EEM.scmA
Satellite Communications A
Part 3
Link planning / budgetting
-Professor Barry G Evans-
Autumn2004 © University of Surrey
SatComms A - part 3 - B G Evans
3.1
Link budget & system planning
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SatComms A - part 3 - B G Evans
3.2
Mobile System
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3.3
Performance
• (i) QoS – b.e.r.
– 10-4 if speech
– 10-6 – 10-8 data (extra coding)
• (ii) Availability
– 95%
– Channel conditions
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3.4
Basic Transmission
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3.5
Carrier Transmission Budget
-Antenna GainThe antenna gain is defined as the ratio of the power per unit solid angle received/radiated by the antenna
in a given direction to the power per unit solid angle received/radiated by an isotropic antenna supplied
with the same power.
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3.6
Basic Transmission
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3.7
Basic Transmission
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3.8
Antenna radiation pattern
Antenna radiation pattern = gain variations as a function of the angle 
relative to boresight
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3.9
Transmitted power in a given direction
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3.10
Predicted coverage areas for the
HOTBIRD satellites
(a) Superbeam
(b) Widebeam
(courtesy of EUTELSAT)
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3.11
Effective isotropically radiated power
(EIRP)
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3.12
Exercise (1) - Carrier Transmission
Budget
• Given
– Power fed to antenna: PT = 10W
– Antenna gain (at boresight): GTmax = 40dB
– Distance: R = 36000km (earth to geostationary satellite
• Calculate
– Transmitter EIRP in dB(W)
– Flux density at receiver in dB(W/m2)
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3.13
Down Path
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3.14
GEO - Geometry
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3.15
Earth station from the geostationary orbit
•
•
Satellite
–
Height h above the equator
–
Sub-satellite point, longitude ΦS
Earth station
– Latitude E, longitude ΦE
–
Relative longitude satellite = (ΦE – ΦS) = ΦES
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3.16
Exercise (2) – Carrier Transmission
Budget
• Given
– Uplink frequency = 14GHz
– Eart station
• Power fed to the antenna: PT=100W
• Antenna diameter: D=4 (efficiency =0.6)
• Location: Bercenay (France)
 Latitude = 48º13’07”N
 Longitude = 03º53’13”E
– Satellite
• Receiving antenna gain at boresight: GRmax=40dB
• Location: 7ºE (EUTELSAT 1-F2)
• Calculate
– EIRP of earth station
– Free space loss
– Received power
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3.17
Noise in an Earth Station
G/T Ref
rf
Ta
if
Tf
TD/L
IPA
LNA
TLNA
DEMOD
TIPA
Lo
BASEBAND
QoS
(BER)
DOWN CONV
C/NOD
Ts
– Noise comes from:
•
•
•
•
Pa
Ta= picked up by antenna from outside ( kB=effective noise)
Tf= lossy feeder
TLNA, TIPA= amplifiers in receiver chain
TD/C= down converter
– Refer all noise to a reference plane into the LNA
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SatComms A - part 3 - B G Evans
3.18
Noise in a Payload
G/T Ref
CD
Cu
D/C
C/Nou
eirps
• Noise comes from:
– Antenna received noise –earth + galaxy
– Feeder lossy noise (nb.290K)
– Equipment noise –amps / D/C etc. added in same way as for earth
station.
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3.19
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3.20
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3.21
Noise Characterisation (1)
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3.22
Noise Characterisation (2)
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3.23
Noise contribution of an attenuator
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3.24
Earth-station system G/T
and noise temp.
Ref
Ta Tf TLNA
LdB
LNA
GLNA
TLNA
TIPA
TIPA
TD/C
IPA
D/C
GIPA
g LNA
LD/C
TD/C
1
( 1 )Tf
l
g LNA xg IPA
1
xTa
l
TIPA
T DC
Ts  Ta  (1 -  )Tf  TLNA 

 ...
gLNA gLNA x gIPA
LdB  10log(l), α  1
l
GdB  10log(g)
Gain of antenna at reference  (Ga - L)dB
G
Autumn2004 © University of Surrey
T
 (Ga  L)  10Log(Ts)d B/K
SatComms A - part 3 - B G Evans
3.25
Earth station antenna noise temperature
Examples (clear sky conditions)
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3.26
Exercise (3) - Noise Contribution
Budget
•
•
•
•
Operating frequency = 12 GHz
LNA: TLNA = 150K, GLNA = 50dB
MIXER: TMX = 850K, GMX = -10dB
IF AMP: TIF = 400K, GIF = 30dB
• Calculate
– Receiver effective input noise temperature TR
– Receiver noise figure
Autumn2004 © University of Surrey
SatComms A - part 3 - B G Evans
3.27
Exercise (4) - G/T of C-band earth
station
•
•
•
•
•
•
•
•
•
•
Dish=15m, n=70%
Ta=30K
Tf=290K
Loss f=0.5dB
TLNA=35K
GLNA=30dB
FIPA=3dB
GIPA=20dB
TD/C=1000K
Loss D/C=-10dB
Feeder
LNA
IPA
D/C
if
• Calculate the earth station G/T
– What are the advantages of trading off dish size and LNA
temp.?
Autumn2004 © University of Surrey
SatComms A - part 3 - B G Evans
3.28
Propagation
-Effects to be considered• Radio noise
• Ionospheric effects
– Absorption
– Total electron content effects (group delay, refraction,
polarisation rotation)
– Scintillation
• Tropospheric effects
– Attenuation by rain
– Depolarisation
– Refraction effects
• Shadowing and multipath effects
Autumn2004 © University of Surrey
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3.29
Clear Sky Noise Temperature
• Any ATTENUATION process which involves energy
absorption is associated with THERMAL NOISE
GENERATION from the medium
• Absorption by atmospheric gases is frequency dependent,
hence clear sky noise temperature exhibits similar variations
with frequency
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3.30
Attenuation by atmospheric gases
• See CCIR Rep.719 for a detailed description of practical
techniques of calculation for LAG. The following curve
displays AAG(E) versus frequency; E is the elevation angle.
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3.31
Noise temperature of the sun
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3.32
Ionospheric effects
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3.33
Attenuation due to rain, etc.
•
•
•
•
Mist
Clouds
Snow
Ice
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3.34
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3.35
References for calculation
methodology
• Course notes or chapter 8 of the book
• ITU-R PN 618-3 splant path rain induced
attenuation and depolarisation and scintillatin
(available from lending libraries or ITU, Geneva)
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3.36
Attenuation due to precipitation and clouds
Relevant techniques described in CCIR (see rep.563, 564, 721, 723)
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3.37
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3.38
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3.39
Maps of rainfall contours (1/3)
Contours of RAINFALL RATE
R₀․₀₁ (mm/h) exceeded for
0.01% OF AN AVERAGE YEAR:
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3.40
Maps of rainfall contours (2/3)
Contours of RAINFALL RATE
R₀․₀₁ (mm/h) exceeded for
0.01% OF AN AVERAGE YEAR:
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3.41
Maps of rainfall contours (3/3)
Contours of RAINFALL RATE
R₀․₀₁ (mm/h) exceeded for
0.01% OF AN AVERAGE YEAR:
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3.42
Nomogram for determination of
specific attenuation
 with circular polarization use the arithmetic mean of attenuation with horizontal and
vertical polarization
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3.43
Typical values of rain attenuation
Comments:
30/20 GHz systems face a problem, especially in tropical regions where rainfall rate is
very high during small percentage of time.
Performance objective must be achieved when rain occurs. The link will probably be over
dimensioned during most of the time (margin).
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3.44
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3.45
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3.46
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3.47
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3.48
DEPOLARISATION
• Rain and ice cause this due to shape of
particles
– Need to know shape and orientation of particles
– Linear and circular POLN different
– Circular POLN is worst case
– Can form a model linking depolarisation (XPD)
and attenuation
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3.49
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3.50
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3.51
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3.52
XPD STATISTICS
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3.53
Raininduced XPD circular polarisation
(for 1% worsth month)
CO-POLAR ATTENUATION
dB
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3.54
Other tropospheric effects
• Snow
– Dry snow –ok (little effect)
– Wet snow –as bad as rain
– Problem if snow builds up on antenna
• Atmospheric absorption
– Gas and particle absorption (worse at low
elevation angles)
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SatComms A - part 3 - B G Evans
3.55
Noise Contribution Budget
-Satellite Antenna Noise Temperature-(1)
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3.56
Noise Contribution Budget
-Satellite Antenna Noise Temperature-(2)
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3.57
Influence of Rain
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3.58
Noise
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3.59
Exercise (5.a) - Carrier Transmission
Budget
•
•
•
•
•
Ta=50K, =0.9, Tf=290k
Pointing loss = 0.7dB
Atmospheric loss = 0.3dB
Rain loss = 3dB for 99% lime
Rain temp = 275K
• Calculate the G/T of the earth station under worst weather
conditions
• Calculate the down link C/No
• Calculate the down link C/N if the link bandwidth is 100KHz
• Complete the link budget sheet
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3.60
Exercise (5.b) – Link budget sheet
• Link budget sheet – Downlink
Satellite EIRP
dBW
Pointing loss
dB
Atmospheric loss
dB
Rain loss (99%)
dB
Free space loss
dB
Gain E/S
dB
Downlink carrier
dBW
E/S noise temp.
dB-K
E/S G/T
dB/K
Boltzmann constant
-228.6
dBW/Hz/K
Downlink noise
density (NOD)
dBW/Hz
C/NOD
dB-Hz
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3.61
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3.62
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3.63
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3.64
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3.65
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3.66
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3.67
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3.68
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3.69
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3.70
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3.71
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3.72
DOWNLINK
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3.73
UPLINK
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3.74
Up Path
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3.75
Exercise (6) – Up-link
Cu
•
•
•
•
•
•
•
•
•
•
•
•
Ku-band uplink 14GHz
Dish size=5m, =0.65
Distance to satellite=38,000km
Uplink atmospheric loss=0.3dB
Uplink pointing loss=0.7dB
Uplink rain loss=3dB
Tx e/s w.g. feed loss=3dB
Satellite Rx antenna gain=26dBi (from Tx e/s)
Satellite Tx antenna gain=25dBi (at boresight)
Rx earth station AR=-2dB
Satellite Tpdr gain=120dB
The satellite transponder has a single carrier saturation condition

•
120dB
SAT
eirps
PFDi=-76dBW/m2, eirp sut=50dBW
The transponder’s is operated at 8dB input and 5dB output back off
Calculate
1.
2.
3.
The uplink HPA rating if this has to operate at 6dB back off
The uplink carrier at the satellite Cu
The downlink carrier eirp from the satellite
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3.76
Characteristics of intermodulation
products
• The order of any intermodulation product is defined as ‘(n+m) where the
IMP’s are:
(n f 1  m f 2) where n, m= 1,2,3,…
•
•
When the center frequency of the amplifier is large compared to its bandwidth,
odd-order intermodulation products are the only ones falling within the useful
frequency band
Intermodulation product power decreases with the order of the product. So only
third and fifth order intermodulation products are concerned
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3.77
Link Performance
-Intermodulation noise
Intermodulation products may appear at:
- the output of the transmitting earth station non linear power amplifier
- the output of the satellite repeater
These intermodulation products can interfere with the desired carriers, and hence be considered
as noise called “intermodulation noise”.
With modulated carriers, the intermodulation noise is distributed over the entire frequency band.
Example: Intermodulation noise spectrum for a typical TWT with 10 carriers. (6 central carriers modulated by a
multiplex of 24 telephone channels, two 64 channels carriers and two 132 channels carriers)
Intermodulation products can be considered as filtered white noise with constant spectral
density (No)IM
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3.78
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3.79
Intermodulation
• (nf1  mf2), order = (n+m)
• IMP’s vary (order-1)dB/dB with carrier.
– E.g. 3rd – 2dB/dB
5th – 4dB/dB
• Payloads –linearisers to reduce IMP’s
• Ku-band transponders
– TV
– 3rd order important
• L/S-band transponder –1000’s small mobile
carriers. 5th and 7th important
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3.80
Total Link Operation
(link from earth station to earth station)
1 – LINEAR OPERATION: PT‹(PT)max’ (NO)IM = O
Repeater power gain GS is constant. Satellite transmitter output power
is shared between:
- amplified carriers
- amplified input noise
2 – SATURATION REGION OPERATION:
Available power from satellite repeater is limited.
Output power is shared between:
- amplified carriers
- amplified input noise
- intermodulation products
Power gain value depends on operating point.
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3.81
Total Link Budget
-Non linear operation-
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3.82
Interference
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3.83
Interference Management (1)
• Between Satellite and Terrestrial systems –limit
PFD’s satellites and terrestrial Tx’s
• Radio Reg’s –Appendix S7
• 1st stage
– Calculate coordination contour
– Calculate all Tx’s inside contour
• 2nd stage
–
–
–
–
If needed
Detailed calc’s using all parameters
Site shielding
Energy dispersal etc.
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3.84
Radio regulations
(Appendix S7)
EARTH STATION: MADLEY
SAT: INTELSAT 5
LONGITUDE 3415
RX FREQUENCY: 4.18 GHZ
- CO-ORDINATION CONTOUR
- MODE 1 CONTOUR
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3.85
Interference
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3.86
Interference Management (2)
• Between satellite networks
• Radio Reg’s –Appendix S8
• Analyse noise increase ΔT6% (otherwise go to second
detailed stage)
S2
S1
I
C
E2
E1
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3.87
Total Link Budget
-Non Linear OperationTotal noise at receiver input = uplink retransmitted noise + intermodulation
noise + downlink noise:
1 – Assuming that all incoming carriers at repeater input have SAME
POWER(as with controlled uplink power FDMA for instance):
(C/N0)T-1 = (C/N0)U-1 + (C/N0)D-1 + (C/N0)IM-1+ (C/I0)U/D-1
2 – If incoming carriers at repeater input DO NOT HAVE SAME POWER:
There is a CARRIER SUPPRESSION EFFECT: large power carriers tend
to suppress small power carriers.
Generally speaking:
- for SMALL POWER carriers:
(C/N0)T is smaller than in the case of equal power carriers.
- for LARGE POWER carriers:
(C/N0)T is larger than in the case of equal power carriers.
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3.88
Exercise (7) – Link Performance
SAT
Downlink
interference
Uplink
interference
Uplink path
•
Given
–
–
–
–
–
–
•
Downlink path
Uplink carrier power-to-noise power spectral density:
Downlink carrier power-to-noise power spectral density:
Carrier power-to-intermodulation noise power spectral density:
Uplink carrier power-to-interference power spectral density:
Downlink carrier power-to-interference power spectral density:
Noise equivalent bandwidth of earth station receiver:
(C/No)U=85dB(Hz)
(C/No)D=83dB(Hz)
(C/No)IM=87dB(Hz)
(C/No)I,U=90dB(Hz)
(C/No)I,D=90dB(Hz)
BN=5MHz
Calculate
– Overall link carrier power-to-noise power spectral density:
– Overall link carrier power-to-noise power ratio:
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(C/No)T
(C/N)T
3.89
Total Link Budget
-Non linear operation with interference
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3.90
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3.91
Figure 6.11 Gains and losses in power of signals being relayed by satellite. The signal falls to
about one hundred billion billionth of its strength (10-34) on each of its 25,000-mile journeys
through space. This great loss is balanced by the grains of the antennas and amplifier
Autumn2004 © University of Surrey
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3.92
Setting out Link budgets
Uplink
EIRP
Satellite
C/Nou
C/IM o
C/IU
C/ID
C/ND
Increase EIRP
And Repeat
Sat. Link Performance
C/NTOT
Requirements for QoS
If Not 2-3 dB
C/No.Req
Margin
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=C/NTOT – C/NoReq
SatComms A - part 3 - B G Evans
3.93
Types of Objectives
• SIGNAL QUALITY OBJECTIVES:
In terms of thresholds which must not be exceeded for more than a given
percentage of time.
• SYSTEM AVAILABILITY OBJECTIVES:
Asys = (required time – down time) / required time
Required time = period of time during which the user requires the link to
be in condition to perform a required function
Down time = cumulative time of link interruption within the required time
Interruption is a period in which there is a complete or partial loss of
signal, excessive noise, or a discontinuity or severe distortion of the
signal.
• PROPAGATION TIME:
The overall link propagation time should not overstep a maximum value
depending on the user’s requirement.
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3.94
System Availability
SYSTEM AVAILABILITY ASYS implies that the quality objectives be met
during a given percentage of time (typically between 99 and 99.9%).
This requires the link C/N0 ratio to be larger or equal to a given value for
the considered percentage of time.
C/N0 varies according to:
- propagation effects (mainly influence of rain)
- implementation losses (mainly antenna depointing or equipment failure)
ASYS = ATX Asat Alink ARX
where:
ATX = transmitting earth station availability
Asat = satellite availability
Alink = link availability
ARX = receiving earth station availability
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3.95
Link Availability
RAIN INDUCED attenuation and depolarization can reduce the
C/N0 value, and cause link outage.
A LARGER MARGIN value leads to a HIGHER LINK
AVAILABILITY, as C/N0 will understep the required value during
a shorter time interval.
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3.96
Cost of System Availability
System cost increases rapidly with system availability:
CUSTOMER SHOULD NOT ASK FOR TIGHT SPECIFICATIONS,
UNLESS STRICTLY NEEDED.
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3.97
Digital Transmission Techniques
-System Model-
PERFORMANCE:
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- BIT ERROR RATE
- BANDWIDTH
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3.98
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3.99
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3.100
Time Division Multiplexing
Digital signals are organized in bursts by means of buffers
where bits are stored and then read at a higher clock rate.
Bursts are transmitted sequentially within time slots
according to a time frame structure.
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3.101
Time Division Multiplex Standards
(CCITT,Rec. G702, G732, G733):
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3.102
Data Encryption
DATA ENCRYPTION entails two aspects:
- confidentiality: avoid access to message by an unauthorized party.
- authentication: protection against someone changing the message content.
Two types of encryption techniques:
- stream cipher: each bit of the plain text is combined bit per bit with the keystream,
- block ciphering: the plain text is modified block per block.
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3.103
Scrambling
•
At receiver side CLOCK TIMING for bit detection is extracted from DATA SYMBOL
TRANSITIONS. Long data streams of 0’s and 1’s can result in the loss of data
synchronization.
DIGITAL DATA CSRAMBLING at transmitter side provides a data symbol transition
probability close to 0.5. At receiver side DESCRAMBLING is performed to restore
original data.
•
SCRAMBLING also removes any periodic pattern in the baseband pulse train.
Hence it CANCELS any DISCRETE LINE COMPONENT in the modulated RF
spectrum. This offers better protection against overstepping the permissible level
of radiated power flux density: scrambling is an ENERGY DISPERSAL technique.
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Channel encoding
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Decoding gain
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Digital Speech Interpolation (DSI)
•
A talker has an activity factor which is less than 1. By INSERTING BITS from
another channel INTO PAUSES of a given channel, DSI compresses a number m
of voice channels into a SMALLER number n of satellite channels.
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Performance objectives
•
Quality objectives for telephony (CCIR Rec.522)
DIGITAL TRANSMISSION
–
a)
b)
c)
•
Quality objectives for data transfer (CCIR Rec.614)
–
•
The BIT ERROR RATE (BER) should not exceed:
10-6, 10-minute mean value, for more than 20% of any month
10-4, 1-minute mean value, for more than 0.3% of any month
c) 10-3, 1-second mean value, for more than 0.01% of any year
for 64 kbit/s channels as part of ISDN:
The BIT ERROR RATE (BER) should NOT EXCEED:
a) 10-7, for more than 10% of any month
b) 10-6, for more than 2% of any month
c) 10-3, for more than 0.03% of any month
No standard yet for bit rates in excess of 64 kbit/s. Likely
10-9 to 10-12.
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Noise performance
• Problems
– Additive white Gaussian noise
– Co-channel interference
• Frequency re-use
– Adjacent channel interference
• From other signals
– Intersymbol interference
• Due to band limiting
– Phase noise
• From carrier recovery
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Which modulation?
ASK
FSK
BER
PSK
minimum power from satellite
Eb/No
• Power limited satellite use B/QPSK
• Mobiles need OQPSK/MSK to avoid non linear amp problems
• Bandwidth limited satellite –16 QAM etc.
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Digital transmission techniques
M-PSK modulation
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Carrier-to-noise power ratio at
demodulator input
The noise equivalent bandwidth
BN of their receiver is assumed
to be matched to the modulated
carrier bandwidth B
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BPSK
QPSK
1
+/2
01
11
Vn=AWGN
VR
DECN
VR
0
10
-/2
2 x errors
Bw=1/2 BPSK
Result same
00
Prob(Error) = BER
  SIGNAL AWGN

1
BER  erfc Eb
No
2
BER 


Rs= Rb/2
Rs= Rb
•
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
1
erfc Eb
No
2
QPSK is half bandwidth of BPSK
• PSD in QPSK is 3dB higher
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Theoretical Bit Error Probability (BEP)
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Bit Error Probability (BEP)
Useful values
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Theoretical Bit Error Probability(BEP)
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Carrier & Bit Error Probability (cont’d)
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Demodulation of digital signals
CONCLUSION
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M-PSK modulation
Power spectral density
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Matched filtering
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Bit Rates and Bandwidth
• Example
PCM
coder
Rb
=1/2
FEC coder
Rc
QPSK
MOD
Rs
– What is Rb, Rc and Rs?
– If filtering is Rc, =0.5, what is the bandwidth?
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Spectral efficiency
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Exercise (8) – Digital Transmission
Techniques
satellite transponder
bandwidth B=36MHz
PT=10W
EIRP=40dB(W)
GT=30dB
Free space loss L=200dB
G/T=14dB(K-1)
receiver bandwidth BIF
•
C/No = EIRP x 1/L x G/T x 1/k
Given
– Type of modulation: coherent QPSK (spectral efficiency r = 1.5 bits/s.Hz)
– Received information bit rate: Rb = 36 Mbit/s
– Required BER = 10-5
•
Calculate required value of C/No and bandwidth:
– 1. Without coding
– 2. With coding (code rate  = 3/4)
– Could you use a smaller code rate (for instance 2/3 or 1/2)?
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Power/Bandwidth
trade off and coding
•
•
•
Power and bandwidth limitations are complimentary
A transponder has finite bandwidth BT and hence traffic limit = BT/BC (BC =
channel spacing)
Bandwidth limit case
A transponder has fixed power so can only support ‘n’ channels at a given
QoS (ber)
– Traffic limit  (PTPD-Pc)=10log(n)
•
(Pc=power per channel)
Power limit case
Coding allows trade-off between bandwidth and power to optimise throughput
B  Rb
 
1

 Eb 
 Eb  
Power  



  
 No  nc  No c 
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Exercise (9) – Overall Link Budget
• The attached link budget has been calculated for a 9.6 kb/s
email service for a VSAT into a hub. The modulation used is
BPSK and the coding gives a coding gain of 4dB. The
desired quality of service is a BER of 10-6.
• The hub available has the following parameters:
–
–
–
–
–
–
Antenna diameter
Efficiency
=
Feeder loss
Skynoise
=
LNA temp
Rain temp
=
65%
=
50K
=
=
4m
0.5dB
75K
275K
• Fill in the missing components of the budget.
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Exercise (9) cont’d
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Exercise A – Earth Station
• An INTELSAT-A (4/6 GHz) earth-station is required to transmit two IDR
carriers (eirp = 65 dBW/carrier). The specification of the station is:
– G/T >35 dB/K at 5° elevation
– 2 carrier IDR, intermodulation eirp is not to exceed 10dBW/4kHz.
• A list of major available equipment is shown in Table next page.
• The earth-station waveguide feed loss is 0.5dB on receive and 3dB on
transmit. All components beyond the LNA can be neglected for noise
calculation purposes and all antennas have a 70% efficiency. The output
back-offs of HPAs can be taken as 10dB for multicarrier operation and
the IMP eirp is given by;
• E12 = 2E1 + E2 – 2(GTX – LTX) + D - SF
• Where:
– (GTX – LTX) is the effective atenna gain at the HPA flange.
– D = (-2.PSAT – 28 + 2 x BOo)dBW2.
– SF (Spreading Factor) = 20 dBW/4kHz.
• Calculate the minimum cost earth-station configuration to meet the
specification.
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Exercise A – Earth Station (cont.)
• List of equipment
Equipment
Antenna
13.0 m
15.5 m
18.0 m
Cost (£k)
Noise Temp
30 K
25 K
20 K
HPA
125 W
400 W
700 W
160
200
300
50
60
80
LNA
33 K
55 K
80 K
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6
3
3.133
Exercise B – Payload
•
Figure A shows a 20/30 GHz payload with specification
–
–
–
•
G/T  16.5 dB/K
eirp  50 dBW
C/I3  20 dB
The input power at the antenna receive terminals is –111 dBW. There
is an input feeder loss of 1dB at a temperature of 75K.
i.
ii.
iii.
iv.
Determine the noise specification for the payload.
20 GHz LNAs of gain 10, 13 and 20 dB with noise figure of 3, 4 and 5 dB
respectively are available. Determine the LNA configuration to be used.
Estimate whether the noise specification is achievable.
Describe how you would check the linearity specification.
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