NPI Training - Accessibility
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Transcript of NPI Training - Accessibility
Slide titleIn CAPITALS
50 pt
Slide subtitle 32 pt
NPI TrainingAccessibility
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Limited Internal NPI Training - Accessibility 2005-09-202
Agenda
Objective Accessibility Time Plan Key Performance Indicators – KPIs Benchmark concept – NETQB Accessibility Definition Accessibility KPIs
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Limited Internal NPI Training - Accessibility 2005-09-203
Objective
On completion of this section the attendants should be able to:
Understand the Accessibility Concept Have a good knowledge of the Accessibility KPIs Understand the impact of parameter settings and the radio
network configuration on Accessibility performance Be able to do an Accessibility Network Performance Audit
and provide high level recommendations Be able to identify and correct Accessibility performance
problems
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Limited Internal NPI Training - Accessibility 2005-09-204
Accessibility – Time plan
Accessibility – 10 days
Day 1:– Objective– Key Performance Indicators – KPIs– Benchmark concept – NETQB– Accessibility Definition– Accessibility KPIs– Paging– Location Area Update
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Limited Internal NPI Training - Accessibility 2005-09-205
Accessibility – Time plan
Day 2&3:– Random Access Failures– SDCCH Congestion– SDCCH Drop
Day 4&5:– TCH Assignment Failures– Start of Accessibility practical exercise
Day 6 to 10:– Accessibility practical exercise– Review of exercise accessibility reports
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Limited Internal NPI Training - Accessibility 2005-09-206
Key Performance Indicators - KPIs
Key Performance Indicators (KPIs) are used to categorize the Network elements such as MSCs and BSCs.
The KPI values allow the operator to visually compare
their network with other networks, and also highlight areas that may require focusing for improvements.
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Limited Internal NPI Training - Accessibility 2005-09-207
Key Performance Indicators - KPIs
KPI TOP 25% TOP 50% Below TOP 50%Paging Succes Rate (1st
+2nd
page) > 95.10 >= 93.24 < 93.24Location Update Success Rate > 98.23 >= 97.12 < 97.12
Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114
SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38
TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34
Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
Accessibility
Retainability
Voice Quality
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Limited Internal NPI Training - Accessibility 2005-09-208
Benchmark Concept - NETQB
In the Quality Benchmark report performance from an operator’s radio network individual nodes (BSCs and MSCs) are compared and rated in relation to world references from Ericsson Global Benchmarking database.
Ericsson Benchmarking database is periodically updated with data from its installed basis, i.e. Ericsson MSCs and BSCs installed in mobile telephony networks around the world.
The KPI references are calculated on all BSCs in Ericsson global database carrying more than 600 Erlangs. The total number of BSCs in Ericsson benchmarking database in July 2005 was 1166. From those, 927 BSCs were selected with traffic above 600 Erl.
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Benchmark Concept - NETQB
Top 25%: Performance level of 25th percentile of all nodes in the world above 600 Erl. Nodes color-coded in green have world-best-in-class performance in the related indicator.
Top 50%: Performance level of 50th percentile of all nodes in the world above 600 Erl. Nodes color-coded in yellow have world-average performance in the related indicator. These nodes could be addressed when time and resources are available
Below Top 50%: Performance level below the 50h percentile of all nodes in the world above 600 Erl. Nodes color-coded in red have poor performance compared to the world references. Prioritization of improvement actions and Network Performance Improvement (NPI) services to these nodes are recommended.
KPI TOP 25% TOP 50% Below TOP 50%Paging Succes Rate (1st+2nd page) > 95.10 >= 93.24 < 93.24Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
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Limited Internal NPI Training - Accessibility 2005-09-2010
Accessibility Definition
Service Accessibility is defined by ITU-T E.800 as:
“The ability of a service to be obtained, within specified tolerances and other given conditions, when requested by the user.”
Total number of successful calls set up/Total call accesses to the network
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Accessibility DefinitionCall to an MS
9805024
BSC
MSC/VLR
TRC
BTS
BTS
1
2
4
5
2
2
2
3
1
4
35
6
1. MSC/VLR sends paging command to all BSCs belonging to the location area (LA) where MS is located
2. BSC forwards the paging command to all BTSs in that LA, and the BTSs in their turn page the MS on the PCH
3. The MS responds to the BTS on the RACH and the BTS forwards the response to the BSC (forward to MSC)
4. The BSCs checks with the BTS if it has an SDCCH available and the BTS grants the MS an SDCCH by using the AGCH
5. The MS and the BTS signal on the SDCCH, measurement reports sent on SACCH are forwarded from the BTS to the BSC and once the signalling is done the BSC decides which TCH to use
6. TCH connection established between MS and BTS
Accessib ili ty
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Accessibility KPIs
KPI TOP 25% TOP 50% Below TOP 50%Paging Succes Rate (1st+2nd page) > 95.10 >= 93.24 < 93.24Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
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Paging
KPI TOP 25% TOP 50% Below TOP 50%Paging Succes Rate (1st+2nd page) > 95.10 >= 93.24 < 93.24Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
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Paging – Overview
All BSC in the MSC
BSC wt cells using
specified LAC
MSC
local
global
Paging message Cells with specified LAC
Paging command
Paging command
Paging Request
Paging Request
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Paging – Overview
MS can be paged by IMSI or TMSI Up to 4 Paging Requests per Paging block
MS only listens for paging at particular PCH sub-channel corresponding to its Paging Group
IMSI IMSI T T TTor
Note: T = TMSI
TTIMSIor
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Paging - Overview
9702690
Listeningto PCH
Listeningto PCH
1 53 4207 2 3 4 57 0 16
Sleep mode
7 0 1
Sleep modeMeasuring on
neighbors
Listeningto PCH Measuring on
neighbors
TDMAframes
BSF S CFC FC S
Paging group
F (FCCH): Frequency Correction ChannelS (SCH):Synchronization ChannelB (BCCH):Broadcast Control ChannelC (CCCH):Common Control Channel;Paging Channel (PCH) or Access Grant Channel (AGCH)
BCCH + CCCH(downlink)
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Paging - Overview
2nd page according to PAGREPGLOB
2nd page according to PAGREP1LA
Local Paging?
Paging in one LA. Wait for response:
PAGTIMEFRST1LA
Paging in MSC area. Wait for response:
PAGTIMEFRSTGLOB
yes no
VLR has an LAI (normal case) LAI is missing
Answer? Successful
Answer?Answer?
Paging in one LA. Wait for response: PAGTIMEREP1LA
Paging in MSC area. Wait for response:
PAGTIMEREPGLOB
Paging in MSC area. Wait for response:
PAGTIMEREPGLOB
No repeated paging
Successful
unsuccessful
Either TMSI/IMSI
1 2 3 0
IMSI used
Answer?
10
yes
yes yes
yes
no no
nono
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Paging – Overview
Upon receipt of a paging request message and if access to the network is allowed, the addressed MS shall initiate within 0.5 s the immediate assignment procedure. The establishment of the main signaling link is then initiated by use of an SABM with information field containing the PAGING RESPONSE message
Upon receipt of the PAGING RESPONSE message the network stops timer PAGTIMERFRST1LA (PAGTIMEFRSTGLOB).
If timer PAGTIMERFRST1LA (PAGTIMEFRSTGLOB) expires and a PAGING RESPONSE message has not been received, the network may repeat the paging request message and start timer PAGREP1LA (PAGREPGLOB).
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Paging - Overview
1
2
PAGING
PAGING COMMAND
PAGING REQUEST
MSC BSC BTS MS
A-interface
Processor Load too high?
YN
Paging queue full?
NY
Step NPAG1GLTOT or NPAG1LOTOT
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Paging - Overview
MSMSC BSC BTS
Channel RequestChannel Required
Establish Indication (Paging Resp.)SCCP Conn. Req (Paging Resp.)SCCP Conn. Conf.
SABM, Page Response
Channel Activation
Channel Activation Ack.
Immediate Assignment Command
Immediate Assignment
Paging Paging CommandPaging Request
UA
PCH
RACH
AGCH
SDCCH
SDCCH
Random Access
Step NPAGE1RESUCC or NPAGE2RESUCC
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Paging - Overview
BTS
BSC
MSC
LA 1
Paging
Paging
Paging
Removed due to overflow
Removed due to overflow
Removed due to time-out
Removed due to time-out
Monitor and detect congestion on paging channel
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Paging – Strategy
Recommended paging strategy is:– First page as local page the MS by TMSI– Second page as global page the MS by IMSI
Other strategies and constraints:– No second page: Less paging load, but risk more unsuccessful
paging– Second local page: Less paging load, risk more unsuccessful
paging– Second page by TMSI: Utilize less paging capacity, but some
pages maybe unsuccessful if TMSI of MS is wrong in VLR
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Paging – BSC Capacity
It is difficult to estimate BSC Paging Capacity Rule of thumb: BSC can accommodate 8500 Paging
Commands/sec To further optimize the BSC paging capacity, paging
queue overflow can be monitored with the following formula:
Where TOTCONPAG - step for every discarded paging message when paging queue is full
TOTPAG - paging messages received from MSC
%100TOTPAG
TOTCONPAGFAIL_PAG
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Paging – BTS Capacity
CCCH consists of 2 sub-channels for DL: PCH & AGCH AGCH used to allocate resource to MS during call setup PCH used to send paging request to MS Two types of Channel Configuration:
– Combined BCCH/SDCCH 3 CCCH blocks
– Non combined BCCH/SDCCH 9 CCCH blocks
AGCH can have dedicated blocks or work by stealing mode
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Paging – BTS Capacity
Incoming paging command are buffered in a queue One queue for each paging group When paging blocks are available, BTS will send these
paging commands as paging requests over the air interface
If queue is full, further incoming pages are discarded If queue at BTS for too long time, the page may be lost
since MSC do not receive any page response after timer expired
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Paging – Reducing Paging
IMSI attach/detach– If ATT = ON, MS will send attach/detach information to
MSC/VLR when it is powered on/off. – Decrease unnecessary paging to MS not connected to network– Constraint is higher SDCCH utilization
Periodic Registration– Avoid paging MS which lost coverage and not able to inform the
system that it is inactive– Timer T3212 specifies the period for periodic registration– Shorter T3212 leads to less paging, but higher utilization of
SDCCH
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Paging Capacity Impacting parameters
BCCHTYPE: NCOMB or COMB– Non-combined BCCH will give higher paging capacity than
combined BCCH
AGBLK: 0 – 1– AGBLK=0 gives higher paging capacity than AGBLK=1
MFRMS: 2 – 9– The lower value for MFRMS, the higher paging capacity due to
trunking efficiency– MFRMS setting is a trade off between battery consumption and
call set up time
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Paging – Optimization
Analyze the following issues that could be possible reasons for poor Paging Performance:
– Insufficient coverage– High interference– Non-optimum Paging Strategy– Non-optimum Paging parameter settings– Paging Congestion in MSc, BSC or BTS– De-activated or incorrect use of Paging features
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Paging – Optimization
The following actions can improve Paging Congestion:
MSC Paging Congestion– Increase SAE
BSC/BTS Paging Congestion– Check Paging Strategy– Increase number of Location Areas (This will increase SDCCH
load)– Set BCCHTYPE to NCOMB– Use TMSI paging requests– Ensure IMSI attach/detach is activated (ATT = yes)– Decrease T3212/BTDM (This will increase SDCCH load)
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Paging – OptimizationLow Paging Success
N o TM S I A ttach / D etach?
A ctiva te
W rong period ic loca tionupdating se tting?
C orrect T3212 in B S C ,B TD M & G T D M in M S C
S D C C HC ongestion?
Increase S D C C H channe l A daptive configura tion fea ture
P agingcongestion?
P lan m ore LA U se TM S I paging
TM S I pagingnot use?
A ctiva te
afte r no t period icregistra tion not use? A ctiva te
E N D
Yes
No
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
Im p lic it de tach
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Paging - KPI
Paging Success Rate is measured on MSc level and calculated with the following formula:
Paging Success Rate (1st+2nd page)
– Successful First and Second Pages of Total Number of First Pages
This is the End-User perceived Paging Success Rate, which is used as the Paging KPI.
[%]100*
1
NPAG1LOTOTNPAG1GLTOT
CNPAG2RESUCCNPAG1RESUC1
TOTALCELLS
TOTALCELLS
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Paging – Additional indicators
The following Paging indicator is useful when studying paging performance (MSc level):
Paging Success Rate (1st page)
Successful First of Total Number of First Pages
This is the formula showing the system behavior
[%]100*
1
NPAG1LOTOTNPAG1GLTOT
CNPAG1RESUC1
TOTALCELLS
TOTALCELLS
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Paging – STS Counter Summary
Paging Success STS counters– NPAG1GLTOT: The number of first global page attempts over A-Interface– NPAG1LOTOT: The number of first page attempts to a location area over
A-Interface– NPAG1RESUCC: The number of page responses to first page attempt on
A-interface– NPAGE2RESUCC: The number of page responses to repeated page over
A-interface
Paging Congestion STS counters– TOTPAG: Number of paging messages received from the MSC – TOTCONGPAG: Number of Paging messages discarded due to congestion– PAGPCHCONG: Number of discarded paging messages due to full paging
Queue. – PAGETOOOLD: Number of discarded paging messages due to old paging
messages.
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Paging – Parameter SummaryParameter Range Recommended Description
MFRMS 2-9 CCCHMultiframe
4 MF period betweentransmission ofpaging message tosame paging group
AGBLK 0-7 0 Reserved CCCHblocks for AGCH
BCCHTYPE COMB,COMBC,NCOMB
- Channel configuration
T3212 0-255 40 Time between periodregistration
ATT YES, NO YES IMSI Attach/ detachallowed
CRH 0-14 (steps of2) dB
4 Hysteresis used whenMS in idle crosses aLA area
GPRSNWMODE 0-3 2 (No Gs-Interface & noMPDCH used)
Whether or not Gs-interface & MPDCHused
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Paging – Parameter SummaryParameter Recommended Description
BTDM T3212 * 6 Implicit detach supervisionGTDM 6 min
Range: 0-255Extra guard time beforesubscriber set to detached
TDD OFF (default) Time inactive IMSI in VLRbefore it is removed
PAGTIMEFRST1LA 4sec (default)Range: 2-10sec
Time supervision for pageresponse for first page
PAGTIMEFRSTGLOB 4sec (default)Range: 2-10sec
Time supervision for pageresponse for first global page
PAGREP1LA 2 (recommend)Range: 0-3
How second page is sent
PAGEREPGLOB 0Range: 0-1
How global page is repeated
PAGTIMEREP1LA 7sec (default)Range: 2-10sec
Time supervision for pageresponse for second page
PAGTIMEREPGLOB 7sec (default)Range: 2-10sec
Time supervision for pageresponse for second globalpage
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Paging – Parameter Summary
Parameter Recommended DescriptionTMSIPAR 1 or 2 TMSI should be used or notTMSILAIMSC 0 (default)
Range: 0-1New TMSI to be allocated atchange or LAI withinMSC/VLR
SECPAGEPATH 1 (recommend)Range: 0-2
Define which interface 2nd
paging is sentTIMPAGINGM 9 sec
Range:2-20secTime supervision for 1st CSpaging sent over Gs interface
SGSN Parameter Parameter Recommended Description
T3133 5 secFixed
Time supervision for PSPaging
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Location Update
KPI TOP 25% TOP 50% Below TOP 50%
Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
KPI TOP 25% TOP 50% Below TOP 50%
Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
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Location Update – Overview
In Idle Mode the MS is powered on but not allocated a dedicated channel
The purpose of Idle Mode is for the MS to be able to access the system and be reached by the system any time and anywhere
Idle Mode behavior is managed by the MS Idle Mode is controlled by the parameters which the MS
receives on BCCH. Location Updates enable the to register its current location
to the network so that the network knows where to route incoming calls.
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Location Update – Overview
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Location Update – Overview
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Location Update – Overview
9702628
Good enoughdownlink
To ensure good enough uplink
C1=(received_signal_level-ACCMIN)-max(CCHPWR-P,0)
ACCMIN - minimum received signal in MS to allow access
CCHPWR - maximum MS power at access
P - maximum power output of MS according to its class
C1>0
Cell selection process
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Location Update – Overview
9702629
C21 = C1+CRO-TO* q(PT-T); PT=31
C21 = C1-CRO PT=31
CRO - Cell reselection offset
TO - Temporary negativ offset
PT - Time for application of a temporary offset
T - Timer1 C2 is only supported by phase 2 mobiles
Cell reselection process
q(x) = 0, x <01, x 0
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Location Update – Overview
9702630
• The serving cell becomes barred
• Repeated unsuccessfull access attempts(MAXRET)
• Downlink signalling failure
• C1<0 for serving cell more than 5s
• C2neighbour>C2serving(+CRH) more than 5s
Cell reselection process
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Location Update – Overview
Cell Reselection Hysteresis (CRH) Receiving signal strength (RXLEV) hysteresis for required cell re-
selection over a location area border. Each change of location area requires a location update to be
performed, which increases signaling load. CRH is used in order to prevent ping-pong effects for cell selection
across location area borders If the CRH value is set too low, the fluctuations in signal strength may
lead to a ping-pong effect for location updating.This will cause an undesired increase in the signaling load on the SDCCH
If the parameter is set too high, the mobile may camp on the wrong cell (not the strongest one) for too long when entering a new location area.
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Location Update – Overview
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Location Update – Overview
9702631
• PLMN not allowed
• No SIM card inserted
• Illegal MS
• IMSI unknown in HLR
• .....
• Emergency calls only
• Cell reselection as normal,but CRH is ignored
• No updating
Limited service state
Cell selection process
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Location Update – Overview
9702632
• Normal - at change of Location area
• Periodic - according to T3212
• IMSI attach/detach, ATT
Location updating process
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Location Update – Strategy
Location Area Code (LAC) is part of Cell Global Identity Circuit Switched (CS) paging done based on LAC
Larger LA – Higher paging load– Less LAC update, lower SDCCH utilization
Smaller LA– Lower paging load– More LAC update, higher SDCCH utilization
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Location Area – Strategy
Location Area (LA) dimensioning strategies: Size of a LA must not exceed the maximum paging capacity for the BTS /
BSC In a rural area, it is easy to find LA border cells. But there’s no reason to
have a smaller LA than required General rule of thumb : 1 LAC per BSC If a BSC covers a large area with high traffic, consider splitting the LA. This
will reduce the paging load in BTS and BSC In larger cities, SDCCH load will be higher for LA border cells. If difficult is
experienced to find LA border cells and the BSC coverage area is small, several BSCs can share one LA
Define LA border at cells with low subscriber density
Good information is available in the Location Area Dimensioning Guideline
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Location Update – Optimization
Analyze the following issues that could be possible reasons for poor Location Update success rate:
– Insufficient coverage– High interference– Location Area borders not optimum– Low CRH Hysteresis– Short time for periodic registration (T3212)– Insufficient SAEs– SDCCH congestion
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Location Update – OptimizationLow Location Updating
Success
borderce ll?
R eallocate to another LA or M SC Increase C R H
Low C R HH ysteris is? Increase C R H
Bad LAD em ension ing?
R e-d im ension ing LA
Short perod icregistra tion?
C heck T3212 in BSC &BTD M in M SC
Interference? C heck frequency p lan Activa te rad io feature
Software F ileC ongestion?
C orrect se ttings for S AE 500 B lockM LU AP, M LC A P,M LV AP,M M M LR
SD C C HC ongestion?
Increase SD C C H channel Adaptive configura tion feature
Autom aticderegistra tion?
Activa te autom aticde-registra tion
EN D
Yes
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
No
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Location Area Update - KPI
Location Area Update Success Rate is calculated using the following formula:
Location Update Success Rate
– Successful Location Updates of Total Number of Location Updates
[%]100*1
NLOCNRGTOT NLOCOLDTOT
CNLOCNRGSUC CNLOCOLDSUC
1
TOTALCELLS
TOTALCELLS
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LA – STS Counter Summary
OBJECT TYPE: LOCAREAST Events are counted per Location Area
– NLAPAG1LOTOT = # of first page attempt to a LA– NLAPAG2LOTOT = # of repeated page attempt to a LA– NLAPAG1RESUCC = # of page response to first page to a
LA– NLAPAG2RESUCC = # of page response to repeated
page to a LA– NLAPAGERR = # of unsuccessful page response to
a LA
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Random Access
KPI TOP 25% TOP 50% Below TOP 50%
Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
KPI TOP 25% TOP 50% Below TOP 50%
Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
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Random Access – Overview
The measurements are done per cell for random access channels. For every cell there are counters registering the number of random
access attempts received in the BSC.
Random Accesses can be distributed into the following types: MS Originated RA Call Re-establishment Emergency Calls Answer to Paging All Other Cases
– IMSI Attach/Detach– Location Updates– Period Registration
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Random Access – Overview
The failed random access counter (RAACCFA) is incremented when an access attempt is failed.
There is also a counter for all accepted random accesses (CNROCNT) that means all except failed random access.
A failed random access burst does not necessarily lead to a call setup failure, as the MS sends many RA bursts each time it tries to connect to the network. This counter always incremented in an accepted random access.
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Random Access – Overview
MSMSC BSC BTSChannel Request
Channel Required
1
2
3
Immediate Assignment RejectY
4 Channel Activation
5n6
Channel Activation Ack.
Channel ActivationChannel Activation Ack.
6n
Chan. Neg. Ack.
Chan. Neg. Ack.Immediate Assignment
Establish IndicationSCCP Conn. ReqSCCP Conn. Conf.
SABM, UA
5
N
Too high TA ?Wrong Cause Code? SW file congestion?
Step CNROCNT or RAACCFA
Y
NToo high processor load ?
Step related RA counter
Free ch. Available?
YNActivation of channel successful?
Y
N
Random Access
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RA – Important parameters
ACCMIN– ACCMIN controls the access threshold to the system– Often the setting of ACCMIN is decided by non-technical reasons– A low setting of ACCMIN can cause RA failures, TCH drops and bad
quality– A high setting of ACCMIN can stop users accessing the system
resulting in lost revenue
MAXRET– MAXRET controls the number of Random Access retries allowed when
the MS accesses the system– A lower setting of MAXRET can improve RA performance but also
result in MSs not being able to access the system
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RA – Important parameters
CRH– Cell reselection hysteresis between different location areas– CRH can be adjusted for cells on LA borders to reduce the amount of
RA attempts
T3212– T3212 determines the time between periodic updates
ATT– ATT indicates if IMSI attach/detach is active
CB– CB indicates if a certain cell is barred for access
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Random Access – Optimization
Analyze the following issues that could be possible reasons for high Random Access failure rate:
– High interference– Lack of Coverage– High Timing Advance– Handover access burst mistaken as random access burst– Non-optimized parameter settings– Software Congestion (SAE)– Unbalanced link budget
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Random Access – OptimizationNot Approved Random Accesses
C heck B S IC a lloca tion
C heck frequency p lan
A ccess burst fromanother co-channel
ce ll
C heck ce ll param eter se tting
M A XTA toolow?
C heck S A E (C O FLP ,D B TS P :T A P =S A A C TIO N ;)
S oftware filecongestion?
C heck in te rfe rence
H igh no isefloor?
END
R educe in te rfe rence
Increase S A E
IncreaseM A XTA
C hange B S IC or
frequency p lan
C heck if unknown access code
YES
NO
NO
YES
NO
YES
NO
YES
C heck s ite loca tion
H igh loca tedsite?
C onsider tilting orlowering s ite
NO
YES
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Random Access – Optimization
f1
BSIC xxf1
BSIC xx
f2
BSIC yy
Random Access
Handover Access
Random Access
5 33-4 bits established cause4-5 bits random number 8
8 6
Info Parity
8 6
6
X 8 6
14 4
Tail Coded2 x 18
Final Burst Tail Synch Info
BSIC
Handover Access
Base Station Identity Code
Handover access burst mistaken as random access burst
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Random Access Failure - KPI
The Random Access Failure rate is calculated using the following formula:
Random Access Failure Rate
– Failed Random Accesses of Total Number of Random Access Attempts
[%]100*)(
1
1
PDRACRAACCFACNROCNT
RAACCFA
TOTALCELLS
TOTALCELLS
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Random Access Failure - KPI
RAACCFA
CNROCNT +PDRAC+ RAACCFA100 [%]
Number of accepted random
accesses (CS)
Packet Data Random Access per cell
)
Number of Failed random accesses
PS+CS
Number of Failed random accesses
PS+CS
TA>MAXTA -> RAACCFA incr
The Random Access Failure rate is calculated using the following formula:
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RA – Additional indicators The following Random Access indicators are useful when studying
RA performance:
– RA_LOA_REJ: Rejected Random Accesses due to load regulation of Total Number of Accepted Random Accesses
– RA_ANSWPAG: Random Accesses with Cause “Answer to Paging” of Total Number of Accepted Random Accesses
100
CNROCNT
RATRHFAREG
ERRATRHFAOTHALRATRHFAEMC
100
21
21
2
1
RACALRRACALRRACALRE
RAEMCALRAOTHERRAORDAT
RAORSPERAOSREQRAAPOPS
RAAPAGRAAPAGRAANPAG
RAAPOPSRAAPAG
RAAPAGRAANPAG
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RA – Additional indicators The following Random Access indicators are useful when studying RA
performance:
– RA_SERVICE: Mobile Originated RA (i.e. Random accesses caused by the MS user) of Total Number of Accepted RA
– RA_OTHER: RA with Cause “All Other Cases”, e.g. Location Updating, Detach, Attach, etc. of Total Number of Accepted RA
100
21
21
RACALRRACALRRACALRE
RAEMCALRAOTHERRAORDAT
RAORSPERAOSREQRAAPOPS
RAAPAGRAAPAGRAANPAG
RAORDATRAORSPERAOSREQ
100
21
21
RACALRRACALRRACALRE
RAEMCALRAOTHERRAORDAT
RAORSPERAOSREQRAAPOPS
RAAPAGRAAPAGRAANPAG
RAOTHER
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RA – Additional indicators The following Random Access indicators are useful when studying RA
performance:
– RA_EMERG: RA with Cause “Emergency Calls” of Total Number of Accepted Random Accesses
– RA_CALLREE: RA with Cause “Call Reestablishments”of Total Number of Accepted Random Accesses
–
100
21
21
RACALRRACALRRACALRE
RAEMCALRAOTHERRAORDAT
RAORSPERAOSREQRAAPOPS
RAAPAGRAAPAGRAANPAG
RAEMCAL
100
21
21
21
RACALRRACALRRACALRE
RAEMCALRAOTHERRAORDAT
RAORSPERAOSREQRAAPOPS
RAAPAGRAAPAGRAANPAG
RACALRRACALRRACALRE
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RA – Examples in ESPA
Random Access examples in ESPA
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SDCCH Congestion
KPI TOP 25% TOP 50% Below TOP 50%
Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
KPI TOP 25% TOP 50% Below TOP 50%
Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
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SDCCH Congestion – Overview
SDCCH Activities:
Mobility Management– Normal Location update– Periodic Registration– IMSI Attach / Detach
Connection Management– Call setup– SMS Point to Point– Fax Setup– Supplementary Services
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SDCCH Congestion – Overview
Channel Configuration:
Channel Configuration can be done as follow
– Combined BCCH/SDCCH on 1 TS (SDCCH/4)– Non-Combined BCCH and SDCCH on 2 TS (SDCCH/8)
Cell Broadcast Channel (CBCH)– The Cell Broadcast service provides the transmission of an SMS from
a message-handling centre to all MSs in the serving area of the BTS. – If the Cell Broadcast service is active in a cell, one signaling sub-
channel is replaced by one CBCH resulting in a SDCCH/7
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SDCCH Congestion – Overview
SDCCH Channel Allocation Profile (CHAP)
Channel Allocation is the feature that selects and allocates suitable channels when one or more channels are required
Channel Allocation Profile (CHAP) is the parameter that provides different channel allocation strategies
For SDCCH assignments, CHAP 8 prioritize new assignments as follows:
1. OL/SDCCH2. UL/SDCCH (if OL/SDCCH is congested)
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SDCCH Congestion – Overview
OL (CHGR 0)
UL (CHGR 1)TT T T T T T T
ST T T T T T T
TT T T T T T T
SB T T T T P P
A new assignment will use the SDCCH in OL first
OL (CHGR 0)
UL (CHGR 1)TT T T T T T T
ST T T T T T T
TT T T T T T T
SB T T T T P P
If the OL is congested, the SDCCH in UL will be used
NoteSDCCH congestion in the OL will increment, but this is not customer perceived since the SDCCH in UL will then be utilized
B
S
T
P
BCCH timeslot
SDCCH timeslot
TCH timeslot
PDCH timeslot
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SDCCH Capacity Features
Adaptive Configuration of Logical Channels (ACLC):
Dynamic dimensioning of Logical Channel (SDCCH) on demand
Adaptive configuration of logical channels will dynamically dimension the cell with more (or less) SDCCH/8s on demand.
Reduced SDCCH congestion Increase in Network Capacity SDCCH dimensioning becomes less critical
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SDCCH Capacity Features
Adaptive Configuration of Logical Channels (ACLC):
Number of intra-cell handovers might increase slightly The reason is that when a timeslot is to be reconfigured,
any ongoing traffic on that timeslot is handed over to other idle channels.
With OL/UL subcell structure in the site with normal and extended range cells, ACLC will place all additional SDCCH/8 in the UL.
In the OL/UL subcell structure UL need to have one SDCCH configured
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SDCCH Capacity Features
ACLC:
SDCCH Increase
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SDCCH Capacity Features
ACLC:
SDCCH Decrease
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SDCCH Capacity Features
Increased SDCCH Capacity (MAXNOSDCCHTRX):
Double number of SDCCH/8 per cell– 2 x no of TRX per cell– maximum 32 SDCCH/8 per cell
Increased signaling capacity
B S S
S S
S S
S S
TRX 1TRX 2
TRX 3TRX 4
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SDCCH Capacity Features
Flexible SDCCH Allocation:
Allocate SDCCH where most suitable in a cell
Up to 4 SDCCH/8 per TRX (impacts TRH dimensioning)
TRX HW mapping
Carrier (Air-Interface) mappingB
S S S S S S S S
B
S S S S
S S S S
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LAPD Concentration/Multiplexing Concentrates up to four LAPD signaling links upon one 64
kbit/s A-bis time slot The concentration ratio is the number of TRXs sharing the
same 64 kbit/s A-bis time slots for LAPD signaling. Max no of SDCCH/ TRX is limited by the use of LAPD
Concentration/Multiplexing
SDCCH Capacity Features
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LAPD Concentration
SDCCH Capacity Features
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Immediate Assignment on TCH Feature
When a connection is to be established, normally the immediate assignment procedure allocates a Stand alone Dedicated Control CHannel(SDCCH) for the call set-up signaling. This feature allows signaling to be done on a Traffic CHannel (TCH).
For speech/data connections, the operator can choose between three general strategies:
– Immediate assignment on TCH is not allowed. – Immediate assignment on TCH as last preference.– Immediate assignment on TCH as a first preference.
SDCCH Capacity Features
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SDCCH Dimensioning Strategy
GOS Approach: SDCCH should be dimensioned for better GOS compare to TCH.
Typical range is 0.5% - 1%. Immediate Assignment of TCH with “TCH as last option strategy” is
recommended. It is recommended to add SDCCH when 0.5 Erlang of signaling traffic
is carried by TCH. Half Rate penetration, usage of Extended Range cell and HSCSD
should be taken into consideration.
STS Approach: Accurate dimensioning is achieved by using STS cell statistics
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SDCCH Congestion Optimization
Analyze the following issues that could be possible reasons for SDCCH Congestion:
SDCCH Dimensioning Incorrect use of SDCCH capacity features such as
Adaptive Configuration of Logical channels TCH Congestion Location Areas not optimized SMS usage and Cell Broadcast channel SDCCH Availability
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SDCCH Congestion Optimization
The following recommendations will have a positive impact on SDCCH congestion
Try not to use combined BCCH/SDCCH (SDCCH/4) Use the optional SDCCH capacity features such as the Adaptive
Configuration of Logical Channel feature when available. Use Immediate Assignment on TCH, SDCCH first. For manual dimensioning, use STS cell statistics Configure one SDCCH on the BCCH carrier and the others on the
hopping layer (Non-BCCH) Use the Ericsson SDCCH Dimensioning guideline.
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SDCCH Congestion Optimization
The following issues are worth taking into account when analyzing SDCCH Congestion:
Use LAPD STS statistics to evaluate LAPD congestion and optimize the LAPD Concentration factor
Analyze border cells with a large amount of random access attempts resulting in SDCCH congestion.
– Use Random Access optimization to solve the SDCCH congestion
Take into account Timeslot priority when deciding where to configure SDCCH/8
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SDCCH Congestion OptimizationSDCCH Congestion
C heck s ite position
Location area
border?C hange Location
A rea Border
C heck and increaseC R H
C heck TC H tra ffic
TC HC ongestion?
C heck S M S activity
M any SM Sm essages?
E
C heck period icregistra tion
Too frequentregistra tion?
C heck H W ava ilab ilty
Lowava ilab ility?
See TC H & SD C C H
Availab ility
Add TC Hcapacity
R edim ension SD C C H
C hange registra tionin terva l tim ers
NO
YES
NO
NO
NO
YES
YES
YES
NO
YES
YES
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SDCCH Congestion OptimizationC heck channel configura tion
C om binedSD C C H ?
C heck tra ffic trend
Short te rmtra ffic growth?
C heck S D C C H d im ension ing
E
U nderd im ensionedSD C C H ?
C heck S D C C H m ean ho ld ing tim e
Long m ean ho ld ingtim e?
Is ce ll b roadcastused?
Avoid ce ll b roadcast ifpossib le
M ake channelnon-com bined
N o activity
C heck H W and num berof Fa lse Accesses
R edim ensionSD C C H
END
NO
NO
YES
YES
YES
YES
YES
NO
NO
NO
C heck A daptive configuration o flogica l channel and param eters
AC STATE off? Sw itch onYES
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SDCCH Congestion - KPI
The SDCCH Time Congestion is calculated using the following formula:
SDCCH Time Congestion
– SDCCH Time Congestion of Total Measurement Interval
[%]100*_
60*1
CELLSNBPERIOD
CTCONSUBCTCONGSTOTALCELLS
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SDCCH Congestion – STS Counter Summary
OBJECT TYPES: – CLSDCCH, CELLCONF
– CCALLS: Allocation attempt counters (incremented at signaling connection setup, at handover and at assignment).
– CCONGS: incremented when an allocation attempt fails due to no idle channels.
– CTCONGS: When the last available channel is allocated, the counter is incremented each second until a channel becomes idle.
– CTRALACC: Traffic level accumulator. – CNSCAN: Scanning counter. Incremented one by one at each time
CTRALACC is updated.– CNDROP: Number of abnormally terminated SDCCH connections.– CNUCHCNT: Number of SDCCH channels defined (adaptive
configuration of logical channels is not considered).
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SDCCH Congestion – STS Counter Summary
OBJECT TYPES: – CLSDCCH, CELLCONF
– CAVAACC: Every tenth second the number of available channels is scanned and the value is added to CAVAACC.
– CAVASSCAN: Scanning counter. Counts the number of times CAVAACC is updated.
– CMSESTAB: successful connection establishments on the SDCCH (incremented at signaling connection setup, at handover and at assignment).
– CNRELCONG: Incremented when a connection on SDCCH is released due to radio resource congestion, that is when there is congestion on TCH or congestion on transcoder resources (CNDROP is incremented at the same time).
– CONFATTC: Number of reconfiguration attempts from SDCCH to TCH.
– CONFATTT: Number of reconfiguration attempts from TCH to SDCCH.
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SDCCH Congestion – Examples in ESPA
SDCCH Congestion examples in ESPA
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SDCCH Drops
KPI TOP 25% TOP 50% Below TOP 50%
Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
KPI TOP 25% TOP 50% Below TOP 50%
Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
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SDCCH Drops – Overview
SDCCH Drops are classified into one of the following categories:
SDCCH Drops because of Timing Advance SDCCH Drops because of Low Signal Strength SDCCH Drops because of Bad Quality SDCCH Drops due to Other Reasons
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SDCCH Drops – Overview
MSMSC BSC BTSChannel Request
Channel Required
1
2
3
Immediate Assignment RejectY
4 Channel Activation
5n6
Channel Activation Ack.
Channel ActivationChannel Activation Ack.
6n
Chan. Neg. Ack.
Chan. Neg. Ack.Immediate Assignment
Establish IndicationSCCP Conn. ReqSCCP Conn. Conf.
SABM, UA
Signaling Connection Set-up
5
N
Too high TA ?Wrong Cause Code?
Y
NToo high processor load ?
Step related RA counter
Free ch. Available?
YNActivation of channel successful?
Y
N
Random Access
Step CMSESTAB counter
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SDCCH Drops – OverviewAssignment: Assignment to Serving Cell
MSC BSC BTS MS
Assignment Request
N
Y
SABMUAEstablish Indication
Assignment Command
Assignment Complete
Assignment Compl.
Channel Activation
XChannel Act. Ack.
Channel Act. Neg. Ack.
RF Channel Release, old channel
RF Channel Release Ack.
Possible to assign channel?
If TCH Congestion CNRELCONG is stepped (time out).
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SDCCH Drops – OverviewConnection Release, Normal Disconnection
MSC BSC BTS MS
Clear Command
Channel ReleaseClear Complete
Deactivate SACCH
DISC
UARelease Indication
RF Channel Release
RF Channel Release Ack
SCCP Rel.
SCCP Rel. Ack.
1
Check Cause codes, if not HO successful or Call Control, step drop call counter, CNDROP
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SDCCH Drops – OverviewConnection Release, Abnormal Disconnection
MSC BSC BTS
Clear Command
Channel Release
Clear CompleteDeactivate SACCH
DISC
UARelease Indication
RF Channel Release
RF Channel Release Ack
SCCP Rel.
SCCP Rel. Ack.
Clear Request Step drop call counter, CNDROP
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SDCCH Features
SDCCH Power Regulation
BTS and MS power regulation for the SDCCH can be activated on the system with the parameter SDCCHREG.
Power regulation will decrease the interference in tight re-use networks
SDCCH power regulation should not be used in coverage limited networks
Remember that DL power regulation is never performed on the BCCH carrier
For SDCCH power regulation the “Full” measurement set is always used
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SDCCH Features
Handover on the SDCCH:
SCHO switches on and off the possibility of performing handovers on the SDCCH. It is defined per cell. If SCHO is set to OFF, handover to as well as from that cell is inhibited on the SDCCH.
IBHOSICH switches on and off the possibility of making inter-BSC handover on SDCCH. It is defined per BSC.
IHOSICH switches intra-cell handover on SDCCH on/off. It is defined in the BSC.
SDCCH Handovers should not be used in coverage limited networks
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SDCCH Drop Optimization
Analyze the following issues that could be possible reasons for SDCCH Drops:
Low signal strength Interference Pathloss Imbalance between UL/DL High Timing Advance MS error or Subscriber behavior TCH Congestion Transmission Congestion (LAPD Concentration) Hardware or Transmission failures
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SDCCH Drop Optimization
The following issues are worth taking into account when analyzing SDCCH Drops:
SDCCH Drops and TCH Drops often drop because of the same RF reasons, such as for example insufficient coverage
Only use SDCCH power regulation and SDCCH HO when the network has good coverage
BSC and transmission problems can impact SDCCH drops so investigate Transcoders, A-interface and LAPD
SDCCH Drops on the hopping layer are normally showing worse values than SDCCH on the BCCH
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SDCCH Drop OptimizationC h e c k S D C C H D r o p p e d P e r C e ll
C h eck d ro preaso n
B adq u a lity ?
C h eck IC M C h eck freq u en cy P lan
F req u en cy scanR u n M R R & F A S
L o wS S ?
R efe r to L o w S San a ly s is f lo w ch a rt.
H ig hT A ?
C h eck s ite lo ca tio n& T A L IM
T C HC o n g es tio n ?
C h eck S _ D R -S _ N T C In c rease T C H o r u s in g
C h eck B T S e rro rlo g
H Wfau lt?
S w ap &R ep a ir H W
B
N O
Y E S
Y E S
Y E S
Y E S
Y E S
N O
N O
N O
N O
R ad io F ea tu res , C L S , H C S
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SDCCH Drop OptimizationB
T ra n sm iss io n fa u lt?
P e rfo rm lin kin v e s tig a tio n
C h e c k L in k Q u a lity
C h e c k M S fle e t
P e r fo rm D r iv e T e s t
P e r fo rm M T R /C T R /M R R
P e rfo rm s ite su rv e y
C h e c k a n te n n a in s ta lla tio n
E N D
Y E S
N O
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SDCCH Drop Rate - KPI
The SDCCH Drop Rate is calculated using the following formula:
SDCCH Drop Rate
– Dropped SDCCH Connections of Total Number of SDCCH Connections
[%]100*
1
1
TOTALCELLS
TOTALCELLS
CMSESTAB
CNRELCONGCNDROP
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SDCCH Drop Rate - KPI
The SDCCH Drop Rate is calculated using the following formula:
CNDROP - CNRELCONG
CMSESTAB100 [%]
Successful MS channel establishment on SDCCH (SDCCH HOs counts twice)
Dropped SDCCH connections and TCH & TRA
congestion releases
Number of SDCCHs released due to TCH or TRA congestion (OL & UL)
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SDCCH Drop – Additional indicators The following SDCCH Drop indicators are useful when studying
the SDCCH Drop performance:
– S_DR_SS_OU: Dropped SDCCH Connections due to Low Signal Strength of Total Number of Dropped SDCCH Connections in OL/UL subcell
– S_DR_BQ_OU: Dropped SDCCH Connections due to Bad Quality of Total Number of Dropped SDCCH Connections in OL/UL subcell
100
CNDROP
CDISSSSUBCDISSS
100
CNDROP
CDISQASUBCDISQA
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SDCCH Drop – Additional indicators The following SDCCH Drop indicators are useful when studying
the SDCCH Drop performance:
– S_DR_TA_OU: Dropped SDCCH Connections due to Excessive Timing Advance of Total Number of Dropped SDCCH Connections in OL/UL subcell
– S_DR_OTHOU: Dropped SDCCH Connections due to Other Reasons of Total Number of Dropped SDCCH Connections in OL/UL subcell
100CNDROP
CDISTA
100
CNDROP
CDISTACDISQASUBCDISQACDISSSUBCDISSSCNDROP
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SDCCH Drops – STS Counter Summary
OBJECT TYPES: CELLCCHDR, CLSDCCH, CELLCCHHO
– CMSESTAB: Successful MS channel establishment on SDCCH– CNDROP: Dropped SDCCH connections – CNRELCONG: Number of SDCCHs released due to radio
resource congestion– CDISSS: Number of Dropped SDCCH connections due to Low
Signal Strength– CDISQA: Number of Dropped SDCCH connections due to Bad
Quality– CDISTA: Number of Dropped SDCCH connections due to
excessive Timing Advance
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SDCCH Drops – Examples in ESPA
SDCCH Drop examples in ESPA
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TCH Assignment Failure
KPI TOP 25% TOP 50% Below TOP 50%
Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
KPI TOP 25% TOP 50% Below TOP 50%
Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49
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TCH Assignment Failure – Overview
The TCH assignment success rate measures how often a call set-up, ordered by the MSC, has been successful
The major issues impacting TCH assignment failures are:– TCH congestion– Radio reasons such as coverage and interference– Hardware or transmission problems
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TCH Assignment Failure – Overview
Capacity and Grade of Service
When designing a network one of the important decisions to make is what Grade of Service (GOS) to dimension the network for
The GOS will determine the amount of sites needed and the capacity installed in each site
Grade of Service (GOS) is defined as:– The probability of a lost call due to the reliability of the system and the
availability of circuits and other equipment– Most networks are dimensioned for a GOS = 2%
Capacity are planned to ensure low congestion by using the Erlang B model
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TCH Assignment Failure – Overview
Erlang
An Erlang is a unit of telecommunications traffic measurement. Strictly speaking, an Erlang represents the continuous use of one voice path. In practice, it is used to describe the total traffic volume of one hour
One Erlang represents a circuit occupied for one hour. – 1 Erlang = 1 call Hour/ Hour
Several traffic models exist which share their name with the Erlang unit of traffic. They are formulae, which can be used to estimate the number of channels required in a network
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TCH Assignment Failure – Overview
Erlang B
The most commonly used traffic model in radio networks is Erlang B The Erlang B traffic model is used to work out how many channels are
required if the traffic figure (in Erlangs) during the busiest hour is known. The model assumes that all blocked calls are immediately cleared
The three variables involved are Busy Hour Traffic (BHT), Congestion (Blocking) and Channels:
– Busy Hour Traffic (in Erlangs) is the number of hours of call traffic there are during the busiest hour of operation of a telephone system.
– Blocking is the failure of calls due to an insufficient number of channels being available.
– Channels are the available capacity.
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TCH Assignment Failure – Overview
Hardware Capacity and Configuration
SB T T T E E T BCCH (CHGR 0)
TT T T T T T T Hopping (CHGR 1)
SB
T
TRXBCCH timeslotSDCCH timeslotTCH timeslotEDGE timeslot
Legend
E
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TCH Assignment Failure – OverviewHourly Traffic
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TCH Assignment Failure – OverviewHourly Traffic
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TCH Assignment Failure – Overview
Congestion
Congestion can be defined as follow:– The probability that a call attempt cannot be handled
successfully, because of not enough free circuits and other switching equipments
– The Congestion (Blocking) Probability represented by B (n, A) is determined by Offered traffic A and the number of available circuits n
STS are used to calculate congestion but different formulas exist each showing a different view of congestion
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TCH Assignment Failure – Overview
Congestion – Subscriber congestion
Good to show impact on customer but may hide capacity shortage
STS Formula: Compares failed TCH assignment attempts due to congestion with total number of TCH assignment attempts
100
TASSALL
TxNRELCONGCNRELCONG
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TCH Assignment Failure – Overview
Congestion – TCH Time congestion
When the last idle channel used for speech with a specific speech version is allocated and a new allocation attempt is done irrespective if pre-emption is successful or not, the 'TCH congestion time counters' are started incrementing each second until a channel becomes idle.
The counters TFTCONGS, TFTCONSUB, THTCONGS and THTCONSUB are not started if the allocation attempt is done for intra cell handover due to channel rate change or half rate packing.
Good for optimization but values are worse than what customer perceive
STS Formula: TCH Time Congestion in Underlaid Subcell of Total Measurement Interval
10060
PERLEN
TxTCONGS
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TCH Assignment Failure – Overview
Congestion – Attempt congestion
The 'TCH congestion at assignment' counters are incremented when an allocation attempt of a channel for assignment or immediate assignment fails due to no idle channels available
STS Formula:
100
TxCALLS
TxCONGSHOTxCONGSAS
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TCH Assignment Failure – Overview
Congestion – TCH Hard Time congestion Hard Time congestion counters are only valid for FR The hard time congestion counter is incremented each
second when all radio resources are occupied and when it is not possible to free any resources with help of pre-emption of any kind
STS Formula: TCH Hard Time Congestion in Underlaid Subcell of Total Measurement Interval
10060
PERLEN
GSTFTHARDCON
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TCH Assignment Failure – Overview
Congestion – Congestion at Handover
The 'TCH congestion at handover' counters are incremented when an allocation attempt of a channel for handover fails due to no idle channels available in target cell.
STS Formula: Congestion At Handover of Total Number of Handover Decisions in OL/UL Subcell
100
SUMIHODEC
UBTxCONGSHOSTxCONGSHO
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TCH Assignment Failure – Overview
• Time congestion (GoS for a cell)
• Subscriber perceived congestion (Subscriber Percieved GoS)
Transcoder resource congestion during imm ass on TCH (4 counters FR/HR/SUB). TFNDROP also steps.
Number of SDCCHs released due to TCH or TRA congestion (OL & UL)
TASSALL steps in target cell at successful assignment and in originating cell if assignment fails.
TFTCONGS
PERLEN * 60100 [%]100 [%]
TCH FR congestion time (sec) Starts when congestion and one more allocation attempt is done.
Measurement Time in Minutes AFR UL: TFV3TCONGS
TCASSALL
TASSALL100 [%]100 [%](1- )Failed first TCH assignments:
Alternative:
CNRELCONG + TxNRELCONG
TASSALL - Inc(AB+AW) + Outg(AB+AW)100 [%]100 [%]
Not needed on BSC level
TFTHARDCONGS
TFTCONGS:
TFTHARDCONGS:
B/S T T T T P P P Allocation is still possible.
B/S T T T T P P P When allocation fails.
Also for OL but not for HR
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Limited Internal NPI Training - Accessibility 2005-09-20126
TCH Assignment Failure – Overview
Congestion – Formula comparison
0
10
20
30
40
50
60
70
80
90
100
1 2 3 4 5 6 7 8 9
Cell
Co
ng
es
tio
n
Attempt congestion
Time Congestion
GOS
Subs. Perceived cong.
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Limited Internal NPI Training - Accessibility 2005-09-20127
TCH Assignment Failure – Overview
Congestion Improvement
Congestion can be improved by short, medium and long term actions
Medium and Long term:– Expansions: Add capacity to existing cells– Sectorize omni cells– Indoor and capacity microcells– Additional macro sites
Short term:– Optimization of access parameters– Activation and optimization of capacity features
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Limited Internal NPI Training - Accessibility 2005-09-20128
TCH Assignment Failure – Overview
Congestion Improvement - Expansions Expansions need to be planned in advance – Before
capacity is needed Important for operators to have an expansion procedure in
place Expansions can be limited by a variety of issues, for
example available spectrum The following presentation take a more detailed look at
traffic and capacity management
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Limited Internal NPI Training - Accessibility 2005-09-20129
TCH Assignment Failure – Overview
Congestion Improvement – Short Term
The following features can be used to ensure efficient use of installed capacity and to reduce congestion:
– Overlaid/Underlaid subcells– Cell Load Sharing (CLS)– AMR Half-rate (AHR)– Assignment to Worse Cell– Hierarchical Cell Structures (HCS)
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TCH Assignment Failure – Features
Overlaid/Underlaid Subcells
Cells are split into OL/UL subcell pairs OL and UL share the same BCCH The fundamental idea is that traffic close to the site is
moved to the Overlaid subcell while traffic closer to the edge of the cell is carried on the Underlaid
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TCH Assignment Failure – Features
Overlaid/Underlaid Subcells
Parameter settings available on a subcell level:– Intra Cell Handover– Power Control– Output power– Urgency conditions– Training Sequence Code
Additional statistics and recordings on a subcell level Ability to differentiate and prioritize between hopping and
non-hopping (BCCH) layers
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TCH Assignment Failure – Features
OLUL
OLUL
Only mobiles near the site are allowed on the OL to maximize quality on OL
Allows tighter reuse of channels in the OL
Overlaid/Underlaid Subcells
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TCH Assignment Failure – Features
Overlaid/Underlaid Subcells – Frequency Re-use A tighter frequency re-use is possible on the OL subcell
since the OL channels cause and receive less interference
Fu
Fu
Fu
Fo
Fo
Fo
Fo
Fo
Fo
Fo
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TCH Assignment Failure – Features
Overlaid/Underlaid Subcells - Configuration BCCH in UL, TCH in OL
Chgr 1
Chgr 2 Normally used with high FL
Higher Re-use of TCH channels
OL Subcell
BUL Subcell Chgr 0
BCCH TRX
With Subcell Load Distribution, both CHGR1 and 2 will take traffic close to the site
Lower power on CHGR1 and 2 possible
If CHGR 1 has more freq than CHGR 2, assignments will be made to CHGR 1 first (see channel admin)
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TCH Assignment Failure – Features
Overlaid/Underlaid Subcells - Configuration BCCH in OL, TCH in UL
Chgr 1
Chgr 2
Normal configuration
Tight BCCH re-use
UL Subcell
BOL Subcell Chgr 0
BCCH TRX
The hopping channels in the UL subcell are used during low and normal traffic
At high traffic load, SCLD will move the mobiles with the lowest path loss to the OL subcell
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TCH Assignment Failure – Features
Overlaid/Underlaid Subcells – BCCH in OL Configuration BCCH has many disadvantages relative to TCH’s
– Non-frequency hopping (no frequency diversity)– No power control
BCCH OL is still covering same area as the UL
OL
UL
BCCH
TCH
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TCH Assignment Failure – FeaturesOverlaid/Underlaid Subcells – Subcell change UL to OL
9702676
• A subcell change will be requested when:downlink path loss is equal or below LOL - LOLHYSTANDtiming advance is lower than TAOL - TAOLHYST.
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TCH Assignment Failure – FeaturesOverlaid/Underlaid Subcells – Subcell change OL to UL
9702677
• A subcell change will be requested when:Downlink path loss exceeds LOL + LOLHYST ORtiming advance is equal to or increases above TAOL +TAOLHYST.
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TCH Assignment Failure – FeaturesOverlaid/Underlaid Subcells – DTCB
Equal signal strength border
Pathloss border, LOLPathloss border, LOLPathloss border, LOLPathloss border, LOLPathloss border, LOLPathloss border, LOL
Distance to Cell Border, Distance to Cell Border, DTCB DTCB Distance to Cell Border, Distance to Cell Border, DTCB DTCB
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TCH Assignment Failure – Features
Overlaid/Underlaid Subcells – LOL, TAOL, DTCB
UL -> OL
If ( SSdiff DTCB + DTCBHYST )andIf ( L LOL – LOLHYST )andIf ( ta TAOL – TAOLHYST )
OL -> UL
If ( SSdiff DTCB - DTCBHYST )orIf ( L LOL + LOLHYST )orIf ( ta TAOL + TAOLHYST )
Only if NNCELLSis fulfilled
DTCB = wanted subcell border, set by command per cellSSdiff = SSs- SSstrongest neighbour
Counters for reason for subcell change
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TCH Assignment Failure – FeaturesOverlaid/Underlaid Subcells – Subcell change, LOL/TAOL/DTCB
UL subcell
OL subcell
Traffic taking area
LOL, TAOL, DTCB
SCLD=OFFSCLD=OFF
OL subcell B
UL subcell
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TCH Assignment Failure – Features
Overlaid/Underlaid Subcells – Subcell change with SCLD
Aims to keep traffic on the UL layer until threshold is reached
Without SCLD, mobiles that qualify (LOL, TAOL) will always be on OL even if site is not busy – this minimizes advantage of high reuse layer
With SCLD, when site is not busy, all traffic is carried on UL. When site is busy, mobiles that qualify are promoted to OL.
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Limited Internal NPI Training - Accessibility 2005-09-201439804684
Percentage ofactive TCHs
SCLDUL
SCLDLL
Subcell change OL to UL(no other condition)
No subcell change
Subcell change UL to OL(L < LOL, ta < TAOL)
When the percentage of idle full rate capable TCHs in the UL subcell equals orfalls below SCLDLL subcell changes from the UL to the OL subcell are initiated.When the same percentage exceeds SCLDUL then subcell changes from the OLto the UL are initiated. In between no subcell changes are initiated.
Percentageof idle TCHs
TCH Assignment Failure – Features
Overlaid/Underlaid Subcells – Subcell change with SCLD
Based upon the LOL, TAOL, and DTCB thresholds
Mobiles with highest pathloss are migrated first
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TCH Assignment Failure – FeaturesOverlaid/Underlaid Subcells – Subcell change with SCLD
B
UL subcell
OL subcellLOL, TAOL, DTCBLOL, TAOL, DTCB
SCLD=ONSCLDLL=35 % of idle TS’sSCLDUL=40 % of idle TS’s
SCLD=ONSCLDLL=35 % of idle TS’sSCLDUL=40 % of idle TS’s
OL subcell
UL subcell
Time
Traffic
Time
Traffic
UL CapacityUL Capacity
OL CapacityOL Capacity
OL traffic will be close to the site
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TCH Assignment Failure – Features
Overlaid/Underlaid Subcells – MRR Pathloss
PDF of downlink pathloss. 1 BSC in an urban area with BCCH in OL feature
0
0,05
0,1
0,15
0,2
0,25
Pathloss [dB]
PD
F
OL Subcell
UL Subcell
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TCH Assignment Failure – Features
Overlaid/Underlaid Subcells – Handovers
9702679
CS = YES
9702680
CS = NO
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TCH Assignment Failure – Features
Overlaid/Underlaid Subcells – Parameters
9702683
Main controlling parameters• SCTYPE identifies the subcell type, overlaid or
underlaid, within a cell.
• LOL is the path loss threshold for the serving area ofthe overlaid subcell within a cell. This parameter is setper overlaid subcell.
• TAOL is the timing advance threshold for the servingarea of the overlaid subcell within a cell. Thisparameter is set per overlaid subcell.
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TCH Assignment Failure – Features
Overlaid/Underlaid Subcells – Parameters
9702684
• LOLHYST is the path loss hysteresis for the serving areaof the overlaid subcell within a cell. This parameter is setper overlaid subcell.
• TAOLHYST is the timing advance hysteresis for theserving area of the overlaid subcell within a cell. Thisparameter is set per overlaid subcell.
• BSTXPWR is the base station power at the reference pointfor the locating algorithm on the non-BCCH frequencieswithin a cell. This parameter is set per subcell.
• BSPWRT is the base station output power after the poweron the non BCCH frequency within a cell. This parameteris set per subcell.
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TCH Assignment Failure – Features
Overlaid/Underlaid Subcells – Parameters
9702685
• TSC is the Training Sequence Code for the specifiedsubcell within a cell. This parameter is set per subcell, butit is not available for cells without an overlaid/underlaidsubcell structure. Note that it is recommended not tochange TSC in the underlaid subcells.
• CS indicates if a cell shares the same site as itsNeighbour. This parameter is set per neighboring cellrelation and it can take the values:
• YES, the cell is co-sited with its Neighbour.
• NO, the cell is not co-sited with its Neighbour.
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TCH Assignment Failure – Features
Cell Load Sharing (CLS)
9702744
• the traffic load in the cells are monitored
• if a cell has too high load, MSs close to the cellborder are made to perform a handover
• the handovers are carried out if the receiving cell haslow enough load
Note: Load share evaluations are only performed for existing TCH-connections, i.e. it is not applied during the assignment phase.
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TCH Assignment Failure – Features
Cell Load Sharing (CLS)
9702745
The measure of the load is the percentage of idle TCHs
There are two levels:
• CLSLEVELif the amount of idle traffic channels is equal to ordecreases below CLSLEVEL in a cell, that cell triesto rid itself of some traffic by initiating load sharinghandover to neighboring cells
• CLSACCif the amount of idle traffic channels is above loadCLSACC in a cell, that cell is prepared to acceptincoming load sharing handovers from other cells.
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TCH Assignment Failure – Features
Cell Load Sharing (CLS)
9702897
Locating conditions•CLS HO is not allowed during assignment•CLS HO is not allowed if there is an urgency condition
Conditions for neigboring cell•The cell belongs to the same BSC•The cell belongs to the same HCS-layer•Incoming CLS handovers are allowed (HOCLSACC=ON)
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TCH Assignment Failure – Features
Cell Load Sharing (CLS)
9702749
RHYST:
0 % no reduction of the hysteresis50 % all hysteresis removed, the border
reduced to the nominal cell border100 % negative hysteresis
CLSRAMP: The time it takes to fully decrease the hysteresis
nominal cell border
Hysteresis area
(cell A=serving cell)(cell B=target cell)
Handover border,cell A to cell Bwithout reduction
RHYST = 75%RHYST = 50%
RHYST = 100%
RHYST = 25%
RHYST = 0%
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TCH Assignment Failure – Features
Cell Load Sharing (CLS)
Normal Handover
Nominal cell border
HO border to cell A
HO border to cell B
Cell A Cell B
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Limited Internal NPI Training - Accessibility 2005-09-20155
TCH Assignment Failure – Features
Cell Load Sharing (CLS)
Normal Handover
Nominal cell border
HO border to cell A
HO border to cell B
Cell A Cell B
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TCH Assignment Failure – Features
Cell Load Sharing (CLS)
HO with CLS
Nominal cell border
HO border to cell A
HO border to cell B
Cell A Cell B
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TCH Assignment Failure – Features
Cell Load Sharing (CLS)
Advantage of feature: Does not degrade performance Helps avoiding congestion at pre-defined load Easy usage
Disadvantage of feature: Does not work on cells where there is no traffic on the border If neighbor cell is congested - no off-load
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TCH Assignment Failure – Features
Cell Load Sharing (CLS)
Parametername
Defaultvalue
Recommen-ded value
Valuerange
Unit
CLSLEVEL 20 – 0 to 99 %
CLSACC 40 – 0 to 100 %
CLSRAMP 5 8 0 to 30 s
HOCLSACC OFF ON ON,OFF
RHYST 75 100 0 to 100 %
CLSTIMEINTERVAL 100 100 100 to 1000 ms
ERBANDSINCLUDED OFF – ON,OFF
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TCH Assignment Failure – Features
AMR Half-rate (AHR)
Avoid congestion by using AMR HR instead of AMR FR at high load
Possibility of doubling the AMR capacity by using AHR instead of AFR
Gain in capacity is achieved at a cost to speech quality Traffic changed between HRFR with:
– Dynamic Half Rate Allocation– Dynamic Mode Adaptation
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TCH Assignment Failure – Features
AMR Half-rate (AHR) – Dynamic Half Rate Allocation
DHA allocates AMR HR at call set-up and handover when few idle TCHs remain in the cell
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TCH Assignment Failure – Features
AMR Half-rate (AHR) – Dynamic Half Rate Allocation
Traffic threshold:New calls allocatedHR
Operator setable
EFR
AMR
EFR
AMR
EFR
AMR
EFR
AMR
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TCH Assignment Failure – Features
AMR Half-rate (AHR)
Dynamic HR Allocation
NO
NOYES
YES
NOYES
YESNO
Is the amount of idleFR below theDTHNAMRthreshold?
Is the amount of idleFR below theDTHAMRthreshold?
Is the mobile dualrate?
AllocateAMR HR
Allocatewanted FR
Allocate HR
Is the mobile AMRHR capable?
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TCH Assignment Failure – Features
AMR Half-rate (AHR) – DHA parameters
DHA - Dynamic Half Rate (HR) Allocation DTHAMR - Dynamic HR Allocation threshold for Adaptive
Multi Rate(AMR) capable mobiles DTHNAMR - Dynamic HR Allocation threshold for mobiles
not capable of AMR
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TCH Assignment Failure – Features
AMR Half-rate (AHR) – Dynamic Mode Adaptation Changes channel rate from FR to HR on ongoing calls
when few idle TCHs remain in the cell. From FR to HR, chooses calls with the best reported
quality (both uplink and downlink considered). Changes from HR to FR when the reported quality is below
certain threshold.
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TCH Assignment Failure – Features
AMR Half-rate (AHR) – Dynamic Mode Adaptation
Congestion threshold:Existing calls reallocated HR
Operator setable
EFR
AMR
EFR
AMR
EFR
AMR
EFR
AMR
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TCH Assignment Failure – FeaturesAMR Half-rate (AHR) – Dynamic Mode Adaptation, FR>HR
The total number of idle timeslots in a cell are below the DMTHAMR
and quality for a candidate is better than DMQGAMR . An attempt for FR->HR allocation is
performed.
+HOATFRHRAMR
The allocation is considered a success when the OLD CHANNEL is released. Last
message that arrived to the BSC was ASSIGNMENT COMPLETE
+HOSUCFRHRAMR
The total number of idle timeslots in a cell are below the DMTHNAMR and quality for a candidate is better than DMQGNAMR . An attempt for
FR->HR allocation is performed.
+HOATFRHRNAMR
The allocation is considered a success when the OLD CHANNEL is released.
Last message that arrived to the BSC was ASSIGNMENT COMPLETE
+HOSUCFRHRNAMR
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TCH Assignment Failure – FeaturesAMR Half-rate (AHR) – Dynamic Mode Adaptation, HR>FR
When the quality for a HR connection is considered
poor, rxqual below DMQBAMR. An attempt for
HR->FR allocation is performed.
+HOATHRFRAMR,
The allocation is considered a success when the OLD CHANNEL is released. Last message that
arrived to the BSC was ASSIGNMENT COMPLETE
+HOSUCHRFRAMR, +HOSUCHRFRNAMR.
When the quality for a HR connection is considered poor, rxqual below
DMQBNAMR. An attempt for HR->FR allocation is performed.
+HOATHRFRNAMR
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TCH Assignment Failure – Features
AMR Half-rate (AHR) – DYMA parameters
DMSUPP – Activates dynamic FR/HR mode adaptation, set per cell DMQB - Dynamic Half Rate (HR) to Full Rate (FR) Mode Adaptation due
to bad quality. Values on or off. DMQBAMR - Threshold triggering a switch from a HR channel to a FR if
RXQUAL (DL or UL) for AMR MS is exceeding DMQBAMR, set per cell. DMQG - Dynamic FR to HR Mode Adaptation quality evaluations.
Values on or off. DMQGAMR - Threshold triggering a switch from FR to HR channel if
RXQUAL (DL or UL) is less than DMQGAMR, set per cell DMTHAMR - Dynamic FR to HR Mode Adaptation threshold for AMR
capable mobiles.
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TCH Assignment Failure – Features
AMR Half-rate (AHR) – Example
DYMA load threshold = 30% => 2TS, assuming 8 TCH DHA load threshold = 15% => 1 TS, assuming 8 TCH
With quality-based channel rate change active FR -> HR quality threshold = 15 dtqu HR -> FR quality threshold = 35 dtqu
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TCH Assignment Failure – Features
AMR Half-rate (AHR) – Example
3RxQual : 02023RxQual : 0202 -0
Traffic limit exceeded, move MS from FR to HR
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TCH Assignment Failure – Features
AMR Half-rate (AHR) – Example
3RxQual : 0202 1 -/
Traffic limit still exceeded, move MS from FR to HRTraffic limit still exceeded, move MS from FR to HR
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TCH Assignment Failure – Features
AMR Half-rate (AHR) – Example
RxQual : 3 202 1 0/-3 202 1 0/-
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RxQual : 3 202 1 0/43 202 1 0/4
Quality Threshold exceeded, move MS from HR to FR
Quality Threshold exceeded, move MS from HR to FR
TCH Assignment Failure – Features
AMR Half-rate (AHR) – Example
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TCH Assignment Failure – Features
AMR Half-rate (AHR) – Example
3RxQual : 202 1 0/-
Traffic limit exceeded, move MS from FR to HR
Traffic limit exceeded, move MS from FR to HR
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TCH Assignment Failure – Features
AMR Half-rate (AHR) – Example
RxQual : 3 22 1 0/103 22 1 0/10
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TCH Assignment Failure – Features
AMR Half-rate (AHR) – Example
RxQual : 3 22 0/10/01/00/23 22 0/10/01/00/2
Dyn. HR Allocation allocates HR directly if threshold is exceeded
0/
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TCH Assignment Failure – Features
AMR Half-rate (AHR) – Example
RxQual : 3 22 0/10/01/00/2 0/
Pack HR calls Pack HR calls
-
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TCH Assignment Failure – Features
Assignment to Other/Worse Cell:
The feature operates at call setup when a TCH is to be assigned
The feature makes it possible to assign a TCH in another cell than the one currently serving in the following cases:
– Assign to another cell (preferred) if the other cell is ranked higher by locating
– Assign to worse cell if the call cannot connect to the current cell due to congestion
– Assign to worse cell if locating detects an urgency condition during call setup
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TCH Assignment Failure – Features
Assignment to Other/Worse Cell
Assignment to better cell advantages
– Unnecessary HOs are prevented– Less Interference since call are on best server
Assignment to worse cell advantages– Less TCH congestion – Improved possibility of successful connection– Improved utilization of capacity
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TCH Assignment Failure – Features
Assignment to Other/Worse Cell
9702700
Main controlling parameters
• ASSOC is the parameter that turns the featureAssignment to another cell ON or OFF. Theparameter is set per BSC.
• AW is set per cell and determines if an assignment toa worse cell is allowed from that cell. However, toallow assignment to a worse cell, the parameterASSOC (see above) has to be set to ON as well.
• IBHOASS determines whether assignment to anotherBSC can be performed during assignment
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TCH Assignment Failure – Features
Assignment to Other/Worse Cell
9702886
• AWOFFSET is a signal strength offset parameter used to define therange around the original cell border where an assignment to a worsecell is allowed. It is set per neighbor relation.
• CAND is set per neighbor relation and specifies if the neighbor cellshall be treated as a possible candidate at assignment and athandover. The parameter can take the values:
* AWN, the cell is only a possible candidate at assignment to aworse cell. Note: The cell is not a candidate for assignmentto better cell or handover.
* NHN, the cell is a possible handover candidate in case of an assignment to a better cell and normal handover.
* BOTH, the cell is always a possible candidate, at assignment aswell as at handover.
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TCH Assignment Failure – Features
Assignment to Other/Worse Cell
9702887
• TINIT is a timer used to inhibit locating for a time interval afterImmediate assignment, Assignment or Handover in order to stabilizethe ranking values. The timer is set per BSC.
• TALLOC is used when there is an assignment failure due tocongestion or due to bad radio conditions as a result of the firstcandidate list. A new list is sent after the timer has expired. The timeris set per BSC.
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TCH Assignment Failure – Features
Hierarchical Cell Structures (HCS)
The priority of a cell is given by associating a layer to the cell.
Each layer is also belonging to a HCS band. The lower the layer (and HCS band), the higher is the priority.
This provides a mechanism where by the traffic may be directed towards cells belongings to the lower layer, so as the lower layer cells can serve all the traffic with sufficient signal strength
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TCH Assignment Failure – Features
Hierarchical Cell Structures (HCS)
Small cells have limited coverage Large cells have limited capacity Locating is primarily based on “best server” In certain situations we want to favor a “weaker cell”
– Combined microcell / macrocell network– Multiband GSM 900 / GSM 1800
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TCH Assignment Failure – Features
Hierarchical Cell Structures (HCS)
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TCH Assignment Failure – Features
Hierarchical Cell Structures (HCS)
Congestion
Layer 4
Layer 2
Layer 4
Layer 4
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TCH Ass. Failure – Optimization
Analyze the following issues that could be possible reasons for TCH Assignment failures:
Low Signal strength or no dominant serving cell Interference Congestion on TCH Incorrect use of Capacity features Faulty Hardware or transmission Incorrect Output power
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TCH Ass. Failure – Optimization
It is worth taking into account the following issues when optimizing TCH Assignment failures:
Make sure that problems with network availability are not the cause of congestion
Often congestion problems are caused by network design issues such as cells covering a large area
Try to make sure that as far as possible calls are made on the best serving cell to reduce the negative impact on Retainability and Voice Quality
Radio capacity features such as for example CLS should preferably be only used as short or medium term solutions for congestion.
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TCH Ass. Failure – OptimizationCheck TCH congestion
Low TCH Assignment Success Rate
Congestion on TCH ?
Check output power
Low outputpower?
Check output powerparam eters
Corrupt param etersetting?
Check S igna l S trength o fBC CH and TC H
Low SS for ca llaccess?
Check BTS E rror Log
HWfault?
NO
YES
END
Correct param eters
Swap & repa irHW
Check coverage p lo ts
Perform drive tests
Dom inantserver exists?
YES
NO
YES
AddBTS
NO
Add trance ivers or BTSYES
NO
YES
YES
NO
Adjust TCH outputpower
NO
Check In terference
D isturbanceon SDC CH ortarget TCH?
Im prove & ad justfrequency p lan
NO
YES
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TCH Assignment Failure – KPI
The TCH Assignment Failure Rate is calculated using the following formula:
TCH Assignment Failure Rate
[%]100*1
1
1
TOTALCELLS
TOTALCELLS
TASSALL
BTHCASSALSUTHCASSALLUBTFCASSALLSTFCASSALL
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TCH Ass. Failure – Examples in ESPA
TCH Assignment Failure (Service Denied) examples in ESPA
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Accessibility - Exercise
Accessibility Exercise
Perform an Accessibility Audit on a network using ESPA Create an Accessibility document summarizing findings and
recommendations Review of Accessibility documents
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Acknowledgement
The material used in this presentation has been obtained from various sources, documents and presentations in the Ericsson world, created by a large variety of people
I would like to acknowledge all the authors/creators of the used material
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Limited Internal NPI Training - Accessibility 2005-09-20194