Project 2

Report

Regional Multibeam Satellite System

Submitted by:

Juan Pablo CUADROMatias PRIETO

Under the guidance of:

Michel BOUSQUET

Abstract

Project 2 consists of the design of an earth-station and dimensioning of a satcom systemto route traffic demand with certain performance requirements while minimizing the costof the earth segment.

S U P A E R OS U P A E R O

SCS Program 2014/2015Telecom Bretagne, ENSEEIHT, ISAE

Toulouse, France

Contents1 System 1

1.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.1 Coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.2 Carrier assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.3 Modulation and Coding . . . . . . . . . . . . . . . . . . . . . . . . 11.1.4 Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.1.5 Allocated Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2 Satellite Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2.1 Attitude and Orbit Control Subsystem . . . . . . . . . . . . . . . . 3

1.2.1.1 Attitude Control . . . . . . . . . . . . . . . . . . . . . . . 31.2.1.2 Station Keeping . . . . . . . . . . . . . . . . . . . . . . . 3

1.2.2 Communication Payload . . . . . . . . . . . . . . . . . . . . . . . . 31.2.2.1 Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2.2.2 Satellite Channels . . . . . . . . . . . . . . . . . . . . . . 4

1.3 Earth Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.3.1 Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.3.2 Radio-Frequency Equipment . . . . . . . . . . . . . . . . . . . . . . 4

1.3.2.1 Transmitting Side . . . . . . . . . . . . . . . . . . . . . . 41.3.2.2 Receiving Side . . . . . . . . . . . . . . . . . . . . . . . . 5

2 Performance Objectives 62.1 Coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.2 Link Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.3 Provision for External Interference . . . . . . . . . . . . . . . . . . . . . . 6

3 Design 73.1 Transponder Usage and Carrier Capacity . . . . . . . . . . . . . . . . . . . 7

3.1.1 Transponder Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.1.2 Available Carrier Bitrate . . . . . . . . . . . . . . . . . . . . . . . . 73.1.3 Depointing and Antenna Dimensioning . . . . . . . . . . . . . . . . 7

3.1.3.1 Depointing . . . . . . . . . . . . . . . . . . . . . . . . . . 83.1.3.2 Antenna Diameter . . . . . . . . . . . . . . . . . . . . . . 8

3.2 Frequency Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.2.1 Downlink frequency plan selection . . . . . . . . . . . . . . . . . . . 93.2.2 Selection criterion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.3 ACI and CCI interferences . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.3.1 Cross polarization discrimination and isolation . . . . . . . . . . . . 113.3.2 CCI computation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.3.2.1 Free space losses . . . . . . . . . . . . . . . . . . . . . . . 143.3.2.2 Antenna gain variations . . . . . . . . . . . . . . . . . . . 153.3.2.3 Overall results . . . . . . . . . . . . . . . . . . . . . . . . 16

3.4 Carrier-to-Noise Ratio Requirements . . . . . . . . . . . . . . . . . . . . . 163.4.1 Clear Sky Condition Requirements . . . . . . . . . . . . . . . . . . 163.4.2 Rain Condition Requirements . . . . . . . . . . . . . . . . . . . . . 17

3.5 Contributions to Total Carrier-to-Noise Ratio . . . . . . . . . . . . . . . . 18

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3.6 Relationship between overall C/N and IBO . . . . . . . . . . . . . . . . . . 183.6.1 Uplink Carrier-to-Noise Ratio . . . . . . . . . . . . . . . . . . . . . 18

3.6.1.1 Set of attenuators and gains within the path of the carrier 193.6.1.2 Receiver noise factor and noise figure . . . . . . . . . . . . 193.6.1.3 System noise temperature . . . . . . . . . . . . . . . . . . 203.6.1.4 AU numerical value . . . . . . . . . . . . . . . . . . . . . . 21

3.6.2 Downlink Carrier-to-Noise Ratio . . . . . . . . . . . . . . . . . . . . 213.6.2.1 Assessments for AD calculation . . . . . . . . . . . . . . . 223.6.2.2 Losses from the HPA and transmitting antenna gain . . . 233.6.2.3 Free space losses . . . . . . . . . . . . . . . . . . . . . . . 243.6.2.4 Atmospheric gases attenuation . . . . . . . . . . . . . . . 243.6.2.5 AD numerical value . . . . . . . . . . . . . . . . . . . . . . 24

3.6.3 Carrier-to-Intermodulation-Noise Ratio . . . . . . . . . . . . . . . . 243.6.4 Carrier-to-Interference Ratio . . . . . . . . . . . . . . . . . . . . . . 253.6.5 Overall Carrier-to-Noise Ratio . . . . . . . . . . . . . . . . . . . . . 25

3.7 Earth station EIRP vs. G/T trade-off . . . . . . . . . . . . . . . . . . . . . 283.7.1 Uplink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283.7.2 Receiving satellite antenna gain . . . . . . . . . . . . . . . . . . . . 283.7.3 AES numerical value . . . . . . . . . . . . . . . . . . . . . . . . . . 283.7.4 Uplink trade-off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3.8 Cost Effective Design of the Earth Station . . . . . . . . . . . . . . . . . . 313.8.1 Antenna Tracking System . . . . . . . . . . . . . . . . . . . . . . . 31

3.8.1.1 Fixed Mount Antenna . . . . . . . . . . . . . . . . . . . . 313.8.1.2 Step Tracking Antenna . . . . . . . . . . . . . . . . . . . . 323.8.1.3 Monopulse Tracking Antenna . . . . . . . . . . . . . . . . 32

3.8.2 Antenna System Cost . . . . . . . . . . . . . . . . . . . . . . . . . . 323.8.3 Figure of Merit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323.8.4 Earth Station Architecture and Cost . . . . . . . . . . . . . . . . . 33

3.9 Rainy conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333.9.1 Rain attenuation for the downlink . . . . . . . . . . . . . . . . . . . 343.9.2 Rain attenuation for the uplink . . . . . . . . . . . . . . . . . . . . 343.9.3 Carrier-to-Interference Ratio with rainy conditions . . . . . . . . . . 343.9.4 Earth station G/T degradation due to the rain . . . . . . . . . . . . 363.9.5 Link performance degradation due to rain . . . . . . . . . . . . . . 38

3.10 Performance summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393.10.1 Performance with 0 dB margin . . . . . . . . . . . . . . . . . . . . . 393.10.2 Performance with 2 dB margin . . . . . . . . . . . . . . . . . . . . . 403.10.3 Overall Performance . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3.11 Complete frequency plan analysis and carriers allocation . . . . . . . . . . 423.12 Digital Transmission Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . 493.13 Conclusions and Final Design . . . . . . . . . . . . . . . . . . . . . . . . . 50

Appendices 52

A Satellite Depointing 53

B Link performances dependence on frequency 56B.1 Antenna gains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56B.2 Losses under clear sky conditions . . . . . . . . . . . . . . . . . . . . . . . 56

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B.3 Overall link performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

C Atmospheric gases attenuation 59

D Rain attenuation 61D.1 Rain attenuation model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61D.2 Predicted attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

E Carrier-to-Interference Ratio with rainy conditions 64E.1 Carrier-to-Interference Ratio dependency analysis . . . . . . . . . . . . . . 64E.2 Cross-polarisation discrimination with rainy conditions XPDrain . . . . . . 65E.3 XPDrain influence on the link . . . . . . . . . . . . . . . . . . . . . . . . . 66

F Earth Station 68F.1 Antenna System Cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68F.2 EIRP and Figure of Merit Results . . . . . . . . . . . . . . . . . . . . . . . 68F.3 RF Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69F.4 High Power Amplifier Costs . . . . . . . . . . . . . . . . . . . . . . . . . . 71

G Earth-station-to-satellite distance and elevation angles 73

H Satellite HPA in/out power transfer curves 74

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List of Figures1.1 Geographical location of coverage zones. . . . . . . . . . . . . . . . . . . . 2

3.1 Selected frequency plan for downlink . . . . . . . . . . . . . . . . . . . . . 103.2 Frequency reuse by linear polarization . . . . . . . . . . . . . . . . . . . . 123.3 Possible source and interferer positions for the lowest C/NI . . . . . . . . . 133.4 Antenna radiation pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.5 Contributions on the overall (C/N)t with (G/T )es = 12 dBK

1 . . . . . . . 263.6 Contributions on the overall (C/N)t with (G/T )es = 30 dBK

1 . . . . . . . 273.7 Overall (C/N)t vs IBO for different values of (G/T )es . . . . . . . . . . . . 273.8 Relationship between C/NT , required EIRPes and (G/T )es . . . . . . . . . 303.9 Curves of min. required EIRPes and (G/T )es for margins of 0 dB and 2 dB 313.10 Average temperature by geographical location in C . . . . . . . . . . . . . 383.11 Allocated spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433.12 Complete frequency plan for uplink and downlink . . . . . . . . . . . . . . 443.13 Carriers allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443.14 Communication payload with connections between OMUX outputs and

antenna feeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

A.1 Projection of a point on the xy reference plane. . . . . . . . . . . . . . . . 53

C.1 Attenuation by atmospheric gases and water vapor for different elevationangles E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

D.1 Nomogram to determine the specific rain attenuation R . . . . . . . . . . 62D.2 Computation of R for different values of R001, f and polarisations . . . . . 63

E.1 XPD/XPI model for clear sky and rainy conditions . . . . . . . . . . . . . 66

F.1 Antenna system cost as a function of effective gain and tracking system.Markers show antenna diameters of 1.5, 2, 2.5, 3, 3.5, 4 and 5 meters . . . 68

F.2 Pre-amplification coupling architecture. . . . . . . . . . . . . . . . . . . . . 69F.3 Post-amplification coupling architecture. . . . . . . . . . . . . . . . . . . . 70F.4 HPA power versus cost curves for solid-state (SS), travelling-wave tube

(TWT) and klystron (KLY) amplifier types. . . . . . . . . . . . . . . . . . 71

H.1 HPA power transfer curves for 3 carriers per transponder . . . . . . . . . . 74

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List of Tables1.1 Attitude control uncertainty. . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.1 Transponder and carrier configuration. . . . . . . . . . . . . . . . . . . . . 73.2 Required half-power beamwidths and associated maximum antenna diam-

eters for downlink coverage zones. . . . . . . . . . . . . . . . . . . . . . . . 83.3 Partial frequency plan performance dispersion . . . . . . . . . . . . . . . . 103.4 Complete frequency plan performances dispersion . . . . . . . . . . . . . . 103.5 Relative free space losses between the source and the interference . . . . . 143.6 (C/N)I values for any combination source-interference with clear sky con-

ditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.7 List of communication payload components from the RX antenna to the

HPA input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.8 Cascade components contributing to the receiver noise factor . . . . . . . . 203.9 List of communication payload components from the HPA output to the

TX antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243.10 AD values for each zone for each polarisation . . . . . . . . . . . . . . . . . 253.11 Rain attenuation exceeded for p = 0.075% on an average year: A0075, on

the downlink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343.12 Rain attenuation exceeded for p = 0.075% on an average year: A0075, on

the uplink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353.13 Contributions of the (C/N)I from the interferences . . . . . . . . . . . . . 353.14 Contributions of the (C/N)I from the source . . . . . . . . . . . . . . . . . 363.15 (C/N)I values for any combination source-interference with rainy conditions 363.16 G/T degradation due to rain by zone . . . . . . . . . . . . . . . . . . . . . 383.17 Uplink contributions summary for clear sky and rainy conditions, with 0 dB

margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393.18 Downlink contributions summary for clear sky and rainy conditions, with

0 dB margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403.19 Uplink contributions summary for clear sky and rainy conditions, with 2 dB

margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403.20 Downlink contributions summary for clear sky and rainy conditions, with

2 dB margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413.21 Overall link performance summary for clear sky and rainy conditions . . . 413.22 Carriers assignment per earth station. It should be read: 5H = carrier

number 5 with horizontal polarisation in both links . . . . . . . . . . . . . 453.23 Carriers details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463.24 Worst case link performances summary for rainy conditions with the se-

lected frequency plan and 2 dBmargin . . . . . . . . . . . . . . . . . . . . . 473.25 Different FEC and modulation schemes. . . . . . . . . . . . . . . . . . . . 493.26 Carrier bitrate and network capacity for 0dB margin design . . . . . . . . . 503.27 Carrier bitrate and network capacity for 2dB margin design . . . . . . . . . 503.28 Earth-station final design parameters. No margin. . . . . . . . . . . . . . . 503.29 Earth-station final design parameters. 2dB margin. . . . . . . . . . . . . . 51

A.1 Depointing components for all downlink beams (A, B, C) and uplink (U)antenna. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

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E.1 Depolarisation with rainy conditions for p = 0.075% for interferences . . . . 66E.2 Equivalent cross-polarisation isolation (XPI*) for the interferences under

rainy conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

F.1 Numerical results for the earth station antenna system taking a 0dBmargin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

F.2 Numerical results for the earth station antenna system taking a 2dBmargin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

F.3 Earth-station RF equipment and antenna costs with pre-amplificationcoupling taking a 0dB margin. . . . . . . . . . . . . . . . . . . . . . . . 71

F.4 Earth-station RF equipment and antenna costs with pre-amplificationcoupling taking a 2dB margin. . . . . . . . . . . . . . . . . . . . . . . . 72

F.5 Earth-station RF equipment and antenna costs with post-amplificationcoupling taking a 0dB margin. . . . . . . . . . . . . . . . . . . . . . . . 72

F.6 Earth-station RF equipment and antenna costs with post-amplificationcoupling taking a 2dB margin. . . . . . . . . . . . . . . . . . . . . . . . 72

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1. SystemIn this project a satellite system is designed in order to meet certain performance require-ments while being subject to certain constraints (cost, allocated spectrum, etc.).

1.1 Description

The system provides digital services to a set of users which are located in 3 distinctgeographical zones. Withing each zone, user stations are evenly connected to each of the8 stations that are installed.

Zone A 8 stations located in Western Europe (France and United Kingdom)

Zone B 8 stations located in Eastern Europe (Italy)

Zone C 8 stations located in Northern Africa

1.1.1 Coverage

There are 3 beams for downlink each one serving one geographical zone. On the otherhand, there is only one uplink beam covering all zones. This is shown in figure 1.1. Eachof the three zones A, B and C are viewed from the satellite within a cone with apex angleequal to 0.75. The global uplink zone from which the satellite receives is viewed fromthe satellite with an apex angle of 2.78.

1.1.2 Carrier assignment

One carrier is to be assigned to each one-way link from one station to each zone. It will beassumed that traffic from a given station is equally distributed among all carriers. Trafficrequirements are identical for all stations.

1.1.3 Modulation and Coding

Quadrature Phase Shift Keying (QPSK) modulation with a spectral efficiency = 1.45 bit s1 Hz1

is to be used.

Demodulators introduce a 1.5dB degradation with respect to the theoretical gray-codedQPSK performance.

Forward error correction (FEC) is to be implemented using a 7/8 code rate resulting in a2.2dB coding gain at BER = 106

1

Figure 1.1: Geographical location of coverage zones.

1.1.4 Polarization

In order to double capacity over a given frequency band, transmission using vertical andhorizontal polarization will be used. Carriers are to be equally distributed among allpolarizations

1.1.5 Allocated Spectrum

Available spectrum consists of two paired 500 Mhz blocks that have been allocated inaccordance to ITU specifications in the Ku band:

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Uplink 12.75-13.25 GHz band

Downlink 11.20-11.70 GHz band

Carriers should be equally distributed among all available satellite resources leading to anequal distribution of carriers among all available spectrum. Total bandwidth devoted toguard bands between modulated carriers accessing a common satellite channel represents10% of channel bandwidth.

1.2 Satellite Characteristics

The satellite is a body-stabilized GEO satellite positioned at longitude 500E.

1.2.1 Attitude and Orbit Control Subsystem

1.2.1.1 Attitude Control

Attitude control refers to the controlling of the satellites orientation with respect to earth.Maintaining attitude is very important for the different subsystems and their correctfunctioning. In particular, the narrow beam antennas used for downlink transmission areparticularly sensitive to depointing due to imperfect attitude control. Uncertainty valuesfor satellite attitude control are shown in Table 1.1.

Axis UncertaintyRoll 0.05

Pitch 0.02

Yaw 0.3

Table 1.1: Attitude control uncertainty.

1.2.1.2 Station Keeping

Station keeping uncertainty is 0.05from nominal position both in latitude (East-Weststation keeping) and longitude (North-South station keeping). Maximum specified valuesof eccentricity and inclination are e = 5 104 and i = 0.03. The actual position of thesatellite within the station-keeping box is known from the station control centre with anerror of 0.02.

1.2.2 Communication Payload

1.2.2.1 Antennas

The satellite is fitted with two antennas:

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A 3-beam reflector antenna operating in both horizontal and vertical polarizationsto achieve 3dB downlink coverage on each of the three geographical zones A, B andC.

A single beam reflector antenna operating in both horizontal and vertical polariza-tions to achieve 3dB uplink coverage on the global zone.

Each of these has an efficiency factor = 0.55 and cross-polarization isolation is betterthan 25dB.

1.2.2.2 Satellite Channels

The communications payload comprises twenty-four 36MHz active channels (12 transpon-ders numbered from 1 to 12 for each polarization), equipped with 50W travelling-wavetube (TWT) amplifiers. Block diagram of the communications payload can be seen in thedesign section of this document (figure 3.14).

1.3 Earth Stations

1.3.1 Antennas

Earth station antennas have 60% efficiency when receiving and 50% when transmitting.Cross-polarization isolation at reception and transmission is better than 35dB. Side-lobecontribution to antenna noise temperature is 50K. Three types of antenna mountingsystems are considered:

Fixed mount antenna system (FMA) Step tracking antenna system (STA) Monopulse tracking antenna system (MPA)

1.3.2 Radio-Frequency Equipment

1.3.2.1 Transmitting Side

Each station transmits several carriers. All carriers from a given station are radiatedusing the same polarization. Two design solutions shall be considered:

Pre-amplification coupling: All carriers are amplified together with the same poweramplifier (HPA). A total output back-off of -8dB is used to operate the amplifier in thelinear part of its characteristics so as to keep intermod noise at a negligible level. A one-to-one redundancy scheme is to be considered. The cost of switching devices per installedHPA is one fourth of the cost of one amplifier.

Post-amplification coupling: Each carrier is power amplified using a dedicated HPAoperated at saturation. Carrier coupling is achieved after power amplification using a3-input port coupling device using band-pass filters and circulators. Coupling device

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insertion loss is 0.3dB and its cost is one third of the amplifier cost per input port. Aone spare for three active amplifier redundancy scheme (3/4) is considered. The cost ofswitching devices per installed HPA is one fourth of the cost of one amplifier.

For both solutions, feeder loss between HPA coupler output and transmit antenna inputis 1dB.

1.3.2.2 Receiving Side

Low noise amplifiers (LNA) with a noise effective input temperature TR=65K are used.A one-to-one redundancy scheme is considered. Insertion loss between antenna outputand LNA is 0.2dB including switches.

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2. Performance Objectives

2.1 Coverage

Beamwidth of all beams must be such that the coverage zone remains within the 3dBbeamwidth regardless of depointing of antennas. Depointing may arise from the followingphenomena:

Satellite motion about its center of mass (rotations about yaw, pitch and roll axes). Satellite motion within its station-keeping box (North-South and East-West). Alignment error of the antenna beams due to initial boresight misalignment.

2.2 Link Performance

The link performance objectives for clear-sky conditions and rainy conditions will bedefined considering ITU recommendation ITU-R S.522 [1]:

The ITU Radiocommunication Assembly [...] recommends

1.That the bit-error ratio at the output of the HRDP [Hypothetical ReferenceDigital Path], as defined in Recommendation ITU-R S.521, should not exceedthe provisional values given below:

1.1 - One part in 106, 10 min mean value for more than 20% of any month;

1.2 - One part in 104, 1 min mean value for more than 0.3% of any month;

2.3 Provision for External Interference

The system design should incorporate a provision of 1.5dB on the overall link perfor-mance to accommodate degradations not taken into account in the system description(interference from other satellites).

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3. DesignThis section contains a detailed explanation of all steps and calculations that were neces-sary for the correct dimensioning and design of the system.

3.1 Transponder Usage and Carrier Capacity

This section explains the distribution of carriers among all available satellite transpondersas well as carrier capacity and antenna dimensioning.

3.1.1 Transponder Usage

As stated in section 1.1.2, a single carrier is assigned to each one-way link from onestation to each zone. Since there 8 stations inside each of the 3 zones, we will needa total of 8 3 3 = 72 carriers. On the other hand, there are 24 available satellitechannels (transponders) each having a bandwidth of 36 MHz of which 10% is used forFDM guardbands between carriers. Table 3.1 summarizes transponder usage and availablebandwidth per carrier.

Number of carriers (NC) 72Number of transponders (NT ) 24Carriers per transponder (NCT ) 3Transponder bandwidth (BT ) 36 MHzCarrier bandwidth (BC) 10.8 MHz

Table 3.1: Transponder and carrier configuration.

3.1.2 Available Carrier Bitrate

Carrier capacity is a function of the coding rate and the spectral efficiency of themodulation scheme , all of which were defined in section 1.1.3. Available informationbitrate per carrier is thus the following:

Rcb = BC = 13.70 Mbit s1 (3.1)

3.1.3 Depointing and Antenna Dimensioning

In order to dimension the parabolic reflectors of satellite, beamwidths need to be defined.In section 1.1.1 the apex angles under which each zone is seen from the satellite werespecified. Naturally one would set beamwidths to these values. However, this approachwill not guarantee full coverage since antenna boresight is not always aligned with thecoverage center. It is of interest then to calculate the maximum depointing angle due tostation keeping and attitude control uncertainty. Necessary beamwidth for full coveragewill then be calculated and antenna dimensions will be defined.

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3.1.3.1 Depointing

A thorough analysis on the method for calculating depointing values of the geostationarysatellite is discussed in appendix 1.2. To summarize, the following values were obtainedfor all coverage zones:

Total depointing values

A = 0.0906

B = 0.0887

C = 0.0842

U = 0.0869

(3.2a)

(3.2b)

(3.2c)

(3.2d)

3.1.3.2 Antenna Diameter

As described in section 1.2.2.1, coverage zones A, B and C are seen from the satellitedownlink antenna with an apex of = 0.75. In order to guarantee coverage, depointing() should be taken into account. This way the following half-power beamwidth shouldbe attained:

3dB = + 2 (3.3)

Half-power beamwidth in a parabolic reflector is approximately given by the followingexpression:

3dB = 70 D

(3.4)

Where denotes wavelength and D antenna diameter. Downlink antenna diameter isnow dimensioned so that all coverage zones are within the 3dB.Table 3.2 shows maximumantenna diameter values for the previous condition to hold. Note that frequency used forcalculations is the maximum downlink frequency1 11.7 GHz.

Zone 3dB Dmax

A 0.9313 1.90 mB 0.9275 1.90 mC 0.9184 1.92 m

Table 3.2: Required half-power beamwidths and associated maximum antenna diametersfor downlink coverage zones.

Downlink and uplink maximum antenna diameters are thus:

DDLmax = 1.9 m

DULmax = 0.53 m

(3.5)

(3.6)

1Higher frequencies lead to more selective beamwidths.

8

3.2 Frequency Planning

The frequency plan for clear sky conditions is selected by taking into account the depen-dence of C/N on the choice of carrier frequency. It can be shown that C/N performancesare better for higher frequencies (see appendix B).

3.2.1 Downlink frequency plan selection

This section only analyses the choice of the downlink frequency plan, which determinesthe carriers to be used as function of the destination zone. For this first analysis, uplinkcarriers are assumed to be spread among all the available carriers since any station isable to reach any zone. In section 3.11, carrier allocation is analyzed in detail in order tooptimize system performances.

Results from appendix let link performance computation of the three zones with differentfrequency assignments. After assigning a given frequency band for each zone, link C/Ncan be computed for each zone. Then, the overall system performance is evaluated withsome selection criterion.

3.2.2 Selection criterion

A frequency plan selection criterion needs to be defined. At first sight, the mean C/N overall the coverage zones seems to be a good criterion. However, it can be shown that thismean is the same (considering clear sky conditions) for all possible combinations.

Since the mean performance (i.e. mean value of C/N) will not vary despite the frequencycarrier assignment, the dispersion of the C/N over the coverage zones seems to be a moreappropriate criterion. One suitable indicator of the dispersion is the variance. Therefore,the selection criterion is the variance of the C/N per zone for a given frequency plancombination.

Let be ABC the frequency plan which assigns:

the lowest frequency band to the zone A (11.20-11.36 GHz), the middle frequency band to the zone B (11.36-11.53 GHz) and the highest frequency band to the zone C (11.53-11.70 GHz).

Then the computation of the dispersion is as follows:

From table 3.4, the option with the lowest C/N dispersion is BCA + CAB (highlighted).Consequently, the frequency plan for the downlink is shown in the figure 3.1.

9

Frequency Plan C/NdB Variance

CBA 0.0101CAB 0.0258BCA 0.0301BAC 0.0656ABC 0.0815ACB 0.0618

Table 3.3: Partial frequency plan performance dispersion

Complete Frequency Plan C/NdB Variance

Horizontal: CBA + Vertical: BAC 0.0757Horizontal: CBA + Vertical: ACB 0.0719Horizontal: BCA + Vertical: ABC 0.1116Horizontal: BCA + Vertical: CAB 0.0559Horizontal: ACB + Vertical: BAC 0.1274Horizontal: ABC + Vertical: CAB 0.1073

Table 3.4: Complete frequency plan performances dispersion

11.20 GHz 11.70 GHz1 2 3 4 5 6 7 8 9 10 11 12

Horizontal pol. Zone B Zone C Zone A

11.20 GHz 11.70 GHz1 2 3 4 5 6 7 8 9 10 11 12

Vertical pol. Zone C Zone A Zone B

Figure 3.1: Selected frequency plan for downlink

3.3 ACI and CCI interferences

Since the multiple access strategy being implemented is based on an FDMA architectureand the frequency bands are reused thanks to quasi-orthogonal polarization, adjacentchannel interference (ACI) and co-channel interference (CCI) need to be considered.

Adjacent channel interference depends on the filter characteristics and it can beminimized by adopting larger guard bands. The guard bands have been previouslydefined by a design constraint: 10% of the channel bandwidth is to be dedicated toguards.

Because of the lack of data and specifications over the filter banks and multiplexersused on the satellite payload and the earth stations, these types of interferences arenot taken into account.

Co-channel interference is crosstalk from two different radio transmitters using thesame frequency channel. This means that while one transmitter is emitting on onespecific channel, power of another transmission using the same frequency channelinterferes with it.

10

The non-ideal polarization isolation/discrimination of the antennas (both, trans-mitting and receiving) translates into CCI when two stations use the same carrierfrequency with different (horizontal and vertical) polarizations.

3.3.1 Cross polarization discrimination and isolation

Cross polarization discrimination (XPD) is defined as follows:

Assuming two waves with the same power, the same frequency fc and different linearpolarization. Then, XPD is the power ratio at the output of the receiving antenna betweenthe signal of wanted polarization and the signal of the opposite polarization.

XPD =Cfc,vrx,wanted

Cfc,hrx=Cfc,hrx,wanted

Cfc,vrx(3.7)

Where Cfc,vrx is the power of the signal at the output of the receiving antenna, at frequencyfc and vertical polarization.

In dB, XPDdB = 10 log(XPD)Cross polarization isolation (XPI) is defined as follows. A non-ideal antenna designed totransmit waves in a specific linear polarization, fed by a source at frequency fc, transmitswaves in both polarizations. In this context, XPI is the power ratio between the signalwith the wanted polarization and the signal with the opposite.

XPI =Cfc,vtx,wanted

Cfc,htx=Cfc,htx,wanted

Cfc,vtx(3.8)

Where Cfc,vtx is the power of the signal at the output of the transmitter antenna, atfrequency fc and vertical polarization.

In dB, XPIdB = 10 log(XPI)

3.3.2 CCI computation

For the specified frequency plan, the problem of CCI relies on frequency reuse by linearpolarization. On the downlink, frequency reuse is achieved by spatial separation, so thereis no CCI. However, on the uplink, frequency reuse is achieved by dual linear polarization.Therefore, with the aforementioned constraints and assumptions, (C/N)I is determinedonly by CCI on the uplink channel.

Now, lets assume two earth stations transmitting with the same carrier frequency butdifferent polarizations and one of these carries the wanted signal.

Diagram 3.2 shows the relationship between the different signals at the transmitter side,the channel and the receiver side.

Where:

11

Figure 3.2: Frequency reuse by linear polarization

For the transmitting antennas, the relationship between the polarised signals are:XPI1 =

TxH,1

TxV,1and XPI2 =

TxV,2

TxH,2

At the channel, the signals are attenuated by free space losses:Rxi =

Txi

LZ

For the receiving antenna, the relationship between the different components at theoutputs are:

PRX,H =RxH +

RxV

1

XPD

PRX,V =RxV +

RxH

1

XPD

At the horizontal receiver, the following components are found:

PRX,H =

RxH +

RxV 1XPD

=TxH,1

LZ,1+

TxV,1

XPD LZ,1 +TxH,2

LZ,2+

TxV,2

XPD LZ,2=TxH,1

LZ,1+

TxH,1

XPI1 XPD LZ,1 +TxV,2

XPI2 LZ,2 +TxV,2

XPD LZ,2

=TxH,1

LZ,1(

1 +1

XPI1 XPD

)+TxV,2

LZ,2(

1

XPI2+

1

XPD

)(3.9)

For PRX,H , the wanted signal is composed of all the components coming from PTX,1 and theinterference is composed of all the components coming from PTX,2. The same reasoningcan be applied to the other receiver.

Finally, the value of (C/N)I is given by the power ratio between the useful and theinterfering components.

12

CN

I

=TxH,1

TxV,2 LZ,2LZ,1

1 +1

XPI1 XPD1

XPI2+

1

XPD

(3.10)

Assuming that all sources transmit with the same power, then:

C

N

I

=LZ,2

LZ,1

1 +1

XPI1 XPD1

XPI2+

1

XPD

(3.11)

In dB,

C

N

I,dB

= LZ,2,dB LZ,1,dB + 10 log(

1 + XPI11 XPD1XPI12 + XPD

1

)(3.12)

In order to find the lowest value of (C/N)I , the worst case condition will be assumed.This means that the source signal comes from the furthest position with respect to theboresight (lowest receiving antenna gain) and the interfering signal comes from the nearestposition (highest associated antenna gain). Figure 3.3 shows all the possible locations ofthe source and interferer in the previously mentioned scenario.

Figure 3.3: Possible source and interferer positions for the lowest C/NI

13

For the sake of simplicity, only free space losses (Lfs) and receiving antenna gain vari-ations (Grx) are considered in the computation of Lz,dB. Where Lz,dB = LZ,2,dB LZ,1,dB.

This means that:Lz,dB = Grx,dB + Lfs,dB (3.13)

3.3.2.1 Free space losses

Free space losses depend on the carrier frequency f and the distance of the link R, whichis related to the location of the earth station on Earth.

Lfs,dB = 10 log(

(4piRinterference f/c)2(4piRsource f/c)2

)

= 10 log(R2interferenceR2source

)

= 10 log(

1 + 0.42 (1 cos lI cosLI)1 + 0.42 (1 cos lS cosLS)

)

= 10 log(rI

rS

)= 10 log rI 10 log rS

(3.14)

Where:

LS and LI are the earth station-to-satellite relative longitude of the source and theinterference respectively.

lS and lI are the earth station latitude of the source and the interference respectively. r = 1 + 0.42 (1 cos l cosL); with rS for the source and rI for the interference.

Source locationZone l L r rdB

A 52.8 -5.7 1.167 0.67B 43.2 10.8 1.119 0.49C 31.3 -5 1.062 0.26

Interference locationZone l L r rdB

A 45.2 -2.1 1.124 0.51B 41.4 5 1.106 0.44C 36.7 -2.4 1.084 0.35

Table 3.5: Relative free space losses between the source and the interference

The smallest value of Lfs,dB is reached when rI is minimum and rS is maximum. Fromthe table 3.5, those minimum and maximum values can be found.

14

Thus,Lfs,dB = min (rI,dB)max (rS,dB)

= 0.35 dB 0.67 dB= 0.32 dB

(3.15)

3.3.2.2 Antenna gain variations

The antenna gain is maximum at boresight. In direction , the gain falls and the attenu-ation for small off-axis angles is given by:

AdB = 12 (

3dB

)2(3.16)

Figure 3.4: Antenna radiation pattern

Since all the possible source locations are placed on the edge of coverage, their attenuationare 3 dB by design.

AS,dB 3 dB

Then, all the possible interference locations are placed at the same direction angle Ifrom the boresight.

I = 3dB/2 zone3dB (uplink) 2.9538

zone 0.75

I 0.727

AI,dB 0.727 dB

Finally, it is possible to compute the difference between the gains at the interference andthe source:

Grx,dB = AI,dB AS,dB = 0.727 dB 3 dB = 2.273 dB (3.17)

15

3.3.2.3 Overall results

The smallest value (i.e. worst case) of (C/N)I can be calculated as follows:

C

N

I,dB

= Grx,dB + Lfs,dB + 10 log(

1 + XPI1 XPD1XPI1 + XPD1

)(3.18)

XPI1 = XPI2 35 dBXPD 25 dBGrx,dB 2.273 dBLfs,dB 0.32 dB

C

N

I,dB

= Grx,dB + Lfs,dB + 24.586 dB

= 2.273 dB 0.32 dB + 24.586 dB= 21.99 dB

(3.19)

This value is met when the source comes from zone A and the interference comes fromzone C.

(C/N)I values can be computed for any combination source-interference. Table 3.6 pro-vides these for all possible cases.

Source InterferenceA B C

A 22.15 dB 22.08 dB 21.99 dBB 22.33 dB 22.26 dB 22.17 dBC 22.56 dB 22.49 dB 22.40 dB

Table 3.6: (C/N)I values for any combination source-interference with clear sky conditions

3.4 Carrier-to-Noise Ratio Requirements

Total carrier-to-noise ratio requirements for a station-to-zone link can be derived fromBER objectives under clear-sky conditions. Rainy conditions impact service availabil-ity.

3.4.1 Clear Sky Condition Requirements

In order to meet BER objectives (BER = 106), a certain Eb/N0 value is required at thestation receiver input. It can be calculated taking modulation scheme, receiver degrada-tion and FEC gain into account (section 1.1.3):

16

Eb

N0= 10.53 dB + 1.50 dB 2.20 dB = 9.83 dB (3.20)

Using previously calculated carrier bitrate and carrier bandwidth values, carrier-to-noise-spectral-density and carrier-to-noise ratios can be obtained. Note that a 1.5 dB marginis incorporated as per section 2.3:

Total CNR requirements under clear-sky conditions(C

N0

)T

=Eb

N0 10 logRcb + 1.5 dB = 82.70 dB Hz(

C

N

)T

=

(C

N0

)T

10 logBC = 12.36 dB

(3.21a)

(3.21b)

3.4.2 Rain Condition Requirements

Under rainy conditions the targeted BER is (BER = 104). Modulation scheme andreceiver degradation are the same as for clear sky conditions. However, FEC gain changesbecause it is defined with respect to a BER value.

Since FEC gain at the targeted BER is unknown and the FEC scheme is not madeexplicit, the gain value can be approximated by assuming that the coding gain curve hasthe same behaviour as a Convolutional-Viterbi coding scheme with the same coding rate(i.e. = 7/8). Then:

GFEC(BER = 104) GFEC(Vit = 10

4)GV it(BER = 106)

GFEC(BER = 106) 1.65 dB

(3.22)

The required Eb/N0 is:

Eb

N0= 8.40 dB + 1.50 dB 1.65 dB = 8.25 dB (3.23)

Then, required carrier-to-noise-spectral-density and carrier-to-noise ratios can be ob-tained.

Total CNR requirements under rainy conditions(C

N0

)T

=Eb

N0 10 logRcb + 1.5 dB = 81.12 dB Hz(

C

N

)T

=

(C

N0

)T

10 logBC = 10.78 dB

(3.24a)

(3.24b)

17

3.5 Contributions to Total Carrier-to-Noise

Ratio

Total carrier-to-noise ratio can be seen as the contribution of several factors:(C

N

)1T

=

(C

N

)1U

+

(C

N

)1D

+

(C

N

)1IM

+

(C

I

)1U

+

(C

I

)1D

(3.25)

Where:(CN

)1T

= Total carrier-to-noise ratio.(CN

)1U

= Uplink carrier-to-noise ratio.(CN

)1D

= Downlink carrier-to-noise ratio.(CN

)1IM

= Carrier-to-intermodulation-noise ratio.(CI

)1U

= Uplink carrier-to-interference ratio.(CI

)1D

= Downlink carrier-to-interference ratio.

In the following subsections each of these components will be studied separately.

3.6 Relationship between overall C/N and IBO

Since the overall available carrier-to-noise ratio, (C/N)T , depends on different compo-nents, the behaviour of each component w.r.t. the operation point of the high poweramplifier (HPA) needs to be analyzed.

3.6.1 Uplink Carrier-to-Noise Ratio

The HPA operation point is determined by the Input Back-Off (IBO) and Output Back-Off (OBO) parameters. Components in the path between the receiver input and HPAinput determine the relationship between the available C/NU and the operation point ofthe amplifier.

Since,

IBO = Pi,3Pi,1,sat

= Pi,3 = IBO Pi,1,sat

Pi,3 = CU

i L1i

iGi

Where, Li and Gi are respectively the losses and gains from the satellite receiverinput to the HPA input.

18

Then,C

N

U

=CU

NU=Pi,1,s

i Li

NU

iGi IBO = Pi,1,s

i Li

k Trx,s Bn

iGi IBO (3.26)

Therefore,C

N

U

= AU IBO (3.27)

AU is the required single carrier C/NU at the satellite receiver input which sets the HPAin saturated operation point (i.e. IBO = 0 dB).

As defined before, AU is composed of two elements: first, the power at the receiver inputwhich determines saturation in the HPA and, second, the noise power measured at thereceiver input.

It is calculated as follows:

AU =Pi,1,sat

i Li

k Trx,s Bn

iGi(3.28)

In dB,

AU,dB = Pi,1,sat,dB 10 log(k Trx,s Bn) +i

Li,dB i

Gi,dB (3.29)

3.6.1.1 Set of attenuators and gains within the path of the carrier

With the block diagram of the satellite communication payload, it is possible to find allthe main components in the path followed by each carrier. This is shown in the figure3.14.

All those components placed in the path from the antenna down to the HPA input (Liand Gi) have to be taken into account to compute the value AU as explained before (seeequations 3.28 and 3.29). These components are listed in table 3.7.

3.6.1.2 Receiver noise factor and noise figure

Friiss formula is used to calculate the total noise factor of any system modeled as a setof components in cascade, each one with its own noise factor Fi and gain Gi.

Fsys = F1 +F2 1G1

+F3 1G1 G2 +

F4 1G1 G2 G3 + . . .

(3.30)

Also, it is possible to define the noise figure NF, which is linked to the noise factor F by:NF = 10 log(F ).Here, the system is the receiver which is composed by a set of subsystems or componentsin cascade. In order to determine the value of Fsys, Friiss formula is used taking intoaccount all the components inside the receiver which contribute to the system noise factor.Those components are listed in table 3.8.

19

Item Subsystem Gi [dB] Li [dB]

1 Antenna to receiver feeder loss 0.72 Input filter (FLT) 0.23 Switch 0.14.1

Receiver

LNA 204.2 13 GHz amplifier 204.3 Frequency converter 104.4 11.5 GHz amplifier 105 Hybrid coupler (H) 3 + 0.16 IMUX 1.17 Switch (S 2/3) 0.18 Receiver to driver feeder loss 0.29 Attenuator (A) 510 Driver (D) 25

Total 75 20.5

Table 3.7: List of communication payload components from the RX antenna to the HPAinput

Item Subsystem Gi [dB] NFi [dB]

1 Low noise amplifier 20 4.52 13 GHz amplifier 20 6.03 Frequency converter -10 7.04 11.5 GHz amplifier 10 6.05 Driver (D) 25 7.06 HPA at saturatioin 55 28.0

System (receiver) 4.55

Table 3.8: Cascade components contributing to the receiver noise factor

Then the resulting system noise factor and noise figure give the receiver equivalent tem-perature:

Fsys = 2.85

NFsys = 4.55 dB

TR = 537.13 K

(3.31)

3.6.1.3 System noise temperature

The noise temperature, T , is one way of expressing the level of present noise power, N .The power spectral density of the noise is expressed in terms of the temperature as follows:N0 = k T .The system noise temperature is the equivalent temperature which would produce thesame noise power density measured at the receiver input.

Tsys =TA

LFRX+ TF

(1 1

LFRX

)+ TR (3.32)

20

This temperature takes into account all the noise sources:

Noise power received by the antenna, determined by TA. Noise power generated by the feeder (modeled as an attenuator LFRX), determined

by TF .

Equivalent noise power added by the receiver, determined by TR = T0 (F 1).Where F is the system noise factor of the receiver and T0 = 290 K.

For the receiving antenna at the satellite, it can be assumed:

TA = 250 K TF TA = Tsys TA + TR

Which gives the system noise temperature:

Tsys = 787.13 K (3.33)

Also, for the HPA, the input power is linked to the output power by the gain. Thisgives the relationship between the powers at the input and output at saturated operationpoint.

Pi,1,sat =Po,1,sat

GHPAPi,1,sat,dB = 10 log(Po,1,sat)GHPA,dB

(3.34)

Parameter valuePo,1,sat 50 WGHPA,dB 55 dBPi,1,sat,dB 38.01 dB W

3.6.1.4 AU numerical value

Finally, to obtain the value of AU,dB, the equation 3.29 is used with the following param-eters values.

Parameter valuePi,1,sat,dB 38.01 dB WTrx,s 787.13 KBn 10.8 MHzLi 20.5 dBGi 75 dB

AU,dB 36.79 dB

3.6.2 Downlink Carrier-to-Noise Ratio

The OBO parameter is defined by the HPA operation point and depends on the IBO.Available EIRP at the transmitting antenna depends on the HPA output power, which is

21

related to the OBO. Therefore, downlink performances are linked to the OBO, then theyare linked to the IBO too.

Since,

OBO = Po,3Po,1,sat

= Po,3 = OBO Po,1,sat

Then,C

N

D

=CD

ND=Po,1,sat OBO Gtx,s Grx,es

k Trx,es Bn

i Li(3.35)

C/ND depends on the EIRP but also on the G/T at the receiver antenna and pathlosses.

C

N

D

=Po,1,sat Gtx,sk Bn

i Li(G

T

)rx,es

OBO (3.36)

Therefore,

C

N

D

= AD (G

T

)rx,es

OBO (3.37)

With,

AD =Po,1,sat Gtx,sk Bn

i Li

(3.38)

Where the OBO is a function of the IBO as defined in appendix H (equation H.1).

In dB,

AD = 10 log(Po,1,sat

k Bn

)+Gtx,s,dB

i

Li,dB (3.39)

3.6.2.1 Assessments for AD calculation

In order to calculate the value of AD, all gains and losses from the HPA output to thereceiving antenna at the earth station must be taken into account. These components arelisted below:

Losses from the HPA output to the transmitting antenna at the satellite. Transmitting antenna gain at the satellite, for the worst case. It means that the

receiving antenna is situated at the EOC.

Free space (F.S.) losses: LFS. The worst condition is given by the earth stationsituated on the furthest position w.r.t. the satellite. It can be assumed that thiscondition is met when the earth station is located on the north of the zone at theEOC.

Losses by atmospheric gases attenuation (A.G.): LAG. Since the smaller the eleva-tion angle is, the higher the atmospheric gases attenuation is, the worst condition ismet for the furthest location of the earth station w.r.t the satellite. Thus, the worst

22

condition for free space losses implies meeting the worst condition for atmosphericgases.

Also, regarding the carrier frequency, from the previously defined frequency plan, it shouldbe chosen the worst condition for each zone (i.e. the worst conditions w.r.t. the linkperformance). It means that the computation for each case should be done with thelowest frequency in the corresponding frequency band.

3.6.2.2 Losses from the HPA and transmitting antenna gain

Since, at the satellite, the transmitting antenna dish is the same for all the frequencybands, the value of 3dB is different for each zone depending on the carrier frequency.

This is,

3dB = 70

D

= 70 cf D

(3.40)

Then, the maximum antenna gain is,

Gtx,max = (piD

)2

= 4836123dB

(3.41)

Where, D is the antenna dish diameter, f = c/ is the carrier frequency, is the antennaefficiency and 3dB is given in degrees.

Taking into account the depointing angles of the transmitting antenna for each zone, theantenna gain variation at the edge of coverage (EOC) is given by the roll-off:

Geoc,dB = 3 ( + 2

3dB

)2(3.42)

Where, = 0.75 is the cone apex angle of the zone viewed from the satellite and isthe depointing angle.

Finally, adding the losses Ltx from the HPA output to the antenna input:

Gtx,eoc,dB = Gtx,max,dB Geoc,dB Ltx,dB (3.43)

Ltx is composed of all the losses added by the components within the path of the carrierfrom the HPA output to the antenna. These subsystems are listed in the table 3.9.

23

Item Subsystem Li [dB]

1 Switch (S 3/2) 0.12 OMUX 0.53 Output filter (HF) 0.14 HPA to antenna feeder loss 0.3

Total Ltx 1.0

Table 3.9: List of communication payload components from the HPA output to the TXantenna

3.6.2.3 Free space losses

Free space losses are given by the following expression as explained in section B.2:

LFS = (4pi R0 f/c)2 (R/R0)2(R/R0)

2 = 1 + 0.42 (1 cos l cosL) (3.44)

3.6.2.4 Atmospheric gases attenuation

Calculation of atmospheric losses due to gases are detailed in appendix C.

3.6.2.5 AD numerical value

Under the aforementioned conditions, it is possible to compute the value of AD for eachzone for each polarisation. The results are shown in table 3.10.

The values of the elevation angles, latitudes and longitudes of the earth stations are takenfrom appendix G.

Thus, the selected value is the minimum of all the cases, i.e. each zone with both polari-sations:

AD = 10.5 dB K (3.45)

3.6.3 Carrier-to-Intermodulation-Noise Ratio

Intermodulation (IM) noise is generated by the intermodulation products, which increasesfor higher values of IBO.

C/NIM is measured at the HPA output, considering that its input is noiseless. Oncethe IBO is defined, output power is detrmined by the OBO and intermodulation noise isdetermined by IM.

Since,

IM = Po,1,IMPo,1,sat

= Po,1,IM = IBO Po,1,sat

24

Earth station position Zone A, north Zone B, north Zone C, north UnitPolarisation Hor Ver Hor Ver Hor VerBand min. frequency 11.53 11.37 11.20 11.53 11.37 11.20 GHz

Depointing 0.091 0.091 0.089 0.089 0.084 0.084 deg + 2 0.932 0.932 0.928 0.928 0.918 0.918 deg3dB 0.963 0.978 0.992 0.963 0.978 0.992 degLosses Tx Ltx 1.00 1.00 1.00 1.00 1.00 1.00 dBGtx,max 44.57 44.45 44.32 44.57 44.45 44.32 dBRoll-off at EOC 2.81 2.73 2.63 2.78 2.65 2.57 dBGtx,eoc 40.76 40.72 40.69 40.79 40.80 40.75 dBLat. 53.00 53.00 45.50 45.50 36.50 36.50 degLon. 1.25 1.25 12.80 12.80 1.25 1.25 degLon. (relative) -3.75 -3.75 7.80 7.80 -3.75 -3.75 degElevation angle E 29.40 29.40 37.11 37.11 47.52 47.52 degF.S. losses LFS 205.43 205.30 205.02 205.28 204.98 204.85 dBA.G. losses LAG 0.10 0.10 0.08 0.08 0.07 0.07 dB

Ad 10.49 10.57 10.84 10.69 11.02 11.09 dBK

Table 3.10: AD values for each zone for each polarisation

Then,C

N

IM

=Po,3

Po,1,IM=Po,1,sat OBOPo,1,sat IM =

OBO

IM(3.46)

Where the IM is a function of the IBO. This relation as well as amplifier models aredefined in appendix H.

3.6.4 Carrier-to-Interference Ratio

(C/N)I takes into account the interferences originated by ACI and CCI. As explainedin section 3.3, the problem is principally due to frequency reuse in the uplink. Thismeans that it mainly depends on the cross-polarisation isolation of the antennas at thetransmitter and the receiver and their positions in the coverage zone.

Then, the value for (C/N)I is calculated for the worst case, which doesnt depend on theIBO parameter and, therefore it is assumed constant.

The value previously obtained is:

C

N

I,dB

= 21.99 dB (3.47)

3.6.5 Overall Carrier-to-Noise Ratio

After computing the contribution of each C/N component, it is possible to obtain theoverall C/N curve as a function of the IBO.

25

Figure 3.6 shows the different contributions for the overall C/N . In this case, becauseof the small value of (G/T )es = 12 dBK

1, the curve of (C/N)D is more limiting thanthe curve of (C/N)U . Therefore, the overall C/N is mainly defined by (C/N)D and(C/N)IM .

In the other hand, the higher the (G/T )es, the smaller the contribution of (C/N)D. Figure3.6 shows the different contributions for the overall C/N for (G/T )es = 30 dBK

1. Inthis case, the curve of (C/N)U is more limiting than the curve of (C/N)D. Therefore, theoverall C/N is mainly defined by (C/N)U and (C/N)IM .

As (G/T )es gets higher, the influence of (C/N)D in the overall C/N gets smaller. If(G/T )es tends to infinity, then there will not be noise contribution from the downlink.Then, the C/NT curve will be defined only by (C/N)U , (C/N)IM and (C/N)I .

Taking different values of G/T at the earth station, overall C/N is computed and theresults are shown in the figure 3.7.

30 25 20 15 10 510

0

10

20

30

40

50

IBO (dB)

C/N

(dB

)

(C/N)U

(C/N)D with (G/T)

ES = 12 dBK1

(C/N)IM

(C/N)I

(C/N)T

Figure 3.5: Contributions on the overall (C/N)t with (G/T )es = 12 dBK1

For small IBO values, there is a small noise contribution from intermodulation products(IM). Then, the main limitation comes from either the uplink or the downlink, dependingon the G/T contribution.

For higher IBO values (closer to 0 dB), noise contribution from IM is bigger than contri-butions from the uplink or downlink. This is because IM increases with the IBO (moreIM noise) and uplink/downlink performances are better for higher IBOs.

Also, interference noise contribution (by frequency reuse) does not depend on the IBOand it is kept constant for any operation point (OP) at the HPA. This sets a limitationon the overall performance that cannot be overcome by changing the OP.

The table presented below summarizes minimum required G/T values, maximum availableC/NT and IBO parameter for required C/NT with 0 dB and 2 dB margins.

26

30 25 20 15 10 50

5

10

15

20

25

30

35

40

45

50

IBO (dB)

C/N (dB)

(C/N)U

(C/N)D with (G/T)

ES = 30 dBK1

(C/N)IM

(C/N)I

(C/N)T

Figure 3.6: Contributions on the overall (C/N)t with (G/T )es = 30 dBK1

Figure 3.7: Overall (C/N)t vs IBO for different values of (G/T )es

Margin 0 2 dBRequired C/NT 12.36 14.36 dBMin. G/TES 13.70 18.00 dBRelated IBO -12.97 -14.27 dBLargest C/NT 17.02 dBRelated IBO -5.97 dB

27

3.7 Earth station EIRP vs. G/T trade-off

3.7.1 Uplink

With regards to the uplink, there is a relationship between the IBO and the available(C/N)U , which is defined by the receiver characteristics in the satellite transponder.

This relationship is given by:(C/N)U = AU IBO (3.48)

On the other hand, the (C/N)U is determined by the link budget as follows:

(C/N)U = EIRPES (G/T )rx,s 1

k BN 1i Li

(3.49)

Therefore, there exists an underlying relationship between the earth station EIRP andthe IBO of the satellite transponders.

EIRPES =AU k BN

i Li

(G/T )rx,s IBO

= AES IBO(3.50)

With,

AES =AU k BN

i Li

(G/T )rx,s(3.51)

In dB,

AES,dB = AU,dB + 10 log(k BN) (G/T )rx,s,dB +i

Li,dB (3.52)

3.7.2 Receiving satellite antenna gain

As described in section 3.1.3.2 the receiving antenna diameter at the satellite needs to belower than 0.53 m in order to achieve the required coverage zone. This maximum valuewill be used since it is of interest to maximize the antenna gain as well. The antenna gainfor the lowest frequency is thus:

Grx,s,max = 10 log( (pi D f/c)2)

Grx,s,max = 34.38 dB(3.53)

3.7.3 AES numerical value

In order to calculate the value of AES, the following conditions will be considered :

The analysis is done in the uplink for the worst condition (highest losses);

28

The transmitting earth station is situated on the edge of coverage of the receiverantenna (on the satellite);

The transmitting earth station is situated on the furthest location with respect tothe satellite (highest R);

The carrier frequency is the lowest in the uplink frequency plan (the lower thefrequency is, the lower the available C/N);

Losses under clear sky conditions: Free space losses;

Atmospheric gases losses (oxygen plus water vapor);

Under the previously mentioned conditions:

Parameter Value

Carrier frequency f = 12.75 GHzEarth station position Zone A, north(R/R0)

2db 1.17 dB

Elevation angle E = 29.40

Free space losses Lfs = 206.31 dBAtmospheric gases attenuation2 LAG 0.15 dBTotal losses Lfs + LAG = 206.46 dB

For the receiver antenna, at the satellite:

Parameter Value

Receiving antenna diameter 0.53 mReceiving antenna max. gain Grx,s,max = 34.38 dBReceiving antenna gain Grx,s,max 3 dB = 31.38 dBEquivalent system temperature3 Tsys = 787.13 KG/Trx,s,dB 5.42 dBK

1

Also,

Parameter Value

AU 36.79 dBEquivalent noise bandwidth Bn = 10.8 MHz10 log(k Bn) 158.26 dBWK1

Finally,

AES = 82.57 dB.

3.7.4 Uplink trade-off

Previously, in the downlink budget analysis it has been shown that the available (C/N)Dis linked to the IBO parameter at the satellite transponder HPA and the earth station

2See figure C.13The equivalent noise temperature is measured at the receiver input (see section 3.6.1)

29

(G/T )es.

Furthermore, the overall link budget depends on the IBO and the (G/T )es. For a given(G/T )es,i, the available (C/N)T,i reaches the required (C/N)T at a certain point linkedto a certain value of IBOi.

Since EIRPes = Aes IBO, the value of IBOi gives the minimum EIRP required for(G/T )es,i.

Figure 3.8: Relationship between C/NT , required EIRPes and (G/T )es

In the figure 3.8, the minimum required EIRP is given by:

For (G/T )es,1, (C/N)T,1 = (C/N)T,0 at IBO1 = EIRPes,1 For (G/T )es,2, (C/N)T,2 = (C/N)T,0 at IBO2 = EIRPes,2

With a simple Matlab script, the value of minimum required EIRP for a given (G/T )es)is computed. Doing so, for a set of values, reusing the data on the available (C/N)T , itresults in the curves shown in the figure 3.9.

30

10 15 20 25 30 35 40 45 5058

60

62

64

66

68

70

G/TES (dB)

Min. EIRP

ES (dB)

Margin = 0 dBMargin = 2 dB

Figure 3.9: Curves of min. required EIRPes and (G/T )es for margins of 0 dB and 2 dB

3.8 Cost Effective Design of the Earth Station

3.8.1 Antenna Tracking System

There are three different tracking systems available to choose from for the earth stationdesign:

Fixed mount antenna system (FMA) Step tracking antenna system (STA) Monopulse tracking antenna system (MPA)

These different systems will induce different depointing angles. The following subsectionsexplain the matter in which these are calculated.

3.8.1.1 Fixed Mount Antenna

In the case of a fixed antenna, maximum depointing angle is given by the followingformula:

max =

2 SKW + SPO + 0.23dB (3.54)

Where SKW is the station-keeping box half-width, SPO is the uncertainty in the satelliteposition determination and 0.23dB is the initial depointing error term.

31

3.8.1.2 Step Tracking Antenna

In this case, tracking is performed by analyzing variations of the received signal level dueto depointing. Typical depointing value is:

max = 0.23dB (3.55)

3.8.1.3 Monopulse Tracking Antenna

Signals caused by azimuth and elevation misalignment are measured from error antennafeed output ports specifically used for this purpose and later processed by a monopulseprocessor. Typical depointing value is:

max = 0.13dB (3.56)

3.8.2 Antenna System Cost

Antenna gain of the earth station receiver calculation takes into account losses due to thedepointing angle . Antenna gain is thus calculated as follows (in dBi):

GdBi = 10 log [ (piDES

)2] 12(/3dB)2

Antenna diameter DES and tracking system are the parameters which will affect theoverall cost of the antenna system. Figure F.1 shows cost vs antenna gain for all availabletracking solutions and antenna diameters (1.5, 2, 2.5, 3, 3.5, 4, 5 meters).

3.8.3 Figure of Merit

The earth station figure of merit (G/T )ES depends on the antenna diameter DES as wellas the tracking system. It is given by the following expression:

(G/T )dBi = 10 log [ (piDES

)2] 12(/3dB)2 10 log T

The equivalent noise temperature T can be calculated as follows:

T = (TSKY + TGROUND)/LFRX + TF(1 1/LFRX) + TRWhere TSKY is the clear-sky contribution to antenna noise temperature (7K at a minimumelevation angle of 30and a downlink minimum frequency of 11.20GHz), TGROUND is theside-lobe contribution to antenna noise temperature (50K), LFRX is the feeder loss, TFRXis the temperature of feeder (considered as 290K) and TR is the receiver effective inputtemperature (65K).

Tables F.1 and F.2 show requirements (antenna gain, figure of merit, EIRP and powerper carrier) for a 0dB and 2dB margin respectively.

32

3.8.4 Earth Station Architecture and Cost

There are two design solutions that can be considered for the earth station design. Bothare illustrated in appendix F.3; figure F.2 shows the pre-amplification coupling variantwith a 1 to 1 redundancy scheme. In this case all 3 carriers are amplified together withonly one power amplifier (HPA). This approach leads to higher power requirements onthe HPA and a total output back-off of 10dB has to be taken in order for it to work in itslinear zone so as to keep intermodulation noise as low as possible. Figure F.3 on the otherhand, shows the post-amplification coupling solution with a 3 to 4 redundancy scheme.For this case, power requirements for each HPA should be considerably lower than in thepre-amplification coupling scheme.

Regarding the choice of HPA, there are 3 technologies to choose from depending on theoutput power requirements:

Solid State (SS) amplifier: 1 to 10 Watts Travelling Wave Tube (TWT) amplifier: 10 Watts and higher Klystron amplifier: 300 Watts and higher

The choice ultimately will depend on the overall cost for the whole earth station. Thedesign should be cost-effective thus overall cost (antenna plus RF equipment) shouldbe as low as possible. Individual amplifier cost and all combinations for chosen antennadiameters as well as their associated costs are shown in appendix F.4. Final system choiceis as follows:

0dB margin: 3 meter fixed-mount antenna, Klystron-type HPA with pre-amplificationcoupling.

2dB margin: 3 meter fixed-mount antenna, Klystron-type HPA with pre-amplificationcoupling.

3.9 Rainy conditions

Under rainy conditions the link budget is affected by several factors. The main onesare:

Attenuation due to the rain which causes degradation on the link performance C/N . Depolarisation which increases co-channel interferences by frequency reuse with lin-

ear polarisation.

Noise temperature increment at the receiving antenna on the downlink.For the sake of simplicity, other less significant atmospheric effects are neglected. Thisis the case for attenuation by fog, ice clouds and sandstorms, scintillation and Faradayrotation.

33

3.9.1 Rain attenuation for the downlink

Rain attenuation model is described in detail in appendix D.

Then, from the models, attenuation due to rain for each zone in the downlink can becalculated.

Analyzing the link performance under rainy conditions, the higher the frequency, thehigher the rain attenuation. However, the C/N has better performances with higherfrequencies when there is not rain. So, in order to determine the worst condition, linkperformance for both frequency limits (max. and min.) is needed to be computed.

Therefore, the rain attenuation will be analysed for both cases: highest and smallestfrequencies inside the considered band.

The resulting rain attenuation values are shown in table 3.11. AN , BN and CN are thepositions of the earth stations on the EOC at the north of each zone. For more details,see section G.

Zone f Pol. LG R001 R r001 v001 LR LE A001 A0075GHz km mm/h dB/km km km dB dB

AN

11.53H

4.19

35

1.34 0.86 0.94 4.13 3.86 5.18 1.9111.70 4.19 1.38 0.86 0.94 4.12 3.87 5.34 1.9711.36

V4.19 1.09 0.90 0.95 4.32 4.11 4.47 1.62

11.53 4.19 1.11 0.90 0.96 4.31 4.13 4.60 1.68

BN

11.20H

3.12

50

1.94 0.84 0.88 3.28 2.89 5.60 2.0811.36 3.12 2.02 0.83 0.89 3.26 2.88 5.82 2.1711.53

V3.12 1.73 0.87 0.92 3.39 3.11 5.38 1.99

11.70 3.12 1.78 0.86 0.92 3.38 3.12 5.56 2.06

CN

11.36H

2.16

25

0.86 1.06 1.05 3.20 3.35 2.88 1.0111.53 2.16 0.88 1.06 1.05 3.20 3.37 2.97 1.0411.20

V2.16 0.70 1.10 1.07 3.20 3.44 2.41 0.83

11.36 2.16 0.72 1.09 1.08 3.20 3.45 2.49 0.86

Table 3.11: Rain attenuation exceeded for p = 0.075% on an average year: A0075, on thedownlink

3.9.2 Rain attenuation for the uplink

With the same assumptions done for the downlink, the rain attenuation on the uplink iscalculated for the highest and lowest frequencies in the considered band.

The results are shown in table 3.12.

3.9.3 Carrier-to-Interference Ratio with rainy conditions

As it was seen in section 3.3.2, (C/N)I depends on the differences of the link lossesbetween the source signal and the interference signal, and also it depends on the XPI/XPDproperties of the transmitting and receiving antennas.

34

Zone f Pol. LG R001 R r001 v001 LR LE A001 A0075GHz km mm/h dB/km km km dB dB

AN

12.75H

4.19

35

1.62 0.84 0.97 4.04 3.94 6.38 2.3913.25 4.19 1.76 0.83 0.99 4.00 3.95 6.95 2.6312.75

V4.19 1.38 0.87 0.99 4.20 4.17 5.76 2.14

13.25 4.19 1.48 0.87 1.01 4.17 4.20 6.22 2.33

BN

12.75H

3.12

50

2.48 0.81 0.94 3.18 2.99 7.40 2.8213.25 3.12 2.62 0.81 0.96 3.17 3.03 7.95 3.0412.75

V3.12 2.08 0.85 0.96 3.32 3.20 6.65 2.50

13.25 3.12 2.24 0.84 0.98 3.29 3.22 7.21 2.74

CN

12.75H

2.16

25

1.08 1.04 1.09 3.20 3.49 3.76 1.3513.25 2.16 1.18 1.03 1.10 3.20 3.52 4.16 1.5012.75

V2.16 0.90 1.08 1.12 3.20 3.59 3.23 1.14

13.25 2.16 0.99 1.07 1.13 3.20 3.62 3.59 1.28

Table 3.12: Rain attenuation exceeded for p = 0.075% on an average year: A0075, on theuplink

However, rain introduces depolarisation and attenuation which must be taken into accountto compute (C/N)I . A detailed analysis is done in appendix E.

Regarding the carrier-to-interference computation, from appendix E.1 it was seen thatthe overall value of (C/N)I can be decomposed in the contributions from the interferenceI and the contributions from the source S (see equation E.3).

Regarding the contributions of the interference, the value of interest is when the contri-butions are minimum:

I = rI,dB + Arain,I,dB + (3.57)

So, there will be analysed both conditions: clear sky (Arain,I,dB = 0) and rainy conditions( degraded).

Condition Interference XPI* XPD rI Arain,I Slocation dB dB dB dB dB dB

A 34.02 25 24.40 0.51 2.63 27.54Rainy B 33.86 25 24.45 0.44 3.04 27.93

C 34.72 25 24.57 0.35 1.50 26.42A 35 25 24.59 0.51 0.00 25.10

Clear sky B 35 25 24.59 0.44 0.00 25.03C 35 25 24.59 0.35 0.00 24.94

Table 3.13: Contributions of the (C/N)I from the interferences

The minimum value for I is met when the interference is located in zone C with clearsky conditions.

min(I) = 24.94 dB (3.58)

Regarding the contributions of the source, the value of interest is when the contributions

35

are maximum:S = rS,dB + Arain,S,dB (3.59)

So, only rainy conditions are taken into account (Arain,S,dB > 0). Table 3.14 summarizesthe main values.

Condition Source rI Arain,I Slocation dB dB dB

A 0.67 2.65 3.33Rainy B 0.49 2.94 3.43

C 0.26 1.42 1.68

Table 3.14: Contributions of the (C/N)I from the source

The maximum value for S is met when the source is located in zone B.

max(S) = 3.43 dB (3.60)

Finally, from equation E.4 and previous results, the worst condition for (C/N)I is:

C

N

I,dB

= Grx,dB + min(I)max(S)

= 2.27 dB + 24.94 dB 3.43 dB= 19.24 dB

(3.61)

This value is found when the source comes from zone B with rainy conditions and theinterference comes from zone C with clear sky conditions.

(C/N)I value can be computed for any combination source-interference. Table 3.15 pro-vides the values for all possible cases.

Source InterferenceA B C

A 19.50 dB 19.43 dB 19.34 dBB 19.40 dB 19.33 dB 19.24 dBC 21.15 dB 21.08 dB 20.99 dB

Table 3.15: (C/N)I values for any combination source-interference with rainy conditions

3.9.4 Earth station G/T degradation due to the rain

As it was mentioned before, rainy conditions modify the antenna noise temperature atthe earth station. More precisely, the antenna noise temperature increments with rain.Therefore, it results in a degradation of the figure of merit G/T of the receiving an-tenna.

36

The equivalent system noise temperature T is calculated as follows 4:

T =TA

LFRX+ TF

(1 1

LFRX

)+ TR (3.62)

Where TA is the antenna noise temperature:

Under clear sky conditions,TA,clearsky = TSKY + TGND

Under rainy conditions,

TA,rain =TSKY

Arain+ Tm

(1 1

Arain

)+ TGND

Tm is the mean thermodynamic temperature of the formations such as clouds andrain. It can be calculated as follows:

Tm 1.12 TAMB 50 K, expressed in K.The receiving antenna at the earth station is described by its figure of merit G/T , thenthe degradation due to rain is:

(G/T )dB = 10 log(

(G/T )rain

(G/T )clearsky

)

= 10 log(Tclearsky

Train

) (3.63)

In order to compute the degradation due to the rain, the following conditions are consid-ered (see section 3.8.3):

Parameter Value

Feeder losses LFRX = 0.2 dBFeeder temperature TF = 290 KReceiver noise effective input temp. TR = 65 KGround side lobes noise temperature TGND = 50 KSky noise temperature TSKY = 7 KAmbient temperature TAMB = 293 KMean formations temperature Tm = 278 K

Figure 3.10 shows the average temperature by geographical location, where it can befound that, for all the coverage zones, 15 C < TAMB < 20 C.

Table 3.16 summarizes antenna temperature modifications and G/T degradation due torainy conditions.

4See section 3.8.35Worst attenuation cases are considered

37

Figure 3.10: Average temperature by geographical location in C

Zone A B C

Arain5 1.97 2.17 1.04 dB

TA,clearsky 57.00 57.00 57.00 KTA,rain 155.88 163.64 114.74 KTclearsky 130.49 130.49 130.49 KTrain 224.92 232.32 185.63 K(G/T ) -2.36 -2.51 -1.53 dB

Table 3.16: G/T degradation due to rain by zone

3.9.5 Link performance degradation due to rain

Uplink performances with rainy conditions are deteriorated by the increment on the linklosses due to rain attenuation. This is:

C

N

U,rain,dB

=C

N

U,clearsky,dB

Arain,dB (3.64)

If no gain control technology is used in the transponders, the preset operation point ofthe HPA may be affected by attenuation in the uplink. This changes the IBO parameterand produces a reduction in the IM and the OBO.

Downlink performances are deteriorated by attenuation and antenna temperature incre-ment at the earth station. This is:

C

N

D,rain,dB

=C

N

D,clearsky,dB

Arain,dB (G/T ) (3.65)

As a consequence of the reduction in the OBO (caused by attenuation in the uplink),the EIRP at the transmitting antenna output of the satellite is decremented. So, thedownlink performance is affected by this phenomenon and it should be taken into accountin the link budget.

38

Carrier to interference ratio by frequency reuse is decremented as explained in section3.9.3.

Carrier to intermodulation noise ratio may be improved by rainy conditions asa result of the IBO modification which derives in a reduction of the intermodulationproducts.

3.10 Performance summary

From previous analysis and calculations, link performance is verified and boiled down inorder to provide a better understanding of the system behaviour under different condi-tions.

3.10.1 Performance with 0 dB margin

Table 3.17 summarizes uplink performance for different zones and frequencies. It can befound that the worst case for clear sky conditions is located at zone A with availableC/NU = 14.34 dB. The worst case for rainy conditions is located at zone B with availableC/NU = 11.54 dB.

Zone f Pol. 3dB GEOC EIRP G/TEOC Lfs + Lag Arain C/NU C/NU(RX) (RX) (TX) (RX) (c. sky) (rainy)

GHz deg dB dBW dBK1 dB dB dB dB12.75 H 3.12 2.84 59.90 2.58 206.40 2.39 14.34 11.95

A V 3.12 2.84 59.90 2.58 206.40 2.14 14.34 12.2013.25 H 3.00 2.95 60.23 2.75 206.73 2.63 14.52 11.89

V 3.00 2.95 60.23 2.75 206.73 2.33 14.52 12.1912.75 H 3.12 2.84 59.90 2.42 206.23 2.82 14.35 11.54

B V 3.12 2.84 59.90 2.42 206.23 2.50 14.35 11.8513.25 H 3.00 2.95 60.23 2.75 206.56 3.04 14.69 11.65

V 3.00 2.95 60.23 2.75 206.56 2.74 14.69 11.9512.75 H 3.12 2.84 59.90 2.42 206.05 1.35 14.53 13.19

C V 3.12 2.84 59.90 2.42 206.05 1.14 14.53 13.3913.25 H 3.00 2.95 60.23 2.75 206.38 1.50 14.87 13.37

V 3.00 2.95 60.23 2.75 206.38 1.28 14.87 13.59

Table 3.17: Uplink contributions summary for clear sky and rainy conditions, with 0 dBmargin

Table 3.18 summarizes downlink performance for different zones and frequencies. It canbe found that the worst case for clear sky conditions is located at zone A with availableC/ND = 20.20 dB. The worst case for rainy conditions is located at zone B with availableC/ND = 12.97 dB.

6Calculated at the minimum OBO for clear sky conditions. This is OBO = 17.44 dB7Calculated at the minimum OBO for rainy conditions. This is OBO = 20.04 dB

39

Zone f Pol. AD G/T Arain G/T C/ND C/ND(RX) (RX) (c. sky)6 (rainy)7

GHz dBK dBK1 dB dB dB dB11.53 H 10.49 26.35 1.91 2.36 20.24 13.23

A 11.70 10.41 26.48 1.97 2.36 20.29 13.2111.37 V 10.57 26.23 1.62 2.36 20.20 13.4711.53 10.49 26.35 1.68 2.36 20.24 13.4611.20 H 10.84 26.10 2.07 2.51 20.34 13.01

B 11.37 10.77 26.23 2.17 2.51 20.40 12.9711.53 V 10.69 26.35 1.99 2.51 20.44 13.2011.70 10.61 26.48 2.06 2.51 20.49 13.1711.37 H 11.02 26.23 1.00 1.53 20.65 15.37

C 11.53 10.94 26.35 1.04 1.53 20.69 15.3811.20 V 11.09 26.10 0.83 1.53 20.59 15.4811.37 11.02 26.23 0.86 1.53 20.65 15.51

Table 3.18: Downlink contributions summary for clear sky and rainy conditions, with0 dB margin

3.10.2 Performance with 2 dB margin

As previously done for 0 dB margin, performance of the system with 2 dB margin is donebelow.

Table 3.19 summarizes uplink Performance. The worst case for clear sky conditions islocated at zone A with available C/NU = 16.74 dB. The worst case for rainy conditionsis located at zone B with available C/NU = 13.94 dB.

Zone f Pol. 3dB GEOC EIRP G/TEOC Lfs + Lag Arain C/NU C/NU(RX) (RX) (TX) (RX) (c. sky) (rainy)

GHz deg dB dBW dBK1 dB dB dB dB12.75 H 3.12 2.84 62.30 2.58 206.40 2.39 16.74 14.35

A V 3.12 2.84 62.30 2.58 206.40 2.14 16.74 14.6013.25 H 3.00 2.95 62.63 2.75 206.73 2.63 16.92 14.29

V 3.00 2.95 62.63 2.75 206.73 2.33 16.92 14.5912.75 H 3.12 2.84 62.30 2.42 206.23 2.82 16.75 13.94

B V 3.12 2.84 62.30 2.42 206.23 2.50 16.75 14.2513.25 H 3.00 2.95 62.63 2.75 206.56 3.04 17.09 14.05

V 3.00 2.95 62.63 2.75 206.56 2.74 17.09 14.3512.75 H 3.12 2.84 62.30 2.42 206.05 1.35 16.93 15.59

C V 3.12 2.84 62.30 2.42 206.05 1.14 16.93 15.7913.25 H 3.00 2.95 62.63 2.75 206.38 1.50 17.27 15.77

V 3.00 2.95 62.63 2.75 206.38 1.28 17.27 15.99

Table 3.19: Uplink contributions summary for clear sky and rainy conditions, with 2 dBmargin

Table 3.20 summarizes downlink Performance. The worst case for clear sky conditions islocated at zone A with available C/ND = 22.53 dB. The worst case for rainy conditionsis located at zone B with available C/ND = 15.33 dB.

40

Zone f Pol. AD G/T Arain G/T C/ND C/ND(RX) (RX) (c. sky)8 (rainy)9

GHz dBK dBK1 dB dB dB dB11.53 H 10.49 26.35 1.91 2.36 22.57 15.58

A 11.70 10.41 26.48 1.97 2.36 22.61 15.5711.37 V 10.57 26.23 1.62 2.36 22.53 15.8311.53 10.49 26.35 1.68 2.36 22.57 15.8111.20 H 10.84 26.10 2.07 2.51 22.66 15.37

B 11.37 10.77 26.23 2.17 2.51 22.73 15.3311.53 V 10.69 26.35 1.99 2.51 22.77 15.5511.70 10.61 26.48 2.06 2.51 22.81 15.5311.37 H 11.02 26.23 1.00 1.53 22.98 17.73

C 11.53 10.94 26.35 1.04 1.53 23.02 17.7311.20 V 11.09 26.10 0.83 1.53 22.91 17.8411.37 11.02 26.23 0.86 1.53 22.98 17.87

Table 3.20: Downlink contributions summary for clear sky and rainy conditions, with2 dB margin

3.10.3 Overall Performance

Table 3.21 summarizes overall link performance and operation point at the HPA for theworst case, with 0 dB and 2 dB margins.

Margin 0 2 dBCondition Clear sky Rainy Clear sky RainyMin. C/NU 14.34 11.54 16.74 13.94 dBIBO -22.45 -25.25 -20.05 -22.85 dBOBO -16.60 -19.35 -14.28 -16.99 dBIM -51.48 -59.47 -44.80 -52.61 dBMin. C/ND 20.20 12.97 22.53 15.33 dBMin. C/NIM 34.87 40.13 30.53 35.62 dBMin. C/NI 21.99 19.24 21.99 19.24 dBMin. C/NT 12.76 8.77 14.69 10.87 dB

Table 3.21: Overall link performance summary for clear sky and rainy conditions

The results show that the system with 2 dB margin fulfills completely the requirementsfor every condition. However, the system designed with 0 dB margin does not fulfill therequirements under rainy conditions. This is: 8.77 dB < 10.78 dB.

Then, the margin required is:

C/NT = 10.78 dB 8.77 dB = 2.01 dB

From table 3.17, it can be found that between the worst and best cases in zone B (mostlimiting zone under rainy conditions), there is no more than half dB difference. Further-

8Calculated at the minimum OBO for clear sky conditions. This is OBO = 14.28 dB9Calculated at the minimum OBO for rainy conditions. This is OBO = 16.99 dB

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more, if gain is achieved in the uplink, it will imply a modification of the HPA operationpoint (IBO-OBO), which will give a gain in the downlink of the same order of magnitude.Therefore, a gain close to 0.5 dB can be achieved by arranging the frequency plan.

No frequency plan arrangement can provide the needed gain in order to fulfill the re-quirements with 0 dB margin. In addition, the solution with 2 dB margin fulfills properlyall requirements in all situations. So, this option is the chosen solution to provide therequired services in all conditions.

Design with 2 dB margin is chosen

Up to this point calculations do not take into account carriers allocation on the uplink.However, once uplink carriers are assigned, only actual cases must be considered. Then,in section 3.11, a complete frequency plan analysis and carriers allocation is performed inorder to minimize rain effects and get actual performance.

3.11 Complete frequency plan analysis and carriers

allocation

Since the uplink and downlink frequency plans are related by the frequency offset givenby the frequency converter. Each uplink channel will be mapped into another downlinkchannel respecting the same offset for all the channels.

fc,down = fc,up fWhere,

fc,down is the carrier frequency for downlink; fc,up is the carrier frequency for uplink; and f is the frequency offset introduced by the frequency converter.

For the project, the uplink frequencies are in the 12.75-13.25 GHz band and thedownlink frequencies are in the 11.20-11.70 GHz band. Therefore, the offset isf = 1.55 GHz.

This means that the choice of the downlink frequency plan will set constraints in theuplink frequency plan, and vice-verse.

Taking the actual downlink frequency plan and, since the overall link performance islimited by the uplink, the design work-flow is as follows:

1. Select the worst uplink zone.

2. Assign the best frequency band for the worst link condition (i.e. worst source zoneto worst destination zone).

3. Complete the assignment for the rest of destination zones, giving the best availableoption to the worst downlink condition.

4. Select the uplink zone with intermediate performances and repeat the previous steps.

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5. Complete the design by selecting the best uplink zone and assigning the downlinkcarriers.

Under clear sky conditions, the best carriers are the ones with the highest frequen-cies.

However, under rainy conditions, the best carriers are the ones with the smallest rainattenuation and highest frequencies. This means that it is necessary to evaluate the linkperformances for the whole frequency range for both polarisations (rain attenuation de-pends on frequency and polarisation) in order to determine which is the best option.

The design is done by following the aforementioned steps and considering that horizontalpolarised carriers in the uplink are mapped to horizontal polarized carriers in the downlink,and the same for vertical carriers 10.

The assignment for rainy conditions is chosen in order to minimize rain effects. Figures3.12 and 3.13 show a good carriers allocation under rainy conditions derived from previousanalysis.

Figure 3.11 details allocated spectrum, bandwidths and guards for channels and carri-ers.

Figure 3.11: Allocated spectrum

Then, tables 3.22 and 3.23 show detailed carriers assignment.

Now, link attenuation is constrained and limited by carriers allocation. As a result, perfor-mances should be recalculated, expecting an overall performance improvement. Table 3.24summarizes worst link performances under rainy conditions with the selected frequencyplan for 2 dB margin.

The actual design shows that the worst case provides C/NT = 11.28 dB. The availablemargin is:

C/NT = 11.28 dB 10.78 dB = 0.5 dB

From proper frequency planning on the uplink, performances are improved around halfdB as expected, which is left as a margin in the overall link budget.

10The connection matrix between the OMUX output and antenna feeds allows any combination ofchanging (or not) polarisation from the uplink to the downlink. Since rainy conditions are worse forhorizontal polarisation, it is desired to use vertical polarisation in both uplink and downlink for the worstcase source zone to destination zone. Therefore, as a design choice, carriers do not change polarisationbetween the uplink and downlink.

11Changes in C/NI by uplink carriers assignment are not analysed here. So the worst value is takeninto account, which represents the worst case for any uplink frequency plan.

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Figure 3.12: Complete frequency plan for uplink and downlink

Figure 3.13: Carriers allocation

Figure 3.14 shows the communication payload with the connections between OMUX out-puts and feeds of transmit antenna.

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Source Earth Destination zonezone station A B C

1 33H 9H 21H2 34H 10H 22H3 35H 11H 23H

A 4 36H 12H 24H5 13V 25V 1V6 14V 26V 2V7 15V 27V 3V8 16V 28V 4V1 17V 29V 5V2 18V 30V 6V3 19V 31V 7V

B 4 20V 32V 8V5 21V 33V 9V6 22V 34V 10V7 23V 35V 11V8 24V 36V 12V1 25H 1H 13H2 26H 2H 14H3 27H 3H 15H

C 4 28H 4H 16H5 29H 5H 17H6 30H 6H 18H7 31H 7H 19H8 32H 8H 20H

Table 3.22: Carriers assignment per earth station.It should be read: 5H = carrier number 5 with horizontal polarisation in both links

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Carrier Transponder fUP fDOWN Carrier Transponder fUP fDOWNID (GHz) (GHz) ID (GHz) (GHz)

1V #1 12.7554 11.2054 1H #13 12.7554 11.20542V #1 12.7680 11.2180 2H #13 12.7680 11.21803V #1 12.7806 11.2306 3H #13 12.7806 11.23064V #2 12.7976 11.2476 4H #14 12.7976 11.24765V #2 12.8102 11.2602 5H #14 12.8102 11.26026V #2 12.8228 11.2728 6H #14 12.8228 11.27287V #3 12.8398 11.2898 7H #15 12.8398 11.28988V #3 12.8524 11.3024 8H #15 12.8524 11.30249V #3 12.8650 11.3150 9H #15 12.8650 11.315010V #4 12.8819 11.3319 10H #16 12.8819 11.331911V #4 12.8945 11.3445 11H #16 12.8945 11.344512V #4 12.9071 11.3571 12H #16 12.9071 11.357113V #5 12.9241 11.3741 13H #17 12.9241 11.374114V #5 12.9367 11.3867 14H #17 12.9367 11.386715V #5 12.9493 11.3993 15H #17 12.9493 11.399316V #6 12.9663 11.4163 16H #18 12.9663 11.416317V #6 12.9789 11.4289 17H #18 12.9789 11.428918V #6 12.9915 11.4415 18H #18 12.9915 11.441519V #7 13.0085 11.4585 19H #19 13.0085 11.458520V #7 13.0211 11.4711 20H #19 13.0211 11.471121V #7 13.0337 11.4837 21H #19 13.0337 11.483722V #8 13.0507 11.5007 22H #20 13.0507 11.500723V #8 13.0633 11.5133 23H #20 13.0633 11.513324V #8 13.0759 11.5259 24H #20 13.0759 11.525925V #9 13.0929 11.5429 25H #21 13.0929 11.542926V #9 13.1055 11.5555 26H #21 13.1055 11.555527V #9 13.1181 11.5681 27H #21 13.1181 11.568128V #10 13.1350 11.5850 28H #22 13.1350 11.585029V #10 13.1476 11.5976 29H #22 13.1476 11.597630V #10 13.1602 11.6102 30H #22 13.1602 11.610231V #11 13.1772 11.6272 31H #23 13.1772 11.627232V #11 13.1898 11.6398 32H #23 13.1898 11.639833V #11 13.2024 11.6524 33H #23 13.2024 11.652434V #12 13.2194 11.6694 34H #24 13.2194 11.669435V #12 13.2320 11.6820 35H #24 13.2320 11.682036V #12 13.2446 11.6946 36H #24 13.2446 11.6946

Table 3.23: Carriers details

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Source zone B B BDestination zone A B CWorst carrier 17V 29V 5VfUP 12.9789 13.1476 12.8102 GHzfDOWN 11.4289 11.5976 11.2602 GHzC/NU 14.30 14.35 14.25 dBIBO -22.49 -22.44 -22.54 dBOBO -16.64 -16.59 -16.69 dBIM -51.59 -51.45 -51.73 dBC/ND 16.17 15.94 18.14 dBC/NIM 34.95 34.86 35.04 dBC/NI

11 19.24 19.24 19.24 dBC/NT 11.33 11.28 11.86 dB

Table 3.24: Worst case link performances summary for rainy conditions with the selectedfrequency plan and 2 dBmargin

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Figure 3.14: Communication payload with connections between OMUX outputs and an-tenna feeds

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3.12 Digital Transmission Scheme

As was explained in section 1.1.3, the designed system uses constant coding and modu-lation (QPSK and 7/8 code rate). While the design steps that were followed guaranteelink-closure to meet availability requirements for the worst-case propagation conditions,high margins in CNR ratios occur in the majority of cases when favourable propagationconditions allow for it.

In the case of broadcasting services, where we have a multitude of users spread over verylarge areas, this waste of power cannot be easily avoided. However, in this scenario, if areturn channel is present it is possible to report channel