Fundamentals of Microwave &
Satellite Technologies
TEL 117
Telekomunikasi Dasar
Historical Perspective
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Founded during WWII
Used for long-haul telecommunications
Displaced by fiber optic networks
Still viable for right-of-way bypass and
geographic obstruction avoidance
Microwave Spectrum
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Range is approximately 1 GHz
to 40 GHz
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Total of all usable frequencies under
1 GHz gives a reference on the
capacity of in the microwave range
Microwave Impairments
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Equipment, antenna, and waveguide
failures
Fading and distortion from multipath
reflections
Absorption from rain, fog, and other
atmospheric conditions
Interference from other frequencies
Microwave Engineering
Considerations
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Free space &
atmospheric
attenuation
Reflections
Diffractions
Rain attenuation
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Skin affect
Line of Sight (LOS)
Fading
Range
Interference
Free Space & Atmospheric
Attenuation
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Free space & atmospheric attenuation is
defined by the loss the signal undergoes
traveling through the atmosphere.
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Changes in air density and absorption by
atmospheric particles.
Reflections
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Reflections can occur as the microwave
signal traverses a body of water or fog
bank; cause multipath conditions
Diffraction
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Diffraction is the result of variations in
the terrain the signal crosses
Rain Attenuation
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Raindrop absorption or scattering of the
microwave signal can cause signal loss
in transmissions.
Skin Affect
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Skin Affect is the concept that high
frequency energy travels only on the
outside skin of a conductor and does
not penetrate into it any great distance.
Skin Affect determines the properties of
microwave signals.
Line of Sight
Fresnel Zone Clearance
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Fresnel Zone Clearance is the minimum
clearance over obstacles that the signal
needs to be sent over. Reflection or
path bending will occur if the clearance
is not sufficient.
LOS & FZC-cont’d
Fresnel Zone
D1 X D2
72.2
FxD
secret formula
Microwave Fading
Normal Signal
Reflective Path
Caused by multi-path reflections and heavy rains
Range
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The distance a signal travels and its
increase in frequency are inversely
proportional
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Repeaters extend range
 Back-to-back antennas
 Reflectors
Range-cont’d
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High frequencies are repeated/received
at or below one mile
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Lower frequencies can travel up to 100
miles but 25-30 miles is the typical
placement for repeaters
Interference
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Adjacent Channel Interference
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digital not greatly affected
Overreach
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caused by signal feeding past a repeater to
the receiving antenna at the next station in
the route. Eliminated by zigzag path
alignment or alternate frequency use
between adjacent stations
Components of a Microwave
System
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Digital Modem
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Radio Frequency (RF) Unit
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Antenna
Digital Modem
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The digital modem modulates the
information signal (intermediate
frequency or IF).
RF Unit
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IF is fed to the RF unit which is
mounted as close physically to the
antenna as possible (direct connect is
optimal).
Antenna
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The antenna is a passive device that
radiates the modulated signal. It is fed
by direct connect of the RF unit, coaxial
cable, or waveguides at higher
frequencies.
Waveguides
Waveguides are hollow channels of
low-loss material used to direct the
signal from the RF unit to the
antenna.
Modulation Methods
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Primarily modulated today with digital
FM or AM signals
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Digital signal remains quiet until failure
threshold bit error rate renders it unusable
Bit Error Rate (BER)
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The BER is a performance measure of
microwave signaling throughput
10 or one error per million transmitted bits
-6of information
 Data fail over is at 10; voice traffic can
withstand this error-3rate
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Diversity
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Space Diversity
Frequency Diversity
Hot Standby
PRI
Space Diversity
Normal Signal
Transmitter
Receiver
Space Diversity-cont’d
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Space Diversity protects against multipath fading by automatic switch over to
another antenna place below the
primary antenna. This is done at the
BER failure point or signal strength
attenuation point to the secondary
antenna that is receiving the
transmitted signal at a stronger power
rating.
Frequency Diversity
Rx
Frequency #1
Active Tx
Frequency #1
Rx
Frequency #2
Protect Tx
Frequency #2
Transmitter
Receiver
Frequency Diversity-cont’d
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Frequency Diversity uses separate
frequencies (dual transmit and receive
systems); it monitors primary for fail
over and switches to standby.
Interference usually affects only one
range of frequencies. Not allowed in
non-carrier applications because of
spectrum scarcity.
Hot Standby*
Active Rx
#1
System Tx
Primary #1
Standby Rx
#2
System Tx
Standby #2
failure switch
Transmitter
Receiver
*Hot standby is designed for equipment failure only
PRI (Primary Rate Interface)
PRI is an ISDN service providing user with 23,64 kbps for channel message and 1,64
kbps data channel for control & signalling. PRI is ISDN E1 interface.
System
Transmission
Facilities
System
Receiver
Facilities
Connect to
PRI interface
& PSTN
Connect to
PRI interface
& PSTN
Transmitter
To PSTN
Receiver
To PSTN
Availability Formula
Percent Availability equals:
1 – (outage hours/8760 hours per year)
Private microwaves have 99.99% availability
Microwave Path Analysis
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Transmitter output power
Antenna gain
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proportional to the physical characteristics
of the antenna (diameter)
Free space gain
Antenna alignment factor
Unfaded received signal level
Microwave Radio Applications
Satellite Communications
Satellite-Related Terms
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Earth Stations – antenna systems on or near earth
Uplink – transmission from an earth station to a
satellite
Downlink – transmission from a satellite to an
earth station
Transponder – electronics in the satellite that
convert uplink signals to downlink signals
Ways to Categorize
Communications Satellites
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Coverage area
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Service type
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Global, regional, national
Fixed service satellite (FSS)
Broadcast service satellite (BSS)
Mobile service satellite (MSS)
General usage
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Commercial, military, amateur, experimental
Classification of Satellite Orbits
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Circular or elliptical orbit
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Orbit around earth in different planes
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Circular with center at earth’s center
Elliptical with one foci at earth’s center
Equatorial orbit above earth’s equator
Polar orbit passes over both poles
Other orbits referred to as inclined orbits
Altitude of satellites
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Geostationary orbit (GEO)
Medium earth orbit (MEO)
Low earth orbit (LEO)
Geometry Terms
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Elevation angle - the angle from the
horizontal to the point on the center of the
main beam of the antenna when the antenna
is pointed directly at the satellite
Minimum elevation angle
Coverage angle - the measure of the portion
of the earth's surface visible to the satellite
Minimum Elevation Angle
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Reasons affecting minimum elevation angle
of earth station’s antenna (>0o)
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Buildings, trees, and other terrestrial objects
block the line of sight
Atmospheric attenuation is greater at low
elevation angles
Electrical noise generated by the earth's heat
near its surface adversely affects reception
GEO Orbit
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Advantages of the the GEO orbit
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No problem with frequency changes
Tracking of the satellite is simplified
High coverage area
Disadvantages of the GEO orbit
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Weak signal after traveling over 35,000 km
Polar regions are poorly served
Signal sending delay is substantial
GEO : Geosynchronous equatorial orbit
LEO Satellite Characteristics
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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
Maximum satellite visible time up to 20 min
System must cope with large Doppler shifts
Atmospheric drag results in orbital deterioration
LEO : Low earth orbit
LEO Categories
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Little LEOs
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Frequencies below 1 GHz
5MHz of bandwidth
Data rates up to 10 kbps
Aimed at paging, tracking, and low-rate messaging
Big LEOs
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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
MEO Satellite Characteristics
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Circular orbit at an altitude in the range of 5000 to
12,000 km
Orbit period of 6 hours
Diameter of coverage is 10,000 to 15,000 km
Round trip signal propagation delay less than 50
ms
Maximum satellite visible time is a few hours
MEO : Medium Earth Orbit
Satellite Systems
GEO
GEO (22,300 mi., equatorial)
high bandwidth, power, latency
MEO
M EO
LEO
high bandwidth, power, latency
LEO (400 mi.)
low power, latency
more satellites
small footprint
V-SAT (Very Small Aperture
Terminal)
private WAN
SATELLITE MAP
SOURCE: WASHINGTON UNIV.
Geostationary Orbit
SOURCE: BILL LUTHER, FCC
GPS Satellite Constellation
• Global Positioning
System
• Operated by USAF
• 28 satellites
• 6 orbital planes at a
height of 20,200 km
• Positioned so a
minimum of 5 satellites
are visible at all times
• Receiver measures
distance to satellite
SOURCE: NAVSTAR
Frequency Bands Available for
Satellite Communications
Satellite Link Performance Factors
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Distance between earth station antenna and
satellite antenna
For downlink, terrestrial distance between earth
station antenna and “aim point” of satellite
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Displayed as a satellite footprint (Figure 9.6)
Atmospheric attenuation
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Affected by oxygen, water, angle of elevation, and
higher frequencies
Satellite Footprint
Satellite Network Configurations
Capacity Allocation Strategies
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Frequency division multiple access
(FDMA)
Time division multiple access (TDMA)
Code division multiple access (CDMA)
Frequency-Division Multiplexing
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Alternative uses of channels in point-to-point
configuration
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1200 voice-frequency (VF) voice channels
One 50-Mbps data stream
16 channels of 1.544 Mbps each
400 channels of 64 kbps each
600 channels of 40 kbps each
One analog video signal
Six to nine digital video signals
Frequency-Division Multiple
Access
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Factors which limit the number of
subchannels provided within a satellite
channel via FDMA
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Thermal noise
Intermodulation noise
Crosstalk
Forms of FDMA
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Fixed-assignment multiple access (FAMA)
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The assignment of capacity is distributed in a fixed
manner among multiple stations
Demand may fluctuate
Results in the significant underuse of capacity
Demand-assignment multiple access (DAMA)
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Capacity assignment is changed as needed to respond
optimally to demand changes among the multiple
stations
FAMA-FDMA
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FAMA – logical links between stations are
preassigned
FAMA – multiple stations access the
satellite by using different frequency bands
Uses considerable bandwidth
DAMA-FDMA
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Single channel per carrier (SCPC) – bandwidth
divided into individual VF channels
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Attractive for remote areas with few user stations near
each site
Suffers from inefficiency of fixed assignment
DAMA – set of subchannels in a channel is treated
as a pool of available links
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For full-duplex between two earth stations, a pair of
subchannels is dynamically assigned on demand
Demand assignment performed in a distributed fashion
by earth station using CSC
Reasons for Increasing Use of TDM
Techniques
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Cost of digital components continues to
drop
Advantages of digital components
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Use of error correction
Increased efficiency of TDM
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Lack of intermodulation noise
FAMA-TDMA Operation
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Transmission in the form of repetitive sequence of
frames
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Earth stations take turns using uplink channel
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Sends data in assigned time slot
Satellite repeats incoming transmissions
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Each frame is divided into a number of time slots
Each slot is dedicated to a particular transmitter
Broadcast to all stations
Stations must know which slot to use for
transmission and which to use for reception
FAMA-TDMA Uplink
FAMA-TDMA Downlink