Interference analysis

Interference Analysis For

LAND MOBILE

Interference in HistoryInterference in History عام قاتل أجاممنون 30003000منذ أكثر من •

الملك األغريقي القديم ”تروي“ خاطف إبنة أخيه ”إيلينا“ وقام بأسره، و أحب أن يزف هذا الخبر إلى زوجته ”كليتيميسترا“

ميل من مدينة 800800وهو على بعد ”ميسيني“ بمملكة ”أرجوليس“ )باليونان

حاليا(!!. فاستخدم أعقد طرق االتصاالت في ذلك •

نيران على قمم سلسلة نيران على قمم سلسلة الوقت، وبواسطة بينه وبين مكان مملكته، استطاع الجبالالجبال

مع سائر InterferenceInterferenceمعالجة التداخل المصادر الضوئية األخرى. واستغل حركة

النيران في تشفير رسالته إلى زوجته ليطلعها على الخبر السعيد.

A Basic Radio SystemA Basic Radio System

Generalized Block Diagram of a Generalized Block Diagram of a Communication systemCommunication system

The The SPECTRUMSPECTRUM of a of a SIGNALSIGNAL

HOW MUCHHOW MUCH “SINUSOIDS”“SINUSOIDS” are present in that signal ? are present in that signal ?

→ → The theoretical Origin is The theoretical Origin is FOURIER TheoryFOURIER Theory in in

mathematical analysis: “mathematical analysis: “Any signal can be Any signal can be

DECOMPOSED into SUMS of SINUSOIDAL signalsDECOMPOSED into SUMS of SINUSOIDAL signals””

Types of SignalsTypes of Signals• Base-bandBase-band: Its Spectrum is concentrated AROUND f=0. Example: Voltage at the output of a handset handset

• Band-PassBand-Pass: Its Spectrum is translatedtranslated FAR from f=0 )around a

CARRIER(Example: Voltage from the Low Noise Block of a Dish

Base Band: Telephone Voice : Telephone Voice ChannelChannel

What is “MODULATION”

AMAM of A CARRIER of A CARRIER

Modulation Index “m”

Angle ModulationAngle Modulation

Frequency and Phase ModulationFrequency and Phase Modulation

Modulation index of FM Signal

Mathematical ToolAny Bandpass signal may be represented as:

( ) ( ) cos ( )

or: ( ) ( ) cos( ) ( )sin( )c

c c

v t R t t t

v t x t t y t t

or in a Complex form:( ) ( )

2 2

1

( ) ( ) ( ) ( ) ( )

:

( ) ( ) ( ) ( )

( )( ) tan ( )

( )

j g t j tg t x t jy t g t e R t e

Where

R t g t x t y t

y tt

x t

Modulated SignalModulated Signal

The SOURCESOURCE of information )Modulating signal or BasebandBaseband signal( m(t) is ENCODEDENCODED into a Bandpass signal )Modulated signal( s(t)s(t) given by:given by:

( ) Re ( ) cj ts t g t e

Generalized TransmitterGeneralized TransmitterAM-PM techniqueAM-PM technique

Generalized TransmitterQuadrature Technique

Side Bands of Side Bands of AM AM SignalSignal

Power of AM Signal Delivered Power of AM Signal Delivered to a resistive loadto a resistive load

Visualization in the Visualization in the Time Time and and FrequencyFrequency Domains Domains

The spectrum analyzer is to the frequency domain as the oscilloscope The spectrum analyzer is to the frequency domain as the oscilloscope is to the time domain. It can also be used in the is to the time domain. It can also be used in the fixed-tune modefixed-tune mode ))zero spanzero span( to provide time-domain measurement capability much ( to provide time-domain measurement capability much like that of an like that of an oscilloscopeoscilloscope..

SPECTRUMSPECTRUM

Time Domain Signal SPECTRUM )Frequency Domain(

More ExamplesMore Examples

Need for DECIBELS

0.001

SMALL and LARGE Signals on the SAME Scale

There are two basic forms of spectrum analyzers:

•Swept tuned:is tuned by electronically sweeping its inputelectronically sweeping its input over the desired frequency range thus, the frequency components of a signal are sampled sequentially in time.

Types Of Spectrum AnalyzersTypes Of Spectrum Analyzers

Real time analyzers:They sample the total frequency range simultaneously, thus preserving the time dependency between signals. This technique allows both transient and periodic / random signals to be displayed.

Basic Operation of Basic Operation of Swept Swept TunedTuned Spectrum Analyzers Spectrum Analyzers

Swept Tuned spectrum analyzers Swept Tuned spectrum analyzers are based on a are based on a Super Super HeterodyneHeterodyne receiver principle. receiver principle.

The The input Frequencyinput Frequency ffin in is converted is converted

to an to an Intermediate FrequencyIntermediate Frequency, , ffIFIF , via a mixer )Multiplier( and a , via a mixer )Multiplier( and a

tunable local oscillator tunable local oscillator ffLOLO . When . When

the frequency difference the frequency difference between the input signal and the between the input signal and the local oscillator is equal to the local oscillator is equal to the intermediate frequency then intermediate frequency then there is a response on the there is a response on the displaydisplay..

fIN = fLO ++ f fIFIF

Block Diagram of SWEPT Spectrum Analyzer

MultipleMultiple Frequency Translation via Frequency Translation via Multi-stage MixersMulti-stage Mixers and and Multiple Local Oscillators Multiple Local Oscillators )derived from the )derived from the HARMONICSHARMONICS of the Local Oscillator( of the Local Oscillator(

Characteristics of Spectrum Characteristics of Spectrum AnalyzersAnalyzers

a( Wide frequency range. b( Amplitude and frequency calibration via internal

calibration source and error correction routines. c( Flat frequency response where amplitude is

independent of frequency. d( Good frequency stability using synthesized local

oscillators and reference source. e( Low internal distortion. f( Good frequency resolution. g( High amplitude sensitivity. h( Linear and logarithmic display modes for amplitude

)voltage and dB scaling(. i( Absolute and relative measurement capabilities.

Frequency RangeFrequency Range

The The lower frequencylower frequency limit of a spectrum analyzer is determined by limit of a spectrum analyzer is determined by the the sideband noisesideband noise of the of the local oscillatorlocal oscillator. The local oscillator feed . The local oscillator feed through occurs even when there is no input signal present. through occurs even when there is no input signal present.

The The sensitivitysensitivity at the at the lower frequencylower frequency is also limited by the LO is also limited by the LO

sideband noisesideband noise..

COUPLINGCOUPLING

As the As the IF bandwidthIF bandwidth is is reduced,reduced, the time to the time to sweepsweep a given frequency range a given frequency range increasesincreases since the since the charge time of the IF filtercharge time of the IF filter increases. increases.

This means that the This means that the sweep time is increasedsweep time is increased to to allow the allow the IF filter to respondIF filter to respond and therefore and therefore present an undistorted signal to the detector. present an undistorted signal to the detector. These variables are generally taken into These variables are generally taken into account automatically within a spectrum account automatically within a spectrum analyzer and are referred to as analyzer and are referred to as ‘COUPLING’.‘COUPLING’.

Zero FrequencyZero Frequency Span mode Span modeOscilloscope ModeOscilloscope Mode

If the local oscillator is manually manually tunedtuned, the

spectrum analyzer becomes a fixed-tunedfixed-tuned receiver

► whose frequency is determined by that of the local oscillator. In this mode the analyzer will display the time domain function since the frequency component is fixed even though the scan generator is still sweeping the display.

Frequency ResolutionFrequency Resolutioncalled “called “resolution bandwidthresolution bandwidth” is:” is:

““The ability to separate and The ability to separate and measure two signals in close measure two signals in close

proximityproximity”. ”. It is determined by 3 primary factors: It is determined by 3 primary factors: a( the a( the IF filter bandwidth..b( the b( the shapeshape of the IF filter. of the IF filter.c(c( the the sideboard noisesideboard noise of the IF filter. of the IF filter. The IF bandwidth is normally specified by The IF bandwidth is normally specified by

ff at at -3dB-3dB

The RESOLUTION The RESOLUTION ↑↑as as f f ↓, ↓, BUT !! BUT !! Remember:Remember:

The CHARGE time of the IF filter → The CHARGE time of the IF filter → INCREASE SWEEP time.INCREASE SWEEP time.

Example of Narrow IF FilterExample of Narrow IF FilterNarrow IF bandwidths are required to distinguish the Narrow IF bandwidths are required to distinguish the

sidebandssidebands of AM and FM signals. of AM and FM signals.

Filter Filter Skirt InclinationSkirt Inclinationor the ‘or the ‘SHAPE FACTORSHAPE FACTOR’’

When measuring close-When measuring close-in in spurious spurious componentscomponents, the , the shapeshape of the IF filter of the IF filter becomes important.becomes important.

The The skirt inclinationskirt inclination is: is:

the the ratioratio of the filter of the filter bandwidth at bandwidth at -60dB-60dB to that at to that at

-3dB-3dB

Scanning TOO FASTScanning TOO FASTGaussian filtersGaussian filters have have SFSF 12:112:1

Some spectrum analyzers utilize digital digital

filtersfilters with shape factor as low as 3:13:1 because sometimes they are better in better in

terms of frequency resolution, but they terms of frequency resolution, but they

do have the drawback of do have the drawback of sharply sharply

increasing the scan time.increasing the scan time.

As the scan time decreases, the As the scan time decreases, the

displayed amplitude decreases and displayed amplitude decreases and

the the apparent bandwidth increasesapparent bandwidth increases. .

ConsequentlyConsequently, frequency , frequency resolution resolution and and

amplitude uncertaintyamplitude uncertainty get worse, and get worse, and

some analyzers will warn you that you some analyzers will warn you that you

are now in an ‘are now in an ‘UNCALUNCAL’ )Uncalibrated( ’ )Uncalibrated(

mode. mode.

Sensitivity and Noise FigureSensitivity and Noise Figure

The sensitivity of a spectrum analyzer is: its ability to detect signals of low amplitude

The maximum sensitivity of the analyzer is limited by the The maximum sensitivity of the analyzer is limited by the noise noise PPNN generated internally: generated internally:

Noise Increases with BANDWIDTH →→

NOISE FIGURE FN

:

( / ) / ( / )

: ,

dim :

F 10log( ) dB

N IN OUT

N

It isdefinedas

F S N S N

Where S Signal andN Noise

ina ensionlessquantity

F

Video Filtering - AveragingVideo Filtering - AveragingVery low level signals can be difficult Very low level signals can be difficult

to distinguish from the internal to distinguish from the internal noise; since analyzers display noise; since analyzers display signal plus noise. some form ofsignal plus noise. some form of averaging or filtering is required to averaging or filtering is required to assist the visual detection process. assist the visual detection process.

So we use a So we use a post-detection video filter post-detection video filter )Low Pass Filter()Low Pass Filter( that averages the that averages the internal noise of the analyzer. The internal noise of the analyzer. The minimum signal power that can be minimum signal power that can be

displayed = displayed = the average noisethe average noise

power power

( ) 2

( ) / 2

10log 2 3

S N N

S N N

MinimumSignal level

dB

Signal Display RangeSignal Display Rangeis dependent on is dependent on two key two key

parameters:parameters: a( The a( The minimum resolution minimum resolution

bandwidthbandwidth available and available and hence the average noise hence the average noise level. level.

b( The b( The maximum signal maximum signal level at the first mixerlevel at the first mixer that does not introduce that does not introduce distortion or inflict distortion or inflict permanent damage to permanent damage to the mixer performance.the mixer performance.

The Dynamic RangeThe Dynamic RangeIt is determined by 4 key factors: i. Average noise levelAverage noise level: Which is generated within the RF section. ii. Residual spurious componentsResidual spurious components: The harmonics harmonics of various signals are mixed together in a complex

form and converted (via the MIXERS) to the IF signal componentsconverted (via the MIXERS) to the IF signal components which are then displayed regardless of whether or not a signal is displayed regardless of whether or not a signal is present at the input.present at the input.

iii. Distortion due to higher order harmonicsDistortion due to higher order harmonics: When the inputinput signal level is highhigh, spurious images of the input spurious images of the input

signal harmonicssignal harmonics are generated due to the non-linearity of the non-linearity of the mixer conversion!!! mixer conversion!!!

iv. Distortion due to 3rd order intermodulation products: • When two adjacent signals at high powerhigh power are present as inputsinputs to

a spectrum analyzer, intermodulationintermodulation occurs in the mixers, so Spurious signalsSpurious signals, separated by the frequency difference of the

input signals are generated above and below the input signals. above and below the input signals. The The range over which measurements can be performed without interference range over which measurements can be performed without interference

from anyfrom any of these factors is the of these factors is the dynamic rangedynamic range

AM MeasurementsAM MeasurementsFor an AM signal there are

three signal elements: a( the unmodulated

carrier. b( the upper sideboard

whose frequency is the sum of the carrier and the modulation frequency.

c( the lower sideboard whose frequency is the difference between the carrier and the modulation frequency.

InterferenceInterference

In mobile radio communications, the emitted electromagnetic waves often do not reach the receiving antenna directlydirectly due to obstaclesobstacles blocking the line-of-sight path. In fact, the received waves are a superposition of waves coming from all directions due to reflection, diffraction, and scattering caused by buildings, trees, and other obstacles. This effect is known as multipath multipath propagationpropagation.

The received signal consists an infinite sum The received signal consists an infinite sum of:of:1- 1- attenuatedattenuated 2- 2- delayeddelayed3- and 3- and phase-shiftedphase-shifted replicas of the transmitted signal, replicas of the transmitted signal, ►►► ►►► each influencing each othereach influencing each other..

Consequences of MultiPath Consequences of MultiPath Propagation !!Propagation !!

Importance of Angle of Arrival

f →→ f cos)α) !!!

Typical Received SignalTypical Received Signal

A Wireless NetworkA Wireless Network

An Analog Transmission system

Characteristics of Analog Characteristics of Analog TransmissionTransmission

Analog transmission is characterized by the following:1. Signal processing. Processing is performed on the baseband

signal before modulation and after demodulation in order to improve the quality of the link.

2. The number of communication channels supported by the carrier. In the case of a single communication channel, one refers to single channel per carrier )SCPC( transmission. Several communication channels combined by frequency division multiplexing )FDM( is referred to as FDM transmission.

3. The type of modulation used. The most widely used is FM. For this type of modulation, the carrier amplitude is not affected by the modulating signal; thus, it is robust with respect to the nonlinearities of the channel.

Typical Requirements

The signal received at the demodulator of a receiver is always accompanied by noise, including that generated in preceding stages of the receiver itself. Furthermore, there may be interfering signalsinterfering signals in the desired band that are not rejected by the bandpass filter HR)f (. Both noise and interference give rise

to undesired components at the detector output. When interference or noise is included, the contaminated signal u)t ( is given by:

Noise and Interference in Analog Transmission

Simple Interference ExampleSimple Interference Example

A sinusoidal carrier fc and an interference signal fI

Let the interference signal have amplitude Ai and frequency fc + fi . The total signal entering the demodulator is the sum of two sinusoids, given by:

Following the phasor construction:

If the interference is small compared to the carrier, thephasor diagram shows that the resultant envelope is essentially the sum of the inphase componentsinphase components, while the quadrature component determines the phase anglephase angle. That is, if Ai << A, then:

we can see that the interfering wave performs an AM modulation and phase modulation of a carrier just like a modulating tone of frequency f i with modulation index mI

Electromagnetic BandElectromagnetic Band

The Electromagnetic WavesThe Electromagnetic Waves

The Plane WaveThe Plane Wave

Propagating Wave

Wave Polarization !!!!

Linear Polarization

Refraction )Transmission( and Reflection

TOTAL REFLECTION

TOTAL TRANSMISSION

BRWESTER Angle

Fundamental Parameter

Typical Values

dB and dBm

More Parameters

FAR Zone - FAR Field

REFERENCE ANTENNA REFERENCE ANTENNA ISOTROPIC !ISOTROPIC !

Basic Types of Basic Types of AntennasAntennas

SMALLSMALL Dipole Antenna Dipole Antenna

FINITE Dipole = Sum of SMALL DIPOLES

SPACE FACTOR

HALF-Wave Dipole

Effect of Reflected Wave

Propagation Effects )Flat Earth(Propagation Effects )Flat Earth(

ANRITSU Spectrum Analyzer