analysis & optimization
TRANSCRIPT
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Topics Covered
This document will provide you the basic methodology used in Analyzing & Rectifying differentkind of problems which effect the performance of the network. These include Analyses of Drivedata on CNA. Identifying the problems with the help of plots and also through Layer 3 analyses.These scenarios mainly focus on types of RF Failure faced based on Coverage issues &
Handoff Issues. Also are provided their resolutions for rectification.
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RF Failure Reasons
Coverage (Bad Rx, Bad Ec/Io, Bad FER & Bad PN Ec/Io)
Handoff issue (Undefined Neighbor & Low Search Priority)
Resource Unavailable (Walsh Code & Traffic Channel Blocking)
Power Overload (BTS output power)
RF Parameter Configuration (RF parameters defined in System (BSC))
Timer Expiration (Channel Allotment, Acknowledgement, etc)
PN Conflict (PN reuse)
Interference (Forward & Reverse)
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COVERAGE
The Performance of a Network is based on two different criteria. One of them is Coverage & other
is Capacity. The Coverage is based on different criteria. This includes Mobile Receive Power (Rx),Mobile Transmit Power (Tx), Pilot Strength (Ec/Io), Forward Frame Error Rate (FER).
Rx: The Mobile Receive Power is the total power being received by the MS from all the BTS
around it. In order for a good indoor coverage 85-90% of bins should lie below -75dBm value.
Tx: The Mobile Transmit Power is the power that MS radiates to the BTS. The transmit power
depends upon the Mobile Receive Power & TxAdj (Power Control).
Ec/Io: This the received Pilot Strength of Dominant PN with respect to total power received (which
appears to be interference to the decoded PN). This ranges from (0 to -13dBm)
FER: This is the factor which indicates the quality of voice of the system. The FER value should be
below 2% Threshold.
The Coverage of a system can be improved and optimized with the help of Physical as well asSystem Optimization. This requires On Field Drive Test, Data Analysis, Physical changes &
Parameter Optimization. The results can be seen by Drive Test Results as well as KPI of theNetwork.
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Bad Coverage Rx (Mobile Receive Power)
Bad Coverage (Rx Plot) can be due to different reasons. It can be due to VSWR, Connector, Interferenceor
Incorrect Orientation of Antenna. The Clutteralso plays a major role in the coverage. A dense clutter can also
be reason for a bad coverage area.
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Good Coverage after Optimization
The Coverage can be improved by Physical Optimization, i.e., by Re-Orienting the Antenna according to
clutter or adjusting the tilt on the Antenna.
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Checking Sector Radiation
In order to check if a particular sector is radiating properly or not we see the PN,s Ec/Io plot for a
particular PN. In th is case we can see the radiation pattern of the PN 114. The Sector is radiating good
in its defined Orientation.
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Pilot Pollution
One of the most common cause of Bad Coverage is Pilot Pollution . This is the area where no particular PN
is dominant. Such area is under constant handoff and degrades the Ec/Io of the Best PN.
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Pilot Pollution Correction
Pilot Pollu tion gives rise to High Handoff count (high secondary traffic) & also degrades the Coverage
(Ec/Io). As we can see all the Active Set has been Occupied by Pilots with weaker Strength. The PN
with better Strength cannot be accommodated as the Active Set is already full. In order to rectify the
Pilot Pollution we remove the weaker pilots. This can be done by Re-Orienting the Antenna or Giving Tilt,
to the particular sector.
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Degraded - FER
Generally FER is degraded wherever Ec/Io is Degraded. If however such is not the case then check for
Forward Power Control Parameters configuration.
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Incorrect RF Parameter
As seen in previous case of Bad FER, we check for System Configuration. Forward Power Control
Parameter can be found in Power Control Message in Layer 3 Messages. It can be seen that the set
point of FER is set as 4. However the Optimized value is 2. Such incorrect configurations in system
can effect the Coverage & Performance of the Network.
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DIFFERENT CALL SCENARIO
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CALL FLOW
If at any point after the Traffic Channel assignment we get a Sync Channel Message without a
Release Order message, the call is termed as dropped call
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Call Drop Analysis Coverage Issue (Ec/Io)
The Example shown
demonstrates a call drop
scenario. From the point
info option in CNA we can
see that at the time of drop
none of the active PN were
dominant. Which in turn led
to a call drop. This can be
termed as coverageproblem.
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Call Drop Analysis Coverage Issue (Ec/Io)
Call Drop can be viewed in
Layer 3 Message Analysis
also. As we can see the
last PSMM message sent
contains active pilots along
with their Ec/Io level. In
case of a call drop we
directly get a Sync
Channel Message aftertraffic channel. However in
case of a normal released
call we get a Release
Order message before a
Sync Channel Message
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HANDOFF PROCESS
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HANDOFF
Handoff is a process in which a call is transferred from one sector to another (Softer Handoff) or
from one BTS to another (Soft Handoff). In CDMA system this process is done without breakingthe circuit (call is not disconnected). A CDMA mobile handset has 3 rake receiver which can
decode different PNs at a time. These PNs have different Pilot Strength and the call is latchedonto the strongest PN. However if another Stronger PN is decoded by mobile it request for ahandoff in order to move the call onto this PN. This information is sent over to BTS through Pilot
Strength Measurement Message (PSMM). The Handoff is based on a certain Thresholds. Theseinclude Tadd,Tdrop,Tcomp& Ttdrop.
Tadd: This is the threshold level (in dBm) above which a PN is added into Active Set for handoff.
Tdrop:This is the threshold level (in dBm) below which a PN is removed from the Active Set.
Tcomp: This is the comparison between the Strength of PN in between Active Set & CandidateSet. Incase of a full Active Set this value is used to replace better PN from Candidate Set.
Ttdrop: This is the timer used to remove the PN from Active Set after it goes below the Tdropvalue.
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INTER FREQUENCY HANDOFF (IFHO)
Inter Frequency Handoff is used where the adjoining sites have different carriers, E.g.: 2 Carrier
BTS along with a 3 Carrier BTS. This is based on two methods.
1) MAHO: In Mobile Assisted Handoff (MAHO) process, mobile scans for PN in adjoining CarrierFrequency. If a Stronger PN is encountered the IFHO takes place.
2) DAHO: In Database Assisted Handoff (DAHO) process, the PN of target Carrier for adjoiningBTS are defined in system. In order for IFHO to take place we define two different thresholds.
One of them is distance based (RTD Threshold) & another is based on Pilot Strength (Ec/Io).
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Handoff Failure Undefined PN in Neighbor List
The handoff fail scenario
can be seen in this case.
As we can see the Pi lot
Strength of Candidate Pilot
is better than Active set, the
Handoff is not taking place.
This ultimately leads to a
call drop. The defined
neighbor list can seen inNeighbor List Update
Message in Layer 3
Analysis.
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Checking Defined Neighbor List
In order to check the Missing PN in Neighbor List, go to Neighbor List Update Message and
look at the Defined Neighbor List. You can also see the Priority in this list. The Handoff takes
place according to PN with Higher Priority (0,1,2 .. Ascending).
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Well Optimized System
In order for a system to be well Optimized our main aim should be make PN Dominant in theirServing Area.
We should avoid overlapping of different PN at a same area. This will reduce the Secondary Traffic as well
as the Interference within the system.
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Good Coverage Plots
Good Drive Plots can be seen in the above figures. Each sector has to be covered. Maximum bins should lie in
its respective good range.
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Checking cable swap Issues
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2 Sectors Radiating in
same direction
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Checking cable swap Issues.contd
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Checking cable swap Issues.contd
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Cable Swap between 2 Sectors
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Cable Swap between 3 Sectors
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Cable Swap between Rx cables
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Physical Optimization of sites
Why Physical Optimization is required?
1. To re-direct the radiation of signals in desired area.
2. To control the extent of radiation of a sector.
3. To control the load sharing of sectors.
4. To control the soft handoff %.
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Types of Physical optimization
1. Mechanical tilt
2. Electrical Tilt
3. Antenna Ht change
4. Antenna Change
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Antenna Downtilt
Mechanical Downtilt
Physically tilt the antenna. The
pattern in front goes down, andbehind goes upElectrical Downtilt
more elegant is the electricaldowntilt with the antenna
remaining upright;
instead of equal phases on the
dipoles, particular phasedistributions are
selected by varying the cablelengths to the dipoles
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Load Optimization using Physical Changes
Begin Time BTS IDCEL
L
1X:
VoiceCall
Traffic
(Erl)
%PrimaryTraffic
2008-05-2719:00:00
JIYAGUDA 502 072.663
368.8099
4
2008-05-2819:00:00
JIYAGUDA 502 069.998
166.2860
8
2008-05-2919:00:00
JIYAGUDA 502 068.769
465.1225
4
2008-05-2719:00:00
DHOOLPET 114 252.258
149.4868
4
2008-05-2819:00:00
DHOOLPET 114 250.591
747.9088
1
2008-05-29
19:00:00DHOOLPET 114 2
51.150
348.4377
8
2008-05-2719:00:00
TAPACHAPUTRA
156 016.833
915.9411
9
2008-05-2819:00:00
TAPACHAPUTRA
156 016.838
615.9456
4
2008-05-29
19:00:00
TAPACHAPU
TRA
156 017.566
4
16.6348
5
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Site
BTS
ID
C
e
ll
Azi
mut
h
Prese
nt M
Tilt
Recom
mended
M Tilt
Jiyaguda 502 0 40 0 3
Tapachabutra 156 0 140 5 4
Dhoolpet 114 2 240 5 5
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Reducing overshoots by Antenna Ht reduction
For antennae having total tilt (Mechanical + Electrical) of 9
degrees or more, further down tilting is not recommended.
For further physical optimization of this sector antenna ht
reduction is recommended
O h t d ti b A t Ht d ti
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Overshoot reduction by Antenna Ht reduction
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