Satellite communications systems allow communication between two points on Earth via satellites. A signal is transmitted from an earth station to a satellite, which then relays the signal to another earth station. Satellites provide large area coverage and can bypass terrestrial networks. They are used for voice calls, television, radio, internet access, and more. Higher frequency bands like Ku-band provide more flexibility than C-band but are more susceptible to rain fade. Modern systems use modulation techniques like QPSK and 8-PSK along with error correction coding to optimize bandwidth use on satellites.

2. INTRODUCTION
 Satellite communications systems exist because earth is a sphere.
 Radio waves travel in straight lines at the microwave frequencies
used for wideband communications.
 Satellites are important in: voice communications, video & radio
transmission, navigation (GPS),remote sensing (maps, weather
satellites) etc.
 They cover large areas.
 Inherent broadcast.
 Inherent capability of by-passing the whole terrestrial system.

3. HOW DO SATELLITES WORK?
Two Stations on Earth want to communicate through radio
broadcast but are too far away to use conventional means.
The two stations can use a satellite as a relay station for their
communication.
One Earth Station transmits the signals to the satellite. Up link
frequency is the frequency at which Ground Station is
communicating with Satellite.
The satellite Transponder converts the signal and sends it down
to the second earth station. This frequency is called a Downlink.

4. ADVANTAGES OF SATELLITE
COMMUNICATIONS
 LARGE COVERAGE
 HIGH QUALITY
 HIGH RELIABILITY
 HIGH CAPACITY
 FLEXIBILITY
 SPEED OF INSTALLATION
 EMERGENCY COMMUNICATION

5. APPLICATIONS OF SATELLITE
COMMUNICATION
 TELEPHONE
 SATELLITE TELEVISION
 FIXED SERVICE SATELLITE
 DIRECT BROADCAST SATELLITE
 MOBILE SATELLITE TECHNOLOGIES
 SATELLITE RADIO
 SATELLITE INTERNET ACCESS
 MILITARY USES

7. Ku Band
The Ku band is a portion of the electromagnetic spectrum that ranges from 10.95-
14.5 GHz
More flexibility
For the End users Ku band is generally cheaper and enables smaller antennas
The satellite operator's Earth Station antenna do require more accurate position
control when operating at Ku band than compared to C band.

8. C Band
Range : 4 – 8 GHz
At frequencies higher than 10 GHz in heavy rain fall areas, a noticeable
degradation occurs
The C-band perform better in comparison with Ku band under adverse weather
conditions
The Ku band satellites typically require considerably more power to transmit than
the C-band satellites.

9. •Available bandwidth is limited and insufficient to meet demand
• Existing capacity is usually running at maximum capacity
– As a result it is often unusable
– Universal flat lining during working hours
•The cost of bandwidth is extremely high
•Expanding bandwidth capacity is limited due to finances, supply,
technology
THE BANDWIDTH CHALLENGE

10. optimizing the traffic
advanced modulation techniques to reduce the
bandwidth allocated to a given service
HOW TO REDUCE BANDWIDTH

11. Who Benefits from BANDWIDTH OPTIMIZATION SOLUTIONS
 SATELLITE SERVICE PROVIDERS
 MARITIME INDUSTRIES
 OIL and GAS COMPANIES
 CONSTRUCTION and MINING INDUSTRY
 MILITARY and GOVERNMENT OPERATIONS
 DISASTER RECOVERY , EMERGENCY AID
 BROADCASTING COMPANIES

12. BLOCK DIAGRAM

14. MODULATION TECHNIQUES
 Modulation is the process by which information is conveyed by
means of an electromagnetic wave.
 The power and bandwidth necessary for the transmission of a
signal with a given level of quality depends on the method of
modulation.
1. QPSK
2. 8-PSK

15. QPSK v/s 8PSK
QPSK occupies 1/2 of the bandwidth of BPSK whereas 8PSK uses 1/3rd
of the bandwidth that BPSK for a given bit rate
With a 8PSK capable satellite receiver you can demodulate QPSK as
well as 8PSK
8PSK makes better use of bandwidth than QPSK
8PSK is not as phase-tolerant as QPSK and has a slightly longer
acquisition time

17. UP/DOWN CONVERTER
Up converter accepts IF signal in the 70±18 MHz band
Convert to an RF signal in 5.925-6.425 GHz band
Down converter accepts RF signal in 3.7-4.2 GHz band
convert to an IF signal in 70±18 MHz band
Same transponder is used for transmitter and receiver channels

18. HIGH POWER AMPLIFIER
Obtain Necessary EIRP (Equivalent Isotropic Radiated Power) from an earth
station
Three types:
- klystron power amplifier(KPA)
- traveling wave tube amplifier(TWTA)
- solid state power amplifier(SSPA)
For large power of the order of few kilowatts, traveling wave tube amplifiers
(TWTAs) or Klystron are used
Klystrons amplifiers are used in ONGC
Klystrons have narrow instantaneous bandwidth around 40MHz tunable over
500MHz range
TWTAs have wide bandwidth typically around 500MHz

19. LOW NOISE AMPLIFIER
Amplify very weak signals
Located very close to the detection device
Placed at the front-end of a radio receiver circuit
The effect of noise from subsequent stages of the receive chain is reduced
Low NF (like 1db)
Large enough gain (like 20db)
Large enough intermodulation and compression point (IP3 and P1dB)
The gain of the LNA That is used in satellite earth station, ONGC is 60db

20. Modems
Modems currently in use at ONGC :
- DMD15 Universal Satellite Modem
- DMD20 Universal Satellite Modem

21. DMD15 Universal Satellite Modem
Main Features:
•BPSK and QPSK modulation.
•9.6 Kbps to 8.448 Mbps in 1 bps steps.
•Configuration, monitor and control features are fully user-programmable.
•Excellent spurious performance.
•Fully-compliant with IESS 308/309.
•Industry standard I/O interfaces.
•Customize for closed network applications.
•50-90,100-180 MHz IF in 1 Hz steps.

22. DMD20 Universal Satellite Modem
Highlights:
•BPSK/QPSK/OQPSK/8-PSK/8-QAM/16-QAM Operation
• 2.4 Kbps to 20 Mbps in 1 bps Steps
• FEC - Viterbi, Reed-Solomon, Sequential, Trellis, Turbo Product Code, Low
Density Parity Check Code
• Configuration, Monitor and Control Features Fully User-Programmable
• Excellent Spurious Performance
• Fully Compliant with IESS 308/309/310/314/315
•Industry-standard Universal Interface Module
•50 to 90 MHz and 100 to 180 MHz IF, and 950 to 2050 MHz L-Band in 1 Hz Steps
• Standard Features Include: Reed-Solomon,Asynchronous Overhead, Satellite
Control Channel and Automatic Uplink Power Control

23. The required occupied bandwidth is
B = k ( Rb / m )(1/ r )
Where,
Rb = information bit rate
m = number of bits per symbol
r = code rate
K = bandwidth expansion factor used
to minimize intersymbol interference

24. Link Design, Link Budget and
Power

25. Link Power Budget
25
Transmission:
HPA Power
Transmission Losses
(cables & connectors)
Antenna Gain
EIRP
Tx
Antenna Pointing Loss
Free Space Loss
Atmospheric Loss
(gaseous, clouds, rain)
Rx Antenna Pointing Loss
Rx
Reception:
Antenna gain
Reception Losses
(cables & connectors)
Noise Temperature
Contribution
Pr

26. Link Budgets
 The transmission formula can be written in dB as:
 The calculation of received signal based on transmitted
power and all losses and gains involved until the receiver is
called “Link Power Budget”, or “Link Budget”.
 The received power Pr is commonly referred to as “Carrier
Power”, C.
26
rrotherrapolaptar LGLLLLLLEIRPP

27. Why calculate Link Budgets?
 System performance tied to operation
thresholds.
 Operation thresholds Cmin tell the minimum
power that should be received at the
demodulator in order for communications to
work properly.
 Operation thresholds depend on:
 Modulation scheme being used.
 Desired communication quality.
 Coding gain.
 Additional overheads.
 Channel Bandwidth.
 Thermal Noise power.
27

28. Simple Link Power Budget
28
Parameter Value Totals Units Parameter Value Totals Units
Frequency 11.75 GHz
Transmitter Receive Antenna
Transmitter Power 40.00 dBm Radome Loss 0.50 dB
Modulation Loss 3.00 dB Diameter 1.5 m
Transmission Line Loss 0.75 dB Aperture Efficiency 0.6 none
Transmitted Power 36.25 dBm Gain 43.10 dBi
Polarization Loss 0.20 dB
Transmit Antenna Effective RX Ant. Gain 42.40 dB
Diameter 0.5 m
Aperture Efficiency 0.55 none Received Power -98.54 dBm
Transmit Antenna Gain 33.18 dBi
Slant Path Summary
Satellite Altitude 35,786 km Transmitted Power 36.25 dBm
Elevation Angle 14.5 degrees Transmit Anntenna Gain 33.18 dBi
Slant Range 41,602 km EIRP 69.43 dBmi
Free-space Path Loss 206.22 dB Path Loss 210.37 dB
Gaseous Loss 0.65 dB Effective RX Antenna Gain 42.4 dBi
Rain Loss (allocated) 3.50 dB Received Power -98.54 dBm
Path Loss 210.37 dB

29. BANDWIDTH OPTIMIZATION
Transponder bandwidth is usually the most expensive resource
in a satellite communication link. For maximum efficiency, a
satellite link should be engineered to balance bandwidth and
power.
Available bandwidth can be optimized by using one of the
following techniques:
•Using higher modulation
•lower order FEC technique
•Increased Antenna size
Our project is based on using higher order modulation
techniques for efficient utilization of available bandwidth.

30. FORWARD ERROR CORRECTION
 In communication forward error
correction(FEC) a system of error control for data
transmission, whereby the sender adds systematically
generated redundant data to its messages, also known as
an error-correcting code (ECC).
 The carefully designed redundancy allows the receiver to
detect and correct a limited number of errors occurring
anywhere in the message without the need to ask the sender for
additional data. FEC gives the receiver an ability to correct
errors without needing a reverse channel to request
retransmission of data.

31. Benefits of Forward Error
Correction (FEC)
Reduce bandwidth by 50%.
Increase data throughput by a factor of 2.
Reduce antenna size by 30%.
Reduce transmitter power by a factor of 2.
Provide 3dB more link margin.

32. if we have bandwidth to spare, then use a lower order modulation or a
higher rate FEC (like 1/2 or 2/3) to spread the signal out.
 If we have power to spare then use a higher order modulation and/or
lower rate FEC (like 3/4 or 7/8).
Ideally use all of both the available bandwidth and power simultaneously
to obtain the highest user information rate.
Bandwidth-Power Trade-Off

33. RESULTS
The following results were derived from these calculations:
Bandwidth requirement has been reduced by a considerable
amount when 8PSK is used as compared to QPSK.
Different FEC rates used also has an effect on the bandwidth
requirement of the transmission and receiving link.
By using a proper combination of modulation technique
and FEC rate we can achieve efficient utilization of
bandwidth.

34. Allocated Bandwidth
Bandwidth, Allocated Bandwidth or Occupied Bandwidth is the
frequency space required by a carrier on a transponder.
E.g. : a duplex E1 (2.048 Mbps) circuit with 8-PSK modulation, FEC
rate 3/4 and 1.4 spacing requires:
Bandwidth = data rate/(no. of bits per symbol * FEC)* frequency
spacing * 2 [for duplex circuit]
B = 2.048 / (3 * 0.75) * 1.4 * 2 = 2.548 MHz
 For a 36 MHz transponder, 2.548 MHz corresponds to 7.078%
bandwidth utilization.

35. Power Equivalent Bandwidth
Power Equivalent Bandwidth (PEB) is the transponder power used
by a carrier, represented as bandwidth equivalent.
PEB calculation example:
• Transponder EIRP = 37 dBW
• Output Backoff (OBO) = 4 dB
• Available EIRP = 37 – 4 = 33 dBW = 10^3.3= 1995.26 Watts
• Transponder Bandwidth = 36 MHz
• Power Available / MHz = 1955.26 / 36 = 55.424 W
• If a carrier uses 24 dBW, then
PEB = Power used by your carrier/transponder saturated power
PEB = 10^2.4/ 55.424 = 4.532 MHz
This corresponds to 12.59% of available transponder power.

36. CONCLUSION
In the design of a communication system, the choice of modulation is of
fundamental importance and always involves tradeoffs between power and
bandwidth.
In the past, frequency spectrum was relatively plentiful but the power
available on a satellite was limited. Today, the equation has been reversed.
Spectrum is now scarce.
More spectrum efficient forms of digital modulation such as 8PSK and
16QAM are becoming more attractive, even though the power
requirements are higher.
Coupled with powerful coding methods such as concatenated Reed
Solomon/Viterbi coding, these methods offer the prospect of enhanced
spectral efficiency with virtually error-free digital signal transmission.

37. Thank You