Og 103 test and analysis of gsm electromagnetic background issue1.0

HUAWEITECHNOLOGIES CO., LTD.
www.huawei.com
HUAWEIConfidential
Security Level:
Test and Analysis of
GSM
Electromagnetic
Background
ISSUE 1.0

HUAWEITECHNOLOGIES CO., LTD. Page 2HUAWEIConfidential
Foreword
 In the GSM system, to extend the capacity, perform
frequency reuse. If the frequency reuse is more
aggressive, the network capacity becomes more
large. If the reuse distance is shorter, the
interference becomes stronger.
 The interference has obvious impacts on call quality,
call drop rate, handover, and congestion. If there is a
strong interference in the band, clear frequency or
apply for new frequency.

Purpose
 Interference source of
electromagnetic background
 Test methods of electromagnetic
background
 Use of spectrum test instrument
After learning this course, you should be
familiar with:

Contents
Training.huawei.com
Chapter 1 Impacts of Electromagnetic Interference on System
Chapter 2 Interference Source of Electromagnetic Background
Chapter 3 Introduction to Interference Test Tool
Chapter 4 Test Methods of Electromagnetic Background
Chapter 5 Use of YBT250

Channel interval: 200kHz
890 915 935 960
Duplex distance: 45 MHz
GSM 900 :
1710 1785 1805 1880
Duplex distance: 95 MHz
GSM 1800 :
Frequency of GSMSystem
EGSM: Uplink: 880MHz - 915MHz Downlink: 925MHz - 960MHz
RGSM: Uplink: 876MHz - 915MHz Downlink: 921MHz - 960MHz

Impacts of Electromagnetic Interference on System
Impacts on Calls
If calls are failed, the calling parties hear beeps, and then hear call
drop sounds. (The prompt tones of different mobile phones may be
different.)
In the courses of calls, voice discontinuity, noise, silence, and call drop
often occur.
Impacts on System
Failures of SDCCH assignment and TCH assignment
Frequent call drop or high call drop rate
Low handover success rate
Much statistics of high level and low quality in the receiver level
performance measurement and the quality performance measurement

Contents

Category of Interference Source
 Nature Noise
Atmospheric noise
Galaxy noise
Sun noise (quiet period)
Human Noise
Interferences of automobiles or the engine systems
Interferences of communication equipment
Interferences of electrical power cables
Interferences of industrial equipment, scientific equipment,
medical equipment, and home appliances

Ambient Noise

Analysis of Interference Source
Equipment Faults
Faults of TRX, CDU, or Splitter
Out-of-band Spurious emission and intermodulation
Network Interference
Intra-frequency and neighboring-frequency interferences
owning to improper frequency planning
Repeater interference
Intermodulation interference
Off-net interference
Radar, intra-frequency radio equipment, interference
generator, Cordless Telephone, analog BTS, and CDMA
BTS

Contents

Tools forTesting Interference
 Spectrum Analyzer
 Antenna
 Low-noise
amplifier/attenuator

Spectrum Analyzer
The spectrum analyzer is used to test the features of frequency
domains of signals, including spectrum, adjacent-channel power,
fast time-domain sweep, parasitic radiation, and intermodulation
attenuation.
Key indexes
− F0
− Sensitivity
− RBW
− VBW
− SPAN
− ATT
− RefLv
− RMS
− Sweep Time

Specifications of Various Spectrum Analyzers
Model Operating Band Sensitivity
(1Hz)
Minimum
resolution band
HP8591E 30Hz-1.8GHz -145dBm 30Hz
YBT250 30-2500MHz -132dBm 1KHz

Antenna
Omni-directional antenna: Being convenient for measuring
interference and not being convenient for locating interference
Directional antenna: Being used for searching interference
source; The searching capability is determined by the
directionality and gain.
Directional antenna:
− Flat-antenna
− Yagi antenna
− Log-periodic antenna

Low-Noise Amplifier (LNA)
It is used for testing the receiver sensitivity of test appliance.
The LNA with 30dB gain and 5dB noise factor can be used.
LNA needs external power supply. Some appliances are equipped
with built-in LNA, such as YBT250.
In a cascading network, if the front of the system is configured with
high-gain amplifier, the noise factor of the system is determined by
the first-class noise factor.
Attenuator
It is used for attenuating the power of input signals to protect
spectrum analyzer against strong signals.

Contents

Chapter4 Test Methods of Electromagnetic Background
 Section 1 PreparationSection 1 Preparation
 Section 2 Setting of Basic Parameters
 Section 3 Measurement Course
 Section 4 Data Processing

Preparations
 Being familiar with the planning of local radio frequency band and
usage of radio equipment
Pilot office
− The available frequencies are not confirmed. The test frequency
band is distributed temporarily. For the noise test, you should
sweep the full frequency band or choose several available
frequency bands based on the local frequency resources.
Commercial stage
− The available frequencies are confirmed. To eliminate the
interferences in bands, mainly test the available frequency bands
of carriers.

Preparations
 Confirming time and place of test
Test for electromagnetic interference of uplink
− Test place: position of installing antenna
− Test angle: North by east 0°, 120°, and 240°
− Available antenna: Portable antenna and BTS antenna
Test for electromagnetic interference of downlink
− Test place: typical positions in the cell
− Test angle: North by east 0° ， 120° ， 240°
− Portable antenna
− Testing the places with strong interferences

Preparations
Ensure that the following tools are ready:
Spectrum Analyzer
GPS satellite receiver
Compass
Antenna
Vehicle

Preparations
Ensure the following tools are available:
If a spectrum analyzer has weak receiver sensitivity, the low-
noise amplifier (LNA) is required.
Check whether connectors are matching and whether meters
can be supplied power all the time.
Antenna type Model of connector
Portable omni-directional
mini antenna
N-shaped male
connector
Yagi antenna N-shaped male
connector
Common BTS antenna DIN female
connector
7/8 feeder DIN female
connector
Small jumper DIN male connector
Common spectrum analyzer N-shaped female
connector

 Section 1 Preparation
 Section 2 Setting of Basic ParametersSection 2 Setting of Basic Parameters

Set the basic parameters that are listed in the following table:
Setting of Basic Parameters
Parameter Description Remarks
Fo Setting based on test results Central frequency of
tested spectrum
SPAN Setting based on test results Width of tested
spectrum
Trace Choosing MaxHold or Average based
on accidental interference or
continuous interference
Maximum value or
average value
RefLvl Setting based on the tested signals;
making signals in the middle of
spectrum analyzer
Reference level

 Section 3 Measurement CourseSection 3 Measurement Course

Test Course
Confirming Test Azimuth
Choose the position where the antenna is installed. Often make tests in
three azimuths. If the azimuth of antenna is confirmed, ensure the
azimuth of test antenna is the same as that of BTS antenna.
Search Interference
Search for interference in the uplink band, and then in the downlink
band.
Operations
− Enter the noise test interface of the YBT250, and then set Fo and SPAN.
− Fill in the record table, save data file, and check whether interferences exist.
Judging principle: Check whether there are interference waves that
are higher than the back noise

Test Course
 Confirming Interference
In the course of searching interferences, if interferences exist, make test for
confirming the interferences.
To confirm interferences, proceed as follows:
− Enter the interface of testing YBT250, and then set Fo to the central
frequency that nears to interferences and set SPAN to 3×interference.
Analyze the distribution of signal spectrum. Confirm the interference
signals. Record the strengths of signals and azimuth angle and elevation of
directional antenna beam.
− Search new test point along the direction of antenna beam. Then, perform
the preceding step to find interference source.
− If two places in different directions may have interference sources, the
intersection of the two places is the position where the interface source is.
Thus, perform search near the intersection.

Test Course
Downlink Drive Test
Drive slowly on the main streets where the signals of cell are covered.
If you find strong interferences, make downlink pointing test to confirm
interference source.
To confirm interference source, proceed as follows:
− Enter the noise test interface of the
− Set the Fo and SPAN. Drive at less than 15KM/H speed to
perform interference search.
− In the course of searching, if you find interferences, confirm the
interferences.

 Section 4 Data ProcessingSection 4 Data Processing

Data Processing
Filling test results
 After constructing the test region,
fill in the Electromagnetic
Interference Test Table.
 After constructing the entire
network, fill in the
Electromagnetic Interference
Test Report.

FAQs-Question
 Whether the interference level obtained
from the electromagnetic interference test
is the actual interference level that affects
the BTS or mobile station?

FAQs-Answer
 Because the test system and the actual
system may use different antennae and
feeders, confirm the interference level of
BTS or mobile station based on test data.

FAQs-Answer
 Test System
 Antenna gain: 3dBi
 Feeder loss: 1dB
 Interference level: -90dBm
 BTS System
 Antenna gain: 10dBi
 Feeder loss: 2dB
 Interference level: － 90 － (3 － 1)+(10 － 2) ＝－
84dBm

Contents

Use of YBT250
 Connecting System
 Switching on
 Test
 Test Setting
 Test Result

Use Description of YBT250
 Before carrying out survey, use proper appliance to
make noise test.
 Use the YBT250 of Tektronix
 Features of the YBT250
 Being convenient for taking
 Integrated system with built-in LNA

 Connecting System
 The YBT250 is configured with yagi directional antenna.
 Use portable mini antenna to make electromagnetic background
test.
 The YBT250 is equipped with battery or can be connected
external power.
 Switching on
 Press Power and enter the Windows CE operating system.
 Use the touch screen of the YBT250 to enter the test interface.

 Test
 The YBT250 has three test functions:
BTS information test
Noise test
Interference source searching
 The noise test has two kinds of shown modes:
− Spectrum mode
− Spectrogrum mode

 Test
The Spectrum mode is used for real-time test.
− Confirming the frequency band for test and setting the Fo of the
central frequency
− Modifying SPAN
− Checking the spectrum figure, modifying Fo and SPAN, and
checking for interferences
− Options of the TRACE menu
▪ Normal, Max Hold, Min Hold, Max/Min Hold
− Saving the spectrum figure
Note: Set RefLvl and ensure that the test level is not more than
70dB
(Proper level of YBT250: 70dB)

Test
The Spectrogrum mode is used to check whether
interferences exist in the frequency bands. The
horizontal axis represents frequency band and the
vertical axis represents time.
Operations:
− Setting automatic storage option and file name
− Setting the frequency band (Fo, SPAN)
− Opening the saved file and checking for
interference
To check interference value, export the file:
− Exporting the figure
− Exporting data and saving it as a *.txt file, or a
*.csv file

 Setting Measurement Parameters
− Fo: central frequency of tested signals, MHz
− SPAN: 100MHz, 10MHz, and 5MHz
− RBW: Setting automatically based on SPAN
− MaxHold/Average: Maximum value, average value
− RefLvl: Setting based on interference level
 Output
Electromagnetic Interference Test Table
Electromagnetic Interference Test Report

Summary
In this course, we have learnt:
 Impacts of interference on the mobile network
system
 Source of interference
 Test method of electromagnetic background
 Use of YBT250

Og 103 test and analysis of gsm electromagnetic background issue1.0

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