FALL 2010
Innovation Hall Room 338 Thursdays 4:30 – 7:10 p.m.
Dr. Jeremy Allnutt
jallnutt@gmu.edu
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
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General Information - 1
 Course Outline
 Go to http://ece.gmu.edu/
 Hover over Courses
 Select Course Web Pages
 Scroll down to TCOM 707 Fall 2010
 Severe weather days: call (703) 993-1000
 You MUST have a Mathematical Calculator –
please, simple ones only
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
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General Information - 2
 Homework Assignments
 Feel free to work together on these, BUT
 All submitted work must be your own work
 Web and other sources of information
 You may use any and all resources, BUT
 You must acknowledge all sources
 You must enclose in quotation marks all parts copied
directly – and you must give the full source information
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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General Information - 3
 Homework Answers
 For problems set, most marks will be given for
the solution procedure used, not the answer
 So: please give as much information as you can
when answering questions: partial credit cannot
be given if there is nothing to go on
 If something appears to be missing from the
question set, make – and give –assumptions
used to find the solution
Fall 2010
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General Information - 4
 Class Grades
 Emphasis on overall effort and results
 Balance between homework, tests, and project:
 Homeworks (total of 6)
 Mid-Term (project PDR)  Final exam (project CDR) -
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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35%
25%
40%
5
TCOM 707 Course Plan
 Up to 13 formal lectures
 2 half-class guest lectures
 CISCO (Router in orbit)
 Orbital Sciences (Networked satellites)
 Major class project
 Preliminary Design Review October 14th, 2010
 Critical Design review December 16th, 2010
 Possible “CDR Dry Run on December 7th, 2010)
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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TCOM 707 Lecture 1 Outline
 Project SCION
 Satellite Orbits Review
 Earth Coverage Review
 Connectivity Issues
 Linking the Satellites
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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TCOM 707 Lecture 1 Outline
 Project SCION
 Satellite Orbits Review
 Earth Coverage Review
 Connectivity Issues
 Linking the Satellites
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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TCOM 707 Project SCION – 1
Additional details of the project will be provided to the class at this
point in the first lecture and there will be a short discussion of the
primary goals. The next 20 slides give an outline of the class project:
SCION – Satellite Clusters In Orbital Networks.
The first half hour of each subsequent lecture will be devoted to
clarification of the project goals, setting up the team(s), and then time
for the team(s) to meet before class to discuss elements of their project
work. There will also be two half-class guest lectures in the first three
weeks from industry experts.
The lecture on December 9th may be rescheduled as a dry run for
students to go through their final presentation.
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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TCOM 707 Project SCION – 2
 Earth satellites have grown larger and larger
due to increased mission requirements
 This has led to
 The need for very large launch vehicles
 Long procurement lead times
 Degraded performance as mission needs change


Fall 2010
Large satellites generally means > 10 year lifetime
Technological changes are in a <5 year cycle
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
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TCOM 707 Project SCION – 3
 Earth satellites have grown larger and larger
due to increased mission requirements
 This has led to
 The need for very large launch vehicles
 Long procurement lead times
 Degraded performance as mission needs change


Fall 2010
Large satellites generally means > 10 year lifetime
Technological changes are in a <5 year cycle
TCOM 707 Advanced Link Design Lecture No. 1
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http://en.wikipedia.org/wiki/Delta_IV
TCOM 707 Project SCION – 4
Size
Height
63 - 72 m (206 235 ft)
Diameter
5 m (16.4 ft)
Mass
249,500 - 733,400
kg (550,000 1,616,800 lb)
Stages
2
Capacity
Payload to LEO
8,600 - 25,800 kg
(18,900 - 56,800
lb)
Payload to GTO
3,900 - 10,843 kg
Delta IV core vehicle
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TCOM 707 Advanced Link Design Lecture No. 1
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http://www.nasa.gov/mission_pages/newhorizons/launch/atlasv101.html
TCOM 707 Project SCION – 5
Size
Height
55 - 61 m (180 200 ft)
Diameter
5 m (16.4 ft)
Mass
334,054 – 961,451
kg (734,850 –
2,120,000 lb)
Stages
2
Capacity
Payload to LEO
c. 11,025 – 33,000
kg (24,800 74,423 lb)
Payload to GTO
5,000 - 13,605 kg
Atlas “Heavy” with 5 strap-on boosters
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TCOM 707 Advanced Link Design Lecture No. 1
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http://en.wikipedia.org/wiki/Ariane_5
TCOM 707 Project SCION – 6
Size
Height
46 - 62 m (151 170 ft)
Diameter
5.4 m (17.7 ft)
Mass
777,000 kg
(1,712,000lb)
Stages
2
Capacity
Payload to LEO
16,000 - 21,000 kg
(36,000 – 47,250
lb)
Payload to GTO
6,200 - 10,500 kg
Ariane 5 with 2 liquid strap-on boosters
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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TCOM 707 Project SCION – 7
 Earth satellites have grown larger and larger
due to increased mission requirements
 This has led to
 Need for very large launch vehicles
 Long procurement lead times
 Degraded performance as mission needs change


Fall 2010
Large satellites generally means > 10 year lifetime
Technological changes are in a <5 year cycle
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
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TCOM 707 Project SCION – 8
 Procurement lead time for a large satellite
 System architecture – one year
 Satellite design – one year with existing bus
 Satellite construction – two to three years
 Total time-to-launch is 4 to 5 years
 In-Orbit Lifetime – 10 to 15 years
 Total time elapsed 14 to 20 years
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TCOM 707 Project SCION – 9
 Procurement lead time for a large satellite
 System architecture – one year
 Satellite design – one year with existing bus
 Satellite construction – two to three years
 Total time-to-launch is 4 to 5 years
 In-Orbit Lifetime – 10 to 15 years
 Total time elapsed 14 to 20 years
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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Internet
lifetime is about
20 months!!
17
TCOM 707 Project SCION – 10
 Earth satellites have grown larger and larger
due to increased mission requirements
 This has led to
 Need for very large launch vehicles
 Long procurement lead times
 Degraded performance as mission needs change


Fall 2010
Large satellites generally means > 10 year lifetime
Technological changes are in a <5 year cycle
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
18
TCOM 707 Project SCION – 11
 Need for very large satellites and very large
launch vehicles has led to:
 Only 2 or 3 US large satellite manufacturers
 Only two large US rocket suppliers
 The corollary has been only the US government
can afford to pay the research efforts for such
large satellites and rockets.
 And, just as importantly
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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TCOM 707 Project SCION – 12
 Putting too many (very expensive) eggs in one
basket can lead to critical vulnerabilities of
both civilian and military space assets
RIM-161 Standard Missile 3 launched from
the US Navy USS Lake Erie Ticonderoga
class cruiser, 2005.
http://en.wikipedia.org/wiki/Antisatellite_weapon
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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TCOM 707 Project SCION – 13
 Need for very large satellites and very large
launch vehicles has led to:
 Only two or three US satellite manufacturers
 Only two large rocket supplier
 The corollary has been only the US government
can afford to pay the research efforts for such
large satellites and rockets.
 Possible solution?
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TCOM 707 Advanced Link Design Lecture No. 1
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TCOM 707 Project SCION – 14
 Possible Solution:
Use a cluster of satellites, networked together,
to perform the mission of one large satellite
 Advantages
 Much lower vulnerability
 Smaller satellites and launchers – more competition
 Technical advances can be met with more rapid
satellite deployments as needed
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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BUT
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TCOM 707 Project SCION – 15
 Major Technical Issues need to be solved:
 How do you split the payloads amongst how
many satellites?
 How do you inter-connect the satellites?
 How do you control the satellites?
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TCOM 707 Project SCION – 16
 Major Technical Issues to be solved
 How do you split the payloads amongst how
many satellites?
 How do you inter-connect the satellites?
 How do you control the satellites?
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TCOM 707 Advanced Link Design Lecture No. 1
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TCOM 707 Project SCION – 17
 Some payload split questions:
 Does each satellite have its own Earth/Space
communications capabilities or will this be
provided by one core satellite? Which leads to –
 Are the satellite buses common or of different
sizes?
 Will one satellite act as the control hub or will
there be a distributed architecture?
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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TCOM 707 Project SCION – 18
 Major Technical Issues to be solved
 How do you split the payloads amongst how
many satellites?
 How do you inter-connect the satellites?
 How do you control the satellites?
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TCOM 707 Advanced Link Design Lecture No. 1
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TCOM 707 Project SCION – 19
 Linking the satellites
 Physical layer


Microwave
Optical
 Network layer


Fall 2010
TCP/IP
Other?
TCOM 707 Advanced Link Design Lecture No. 1
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TCOM 707 Project SCION – 20
 Major Technical Issues to be solved
 How do you split the payloads amongst how
many satellites?
 How do you inter-connect the satellites?
 How do you control the satellites?
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TCOM 707 Project SCION – 21
 Satellite control
 Direct control of each satellite from the ground

Man-power intensive
 Direct control of one satellite and then distributed
control

Redundancy issues
 Semi-autonomous control

But which bits are left to the satellite cluster?
 Fully automated control

Fall 2010
Software nightmare
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
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TCOM 707 Lecture 1 Outline
 Project SCION
 Satellite Orbits Review
 Earth Coverage Review
 Connectivity Issues
 Linking the Satellites
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
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Satellite Orbits – 1
 Earth satellites are typically in four orbits
 Low Earth Orbit (LEO)
 Medium Earth Orbit (MEO)
 Geostationary Earth Orbit (GEO)
 Highly Elliptical Earth Orbit (HEO)
These are usually highly
elliptical; eccentricity > 0.1
Fall 2010
These are usually circular;
eccentricity < 0.001
TCOM 707 Advanced Link Design Lecture No. 1
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http://www.thetech.org/exhibits/online/satellite/4/4d/4d.1.html
HEO
Equatorial
LEO
Polar LEO
GEO
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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Satellite Orbits – 2A
 Orbit ranges (altitudes)
 LEO
 MEO
 GEO
250
to 1,500 km
2,500 to 15,000 km
35,786.03 km
examples:
Mean earth radius is
6,378.137 km
Period of one-half
sidereal day
 HEO
 500 to 39,152 km Molniya (“Flash of lightning”)
  16,000 to  133,000 km Chandra
Period of 64 hours
and 18 minutes
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TCOM 707 Advanced Link Design Lecture No. 1
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http://www.centennialofflight.gov/essay/Dictionary/SUN_SYNCH_ORBIT/DI155.htm
Satellite Orbits – 2B
 Some special orbits
 Sun synchronous
Sometimes called
a “retrograde”
orbit as it is
effectively
launched more
than 90o to the
equator
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TCOM 707 Advanced Link Design Lecture No. 1
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http://www.stk.com/corporate/partners/edu/AstroPrimer/primer96.htm
Satellite Orbits – 2C
 Some special orbits
 Molniya
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Satellite Orbits – 2D
 Some
Apogee: moving slowly
special
orbits
 Molniya
(contd.)
Perigee: moving quickly
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TCOM 707 Advanced Link Design Lecture No. 1
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http://www.stk.com/corporate/partners/edu/AstroPrimer/primer96.htm
Satellite Orbits – 2E
 Some special orbits
 Molniya (contd.)
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TCOM 707 Advanced Link Design Lecture No. 1
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MOLNIYA APOGEE VIEW
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TCOM 707 Advanced Link Design Lecture No. 1
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http://chandra.harvard.edu/about/tracking.html
Satellite Orbits – 2F
 Some special orbits
 Chandra
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TCOM 707 Advanced Link Design Lecture No. 1
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Satellite Orbits – 3
 Orbit period, T (seconds)
2a
 is Kepler’s
constant
T2 = (42a3)/
 = 3.986004418  105 km3/s2
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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Satellite Orbits – 4
 Orbit period, T – examples
Orbital height
500 km
1,000 km
5,000 km
10,000 km
35,786 km
402,000 km
148,800,000 km
Fall 2010
Orbital period
1 h 34.6 min
1 h 45.1 min
3 h 21.3 min
5 h 47.6 min
23 h 56.04 min
28 days
365.25 days
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
Typical LEO
Typical MEO
GEO
Moon’s orbit
Earth’s orbit
41
One-Way Delay Times – 1
GEO satellite: 35,786 km
One-way delay:
119.3 ms
MEO satellite: 10,355 km
One-way delay:
34.5 ms
LEO satellite: 800 km
One-way delay:
2.7 ms
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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One-Way Delay Times – 2
Path Loss Issues:
LEO = MEO – 22dB
LEO = GEO – 33dB
GEO satellite: 35,786 km
One-way delay:
119.3 ms
MEO satellite: 10,355 km
One-way delay:
34.5 ms
LEO satellite: 800 km
One-way delay:
2.7 ms
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
Beware:
Propagation delay
does not tell the
whole story!
43
Satellite Orbits – 5
 Orbit velocities (m/s)
 LEO
 MEO
 GEO
 7 km/s
 5 km/s
= 3.0747 km/s
v = (/r)1/2
where r = radius
from center of earth
GEO Orbital radius = 35,786.03 + 6,378.137 km
Orbital circumference = 2  42,164.167 km
Orbital period = (2  42,164.167)/3.0747 seconds
= 86,162.96699 seconds
= 23 hours 56.04 minutes
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
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TCOM 707 Lecture 1 Outline
 Project SCION
 Satellite Orbits Review
 Earth Coverage Review
 Connectivity Issues
 Linking the Satellites
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
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Satellite Orbits – Coverages – 1
LEO
Track of the subsatellite point along
the surface of the
Earth
Movement of the
coverage area
under the satellite
Orbital
path of
satellite
The Earth
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
Fig. 10.14
Pratt et al.
46
Satellite Orbits – Coverages – 2
Multiple
beams
Spectrum A
Spectrum B
Spectrum C
Fig. 10.15
Pratt et al.
Instantaneous
Coverage
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
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Satellite Orbits – Coverages – 3
Iridium
Fig. 10.16(a)
Pratt et al.
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TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
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Satellite Orbits – Coverages – 4
New ICO
Fig. 10.16(b)
Pratt et al.
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
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Satellite Orbits – Coverages – 5
 Satellite coverages – 1
 Determined by two principal factors
 Height of satellite above the Earth
 Beamwidth of satellite antenna
Same beamwidth,
different altitudes
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
Same altitude,
different beamwidths
50
Satellite Orbits – Coverages – 6
 Satellite coverages – 2
 Orbital plane usually optimized
 Equatorial orbits – simplest, equal N-S coverage
 Inclined orbits – cover most of populated Earth
 Polar orbits – cover all of the Earth at some point
 Retrograde orbits – gives sun synchronized orbit
 LEO chosen for two reasons usually
 Low link power needed
 good optical resolution
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Satellite Orbits – Coverages – 7
 Satellite coverages – 3
 MEO chosen for a variety of reasons
 GPS half sidereal orbit covers same tracks alternately
 Compromise between LEO and GEO delay
 Compromise between LEO and GEO total number
 GEO chosen for two reasons mainly
 Optimizes broadcast capabilities
 Simplest earth terminal implementation
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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Satellite Orbits – Coverages – 8
 We will now look at one of the most important
figure that will help you calculate satellite
coverages, look angles, required beamwidths,
separation angles between satellites, and
distances between earth stations and satellites,
and between satellites in a constellation.
Fall 2010
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Satellite Orbits – Coverages – 9
Local
horizontal
S
rs
Satellite
d
Z
El


Earth
station
El = elevation angle = θ
E = earth station location
Z = point on the surface
of the Earth where the
radius SC cuts the earth
E
re
C
Earth
Fig 2.12 in Pratt et al.
TCOM 607
Spring 2010
TCOM 607 Satcom Lecture number 2
© Tim Pratt and Jeremy Allnutt January 2010
Geometry for El angle
calculation 54
Look Angles and Coverages
Let’s look at each
of the critical
parameters in the
previous slide again
TCOM 607
Spring 2010
TCOM 607 Satcom Lecture number 2
© Tim Pratt and Jeremy Allnutt January 2010
55
This curve allows
you to calculate
coverages
S
rs
Satellite
This angle allows
you to calculate the
antenna beamwidth
This allows you
to calculate
elevation angles
Local
horizontal
d
Z
El


Earth
station
E
re
C
Earth
Fig 2.12 in Pratt et al.
TCOM 607
Spring 2010
This angle allows
you to calculate
the number of
satellites required
for full coverage
in one plane
TCOM 607 Satcom Lecture number 2
© Tim Pratt and Jeremy Allnutt January 2010
Geometry for El angle
calculation 56
Satellite Orbits – Coverages – 9
 Satellite coverages – 4: Calculation contd.
 Using the sine rule
[ rs / sin (90 + ) ] = [ d / sin () ]
  will yield coverage on surface assuming symmetrical
coverage about nadir
 d will determine path loss
  will determine G/T, blockage, level of propagation
impairments
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Satellite Orbits – Coverages – 10
 Satellite coverage example – 1
 Given an orbital height of 750 km what are
 Length of coverage arc
 Gain of satellite antenna to cover this area
 Number of satellites to cover one plane
 Number of satellites to cover the globe
 Assume a minimum elevation angle of 10o
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Satellite Orbits – Coverages – 11
 Satellite coverage example – 2
 Rs = re +750 = 6378 + 750 = 7128 km
 Angle SEC = 90 + 10 = 100o
 sin () / re = sin (angle SEC) / rs , which yields
 = 61.79o
 If  = 61.79o, then  = 180 – 100 – 61.79 =
18.21o
 Arc EZ is therefore given by re   (with  in
radians) = 2027.1 km.
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Satellite Orbits – Coverages – 12
 Satellite coverage example – 3
 The diameter of the instantaneous coverage region
is therefore 2  2,027 = 4054 km and the
coverage angle measured at the center of the earth
is 36.42o
 The angle  is half of the antenna beamwidth
(assuming symmetrical coverage about nadir)
 Beamwidth therefore = 2 = 61.79o  2 = 123.6o.
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Satellite Orbits – Coverages – 13
 Satellite coverage example – 4
 The gain of an antenna can be related to the 3dB
beamwidth using the approximate relationship Gain
ratio = 33,000 / (3dB beamwidth in degrees)2 = G
 Therefore G = 33,000 / (123.6o)2 = 2.16  3.3 dB
If we had used 30,000
instead of 33,000, G  3 dB
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Satellite Orbits – Coverages – 14
 Satellite coverage example – 5
 Number of satellites required for one plane is
360/36.42  10
 By the same logic used above, if 10 satellites are
required to complete coverage around (say) the
equator, 5 complete planes of satellites will be
needed to complete the full global coverage.
 The total minimum number of satellites needed is
therefore 50
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Satellite Orbits – Coverages – 15
 Satellite coverage example – 6
 Analysis
 The example assumed a polar orbit. If an inclined orbit
were to be adopted, or a limited population targeted,
fewer satellites are needed
 The coverage example did not allow any overlap between
satellite coverages nor for in-orbit failures
 No consideration was taken of the number of smaller
beams within the instantaneous coverages that would be
required for frequency re-use
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Repeat of Slide 47
Satellite Orbits – Coverages – 16
Multiple
beams
Spectrum A
Spectrum B
Spectrum C
Individual beams
developed by the
multi-beam antenna
Fall 2010
Fig. 10.15
Pratt et al.
Instantaneous
Coverage
TCOM 707 Advanced Link Design Lecture No. 1
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Satellite Orbits – Coverages – 17
 Multiple beams lead to path loss differences
If a phased array antenna
is used, you can have
additional scan loss
Individual beams that
develop the total
instantaneous coverage
dnadir
dedge of coverage
Instantaneous coverage region
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Satellite Orbits – Coverages – 18
 Also need to look at coverage losses
6 dB beamwidth
3 dB beamwidth
1 dB beamwidth
Need to adjust
received power level
by coverage loss
VSAT Community within the satellite coverage
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TCOM 707 Lecture 1 Outline
 Project SCION
 Satellite Orbits Review
 Earth Coverage Review
 Connectivity Issues
 Linking the Satellites
Fall 2010
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Satellite Connectivity – 1
 Connectivity issues
 The more beams there are, the better the frequency
re-use, but …
 …. The more connectivity is required to
interconnect the many beams either within the
satellite or through the hub station, and …
 … The more the connectivity requirements
increase, the more complex the payload becomes
 But first, let’s look at multiple access techniques
Fall 2010
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Satellite Connectivity – 2
 There are three basic ways that a number of
signals can simultaneously access a common
resource (e.g. a transponder)
 FDMA, TDMA, CDMA
 Each of these will require transponder
connectivity through either:
 On-board switching; or
 On-board processing
Fall 2010
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69
Satellite Connectivity – 2A
 We will first review multiple access techniques
and then move on to discuss how the signals
arriving at a satellite can be moved among
various transponder/antenna beam options on the
down-link (or cross-link) paths
Fall 2010
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70
Satellite Connectivity – 3
 Multiple access techniques
 FDMA, TDMA, CDMA
 Connectivity issues
 On-board switching
 On-board processing
Fall 2010
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Multiple Access Techniques – 1
 What is Multiple Access?
 Multiple Access is a technique whereby a variable
number of users can access a common resource for
the purpose of communications
Common
Resource
Fall 2010
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For satellites, the common resource is a transponder
Multiple Access Techniques – 2
 What is Multiple Access?
 Multiple Access is a technique whereby a variable
number of users can access a common resource for
the purpose of communications
Common
Resource
Fall 2010
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73
From Pratt, et al., Fig.
3.12
Multiple Access Techniques – 3
LNA
BPF
Mixer
BPF
HPA
Uplink
Downlink
LO
A simple linear transponder for an FSS Satellite
Fall 2010
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74
Multiple Access Techniques – 4
 Why do you need Multiple Access?
 Multiple Access has many advantages
 Increases efficiency for provider
 Reduces costs to user
 Enhances network control
 Enables more flexible designs
Fall 2010
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Multiple Access Techniques – 5
Amplitude
User 1
Common resource
User 2
User 3
User 4
Frequency
Frequency Division Multiple
Access (FDMA)
Each user may transmit all of the time, but on a different frequency
Fall 2010
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Multiple Access Techniques – 6
Amplitude
User 1
Common resource
User 2
User 3
User 4
Time
Time Division Multiple
Access (TDMA)
Each user may transmit on the same frequency, but not at the same time
Fall 2010
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77
Multiple Access Techniques – 7
Code and
Amplitude
Common resource
User 4
User 3
User 2
User 1
Time and
Frequency
Code Division Multiple
Access (CDMA)
Users transmit with the same frequency and time, but with a different code
Fall 2010
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78
Multiple Access Techniques – 8
MF-TDMA Internet Spacecraft
In-bound, downlink TDM stream to the hub
In-bound, uplink MFTDMA VSAT bursts
Hub
From Pratt, et al.,
Fig. 9.15
A
Fall 2010
TCOM
707 Advanced Link
B
C Design Lecture No. 1D
© Jeremy Allnutt August 2010
E
79
VSAT System Trade-Offs – 3
 Multiple access techniques
 FDMA, TDMA, CDMA
 Connectivity issues
 On-board switching
 On-board processing
Fall 2010
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Connectivity Issues – 1
 Satellites can “see” a lot of the earth, and so
offer a means to interconnect a large number
of terminals
 The simplest method is to use a broadband,
linear transponder with the spectrum shared
amongst all the users
 The simplest of all approaches is to have all
users in the same beam
Fall 2010
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81
Connectivity Issues – 2
 With few users, beams can be very broad and
operate with few transponders
If capacity is
low, could have
just one
transponder
and one beam
Satellite
Earth station
1
Fall 2010
2
3
TCOM 707 Advanced Link Design Lecture No. 1
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4
82
Connectivity Issues – 2
 Single beam, single transponder
The four users exist in the same beam and
transponder and so no switching is required
1
2
3
Lowest
frequency of
transponder
Fall 2010
4
Highest
frequency of
transponder
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
83
Connectivity Issues – 3
 As demand rises, more transponders are needed
We now have 20 users, with four per transponder.
How will user 1 communicate with user 14, say?
1
2
f1
Fall 2010
3
4
5
f2 f3
6
7
8
9
f4 f5
10 11 12
13 14 15 16
f6 f7
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
17 18 19 20
f8 f9
f10
84
Connectivity Issues – 4
 As demand rises still further, additional frequency
re-uses are needed via new beams
Here we have three beams – how do the users interconnect?
1
2
3
f1
4
5
6
7
f2 f3
1
2
3
f1
4
5
2
f1
Fall 2010
3
4
5
f2 f3
9
f4 f5
6
7
f2 f3
1
8
8
9
f4 f5
6
7
8
9
f4 f5
10 11 12
13 14 15 16
f6 f7
10 11 12
10 11 12
f10
17 18 19 20
f8 f9
13 14 15 16
f6 f7
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
f8 f9
13 14 15 16
f6 f7
17 18 19 20
f10
17 18 19 20
f8 f9
f10
85
Connectivity Issues – 5
 As demand rises even further, the need to re-use
spectrum several times becomes essential
 Spectrum can be re-used by isolating beams from
one another through using non-overlapping
coverages (spatial re-use) or by isolating beams
from one another using orthogonal polarizations
in overlapping coverages (polarization re-use)
Fall 2010
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86
Connectivity Issues – 6
 Frequency re-use
coverages
Example of multiple
coverages with six-fold
frequency re-use
Hemi-beam coverage
in polarization “A” –
spatial isolation
Earth viewed from GEO
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
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Zone-beam coverage
in polarization “B” –
polarization isolation
87
Connectivity Issues – 7
 How do we connect together six coverages?
H1
H2
Z1
Z3
Z2
Z4
Fall 2010
Here we have a typical six-fold
GEO frequency re-use scheme.
There are two hemi-beams and
four zone beams, each using
exactly the same spectrum. The
hemi-beams use the same
polarization and are spatially
isolated from each other while
the zone beams all use a
polarization sense orthogonal to
the hemi-beams to achieve
polarization isolation from them.
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Connectivity Issues – 8
 What happens if your satellite is not in
Geostationary or Highly elliptical Orbit?
 A Medium Earth Orbit (MEO) satellite will see
about one-sixth that of a GEO satellite
 A Low Earth Orbit Satellite will see about onetwentieth that of a GEO satellite
 We will look at the Iridium LEO system
Fall 2010
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89
http://info.ee.surrey.ac.uk/Personal/L.Wood/constellations/iridium.html
Connectivity Issues – 9
The Iridium
Constellation of
66 LEO satellites
Fall 2010
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90
http://info.ee.surrey.ac.uk/Personal/L.Wood/constellations/iridium.html
Connectivity Issues – 10
“Warming the fishes”!
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Connectivity Issues – 11
 Multiple access techniques
 FDMA, TDMA, CDMA
 Connectivity issues
 On-board switching
 On-board processing
Fall 2010
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92
On-Board Switching – 1
 Each of the six beams
shown in slide 87 needs
to be connected to every
other beam
 There is therefore a need
for a six-by-six switch
matrix to be on the
satellite
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
H1
H1
H2
H2
Z1
Z2
66
Switch
Matrix
Z1
Z2
Z3
Z3
Z4
Z4
Switch Control
93
Limit for RF or IF switch matrices is about 10 beams
On-Board Switching – 2
 The switch matrix can be at RF, at IF, or at
baseband
 The key link design point lies in knowing if
the satellite acts as a linear transponder or as a
processing transponder
 RF and IF switch matrices are usually part of
linear transponders
 Baseband switch matrices are usually part of
processing transponders
Fall 2010
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94
Connectivity Issues – 12
 Multiple access techniques
 FDMA, TDMA, CDMA
 Connectivity issues
 On-board switching
 On-board processing
Fall 2010
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95
Surface Acoustic Wave
On-Board Processing – 1
 Early (analog) on-board processing designs
used SAW to generate a space-time switch
 With the move to digital systems, on-board
processing (OBP) takes place at baseband
 The OBP payload therefore has to demodulate
the carrier and decode the signal before any
processing can take place
Fall 2010
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96
From Pratt, et al., Fig. 3.14
On-Board Processing – 2
 A simplified OBP payload is shown below
Rx
Multi-beam
Uplink
Fall 2010
Demod
FEC
decode
OBP
FEC
encode
On-board
controller
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
Mod.
Tx
Multi-beam
Downlink
97
From Pratt, et al., Fig. 3.14
For full on-board processing, a demultiplexer
and a multiplexer are also required
On-Board Processing – 2A
DEMUX MUX
 A simplified OBP payload is shown below
Rx
Multi-beam
Uplink
Fall 2010
Demod
FEC
decode
OBP
FEC
encode
On-board
controller
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
Mod.
Tx
Multi-beam
Downlink
98
From Pratt, et al., Fig. 3.14
This is abbreviated to MCDDD:
Multi-Carrier Demodulation, Decoding, and
Demultiplexing
On-Board Processing – 2A
DEMUX MUX
 A simplified OBP payload is shown below
Rx
Multi-beam
Uplink
Fall 2010
Demod
FEC
decode
OBP
FEC
encode
On-board
controller
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
Mod.
Tx
Multi-beam
Downlink
99
On-Board Processing – 3
 OBP provides orders of magnitude more
flexibility than a linear transponder, but at a
price
 OBP
 Is very expensive and heavy
 Requires a priore knowledge of future markets
 Requires very high component reliability
 separates the uplink from the downlink
Sometimes good; sometimes bad
Fall 2010
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100
On-Board Processing – 4
 OBP separation of up- and downlinks – 1
Output
power
Satellite
transponder
linear
amplifier
characteristic
Downlink
power range
Input
power
Uplink power
range
Fall 2010
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© Jeremy Allnutt August 2010
101
Good between about 10 and 40
GHz, away from the 22 GHz line
On-Board Processing – 5
 OBP separation of up- and downlinks – 2
 Uplink attenuation is usually higher than
downlink attenuation for a given rain event
 Uplink and downlink rain fades are nearly
always uncorrelated
Rule of thumb
(f2fade)/(f1fade) = (f2)2/(f1)2
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
Example
102
Rain Attenuation example
 A VSAT operates at 14.5 GHz on the uplink
and 12.15 GHz on the downlink
 Rain causes an uplink attenuation of 8 dB,
what is the downlink fade in the same storm?
 f2 = 14.5 GHz, f1 = 12.15 GHz, f2fade = 8 dB, since
(f2fade)/(f1fade) = (f2)2/(f1)2
f1fade = (f2fade)(f1)2/(f2)2 = 8(12.15)2/(14.5)2
= 8(147.6255)/(210.25) = 5.6170273 = 5.6 dB
Fall 2010
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103
On-Board Processing – 6
 Uplink margin in a linear transponder has to
allow for the connection to work even in an
uplink rain event, so the downlink margin is
higher than necessary
 OBP payload separates the links and so the
additional uplink margin is not present on the
downlink
 This has implications in link design
Fall 2010
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104
On-Board Processing – 7
 But OBP has moved on dramatically with the
orbiting of INTELSAT 14 in November 2009
 INTELSAT 14 carried an IRIS payload:
Internet Router In Space (CISCO Router)
 IRIS is connected to up to three transponders
and can provide multicasting opportunities
without double-hops normally used in satellites
that have only linear transponders
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
105
On-Board Processing – 8
Therefore slide 99 now becomes
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
106
From Pratt, et al., Fig. 3.14
This is abbreviated to MCDDD:
Multi-Carrier Demodulation, Decoding, and
Demultiplexing
On-Board Processing – 2A
DEMUX MUX
 A simplified OBP payload is shown below
Rx
Multi-beam
Uplink
Fall 2010
Demod
FEC
decode
OBP
On-board
controller
FEC
encode
Mod.
Internet Router
In Space
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
Tx
Multi-beam
Downlink
107
On-Board Processing – 10
Given that you can conduct
on-board processing on each
satellite, how do you link a
cluster of satellites together?
Fall 2010
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108
TCOM 707 Lecture 1 Outline
 Project SCION
 Satellite Orbits Review
 Earth Coverage Review
 Connectivity Issues
 Linking the Satellites
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
109
Linking the Satellites – 1
 Repeating Slide 27 we have –
 Linking the satellites
 Physical layer


Microwave
Optical
 Network layer


Fall 2010
TCP/IP
Other?
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
110
Linking the Satellites – 2
 Repeating Slide 27 we have –
 Linking the satellites
 Physical layer


Microwave
Optical
 Network layer


Fall 2010
TCP/IP
Other?
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
111
Microwave Links – 1
 Microwave transmission requires an antenna
 The antenna can be directive or omni-directional
 Directive antenna will require tracking
 Omni-directional antenna does not need steering
 Examples of some microwave antennas are
shown in the next few slides
Fall 2010
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© Jeremy Allnutt August 2010
112
Antenna Types – 1
 There are many types of antennas
 Dipole antennas
 Yagi-Uda antennas
 Short Backfire antennas
 Patch antennas
 Array antennas
 Parabolic antennas
TCOM 551
2009
Fall
Lectures number 6 and 7
113
Dipole Antenna
Dipole
antenna
“WalkieTalkie”
radio
handset
Fall 2010
A dipole antenna is either extended
from the body of the handset or
vehicle and it generates a fairly
uniform field about the axis of the
antenna. The gain is unity (i.e. 1)
which translates to a gain of 0 dB.
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
114
Yagi-Uda Antenna
The square metal grid is used to
enhance the reflector element’s
performance, giving more gain
along the axis of the support pole
TCOM 551
2009
Fall
Lectures number 6 and 7
115
http://oasis.dit.upm.es/~jantonio/personal/eb4gpe/images/complete_antenna1.jpg
Short-Backfire Antenna
TCOM 551
2009
Fall
Lectures number 6 and 7
116
http://en.wikipedia.org/wiki/Image:Patch_antenna_w_cutaway.gif
Patch Antenna
TCOM 551
2009
Fall
Lectures number 6 and 7
117
http://en.wikipedia.org/wiki/Phased_array
Phased Array Antenna
PAVE PAWS
Antenna in Alaska
TCOM 551
2009
Fall
Lectures number 6 and 7
118
Antenna Types – 2
 There are many types of antennas
 Dipole antennas
 Yagi-Uda antennas
 Short Backfire antennas
 Patch antennas
 Array antennas
 Parabolic antennas
These provide the highest gain
TCOM 551
2009
Fall
Lectures number 6 and 7
119
Parabolic Antennas - 1
 A Parabola has two focal points: one close to
the antenna and the other at infinity
 Parallel rays (essentially flux from infinity –
the second focal point) will all reflect back to
the focal point near the antenna – the focus
Parabolic
Antenna
TCOM 551
2009
Focus
Parallel “rays”
Flux
arriving
from a
distant
source
Fall
Lectures number 6 and 7
120
Parabolic Antennas - 2
 There are two basic types of parabolic
reflectors
 Axially-fed
and
Offset-fed
Focus
Focus
Aperture diameter, D
TCOM 551
2009
Fall
Lectures number 6 and 7
121
Examples of Axially-fed and
Offset-fed Parabolic Antennas
TCOM 551
2009
Fall
Lectures number 6 and 7
122
Parabolic Antennas - 3
 Parabolic antennas can sometimes have more than
one reflecting surface
Front-fed antenna
Cassegrain antenna
Gregorian antenna
Sub-reflector must be >10
Feed
horn
Hyperbolic
sub-reflector
TCOM 551
2009
Elliptical
subreflector
Fall
Lectures number 6 and 7
123
Parabolic Antennas - 4
 These three antenna types can also be offset-
fed
Offset
Front-fed antenna
TCOM 551
2009
Offset
Cassegrain antenna
Offset
Gregorian antenna
Fall
Lectures number 6 and 7
124
Basic Theory – Antenna Beamwidth 1
 There are two general beamwidths used for
antennas
Maximum
Gain
 The 1 dB beamwidth
1
dB
 The 3 dB beamwidth
3 dB
Electrical
axis
Fall 2010
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© Jeremy Allnutt August 2010
125
1 dB beamwidth is normally
the tracking beamwidth
3 dB beamwidth is normally the
communications beamwidth
Basic Theory – Antenna Beamwidth 2
 There are two general beamwidths used for
antennas
Maximum
Gain
 The 1 dB beamwidth
 The 3 dB beamwidth
3 dB
1
dB
Electrical
axis
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
126
Antenna Beamwidth – 2A
 The half-power (3 dB) beamwidth of a
parabolic antenna is given by
Beamwidth3dB = (1.2 ) / D
Assumes
  0.60
radians
Example:
A 3m antenna with an efficiency of 65% operates at
a frequency of 12 GHz. What is the beamwidth?
TCOM 551
2009
Fall
Lectures number 6 and 7
127
Antenna Beamwidth – 2B
 Answer
Beamwidth3dB = (1.2  / D) = 1.2  0.025 / 3
= 0.01 radians
= 0.01  180/
= 0.57 degrees
Alternatively:
Antenna gain ratio = 30,000/(3dB beamwidth in
degrees)2
Gain = (D/)2  0.65 = 92,379.5
TCOM 551
2009
Fall
Lectures number 6 and 7
128
Antenna Beamwidth – 2C
 Answer (contd.)
Efficiency, 
Gain as a ratio
Gain =
 0.65 = 92,379.5
But Gain = 30,000/(3dB beamwidth in degrees)2
(D/)2
(3dB beamwidth in degrees)2 = 30,000 / 92,379.5
= 0.3247474
3dB beamwidth in degrees = 0.57 degrees
TCOM 551
2009
Fall
Lectures number 6 and 7
129
Antenna Beamwidth – 2D
 Another (more approximate) method is
3dB = 70/D in degrees
 From the example before, with  = 0.025 and
D = 3m, which gives 0.583 degrees
 However, 3dB = 70/D in degrees is not the
whole story
TCOM 551
2009
Fall
Lectures number 6 and 7
130
Antenna Beamwidth – 2E
 In actual fact
3dB = N/D , degrees
where N is the beamwidth factor dependent on the
aperture illumination distribution
 In general 58  N  75
Uniform
Tapered
Uniform
distribution
TCOM 551
2009
Tapered
distribution
Field in aperture of antenna
Fall
Lectures number 6 and 7
131
Note: Sometimes you will find 3dB = 75/D and antenna gain ratio = 33,000/(3dB
beamwidth in degrees)2. It depends on the aperture distribution of the antenna.
Antenna Beamwidth – 2F
 Most antennas have their aperture distribution
tapered to reduce spill-over problems and so N
= 70 to 75 are the normal values
 The aperture distribution will also affect the
antenna gain ratio
 The power (watts) being fed into an antenna
with a given gain provides a parameter called
the EIRP, where EIRP = Power × Gain
TCOM 551
2009
Fall
EIRP = Equivalent Isotropic Radiated Power
Lectures number 6 and 7
132
EIRP - 1
 The transmit power being fed into an antenna,
Pt , is multiplied by the transmit gain of the
antenna, Gt , to give a product called the
Effective Isotropically Radiated Power, or
EIRP
 EIRP = Pt Gt watts
Example
TCOM 551
2009
Fall
Lectures number 6 and 7
133
EIRP - 2
 An antenna with a gain of 50 dB is fed by an
amplifier with a power of 20 watts, what is the
EIRP, ignoring any losses, in dBW?
 Answer:
First: convert 20 watts  13 dBW
Second: add the power to the gain, giving
EIRP = 13 + 50 = 63 dBW
 Alternatively:
TCOM 551
2009
Fall
Lectures number 6 and 7
134
EIRP - 3
 Alternative Answer:
First: Convert 50 dB to a ratio  100,000
Second: Amplifier power of 20 W is multiplied by the
gain of the antenna, yielding 2,000,000 W
Third: Turn the 2,000,000 W into a dB value
referenced to 1W, thus
EIRPdB = 10 log (2,000,000/1)
= 10  6.3010300
= 63 dBW
TCOM 551
2009
Fall
Lectures number 6 and 7
135
EIRP - 4
 Note: maximum EIRP will only exist along the
electrical axis of the antenna (called the
electrical boresight or the main beam axis)
 Communications systems often have a
misalignment between the receiving and
transmitting antennas
 The System design must allow for this
misalignment
TCOM 551
2009
Fall
Lectures number 6 and 7
136
Basic Theory – Link Budget 1
Pr = (EIRP  Gr)/Lp watts
EIRP = PtGt
D is the physical
distance, in meters,
between the
transmitting and
receiving antennas
Fall 2010
(Pr)dB = EIRPdB + (Gr)dB – (Lp)dB
Antenna Gain,
Gr
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
Received power,
Pr
137
Linking the Satellites – 1
 Repeating Slide 27 we have –
 Linking the satellites
 Physical layer


Microwave
Optical
 Network layer


Fall 2010
TCP/IP
Other?
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
138
λ = wavelength in meters
D = aperture diameter in meters
Optical Links – 1
 Optical links are usually generated using solid-
state, infra-red lasers
 The amplitude distribution across the aperture
of a solid state laser provides a beamwidth that
can be taken as λ/D (in radians)
 The beam has a Gaussian shape in most cases
and so collimation is needed if a high gain
antenna (telescope) is to be used
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Optical Links – 2
 The calculation of path loss for optical links is
the same as for microwave links
 The links budget calculation is the same as for
microwave links
 Where the microwave and optical links differ is
if the transmission occurs through the
atmosphere (more of this in later lectures). For
a cross-link in space, this is not a factor.
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Optical Links – 3
 Current fiber-optic laser links tend to use On-
Off keying, which reduces the C/N by about 3
dB
 Optical links in space will probably utilize a
form of pulse position modulation in order to
maintain a constant envelope
 Other modulation schemes could be feasible,
depending on the separation between spacecraft
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141
Linking the Satellites – 1
 Repeating Slide 27 we have –
 Linking the satellites
 Physical layer


Microwave
Optical
 Network layer


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TCP/IP
Other?
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TCP/IP
 Standard router techniques could be assumed
for a router operating in space, the only
difference being in the need to qualify the
router for space, and in particular for the
launch environment
 It may well be that a LAN or WAN operation
could be set up between satellite routers
 Is a BGP or IGP mode feasible?
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
143
Linking the Satellites – 1
 Repeating Slide 27 we have –
 Linking the satellites
 Physical layer


Microwave
Optical
 Network layer


Fall 2010
TCP/IP
Other?
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
144
Other
 There may be other network layers to consider,
depending on the round-trip delays between
spacecraft
 Is a scheme like Blue Tooth an option?
Fall 2010
TCOM 707 Advanced Link Design Lecture No. 1
© Jeremy Allnutt August 2010
145