microsoft powerpoint - drop call analysis presention

8/9/2019 Microsoft PowerPoint - Drop Call Analysis Presention

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Summary

Introduction

Drop call reasons.

Drop call examples

Call setup failures reasons

Call setup failures examples

Mainly focused on LTE call analysis.



Network Optimization Flowchart



INTRODUCTION

RF Drop Call Analysis is a part of Network/RF Optimization.

Drop Call Analysis Objectives:

o To reduce access failures/Blocked Call (Accessibility).

o To reduce drop calls (Retainability).

o To enhance service quality.

o RF Optimization Objectives:

To optimize coverage

To minimize pilot pollution

To optimize cell dominance

To optimize neighbor cell list (LTE - ANR)

To resolve/minimize RF related drop calls



Drop Call Reasons

1) Coverage problems

2) Lack of a Dominant Cell/Server

3) Overshooting Cells

4) Unbalanced Downlink & Uplink

5) Handover problems

6) Missing neighbors

7) Pilot pollution (UMTS) / PCI Pollution (LTE)



Factors affecting Coverage

Downlink:

EIRP-Equivalent Isotropic Radiated Power

Total transmit power

Path Loss

Frequency band

Scenarios: urban & suburban areas Terrains: plains, mountains & hills

Antenna gain, height parameters, tilt &

azimuth

Uplink:

eNodeB receiver sensitivity

Antenna diversity gain

UE transmit power

Propagation loss of uplink radio signals

Impact of Tower Mounted Amplifiers(TMAs) on uplink



Call Failures: Poor Coverage Area

Diagnosis:

RSRP is poor (< -95 dBm)

SINR degrades very rapidly (<0 dB)

Solution:

Check antenna configuration

Esure there is no hardware issues related

to antenna

Adjust the antenna tilts/azimuth to increase

the coverage

Check presence of shadowing obstacles



Drop Calls : Coverage Issue

Weak Coverage

In this region, Signal quality of the cells are poor UEs cannot be registered with the

network .

Coverage Holes

o In this region, Receive signal level of a UE is less than minimum access level Low levels of

signal quality Service/Call drops occur.

Solutions:

Analyze surrounding geographical environment such as water bodies, vegetation, terrains, etc.

( Using Google Earth)

Recommend changes in antenna azimuths & tilts to increase the coverage.

Increase coverage by increasing antenna tilts/power of adjacent eNodeBs.

Replace antenna with higher gain/power.



Lack of a Dominant Cell

Receive level of the serving cell = Receive levels of its neighboring cells ~ Cell reselection

thresholds Results in poor SINR of the serving cell.

Poor signal quality Frequent handovers in connected mode ‘Ping Pong effect’

Service drops

Area with out dominant cell = Weak coverage area

Mostly happens in the cell borders = No any best server to keep the call.



Lack of a Dominant Cell : Example

Areas along the cells border

in red have high chance of

having issues of lack of

dominant cell.



Lack of a Dominant Cell

Diagnosis

- UEs frequently perform cell reselections or handovers between cells.

- PCIs alternate in two or more colors if there is no dominant cell within a small distance

Solutions

- Increase coverage of the serving cell by adjusting antenna tilts to increase coverage.

- Decrease coverage of other cells with weak signals by recommending down-tilting ET of those cells.

- Up tilt nearest cell to make it more dominant.



Overshooting Scenario

Height of a site >>> Average height of surrounding

Its transmit signals propagate far forming dominant coverage in the coverage scope of

other eNodeBs Overshooting Coverage

Analogy – Island phenomenon

o Call is connected to an island that is far away from an eNodeB

o But is still served by the eNodeB, and cells around the island are not configured as neighboring cells of the

current cell

o Then call drops immediately once UEs leave the island.

Drop CallDrop Call

Drop Call

Overshooting

Coverage



Overshooting Coverage : Solutions

Adjust Electrical Tilts (ET) / Mechanical Tilt (MT) of overshooting cells.

If ET max out, replace antennas with large ET

If possible, decrease the antenna height for a high site.

Decrease the Cell Radius of overshooting cell.

eNodeB can only

handover to other cells

within the Cell Radius



Drop Calls : Overshooting Cell

Problems: Contribute to downlink interference.

Susceptible to uplink interference which

reduces cell capacity.

Diagnosis: Overshooting cell come temporarily and forces a

suitable serving cell to be dropped out.

Later RSRP suddenly drops in the ‘wrong cell’ and

causes a dropped call .

Solution: Down tilt EDT/MDT of overshooting cells

Decrease the Cell Radius of overshooting

cell



PCI 292, MDL04566_7B_1 (DL Frequency : 5815) is over shooting from 12 miles.

RECOMMNENDATION: Down tilt PCI 292 to avoid drops.

Drop Call due to Overshooting Cell : Example 1



Serving Frequency Plot PCI Plot

Drop Call due to Overshooting Cell : Example 1



Unbalanced Downlink & Uplink

Downlink Downlink coverage is restricted.

Downlink transmit power reaches the

maximum which still cannot meet

minimum quality level DL requirements.

Uplink Downlink coverage is good but the uplink

coverage is restricted

UE transmit power reaches the maximum

which still cannot meet minimum quality

level for UL requirements.

Solutions:- Check for interference by monitoring RTWP alarms of eNodeBs.

- Check hardware issues such as gain of repeaters & amplifiers are faulty, antenna feeder

system is faulty, etc.



LTE ANR

ANR – Automatic Neighbor Relation = Automatic adding/deleting of neighbor list

If ANR function is enabled, there will be no missed definition of neighboring cells.



Missing Neighbor

Diagnosis: A good usable neighbor cell present within

cells coverage area but not defined in

neighbor list.

If not defined in neighbor list (active set),

that cell can cause DL interference

(UMTS).

Solutions: Analyze layer 3 messages in ACTIX to see

if there is a good usable neighbor cell

present but UE cannot hand over to that

cell.

Comparing UE received neighbor list with

scanner receiver pilots.

The pilots seen from the scanner but not

in the UE neighbor list can be classified as

potential missing neighbor (UMTS).



LTE Handover

Entire handover procedure is controlled by the network (eNodeB).

UE send Measurement Reports to the network with the quality of the radio environment.

eNodeB send RRCConnectionreconfiguration to UE ordering UE to make necessary adjustment to change

in radio environment.



Handover in ACTIX

Observe signaling messages starting from ‘Measurement Report’ triggering handover to

‘RRCConnectionreconfigurationComplete’ message. ( Both messages sent by UE)

o Change of PCI if a handover success.

o Service drops & RRC connection reestablishment if there is a handover failure.



Identifying Handover Command in ACTIX

Search for the RRCConnectionReconfiguration message after the Measurement Report message

over the Uu interface.

Handover command if RRCConnectionReconfiguration message contains the targetPhysCellId

IE.



Handover Failure Case I : Weak Coverage

RSRPs of both the serving cell & neighboring cell are weak.



Handover Failure Case II : Missing Neighbor



Handover Failure Case III: Loss of Handover Command

1. UE sends Measurement Reports.

2. eNodeB receives Measurement Reports.

3. eNodeB delivers a Handover command.

4. UE fails to receive that command

Cause:

- Target cell fails to receive the handover completion message after eNodeB receivesmeasurement reports and delivers a handover command.



Handover Failure Case IV : UE Fails to access Target Cell

1. UE sends Measurement Reports to eNodeB

2. eNodeB receives the Measurement Reports & delivers a Handover Command to UE

3. UE receives the Hand over command & accesses Target cell.

4. Target cell fails to receive RRCConnectionReconfiguration message.

Cause:

- RRCConnectionReconfigurationComplete message sent by UE to Target cell is lost during

transmission.



Handover Failure Case V: Caused by Uu interface

1. After UE sends Measurement Reports,

2. UE sends RRCConnectionRequest or RRCConnectionReestablishmentRequest message or

UE enters idle state.



Call Drop due to Handover Failure : Example 1

UE initiated HO from PCI 314 (2C) to PCI 380 (2C). RACH failed resulted in RRC drop.



Drop Call due to Handover Failures : Example 2

Call dropped due to loss in handover command.



Pilot Pollution (UMTS)

In LTE, pilot pollution is calculated in terms of how many servers are serving within given

threshold.

For example, if 6 servers are serving within 10dB power difference pilot pollution in LTE



Pilot Pollution (UMTS)/ PCI Pollutions (LTE)

Diagnosis: Bad SINR level even if RSRP is good.

Solution: Find interfering cells from PCI plots.

Down tilt interfering cells without breaking

the dominance

Check if high site in the neighborhood

causing interference

Check current tilt implemented to

estimate tilt change needed.



PCI Pollution : Example 1

- Poor CINR marked by red circles is caused by pilot pollution.

- poor CINR marked by black circle is caused by poor RF conditions.



PCI Pollution : Example 1



Poor RF Coverage near to Site

Possible reasons:

1. Wrong antenna azimuth implementation

2. Improper EDT/MDT settings/implementation

3. Near field obstructions

eNodeBs hardware/feeder/connector issues.



Call Setup Failure: Poor DL coverage

Mostly because of ‘Fake coverage’

= User can see good signal on UE

= Overshooting cells

= UE cannot pass an RRC to the network

Solutions:

Adjust antenna azimuth

Down-tilt the overshooting cells

Add repeaters & RRUs, micro cells to improve the coverage if not overshooting case

Improve best server/cell



Call Setup Failure due to Poor Coverage : Example 1

- UE sent multiple RRC connection setup request on 485 SC

- But due to bad coverage (RSRP) resulted in setup fail.

Poor RF condition



Call Setup Failure due to Routing Area Update: Example 2

Call setup failure occurred due to routing area update during the connection setup

RRC Connection setup

request

Routing areaUpdate



Call Setup Failures due to Routing Area Update : Example 3

RRC Connection setup

request

Routing areaUpdate

Call setup failure occurred due to routing area update during the connection setup



Ambient Factors

High buildings or mountains block signals from spreading.

Water bodies nearby reflect radio signals.

Dense vegetation/forest & rain scatter radio signals.

High buildings with glass windows reflect radio signals.

May lead to Drop/Block Calls.



Network Optimization Methods

Preferred

Prefer

Less

Preferred

ast

rred

Least

Preferred

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