analysis & optimization

7/28/2019 Analysis & Optimization

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2006, ZTE Corpo ration. All rights reserved.

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.


7/40 2006, ZTE Corpo ration. All rights reserved.

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.



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.



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.



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.



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.



DIFFERENT CALL SCENARIO



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



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.



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



HANDOFF PROCESS



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.



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).



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.



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).



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.



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.



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


166.2860

8

2008-05-2919:00:00


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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