Basics-of-Satellite-Communications-1.pdf

Basics of Satellite Communications (Duration: 90 Minutes) Note: Please ask Questions Anytime! Presenter: E. Kasule Musisi ITSO Consultant Email: [email protected] Cell: +256 772 783 784...

Basics of Satellite Communications (Duration: 90 Minutes) Note: Please ask Questions Anytime! Presenter: E. Kasule Musisi ITSO Consultant Email: [email protected] Cell: +256 772 783 784 Skype: ekasule  Topics in this Module Birth of Satellite Communications Communication Links The Space Segment Satellite Design The Ground Segment Satellite Orbits Earth Station Registration Orbital Positions and Radio Interference Services Satellite Lifecycle Management Technology Trends Polarisation Introduction to Satellite Link Analysis  Birth of satellite communications 1/11 Communications satellites may be used for many applications: relaying telephone calls providing communications to remote areas of the Earth, TV direct-to-user broadcasting providing communications to ships, aircraft and other mobile vehicles etc.  Birth of satellite communications 2/11 Network Services Cell Maritime Disaster Oil & Gas Aeronautical Enterprise Backhaul Communications Recovery Media Services Cable MCPC Satellite DTH Special Events News Mobile Video Distribution Platforms Gathering Government Services Space Military Hosted End-to-End Embassy Situational ISR Mobility Payloads Communications Networks Awareness  Birth of satellite communications 3/11 A communications satellite acts as a repeater  Birth of satellite communications 4/11 Frequently Asked Questions (FAQs) Who invented satellites? − Arthur C. Clarke, who went on to be a well-read author of science fiction novels. When were satellites invented? − The first satellites were experimented with in the late 1950’s and early 1960’s. Intelsat’s first satellite, which was called ‘Early Bird’, was launched on 6 April 1965. How big is a satellite? − (Based on the Intelsat 9 series) Before liftoff it’s, about 4,500 kilograms! Without fuel, it’s about 2,000 kilograms! The body is 5.6 meters …and the solar panels are 31 meters wide – more than a 10-story building! How many years can a satellite last? − It varies by satellite type. The type of satellites owned by Intelsat can last over 20 years, but typically their work life is approximately 15 years.  Birth of satellite communications 5/11 Frequently Asked Questions : How do you fix satellites if they get broken? − The satellites send back ‘health check’ information to ground engineers all the time. Pre- developed commands are sent to the satellite to perform certain functions, such as firing a booster or changing the angle of a solar panel, so that it can repair itself. How does a satellite get its power? − Mostly solar power collected by the solar arrays/panels. There are also batteries on the satellites for the times when the satellite passes through the earths shadow. This is called eclipse. How much power does it take to transmit a signal? − The power used to send a communications signal to the Earth from a satellite is about the same as a typical 60W light bulb, just like you have at home. What kinds of people work in the satellite industry? − All kinds! Engineers, rocket scientists, sales people, writers, accountants and lawyers.  Birth of satellite communications 6/11 In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavor. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon.  Birth of satellite communications 7/11 First satellite was launched in 1957 by Russia. It was named “Sputnik 1”  Birth of satellite communications 8/11 INTELSAT I (nicknamed Early Bird for the proverb "The early bird catches the worm") was the first (commercial) communications satellite to be placed in geosynchronous orbit, on April 6, 1965.  Birth of satellite communications 9/11 Benefits of Satellites Adaptable to customer requirements Mobility Cost advantage Not affected by geographical obstructions Quick implementation Alternate routing or redundancy Cost is independent of distance Cost effective for short term requirements  Birth of satellite communications 10/11 Satellites are complementary to cable for the following reasons: Submarine cables (and landline fibre) are subject to cuts Interim solutions for cellular backhaul and internet trunking Satellite systems utilizing MEO (medium Earth orbit) have both high capacity and high quality (low latency) and cost.  Birth of satellite communications 11/11 Types of satellites Communications satellites Weather satellites: provide meteorologists with scientific data to predict weather conditions and are equipped with advanced instruments Earth observation satellites Navigation satellites: Using GPS technology these satellites are able to provide a person's exact location on Earth to within a few meters Broadcast satellites: broadcast television signals from one point to another (similar to communications satellites). Scientific satellites : perform a variety of scientific missions e.g. the The Hubble Space Telescope Military satellites  Communication Links 1/4 Uplink Uplink - The transmission of signals to the satellite  Communication Links 2/4 Downlink s Downlink - The transmission of information from the satellite. Many Earth Stations can be covered by one satellite beam footprint Communication Links 3/4 NOTE: − Satellites receive at a different frequency than they transmit at − Different wavelengths give different radiation patterns on the antennae − This causes slightly different footprints for uplink and downlink − For marketing reasons the patterns may be different  Communication Links 4/4 A satellite beam “footprint”  The Space Segment 1/6 A satellite communications (satcom) system maybe looked at as comprising of three parts “space segment”, the “ground segment” and the transmission medium ( the space between the Earth and the satellite)  The Space Segment 2/6 A telecommunications satellite comprises: − A platform (or bus): propulsion system, fuel tanks, batteries, solar panels, attitude and orbit control functions, etc. It is usually standardized by the manufacturer. − A payload: the equipment used to provide the service for which the satellite has been launched. It is customized for a given mission.  The Space Segment 3/6 The Transponder: This is the equipment which provides the connecting link between the satellite’s transmit and receive antennas. It forms one of the main sections of the payload, the other being the antenna subsystems.  The Space Segment 4/6 Block Diagram of a Communications Satellite Propulsion System Telemetry, Attitude Control, Solar Arrays Commanding, Fuel, Batteries Solar Arrays Power System/Thermal System Down High Doe Converter Power Transponder Amplifier Transponder Receiver Section Transmitter Section Communications Pre- Filter Amplifier Payload Filter Rx Antennas Tx Antenna  The Space Segment 5/6 Satellite Capacity Typically satellites have between 24 and 72 transponders. A single transponder is capable of handling up to 155 million bits of information per second (155 Mbps)  The Space Segment 6/6 A closer look at the Transponder  Satellite Design1/1 Key aspects of Satellite Design: Electrical Power Station Keeping Attitude Control Orbital Control Thermal Control Satellite Design1/2 Orbital Control Necessary keep the satellite stationary with respect to all the earth station antennas that are pointed at it. Each satellite carries a thrust subsystem to give it an occasional nudge to keep it "On Station." Questions so far?  The Ground Segment 1/15 Topic Outline: Earth station components Factors governing antenna sizes The differences between a major earth station and a VSAT Permissions required to install and operate a VSAT / Earth station  The Ground Segment 2/15 Indoor Outdoor Equipment Rack Feed Horn Contains: Modems, RF Power Amplifiers Data Communications IFL Reflector Equipment Data Networking Eqpt UPS etc Rigid Mounting Earth Station Components – generic simplified diagram The Ground Segment 3/15 Earth Station Components- simplified list Reflector – Physical reflecting piece – focuses signal into the LNB assembly and / or focuses the transmission signal towards the satellite Feed horn – Device to accept the focussed RF signals into the LNB or conversely to output the RF signal to the satellite Power amplifier – Device that accepts a signal from the modem and boosts it to a suitable level for onward transmission to the satellite LNA,B or C – Low Noise Amplifier – Receives the signal from the satellite, Modem – Converts a data signal to one suitable for transmission to the satellite Up Converter– Converts the modulated signals from RF to RF frequency Down Converter– Converts the modulated signals from RF to RF frequency Mounting – Some form of mounting to hold the antenna assembly vertical and pointed correctly under most normal condition The Ground Segment 4/15 Uplink Block Diagram Antenna Modem IFL Up-Converter IFL Transmitter IFL Feed Simplified Uplink Block Diagram The Ground Segment 5/15 Downlink Block Diagram Modem IFL Down-Converter IFL LNA Feed Simplified Downlink Block Diagram The Ground Segment 6/15 Picture of a VSAT Reflector Ground Mount with weights  The Ground Segment 7/15 Picture of a VSAT components Feed horn assembly RF Power amplifier (SSPA) LNB Transmit cable Receive cable From indoor modem From LNB modem  The Ground Segment 8/15 Factors governing Reflector sizes Why install a large antenna when a small one would do the job? Transmission: ✓Large earth stations have smaller BEAM Width's therefore point more accurately ✓ Less RF signal wastage ✓ Less co-satellite interference ✓ Link budget requirement ✓ Cost factors − Larger antenna may be less than the cost of a lease with a smaller antenna The Ground Segment 9/15 3D Antenna Radiation Pattern The Ground Segment 10/15 Receiving: ✓Antenna Gain dictated by the Link Budget ✓Large earth station can receive a weaker signal than the equivalent small antenna ✓Cost implications with the Link Budget ✓Planning permission e.g. Europe 0.9M is the minimum size  The Ground Segment 11/15 The differences between a Major Earth Station and a VSAT VSAT – Very Small Aperture Terminal A VSAT is typically a small earth station 0.7M to 3.7M Usually operates a single service or application Major Earth Station Typically A Major Earth station is sized from 3.7M to 16M+ weighing 20 T or mo re costing $1M+ Basically same components in each station Supports multiple services All components redundant Can transmit and receive in multiple polarisations Usually configured with large RF power amplifiers Always connected to suitable Power supplies Usually connected to multiple terrestrial paths  The Ground Segment 12/15 Photos of Large earth station antennas  The Ground Segment 13/15 Permissions required to install & operate a VSAT / Earth station Just because it can work does not necessarily mean you may go out install and operate! Planning permission ✓ Local Authority building departments ✓ Zoning issues Landlord’s permission Will the landlord permit your activity? Regulatory authority Does the law allow you to build and operate? The Ground Segment 14/15 Teleports: Multiple large earth stations Well specified antennas Good power systems Ample Rack space for ancillary equipment 24X7 staff on-site to maintain systems Quality support and technical staff to assist with design, install and operation Good terrestrial connectivity Preferably to more than a single fibre supplier The Ground Segment 15/15 A Typical Teleport Questions so far? Satellite Orbits 1/7 MEO LEO GEO  MEO Satellite Orbits LEO 2/7 GEO Type LEO MEO GEO Low Earth Orbit Medium Earth Orbit Geostationary Earth Orbit Description Equatorial or polar Equatorial or Polar orbit Equatorial orbit orbit Height 100-500 miles 6000-12000 miles 22,282 miles Signal Visibility / 15 min 2-4 hrs 24 hrs orbit Lower launch costs Covers as much as 42.2% of Short round trip signal Moderate launch cost the earth's surface Ease of Advantages delay Small round trip delays tracking Small path loss No problems due to doppler Tracking antenna Tracking antenna required required Larger delays Large round trip delays Disadvantages Short life, 5-8 years Greater path loss than Weaker signals on Earth Encounters radiation LEO's belts Satellite Orbits 3/7 Applications Low Earth Orbit: − Earth Observation − International Space Station − Satellite communications (constellations) Medium Earth Orbit: − Navigation: GPS, Galileo, GLONASS, etc − Satellite communications (constellations) Geostationary Earth Orbit: − Satellite communications − Meteorology Satellite Orbits 4/7 Satellite Orbits 5/7 Inclined Orbits: Implications for earth station tracking: Stations must have tracking systems so that their pointing is adjusted to aim at the satellite all during the day. Satellite Orbits 6/7 Orbital Slot Registration The ITU Member States have established a legal regime, which is codified through the ITU Constitution and Convention, including the Radio Regulations. In 1988, the ITU acknowledged that all countries, including lesser developed countries, have an equal right to orbital slots. However, Article II of the Outer Space Treaty forbids any claim of sovereignty by any country in space, which would not allow countries to establish dominion over the orbital slots above their territory. At conferences in 1985 and 1988, the ITU did give all countries the rights to an orbital slot directly over their territory, which would ensure at least some access to these satellites to all countries. Satellite Orbits 7/7 Building and launching a telecommunications satellite 1/3 It takes about 3 years to get a GEO telecom satellite built and launched. Satellite payloads are customized for a given mission. Satellites are heavily tested on the ground in facilities that reproduce the space environment: − Mechanical, Thermal, Noise and RF tests Typical cost of a satellite is $150-$250 million − Some satellites can cost as much as $500 million. − Not including launch services ($55-$100 million) and insurance. Building and launching a telecommunications satellite 2/3 GEO Satellite Launch Multiple burns to achieve GEO orbit Building and launching a telecommunications satellite 3/3 Generic Transfer Orbit Profile Generic Transfer Profile  Earth Station and VSAT Registration 1/5 A licence is required by the national telecommunications authority of a country where any earth station as a part of a network, be it the hub, a control station or a VSAT, is planned to be installed and operated. Earth Station and VSAT Registration 2/5 In the past, national telecommunication authorities have required licensing of individual VSAT terminals in addition to requiring a network operator’s license. Then, the US Federal Communication Commission (FCC) implemented with success a blanket licensing approach for VSATs operated within the US. Earth Station and VSAT Registration 3/5 In the past, national telecommunication authorities have required licensing of individual VSAT terminals in addition to requiring a network operator’s license. Then, the US Federal Communication Commission (FCC) implemented with success a blanket licensing approach for VSATs operated within the US. Earth Station and VSAT Registration 4/5 Blanket licensing has since gained interest among national telecommunications authorities all over the world, as a result of equipment manufacturers complying with the recommendations issued by international standardization bodies, such as the International Telecommunication Union (ITU) and the European Telecommunications Standards Institute (ETSI). Earth Station and VSAT Registration 5/5 A licence usually entails the payment of a licence fee, which is most often in two parts: a one-time fee for the licensing work and an annual charge per station. The licensing procedure is simpler when the network is national, as only one telecom authority is involved. For transborder networks, licences must be obtained from the national authorities of the different countries where the relevant earth stations are planned to be installed and operated, and rules often differ from one country to another. Orbital positions and radio interferences Control of Interference ALLOCATION POWER LIMITS Frequency separation of stations of PFD to protect TERR services / EIRP to different services protect SPACE services / EPFD to protect GSO from Non-GSO REGULATORY PROTECTION e.g. No. 22.2: Non-GSO to protect GSO COORDINATION (FSS and BSS) between Administrations to ensure interference-free operations conditions Radio Regulatory Organisations 1/3 National Regulation Ultimately the responsibility for licensing falls to a National Regulatory Authority (a Government department), e.g. – Ofcom in the United Kingdom – FCC & NTIA in the USA Radio regulatory organisations 2/3 ITSO ITSO is the continuation of INTELSAT, the intergovernmental organization established by treaty in 1973.On July 18, 2001, the satellite fleet, customer contracts and other operational assets of the Organization were transferred to Intelsat Ltd, a new private company now registered in Luxembourg and various amendments to the ITSO Agreement took effect. Under the ITSO Agreement, as amended , ITSO’s primary role was that of supervising and monitoring Intelsat’s provision of public telecommunications satellite services as specified in the Public Services Agreement(PSA) entered into between ITSO and Intelsat. In addition, the Director General , on behalf of the Organization, must consider all issues related to the Common Heritage. ITSO currently has 149 Member States.” Radio regulatory organisations 3/3 ITSO The International Telecommunications Satellite Organization is an intergovernmental organization charged with overseeing the public service obligations of Intelsat. GVF Global VSAT Forum is an association of key companies involved in the business of delivering advanced digital fixed satellite systems and services. Satellite Operators Satellite Operators Intelsat, Ltd. is a communications satellite services provider. Originally formed as International Telecommunications Satellite Organization (INTELSAT), it was an intergovernmental consortium owning and managing a constellation of communications satellites providing international broadcast services. As of March 2011, Intelsat owned and operated a fleet of 52 communications satellites. Eutelsat S.A. is a French-based satellite provider. Providing coverage over the entire European continent, as well as the Middle East, Africa, India and significant parts of Asia and the Americas, it is one of the world's three leading satellite operators in terms of revenues. Satellite Operators O3b is building a next-generation network that combines the reach of satellite with the speed of fiber. Higher capacity O3b’s satellite transponders have on average three to four times the capacity of those offered by GEO satellite systems. This translates into three to four times more bandwidth – and a fiber-like experience for customers. Greater coverage Satellite technology can deliver Internet connectivity to any location on the planet. O3b’s next-generation satellite network will reach consumers, businesses and other organisations in more than 150 countries across Asia, Africa, Latin America and the Middle East. Satellite Operators Lower latency O3b’s unique network of Medium Earth Orbit (MEO) satellites virtually eliminates the delay caused by standard Geosynchronous (GEO) satellites. Round-trip data transmission time is reduced from well over 500 milliseconds to approximately 100 milliseconds. This creates a web experience significantly closer to terrestrial systems such as DSL or Optical Fiber.  Satellite Operators International Organization The International Mobile Satellite Organization (IMSO) is the intergovernmental organization that oversees certain public satellite safety and security communication services provided via the Inmarsat satellites. These public services include: services for maritime safety within the Global Maritime Distress and Safety System (GMDSS) established by the International Maritime Organization (IMO) distress alerting search and rescue co-ordinating communications maritime safety information (MSI) broadcasts general communications  Satelite Services The Commercial Satellite Industry GPS/Navigation Voice/Video/Data Communications Position Location Rural Telephony Timing News Gathering/Distribution Search and Rescue Internet Trunking Mapping Corporate VSAT Networks Fleet Management Tele-Medicine Security & Database Access Distance-Learning Emergency Services Mobile Telephony Videoconferencing Business Television Remote Sensing Broadcast and Cable Relay Pipeline Monitoring VOIP & Multi-media over IP Infrastructure Planning Forest Fire Prevention Urban Planning Direct-To-Consumer Flood and Storm watches Broadband IP Air Pollution Management DTH/DBS Television Geo-spatial Services Digital Audio Radio Interactive Entertainment & Games Video & Data to handhelds  Technology trends Market trends for capacity – continues to grow despite fibre deployment Potential shortage of capacity in some areas for certain types of capacity due to heavy cutbacks in launches Bandwidth is ever increasing on a per link basis Technology trends User demands Smaller terminals High throughput Enhanced capability Constellations Responsive space Lower costs - $1000 now and lower! Easier access to space segment Easier licensing regimes Open standards Technology trends Open Standards? Industry Players (Satellite Operators, Network Operators, Equipment manufacturers and=End-users) agree that Open Standards are good for everyone But which one is the best one or is it a multitude of answers and solutions? 8- Technology trends Global usage and coordination Ka / Ku/ C Band Interference issues Global Regional frequency coordination Questions so far?  Polarization 1/5 Linear Polarization Circular Polarization Polarization Frequency Re-use  Polarization 2/5 Electromagnetic waves have an electrical field and a magnetic field which are orthogonal to each other and to the direction of propagation Polarization of a signal is defined by the direction of the electrical field. Polarization can be: − Linear: Horizontal (H) or Vertical (V) − Circular: Right Hand Circular (RHCP) or Left Hand Circular (RHLP)  Polarization 3/5 The electrical field is wholly in one plane containing the direction of propagation Horizontal: the field lies in a plane parallel to the earth’s surface Vertical: the field lies in a plane perpendicular to the earth’s surface Polarization 4/5 Circular Polarization The electrical field radiates energy in both the horizontal and vertical planes and all planes in between Right-Hand Circular Polarization: The electrical field is rotating clockwise as seen by an observer towards whom the wave is moving Left-Hand Circular Polarization: The electrical field is rotating counterclockwise as seen by an observer towards whom the wave is moving  Polarization 5/5 Polarization frequency re-use A satellite can get twice the capacity on the same frequency channels by using opposite polarizations over the same coverage area. − E.g. Transponder A using 6,000-6,072 MHz in vertical polarization Transponder B using 6,000-6,072 MHz in horizontal polarization In case of misalignment of polarization between transmitter and receiver, there is cross-pol interference. Cross-pol discrimination (XPD) is defined as the ratio of power transmitted on the correct polarization to the power transmitted on the incorrect polarization. The specified XPD is usually in the range of 20-30 dB for VSATs. Questions so far? Introduction to Satellite Link Analysis1/9 Components of a satellite circuit The satellite receives the signals, filters them, converts the frequencies then amplifies them for Satellite transmission down to the Earth The antenna Antenna transmits/receives and Antenna focuses the energy of the signal towards/from the satellite. The BUC amplifies and converts up the signal for BUC LNB The LNB amplifies the BUC LNB transmission by the received signal and antenna converts down its frequency for reception by The modem modulates the modem and demodulates the Modem signal and is connected to Modem other user equipment (router, TV, etc)  Introduction to Satellite Link Analysis2/9 Simplified digital communications chain: Analog Analog- Digital Channel Channel Digital Modulat Information Digital Encoder Coded ed Signal Converter Information Modulat Informat ion or Voice, Video … 1001010101 1001010101101 Satellite Transmissi Mbps MHz on Mbps Analog Analog- Channel Demodula Digital Received Information Digital Decoder Digital Informat ted Signal Demodulat Signal Converter ion or Introduction to Satellite Link Analysis3/9 Modulation is the process of varying some characteristics of a periodic waveform, Carrier signal Modulating signal (no information) (with information) called the carrier signal, with a modulating signal that contains information. Characteristics that can vary are the amplitude, frequency and phase. Typical modulations used in satellite communications are PSK and QAM. The order of the modulation how many different symbols can be transmitted with it. E.g. Order 2: BPSK Order 4: QPSK, 4-QAM Order 8: 8-PSK, 8-QAM Order 16: 16-PSK, 16QAM Constellation diagram for QPSK Introduction to Satellite Link Analysis4/9 Channel coding (FEC: Forward Error Correction) consists of adding red bits to the useful information to allow detection and correction of er caused by the transmission channel. 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑢𝑠𝑒𝑓𝑢𝑙 𝑏𝑖𝑡𝑠 The FEC is usually given as a fraction 𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑏𝑖𝑡𝑠 The FEC is usually given with the modulation scheme. E.g.: QPSK 3/4 means that: − A QPSK modulation is used (order 4) − And for every 3 bits of useful information, 1 redundant bit is added. Said otherwise, 4 bits are required to send 3 bits of information Or 25% of the bits sent are useless from the user point of view (but still necessary to detect an errors)  Introduction to Satellite Link Analysis 5/9 On the importance of efficiency From user point of view, the key parameter is Information Rate (IR) (in Mbps or kbps) The required bandwidth in MHz for a given information rate is directly related to the modulation and coding scheme (modcod). − The higher the modulation order (2𝑛 ), the less bandwidth is required − The higher the FEC ratio, the less bandwidth is required − Other parameters also matter: roll-off factor (α), Reed-Solomon coding (RS) 𝑀𝑏𝑝𝑠 The efficiency is defined as the ratio : that is the number of Mbps that can 𝑀𝐻𝑧 be transmitted in a given MHz. The unit is bit per second per Hz (bps/Hz) The higher the efficiency, the more cost-effective a service is.  Introduction to Satellite Link Analysis 6/9 $/𝑀𝐻𝑧 $/𝑀𝑏𝑝𝑠 = 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 On the importance of efficiency – Examples 2 Mbps link using QPSK-3/4 (order 4 = 22 ), with 25% roll-off factor and no Reed- Solomon: 4 − Required bandwidth is: 2 × 1 + 0.25 × 3 ÷ 2 = 1.67 𝑀𝐻𝑧 − Efficiency is 1.20 bps/Hz Same 2 Mbps link using 8PSK-3/4 (order 8 = 23 ), with 25% roll-off factor and no Reed-Solomon: 4 − Required bandwidth is: 2 × 1 + 0.25 × 3 ÷ 3 = 1.11 𝑀𝐻𝑧 − Efficiency is 1.80 bps/Hz Same 2 Mbps link using 8PSK-7/8 (order 8 = 23 ), with 25% roll-off factor and no Reed-Solomon: 8 − Required bandwidth is: 2 × 1 + 0.25 × 7 ÷ 3 = 0.95 𝑀𝐻𝑧 − Efficiency is 2.10 bps/Hz Introduction to Satellite Link Analysis7/9 The selection of a modcod is constrained by the signal over noise ratio at reception: − The higher the modulation order, the higher the signal to noise ratio must be for the modem to be able to demodulate it. Signal over noise ratio is affected by: − Link conditions – propagation attenuation and impairments − Available power – on ground and on the satellite (PEB) − Performance of the satellite − Antenna size at reception − Capabilities of the modem A satellite link budget analysis will determine what modcod can be used and what are the required bandwidth and power. Introduction to Satellite Link Analysis8/9 What is a good efficiency? In general, the higher the efficiency, the better, but … − Efficiency is not the only parameter to consider − Service availability, cost of equipment, network topology, … are also key factors Sometimes a lower efficiency is acceptable to reduce required investment or size of equipment. − Example: a Direct-To-Home service with small receiving antennas and cheap demodulators will typically have a lower efficiency than a CBH service using large antennas and efficient modems. Introduction to Satellite Link Analysis9/9 Summary A signal transmitted by satellite has to be modulated and coded (modcod). The modcod scheme determines the efficiency which tells how many MHz are required to transmit one Mbps. The achievable efficiency is constrained by link conditions, satellite characteristics and available ground equipment. A link budget analysis is required to determine the maximum efficiency. Efficiency can be increased with better ground equipment (antenna, modem, amplifier) → tradeoff to be made between investment (CAPEX) and cost of bandwidth (OPEX)  End of Module 1 Thank You! Final Questions?