Link Budget: Comunicaciones Satelitales

Comunicaciones Satelitales
LINK BUDGET
L.A.F.S
L.A.F.S
LINK BUDGET
• Introduction:
• A satellite link is defined as an Earth station - satellite -

Earth station connection. The Earth station - satellite
segment is called the uplink and the satellite - Earth
station segment is called the downlink.
• The Earth station design consists of the Transmission
Link Design, or Link Budget, and the Transmission
System Design.
• The Link Budget establishes the resources needed for a
given service to achieve the performance objectives.
L.A.F.S
LINK BUDGET
• Performance objectives for digital links consist

of:
• BER for normal operating conditions
• Link Availability, or percentage of time that the

link has a BER better than a specified threshold
level
L.A.F.S
LINK BUDGET
• The satellite link is composed primarily of three

segments:
• (i) the transmitting Earth station and the uplink media;
• (ii) the satellite; and
• (iii) the downlink media and the receiving Earth station.
• The carrier level received at the end of the link is a
straightforward addition of the losses and gains in the
path between transmitting and receiving Earth stations.
L.A.F.S
Typical Satellite Link L.A.F.S

LINK BUDGET
• The basic carrier-to-noise relationship in a system
establishes the transmission performance of the RF
portion of the system, and is defined by the receive
carrier power level compared to the noise at the
receiver input. For example, the downlink thermal
carrier-to-noise ratio is:
C/N = C -10log(kTB) (1)
• Where:
• C = Received power in dBW
• k = Boltzman constant, 1.38*10-23 W/°K/Hz
• B = Noise Bandwidth (or Occupied Bandwidth) in Hz
• T = Absolute temperature of the receiving system in °K
L.A.F.S
Link Parameters’ Impact on Service Quality Comunicaciones Satelitales
L.A.F.S
LINK BUDGET
• The link equation in its general form is:
C/N = EIRP - L + G - 10log(kTB) (2)
Where:
• EIRP = Equivalent Isotropically Radiated Power (dBW)
• L = Transmission Losses (dB)
• G = Gain of the receive antenna (dB)
L.A.F.S
LINK BUDGET
Equivalent Isotropically Radiated Power:
The gain of a directive antenna results in a more

economic use of the RF power supplied by the source.
Thus, the EIRP is expressed as a function of the antenna
transmit gain GT and the transmitted power PT fed to
the antenna.
EIRPdBW = 10 log PT dBw + GT dBi (3)

Where:
PT dBw = antenna input power in dBW
GT dBi = transmit antenna gain in dBi
L.A.F.S
LINK BUDGET
Equivalent Isotropically Radiated Power:
Maximum power flux density at distance r from a transmitting

antenna of gain G:
ΨM = (G*Ps) / (4πr2)
An isotropic (omnidirectional) radiator would generate this flux
density
EIRP is defined as G*Ps
When expressed as dBW, Ps in W, G in dB:
EIRP = Ps + G
e.g., transmit power of 6 W and antenna gain of 48.2 dB:
EIRP = 10 log 6 + 48.2 = 56 dBW
Free Space Loss: PR = EIRP + GR - 10 log (4πr/λ)2 (dBW)

L.A.F.S
Receiver Power Equation
L.A.F.S
Antenna Gain.
The antenna gain, referred to an isotropic

radiator, is defined by:
GdBi = 10log(η)+20log(f)+20log(d)+20.4 dB
(4) Where:
η = antenna efficiency (Typical values are 0.55 - 0.75)
d = antenna diameter in m
f = operating frequency in GHz
L.A.F.S
L.A.F.S
Transmission losses,
generally consist of four components:
L = Lo + Latm + Lrain + Ltrack (5)
Where:
Lo = free Space Loss
Latm = atmospheric losses
Lrain = attenuation due to rain effects
Ltrack = losses due to antenna tracking errors
L.A.F.S
LINK BUDGET
If an isotropic antenna radiates a power PT, the beam

power will spread as a sphere in which the antenna
is the center. The power at a distance “D” from the
transmission point is given by the next equation.
W = PT/4πD2. . . . . (W/m2) (6)
As the transmit antenna focuses the energy (i.e., has
a gain), the equation changes to:
W = GTPT/4πD2. . . . . (W/m2) (7)
L.A.F.S
LINK BUDGET
or
WdBW/m2 = EIRPdBW - 20 log D – 71 dB (8)
Where:
GTPT = EIRP
W = illumination level
D = distance in km
71 dB = 10 log (4π*106)
L.A.F.S
L.A.F.S
LINK BUDGET
As a receiver antenna 'collects' the signal, the amount

of 'collected' signal will depend on the receiver
antenna size. The received power PR will be:
PR = W*Ae (9)
Where:
Ae = effective aperture of the receive antenna
= (λ2/4π)/GR
Then,
PR = [GTPT/4πD2]*[(λ2/4π)/GR] (10)
PR = GTPT*(λ/4πD)2*GR (11) L.A.F.S
LINK BUDGET
The expression [4πD/λ]2 is known as the basic free
space loss Lo. The basic free space loss is
expressed in decibels as:
Lo = 20log(D) + 20log(f) + 92.5 dB (12)
Where:
D = distance in km between transmitter and receiver,
or slant range
f = frequency in GHz
92.5 dB = 20 log {(4π*109*103)/c}
L.A.F.S
Free Space Loss
FSL = 10 log (4r/)2
in dBW , FSL = 32.4 + 20 log r + 20 log ƒ
e.g., ES to satellite is 42,000 km, ƒ is 6 GHz, what is FSL?
» FSL = 32.4 + 20 log 42000 + 20 log 6000 = 200.4 dB
» Very large loss!!
e.g., EIRP = 56 dBW, receive antenna gain 50 dB
» PR = 56 + 50 - 200.4 = -94.4 dBW = 355 pW
• Other sources of losses
– Feeder losses
– Antenna misalignment losses
– Fixed atmospheric and ionospheric losses
– Effects of rain
• PR = EIRP + GR - Losses, in dBW L.A.F.S
Path Loss
• Depends on:
– Distance and frequency
– About 200 dB at C-band
– About 206 dB at Ku-band
L.A.F.S
LINK BUDGET
Expressing equation (11) in dB:
PR dBW = EIRP - Lo + GR (13)
In equation (13), if GR were the gain for a 1m2

antenna with 100 percent efficiency, PR will become
the illumination level per unit area in dBW/m2;
therefore, the illumination level in equation (8) can
also be expressed as:
WdBW/m2 = EIRP - Lo + G1m2 (14) L.A.F.S
Atmospheric Losses
Losses in the signal can also occur through
absorption by atmospheric gases such as
oxygen and water vapor. This characteristic
depends on the frequency, elevation angle,
altitude above sea level, and absolute
humidity. At frequencies below 10 GHz, the
effect of atmospheric absorption is negligible.
Its importance increases with frequencies above
10 GHz, especially for low elevation angles.
L.A.F.S
Atmospheric Losses
• Table shows an example of the mean value of

atmospheric losses for a 10-degree elevation
angle.
L.A.F.S
Atmospheric Attenuation
L.A.F.S
Atmospheric Attenuation
L.A.F.S
Atmospheric Absorption
Contributing Factors:
– Molecular oxygen Constant
– Uncondensed water vapor
– Rain
– Fog and clouds Depend on
weather
– Snow and hail
• Effects are frequency dependent
– Molecular oxygen absorption peaks at 60 GHz
– Water molecules peak at 21 GHz
• Decreasing elevation angle will also increase absorption loss
L.A.F.S
Atmospheric Absorption
1% of the time, rain attenuation exceeds 0.3 dB

(99% of the time, it is less than or equal to 0.3 dB)
0.5% of the time, it exceeds 0.5 dB
0.1% of the time, it exceeds 1.9 dB
L.A.F.S
Sky-Noise and Frequency Bands Comunicaciones Satelitales
L.A.F.S
Transmission Losses
Up-Link (Geosync)
– Up-link ƒ = 6.175 GHz, D = 36,000 km
– Path loss is a function of frequency and distance minus
transmitter and receiver antenna gain
– Loss = 132.7 - 20 log dt - 20 log dr
dt transmitter antenna: 30 m
dr satellite receiver antenna: 1.5 m
– Loss = 132.7 - 29.5 - 3.5 = 94.7 dB
Transmitted pwr/received pwr = 2.95 x 109
• Down-Link
– Down-link ƒ = 3.95 GHz
– Footprint of antenna affects its gain; wide area footprint yields a
lower gain, narrow footprint a higher gain
– Loss = 136.6 - 20 log dt - 20 log dr
Loss = 136.6 - 3.5 - 29.5 = 103.6 dB
L.A.F.S
Rain Effects
• An important climatic effect on a satellite link is the rainfall. Rain results in

attenuation of radio waves by scattering and by absorption of energy from the
wave.
• Rain attenuation increases with the frequency, being worse for Ku-band than
for C-band. Enough extra power must be transmitted to overcome the
additional attenuation induced by rain to provide adequate link availability.
L.A.F.S
Tracking Losses
When a satellite link is established, the ideal situation

is to have the Earth station antenna aligned for
maximum gain, but normal operation shows that
there is a small degree of misalignment which
causes the gain to drop by a few tenths of a dB.
The gain reduction can be estimated from the
antenna size, the tracking type, and accuracy.
• This loss must be considered for the uplink and
downlink calculations.
L.A.F.S
Tracking Losses
Earth Station Performance Characteristic (C-band, Antenna Efficiency 70%)
L.A.F.S
Tracking Losses
Earth Station Performance Characteristic (Ku-band, Antenna Efficiency 60%)
L.A.F.S
Typical Losses
L.A.F.S
Typical Losses (4/6 GHz)
L.A.F.S
System Noise Temperature
The system noise temperature of an Earth station consists of the

receiver noise temperature, the noise temperature of the
antenna, including the feed and waveguides, and the sky noise
picked up by the antenna.
Tsystem = Tant/L + (1 - 1/L)To + Te (15)
Where:
L = feed loss in numerical value
Te= receiver equivalent noise temperature
To= standard temperature of 290°K
Tant = antenna equivalent noise temperature as provided by the
manufacturer
L.A.F.S
Noise
• Shannon’s Law: B = BN log2 (PR / PN + 1)
• Where B = information-carrying capacity of the link (bits/unit bandwidth)
• BN = usable bandwidth (hertz)
• PR/PN must not get too small!
• Noise power usually quoted in terms of noise temperature: PN = k TN BN
• The noise temperature of a noise source is that temperature that produces the
same noise power over the same frequency range: TN = PN / k BN
• Noise density (noise per hertz of b/w): N0 = PN / BN = k TN
• Carrier-to-Noise: C/N0 = PR / N0 = PR / k TN : EIRP + G/T - k - Losses in dB
• Receiver antenna figure of merit: increases
• with antenna diameter and frequency;
• More powerful xmit implies cheaper receiver
• Sun, Moon, Earth, Galactic
• Noise, Cosmic Noise, Sky
• Noise, Atmospheric Noise,
• Man-made Noise
L.A.F.S
Noise Sources
System Noise
– Received power is very small, in picowatts
– Thermal noise from random motion of electrons
– Antenna noise: antenna losses + sky noise (background microwave radiation)
– Amplifier noise temperature: energy absorption manifests itself as heat, thus
generating thermal noise
• Carrier-to-Noise Ratio
– C/N = PR - PN in dB
– PN = k TN BN
– C/N = EIRP + GR - LOSSES - k -TS - BN
where k is Boltzman’s constant, TS is system noise temperature, TN is equivalent
noise temperature, BN is the equivalent noise bandwidth
– Carrier to noise power density (noise power per unit b/w):
C/N0 = EIRP + G/T - Losses - k
L.A.F.S
Antenna Noise Temperature
• The noise power into the receiver, (in this case the LNA),
due to the antenna is equivalent to that produced by a
matched resistor at the LNA input at a physical temperature
of Tant.
• If a body is capable of absorbing radiation, then the body
can generate noise. Thus the atmosphere generates some
noise. This also applies to the Earth surrounding a receiving
ground station antenna. If the main lobe of an antenna can
be brought down to illuminate the ground, the system noise
temperature would increase by approximately 290°K.
L.A.F.S
Antenna Noise Temperature

Noise Temperature of an Antenna as a Function of Elevation Angle
L.A.F.S
Antenna Temperature Comunicaciones Satelitales
L.A.F.S
Figure of Merit (G/T)
In every transmission system, noise is a factor that

greatly influences the whole link quality.
The G /TdBK is known as the "goodness"

measurement of a receive system.
This means that providing the Earth station meets

the required G/T specification, INTELSAT will
provide enough power from the satellite to meet the
characteristic of every service.
L.A.F.S
Figure of Merit (G/T)
G/T is expressed in dB relative to 1°K. The same

system reference point, such as the receiver input,
for both the gain and noise temperature must be
used.
G/T = Grx - 10log(Tsys) (16)
Where:
Grx = receive gain in dB
Tsys = system noise temperature in °K
L.A.F.S
Carrier to Noise Ratio
In the link equation, by unfolding the kTB product under the

logarithm, the link equation becomes:
C/N = EIRP - L+ G - 10log(k) - 10log(T) - 10log(B) (17)

The difference, G - 10logT, is the figure of merit:
C/N = EIRP - L+ G/T - 10log(k) - 10log(B) (18)

Where:
L = transmission losses
G/T = figure of merit of the receiver
k = Boltzmann constant
B = carrier occupied bandwidth
L.A.F.S
Because the receiver bandwidth (B) is often dependent on

the modulation format, isolate the link power parameters by
normalizing out the bandwidth dependence. The new
relation is known as Carrier-to-Noise Density ratio (C/No).
C/No = EIRP - L + G/T - 10log(k) (19)

Note that:
C/N = C/T - 10logkB (20)
Expressing C/T as a function of C/N, and replacing C/N with
the right side of the link equation, results:
C/T = EIRP - L + G/T (21)
L.A.F.S
The ratio C/No allow us to compute directly the

receiver Bit energy-to-noise density ratio as:
Eb/No = C/No - 10log(digital rate) (22)
The term "digital rate" is used here because Eb/No

can refer to different points with different rates in
the same modem.
L.A.F.S
Carrier-to-Noise Ratio
Example Calculation
– 12 GHz frequency, free space loss = 206 dB,

antenna pointing loss = 1 dB,
atmospheric absorption = 2 dB
– Receiver G/T = 19.5 dB/K,
receiver feeder loss = 1 dB
– EIRP = 48 dBW
• Calculation:
– C/N0 = -206 - 1 - 2 + 19.5 - 1 + 48 + 228.6 = 86.1
(Note that Boltzmann’s constant k
= 1.38x10-23 J/K = -228.6 dB)
L.A.F.S
Link Budget
The interpretation of equation (21) is that a given
C/T required by a certain type of carrier and quality
of service, can be obtained for different
combinations of EIRP and G/T.
EIRP represents the resource usage and finally is
reflected in the operating costs because higher
satellite EIRP means higher operating costs. On the
other hand the G/T represents the capital
expenditure, because higher G/T means larger
antenna and/or better LNA, reflected in the cost of
the equipment.
L.A.F.S
Link Budget
Note that in some cases the Earth station G/T
could be improved by using a better LNA. For
example, an Earth station with a receive gain of 53
dBi,
antenna noise of 25°K at 25° in C-band, feeder
noise temperature of 5°K and LNA noise
temperature of 80°K would have:
G/T = Gant -10log(Tant+Tfeed+TLNA) (23)

G/T = 53-10log(25 + 5 + 80) = 32.6 dB/°K
This antenna would be classified as a standard B

L.A.F.S
antenna.
Link Budget
Removing the LNA and replacing it with a 30°K
LNA, the G/T is:
G/T = 53 - 10log(25 + 5 + 30) = 35.2 dB/°K
This reclassifies the antenna as a standard A.
For elevation angles below 25°, the antenna noise

would increase and the overall G/T would be too
low for standard A.
L.A.F.S
Simplified Link Equation

10 log (C/N0) = PS + GS - FSL + GR - TR - k - L (dB) where:
– C/N0: ratio of signal pwr to noise pwr after being received (Hz)
– PS: RF pwr delivered to transmitting antenna (dBW)
– GS: Gain of the transmitting antenna relative to isotropic rad (dBi)
– FSL: Free space loss (dB)
– GR: Gain of the receiving antenna (dBi)
– TR: Composite noise temperature of the receiver (dBK)
– k: Boltzmann’s constant (-288.6 dBW/K-Hz)
– L: Composite of propagation loss (dB)
• G = 10 log (ηπ2D2/λ2) dBi
– η: antenna efficiency, D: diameter
• FSL = 10 log [(4πr)2/λ2] dB
– r is distance
Path loss and antenna gain increase with square of radio frequency
L.A.F.S
Frequency vs. Losses vs. BER
Higher transmission frequency has the

advantage of requiring a smaller receiver
antenna BUT suffers from higher attenuation
losses through atmosphere
• To achieve the same C/N0 performance,
which is related to BER, actually needs a
LARGER antenna than same transmission
power at a lower frequency
• But still frequency allocation advantages for
high frequencies solution is to use higher
transmitter power at the satellite and earth
station for the higher frequency
transmissions
L.A.F.S
Time Delay
• The total Earth-satellite-Earth path length may be as much as

84,000km thus giving a one-way propagation delay of 250ms.
The effect of this delay on telephone conversations, where a
500ms gap can occur between one person asking a question
and hearing the other person reply.
• This phenomenon is minimized with the use of "Echo

cancelers". With geostationary satellites, a two-hop operation
is sometimes unavoidable and results in a delay of over 1
second.
L.A.F.S
Geographical Advantage
• A station which is located near the center of a
satellite beam (footprint), will have an advantage in
the received signal compared to another located at
the edge of the same beam of the satellite.
• The satellite antenna pattern has a defined beam

edge to which the values of the satellite Equivalent
Isotropically Radiated Power (EIRP), Gain-to-Noise
Temperature ratio (G/T), and flux density are
referenced.
L.A.F.S
Geographical Advantage
Beam Peak 48.7 dBW
e.i. r.p. Levels

47.7 dBW
46.7 dBW
45.7 dBW
44.7 dBW
43.7 dBW
42.7 dBW
41.7 dBW
7/04/0515M
40.7 dBW
L.A.F.S
Sun Interference
• Sun interference is due to the satellite, the Sun, and
the Earth station antenna being aligned, causing the
antenna to receive solar noise.
• The Sun represents a transmitter with significantly

more power than the satellite, and the solar noise
will overwhelm the signals coming from the satellite,
causing a total loss of traffic.
L.A.F.S
Spring
Summer
SUN
INTERFERENCE
Autumn
Winter
L.A.F.S
Sun Outage
L.A.F.S
Sun
Outage
L.A.F.S
Tropospheric Scintillation
• At unpredictable times the levels of receive signals

from the satellite rapidly fluctuate up and down. This
is called scintillation.
• Scintillation is brought about by the turbulent mixing
of air mass at different temperatures and humidities,
and by the random addition of particles such as rain,
ice, and moisture.
L.A.F.S

Link Budget: Comunicaciones Satelitales

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What are the three main segments of a satellite link?

What are the three main segments of a satellite link?

What factors impact the carrier-to-noise ratio of a satellite link?

What factors impact the carrier-to-noise ratio of a satellite link?

Comunicaciones Satelitales

• A satellite link is defined as an Earth station - satellite -

• Performance objectives for digital links consist

• BER for normal operating conditions

• Link Availability, or percentage of time that the

• The satellite link is composed primarily of three

Typical Satellite Link L.A.F.S

C/N = EIRP - L + G - 10log(kTB) (2)

The gain of a directive antenna results in a more

EIRPdBW = 10 log PT dBw + GT dBi (3)

Maximum power flux density at distance r from a transmitting

Free Space Loss: PR = EIRP + GR - 10 log (4πr/λ)2 (dBW)

Receiver Power Equation

The antenna gain, referred to an isotropic

L = Lo + Latm + Lrain + Ltrack (5)

If an isotropic antenna radiates a power PT, the beam

W = GTPT/4πD2. . . . . (W/m2) (7)

As a receiver antenna 'collects' the signal, the amount

PR dBW = EIRP - Lo + GR (13)

In equation (13), if GR were the gain for a 1m2

• Table shows an example of the mean value of

1% of the time, rain attenuation exceeds 0.3 dB

• An important climatic effect on a satellite link is the rainfall. Rain results in

When a satellite link is established, the ideal situation

Earth Station Performance Characteristic (C-band, Antenna Efficiency 70%)

Earth Station Performance Characteristic (Ku-band, Antenna Efficiency 60%)

Typical Losses (4/6 GHz)

System Noise Temperature

The system noise temperature of an Earth station consists of the

Antenna Noise Temperature

Antenna Noise Temperature

Figure of Merit (G/T)

In every transmission system, noise is a factor that

The G /TdBK is known as the "goodness"

This means that providing the Earth station meets

Figure of Merit (G/T)

G/T is expressed in dB relative to 1°K. The same

Carrier to Noise Ratio

In the link equation, by unfolding the kTB product under the

C/N = EIRP - L+ G - 10log(k) - 10log(T) - 10log(B) (17)

C/N = EIRP - L+ G/T - 10log(k) - 10log(B) (18)

Carrier to Noise Ratio

Because the receiver bandwidth (B) is often dependent on

C/No = EIRP - L + G/T - 10log(k) (19)

Carrier to Noise Ratio

The ratio C/No allow us to compute directly the

Eb/No = C/No - 10log(digital rate) (22)

The term "digital rate" is used here because Eb/No

– 12 GHz frequency, free space loss = 206 dB,

G/T = Gant -10log(Tant+Tfeed+TLNA) (23)

This antenna would be classified as a standard B

G/T = 53 - 10log(25 + 5 + 30) = 35.2 dB/°K

This reclassifies the antenna as a standard A.

For elevation angles below 25°, the antenna noise