JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN ELECTRONICS AND
COMMUNICATION ENGINEERING
A System Design And An Analysis On Satellite Mobile
Communication Link
1
ARTI J JANSARI , 2 PROF.KUNAL ACHARYA
1
2
Department of Electronics & communication, L.D.Engineering College, Ahmedabad.
Department of Electronics & communication, L.D.Engineering College, Ahmedabad.
artijansari@yahoo.com, acharyakunal@yahoo.com
ABSTRACT : A satellite mobile communication link between user terminal is analyzed based on a simple fundamental equations
by systematic approach in this paper. With the given fundamental design parameter, the important parameters are calculated
step by step and three communication characteristics such as carrier-to-noise density ratio, Energy per bit to noise density ratio,
carrier-to-noise ratio (CNR) at the satellite and gateway station are analyzed. It gives very useful information to the system
engineers for designing and analyzing the overall satellite mobile communication system in the conceptual design phase.
Key word— satellite ,RF link
The product PTGT is called Equivalent Isotropic Radiated
Power (EIRP).It is express in W. The EIRP serves as a single
1. INTRODUCTION
Geostationary Earth Orbit (GEO) have been used to support all
forms of communication via satellite, voice, data, multimedia
services, higher gain, voice conference etc. Geostationary
Earth Orbit satellite is in a circular orbit 35,876km above the
earth’s surface and rotates in the equatorial plane of the earth.
It will therefore rotate at exactly the same angular speed as the
earth. The major advantages of these systems is their
unchanging position with respect to the earth surface, thus no
control overhead is required to track the satellites. For this link
design s band frequency is used between user terminal and
satellite station and C band frequency is used between satellite
station and gateway station. The overall receiver noise
temperatures available today range from as little as about 30 K
to thousands of degrees Kelvin. Power output of the
transponders in differing communication satellite may vary by
an order of magnitude or more. For satellite mobile
application, mesh reflector antenna is used between user
terminal and satellite station. In practical case, it necessary to
consider additional losses due to system design such as
atmospheric loss, polarisation loss, antenna mismatches loss
etc.
parameter ‘figure of merit’ for the transmit portion of the
communication link.
2.1.2 Power Flux Density
The power flux density, usually expressed in Watts/m2, at the
distance r from the transmit antenna with a gain GT, is defined
as the power flux density which is shown in figure 2.1.
Power flux density Φ =
(W/m2)
Æ
2. FUNDAMENTAL DESIGN PARAMETERS
2.1 Transmission basis
2.1.1 Effective Isotropic Radiated Power
The power radiated by an isotropic antenna fed from a radio
frequency source of power PT. In direction where the value of
transmission gain is GT.
EIRP
P T GT
Figure 2.1: power flux density
Where PT, GT and EIRP are the transmit power, transmit
antenna gain, and effective radiated power, all expressed in
dB. Φ is called power flux density.
2.1.3 Saturation flux density
If you transmit an uplink signal with sufficient power to
produce the pfd/sat specified above you will saturate the
transponder. This is applicable only if you are using one
carrier in the transponder. In such a case the input and output
back offs would both be zero. For two carriers an input back
off of 0.5 dB is suggested, with an output back off of about 1.5
dB due to the production of second order intermodulation
products (A+B) which are hopefully absorbed in the satellite
before the output filter. In many cases 3 or more carriers are
transmitted through the transponder and to avoid unacceptable
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JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN ELECTRONICS AND
COMMUNICATION ENGINEERING
intermodulation interference levels, it is necessary to operate
the transponder power backoff.
2.2 Losses
In practical case, it necessary to consider additional losses due
to system design.
a) Losses occurs in atmosphere
In the atmosphere, the attenuation of waves, express by LA, is
during the presence of gaseous component in troposphere,
water and ionosphere. The overall effect on the power of
received signal can be taken into account by replacing LFS,
L
LFS LA
Where L is path loss and LFS is free space loss. LFS is not a loss
in sense of power being absorbed. It accounts for the way
energy spread out as an electromagnetic wave away from a
transmitting source in three dimensional spaces.
b) Losses in transmitting and receiving component
The loss occurs between the transmitter and antenna, denoted
by LFTX. At the output of the transmission amplifier, power PTX
is,
PTX
PT LFTX
Where PT is transmitting power in watts and LFTX is transmitter
feeder loss. The loss LFRX occurs between the antenna and the
receiver, at the input of receiver, signal power P RX is,
PRX
PR/LFRX
Where PR is receiving power in watts and LFRX is Receiver
feeder loss.
c) Imperfect alignment of the antennas
The loss of antenna gain which can be inserted in the form
of a misalignment loss LT on transmission and misalignment
loss in reception. These losses are a function of
misalignment angle of transmission αT and reception αR.
LT
LR
12(αT /θ3dB) 2
12(αR /θ3dB) 2
d) Polarisation Mismatch loss
When the receiving antenna is not oriented with the
polarisation of received wave, the polarisation mismatch loss
occurs. In link with circular polarisation, the transmitted wave
circularly polarised only on the axis of antenna and elliptical
of this axis. Propagation through the atmosphere can also
change circular in to elliptical polarisation. In a linear
polarisation, the wave can be rotate of its plane of polarisation
as it propagates through the atmosphere.
2.3 System Noise Temperature
The four sources of noise in the front-end area are the receiver
front end, the receiver antenna, the connecting elements
between them and noise entering from the free space path. The
receiver antenna, receiver front end, and the connecting
elements between them are the subsystems that must be
designed to minimize the effects of noise on the performance
of the satellite link. Both the ground terminal antenna/receiver
and the satellite antenna/receiver are possible sources of noise
degradation. The received carrier power at the receive antenna
terminals, PR, if is very low (picowatts) then very little noise
introduced into the system at that point is needed to degrade
the performance.
The major contributor of noise at radio frequencies is thermal
noise, caused by the thermal motion of electrons in the devices
of the receiver. The noise introduced by each device in the
system is quantified by the introduction of an equivalent noise
temperature. The equivalent noise temperature, T e, is defined
as the temperature of resistor producing a noise power per unit
bandwidth that is equal to that produced by the device.
The noise power, nN, is defined by the Nyquist formula as
nN
k Te BN watts
Where k
Boltzmann’s Constant = 1.39 × 10−23 Joules/K
−228.6 dBw /K/Hz
Te
equivalent noise temperature in K
BN
noise bandwidth, in Hz
Antenna losses are absorptive losses produced by the
physical structure main reflector, sub reflector, struts, etc.,
which effectively reduce the power level of the radiowave.
Antenna losses are usually specified by an equivalent noise
temperature for the antenna. The antenna loss is usually
included as part of the antenna aperture.
In clear condition ,at the frequencies greater than 2 GHz the
greater contribution is that of the non-ionized region of
atmosphere which being an absorbent medium ,is noise source.
In the absence of meteorological formation the antenna noise
temperature contains contributions due to the sky and
surrounding ground. The antenna noise temperature TA of
receiver can be expressed as
TA
TSKY TGROUND
System noise temperature is
TS
TA /LFRX T0 (1 1/LFRX) TR
2.4 Figure of Merit (G/T ratio)
It is defined as the ratio of receiver antenna gain to the receiver
system noise temperature. Regarding the antenna gain GR and
equivalent input noise temperature TS can be denoted as,
(G/T)
GR − T S
GR − 10 log10 (TS)
Where TS is the system noise temperature. The (G/T) is a
single parameter measure of the performance of the receiver
system, and is analogous to EIRP as the single parameter
measure of performance for the transmitter portion of the link.
(G/T) values cover a wide range in operational satellite
systems, including negative dB values. The lower values are
typically found in satellite receivers (uplinks) with broad beam
antennas where the gain may be lower than the system noise
temperature expressed in dB.
2.5 Link performance parameter
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COMMUNICATION ENGINEERING
2.5.1 Carried-to-noise Ratio
The ratio of average RF carrier power C to the noise power N
in the same bandwidth is called carrier-to-noise ratio. It
express in (C/N). It is the primary parameter of interest for
defining the overall system performance in a communications
system. It can be defined at any point in the link, such as at the
receiver antenna terminals, or at the input to the demodulator.
The (C/N) can be expressed in terms of the EIRP, G/T, and
other link parameters developed earlier. Consider the link with
a transmit power PT, transmit antenna gain GT, and receive
antenna gain GR .In practical case, we define the losses on the
link by two components, the free space path loss.
LFS
(4πR/λ) 2
The received power at the input,
PR
PTGTGR(1/LFSL0)
EIRP
(G/T)
(LFS
Σ other losses)
228.6
BN
Where the EIRP is in dBW, the bandwidth B N is in dBHz, k =
−228.6 dBw/K/Hz.
The (C/N) is the single most important parameter that defines
the performance of a satellite Communications link. The larger
the C/N, the better the link will perform. Some modern
communications systems that employ significant coding can
operate at much lower values. Spread spectrum systems can
operate with negative C/N values and still achieve acceptable
performance. The performance of the link will be degraded in
two ways: if the carrier power, C, is reduced, and/or if the
noise power, Nn, increases. Both factors must be taken into
account when evaluating link performance and system design.
2.5.2 Carrier-to-Noise Density
A related parameter to the carrier-to-noise ratio often used in
link calculations is the carrier to- noise density, or carrier-tonoise density ratio, C/No. The carrier-to-noise density is
defined in terms of noise power density, No, defined by
Equation
N0
The carrier-to-noise density behaves similarly to the carrier-tonoise ratio in terms of system Performance. The larger the
value, the better the performance. The C/No tend to be much
larger in dB value than the C/N because of the large values for
BN that occur for most communications links.
2.5.3 Energy-Per-Bit to Noise Density
For digital communications systems, the bit energy, Eb, is more
useful than carrier power in describing the performance of the
link. The bit energy is related to the carrier power from,
Eb
C Tb
Where C is the carrier power and T b is the bit duration in s.
The energy-per-bit to noise density ratio, Eb/No, is the most
frequently used parameter to describe digital communications
link performance. Eb/ No is related to (C/N0) by
Eb/N0
Tb (C/N0)
(1/Rb) (C/N0)
Where Rb is the bit rate, in bits per second (bps). This relation
allows for a comparison of link performance of both analog
and digital modulation techniques, and various transmission
rates, for the same link system parameters.
2.5.4 Uplink
Satellite link performance evaluation for an uplink includes
additional considerations and parameters. If we represent the
uplink parameters by the subscript U.
Satellite telephone handsets are restricted to transmitter power
level below 1 w because of the risk of EM radiation hazard. In
mobile system the uplink from the satellite telephone is usually
the link with lowest C/N ratio.
Where LU is the sum of other losses on the uplink. Uplink
performance is often specified in terms of a power flux density
requirement at the satellite receiver antenna to produce a
desired satellite output transmit power.
2.5.5 Downlink
+
+ 228.6
Where LD is the sum of other losses on the downlink. When
input backoff is employed for multiple carriers or for linear
operation, a corresponding output backoff must be included in
the link performance equations. The downlink EIRP that is the
EIRP from the satellite, resulting from operation at an output
backoff of BOo is given by
EIRPD M
EIRPDS − BOo
S
Where EIRPD is the downlink EIRP for a single carrier
saturated output. BOo is on linearly related to BOi.
3 COMMUNICATION SATELLITE SYSTEM DESIGN
The RF communication links of communication mobile
satellite systems between two handheld terminal have been
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JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN ELECTRONICS AND
COMMUNICATION ENGINEERING
designed and analyzed using the fundamental parameters and
losses in this section.
Input data of return link are given below.
3.1 Return link
At user terminal
Transmitting Amplifier Power = PT(MAX)
Antenna Gain = GTMAX
Distance = R
Atmospheric Wave Attenuation = LA
At satellite station
Antenna Diameter = D
Antenna Noise Temperature = TA
Absolute Temperature = T0
Noise Figure = NF
Transmitting Amplifier Power = PT(MA
Antenna Diameter = DSL
At gateway station
Antenna Diameter = D
Maximum Pointing Error at Earth Station= αR
Antenna Noise Temperature = TA
Absolute Temperature = T0
Noise Figure = NF
2 watt
3 dBi
40000Km
0.3 dB
12 meter
290 ˚K
290˚K
3 dB
15 Watt
0.7 meter
6 meter
0.1
65˚K
290 ˚K
2.2 dB
Calculation
Power Flux Density=Φ
-157.02
dB(w/m2)
EIRP at user terminal
6.01 dBi
Maximum Receiver Gain at satellite 47.68dBi
station = GR(Max)
System Noise Temperature at satellite 27.62 dB(˚K)
station = T
(G//T) ratio at satellite station
16.05 dB(1/˚K)
Maximum Transmitting Gain at
26.74dBi
satellite station = GT(Max)
EIRP at satellite station
6.01 dBW
Maximum Receiver Gain at Gateway 45.78dBi
station = (GRMAX)Es
System Noise Temperature at Gateway 24.48dB
station = T
Carrier to noise density ratio at Uplink= 57.59dB(Hz)
(C/N0)U
Carrier to noise density ratio at
58.61dB(Hz)
Downlink= (C/N0)D
(C/N0)Total Ratio
55.06 dB(Hz)
Data rate
64 Kbps
(Eb/n0)
7.001dB
Input data of forward link are given below.
3.2 Forward link
At gateway station
Transmitting Amplifier Power = PT(MAX)
Antenna Diameter = D
0.35 watt
6 meter
Distance = R
At satellite station
Antenna Diameter = D
Antenna Noise Temperature = TA
Absolute Temperature = T0
Noise Figure = NF
Transmitting Amplifier Power = Pt(MAX)
Antenna Diameter = DSL
At user terminal
Antenna Diameter = D
Maximum Pointing Error at Earth Station= αR
Antenna Noise Temperature = TA
Absolute Temperature = T0
Noise Figure = NF
40000Km
0.7 meter
290 ˚K
290˚K
3 dB
230 watt
12 meter
0.1 meter
0.1˚
65˚K
290˚K
2.2 dB
Calculation
Power Flux Density=Φ
-118.28
dB(w/m2)
Maximum Gain
49.303 dBi
EIRP at gateway station
43.89dBW
Maximum Receiver Gain at satellite 30.26dBi
station = GR(Max)
System Noise Temperature at satellite 27.62 dB(˚K)
station = T
Maximum Transmitting Gain at
26.74dBi
satellite station = GT(Max)
EIRP at satellite station
43.41 dBW
Maximum Receiver Gain at user 0 dBi`
terminal = (GRMAX)Es
System Noise Temperature at user 24.08 dB(1/˚K)
terminal = T
Carrier to noise density ratio at
70.79 dB(Hz)
Uplink= (C/N0)U
Carrier to noise density ratio at
55.18 dB(Hz)
Downlink= (C/N0)D
(C/N0)Total Ratio
55.06 dB(Hz)
Data rate
64 Kbps
(Eb/n0)
7.004 dB
4 CONCLUSIONS
A satellite RF communication link between user terminal is
analyzed based on a simple fundamental equations by
systematic approach in this paper. In general, the above
procedures are applicable to LEO (Low Earth Orbit), MEO
(Medium Earth Orbit), and GEO satellite systems, and also are
valid in satellite and ground station since the two points which
communicate with each other are symmetrical in the sense of
uplink and down link. The key parameters are operating
frequency (up-link and down-link), transmitter power output,
antenna gain, satellite altitude, receiver noise temperature, and
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JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN ELECTRONICS AND
COMMUNICATION ENGINEERING
system . Other important parameters may be calculated by
combining the key parameters.
It is very informative to estimate the overall mobile satellite
communication systems. However, the more detailed analysis
will be required by taking RF circuits into account.
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