gsm-kpi-optimization

ALUMS‐OMP‐L2‐014 ALUMS OPERATIONAL PROCESS MANUAL
EDITION 1.2 EFFECTIVE DATE: 01January 2011

KPI Optimization Process
Appendix‐3
refers to page 15 of Network Performance Monitoring & Optimization Process
Huwaei


PROCESS for SDCCH Assignment Success Rate Optimization:
Definition: When From the MS SDCCH Request is sent to Base Station and if MS
successfully gets the SDCCH in response SDCCH Assignment has done successfully.
PROCESS for Optimization:
1. Identify the Bad performing Cells for SDCCH Assignment Success Rate
2. Take the detailed report showing (Ex. Total SDCCH Assignment Request, Total SDCCH
Assignment Successful)
3. Follow the below mentioned Process after Analyzing detailed report...
4. From Report Check whether you have Idle SDCCH available in cell or not for SDCCH
Assignment; because the Main factor for lowering SDCCH Assignment success rate is
SDCCH congestion.
5. SDCCH Congestion:
a. Check The SDCCH Requests (Immediate Assignment Measurement Per Cell
Report form M200)
b. Ex. Call purpose, SMS, Location Update
c. If you find High SDCCH Request and low TCH utilization Check “SDCCH
Dynamic Allocation Allow” feature is enabled or not? if not enable this feature.
d. If you have very High SDCCH Request for Location Updating; optimize the LAC
boundary.
e. Only For some exceptional cases you can increase the Static SDCCH Time Slots.
6. Check Hardware/Transmission alarms; Resolve if find any.
7. Audit for any parameters related discrepancies and define as per standard parameters set.
8. RF and Environmental Factors:
a. Low Coverage Areas (Try to reduce low coverage patches with physical
optimization; New sites)
b. Interference/ Bad quality/ UL-DL Imbalance;
c. Check the states for TRx on which SDCCH is configured can be issue of TRx
also; Change TRx if you found random behavior of TRx.
9. After all rectification observe the subsequent days report if you still find the problem
repeat the same process with due care to Pin Point the actual cause.


Fish bone diagram for the root cause analysis high SDCCH congestion rate
PROCESS for SDCCH DROP Rate Optimization:
Definition: When MS is already on SDCCH and in-between communication with Base
station SDCCH channel got disconnected abruptly then SDCCH Drop has occurred.
1. Identify the Bad performing Cells for SDCCH Drop Rate
2. Take the detailed report showing (Ex. Total SDCCH Assignment Successful, Total
SDCCH Dropped)


4. The Main Reasons for High SDCCH Drop Rate are improper Parameters Configuration
and Bad RF & Environmental factors.
5. First Audit for any parameters related discrepancies and define as per standard
parameters set.
6. Check for Neighbor Relations and correct if it is not proper.
7. For counter level analysis refer “Call Drop Measurement per Cell” report from M2000.
8. Low Coverage: Through Drive Test Find out the low coverage patched and try to
improve with physical optimization; New site; coverage enhancement features for some
cases(Ex. Power Boost Tech, No Combining, TMA/TMB)
9. Interference: Check for interference from repeaters, Intra-Network interference due to
aggressive reuse or improper Freq., Inter-Network can also be the case. Find out the
actual cause and rectify it.
10. Antenna System: High VSWR due to feeders, Improper antenna configuration(Ex. Sector
cable Swap)
11. Check for Hardware Issue and rectify if you found any.
12. After the activity check the subsequent days report and repeat the procedure for pin
pointing the actual cause.

Fish bone diagram for the root cause analysis for high SDCCH drop rate


PROCESS for RACH (Random Access Channel) Success Rate
Optimization:
Definition: Random Access Channel (RACH) is used by the MS on the “uplink” to request
for allocation of an SDCCH. This request from the MS on the uplink could either be as a page
response (MS being paged by the BSS in response to an incoming call) or due to user trying to
access the network to establish a call. For all services there will CH REQ (Channel Request)
from MS and in the response of CH REQ if MS will get the IMM ASS CMD (Signaling Ch)
Access to system is successful. Nature of this Access REQ is random so it is call Random Access
Channel Request.
1. Identify the Bad performing Cells for RACH Success Rate
2. Take detailed report and analyze for no of failure of Request and failures.
3. The main reasons for bad RACH success rate could be access from very distant place
with very low coverage; Parameters Configuration discrepancies.
4. First Check for Parameters Configuration discrepancies and correct as per standard
parameter set.
5. The main parameters to look for Huawei
a. “MS MAX Retrans” can set depending upon Traffic and Clutter.
b. “Tx-Interger” will reduce the RACH collision and can improve RACH success
rate.
c. “T3122” waiting time for next network access.
d. “RACH Min.Access Level(dbm)” very important parameter for low coverage
rural areas.
e. “CCCH conf” & “BS_AG_BLKS_RES” check properly defined or not? Because
if you have overload with AGCH “IMM ASS” can’t be send in the response of
CH REQ.
6. Check for Hardware Issues (Ex. BTS sensitivity has very crucial role to play here)
7. Check for Uplink Interference and quality.
8. Check for UL-DL imbalance and correct if any problem.


9. After the activity check the subsequent days report and repeat the procedure for pin
pointing the actual cause.

Fish Bone diagram for the root cause analysis of poor Random Access Success


PROCESS for TCH Assignment Success Rate Optimization:
Definition: When From the MS TCH Request is sent to Base Station and if MS successfully
gets the TCH in response TCH Assignment has done successfully.
1. Identify the Bad performing Cells for TASR( TCH Assignment Success Rate)
2. Take the detailed report showing (Ex. Total Assignment Request, Total Assignment
Successful)
4. From Report Check whether you have Idle TCH available in cell or not for Assignment
and follow the below process.


A & B in above Flow chart are measurement Points for TCH Assignment Failures...
5. As per the Above Process If you have already used “Re-Assignment”, “Directed Retry”
and “Queuing” features and still you are having issue with TCH Congestion (No Idle
TCH)... Try to Decrease Half Rate Triggering Thresholds...
6. Ex. Below Parameters for Huawei System
“TCH Busy Traffic Threshold (%)”
“AMR TCH/H Prior Allowed”
“AMR TCH/H Prior Cell Load Threshold”
7. Check for discrepancies with Parameter Configuration and set as per Standard Parameters
set available.
8. If you find Issue is not with High Traffic and Congestion... Check Hardware Issue (Ex.
BTS/BSC/MSC hardware / UL-DL Imbalance due to VSWR) resolve if you find any.
9. Transmission Issues at A-bis/A-ter/A links
10. If Hardware is Ok check for Bad RF Environment... (Very low Coverage, High
Interference, Bad Quality, Call from Distant Place (TA).
11. Follow below Process for Above Points... You can check the counters Report for Pin
pointing the actual cause. (Ex. Assignment Per Cell Report from M2000)


12. Correct the affected area (Ex. If call is getting originated from High TA and getting failed
due improper strength ; Optimize the Site Coverage with Physical Optimization) and
check the subsequent days Report; If you still find the issue follow the same flow right
from the starting with due care to PIN Point the Actual cause..
13. TBF Success Rate
14. Average GPRS RLC throughput & Average EDGE RLC Throughput
15. Downlink Multislot Assignment Success Rate
16. SDCCH Assignment Success Rate
17. SDCCH DROP Rate
18. ACH (Random Access Channel) Success Rate
19. Assignment Success Rate


PROCESS for Rx Quality Optimization:
• Definition : Rx Quality is measure of BER of radio link between MS and BTS
• Poor Speech Quality could be due to
• Patchy Coverage ( holes)
• No Target cell for Handover
• Echo , Audio holes, Voice Clipping
Interference ---:
• Co-channel
• Adjacent channel
• External
• Multipath
• Noise
Speech Quality Parameters
• RxQUAL: Measured on the midamble.
• Indicates poor speech quality due to radio interface impairments
• FER : Measured on the basis of BFI ( Ping -Pong effect on speech )
• Preferred under Frequency Hopping situation
• Audio holes: Blank period of speech, due to malfunctioning of Transcoder boards or
PCM circuits.
• Mean Opinion Score (MOS) : ITU standard for estimating speech quality


1) Physical optimization
2) New cell dependency
3) Overshooting
4) Neighbor list tuning
5) BCCH tuning (Freq plan)

From M2
Quality.
ALUMS‐O
       EDITION 1.2
2000 extract
OMP‐L2‐014 ALU
2           EFFECTIV
Rx Quality
UMS OPERATIO
VE DATE: 01Janu
measuremen
ONAL PROCESS M
uary  2011
nt distributio
MANUAL
on Counters to know Trx

x –cell wise Rx


PROCESS for HOSR Optimization:
Definition: HO activity is performaed to maintain – Call continuity and call quality . The
inputs that the BSC uses for making a handover decision, from the received MRs from the MS is
the DL signal strength, DL quality, and the signal strength of the six best reported neighbours.
From the serving BTS, for the same MS the BSC will use UL signal strength, UL quality and
TA.
Handover Process:
The GSM handover process uses a mobile assisted technique for accurate and fast
handovers, in order to:
- Maintain the user connection link quality.
- Manage traffic distribution
The overall handover process is implemented in the MS,BSS & MSC.
Measurement of radio subsystem downlink performance and signal strengths received
from surrounding cells, is made in the MS.
These measurements are sent to the BSS for assessment.
The BSS measures the uplink performance for the MS being served and also assesses
the signal strength of interference on its idle traffic channels.
Initial assessment of the measurements in conjunction with defined thresholds and
handover strategy may be performed in the BSS. Assessment requiring measurement
results from other BSS or other information resident in the MSC, may be perform. in
the MSC.
The MS assists the handover decision process by performing certain measurements.
When the MS is engaged in a speech conversation, a portion of the TDMA frame is idle
while the rest of the frame is used for uplink (BTS receive) and downlink (BTS transmit)
timeslots.


During the idle time period of the frame, the MS changes radio channel frequency and
monitors and measures the signal level of the six best neighbor cells.
Measurements which feed the handover decision algorithm are made at both ends of the
radio link.
Classification By Reason:
• Emergency HO
– Timing advance (TA) Emergency HO
– Bad quality (BQ) Emergency HO
– Rx Level Drop Emergency HO
– Interference emergency HO
• load HO
• Normal HO
– Edge HO
– Layer HO
– Power budget (PBGT) HO
• Fast moving MS HO (Speed-sensitive HO )
10. Identify the Bad performing Cells for HOSR
11. Take the detailed report showing cause & target cell
12. Check congestion; hardware Alarm; Quality; Rx level
13. Late Handover – Handover margin (like Rx level-Rx Qual etc )need to define properly.
14. Ping-Pong Handover – A proper Hysteresis is used to prevent the Ping Pong effect. This
can be caused by fading
15. Unnecessary Handover – more number of handovers, higher risk of facing quality
problem and even in call drop


16. Missing neighbor – Best server is not in there in neighbor list
17. BCCH Missing
18. Same BCCH & BSIC combination
19. one way neighbor handover
20. Neighbor cell in other BSC- need to define correct CGI,BCCHNO,BSIC
21. Congestion on other cell
Fish bone diagram for the root cause analysis for high handover failure rate
PROCESS for TCH drop Optimization:
Definition: TCH drop (or a dropped call) could be broadly classified into 3 sub classes:
1. Degradation of the links (Uplink and Downlink): either degradation of Signal Strength
which falls near or lower than the sensitivity of the base station (around to -110 dBm) or
that of the mobile (around -104dBm) or degradation of quality of the links (Uplink and
Downlink) often due to interference.
2. Excess TA (TA>63 or excess path imbalance due to high TA).
3. Other Reasons.


Call drops are identified through SACCH messages. A Radio Link Failure Counter value
is broadcast on the BCH. The counter value may vary from network to network. At the
establishment of a dedicated channel, the counter is set to the broadcast value (which will
be the maximum allowable for the connection). The mobile decrements the counter by 1
for every FER (unrecoverable block of data) detected on the SACCH and increases the
counter by 2 for every data block that is correctly received (up to the initial maximum
value). If this counter reaches zero, a radio link failure is declared by the mobile and it
returns back to the idle mode.
If the counter reaches zero when the mobile is on a SDCCH then it is an SDCCH Drop.
If it happens on a TCH, it is a TCH drop.
Sometimes an attempted handover, which may in itself have been an attempt to prevent a
drop, can result in a dropped call.
When the quality drops, a mobile is usually commanded to perform a handover.
Sometimes however, when it attempts to handover, it finds that the target cell is not
suitable. When this happens it jumps back to the old cell and sends a Handover Failure
message to the old cell. At this stage, if the handover was attempted at the survival
threshold, the call may get dropped anyway. If on the other hand the thresholds were
somewhat higher, the network can attempt another handover.
1 2
C h a n n e l R e q u e s t C h a n n e l R e q u e s t
Im m A s s ig n m e n t Im m A s s ig n m e n t
S e rvic e R e q u e s t S e rvic e R e q u e s t
S ig n a llin g S D C C H S ig n a llin g
: :
S ig n a llin g S p e e c h
T C H
R L T = 0 ; D R O P S R L T = 0 ; D R O P S
S D C C H D R O P ! T C H D R O P !
3 S D C C H / T C H
H a n d o ve r C o m m a n d
H a n d A c c e s s
H a n d o ve r F a ilu re

From M2
ALUMS‐O
       EDITION 1.2
2000 extract
OMP‐L2‐014 ALU
2           EFFECTIV
Call Drop M
UMS OPERATIO
VE DATE: 01Janu
Measuremen
ONAL PROCESS M
uary  2011
nt counters to
MANUAL
o know cause.


8.3.1 Fish bone diagram for the root cause analysis for high TCH Drop Rate
Figure 1: Fish bone diagram for the root cause analysis for high TCH Drop Rate
Figure 2: Fish bone diagram for the root cause analysis for high TCH Drop Rate
T C H D r o p R a te
L o w S ig n a l S tr e n g th D L L o w S ig n a l S tr e n g th U L
B a d Q u a lity D L B a d Q u a lity U LH ig h T A /R F S p illa g e /P a th Im b a le n c e
E x te r n a l In te r fe r e n c e
TCH Drop Rate
Hardware Faults Drops due to Other Reason
Power Control Sudden Lost ConnectionHandover Failures
HCSCLS
Assignment to another cell


PROCESS for SCR:
Definition: SCR = ((Total Call - INTERNAL_FAILURES)/TOTAL CALLS) x 100%...
Total Call = BSS Originate Call->2G ORG CALL ATTEMPT TIMES
+ Trunk Office Direction Incoming Office Traffic->SEIZURE TIMES
INTERNAL_FAILURES = Failure Reason Traffic-> CAUSE013_switch equipment congestion
+ CAUSE016_temporary failure
+ CAUSE027_switch equipment failure
+ CAUSE061_no CR resource
+ CAUSE062_no CCB resource
+ CAUSE166_network error
+ CAUSE169_temporary error
+ CAUSE170_device congestion
+ CAUSE201_IWF resource unavailable
1. Identify the Failure reasons count for each internal failure reason.
2. Check detailed explanation of cause values those contributing the major factor.


PROCESS for Paging Success Rate:
Definition: Paging Success rate is the percentage of valid page responses received by the
system
PSR = ( CC service first paging response number + CC service repeat paging response number+
SMS service first paging response number + SMS service repeat paging response number) / (CC
service first send paging number + SMS service first send paging number)*100
1. Removal of non existing Cell site database created in BSCs
2. Correcting the number of LACs per BSC (Minimizing the number of LAC per BSC)


3. Standard template of Cell site database in each BSC.
1 Fish bone diagram for the root cause analysis of poor Paging Success Rate
Figure 1 : Root Cause for Poor Paging Succ Rate (1)
Figure 2 : Root Cause for Poor Paging Succ Rate (2)
P o o r P a g in g S u c c R a te
1 . In c o rre c t C e ll P a ra m e te rs
4 . P o o r R F 2 . E x c e s s p a g in g D is c a rd s
3 . In c o rre c t M S C P a ra m e te rs
5 . P o o r P a g in g S tra te g y
Poor Paging Succ Rate
8. incorrect LAC Dimension 6. SDCCH Congestion
9. ABIS , A interface Congestion 7. Combined BCCH
10. ABIS , A interface fluctuations, Errors
11. decrease signalling load on CCCH


PROCESS for SS7 Signaling Load:
Definition:
1. TRANSMITT LINK OCCUPANCY (%)= ((( NO. OF SIGNALLING OCTETS
TRANSMITTED + 6 *(MSU TRANSMITTED + MSU RETRANSMITTED) ) /
(248000 * 3600 * 0.2) ) * 100) -----> HSL
2. TRANSMITT LINK OCCUPANCY (%)= ((( NO. OF SIGNALLING
OCTETSTRANSMITTED + 6 *(MSU TRANSMITTED + MSU RETRANSMITTED) )
/ (8000 * 3600 * 0.4) ) * 100) -----> OTHER THAN HSL
3. RECEIVE LINK OCCUPANCY (%)= ((( NO. OF SIGNALLING OCTETS RECEIVED
+ 6 *(MSU RECEIVED) ) / (248000 * 3600 * 0.2) ) * 100) -----> HSL
4. RECEIVE LINK OCCUPANCY (%)= ((( NO. OF SIGNALLING OCTETS RECEIVED
+ 6 *(MSU RECEIVED) ) / (8000 * 3600 * 0.4) ) * 100) -----> OTHER THAN HSL
1. Identify the signaling links whose utilization is going above 80%.
2. Prepared Plan for additional signaling links as per requirement…


PROCESS for TBF Success Rate Optimization:
Definition: Temporary Block Flow (TBF) is a physical connection used by the two Radio
Resource entities to support the unidirectional transfer of PDUs on packet data physical
channels. The TBF is allocated radio resource on one or more PDCHs and comprises a number
of RLC/MAC blocks carrying one or more LLC PDU. TBF Success Rate is when during a
data session, TBFs are successfully established on UL and DL.
22. Identify the Bad performing Cells for TBF Success Rate.
23. Identify the bifurcation of Poor TBF Success Rate: whether UL or DL is poor or it is poor
in both directions.
24. Take the detailed report showing (Ex. Total TBF Requests, Total TBF Success, Failure
reasons)
25. Identify the failure reasons after analyzing detailed report and follow the below
mentioned process. Failure is mainly due to TBF Congestion or MS No response.
26. TBF Congestion:
a. Check The Static and Dynamic PDCH definition from BSC Configuration data)
b. If you find Zero Static or Dynamic PDCH, define the same.
c. If PDCH definition is sufficient as per the guidelines, then check whether the TBF
requests are high. If requests are high, then we need to define more PDCHs in the
cell. But before defining more PDCHs, check whether the Voice Utilization is not
high and there is no TCH Congestion in the cell..
27. Check Hardware/TRX alarms; Resolve if find any.
29. MS No Response: RF and Environmental Factors:
a. Low Coverage Areas (Try to reduce low coverage patches with physical
optimization; New sites)
b. Interference/ Bad quality/ UL-DL Imbalance;


c. Check the states for TRx on which PDCH is configured can be issue of TRx also;
Change TRx if you found random behavior of TRx.
After all rectification observe the subsequent days report if you still find the problem repeat the
same process with due care to Pin Point the actual cause.
PROCESS for Optimization of Average GPRS RLC throughput and
Average EDGE RLC Throughput:
Definition: Throughput is the amount of data uploaded/downloaded per unit of time.
1. Identify the Bad performing Cells for Poor GPRS/EDGE Throughput.
2. Identify the bifurcation of Poor Throughput: whether UL or DL is poor or it is poor in
both directions.
3. Take the detailed report showing (Ex. Total TBF Requests, Coding Scheme Utilization)
4. Identify the cells after analyzing detailed report and follow the below mentioned process.
5. Take the configuration dump of the poor cells:
high and there is no TCH Congestion in the cell.
d. Check whether there are enough Idle TS defined at the site. If not, definition to be
done.
6. Check whether it is due to poor radio conditions/interference; check C/I. Perform a drive
test to analyze the cell in more detail.
7. Check Gb Congestion/Utilization at the BSC/PCU.


PROCESS for Optimization of Downlink Multislot Assignment
Success Rate:
Definition: User timeslot request based on traffic types and MS multi-timeslot capability
and the actual timeslot allocated by the system which can also be termed as Downlink Multislot
Assignment Success rate.
1. Identify the Bad performing Cells for Poor DL Multislot Assignment.
2. Take the detailed report showing (Ex. Total TBF Requests, Failure in terms of TS
requests)
3. Identify the cells after analyzing detailed report and follow the below mentioned process.
4. Take the configuration dump of the poor cells:
high and there is no TCH Congestion in the cell.
d. Check the multiplexing thresholds and upgrade/downgrade reports.
5. Check whether it is due to poor radio conditions/interference; check C/I. Perform a drive
test to analyze the cell in more detail.


6. Check Gb Congestion/PCU-DSP Utilization.


KPI Optimization Process
Appendix‐3 (contd..)
refers to page 15 of Network Performance Monitoring & Optimization Process
Alcatel & ZTE

The document covers the TCH Assignment Success rate & SDCCH Congestion optimization process for
Alcatel & ZTE GSM Radio Networks to be complaint by Alcatel‐Lucent Managed Solutions India Pvt. Ltd
Radio Optimization Engineers & associated staff.


Contents
1. PURPOSE………………………………………………………………………………………….4
2. SCOPE………………………………………………………………………………………………4
3. INTRODUCTION……………………………………………………………………………….4
4. DEFINITION……………………………………………………………………………………..5
4.1 TCH ASSIGNMENT SUCCESS RATE (TASR)
4.2 SDCCH CONGESTION (SD CONG)
5. VENDOR WISE COUNTER BASED DESCRIPTION
5.1.1 ALCATEL TASR DESCRIPTION
5.1.2 ZTE TASR DESCRIPTION
5.2.1 ALCATEL SD CONG DESCRIPTION
5.2.2 ZTE SD CONG DESCRIPTION
6. VENDOR WISE ROOT CAUSE ANALYSIS & OPTIMIZATION STEPS
6.1.1 ALCATEL TASR ANALYSIS
6.1.2 ZTE TASR ANALYSIS


6.2.1 ALCATEL SD CONG ANALYSIS
6.2.2 ZTE SD CONG ANALYSIS
7. APPENDIX
7.1 SDCCH DIMENSIONING
7.1.1 ALCATEL SD DIMENSIONING METHOD
7.1.2 ZTE SD DIMENSIONING METHOD

8. Optimization Process for other Radio KPIs


1. PURPOSE
This document serves as a process guideline for key performance indicator (KPI)
optimization such as TCH Assignment Success Rate (TASR) and SDCCH (SD)
Congestion in advanced wireless GSM 2G networks in multi‐vendor scenario
comprising of Alcatel (B10 version) & ZTE (ZXG10‐2.97) Radio systems.

2. SCOPE
This document is meant for experienced wireless 2G GSM professionals involved
in key performance indicator (KPI) optimization specifically TCH Assignment Success
Rate (TASR) and SDCCH (SD) Congestion in multi‐vendor scenario comprising of
Alcatel (B10 version) & ZTE (ZXG10‐2.97) Radio systems.
Also, the document targets the internal customers of ALUMS with sufficient
background in GSM.
3. INTRODUCTION
Dynamic network configuration changes, operation & maintenance activities
with exponentially rising curve of subscriber density for wireless services prompts
the radio engineers to be quick & effective to retain the Quality of Services (QoS) in
current scenario.
TCH Assignment Success Rate (TASR) and SDCCH congestion are two critical
pointers to quality of network accessibility during busy hours & non busy hours for
the subscribers.
Ideally, cells in the network needs to be designed for 0% SDCCH congestion &
100% TASR to ensure 100 % error‐free subscriber services initiated from the MS to
the MSC. Practically, the real time radio environment (changing clutters), high level
of faults/outages in network elements (MSC/BSC/TRAU/BTS) and higher subscriber
services (Voice/Data) demands destabilizes the designed network capacity to result
in degradation of TASR & SDCCH congestion.


In order to achieve sustainable demand, the network resources are re‐
dimensioned periodically with coverage/capacity/KPI optimization as when required
basis and TASR / SD Congestion stands prime focus area as to be discussed.

4. DEFINITION
In general, TASR is defined as percentage ratio of successful TCH
Attempts to TCH Attempts over an observed period of time. It measures how
often setup message sent from MS for Mobile Originating Call (MOC) or Mobile
Terminating Call (MTC) is successful during TCH allocation procedure from MSC.
General Equation:‐
TASR (%) = (TCH Attempt seizures/TCH Attempts) *100
GSM Layer 3 Equation:‐
TASR (%) = (No. of Assignment Complete msg. /Assign Requests.)*100
Figure 1 Successful TCH Assignment phase


Although, TASR indicates successful TCH seizures for MS connectivity with
the network during call phase. Better way to approach TASR improvement is to
focus on TCH Assignment failure rate which is equally important.

High TCH Assignment failures can be observed for under reasons:
• Hardware faults in Network elements (BTS/BSC/MSC)
• Software & Network configuration database discrepancy
• Low Coverage zone
• Path loss issue
• High Interference from internal/external sources
• Transmission issues in A‐bis/A‐ter links
• CIC mismatches between BSC‐MSC
• BTS wiring diagram issue
• Incorrect Feature, Parameters & Timer usages
• Mismatch in TRX radio timeslots mapping on RSL
• Sector blocking due to clutter issues
• TCH Congestion
• High Traffic Utilization
TCH
ASSIGN‐
MENT
PHASE


• Wrong antenna type deployments for required clutters
• Invalid counter pegging
• Incorrect counter selection for failure monitoring
TASR improvement based on above mentioned causes is covered in
Vendor wise root cause analysis & Optimization steps section.  Many internal
system reports based on measurable counters are required to co‐correlate to
arrive at certain conclusion for improvement action and are covered in up‐
coming sections. Assignment failure cause points are shown in figure as under:
Figure 2 TCH Assignment failure cause points
MS            BTS                      BSC    TRAU            MSC
Um A‐bis A      A‐ter


Legend:
Assignment failure cause point:‐
In general, SDCCH Congestion is defined as the percentage ratio of SDCCH
Blocks to total SDCCH Attempts over an observed period of time. It measures
how often Mobile Station (MS) is unable to access the network for various
signaling (MM/CC) procedures to ensure subscriber service establishment.
General Equation:‐
SD CONG (%) = (SD Blocks/SD Attempts) *100
GSM Layer 3 Equation:‐
SD CONG (%) = (Immediate Assign. Rejects /Channel Required) *100

Figure 3 SDCCH Assignment phase

In case of SDCCH
Congestion,
IMMEDIATE
ASSIGNMENT
REJECT message
flows from BTS to
MS on AGCH


Various Mobility Management (MM) sub‐layer and Connection
Management (CM) sub‐layer procedures require usage of SDCCH channel
between MS and MSC. Some of the commonly observed signaling procedures
on SDCCH are as under:
• Normal Location Update (LU)
• Periodic Registration
• IMSI Attach/Detach
• Call Setup (MOC/MTC)
• SMS point to point (MO/MT)
• Fax Setup
• Supplementary services (USSD)
Most of the root causes for SD Cong % are listed under:
• Improper SDCCH Dimensioning
• Incorrect usage of available features,  parameters & timers
• High TCH Utilization
• Non optimized LAC Borders (Inter cell/Inter BSC/Inter MSC)
• Configured but out of service SDCCHs
• Phantom RACHs (Co BCCH/BSIC )
SDCCH
ASSIGN‐
MENT
PHASE


• Overshooting cells inside the clutter
• Equipment failure (Cell/TRE/BSC)
• Increased mean hold time of SDCCH due to large no. of Layer 3
message flows between MS‐MSC
• LAPD congestion in A‐bis interface

SDCCH Congestion cause points are shown in figure as under:
Figure 4 SDCCH Congestion cause points
MS            BTS                      BSC    TRAU            MSC
Um A‐bis A      A‐ter


Legend:
SDCCH Congestion cause point:‐
SDCCH Congestion cause points are the locations where probable event
failures are observed due to various reasons mentioned above.
SDCCH Congestion improvement based on above mentioned causes is
covered in Vendor wise root cause analysis & Optimization steps section.  Many
internal system reports based on measurable counters are required to co‐
correlate to arrive at certain conclusion for improvement action and are covered
in up‐coming sections.

5. VENDOR WISE COUNTER BASED DESCRIPTION


5.1.1 ALCATEL TASR DESCRIPTION
Alcatel BSS system (B10) evaluates the TASR based on certain measurable
counters from NPO with below relation:
TASR (%) = MC718 / [MC140a‐(MC142e+MC142f)*100.
Also, MC142e=C142a+C142c & MC142f=C142b+C142d.
Counters increment or decrement based on various factors governing the
network operator settings and real time operational status. It is important to be
aware of TASR % value on cell basis to visualize the impact & validity of these
counters.

5.1.2 ZTE TASR DESCRIPTION
ZTE BSS system (ZXG10‐V2.97) evaluates the TASR based on certain
measurable counters from OMCR with below relation:
TASR % = {(C11609‐C11696) ‐ (C11610+C11654+C11658‐C11697‐
C116101‐C116133)} * 100 / (C11609‐C11696)
Counter description & details can be found in Appendix section or on
click to respective counter in quicker way.

5.2.1 ALCATEL SD CONG DESCRIPTION
Alcatel BSS system (B10) evaluates the SD CONG based on certain
measurable counters from NPO with below relation:
SD CONG (%) = [MC04] / [MC04 + MC148]*100
Counter description & details can be found in Appendix section or on
click to respective counter in quicker way.


5.2.2  ZTE SD CONG DESCRIPTION
ZTE BSS system (ZXG10‐V2.97) evaluates the SD CONG based on certain
measurable counters from OMCR with below relation:
SD CONG % = (C11625 ‐ C11626 + C11697) *100 / (C11625 + C11696)

6. VENDOR WISE ROOT CAUSE ANALYSIS & OPTIMIZATION STEPS

6.1.1 ALCATEL TASR ANALYSIS
Alcatel (BSS 10 release) TASR analysis requires monitoring of the KPI from
BBH report circulated from localcentral MIS team on daily basis at cell level.
It involves clear understanding of associated counter based internal
system reports from NPO/OMC server as under which reflect the root causes for
poor TASR % values and needs study of these reports in following sequence
based on degradation severity:
• Active alarms report
• Path balance report
• RTCH Assignment report
• Quality/Level report
• Timing Advance (TA) report
• Network parameter checks
Refer Appendix Sample Reports section for screenshot.
Flow‐diagram for TASR improvement report checks:

TASR CYCLE


Below Flowchart 1 represents the TASR% improvement cycle based on
trigger condition and root causes:


                                                                  Yes                                   No



START
Identify & filter TASR
% from BBH report
for analysis
TASR %
<98.75%
No further
investigation reqd.
Check & clear
active alarms
Check for TRE
Path bal.  >5 dB
without TMA
Verify the
Tx/Rx path &
rectify it
Active Alarms
Path Balance
RTCH Assign
Quality/Level
Timing advance
N/w parameter
BSS problem, check Abis
media stability with any
CIC mismatch at Ater
front (GTCNAAFLCPMR)


                                     No

               Yes

                                                     Yes

STOP
Check failure
phase in RTCH
Assign report
Check BBH report
for TASR % value
after problem
correction
TASR %
>=98.75
Active Alarms
Path Balance
IOI
BER (U/L‐D/L)
Timing advance
N/w parameter
GTCNAFLRR
>GTCNAFLBR
Radio problem, check
Quality/Level/TA RMS
reports with any TCH
congestion (GTCNACGR)
Revisit the
improvement
cycle to START
MSC/BSC/Cell
Parameters, Timers &
Features audit for fine
tuning purpose




                                                                  Yes                                   No



No


START
% from BBH report
for analysis
TASR %
<98.75%
No further
investigation reqd.
Check & clear
active alarms
Check RTFs
Path loss <105
& >115 no TMA
Check BBH report
for TASR % value
after problem
correction
Verify the
Tx/Rx path &
rectify it
Check IOI
report for
Uplink Intrf.
MSC/BSC/Cell
tuning purpose


                Yes


                                                     Yes

6.1.2  ZTE TASR ANALYSIS
ZTE (ZXG10‐V2.97) TASR analysis requires monitoring of the KPI from BBH
report circulated from localcentral MIS team on daily basis at cell level.
It involves clear understanding of associated counter based internal
system reports from OMCR as under which reflect the root causes for poor TASR
% values and needs study of these reports in following sequence based on
degradation severity:
• Active alarms report
• Path Balance report
• Basic Measurement report
• Timing Advance (TA) report
• Network parameter checks
Refer Appendix Sample Reports section for screenshot.
Flow‐diagram for TASR improvement report checks:

Active Alarms
TASR CYCLE
Path Balance
IOI
STOP
TASR %
>=98.75
Revisit the
improvement
cycle to START




                                                                  Yes                                   No



BER (U/L‐D/L)
Timing advance
N/w parameter
START
% from BBH report
for analysis
TASR %
<98.75%
No further
investigation reqd.
Check & clear
active alarms
Check for TRE
Path bal.  >5 dB
without TMA
Verify the
Tx/Rx path &
rectify it


                                     No

               Yes

                                                     Yes

6.2.1 ALCATEL SD CONG ANALYSIS
Alcatel (BSS 10 release) SD CONG analysis requires monitoring of the KPI
from BBH report circulated from localcentral MIS team on daily basis at cell level.
It is highly critical to understand the radio network configuration & spatial location of cells
based on which certain implications can be made for high SD Cong %.
STOP
Check failure
phase in RTCH
Assign report
Check BBH report
for TASR % value
after problem
correction
TASR %
>=98.75
GTCNAFLRR
>GTCNAFLBR
Revisit the
improvement
cycle to START
MSC/BSC/Cell
tuning purpose


It is advised not to confuse with OMCR Counters & NPO Indicators in
Alcatel (BSS 10 release). NPO Indicators can be direct OMCR Counters or Indirect
Counters based on computation.
Below Flowchart 4 represents the SD CONG% improvement cycle based
on trigger condition and root causes:

             No                                                   Yes

START
Identify & filter SD
CONG   % from BBH
report for analysis
SD CONG
%! = 0.00
Check HW availability


7. APPENDIX
7.1 SDCCH DIMENSIONING
SDCCH Dimensioning is the need for signaling resource optimization
based on carried SDCCH & TCH traffic in a cell. Different vendors provide various
solutions for dimensioning based on network settings & traffic requirements. Two
methods available for SD dimensioning are:
• Automatic ( Load based increase/decrease of SDCCH/8)
• Manual ( Traffic Estimations and Cell Statistics)
Automatic SD dimensioning is dependent on feature availability in the system
although most of systems have dynamic SDCCH configuration feature to control SD
traffic in peak hours. Dynamic SDCCH feature activation is network operator
dependent & is highly recommended when flow monitoring of LAPD layer 2
messages is available.
Manual SDCCH dimensioning is based on two following methods
• Traffic Estimations:‐
Various Layer‐3 events (LU/IMSI ATTACH‐DETACH/Call set‐
up/SMS/FAX etc require average mean holding time (seconds)
based on which SDCCH traffic estimation is done. This method is
largely ignored in real networks due to varying probability of
mean holding times of Layer 3 (MM/CM) messages and SD traffic
estimation.

STOP


• Cell Statistics:‐
Cell Statistics based SD dimensioning is highly recommended in
current real time dynamic networks due to high demand for
SDCCH resources and forms valid part of discussion in the manual.

Cell statistic based approach considers maximum SDCCH channel
occupancy in 24 hours or peak SD traffic for SD dimensioning as a
critical input besides configured total SDCCH channels including
(SDCCH/4, SDCCH/8) with or without CBCH. SD carried traffic or
busy channels must be average of minimum 3 weeks to capture
cell behavior on long term basis for effective dimensioning.

As a Thumb rule, Designed SDCCH Grade of Service (G.O.S) can be
calculated as under:
SDCCH G.O.S (%) = ¼* TCH G.O.S (%)
GSM wireless networks consider TCH capacity dimensioning at 2
% G.O.S, hence SD capacity is dimensioned at 0.5% G.O.S.
Common flowchart 5 for SD dimensioning based on cell statistic
approach is as under and same is applicable in
Alcatel/Motorola/ZTE vendors as well.



        Yes                                                                     No

SD
Dimensioning
reqd.
Check for Counter
with max SD traffic
or busy channels
START
Max SD
traffic
available
Max SD busy
sub‐channels
available



                    No                                                                        No


                                  Yes                                                                      Yes

Note: 8 SDCCH sub‐channels correspond to one hard coded SDCCH/8
7.1.1 ALCATEL SD DIMENSIONING METHOD
Alcatel (B10 release) SD Dimensioning is done using NPO
indicator GSDTRE which gives SD Erlang hourly basis for a day. Minimum
3 weeks data average with maximum SD Erlang observed in daily busy
hour must be taken into account before further analysis.
Refer steps as mentioned in Flowchart 5 for SD dimensioning.

7.1.2 ZTE SD DIMENSIONING METHOD
ZTE (ZXG10‐V2.97) SD Dimensioning is done using Basic
Measurement report.xls available in OMCR with counter C11627
(Maximum Number of Busy SDCCH). Minimum 3 weeks data average (If
available) with maximum SD busy channels in 24 hours must be taken
into account before further analysis.
STOP
Compute channels
frm carried SD traffic
using 0.5 % G.O.S
from Erlang B table
Check for configured
& required SDCCH
sub‐channel with
40% excess addition


Refer steps as mentioned in Flowchart 5 for SD dimensioning.


8. Optimization Process for other Radio KPIs

SDCCH Drop Rate

Definition: SDCCH Call Drop Rate indicates the probability of call drops that occur when MSs
occupy SDCCHs. This KPI reflects the seizure condition of signaling channels. If the value of this
KPI is high, user experience is adversely affected.

SDCCH Call Drop Rate = Call Drops on SDCCH/ Successful SDCCH seizures

Causes:
30. Due to Blind spot, low coverage level, or cross coverage.
31. High VSWR due to feeders leads to the reduction in the transmit power and in the
receiver sensitivity.
32. Poor transmission quality and unstable transmission links over the Abis interface
33. Unavoidable inter‐network interference, interference from repeaters, or high and
unavoidable intra‐network interference caused by aggressive frequency reuse
Interference
34. unavailable terrestrial resources or faulty devices

Action:
1. Reduce Coverage hole, Blind spots by physically optimization.
2. By maintaining balance between Uplink Downlink path by achieving less VSWR value,
proper tuning of RxLevAccessMin and RachLevAccessMin Parameter.
3. Stable Transmission – Minimum LapD failures
4. Proper Frequency plan to reduce Inference level by retuning frequency, Maio, HSN,
reducing Overshooting.
5. Reshuffling of SDCCH Timeslot as per TRX efficiency. Rectification of Faulty TRX’s.
6. Timer T200 can be optimized as per transmission efficiency.


Handover Success Rate

Definition: The purpose of handover is to ensure the call continuity, improve the speech
quality, and reduce the cross interference in the network, thus providing better services for the
subscribers. Success ratio of handover is the ratio of the total number of successful handovers
to the total number of handover requests.

Success Rate of Handover = Successful Handovers/Handover Requests

HSR is impacted due to
1. Blind spot, low coverage level, or cross coverage.
2. Unavoidable interference can be the inter‐network interference, interference from
repeaters, or intra‐network interference resulting from aggressive frequency reuse.
4. Faulty devices, or asynchronous clocks
5. Imbalanced distribution of traffic volume in the network. If the network is congested
badly, the handover failures increase because of no available TCHs and the handover
success rate decreases. The network congestion does not affect the success rate of radio
handover.
Action
1. Proper neighbor definition (1st
tier mandatory and 2nd
tier definition as per requirement)
2. Maintaining proper footprint by physical optimization.
3. Reducing Interference level by smooth frequency plan
4. Stable error free transmission links
5. Avoiding Ping‐pong HO by defining proper HO margin parameter which may be due
Level or Quality.
6. Providing appropriate time frame for clear msg or Establish msg between BTS’s by T8
timer
7. For intra Bsc HO, time to receives HO complete msg from BSC should be optimized by
T3103 timer
8. Maximizing the HO cause due to Power budget.
9. Maintaining proper traffic distribution by physically, DR, queuing parameters to avoid
HO failure due to neighbor cells congestion
10. Clock drift should be avoided.


TCH Call Drop Rate

Call Drop Ratio on TCH indicates the ratio of the number of call drops to the number of
successful TCH seizures after the BSC successfully assigns TCHs to MSs.

TCH Call drops due to
1. Blind spot, low coverage level, or cross coverage.
2. Unavoidable interference can be the inter‐network interference, interference from
repeaters, or intra‐network interference resulting from aggressive frequency reuse.
4. Faulty devices and high VSWR
5. If the target cell involved in the Directed Retry procedure is under another BSC
6. During intra Bsc handover
7. If preemption is used in MSC  then lower priority MS will face call drop.

Action
1. Clean frequency plan viz. achieve minimum interference level by clean BCCH (CO/ADJ),
MAL, MAIO, MS Plan.
2. Minimizing coverage holes by physical optimization (Orientation, Height, E.Tilt, M.Tilt).
3. Setting Radio link timeout parameter as per inter‐site distance viz. for rural sites RLT can
be of higher value.
4. Similar for Rural site where uplink quality is poor, Rxlev Access min, Rach Access min
parameter can be set appropriately. Proper balance should be maintained for this
parameter else path imbalance will result and TCH drop will increase. TMA/TMB can be
planned appropriately.
5. Minimize Ater Abis fluctuation – Link stability plays very vital role.
6. Ater Congestion further results in TCH call drops. Sufficient Ater argument should be
maintained.
7. Power control used for HO should be properly designed to avoid drop where ever there
is sudden RxLev drop.
8. During HO to neighbor cells should be having free TCH resources else call drop may
increase. For this proper half rate thresholds should be defined as per traffic pattern,
decongestion of these cells by capacity argument.
9. Queuing length should not made too long/short.
10. Drop due to intra Bsc HO, congestion free Ater argument should be maintained


11. Timer T305 and T308 interval should be well enough to receive the Disconnect and
Release message from Msc and Bsc respectively.
12. Proper Neighbor definition should be maintained – some handovers cannot be
performed and thus call drops.
13. By maximizing Power control HO’s reduces the interferences level, which further
reduces TCH drop rate.
14. By DTX feature further Interference levels are reduced, reducing TCH drop.

RACH Success rate

Def : Random Access Channel (RACH) is used by the MS on the “uplink” to request for
allocation of an SDCCH. This request from the MS on the uplink could either be as a page
response (MS being paged by the BSS in response to an incoming call) or due to user trying
to access the network to establish a call.

RACH Failure can be due to :‐
1.  AGCH Overload at Base Station
2.  RACH Collisions
3.  MS out of Range
4.  Poor Uplink quality
5.  BTS Receiver Problem

Action
1. Appropriate no. of CCCH blocks should be designed as per Traffic pattern. Signaling link
should be increased from 16k to 32k as per requirement to avoid overloading.
2. Minimum Coverage hole is first requirement for greater RACH success rate.
3. Use of DTX mode in Uplink reduces the interference level making less probability for
RACH collision
4. Hardware alarm like difference in uplink and downlink path balance heavily impacts
RACH success rate. H/W alarm should be minimized
5. Max. No Of Retransmission parameter allows the MS to retransmit again for AGCH by
not incrementing the RACH access failure counter.
6. RACH Access min and RACH Busy Threshold parameter can be tuned to restrict the MS
in out of range. If this parameter is set to a higher value, the actual coverage area of the
network becomes small; if this parameter is set to a lower value; all drops are likely to


occur because of invalid access or too weak access signals, thus decreasing the success
rate.
7. Fluctuation in transmission media further decreases the success rate. Stable media need
to be maintained.
8. Uplink quality can be further boosted by TMA/TMB.

Rx Quality

Samples carried within 0 to 4 Level by sum of samples carried within 0 to 7 Levels, is termed as
Rx Quality for the TRX/cell.

Poor Speech Quality could be bad due to
1. Coverage holes
2. No Target cell for Handover
3. Interference ‐
• Co‐channel
• Adjacent channel
• External
• Multipath
• Noise
4. E1 fluctuation – poor FER
5. Path balance, VSWR , Hardware issue at BTS
6. Poor power budget thresholds
7. Half rate penetration
8. Repeater used – broadband/narrow/manual

Action

1. Both Uplink and Downlink good quality, proper uniform coverage patterns are
prerequisite.
2. Clean frequency plan viz. achieve minimum interference level by clean BCCH (CO/ADJ),
MAL, MAIO, MS Plan
3. Overshooting should be avoided by E/M tilt, height reduction and reorientation e.g. cells
from high altitude (mountain) are tending to overshoot even with maximum tilt and
height. Sector facing towards water (sea, pond) causes reflection and further
interference in the surrounding. Proper orientation or isolated frequency plan need to
be considered for these sites.


4. Missing neighbor’s further causes HO due to interference. Proper 1st
tier neighbor
should be defined
5. Poor FER further degrades the quality, by making MS to go to lowest codec supported.
Error free E1 link should be maintained.
6. Difference in uplink and downlink path causes further quality in uplink and downlink
respectively. Call served by faulty/alarmed timeslot/TRX causes quality degradation.
Minimum Hardware alarms should be maintained.
7. Aggressive Half rate utilization makes MS to use lowest EFR or AMR codec maximum
times making subscriber to put their efforts to understand about the clearly of
conversation.
8. Repeater’s frequencies are not updated automatic whenever an RF engg. changes
frequency plan of serving macro site since maximum repeaters are manually tuned
repeaters.
9. Quality is found poorer at places where external interferences are present viz. close by
CDMA sites, restricted zones due to jammers/frequencies used by them. Notch filters
can be proposed to reduce CDMA frequency effects.
10. TMA/TMB can be used at Highway sites to achieve good uplink path.
11. MS should access network with proper uplink and downlink lev which are set by
Rxlevaccess min and Rach accesmin parameter.

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