

Conducting a Link BudgetIntroductionLink analysis is the process of calculating the carrier power levels to be transmitted from the Earth Station and the satellite in order to provide the required overall carrier to noise ratio at the receive end of the link. The power levels will depend on the type of service, the coding rate, the Earth Station locations, the satellite’s characteristics, and so on.

The design process will also be concerned with the allocation of sufficient link margin to provide an acceptable propagation availability. Trade-offs between Earth Station costs and satellite utilization costs must be carried out to define the minimum overall system cost. The Earth Station power amplifiers, antenna diameters and low noise receiver characteristics will be optimized to arrive at a minimum cost solution.

Vol 5: Link Analysis

5.3: Conducting a Link Budget



Conducting a Link Budget1. Static Or "Clear Weather" Design Concerns• Thermal noise in the Earth and satellite receivers

• Earth Station antenna characteristics

• Satellite antenna patterns

• Uplink and downlink path losses

• Multicarrier intermodulation noise

• Interference from cross-polarized RF channels

• Interference from adjacent satellite systems

• Interference from adjacent RF channels





Conducting a Link Budget2. Link Margin (Fade Margin) Allocations

• Signal absorption due to rain

• Receiver noise enhancement due to rain

• Earth Station transmitter power level variations with time and temperature

• Earth Station antenna pointing errors

• Satellite antenna pointing errors

• Satellite gain loss with age, requires Earth Station HPA margin for future carrier level increases

(Note: most modern satellites are equipped with gain adjustment pads)





TYPICAL SATELLITE COMMUNICATIONS LINK

SATELLITE

TRANSMIT EARTH STATION RECEIVE EARTH STATION

PTE

GTE

GRS

NOS GS

PTS

GTS

GRE

NOE



Figure 5.3 Typical Satellite Communications Link




Receive System Considerations

Part 1




Receiver System Noise Due To AntennasThe antennas used in satellite communication systems not only intercept the signal energy, they also receive radio frequency noise from a variety of sources.

The mainlobe of an Earth Station antenna is pointing toward "cold" space which has a very low radio noise background.

For antennas operating above a frequency of 1 GHz, the noise source is primarily absorption noise due to oxygen and water vapour in the atmosphere.

The antenna backlobes and some of the sidelobes receive noise radiation from the "warm" Earth which adds to the atmospheric noise.

Part 1: Receive System Considerations

5.3.1.1: Receiver System Noise Due to Antennas

Vol 5: Link Analysis, Sec 3: Conducting a Link Budget



Receiver System Noise Due To Antennas




Figure 5.3.1.1a Sky Noise Temperature Vs. Frequency



AntennaNoiseTemperature[deg K]




Figure 5.3.1.1b Antenna Noise Temperature Vs Elevation Angle

Receiver System Noise Due To Antennas




5.3.1.2: Rain Effect Reminder


Rain Effects, AttenuationAs we have seen, when rain occurs along the propagation path, the resultant link performance degradation can be reliably estimated.

However, due to the inherent inaccuracy in rainfall prediction, only statistical predictions can be made of the effect on the design.

Rain attenuation depends on carrier frequency, rain rate, elevation angle and the length of the path that is within the rain zone.

The required rain margin allocation can be calculated with computer programs using various prediction models. A detailed discussion of propagation effects and rainfall modeling was given in Section 5.2.






Figure 5.3.1.2 Rain Effect, Canadian Locations






Rain Effects, NoiseIn addition to attenuating the radio signal, rain also degrades the system noise temperature of the receive Earth Station. The net result is a reduction in the effective station G/T.

This factor is included automatically in the Telesat’s CKLINK and other link budgeting computer programs, but the additional noise temperature can also be estimated manually for a given rain attenuation.

Rain Attenuation (dB)130 K System 300 K System

0.5 0.9 0.41.0 1.5 0.72.0 2.5 1.24.0 3.5 1.96.0 4.1 2.2

Increase in System Noise Temperature (dB)



Sun TransitsA special case of antenna noise reception occurs during a sun transit. The mainlobe of the antenna is pointing directly at the sun which has a noise temperature in the order of 100,000 K. This high level of noise can dominate the receiver and usually leads to an outage.

This effect was also dealt with in the section on propagation.


5.3.1.3: Sun Transit Effect Reminder




Dust StormsDust storms are associated with the dry, windy seasons in arid and semi-arid parts of the world. In these parts of the world, depending on historical and trend data with respect to the frequency, duration, and magnitude of dust storms, it may be considered prudent to allocate margins for this event.

Airborne dust attenuates microwave energy passing though it by means of diffusion, diffraction, scattering and depolarization. As always with attenuation, an increase in system noise and decrease in G/T will also result.

The amount of attenuation will depend on the frequency of operation, the polarization, the vertical extent of the airborne dust, the density of airborne dust, particulate size, and the moisture content of the particles.


5.3.1.4: Dust Storm




Dust StormsStudies have estimated that the attenuation from dust storms could reach 1.83 dB/km, depending on the factors listed above.

Work done on this subject has resulted in some agreement on the applicability of this formula for P, the amount of attenuation, in dB/km, caused by airborne dust:


5.3.1.4: Dust Storm


2223189

ic

i

i KKKa

VP

This formula relates visibility (Vi), probably the best way to estimates a dust storm’s intensity and magnitude, to microwave attenuation through the optical power density attenuation constant a. The K’s a dielectric constants.



Receiver System - Total Noise CalculationThe noise contribution of the total receiver system can now be calculated. Consider the following model:

Where

Ta is the antenna noise temperature.

T1 is the noise temperature of the LNA.

G is the gain of the LNA.

f is the noise figure of the remaining receiver equipment.


5.3.1.5: Receiver System - Total Noise Calculation


RECEIVER

LNALOSS

GL f

Ta Tl

ANTENNA

Figure 5.3.1.5 Receiver System



Receiver System - Total Noise CalculationUsing the input of the Low Noise Amplifier (LNA) as a reference point, the total system noise temperature is calculated as follows:

ExampleConsider the following typical specifications for a C-Band satellite Earth Station:

Ta = 35 KLoss = 0.5 dB (L = 1.12)T1 = 80 K ; Gain = 50 dB (G = 100,000)F = 20 dB (f = 100)

Gf

LL

La

sys)1()1( 0

10






Receiver System - Total Noise CalculationPlugging the values into the formula we get:




000,100)99(2908012.1

)112.1(29012.1

35 sys

= 31 + 31 + 80 + 0.3 142 K



Receiver System - Figure of MeritReceiver systems for satellite and terrestrial radio stations are often specified in terms of their gain to temperature ratio, or receive figure of merit. This ratio results in a single number defining the system’s receive capability.

This specification is easy to use in design work as will be demonstrated later. The reference point for G/T calculation is usually the input to the LNA, but it is important to realize that the value of G/T is independent of the reference point actually used.

Considering our model:


5.3.1.6: Receiver System Figure of Merit


RECEIVER

LNALOSS

GL f

ANTENNA

Ga = 45 dB

= 0.5 dB

TSYS= 142 K Figure 5.3.1.5 Receiver System



Receiver System - Figure of MeritG/T = Ga - L - 10 log (Tsys)

= 45 - 0.5 - 21.5 = 23 dB/K

The noise temperature and figure of merit for the satellite receiver are calculated in the same way as those of the Earth Station.

A special consideration for the satellite is the antenna noise temperature. Unlike Earth Station antennas that are looking into "cold" space, the satellite antenna which is designed for coverage of a portion of the Earth, is looking only at the "warm" Earth.






Receiver System Figure of MeritAs viewed from space, the Earth has a noise temperature of about 290 k and this is a major factor in setting the G/T of a satellite. The following are typical values for Telesat satellites:

SATELLITE ANIK C ANIK D

Frequency Band (GHz) 14/12 6/4

Receive Antenna Gain (dBi) 36 33

Receive Losses (dB) 0.5 0.5

Receiver Noise Figure (dB) 5.3 4

Satellite G/T 3.5 1.7

The satellite G/T is specified by the manufacturer and does not have to be calculated as part of the link analysis.







5.3.1.7: Antenna Equations


Antenna EquationsThe flux density, or power per unit area at a distance d from an isotropic radiator is:

dBW/m2

Where PT is the power into the antenna.

For a non-isotropic radiation, the transmit antenna gain is given by:

24 dP

22

222 4444

DDAAG e



Antenna EquationsTherefore the flux density is increased by the antenna gain in the direction of interest. A 55% efficient antenna of D meters at f GHz has gain:

G = 17.8 + 20 log (D) + 20 log (f) dBi


5.3.1.7: Antenna Equations





The Radio LinkEquation

Part 2




Sec 3: Conducting a Link Budget

5.3.2: The Radio Link Equation


The Radio Link Equation

Consider the simple model shown above in which a signal is transmitted from an antenna, propagates through free space, and is received by another antenna.

P A T H L O S S

PT

GT GR

C

Figure 5.3.2 Radio Link Equation



The Radio Link EquationThe radiated flux density, or power per unit area, at a distance d from the transmitter is

dBW/m2

Where PT is the power into the antenna

and GT is the antenna gain, with respect to isotropic gain, in

the direction of the receive antenna.

24 dGP









The Radio Link EquationAs we have seen in a previous section, the product of transmit power and antenna gain is called the "Equivalent Isotropically Radiated Power" and is a figure of merit of the transmitting station. We can therefore write:

dBW/m2

The received carrier power collected by the receiving antenna having an effective aperture area Ae is given by:

dBW

24 dEIRP

)(4 2 ee A

dEIRPAC



The Radio Link EquationRecall that the receive antenna gain is given in terms of its effective aperture by

Therefore we can write the received power as

dBW

Where FSL is the “Free Space Loss”,

)(42 eR AG

RRRR G

FSLEIRPGdEIRPG

dEIRPG

dEIRPC

222

2

4444

24

d






The Radio Link EquationNote once again that this FSL term is a function of frequency and is not just the inverse square law energy spreading loss. This form is very convenient for use in link analysis. Since the total path is not in free space, but passes through the atmosphere, a loss term for atmospheric absorption must be added. The equation now becomes:

dBW

The actual level of the carrier received is not critical since the receiver has gain to restore the signal to a workable level.

LG

FSLEIRPC R






The Radio Link EquationThe ratio of carrier to noise power density is the significant measure of the capability of the system to pass information from the transmitter to the receiver. This ratio can be written as:

dB-Hz

This ratio is expressed in Decibel terms using the following notation:

dB-Hz

or C/NoC/No = EIRP - FSL - L + G/T= EIRP - FSL - L + G/Tsyssys + 228.6 + 228.6 dB-Hz

sys

R

kLG

FSLEIRPNC

1/ 0

)log(10log101log10/ 0 kGLFSL

EIRPNCsys

R






The Radio Link EquationIn the previous Basic Link EquationBasic Link Equation:

EIRP, is the transmitter EIRP in dBW

FSL, is the path free space loss in Decibels = 20 log (4 d/ ) dB

L, is the atmospheric loss in Decibels

G/Tsys, is the receiver Figure of Merit,dB/K

10 log (k) is the Boltzmann’s Constant in Decibel terms = 228.6 dBW/K/Hz

In general, from now on, the symbols used will refer to the Decibel equivalents of the terms.






The Radio Link EquationAnother very useful equation is that expressing the flux density at the receiver in terms of the free space loss term.

Where G1 is the gain of a 1 m2 antenna.

This gain term is an engineering convenience, remaining constant for any particular frequency. Together with the free space loss term, which is used in the link analysis, it enables the flux density at the receiver to be easily calculated.

1222

4)/4(4

GFSLEIRP

dEIRP

dEIRP






The Radio Link EquationThis is most commonly written in decibel terms as follows where the atmospheric absorption loss has been included:

= EIRP - FSL - L + G1

Thus we can also write

C/N0 = - G1 + G/Tsys + 228.6 dB-Hz







Satellite LinkCalculations

Part 3





5.3.3: Satellite Link Calculations


S A T E L L IT E

U P L IN K D O W N L IN K

Satellite Link Calculations

The overall satellite link consists of two basic parts: the uplink effects and the downlink effects. In addition to the thermal noise, there are a number of interference terms to be included. For the moment, these will be ignored.

Figure 5.3.3 Satellite Link



Satellite Link CalculationsThe satellite amplifies the received signal (along with the noise and interferences), performs a frequency translation and re-transmits some amount of power back down to the receiving Earth Station.

The frequency translation will be ignored since it does not affect the carrier to noise power density ratio. The satellite will be treated, for now, simply as a device with some gain.

Although the TWT amplifier is not linear, it is possible to easily calculate the output power for any particular level of input power.

We will consider the uplink first.


5.3.3: Satellite Link Calculations




5.3.3.1.1 The Uplink EquationThe uplink equation for transmissions to the satellite may now be written by directly substituting the appropriate values into the basic link equation:

C/N0 = EIRPES - FSLUP - LABS + G/TSAT + 228.6 dB-Hz

The G/T of the satellite can be found using the SFD pattern on the following page. The SFD and G/T are related by a constant which is provided by the satellite operator. As a result, operators only need to publish one receive pattern and a constant instead of two receive patterns.

Part 3: Satellite Link Calculations

5.3.3.1: The Uplink




5.3.3.1.2 The Uplink Power Flux Density EquationThe next step is to find the PFD at the satellite using the equation:

PFD = EIRPES - FSLUP - LABS + G1 dBW/m2

Once again, remember that the G1 term is the gain of a 1 meter antenna.


5.3.3.1: The Uplink




5.3.3.2.1 Power Flux Density to Input Back-OffThe relationship between the satellite input power flux density and the input back-off is done using the saturated flux density pattern such as the one on Slide 37. These patterns show the amount of energy density required at the satellite from a given location on Earth in order to saturate the amplifier. Finding the carrier input back-off is done by comparing the SFD for a given direction to the energy actually received.

IBO = SFD - PFD

5.3.3.2.2 Output Back-OffThe Output Back-Off (OBO) is found by referring to the appropriate satellite TWT amplifier AM/AM curve, much like the one on the next slide. The input and output powers are usually specified in terms of their backoff from the single saturating carrier levels.


5.3.3.2: At the Satellite




INPUT POWER, dB RELATIVE TO SINGLECARRIER SATURATING POWER

100-10-20-30-20

-10

0

OU

TPU

T PO

WER

, dB

REL

ATI

VE T

O

SIN

GLE

CA

RR

IER

SA

TUR

ATE

D O

UTP

UT

AM/AM TRANSFERCHARACTERISTIC

OBO

IBO




Figure 5.3.3.2a Carrier Saturating Power



5.3.3.2.3 Satellite Carrier EIRPThe pattern of the satellite transmit antenna is needed in order to find the satellite carrier EIRP. These patterns, like the one in the next page, show the EIRP contours for the case when the amplifier is saturated. As a result the carrier EIRP is:

EIRPCXR = EIRPSAT - OBO




Figure 5.3.3.2.3 Typical Telesat ANIK E EIRP Pattern



The Downlink EquationThe downlink portion of the link calculation is then obtained by again substituting the appropriate values into the basic link equation:

C/N0 = EIRPCXR - FSLDN - LABS + G/TES + 228.6

Also, as before, the PFD at the Earth Station antenna is:

PFD = EIRPCXR - FSLDN - LABS + G1 dBW/m2


5.3.3.3: The Downlink Equation




Overall System C/No, Uplink and Downlink CombinedThe analysis is completed by appropriately combining the two carrier to noise power density ratios. For a given carrier passing through the satellite, the satellite can be modeled as a noiseless device with gain and equivalent input noise power density.

For this model, consider the downlink losses to be included in the satellite gain term. The carrier level, CD , at the receiving Earth Station is then just the carrier level at the satellite input, CU , multiplied by the satellite gain, GS. Since the uplink noise power density will also appear at the receiving Earth Station multiplied by this gain, we may write the following equations:

The downlink carrier level is: CD = CU GS

The total noise at the receive station is: NT = ND + NU GS


5.3.3.4: Overall System C/No, Uplink and Downlink Combined




Overall System C/No, Uplink and Downlink CombinedCombining these equations for carrier power and noise we get:

This relationship can be generalized to include as many noise and interference terms as are required to complete the link calculation.




D

D

U

U

D

D

SU

SU

D

DSUT

CN

CN

CN

GCGN

CNGN

CN

111

U

U

D

D

T NC

NC

NC

11111

X

X

X

X

U

U

D

D

T IC

NC

NC

NC

NC



Overall System C/No, Uplink and Downlink CombinedBy recognizing the above relationship, it is not necessary to labouriously carry all the signal and noise terms through all the gains and losses in the system and do a final carrier to noise calculation.

This is especially important because the satellite non-linearity would make the numerous calculations required for trade-off analyses very time consuming.







Satellite and TerrestrialLink Comparison

Part 4




Satellite and Terrestrial Link Comparison It is interesting to compare a typical terrestrial microwave hop with a satellite downlink to see where the major differences are.

For simplicity, assume a saturated signal from the satellite compared to a 50 km terrestrial link, both operating at 4 GHz.

The objective is to obtain the same C/N ratio for both systems, taking into account all major link factors.

The satellite uplink will be ignored since it is not a major contributor to the link performance in this example.


5.3.4: Satellite and Terrestrial Link Comparison




Satellite and Terrestrial Link ComparisonThe basic link equation applies to both systems:

C/No = EIRP - FSL - L - FADE + G/T - 228.6 dB-Hz

DOWNLINK

38,000 KM PATH

50 KM PATH




Figure 5.3.4 Satellite and Terrestrial Link Comparison



Satellite and Terrestrial Link ComparisonSatellite Terrestrial

Link Parameter System SystemTransmit Power (dBW) 9.0 5.0Transmit Gain (dBi) 30.0 35.0 EIRP (dBW) 39.0 40.0Free Space Loss (dB) 196.0 138.5Atmos. Abs. (dB) -- 2.5Propagation Fading (dB) 1.0 35.01 m2 Gain (4 GHz) (dBi) 33.5 33.5Flux Density (dBW/m2 ) -124.5 -102.5Receive Ant. Gain (dBi) 48.0 (15 ft ant.) 35.0 (6 ft ant.)Receiver Temp. (dB/K) 20.5 29.5Receiver G/T (dB/K) 27.5 5.5Boltzmann's Const. (dB/K/Hz) 228.6 228.6C/No (dB-Hz) 98.1 98.1C/N (36 MHz bandwidth) (dB) 22.5 22.5









Satellite and Terrestrial Link ComparisonNotes• The satellite used is Telesat's Anik E, typical of C-Band

domestic satellites.• The terrestrial system is assumed to use 1.8 m antennas on

each end of the link. Satellite receive uses a 4.5 m antenna.• The terrestrial transmitter is a 5 watt TWT or solid state

amplifier with 2 dB of cable loss.• The 35 dB fade margin for the terrestrial link is typical; larger

margins may be required on some links.• The receive Earth Station noise temperature is composed of an

80K LNA, 25K of antenna noise, and 7K from a 0.1 dB loss between the antenna and the LNA.

• The terrestrial receive noise consists of a 600K LNA and 300K of antenna noise.




Review of FactorsAffecting Link Performance

Part 5





5.3.5: Review of Factors Affecting Link Performance


Review of Factors Affecting Link PerformanceWe have now identified the basic parameters of a link analysis. Before going into detailed examples, we will review typical values and their effect on the link performance. This review will cover the following:

• Required C/No and C/N (System Bandwidths)

• Earth Station Antenna

• Earth Station LNA and G/T

• Earth Station HPA and EIRP

• Satellite Antenna Patterns

• Satellite EIRP and G/T

• Path FSL and Atmospheric Absorption



Part 5: Review of Factors Affecting Link Performance

5.3.5.1: Required C/No


Required C/NoThe objective of link analysis is to design a system that meets the specified performance threshold carrier to noise density ratio.

This C/No value is selected based on the type of voice, data, audio or video service to be carried, the modulation technique used, the performance of the modems and associated forward error correction codes, and so on.

A link or fade margin must be added to the static link design to ensure that the threshold will be exceeded for the required percentage of the time.



Earth Station Antenna DesignsThe antenna is the major Earth Station design parameter, since it affects the receive and transmit capabilities, and the sidelobe gains used in interference calculations.

The antenna parameters are given by the manufacturer. In the tradeoff analyses, the antenna diameter is varied by selecting an available antenna size and substituting its gain values into the appropriate equations.

For cost tradeoff studies, the cost of the mounting structure and foundation civil works must be included in the analysis. For large antennas, these costs are significant.

In addition, some applications may have size limitations imposed by the site location, or by a roof mounting requirement.


5.3.5.2: Earth Station Antenna Designs




Earth Station Antenna DesignsTypical antenna sizes at C-Band range from 2.4 to 16 meters in diameter, with adjacent satellite interference being one limitation of the smaller sizes.

At Ku-Band, the satellites usually have greater gain and the antenna sizes are smaller, ranging from 1.2 to 8 meters in diameter. Some specialized systems use antennas as small as 0.5 meters.

There are three main styles of antenna design based on the type of feed structure.

• Gregorian• Focal Fed Antennas• Offset Fed Antennas

These designs have been covered in Part 4.5.2 of this course.


5.3.5.2: Earth Station Antenna Designs





5.3.5.3: Earth Station LNA and G/T


Earth Station LNA and G/TIn combination with the antenna gain, the LNA noise temperature is the major factor that determines the receive performance of an Earth Station.

Today, virtually every LNA is a solid state device and the costs have come down to the equivalent of a few hundred dollars.

Typical noise temperatures at C-Band are in the range of 35 to 85 K, and at Ku-Band the range is 85 to 250 K. The cost and reliability differences between these amplifiers are small.




5.3.5.4: Earth Station HPA and EIRP


Earth Station HPA and EIRPOne of the results of the link analysis is the required EIRP from the Earth Station. In combination with the antenna chosen, HPA size is selected to meet the system transmit power requirement, including any margin allocated for satellite gain reductions with age.

Often a tradeoff of antenna size, LNA cost and HPA cost is done to find the optimum combination for a transmit/receive station.

Where transmit power requirements are low enough, a solid state HPA is desirable because of its high reliability. If power requirements preclude the use of an SSPA, then TWT amplifiers up to 600 Watts and Klystron amplifiers up to 3 kilowatts are available in both bands.




5.3.5.5: Satellite Antenna Patterns, EIRP and G/T


Satellite Antenna Patterns, EIRP and G/TSatellite performance data is available in terms of three antenna patterns:

• Saturating Flux Density (SFD)

• Satellite G/T (may be combined with SFD pattern)

• Downlink EIRP

The characteristics of these patterns are fixed primarily by the required coverage area, which determines the size of the antenna on board the satellite.

The primary design limitation is with respect to the locations of the Earth Stations within the coverage pattern. For design purposes, the values are read from the published patterns and substituted into the appropriate equations.





Satellite Antenna Patterns, EIRP and G/TA secondary consideration is the satellite antenna pointing error that occurs with small motions of the satellite in its orbit. Locations near the edge of coverage will experience larger gain changes than those near the center of the coverage area. This must be included in final calculations.

The satellite G/T is not usually a significant factor in system design, except possibly for single saturating carrier systems.

The SFD is important because it affects, dB for dB, the uplink EIRP required and therefore the selection of antenna and HPA sizes.






Satellite Antenna Patterns, EIRP and G/TMany satellites have an adjustable SFD setting which may be optimized in a tradeoff of reduced Earth Station HPA sizes against increased uplink interference sensitivity and increased thermal noise.

For systems with a large number of transmit stations, this could result in considerable cost savings by reducing all the HPA ratings.

The satellite EIRP is significant since it affects downlink performance and therefore the Earth Station antenna gain and LNA temperature design specifications.

The type of satellite access is important since it will determine how much of the saturated EIRP is available to be used in the design.





5.3.5.6: Path FSL and Atmospheric Absorption

Path FSL and Atmospheric AbsorptionThe path free space loss depends on the operating frequency, increasing with an increase in frequency.

FSL also depends on the actual distance between the transmitter and the receiver and therefore on the station locations in the satellite pattern.

Remember that FSL is an engineering term used to make radio link designs easier in combination with transmit and receive antenna gains. It should not be confused with the inverse square law for spreading loss.





5.3.5.6: Path FSL and Atmospheric Absorption

Path FSL and Atmospheric AbsorptionThe mean atmospheric absorption of the signal due to water vapour and oxygen depends on location as well, since the elevation angle to the satellite determines the amount of atmosphere along the path.

Another location sensitive variable is the local climate. While this primarily affects the rain margin, the moisture content also affects the mean absorption factor. Typical absorption values are less than 0.5 dB for C- or Ku-Band systems with elevation angles greater than 5 degrees.





Static Link Design

Part 6





5.3.6: Static Link Design


Static Link DesignWe will now work some examples of satellite links using typical values for the various parameters and examining their effects on the overall system performance.

The idea behind “static” link design is that all system parameters are considered static, or unchanging, so that there is no need to build margins into the links.

To begin with, a single carrier example will be considered. Next, a multi-carrier, FDMA channel example will be worked. Finally, an exercise will be included, permitting the student to work out a link budget for themselves.



Part 6: Static “Clear Weather” Link Calculations

5.3.6.1: Single Carrier

Single CarrierFirst, a single carrier example.

Satellite CharacteristicsFrequency Band 6/4 GHz

SFD -82 dBW/m2

G/T -2 dB/K

Saturated EIRP 36 dBW

FSL (6/4 GHz) 199.5/196 dB

Receive Earth Station CharacteristicsReceive Gain 45 dBi

LNA Noise Temp 80 K







Single CarrierTransmit Earth Station

Assume EIRP is given as 60 dBW.

The objective of this example is to calculate the total link C/No ignoring interferences and link margin. Assume the mean absorption is 0.3 dB.

First, calculate the uplink C/No. Recall:

C/No = EIRPES - FSLUP - LABS + G/TSAT + 228.6 dB-Hz

= 60 - 199.5 - 0.3 - 2 + 228.6 dB-Hz

= 86.8 dB-Hz



Single CarrierThe input backoff is given by:

IBO = SFD - PFD

= SFD - EIRPES + FSLUP + LABS - G1

= -82 - 60 + 199.5 + 0.3 - 37

= 20.8 dB

The output backoff is found by referring to a table or curve for single carrier AM/AM performance of the satellite TWT.

From the sample curve presented on slide 66, for an IBO of 20.8, the output backoff will be approximately 14 dB.

The satellite downlink EIRP is then:

EIRP = 36 - 14 = 22 dBW






Single CarrierThe downlink C/No calculation requires the G/T of the Earth Station to be calculated. The total receiver noise, Tsys, can be estimated as 80 K for the LNA plus, say, 35 K for the antenna. Assume the LNA is right at the antenna flange so that there is no receive loss.

ThereforeG/T = Ga - 10 Log (Tsys)

= 45 - 10 log (115) = 24.4 dB/K

From the downlink equation,

C/No = EIRPSAT - FSLDN - LABS + G/TES + 228.6 dB-Hz

= 22 - 196 - 0.3 + 24.4 + 228.6 dB-Hz

= 78.7 dB-Hz






Single CarrierThe total link C/No then becomes:

Recalling that we cannot add dB to dB directly, we first convert to linear values:

= 2.09 x 10-9 + 1.35 x 10-8

= 1.558 x 10-8

Total C/No is therefore equal to linear (1.559 x 10-8)-1 or, when converted back to dB, 78.1 dB-Hz for the total link.




111

U

U

D

D

T NC

NC

NC

17171

10413.710863.47

TNC



INPUT POWER, dB RELATIVE TO SINGLECARRIER SATURATING POWER

100-10-20-30-20

-10

0

OU

TPU

T PO

WER

, dB

REL

ATI

VE T

O

SIN

GLE

CA

RR

IER

SA

TUR

ATE

D O

UTP

UT

SINGLECARRIER

MULTIPLECARRIERS

OBO

IBO


5.3.6.2: Multicarrier Input/Output Back-Off


Figure 5.3.6.2 Carrier Saturating Power






Multicarrier Input/Output Back-OffTo calculate the performance of an individual carrier, we introduce the idea of a power fraction, F, that defines the fraction or portion of the operating point power that the individual carrier represents. For example, if the RF channel has 100 equal carriers, then:

F = -20 dB

The individual carrier has the same fraction of the output power as it has of the input power. We have then:

IBO RF channel input backoff

OBO RF channel output backoff

IBOi Individual Carrier input backoff

OBOi Individual Carrier output backoff





Multicarrier Input/Output Back-OffNote that all backoffs are defined with respect to the single saturating carrier point on the AM/AM curve. The input backoff is the difference between the SFD and the actual flux density of the signal being considered.

The fraction of the input power is therefore expressed as:

F = IBO - IBOi dB

And the output backoff is:

OBOi = OBO - F dB






Multicarrier Input/Output Back-OffExample

Satellite IBO = 10 dB

Satellite OBO = 5.1 dB

Suppose the calculated IBOi = 30 dB, then:

F = 10 - 30 = -20 dB

And the carrier output backoff is:

OBOi = 5.1 - (-20)

= 25.1 dB





5.3.6.3: Multicarrier FDMA Channel Example

Multicarrier FDMA Channel ExampleNow consider an example with an FDMA channel. Assume the satellite RF channel is loaded with a large number of carriers such that the total input power is 10 dB below the saturation point. That is, IBO = 10 dB.

Objective: Using the same satellite and Earth Station data as in the previous example, calculate the total link C/No including the effects of the multicarrier intermodulation noise.

Note: To accommodate the multicarrier IBO, change the uplink EIRP from 60 dBW to 50 dBW.

First find the uplink C/No:

C/No = 50 - 199.5 - 0.3 - 2 + 228.6

= 76.8 dB-Hz






Multicarrier FDMA Channel ExampleThe individual carrier flux density is:

= 50 - 199.5 - 0.3 + 37 = -112.8 dBW/m2

And the individual carrier backoff is:

IBOi = -82 - (-112.8) = 30.8 dB

Since the IBO = 10 dB, the power fraction is:

F = 10 - 30.8 = -20.8 dB

The individual carrier output backoff is therefore:

OBOi = OBO - F

= 5.1 - (-20.8) = 25.9 dB

where the OBO value is taken from a table or multicarrier AM/AM transfer characteristic.






Multicarrier FDMA Channel ExampleThe downlink EIRP is then:

= 36 - 25.9 = 10.1 dBW

And the downlink C/No = 10.1 - 196 - 0.3 + 24.4 + 228.6

= 66.8 dB-Hz

The value of saturated output carrier to intermodulation noise power density can be obtained from a table or curve such as the one on the following slide as:

CSAT/Io= 96 dB-Hz

Therefore: C/Io = CSAT/Io - OBOi

= 96 - 25.9 = 70.1 dB-Hz






Multicarrier FDMA Channel ExampleFDMA SATELLITE CHANNEL INTERMODULATION

(Based On A Typical TWTA Characteristics)Saturated Carrier

Input Backoff Output Backoff To Intermodulation Noise IBO (dB) OBO (dB) Density (dB-Hz) 14 8.1 102 13 7.2 100.5 12 6.5 99 11 5.8 97.5 10 5.1 96 9 4.5 94.5 8 3.9 93 7 3.4 91.5 6 2.9 90 5 2.5 89 4 2.3 88 3 2.1 86.5






Multicarrier FDMA Channel ExampleSummarizing:

Uplink C/No 76.8 dB-Hz

Downlink C/No 66.8 dB-Hz

Intermod C/Io 70.1 dB-Hz

Net link C/No 64.8 dB-Hz

Notice that the intermodulation noise is a significant contributor to the overall link performance.

Objective: Find the required G/T at the receive Earth Station to give an overall link C/No of 50 dB-Hz.

Solution: Since the uplink C/No and the C/Io will be unchanged, calculate the required downlink C/No which will give an overall C/No of 50 dB-Hz.






Multicarrier FDMA Channel ExampleDownlink C/No = 50.1 dB-Hz.

The required G/T is then calculated from the downlink equation

50.1 = 10.1 - 196 - 0.3 + G/T + 228.6

Thus G/T = 7.7 dB/K

Notice that for this design, the downlink thermal noise dominates the performance.

Objective: Keeping the original G/T of 24.4 dB/K, calculate the required new uplink EIRP to give an overall link C/No of 50 dB-Hz.

At first, it may appear that it would be necessary to work with some complex equations involving the uplink EIRP as a parameter and solve for the EIRP value.






Multicarrier FDMA Channel ExampleWhile this could be done, an easier way is to estimate the uplink EIRP and do a calculation of the performance. Since the total link C/No is proportional to the EIRP, the final value can be easily obtained from the first estimate.

For an uplink EIRP of 50 dBW we obtained:




Net Link C/No 64.8 dB-Hz






Multicarrier FDMA Channel ExampleSince the link performance scales with uplink EIRP, reducing the EIRP by 14.8 dB to 35.2 dBW will reduce the overall C/No to 50 dB-Hz. This approach is a general one which makes the analysis more straightforward and easier to calculate.

As long as the overall result scales linearly with some parameter, it does not matter whether or not the initial "guess" is close to the final answer. A simple correction at the end will yield the desired result without working with large awkward equations.

This is an important technique that will be used throughout this course.





Optimization of SatelliteOperating Point

Part 7





5.3.7: Optimization of Satellite Operating Point


Optimization of Satellite Operating PointFor multicarrier RF channel operation (FDMA) the satellite operating point must be selected before the link design can be finalized. This is determined by the composite input power to the satellite amplifier, or the total input backoff, IBO.

If the individual IBOi for each carrier is reduced by increasing the uplink EIRP, then the uplink C/No will be increased proportionally. This will also decrease the output OBOi and increase the downlink EIRP which increases the downlink C/No.

The decreases in IBOi also decrease the overall IBO and OBO. As this occurs, the intermodulation noise increases, or the saturated C/Io decreases and each individual carrier C/Io decreases.





Optimization of Satellite Operating PointTherefore, as the carrier levels are increased and the transponder operating point changes, the carrier to noise ratios increase. However, the carrier to intermodulation noise decreases and a tradeoff occurs.

Therefore, there is an optimum selection of IBO that will maximize the overall C/No.







UPLINK C/No

C/Io

TOTAL C/No

CARRIERTO NOISE

POWERDENSITYRATIO

(dB-Hz)

SATELLITE IBO (dB)0-10-20

DOWNLINK C/No

Figure 5.3.7a Satellite Operating Point






Optimization of Satellite Operating PointThe optimum is usually very broad and other considerations such as uplink EIRP requirements may dictate moving away from the optimum point. For a given carrier overall C/No, the number of carriers, or the RF channel capacity, varies with IBO as illustrated below. The maximum capacity is usually found by trying several IBO values and iterating toward the optimum operating point.

0

RFCHANNELCAPACITY

-10-20SATELLITE IBO (dB)

Figure 5.3.7b Satellite Operating Point






Optimization of Satellite Operating PointConsider the previous system data with the Earth Station G/T of 24.4 dB/k. Could the satellite operating point (IBO, OBO) be changed to provide a higher overall C/No by changing the uplink EIRP of all the carriers? What is the optimum operating point?

Try 8 dB IBOIf the carrier levels are all increased by 2 dB, then the satellite IBO will change from 10 dB to 8 dB. The corresponding OBO becomes 3.9 dB and the saturated C/Io becomes 93 dB‑Hz.

Since the uplink EIRP is 2 dB higher, the uplink C/No is increased by 2 dB to 78.8 dB-Hz, and the IBOi is decreased 2 dB to 28.8 dB.

F = 8 - 28.8 = -20.8 dB (same as before)

OBOi = 3.9 + 20.8 = 24.7 dB (1.2 dB less)





Optimization of Satellite Operating PointDownlink EIRP is increased 1.2 dB to 11.3 dBW.

The downlink C/No is increased 1.2 dB to 68.0 dB-Hz.

The C/Io = 93 - 24.7 = 68.3 dB-Hz.

Using this approach, the following table summarizes the overall C/No for several values of satellite IBO.






Optimization of Satellite Operating PointUplink Sat'd Uplink Down TotalEIRP IBO OBO C/ Io C/No C/No C/ Io C/No(dBW) (dB) (dB) (dB-Hz) (dB-Hz) (dB-Hz) (dB-Hz) (dB-Hz)

48 12 6.5 99 74.8 65.4 71.7 64.149 11 5.8 97.5 75.8 66.1 70.9 64.550 10 5.1 96 76.8 66.8 70.1 64.851 9 4.5 94.5 77.8 67.4 69.2 65.052 8 3.9 93 78.8 68.0 68.3 65.054 6 2.9 90 80.8 69.0 66.3 64.356 4 2.3 88 82.8 69.6 64.9 63.6


The optimum operating point occurs around 9 dB IBO. Notice that the optimum range is very broad with little change in the overall C/No as IBO varies from 8 dB to 10 dB.


Slide Number 90Rev -, July 2001 Vol 5: Link Analysis



Optimization of Satellite Operating PointSuppose that the Earth Station G/T were much lower, say, 19 dB/k. What would be the new optimum satellite operating point? Modifying the downlink C/No in the previous table, we have:

Uplink Sat'd Uplink Down TotalEIRP IBO OBO C/ Io C/No C/No C/ Io C/No(dBW) (dB) (dB) (dB-Hz) (dB-Hz) (dB-Hz) (dB-Hz) (dB-Hz)

50 10 5.1 96 76.8 61.4 70.1 60.752 8 3.9 93 78.8 62.6 68.3 61.554 6 2.9 90 80.8 63.6 66.3 61.756 4 2.3 88 82.8 64.2 64.9 61.5

The optimum operating point now occurs around 6 dB IBO.


Slide Number 91Rev -, July 2001 Vol 5: Link Analysis



Optimization of Satellite Operating PointAs shown above, the link performance is dominated by the downlink thermal noise component; consequently, more intermodulation noise can be tolerated before it begins to dominate the performance.

In general, for an FDMA RF channel, the lower the receive stations' G/T, the smaller the optimum IBO.

When the Earth Station characteristics are all known in advance, it is possible to optimize the IBO of the RF channel as shown in the previous examples. This can be done even for a mix of Earth Station types and a mix of different carrier types.





Optimization of Satellite Operating PointHowever, the final RF channel traffic configuration may not be known in advance. It is then necessary to make an estimate of the optimum operating point. This fixes the level of intermodulation noise that will be present when the RF channel is loaded to capacity, and allows link designs to be carried out.

The optimum is usually fairly broad as a function of IBO, so the selection is not too critical. In Telesat's experience, typical optimum operating points for FDMA RF transponders based on transponder type would be:

TWT SSPA Linearized TWT

IBO 8 dB 3.5 dB 5.5 dB

OBO 4 dB 3.0 dB 3.5 dB





RF Utilization: RF vsPower Limited Links

Part 8





5.3.8: RF Utilization: Bandwidth vs Power Limited Links


RF Utilization: Bandwidth vs. Power Limited LinksIn an RF channel that has multiple carriers sharing the available power and bandwidth, we can define the RF utilization of each carrier in terms of the percentage of the available power it uses, and in terms of the percentage of the available bandwidth that it occupies. The final value of RF utilization is usually defined as the larger of the percentage of power or bandwidth.

ExampleFrom the previous example, the power fraction is:

F = -20.8 dB

Therefore the power utilization is:

= 10-20.8/10 x 100 = 0.83 %

The bandwidth of the carrier and of the RF channel were not specified, but assume the RF channel BW is 36 MHz and the assigned carrier bandwidth is 100 kHz.





RF Utilization: Bandwidth vs. Power Limited Links

The bandwidth utilization is

Therefore the RF utilization is power limited at 0.83 %.

In general, for a system with several carriers operating in an FDMA RF channel, the system utilization is calculated as follows:

Power Utilization:

%28.0100103610100

6

3

xxx

Output At Satellitexwer Carrier PoTotal Usable

erCarrier Pow % 100






RF Utilization: Bandwidth vs. Power Limited LinksBandwidth Utilization:

Transponder Utilization:The larger of the percent of usable carrier power or the percent of of usable bandwidth is considered to be the Transponder Utilization figure for that carrier.

%100Bandwidth UsableBandwidthCarrier x





Useable RF ChannelPower

Part 9





5.3.9: Usable RF Channel Power


Usable RF Channel PowerWhen only one carrier occupies an RF channel, the full saturated output power of the channel is available to that carrier. When two or more carriers share an RF channel, the total usable power is less than the saturated value, as shown by the TWT AM/AM characteristic.

For FDMA RF channels, there is an optimum RF channel operating point that results in approximately only one third of the total saturated output power being available to share among the carriers. Telesat typically operates Ku-Band FDMA RF transponder with an IBO of 8 dB and a corresponding OBO of 4 dB.





Usable RF Channel PowerTelesat also operates some 54 MHz Anik E RF transponders with two equal FM TV carriers. In this arrangement, each TV carrier has an IBOi of 8 dB, and an OBOi of 5.2 dB. Thus, the total power used is 2.2 dB below the saturated output power.

The system is not operated at the two carrier saturation point because of the cross-modulation between the carriers due to satellite AM/PM, and because the level of the intermodulation products falling into adjacent RF channels would become excessive.

Thus the actual usable power for a system is one of the factors to be determined by a performance analysis.






Usable RF Channel PowerWhen a single carrier occupies an RF channel, it can normally use the total available bandwidth. Thus a 60 Mbps TDMA carrier will occupy essentially the full 36 MHz of a C-Band satellite RF channel.

For FDMA RF channels that carry low power carriers, there may be portions of the RF channel where interferences are too high for a carrier to meet its performance objectives.

Referring back to the sections on interference, it can be seen that portions of the RF channel may be made unusable by high levels of interference from adjacent satellite TV carriers, TV carriers on cross-polarized RF channels, or from adjacent RF channel interference.






Usable RF Channel PowerThe exact interference environment is difficult to estimate.

Telesat has carried out detailed studies of its interference environment and based on typical system designs has derived a set of interference allocations to use both for FDMA RF channels and for RF channels that may carry large carriers, such as a TV signal.

From this work it has been estimated that a 36 MHz C-Band satellite RF channel will have about 28 MHz of usable bandwidth when occupied by FDMA carriers, and that a 54 MHz Ku-Band RF channel will have about 44 MHz of usable bandwidth for FDMA operation.

Now that analog TV is disappearing, there will be less likelihood of high level interference and the useful bandwidth figures are now more like 32 MHz for C-Band and 24 MHz for Ku-Band.





Interference Allocations

Part 10





5.3.10: Interference Allocations

Interference AllocationsThis portion of the course will deal with various interference signals generated within the satellite system and from outside sources.

The methods of estimating the interference levels for these signals will be derived, and examples will be provided from operating systems. The analysis will cover the following types of interference:

Adjacent Satellite System Interference. Adjacent RF Channel Interference. Earth Station Uplink Intermodulation Noise. Cross-polarized RF Channel Interference Interference From FMTV Into FDMA Terrestrial Microwave System Interference




Part 10: Interference Allocations

5.3.10.1: Adjacent Satellite System Interference

Adjacent Satellite System InterferenceInterference from other satellite systems arises on the uplink from the sidelobes of the transmitting Earth Stations. Interference occurs on the downlink into the receive Earth Station sidelobes from other satellites in the geostationary orbit that have similar coverage patterns on the earth.

The accurate calculation of interference levels requires knowledge of the following system characteristics:

• Earth Station antenna sidelobes

• Antenna coverage patterns of the adjacent satellites

• Uplink and downlink carrier levels in the other systems

• The carrier frequencies and the types of modulation used

• The sensitivity of one carrier type to interference from another type







AD JAC E NTS ATELLITE

AD J AC ENTS ATELLITE

O PER ATIN GS ATELLITE

U PLIN KIN TER FE R EN C E

U PLINKIN TERFEREN CE

D O W N LINKINTERFERENCE DO W N LIN K

IN TER FER EN C E

O PER ATIN GE AR TH STATION

Figure 5.3.10.1a Adjacent Satellite System Interface






Adjacent System Interference CalculationsThe next few pages will illustrate the interference calculation process with several simple examples.

For simplicity, it is assumed that the satellite uplink and downlink characteristics are identical for both the operating satellite and the adjacent interfering satellites (that is, the saturating flux density and saturated EIRP are the same). It is also assume that the transmit and receive sidelobes of the antennas follow the latest ITU Recommendation 580 values given by:

G () = 29 - 25 Log10 () dBi

Where G () is the sidelobe gain of the antenna and is the off-axis angle in degrees measured from the antenna boresight.





Adjacent System Interference CalculationsMany existing antennas meet the older CCIR recommendation:

G () = 32 - 25 Log10 () dBi

If that is the case, interference allocations must be calculated using this sidelobe specification.

ADJACENT SYSTEM INTERFERENCE EXAMPLES

The next several pages present some simplified sample calculations for adjacent satellite interference to illustrate the calculation process. The following examples will be covered:

• Uplink interference between TV carriers

• Uplink interference from a TDMA system

• Downlink interference from TV carriers

• Downlink interference from TDMAVol 5: Link Analysis, Sec 3: Conducting a Link Budget





Adjacent System Interference CalculationsUplink Interference - TV carriers: Consider the adjacent satellite interference between systems transmitting TV carriers. The wanted signal uplink EIRP toward the operating satellite is given by:

EIRP = P + G dBWWhere:

P dBW is the power into the antenna and

G dBi is the boresight gain of the antenna

The interfering uplink EIRP from each adjacent system toward the operating satellite is given by:

EIRP = P + {29 - 25 Log ()} dBW






Adjacent System Interference CalculationsAssuming the same antenna size for the operating and adjacent system Earth Stations, the ratio of wanted to unwanted signals is:

C/I = P + G - P - {29 - 25 Log ()} dB

= G - 29 + 25 Log () dB

If there is interference from a similar adjacent system on both sides, the ratio becomes:

C/I = G - 29 + 25 Log () - 3 dB

= G - 32 + 25 Log () dB






Adjacent System Interference CalculationsAssume the satellite spacing is 2 degrees and that the uplinks are at 6 GHz transmitted from 7.3 meter antennas. The boresight gain is about 51.5 dBi. For two adjacent systems the C/I becomes:

C/I = 51.5 - 32 + 25 log (2)

= 51.5 - 32 + 7.5 = 27 dB.

Since a typical "clear weather" operating carrier to noise ratio for FM television signals may be in the order of 13 dB, the effect of this interference will be very small (0.2 dB).

Uplink Interference - from TDMA: As another example of adjacent satellite interference, assume that the interference comes from wideband saturating carriers occupying 30 MHz of bandwidth (60 Mbps TDMA).






Adjacent System Interference CalculationsAssuming that the transmit antennas are 7.3 meters in diameter, we know from the previous calculation that the interference power at the input to the desired satellite will be 27 dB below saturation. The interference noise power density, Io, will be:

Io = 27 + 10 Log (30 x 106 ) = 101.8 dB/Hz

below the saturating input power.

Another way to express this is to say that:

Csat/Io = 101.8 dB/Hz

Detailed values for uplink adjacent satellite interference allocations will be reviewed in a later section of the course.






Adjacent System Interference CalculationsDownlink Interference - TV carriers: Consider the interference that occurs on the satellite downlink. For systems of the same configuration all using saturated carriers, the ratio of carrier to interference power at the receive Earth Station is again a function of the ratio of the boresight receive gain to the sidelobe receive gain. For two interfering systems, each at a 2-degree spacing, this becomes:

C/I = G - {29 - 25 Log (2)} - 3 dB

Assume that the receive antennas are 3.7 meters in diameter, having a typical receive gain of 41.5 dBi. Therefore,

C/I = 41.5 - 29 + 7.5 - 3 = 17 dB.






Adjacent System Interference CalculationsFor an overall clear weather C/N of 13 dB, this level of interference would degrade the system by 1.5 dB. This method of estimating carrier to interference ratios involving TV carriers is appropriate since both are TV signals.

However, the interference density from FM TV carriers into FDMA RF channels is so high that a bandwidth of several MHz must usually be left vacant near the TV carrier frequency. This will be covered in more detail later.

Downlink Interference - from TDMA: Following on from the previous interference example, since the TDMA carriers are assumed to be operating at saturation, the ratio of saturated output power to total interference power is:

Csat/I = 17 dB






Adjacent System Interference CalculationsAssuming that the TDMA power is uniformly spread over 30 MHz, we have:

Csat/Io = 17 + 10 Log (30 x 106) = 91.8 dB-Hz

In general, the interference will not be of the same type from each adjacent satellite system, and interference may arise from more than one system on each side. This situation will require a detailed calculation of the net interference by adding up the contributions from each system.

The trend toward reduced satellite spacing and the use of small Earth Station antennas has increased the effects of adjacent system interference.

The values used by Telesat for the specific Canadian interference environment will be shown as examples in a later section of this course.





5.3.10.2: Adjacent RF Channel Interference

Adjacent RF Channel InterferenceInterference from adjacent RF channels is caused mainly by the following types of signals:

Large digital carriers such as full channel TDMA Multiple carriers across the RF channel

Large Digital Carriers: Carriers such as TDMA, which occupy the total RF channel bandwidth, are usually operated with the RF channel near saturation.

Since these filtered carriers have some small amplitude modulation, the AM/PM effects of the satellite amplifier cause the sidebands to be regenerated at the TWT output.

Although these sidebands are filtered by the satellite output multiplexer, they still spread into the ends of adjacent RF channels.






Adjacent RF Channel Interference


Figure 5.3.10.2a Wideband Digital Energy Spreading







SPECTRUM SPREADING45 MSPS PSK SIGNAL

1801501209060300-30-60-90-120-150-180-150

-140

-130

-120

-110

-100

-90

-80

-70

FREQUENCY OFFSET FROM CENTER (MHZ)

Pow

er S

pect

ral D

ensi

ty (d

Bc/

Hz)

O DB OPBO

1 DB OPBO

2 DB OPBO

3 DB OPBO

4 DB OPBO

Figure 5.3.10.2b Spectrum Spreading





Adjacent RF Channel InterferenceSpectrum SpreadingThe spectral spreading caused by the Earth Station HPA is subject to Intelsat specifications for Earth Stations accessing Intelsat satellites. For example, Intelsat specifies that the spectral sidelobes of digital carriers must be at least 26 dB down from the main carrier’s spectral power.

As another example, Intelsat specifies that the uplink out-of-band emission limits for the Intelsat V 120 Mbps TDMA system must not exceed an EIRP density of 23 dBW/4 kHz.

The measured performance of typical HPAs shows that the spectral spreading specifications can usually be met by operating the amplifier with a 3-dB output backoff.






Adjacent RF Channel InterferenceMultiple Carrier RF ChannelsSome RF channels may be operated with multiple carriers, such as FDMA systems, or with two TV carriers in one RF channel. The intermodulation products generated in the satellite by these carriers are spread over a bandwidth of about three times the bandwidth occupied by the carriers (considering only third order intermodulation products).

Although these interferences are filtered by the satellite output multiplexer, which follows the TWT amplifier, considerable energy may still be transmitted into the frequency bands at the edges of adjacent RF channels.








Figure 5.3.10.2c Multiple Carrier Intermodulation and 2 Carrier Television Intermodulation





Adjacent RF Channel InterferenceThe next two figures illustrate typical adjacent satellite interferences generated by operating the RF channel with more than one carrier. Telesat’s computer program IMSHI generated these plots.

The first shows the modulated intermodulation noise power density spectrum for two FM modulated television carriers in one 54 MHz RF channel. The satellite-input power of each carrier is 8 dB below the saturating value, and the rms deviation of each carrier is 6 MHz.

The effects of the satellite output multiplexer filtering are not included here.






Adjacent RF Channel InterferenceThe second figure shows the intermodulation noise power density spectrum for an FDMA RF channel loaded to 9.5 dB below input saturation.

For illustrative purposes, assigning 15 FM carriers uniformly across the 36 MHz RF channel bandwidth made this plot. Each carrier has an rms deviation of 630 kHz.

Because the interference density decreases toward the edges of the RF channel, when two FDMA RF channels are adjacent, the sum of their intermodulation noises is approximately uniform.

In this instance, the effects of the adjacent RF channel are normally covered by the channel's own intermodulation allocation, which is based on the peak center of channel value.








Figure 5.3.10.2d 2TV Carrier Intermodulation Spectrum







Figure 5.3.10.2e FDMA Intermodulation Spectrum




5.3.10.3: Earth Station Uplink Intermodulation Noise

Earth Station Uplink Intermodulation NoiseSimilar to the satellite amplifier, the Earth Station amplifiers are not linear, and they also generate intermodulation products when operated in a multicarrier mode. The effect here is potentially much worse, since the Earth Station amplifier output is often not restricted by a channel filter.

Since the cost of transmit power is lower on the Earth, these amplifiers are operated with larger output backoffs than those on the satellite in order to reduce the level of the intermodulation products.

A typical value of output backoff is 7 dB, which will yield a two-carrier C/I ratio of about 25 dB. This is a reasonable compromise between the cost of the amplifier and the level of intermodulation products generated.






Earth Station Uplink Intermodulation NoiseThe actual spectrum of the interference is complex to calculate and is best estimated with a computer, but the analysis is essentially the same as that carried out for a satellite amplifier.

An allocation for this uplink interference must be made for any system using multiple carriers in the Earth Station amplifiers.

Even if a particular link uses only single carriers in the amplifiers, other Earth Stations sharing the RF channel in an FDMA system may cause uplink intermodulation noise to fall on the carriers.

Therefore, it is recommended to make an allocation for this interference into all carriers in FDMA RF channels.






Earth Station Uplink Intermodulation NoiseIntelsat provides a number of specifications for the permitted level of out-of-band intermodulation products transmitted from an HPA.

These EIRP densities range from 12 dBW/4 kHz at Ku-Band to 23.4 dBW/4 kHz at C-Band depending upon the satellite in use.

These allocations are normally not required for single carrier RF channels, such as television systems.





5.3.10.4: Cross-Polarized RF Channel Interference

Cross-Polarized RF Channel InterferenceThe bandwidth available for satellite use at a specific orbital location is a limited resource. Most current satellites increase the available bandwidth through frequency re-use by means of orthogonal polarized RF channels.

North American satellites use linear polarization, with half of the channels transmitting in the vertical polarization, and the other half in the horizontal polarization. Other satellites may use left and right circular polarizations.

In general, the satellite re-transmits a signal on the opposite polarization to that on which it was received.

The atmosphere can affect the orthogonal relationship of the two polarizations resulting in some cross talk between RF channels.






Cross-Polarized RF Channel InterferenceNonspherical water droplets cause depolarization, and the level of this effect depends on the rainfall rate, the droplet size, the raindrop orientation, and the frequency of transmission.

Circularly polarized signals are somewhat more sensitive to atmospheric depolarization, but the effects are negligible at frequencies below 10 GHz. C-Band systems can therefore ignore the effects of the atmosphere on polarization isolation.

The antennas used on the satellite and at the Earth Stations should be able to meet cross-polarization isolation specifications of about 35 dB.

A typical cross-polarization isolation of better than 30 dB can usually be maintained on an uplink or downlink including the effects of both the Earth Station and the satellite.






Cross-Polarized RF Channel InterferenceCare must be taken to maintain proper alignment of the Earth Station feeds to meet this level of performance.

The RF channel frequencies of the two polarizations are often offset by some amount in order to minimize the effects of interference from high level signals into the opposite polarization (at C-Band, this is usually half a channel, or 20 MHz).

The spectral densities of the different types of traffic must be included in any interference analysis, and in general it is preferable to assign similar types of carriers on RF channels of opposite polarization.







Cross-Polarized RF Channel Interference

Figure 5.3.10.4a Cross Polarization RF Channel Interference






Cross-Polarized RF Channel InterferenceCross-polarized Interference CalculationThe following pages show some simple examples that will illustrate the procedure for estimating the levels of interference between cross-polarized RF channels.

The examples are as follows:

• Uplink interference from an FDMA RF channel

• Uplink interference from a TDMA RF channel

• Uplink C/I for a TV carrier due to FDMA or TDMA on the cross-polarized RF channel





Cross-Polarized RF Channel InterferenceCross-polarized Interference Examples

Uplink Interference From FDMA Assume that cross-polarized interference occurs on the uplink from an FDMA RF channel on a C-Band satellite. If the FDMA channel is fully loaded, the input backoff will be about 9 dB, and we will assume that the uplink carrier energy is uniformly spread over the 36 MHz bandwidth.

Based on a net uplink cross-polarization isolation of 30 dB, the ratio of saturating input power to cross-polarized interference noise power density in the opposite polarized RF channel is:

Csat/Io = 0 - {-9 - 30 - 10 Log (36 x 106)} dB-Hz= 9 + 30 + 75.6 dB-Hz= 114.6 dB-Hz.






Cross-Polarized RF Channel InterferenceUplink Interference From TDMA As another example, consider the uplink cross-polarized interference from a wideband digital signal such as a TDMA carrier. Assume the TDMA carrier operates the RF channel at saturation, and that its energy is uniformly spread over 30 MHz of bandwidth.

If the net uplink cross-polarization isolation is 30 dB, then as in the previous example, the ratio of saturating input power to cross-polarized interference noise power density in the opposite polarized RF channel is:

Csat/Io = 0 - {0 - 30 - 10 Log (30 x 106)} dB-Hz= 30 + 74.8 dB-Hz= 104.8 dB-Hz.






Cross-Polarized RF Channel InterferenceUplink Interference Into A TV Carrier: Consider the effect of the cross-polarized interference on a TV carrier. The TV signal will typically operate the RF channel at saturation (input backoff 0 dB) and the TV channel receivers have a typical RF bandwidth of 25 MHz.

For the FDMA interference:

C/I = 114.6 - 10 Log (25 x 106) = 114.6 - 74.0 = 40.6 dB

For the TDMA interference:

C/I = 104.8 - 10 Log (25 x 106) = 104.8 - 74.0 = 30.8 dB





5.3.10.5: Interference From FM TV Into FDMA

Interference From FM TV Into FDMAIn most cases, the interference noise power can be treated in the same way as thermal noise and added, on a power basis, with other noise and interference terms.

Interference from FM modulated TV carriers into narrow band carriers (such as SCPC voice or data carriers) is a special case.

Because of the time-varying nature of the TV signal, much of the RF carrier energy can be instantaneously concentrated in a very narrow bandwidth. This results in interference power densities that greatly exceed the rms values derived by conventional analysis.

The figure on the next page illustrates the power distribution of a typical video carrier for various percentages of the time.






Interference From FM TV Into FDMA


Figure 5.3.10.5a Pow

er Density D

istribution of an FM TV

Carrier





Interference From FM TV Into FDMAThe effect of this type of interference on narrow-band carriers can only be determined by measurement, and the results are specific to the type of equipment used.

Telesat has carried out a number of measurements on the effects of FM TV carrier interference into QPSK carriers. In these tests, the degradation in bit error rate was measured and the equivalent interference noise power density that would produce the same degradation was calculated.

By doing measurements at various frequency offsets from the TV carrier, an equivalent interference noise power density spectrum was estimated for the TV carrier.






Interference From FM TV Into FDMAThe figure on the following page shows the results of Telesat’s tests. The masks were derived from the 85% NTSC FM video histogram, which was found to offer the closest BER performance estimate to the measured BER performance.

ITU-R Report 867 provides details of Telesat's FMTV masks and those of other organizations.

Telesat uses these masks to estimate the interference effects of TV carriers into narrow band carriers. The area a few MHz on either side of the TV center frequency (more than just the energy dispersion bandwidth) must normally be avoided due to the high interference power density.

Similar work using PSK carriers with data rates up to 1.544 Mbps, including the effects of forward error correction coding, have also been reported.







Interference From FM TV Into FDMA

Figure 5.3.10.5b Equivalent TV Interference Power

Spectrum




5.3.10.6: Terrestrial Microwave System Interference

Terrestrial Microwave System InterferenceFixed satellite systems currently operate in the following frequency bands:

North America Saudi Arabia

Uplink 5.925 - 6.425 GHz 5.925 - 6.665 GHz

Downlink 3.700 - 4.200 GHz 3.400 - 4.200 GHz

Uplink 14.00 - 14.5 GHz 14.00 - 14.50 GHz

Downlink 10.95 - 11.2 GHz 10.95 - 11.20 GHz

11.45 - 11.7 GHz 11.45 - 11.70 GHz

11.70 - 12.2 GHz 12.20 - 12.75 GHz






Terrestrial Microwave System InterferenceIn Canada, the Ku-Band frequencies are dedicated to satellite transmissions and there is no mutual interference problem with terrestrial systems.

However, the C-Band is shared with terrestrial microwave systems, as it is in Saudi Arabia, and therefore all Earth Station or microwave system installations must be made with appropriate allowance for interference as follows:

• 6 GHz Earth Stations into terrestrial stations.• 4 GHz terrestrial stations into Earth Stations.

Interference ObjectiveA typical approach to handling terrestrial interference into a satellite Earth Station is to define an acceptable interference level or C/I ratio and ensure that the station is located such that this criterion is met.






Terrestrial Microwave System InterferenceTelesat usually uses a C/I ratio of 25 dB. This renders the interference essentially negligible.

A lower C/I can be used if it is properly accounted for in the design. However, caution should be exercised in allocating large interferences since their levels are not as predictable or as stable as the thermal noise components.

In Canada, the Earth Station interference analysis and frequency coordination involves the following steps:

• Analyze the potential for interference

• Account for terrain characteristics

• Carry out field testing if required

• Shield or relocate the station if necessary






Terrestrial Microwave System InterferenceEarth Station Frequency Coordination

• Required for 6/4 GHz systems

• Ensures that the operation of the Earth Station and the terrestrial system are within specifications

• Usually required by a government licensing authority

• Coordination must be carried out with terrestrial and satellite system users within an appropriately defined coordination zone

• This coordination could involve users in other countries

• Note that this is different from the international coordination of satellites which is carried out through the International Telecommunications Union (ITU)






Terrestrial Microwave System InterferenceStep 1 In Canada, due to the very large number of terrestrial stations, the initial analysis is carried out by computer. The Frequency Coordination System Association administers the program. It contains:

• A master database of licensed terrestrial and satellite stations and their characteristics

• Software for the calculation of interference levels

• Mutually agreed interference objectives (for Earth Stations this is typically a desired C/I ratio)






Terrestrial Microwave System InterferenceThis procedure is very conservative because it assumes:

• A flat Earth within the coordination zone

• No natural or man-made objects are in the path

• The two systems are co-polarized

• Guaranteed antenna pattern envelopes are used rather than the fine sidelobe structure

If the program predicts no interference, then the site is considered to be interference free. If there is some interference predicted, then proceed to step 2.






Terrestrial Microwave System InterferenceStep 2

• Draw path profiles on topographical contour maps to assess the effect of blockages due to hills, etc.

• Carry out a calculation of the attenuation provided by the objects in the path. This is usually done with the aid of computer programs.

This may clear the site of interference effects. If not, proceed to Step 3.

Step 3 • Carry out field measurements with a transportable antenna.

This will assess protection provided by buildings and the fine structure of the antenna sidelobes.

If this is not successful in achieving the C/I objective, then shielding is the next alternative.






Terrestrial Microwave System InterferenceSite Shielding Interfering signals may sometimes be blocked by the use of site shielding using:

• Wire mesh screen• Earth berm• Solid wall built of concrete or steel

In Telesat's experience, shielding will yield the following signal attenuations:

• Buildings 6 - 20 dB• Wire mesh screen 6 - 10 dB• Wall or Earth berm 10 - 20 dB

If these techniques do not result in the C/I objective being met, the only alternative left is to relocate the Earth Station.





Detailed LinkBudget Calculations

Part 11





5.3.11: Detailed Link Budget Calculations


Detailed Link Budget CalculationsThis portion of the course is a detailed review of the link calculation process dealing with a number of typical service examples including all interference and margin components of the links.



Detailed Link Budget CalculationsAs we have seen, interferences into the satellite RF channel include:

• Interference from cross-polarized RF channels• Interference from adjacent satellite systems• Interference from adjacent RF channels• Interference from uplink intermodulation noise

The way in which these interferences arise and the approach to calculating them has been covered in the previous section.

As one example of the magnitude of interference terms, consider the values used by Telesat in its standard FDMA design procedures.

Part 11: Detailed Link Budget Calculations

5.3.11.1: Interference Allocations




The Detailed Link ModelThe actual calculations depend on the traffic carried on adjacent satellites, their relative orbital locations, and the equivalent effect of the interfering modulations on FDMA carriers. Often, this requires measured data to provide a model.

The interferences are all expressed as equivalent noise power densities, relative to either saturated input or saturated output satellite power. This makes it easy to include in the analysis since IBOi and OBOi are calculated as part of the link analysis.

Note, however, that downlink adjacent satellite interference is an exception to this. It is expressed as an equivalent downlink EIRP power density that is a function of the receive antenna gain.



5.3.11.2: The Detailed Link Model



The Detailed Link Model



5.3.11.2: The Detailed Link Model

TYPICAL EXAMPLE OF INTERFERENCE ALLOCATIONSFor 14/12 and 6/4GHz (FDMA RFChannels Only

Up Adj. SatDN Adj. Sat EIRPUplink X-pol.Downlink X-pol.Dn Adj. ChannelSat Intermod.E Stn. Int'd(s)*E Stn. Int'd (m)*

-105-5 - Go

-107-106-110-96-105-102

-103-13 - Go

-106-101n/a

-94.5-104-101

dB/Hz relative to sat input powerdBW/Hz (Go is receive gain)dB/Hz relative to sat input powerdB/Hz relative to sat output powerdB/Hz relative to sat output powerdB/Hz relative to sat output powerdB/Hz relative to sat input powerdB/Hz relative to sat input power

Intereference Parameter UnitsFrequency Band14/12 6/4





5.3.11.3: ITU Interference Allocations

ITU Interference AllocationsIn lieu of carrying out detailed calculations on the interference between adjacent satellite systems, the ITU provides recommendations that may be used in designs.

These are usually treated as an initial guideline until detailed coordination activities are carried out.

These guidelines are usually used for services on an Intelsat satellite.

In addition, Intelsat provides many interference recommendations which vary for different satellites and different services. This data should be consulted for services on Intelsat satellites.

It is still necessary to make estimates of the interferences, such as cross-polarized interference, that occur from within the satellite system itself.




ITU Interference AllocationsWe have seen that, in the absence of detailed data, the current ITU 580 recommendation allocations for adjacent satellite interference is based on the assumption that the receiving Earth Station antennas have a sidelobe pattern that meets the following:

G(a) = 29 - 25 log ( A )

Where A is the off-axis angle having values between 1 and 48 degrees

If the actual sidelobe gain is known, it should be used for calculations.







ITU Interference AllocationsThe following data gives the essence of three of the ITU recommendations. The actual text should be referred to for the details.

RECOMMENDATION 483-1: MAXIMUM PERMISSIBLE LEVEL OF INTERFERENCE INTO A TELEVISION CHANNEL EMPLOYING FREQUENCY MODULATION

• The interference noise power caused by the aggregate of Earth Station and space station transmitters of other networks should not exceed 10% of the permissible video noise.

• The interference caused by any one satellite network should not exceed 4% of the permissible video noise.

Note that this recommendation deals with the sum of the uplink and downlink interferences.






ITU Interference AllocationsRECOMMENDATION 523-2: MAXIMUM PERMISSIBLE LEVEL OF INTERFERENCE INTO 8-BIT PCMENCODED TELEPHONY LINKS

The interference noise power caused by the aggregate of Earth Station and space station transmitters of all other networks should not exceed the following limits:

• If the system does not have frequency re-use, the level should not exceed 25% of the total noise power at the demodulator input that would result in a bit error ratio of 1 in 106.

• If the system has frequency reuse, the limit is 20% of the total noise power at the demodulator.






ITU Interference Allocations• The interference caused by any one satellite network

should not exceed (provisionally) 6% of the total noise power at the demodulator input that would result in a bit error ratio of 1 in 106.

In general, these guidelines can be used as interference estimates for any analog or digital SCPC carrier.






ITU Interference AllocationsRECOMMENDATION 524-2 (MOD I): MAXIMUM PERMISSIBLE LEVELS OF OFF-AXIS EIRP DENSITY FROM EARTH STATIONS IN THE 6 AND 14 GHz FIXED SERVICE BANDS

6 GHzOff-Axis Angle Maximum EIRP Density A (Degrees) (dBW/4 kHz)

2.5 - 7 32 - 25 log(A)

7 - 9.2 11

9.2 - 48 35 - 25 log(A)

48 - 180 -7






ITU Interference Allocations14 GHz

Off-Axis Angle Maximum EIRP Density A (Degrees) (dBW/4 kHz)

2.5 - 7 39 - 25 log(A)

7 - 9.2 18

9.2 - 48 42 - 25 log(A)

48 - 180 0





5.3.11.4: Link Example With Interference Allocations

Link Example With Interference AllocationsBefore proceeding to the section on link margins, we will add interferences to a design example and assess their effect on the overall performance.

For an uplink EIRP of 50 dBW, a carrier passing through an FDMA RF channel and received by an Earth Station with a G/T of 24.4 dB/K has the following link design information:

Satellite IBOi 30.8 dB

Satellite OBOi 25.9 dB

Downlink EIRP 10.1 dBW





Link Example With Interference AllocationsLink Summary





We will use the C-Band typical example of interference allocations as an example for further calculation.

Uplink Adjacent Satellite Interference

C/Io = CSAT/Io - IBOi

= 103 - 30.8 = 72.2 dB-Hz






Link Example With Interference AllocationsUplink Cross-Pol Interference


= 106 - 30.8 = 75.2 dB-Hz

Uplink Earth Station Intermodulation (Assume Single Carrier Transmission)


= 104 - 30.8 = 73.2 dB-Hz





5.3.11.4: Link Example With Interference AllocationsPart 11: Detailed Link Budget Calculations

Link Example With Interference AllocationsContinuing with the downlink interferences:

Downlink Adjacent Satellite Interference

The ratio of carrier EIRP to interference EIRP density

= 10.1 - ( - 13 - Go)

= 10.1 + 13 + 45 = 68.1 dB-Hz

Downlink Cross-Pol Interference

C/Io = CSAT/Io - OBOi

= 101 - 25.9 = 75.1 dB-Hz






Link Example With Interference AllocationsA downlink adjacent RF channel allocation is often not required; adjacent FDMA RF channel interference would be included in the satellite intermodulation allocation. If the traffic in the adjacent RF channel were a source of interference, this factor could easily be added to the link calculation.

The link summary is now as follows:

UPLINKThermal C/No 76.8 dB-HzAdjacent Satellite C/Io 72.2 dB-HzCross-Pole C/Io 75.2 dB-Hz

Earth Station Int'd C/Io 73.2 dB-HzNet Uplink 68.0 dB-Hz






Link Example With Interference AllocationsDOWNLINK

Thermal C/No 66.8 dB-HzIntermod C/Io 70.1 dB-HzAdjacent Satellite C/Io 68.1 dB-HzCross-Pole C/Io 75.1 dB-HzNet Downlink 63.1 dB-Hz


Comparing this result with the design without interference allocations, it can be seen that the performance has been reduced by 2.9 dB. Thus, the allocation of interferences can have a significant effect on link performance compared to thermal noise and satellite intermodulation effects alone.






Link Example With Interference AllocationsA major concern, as interferences come to be more dominant in link performance, is that, in general, the interferences can not be estimated with the accuracy of the thermal noise components of the link.

This means that the performance could easily differ from the calculated value if one of the dominant interferences is even slightly larger than expected.






Link Margin AllocationsSo far we have looked at "clear weather" link designs. We will now consider the margins required to compensate for signal variations with time. Some of these, such as the satellite motion effects, are regular and easily calculated; others, such as the effects due to rain, can only be described statistically. We will include allocations for the following:

• Signal absorption due to rain• Receiver noise enhancement due to rain• Earth Station transmitter power level variations with time and

temperature• Earth Station antenna pointing errors• Satellite antenna pointing errors• Satellite gain loss with age (requires Earth Station HPA margin for

future carrier level increases)

5.3.11.5: Link Margin Allocations





Link Margin AllocationsLink Design Examples To Be Reviewed

The remainder of this portion of the course will cover detailed satellite system examples for the following types of designs:

• Ku-Band FDMA Mesh Networks• C-Band FDMA Star Networks• C-Band Television Broadcast Networks• C-Band TDMA System • C-Band CDMA Data Broadcast System• Ku-Band "VSAT" System Designs







5.3.11.5.1 Example 1 - Ku-Band MESH Network LinksConsider a point-to-point Ku-Band link design between two locations operating at 56 kbps. Use 3 meter antennas on each end of the link and assume that the Earth Station and satellite characteristics are the same for both locations. Using rate 1/2 FEC, the required Eb/No is 6.5 dB for a 10-7 BER and the objective clear weather C/No is:

6.5 + 10 log (56,000) = 54 dB-Hz.

Earth Station CharacteristicsAntenna Diameter 3.0 mTransmit Gain 50.8 dBiReceive Gain 49.3 dBiG/T 24.7 dB/KPointing Error Uplink 0.3 dBPointing Error Downlink 0.3 dB






5.3.11.5.1 Example 1 - Ku-Band MESH Network Links

Assume each station transmits multiple carriers as part of a mesh network.

Satellite CharacteristicsSFD (dBW/m2) -83.0

Saturated EIRP (dBW) 45.0

G/T (dB/K) 3.8

Sat Up Point Error (dB) 0.5

Sat Dn Point Error (dB) 0.5

Satellite IBO (dB) 9

Satellite OBO (dB) 4.5







Link ParametersUplink FSL (dB) 207.5

Downlink FSL (dB) 206.2

Uplink Absorption (dB) 0.3

Down Absorption (dB) 0.3

Uplink Rain Loss (dB) 2.0

Down Rain Loss (dB) 1.5







UPLINK EQUATION

C/No = EIRPES - FSLUP - LABS + G/TSAT + 228.6 dB-Hz

In order to start the analysis, an initial estimate of the uplink EIRP must be made - say 50 dBW.

C/No = 50 - 207.5 - 0.3 + 3.8 + 228.6 = 74.6 dB-Hz.

INPUT BACKOFF

IBOi = SFD - EIRPES + FSLUP + LABS - G1 dB

IBOi = - 83 - 50 + 207.5 + 0.3 - 44.4 = 30.4 dB







The uplink interferences can now be calculated:

C/Io Up Adj Sat = - 30.4 - (- 105) = 74.6 dB-Hz

C/Io Uplink X-Pol = - 30.4 - (- 107) = 76.6 dB-Hz

C/Io E Stn Int'd = - 30.4 - (- 102) = 71.6 dB-Hz

C/No Up Total = 67.9 dB-Hz

To begin the downlink calculations, the satellite output power must first be calculated. The power fraction is:

F = IBO - IBOi = 9 - 30.4 = - 21.4 dB

The output backoff is then:

OBOi = OBO - f = 4.5 - (- 21.4) = 25.9 dB







Therefore the downlink EIRP is:

EIRPDN = EIRPSAT - OBOi = 45 - 25.9 = 19.1 dBW

The downlink thermal noise is:

C/No = EIRPDN - FSLDN - LABS + G/TES + 228.6 dB-Hz

= 19.1 - 206.2 - 0.3 + 24.7 + 228.6 = 65.9 dB-Hz

The downlink interferences are then:

C/Io Dn Adj Sat = 19.1 - (- 5 - 49.3) = 73.4 dB-Hz

C/Io Dn Adj Channel = -25.9 - (- 110) = 84.1 dB-Hz

C/Io Sat Intermod = -25.9 - (- 96) = 70.1 dB-Hz

C/No Down Total = 63.9 dB-Hz

C/No Total Link = 62.5 dB-Hz.Vol 5: Link Analysis, Sec 3: Conducting a Link Budget






Recall that the clear weather threshold C/No was calculated as 54 dB-Hz. Since the link performance scales with uplink EIRP, the EIRP required to yield a clear weather C/No of 54 dB-Hz would be:

50 - (62.5 - 54) = 41.5 dBW.

This demonstrates how the scalability of these values can be used to advantage. By making only one assumption about uplink EIRP, we can arrive back at the actual, required EIRP without a lengthy iteration process.







To continue, we must now add the appropriate link margin to allow for all the degradations expected within the required propagation availability. First consider only uplink rain:

Transmit Level Variation 1.5 dB

Transmit Antenna Pointing Loss 0.3 dB

Satellite Uplink Pointing Loss 0.5 dB

Uplink Rain Loss 2.0 dB

Total Uplink Losses 4.3 dB

Satellite Downlink Pointing Loss 0.5 dB

Receive Antenna Pointing Loss 0.3 dB

Total Downlink Losses 0.8 dB







Note that, in bent pipe satellite design, the uplink losses affect every component of the link, while the downlink losses affect only the downlink thermal C/No and the adjacent satellite C/Io components.

Based on our initial estimate of 50 dBW uplink EIRP, we will now determine the link margin required by calculating the amount of link degradation caused by the various loss components.

Uplink Original Degraded

C/No Uplink Thermal 74.6 70.3 dB-Hz

C/Io Up Adj Sat 74.6 70.3 dB-Hz

C/Io Uplink X-Pol 76.6 72.3 dB-Hz

C/Io E Stn Int'd 71.6 67.3 dB-Hz

C/No Up Total 67.9 63.6 dB-HzVol 5: Link Analysis, Sec 3: Conducting a Link Budget






Downlink

C/No Down Thermal 65.9 60.8 dB-Hz

C/Io Dn Adj Sat 73.4 68.3 dB-Hz

C/Io Dn Adj Channel 84.1 79.8 dB-Hz

C/Io Sat Intermod 70.1 65.8 dB-Hz

C/No Down Total 63.9 59.0 dB-Hz

Total Link C/No 62.5 57.7 dB-Hz

The required link margin, the difference between the clear weather total C/No and the degraded C/No, is 4.8 dB. Since we know that a 50 dBW uplink EIRP gives a total C/No of 57.7 dB-Hz with all degradations in, and we require a threshold C/No of 54 dB-Hz, the actual uplink EIRP must become 50 + (54 - 57.7) = 46.3 dBW. All the C/No and C/Io terms scale down accordingly.Vol 5: Link Analysis, Sec 3: Conducting a Link Budget






RF UTILIZATION

The power utilization is found directly from the power fraction. For an uplink EIRP of 46.3 dBW, F = -25.1 dB, which gives 0.3% power for each 56 kbps carrier.

The bandwidth required for a QPSK carrier operating at 56 ksps is 1.5 x 56,000 = 84 kHz. Since the modem synthesizer can be set only in 25 kHz steps, the allocated bandwidth becomes 100 kHz.

Since the available RF channel bandwidth is 44 MHz, the utilization is

The RF utilization is therefore 0.3 % (power limited).

%23.0100104410100

6

3

xxx







Downlink Rain Effects

Up to this point, we have considered the effects of rain on the uplink only.

Usually the uplink loss will dominate a link availability, and since fading at both ends is very unlikely to occur at the same time, the uplink rain loss margin is sufficient to cover the rain fade effects at the receive end.

However, sometimes the downlink will dominate the link performance, so the effects of downlink rain on the link margin must be checked.

The overall link margin is taken as the larger of the two margins that are independently based on uplink or downlink rain.







We will continue our example by calculating the margin required when rain occurs on the downlink only. Note that all of the other losses except uplink rain are also included. The table below summarizes the components of the margin.

Transmit Level Variation 1.5 dB

Transmit Antenna Pointing Loss 0.3 dB

Satellite Uplink Pointing Loss 0.5 dB

Total Uplink Losses 2.3 dB

Satellite Downlink Pointing Loss 0.5 dB

Receive Antenna Pointing Loss 0.3 dB

Downlink Rain Loss 1.5 dB

Total Downlink Losses 2.3 dB







Note that the uplink losses affect every component of the link, while the downlink pointing losses affect only the downlink thermal C/No and the adjacent satellite C/Io components.

The downlink rain loss affects only the downlink thermal component; the adjacent satellite interference is assumed to be attenuated by the rain as well.

Note also that the downlink rain loss will cause a receive system noise enhancement to occur.

Based on our initial estimate of 50 dBW uplink EIRP, we will again determine the link margin required by calculating the amount of link degradation caused by the various loss components with downlink rain.







Uplink Original DegradedC/No Uplink Thermal 74.6 72.3 dB-Hz

C/Io Up Adj Sat 74.6 72.3 dB-Hz

C/Io Uplink X-Pol 76.6 74.3 dB-Hz

C/Io E Stn Int'd 71.6 69.3 dB-Hz

C/No Up Total 67.9 65.6 dB-Hz







Downlink

C/No Down Thermal 65.9 60.2 dB-Hz

C/Io Dn Adj Sat 73.4 70.3 dB-Hz

C/Io Dn Adj Channel 84.1 81.8 dB-Hz

C/Io Sat Intermod 70.1 67.8 dB-Hz

C/No Down Total 63.9 59.1 dB-Hz

Total Link C/No 62.5 58.3 dB-Hz

The required link margin, the difference between the clear weather total C/No and the downlink rain degraded C/No, is 4.2 dB.

Therefore, the margin is determined by the uplink rain effects for this example.





The downlink thermal C/No on the previous page included a G/T degradation due to the rain noise which is calculated as follows:

TSYS = 288 K and the rain loss = 1.5 dB

The degradation =



KxxL

LTRAIN 8529041.1

141.12901

dBLog 1.1288

8528810




5.3.11.5.2 Example 2 (Exercise 1) - C-Band Star Network Links

This example is based on an SCPC voice network that operates in a star configuration from a large hub station to about 50 sites in Canada’s Arctic providing trunk circuit interconnection to telephone company small central offices in the villages.

The system uses delta encoded voice at 40 kbps and QPSK modulation. The performance threshold BER is 1 in 1000 which requires an Eb/No of 9.5 dB. The objective clear weather C/No is therefore:

9.5 + 10 log (40,000) = 55.5 dB-Hz.







Earth Station Characteristics HUB REMOTES Antenna Diameter (m) 10.0 4.5

Transmit Gain (dBi) 53.7 46.8

Receive Gain (dBi) 50.2 43.3

G/T (dB/K) 29.1 22.1

Pointing Error Uplink (dB) 0.6 0.3

Pointing Error Downlink (dB) 0.6 0.3

Assume all stations transmit multiple carriers.







SATELLITE PARAMETERS (TYPICAL TELESAT ANIK D)HUB REMOTES

SFD (dBW/m2) -86.0 -84.0

EIRP (Sat'd) (dBW) 39.5 36.0

G/T (dB/K) 1.4 -0.6

Sat Up Point Err (dB) 0.2 0.5

Sat Dn Point Err (dB) 0.2 0.5

Satellite IBO (dB) 9

Satellite OBO (dB) 4.5







LINK PARAMETERS Hub RemoteUplink FSL (dB) 199.8 200.3

Downlink FSL (dB) 196.2 196.7

Uplink Absorption (dB) 0.1 0.1

Down Absorption (dB) 0.1 0.1

Uplink Rain Atten (dB) 0.3 0.3

Down Rain Atten (dB) 0.3 0.3




It is now your turn. Find the uplink EIRP required for the It is now your turn. Find the uplink EIRP required for the target C/No, including all allocations and margins. target C/No, including all allocations and margins.




Solution for Inbound LinkAs usual, pick an uplink EIRP value to start the analysis: say 50 dBW.

C/No(Uplink Thermal) = EIRP - FSL - ABS + G/T + 228.6= 50 - 200.3 - 0.1 + (-0.6) + 228.6= 77.6 dB-Hz

Uplink flux density at the satellite is:

PFD(Uplink) = EIRP - FSL - ABS + G1

= 50 - 200.3 - 0.1 - 37= -113.4 dBW/m2

Now, SFD from the remote is -84 dBW/m2. Therefore:

IBOi = -84 - (-113.4)= 20.4 dB







Solution for Inbound LinkWe can now calculate the Power Fraction:

Power Fraction = IBO - IBOi= 9 - 29.4= 20.4 dB

From here, the next step is to arrive at the OBOi, as:

OBOi = OBO - F= 4.5 - (-20.4)= 24.9 dB







Solution for Inbound LinkNow let’s begin working with the interferences, starting with Uplink Adjacent Satellite Interference. The interference parameters used here are drawn from Slide 143.

C/Io (Uplink Adjacent) = CSat/Io - IBOi= 103 - 29.4= 73.6 dB-Hz

Uplink crosspole would be:

C/Io (Uplink Xpole) = CSat/Io - IBO= 106 - 29.4= 76.6 dB-Hz







Solution for Inbound LinkEarth Station Uplink Intermodulation is:

C/Io (Uplink Intermod) = CSat/Io - IBOi= 101 - 29.4= 71.6 dB-Hz

Therefore, Total Uplink C/No is 68.2 dB-Hz.

Now, saturated EIRP toward the Hub is 39.5 dBW. Consequently, downlink carrier EIRP is calculated as:

EIRP(Down) = EIRP(Sat) - OBOi= 39.5 - 24.9= 14.6 dBW







Solution for Inbound LinkWe are now in a position to calculate the downlink C/No:

C/No(Downlink Thermal) = EIRP - FSL - ABS + G/T + 228.6= 14.6 - 196.2 - 0.1 + 29.1 + 228.6= 76.0 dB-Hz

Once again we look at the interferences:

C/Io (Adjacent Satellite) = EIRP - (-13 - Go) — Go being RX Gain= 14.6 + 13 + 50.2= 77.8 dB-Hz

C/Io (Downlink Xpole) = CSat/Io - OBOi

= 101 - 24.9= 76.1 dB-Hz







Solution for Inbound Link

C/Io (Satellite Intermod) = CSat/Io - OBOi= 94.5 - 24.9= 69.6 dB-Hz

Therefore, Total Downlink C/No is 67.5 dB-Hz. Note that adjacent channel interference is not considered a factor in this example.

The inverse squared addition of the uplink and downlink C/No values gives us the total link C/No of 64.8 dB-Hz.

We must now determine the amount of link margin required based on pointing, rain, and other losses. Usually, the calculation includes only the uplink or downlink rain fade loss, as both Earth Stations are unlikely to experience rain at the same time.







Solution for Inbound LinkThe uplink and downlink rain attenuations are calculated and the worst case result is used.

Since, in this case, the rain loss is given as 0.3 dB for both uplink and downlink, we know that the uplink rain loss will dominate. Thus, only the uplink rain loss will be included here.

Factors affecting the inbound uplink are:

• Transmit level variation (typical) 1.5 dB• Transmit antenna pointing (Slide 178) 0.3 dB• Satellite uplink pointing (Slide 179) 0.5 dB• Uplink rain attenuation 0.3 dB

Total Uplink Effects 2.6 dB







Solution for Inbound LinkThis 2.6 dB loss affects all of the C/Io components since it directly reduces the value of carrier power at the satellite. Therefore, we can just apply it to the total uplink C/No:

Faded Uplink C/No = 68.2 - 2.6 = 65.6 dB-Hz

The downlink impairments do not change some of the C/Io values since they affect both the carrier and the interference power.

The downlink impairments are:

• Satellite downlink pointing error 0.2 dB• Receive Earth Station pointing error 0.6 dB• Downlink rain fade 0.3 dB







Solution for Inbound LinkAs indicated earlier, we will not include the downlink rain fade value as we have decided to use the uplink value instead.

In addition, when considering the downlink, we must remember that the uplink carrier level reduction of 2.6 dB also translates directly into a downlink carrier reduction of 2.6 dB. Therefore, all of the link components are affected by this factor as well.

The downlink thermal C/No, with uplink rain fading, will now be changed to:

C/No(Downlink Thermal) = Unfaded Value - U/L Effects - D/L Effects= 76.0 - 2.6 - (0.2 + 0.6)= 72.6 dB-Hz







Solution for Inbound LinkSince the C/Io values are affected as well, we can now make similar adjustments to them:

C/Io(Adjacent Satellite Int.) = Unfaded Value - U/L Effects - D/L Effects = 77.8 - 2.6 - (0.2 + 0.6) = 74.4 dB-Hz

C/Io(Crosspole.) = Unfaded Value - U/L Effects = 76.1 - 2.6 = 73.5 dB-Hz

C/Io(Satellite Intermod.) = Unfaded Value - U/L Effects = 69.6 - 2.6 = 67.0 dB-Hz

Note that the final two values are not affected by the downlink impairments.







Solution for Inbound LinkSummary:

Uplink C/No = 65.6 dB-Hz

Downlink C/No = 64.7 dB-Hz

Net Link C/No = 62.1 dB-Hz

Recall that the clear weather net link C/No was 64.8 dB-Hz. Therefore:

Required Link Margin = 64.8 - 62.1= 2.7 dB







Solution for Inbound LinkWe can now complete the exercise. From Slide 177, recall that the threshold C/No is 55.5 dB-Hz. Adding the 2.7 dB link margin gives a clear weather link requirement of C/No = 58.2 dB.

Since the arbitrary uplink EIRP of 50 dBW that we started with gives a clear weather link total of 64.8 dB-Hz, then the required uplink EIRP at a remote site is 50 - (64.8 - 58.2) = 43.4 dBW.

The outbound link will not be calculated here, as the calculation method is just the same as for the inbound link.

The following slide restates all the link parameters based on the new uplink EIRP of 43.4 dBW. The output is actually from Telesat’s program CKLINK.









IN OUT BOUND BOUND

Rx Ant Diameter (m) 10.0 4.5E.S. G/T (dB/K) 29.1 22.1

(EIRP)up (dBW) 43.4 45.2Carrier IPBO (dB) 36.0 31.7(C/No)up Thermal (dB-Hz) 71.0 75.3(C/ Io)up Adj Sat (dB-Hz) 67.0 71.3(C/ Io)up X-Pol (dB-Hz) 70.0 74.3(C/ Io)imd E.S. (dB-Hz) 65.0 69.3(C/No)up Total (dB-Hz) 61.6 65.9

(EIRP)down (dBW) 8.0 8.8CARRIER OPBO (dB) 31.5 27.2(C/No)down Thermal (dB-Hz) 69.4 62.8(C/ Io)down Adj Sat (dB-Hz) 71.2 65.1(C/ Io)down Adj Ch (dB-Hz) 168.5 172.8(C/ Io)down X-Pol (dB-Hz) 69.5 73.8(C/ Io)imd Sat (dB-Hz) 63.0 67.3(C/No)down Total (dB-Hz) 60.9 59.7

(C/No) Total (dB-Hz) 58.2 58.8

(C/No) Threshold (dB-Hz) 55.5 55.5System Margin (dB) 2.7 3.3

% Of RF Power Util One Way .20 .54




% Of RF Power Util Two Way .74

51ENTER REMOTE SITE SAT EIRP (dBW)36HOME SITE NAME 10: HUBREMOTE SITE NAME 11: REMOTE# OF REM SITE G/T's CONSIDERED 12: 1

HOM REM HOM REMU/L FSL (dB) 20: 199.8 30: 200.3 SFD (dBW/m**2) 40: -86.0 50: -84.0D/L FSL (dB) 21: 196.2 31: 196.7 SAT EIRP(dBW) 41: 39.5 51: 36.0U/L ABS (dB) 22: .1 32: .1 U/L P.E. (dB) 42: .2 52: .5D/L ABS (dB) 23: .1 33: .1 D/L P.E. (dB) 43: .2 53: .5U/L R.ATT.(dB) 24: .3 34: .3 M-IPBO (dB) 60: 9.0D/L R.ATT.(dB) 25: .3 35: .3 M-OPBO (dB) 61: 4.5

BIT RATE (kbps) 70: 40.0 MODULATION l/FM, 2/PSK 73: 2(Eb/No)TH (dB) 71: 9.5 FREQ BAND 74: CE.S. LEV VAR(dB) 72: 1.5 SATELLITE USED 75: D

HOM REMRX ANT DIA (m) 80: 10.0 90: 4.5RX GAIN (dBi) 81: 50.2 91: 43.3E.S. G/T (dB/K) 82: 29.1 92: 22.1E.S. ANT P.E.(dB)83: .6 93: .3TX ANT G (dBi) 84: 53.7 94: 46.8E.S. TX > 1 CARR87: Y 97: YENTER PARAMETER NUMBER TO BE MODIFIED (O TO EXIT)







5.3.11.5.3 Example 3 (Exercise 2) - C-Band Television LinksIn general, there are no trade-offs involving satellite utilization for TV networks because, for systems with one carrier in an RF channel, the carrier level is fixed, usually near saturation.

Therefore, the uplink and downlink can be separated in most TV system designs. Fades on the uplink, usually, have very little effect on the downlink carrier level because of operation near saturation.

We will work some examples for a typical C-Band service. The objective is to determine the typical antenna sizes required to receive the signal from the satellite and provide three different video signal to noise ratios:

• 45 dB S/N• 50 dB S/N• 54 dB S/N






5.3.11.5.3 Example 3 (Exercise 2) - C-Band Television Links

Assume the Earth Stations have an 80 K LNA with a receive system noise temperature of 130 K. For this example, we will simply design for an overall margin of 2 dB above the performance threshold value rather than work with specific pointing and other fade effects.

Satellite and Link ParametersSatellite IBO (dB) 1.0Satellite OBO (dB) 0.2Satellite SFD from hub (dBW/M2) -86.0Satellite G/T from hub (dB/K) 1.4Uplink FSL from hub (dB) 199.8Uplink absorption from hub (dB) 0.1Satellite saturated EIRP (dBW) 39.0Downlink FSL to receivers (dB) 196.7Downlink absorption to receivers (dB) 0.1







Interference Allocations For TV Links

The interference allocations for TV carriers are different from those for FDMA RF channels. For simplicity, assume the following typical power densities:

Net uplink interference -103 dB/Hz rel. to sat input Net downlink interference -99 dB/Hz rel. to sat

output

(This ignores the effect of receive sidelobes on adjacent satellite interference.)







The relationship between video S/N and link C/No is as follows:

Wherefpk is the carrier peak deviation due to the video signal (typically

9.85 MHz at C-Band).Fv is the top video baseband frequency (4.25 MHz for NTSC; 5

MHz for PAL B,G).PW is the emphasis plus weighting factor (12.8 dB for NTSC;

16.3 dB for PAL B,G).IM is the implementation margin (about 1 dB)CF is the RMS to peak-to-peak conversion factor (6 dB)



CFIMPWff

LOGNCNSv

pko

3

2

23

10//





Substituting the parameters into the equation we have:

= - 38.0 dB For PAL B, G Systems

Similarly, we have:

- 39.4 dB For NTSC Systems



613.16

10521085.9310 36

26

LOG

NC

NS

o

oNC

oNC

NS





Recall the uplink equation for C/No Thermal:

C/No = - G1 + G/TSYS + 228.6 dB-Hz

Where is the Flux Density, here 1 dB below saturation. Therefore,

C/No = -87 - 37 + 1.4 + 228.6 = 106 dB-Hz

The net uplink interference is given as:

C/Io = -1 - ( -103) = 102 dB-Hz

Thus the uplink total C/No = 100.5 dB-Hz.

Assuming a PAL B,G system with video S/N ratios of 45, 50 and 54 dB we can calculate the required overall link C/No values, the downlink total C/No values, the downlink thermal C/No values, and finally the required G/T and antenna diameters.







For example, for a 45 dB S/N ratio, the required overall C/No ratio is:

45 + 2 + 38.0 = 85.0 dB-Hz.

Since the total uplink C/No is 100.5 dB-Hz, and the downlink net interference C/Io is 98.8 dB-Hz, the required downlink thermal C/No becomes 85.3 dB-Hz.

The Earth Station G/T is found from the following, familiar equation:

C/No = EIRPDN - FSLDN - LABS + G/TES + 228.6dB-Hz

G/TES= 85.3 - 38.8 + 196.7 + 0.1 - 228.6

= 14.7 dB/K







Based on a receive system noise temperature of 130 K, the required antenna diameter is 1.8 M. This value can be found by referring to receive gains for available antennas, or approximately from the formula:

The following table summarizes the results for the PAL B, G examples.



22

222 4444

DDAAG e

S/N(dB)

Total C/No(dB-Hz)

Down ThermC/No (dB-Hz)

RequiredG/T (dB/K)

AntennaDiam. (M)

45 85.0 85.3 14.7 1.8

50 90.0 91.1 20.5 3.7

54 94.0 97.5 26.9 7.6





1) Satellite saturated EIRP = 36 dBW

2) 40 K LNA (90 K receive system temperature)




Your turn again. For additional examples, repeat this Your turn again. For additional examples, repeat this exercise for the following two system parameter exercise for the following two system parameter

changes.changes.



5.3.11.5.4 Example 4 (Exercise 3) - C-Band TDMA LinksThis example describes the link budgets for a 60 Mbps TDMA system between three locations A, B, and C. Such a system will occupy a 36 MHz RF channel and is assumed to be on an Intelsat V type satellite with an east hemispheric beam.

The satellite characteristics are assumed to be as follows:Saturating Flux Density -79.6 dBW/m2

Satellite G/T -7 dB/KSaturated EIRP 28 dBWSatellite IBO 3 dBSatellite OBO 1 dB

The following pages provide the detailed link calculations for the TDMA network based on an Earth Station with a 12 meter antenna. The satellite’s characteristics are assumed to be the same at all three locations.






5.3.11.5.4 Example 4 (Exercise 3) - C-Band TDMA Links

This performance assumes 1 dB implementation margin from the IF loopback performance.

Adjacent Satellite InterferenceThe adjacent satellite interference in the link analysis will be calculated on the following basis:

Assume two adjacent satellites at 2 degree spacing carrying saturated carriers transmitted from 12 meter Earth Station antennas meeting the 29 - 25 log(A) pattern.

Off-axis gain at 2 degrees is 21.5 dBi. Satellite SFD = -74.6 dBW/m2 (low gain edge of

coverage). Satellite saturated EIRP = 28 dBW.







Uplink interference Antenna gain at 6 GHz is 56.3 dBi; thus the antenna

discrimination is 34.8 dB. Interfering Flux Density = -74.6 - 34.8 - 75.6 = -185

dBW/m2/Hz. For two satellites Flux Density = -182 dBW/m2. Uplink adjacent C/Io = -82.6 - ( -182) = 99.4 dB-Hz.







Downlink Interference Antenna gain at 4 GHz is 52.3 dBi; Thus the antenna

discrimination is 30.8 dB. Downlink EIRP density = 28 - 75.6 = - 47.6 dBW/Hz. For two satellites EIRP density = - 44.6 dBW/Hz. Downlink adjacent C/Io = 27 - ( -44.6 - 30.8) = 102.4

dB-Hz.









TDMA Modem IF Loopback PerformanceEb/No

10.311.713.0

Uncorrected BER1 x 101 x 101 x 10

Input BER1 x 101 x 101 x 10

Ouput BER2 x 102 x 102 x 10

FEC Codec Performance

-4

-5-6

-8

-11-14

-4

-5-6


Okay, that’s all you need to know. See if you can arrive Okay, that’s all you need to know. See if you can arrive at the same values given in the next 2 slides.at the same values given in the next 2 slides.






PARAMETER VALUE UNITSEarth Station

Antenna DiameterTransmit GainWaveguide and Hybrid LossesHPA Ouput PowerReceive GainReceive Noise TemperatureG/TTransmission Bit RateIF Bandwidth

12.056.36.0

30.352.319.233.160.036.0

MdBidB

dBWdBi

dB-KdB/KMpbsMHz

UplinkEarth Station EIRPUplink FSLPointing and Absorption LossesUplink Thermal C/No

Adjacent Satellite C/IoCo-Channel Interference C/ICo-Channel Interference C/Io

Uplink Total C/No

80.0200.0

0.2102.099.425.2100.8

95.8

dBWdBdB

dB-HzdB-Hz

dBdB-Hz

dB-Hz







PARAMETER VALUE UNITSDownlink

Carrier EIRPDownlink FSLPointing and Absorption LossesDownlink Thermal C/No

Intermodulation EIRP DensityIntermodulation C/No

Adjacent Satellite C/IoCo-Channel Interference C/ICo-Channel Interference C/Io

Downlink Total C/No

27.0196.3

0.292.2-40.0103.0102.425.2100.8

91.0

dBWdBdB

dB-HzdBW/4kHz

dB-HzdB-Hz

dBdB-Hz

dB-HzCombined Link

Total Link C/No

Eb/No

BER Performance (No FEC)BER Performance (With FEC)

89.812.0

3 x 101 x 10

dB-HzdB

(Typical)(Typical)

-5-9

This performance assumes 1 dB implementation margin from the IF loopbackperformance




5.3.11.5.5 Example 5 (Exercise 4) - CDMA Data Broadcast Links

This example covers a C-Band system for one-way data broadcasting using a CDMA spread spectrum system. The performance of the system can be calculated as if CDMA were not used as long as the required Eb/No is specified.

The object is to calculate the coverage area (the required satellite saturated downlink EIRP contour) to provide satisfactory performance into a 0.8 meter antenna with a G/T of 5.7 dB/K.

A performance threshold Eb/No of 12.7 dB provides a BER of 1 x 10e-7 after the built-in block decoding. The information bit rate is 19.2 kbps; thus the performance threshold C/No is 55.5 dB-Hz.

The 19.2 kbps PSK signal is spread by a 2.5 Mbps BPSK signal to occupy a bandwidth of 5 MHz. For a satellite with 28 MHz useful bandwidth for FDMA services, this represents a bandwidth utilization of 18%.







The design will ultimately allow for three overlapping carriers. Thus, the bandwidth utilization attributable to each one is 6%. Therefore, the coverage area will be defined as that which also results in a power utilization of 6% for each carrier.

This design was completed using Telesat’s computer program CKLINK by varying the satellite saturated EIRP specification until the power utilization for the outbound link became 6%.

Normally an allowance would be made for degradation due to mutual interference between the CDMA carriers—in this case 1.4 dB, as measured. However, the computer program interference allocations are suitable only for narrow-band signals and are excessive for a 5 MHz carrier. Thus these allocations will be assumed to make allowance for the mutual interference effects as well.







The printout on the next page shows that the performance can be met with about 3 dB of margin on a satellite saturated EIRP contour of 39.3 dBW.

When you have reviewed the output of CKLINK, try switching this service to an Arabsat satellite, and use an Earth Station antenna of 1.2 meters. This station will have a G/T of 9.7 dB and a receive gain of 31.8 dBi.

Assume that the other system characteristics are the same as in this printout and find the new contour that gives 6% power utilization.









RX Ant Diameter (m) 0.8E.S. G/T (dB/K) 5.7

(EIRP)up (dBW) 55.7Carrier IPBO (dB) 21.2(C/No)up THERMAL (dB-Hz) 85.8(C/Io)up ADJ SAT (dB-Hz) 81.8(C/Io)up X-POL (dB-Hz) 84.8(C/Io)imd E.S. (dB-Hz) 82.8(C/No)up TOTAL (dB-Hz) 77.5(EIRP)down (dBW) 22.6Carrier OPBO (dB) 16.7(C/No)down THERMAL (dB-Hz) 60.1(C/Io)down ADJ SAT (dB-Hz) 63.3(C/Io)down ADJ CH (dB-Hz) 183.3(C/Io)down X_POL (dB-Hz) 84.3(C/Io)imd SAT (dB-Hz) 77.8(C/No)down TOTAL (dB-Hz) 58.4

(C/No) TOTAL (dB-Hz) 58.3

(C/No) THRESHOLD (dB-Hz) 55.5System Margin (dB) 2.8

% of RF Power Util. ONE WAY 6.06








Home Remote Home RemoteU/L FSL dB 199.8 200.3 SFD dB/Wm2 -86.0 -84.0D/L FSL dB 196.2 196.7 Sat. EIRP dBW 39.5 39.3U/L ABS dB 0.1 0.1 U/L P.E. dB 0.2 0.5D/L ABS dB 0.1 0.1 D/L P.E. dB 0.2 0.5U/L R.ATT dB 0.2 0.2 M-IPBO dB 9.0D/L R.ATT dB 0.1 0.1 M-OPBO dB 4.5Bit Rate kbps 19.2 Modulation PSKEb/No TH dB 12.7 Freq. Band CE.S. Lev Var dB 1.0Rx Ant Dia m 10.0 0.8Rx Gain dBi 50.2 27.7E.S. G/T dB/K 29.1 5.7E.S. Ant P.E. dB 0.6 0.3Tx Ant. Gain dBi 53.7 31.2



5.3.11.5.6 Example 6 (Exercise 5) - Ku-Band VSAT System Links

There are many different "Very Small Aperture Terminal" (VSAT) systems in use. This example will show a typical link analysis for a Ku-Band system.

The major characteristic of a VSAT system is that a large hub station is used to connect to many small, low traffic stations.

Each out-route is a time division multiplexed broadcast signal received by many VSATs, and each in-route signal is time shared by the VSATs in a TDMA mode of access.







Two standard VSAT Earth Stations are used:

OPTION 1 OPTION 2Antenna diameter (m) 1.0 1.8

Transmit gain (dBi) 41.5 46.5

Receive gain (dBi) 39.7 45.0

VSAT G/T (dB/k) 17.0 22.0

The hub station has a 5.6 meter antenna with a G/T of 30 dB/k. The system is carried on an FDMA satellite RF channel with a standard IBO of 8 dB and an OBO of 4 dB.







This VSAT system operates with out-routes (to the VSAT terminals) of 512 kbps and inroutes (from the VSATs to the hub) of 128 kbps.

The required performance threshold Eb/No is 6.5 dB for a BER of 1x10e-7 in each direction.

The carriers all use BPSK modulation. The bandwidth allocations are 1.6 MHz for each out-route carrier and 400 kHz for each in-route carrier. The RF channel utilization is power limited for the out-route carrier and bandwidth limited for the in-route carrier.




The CKLINK printouts attached on the next two pages The CKLINK printouts attached on the next two pages show the results of the link analysis. See if you can show the results of the link analysis. See if you can duplicate the results. duplicate the results. (Hint: you will need the typical Ku-Band FDMA (Hint: you will need the typical Ku-Band FDMA

parameters from Slide 143).parameters from Slide 143).






INBOUND

RX ANT DIAMETER (m) 5.6E.S. G/T (dB/K) 3.0

(EIRP)up (dBW) 41.5CARRIER IPBO (dB) 32.4(C/No)up THERMAL (dB-Hz) 69.3(C/Io)up ADJ SAT (dB-Hz) 74.6(C/Io)up X-POL (dB-Hz) 72.6(C/Io)imd E.S. (dB-Hz) 72.6(C/No)up TOTAL (dB-Hz) 65.8(EIRP)down (dBW) 22.1CARRIER OPBO (dB) 28.4(C/No)down THERMAL (dB-Hz) 74.8(C/Io)down ADJ SAT (dB-Hz) 82.2(C/Io)down ADJ CH (dB-Hz) 81.6(C/Io)down X-POL (dB-Hz) 74.6(C/Io)imd SAT (dB-Hz) 66.6(C/No)down TOTAL (dB-Hz) 65.2


(C/No) Threshold (dB-Hz) 57.6SYSTEM MARGIN (dB) 4.9

% OF RF POWER UTIL ONE WAY .36% OF RF POWER UTIL TWO WAY







OUTBOUND

RX ANT DIAMETER (m) 1.0E.S. G/T (dB/K) 17.0

(EIRP)up (dBW) 54.0CARRIER IPBO (dB) 19.5(C/No)up THERMAL (dB-Hz) 82.2(C/Io)up ADJ SAT (dB-Hz) 87.5(C/Io)up X-POL (dB-Hz) 85.5(C/Io)imd E.S. (dB-Hz) 82.5(C/No)up TOTAL (dB-Hz) 77.9(EIRP)down (dBW) 33.0CARRIER OPBO (dB) 15.5(C/No)down THERMAL (dB-Hz) 72.7(C/Io)down ADJ SAT (dB-Hz) 77.7(C/Io)down ADJ CH (dB-Hz) 94.5(C/Io)down X-POL (dB-Hz) 87.5(C/Io)imd SAT (dB-Hz) 79.5(C/No)down TOTAL (dB-Hz) 70.8


(C/No) Threshold (dB-Hz) 63.6SYSTEM MARGIN (dB) 6.4

% OF RF POWER UTIL ONE WAY 7.1% OF RF POWER UTIL TWO WAY


conducting a link budget in satellite communications

Engineering