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
They cover large areas.
Inherent capability of by-passing the whole terrestrial system.
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
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.
ADVANTAGES OF SATELLITE
SPEED OF INSTALLATION
APPLICATIONS OF SATELLITE
FIXED SERVICE SATELLITE
DIRECT BROADCAST SATELLITE
MOBILE SATELLITE TECHNOLOGIES
SATELLITE INTERNET ACCESS
The Ku band is a portion of the electromagnetic spectrum that ranges from 10.95-
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.
Range : 4 – 8 GHz
At frequencies higher than 10 GHz in heavy rain fall areas, a noticeable
The C-band perform better in comparison with Ku band under adverse weather
The Ku band satellites typically require considerably more power to transmit than
the C-band satellites.
•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,
THE BANDWIDTH CHALLENGE
optimizing the traffic
advanced modulation techniques to reduce the
bandwidth allocated to a given service
HOW TO REDUCE BANDWIDTH
Who Benefits from BANDWIDTH OPTIMIZATION SOLUTIONS
SATELLITE SERVICE PROVIDERS
OIL and GAS COMPANIES
CONSTRUCTION and MINING INDUSTRY
MILITARY and GOVERNMENT OPERATIONS
DISASTER RECOVERY , EMERGENCY AID
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
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
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
HIGH POWER AMPLIFIER
Obtain Necessary EIRP (Equivalent Isotropic Radiated Power) from an earth
- 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
TWTAs have wide bandwidth typically around 500MHz
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
Modems currently in use at ONGC :
- DMD15 Universal Satellite Modem
- DMD20 Universal Satellite Modem
DMD15 Universal Satellite Modem
•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.
DMD20 Universal Satellite Modem
• 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
The required occupied bandwidth is
B = k ( Rb / m )(1/ r )
Rb = information bit rate
m = number of bits per symbol
r = code rate
K = bandwidth expansion factor used
to minimize intersymbol interference
Link Power Budget
(cables & connectors)
Antenna Pointing Loss
Free Space Loss
(gaseous, clouds, rain)
Rx Antenna Pointing Loss
(cables & connectors)
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
Why calculate Link Budgets?
System performance tied to operation
Operation thresholds Cmin tell the minimum
power that should be received at the
demodulator in order for communications to
Operation thresholds depend on:
Modulation scheme being used.
Desired communication quality.
Thermal Noise power.
Simple Link Power Budget
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
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
Available bandwidth can be optimized by using one of the
•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.
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.
Benefits of Forward Error
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.
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.
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, 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%
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.
In the design of a communication system, the choice of modulation is of
fundamental importance and always involves tradeoffs between power and
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.