Module 2

Amity School of Engg &
Technology
M.Tech ECE, Semester II
Satellite Communication
Module 2 Lecture 1
Dr Sanmukh Kaur
1
Learning Objectives & Outcomes
 To develop the Link equation of a Satellite at Earth station.
 Ability to derive the link equation and analyze various factors affecting the quality of
received signal at Earth station.
2
Module II Satellite link design
power received by an earth station from a satellite transmitter
 Consider a transmitting source, in free space, radiating a total power P t watts

uniformly in all directions as shown in Fig.1.
 Such a source is called isotropic. At a distance R meters from the hypothetical

isotropic source transmitting RF power Pt watts, the flux density crossing the surface
of a sphere with radius R m is given by:
(1)
 For a transmitter with output Pt watts driving a lossless antenna with gain Gt, the
flux density in the direction of the antenna boresight at distance R meters is
(2)
3
Developing the equation of the orbit
4
Fig.1: Flux density from an isotropic source with EIRP P t watts
Power received by an earth station
 The product Pt Gt is often called the effective isotropically radiated power (EIRP),
 If we had an ideal receiving antenna with an aperture area of A m2, we would collect
power Pr watts given by:
(3)
 A practical antenna with a physical aperture area of Ar m2 will not deliver the power
given in Eq. (3).
 Some of the energy incident on the aperture is reflected away from the antenna,
referred to as scattering, and some is absorbed by lossy components.
 This reduction in efficiency is described by using an effective aperture Ae where :
5 (4)
Power received by an earth station
 ηA is the aperture efficiency of the antenna,
Fig.2: Calculation of received power by an antenna.
 Thus the power received by a real antenna with a physical receiving area Ar and effective
aperture area Ae at a distance R from the transmitter is:
(5)
6
Link equation
 A fundamental relationship in antenna theory is that the gain and area of an antenna
are related by:
(6)
 Where λ is the wavelength (in meters for Ae in square meters) at the frequency of
operation. Substituting for Ae gives:
(7)
 This expression is known as the link equation, and it is essential in the calculation
of power received in any radio link.
7
Link equation
 In communication systems, decibel quantities are commonly used to simplify
equations like (7). In decibel terms, we have:
(8)
 Where
 Path loss LP is given by:
(9)
8
Link equation
 In practice, we will need to take account of a more complex situation in which we
have losses in the atmosphere due to attenuation by oxygen, water vapor, and rain,
losses in the antennas at each end of the link, and possible reduction in antenna gain
due to mispointing.
 More generally, Eq. (8) can be written as
(10)
 Where
9
System Noise Temperature and G/T Ratio
 The noise power is given by:
(1)
 Where
-k = Boltzmann’s constant = 1.39 x 10-23 J/K= −228.6 dBW/K/Hz
-Tp = physical temperature of source in kelvin degrees
-Bn = noise bandwidth in which the noise power is measured, in hertz
 Pn is the available noise power (in watts) and will be delivered only to a load that is
impedance matched to the noise source.
 The term kTp is a noise power spectral density, in watts per hertz. The density is
constant for all radio frequencies up to 300 GHz.
10
Fig.3 Simplified receiver with single frequency conversion.

11
Earth Station Receivers
 Fig.3 shows a simplified communications receiver with an RF amplifier and single
frequency conversion, from its RF input to the IF output.
 The superhet receiver has three main subsystems:

-A front end (RF amplifier, mixer and local oscillator [LO]) an IF amplifier (IF
amplifiers and filters), a demodulator, and a baseband section.
Calculation of System Noise Temperature
 Fig 4a can be used to represent equivalent circuits of a receiver for the purpose of
noise analysis.
 The noisy devices in the receiver are replaced by equivalent noiseless blocks with
the same gain and noise generators at the input to each block such that the block
produces the same noise at its output as the device it replaces.
12
Fig 4a Noise model of receiver

13
 The entire receiver is then reduced to a single equivalent noiseless block with the same end-to-
end gain as the actual receiver and a single noise source at its input with temperature Ts, called
the system noise temperature.
 The total noise power at the output of the IF amplifier of the receiver in Fig. 4 is given by:
(2)
 where GRF, Gm, and GIF are respectively the gains of the RF amplifier, mixer, and IF amplifier,
and TRF, Tm, and TIF are their equivalent noise temperatures.
 Tin is the noise temperature of the antenna, measured at its output port. It accounts for noise
radiated into the antenna from the signal path through the atmosphere and also any noise
radiated from the earth into the sidelobes of the antenna pattern.
14
 Fig.4a shows a model of a noiseless receiver in which each block in the receiver is replaced by a
noiseless block followed by an equivalent noise source at the output of the block.
 The noise source in each case has a noise temperature that results in the same output noise
power as the noisy device, measured in the receiver noise bandwidth.
 In Fig.4b, the noise sources are combined into a single equivalent system noise source with a
noise temperature Ts at the input of the receiver, and the receiver is represented as a single
noiseless block that has the same end to end gain as the receiver in Fig.4a.
 Fig.4c is an alternative configuration to Fig.4b with a single equivalent noise source with noise
temperature Tno at the output of the receiver.
15
Fig.4bNoise model of receiver with a single noise source
16
Fig.4c Noise model of receiver with a single noise source
17
 Equation (2) can be rewritten as:
(3)
 The single source of noise shown in Fig.4b with noise temperature Ts generates the same noise
power Pn at its output as the model in Fig.4a.
(4)
 The noise power at the output of the noise model in Fig.4b will be the same as the noise power
at the output of the noise model in Fig.4.a if
18
(5)
Or
(6)
 Succeeding stages of the receiver contribute less and less noise to the total system noise
temperature.
 Noise figure is frequently used to specify the noise generated within a device.
(7)
19
G/T Ratio for Earth Stations
 The link equation can be rewritten in terms of CNR at the earth station
(8)
 Thus CNR ∝ Gr/Ts, and the terms in the square brackets are all constants for a given satellite
system.
 The ratio Gr/Ts , which is usually quoted as simply G/T in decibels with units dBK-1, can be used
to specify the quality of a receiving earth station or a satellite receiving system, since increasing
Gr/Ts increases the received CNR.
20
Technology
Module 2 Lecture 2
Dr Sanmukh Kaur
21
 To identify the parameters to be considered for the design of the satellite links
 Ability to analyze and design uplink and downlink power budget .
22
Design of downlinks and uplinks with examples
Design of downlinks considerations
 The design of any satellite communication is based on two objectives:

- Meeting a minimum C/N ratio for a specified percentage of time
- Carrying the maximum revenue earning traffic at minimum cost.
 Any satellite link can be designed with very large antennas to achieve high CNRs
under all conditions, but the cost will be very high.
 The art of good system design is to reach the best compromise of system parameters
that meets the specification at the lowest cost.
 If a satellite link is designed with sufficient margin to overcome a 20 dB rain fade

rather than a 3 dB fade, an earth station antenna with seven times the diameter is
required.
23
Rain attenuation
 In the 6/4 GHz band the effect of rain on the link is small.
 In the 14/11 GHz Ku-band, and even more so in the 30/20 GHz Ka-band and higher
frequency bands, rain attenuation becomes all important.
 Satellite links are typically designed to achieve reliabilities of 99.5–99.99%,

averaged over a long period of time, typically a year.
 This means the CNR in the receiver will fall below the minimum permissible value
for proper operation of the link for between 0.5% and 0.01% of the specified time;
the link is then said to suffer an outage.
24
 C-band links can be designed to achieve 99.99% reliability because the rain
attenuation rarely exceeds 1 or 2 dB.
 The time corresponding to 0.01% of a year is 52minutes;
 Rain attenuation can be overcome in many cases by using a small clear sky link
margin and changing the forward error correction (FEC) coding rate and modulation
when rain attenuation occurs.
 GEO Ka-band satellite links are currently becoming widespread in aeronautical

services for aircraft crossing the oceans to provide internet access for passengers.
 Aircraft avoid flying through heavy rain and thunderstorms, and long distance
flights are at altitudes above clouds and rain, except for thunderstorms
25
Link Budgets
 The link budget must be calculated for an individual transponder,
 In a two-way satellite communication link, there will be four separate links, each
requiring a calculation of CNR.
 When a bent pipe transponder is used the uplink and downlink CNRs must be
combined to give an overall CNR.
 The calculation of CNR in a satellite link is based on the two equations for received
signal power and receiver noise power.
 We have derived the Eq. for received carrier power in dB watts as:
(1)
26
 The receiving terminal with a system noise temperature Ts K and a noise bandwidth
Bn Hz has a noise power Pn watts
(2)
 It is usually written in decibel units as
(3)
 where k is Boltzmann’s constant (−228.6 dBW/K/Hz), Ts is the system noise

temperature in dBK, and Bn is the noise bandwidth of the receiver in dBHz.
(dB) Downlink (4)

27
Design of downlinks and uplinks with examples
Uplink Design
 The design of the uplink is easier than the downlink in many cases, since an
accurately specified carrier power must be presented at the satellite transponder and
it is often feasible to use much higher power transmitters at earth stations than can
be used on a satellite
 The cost of transmitters tends to be high compared with the cost of receiving
equipment in satellite communication systems.
 The major growth in satellite communications has been in point-to-multipoint

transmission, as in cable TV distribution and DBS-TV.
 One high power gateway earth station provides service via a DBS-TV satellite to
many low-cost receive-only stations, and the high cost of the transmitting station is
28 only a small part of the total network cost.
Uplink Design
 Earth station transmitter power is set by the power level required at the input to the
transponder
 The link equation is used to determine uplink C / N ratio.
 Let (CNR)up be the specified CNR in the transponder, measured in a noise

bandwidth Bn Hz.
 Uplink CNR be calculated in the bandwidth of the receiver, not the bandwidth of the
transponder.
 The noise power referred to the transponder input is Nxp watts. In dB units:
(5)
29
Uplink Design
 Where Txp is the system noise temperature of the transponder in dBK and Bn is in
units of dBHz.
 The power received at the input to the transponder is Prxp where
(6)
 Where Pt +Gt is the uplink earth station EIRP in dBW, Gr is the satellite antenna gain
in dB in the direction of the uplink earth station and Lp is the path loss in dB.
 The factor Lup accounts for all uplink losses other than path loss. The value of
(CNR)up at the LNA input of the satellite receiver is given by
(7)
30
Uplink Design
 The received power at the transponder input is also given by:
(8)
 With small-diameter earth stations, a higher power earth station transmitter is

required to achieve a similar satellite EIRP.
 This has the disadvantage that the interference level at adjacent satellites rises, since
the small earth station antenna inevitably has a wider beam.
 Thus it is not always possible to trade off transmitter power against uplink antenna
size.
 There are also specifications for transmit station antenna pattern, designed to
minimize interference from adjacent uplinks.
31
Uplink Design
 At frequencies above 10 GHz, for example, 14.6 and 30 GHz, propagation
disturbances in the form of fading in rain cause the received power level at the
satellite to fall.
 This lowers the uplink CNR in the transponder, which lowers the overall (CNR)o
ratio in the earth station receiver when a linear (bent pipe) transponder is used on the
satellite.
 Uplink power control (UPC) can be used to combat uplink rain attenuation
 The transmitting earth station monitors a beacon signal from the satellite, and
watches for reductions in power indicating rain fading on the uplink and downlink.
 Automatic monitoring and control of transmitted uplink power is used in 14 and 17

GHz uplink earth stations to maintain the uplink CNR in the satellite transponder
32 during rain periods.
Uplink Design
 Since the downlink is always at a different frequency from the uplink, a downlink
attenuation of A dB must be scaled to estimate uplink attenuation.
 The scaling factor used is typically (fup/fdown)a where the exponent a is typically
between 2.0 and 2.4.
 For example, an uplink station transmitting at 14.0 GHz to a Ku-band satellite

monitors the satellite beacon at 11.45 GHz.
 The uplink attenuation is therefore given by:
(9)
 Where Aup is the estimated uplink rain attenuation and Adown is the measured downlink rain
attenuation.
 For a value of a = 2.2 and (fup/fdown) = 1.222, the factor (fup/fdown)a is 1.56.
33
Technology
Module 2 Lecture 3
Dr Sanmukh Kaur
34
 To study various propagation effects affecting the satellite link performance.
 Ability to identify causes of attenuation in satellite link due to different propagation

effects.
35
Propagation effects and their impact on satellite
earth links
 There are many phenomena that lead to signal loss on transmission through the
earth’s atmosphere.
 These include:
- Atmospheric absorption (gaseous effects);
- Cloud attenuation (aerosol and ice particle effects);
- Tropospheric scintillation (refractive effects);
- Faraday rotation (an ionospheric effect);
- Ionospheric scintillation (a second ionospheric effect);
- rain attenuation;
- Rain and ice crystal depolarization.
36
Rain attenuation
earth links
 Rain attenuation is by far the most important of these losses for frequencies above
10 GHz, because it can cause the largest attenuation and is usually, therefore, the
limiting factor in satellite link design in Ku-band and at higher frequencies.
 Raindrops absorb and scatter electromagnetic waves.
 In the Ku- and Ka-bands, rain attenuation is almost entirely caused by absorption.
 At Ka-band, there is a small contribution from scattering by large raindrops.
 The various propagation loss mechanisms are illustrated in Fig.1.
37
earth links
38 Fig.1. various propagation loss mechanisms on a typical earth-space path

Rain attenuation
 Signal loss – attenuation – affects all radio systems; those that employ orthogonal
polarizations to transmit two different channels on a common, or partially
overlapping, frequency band may also experience degradations caused by
depolarization.
 There is conversion of energy from the wanted (i.e., the co-polarized) channel into
the unwanted (i.e., the cross-polarized) channel.
 Under ideal conditions, depolarization will not occur.
 When depolarization does occur, it can cause co-channel interference and cross-talk
between dual-polarized satellite links.
 Rain is a primary cause of depolarization.
39
Rain attenuation
 Both attenuation and depolarization come from interactions between the propagating
electromagnetic waves and whatever is in the atmosphere at the time.
 The atmospheric constituents may include free electrons, ions, neutral atoms,
molecules, and hydrometeors (a term that conventionally describes any falling
particle in the atmosphere that contains water: raindrops, snowflakes, sleet, hail, ice-
crystals, graupel, etc.); many of these particles come in a wide variety of sizes.
 Their interaction with radio waves depends strongly on frequency, and effects that
dominate 30 GHz propagation, for example, may be negligible at 4 GHz.
 The converse is also true. With one major exception (ionospheric effects) almost all
propagation effects become more severe as the frequency increases.
40
Technology
Module 2 Lecture 4
Dr Sanmukh Kaur
41
 To understand Analog FM transmission through satellite
 Ability to analyze Analog FM transmission through satellite links
42
Analog FM transmission
 Communications satellites are used to carry telephone, video, and data signals, and
can employ both analog and digital modulation techniques.
 When geostationary earth orbit (GEO) satellites were first used for communications
in the 1960s and 1970s, the signals were mainly analog [For first 20 years].
 The modulation and multiplexing techniques that were used at that time were
analog, adapted from the technology developed for microwave links.
 Frequency modulation (FM) was the modulation of choice and frequency division
multiplexing (FDM) was used to combine hundreds or thousands of telephone
channels onto a single microwave carrier.
43
 Prior to the availability of satellites for video signal distribution , hundred's of

microwave links were needed to deliver television signals throughout the US.
 The lower cost and wide distribution of video signals by satellite led to creation of
many networks and TV program channels which initially were available through
cable TV systems.
 Regional domestic and international satellite systems were developed to exploit the
high capacity and bandwidth that satellites offered.
 In the 1980s, optical fibers came into widespread use, and GEO satellites were no
longer used for telephony within the United States.
44
 The long round trip delay of 500ms in a typical GEO satellite voice link could cause
echoes that were unsettling to many telephone users, so GEO satellite telephone
links were restricted to routes that cannot use optical fibers over the majority of the
route.
 On a terrestrial telephone link, echoes typically occur with a delay of a few

milliseconds and are not noticeable.
 Long distance telephone links using optical fibers are digital, so all telephone signals
sent via optical fiber have to be in digital form.
 This forced telephone signals to be converted to digital form at the telephone

exchange, and rendered all the analog multiplexing methods obsolete.
45
 FDM has disappeared as a way to combine analog telephone signals, replaced by
time division multiplexing (TDM) of digital voice signals.
 There may be parts of the world where the older analog technology is still in use.
 An internet search for FDM/FM/FDMA will provide a multitude of sources that

describe analog communication technology, and many texts on communication
systems cover this technology.
 Analog multiplexing in the form of FDM has virtually disappeared, but frequency
division multiple access, FDMA, remains one of the major ways in which
transponder capacity is shared among users.
 FDMA divides up the frequency band in the transponder into channels which are
allocated to different signals on a fixed or on-demand basis.
46
Analog Versus digital transmission
 Video transmission of signals for cable TV providers used analog FM from mid
1970 through mid 1990s at C and Ku band, using a full transponder per video signal.
 The typical cost of leasing a C band or Ku band transponder was $ 1M per year.
 Once an analog signal is in digital form, it can be transmitted over any digital
communication link, multiplexed with other digital signals, and sent very long
distances without degradation.
 One major advantage of digital transmission systems over analog is that error free
transmission is possible.
47
Analog Versus digital transmission
 Digital signals can be compressed to reduce the bandwidth required to transmit the
signal, an essential feature in mobile telephones and in the transmission of video
signals.
 Digital signals can easily be encrypted to maintain security of the message content,
while effective encryption of analog signals is very difficult.
 Several such digital compressed video signals can fit into one transponder, saving
distribution companies millions of dollars each year.
 In a digital telephone system, error free transmission means that no noise is injected
into the baseband channel, regardless of the transmission distance, so a telephone
call over a distance of 10 000 km has the same quality as a call over a distance of 10
km. This is not the case when analog transmission is used.
48
TV signals
 Two most common transmission standards for video signal transmission are North
American and Japanese 525 line / 60 Hz NTSC system and European 625/50Hz
PAL system.
 The video signal of a monochrome TV transmission carries an analog representation

of the brightness (amount of white light) in the picture along with a series of
horizontal scanning lines .This is called luminance signal
 Along with the luminance signal, synchronization pulses are transmitted so that TV
receiver can recreate the scanning process of camera.
 Later colour information was added to monochrome transmission without degrading

the performance of existing black and white receivers.
49
TV signals
 Colour components of picture are not separately transmitted as it would require
excessive bandwidth.
 The luminance Y is related to the colour voltage levels by
Y = 0.30 R + 0.59 G + 0.11 B
 The luminance signal is transmitted so that monochrome receivers can receive a

color image
 For colour reconstruction , two other linear combinations of R,G & B (I & Q
signals) must be transmitted along with Y so that all color components can be
recovered.
50
TV signals
 The letters I and Q stand for in phase and quadrature components and together carry
the chrominance information about the colour at each point in picture
I = 0.60 R - 0.29 G - 0.32 B

Q = 0.21 R – 0.52 G + 0.31 B
 The I and Q signals modulate a color (or chrominance) subcarrier in such a way that
the amplitude of resulting chrominance signal determines the saturation (degree of
purity) of the colour at a point and the phase of the chrominance signal determines
the hue (perceived shade) of the color.
 From the luminance signal it determines how bright the colour should be. Y = 0.30
R + 0.59 G + 0.11 B
51
TV signals
 In terrestrial broadcasting, Y signal is filtered to occupy the band from 0 to 4.2 MHz,
modulates the video carrier with VSB modulator [Fig.1].
 The upper sideband is transmitted in full, the lower sideband is partially removed.
 The chrominance information is transmitted by color subcarrier at 3.579545 MHz.
 This was chosen to place it at a relatively empty part of the luminance spectrum and
minimize color interference with B & W reception
 The baseband audio signal extends from 50 Hz to 15 KHz.
 It frequency modulates an audio subcarrier and the resulting FM waveform is added

to the video baseband signal.
 In US 6.8 MHz is used as standard audio subcarrier frequency.

52
[Fig.1 (a) Baseband video signal (b) The composite (video plus audio) TV signal as transmitted by
U.S. domestic satellites ]
53
Terrestrial Broadcasting Satellite Transmission
 The audio and video signals are  The baseband video signal (luminance
combined and shifted in frequency to an and chrominance) frequency modulates
appropriate part of VHF and UHF band a video carrier and two stereo audio
for transmission. signals frequency modulate two audio
carrier.
 The radiated signal is a complex

combination of FM (sound), VSB  The details of video modulation
(luminance), and quadrature DSB SC depends upon transponder BW
(chrominance) signals occupying a 6 available.
MHz bandwidth.
54
Technology
Module 2 Lecture 5
Dr Sanmukh Kaur
55
 To analyze the expression for S / N ratio calculation for satellite TV links.
 Ability to analyze S / N ratio consideration for satellite TV links.
 To understand digital baseband signal and be able to distinguish analog and digital
baseband signals.
56
TV signals/N ratio for FM video Transmission
 Baseband S/N ratio for FM signals is given by:
(S/N)U = C / N + 10 log10 (BRF / fmax) + 20 log10 (Δfpk / fmax) + 1.8 +P dB (1)
 Typical values Δfpk (peak deviation)= 10.7 MHz

fmax (max video modulating frequency)=4.2 MHz
 By carson’s rule required transponder BW is:

B = 2 (Δfpk + fmax ) Hz
= 2 (10.75 + 4.2) = 29.9 MHz
 A TV signal from satellite is quite different from broadcast TV signal.
57
 Converters (set top boxes) that allow reception of satellite television transmission on
conventional home TV receiver must demodulate the incoming FM signals , recover
the baseband video and audio channels, and send separate video and audio signals to
TV receivers.
 The S /N ratio in the baseband channel of an analog FM satellite TV receiver is

given by:
(S/N)W = C / N + 10 log10 (BRF / fmax) + 20 log10 (Δfpk / fmax) + 1.8 +P + Q dB (2)
 The baseband S / N ratio is increased by a factor P dB with de-emphasis in the

receiver.
 The value of P depends on the nature of the signal and baseband bandwidth.
 P is different for voice and video signals.

58
 As the FM demodulator has low baseband noise power at low frequencies,

appearance of FM noise on a TV screen is less annoying than white noise.
 The S / N given by Eq. (2) has to be increased by the subjective factor Q to account
for these effects.
59
Digital transmission
 Virtually all signals sent via satellites are now digital.
 Familiar examples are

-data transmissions to and from internet hubs,
- communications between remote terminals and computers
- digital telephony
- TV signals in digital form, such as high definition television (HDTV) and DBS-
TV.
 Digital transmission lends itself naturally to TDM and time division multiple access
(TDMA).
 Thus a digital satellite link can carry a mix of telephone, video, and data signals that
varies with traffic demand.
60
 All digital links are designed in much the same way, using a specific symbol rate,
and specific filters and waveforms that minimize intersymbol interference (ISI).
 A symbol is a pulse of current or voltage.
 In a digital radio link, a symbol is almost always a phase state (BPSK and QPSK) or
a phase and amplitude state (QAM).
 Binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) send
one bit and two bits per symbol as phase states of a radio wave, called a carrier.
 Higher levels carrying more bits per symbol are also used, for example, 8-PSK has
eight phase states and carries three bits per symbol.
61
 A combination of multiple voltage levels and phase states can be employed to carry
a large number of bits per symbol using quadrature amplitude modulation (QAM) or
amplitude phase shift keying (APSK).
 It is important to distinguish between symbols and bits.
 With binary modulations, such as BPSK, the symbol rate and bit rate are the same.
 Symbol rates are given in baud (largely obsolete) or in symbols per second,
abbreviated to sps.
Baseband transmission of digital data signals
 Satellite links always consist of RF signals, which requires that data be modulated
onto a radio frequency carrier for transmission.
62
 In a baseband link, the frequency response of the link is assumed to extend from DC
to an upper limit fmax, where fmax is equal to the bandwidth of the link, B Hz.
 Data is transmitted in the form of polar pulses; in a binary system, the pulses have
amplitudes +V and −V volts, where V can take any value.
 The average number of +V and −V pulses is made equal so that the average DC
voltage on the transmission line is zero.
 Otherwise all circuits that carry this signal must have a frequency response that
extends to DC, and this is difficult to achieve since many communication circuits
contain transformers.
63
 Fig.1 shows some kind of digital baseband signals.
 Thus if Sk (k = 0, 1, M-1) represents M baseband signals each of duration T, then

their collection is called the baseband signal set.
 The energy in the kth signal is denoted by Ek.
 If all of the signals in the set have same energy, the common value is denoted by E.
 For two signals Sk (t) and Sj (t) , their inner product (Sk , Sj) is defined as :
∞
(Sk , Sj) = ‫׬‬−∞ Sk (t) Sj* (t) dt (1)
64
 For orthogonality (Sk , Sj) = 0 k ≠ j

= E k = j
 The signal sets are of two kinds namely orthogonal signal sets and binary antipodal
signal sets.
 A signal set is said to be orthogonal signal set if (Sk , Sj) = 0 for all k ≠ j.
 A binary signal set is antipodal if So (t) = - Si (t) for all t in the interval [0 , T]
 Antipodal signals have equal energy E and their inner product is (So , S1) = -E
65
Fig.1Typical examples of digital baseband signals (a) and (b) Rectangular pulse waveforms
(c) Split phase pulse waveform (d) Sine pulse waveform
66
 The baseband signal sets can be represented in terms of a signal waveform v (t).
 For the signal sets of fig (a) and (b) , the waveform is a rectangular pulse of duration
T.
 Fig (c) is the split phase or Manchester coded pulse.
 Fig (d) is the basic waveform of sine pulse which is one half of a full period of sine
wave.
 There are several binary and M ary baseband signal sets which cannot be described
in terms of a single waveform of duration T.
67

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Amity School of Engg &

 To develop the Link equation of a Satellite at Earth station.

 Consider a transmitting source, in free space, radiating a total power P t watts

 Such a source is called isotropic. At a distance R meters from the hypothetical

 This reduction in efficiency is described by using an effective aperture Ae where :

Fig.2: Calculation of received power by an antenna.

 Path loss LP is given by:

 More generally, Eq. (8) can be written as

Fig.3 Simplified receiver with single frequency conversion.

 The superhet receiver has three main subsystems:

Calculation of System Noise Temperature

Fig 4a Noise model of receiver

Fig.4bNoise model of receiver with a single noise source

Fig.4c Noise model of receiver with a single noise source

 Equation (2) can be rewritten as:

 Ability to analyze and design uplink and downlink power budget .

 The design of any satellite communication is based on two objectives:

 If a satellite link is designed with sufficient margin to overcome a 20 dB rain fade

 Satellite links are typically designed to achieve reliabilities of 99.5–99.99%,

 The time corresponding to 0.01% of a year is 52minutes;

 GEO Ka-band satellite links are currently becoming widespread in aeronautical

 It is usually written in decibel units as

 where k is Boltzmann’s constant (−228.6 dBW/K/Hz), Ts is the system noise

(dB) Downlink (4)

 The major growth in satellite communications has been in point-to-multipoint

 The link equation is used to determine uplink C / N ratio.

 Let (CNR)up be the specified CNR in the transponder, measured in a noise

 The power received at the input to the transponder is Prxp where

 With small-diameter earth stations, a higher power earth station transmitter is

 Automatic monitoring and control of transmitted uplink power is used in 14 and 17

 For example, an uplink station transmitting at 14.0 GHz to a Ku-band satellite

 The uplink attenuation is therefore given by:

 To study various propagation effects affecting the satellite link performance.

 Ability to identify causes of attenuation in satellite link due to different propagation

 Raindrops absorb and scatter electromagnetic waves.

 At Ka-band, there is a small contribution from scattering by large raindrops.

 The various propagation loss mechanisms are illustrated in Fig.1.

38 Fig.1. various propagation loss mechanisms on a typical earth-space path

 Under ideal conditions, depolarization will not occur.

 Rain is a primary cause of depolarization.

 To understand Analog FM transmission through satellite

 Ability to analyze Analog FM transmission through satellite links

 Prior to the availability of satellites for video signal distribution , hundred's of

 On a terrestrial telephone link, echoes typically occur with a delay of a few

 This forced telephone signals to be converted to digital form at the telephone

 An internet search for FDM/FM/FDMA will provide a multitude of sources that

 The video signal of a monochrome TV transmission carries an analog representation

 Later colour information was added to monochrome transmission without degrading

 The luminance Y is related to the colour voltage levels by

Y = 0.30 R + 0.59 G + 0.11 B

 The luminance signal is transmitted so that monochrome receivers can receive a

I = 0.60 R - 0.29 G - 0.32 B

 The chrominance information is transmitted by color subcarrier at 3.579545 MHz.

 The baseband audio signal extends from 50 Hz to 15 KHz.

 It frequency modulates an audio subcarrier and the resulting FM waveform is added

 In US 6.8 MHz is used as standard audio subcarrier frequency.

 The radiated signal is a complex

 To analyze the expression for S / N ratio calculation for satellite TV links.