1.1 GENERAL
Satellite communication networks are now an indispensable part of major telecommunication networks. Satellites offer a unique capability of providing coverage over large geographical areas. The resulting interconnectivity between communication sources provides major advantages in wide-area telecommunication applications. The advantages offered have enabled this technology to mature within just three decades. The phenomenal growth of satellite technology continues, the major growth now being in those areas where satellites can provide unique advantages. Such applications include service provision directly to customers using small, low cost earth stations; mobile communication to ships, aircrafts, railways and land vehicles; direct-to-individual television/sound broadcasts and data distribution/gathering from widely distributed terminals. In many applications such as video distribution, service providers are combining the benefits of satellite communications with optical fibre systems to produce the best solution to users’ needs. Similarly, systems have emerged which combine the advantages of satellite mobile communication with those of terrestrial mobile system to provide a seamless coverage – terrestrial systems providing service in populated areas and satellite systems in those areas outside of terrestrial systems.
We begin with a brief history of satellite communications and an overview of the main components of a satellite communication system follows. Major design considerations are then discussed and the present status and future trends of the technology are briefly reviewed.
1.2 BACKGROUND
The first known use of a device resembling a rocket is said to have been reported in China in the year 1232. A number of instances of use of such devices were subsequently reported over the next centuries. However, significant progress in the field was not made until the work of a Russian school teacher, Konstantin E Tsiolkovsky (1857 – 1935), propounded the basis of liquid propelled rockets. He went further and put forward ideas of multi-stage launchers, manned space vehicles, space walks by astronauts and large space platforms that could be assembled in space complete with their own biological life support systems. His theoretical work on liquid propelled rocket engines was verified when in 1926 Robert H Goddard launched the first liquid propelled rocket in the United States. Other rocket pioneers also corroborated and extended Tsiolkovsy’s ideas – notable being the brilliant work of Slovene rocket engineer Herman Potočnik (pseudonym Hermann Noordung).
In his book, Das Problem der Befahrung des Weltraums – der Raketen-Motor, (Translated as: The Problem of Space Travel – The Rocket Motor) published in 1929 he conceptualized the design of a space station and recognized the significance of the geostationary orbit with detailed calculations of the orbit (Wikipedia, 2015). He also described the use of spacecrafts for Earth observation and scientific experiments. His concepts were extended in Germany by a small amateur group to lay the foundations of the present rocket technology. Their effort was later supported by the German military, leading to the successful launch of V-2 rockets in 1942 (Gatland, 1975). Recognising the potential of V-2 rockets, Arthur Clark suggested the use of geostationary satellites for worldwide voice broadcasts (Clark, 1945). The technology of V-2 rockets, extended in the United States and Russia after the war, led to the development of first satellite launchers. The satellite era began in October 1957 with the launch of Sputnik-1, a former Soviet Union satellite, followed by the launch of an American satellite, Explorer-1, in 1958.
Communication by moon reflections was demonstrated and used in the United States in 1940s and 1950s. The early years of satellite communications exploited similar techniques. Satellites were used as passive reflectors of radio waves for establishing communication. An immediate problem with the use of satellite reflectors was the extremely low level of received signal strength, resulting in the need of very sensitive and hence costly receivers. It was recognized that use of satellites, capable of amplifying the received signal on-board before re-transmission, could greatly enhance the capability of satellites for communications. However, the concept could not be implemented due to lack of space-qualified electronics. Therefore considerable research and development effort was spent during the next few years in the development of space qualified electronics, eventually leading to the introduction of active repeaters. In 1963 the first geostationary satellite, Syncom III, was successfully launched. The first commercial satellite for international communication, Early Bird, was launched in 1965.
The breakthrough provided by satellites in telecommunications resulted in major research and development effort in all the related technologies. Most of the early work concentrated on international point-to-point telecommunications applications. Later, the application of satellite communication extended to direct satellite broadcasts (1970s), mobile communications (1980s,) personal narrowband communication, radio and multimedia broadcast (1990s), personal broadband in 2000s and beyond.
The healthy revenues permitted large investments in research and development of both space and ground segment hardware, resulting in a steady reduction in the space and ground segment costs and several orders of magnitude improvements in performance.
In addition to international telecommunications, the use of satellite technology extended to regional and domestic telecommunication networks. Regional networks refer to networks formed by grouping countries in a region – such as Europe, and domestic network refers to an intra-country network.
INTELSAT, which was founded in 1964 to develop commercial uses of satellite communications, is a leading provider of international fixed satellite service. Examples of other international operators include SES, a European international operator that covers 99% of the world; and International Mobile Satellite Organization (INMARSAT), a UK operator which provides world-wide mobile communications. Examples of regional system operators are, the European Telecommunication Satellite Organisation (EUTELSAT) and the Asian Satellite Telecommunication Company Ltd (AsiaSat) which provides services in the European and the Asian regions respectively. Several countries now use domesic satellite systems – for example, North America, Canada, India and Indonesia.
A summary of notable milestones in the development of satellite systems is given at the end of the chapter (see Table 1.1).
The fact that satellites have a wide view of the Earth makes them useful for a variety of applications besides telecommunication. These applications are in the fields of meteorology, navigation, astronomy, management of earth resources such as forestry and agriculture, military reconnaissance, amateur radio and others. To coordinate the operation of different types of radio systems, an international body, the International Telecommunications Union (ITU), has categorised radio services on basis of offered service and set guidelines for the design and operation of each service. Telecommunication is provided by the Fixed Satellite Service (FSS) for communication between fixed points on the Earth; Mobile Satellite Service (MSS) for communication with moving terminals; and the Broadcast Satellite Service (BSS) which deals with television and sound broadcasts directly to customers.
1.3 SYSTEM
A satellite communication system consists of a space segment serving a ground segment confined within its service area. The characteristics of the ground segment depend on whether the service is for fixed, mobile or direct broadcast applications. The features and the related issues of these services are briefly addressed in this section.
The establishment of end-to-end connection and subsequent message exchange whether it is for voice, internet, or data exchange requires numerous distinguishable functions such as physical transport of the packet, signalling to initiate a session, handshake to establish an error-free connection followed by application-specific task and finally a tear down at the end of the session. These functions are partitioned according to their role into seven ‘layers’ formalised by the ITU in recommendation X.200 for information system in order to provide a common platform for the coordination of standards development in this area and to set a perspective for existing standards (ITU-T, 07/94). Within this model the entity such as a cable or satellite radio link that transports the fully potent packet belongs to layer 1. Here we will deal primarily with the physical layer.
The main elements of a satellite communication system for point to point communication between fixed sites are shown in figure 1.1. Ground stations (also called earth stations) in a network, transmit radio frequency (RF) signals to the operational satellite; the received signals are amplified, translated to another radio frequency, and after further amplification, transmitted back towards the service area. The destination earth station receives these signals, extracts the messages and flow them out to the user. Communication can thus be established between earth stations located within the service area.
Space Segment
The space segment consists of one or more satellite(s) in suitable orbit(s). Satellite and orbital characteristics depend on the application needs. The satellites are controlled and their performance monitored by the Telemetry Tracking and Command (TT&C) stations. In an operational system the satellite in use is usually backed up by another satellite to cover the risk of satellite failure. Most of the present communication satellites are in the geostationary orbit. In the year 2015, 80% of the commercial communication satellites were in geo-stationary orbit (Satnews Daily, August 26, 2015). A circle at an altitude of ~ 35,786 km above the equator is known as the geostationary orbit. Satellites orbiting the Earth in such an orbit rotate in unison with the Earth, appearing almost stationary to an observer on the ground. A satellite that appears stationary simplifies the design, operation and maintenance of earth stations. Earth station antennas need not track such a satellite or use simple and low cost tracking systems; RF signals do not suffer significant Doppler frequency shift; and the signal and interference environment remain stable. Further, a single geostationary satellite can provide communication to large areas (about one-third of the Earth), permitting easy interconnection between distant ground terminals. Thus three geostationary satellites placed 120o apart can provide coverage to almost all (~99%) the populated areas of the world. Figure 1.2 conceptualises the coverage by a combination of three geostationary satellites and satellites in another class of orbit known as Molniya. A Molniya orbit has an inclination of 63.4o with high eccentricity such that satellites provide good coverage in the polar and high-latitude regions where geostationary satellites signals are unreliable. Signals from geostationary satellites are unstable beyond latitudes of ± ~ 76.35o (~ 5o elevation from ground) and unavailable beyond latitudes of ± 81.3 o.
(©Knowledge Space Ltd)
Figure 1.3 shows visibility contours of 0o, 5o and 10o elevation angles of a single geostationary satellite located at 142o W longitude [Note: Elevation angle of a satellite from a given location on the Earth is the satellite’s elevation above the horizon].
Signal quality of received signals below ~ 5o elevation degrades due to tropospheric effects (caused by longer path through the troposphere) and rapid signal fluctuations caused by multiple signal entries at the receiver from reflections/diffraction of the signal from the local environment. The condition is worse for land mobiles as number and depth of obstructions increase at low elevation angles resulting in a considerable increase in the depth and probability of shadowing.
Satellites in Molniya or similar orbit (there are other variants of this orbital class) appear nearly stationary at high elevation angles for periods of 8 to 12 hours from earth stations located at high latitude. Thus three satellites operating in tandem can provide continuous service by periodic handover of traffic from the setting satellite to the rising satellite. This class of orbit has been favoured for mobile communication and direct broadcasts in mid and high latitude areas.
The use of low and medium earth orbits was considered actively during the early stages in the development of satellite communications but abandoned because of the resulting complexity in earth station antenna and receiver systems as well as network architecture. A number of satellites are needed for global or regional coverage; frequent handovers are necessary to maintain communication continuity as satellites constantly appear and set; and complex routing arrangements are necessary to establish end-to-end connectivity. However as technology matured, solutions to these technicalities emerged at affordable costs, making low and medium earth system technically and economically viable. Interest in the use of low and medium earth orbit for mobile communications was therefore revived in 1990s (e.g., Richharia et al., 1989, Maral et al. 1992). Some of the main advantages include:
a) Satellites are closer to the Earth and can therefore provide stronger signal amenable for hand-held user terminals; the advantage can best be exploited by using ‘spot’ beam antennas and a rather complex network architecture; (Note: spot beams provide highly focussed transmissions);
b) Frequencies are reused more frequently compared to geostationary orbit because the illuminated area from low and medium earth orbit is smaller, allowing a denser frequency reuse;
c) Due to a shorter signal path, propagation delay is less than that of geostationary satellite links and, depending on orbital altitude, approaches those of terrestrial system [Note: Large propagation delay affects interactive communication adversely].
Various types of communication satellites are in use depending on the anticipated traffic load, service type, and service area – ranging from small satellites for domestic communications or as a unit of a non-geostationary constellation to large and complex satellites such as those used for mobile or consumer applications. Radio regulations permit higher power satellite transmissions to services of the consumer sectors than from satellites serving the fixed network sector. Essentially, the complexity is shifted to the space segment in order to simplify the ground segment amenable to the consumer segment. For example, Inmarsat-5 satellites, launched during 2014-15, have a lifetime of 15 years; a launch mass of 6100 Kg; solar panel of 33.8 m span capable of generating 15 kW power at the beginning of life; and comprise huge 8.08 m antennas, which illuminate the Earth with 89 Ka band reconfigurable spot beams to support broadband on portable, mobile and fixed ground terminals.
Figure 1.4 illustrates picture of a 3-axis stabilized satellite typical of a modern system. The stabilized platform contains equipment that processes received signals and readies them for transmission. The antenna systems receive and transmit signals towards the service area. Solar cells provide DC power for functioning of the repeater and other support system. The support systems keep temperature of equipment within tolerance; maintain stability and orbital location of the satellite; and perform telemetry and command functions, which include transmission of health of each sub-system and reception of commands from ground to execute on-board tasks like equipment reconfiguration and manoeuvres such as firing on-board thrusters for attitude and orbit corrections.
Low and medium Earth orbit satellites view a narrower geographical area than geostationary satellites and are, therefore, smaller in size as the load captured per satellite is lower. However, the constellation size can be large, depending on the orbital altitude and service area. For example, the largest constellation in use today comprises 77 satellites to provide global mobile service. A few providers plan to deploy hundreds of small, low-cost satellites in low earth orbit for global low-cost Internet and other services.
Ground Segment
The ground segment of each service has distinct characteristics. The ground segment of a fixed satellite service (FSS) illustrated in figure 1.1 consists of several types of fixed earth stations, depending on the application. For example, earth stations for handling international traffic use large antennas (typically, 11m) together with complex RF and baseband sub-systems (Figure 1.5(a)), whereas terminals for communication directly to customer’s premises deploy non-tracking antenna of 1-3 m diameter with simple RF and baseband hardware (Figure 1.5(b). The user is connected to earth station either directly or through a regional or a national public switched network. The interface between an earth station and user (i.e., fixed network or end-user) is an important feature.
The main components of a mobile satellite service (MSS) are shown in Figure 1.6.
The ground segment consists of several types of mobile terminals connected wirelessly with the fixed telecommunication networks. Mobile satellite systems can be categorized into three classes according to their respective service environment – maritime, aeronautical and land-based. Ground terminals serving each category of mobiles differ to varying extents. Differences occur because the mounting space available for the antenna and receiver depends on the size and shape of the mobile (e.g., ship has more space than a truck); the communication needs and terminal cost target differ (e.g., a personal communicator must have a lower cost with moderate communication capability relative to an aeronautical terminal); and the behaviour of the signals are affected significantly by the environment in the proximity of the mobile. Consequently, maritime and portable fixed terminals can potentially provide the largest communication capability, followed by aeronautical terminals. At present on-move land terminals (in contrast to portable terminals) provide a rather limited communication capability because of severe limitations on antenna size, harsh propagation environment and technological limitations of space segment. Nevertheless, hybrid terrestrial-satellite systems can overcome such limitations. Radical improvements in satellite and handset technology and system architecture have enabled the availability of hand-held satellite terminals resembling cellular telephone, while portable communicators can provide broadband communication from anywhere on the globe.
A rescue co-ordination centre can be included in the MSS network to respond to distress calls from mobiles in the network.
Figures 1.7(a) and (b) respectively illustrate a mobile wideband terminal and a satellite handheld terminal.
Figure 1.8 shows the main elements of a broadcast satellite service (BSS). The video component of the service is often referred to as Satellite Television in general terms. Direct to Home (DTH) television and Direct Broadcast Satellite (DBS) television are variants of the same technology with slightly different historical background and technical specifications. DTH television refers to the generic satellite television technology which uses an operator-chosen set of system parameters and frequency bands which may not be designated for broadcasts – dating it back to the years when individuals intercepted low power transmissions of cable distribution network. The receivers had to use large dishes in those days as the technology was not matured; but over the years the technology has evolved and receivers are similar to DBS television sets and such systems have been legalised.
DBS technology refers to transmissions in compliance to a plan introduced by the International Telecommunication Union (ITU) in which system parameters including orbital slot and frequencies (in Ku band: 14 GHz uplink/11 GHz downlink) have been assigned to each country to provide high quality reception directly to consumers’ and guarantee availability of orbital slot and frequencies to each country. Transmissions can only be made on designated frequencies and the specified system parameters.
There is thus a combination of these two technologies in operation across the world.
Programmes (originating in a studio or captured live) are transmitted through a large gateway earth station and a high power satellite to subscribers dispersed throughout the service area who receive the programmes on low-cost receivers typically using 50-90 cm roof-mounted antenna interfaced to television set shared with other applications (figure 1.8). The cost of the direct broadcast receiver is comparable to other home entertainment appliances.
Commercial cable systems use larger and more sensitive satellite receivers and provide to their subscribers a better signal quality with a larger choice of programmes at lower cost than is possible on direct-to-home receivers.
Majority of revenue in the satellite service and consumer segments comes from the satellite television sector. The sector contributed 78% of total satellite services revenue with about 200 million subscribers worldwide in 2013 (SIA, 2014).
Direct-to-individual satellite broadcast systems are a recent addition to the broadcast service portfolio. They provide sound, multimedia, television and similar services directly to consumers on small portable or mobile user terminals. Examples of associated applications include customised audio or video content (e.g., podcasts), data delivery (e.g., ring tones), location-based information (e.g. traffic), etc. These services are known variously as satellite radio, Satellite Digital Audio Radio Services (SDARS) and Satellite-Digital Radio Broadcast (S-DAB).
Figure 1.9 (a) illustrates a cluster of direct broadcast dishes installed in a housing complex. Figures 1.9(b) and 1.9(c) respectively show a hand-held direct-to-individual television receiver and a satellite radio.
1.4 SYSTEM ELEMENTS
The structure of a satellite network depends on the service provided (e.g., voice, data, fixed, mobile, television, radio, etc.), the service area, anticipated traffic load, the addressed market and the business goal. The objective is to meet the mission goals such as signal quality objectives and economics, respecting all system and implementation constraints such the state of technology and time scales. Moreover, a satellite link may only be a subset of a larger network comprising other types of links (microwave radio relays, optical fibres, etc.). In such cases the satellite portion cannot be considered in isolation from the rest of the network. Further, characteristics and hence optimisation criteria are different for fixed, mobile and broadcast satellite services.
An important system consideration is the selection of radio frequency (RF). The choice is governed by type of service, radio wave propagation characteristics, state of technology, prevalent radio regulations, and spectrum availability in face of competition. Radio regulations promulgated by the ITU specify frequencies for radio services and methods to avoid excessive interference between users.
Another consideration related to the physical layer relates to the selection of an optimum modulation and coding scheme. [Note: physical layer in this context refers to all aspects of radio frequency transmissions]. The choice is governed by characteristics of the messages (e.g. video, telephony, and data, interactive, non-interactive, error tolerance, etc.), radio link, earth stations; and a power-bandwidth trade-off. The latter refers to the inverse relationship between the power and bandwidth – in general, bandwidth reduces with an increase in transmitted power and vice versa allowing the designer to select the best combination in relation to the available power-bandwidth. It is worth noting that characteristics of baseband signals also influence the choice of modulation and coding schemes.
A satellite network consists of a few to several thousand earth stations and hence a provision is made to ensure that satellite resources are shared equitably. Various accessing schemes have been developed to optimise the use of satellite capacity, while satisfying the end-user. For example, interactive services like voice require a dedicated access whereas delay-tolerant applications can use a discontinuous access, giving precedence to interactive users.
The size and shape of service area determines the characteristics of satellite antenna system; the prevailing technology in relation to spacecraft and ground stations govern the achievable limits of throughput, user terminal size, and crucially, the economics. The overall trade-offs are constrained by numerous real-world considerations, e.g. funding, politics, business goals, etc. A unique solution may not exist, and a solution used by one administration may not be applicable to another.
1.5 Applications
A few generic applications of satellite communication system were mentioned in the introductory paragraph – here we provide a wider perspective. In addition to these examples, numerous other applications are possible and the interested readers are encouraged to consider imaginatively how best satellite communications can be utilized for their needs based on the advantages and limitations of satellite communications. The main limitations of satellite communications are, therefore, included here for obtaining a balanced perspective.
Satellite communications is traditionally used for connecting large traffic nodes such as switching centres when distances are of the order of hundreds of kilometres and in special situations such as the presence of difficult terrains or a large span of sea in-between traffic nodes.
Satellites prove attractive for rapid deployment of telecommunication services between or with isolated communities. Hence several countries, where populated areas are separated by vast distances, difficult terrain (e.g. mountains) or sea (e.g., an archipelago), use satellite systems effectively.
VSATs are a popular choice for thin and remote routes, dedicated applications, personal and mobile broadband service. Since VSAT networks can bypass the public switched network (PSN), they are often more cost-effective and reliable than the PSNs; by eliminating delays associated with the PSN, users can access services and applications quickly. VSATs are, therefore, used universally in auto, retail and business sectors. Due to a dramatic reduction in size and cost, VSATs are beginning to penetrate the personal and mobile broadband markets.
One of the fastest growth areas is that of mobile satellite communications. Satellites provide unbiased coverage over a significantly wider area than terrestrial mobile systems, including oceans, inter-continental flight corridors and large expanses of sparsely populated land masses. Satellites are, therefore, used to provide voice and broadband data communications to aircrafts, ships and land vehicles. Examples of mobile applications include broadcasting live televisions to ships using advanced picture compression techniques; providing multimedia and voice communications to portable and hand-held terminals; tracking movements of truck fleets or yachts in conjunction with location information; supporting relief operations in remote areas; supporting first-responders; providing instant contact with news reporters covering events in a war zone or in remote areas; responding to distress calls from mobiles; and offering world-wide paging service.
Satellites broadcasts can cover large hitherto unserved geographical areas in a single sweep. Although the time taken from planning stage to system implementation typically takes 4-5 years, service is available simultaneously throughout the coverage spanning hundreds to thousands of kilometres as soon as a broadcast satellite is brought into service. Coverage by terrestrial means in the same areas would be tedious, time-consuming and expensive and even then many pockets would remain unserved. Developing countries, such as India, use satellite broadcasts extensively. Satellite television has proven equally popular in developed regions such as Europe, despite strong competition from other television delivery medium. Satellite radio and multi-media broadcast systems have gained popularity in some regions of the world despite competition from terrestrial delivery medium but have so far failed to take off on a global scale.
Let us now summarise limitations of satellite communications. Most significantly, satellite networks are expensive to install, particularly if a single entity attempts to take responsibility of the space and ground segment. A careful techno-economic study is therefore essential before taking such a decision. The space segment cost can be scaled down considerably by leasing transponders from specialist satellite capacity providers.
There is potentially a sudden loss of service to vast areas if an operational satellite were to fail or malfunction. Similarly, the reliability of satellite hardware has increased considerably. Many satellites continue to provide good service far beyond their design lifetime. The problem of in-orbit catastrophic failure is mitigated by deploying an in-orbit spare, often leased from another organisation to minimise cost. To make a better utilization of the idle spare capacity it is sometimes leased on a pre-emptible basis. In a non-geostationary the dynamic coverage gap can be patched up quickly by re-phasing other satellites of the constellation while the spare satellite is brought into service; note that unlike the case of a failure of a geostationary satellite the coverage gap does not remain static due to constellation dynamics.
Launch failure is yet another risk area. Fortunately, the reliability of launchers has improved vastly and present launchers typically have reliabilities better than 99%.
Geostationary satellite systems exhibit a large end-end transmission delay due to a long propagation path. The problem is exacerbated when the delay is accompanied with echo caused by a mismatch at the interface between terrestrial and satellite system. Under these circumstances telephone users suffer the worst annoyance. Advances in echo suppressors/cancellers technology have reduced the echo problem. Fortunately, transmission delay does not pose a problem in applications insensitive to transmission delays – such as transfer of large data files.
Low and medium Earth satellite system exhibit a much lower propagation delays due to closer proximity of the satellites from the Earth, and hence, such orbits are favoured for applications where propagation delay must be minimised.
1.6 TRENDS
Satellite industry revenue has grown at an average annual growth of 11% between 2004 and 2013 equating to an increase by 2.6 times in absolute terms [SIA, 2014]. In order to develop research and development focus, refine capabilities of existing products and shape strategy, industrial forecasts are made regularly by specialists, taking into consideration external influences (other industries, societal changes, etc.) , demand drivers, market trends, technology innovation across the industry, emerging applications (including those provided by terrestrial systems), regional disparity, customer base, etc.
One of the primary drivers in the growth of satellite communication is the stupendous uptake of internet applications. One estimate puts the global compounded internet-driven market growth in communication for the period 2015-2022 as 68% covering both commercial and military sectors.
According to forecasts the compounded annual growth rate for the Fixed Satellite Service (FSS) as a whole is anticipated to average around 5% per year up to the year 2019. The FSS, can be segmented in to sectors, for example, video (direct to home, video distribution, etc.); network support (enterprise, direct user access, etc.); backhaul (carrier, cellular, etc.); and mobile applications in regions where FSS mobility is permissible. The growth is anticipated to vary by sector as well as region. Demands from the matured markets are anticipated to drive innovation such as direct user access and mobile applications, while developing regions are expected to foster demands on traditional services such as wholesale carrier services as their infrastructure builds up.
An interesting trend in FSS is the inroad of the service, formally covering only fixed installations, into the mobile domain that is dealt primarily by mobile satellite services (MSS). Due to differences in the radio link characteristics of fixed and mobile users, differing user terminal characteristics and interference mechanisms, these services are governed by different radio regulations. This changing paradigm is attributed to:
– demands of low-cost broadband communications from the mobile community – a requirement which cannot be fully met by mobile satellite service operators ;
– modifications to FSS radio regulations allowing maritime mobility in limited areas;
– a remarkable reduction in size and costs of VSAT user terminals;
– availability of relatively cheap satellite capacity across the globe.
Mobile VSATs are increasingly being deployed in maritime, aviation and railway applications in geographical regions where regulatory barriers were relaxed.
The traditional mobile satellite services have grown robustly in recent years and are expected as a major growth area in the next decade due to an escalating demand for ubiquitous data. Mobile satellite systems using non-geostationary orbit are poised for further inroads into broadband applications with introduction of new satellite generation. Emerging applications include machine-to-machine communication, cellular backhaul from mobiles such as aircrafts, aircraft traffic and management, etc.
Active MSS terminal base has grown at a compounded aggregate growth rate (CAGR) of 9% over the past five years (2014 base) with projection that the base – excluding the recent Ka-band MSS emergence – is likely to grow at an annual rate of 7% up to 2024, while the wholesale service revenue is predicted to grow at a CAGR of 4% over the assessment period (2014-2024). The land sector is anticipated as the largest segment by 2024, while the aeronautical segment is likely to provide the fastest growth in revenue, projected as 9% per year (Satnews Daily, April 20, 2015).
Recent innovations, promoting these trends, include introduction of high throughput satellites (HTS) which utilize various innovations to more than double the capacity of traditional satellites. These techniques include enhanced frequency reuse through dense spot-beam technology (well over 50 narrow beams from a satellite), on-board processing and introduction of HTSs in non-geostationary orbit. The end-user benefits by a significant reduction in communication and terminal costs. Another notable innovation is the electrical propulsion system, which reduces the weight of satellites by minimising the use of traditional fuel for orbital manoeuvres. A further dimension to innovations is an increasing use of flexible payload incorporating software reconfigurable elements in the payload executable from the ground.
There is an increasing use of small satellites in recent years – some measuring less than a metre (and as small as 10 cm) – at present mainly for research and development, government applications, etc. Such satellites are low in cost with highly compact electronics and powerful processing capabilities; and their launch cost is very competitive thus fostering an era of low-cost constellations. There are a number of proposals of low-cost large constellations comprising hundreds of small non-geostationary satellites targeting communication to remote communities.
Other areas in investigation include, as yet un-utilized, high radio frequency Q/V bands extending beyond 40 GHz to alleviate frequency congestion problems of existing bands; inter-satellite links in space to increase space segment capacity and connectivity; advanced antenna concepts; adaptation of terrestrial mobile system technologies and others
Standardization of a number of key air-interfaces (i.e. the satellite radio link), based on years of intense worldwide collaborative effort, is promoting a robust growth through competition and economies of scale. Availability of the base technology to manufacturers through standardisation (as opposed to propriety solutions) encourages competition and forces down cost which in turn fosters uptake by the end users eventually leading to large economies of scale. Digital video broadcasting over satellite is one example of the accrued benefit which has brought direct broadcasts in the consumer mainstream.
Introduction of Ultra high definition television is likely to spurt the growth in satellite and ground segments through large demands for bandwidth.
Innovative hybrid network infrastructure combining satellite and terrestrial system seamlessly has already proven itself in satellite radio broadcast systems; this architecture is poised to pervade the mobile satellite services.
Rapid evolution of terrestrial mobile technologies has been a strong driver towards similar innovations in satellite communication system technology. Satellite systems continue to be inspired by and leverage from technology of these extraordinary developments.
| Year | Milestone | Credit |
| 1926 | First liquid propellant rocket launched by R H Goddard in the USA | |
| 1942 | First successful launch of a V-2 rocket in Germany, which led to development of satellite launchers | |
| 1945 | Arthur Clarke publishes his ideas of geostationary satellites for world- wide broadcast | |
| 1957 | Launch of first satellite | Former Soviet Union |
| 1958 | First American satellite launchedFirst voice communication via satellite demonstrated | USA |
| 1960 | First communication satellite (passive) launchedFirst successful launch by DELTA Launch VehicleFirst remote sensing satellite TIROS-1 launched | USA |
| 1961 | Formal start of TELSTAR, RELAY, and SYNCOM Programs which led to the beginning of satellite communication as we know it | USA |
| 1962 | First active communication satellite launchedTELSTAR and RELAY satellite launchedFirst trans-Atlantic live television broadcast (TELSTAR-1)RELAY satellite used for live trans-Atlantic television broadcasts of important US events | USA |
| 1963 | SYNCOM 1 and 2 launched to develop technology for geostationary orbit | USA |
| 1964 | First satellite launched into geostationary orbit (SYNCOM-3)INTELSAT founded | USA |
| 1965 | First commercial geostationary satellite system launched (Early Bird: INTELSAT-1) | Comsat, USA |
| 1969 | Global coverage available through INTELSAT-III satellite series | INTELSAT |
| 1972 | First domestic satellite system operational (ANIK)INTERSPUTNIK foundedLandsat-1 (remote sensing) satellite launched | CanadaFormer USSRUSA |
| 1974 | First U.S. domestic communications satellite (WESTAR) | USA |
| 1975 | First use of dual-polarization (INTELSAT-IVA)Launch of first Indian satellite (Arya Bhatt) | INTELSATIndian Space Research Organization (ISRO) |
| 1975 | First successful wide-area direct broadcast demonstrations ( 1 year duration, Satellite Instructional Television Experiment) | USA/India |
| 1975 | First body-stabilized operational communication satellite | RCA/USA |
| 1976 | First mobile communications satellite launched (MARISAT)Indonesia, third country, launches domestic communication satellite system (PALAPA system) | USAIndonesia |
| 1976 | First demonstration of inter-satellite link using LES-8 satellite | USA |
| 1977 | A plan for direct-to-home satellite broadcasts assigned by the International Telecommunication Union (ITU) in regions 1 and 3 (most of the world except Americas). | ITU |
| 1977 | Mobile experiments conducted using ATS-6 | NASA, USA |
| 1978 | Start of GPS introductionFists demonstration of Internet connection | USAINTELSAT |
| 1979 | Inmarsat formation | International Maritime Satellite Organization/IMO/UN |
| 1980 | IMO decides to deploy satellite communications for maritime safety | UN |
| 1981 | First re-useable launch vehicle flight (American Space Shuttle) | USA |
| 1982 | Start of GLONASS introduction | Former Soviet Union |
| 1982 | First civilian mobile satellite system introduced for maritime use | Inmarsat |
| 1983 | ITU direct broadcast plan extended to region 2Beginning of Indian domestic satellite system INSAT | ITUIndia |
| 1984 | First direct-to-home broadcast system operational | Japan |
| 1987 | Successful trials of land mobile communications | Inmarsat |
| 1988 | Launch of Indian Remote Sensing Satellite–1 (IRS-1). [IRS constellation is world’s largest constellation of civilian remote sensing satellites.] | ISRO |
| 1987-89 | An architecture of LEO for mobile satellite communication proposed | University of Surrey, UK |
| 1989 | First international high definition link established (USA-Japan) | INTELSAT |
| 1989-90 | Global mobile communication commercial service extended to land mobile and aeronautical environments | Inmarsat |
| 1990 | First commercial satellite radio broadcast system filed | CD Radio Inc., USA |
| 1990 | First commercial non-GEO hand-held system announced | Motorola/Iridium |
| 1990-91 | Commercial land and aeronautical mobile satellite services (MSS) introduced | Inmarsat |
| 1990-92 | Several organizations/companies propose non-geostationary satellite systems for mobile communications – following Motorola. | Various |
| 1992 | GSM terrestrial mobile system introduced (Architecture used later as basis for mobile satellite systems) | Europe |
| 1992 | Major changes to mobile satellite frequency allocation | ITU (WARC 1992) |
| 1992 | Successful retrieval and re-boost of INTELSAT 603 spacecraft in space | NASA/INTELSAT |
| 1993 | Announcement of first commercial little-LEO satellite system (with secure finance) | Orbital Sciences Corporation – ORBCOMM system; USA |
| 1994 | First non-GEO fixed satellite service system announced (However, the system failed to materialize) | Teledesic Corporation; USA |
| 1994-96 | Several regional ‘super-geostationary’ satellite systems announced | Agrani (Indian Consortium) ; APMT (China/Thailand); ACes; Thuraya, etc. |
| 1995 | GPS navigation system fully operational (Project start: 1973)GLONASS (Start of development 1976) | US GovernmentFormer Soviet Union |
| 1996 | Satellite paging services announced | Inmarsat |
| 1997 | Desktop-sized mobile terminals introduced | Inmarsat |
| 1997 | First non-geostationary little-LEO satellite system introduced | ORBCOMM |
| 1997 | Frequency allocated for non-GEO fixed system | WRC 1997 |
| 1997 | Launch of first batch of LEO satellite system for voice communications (so called ‘big-LEO’) | Iridium |
| 1997 | Launch of first batch of non-geostationary satellite system for low bit rate data communications (‘little-LEO’) | ORBCOMM |
| 1997 | Mobile experiments conducted using ACTS | NASA |
| 1997 | Navigation system : geostationary overlay capability available | Inmarsat |
| 1997-98 | Start of world-wide spot beam operation for MSS | Inmarsat |
| 1998 | Introduction of first big-LEO satellite system | Iridium |
| 1998 | Introduction of dual-mode satellite-terrestrial handsets (i.e., combined satellite and terrestrial handset) | Iridium |
| 1998 | Safety of life at sea (SOLAS) treaty introduced | UN |
| 1998 | Introduction of extensive on-board processing satellites for MSS | Iridium |
| 1999-2000 | Serious financial difficulty experienced by new and proposed non-GEO MSS systemsIntroduction of Globalstar | IridiumGlobalstar |
| 2000-05 | Consolidation of new mobile satellite system operators despite financial losses | Various |
| 2005 | Launch of Inmarsat 4 – first L band high throughput mobile satellite | Inmarsat |
| 2005 | Introduction of wide-band portable land mobile communication system | Inmarsat |
| 2006-2008 | Extension of portable broadband system to mobile platforms | Inmarsat |
| 2008 onwards | Growing trend of FSS satellite system usage in mobile environment (maritime/aeronautical) | |
| 2009-10 | Announcement of next generation systems | Inmarsat, Iridium, Globalstar, ORBCOMM |
| 2009 | LightSquared proposes ATC services in USA (Satellite-terrestrial hybrid system) | LightSquared |
| 2011 | Launch of Viasat-1 : Beginning of High Throughput Satellite fixed satellite service era | Built on Space Systems/Lora |
| 2012 | ATC service license suspended in USA due to interference issues to GPS | LightSquared |
| 2012 -15 | Escalation of mobile usage in FSS band due to growing demands | Worldwide |
| 2014 | Introduction of Ka band mobile broadband | Inmarsat |
| 2015 | Start of India’s Satellite-based augmentation system (GAGAN) | Indian Government |
| 2015 | Introduction of first medium Earth orbit satellite communication system for space segment capacity lease | O3b, USA |
| 2015 | Revival of dense LEO constellation concept through several announcement for global Internet provision | |
| 2016 | LEO Next generation broadband L-band system roll out planned | Iridium |
| Forecast up to 2014 | 550 commercial satellites estimated to be launched up to 2024 (Excludes new dense constellation announcements and satellites < 50 kg by weight) | Euroconsultant (Satnews Daily, 26 August, 2015) |
TABLE 1.1 Milestones in evolution of satellite systems.
ACRONYMS
| ATC | Ancillary Test Component |
| BSS | Broadcast satellite service |
| CAGR | Compounded Aggregate Growth Rate |
| DBS | Direct Broadcast Satellite |
| DTH | Direct to Home |
| FSS | Fixed Satellite service |
| GEO | Geostationary Earth Orbit |
| GPS | Global Positioning System |
| Inmarsat | International Mobile Satellite Organisation |
| Intelsat | International Telecommunication Satellite Organisation |
| IRS | Indian Remote Sensing |
| ITU | International Telecommunication Union |
| LEO | Low Earth Orbit |
| MEO | Medium Earth Orbit |
| MSS | Mobile Satellite Service |
| OSI | Open System Interconnection |
| RF | Radio Frequency |
| SOLAS | Safety of life at sea |
| TT & C | Telemetry Tracking and Command |
| VSAT | Very Small Aperture Terminal |
REFERENCES
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