WC-Lecture-1, 2, 3.ppt

TLC509
Wireless Communication and Networks

Wireless Communication and
Wireless Networks:
 Communication via Satellites
 GSM/Cellular communication
 Wireless LANS
 Wi-Max/Wi-Fi communication
 Bluetooth communication
 Wireless WANS

A satellite is any object that revolves around a planet
• there are many manmade (artificial) satellites,
– ~13,000 satellites are tracked in real time
• some are inactive, some are debris from space missions …
• the path a satellite follows is called an orbit,
• to access a satellite requires a ‘line of sight’ communication
– the receiver (satellite dish) must be in the satellite’s ‘footprint’
Satellite communications systems exist because earth is a sphere:
– Radio waves travel in straight lines at the microwave
frequencies used for communications
Introduction: Communication via Satellites

Generally:
• there is a transmitter on the ground
• the transmitter sends signals to a satellite
– using microwaves
• signal is received & amplified by the satellite
• signal is retransmitted back to Earth
• signal reaches its recipient
– or is 'bounced back' to another satellite

• Different kinds of satellites use different
frequency bands:
 L–Band: 1 to 2 GHz,
 S-Band: 2 to 4 GHz,
 C-Band: 4 to 8 GHz,
 X-Band: 8 to 12.5 GHz,
 Ku-Band: 12.5 to 18 GHz:
 K-Band: 18 to 26.5 GHz:
 Ka-Band: 26.5 to 40 GHz:

Satellite Footprint

ECHO1

TELSTAR

SYNCOM2

Meteosat weather satellite
Weight: 2000kg

Types of Satellite
• Based on the inclination, i, over the equatorial plane:
– Equatorial Orbits above Earth’s equator (i=0°)
– Polar Orbits pass over both poles (i=90°)
– Other orbits called inclined orbits (0°<i<90°)
• Based on Eccentricity (how much a conic section (a circle, ellipse,
parabola or hyperbola) varies from being circular. A circle has an eccentricity of zero, so
the eccentricity shows you how "un-circular" the curve is.
– Circular with centre at the earth’s centre
– Elliptical with one foci at earth’s centre

• Based on the Satellite Altitudes:
– GEO – Geostationary Orbits
• 36000 Km = 22300 Miles, equatorial, High latency
– MEO – Medium Earth Orbits
• High bandwidth, High power, High latency
– LEO – Low Earth Orbits
• Low power, Low latency, More Satellites, Small Footprint
– VSAT
• Very Small Aperture Satellites
Types of Satellite

GEO satellites
• Originally proposed by Arthur C. Clarke
• Their period of rotation exactly matches the Earth's
rotation
• Orbital height above the earth about 23000 miles or
35000km
Geosynchronous:
• their plane of orbit for these satellites is generally not the
equatorial plane
Geostationary:
• positioned directly over the equator and their path follows
the equatorial plane of the Earth.
• majority of communications satellites are in fact
geostationary satellites

16
MEO Satellites
• Medium Earth orbit (MEO), sometimes called intermediate
circular orbit (ICO), is the region of space around the Earth
above low Earth orbit (altitude of 2,000 kilometres (1,243 mi))
and below geostationary orbit (altitude of 35,786 kilometres
(22,236 mi))
• Diameter of coverage is 10,000 to 15,000 km
• Round trip signal propagation delay less than 50 ms
• Most common use for satellites in this region is for navigation,
communication, and geodetic/space environment science
• Example: Global Positioning System (GPS)

17
LEO Satellites
• A low Earth orbit (LEO) is an orbit around Earth with
an altitude between 160 kilometers (99 mi)
• Circular/slightly elliptical orbit under 2000 km
• Orbit period ranges from 1.5 to 2 hours
• Diameter of coverage is about 8000 km
• Round-trip signal propagation delay less than 20 ms
• Atmospheric drag results in orbital deterioration

• Earth observation satellites and spy satellites use
LEO as they are able to see the surface of the Earth
more clearly as they are not so far away
• The International Space Station is in a LEO about
400 km (250 mi) above the Earth's surface
• LEO satellite needs less powerful amplifiers for
successful transmission
• Envisat is one example of an Earth observation
satellite that makes use of this particular type of LEO
LEO Satellites

19
LEO satellites
• Little LEOs
– Frequencies below 1 GHz
– 5MHz of bandwidth
– Data rates up to 10 kbps
– Aimed at paging, tracking, and low-rate messaging
• Big LEOs
– Frequencies above 1 GHz
– Support data rates up to a few megabits per sec
– Offer same services as little LEOs in addition to
voice and positioning services

Prime objective of satellite:-
“provide reliable communication and other services to
earth stations and relay to other satellites”
They must be controlled and monitored and ensured that:
 The antennas are mounted properly
 Are rotating in respective orbits
 having the required electrical power
 Maintaining the controlled temperatures
 keeping communication active and reliable etc.
Each satellite has multiple components for different purposes; mainly are those
that provide communication and others are for support and control

A satellite has generally following subsystems:
 Attitude and Control System (AOCS)
 Telemetry, Tracking, Command and Monitoring (TTC&M)
 Power system
 Communication-subsystem
 Satellite antennas
Satellite Subsystem

Satellite Subsystem
Attitude and Control System (AOCS):
Attitude control is controlling the orientation of satellite w.r.t
some objects or fields exerting on
Satellites have sensors (to detect, measure the vehicle
change in its orientation etc.) and actuators to apply the
torques/forces needed to re-orient the vehicle to a desired
attitude
Factors that affect the orientation:
 Gravitational fields of moon/sun
 Solar effects due to its pressure
 Variation in earth’s magnetic field

Attitude and Orbit Control--AOC
Gravitational fields of sun and moon
The effect of the sun's radiation pressure, Residual air drag and
asteriods/meteoroids.
 cause the satellite to change its position, resulting in
change in its inclination
Orbital control must be able to pull-back the satellite
 Satellites must be periodically accelerated, in the opposite direction of
the forces acting on it
It is done by:
small rocket-motors (gas-jets or thrusters) as a sequence of
station-keeping maneuvers(orbit-control) from earth-station
LEOs/MEOs are less affective: as they are far away from sun/moon
orbits

Stabilizing a satellite in its orbit, requires us to determine first:
 Where satellite is
 Where it must be
 What means to be used to stabilize its position
Attitude and Orbit Control--AOC

Telemetry, Tracking, Command
and Monitoring of the
satellites

Telemetry and Monitoring:
Monitoring systems collect data from sensors and
send back to controlling earth-stations.
Data can be:
pressure in fuel tank, voltage and current levels in each
communication systems, temperature, drawn electrical
power, propulsion system, altitude, position etc.
The sensor data, status of each subsystem and related
information is reported back through the Telemetry system via
Telemetry-link.
Telemetry, Tracking, Command and
Monitoring:

Command System
 The ground station uses the Telemetry inputs in control
systems to compare the satellite’s actual status and desired
status
 It transmits the control signals back to satellite onboard
actuators
to perform control functions like:
• station-keeping, orbital positioning
• antenna adjustments, altitude
• attitude control, energy-management etc.
Monitoring:

Command System
 Command structure must be able for:
• Encryption of control signals
• Secured system-unauthorized use
• successful launch and operation
• minimized risk of errors
 Command and Telemetry links are usually separate, they may
operate in same frequency band ( 6 and 4 GHz)
In launch phase--- the main TTC&M is operate-able once satellites
reach in their orbits, during this time – back command system is utilized
Monitoring:

Tracking System
 Determines the current and updated status
• Velocity and acceleration
• Change in the orbit from last position
• Last-know position, satellite health
• Electrical power and command and control signals etc.
 Ranging tones are also used to detect the range – the rate of
change of its position/location etc.
With precision equipment at the earth station, the overall
tracking can be carried out to determine the current parameters of
the satellite
Monitoring:

Power System
 Major source is sun’s radiation – solar cells
• Radiation intensity falling on satellites – 1.39Kw/m-square
• Solar cells – 20 to 30 % at beginning but reduces with time
• 15% extra-area is provided for end-of-life time
 Satellites must carry batteries to power the system during
launch and eclipses
 different satellites use different types of areas – cylindrical, flat-
panels etc. for cell arrangements
Monitoring:

Typically composed of:
• An input band limiting device (band pass filter)
• An input low-noise amplifier (LNA), designed to amplify
the (normally very weak, because of the large distances
involved) signals received from the earth station
• Frequency translator (normally composed of an oscillator
and a frequency mixer) used to convert the frequency of
the received signal to the frequency required for the
transmitted signal
• An output band pass filter
Transponders
Series of interconnected units that form a communications
channel between the receiving and the transmitting antennas to
transfer the signals
---- receives, modulates, amplifies and re-transmits the signals.

Most communication satellites carry dozens of
transponders:
• Each with a bandwidth of tens of megahertz.
• Most transponders operate on a bent pipe principle, sending
back to earth of what goes into the conduit with only
amplification and a shift from uplink to downlink frequency.
• Modern satellites use on-board processing:
signal is demodulated, decoded, processed, re-encoded and
modulated aboard the satellite. This type, called
"regenerative" transponder, has advantages, but is more
complex.
• With data compression and multiplexing, several video
(including digital video) and audio channels may travel through
a single transponder on a single wideband carrier
Transponders

• Due to technological growth and data demands, successive
satellites have become larger, costlier, but small satellites are
also used
– It is desired to provide the largest capacity possible
• Early communication satellites: transponders of 25- to 500
MHz bandwidth with limited power
– Earth station could not receive adequate SNR at full bandwidth
• Later satellites have transponders of increased output power
upto 200 W (e,g DBS-TV satellites) with improved bandwidth
of around 27, 33, 36, 54 and 72 MHz.
Transponders

Transponder power: derived from two elements:
• Satellite antenna from which the circuit will transmit from and
the HPA assigned to transponder.
– Combination of these two elements develops the downlink Effective Isotropic
Radiated Power (or transponder downlink EIRP) towards the earth.
The satellite antenna, made up of the single feedhorn or a multi feed array (to
transmit the HPA power) and reflector (to direct the HPA power to earth), shapes the
way, downlink power will cover the earth
In some circumstances a multi-feed array can be used to shape the desired radiation
pattern
Transponders

• Signals (carriers) transmitted by earth-station
are received in either:
– Zone beams: anywhere within the coverage area
– Spot beams: limited coverage area
Redundancy is provided, if one component such as LNA fails,
the other one works out, since all the signals (carriers) from one
antenna must pass to LNA
Transponders receive signals from one or more antennas and
send their output to a switch-matrix that directs the each TP
band of frequencies to appropriate antenna/beam
Switch-matrix settings can be controlled from earth station to
reallocate signals to TPs
Transponders

Typical C-band Transponder: uplink-6 GHz, downlink-4 GHz
A BPF in transponder selects the channel’s band frequencies, down converter converts
the uplink 6 GHz to downlink 4 GHz to transmit
Transponders:
C-band

Transponders:
C-band
Channnel banwidth : 36Mhz, the channel spacing is 40Mhz in order to avoid
cochannel interference.
Channels are organized in Horizontal and Vertical polarization. Thus, the first
channel is at 3720 Mhz (H) and the third is at 3760Mhz (H), but the second is at
3740Mhz (Vertical polarization), the forth is at 3780Mhz (V).
Thus, continuing in this way, you will have the 23 channel at 4160Mhz (H), and
the last 24 channel at 4180Mhz (V). So, for the downlink transponder at (3700-
4200) Mhz, you have 24 channels, 12 on horizontal and 12 on vertical
polarization. The same logic is applied for the uplink transponder at the band of
(5925-6425) Mhz, having also 24 channels (both polarizations) within an uplink
transponder.

Single-convertion transponder
Typical
Transponders

Double--convertion transponder
Typical
Transponders

For an electromagnetic wave, polarization is effectively the plane in which the electric wave
vibrates
Polarization

Linear Polarization (mostly used
in RF communications)
Polarization

Circular Polarization: Two E-field components (same
magnitude and perpendicular) rotate in a circle
Polarization

General configuration of
a satellite

• Sub-satellite point: The imaginary point on the earth’s surface
created by a normal drawn from the centre of satellite to the
centre of earth (2.4)
• Slant angle: The line of sight distance from a particular point on
earth to satellite (2.4)
• Elevation angle: The angle subtended by antenna looking at
satellite from horizontal plane in vertical direction (2.5)
• Look angle: The angle determined by azimuth and elevation
angle for the antenna to look at the satellite
• Height of satellite: It is the height h or altitude of satellite from
the earth surface. Radius of orbit is h plus earth radius r
• Ascending node: The point of intersection t of orbit path with
equatorial plane while travelling from south to north (2.6)
• Descending node: The point of intersection t of orbit path with
equatorial plane while travelling from s north to south (2.6)
Basic definitions..

• Perigee: In an elliptical orbit, the nearest distance of satellite
from primary body or earth, is called Perigee. It depends
upon the eccentricity
• Apogee: In an elliptical orbit, the farthest distance of satellite
from primary body or earth, is called Apogee.
– If circular orbit, then apogee and perigee coincide
• Inclination angle: The angle between orbital plane and
earth’s equatorial plane is called the angle of Inclination (2.6)
• Satellite axes: These axes are defined to keep the satellite at
proper position: (2.7)
– Roll: The tangent along the orbit path is called the roll axis
– Pitch: The axis perpendicular to the orbit path is called the pitch
axis
– Yaw: The axis which is directed toward s the centre of earth.
The satellite can rotate clockwise or anticlockwise (Yawing)
Basic definitions..

Orbit Plane
– The plane in which the satellite orbits. It can lie in any
of the following planes:-
• Polar plane: plane which is assumed to be cut along the
poles (a)
• Equatorial plane: plane which is assumed to be cut along
equator (b)
• Inclined plane: plane which is at an angle to both polar
plane and equatorial plane (c)
• Prograde: when satellite orbits in the same direction as
the direction of earth revolution (d)
• Retrograde: when the satellite orbits in the opposite
direction than that of earth revolution (d)
Basic definitions..

Bands also have subdivisions (this is particularly true of the radio
spectrum).
In the frequency scale T=1012, P=1015, E=1018
In the wavelength scale μ=10-6, n=10-9, p=10-12
THE ELECTROMAGNETIC
SPECTRUM

THE
ELECTROMAGNETIC
SPECTRUM
Presently, US and ITU have allocation up to 275 GHz for highly specialized
scientific
and engineering applications
According to FCC and ITU, radio spectrum encompasses all frequencies
below 3000 GHz, which is extra-ordinary high.

• Fixed satellite service:
Provides Links for existing Telephone Networks Used for
transmitting television signals to cable companies
• Broadcasting satellite service:
Provides Direct Broadcast to homes. E.g. Live Cricket
matches etc
• Mobile satellite services:
This includes services for: Land Mobile Maritime Mobile
Aeronautical mobile
• Navigational satellite services:
Include Global Positioning systems
• Meteorological satellite services:
They are often used to perform Search and Rescue
service
Satellite Services:

Frequencies allocation to satellite services is a complicated
process which requires international coordination and
planning.
It is done as per International Telecommunication Union (ITU).
To implement this frequency planning, the world is divided into
three regions:
Region1: Europe, Africa and Mongolia
Region 2: North and South America and Greenland
Region 3: Asia , Australia and south-west Pacific.
Within these regions, the frequency bands are allocated to
various satellite services.
Frequency Allocation

The spectrum allocations are given in the following approximate
ranges::
• L-band: 1.5 to 1.65 GHz
• S-band: 2.4 to 2.8 GHz
• C-band: 3.4 to 7.0 GHz
• X-band: 7.9 to 9.0 GHz
• Ku-band: 10.7 to 15.0 GHz
• Ka-band: 18.0 to 31.0 GHz
•V-band: 40.0-75.0 (mm-wave radar and other scientific
areas)
•W-band: 75-110 (mm wave-radar research)
•Mm-band: 110-300 (remote sensing)
•μm-band: 300-3000 (measuring atmospheric ozone)
Frequency Allocation Bands

• VHF Band
– 136 - 138 MHz
This range was used by many different types of satellites in past.
Today most activity is restricted to 137-138 MHz (which is the
current allocation) and consists of meteorological satellites
transmitting data and low resolution images,
– 144 - 146 MHz
Popular band for amateur satellite activity. Most of the links are
found in the upper half of the band (145 - 146 MHz).
–149.95 - 150.05 MHz
Used by satellites providing positioning, time and frequency
services, by ionospheric research and other satellites. Before GPS
it was home to large constellations of US and Russian satellites
that provided positioning information
– 240 - 270 MHz
Military satellites, communications. This band lies in the wider
frequency allocation (225 - 380 MHz) assigned for military aviation.

• UHF Band
– 399.9 - 403 MHz
This band includes navigation, positioning, time and
frequency standard, mobile communication, and
meteorological satellites.
– 432 - 438 MHz
This range includes a popular amateur satellite band as well as a
few Earth resources satellites.
-- 460 - 470 MHz
Meteorological and environmental satellites, includes uplink
frequencies for remote environmental data sensors

• L Band
– 1.2 - 1.8 GHz
This range includes a diverse range of satellites and
have sub-allocations such as GPS and other GNSS
(Global Navigation Satellite Systems - Russian Glonass,
European Galileo, Chinese Beidou).
It also hosts SARSAT/COSPAS search and rescue
satellites which are carried on board US and Russian
meteorological satellites. It also have a mobile satellite
communication band.
-- 1.67 - 1.71 GHz
This is one of the primary bands for high resolution
meteorological satellite downlinks of data and imagery.

• S Band
– 2.025 - 2.3 GHz
It is used in Space operations and research,
including 'deep space' links. This encompasses the
Unified S-band (USB) plan which is used by many
spacecraft, and which was also used by the Apollo
lunar missions.
It also includes military space links including the US
Defense Meteorological Satellite Program (DMSP).
Many Earth resources (remote sensing) satellites
downlink in this band.
-- 2.5 - 2.67 GHz
Fixed (point-to-point) communication and broadcast satellites,
although the broadcast allocation is only used in some Asian
and Middle-eastern countries

• C Band
– 3.4 - 4.2 GHz
Fixed satellite service (FSS) and broadcast satellite service
(BSS) downlinks. International TV broadcast uses this allocation
heavily.
– 5.9 - 6.4 GHz
This is the FSS/BSS uplink for the 3.4-4.2 GHz downlink band.
• X band
– 8 - 9 GHz
This is used heavily for space research, deep space operations,
environmental and military communication satellites. Many
satellites/spacecraft carry complementary S and X band
transmitters.

• Ku band
– 10.7 - 11.7 GHz
Fixed satellite services (FSS)
– 11.7 - 12.2 GHz
Broadcast satellite service (BSS) downlinks. This band is
used for domestic TV programs.
– 14.5 - 14.8 GHz
The uplink for the previous Ku downlink band.
– 17.3 - 18.1 GHz
An alternate 'Ku' band BSS uplink.
• 'Ka' band
– 23 - 27 GHz
Will be used increasingly as fixed links in broadcast,
environmental and space operations satellites in the future

The atmosphere can be divided into several areas.
It is found that the temperature varies according to
the height.
Initially the temperature falls until altitudes of
around 10 km are reached. At this point the
temperature is around -50 or -60 Celsius. It is
around this point that the temperature starts to rise
again. The region below this inflexion point is
known as the troposphere
Atmospheric /layers

• Troposphere:
Lowest atmospheric layer and is about seven miles (11 km) thick.
Most clouds and weather are found in the troposphere.
It is thinner at the poles (averaging about 8km thick) and thicker at
the equator (averaging about 16km thick). Its temperature
decreases with altitude.
• Stratosphere:
It is found from about 7 to 30 miles (11-48 kilometers) above the
Earth’s surface. Here, the atmosphere is ozone layer, which
absorbs most of the harmful ultraviolet radiation from Sun.
The temperature increases slightly with altitude in stratosphere.
The highest temperature in this region is about 32 degrees
Fahrenheit
Atmospheric /layers

• Mesosphere:
The mesosphere is above the stratosphere. Here the atmosphere is
very rarefied, that is, thin, and temperature decreases with altitude,
about –130 Fahrenheit (-90 Celsius) at the top.
• Thermosphere:
The thermosphere starts at about 55 kilometers. Here, the
temperature is quite hot; Temperatures in this region may be as high
as thousands of degrees
• Exosphere:
The exosphere is the region beyond thermosphere.
• Ionosphere:
This layer overlaps the other atmospheric layers above the
Earth. The air is ionized by the Sun’s ultraviolet light. These
ionized layers affect the transmittance and reflectance of radio
waves.
Atmospheric /layers

Behavior of radio waves when they are transmitted or propagated
from one point on Earth to another, or into various parts of the
atmosphere.
• This propagation is affected by the phenomena of reflection,
refraction, diffraction, absorption, polarization and scattering.
1. Ionospheric losses:
• Ionosphere, one of the layers, situated between 90 kms to 400
kms above the surface of the Earth. All the communication
signals between satellites and earth stations have to pass
through this layer.
• It contains free electrons, charged due to solar radiation,
uniformly distributed across the ionosphere. Such clusters are
called clouds of electrons or “travelling ionosphere
disturbances”. When signals pass through such electron
clouds, fluctuations are caused
Satellite signal propagation

2. Atmospheric losses
• Losses may be because of adverse weather conditions or
because of the energy absorption due to various gases present
in the atmosphere. Weather related losses are called
“Atmospheric attenuation”. Absorption losses are called
“Atmospheric absorption”.
• A fading phenomenon, which affects the radio waves because of the
differences in the atmospheric refraction index is called “atmospheric
scintillation”.
a) Absorption
• EM waves are absorbed in the atmosphere according to
wavelength. Two compounds are responsible for the
majority of signal absorption: oxygen and water.
b) Propagation delay
• Propagation delay is the time required for a signal to travel
from the sender (in our case from an earth station or a
spacecraft) to the receiver.

c) Dispersion (scattering of signals)
d) Scintiallation (variation in the amplitude, phase, polarization,
angle of arrival of radio wave)
e) Rayleigh Fading (interference caused to the main signal by
the same signal arriving over many different paths,
resulting in out-of-phase components incident at the receiver
f) Beam-Spreading Loss (spreading of the earth-satellite signals
as they pass through the Earth’s atmosphere
g) Polarization Loss (rotation of the polarization of the signal as
it passes through the Earth's atmosphere
h) Free-Space Loss (It is the major loss suffered by signals in
traveling over the Earth-satellite path. The loss is inversely
proportional to the square of the distance traveled and
inversely proportional to the square of the frequency used.

Propagation concerns of Satellite Communication Systems

WC-Lecture-1, 2, 3.ppt

Recommended

Recommended

More Related Content

Similar to WC-Lecture-1, 2, 3.ppt

Similar to WC-Lecture-1, 2, 3.ppt (20)

Recently uploaded

Recently uploaded (20)

WC-Lecture-1, 2, 3.ppt