Microwave_Fundamentals_ppt.ppt

Proprietary & Confidential Slide 1
Microwave Fundamentals

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

Radio 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
characteristics

characteristics
E
H
P
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.
characteristics
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
characteristics
RI1
RI2
RI1 < RI2
Where RI1 = Refractive index of medium 1
RI2 = Refractive index of medium 2
Medium 2
Medium 1

characteristics
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 Antenna
Receiver
Antenna
Effective Earth
Effective Radio
Optical Line of sight
For K = 0.5
For K = 1
For K = infinity

characteristics
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.

characteristics
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

characteristics
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.

characteristics
Effective Earth
Effective Earth
Effective Earth
Multi path fading
Fading due to earth bulge
Atmospheric duct
Surface duct
Water Body

Trunk Radio Characteristics
 Long distance
 Therefore lower frequencies
 Therefore subject to Multipath fading
 Diversity route compensation
 Lower frequencies less effected by rain

Wave Propagation in Atmosphere
With Atmosphere
No 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

Multipath
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

Diffraction
 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 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
Margin
Rain
Effective
Fade
Margin
Flat
Fade
Margin
Dispersive
Fade
Margin
f ,

Rain 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 & Fields
Energy 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
M
P
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
Polarization

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
E
H
H
P = V P = H
Polarization

Microwave Frequency
Band

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 Range
Corresponding
Metric Subdivision
Metric
Abbreviations for
the band
4 VLF 3 to 30 kHz Myriametric waves B. Mam
5 LF 30 to 300 kHz Kilometric waves B. km
6 MF 300 to 3000 kHz Hectometric waves B. hm
7 HF 3 to 30 MHz Decametric waves B. dam
8 VHF 30 to 300 MHz Metric waves B. m
9 UHF 300 to 3000 MHz Decimetric waves B. dm
10 SHF 3 to 30 GHz Centimetric waves B. cm
11 EHF 30 to 300 GHz Milimetric waves B. mm
12 300 to 3000 GHz Decimilimetric waves

Microwave frequency bands
Band 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 MHz
Voice Channel Capacity 600 384
Max Data Capacity 11.52Mbps 25 Mbps
E1 capacity 10 12
System 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.

Terminologies

i.Azimuth and Importance of North direction
It is angle of antenna direction w.r.t. north in clockwise direction. This is also known as
bearing.
N
ii.AMSL
Above mean sea level. An antenna at AMSL 20m means it is 20meter higher than the mean
sea level.
Terminologies

iii.db, dbm
db=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. miliwatt
1 mW power in dbm is =10 log 1mW/1mW = 10 log 0 = 0dbm
1 W power in dbm is = 10 log 10W/1mW =30dbm
iv) Antenna Gain and Beam width
Beam 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
= 17.6 + 20 * log10 (f *d) dBi
Where d= Antennae Diameter in Meter and f= Frequency in GHz
Beam width
Terminologies

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).
Terminologies

Terminologies
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 Diversity
2. Frequency Diversity

Free Space Propagation

Free 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 propagation

)
log(
20
45
.
92 f
d
Lfs 



d=1km ---> L = 124 dBm
d=2km ---> L = 130 dBm
For 39 GHz, L  118 + 6d
d=1km ---> L = 121 dBm
d=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 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 Beam
Toroidal 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
F
D
q
F
z
r
r4F( 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 (q/2)
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 q = 90°, to F/D =0.5
which gives q = 53°.

The peak gain of the reflector antenna is calculated as :
G = 4P X effective aperture area /  = ( PD /  ) 
Hence more the gain larger will be the size of the antenna used.

1 = 0 dB
2 = 3 dB
3 = 4.7 dB
4 = 6 dB
5 = 7 dB
6 = 7.7 dB
7 = 8.5 dB
8 = 9 dB
9 = 9.5 dB
10 = 10 dB
deciBel
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 Pou
Pout
mW
mW
G 

Pin
Pout
G=?
Gain is a referenced Value without
measurements units
A reminder
LogB
LogA
B
A
Log 

 )
(
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
 Definition
- The device used to guide RF energy from one point to another one, with minimum
attenuation, heat and radiation losses.
Guides the energy
- The structure associated with the region of transition between a guided wave and
a 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 only
a fraction of the wave length) Antenna
(separation between wires
is in the range of one or
more wave lengths)

Directivity
Generator
RCV
17 dBm (50mW)
Isotropic antenna (theoretical)
-
Non-isotropic antenna (real)
Generator
17 dBm (50mW)
RCV
-
The energy fed into the antenna is radiated
in the whole space.
A receiver RCV, located in the far field of the
transmitter, gets the basic element of energy
generated by the presence of 17dBm (50mW) in
the whole space.
The energy fed into the antenna is radiated only
in part of the space.
A receiver RCV, located in the far field of the
transmitter, gets the basic element of energy
generated by the presence of 17dBm (50mW) in
the defined volume, which is equivalent with the
presence of much more energy isotropically
distributed.

For same amount of energy fed into the antenna, a
non-isotropic antenna will transmit its signal over
longer distances.
Non-isotropic antennas are characterized by their
capability to focus the transmitted energy,
expressed by the antenna gain
e.g. - An antenna with 3dBi gain, radiates its energy
into 50% of the space.
Conclusion - A 3dBi antenna fed with
17dBm behaves (in its active field) as an isotropic
antenna fed with 20dBm
Even if, in fact, the antenna radiates only 17 dBm,
it is said that it radiates 20 dBm EIRP (Equivalent
Isotropic Radiated Power)
Antenna gain = 10 Log [dBi]
Volume (radiation) of subject antenna
volume (radiation) of isotropic antenna
Generator
17 dBm (50mW)
Non-isotropic antenna (real)
-
Generator
17 dBm (50mW)
RCV
RCV

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 Pattern
at 3.500000 GHz
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
-180 -120 -60 0 60 120 180

Andrew antenna Specification

VHP2A-220A-241 is:
1. ValuLine High Performance, shielded, single
polarized(VHPX Shielded, Dual Polarized)
2. 2 ft (0.6 m) in diameter
3. Non-compliant to UK RA specifications (blank Compliant to
UK RA Specification)
4. 21.2-23.6 GHz band(142 14.25-15.35 GHz)
5. A Revision
6. PBR220, 1.20 VSWR
7. White antenna, white radome, no flash
8. Standard packing

Fresnel 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 of
all the waves that passed the way: d'1+d'2

Fresnel Zone
The radius of each of the circles in the figure is
calculated using the following equation:
2
1
2
1
d
d
d
d
n
rn



d2: distance from
Terminal: 1.2Km
d1 distance from Base to
obcstacle: 1.8Km
rF: 1st Fresnel zone
radius
Possible obtructor
Base Antenna
site
Terminal
Antenna site

Fresnel Zone
L = 6 dB
L = 20 dB

Fresnel Zone Tables
3.5GHz 50 200 700 1200 1700 2200 2700 3200 3700 4200 4700 5200 5700 6200 6700 7200 7700 8200 8700 9200 97
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
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
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
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 Zone
1 2 3 4 5 6 7 8 9 10
0
10
20
30`
40
50
60
70
80
90
100
Range (km)
height
(m)
3.5GHz
26GHz

Modulations Technologies

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

Modulation Techniques - Basic
Techniques
modulator
message(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
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 - Symbols
unmodulated
carrier
Modulated
carrier
(symbols)
Time domain Frequency domain
A
f
fc
A
f
•
•
1
T
2
T
fc

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)
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).

Quadrature Amplitude
Modulation (QAM)
• 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)

Modulation (QAM)
 =

4
Ks = sin = 0.7

4
Kc = cos = 0.7

4
cos(t - ) = 0.7cos t + 0.7sin t

4
t
A
 =

8
Ks = sin = 0.4

8
Kc = cos = 0.9

8
cos(t - ) = 0.9cos t + 0.4sin t

8
t
A
=

4
I
Q
• I/Q coordinates
• Examples

Modulation (QAM)
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 process
• QAM64 has 64 constellation points
Constellation Point
I
Q
Constelation
point
• 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 process
• The bits to be transmitted are 101111.
I
Q
Constelation
point
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 (QAM)
modulation
technique
number
of
symbols
number
of
bits
per
symbol
bit
rate
/
Baud
rate
number of
amplitudes
phases
constellation
generated using
nr.
of
cosine
amplitudes
nr.
of
sine
amplitudes
64QAM 6
64 6/1 9 52
8
(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.

Q/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 Budget

Link Budget
ii) Link Budget
The 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

Link Budget
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 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.
23
10
38
.
1 -


K
B
T
K
N 


LogB
LogB
T
K
Log
N 10
114
10
)
(
10 
-




SNR
SNR
NF OUT
IN
-

SNR
N
S
NF OUT
IN
IN
-
-

SNR
NF
N
S OUT
IN
IN



SNR
NF
LogB
S OUT
IN



 - 10
114

For correct operation:
 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 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 Frequency
0 300 3400 4000
Energy
Frequency in Hz

Sampling
Voltage
Time
Time
Voltage

Quantization
Time
Fixed
256no’s
Voltage
levels
After Quantization
Before Quantization

Digitization
Each sample will be
represented by 8 bits
0 1 0 0 1 1 0 1

64 kbps Multiplexing
Mu
ltip
lex
er
0
1
2
3
4
25
26
27
28
29
30
31
1 2 3 4 5 27 28 29 31
30
2Mbps stream

PDH
M=Multiplexer
1
2
3
4
2Mbps stream
2 / 8
Multiplexer
8 / 32
Multiplexer
8Mbps stream
2
3
4
32 / 140
Multiplexer
32 Mbps stream
2
3
4
140 Mbps stream

SDH
1
2
21
2Mbps stream
STM-1
20
1
2
21
2Mbps stream
STM-1
20
ADM
2Mbps stream

PDH- Plesynchronous Digital
Hierarchy
Level
0
1
2
3
4
Rate(Mb/s)
0.064
2.048
8.448
34.368
139.264
E1
-
1
4
16
64
i.

SDH-Synchronous digital Hierarchy
Level
STM-1
STM-4
STM-8
STM-16
STM-64
Rate(Mb/s)
155.52
622.08
1244.16
2488.32
~10GHz
E1
63
252
504
1008
4032

Some popular 50 Ohms Coax cable
Type Frequeny
MHz
Power*
Watts
Loss dB
per 100 ft
Diameter
inches
Rel. cost
RG58 0-3000 45 15-20 0.2" low
RG8/RG
213
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
*

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