Microwave Fundamentals

Proprietary & Confidential Slide 1

Microwave FundamentalsMicrowave Fundamentals


Microwave Fundamentals- Microwave Fundamentals-

• Radio Propagation• Terminologies.• Polarization.• Microwave Frequency Bands.• Free space Loss.• Antenna .• Fresnel Zone• Modulation Technologies (QAM).• SDH,PDH,E1


Radio PropagationRadio Propagation


a. Radio Wave Propagation & Its Characterstics

i) Definition of Microwave :

Microwaves in a descriptive term used to identify electromagnetic waves in the frequency

spectrum ranging approx from 1 GHz to 30GHz. This corresponds to wavelength 30cm

to 1 cm. Since the wavelength is small the phase varies rapidly with distance, thus a

signal reaching to a point from two different routes may cause constructive or destructive

interference. Moreover these frequencies contain two energies (Electric and Magnetic)

so also known as ELECTROMAGNATIC WAVES. Propagations of this waves happens

in such a way that direction of propagation, Electric field and Magnetic field always

remains perpendicular to each other. Microwaves frequencies characteristics are very

much similar to light. The same is shown in the figure:

Radio Wave Propagation & Its Radio Wave Propagation & Its characteristicscharacteristics



E

HP

Depending on the topography and the meteorological conditions, radio waves propagate

In different ways causing attenuation to the original wave. Following propagation

mechanisms come into play:

ii) Reflection :

When electromagnetic waves incide on a surface they may be reflected depending on

the smoothness of the surface. When the surface is smooth and its size is greater than

the wavelength of the wave then it is Reflected.


iii) Refraction :

Bending of waves when passing through one media to other media of different refractive

index is called REFRACTION. Radio waves travel with different velocities in different

medium depending on their dielectric constants. The dielectric constant of the

atmosphere decrease with altitude. Thus the waves travel slower in the lower part of

atmosphere where dielectric constant is greater and faster in the upper part where

dielectric constant is lower thus refracting the beam downwards.


Glazy Surface

i r Where i = incident angle

r = reflected angle


iv) K-Factor & Effective Earth Radius:

In a horizontally homogeneous atmosphere where the vertical change of dielectric

constant is gradual, the bending or refraction is continuous, so that the ray is slowly

bent away from the thinner density air towards thicker, thus making the beam tend to

follow the earth’s curvature. This bending can be directly related to the radii of

spheres. The first sphere being the earth itself (radius =6370 km) and the second


RI1

RI2

RI1 < RI2

Where RI1 = Refractive index of medium 1

RI2 = Refractive index of medium 2

Medium 2

Medium 1



sphere is formed by the curvature of the ray beam with its center coinciding the

earth’s center. The K- Factor thus can be defined as the ratio of the radius, r, of the

ray beam curvature to the true earth radius r’.

i.e. K = r / r’, where K is called effective earth radius factor and r is the effective earth

radius.

Transmitter AntennaReceiver

Antenna

Effective Earth

Effective RadioOptical Line of sight

For K = 0.5

For K = 1

For K = infinity



v) Scattering :

When Electromagnetic waves incide on a rough surface having rough edges whose

dimension is less than the wavelength of the wave, it is scattered in different

directions. Scattering is a phenomenon which causes vector distribution of energy as

shown in the figure.

Incident wave Scattered waves

vi) Absorption :

At frequencies above 10 GHz the propagation of radio waves through the atmosphere

of the earth is strongly affected by the resonant absorption of electromagnetic energy

by molecular water vapour and oxygen. The amount of water vapour in the

atmosphere strongly varies from place to place according to the local meteorological

conditions.



vii) Attenuation :

As the EM waves travels it losses its energy, this is due to attenuation. Attenuation is

due to presence of other field (Magnetic or Electric), Due to fog, Due to Rain etc.

Rain Attenuation : Scattering and absorption of the radio wave by raindrops causes

attenuation. Although all frequencies are subject to these effects, rain attenuation is

of practical importance for frequencies above 10 GHz. Due to the random

behaviour of the rain events the same is not included as a contribution to the Link

Budget calculation.

P1 P2

Attenuation = 10 log (P2/P1) db



viii) Fading :

Fading is defined as any time varying of phase, polarization, and/ or level of a

received signal. The most basic propagation mechanism involved in Fading are

reflection, refraction, diffraction, scattering, attenuation and guiding(ducting).

i. Multi path Fading :

It is a common type of fading encountered in LOS radio links. This type of fading

results due to the interference between direct rays and component of ground

reflected wave & partial reflection from atmosphere.

ii. Fading due to Earth Bulge :

iii. Duct & Layer fading : Atmospheric ducts consisting of superrefractive and a

subrefractive layer or vice versa.

iv. Surface duct fading on over water path : It is a combination of multi path fading

due to water body and fading due to atmospheric duct.



Effective Earth

Effective EarthEffective Earth

Multi path fading

Fading due to earth bulge

Atmospheric duct

Surface duct

Water Body


Trunk Radio CharacteristicsTrunk Radio Characteristics

Long distance

Therefore lower frequencies

Therefore subject to Multipath fading

Diversity route compensation

Lower frequencies less effected by rain


Wave Propagation in AtmosphereWave Propagation in Atmosphere

With AtmosphereNo Atmosphere

The highest index of refraction is near the surface of the

earth, the waves are bent towards the ground

K-Value is a common used value to indicate ray bending

with respect to the physical radius of the earth

For a normal atmosphere K value equals 4/3


MultipathMultipath

Direct beam

Delayed beam

Multipath propagation occurs when there are

more then one ray reaching the receiver

Multipath transmission is the main cause of

fading


DiffractionDiffraction Radio path between transmitter and receiver obstructed

by surface with sharp irregular edges

Waves bends around the obstacle, even when line of

sight does not exist


Fade MarginsFade Margins

Fading depends on atmospheric conditions, path climatic

conditions and path terrain (need a path profile)

Rx Threshold level + interference

Rx signal level

Rx Threshold level

Rx signal level - rain

RSL

Thermal

Fade

Margin

Flat

Fade

Margin

Flat fade

MarginRain

EffectiveFade

Margin

FlatFade

Margin

DispersiveFade

Marginf ,


Rain FadingRain Fading

Rain Outage due to water absorption

Increases with frequency

Depends on amount of water in path

Rain rate (mm/hr)

Depends on rain region

How often does that mm/hr occur

Rain falls as flattened droplet

V better than H


i) Electromagnetic Waves & FieldsEnergy in EM waves is in form of Electric and Magnetic field. Energy of any MW wave

is vector sum of its all-electrical and magnetic components. The concept can be better

understood from the following diagrams :

E

MP

E1 E2

E13

E12

E11

E10 E9

E14

E16

E15

E8

E7

E6

E5

E4

E3

H13 H14

H9

H8

H7

H6 H5

H10

H12

H11

H4

H3

H2

H1

H16

H15

PolarizationPolarization


ii) Polarization ( H, V & Circular):

When EM wave contains E and H energies in all direction that is know as circularly

Polarized as shown in the last figure.

When EM waves has got only electrical component perpendicular to Horizon of earth,

is known as Vertical Polarized wave.

When EM waves has got electrical component parallel to Horizon of earth, known as

Horizontally polarized wave.

Vertically polarized wave travels longer distance as compare to horizontally polarized

wave.

Earth

E

EH

H

P = V P = H

PolarizationPolarization


Microwave Frequency Microwave Frequency BandBand


i) Microwave Frequency Bands as per ITU Radio Regulation :

Radio Waves are defined by Radio Regulations of the International telecommunication

Union.The radio spectrum allocated for Microwave are UHF,SHF and EHF as

mentioned below in the table:

Band Number Symbol Frequency RangeCorresponding

Metric Subdivision

Metric Abbreviations for

the band

4 VLF 3 to 30 kHz Myriametric waves B. Mam5 LF 30 to 300 kHz Kilometric waves B. km

6 MF 300 to 3000 kHz Hectometric waves B. hm7 HF 3 to 30 MHz Decametric waves B. dam8 VHF 30 to 300 MHz Metric waves B. m9 UHF 300 to 3000 MHz Decimetric waves B. dm

10 SHF 3 to 30 GHz Centimetric waves B. cm11 EHF 30 to 300 GHz Milimetric waves B. mm

12 300 to 3000 GHz Decimilimetric waves


Microwave frequency bandsMicrowave frequency bandsBand Designator Frequency (GHz Wavelength in Free

Space (centimeters)

L band 1 to 2 30.0 to 15.0

S band 2 to 4 15 to 7.5

C band 4 to 8 7.5 to 3.8

X band 8 to 12 3.8 to 2.5

Ku band 12 to 18 2.5 to 1.7

K band 18 to 27 1.7 to 1.1

Ka band 27 to 40 1.1 to 0.75

V band 40 to 75 0.75 to 0.40

W band 75 to 110 0.40 to 0.27


Prefix Factor Symbol

atto 10-18 a

fempto 10-15 f

pico 10-12 p

nano 10-9 n

micro 10-6 m

milli 10-3 m

centi 10-2 c

deci 10-1 d

deka 101 Da

hecto 102 H

kilo 103 k

mega 106 M

giga 109 G

tera 1012 T


ii) Microwave Frequency Band used in Practical Systems :

2, 6 and 7 GHz Frequency Bands are used for Intercity Backbone routes.

Nominal Hop Distances 25 – 40 Km

15,18 and 23 GHz Frequency Bands are used for Access Network

Nominal Hop Distance 1 – 10 Km.

: Government will allocate spot Frequency. Index of Radios

will be decided by Spot frequency. Channel No will be calculated using allocated spot

frequency. To obtain the same applications have to be forwarded to the following

government bodies :

iii) SACFA (Standing Advisory Committee for Frequency Allocation) –

It is a government Wing which allocates frequency and also gives tower ht clearance.

Before allocation Of frequency it checks not to cause interference to existing users.

Before giving tower


height clearance it checks that it should not cause obstruction to exiting MW link,

should not be in funnel zone of Aircraft etc.

iv) WPC (Wireless Planning Committee) - It is a government wing which takes

charges from operator for use of MW frequency pair. Charges are based on the

and width used and annual gross revenue.


v) Frequency & Bandwidth :

a) Introduction :

The implementation of digital LOS radio links has accelerated due to transition of

telephone network to an all digital network. The digital network is based on a PCM

waveform, which when compared to analog FDM is wasteful of bandwidth. A nominal

4-kHz voice channel on an FDM baseband system occupies about 4-kHz of

bandwidth. On an FDM/FM radiolink, by rough estimation we can say it occupies

about 16 kHz.

In conventional PCM baseband system, allowing 1 bit per Hz of

bandwidth, a 4-KHz voice channel roughly requires 64kHz (64 kbps) of bandwidth.

This is derived using Nyquist sampling rate of 8000 / sec (4000 Hz x 2) and each

sample is assigned an 8-bit code word, thus 8000 x 8 bits per second or 64 kbps.

Thus it is essential to select modulation techniques that are bandwidth conservative.


b) Modulation techniques used :

The digital modulation schemes such as FSK, BPSK/QPSk, 8-ary PSK, 4-QAM, 8 –

QAM and 16-QAM are most commonly used. For eg the table shows comparision of

Analog and digital modulation techniques:600 channel FM Analog 16 QAM Digital

Bandwidth 10 MHz 10 MHzVoice Channel Capacity 600 384Max Data Capacity 11.52Mbps 25 MbpsE1 capacity 10 12System Gain 110.4 dB 111.5 dB

c) Bandwidth Requirement :

As per the no. of channel requirements the bandwidth of the system can be decided.

For example for 4mbps I.e. 60 nos of 64 kbps channels I.e. 4 Mbps , bandwidth of of

3.5MHz is required and so on as mentioned below:

7 MHz for 8 Mbps, 14 MHz for 16 Mbps and so on.


TerminologiesTerminologies


i.Azimuth and Importance of North directionIt is angle of antenna direction w.r.t. north in clockwise direction. This is also known as bearing.

N

ii.AMSLAbove mean sea level. An antenna at AMSL 20m means it is 20meter higher than the mean sea level.



iii.db, dbmdb=it is logarithmic ratio db = 10 log P1/P2.

3db loss of power is power reduced to half.

dbm is the logarithmic ratio of power w.r.t 1. miliwatt1 mW power in dbm is =10 log 1mW/1mW = 10 log 0 = 0dbm1 W power in dbm is = 10 log 10W/1mW =30dbm

iv) Antenna Gain and Beam widthBeam width of an antenna is the angle in which antenna radiates energy. Antenna Gain is measured w.r.t. isotropic antenna. An isotropic antenna radiates power in all direction. In practical system the energy needs to be radiated in the desired direction in desired beam width. Thus the total energy confined in the smaller aperture. Unit of antenna gain is dbi. Antenna Gain

= 17.8 + 20 * log10 (f *d) dBi Where d= Antennae Diameter in Meter and f= Frequency in GHz

Beam width



v) AGC

AGC stands for Automatic Gain Control. Media between two antennae in MW system is variable thus the path loss. MW system is designed in such a way that it can add or reduces the gain to compensate the variation in path loss. This mechanism is known as AGC system.

vi) Spot frequency

MW system transmits information after modulation on carrier frequency from one point to another. The carrier frequency is known as spot frequency. We need to set a spot frequency in MW system (also known as channel number).




Space Diversity

Frequency Diversity

F2

F1

i. Diversity ii. It is used to improve system performance. There are two types of

diversity used. 1. Space Diversity2. Frequency Diversity


Free Space PropagationFree Space Propagation


Free Space propagationFree Space propagation

i. Free Space Propagation :

As described earlier characteristics of Microwave is very much similar to light waves.

Velocity of Microwaves is same as velocity of light waves. Velocity of the light (C) is

3x 108 meter per second.

Also we know that C = F * (F=frequency and = wavelength).

As the EM wave travels in free space it looses energy. Free Space transmission loss

is the least possible loss between a transmitter and a receiver. The same can be

defined by the formula:

P loss = 32.4 + 20 log f *d

where f is Frequency in MHz and d is Distance in KM


ii) Importance of Free Space Loss :

As described free space loss is the loss calculated in space thus it is minimum loss

incurred when EM waves travels a distance. Loss when EM waves travels the same

distance in other media will be higher than the loss in free space. Exact loss can be

calculated by giving other external environmental inputs to planning tool.

Free Space propagationFree Space propagation


)log(2045.92 fdL fs

d=1km ---> L = 124 dBmd=2km ---> L = 130 dBm

For 39 GHz, L 118 + 6d

d=1km ---> L = 121 dBmd=2km ---> L = 127 dBm

For 26 GHz, L 115 + 6d

39 GHz 26 GHz

For 23 GHz, L 120 + 6d For 18 GHz, L 112 + 6d

Examples

Free Space Loss


Antenna BasicsAntenna Basics


vi) Antenna Design for Microwave Systems :

a) Introduction :

Antennas form the link between the guided waves and the free space part of a radio

or microwave system. The guided parts are cables or waveguides to and from the

transmitter and receiver.

b) Purpose of Antennas :

The purpose of a transmitting antenna is to efficiently transform the current in a circuit

or waveguide into radiated radio or microwave energy. The purpose of a receiving

antenna is to efficiently accept the radiated energy and convert it to guided form for

detection and processing by a receiver.

c) Types of Antenna :

Antennas for radio and microwave system falls into two broad categories depending

on the degree to which the radiation is confined.


Microwave and satellite communications use pencil beam antennas where the

radiation is confined to one narrow beam of energy, whereas Mobile communications

and broadcasting use omni directional pattern in the horizontal plane and toroidal

pattern in the vertical plane. At microwave frequencies the most common type of

pencil beam antenna is a medium to large size reflector antenna. This consists of a

reflector, or, mirror which collimates the signal from a feed horn at the focus of the

reflector. These are aperture antennas because the basic radiating element is an

Aperture.

`

Reflector Antenna

& Feed Horn

Pencil BeamToroidal Beam


d) Size and Gain of Microwave Antenna :

The axi-symmetric parabolic reflector with a feed at the focus of the paraboloid is the

simplest type of reflector antenna used in microwave application. The paraboloid has

the property that energy from the feed horn at the focus F goes to the point P on the

surface where it is reflected parallel to the axis to arrive at a point A on the imaginary

aperture plane. The equation describing the surface is :

P A

FD

Fz

r

r4F( F – z ) where F is the focal length. At the

Edge of the reflector the relationship between the

focal length and the diameter D is given by :

F / D = ¼ cot (

The depth of the paraboloid is specified by its F/D ratio.

Common sizes for microwave reflector antennas are

between F/D =0.25 which makes = 90to F/D =0.5

which gives = 53


The peak gain of the reflector antenna is calculated as :

G = 4X effective aperture area / = ( D / )

Hence more the gain larger will be the size of the antenna used.


1 = 0 dB 2 = 3 dB3 = 4.7 dB 4 = 6 dB 5 = 7 dB 6 = 7.7 dB 7 = 8.5 dB 8 = 9 dB 9 = 9.5 dB10 = 10 dB

deciBeldeciBel

When trying to calculate cascade amplifiers in most cases it will be difficult using the linear way (long numbers and most of the time not round ones).This is the reason for working in decibels.

G=10Log(Pout/Pin) [dB]

Pin

Pin Pout

PoutmW

mWG

Pin

PoutG=?

Gain is a referenced Value without measurements units

A reminderLogBLogABALog )(

Power measurements units in a logarithmical world is dBm (in reference to 1mW) or dBW (in reference to 1W).

1mW = -30dBW = 0dBm

1W = 0dBW = 30dBm


Generator

Antennas Basics Antennas Basics

DefinitionDefinition

- The device used to guide RF energy from one point to another one, with minimumattenuation, heat and radiation losses.Guides the energy

- The structure associated with the region of transition between a guided wave anda free space wave, or vice versa.Radiates/receives energy

= wavelength = c/f f = 3.5 GHz = 8.571 cm

- Transmission line

- Radio antenna

Transmission line(spacing between wires is onlya fraction of the wave length) Antenna

(separation between wiresis in the range of one ormore wave lengths)


Directivity Directivity

Generator

RCV

17 dBm (50mW)

Isotropic antenna (theoretical)-

Non-isotropic antenna (real)

Generator17 dBm (50mW)

RCV

-

The energy fed into the antenna is radiatedin the whole space.A receiver RCV, located in the far field of thetransmitter, gets the basic element of energygenerated by the presence of 17dBm (50mW) inthe whole space.

The energy fed into the antenna is radiated onlyin part of the space.A receiver RCV, located in the far field of thetransmitter, gets the basic element of energygenerated by the presence of 17dBm (50mW) inthe defined volume, which is equivalent with thepresence of much more energy isotropicallydistributed.


For same amount of energy fed into the antenna, anon-isotropic antenna will transmit its signal overlonger distances.Non-isotropic antennas are characterized by theircapability to focus the transmitted energy,expressed by the antenna gain

e.g. - An antenna with 3dBi gain, radiates its energyinto 50% of the space.Conclusion - A 3dBi antenna fed with 17dBm behaves (in its active field) as an isotropicantenna fed with 20dBmEven if, in fact, the antenna radiates only 17 dBm,it is said that it radiates 20 dBm EIRP (EquivalentIsotropic Radiated Power)

Antenna gain = 10 Log [dBi] Volume (radiation) of subject antenna

volume (radiation) of isotropic antenna


Non-isotropic antenna (real)-


RCV

RCV


Radiation Patterns for some antennas Radiation Patterns for some antennas

Gain (dBi)

Geometry Radiation Pattern Half Power Beam Width (HPBW)

Horizontal Vertical

18 ±18º ±18º

35 ±2.5º ±2.5º


Antenna PatternAntenna Pattern

at 3.500000 GHz

-50-45

-40-35

-30-25-20

-15-10

-50

-180 -120 -60 0 60 120 180


Andrew antenna SpecificationAndrew antenna Specification


VHP2A-220A-241 is:

ValuLine High Performance, shielded, single polarized(VHPX Shielded, Dual Polarized)

2 ft (0.6 m) in diameter

Non-compliant to UK RA specifications (blank Compliant to UK RA Specification)

21.2-23.6 GHz band(142 14.25-15.35 GHz)

A Revision

PBR220, 1.20 VSWR

White antenna, white radome, no flash

Standard packing


Fresnel ZoneFresnel Zone

A family of ellipsoids that can be constructed between a transmitter and a receiver by joining all the various ways of the destructives electromagnetic waves, in reference to the direct line of transmission.

Transmitter Receiver

d1 d2

d'1 d'2

The circles indicate the geometric place ofall the waves that passed the way: d'1+d'2



The radius of each of the circles in the figure is calculated using the following equation:

21

21

dd

ddnrn

d2: distance fromTerminal: 1.2Km

d1 distance from Base toobcstacle: 1.8Km

rF: 1st Fresnel zoneradius

Possible obtructor

Base Antennasite

TerminalAntenna site



L = 6 dBL = 20 dB


Fresnel Zone TablesFresnel Zone Tables

3.5GHz 50 200 700 1200 1700 2200 2700 3200 3700 4200 4700 5200 5700 6200 6700 7200 7700 8200 8700 9200 9700

50 1.5 1.9 2.0 2.0 2.0 2.0 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1

200 1.9 2.9 3.7 3.8 3.9 4.0 4.0 4.0 4.0 4.0 4.1 4.1 4.1 4.1 4.1 4.1 4.1 4.1 4.1 4.1 4.1

700 2.0 3.7 5.5 6.2 6.5 6.7 6.9 7.0 7.1 7.2 7.2 7.3 7.3 7.3 7.4 7.4 7.4 7.4 7.5 7.5 7.5

1200 2.0 3.8 6.2 7.2 7.8 8.2 8.4 8.6 8.8 8.9 9.1 9.1 9.2 9.3 9.3 9.4 9.4 9.5 9.5 9.5

1700 2.0 3.9 6.5 7.8 8.5 9.1 9.5 9.8 10.0 10.2 10.3 10.5 10.6 10.7 10.8 10.9 10.9 11.0 11.0

2200 2.0 4.0 6.7 8.2 9.1 9.7 10.2 10.6 10.9 11.1 11.3 11.5 11.7 11.8 11.9 12.0 12.1 12.2

2700 2.1 4.0 6.9 8.4 9.5 10.2 10.8 11.2 11.6 11.9 12.1 12.3 12.5 12.7 12.8 13.0 13.1

3200 2.1 4.0 7.0 8.6 9.8 10.6 11.2 11.7 12.1 12.5 12.8 13.0 13.3 13.5 13.6 13.8

3700 2.1 4.0 7.1 8.8 10.0 10.9 11.6 12.1 12.6 13.0 13.3 13.6 13.9 14.1 14.3

4200 2.1 4.0 7.2 8.9 10.2 11.1 11.9 12.5 13.0 13.4 13.8 14.1 14.4 14.6

4700 2.1 4.1 7.2 9.1 10.3 11.3 12.1 12.8 13.3 13.8 14.2 14.5 14.9

5200 2.1 4.1 7.3 9.1 10.5 11.5 12.3 13.0 13.6 14.1 14.5 14.9

5700 2.1 4.1 7.3 9.2 10.6 11.7 12.5 13.3 13.9 14.4 14.9

6200 2.1 4.1 7.3 9.3 10.7 11.8 12.7 13.5 14.1 14.6

6700 2.1 4.1 7.4 9.3 10.8 11.9 12.8 13.6 14.3

7200 2.1 4.1 7.4 9.4 10.9 12.0 13.0 13.8

7700 2.1 4.1 7.4 9.4 10.9 12.1 13.1

8200 2.1 4.1 7.4 9.5 11.0 12.2

8700 2.1 4.1 7.5 9.5 11.0

9200 2.1 4.1 7.5 9.5

9700 2.1 4.1 7.5


3.5 GHz vs. 26 GHz – Fresenel Zone3.5 GHz vs. 26 GHz – Fresenel Zone

1 2 3 4 5 6 7 8 9 100

10

20

30`

40

50

60

70

80

90

100

Range (km)

hei

gh

t (m

)

3.5GHz26GHz


Modulations TechnologiesModulations Technologies


IntroductionIntroduction

Examples for modulation techniques:– Quadrate Phase Shift Keying (QPSK)– Frequency Shift Keying (FSK)– Quadrate Amplitude Modulation (QAM)– Etc.


Modulation Techniques - Basic TechniquesModulation Techniques - Basic Techniques

modulatormessage(t) transmitted

signal

carrier

data bits 0 1 0 0 1

unmodulated carrier

Amplitude Modulation (AM)

Frequency Modulation (FSK)

(Differential) Phase Modulation (DPSK)

• Data bits modulate (modify) a carrier signal• Basic modulation techniques

• Amplitude• Frequency• Phase


• Data bits are represented over the transmission channel by SYMBOLS

• Symbol rate is expressed in Baud

Jean Maurice Emile BAUDOT

- 1874 - Baudot code - 5 bits - for use with telegraphs (more economical than Morse code)

- 1894 - Telegraph multiplexer

(1845 - 1903)

Modulation Techniques - Basic Techniques


Modulation Techniques – Symbols

Modulation Techniques – Symbols

Symbol• Is a sinusoidal signal (carrier) with specific parameters

dictated by the bit(s), transmitted for finite period of time.

• Carrier parameters do not change for the duration of the symbol

• Even if the symbol itself is comprised of one single frequency (the carrier), the fact that it is transmitted over a finite period of time generates an infinite spectrum, centered on the carrier frequency.


Modulation Techniques - SymbolsModulation Techniques - Symbols

unmodulated carrier

Modulated carrier (symbols)

Time domain Frequency domain

A

ffc

A

f••1

T2T

fc


Modulation Techniques - Quadrature Amplitude Modulation (QAM)Modulation Techniques - Quadrature Amplitude Modulation (QAM)

• QAM is a modulation modifying the phase and the amplitude of the carrier signal

• QAM symbols are represented by the carrier signal being transmitted with specific phase / amplitude (dictated by the message), for finite periods of time.


Quadrature Amplitude Modulation (QAM)Quadrature Amplitude Modulation (QAM)

Symbol 1 is a cosine waveform of:

- amplitude A1

- phase A1

A1 cos t

symbol 1

t

A

Symbol 1 = A1cos(t - )

A1cos t (phase 0; reference)

• Polar Coordinates• Symbol presentation

• Amplitude – distance from origin• Phase – Angle from positve x axis

• Symbol Generation• For the generation of such symbols, there is a need for an oscillator

able to modify its phase based on the symbol that has to be transmitted not a very trivial topic.

• Symbol reception• To identify the symbol, the receiver needs a reference carrier, in phase with

the carrier used by the transmitter (coherent demodulation).



• Symbol representation• A cosine waveform of frequency t with any specific phase can be

represented as the sum of a sine and a cosine waveforms of same frequency t.

• The phase of the resultant signal is dictated by the relative amplitudes of the sine and cosine waveforms, through “Kc = cosine amplitude = cos ; Ks = sine amplitude = sin ”

• By controlling Kc and Ks, any phase of the waveform may be generated.

• A cosine waveform may be identified by its

• In phase (I) component amplitude, Kc (cosine)

• Quadrature phase (Q) component amplitude, Ks (sine)

cos(t - ) = cos t*cos + sin t*sin

As is constant :

cos = constant = Kc

sin = constant = Ks

cos(t - ) = Kc*cos t + Ks*sin t

• I/Q coordinates (a bit of trigonometry)



=4

Ks = sin = 0.74

Kc = cos = 0.74

cos(t - ) = 0.7cos t + 0.7sin t4

t

A

=8

Ks = sin = 0.48

Kc = cos = 0.98

cos(t - ) = 0.9cos t + 0.4sin t8

t

A

=4

I

Q

• I/Q coordinates • Examples



Easier to implement

2

cos t cos t

sin t

Kc Ks

symbol

cos(t - ) = Kc*cos t + Ks*sin t

• I/Q coordinates

• Symbol Generation

• Symbol reception• The symbol is identified by the relative amplitude of the sine

and cosine components. there is no need for coherent carrier.


Mapping processMapping process

• QAM64 has 64 constellation points

Constellation Point

I

Q

Constelationpoint

• When the mapping process received the 6 bits needed to be transmitted it divide it to 3 bits for Q signal and the other 3 bits

for the I signal. Then it choose the right constellation point which represent the bits needed to be transmitted.


Mapping processMapping process

• The bits to be transmitted are 101111.

I

Q

Constelationpoint

The bits are divided into 3 bits for Q and 3 bits for I.

101 -> Q 111 -> I

The Q signal are at a certain level defined by the mapping process.

The I signal is handled in the same manner.

Q level

I level



modulation technique

nu

mb

er o

f sy

mb

ols

nu

mb

er o

f b

its

per

sym

bo

l

bit

rat

e / B

aud

ra

te

number of

amp

litu

des

ph

ases constellation

generated using

nr.

of

cosi

ne

amp

litu

des

nr.

of

sin

e am

plit

ud

es

64QAM 664 6/1 9 528

(3 bits)

8

(3 bits)

not all combinations

are used

000101 001101 011101 010101 110101 111101 101101 100101

000111 001111 011111 010111 110111 111111 101111 100111

000110 001110 011110 010110 110110 111110 101110 100110

000010 001010 011010 010010 110010 111010 101010 100010

000011 001011 011011 010011 110011 111011 101011 100011

000001 001001 011001 010001 110001 111001 101001 100001

000000 001000 011000 010000 110000 111000 101000 100000

000100 001100 011100 010100 110100 111100 101100 100100

Q

I-1-3-5-7 +7+5+3+1

+3

+5

+7

+1

-1

-3

-5

-7

• QAM constellations (patterns)


128 QAM Costellation.128 QAM Costellation.


Q/I formatsQ/I formats

• Q and I are 90º difference from each other. • Each one of those signals is basically enhanced

(Quadurate) Amplitude Modulation. • Due to the fact the signals have 90º they will not

interfere each other if they are combined.• Combination of those signals will provide us …..

a signal with Amplitude and Phase changes !


i) Transmit Power, Receiver Sensitivity & Fade Margin

a. Transmit Power :

This is the RF power which is transmitted by RF unit.

b. Receiver Sensitivity :

This is the minimum power, which can be sensed by RF unit and signals can be

received.

c. Fade Margin :

Fade Margin = Receiver Threshold (10E-6) - Actual received power

Link BudgetLink Budget



ii) Link BudgetThe Link Budget sums all attenuations and amplifications of the signal between the

transmitter output and receiver input terminals. This can be illustrated in the figure

below:

Transmitted & Received Power

Output Power

Feeder Loss

Propagation Loss and attenuation

Antenna Gain

Antenna Gain

Feeder Loss

Received Power

Fading Margin

Receiver Threshold

4dB

Power

Distance



As illustrated in the figure the received Power in the radio link terminal can be

calculated as follows :

Pin = Pout – AF + G – ABF – A0 – AG – AL

Where Pin = Received Power (dBm)

Pout = Transmitted Power (dBm)

AF = Antenna Feeder Loss (dB)

G = Antenna Gain (dBi)

ABF = Free space Loss (dB) (between isotropic antennas)

A0 = Obstacle Loss (dB)

AG = Gas Attenuation (dB)

AL = Additional Loss (dB)


Noise and sensitivityNoise and sensitivity

To every transmitted signal a thermal noise is added, the thermal noise is marked by the letter N and defined by Boltsman constant [K] ( ) multiple the temperature in Kelvin [T] (room temperature equal to 290) multiple the bandwidth in MHz [B]. Or in other words… (in the linear way)

in the logarithmical way …

Signal to Noise Ration (SNR) defined as the ratio between the signal strength and the noise strength.

Every active system adds a certain noise to the signal the parameter which described it call Noise Figure (NF). Noise figure defined as the ratio between the input SNR to the output SNR.

231038.1 K

BTKN

LogBLogBTKLogN 1011410)(10

SNRSNRNF OUTIN

SNRNSNF OUTININ

SNRNFNS OUTININ

SNRNFLogBS OUTIN 10114


For correct operation:

Signal to Noise Ratio (SNR)Signal to Noise Ratio (SNR)

External interference

Power received

Noise floor

SNR

Sensitivity SNR

Required received power

Pr interference + SNR

Calculating receiver sensitivity

Power received

SNR

Sensitivity

Noise floor {thermal noise + implementation

noise (NF)} )Note: SNR is a function of rate; values range from 5 dB to 30 dB(


2 Mbps Signal2 Mbps Signal

1. Construction of 2Mbps signal

i. Voice frequency

ii. Sampling

iii. Qunatization

iv. Digitization

v. 64 kbps signal Multiplexing.

vi. PDH

vii. SDH


Voice FrequencyVoice Frequency

0 300 3400 4000

Energy

Frequency in Hz


SamplingSampling

Voltage

Time

Time

Voltage


QuantizationQuantization

Time

Fixed 256no’s Voltagelevels

After QuantizationBefore Quantization


DigitizationDigitization

Each sample will be represented by 8 bits

0 1 0 0 1 1 0 1


64 kbps Multiplexing64 kbps Multiplexing

Multiplexer

0

1

2

3

4

25

26

27

28

29

30

31

1 2 3 4 5 27 28 29 3130

2Mbps stream


PDHPDH

M=Multiplexer

1

2

3

4

2Mbps stream

2 / 8 Multiplexer

8 / 32 Multiplexer8Mbps stream

2

3

4

32 / 140 Multiplexer

32 Mbps stream2

3

4

140 Mbps stream


SDHSDH

1

2

21

2Mbps stream

STM-1

20

1

2

21

2Mbps stream

STM-1

20

ADM

2Mbps stream


PDH- Plesynchronous Digital Hierarchy PDH- Plesynchronous Digital Hierarchy

Level01234

Rate(Mb/s)0.0642.0488.44834.368139.264

E1-141664

i.


SDH-Synchronous digital HierarchySDH-Synchronous digital Hierarchy

LevelSTM-1STM-4STM-8STM-16STM-64

Rate(Mb/s)155.52622.081244.162488.32~10GHz

E16325250410084032


Some popular 50 Ohms Coax cableSome popular 50 Ohms Coax cable

Type Frequeny MHz

Power*Watts

Loss dBper 100 ft

Diameterinches

Rel. cost

RG58 0-3000 45 15-20 0.2" low

RG8/RG213

0-3000 190 9-10 0.4" moderate

Belden 9913

0-1000 275 4-5 0.4" moderate

Times LMR400

0-2000 350 3.5-4 0.4" moderate

1/2" Alum.

0-3000 650 3-3.5 0.6" moderate

1/2" Heliax

0-8000 900 2-2.5 0.6" high

7/8" Heliax

0-5000 2,000 1.25-1.5 1.0" high

*

Microwave Fundamentals

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Transcript of Microwave Fundamentals