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Page 1: RF DT Basics

RF DT BASICS

by

Chika Albert

Gil

Page 2: RF DT Basics

RF DT is the most common and maybe the best

way to analyze Cellular Network performance by

means of coverage evaluation, system

availability, network capacity, network

retainibility and call quality. Although it gives idea

only on downlink side of the process, it provides

huge perspective to the service provider about

what’s happening with a subscriber point of view.

Page 3: RF DT Basics

It is the testing of a network in a particular area to get

the real picture of the network’s performance on the

field using certain tools. It brings about Planning,

Implementation of the plan and optimizing where

necessary.

While statistics give an idea about the real behavior

faced by all end users regardless of their geographical

location, drive testing bring a simulation of end user

perception of the network on the field from one call

perspective. Drive tests give the ‘feel’ of the designed

network as it is

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experienced in the field. The testing process starts

with selection of the ‘live’ region of the network

where the tests need to be performed, and the drive

testing path. Before starting the tests the engineer

should have the appropriate kits that include mobile

equipment (usually three mobiles), drive testing

software (on a laptop), and a GPS (global positioning

system) unit.

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The purposes of RF DT are:

Since RF DT service tools (MS & BTS) are always in

use, the BTS needs constant maintenance to

improve its performance.

The performance of an RF network is only assessed

by collecting and analyzing DT logs.

As a business venture, troubleshooting and

optimization by the operators is needful and can

only be done when DT logs are collected.

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Generally, RF DT is captioned as a planned drive

aimed at testing events, measure KPIs and draw

analysis between the MS and BTS in real time

using pre-defined testing tools.

Based on the above definition, I will discuss RF DT

under the following headings:

Planned Drive

Pre-defined testing tools

MS and BTS

Events KPIs Measurements

Drawing Analysis

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Planned Drive

By planned drive it suffices to say that an indebt

understanding of customer’s demand of what type

of RF DT to be carried-out, pre-defined routes and

updated cell file are really necessary. I will again

discuss planned drive in the following sub-headings:

Types of RF DT

Pre-defined Routes

Updated Cell File

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Types of RF DT

The types of RF DT are generally summarized into

the following:

VIP RF DT: This RF DT normally comes up after

problems of a particular site/cell have been reported

by statistical analyst from the logs of an SSV RF DT.

These areas are also called hotspots and the

analysis is performed simultaneously with the DT.

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Benchmark RF DT: In a region where there is more than

one operator, BM RF DT is used to compare the network

performance of these operators. This RF DT is mostly

done in clusters.

SSV RF DT: Single Site Verification RF DT can also be

called cell coverage analysis DT or the routine DT. It

is a DT used to monitor network performance on

regular basis and on new planned sites in the

network. It tells the coverage area of each sector of

the site.

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Pre-defined Routes

Every operator has their coverage area i.e the area

the sites are expected to cover. Before performing

RF DT, knowledge of the expected area to be

covered is largely important to the RF DT Engineer.

Also, if it is a cluster DT, proper definition of each

cluster route is necessary as a repeated drive of any

route we surely affect the Key Performance

Indicators (KPI’s).

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Updated Cell file

This is an excel sheet showing details of all the sites

of an operator. The sheet contains the cell name,

Absolute Radio Frequency Channel Number (ARFCN),

Base Station Identity Code (BSIC), Latitude,

Longitude, Mobile Network Code (MNC), Mobile

Country Code (MCC), Location Area Code (LAC), Cell

Identity (CI), antenna direction, antenna beam,

mechanical tilt, electrical tilt e.t.c. It is converted to

a cell file format (this is the format TEMS

understands) using the following steps:

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Open another excel sheet

Copy the sheet introduction on the top left of the

sheet also in the first row of the sheet. e.g 2 TEMS_-

_Cell_names

Copy needed information such as cell name, ARFCN,

BSIC, Lat, Lon and antenna direction to the new

sheet.

Save the excel sheet using the text tab delimited

format.

Open the saved file and rename it “any name.cel”

and save.

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Pre-defined Testing Tools

There many testing tools for DT. But when carrying-

out an RF DT project, the testing tools are in most

cases defined by the client/customer. The most used

testing tools are the general products of TEMS. The

acronym expands as Testing Equipments for Mobile

Systems. Her products are grouped into:

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Real time diagnosis tools

Network planning tools

Network monitoring tools

Network Performance Management tools

Also with the TEMS products are:

A laptop the meets task specification.

At least a mobile phone

One (1) GPS

An extension box

AC to DC inverter

A well-ventilated car

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MS and BTS

MS: Mobile Station (MS) is made up of the Mobile

Equipment (International Mobile Equipment Identity

IMEI) and Subscriber Identity Module (International

Mobile Subscriber Identity IMSI). The MS used for RF

DT can either be K790, W995 e.t.c

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Both the K790 and W995 have an almost the same

user approach as the steps below shows:

Power-up the phone (NB: Always remove the battery

from the phone when not in use)

Connect the cable first to the phone and then to the

laptop when already the license (dongle) is up and

running.

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K790

Purely designed for GSM network testing.

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W995

It has the capabilities of perform test on GSM (2G),

WCDMA (3G), GSM and WCDMA (IRAT), Video

streaming e.t.c. It is the MS in vogue as testing for

WCDMA is now everywhere since its deployment.

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BTS: The Base Transceiver Station (BTS) is made up

of the following:

BTS Shelter

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BTS Tower

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Reasons for Tilting Antenna

Reduction of overshoot

Removal of insular coverage

Reducing interference

Improving coverage quality in near areas

Adjusting HO

Types of Antenna Tilt

Mechanical Tilt

Electrical Tilt

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EVENTS and KPI Measurements

Events

In RF DT, the events that will be required by the operator are:

MS Connected and Disconnected

Blocked Calls

Call Initiation

Call Established

Call Set-up

Call end

Cell Reselection

Dedicated Mode

Idle Mode

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Dropped Calls

HO success and failure

PS attached and detached

PDP Context Activated and Deactivated

Location Area Update

Routing Area Update

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MS Connected and Disconnected: This is the voice

prompt when an MS is activated and deactivated on

TEMS.

Blocked Calls: Calls that cannot find their way into the

network are classified as blocked calls. They are used

to ascertain the accessibility of the network. Causes of

blocked calls will be generally classified into the

following:

• Terminating MS is engaged

• System Busy

• No service

• Other causes

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Call Initiation: This happens when the originating MS

seeks TCH allocation of resources. It’s simply put as

when a number is dialed by the originating MS.

Call set-up: This occurs when the terminating MS

receives signal from the BTS of an in-coming call.

This measures the successful TCH assignment to the

total number of TCH assignment attempts.

Call Established: This occurs when both the

originating and the terminating MSs are carrying

traffic.

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Call end: This occurs when the transfer of traffic

between the originating and terminating MSs is

stopped by the users.

Cell Reselection: This occurs when the MS is in idle

mode. The MS measures the kpis of cells it can camp

on while in transit.

Dedicated Mode: When an MS is carrying

traffic/making calls, the MS is said to be in a

dedicated mode.

Idle Mode: A drive test activity in which, the MS is

“ON” but no call occur. A powered on mobile station

(MS) that does not have a dedicated channel

allocated is defined as being in idle mode.

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While in idle mode it is important that the mobile is

both able to access and be reached by the system.

The idle mode behavior is managed by the MS. It is

the mode for performing scanning.

Dropped Calls: This shows the number of abnormal

disconnections during call setup or during

conversation. From a subscriber point of view, the

most serious dropped calls are those that interrupts

an ongoing conversation, i.e. a call dropped on the

TCH.

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This indirectly also defines retainability as a

higher retainability value indicates less dropped

calls.

The causes of dropped calls can be classified into

two viz

Traffic Channel (TCH) Dropped calls

• Excessive Timing Advance 

• Low Signal Strength 

• Bad Quality 

• Sudden Loss of Connection 

• Other Reasons

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SDCCH Dropped calls

• Low signal strength on down or uplink

• Poor quality on down or uplink

• Too high timing advance

• MS error

• Subscriber’s behavior

• MS Battery flaw

• Congestion on TCH

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HO Success and Failure: When a call is made

continuously in transit, it expected that the cell

where the call was initiated and camped-on will not

be cell where the call is terminated. The call is

transferred from one cell to another as the MS is in

transit. Therefore, HO success is the process where

a dedicated call is transferred from one cell to

another without any voice quality dropping using

some well-defined network HO parameter

configuration. If the quality of the call drops or the

call ends impromptly, then the call is said to have

experience HO failure.

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Causes of HO failures

Congestion on the target cell

No synchronization between equipments from

manufacturers

Poor HO parameter configuration

Missing Neighbors

Problem from antenna and feeder system

PS Attached and Detached: It is used to measure the

accessibility in and out of any network while testing

for data service.

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PS Attach and Detach: It is an event used by the MS

to access the network for GRPS service over a

channel. This channel focuses on that packet alone

been transmitted. It can be used to ascertain the

level of accessibility of a network in performing

GPRS service.

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PDP Context Activation and Deactivation: In order for

the MS to send and receive GPRS data the MS must

perform a PDP context activation after the GPRS

attach. The PDP context activation makes the MS

known in the concerned GGSN and communication to

external networks is made possible. The PDP context

activation corresponds from the end users

perspective to "Logging On" to an external network.

The difference from using a dial-up connection over

circuit switched is that in GPRS the end user can have

several PDP contexts activated simultaneously if the

terminal supports several IP addresses.

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Location Area Update: A GSM network is divided into

cells. A group of cells is considered a location area. A

mobile phone in motion keeps the network informed

about changes in the location area. If the mobile

moves from a cell in one location area to a cell in

another location area, the mobile phone should

perform a location area update to inform the

network about the exact location of the mobile

phone.

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Routing Area Update: A routing area is sub-divided

into location area. It is an event used by the MS for

PS attach and detach and PDP context activation

and deactivation services.

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KPI Measurements

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RxLev: Rx-Level is define as The power level

corresponding to the average received signal level

of the downlink as measured by the mobile station.

The range of Rx-level is between -55 to -110.It is

been further classified as Rx-Level Sub and Rx-level

Full. Where Rx-Level sub is based on the mandatory

frames on the SACCH multi frame. These frames

must always be transmitted which means that they

carry intelligent signaling data. Whereas The FULL

values are based upon all frames on the SACCH

multi frame, whether they have been transmitted

from the base station or not.

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This means that if DTX DL has been used, the FULL

values will be invalid for that period since they include

bit-error measurements at periods when nothing has

been sent resulting in very high BER.

RxQual: Rx-Qual is define as the level corresponding to

the mobile station's perceived quality of the downlink

signal. Rx Quality is a value between 0 and 7, where

each value corresponds to an estimated number of bit

errors in a number of bursts. The Rx Quality value

presented in TEMS is calculated in the same way as

values reported in the measurement report sent on the

uplink channel to the GSM network.

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Frame Error Rate (FER): It shows the number of

frames that dropped due to too many bit errors in

the frame. It is the ratio of the number of frame

error to the transmitted frames. It is expressed in

percent. The smaller the speech codec bit rate, the

more sensitive it becomes to frame erasures. FER

plays a major role in troubleshooting of Interference.

Bit Error Rate (BER): It measures the quality of the

network. It is the ratio of the number of bits errors to

the transmitted bits. It is expressed in percent.

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Speech Quality Index (SQI): It measures the voice

quality beyond the RxQual because it also considers

the FER and BER. SQI is an estimate of the perceived

speech quality as experienced by the mobile user, is

based on handover events and on the bit error and

frame erasure distributions.

However, the Rx Quality measure is based on a

simple transformation of the estimated average bit

error rate, and two calls having the same Rx Quality

ratings can be perceived as having quite different

speech quality.

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One of the reasons for this is that there are other

parameters than the bit error rate that affects the

perceived speech quality. Another reason is that

knowing the average bit error rate is not enough

to make it possible to accurately estimate the

speech quality.

Generally Speech Quality Index, which is an

estimate of the perceived speech quality as

experienced by the mobile user, is based on

handover events and on the bit error and frame

erasure distributions.

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The quality of speech on the network is affected by

several factors including what type of mobile the

subscriber is using, background noise, echo

problems, and radio channel disturbances.

Extensive listening tests on real GSM networks have

been made to identify what type of error situations

cause poor speech quality. By using the results from

the listening tests and the full information about the

errors and their distributions, it is possible to

produce the Speech Quality Index. The Speech

Quality Index is available every 0.5 second in and

predicts the instant speech quality in a phone

call/radio–link in real–time.

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DRAWING ANALYSIS

In RF DT, the major analyses to be drawn are:

Coverage Analysis

Interference Analysis

HO Analysis

Neighbor Analysis

Call Analysis

Data throughput rate

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THANK YOU

Failure establishes one thing; that your zeal to succeed was not strong enough.

Gil


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