This document discusses satellite communication systems. It begins by defining a satellite system as a set of radio receivers and transmitters in orbit around Earth. It then describes different types of satellites based on their functions such as communication, weather monitoring, imaging, and more. The document provides historical details on important milestones in satellite technology. It also defines different orbit types used by satellites and discusses concepts such as geostationary orbit. The document outlines the basic components of a satellite system including the uplink, transponder, and downlink. It concludes by describing multiple access techniques for satellite communications including FDMA, TDMA, and CDMA.

1. • A set of radio receivers and transmitters (payload) based on a
space‐based platform (satellite bus / spacecraft) orbiting around
the earth.
• Types of satellite depending on function:
 Communication satellite
 Weather satellite
 Imaging satellite
 Scientific satellite

3. • Arthur C. Clarke published a paper in “ Wireless World ”
in October 1945 that talked about objects that are placed
in space at a distance of 35,800 Km above the equator
have the same period of rotation as the earth.
• It further stated that three such objects can cover the
entire objects can cover the entire surface of the earth.

5. • 1957 First satellite (sub: Synchronous) : Sputnik
• 1962 First telephone and TV broadcast via satellite: Echo 1
• 1962 First telecommunications satellite: Telstar 1
• 1965 First geostationary communications satellite: Syncom3
• 1965 First Intelsat satellite: Early Bird
• 1973 First Domestic satellite network
• 1979 First Mobile satellite applications
• 1982 First small earth stations

6. • Low Earth Orbit (LEO)(500 miles)
• Medium Earth Orbit(MEO)(600-1200 miles)
• Geostationary or Geosynchronous earth orbit (GEO)(>2200
miles)

7. • 36,000 Km or 22,300 miles above the Equator
• Three objects located in space at this altitude will cover the entire
surface of the earth
• Circular orbit parallel to the equator
• All communications satellites are located in GEO orbit
• An object in GEO orbit and the earth have the same period of
rotation (24 hours)
• An object placed in the GEO orbit has a speed of 6,879 miles per
hour

8. • 8,000 - 14,000 Km
• GMPCS satellites
• Speed of object is 11,000 miles per hour
• Takes 5-12 hours to complete one orbit around the earth
• Will need more satellites to provide continuous 24 hour coverage

9. • 200 – 1000 Km above the earth
• Same orbit as the Space Shuttle
• Speed of object is17,000 miles per hour
• Takes 1-2 hours to complete one obit around the earth
• Used by GMPCS systems like Iridium®, Global Star®

11. A Satellite System Basic Sections:
• Uplink
• Satellite Transponder
• Downlink

15. Space segment:
• Contains a satellite as well as terrestrial facilities for
• control and monitoring of Satellite
• It includes tracking, telemetry and command station(TT&C) together with the
satellite control center where all the operation associated with station keeping
and checking the vital functions of the satellite are performed
• Uplink waves transmitted from earth station and received by satellite
• Downlink station transmitting to receiving earth station

16. • Link analysis: Quality of radio link is specified by Carrier‐to‐noise
ratio.
• Multiple Access: Satellite is a nodal point of network access to
satellite or satellite transponder by several carriers implies the use of
multiple access techs.
• A satellite consist of payload and a platform
• Payload consists of the Rx and Tx antennas and all the electronic
equipment which supports Tx of carriers

17. Platform consists of all the sub systems which permit the payload to operate
• These include Architecture of a Satellite Communication System
–Structure
–Electric power supply
–Temp control
–Attitude and orbit control
–Propulsion eqpt
–Tracking, telemetry and control (TT&C)equipment

18. • To amplify the received carriers for retransmission on downlink.
• Carrier power at the input of Satellite Rx is of the order of 100 pW to
1 nW.
• The carrier power at the out put of Tx Amplifier is 10–100W. The
power gain is of the order of 100 to 130 dB.
• Change the frequencies to avoid re injection in to receiver

19. • COLLECT microwave signals from given zone on earth
• AMPLIFY radiofrequency carrier
• CONVERT carrier frequency from uplink to downlink frequency
• TRANSMIT microwave signals to given zone on earth

21. Satellite Frequency Bands
Band Frequencies Available spectrum Applications
L 1.5-1.65 GHz 50 MHz Mobile satellite services
S 2.4 - 2.8 GHz 70 MHz Fixed satellite services
C 3.4 - 7.0 GHz 500 MHz Fixed satellite services
Broadcast service
X 7.9 - 9.0 GHz 30 MHz Military use
Ku 10.7 - 15.0 GHz 2 GHz Fixed satellite services
Broadcast service
Ka 18.0 - 31.0 GHz 2 GHz Broadband services
Q/V 18.0 - 31.0 GHz 3 GHz Broadband services
W 18.0 - 31.0 GHz 3 GHz Broadband services

22. L-Band C-Band Ku-Band
• Only 50 MHz
• Shared extensively with
terrestrial communications
• Used for mobile satellite
communications
• Wider beam width
• Can bend around obstacles
• Can penetrate non metallic
buildings
• 500 MHz
• Dual polarization (Linear or
Circular)
• Low power (EIRP)
• Larger coverage areas
• Larger earth station antennas
• Total bandwidth in use 568 GHz
to 1.44 THz
• Spatial re-use
• Dual polarization
• Frequency re-use
• 800 MHz-BSS; 750 MHz-FSS;
up-to 2 GHz
• Dual polarization (Linear or
Circular)
• Narrower beam
• High power focused beams
• Smaller earth station antennas
• Total bandwidth in use 4 THz
• Spatial re-use
• Dual polarization
• Frequency re-use

24. Satellite Performance Measures
• Footprint
• Transponder Bandwidth
• EIRP(effective isotropic radiated power)
• G/T ratio ( where G= antenna gain & T= antenna temperature)
• SFD(saturation flux density)

25. Multiple Access
• It is a technique in which multiple users can access a common
resource for communications.
• In Satellite Communication,
“How do we share one transponder between earth stations”

26. Multiple Access
NEED TO OPTIMIZE
• Satellite capacity (revenue issue)
• Spectrum utilization (coordination issue)
• Interconnectivity (multiple coverage issue)
• Flexibility (demand fluctuation issue)
• Adaptability (traffic mix issue)
• User acceptance (market share issue)
• Satellite power
• Cost
Very, Very, rarely a simple
optimum; nearly always a
trade-off exercise

27. Types of Multiple Access Methods
• Frequency Division Multiple Access (FDMA)
• Time Division Multiple Access (TDMA)
• Code Division Multiple Access (CDMA)

28. Frequency Division Multiple Access (FDMA)
• Most widely used
• Available satellite bandwidth is divided into portions of non-
overlapping frequency slots , which are assigned exclusively to
individual earth stations.

29. 1)- Multiple Channel Per Carrier (MCPC)
• Each baseband filter is an earth station receiver, which
correspondent to a specific transmitting station.
• Any change in traffic requires retuning of this filter.
2)- Single Channel Per Carrier(SCPC):
• When traffic is low, e.g. service to remote areas, MCPC becomes
wasteful of bandwidth because most of the channels remain
unutilized for a significant part of the time. SCPC is used in this case.
• In SCPC, each carrier transmits a single channel. SCPC may be pre-
assigned or demand-assigned.

30. FDMA
Advantages: Disadvantages:
1. Using well established technology.
2. No need for network timing.
3. No restriction regarding the type of
baseband or the type of
modulation.
1. Inter-modulation noise in the
transponder leads to interference
with other links – satellite capacity
reduction.
2. Lack of flexibility in channel
allocation.
3. Requires up-link power control to
maintain quality.
4. Weak carrier tend to be suppressed.

31. Time Division Multiple Access (TDMA)
• Assigning a short time (time slot) to each earth station in which they
have exclusive use of the entire transponder bandwidth and
communicate with each other by means of non-overlapping burst of
signals.
• In TDMA, the transmit timing of the bursts is accurately
synchronized so that the transponder receives one burst at a time.
Each earth station receives an entire burst stream and extracts the
bursts intended for it.

32. TDMA

33. TDMA
1. As can be seen, each TDMA frame has two reference bursts RB1
and RB2.
2. The primary reference burst (PRB), which can be either RB1 or
RB2, is transmitted by one of the earth stations in the network
designated as the primary reference earth station.
3. For reliability, a second reference burst (SRB) is transmitted by a
secondary reference earth station.
4. To ensure undisrupted service for the TDMA network, automatic
switchover between these two reference stations is provided.

34. TDMA
• The reference bursts carry no traffic information and are used to
provide synchronization for all earth stations in the network.
• The traffic bursts carry information from the traffic earth station.
• Each earth station accessing a transponder may transmit one or two
traffic bursts per TDMA frame and may position them anywhere in
the frame according to a burst time plan that coordinates traffic
between earth stations in the network.
• The Guard time between bursts ensures that the bursts never
overlap at the input to the transponder.

35. TDMA
Advantages Disadvantages
• Satellite power utilizations can be
maximized as inter modulation
noise is minimum.
• Uplink power control is not required.
• Transmission plans and capacity
management is done by the
satellite are very flexible.
• The digital format of TDMA allows
utilization of all advantages of digital
techniques
• It requires a network wide time
synchronization which makes the
entire system very complex.
• Analog of digital conversions are
required.
• Interface with analog terrestrial plan
is expected.

36. Code Division Multiple Access (CDMA)
• In CDMA satellite systems, each uplink earth station is identified by
an address code imposed on its carrier.
• Each uplink earth station uses the entire bandwidth transmits
through the satellite whenever desired.
• No bandwidth or time sharing is required in CDMA satellite systems.
• Signal identification is achieved at a receiving earth station by
recognizing the corresponding address code.
• There are two CDMA techniques:
1. Direct Sequence Spread Spectrum (DSSS)
2. Frequency Hopping Spread Spectrum (FHSS)

37. Direct Sequence Spread Spectrum (DSSS)
• In this technique, an addressed pseudo-noise (PN) sequence
generated by the PN code generator of an uplink earth station
together with the information data are modulated directly on the
carrier.
• The same PN sequence is used synchronously at the receiving earth
station to despread the received signal in order to receive the
original data information
• The bits of the PN sequence are referred to as chips. The ratio
between the chip rate and information rate is called the spreading
factor.
• Phase-shift-keying modulation schemes are commonly used for
these systems.

38. Frequency Hopping Spread Spectrum (FHSS)
• The addressed PN sequence is used to continually change the
frequency of the carrier at the uplink earth station (hopping).
• At the receiver, the local PN code generator produces a
synchronized replica of the transmitted PN code which changes the
synthesizer frequency in order to remove the frequency hops on the
received signal, leaving the original modulated signal untouched.
• Non-coherent M-ary FSK modulation schemes are commonly used
for these systems.