AJAL ASC Chap2 revIew

1. MODULE 2
Satellite Access Methods
AJAL.A.J
Assistant Professor –Dept of ECE,
Federal Institute of Science And Technology (FISAT) TM
MAIL: ec2reach@gmail.com

2. The Earth is divided up into the northern
hemisphere and the southern hemisphere:
Northern
hemisphere
Southern
hemisphere Equator

3. The Earth is tilted on an axis
North pole
South pole

4. The Earth is kept in orbit by the force of…
Gravity
…and by the
fact that is is
moving at a high
velocity

5. The Earth spins on its axis

6. While the Earth is spinning the side that faces the
sun is in -------

7. Day and night

8. The Earth orbits the sun every…
…year (365 1/4 days)

9. The Earth orbits the Sun

10. Because of this spin the sun rises in the
______ and sets in the ______

11. Gravity also keeps the moon in orbit around the
Earth. The moon orbits the Earth every…
…days month (28 )

13. Audio Spectrum
Peak power
Noise floor

14. Analog Signaling

15. Digital Signaling
Example - PCM
(Coder-Decoder)

16. Reasons for Choosing Data and Signal
Combinations
• Digital data, digital signal
– Equipment for encoding is less expensive than digital-
to-analog equipment
• Analog data, digital signal
– Conversion permits use of modern digital transmission,
computational resources and switching equipment
• Digital data, analog signal
– Transmission media will only propagate analog signals
– Examples include optical fiber and POTS (3 kHz
bandwidth limited)
• Analog data, analog signal
– Analog data easily converted to an analog signal via
some form of modulation (AM, FM, etc.)

17. Unguided Media
• Transmission and reception are achieved by
means of an antenna (rcvr + xmtr)
• Configurations for wireless transmission
– Directional (infers gain)
– Omnidirectional
– Polarization (vertical, horizontal, circular)

18. A Simplified Wireless Communications
System – Unguided Media
Antenna
Information
to be Coding Modulator Transmitter
transmitted
(Voice/Data)
Carrier
Antenna
Information
received Decoding Demodulator Receiver
(Voice/Data)
Carrier

19. Modulation Terms
adding data to a radio frequency signal
Baseband – modulation techniques that do not use a
sinusoidal carrier but encodes information directly as the
amplitude, width of position of a pulse. PAM – pulse
amplitude modulation PWM – pulse width modulation
Bandpass – modulation techniques that encode
information as the amplitude, frequency or phase of a
sinusoidal carrier. FSK – frequency shift keying, PSK –
phase shift keying, AM, FM

20. Electromagnetic Spectrum

21. Communication frequencies
• Microwave band terminology
– L band 800 MHz - 2 GHz
– S band 2-3 GHz
– C band 3-6 GHz
– X band 7-9 GHz
– Ku band 10-17 GHz
– Ka band 18-22 GHz

22. • Satellite up links and down links can operate
in different frequency bands:
Band Up-Link Down-link ISSUES
(Ghz) (Ghz)
C 4 6 Interference with
ground links.
Ku 11 14 Attenuation due to rain
Ka 20 30 High Equipment cost
• The up-link is a highly directional, point to point link
• The down-link can have a footprint providing coverage for a
substantial area "spot beam“.

23. Early satellite communications
• Used C band in the range 3.7-4.2 GHz
• Could interfere with terrestrial
communications
• Beamwidth is narrower with higher
frequencies

24. More recent communications
• Greater use made of Ku band
• Use is now being made of Ka band

25. Rain fade
• Above 10 GHz rain and other
disturbances can have a severe effect on
reception
• This can be countered by using larger
receiver dishes so moderate rain will have
less effect
• In severe rainstorms reception can be lost
• In some countries sandstorms can also be
a problem

26. Ku band assignments
• © copyright 1996 MLE INC.

27. Characteristics of some Frequencies
• Microwave frequency range
– 1 GHz to 40 GHz
– Directional beams possible (small)
– Suitable for point-to-point transmission
– Used for satellite communications
• VHF/UHF Radio frequency range
– 30 MHz to 1 GHz (no atmospheric propagation, LOS)
– Suitable for omnidirectional applications
• Infrared frequency range
– Roughly 3x1011 to 2x1014 Hz
– Useful in local point-to-point multipoint applications
within confined areas

28. Terrestrial Microwave
• Description of common microwave antenna
– Parabolic "dish", 3 m in diameter
– Fixed rigidly which focuses a narrow beam
– Achieves a line-of-sight (LOS) transmission path to the
receiving antenna
– Located at substantial heights above ground level
• Applications
– Long haul telecommunications service (many repeaters)
– Short point-to-point links between buildings

29. Satellite Microwave
• Description of communication satellite
– Microwave relay station
– Used to link two or more ground-based microwave
transmitter/receivers
– Receives transmissions on one frequency band (uplink),
amplifies or repeats the signal and transmits it on another
frequency (downlink)
• Applications
– Television distribution (e.g., Direct TV)
– Long-distance telephone transmission
– Private business networks

30. Broadcast Radio
• Description of broadcast radio antennas
– Omnidirectional (HF-vertical polarization, VHF/UHF-
horizontal polarization)
– Antennas not required to be dish-shaped
– Antennas need not be rigidly mounted to a precise
alignment
• Applications
– Broadcast radio
• VHF and part of the UHF band; 30 MHz to 1GHz
• Covers FM radio and UHF and VHF television
• Below 30 MHz transmission (AM radio) is subjected to
propagation effects so not reliable for point-to-point
communications (MUF or max usable freq)

31. Network Architectures
and Protocols
 Systematic Signaling Steps for Information
Exchange
 Open Systems Interconnections (OSI)
 Transmission Control Protocol (TCP)
 Internet Protocol (IP)
 Internet Protocol Version 4 (IPv4)
 Internet Protocol Version 6 (IPv6) – essentially
larger MAC addressing space for the influx of IP based devices
 Mobile IP

32. Ad Hoc Network (peer to peer)
Versus an infrastructure network (centralized) with its AP
(Access Points) which is your WiFi/Hotspot/typical wireless
network normally used to access the Internet.

33. Multiplexing
• Capacity of transmission medium usually
exceeds capacity required for transmission of a
single signal
• Multiplexing - carrying multiple signals on a
single medium
– More efficient use of transmission medium

34. Multiplexing

35. Reasons for Widespread Use of Multiplexing
• Cost per kbps of transmission facility declines with
an increase in the data rate (economy of scale)
• Effective cost of transmission and receiving
equipment declines with increased data rate
(cost per bit)
• Most individual data communication devices with
their associated applications require relatively modest
data rate support

36. Multiplexing Techniques
• Frequency-division multiplexing (FDM)
– Takes advantage of the fact that the useful bandwidth of the
medium exceeds the required bandwidth of a given signal
– Requires guard bands
• Time-division multiplexing (TDM)
– Takes advantage of the fact that the achievable bit rate of the
medium exceeds the required data rate of a digital signal
– Requires accurate clock
• Code-division multiple access(CDMA)
– Use of orthogonal codes to separate users who are all using
the same band of frequencies

37. Frequency-division Multiplexing

38. FDMA Channel Allocation
Frequency 1
User 1
Frequency 2
User 2
… …
Frequency n
User n
Mobile Stations Base Station

39. Time-division Multiplexing

40. TDMA Frame Illustration
for Multiple Users
User 1 Time 1
Time 2
User 2
…
…
…
Time n
User n
Mobile Stations Base Station

41. CDMA
(Code Division Multiple Access)
Frequency
User 1
User 2
. ..
User n
Time
Code

42. Transmitted and Received Signals
in a CDMA System
Information bits
Code at
transmitting end
Transmitted signal
Received signal
Code at
receiving end
Decoded signal
at the receiver
42

43. OFDM
(Orthogonal Frequency Division Multiplexing)
Frequency
Conventional multicarrier modulation used in FDMA
Frequency
Orthogonal multicarrier modulation used in OFDM (normally a single user)

44. Satellite
Microwave Transmission
• a microwave relay station in space
• can relay signals over long distances
• geostationary satellites
– remain above the equator at a height of
22,300 miles (geosynchronous orbit)
– travel around the earth in exactly the time the
earth takes to rotate

45. Satellite Transmission Links
• earth stations communicate by sending
signals to the satellite on an uplink
• the satellite then repeats those signals on
a downlink
• the broadcast nature of the downlink
makes it attractive for services such as the
distribution of television programming

46. Satellite Transmission Process
satellite
transponder
dish
dish
22,300 miles
uplink station downlink station

47. Satellite Navigation
47

50. WORKING
150 MHz
200 MHz
Universiteit Utrecht

51. WORKING
150 MHz
150 MHz
Universiteit Utrecht

52. WORKING
• The receiver only knows
that the satellite is neither
approaching or departing
• So the ship must be on a
line perpendicular to the
orbit of the satellite
• However, farther from the
orbit, the frequency
transition is less
• A calculation will tell the
receiver how far, but not
which side Universiteit Utrecht

53. Local Area Augmentation System (LAAS)

54. Satellite Transmission
Applications
• television distribution
– a network provides programming from a
central location
– direct broadcast satellite (DBS)
• long-distance telephone transmission
– high-usage international trunks
• private business networks

55. Why Satellites remain in Orbits

56. Principal Satellite Transmission
Bands
• C band: 4(downlink) - 6(uplink) GHz
– the first to be designated
• Ku band: 12(downlink) -14(uplink) GHz
– rain interference is the major problem
• Ka band: 19(downlink) - 29(uplink) GHz
– equipment needed to use the band is still very
expensive

57. Fiber vs Satellite

58. Satellite-Related Terms
• 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

59. Ways to Categorize
Communications Satellites
• Coverage area
– Global, regional, national
• Service type
– Fixed service satellite (FSS)
– Broadcast service satellite (BSS)
– Mobile service satellite (MSS)
• General usage
– Commercial, military, amateur, experimental

60. Classification of Satellite Orbits
• Circular or elliptical orbit
– Circular with center at earth’s center
– Elliptical with one foci at earth’s center
• Orbit around earth in different planes
– Equatorial orbit above earth’s equator
– Polar orbit passes over both poles
– Other orbits referred to as inclined orbits
• Altitude of satellites
– Geostationary orbit (GEO)
– Medium earth orbit (MEO)
– Low earth orbit (LEO)

61. Geometry Terms
• 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

62. Minimum Elevation Angle
• Reasons affecting minimum elevation angle of
earth station’s antenna (>0o)
– 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

63. NGSO - Non Geostationary Orbits
 Orbit should avoid
Van Allen radiation
belts:
• Region of charged
particles that can
cause damage to
satellite
• Occur at
 ~2000-4000 km and
 ~13000-25000 km

64. Satellite Orbits

65. GEO Orbit
• Advantages of the the GEO orbit
– No problem with frequency changes
– Tracking of the satellite is simplified
– High coverage area
• Disadvantages of the GEO orbit
– Weak signal after traveling over 35,000 km
– Polar regions are poorly served
– Signal sending delay is substantial
GEO : Geosynchronous equatorial orbit

66. LEO - Low Earth Orbits
• Circular or inclined orbit with < 1400 km altitude
– Satellite travels across sky from horizon to horizon in
5 - 15 minutes => needs handoff
– Earth stations must track satellite or have Omni
directional antennas
– Large constellation of satellites is needed for
continuous communication (66 satellites needed to
cover earth)
– Requires complex architecture
– Requires tracking at ground

67. LEO Satellite Characteristics
• 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

68. LEO Categories
• 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

69. MEO Satellite Characteristics
• 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

70. HEO - Highly Elliptical Orbits
• HEOs (i = 63.4°) are suitable to
provide coverage at high latitudes
(including North Pole in the northern
hemisphere)
• Depending on selected orbit (e.g.
Molniya, Tundra, etc.) two or three
satellites are sufficient for continuous
time coverage of the service area.
• All traffic must be periodically
transferred from the “setting” satellite
to the “rising” satellite (Satellite
Handover)

71. Satellite Systems
GEO
GEO (22,300 mi., equatorial)
high bandwidth, power,
M EO latency
MEO
LEO
high bandwidth, power,
latency
LEO (400 mi.)
low power, latency
more satellites
small footprint
V-SAT (Very Small Aperture
Terminal)
private WAN

72. Geostationary Orbit

73. 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
USAF - United States Air Force

74. Frequency Bands Available for
Satellite Communications

75. Satellite Link Performance Factors
• Distance between earth station antenna and satellite
antenna
• For downlink, terrestrial distance between earth
station antenna and “aim point” of satellite
– Displayed as a satellite footprint (Figure 9.6)
• Atmospheric attenuation
– Affected by oxygen, water, angle of elevation, and higher
frequencies

76. Satellite Footprint

77. Satellite Communications
 Alternating vertical and
horizontal polarisation is
widely used on satellite
communications
 This reduces interference
between programs on the
same frequency band
transmitted from adjacent
satellites (One uses vertical,
the next horizontal, and so
on)
 Allows for reduced angular
separation between the
satellites.

78. Satellite Network Configurations

79. Capacity Allocation Strategies
• Frequency division multiple access (FDMA)
• Time division multiple access (TDMA)
• Code division multiple access (CDMA)

80. Frequency-Division Multiplexing
• Alternative uses of channels in point-to-point
configuration
– 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

81. Frequency-Division Multiple
Access
• Factors which limit the number of subchannels
provided within a satellite channel via FDMA
– Thermal noise
– Intermodulation noise
– Crosstalk

82. Forms of FDMA
• Fixed-assignment multiple access (FAMA)
– 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)
– Capacity assignment is changed as needed to respond
optimally to demand changes among the multiple stations

83. FAMA-FDMA
• FAMA – logical links between stations are
preassigned
• FAMA – multiple stations access the satellite
by using different frequency bands
• Uses considerable bandwidth

84. DAMA-FDMA
• Single channel per carrier (SCPC) – bandwidth
divided into individual VF channels
– 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
– 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

85. Reasons for Increasing Use of TDM
Techniques
• Cost of digital components continues to drop
• Advantages of digital components
– Use of error correction
• Increased efficiency of TDM
– Lack of intermodulation noise

86. FAMA-TDMA Operation
• Transmission in the form of repetitive sequence of
frames
– Each frame is divided into a number of time slots
– Each slot is dedicated to a particular transmitter
• Earth stations take turns using uplink channel
– Sends data in assigned time slot
• Satellite repeats incoming transmissions
– Broadcast to all stations
• Stations must know which slot to use for transmission
and which to use for reception

87. FAMA-TDMA Uplink

88. FAMA-TDMA Downlink

89. Satellite Signals
► Used to transmit signals and data over long
distances
 Weather forecasting
 Television broadcasting
 Internet communication
 Global Positioning Systems

90. Communication Satellite
►A Communication Satellite can be looked
upon as a large microwave repeater
► It contains several transponders which
listens to some portion of spectrum,
amplifies the incoming signal and
broadcasts it in another frequency to avoid
interference with incoming signals.

91. Types of Satellite Orbits
► 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
 Circular with centre at the earth’s centre
 Elliptical with one foci at earth’s centre

92. Intelsat
► INTELSAT is the original "Inter-governmental Satellite organization". It
once owned and operated most of the World's satellites used for
international communications, and still maintains a substantial fleet of
satellites.
► INTELSAT is moving towards "privatization", with increasing
competition from commercial operators (e.g. Panamsat, Loral Skynet,
etc.).
► INTELSAT Timeline:
► Interim organization formed in 1964 by 11 countries
► Permanent structure formed in 1973
► Commercial "spin-off", New Skies Satellites in 1998
► Full "privatization" by April 2001
► INTELSAT has 143 members.

93. Intelsat Structure

94. Advantages of Satellite
Communication
 Can reach over large geographical area
 Flexible (if transparent transponders)
 Easy to install new circuits
 Circuit costs independent of distance
 Broadcast possibilities
 Temporary applications (restoration)
 Niche applications
 Mobile applications (especially "fill-in")
 Terrestrial network "by-pass"
 Provision of service to remote or underdeveloped
areas
 User has control over own network
 1-for-N multipoint standby possibilities

95. Disadvantages of Satellite
Communication
 Large up front capital costs (space
segment and launch)
 Terrestrial break even distance
expanding (now approx. size of
Europe)
 Interference and propagation delay
 Congestion of frequencies and orbits

96. When to use Satellites
 When the unique features of satellite communications
make it attractive
 When the costs are lower than terrestrial routing
 When it is the only solution
 Examples:
• Communications to ships and aircraft (especially safety
communications)
• TV services - contribution links, direct to cable head, direct
to home
• Data services - private networks
• Overload traffic
• Delaying terrestrial investments
• 1 for N diversity
• Special events

97. THANKS FOR YOUR PATIENCE