10.2.1 Geostationary Satellite Communication Systems

The geostationary orbit has been the preferred orbit for satellite communication systems and provides most of the revenue for satellite system operators. The first geostationary communication satellite, named Early Bird (Intelsat 1) was launched by INTELSAT in 1965. Commercial satellites launched in the 1970s and 1980s were all geostationary satellites. These satellites were used for international, regional and domestic telephone and video distribution services. Some of the important geostationary satellite missions include Intelsat, Inmarsat, Telstar, Asiasat, Arabsat, Galaxy, GE, Superbird, Eutelsat, Astra, Palapa and so on. New trends in the field of satellite communication include the launch of satellites in non-geostationary orbits for some specialized applications. The most important applications of geostationary communication satellites in the current scenario include DTH satellite television broadcasting services and VSAT services.

10.2.2 Non-geostationary Satellite Communication Systems

Non-geostationary satellite communication systems are emerging to provide mobile communication services as well as other services like messaging, video, fax and data communication. Constellations of satellites orbiting in LEO or MEO orbits can provide global mobile communication services. However, the cost of building such a constellation of satellites is huge as compared to having a geostationary satellite. Therefore, these systems have not made great progress and are still in the developmental stage. IRIDIUM, Orbcomm, Globalstar and ICO systems are some of the non-geostationary satellite communication systems.

10.4.1 Types of Transponders

Transponders may be broadly classified into two types depending upon the manner in which they process the signal:

1. Transparent or bent pipe transponders
2. Regenerative transponders

10.4.1.1 Transparent or Bent Pipe Transponders

Transparent transponders process the uplink satellite signal in such a way that only their amplitude and the frequency are altered; the modulation and the spectral shape of the signal are not affected. They are also referred to as ‘bent pipe’ transponders as they simply transmit the information back to Earth.

Transparent transponders comprise an input filter, low noise amplifier (LNA), down converter, input multiplexer, channel amplifiers, high power amplifiers and output de-multiplexer (Figure 10.2). The uplink section of the transponder, comprising the input filter, LNA and the down converter is common to all the channels and is shared by all the transponders. The down converter is basically a mixer which provides a fixed frequency translation corresponding to the exact frequency difference between the centre of the uplink and the downlink frequency bands. For example, the down converter for a C band transponder provides a frequency translation of 2.225 GHz as the difference between the centre of the uplink frequency band (5.925–6.425 GHz) and the downlink frequency band (3.7–4.2 GHz) in this case is 2.225 GHz.

The full bandwidth is separated into individual transponder channels by a bank of RF filters called the input multiplexer (IMUX), with each filter being tuned to pass the full bandwidth of a particular channel and reject all other channels. The output of each IMUX filter is then amplified by separate power amplifiers. The power amplifiers employed are travelling wave tube amplifiers (TWTA) for higher power levels (50 W or more) and at higher frequency bands (Ku and Ka bands) and solid state power amplifiers (SSPAs) for lower power applications. The output of all the transponder channels is then combined in an output de-multiplexer, which is composed of specially designed low-loss waveguide filters and then fed to a common transmitting antenna for down-beaming the signal on to Earth. The transponder always has redundant equipment to ensure its proper performance in the case of failure of any one of them.

10.4.2 Transponder Performance Parameters

The product of the transmit antenna gain and the maximum RF power per transponder defines the most important technical parameter of a communication satellite, the transmit effective isotropic radiated power (EIRP). As a general trend, EIRP values for the C band and Ku band satellites are around 40 dBW and 55 dBW respectively. EIRP defines the downlink performance of a transponder and specifies the coverage area of a satellite. The uplink performance of a satellite is defined by the parameter called the relative gain-to-noise temperature (G/T) ratio. It is the ratio of the receive antenna gain and the noise temperature of the satellite receiving system.

10.5.1 Advantages of Satellites Over Terrestrial Networks

Satellites offer certain advantages over terrestrial networks. Some of the advantages are as follows:

1. Broadcast property – wide coverage area. Satellites, by virtue of their very nature, are an ideal means of transmitting information over vast geographical areas. This broadcasting property of satellites is fully exploited in point-to-multipoint networks and multipoint interactive networks. The broadcasting property is one of the major plus points of satellites over terrestrial networks, which are not so well suited for broadcasting applications.
2. Wide bandwidth – high transmission speeds and large transmission capacity. Over the years, satellites have offered greater transmission bandwidths and hence more transmission capacity and speeds as compared to terrestrial networks. However, with the introduction of fibre optic cables into terrestrial cable networks, they are now capable of providing transmission capabilities comparable to those of satellites.
3. Geographical flexibility – independence of location. Unlike terrestrial networks, satellite networks are not restricted to any particular configuration. Within their coverage area, satellite networks offer an infinite choice of routes and hence they can reach remote locations having rudimentary or nonexistent terrestrial networks. This feature of satellite networks makes them particularly attractive to Third World countries and countries having difficult geographical terrains and unevenly distributed populations.
4. Easy installation of ground stations. Once the satellite has been launched, installation and maintenance of satellite Earth stations is much simpler than establishing a terrestrial infra-structure, which requires an extensive ground construction plan. This is particularly helpful in setting up temporary services. Moreover, one fault on the terrestrial communication link can put the entire link out of service, which is not the case with satellite networks.
5. Uniform service characteristics. Satellites provide a more or less uniform service within their coverage area, better known as a ‘footprint'. This overcomes some of the problems related to the fragmentation of service that result from connecting network segments from various terrestrial telecommunication operators.
6. Immunity to natural disaster. Satellites are more immune to natural disaster such as floods, earthquakes, storms, etc., as compared to Earth-based terrestrial networks.
7. Independence from terrestrial infrastructure. Satellites can render services directly to the users, without requiring a terrestrial interface. Direct-to-home television services, mobile satellite services and certain configurations of VSAT networks are examples of such services. In general, C band satellites usually require terrestrial interfaces, whereas Ku and Ka band systems need little or no terrestrial links.
8. Cost aspects – low cost per added site and distance insensitive costs. Satellites do not require a complex infrastructure at the ground level; hence the cost of constructing a receiving station is quite modest – more so in case of DTH and mobile receivers. Also, the cost of satellite services is independent of the length of the transmission route, unlike the terrestrial networks where the cost of building and maintaining a communication facility is directly proportional to the distances involved.

Hence, by virtue of their broadcast nature coupled with uniform services offered within the coverage area and easy installation of ground stations, satellites remain the most flexible means for providing links between all points on the globe with a minimum of terrestrial facilities.

10.5.2 Disadvantages of Satellites with Respect to Terrestrial Networks

For certain applications, satellites are at disadvantage with respect to terrestrial networks:

1. Transmission delay. Transmission delays of the order of a quarter of a second are involved in transmission of signals from one Earth station to another via a geostationary satellite. It may be mentioned here that for satellite-based data communication services, the data communication protocols that require acknowledgement feedback further add to the delay. Hence, GEO satellites are not suited for certain applications like interactive media, which require small transmission delays. Large transmission delays also have an adverse impact on the quality of voice communication and data transmission at high data rates.
2. Echo effects. The echo effect, in which the speaker hears his or her own voice, is more predominant in satellite-based telephone networks as compared to terrestrial networks. This is due to larger transmission delays involved in the case of satellites. However, with the development of new echo suppressors, satisfactory link quality has been provided in the case of single-hop GEO satellite networks. However, for double-hop GEO networks, the problem of echo still exists.
3. Launch cost of a satellite. Although the cost of a satellite ground station is less than that of terrestrial networks and the cost of satellite services are independent of the distances involved, the cost of launching a satellite is huge.

To conclude, although satellites have an edge over terrestrial networks in terms of quality, connectivity and reliability of services offered, the problem they face is that the terrestrial networks already exist and transferring the service over to a satellite network becomes a complex and difficult task. Moreover, due to improvements in the terrestrial network technology, satellites are facing tough competition from terrestrial networks. In fact, satellites correspond to only a small part of communications as a whole, around 2 %. Current trends in the field of telecommunication favour space systems that complement terrestrial networks rather than maintaining their independence from them.

10.6.1 Point-to-Point Trunk Telephone Networks

One of the traditional applications of satellites includes long distance, especially intercontin-ental trunk telephony services, also referred to as thin-route satellite telephony services. Thin route services are used in those regions where installation of terrestrial networks is not feasible either due to low density of population or because of difficult geographical terrain. These services are particularly useful for establishing connections between the company's headquarters and its remote offices, through gateway Earth stations.

Trunk telephony services come under the domain of fixed satellite services (FSS), mainly utilizing C and Ku bands. Generally, GEO satellites are utilized for providing these services. Intelast, Europestar, Eutelsat, PamAmSat are examples of some of the satellites used for the purpose. Although, route telephony services provide reliable and secure communication, but with the expansion of new technologies like fibre optics they are becoming less and less popular.

10.6.2 Mobile Satellite Telephony

One of the important services provided by mobile satellite services (MSS) is the interactive voice communication to mobile users. This service is referred to as mobile satellite telephony. The satellite phones target two specific markets. The first is that of international business users requiring global mobile coverage. Satellites provide them with truly global mobile services with a single mobile phone, which is impossible with terrestrial systems due to the difference in cellular mobile phone standards from region to region. The second market is the unserved regions where the basic telecommunication services are not present.

A glance at the history of mobile satellite services tells us that the first mobile service experiment began in the year 1977 using NASA's satellite ATS-6. Year 1982 saw the launch of the first civilian mobile satellite, Inmarsat. Since then, there has been a steady and gradual growth in the field of MSS until the early 1990s, after which many new MSS services were launched, mainly to provide mobile satellite telephony services. The third quarter of the decade saw the business failure of many MSS operators, but now again there is a spurt in the aggregate worldwide demand for satellite telephones. MSS satellites launched in the periods 1980–1990 and 1990–1998 were GEO satellites, categorized as Generation-I and Generation-II satellites respectively, mainly providing telephony services to relatively large mobile terminals. Third generation mobile satellites, comprising constellations of LEO, MEO, HEO and GEO satellites, provide voice and multimedia services to mobile and hand-held terminals. Moreover, these third generation mobile satellite services have entered the realm of personal communications and are also referred to as global mobile personal communication services (GMPCS).

GMPCS is a personal communication system providing transnational, regional or global two-way voice, fax, messaging, data and broadband multimedia services from a constellation of satellites accessible with small and easily transportable terminals. There are several different types of GMPCS systems: GEO systems, small LEO systems, big LEO systems, MEO systems, HEO systems and broadband GMPCS systems. Except for small LEO satellite systems, which offer only messaging services, all the other systems provide mobile satellite telephony services. Moreover, all these systems operate in the L and S bands allocated for mobile services, except for the broadband GMPCS systems which operate in the Ku band, where MSS services have been allocated a secondary status. Table 10.1 enumerates the features of these various GMPCS systems.

10.7.1 A Typical Satellite TV Network

Satellite television employs GEO satellites acting as point-to-multipoint repeaters receiving a certain telecast from the transmission broadcasting centre and retransmitting the same after frequency translation to the cable TV operators, home dishes, and so on, lying within the footprint of the satellite. Satellites can provide TV programmes either directly to the users (direct-to-home television) or indirectly with the help of cable networks or terrestrial broadcasting networks, where the satellite feeds the signal to a central operator who in turn transmits the programmes to the users either using cable networks or through terrestrial broadcasting. A typical satellite TV network, like any other satellite network, can be divided into two sections: the uplink section and the downlink section.

The uplink section (Figure 10.4) comprises three main components: the programming source, the broadcasting centre and the main broadcasting satellite. The programming source comprises TV channel networks, cable TV programmers, and so on, that provide various TV programming signals, like TV channels, sports coverage, news coverage or local recorded TV programmes, to the broadcasting centre either through terrestrial means, like using the line-of-sight microwave communication and the fibre optic cable, or using satellites referred to as back-haul satellites. As an example, for one-time events like various news events, a vehicle-mounted Earth station generally operating in the Ku band is driven to the site and then the programmes are transmitted to the main broadcast centre using a back-haul satellite on a point-to-point connectivity basis [known as satellite news gathering (SNG)]. In the case of a live telecast of certain events like sports, the signals picked up by the cameras are transmitted to the main broadcasting centre either with the help of a microwave link, a fibre optic link or a point-to-point backhaul satellite link. The broadcasting centre is the hub of the satellite TV system and it processes and beams the signal to the main broadcasting satellite. It also adds commentary or advertisements to the signals from the various programming sources. Generally, the signals are transmitted using analogue techniques in the C band or using a digital format employing various compression techniques in the Ku band. The signals are also generally encrypted before transmission to prevent unauthorized viewing.

The satellite downlink comprises the main broadcasting satellite and the TV receiving network. In fact, the main broadcasting satellite is common in both the uplink and the downlink sections. The receiver network in the case of satellite distributing programmes to the terrestrial broadcast network comprise various terrestrial broadcasting centres that receive the satellite signal and transmit them to the users in the VHF and the UHF bands using terrestrial broadcasting. The user end has directional Yagi antennas to pick up these signals. In the case of satellite distributing programmes to a cable operator, the downlink section comprises the cable–TV head ends and the cable distribution network. For DTH services, receive-only satellite dishes are mounted at the user's premises to receive the TV programmes directly from the satellite.

10.7.2 Satellite–Cable Television

As mentioned earlier, cable TV refers to the use of coaxial and fibre optic cables to connect each house through a point-to-multipoint distribution network to the head end distribution station. Cable TV, originally referred to as CATV (community antenna television) stood for a single head end serving a particular community, like various houses in a large building. The present day cable TV system is more complex and involves a larger distribution area. The head ends receive programming channels from either a local broadcasting link or through satellites. The use of satellites to carry the programming channels to the cable systems head ends is referred to as satellite–cable television (Figure 10.5). The head end in this case consists of various receive-only Earth stations with the capability of receiving telecast from two to six satellites. These Earth stations either have multiple receiving antennas or, a single dish antenna with multiple feeds, with each feed so aligned as to receive telecast from a different satellite.

The transmission from the satellite is either in the analogue format (mainly in the C band) or in the digital format (mainly in the Ku band). In analogue format of transmission, each receiver is tuned to a different transponder channel and the signals from various receivers are multiplexed for transmission to the users. The channels received in the digital format can be transmitted either digitally or in the analogue form as mentioned above. This processed digital or analogue information is then transmitted over a typical cable distribution network to a large number of houses known as subscribers, who pay a monthly fee for the service. The cable operators scramble their programmes to prevent unauthorized viewing. The receiving end then consists of a set top box to descramble and retrieve the original signal. The cable TV operators also transmit the videotaped recorded programmes from other sources in addition to showing programmes received from the satellites.

10.7.3 Satellite–Local Broadcast TV Network

It is the same as the satellite–cable TV network except for the fact that here the satellite distributes programming to local terrestrial broadcasting stations instead of distributing it to the cable head end stations. The broadcasting stations use powerful antennas to transmit the received signals to various users within the line-of-sight (50–150 km) using UHF and VHF microwave bands. The users receive these TV signals using directional antennas like Yagi antennas, reflector antennas or dipole antennas. A typical satellite–local broadcast network is shown in Figure 10.6. Sometimes, a combination of both the satellite-cable TV and the satellite-local broadcast TV networks is used for distributing TV programmes to the users. As an example, one of the possible configurations is where the satellite sends the signals to the local broadcasting stations, which in turn broadcast them to the cable operators.

10.7.4 Direct-to-Home Satellite Television

Direct-to-home (DTH) satellite television refers to the direct reception of satellite TV programmes by the end users from the satellite through their own receiving antennas (Figure 10.7). DTH services can be broadly classified into two types, namely the television receive-only (TVRO) and the direct broadcasting satellite (DBS) services, depending upon the frequency band utilized and the size of the receiving antennas. TVRO systems operate in the C band whereas the DBS systems operate in the Ku band. In the present context, when DTH systems are mentioned, more often than not it refers to the DBS systems only.

10.7.4.2 Direct Broadcasting Satellite (DBS) Services

The DBS service is a relatively recent development in the world of television distribution. The first DBS service, Sky Television, was launched in the year 1989. The DBS service uses high powered Ku band satellites that send digitally compressed television and audio signals to relatively small (45–60 cm across) fixed satellite dishes. DBS satellites transmit signals to Earth in the BSS segment of the Ku band (between 12.2 and 12.7 GHz), making use of MPEG-2 (Moving Picture Experts Group) digital compression techniques. The channel capacity per transponder is five to twelve channels depending upon the data rate and the compression parameters, and hence they can provide about 200 channels from one satellite. Hence, the dishes for DBS services need not be steerable. Figure 10.8 (a) shows the pictorial representation of a typical DBS receiver set-up. The receiver [Figure 10.8 (b)] basically consists of a descrambler that descrambles the digital signals received by the antenna and a converter module that converts the digitally compressed bit stream into analogue TV channels. Then depending upon the channel the user has chosen, that particular channel is split out and sent to the TV screen. Hence one cannot have two television sets viewing different programmes from the same receiver, as in the case of cable TV. They also provide a fully interactive TV guide and automatically feed the billing information to the local computer of the service provider.

DBS systems are completely closed systems that employ some form of encryption techniques, hence enabling only conditional access by authorized users. This also implies that there are no free channels available on DBS systems. Some of the DBS service providers include DirecTV, Echostar, PrimeStar of the USA, TataSky and DishTV of India and Star Choice of Canada. The FCC has allocated eight orbital slots at 61.5°, 101°, 110°, 148°, 157°, 166° and 175° west longitude GEO locations for DBS systems. TVRO systems have better picture quality than DBS or digital cable systems, which tend to use larger amounts of digital signal compression. However, DBS systems are easy to install and are cheaper as compared to TVRO systems.

10.7.5 Digital Video Broadcasting (DVB)

DVB is a family of technology standards defining digital broadcasting and designed to facilitate broadcasting of audio, images and multimedia to allow a large degree of user interaction. These standards are designed to use existing satellite, cable and terrestrial infrastructures for broadcasting.

10.7.6 DVB-S and DVB-S2 Standards

DVB-S was the first digital television satellite standard released by the DVB Project in 1994, providing digital satellite television services to over 100 million subscribers across the world. The world's first digital satellite television services, launched in South Africa and Thailand towards the end of 1994, employed the DVB-S standard. DVB-S2 is an upgraded version of the DVB-S standard. It is the second generation digital satellite transmission system developed by the DVB Project. DVB-S2 is gradually replacing DVB-S because HDTV services are offered by the new standard. Advanced techniques used for channel coding, modulation and error correction have made it possible for many new services to be commercially viable. The launch of HDTV services has been possible due to the availability of the state-of-the-art video compression technology. Some of the key technical features of DVB-S2 are as follows:

1. Modulation schemes used in DVB-S2 include any of the four schemes, namely QPSK, 8PSK, 16APSK and 32APSK. The first two schemes (QPSK and 8PSK) are mainly used for broadcast applications where satellite transponders are driven close to saturation. For professional applications such as news gathering, interactive services etc. requiring a higher carrier-to-noise (C/N) ratio, 16APSK or 32APSK are used.
2. DVB-S2 offers optional backwards compatibility so that DVB-S compliant receivers are not rendered obsolete while the DVB-S2 compliant receivers have the benefit of additional services offered by the new standard.
3. DVB-S2 achieves a high degree of performance in the presence of high levels of noise and interference by using a powerful forward error correction scheme.
4. DVB-S2 uses adaptive coding and modulation, which allow change in transmission parameters on a frame-to-frame basis depending on the delivery path conditions of individual users. This feature is particularly useful in professional applications and in providing interactive services.

Table 10.2 gives a comparison of DVB-S and DVB-S2 satellite television standards for satellite EIRP of 51 dBW and 53.7 dBW.

A large number of major satellite television broadcasters in Europe and the USA are using DVB-S2 in conjunction with MPEG-4 advanced video coding for delivery of HDTV services. DVB-S2 is also used by direct-to-home (DTH) operators in Asia, the Middle East and Africa. DVB-S and DVB-S2 together are offering DVB services to more than 250 million subscribers across the world. Some of the key broadcasters' names in Europe and the USA include DirecTV in the USA, Sky in Italy, Premiere in Germany and BSkyB in UK and Ireland.

10.7.7 DVB-RCS and DVB-RCS2 Standards

DVB-RCS is one of the digital television broadcast standards in the DVB family of standards. Though originally intended to be a broadcast technology, its unique features have interested many users belonging to the wide spectrum of broadband communications. Most of the terrestrial broadband standards are based on the one-to-many concept and therefore involve only a one-way transmission. DVB-RCS, on the other hand, uses a return or uplink channel to enable two-way transmission. The DVB-RCS standard was formulated by the DVB Project in 1999 to provide interactive communication using satellites.

DVB-RCS defines the air interface specification for a two-way satellite broadband scheme and uses a VSAT terminal to provide to the user an ADSL (asymmetric digital subscriber line) type of link that enables two-way communication without the need for a terrestrial network of cables. Interactive broadcasting has been done by having cable connectivity. While this may be economically feasible in urban and built-up areas, providing cable connectivity in remote areas turns out to be far too expensive with very little probability of recovering installation costs for a very long time. DVB-RCS today is an established satellite communication standard created in an open environment with a highly efficient bandwidth management.

To be able to make use of DVB-RCS, the hardware required is a combination of a suitable satellite dish antenna and a satellite interactive terminal (SIT) or satellite modem. The whole process of accessing desired data in the DVB-RCS standard is as follows. The interested user receives the multimedia stream via the satellite downlink. The user then sends the service request signal through their SIT and the return or uplink channel to the satellite, from where it is routed to the service provider. The service provider then responds to the request and the routing from service provider to the satellite is via a standard uplink station. From the satellite, the information is routed to the user's SIT via the satellite's downlink channel.

DVB-RCS is the only multivendor VSAT standard enabling users to keep the choice of terminal vendor open after initial procurement. DVB-RCS has been accepted worldwide for a variety of applications, some of the major ones being in cellular backhaul, voice over IP services, corporate networking, telemedicine, remote monitoring like SCADA and so on.

DVB-RCS2 is the second generation DVB-RCS standard and is more efficient and flexible than DVB-RCS. The new version, published in 2012, adds support for mobility and meshed networks. Table 10.3 gives a comparison of the DVB-RCS and DVB-RCS2 standards.

10.7.8 DVB-T and DVB-T2 Standards

The DVB-T standard, first published in March 1997, is the most widely used digital television broadcast standard worldwide for delivering high quality video. DVB-T allows transmission of several television broadcast channels and audio channels on a single transmission link. The modulation scheme used is orthogonal frequency division multiplexing (OFDM), which gives it the capability to recover signal strength against selective fading from multi-path effects. OFDM uses a large number of carriers modulated with low rate data. The orthogonal nature of the signals makes them immune to any mutual interference. OFDM also allows the network to implement what is termed a single frequency network. A single frequency network allows a number of transmitters to operate on the same frequency without causing any interference. The standard also allows variation of various transmission parameters. This feature can be used by network operators to find the right balance between DVB-T transmission capacity and robustness. These include three modulation options, namely QPSK, 16-QAM and 64-QAM, five different forward error correction (FEC) rates of 1/2, 2/3, 3/4, 5/6 and 7/8, four guard interval options of 1/4, 1/8, 1/16 and 1/32, two carrier options of 2k or 8k, three channel bandwidth options of 6, 7 or 8 MHz and two video refresh rates of 50 Hz or 60 Hz.

Another unique feature of the DVB-T standard is its hierarchical modulation facility, which allows transmission of two completely different data streams on a single DVB signal. A high priority data stream is embedded within a low priority data stream. The operators can use this feature to target two different types of receivers with different services.

DVB-T2 is the second generation DVB-T standard. It offers backwards compatibility so that DVB-T standard compliant receivers are not rendered obsolete. In addition, it provides additional features and services. DVB-T2, like DVB-T, uses OFDM. Table 10.4 gives a comparison of DVB-T and DVB-T2 performance specifications.

10.7.9 DVB-H and DVB-SH Standards

The DVB-H standard provides video and television services for cellular phones and handsets. DVB-H is derived from the well established and widely accepted DVB-T standard. As compared to conventional terrestrial television services, conditions for handheld devices are considerably different:

1. The receiver antennas need to be very small and often integrated in the handset unlike the directional antennas used in television sets.
2. Handheld devices experience high levels of interference and also encounter signal variations due to multipath effects.
3. Handheld devices are often on the move whereas domestic television sets are static.
4. Handheld devices run on batteries whereas domestic television sets operate on AC mains. Battery life is a major concern in handheld devices whereas current consumption is not an issue in domestic television sets.

DVB-H, like DVB-T, uses OFDM. It supports different types of modulation formats, such as QPSK, 16-QAM and 64-QAM, within the OFDM signal. The choice of modulation format is usually a trade-off between data rate and the required signal strength for error-free reception. While QPSK offers better reception under low signal and high noise conditions but at a lower data rate, 64-QAM offers a higher data rate but also requires a higher signal level. The time slicing feature of the DVB-H standard allows the power consumption of a mobile set to be reduced by 90 %, which significantly minimizes the drain on the battery and gives a much longer battery life between charges.

The DVB-SH standard delivers audio, video and data services to handheld devices using frequencies within the S-band from either satellite or terrestrial networks. It complements the DVB-H standard, which delivers mobile video from terrestrial networks in UHF television bands. DVB-SH is targeted for both satellite and terrestrial delivery. While satellite delivery achieves coverage of large areas, terrestrial coverage can be used to fill gaps in built-up areas in cities where tall buildings may shield the satellite signal. Two possible architectures, namely SH-A and SH-B, are used in DVB-SH. SH-A uses OFDM on both satellite and terrestrial links. SH-B uses TDM on the satellite link and OFDM on the terrestrial link. The choice of architecture is governed by satellite characteristics and regulatory considerations.

10.9.1 Satellite Data Broadcasting

Satellite data broadcasting refers to the use of satellites in point-to-multipoint or multipoint interactive configurations for the transmission of information in digital form. Large multi-national companies or international organizations having offices in remote areas make use of satellite broadcasting services for data collection and broadcasting, image and voice transfer, two-way computer interactions and database inquiries between these remote stations and the main head centre.

Point-to-multipoint broadcast services refer to unidirectional data transmission from a single uplink to a large number of remote receiving points within the coverage area of the satellite. A multipoint interactive network is similar to the point-to-multipoint network except for the fact that the remote terminals in this case also have the transmitting capability. Hence, these networks are bidirectional in nature. The broadcast half transmits the bulk information to all the remote points. These points in turn transmit their individual requests back to the main broadcasting station. In general, the amount of data transmitted from the central station to the remote terminals (outbound direction) far exceeds the data transmitted from the remote terminals to the central station (inbound direction). Hence these networks are asymmetrical in form, having higher data rates in the outbound direction as compared to the inbound direction. Interactive data communication is the foundation of most corporate and government networks. Figures 10.9 (a) and (b) show the configurations of typical point-to-multipoint and multipoint interactive networks respectively.

10.9.2 VSATs (Very Small Aperture Terminals)

VSATs, as mentioned above, stand for very small aperture terminals and are used for providing one-way or two-way data broadcasting services, point-to-point voice services and one-way video broadcasting services. VSAT networks are ideal for centralized networks with a central host and a number of geographically dispersed terminals. Typical examples are small and medium businesses with a central office, banking institutions with branches all over the country, reservation and airline ticketing systems, etc. VSATs offer various advantages, like wide geographical area coverage, high reliability, low cost, independence from terrestrial communication infrastructure, flexible network configurations, etc. However, VSATs suffer from a major problem of delay between transmission and reception of data (around 250 ms) due to the use of GEO satellites.

10.9.2.1 VSAT Network

The ground segment of a typical VSAT network consists of a high performance hub Earth station and a large number of low performance terminals, referred to as VSATs. The space segment comprises of GEO satellites acting as communication links between the hub station and the VSAT terminals. A typical VSAT network is shown in Figure 10.10. VSAT networks using non-GEO satellites are still in their conceptual stage. It may be mentioned here that VSATs employ a high performance central station so that the various remote stations can be simpler and smaller in design, thus enabling the VSAT networks to be extremely economical and flexible.

The hub station is usually a large, high performance Earth station comprising an outdoor antenna (with a diameter of between 6 to 9 metres) for transmission, RF terminals for providing a wideband uplink of one digital carrier per network, base band equipment comprising modems, multiplexers and encoders, a control centre for managing the network and various kinds of interfacing equipment to support a wide variety of terrestrial links. These terrestrial links connect the hub station to the head office or to the data processing centre, from where the data has to be broadcasted. In the case of bidirectional networks, the outdoor antenna is also configured for reception of signals and the RF equipment comprises several narrowband downlink channels for reception from various remote VSAT terminals. VSAT terminals are smaller and simpler in design as compared to the hub centre and comprise an outdoor antenna (0.5 to 2.4 m in diameter), an RF terminal comprising an LNB (low noise block) for reception and base band equipment. They also comprise an up-converter and power amplifier for uplinking in the case of bidirectional networks. VSAT networks employ either C band or Ku band frequencies for transmission and reception. Ku band VSAT networks have smaller antenna diameters as compared to C band networks.

It may be mentioned here that most VSAT systems operate in the Ku band with the antenna diameter of the Earth stations being as small as 1 to 2 m. The Earth stations are connected in star network topology. The next decade is expected to see the growth of VSAT networks operating in the Ka band. These VSAT networks may operate in direct-to-home configuration for internet and multimedia applications.

Data transmission through VSATs, as mentioned earlier, is generally asymmetrical in nature because the amount of outbound data to be transmitted far exceeds the inbound data. Generally, VSAT networks can transmit at a rate of 64–1024 kbps (64 kbps per remote terminal) in the outbound direction and 64–256 kbps (1.2 to 16 kbps per remote terminal) in the inbound direction. Hence, VSAT networks generally support data, video and voice services in the outbound direction and only data and voice services in the inbound direction. However, some VSAT networks offer compressed digital video services in the inbound direction also.

10.9.2.2 VSAT Network Topologies

VSAT networks come in various topologies, but the most commonly used topologies are star topology for both unidirectional and bidirectional networks and mesh topology for bidirectional networks.

Unidirectional star networks (Figure 10.11) are those in which the information is transmitted only in one direction from the hub station to the remote terminals. There is no information transfer from the remote station to the hub station or to other remote stations. The Broadcast satellite service (BSS), makes use of this topology. The introduction of digital technology allows the service provider and the user much greater flexibility in the operation of a broadcast network. Different subscribers can access different portions of the downlink transmission meant for them by using proprietary software. This process is referred to as narrowcasting. Bidirectional star networks allow the transmission of information in both the directions, but in this case the information cannot be transmitted directly from one VSAT terminal to another but is routed through the hub station. Figure 10.12 shows part of such a network. It can be seen from the figure that the information from station A to station B (shown by regular line) has to first go to the central hub station and from there it is routed to station B. The same holds for transmission from station B to station A (shown by the dotted line). In the case of mesh VSAT networks, the remote terminals can transmit data directly to each other without passing though the hub (Figure 10.13). These networks are particularly appropriate for large corporations where local facilities need to be in contact with facilities in other regions.

Mesh topology is also more effective if the network is to be mainly used for telephony or video-teleconferencing applications. In certain networks, the hub is owned by a service provider and is shared among large number of users. These networks are referred to as shared hub networks. Each user in these networks is allocated a particular time slot. There are certain networks referred to as mini-hub networks in which each user has a mini-hub, which is smaller than the conventional hub. Thus the user has control over his own communication link. Overall management of the complete network is provided by the service provider who has a super-hub.

Another topology used by the VSAT networks is wherein the high capacity downlink stream is not complemented by an uplink capability from the user terminal. The user transmits via the uplink by employing some other communication channel (such as a telephone line). The VSAT terminal in this case does not require transmit capability which significantly reduces its size and complexity.

A VSAT can either use dedicated bandwidth services or dynamic bandwidth allocation services. Some networks that provide continuous data transfer for critical real time processes employ dedicated bandwidth services, referred to as PAMA (permanently assigned multiple access). Most networks employ dynamic bandwidth allocation services, also referred to as demand assigned multiple access (DAMA), using packet-switching techniques in which the data is broken down into small packets and then transmitted in the form of these packets. Moreover, VSAT networks generally employ a TDM/TDMA scheme for transmission of data. Hence, in most VSAT networks, the outbound data is sent nearly continuously in the form of data packets using the TDM (time division multiplexing) scheme. Each packet contains the source and the destination address and is transmitted through the common outbound link. At the receiving end, each VSAT terminal identifies its packet using the destination address. The inbound data is transmitted from various remote stations using TDMA (time division multiple access), hence allowing many (10–1000) VSATs to share the same communication link. Each VSAT terminal transmits data only for a small time interval in either a preassigned inbound channel slot or in any inbound channel slot, depending on the manufacturer. The main inbound transmission modes are ALOHA, slotted ALOHA, fixed assignment and dynamic assignment. Other schemes used for implementing the VSAT networks include SCPC and CDMA. These schemes have been briefly explained in detail in Chapters 5 and 6.

Non-GEO satellite systems also provide data services like messaging services, pager services, internet services, data services in the store-and-forward mode and some real time data services etc. The non-GEO systems include the little LEO, big LEO and MEO systems. Little LEO satellite systems offer two-way messaging services (including e-mail and paging) in the store-and-forward mode, limited internet, facsimile services and remote data services mainly for emergency situations. Big LEO and MEO systems offer global Internet, fax, real time data services and even broadband multimedia services. Moreover, VSAT networks using LEO satellites will be operational in the near future.

10.10.1 International Satellite Systems

The first and most demonstrable need for commercial satellites is to provide international communication services. Initially all international satellites were GEO satellites but now certain non-GEO satellite constellations that provide global coverage have come to the market. Some of the international satellite missions include Intelsat, PamAmSat, Orion, Intersputnik, Inmarsat, etc., in the category of GEO systems and the Iridium and Globalstar constellations in the non-GEO category. Intelsat, Inmarsat and the Iridium satellite systems are described in detail in the following paragraphs.

10.10.1.1 Intelsat Satellite System

Intelsat Limited is the world's largest commercial satellite communications service provider. Originally, it was formed as the International Telecommunication Satellite Organization (INTELSAT) in 1964 to own and manage a constellation of GEO satellites that could provide international communication services mainly including video, voice and data services to the telecom, broadcast, government and other communications markets. It was an intergovernmental consortium initially having 11 members. In 2001, it became a private company and acquired PamAmSat in 2006. Today, it is the world's largest provider of fixed satellite services, operating a fleet of more than 50 satellites.

To date, more than 80 Intelsat satellites have been launched with each satellite offering a significant upgrade in terms of capability and the quality of services offered over its predecessor. As an example, Intelsat 1 and 2 employed a single isotropic antenna; Intelsat 3 had a de-spinning directional antenna so as to maintain an intense beam on the surface of the Earth. Further innovations were made in Intelsat 4 satellites to shape the beam so that it does not cover the ocean areas. Transponder capacity has also increased with each generation; Intelsat 1 had one C band transponder whereas Intelsat 4 had 12 C band transponders. Intelsat 5 used 4 Ku band transponders in addition to the 21 C band transponders. Intelsat 10, the latest series of Intelsat satellites, has 45 C band and 16 Ku band transponders. Moreover, the services offered have increased many fold in the last four decades: Intelsat 1 had the capability of handling 240 telephone calls or a single TV channel, Intelsat VIII can handle more than 120 000 telephone calls or 500 TV channels. In February 2007, Intelsat changed the names of 16 of its satellites formerly known under the Intelsat Americas and PamAmSat series to Galaxy and Intelsat series respectively. As of October 2013, it operated 28 satellites and supports more than 30 DTH platforms world-wide. Table 10.5 enumerates salient features of the various satellites owned by Intelsat Limited.

Satellite	Transmission Capability	Stabilization	Location
Intelsat 1 (comprising of one satellite Intelsat 1 1)	1 transponder (240 circuits or one TV channel)	Spin	Intelsat 1 1 (332E) over AOR
Intelsat 2 (comprising of four satellites Intelsat 2 1, 2 2, 2 3 and 2 4	2 VHF transponders each (240 two-way telephone circuits or one two-way TV channel)	Spin	Intelsat 2 1, 2 2 and 2 4 over the POR, 2 3 over the AOR
Intelsat 3 (comprising of 8 satellites Intelsat 3 1, 3 2, 3 3, 3 4, 3 5, 3 6, 3 7, 3 8	1500 voice or 4 TV channels	Spin	Intelsat 3 2, 3 6, 3 7 over the AOR, 3 3 over the IOR, 3 4 over the POR. Intelsat 3 1, 3 5 and 3 8 were launch failures
Intelsat 4 (comprising of 8 satellites Intelsat 4 1, 4 2, 4 3, 4 4, 4 5, 4 6, 4 7 and 4 8	12 C band transponders each (4000 voice circuits or 2 TV channels each)	Spin	Intelsat 4 1 initially over IOR then moved to AOR, Intelsat 4 2, 4 3 and 4 7 over AOR, Intelsat 4 4 and 4 8 over POR and Intelsat 4 5 over IOR
Intelsat 4A (comprising of 6 satellites Intelsat 4A 1, 4A 2, 4A 3, 4A 4, 4A 5 and 4A 6	20 C band transponders each (7250 voice or 2 TV channels each)	Spin	Intelsat 4A 1, 4A 2 and 4A 4 over the AOR, Intelsat 4A 3 over the IOR
Intelsat 5 (comprising of 9 satellites Intelsat 501, 502, 503, 504, 505, 506, 507, 508 and 509	21 C band and 4 Ku band transponders each (12000 voice + 2 TV channels)	3-axis	Intelsat 501 first over AOR then POR, 502, 506 over AOR, 503 over AOR then POR, 504, 505, 507, 508 over IOR
Intelsat 5A (comprising of 6 satellites Intelsat 510, 511, 512, 513, 514 and 515)	26 C band and 6 Ku band transponders each (15000 voice + 2 TV channels)	3-axis	Intelsat 510 over POR, Intelsat 511, 515 over IOR and Intelsat 512 and 513 over AOR
Intelsat 6 (comprising of 5 satellites Intelsat 601, 602, 603, 604, 605 and 606)	38 C band and 10 Ku band transponders each (120000 two-way telephone calls + three television channels each)	Spin	Intelsat 602 (178E) and 605 (174E) over POR, 604 (60E) and 601 (47.5E) over IOR, 603 (340E) over AOR
Intelsat 7 (comprising of 6 satellites Intelsat 701, 702, 703, 704, 705 and 709)	26 C band and 10 Ku band transponders each (18000 telephone calls and 3 color TV broadcasts simultaneously or up to 90000 telephone circuits using digital circuit multiplication equipment (DCME))	3-axis	Intelsat 701 (180E) over POR, 702 (55E), 703 (57E), 704 (66E) and 706 (52E) over IOR, 705 (310E) over AOR, 709 (85E) over APR
Intelsat 7A (comprising of 3 satellites 706, 707 and 708)	26 C band transponders and 14 Ku band transponders each (22500 telephone calls and 3 color TV broadcasts simultaneously or up to 112500 telephone circuits using DCME)	3-axis	Intelsat 706 (50E) over IOR, 707 (307E) and 708 (310E) over AOR
Intelsat 8 (comprising of 4 satellites Intelsat 801, 802, 803 and 804)	38 C band transponders and 6 Ku band transponders each (22000 telephone calls and 3 color TV broadcasts simultaneously or up to 112500 telephone circuits using DCME)	3-axis	Intelsat 801 (328.5E), 803 (310E) over AOR, 802 (33E) over IOR and 804 (64E) over IOR
Intelsat 8A (comprising of 2 satellites Intelsat 805 and 806)	28 C band transponders and 3 Ku band transponders each	3-axis	Intelsat 805 (304.5E), 806 (319.5E) over AOR
Intelsat 9 (comprising of 7 satellites Intelsat 901, 902, 903, 904, 905, 906 and 907)	44 C band transponders and 12 Ku band transponders each	3-axis	Intelsat 901 (342E), 903 (325.5E), 905 (335.5E) and 907 (332.5E) over AOR, Intelsat 902 (62E), 904 (60E) and 906 (64E) over IOR
Intelsat 10 (comprising of 1 operational satellite Intelsat 10-02)	45 C band and 16 Ku band transponders	3-axis	Intelsat 10-02 (359E) over AOR
Intelsat 1R (former PAS 1R)	36 C band and 36 Ku band transponders	3-axis	315E over AOR
Intelsat 2 (former PAS 2)	20 C band and 20 Ku band transponders	3-axis	169E over POR
Intelsat 3R (former PAS 3R)	20 C band and 20 Ku band transponders	3-axis	317E over AOR
Intelsat 4 (former PAS 4)	20 C band and 30 Ku band transponders	3-axis	72E over APR
Intelsat 7 (former PAS 7)	14 C band and 30 Ku band transponders	3-axis	68.5E over IOR
Intelsat 8 (former PAS 8)	24 C band and 24 Ku band transponders	3-axis	166E over POR
Intelsat 9 (former PAS 9)	24 C band and 24 Ku band transponders	3-axis	302E over AOR
Intelsat 10 (former PAS 10)	24 C band and 24 Ku band transponders	3-axis	68.5E over IOR
Insalsat 11 (former PAS 11)	16 C band and 18 Ku band transponders	3-axis	317E over AOR
Intelsat 12 (former PAS 12)	30 Ku band transponders	3-axis	45E over IOR
Galaxy 3C	24 C band and 53 Ku band transponders	3-axis	95W over AOR
Galaxy 11	24 C band and 40 Ku band transponders	3-axis	33W over IOR
Galaxy 14	20-24 C band transponders	3-axis	125W over AOR
Galaxy 15	20-24 C band and one L band transponders	3-axis	133W over AOR
Galaxy 16	24 C band and 24 Ku band transponders	3-axis	99W over AOR
Galaxy 17	24 C band and 24 Ku band transponders	3-axis	91W over AOR
Galaxy 18	24 C band and 24 Ku band transponders	3-axis	123W over AOR
Galaxy 19	24 C band and 28 Ku band transponders	3-axis	97W over AOR
Galaxy 23	24 C band, 32 Ku band and 2 Ka band transponders	3-axis	121W over AOR
Galaxy 25	24 C band and 28 Ku band transponders	3-axis	93W over AOR
Galaxy 26	24 C band and 28 Ku band transponders	3-axis	93W over AOR
Galaxy 27	24 C band and 24 Ku band transponders	3-axis	129W over AOR
Galaxy 28	22 C band, 36 Ku band and 24 Ka band transponders	3-axis	89W over AOR
Horizons 1	24 C band and 24 Ku band transponders	3-axis	127W over AOR
Horizons 2	20 Ku band transponders	3-axis	74W over AOR
Intelsat 14	40 C and 22 Ku band transponders, IRIS	3-axis	315EL
Intelsat 15	22 Ku band transponders	3-axis	85EL
Intelsat 16	24 Ku band transponders	3-axis	58W
Intelsat 17	28 C and 46 Ku band transponders	3-axis	66E
Intelsat 18	24 C and 12 Ku band transponders	3-axis	180E
Intelsat 19	24 C and 34 Ku band transponders	3-axis	166E
Intelsat 20	24 C, 54 Ku and 1 Ka band transponders	3-axis	68.5E
Intelsat 21	24 C and 36 Ku band transponders	3-axis	302E
Intelsat 22	24 C, 18Ku and 18UHF transponders	3-axis	72E
Intelsat 23	24 C and 15 Ku band transponders	3-axis	53W
Intelsat 24	9 Ku band transponders	3-axis	31E
Intelsat 25	22 Ku and 38 C band transponders	3-axis	31.5W
Intelsat 26	12 C and 28 Ku band transponders	3-axis	50E
Intelsat 27 (launch failure)	20 C, 20 Ku and 20 UHF transponders	3-axis	304.5E (planned)
Intelsat 28 (New Dawn)	28 C and 24 Ku band transponders	3-axis	32.8E

These satellites basically serve four regions including the Atlantic Ocean Region (AOR) – covering North America, Central America, South America, India, Africa and western portions of Europe; the Indian Ocean Region (IOR) – covering Eastern Europe, Africa, India, South East Asia, Japan and Western Australia; the Asia Pacific Region (APR) – covering Eastern Europe, the former USSR and all the regions from India to Japan and Australia; and the Pacific Ocean Region (POR) – covering Southeast Asia to Australia, the Pacific and the western regions of America and Canada. These coverage regions overlap with each other providing truly global services covering almost every country.

10.10.1.2 Inmarsat Satellite System

INMARSAT, an acronym for the International Maritime Satellite Organization, is an international organization, currently having 85 member countries that control satellite systems in order to provide global mobile communication services. It was established in the year 1979 to serve the maritime industry by providing satellite communication services for ship management, distress and safety applications, but now the horizon of its applications has expanded from providing maritime services to providing land, mobile and aeronautical communication services. INMARSAT operates a global satellite system that is used by independent service providers to offer a range of voice and multimedia communication services for customers on the move and in remote locations. They serve customers from diverse markets including merchant shipping, fisheries, airlines and corporate jets, land transport, oil and gas sector, news media and businessmen whose executives travel beyond the reach of conventional terrestrial communication boundaries. Currently, more than 125 000 Inmarsat mobile terminals are in use.

INMARSAT began its operation in the year 1982 by leasing capacity from the MARISAT, MARECS and the INTELSAT satellites. This formed the first generation of INMARSAT satellites. The first generation of INMARSAT satellites was phased out in the year 1991. The second generation was comprised of four satellites (INMARSAT 2F1, 2F2, 2F3 and 2F4). The third generation of INMARSAT satellites comprises five satellites (INMARSAT 3F1, 3F2, 3F3, 3F4 and 3F5) and the fourth generation comprises of three satellites (INMARSAT 4F1, 4F2 and 4F3). It is being planned to launch three satellites (INMARSAT 5F1, 5F2 and 5F3) in the INMARSAT fifth generation of satellites. INMARSAT has made an agreement with the European Space Agency (ESA) and developed the Alphasat (INMARSAT 4A F4) satellite, which complements the fourth generation INMARSAT satellites.

The Inmarsat satellite system comprises:

1. Space segment: It consists of a constellation of four prime GEO satellites strategically placed at one of the four ocean regions to provide a global coverage [Figure 10.14 (a)]. Two satellites are placed over the Atlantic Ocean Regions East and West (AORE 15.5° W and AORW 55.5° W respectively), one over the Indian Ocean Region (IOR 64.5° E) and one over the Pacific Ocean Region (POR 180° E). There is an overlap between the footprints of each of the satellites. Hence, in many parts of the world the services are provided by two Inmarsat satellites [Figure 10.14 (b)]. Each of these four satellites is backed up by spare operational satellites so that the services are not blocked due to failure of the operational satellites.
2. Ground segment: It comprises a large number of fixed Earth stations (gateways) and mobile Earth stations (MES). Gateways, referred to as land Earth stations (LES) or coastal Earth stations (CES) by the maritime community and as ground Earth stations (GES) by the aeronautical community, serve as interfaces to the terrestrial public switched networks. The ground segment also comprises an Inmarsat network control centre (NCC) and three satellite control centers (SCC). The NCC located in the UK, monitors and controls the complete network of LES, MES and the satellites. SCC are responsible for the physical management of Inmarsat satellites.
3. Subscriber units: These include the satphones, facsimile, telex and data terminals.

Figure 10.15 shows a typical communication network using Inmarsat satellites. The calls can be made between two mobile users and between mobile users and terrestrial phones. Standard Inmarsat satphones and telex terminals are available to make and receive calls using the Inmarsat satellite network. All the calls to the terrestrial phones are routed via the satellite to the gateways from where they are sent directly to the terrestrial public-switched networks. Satellite gateway links, known as feeder links, employ a 6 GHz band in the uplink direction and a 4 GHz band in the downlink direction. The mobile links use 1.6 GHz /1.5 GHz in the uplink/downlink directions. Inmarsat satellites provide various services, namely Inmarsat-A, B, C, D, D+, E, M, mini-M, GAN, R-BGAN, Aero, BGAN, M2M communications, global voice services (ISat Phone Pro, Isat Pro-link, FleetPhone), MPDS (mobile packet data services), XpressLink, FleetPhone, BGAN M2M, Isat Data Pro and other, with each service targeted towards a particular niche market. Table 10.6 enumerates salient features of these services. It may be mentioned here that INMARSAT has withdrawn the Inmarsat-A, E and R-BGAN services.

Service	Communication Capability	Applications
INMARSAT A	Analogue telephony, data and compressed video through desktop PC type terminals	Land and maritime commercial, social and safety related applications
INMARSAT B	Digital telephony, fax, data and full video through briefcase type terminals	Land and maritime commercial, social and safety related applications with better services than INMARSAT A
INMARSAT C	Low bit rate store and forward data communication through briefcase sized terminals	International e-mail services, database access and global telex services
INMARSAT D & D+	Low bit rate two way data communication using personal CD player sized terminals	Data broadcast e.g. financial data, vehicle tracking, personalmessaging
INMARSAT M	World's first personal, portable mobile satellite system providing digital telephony and data services using briefcase sized terminals	Remote and rural fixed communications, mobile communications e.g. business travellers, police and emergency services
INMARSAT mini-M	INMARSAT's most popular service employing the smallest, lightest and the cheapest terminals to provide digital voice and data services	Used by journalists, workers, business people, emergency services, rural telephony
INMARSATAero C	Same services as INMARSAT Cto aircraft	Messaging services to corporate aircraft
INMARSAT Aero-L	Real time duplex digital telephone, fax and data services to aircraft	Real-time flight and passenger related communication e.g. engine monitoring
INMARSAT Aero-H	Telephone, data and fax services to passenger air cabs and cockpits	Medium bit rate real time voice, data and fax communication
INMARSAT Aero-I	Telephone, data and fax services to short and medium-haul aircraft	Passenger voice telephone, facsimile, cockpit voice and data, air traffic control, secure voice access to major air traffic control centers
INMARSAT E	Provides global maritime distress alerting services	Distress and safety-GMDSS compliant
Fleet	Voice, data, ISDN	Ocean-going and coastal vessels
Swift 64	Voice, fax, ISDN and MPDS	Private, business and commercial aircraft
R-BGAN	“Always-on” IP-data service	Land-mobile market
BGAN	internet and intranet solutions, video on demand, video-conferencing, fax, e-mail, telephone and high-speed LAN access	Land-mobile market
FleetBroadband (FB)	Offers similar services to BGAN	Maritime service
SwiftBroadband (SB)	Global voice and high speed data simultaneously at speeds up to 432kbps per channel	Aeronautical service
BGAN HDR (High Data Rate)	High data rate streaming	Broadcasting, media organizations and global governments
XpressLink	High speed broadband for a fixed monthly fee	Maritime service
FleetPhone	Satellite phone service or use when beyond the range of land-based networks	Maritime industry
IsatPhone Pro	Low cost handheld satellite phone	Global services
IsatPhone Link	Low cost global satellite phoneservice	Rural and remote areas outside cellular coverage
M2M (machine to machine service) includes BGAN M2M, Isat Data Pro and Isat M2M	Two-way data connectivity for messaging, tracking andmonitoring of fixed and mobileassets	Global services
BGAN M2M	Global two-way IP data service forlong term M2M management offixed assets	Global services
IsatData Pro	Global two-way SMS service forM2M communication	Global services
Isat M2M	Store and forward low data rateglobal messaging services to and from remote areas	Global services

10.10.1.3 Iridium Satellite Constellation

The Iridium network is a global mobile communication system designed to offer voice communication services to pocket-sized telephones and data, fax and paging services to portable terminals, independent of the user's location in the world and of the availability of trad-itional telecommunications networks. Iridium is expected to provide a cellular-like service in areas where a terrestrial cellular service is unavailable or where the public switched telephone network (PSTN) is not well developed. It has revolutionized communication services for business professionals, travellers, residents of rural or undeveloped areas, disaster relief teams and others to whom it provides global communication services using a single mobile.

The Iridium network can support 172 000 simultaneous users, providing each of them with 2.4 kbps fully duplex channels. The Iridium satellite system comprises the following three principal segments:

1. Space segment
2. Ground segment
3. Iridium subscriber products.

The space segment comprises 66 active communication satellites and 14 spare back-up satellites revolving around Earth, in six LEO orbital planes having 11 satellites each, at an altitude of 780 km. The system was originally supposed to have 77 active satellites (hence the name Iridium, as the element iridium has an atomic number of 77). Each satellite is cross-linked with four other satellites, providing flexibility and independence from the terrestrial networks. The ground segment comprises gateways and a system control segment. Gateways are large fixed Earth stations connected to fixed and mobile terrestrial networks providing an interface between the terrestrial network and the satellites. Terrestrial users access the Iridium satellites through these gateways. They also verify the user account, record call duration and user location for billing purposes. The control segment comprises a ground station that performs TT&C functions, data routing and frequency planning operations. Iridium subscriber products include phones and pagers that allow users to have access to either the compatible cellular telephone network or the Iridium network. Figure 10.16 shows a typical communication set-up of the Iridium satellite constellation. As mentioned earlier, the Iridium network allows the users to have global mobile services using a single subscription number. To accomplish this, each user is associated with a gateway called the ‘home gateway,’ which maintains a record of its profile and location and looks after its services. Each user also has links with two satellites at a time. As the satellite moves out of the range of the user, the link from the user to the satellite is handed off from the satellite, leaving the user's area to the one entering the area.The call from the user is picked up by the satellite and it authenticates the subscriber's account through the nearest land-based gateway. If the user is out of the home gateway region, the gateway will recognize that it is a visiting subscriber and sends information to its home gateway through intersatellite links (ISLs) to view the subscriber's profile and takes permission for making the call. The user-to-satellite service uplink and downlink operate in the same frequency ranges of 1.616 to 1.6265 GHz in the L band. In order to ensure that there is no interference between the uplink and the downlink signals, uplinking and downlinking are not done simultaneously. In order to make efficient use of the limited spectrum, the Iridium system employs a combination of FDMA and TDMA signal multiplexing. The satellite–gateway links, called the feeder links, employ 27.5–30 GHz in the Ka band for uplink signals and 18.8–20.2 GHz in the Ka band for downlink signals. If the destination phone is part of the PSTN, the call is routed from the original satellite to the nearest gateway for transmission through the terrestrial network. If the call is for another Iridium user, it is routed to the neighbouring satellite and so on through ISLs until it reaches the called user's home gateway, which determines the user's location. Depending upon the location of the user, whether he or she is within the home gateway region or in the visiting gateway region, the call is routed to the satellite directly above the user through the home gateway or the visiting gateway. A point to be noted here is that the call set-up information travels through the gateways and the voice information can completely travel over the Iridium ISLs. ISL links employ frequencies of 22.55–23.55 GHz (Ka band) as these frequencies are heavily absorbed by water and hence are not useful for establishing Earth–satellite links. In order to allow easy integration with terrestrial systems and to benefit from the advances made in the field of terrestrial mobile telephony, the architecture of the Iridium system follows the well-established terrestrial standard, the GSM (global systems for mobile communications). The Iridium system once failed financially, mainly due to insufficient demand for the service, the bulkiness and cost of the hand-held devices as compared to cellular mobile phones and the rise of cellular GSM roaming agreements during Iridium's decade-long construction period. The Earth stations were shut down, however, the Iridium satellites were retained in orbit. Their services were re-established in 2001 by the newly founded Iridium Satellite LLC, partly owned by Boeing and other investors. Iridium NEXT, which are second generation Iridium satellites, are scheduled to be launched from 2015. Another mobile satellite system similar to Iridium is the Globalstar satellite system of the USA. It provides global voice, data, fax and messaging services through a constellation of 48 satellites. These satellites orbit at an altitude of 1410 km and are inclined at an angle of 52°.

10.10.2 Regional Satellite Systems

One of the drawbacks of international satellite systems is that they are not optimized to the needs of the individual countries. The first step to meet the focused needs of the countries was to have a regional system that provided services to countries on a regional basis rather than on a global basis. Regional satellite missions were established with the aim of strengthening the communication resources of the countries belonging to the same geographical area. Some of the regional satellite systems include Eutelsat, Arabsat, AsiaSat, Measat, ACeS (Asia cellular satellite), Thuraya, etc. EUTELSAT operates a fleet of satellites that provide communication services to Europe, the Middle East, Africa and large parts of the Asian and American con-tinents. Arabsat satellites provide satellite communication services to the Middle East, Africa and large parts of Europe. The Asia Satellite Telecommunications Company Limited (AsiaSat) and Measat systems are Asia's regional satellite operators, providing satellite services to the Asia Pacific region.

ACeS is another satellite-based regional communication system providing services to Asia. It provides fully digital video, voice and data services throughout Asia. The Thuraya system provides mobile communication services to the Middle East, North and Central Africa, Europe, Central Asia and the Indian subcontinent. In the following paragraphs, the Eutelsat system is described in detail.

10.10.2.1 EUTELSAT (European Telecommunication Satellite Organization)

The EUTELSAT organization was formed in the year 1977 to commission the design and construction of satellites and to manage the operation of regional satellite communication services in Europe. The first communication satellite to be launched by EUTELSAT was the orbital test satellite (OTS) in the year 1978, which carried out link tests with small Earth stations with the help of a powerful antenna on board the satellite. Then came the ECS-1 satellite in the year 1983 to provide communication services to post office and telecommunication administration and to broadcast TV programmes. The ECS satellite programme was renamed the Eutelsat satellite programme. Eutelsat satellites provide television, telephony and data transmission services on a regional basis. The more advanced satellites in this series also provided specific services like business communication services and mobile communication services. In addition to the Eutelsat satellites, other series of satellites, namely the Hot Bird, Eurobird and Atlantic Bird series, were launched to expand the horizon of the services offered and the coverage area of the satellites of the EUTELSAT organization. In 2012, EUTELSAT renamed all the satellite series under the brand name of Eutelsat. Today, the Eutelsat satellite system provides services that include television and radio broadcasting, professional video broadcasting, networking, Internet services, mobile communication services and broadband services for local communities, businesses and individuals.

Table 10.7 enumerates the salient features of the Eutelsat series of satellites.

Satellite	Transmission capability	Stabilization	Location
Eutelsat 12 West A	24 Ku band transponders	3-axis	12.5W
Eutelsat 8 West A	26 Ku band transponders	3-axis	8W
Eutelsat 8 West C	28 Ku and 4 Ka band transponders	3-axis	7.8W
Eutelsat 7 West A	56 Ku band transponders	3-axis	8W
Eutelsat 5 West A	35 Ku and 10 C band transponders	3-axis	5W
Eutelsat 3A	24 Ku band transponders	3-axis	3.3E
Eutelsat 3C	64 Ku band transponders	3-axis	3E
Eutelsat 3D	53 Ku and 3 Ka band transponders	3-axis	3.1E
Eutelsat 4A	28 Ku band transponders	3-axis	4E
Eutelsat 4B	20 Ku band transponders	3-axis	4E
Eutelsat 7A	38 Ku and 2 Ka band transponders	3-axis	7E
Eutelsat 9A	38 Ku band transponders	3-axis	9E
Eutelsat Ka-Sat 9A	82 Ka band spotbeams transponders	3-axis	9E
Eutelsat 10A	46 Ku and 10 C band transponders	3-axis	10E
	and S band payload
Eutelsat Hotbird 13B	64 Ku band transponders	3-axis	13E
Eutelsat Hotbird 13C	64 Ku band transponders	3-axis	13E
Eutelsat Hotbird 13D	64 Ku band transponders	3-axis	13E
Eutelsat 16A	53 Ku and 3 Ka band transponders	3-axis	16E
Eutelsat 16B	20 Ku band transponders	3-axis	15.8E
Eutelsat 16C	18 Ku band transponders	3-axis	16E
Eutelsat 21A	24 Ka band transponders	3-axis	21.5E
Eutelsat 21B	40 Ku band transponders	3-axis	21.5E
Eutelsat 25B	3 Ku and 14 Ka band transponders	3-axis	25.5E
Eutelsat 25C	24 Ku band transponders	3-axis	25.5E
Eutelsat 28A	24 Ku band transponders	3-axis	28.5E
Eutelsat 28B	32 Ku band transponders	3-axis	28.5E
Eutelsat 33A	20 Ku band transponders	Spin	33E
Eutelsat 36A	31 Ku band transponders	3-axis	36E
Eutelsat 36B	70 Ku band transponders	3-axis	35.9E
Eutelsat 48A	20 Ku band transponders	3-axis	48.2E
Eutelsat 48C	24 Ku band transponders	3-axis	48E
Eutelsat 70B	48 Ku band transponders	3-axis	70.5E
Eutelsat 172A	22 C band and 26 Ku band transponders	3-axis	172E
SESAT2	12 Ku band transponders leased to Eutelsat	3-axis	53E
TELSTAR 12	38 Ku band transponders	3-axis	15W

10.10.3 National Satellite Systems

National satellite systems, also referred to as domestic satellite systems, provide services to a particular country. National satellite systems were originally established by developed countries like the USA, USSR and Canada to serve their country's population according to their specific needs. Today, in addition to these developed countries, some developing nations like India, China, Japan, and so on, also have their own national satellite systems. Some of the domestic satellite systems include Galaxy, Satcom, EchoStar and Telestar of the USA, Brasilsat of Brazil, INSAT of India, Optus of Australia and Sinosat of China. The INSAT system is briefly described below.

10.10.3.1 INSAT (Indian National Satellite)

Owned by the Indian Department of Space, named the Indian Space Research Organization (ISRO), INSAT is one of the largest domestic communication satellite networks in the world, providing services in the areas of telecommunications, television broadcasting, mobile satellite services and meteorology including disaster warning. INSAT is a joint venture of the Department of Space (DOS), Department of Telecommunications (DOT), Indian Meteorological Department (IMD), All India Radio (AIR) and Doordarshan. Making a modest beginning with the launch of INSAT-1A in 1982, the INSAT satellite programme has come a long way today. INSAT-1A belonged to the INSAT-1 series, further comprising INSAT-1B, 1C and 1D satellites. The INSAT-1 series was followed by INSAT-2 and INSAT-3 series of satellites. They were superceded by the INSAT-4 series of satellites. In addition to the INSAT series of satellites, GSAT satellites also provide communication services. Table 10.8 lists the salient features of the INSAT series of satellites.

Satellite	Transponders	Position	Stabilization
INSAT 1A	12 C band and 2 S band transponders and VHRR (very high resolution radiometer) meteorological payload	74E	3-axis
INSAT 1B	12 C band and 2 S band transponders and VHRR meteorological payload	74E	3-axis
INSAT 1C	12 C band and 2 S band transponders and VHRR meteorological payload	93.5E	3-axis
INSAT 1D	12 C band and 2 S band transponders	83E	3-axis
INSAT 2A	12 C band, 6 extended C band and 2 S band transponders, 1 data relay transponder, 1 search and rescue transponder and VHRR meteorological payload	74E	3-axis
INSAT 2B	12 C band, 6 extended C band and 2 S band transponders, 1 data relay transponder, 1 search and rescue transponder and VHRR meteorological payload	93.5E	3-axis
INSAT 2C	12 C band, 6 extended C band, 3 Ku band, 2 S band BSS and 1 S band MSS transponders	93.5E	3-axis
INSAT 2DT	25 C band and 1 S band BSS transponders	55E	3-axis
INSAT 2E	12 C band, 5 extended C band transponders, meteorological payloads VHRR and CCD camera. 11 of the C band transponders have been leased to the INTELSAT organization	83E	3-axis
INSAT 3B	12 extended C band, 3 Ku band and 1 S band MSS transponders and 1 Ku band beacon	83E	3-axis
INSAT 3C	24 C band, 6 extended C band, 2 S band BSS transponders and a MSS transponder operating in S band for uplink and C band for downlink	74E	3-axis
INSAT 3A	12 C band, 6 extended C band, 1 S band, 6 Ku band transponders, satellite aided search and rescue (SAS&R) transponder, meteorological payloads of VHRR, CCD camera and 1 data relay (DR) transponder	93.5E	3-axis
INSAT 3E	24 C band and 12 extended C band transponders	55E	3-axis
INSAT 4A	12 C band and 12 Ku band transponders	83E	3-axis
INSAT 4B	12 C band and 12 Ku band transponders	93.5E	3-axis
INSAT 4CR	12 Ku band transponders	74E	3-axis
GSat 4 (failure)	Multi-beam Ka band transponders	3-axis	82E
GSat 5P (failure)	36 G/H band transponders	3-axis	55E
GSat 8 (INSAT 4G)	24 Ku band transponders	3-axis	55E
GSat 12	12 extended C band transponders	3-axis	83E
GSat 10	12C, 6 extended C and 12 Ku band transponders	3-axis	83E
GSat 7 (INSAT 4F)	11 transponders (UHF, S, C and Ku band)	3-axis	74E

Due to the emergence of private satellite operators, the boundaries between the international, national and regional systems are diminishing very fast. As time progresses, the dividing lines classifying these systems will become less and less clear.

10.11.1 Development of Satellite Constellations in LEO Orbits

The future will see the trend of replacing a large single satellite in the geostationary orbit with a large number of co-located and interlinked smaller satellites in LEO orbits as the geostationary satellites cannot support very high data rate services due to an increase in the free space propagation loss with distance. Each satellite will perform its limited function and optical intersatellite links will be used to interface high-speed links between small satellites with a result that as a whole the satellite constellation will work as a single large satellite. Small terminals with antenna diameters of few centimetres will establish Gbits/s links between small satellites and the tracking requirements are minimized as beams with larger beam divergence can be used due to short distances. The services that will be provided by these satellites include broadcasting services to portable hand-held devices, two-way mobile broadband services for the land/aeronautical and maritime sectors and IPTV services.

10.11.2 Development of Personal Communication Services (PCS)

The advent of PCS has given rise to the need to have lower data rate systems supporting many users. The deployment philosophy in this case is to employ tens or hundreds of satellites in LEO orbits rather than employing three to five satellites in the geostationary orbits. The trend will be to have more on-board processing on the satellite and the satellite will support more services including routing, flow control, packet error detection/correction, and so on. In other words, the trend is to increase the application of higher layer protocols on the satellite. In addition to all this, satellite-satellite cross-linking will increase so as to make the satellite based PCS system feasible and realizable. Also, with the advances made in technology, the size of the repeaters on board the satellites will reduce significantly while their capability will increase manyfold.

10.11.3 Use of Higher Frequency Bands

Satellites will employ higher frequency bands like the Ka band to provide their intended services. More sophisticated satellite systems operating in the 21 GHz band will be realized around 2020. With use of higher frequency spectrum becoming common, extension of services provided by VSAT including GSM, IP trunking and broadband services will be possible. Development of robust access technologies will aid in this process. One of the possible developments that can take place is the construction of a common platform based on the internet protocol (IP) including the integration of telephone systems and television broadcasting systems into the internet.

10.11.4 Development of Light Quantum Communication Techniques

Further innovation will be facilitated by the advent of conversion from communication based on electromagnetic waves to that based on light quantum communications. This will offer very secure communication providing high capacity and confidentiality in information communication. The outstanding feature of quantum cryptography communication is that in case some quantum signals are stolen during transmission, the state of quanta changes instantaneously making the data meaningless while at the same time it is recorded at the detector that the data has been stolen. Quantum communications technology utilizes properties such as quantum entanglement and quantum superposition and is quite different from the RF communication technologies being used to date.

10.11.5 Development of Broadband Services to Mobile Users

There will be advancement in the services offered by communication satellites to providing broadband services to mobile users located on aircraft, space planes, boats and vehicles such as high speed trains, buses and cars. Some of the technologies that will be utilized to make these services possible include spatial diversity (such as two receive antenna configuration), time diversity (channel interleaving/ spreading techniques) and upper layer FEC (forward error correction). FEC at upper layers is under study to protect transmitted packets and avoid retransmissions due to limited access or absence of a return channel for a potentially high number of users and to look into the challenges posed by mobile services.

10.11.6 Development of Hybrid Satellite/Terrestrial Networks

Future satellite communications cannot be oblivious to the evolution of terrestrial broadcast and broadband communication systems. Cooperative communication techniques are also being considered for hybrid satellite/terrestrial networks with the aim of extending the satellite coverage and of supporting terrestrial networks unable to provide their services because of lack of coverage, network overloads, terrain constraints or emergency situations. In this perspective, development of new satellite systems tends to align with that of terrestrial communications leading to a full integration between the two networks which enables higher data rates and high quality of service anywhere anytime.

10.11.7 Advanced Concepts

In the paragraphs above, we mentioned the applications of communication satellites that will become a reality in a decade or so. We now shift focus to some interesting concepts which are fiction right now but may become realizable in next two decades or so. Satellites can be used for communicating with submarines to transmit coded information and for establishing an inter-planetary television link and so on. We present in brief these concepts so as to give the readers a glimpse of the potential of this majestic piece of equipment.

Satellite-to-Submarine Communication: Satellites can be used to communicate with many submarines that are submerged in sea water at depths of 100 m or so. This would eliminate the need to have submarines come to the surface to establish communication thus reducing their vulnerability.

The concept is highlighted in Figure 10.17. Satellites in geostationary orbit are used and transmit a large number of narrow beams to create random spots on the ocean, with each beam transmitting encrypted data. Large numbers of spots are generated so as to create empty positions and not give away the location of submarines. Blue-green wavelength laser is used for maximal penetration in sea water.

Interplanetary TV Link: The concept of the interplanetary TV link is shown in Figure 10.18. The set up makes use of a satellite orbiting around a planet with which the link has to be established and a satellite orbiting in geostationary orbit around the Earth. The planetary satellite makes use of a low power laser to transmit the signals. The Earth orbiting satellite will have a sensor to receive the optical signal and process it and convert it into the microwave signal. The signal is converted from the optical spectrum to the microwave spectrum as the optical signals do not penetrate clouds and are highly attenuated by rain. The conversion therefore allows establishing a non-interruptive link. This link would allow monitoring the events happening on different planets on a real-time basis.

Internet Sites

1. www.alcatel.com
2. www.arabsat.com
3. www.asiasat.com
4. www.astrium-space.com
5. www.boeing.com
6. http://electronics.howstuffworks.com/satellite-tv.htm/printable
7. http://en.wikipedia.org/wiki/Satellite_television
8. http://www.ias.ac.in/meetings/annmeet/69am_talks/ksdgupta/img3.html
9. http://www.ddinews.com/DTH
10. http://www.angelfire.com/electronic/vikram/tech/vsattut.html
11. www.esa.int
12. www.eutelsat.org
13. www.globalstar.com
14. www.hughes.com
15. www.inmarsat.org
16. www.intelsat.com
17. www.eads.net
18. www.isro.org
19. www.ssloral.com
20. www.skyrocket.de