How Satellite Technology works

how has satellite technology helped the study of oceanography and how has satellite technology affected modern businesses how do we use satellite technology
Dr.NaveenBansal Profile Pic
Dr.NaveenBansal,India,Teacher
Published Date:25-10-2017
Your Website URL(Optional)
Comment
CHAPTER 1 Evolution of Satellite Technology and Applications Communication satellites, whether in geostationary Earth orbit (GEO) or non- GEO, provide an effective platform to relay radio signals between points on the ground. The users who employ these signals enjoy a broad spectrum of telecommu- nication services on the ground, at sea, and in the air. In recent years, such systems have become practical to the point where a typical household can have its own satel- lite dish. That dish can receive a broad range of television programming and provide broadband access to the Internet. These satellite systems compete directly in some markets with the more established broadcasting media, including over-the-air TV and cable TV, and with high-speed Internet access services like digital subscriber line (DSL) and cable modems. In addition, GEO and non-GEO satellites will con- tinue to offer unique benefits for users on the go with such mobile services as two- way voice and data, and digital audio broadcasting. The accelerated installation of undersea fiber optics that accompanied the Internet and telecom boom of the late 1990s put more capacity into service than markets could quickly absorb. Curiously, these new operators claimed that satellites were obsolescent. Quite to the contrary, satellite communication continues to play an increasing role in backbone networks that extend globally. Just how well we employ satellites to compete in markets depends on our ability to identify, develop, and manage the associated networks and applications. To this end, this book shows how satellite technology can meet a variety of human needs, the ultimate measure of its effectiveness. My first work,Introduction to Satellite Communication 1, established the foundation for the technology and its applications. These have progressed significantly since the late 1980s; however, the basic principles remain the same. Satellite communication applications (which we will refer to as simply satellite applications) extend throughout human activ- ity—both occupational and recreational. Many large companies have built their communications foundations on satellite services such as cable TV, direct-to-home broadcasting satellite (DBS), private data networks, information distribution, mari- time communications, and remote monitoring. For others, satellites have become a hidden asset by providing a reliable communications infrastructure. Examples abound in their use for disaster relief by the Red Cross and other such organiza- tions, and for instant news coverage from areas of conflict. In the public and mili- tary sectors, satellite applications are extremely effective in situations where terrestrial lines and portable radio transceivers are not available or ineffective for a variety of reasons. 34 Evolution of Satellite Technology and Applications We can conclude that there are two basic purposes for creating and operating satellite applications, namely, to make money from selling systems and services (effi - cient communications) and to meet vital communications needs (essential communi - cations). The composition of satellite communication markets has changed over the years. Initially, the primary use was to extend the worldwide telephony net. In the 1980s, video transmission established itself as the hottest application, with data communications gaining an important second place position. Voice services are no longer the principal application in industrialized countries but retain their value in rural environments and in the international telecommunications field. Special- purpose voice applications like mobile telephone and emergency communications continue to expand. The very fact that high-capacity fiber optic systems exist in many countries and extend to major cities worldwide makes satellite applications that much more important as a supplementary and backup medium. Satellites are enjoying rapid adoption in regions where fixed installations are impractical. For example, ships at sea no longer employ the Morse code because of the success of the Inmarsat system. And people who live in remote areas use satellite dishes rather than large VHF antenna arrays to receive television programming. Satellite operators, which are the organizations that own and operate satellites, must attract a significant quantity of users to succeed as a business. As illustrated in Figure 1.1, the fixed ground antennas that become aligned with a given satellite or constellation create synergy and establish a “real estate value” for the orbit position. Some of the key success factors include the following:  The best orbit positions (for GEO) or orbital constellation (for non-GEO);  The right coverage footprint to reach portions of the ground where users exist or would expect to appear;  Service in the best frequency bands to correspond to the availability of low- cost user terminal equipment; Figure 1.1 A neighborhood created by a GEO satellite with many fixed antennas aligned with it.Evolution of Satellite Technology and Applications 5  Satellite performance in terms of downlink radiated power and uplink receive sensitivity;  Service from major Earth stations (also called teleports) for access to the ter- restrial infrastructure, particularly the Public-Switched Telephone Network (PSTN), the Internet, and the fiber backbone;  Sufficient funding to get the system started and operating at least through a cash-flow break-even point. Optimum footprint and technical performance allow a satellite to garner an attractive collection of markets. Importantly, these do not necessarily need to be known with precision when the satellite is launched because new users and applica- tions can start service at any time during the operating lifetime of the satellite (typi- cally 15 years). Anywhere within the footprint, a new application can be introduced quickly once ground antennas are installed. This provides what is called high oper- ating leverage—a factor not usually associated with buried telecom assets such as fiber optic cables and wireless towers. Ultimately, one can create a hot bird that attracts a very large user community of antennas and viewers. Galaxy I, the most successful cable TV hot bird of the 1980s, established the first shopping center in the sky, with anchor tenants like HBO and ESPN and boutiques like Arts & Entertainment Channel (A&E) and The Discovery Channel. Many of the early boutiques have become anchors, and new boutiques, like The Food Network and History International, arrive to establish new market segments. New hot birds develop as well, such as Astra 1 in Europe and AsiaSat 3S in Asia. Users of hot birds pay a premium for access to the ground infra- structure of cable TV and DBS receiving antennas much like tenants in a premium shopping mall pay to be in an outstanding location and in proximity to the most attractive department stores in the city. In the case of cable TV, access is everything because the ground antenna is, in turn, connected to households where cable serv- ices are consumed and paid for. DBS delivers direct access to subscribers, bypassing cable systems. For a new satellite operator to get into an established market often requires them to subsidize users by paying some of the switching costs out of expected revenues. From this experience, those who offer satellite services to large user communities know that the three most important words in satellite service marketing are LOCATION, LOCATION, and LOCATION This refers to the fac- tors previously listed. Stated another way, it is all about connectivity to the right user community. Satellite operators, who invest in the satellites and make capacity available to their customers, generally prefer that users own their own Earth stations. This is because installing antennas and associated indoor electronics is costly for satellite service providers. Once working, this investment must be maintained and upgraded to meet evolving needs. On the other hand, why would users want to make such a commitment? There are two good reasons for this trend toward ownership of the ground segment by the user: (1) the owner/user has complete control of the network resources, and (2) the cost and complexity of ownership and operation have been greatly reduced because of advances in microcircuitry and computer control. A typi- cal small Earth station is no more complex than a cellular telephone or VCR. As a result of strong competition for new subscribers, DBS and the newer S-DARS have6 Evolution of Satellite Technology and Applications to subsidize receiver purchases. Larger Earth stations such as TV uplinks and inter - national telephone gateways are certainly not a consumer item, so it is common for several users to share a large facility in the form of a teleport. User organizations in the public and private sectors that wish to develop their own unique satellite networks have a wide array of tools and technologies at their disposal (which are reviewed in detail in this book). One need not launch and operate satellites as on-orbit capacity may be taken as a service for as long or as short a period as needed. On the other hand, it can be bewildering when one considers the complex - ity of the various satellite systems that could potentially serve the desired region and community. The associated Earth stations and user terminals must be selected, pur - chased, installed, and properly integrated with applications and other networks that they access. Happily for the new user, there are effective methodologies that address this complexity and thereby reduce risk and potentially cost. Satellite communica - tions can also reduce entry barriers for many information industry applications. As a first step, a well-constructed business plan based on the use of existing satellites could be attractive to investors. (More on finance can be found in Chapter 11.) The history of commercial satellite communications includes some fascinating startup services that took advantage of the relatively low cost of entry. The follow- ing three examples illustrate the range of possibilities. The Discovery Channel made the substantial commitment to a Galaxy I C-band transponder and thereby gained access to the most lucrative cable TV market in North America. Another startup, Equatorial Communications, pioneered very small aperture terminal (VSAT) net- works to deliver financial data to investors. Their first receive-only product was a roaring success, and in 1985 the company became the darling of venture capitalists. Unfortunately, they broke their sword trying to move into the much more compli- cated two-way data communication market. Their technology failed to gain accep- tance, and the company disappeared through a series of mergers. SpeedCast was founded in Hong Kong in 2000 to allow content providers and information services to overcome the limited broadband infrastructure in the Asia-Pacific region. Utiliz- ing existing C-band capacity on AsiaSat 3C, SpeedCast built the needed hub in Hong Kong at the terminus of broadband capacity on a trans-Pacific fiber optic cable. Several U.S. corporations attempted to introduce DTH satellite broadcasting at a time when cable TV was still establishing itself. The first entrants experienced great difficulties with limited capacity of existing low- and medium-power Ku-band satellites, hampering the capacity of the networks and the affordability of the home receiving equipment. Europe and Japan had problems of their own in finding the handle on viable DTH systems, choosing first to launch high-power Ku-band satel- lites with only a few operating channels. It was not until BSkyB and NHK were able to bring attractive programming to the public exclusively on their respective satel- lites that consumers moved in the millions of numbers. In the United States, the only viable form of DTH to emerge in the 1980s was through the backyard C-band satellite dish that could pull in existing cable TV pro- gramming from hot birds like Galaxy I and Satcom 3R. In the 1980s there were already millions of C-band receive dishes in North America. This clearly demon- strated the principle that people would vote with their money for a wide range of attractive programming, gaining access to services that were either not available or priced out of reach. Early adopters of the dishes purchased these somewhat1.1 Satellite Network Fundamentals 7 expensive systems because the signals were not scrambled at the time. A similar story can be told for Asia on the basis of Star TV, which continues to provide advertiser-supported C-band satellite television to the broad Asian market. HBO and other cable networks in the United States changed the equation markedly when they scrambled their programming using the Videocipher 2 system, resulting in a halt to the expansion of backyard dishes. This market settled back into the dol - drums for several years. In today’s world, C-band home dishes are rare in the United States and Europe but have a significant following in tropical regions that effectively employ this band. In 1994, Hughes Electronics introduced its DIRECTV service through three high-power satellites colocated at 101º EL (all receivable by a single Ku-band home dish). With more than 150 digitally compressed TV channels, DIRECTV demon - strated that DTH could be both a consumer product and a viable alternative to cable. As an important footnote, DIRECTV shared one of the satellites with another company called USSB; however, the latter was subsequently bought out to aggre - gate all programming under one trademark. An older competing service, PrimeStar, was first introduced by TCI and other cable operators as a means to serve users who were beyond the reach of their cable systems. DIRECTV moved to acquire this com- petitor, resulting in a quantum increase of subscribers. A single competitor remained in the form of EchoStar with their DISH Network. DIRECTV was first to be acquired by DISH, but as a result of U.S. government objections, the acquirer would be News Corp. Satellite communication applications can establish a solid business for compa- nies that know how to work out the details to satisfy customer needs. A stellar example is the mobile satellite service business pioneered by Inmarsat. Through a conservatively managed strategy, Inmarsat has driven its service from initially pro- viding ship-to-shore communications to being the main source of emergency and temporary communications on land. Whether we are talking about reporters cover- ing a conflict in southern Asia or the provision of disaster relief in eastern Europe, lightweight Inmarsat terminals fit the need. 1.1 Satellite Network Fundamentals Every satellite application achieves its effectiveness by building on the strengths of the satellite link. A satellite is capable of performing as a microwave repeater for Earth stations that are located within its coverage area, determined by the altitude of the satellite and the design of its antenna system. The arrangement of three basic orbit configurations is shown in Figure 1.2. A GEO satellite can cover nearly one- third of the Earth’s surface, with the exception of the polar regions. This includes more than 99% of the world’s population and economic activity. The low Earth orbit (LEO) and medium Earth orbit (MEO) approaches require more satellites to achieve this level of coverage. Due to the fact that non-GEO satel- lites move in relation to the surface of the Earth, a full complement of satellites (called a constellation) must be operating to provide continuous, unbroken service. The trade-off here is that the GEO satellites, being more distant, incur a longer path length to Earth stations, while the LEO systems promise short paths not unlike8 Evolution of Satellite Technology and Applications LEO GEO MEO Figure 1.2 The three most popular orbits for communication satellites are LEO, MEO, and GEO. The respective altitude ranges are 500 to 900 km for LEO, 5,000 to 12,000 km for MEO, and 36,000 km for GEO. Only one orbit per altitude is illustrated, even though there is a requirement for constellations of LEO and MEO satellites to provide continuous service. The standard GEO orbit is perfectly circular and lies in the plane of the equator; other 24-hour orbits are inclined and/or elliptical rather than circular. those of terrestrial systems. The path length introduces a propagation delay since radio signals travel at the speed of light. This is illustrated in Figure 1.3, which is a plot of orbit period and propagation delay for various altitudes. Depending on the nature of the service, the increased delay of MEO and GEO orbits may impose some degradation on quality or throughput. The extent to which this materially affects the acceptability of the service depends on many factors, such as the degree of interactiv- ity, the delay of other components of the end-to-end system, and the protocols used to coordinate information transfer and error recovery. This is reviewed in detail in Part III of this book, which consists of Chapters 8–11. Delay, ms 7.5 75 150 225 270 25 20 15 Hours 10 5 0 0 0 10000 10000 20000 20000 30000 30000 40000 40000 Altitude, km Figure 1.3 A graph that plots orbit period in hours versus the mean altitude of the orbit in kilo- meters. One-way (single-hop) propagation delay is indicated at the top in milliseconds.1.1 Satellite Network Fundamentals 9 Three LEO systems have begun service since the publication of the first edition of this handbook: Orbcomm, Iridium, and Globalstar. Orbcomm was designed for two-way messaging service, while Iridium and Globalstar were designed for mobile telephony. Early advertising for Iridium suggested that with one of their handheld phones, you could be reached anywhere in the world. This would be the case only if you remained out of doors with a clear view of the sky from horizon to horizon. Globalstar had a slightly less ambitious claim that its service was cheaper than that of Iridium. While these systems could deliver services, all have resulted in financial failures for their investors. The non-GEO system that has yet to begin operation at the time of this writing is ICO Communications (ICO originally stood for interme - diate circular orbit, but that was subsequently dropped when they spun the com - pany off) and its MEO constellation. The developers of this system explain that their strategy does not rely on service to handheld telephones and such instruments, but rather is a means to provide near-broadband service to small terminals. Except for Orbcomm, which is in VHF band, all of the satellites just discussed have microwave repeaters that operate over an assigned segment of the 1- to 80- GHz frequency range. As microwaves, the signals transmitted between the satellite and Earth stations propagate along line-of-sight paths and experience free-space loss that increases as the square of the distance. The spectrum allocations are given in the following approximate ranges, as practiced in the satellite industry:  L-band: 1.5 to 1.65 GHz:  S-band: 2.4 to 2.8 GHz;  C-band: 3.4 to 7.0 GHz;  X-band: 7.9 to 9.0 GHz;  Ku-band: 10.7 to 15.0 GHz;  Ka-band: 18.0 to 31.0 GHz;  Q-band: 40 to 50 GHz;  V-band: 60 to 80 GHz. Actual assignments to satellites and Earth stations are further restricted in order to permit different services (and the associated user community) to share this valu- able resource. In addition to microwaves, laser systems continue to be under evalua- tion. Rather than being simple repeaters, laser links require modulated coherent light sources and demodulating receivers that include mutually tracking telescopes. An example of such a device is shown in Figure 1.4. So far, commercial laser links are not in use, but there is interest in them principally to allow direct connections between satellites—called intersatellite links or cross links. Applications are delivered through a network architecture that falls into one of three categories: point-to-point (mesh), point-to-multipoint (broadcast), and mul- tipoint interactive (VSAT). Mesh-type networks mirror the telephone network. They allow Earth stations to communicate directly with each other on a one-to-one basis. To make this possible, each Earth station in the network must have sufficient transmit and receive performance to exchange information with its least effective partner. Generally, all such Earth stations have similar antennas and transmitter systems, so their network is completely balanced. Links between pairs of stations10 Evolution of Satellite Technology and Applications Figure 1.4 Illustration of a laser intersatellite link by the Artemis satellite. (Courtesy of ESTECH.) can be operated on a full-time basis for the transfer of broadband information like TV or multiplexed voice and data. Alternatively, links can be established only when needed to transfer information, either by user scheduling (reservation system) or on demand (demand-assignment system). A broadcast of information by the satellite is more efficient than terrestrial arrangements using copper wires, fiber optic cables, or multiple wireless stations. By taking advantage of the broadcast capability of a GEO satellite, the point-to- multipoint network supports the distribution of information from a source (the hub/uplink Earth station) to a potentially very large number of users of that infor- mation (the remote Earth stations, also called receive-only terminals). Any applica- tion that uses this basic feature will usually find that a GEO satellite is its most effective delivery vehicle to reach a national audience. Many applications employ two-way links, which may or may not use the broad- cast feature. The application of the VSAT to interactive data communication appli- cations has proven successful in many lines of business and more recently to the public. As will be covered in Chapter 8, a hub and spoke network using VSATs can be compared to almost any terrestrial wide-area network topology that is designed to accomplish the same result. This is because the satellite provides the common point of connection for the network, eliminating the requirement for a separate physical link between the hub and each remote point. Other interactive applications can employ point-to-point links to mimic the telephone network, although this tends to be favored for rural and mobile services. The incoming generation of satellite and ground equipment, which involves very low-cost VSATs, is reducing barriers to mass market satellite networks. The degree to which satellite communications is superior to terrestrial alternatives depends on many interrelated factors. Experience has shown that the following fea- tures tend to give satellite communication an advantage in appropriate applications:  Wide area coverage of a country, region, or continent;  Wide bandwidth available throughout;  Independent of terrestrial infrastructure;  Rapid installation of ground network;1.1 Satellite Network Fundamentals 11  Low cost per added site;  Uniform service characteristics;  Total service from a single provider;  Mobile/wireless communication, independent of location. While satellite communications will probably never overtake terrestrial tele- communications on a major scale, these strengths can produce very effective niches in the marketplace. Once the satellite operator has placed the satellite into service, a network can easily be installed and managed by a single organization. This is possi- ble on a national or regional basis (including global using at least three GEO satel- lites). The frequency allocations at C-, Ku-, and Ka-bands offer effective bandwidths of 1 GHz or more per satellite, facilitating a range of broadband serv- ices that are not constrained by local infrastructure considerations. Satellites that employ L- and S- bands constrain bandwidth to less than 100 MHz but may propa- gate signals that bend around obstacles and penetrate nonmetallic structures. Regardless of the band, the satellite delivers the same consistent set of services at costs that are potentially lower than those of fixed terrestrial systems. For the long term, the ability to serve mobile stations and provide communications instantly are features that offer strength in a changing world. Originally, Earth stations were large, expensive, and located in rural areas so as not to interfere with terrestrial microwave systems that operate in the same fre- quency bands. These massive structures had to use wideband terrestrial links to reach the closest city. Current emphasis is on customer premise Earth stations—sim- ple, reliable, low cost. An example of a modern small VSAT is illustrated in Figure 1.5. Home receiving systems for DTH service are also low in cost and quite incon- spicuous. The current generation of low-cost VSATs introduced since 2002 encour- age greater use of bidirectional data communications via satellite. As terminals have shrunk in size, satellites have grown in power and sophistication. There are three general classes of satellites used in commercial service, each designed for a particu- lar mission and capital budget. Smaller satellites, capable of launch by the Delta II rocket or dual-launched on the Ariane 4 or 5, provide a basic number of transpond- ers usually in a single frequency band. Satellite operators in the United States, Can- ada, Indonesia, and China have established themselves in business through this class of satellite. The Measat satellite, illustrated in Figure 1.6, is an example of this class Figure 1.5 Example of a VSAT for broadband communications. (Courtesy of Gilat Satellite Communications.)12 Evolution of Satellite Technology and Applications Figure 1.6 The Measat 1 satellite provides services to Malaysia and throughout Southeast Asia. of vehicle. The introduction of mobile service in the LEO involves satellites of this class as well. Moving up to the middle range of spacecraft, we find designs capable of operating in two frequency bands simultaneously. AsiaSat 3S, shown in Figure 1.7, provides 24 C-band and 24 Ku-band transponders to the Asia-Pacific market. A dual payload of this type increases capacity and decreases the cost per transponder. Finally, some satellites serve specialized markets such as GEO mobile satellites that connect directly with specially designed handheld phones. An example of one of these satellites, Thuraya, is shown in Figure 1.8 with its 12-m antenna deployed. Figure 1.7 AsiaSat 3C is a hybrid C/Ka satellite with a total of 48 transponders.1.1 Satellite Network Fundamentals 13 Figure 1.8 Thuraya 1 provides high-power mobile satellite links to handheld terminals. (Courtesy of Boeing Satellite Systems.) Also, the trend to use the smallest possible DTH home receiving antenna and to cover the largest service area combine to demand the largest possible spacecraft. The total payload power of such satellites reaches 15 kW, which is roughly 12 times that of Measat. At the time of this writing, there are drawing board designs for satel- lites that can support payload powers of up to 20 kW. An example of this is the 2020 program from Space Systems/Loral. While most of the money in satellite communications is derived from the broad- cast feature, there are service possibilities where remote Earth stations must trans- mit information back to the hub Earth station (and this is not necessarily by satellite). Examples of such return link applications include:  Control signals to change the content of the information being broadcast (to achieve narrow casting on a broadcast link);  Requests for specific information or browsing of documents (to support Inter- net or intranet services);  Responsive information to update the record for a particular customer;  Point-to-point information that one remote user wishes to be routed to another remote user (like e-mail). Adding the return link to the network tends to increase the cost of the remote Earth station by a significant amount since both a transmitter and controller are required. However, there are many applications that demand a two-way communi- cation feature. The relative amount of information (bandwidth) on the forward and return links can be quantified for the specific application, as suggested in Figure 1.9. Most of the bandwidth on GEO satellites is consumed in the forward direction, as indicated by the area in the lower right for TV broadcast or distribution. There are also uses for transmitting video in both directions, which is indicated in the upper14 Evolution of Satellite Technology and Applications 10K File transfer VSATs and interactive media 1000 Mobile 100 and fixed telephone TV 10 DSL 1 1 10 100 1000 10K 100K Forward link bandwidth, kHz Figure 1.9 The approximate relationship of bandwidth usage between the forward link (hub transmit) and return link (remote transmit) in satellite applications. right-hand corner. Cutting the bandwidth back on the forward link but not on the return link supports an application where bulk data is transferred from a remote to a centralized host computer. Reduced bandwidth in both directions expands the quantity of user channels to offer low data rate switched service for fixed and mobile telephone markets. These general principles lead to a certain set of applications that serve telecom- munication users. In the next section, we review the most popular applications in preparation for the detailed evaluations in the remaining chapters. 1.2 Satellite Application Types Applications in satellite communications have evolved over the years to adapt to competitive markets. Evolutionary development, described in 1, is a natural facet of the technology because satellite communication is extremely versatile. This is important to its extension to new applications yet to be fielded. 1.2.1 Broadcast and Multicast of Digital Content The first set of applications follow the predominant transmission mode of the GEO satellite—that of point-to-multipoint information distribution. We have chosen to focus exclusively on the broadcast and multicast of content in digital form to a com- munity of users. In the past, signals were transmitted in their original analog form using frequency modulation (FM). While some of this equipment is still in use around the world, it is being phased out. One of the main reasons for this is that sig- nals in digital form can be compressed appreciably without impairing their quality. Return link bandwidth (kHz)1.2 Satellite Application Types 15 A bandwidth compression factor of 10 to 20 is now common, with the primary benefit of reducing transponder occupancy per channel of transmission, thereby increasing useful capacity. Rather than paying, say, 1.5 million per TV channel per year, transponder cost is reduced to 250,000 or less. Therefore, analog ground equipment has become expensive to operate even if its sunk cost is zero. Once in digital form, information can be managed in a wide variety of manners and forms. The resulting bit stream can be expanded to include different content, addressable to subsets of users or even an individual user. In addition to the current heavy use of satellites to transmit digital TV channels, we see new applications in digital content distribution appearing and developing. These new applications may employ features of the Internet in terms of permitting Web browsing; however, mul - ticast techniques are better suited to the GEO platform than the Internet itself. 1.2.1.1 Entertainment Television (Network, Cable, and Direct Broadcast Satellite) Commercial TV is the largest segment of the entertainment industry; it also repre - sents the most financially rewarding user group to satellite operators. The four fun- damental ways that the satellite transfers TV signals to the ultimate consumer are:  Point-to-multipoint distribution of TV network programming contribution from the studio to the local broadcast station;  Point-to-point transmission of specific programming from an event location to the studio (alternatively, from one studio to another studio);  Point-to-multipoint distribution of cable TV programming from the studio to the local cable TV system;  Point-to-multipoint distribution of TV network and/or cable TV program- ming from the studio directly to the subscriber (i.e., DTH). It may have taken 10 or more years for the leading networks in the United States and Europe to adopt satellites for distribution of their signals, but since 1985, it has been the main stay. Prior to 1985, pioneering efforts in Indonesia and India allowed these countries to introduce nationwide TV distribution via satellite even before the United States had made the conversion from terrestrial microwave. European TV providers pooled their resources through the European Broadcasting Union (EBU) and the EUTELSAT regional satellite system. Very quickly, the leading nations of Asia and Latin America adopted satellite TV delivery, rapidly expanding this popu- lar medium to global levels. Over-the-Air TV Broadcasting The first of the four fundamental techniques is now standard for TV broadcasting in the VHF and UHF bands, which use local TV transmitters to cover a city or market. The satellite is used to carry the network signal from a central studio to multiple receive Earth stations, each connected to a local TV transmitter. This has been called TV distribution or TV rebroadcast. When equipped with uplink equipment, the remote Earth station can also transmit a signal back to the central studio to allow the station to originate programming for the entire network. U.S. TV net- works like CBS and Fox employ these reverse point-to-point links for on-location16 Evolution of Satellite Technology and Applications news reports. The remote TV uplink provides a transmission point for local sporting and entertainment events in the same city. This is popular in the United States, for example, to allow baseball and football fans to see their home team play an away- from-home game in a remote city. More recently, TV networks employ fiber optic transmission between studio and broadcast station, and between stadium and stu - dio; but the satellite continues to be the alternate flexible routing system. Satellite transmissions have gone digital, as discussed previously, but broadcast stations depend heavily on the conventional analog standards: NTSC, PAL, and SECAM. In developed countries, governments are encouraging broadcasters to dig - itize their signals to open up bandwidth for more TV channels and for use in other radio services such as mobile telephone. In the United States, many local stations provide some quantity of their programming in digital form, offering high-definition television in some cases. Revenue for local broadcast operations is available from two potential sources: advertisers and public taxes. Pay TV services from cable, satellite, and local micro - wave transmissions permit greater revenue when TV watchers become monthly sub - scribers. In some countries, nationally sponsored broadcasters are supported directly through a tax or indirectly by government subsidy. Since its beginnings in the United States, TV provided an excellent medium to influence consumer purchase behavior. In exchange for watching commercials for soap, airlines, and automo- biles, the consumer is entertained for nothing. This has produced a large industry in the United States as stations address local advertisers and the networks promote nationwide advertising. The commercial model was also adopted in Latin America. An alternative approach was taken in many European countries and in Japan, where government-operated networks were the first to appear. In this case, the con- sumer is taxed on each TV set in operation. These revenues are then used to operate the network and to produce the programming. The BBC in the United Kingdom and NHK in Japan are powerhouses in terms of their programming efforts and broad- cast resources. However, with the rapid introduction of truly commercial networks, cable TV, and DTH, these tax-supported networks are experiencing funding difficulties. Public TV in the United States developed after commercial TV was well estab- lished. Originally called Educational TV, this service existed in a fragmented way until a nonprofit organization called the Public Broadcasting Service (PBS) began serving the nation by satellite in 1978. The individual stations are supported by the local communities through various types of donations. Some are attached to univer- sities; others depend on donations from individuals and corporations. PBS itself acquires programming from the member stations and from outside sources like the BBC. Programs are distributed to the members using satellite transponders pur- chased by the U.S. government. It must therefore compete with other government agencies for Congressional support. PBS programming is arguably of better quality than some of the popular shows on the commercial networks. Even though PBS addresses a relatively narrow segment, its markets are under attack by even more targeted cable TV networks like A&E, The Discovery Channel, The Learning Chan- nel, The History Channel, Home and Garden TV, and the Food Network. All of these competitors built their businesses on satellite delivery to cable systems and DTH subscribers.1.2 Satellite Application Types 17 The local airwaves provide a reasonably good medium to distribute program - ming with the added benefit of allowing the local broadcaster to introduce local programs and advertising. Satellite transmission, on the other hand, is not limited by local terrain and thus can be received outside the range of terrestrial trans- mitters, extending across a nation or region. In extreme cases where terrestrial broadcasting has been destroyed by war or conflict, or has not been constructed due to a lack of economic motivation, satellite TV represents the only effective alternative. Cable Television Begun as a way to improve local reception in rural areas, cable TV has established itself as the dominant force in many developed countries. This was facilitated by organizations that used satellite transmission to distribute unique programming for - mats to cable subscribers. The cable TV network was pioneered by HBO in the 1970s. Other early adopters of satellite delivery include Turner Broadcasting, War - ner Communications, and Viacom. By 1980, 40% of urban homes in the United States were using cable to receive the local TV stations (because the cable provided a more reliable signal); at the same time, the first nationwide cable networks were included as a sweetener and additional revenue source. During the 1980s, cable TV became an 8 billion industry and the prototype for this medium in Europe, Latin America, and the developed parts of Asia. By 2002, about 80 million U.S. households were connected to cable for TV, with about 6 million benefiting from broadband Internet access through two- way cable technology. The vitality of the cable industry actually benefited from the digital DTH revolution, which forced cable systems to digitize and expand services. Cable TV networks, discussed in Chapter 4, offer programming as a subscriber service to be paid for on a monthly basis or as an almost free service like commercial TV broadcasting. HBO, Showtime, and the Disney Channel are examples of pre- mium (pay) services, while The Discovery Channel, CNN, and MSNBC are exam- ples of commercial channels that receive most of their revenue from advertisers. The leading premium channels in North America and Europe are successful in financial terms, but the business has yet to be broadly accepted in economies with low- income levels. Cable TV became the first to offer a wide range of programming options that are under the direct control of the service provider. The local cable system operator controls access and can therefore collect subscription fees and service charges from subscribers. If the fees are not paid, the service is terminated. Wireless cable, a con- tradiction in terms but nevertheless a viable alternative to wired cable, uses portions of the microwave spectrum to broadcast multiple TV channels from local towers. It has proven effective in urban areas in developing economies where the density of paying subscribers is relatively high, such as Mexico City and Jakarta, Indonesia. Just as in the case of DTH, wireless cable depends on some form of conditional access control that allows the operator to electronically disconnect a nonpaying user. Theft of signals, called piracy, is a common threat to the economic viability of wired and wireless cable (as it is to DTH, discussed next).18 Evolution of Satellite Technology and Applications Direct-to-Home Broadcasting Satellite The last step in the evolution of the satellite TV network is DTH. After a number of ill-fated ventures during the early 1980s by USCI, COMSAT, CBS, and others, DTH has established its niche in the broadcasting and cable spheres. BSkyB in the United Kingdom, NHK in Japan, DIRECTV and EchoStar in the United States, Sky Latin America, and STAR TV in Asia are now established businesses, with other broad - casters following suit. Through its wide-area broadcast capability, a GEO satellite is uniquely situated to deliver the same signal throughout a country or region at an attractive cost per user. The particular economics of this delivery depend on the fol - lowing factors.  The size of the receiving antennas: Smaller antennas are easier to install and maintain and are cheaper to purchase in the first place. They are also less noticeable (something that is desirable in some cultures).  Thedesignoftheequipment: This is simple to install and operate (this author’s Digital Satellite System (DSS) installation, needed to receive DIRECTV, took only 2 hours—that is, 105 minutes to run the cables and 15 minutes to install and point the dish).  Severaluserscansharethesameantenna: This is sensible if the antenna is rela- tively expensive, say, in excess of 1,000; otherwise, each user can afford his or her own. A separate receiver is needed for each independent TV watcher (the same now applies to digital cable service).  Thenumberoftranspondersthatcanbeaccessedthrougheachantenna(typi- cally32): Due to the high power required as well as concerns for single-point failure, DTH operators place more than one satellite in the same orbit position in order to achieve the desired total transponder count. The more channels that are available at the same slot, the more programming choices that the user will have.  ThenumberofTVchannelsthatcanbecarriedbyeachtransponder(typically 10): Capacity is multiplied through digital compression and statistical multi- plexing techniques discussed in Chapter 6.  Inclusion of local TV channels in the United States: This simplifies home installation and meets a government mandate that satellites “must carry” these channels to all potential markets. The ideal satellite video network delivers its programming to the smallest practi- cal antenna on the ground, has a large number of channels available (200 or more), and permits some means for users to interact with the source of programming. A simple connection to the PSTN allows services to be ordered directly by the sub- scriber; alternatively, a broadband connection is offered either over the satellite or through wireline or wireless access. 1.2.1.2 Content Delivery Networks A content delivery network (CDN) is a point-to-multipoint satellite network that uses the broadcast feature to inject multimedia content (particularly Web pages and specific content files such as software updates and films) into remote servers and1.2 Satellite Application Types 19 other types of caching appliances. The basic structure of a CDN is illustrated in Fig - ure 1.10. The remote cache could be a dedicated server connected to the local infra - structure of the Internet. This greatly reduces the delay associated with accessing and downloading the particular content. Another style of CDN is to put the content directly into the PC hard drive; for this to work, the PC must have a direct electrical connection to the remote CDN terminal. The first CDNs appeared during the Internet boom of 1999–2000; many have not survived the shakeout. However, some organizations are using and developing CDNs as a structure to propagate content to remote locations to bypass the cost and congestion of the terrestrial Internet. The ground equipment and software to create a CDN may be blended with that used for digital TV, as will be discussed in Chapter 5. The fact that the content appears to be local to the user enhances the interactive nature of the service. Thus, the central content store does not directly process requests from users. 1.2.1.3 Satellite Delivered Digital Audio Radio Service We conclude the discussion of point-to-multipoint applications with an introduc - tion to digital audio broadcasting (DARS). By focusing on sound programming without a visual element, S-DARS addresses itself to networks where (1) spectral bandwidth is limited, (2) users are mobile in their cars and boats, and/or (3) iso- lated from major sources of radio and other mass media. While DARS is a term generally reserved for terrestrial digital radio, the version we are interested in is sat- ellite delivered digital audio radio service (S-DARS). The first to introduce S-DARS principally as a solution to (3) was WorldSpace, a startup company with the vision of delivering multichannel radio programming to the underdeveloped regions of Africa and Asia. Subsequently, the FCC auctioned off L-band spectrum for S-DARS for the U.S. market. XM Satellite Radio and Sirius Satellite Radio imple- mented 100 digital audio radio services that are comparable to FM broadcasting. Both companies launched S-band satellites in 2001 and initiated service on a com- mercial basis in 2002. Through a package of subscription radio channels as well as conventional advertiser supported formats, XM and Sirius serve subscribers in their cars and homes. MPEG 2 encoder Broadcast uplink Return channel for lost packets Content IRD Internet Cable server Figure 1.10 Structure of a content delivery network with reliable file transfer. (Courtesy of Scopus.)20 Evolution of Satellite Technology and Applications Satellite construction and launch was hardly a challenge for S-DARS; however, producing the appropriate receiving terminal proved to be more time consuming than the original business plans considered. Examples of the types of units offered for S-DARS service are shown in Figure 1.11. As in any satellite communications service, a line-of-site path is usually required; thus, the antenna must be in plain view of the geostationary orbit. Vehicular installations are best; however, obstructions like tall buildings, trees, tunnels, and overpasses may block the signal. This are coun - tered through three techniques: receiver storage of several seconds of channel stream, allowing for catch-up when a blocked receiver again “sees” the satellite; use of two or more satellites to increase the probability of a line-of-sight path; and rebroadcast of the satellite signal into concrete canyons and inside tunnels through the use of land-based “gap filler” relays. 1.2.2 Voice and Telephony Networks Voice communications are fundamentally based on the interaction between two people. It was recognized very early in the development of satellite networks that the one-way propagation delay of one-quarter second imposed by the GEO tends to degrade the quality of interactive voice communications, at least for some percent- age of the population. However, voice communications represent a significant satel- lite application due to the other advantages of the medium. For example, many developing countries and lightly inhabited regions of developed countries continue to use satellite links in rural telephony and as an integral part of the voice network infrastructure. Furthermore, an area where satellite links are essential for voice com- munications is the mobile field. These developments are treated in detail in Chapters 10 and 11. The PSTN within and between countries is primarily based on the requirements of voice communications, representing something in the range of 50% to 60% of all interactive traffic. The remainder consists of facsimile (fax) transmissions, low- and medium-speed data (both for private networks and access to public network services such as the Internet), and various systems for monitoring and controlling remote facilities. Direct access to the Internet via a dial-up modem will be a supporting fac- tor for the PSTN in coming years. The principal benefit of the PSTN is that it is truly Figure 1.11 Sanyo WorldSpace receiver.1.2 Satellite Application Types 21 universal. If you can do your business within the limits of 3,000 Hz of bandwidth and can tolerate the time needed to establish a connection through its dial-up facil - ity, the PSTN is your best bet. Propagation delay became an issue when competitively priced digital fiber optic networks were introduced in the 1990s. Prior to 1985 in the United States, AT&T, MCI, and others were using a significant amount of analog telephone channels both on terrestrial and satellite links. An aggressive competitor in the form of U.S. Sprint invested in an all-digital network that employed fiber optic transmission. Sprint expanded their network without microwave or satellite links and introduced an all- digital service at a time when competition in long distance was heading up. Their advertising claimed that calls over their network were so quiet “you can hear a pin drop.” This strategy was so successful that both MCI and AT&T quickly shifted their calls to fiber, resulting in rapid turn-down of both satellite voice channels and analog microwave systems. A similar story is told in Europe, Latin America, and Asia, albeit at a slower pace in most countries due to the persistence of local monopolies. In time, fiber links and digital voice switching have become the standard of the PSTN. The economics of satellite voice communications are substantially different from that of the fiber-based PSTN, even given the use of digital technology with both approaches. With low-cost VSAT technology and high-powered satellites at Ku- and Ka-bands, satellite voice is the cheapest and quickest way to reach remote areas where terrestrial facilities are not available. It will be more attractive to install a VSAT than to extend a fiber optic cable over a distance greater than a few hundred meters. A critical variable in this case is the cost of the VSAT, which dropped from the 10,000 level in 1995 to as low as 1,500 in 2003. Fiber, however, is not the only terrestrial technology that can address the voice communication needs of sub- scribers. Fixed wireless systems have been installed in developing countries to rap- idly turn up telephone services on the local loop. Low-cost cordless phones or simple radio terminals are placed in homes or offices, providing access to the PSTN through a central base station. The base stations are concentrating points for traffic and can be connected to the PSTN by fiber or even satellite links. The cost of the base station and network control is kept low by not incorporating the automatic hand-off feature of cellular mobile radio. Instead, user terminals of different types make the connection through the closest base station, which remains in the same operating mode throughout the call. The ability of the wireless local loop to support Internet access at 56 Kbps depends on the degree of compression used to provide sufficient channel capacity. High-speed Internet access has been introduced on wireline local loops through the class of technologies known as DSL. Using the basic approach of frequency divi- sion multiplex (FDM), DSL adds the baseband bandwidth needed to allow bidirec- tional transfer speeds of 100 Kbps to as much as 1 Mbps over copper twisted-pair. In the absence of copper, traditional fixed wireless local loop networks cannot sup- port DSL-like services. More recently, some service providers have begun to offer wireless Internet access using the IEEE 802.11b standard (also called Wi-Fi). The advantage of this approach is that the spectrum is unlicensed in the United States and most other countries and therefore freely available (although potentially crowded); furthermore, many individuals already carry Wi-Fi modems within their22 Evolution of Satellite Technology and Applications laptops. Likewise, to add high-speed access to satellite telephony amounts to provid - ing the appropriate bandwidth over the same or even another VSAT. The notion that bandwidth is free certainly does not apply to wireless systems, whether speak - ing of the local or satellite varieties. New classes of public network services may appear in coming years under the general category of Broadband Integrated Services Digital Networks (B-ISDN). The underlying technology is asynchronous transfer mode (ATM), a flexible high-speed packet-switched architecture that integrates all forms of communications 2. ATM services can be delivered through fiber optic bandwidths and advanced digital switching systems. ATM includes the following capabilities:  High-speed data on demand (384 Kbps to 155 Mbps, and greater);  Multichannel voice;  Video teleconferencing and video telephone;  Video services on demand;  High-resolution color images;  Integrated voice/data/video for enhanced Internet services. Due to the high cost of upgrading the terrestrial telephone plant for ATM serv- ices, many of these services will not appear in many places for some time. However, they represent the capability of the coming generation of public networks being implemented around the globe. Even in the absence of a public B-ISDN, the ATM approach has been applied within private LANs and campus networks, interconnec- tion between LANs to form a WAN, and within the backbone of the Internet itself by Tier 1 Internet service providers (ISPs) like UUNET and Genuity. Fiber optic networks are attractive for intra- and intercity public networks and can offer broadband point-to-point transmission that is low in cost per user. The economics of long-haul fiber dictate that the operator must aggregate large volumes of telephone calls, private leased lines, and other bulk uses of bandwidth in order to make the investment pay. In 2002, the financial failure of several new fiber carriers illustrates the dilemma they face. Yet this is easier to do with a satellite because it provides a common traffic concentration point in the sky. The bandwidth is used more effectively (a principle of traffic engineering), and therefore the network can carry more telephone conversations and generate more revenue regardless of where the demand arises. Satellite networks are very expandable because all points are independent and local terrain does not influence performance. Consider the example of the largest German bank, Deutsche Bank, which needed to offer banking services in the new states of the former East Germany. The telecom infrastructure in East Germany in 1990, while the best in the Soviet Block, was very backward by Western European standards. Deutsche Bank installed medium-sized Earth stations at new bank loca- tions and was then able to offer banking services that were identical to those of their existing branches in the West. In a more recent example, the devastation caused in Afghanistan during years of repression and the ensuing conflict destroyed any sem- blance of telecommunications infrastructure. Existing GEO satellites in the region provide the bandwidth, and low-cost satellite Earth stations are introduced at cities, towns, and villages to restore reliable communications for the entire country.

Advise: Why You Wasting Money in Costly SEO Tools, Use World's Best Free SEO Tool Ubersuggest.