Nokia
test network (predominantly
suburban environment) – averaged
over a large number of calls
• BSIC verification process has the
greatest impact on AMR CM delay
• Little scope for reducing this delay
as BSIC verification always required
– but delay in AMR of less
importance as there is no service
gap to user with AMR calls during
CM
4.5
5
Ta= activation time
© Nokia Siemens Networks
Trssi
3
Trssi= RSSI delay time. By default, the
network only requires the first RSSI
measurements to choose the best GSM
TBSIC=target
Time cell.
for UE to decode the BSIC of the
chosen cell
37
Ta
4
Presentation / Author / Date
2
1
0
2.0
1
Tbsic
1.3
Thandover
0.2
Total delay
ISHO delay, PS
UE
• PS ISHO introduces service affecting
data interrupt (i.e. throughput reduction)
RNC
• In most cases PS calls do not require
BSIC verification during ISHO process
ISHO triggered: Event 6A/1F/
RRC: Measurement control (IE
TGMP=”GSM RSSI”)
RRC: Measurement report
Ta
Trssi
RRC: Cell change Order from UTRAN
• BSIC verification required when 2G
neighbour list contains multiple cells on
same frequency as the ‘best’ RF carrier
chosen by the RNC
• Need to avoid the need for BSIC
verification where ever possible
Tactivation
3
2.5
activation time
Trssi= RSSI delay time. By default, the network only
requires the first RSSI measurements to choose
the best GSM target cell.
seconds
Ta=
1.5
1
0
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Presentation / Author / Date
Trssi
Total
2
0.5
38
2.6
1.4
1.2
Impact of 2G Neighbour List Length
on TRSSI
• UE measures all GSM carriers indicated in the Measurement Control message prior to
sending Measurement Report to RNC
• If UE is not able to measure all GSM carriers within the measurement period it sends
an ‘empty’ Measurement Report
• Once UE has measured all 2G carriers (L1) it reports these measurements to L3 which
reports the top 6 strongest to RNC in Measurement Report
• Tests made with Nokia 7600 UE
• The general trend is that the GSM
RSSI measurement delay increases
as the length of the 2G neighbour list
increases. There is however quite a
large scatter
Number of GSM Neighbours
• In general GSM RSSI measurement delay increases as the length of the 2G neighbour
list increases. There is however quite a large
scatter
35
30
25
20
15
10
5
0
0.0
1.0
2.0
3.0
4.0
5.0
Delay to the first GSM RSSI Measurement (seconds)
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Presentation / Author / Date
6.0
CM Throughput Reduction – HLS
Example
• Throughput will be affected by;
• method of CM used (e.g. HLS)
• poor coverage requiring additional re-transmisisons
• Once UE has been instructed to move to 2G throughput drops to zero until UE
has registered (LAU and RAU) on the 2G network
Throughput
Average = 121 kbps
HLS starts
• Example measurements from the
HLS method applied to the PS data
service
• 7 slot transmission gap
Average = 71 kbps
• Single frame approach
• 4 frame transmission gap pattern
length
Time•
Throughput reductions
• 64 kbps service: 55 to 15 kbps
• 128 kbps service: 121 to 71 kbps
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© Nokia Siemens Networks
Presentation / Author / Date
ISHO Analysis from Network
Statistics
• ISHO counters are found in the Inter-system hard handover measurement table
(M1010Cxx)
• The inter-system handover measurement is carried out in the serving RNC
(SRNC)
• The object of the measurement is the source cell from which the handover is
attempted.
• In case of multiple cells in the AS the object of the measurement is the best cell
of the Active Set during the handover decision (except for
IS_COM_MOD_STA_NOT_POS_(N)RT) where the object is the best active
set cell during the compressed mode preparation phase
• From the measurement point of view the ISHO is divided into two phases:
• Inter-system measurement
• Inter-system handover
41
• Separate
counters
for RT and NRT services
© Nokia Siemens Networks
Presentation / Author / Date
Counters for Triggering
Reasons
If compressed mode can NOT start (before sending
Measurement Control to UE) the following counter is
incremented:
RNC
RRC: Measurement Report
IS_COM_MOD_STA_NOT_POS_(N)RT
The counter is updated when:
RRC: Measurement Control
CHECK TRAFFIC TABLE
COUNTERS
- Admission Control rejects compressed mode request
- Compressed mode can not start due to radio link (or
physical channel) reconfiguration failure (BTS or UE
reasons)
These counters are not
incremented in this
phase but they are
incremented
After RxLev/BSIC
verification phase
together with the
ATTEMPT or NO CELL
FOUND counters
- ISHO is a parallel procedure (especially NRT)
If compressed mode can start the following counters are
incremented:
IS_HHO_W_CMOD_UL_DCH_Q_(N)RT
IS_HHO_W_CMOD_UE_TX_PWR_(N)RT
IS_HHO_W_CMOD_DL_DPCH_(N)RT
Compressed
Mode start
IS_HHO_W_CMOD_CPICH_RSCP_(N)RT
ALSO COUNTERS
FOR ISHO START
WITHOUT
COMPRESSED MODE
EXIST (DUAL
RECEIVER)
IS_HHO_WO_CMOD_
XXX
The counters
are updated
in the best cell of the active set
IS_HHO_W_CMOD_
CPICH_ECNO_(N)RT
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© Nokia Siemens Networks
Presentation / Author / Date
Counters for measurement procedure failure
RNC
If the RNC does not find a suitable cell, one of the following
counters are updated:
IS_HHO_NO_CELL_UL_DCH_Q_(N)RT
IS_HHO_NO_CELL_UE_TX_PWR_(N)RT
IS_HHO_NO_CELL_DL_DPCH_(N)RT
IS_HHO_NO_CELL_CPICH_RSCP_(N)RT
IS_HHO_NO_CELL_CPICH_ECNO_(N)RT
RRC: ”Measurement report”
(3,4,5)
RRC: ”Measurement Control”
RRC: ”Measurement report”
RRC: ”Measurement report”
These counters are updated when either:
• No suitable GSM target cell is found in terms of RSSI
(RxLev)
RRC: ”Measurement report”
• Target cell is suitable (RSSI) but BSIC verification fails
And;
Maximum number of measurement reports have been
Triggered in the referncereceived
cell when:
1) GsmMaxMeasPeriod measurement reports are received with an rx level
not suitable
2) GsmMaxMeasPeriod measurement reports are received with a BSIC not
verified
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Compressed Mode Stopped – Case 1
RNC does receive GsmMaxMeasPeriod ISHO Measurement Reports (meas id = 3)
before the above max_meas_interval time window expires.
-Stop RxLev measurement
-Start BSIC verification phase
-GsmMaxMeasPeriod = 12
13 Measurement Reports:
-GsmMeasRepInterval = 0.5s
-12 with measurementIdentity = 3
-max_meas_interval = (12+4)/2 = 8s
-1 with measurementIdentity =5 (1f EcNo)
meas_interval < 8 s
-Stop BSIC verification phase
(GsmMaxMeasPeriod msg with
measurementIdentity = 3 received
before the max_meas_interval time
window expires)
IS_HHO_W_CMOD_DL_DPCH_RT = +1
IS_HHO_NO_CELL_DL_DPCH_RT = +1
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Counters for ISHO Attempt for RT
If the RNC has found a suitable cell (both RxLev
and BSIC phases), one of the following counters
are updated:
RNC
RRC: ”Measurement report”
(3,4,5)
IS_HHO_ATT_UL_DCH_Q_RT
IS_HHO_ATT_UE_TX_PWR_RT
IS_HHO_ATT_DL_DPCH_PWR_RT
IS_HHO_ATT_CPICH_RSCP_RT
IS_HHO_ATT_CPICH_ECNO_RT
RRC: ”Measurement Control”
RRC: ”Measurement report”
RRC: ”Measurement report”
BSIC verif.
The counters are triggered when the RNC sends
the RANAP: RELOCATION REQUIRED
message to the MSC
MSC
X
Only the SRNC can update the counters.
RELOCATION REQUIRED
RRC: ”Measurement report”
HHO Attempt
Counters
RxLev
meas.
The counters are updated in the best cell of the active set
45
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Presentation / Author / Date
Counters for ISHO Attempt for NRT
If the RNC has found a suitable cell (most
likely only RxLev), one of the following
counters are updated:
RNC
RRC: ”Measurement report”
(3,4,5)
RRC: ”Measurement Control”
RRC: ”Measurement report”
RRC: ”Measurement report”
RxLev
meas.
BSIC
verification only
in case 2 ADJG
with same
BCCH
RRC: ”Measurement report”
CELL CHANGE ORDER
X
HHO Attempt
Counters
IS_HHO_ATT_UL_DCH_Q_NRT
IS_HHO_ATT_UE_TX_PWR_NRT
IS_HHO_ATT_DL_DPCH_PWR_NRT
IS_HHO_ATT_CPICH_RSCP_NRT
IS_HHO_ATT_CPICH_ECNO_NRT
The counters are triggered when the RNC
sends the RRC: CELL CHANGE ORDER
FROM UTRAN message to the UE.
Only the SRNC can update the counters.
The counters are updated in the best cell of the active set
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KPI for ISHO measurement procedure
No Cell Found
Counters
Max measurement interval
not expiring
Compressed
Mode start
CM measurement is not
interrupted
HHO Attempt
Counters
Max measurement interval
expiring OR
It’s not possible to monitor cases like:
1) the UE does not send some
measurement reports
2) Drop during measurement
3) parallel procedure (e.g capacity
request for NRT)
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© Nokia Siemens Networks
ISHO _ Meas _ Fail _ Rate 
It’s not possible to distinguish
between failures in the RxLev
measurement or in the BSIC
verification
 IS _ HHO _ NO _ CELL _ xxx _( N ) RT
 IS _ HHO _ W _ CMOD _ xxx _( N ) RT   IS _ HHO _ WO _ CMOD _ xxx _( N ) RT
Allcauses
Allcauses
KPI is useful for cell
level
Presentation / Author / Date
… measurement not
fail
NO counters
triggering
CM measurement is
interrupted
Accuracy in
GSM neighbour
planning
… measurement fail
Allcauses
Call Duration and ISHO procedure triggered
• Monitoring how often ISHO procedure is started  ISHO Triggering threshold tuning
AVG_RAB_HL D_TM_CS_VOICE/ 6000
 IS_HHO_CMOD_RT  IS_COM_MOD_STA_NOT_POS_RT
Minutes_per_ISHO_procedure_RT 
Allcauses, with& withoutCM
• The KPI on cell level does not take into account user mobility. It does make sense on
cluster/RNC level only
• The KPI can help operators in understanding the ISHO strategy
• Same KPI for NRT
(AVG_DCH_HLD_TM_PS_INTER+AVG_DCH_HLD_TM_PS_BACKG at numerator)
• Service level counter at denominator shall be used because allocation duration
counters (Traffic table) incremented in all the cells within Active Set
• Accuracy of the Indicator affected by:
• the number of ISHO procedures which have no ISHO counter incremented (e.g. drop during
CM, see previous slide)
• number of not successful ISHO procedures during the same call due to e.g. wrong ADJ
parameter, rough mobiles etc.
KPI is useful for cluster level and
cell level as well
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Presentation / Author / Date
ISHO Attempt UTRAN Failure RT
RNC
RRC: ”Measurement report”
(3,4,5)
When the UTRAN is not able to execute an Inter-System
Handover the following counter is triggered:
UTRAN_NOT_ABLE_EXC_ISHHO_RT
RRC: ”Measurement Control”
RRC: ”Measurement report”
RRC: ”Measurement report”
RRC: ”Measurement report”
Relocation Procedure
Handover Command
UTRAN Failure
Counter
49
© Nokia Siemens Networks
The counter is triggered when the ISHO fails before the
SRNC sends the handover command to the UE, in the
same cell where the ISHO attempt has been updated:
• Relocation Preparation Failure or
• TRelocPrep (def. 6s, from Relocation Required to
Relocation Command) expires.
The failure can take place for the following reasons:
• Radio Resource congestion in the target cell
• Radio Link setup/addition failure in the BTS (IFHO)
• Failure during the Relocation preparation procedure in
the CN (for example ciphering parameter not set properly
in 3G MSC, LAC mismatching in RNC/MSC)
• Failure during the Relocation resource allocation
procedure in the target BSC
Presentation / Author / Date
KPI for ISHO Triggering Reasons
RNC
RRC: ”Measurement report”
(3,4,5)
It’s important to know which is the most frequent
triggering reason:
RRC: ”Measurement Control”
xxx _ Cause _ perc 
IS _ HHO _ W _ CMOD _ xxx _( N ) RT
 IS _ HHO _ W _ CMOD _ xxx _( N ) RT
Allcauses
It’s possible to diffentiate between quality and
coverage reasons
The triggerning
reasons must
be enabled:
GSMcause…
Understand the network limiting factors:
• CPICH coverage
• Pilot pollution
• UL/DL Service coverage
KPI is useful for cluster level and cell level as well
50
© Nokia Siemens Networks
Presentation / Author / Date
ISHO UE Failure RT and NRT
RNC
RRC: ”Measurement report”
(3,4,5)
RRC: ”Measurement Control”
RRC: ”Measurement report”
RRC: ”Measurement report”
RRC: ”Measurement report”
When the UE is not able to execute an Inter-System
Handover the following counter is triggered:
UE_NOT_ABLE_EXC_ISHHO_(N)RT
The counter is triggered when the source RNC receives a
failure message from the mobile with the failure cause
“configuration unacceptable”.
The counter is triggered in the same cell where the ISHO
attempt has been updated.
HANDOVER FROM UTRAN
CELL CHANGE ORDER FROM UTRAN
x
HANDOVER FROM UTRAN FAILURE
CELL CHANGE ORDER FROM UTRAN FAILURE
UE Failure
Counter
51
© Nokia Siemens Networks
Presentation / Author / Date
Unsuccessful ISHO RT and NRT
RNC
RRC: ”Measurement report”
(3,4,5)
RRC: ”Measurement Control”
UNSUCC_IS_HHO_UL_DCH_Q_(N)RT
UNSUCC_IS_HHO_EU_TX_PWR_(N)RT
UNSUCC_IS_HHO_DL_DPCH_PWR_(N)RT
UNSUCC_IS_HHO_CPICH_RSCP_(N)RT
UNSUCC_IS_HHO_CPICH_ECNO_(N)RT
RRC: ”Measurement report”
RRC: ”Measurement report”
The counter is triggered in the same cell where the ISHO
attempt has been updated.
RRC: ”Measurement report”
Handover Command
Cell Change Order (PS)
Handover Failure
Cell Change Failure
ISHO Unsuccess
Counters
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© Nokia Siemens Networks
When the RNC receives a failure message from the mobile
and the cause is not “configuration unacceptable”, one of
the following counter is triggered:
x
Reason for failure:
• Physical channel failure (the UE is not able to establish
– in the target RAT – the phy. Channel indicated in the
handover command)
• Protocol error
• Inter-Rat protocol error
• Unspecified
Presentation / Author / Date
Successful ISHO
RNC
RRC: ”Measurement report”
(3,4,5)
RRC: ”Measurement Control”
SUCC_IS_HHO_UL_DCH_Q_(N)RT
SUCC_IS_HHO_EU_TX_PWR_(N)RT
SUCC_IS_HHO_DL_DPCH_PWR_(N)RT
SUCC_IS_HHO_CPICH_RSCP_(N)RT
SUCC_IS_HHO_CPICH_ECNO_(N)RT
RRC: ”Measurement report”
RRC: ”Measurement report”
The counter is triggered in the same cell where the ISHO
attempt has been updated.
During testing the counter is updated in case of failures
(RAB Active failure for RNC internal): for RT use RAB
release due to SRNC relocation (relocation not used at the
moment)
RRC: ”Measurement report”
Handover Command
Cell Change Order (PS)
Handover Complete to BSC
ISHO Success
Counters
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© Nokia Siemens Networks
When the source RNC receives the RANAP message “IU
RELEASE COMMAND” from the core network, one of the
following counter is triggered:
CN
IU Release Command
Presentation / Author / Date
RRC Drop during ISHO RT
When the source RCC Connection drops during the
ISHO, one of the following counter is triggered:
RNC
RRC: ”Measurement report”
(3,4,5)
CON_DRPS_IS_HHO_UL_DCH_Q_RT
CON_DRPS_IS_HHO_EU_TX_PWR_RT
CON_DRPS _IS _HHO_DL_DPCH_PWR_RT
CON_DRPS _IS _HHO_CPICH_RSCP_RT
CON_DRPS _IS _HHO_CPICH_ECNO_RT
RRC: ”Measurement Control”
RRC: ”Measurement report”
RRC: ”Measurement report”
RRC: ”Measurement report”
Handover Command
CN
RRC Drop
Counters
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© Nokia Siemens Networks
IU Release Request
Presentation / Author / Date
For RT:
TRelocOverall (def. 8s, from Relocation Command to
Iu Release Command) expires.
RRC Drop during ISHO NRT
RNC
RRC: ”Measurement report”
(3,4,5)
RRC: ”Measurement Control”
RRC: ”Measurement report”
When the source RCC Connection drops during the ISHO,
one of the following counter is triggered:
CON_DRPS_IS_HHO_UL_DCH_Q_NRT
CON_DRPS_IS_HHO_EU_TX_PWR_NRT
CON_DRPS _IS _HHO_DL_DPCH_PWR_NRT
CON_DRPS _IS _HHO_CPICH_RSCP_NRT
CON_DRPS _IS _HHO_CPICH_ECNO_NRT
RRC: ”Measurement report”
RRC: ”Measurement report”
Cell Change Order (PS)
For NRT:
RRC-TmrlRCC = T309+ InterRATCellReselTmrOffset
expires
where: CN
IU Release Request
RRC Drop
Counters
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© Nokia Siemens Networks
T309 parameter = 5 s (SIB1)
InterRATCellReselTmrOffset is hidden parameter 3s
Presentation / Author / Date
KPI for ISHO Failure Rate
RNC
ISHO _ Fail _ Rate _ Over _ Att _ RT  1 
RRC: ”Measurement report”
(3,4,5)
Nbr _ Success _ RT
 IS _ HHO _ ATT _ xxx _ RT
Allcauses
RAB_ACT_REL_CS_VOICE_SRNC, SRNC Reloc/IFHO
RRC: ”Measurement Control”
Nbr_Success_RT =
RRC: ”Measurement report”
SUM(SUCC_IS_HHO_XXX_RT), SRNC Reloc/IFHO on
RRC: ”Measurement report”
ISHO _ Fail _ Rate _ Over _ Att _ NRT  1 
RRC: ”Measurement report”
Handover Command
Cell Change Order (PS)
 SUCC _ IS _ HHO _ xxx _ NRT
 IS _ HHO _ ATT _ xxx _ NRT
Allcauses
Allcauses
Overall _ ISHO _ Fail _ Rate _ NRT  1 
 SUCC _ IS _ HHO _ xxx _ NRT
Allcauses
 IS_HHO_CMOD_NRT  IS_COM_MOD_STA_NOT_POS_NRT 
Allcauses, with& withoutCM
Overall _ ISHO _ Fail _ Rate _ RT  1 
Nbr _ Success _ RT
 IS_HHO_CMOD_RT  IS_COM_MOD_STA_NOT_POS_RT 
Allcauses, with& withoutCM
KPI are useful for cluster level and cell level as
well
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© Nokia Siemens Networks
Presentation / Author / Date
ISHO Analysis from Network
Statistics
UE
Node B
CN
RNC
RRC: Measurement Control
RRC: Measurement Report
NBAP: Radio Link Reconf iguration Prepare
ISHO triggering
(5 reasons are
possible)
NBAP: Radio Link Reconf iguration Ready
NBAP: Radio Link Reconf iguration Commit
RRC: Physical Channel Reconf iguration
Initial Compressed
Mode
Configuration
RRC: Physical Channel Reconf iguration Complete
NBAP: Compressed Mode Command
RRC: Measurement Control
RRC: Measurement Report
GSM RSSI
Measurement
NBAP: Compressed Mode Command
RRC: Measurement Control
RRC: Measurement Report
GSM BSIC
Identification
RANAP: Relocation Required
RANAP: Relocation Command
RRC: Handover f rom UTRAN Command
RANAP: IU Release Command
RANAP: IU Release Complete
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ISHO Analysis from Network Statistics
UE doesn’t receive HandoverFromUTRAN Command
• ISHO success rate on Beckton3 (URKKT03) had always been poor (<80%) with
UTRAN_NOT_ABLE_EXEC_ISHO_RT the largest failure counter (>90% increments on
<6 cells)
• Similar pattern was observed across a
number of other RNCs
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Presentation / Author / Date
ISHO Analysis from Network Statistics
UE doesn’t receive HandoverFromUTRAN Command
UTRAN_NOT_ABLE_EXEC_ISHHO_RT counter
according to customer documentation
59
© Nokia Siemens Networks
Presentation / Author / Date
ISHO Analysis from Network Statistics
UE doesn’t receive HandoverFromUTRAN Command
PROCEDURE IS
STARTED.....
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Presentation / Author / Date
ISHO Analysis from Network Statistics
UE doesn’t receive HandoverFromUTRAN Command
1
2
GSM SUITABLE CELL IS FOUND
AND BSIC VERIFICATION IS
REQUIRED....
BSIC IS CORRECTLY VERIFIED....
3
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© Nokia Siemens Networks
Presentation / Author / Date
RELOCATION IS REQUIRED TO
MSC...
Timer TRelocPrep (6s) is started
ISHO Analysis from Network Statistics
UE doesn’t receive HandoverFromUTRAN Command
Timer TRelocPrep (6s)
expires
Relocation Cancel msg is
sent
to MSC.....
Note that, in the
meantime, no parallel
procedure is
allowed.....
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ISHO Optimisation - Agenda
• 3G <> 2G Cell Re-selection
• Neighbour planning
• Handover Process & Compressed Mode
• 3G ISHO Analysis
• 3G ISHO Service Optimisation (AMR and PS Data)
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Presentation / Author / Date
Inter System Handover 3G -> 2G Tuning
CPICH RSCP (Event 1F)
•Thresholds:
HHoRscpThreshold
HHoRscpCancel
L3 filter: HHoRscpFilterCoefficient
•Timers:
HHoRscpTimeHysteresis
HHoRscpCancelTime
UE Tx Power (Event 6A)
•Threshold:
GsmUETxPwrThrXX
•L3 filter:
GsmUETxPwrFilterCoeff
•Hysteresis margin:
GsmUETxPwrTimeHyst
•Data rate threshold
HHOMAxAllowedBitrateUL
DL DPCH power
•Threshold:
GsmDLTxPwrThrXX
•Data rate threshold
HHOMAxAllowedBitrateDL
2. GSM measurement reporting
GsmMeasRepInterval
GsmNcellSearchPeriod
GsmMinMeasInterval
GsmMaxMeasPeriod
CPICH Ec/Io (Event 1F)
•Thresholds:
HHoEcNoThreshold
HHoEcNoCancel
•L3 filter:
EcNofilterCoefficient
•Timers:
HHoEcNoTimeHysteresis
HHoEcNoCancelTime
UL Quality
•Timer:
ULQualDetRepThreshold
•Data rate threshold
HHOMAxAllowedBitrateUL
(XX=AMR,CS,NrtPS,RtPS)
3. Decision Algorithm
AdjgTxPwrMaxTCH
AdjgRxLevMinHO (n)
GsmMeasAveWindow
1.
Triggering
2.
GSM measuring
3.
Decision
Handover Execution
2G-to-3G back prevention
GsmMinHoInterval
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© Nokia Siemens Networks
Presentation / Author / Date
Inter System Handover 3G -> 2G Tuning
The IS-HO process consists of several independent sub-processes. Therefore the
optimisation can be applied to each sub-process individually:
1. Triggering process:
• Parameters that belong to this process defines the starting of the GSM measurements:
filters, hysteresis, timers and thresholds
2. GSM Measurement reporting process
• Following parameters control the reporting of the GSM measurements
•
GsmMinMeasInterval: Establish minimum time between successive GSM
measurements
•
GsmMaxMeasPeriod: Maximum duration of the GSM measurements in CM
•
GsmMeasRepInterval: Reporting period of the GSM measurements during CM
3. Decision process:
• Parameters that participate in the selection of the best target cell:
•
AdjgRxLevMinHO(n): Minimum RX level of the GSM cell to do handover
4. ISHO cancellation parameters:
• Cancellation parameters are built for CPICH EcNO and CPICH RSCP triggering
functionality only
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ISHO Triggering Process
• Each triggering procedure makes use of filters, hysteresis and thresholds which
are used to control the inter-system handover behaviour
• The purpose of the hysteresis and filters is to improve the accuracy of the
measurements
• The purpose of the thresholds is to control 3G boundary of the different
services
• Each 3G cell had in average 4 GSM neighbour cells.
• By modifying the network configuration (blocking of cells etc), the radio conditions
in each route was aconditioned so that the need for an inter-system handover
was due to the triggering condition studied
• For example, when the UE Tx power trigger was studied, the radio
conditions along the routes were modified so that the uplink path was the
critical one, in this way the IS-HO performance was not affected by other
reasons e.g. poor CPICH EcNo
• During the tests the following traces were recorded:
-The coordinates where the CM starts
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Presentation / Author / Date
-Unsuccessful/successful
ISHO events
© Nokia Siemens Networks
ISHO Triggering Process – Ec/Io Threshold
Different CPICH EcNo thresholds were used with setting 3:
Routes
EcNo
(IS-HO Success)
% IS-HO
Threshold
/(Attempts)
success rate
Route 2
Route 4
Route 6
Total
-11
-12
-14
-11
-12
-14
-11
-12
-14
-11
-12
-14
12/12
12/12
3/9
7/9
8/9
7/9
13/16
13/16
9/20
32/37
33/37
19/38
100%
100%
33.3%
77.7%
88.8%
77.7%
81.25%
81.25%
45%
86.50%
89.20%
50%
IS-HO performance at threshold values of –11 dB and –12 dB is very similar.
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Presentation / Author / Date
ISHO Triggering Process – RSCP Threshold
Routes
RSCP
(IS-HO Success)
% IS-HO
Threshold
/(Attempts)
success rate
Route 2
Route 3
Route 4
Route 6
Total
-105
-106
-107
-105
-106
-107
-105
-106
-107
-105
-106
-107
-105
-106
-107
9/9
9/9
8/9
10/10
14/15
11/15
8/9
8/9
6/9
21/25
16/20
-48/53
47/53
25/33
100%
100%
88%
100%
93.3%
73.3%
88%
88%
66%
84%
80%
-90.5%
88.7%
75.8%
IS-HO performance at threshold values of –105 dB and –106 dB is very similar.
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ISHO Triggering Process – UE Tx Power Threshold
Routes
UE Tx Pwr
Threshold
(IS-HO Success)
/(Attempts)
% IS-HO
Success rate
-1
-3
-5
-1
-3
-5
-1
-3
-5
-1
-3
-5
-1
-3
-5
6/6
6/6
6/6
10/10
9/9
9/10
6/6
6/6
6/6
22/30
27/30
22/25
44/52
48/51
43/47
100%
100%
100%
100%
100%
90%
100%
100%
100%
73.30%
90.00%
88%
84.60%
94.00%
91.50%
Route 2
Route 3
Route 4
Route 6
Total
The results show that a threshold= -3 dB is large enough to provide a good performance.
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Presentation / Author / Date
ISHO Triggering Process – DL Tx Power Threshold
Routes
RSCP
(IS-HO Success)
% IS-HO
Threshold
/(Attempts)
success rate
Route 2
Route 4
Route 6
Total
-1
-2
-3
-1
-2
-3
-1
-2
-3
-1
-2
-3
0/6
0/6
6/6
1/6
1/6
6/6
6/20
-13/20
7/32
1/12
25/32
0%
0%
100%
16.6%
16.6%
100%
--65%
21.9%
8.3%
78%
Clearly, the IS-HO performance at the threshold GsmDlTxPrwAMR =–3 dB is the best: excellent
performance (100 % success rate) at medium speeds but degradation occurs at high speed (route
6).
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ISHO Triggering Process – Parameter Summary
CPICH EcNo
CPICH RSCP
UL Tx Power
DL DCH
UL Quality
Measurement
Reporting
Parameters
HO
Decision
Algorithm
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Parameter
HHoEcNoThreshold
HHoEcNoCancel
HHoEcNoCancelTime
HHoEcNoTimeHysteresis
EcNoFilterCoefficient
HHoRscpThreshold
HHoRscpCancel
HHoRscpFilterCoefficient
HHoRscpTimeHysteresis
HHoRscpCancelTime
Suggested values
-12 dB
-9 dB
640 ms
100 ms
600 ms
-105 dBm
-103 dBm
200 ms
100 ms
640 ms
GsmUETxPwrThrAMR
-3 dB
GsmUETxPwrFilterCoeff
GsmUETxPwrTimeHyst
GsmDLTxPwrThrAMR
10ms
ULQualDetRepThreshold
GsmMeasRepInterval
GsmNcellSearchPeriod
GsmMaxMeasPeriod
GsmMinMeasInterval
AdjgRxLevMinHO
AdjgTxPwrMaxTCH
GsmMeasAveWindow
Presentation / Author / Date
320ms
-3 dB
0.5s
0.5 s
0
20 meas. report
2s
-98 to -100 dBm
33 dBm
6 meas. report
GSM Measurement Reporting Process
RNC
Triggering
RRC: ”Measurement report”
Details about the
measurements
RRC: ”Measurement Control”
GsmMeasRepInterval
(default 0.5s)
RRC: ”Measurement report”
RRC: ”Measurement report”
GSMMaxMeasPeriod
Max 6 GSM cells
reported
RRC: ”Measurement report”
Handover Command
Handover Complete
Handover Failure
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The first measurement report
has info from the best GSM cell:
BCCH freq & RSSI, no filtering
used in UE
• Inter-system measurement stops if RNC
has not been able to perform intersystem handover after
GSMMaxMeasPeriod (value 10, default
=20, 1…20, step 1 meas report)
• RNC could not initiate inter-system
measurements if:
• The UE has « recently » performed
an inter-system HO:
GSMMinHoInterval / 10s, 0…60, step
1s
• An inter-system HO « recently » fails
for this UE: GSMMinMeasInterval /
10s, 0…60, step 1s
GSM Measurement Reporting Process
• The RNC databuild parameters GsmMeasRepInterval (0.5 s) and
GsmMaxMeasPeriod (10 measurement reports) define the maximum combined
time which may be used for GSM RSSI measurements and BSIC verifcation, i.e.
5 secs
• If GSM RSSI measurements are completed successfully and if there is only a
single GSM neighbour on the strongest GSM RF carrier then the RNC issues the
Cell Change Order from UTRAN message
• If GSM RSSI measurements are completed successfully and if there are multiple
GSM neighbours on the strongest GSM RF carrier then the RNC instructs BSIC
verification only for the neighbours on that RF carrier
• Both RSSI measurements and BSIC verification make use of a 7 slot
transmission gap every 4 radio frames
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GSM Measurement Reporting Process
GsmMeasRepInterval (default value=0.5 seconds)
• The GSM measurement reporting interval given by this parameter should be
kept to 0.5 seconds (default value)
• Increasing the reporting interval would increase the IS-HO process delay
• Besides, accuracy requirements related to the GSM measurements in
compressed mode are given for a reporting interval of 0.5 seconds (480ms TS
25.133)
GsmMaxMeasPeriod ( default value = 20 measurement reports)
• This parameter controls the maximum compressed mode duration time for
each GSM RSSI and BSIC decoding measurement process. The duration of
this parameters in seconds is given by:
max_meas_time (s) = GsmMaxMeasPeriod x GsmMeasRepInterval
• Thus, the default value of GsmMaxMeasPeriod in seconds is 12
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GSM Measurement Reporting Process
GsmMinMeasInterval (default value=10 seconds):
• In case of an unsuccessful IS-HO attempt, the network will deactivate compressed
mode for a time period given by this parameter value
• The network will reactivate automatically compressed mode after the timer has
expired unless a cancellation event is sent by the terminal during that period
• In case IS-HO cancellation event does not occur, and the mobile is leaving clearly the
3G boundary, then there is a death time equal to 10 seconds in which the UE is not
able to attempt new GSM measurements in case of an unsuccessful IS-HO.
• Experience in the field has shown that the probability of having a cancellation event
(event 1B,1E), after an IS-HO was requested, is very low and therefore the
GsmMinMeasInterval is reduced to a lower value (2 seconds) to speed up the
reactivation of the compressed mode
Terminal in
Terminal in
Terminal in
normal
mode
Compressed
mode
Compressed mode
Cancelation threshold
Trigger threshold
8s
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Presentation / Author / Date
10 s
Unsuccessful ISHO
Compressed mode is
reactivated automatically by
the network af ter the
GsmMinMeasInterval timer
expires
Handover Decision Process Optimisation
• The Inter-system handover decision process need to be optimized so that the network
selects the best GSM target cell which compliance with the following formula:
AVE_RXLEV_NCELL(n) > AdjgRxLevMinHO (n) + max( 0, AdjgTxPwrMaxTCH (n) P_MAX )
• AVE_RXLEV_NCELL(n): is the average RSSI level from the cell n
• P_MAX is the maximum power in GSM classmark (+33 dBm)
• AdjgTxPwrMaxTCH (n): is the maximum power of the traffic channel in GSM (default=+33
dBm)
• AdjgRxLevMinHO (n): Minimum required RX level of the target GSM cell to do handover
(default=-95 dBm)
• Thus, if P_MAX and AdjgTxPwrMaxTCH (n) default values are used, then the formula
simplifies to:
AVE_RXLEV_NCELL(n) > AdjgRxLevMinHO (n)
• AdjgRxLevMinHO(n): The sensitivity of a GSM MS is –104/-102 dBm in GSM 900 MS
and –100/-102 dBm for DCS 1800 MS (TS 45.005)
• Since the handover decision process usually only uses one RSSI measurement sample
per neighbour with an accuracy of +/- 6 dB (from specs), it may happen that the terminal
reports a GSM level of –95 dBm when actual level is –101 dBm
Could
consider
using
average
at RNC with lower threshold value
76•
© Nokia Siemens
Networks
Presentation
/ Author / Date
ISHO Cancellation Parameter Optimisation
• The cancellation thresholds 3dB above the triggering works the best
• Values of the cancellation filters (HHoEcNoCancelTime and
HHoRscpCancelTime) depend actually on coverage i.e. in case of fast
changes then the filters values should be relatively long to avoid possible pingpong (initiate IS-HO, cancel, initiate and so on…)
• In case some such ping-pong noted then longer cancellation filters should be
tried
Optimized values
CPICH EcNo
HHoEcNoCancel
HHoEcNoCancelTime
3dB above EcNo threshold
640 ms
CPICH RSCP
HHoRscpCancel
HHoRscpCancelTime
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3dB above RSCP threshold
640 ms
WCDMA <-> GSM PS data inter-working functionality
3G->2G for PS data (network controlled cell reselection)
•Uses compressed mode (in
both RAN & mobile) for measuring how good
2G coverage exists, before RNC moves the control of the call to BSC
•No resources reserved in
BSS in advance; thus the PS data call
continues on best effort basis, like all PS data calls in 2G
•No need
for BSIC identification
2G->3G for PS data (UE controlled cell-reselection)
•Terminal measures neighboring cells
during different time slots (no
compressed mode needed) for measuring how good 3G coverage exists,
before BSC moves the control of the call to RNC
•No resources reserved in RNC in advance; thus the PS data call
continues on best effort basis in 3G
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WCDMA <-> GSM PS data inter-working functionality
• Throughput degradation in the 3G->GSM frontier exists partly due to the CM activation but also due
to the poor 3G radio conditions
• Below is the average throughput in good and poor 3G coverage
• The definition of poor and good coverage is defined as :
• Good 3G coverage: CPICH EcNo>=-10 dB, CPICH RSCP>-100 dBm
• Poor 3G coverage: CPICH EcNo<-10 dB, CPICH RSCP< -100 dBm
kBps
5
4
3
2
1
0
ftp Throughput in ISHO Zones, 64 RAB (server
x.x.x.111 /121)
ftp Throughput in ISHO Zones, 128 RAB (server
x.x.x.111 /121)
Good 3G coverage
Poor 3G coverage
GPRS
50
Poor 3G coverage
6.51
43.03
15.35
45
16
17 %,
GPRS
13.82
5.41
downgrad
10 %,
40
14
e
downgrade
35
12
30
10
25
8
20
2.7
6
15
2.7
4
10
2
5
0
0
1 Service downgrade due to coverage and CM between
1
10 to 17 %
good and poor 3G coverage areas
© Nokia Siemens Networks
Good 3G coverage
Poor 3G coverage
GPRS
Good 3G coverage
18
Throughput in poor coverage
includes throughput during compressed
mode .
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ftp Throughput in ISHO Zones, 384 RAB (server
x.x.x.111 /121)
Presentation / Author / Date
37.76
12 %,
downgrade
kBps
6
128k RAB
kBps
7
384k RAB
64k RAB
2.7
1
Cell Change Order (CCO) to GSM
• Triggers
• GsmUETxPwrThrNrtPS (range -10..0 dB,default: -1 dB): This parameter determines the UE
TX power threshold for a non-real time PS data connection. Values –1 dB and –3dB tested.
• GsmDLTxPwrThrNrtPS (range –10..0 dB,default;- 1 dB): This parameter determines the
downlink DPCH TX power threshold for a non-real time PS data connection. Values –1dB
and –3 dB tested.
• Other Parameters
CPICH EcNo
CPICH RSCP
UL Quality
UL Tx Pow er
DL DCH
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Parameter
HHoEcNoThreshold
HHoEcNoCancel
HHoEcNoCancelTime
HHoEcNoTimeHysteresis
EcNoFilterCoefficient
Default
Values used
-22 dB
-12 dB
- 20 dB
640 ms
-9 dB
640 ms
100 ms
600 ms
600 ms
-105 dBm
-105 dBm
-100 dBm
-103 dBm
200 ms
200 ms
640 ms
100 ms
1280 ms
5s
640 ms
GsmUETxPwrThrNrtPS
-1 dB
-1, -3 dB
GsmUETxPwrFilterCoeff
GsmUETxPwrTimeHyst
10 ms
10ms
1280 ms
320ms
-1 dB
-1, -3 dB
HHoRscpThreshold
HHoRscpCancel
HHoRscpFilterCoefficient
HHoRscpTimeHysteresis
HHoRscpCancelTime
ULQualDetRepThreshold
GsmDLTxPwrThrNrtPS
1280 ms
0.5s
3G/2G Neighbour Verification Process - Example
• Required equipment for 3G/2G neighbour refining
• 2G and 3G scanners + UE in dual mode (outdoor measurements)
• 3G->2G neighbours could be optimized with a prioritization algorithm.
• Priority 1: ISHO failure
• Find the missing neighbours which cause the call failure during the drive test.
• Careful analysis with 2G Scanner and UE data
• Priority 2: poor 3G coverage but good GSM coverage
• 2G and 3G scanner data used to compare signals.
• 3G signal is compared to ISHO triggering parameter values (e.g.
HHoRSCPThreshold, HHoEcNoThreshold)
• GSM neighbor is added if the ISHO condition is met. (2G RSSI>
GsmncellRxLevMinHO)
• Priority 3: good 3G and GSM coverage (probable ISHO when going inside the
building
• 2G and 3G scanner data used to compare signals.
• GSM neighbours of this class are added only when there is still room to reach
the max # of ADJG per cell.
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• GSM RSSI > GSMncellRXLevMinHO +Indoor loss (15-25 dB)
© Nokia Siemens Networks
Presentation / Author / Date
Module 5 – Inter System Handover Optimisation
Summary
• Proper Cell reselection will improve call setup success, it
can be managed with parameters, some margin should be
left to avoid ping-pong
• Good inter-system neighbour planning is key to maintain
the service, the neighbour list should be not too long
• Compressed mode delays the ISHO, for PS data it is
shorter due to no need of BSIC decoding but PS
throughput will be degraded during CM
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Version control
Version
Date
Status
Owner
RAN04
2006
Base version
Mike Roche, Steve Hunt,
Gareth Davies, Pekka Ranta
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