Commercialization of the Ground Segment

The creation of the Communications Satellite Corporation (COMSAT) and the subsequent launch of Early Bird in 1965 ushered in the era of true commercialization of this medium. It has largely gone unnoticed that one of COMSATs greatest legacies is its introduction of major earth stations for telephone and TV services to the general public. The very first transmissions over Early Bird used the same earth stations that were constructed for Telstar; however, these facilities had very limited service capability, both in terms of capacity and physical location. The intention of Early Bird and all of the INTELSAT satellites that followed was to improve the international telecommunications network. This demanded that earth stations be located in essentially every country of the world.

COMSAT worked in cooperation with AT&T, RCA, and others in the United States, and the major post, telegraph, and telephone (PTT) agencies of countries around the world, to standardize the design and operation of these large earth stations. They helped found the International Telecommunications Satellite Organization (INTELSAT), a treaty-based cooperative of national entities around the world. (INTELSAT was created as a quasigovernmental body but spun off its transponder-leasing business to a Netherlands-based satellite operator called NewSkies Satellites.)

A typical INTELSAT earth station of the 1960s, such as the COMSAT facility in Etam, West Virginia, represented a substantial investment yet offered connectivity with other earth stations through the GEO satellites operated by this consortium. While begun and nurtured by COMSAT, INTELSAT set out on its own in the mid-1970s and initiated a broad range of other services and applications of their space segment. The initial Standard A type of station (initially requiring 30-m antennas) was joined by more cost-effective Standard B earth stations (at 15m to 20m) that allowed countries to provide domestic satellite communication networks. Similar stations were installed as part of domestic satellite (DOMSAT) systems, such as the Palapa A network.

The INTELSAT system established its preeminence through the 1960s and early 1970s as the number of earth stations grew from hundreds to thousands.
Using technology and standards originally developed by COMSAT and improved along the way by INTELSAT and its members, the earth stations interoperate effectively. At all times, they maintain quality and order (no small task for a system used by a wide range of operating organizations on every continent).
Headquartered in Washington, D.C., INTELSAT manages the system using its control center, which is connected to TT&C and monitoring stations strategically located around the world. Individual earth stations, which are owned and operated either by members (e.g., the domestic telephone companies or PTTs) or other users who obtain their authority from these entities, are under the direction of INTELSAT’s control staff.
While INTELSAT saw its global system grow rapidly in terms of the number of satellites and earth stations, an important new phase of satellite communication appeared in 1971 when Canada launched its first GEO 
DOMSAT, Anik A (Anik means brother in the native Inuit language). Telesat Canada established the first domestic satellite system, which would become a model for more than twenty other countries. It pioneered applications like rural telephone service to remote regions and national TV broadcasting directly to major cities and small communities far from terrestrial transmitters. While INTELSAT required antennas of at least 15m in diameter, the performance of the Anik satellites allowed Telesat to employ 10m and even 4.5m antennas for these services (see Figure 1.6). This innovative system also spurred Canadian industry, allowing several companies to gain
a viable foothold as international suppliers of satellite and earth station equipment.

The United States, while a pioneer of commercial satellites and earth stations, took a back seat to Canada and only produced its first domestic network in 1974 with the launch of Western Union’s Westar 1 satellite. Being a purely commercial company, Western Union implemented its ground segment to augment its existing terrestrial microwave network. Westar earth stations were located in major cities around the country to support telephone, telex, and data communications. Later, the Public Broadcasting Service (PBS) became the first U.S. television network to use satellites for program  distribution and backhaul (e.g., the point-to-point transmission of video from temporary sites and remote studios at affiliated TV stations).

Integrated ground segments of the day, primarily used analog technology for telephone, telex, and television service, and depended on human operators to control access and manage services. The first domestic satellite system outside of North America was introduced in Indonesia and its neighboring Southeast Asian neighbors in 1976. The Palapa A satellites (named for a mythical fruit that Gajah Mada, an ancient king of Java, refused to eat until all of Indonesia was united) used the same design as Anik A. The ground segment was provided on an integrated basis by an international team consisting of the Indonesian PTT, Hughes Space & Communications Company, Ford Aerospace, ITT, and the TRT division of Philips. Internal to every earth station was a singlechannel per-carrier (SCPC) system that provided telephone service on a demand-assigned (DA) basis. This was directly integrated into the Indonesian direct-distance-dialed (DDD) automated telephone network that ITT
was installing at the time.

The timeline in Figure 1.2 indicates that 1975 was pivotal for mobile satellite communications, since this was the year Marisat 1 was launched.
This L-band GEO satellite was operated by COMSAT as a means to improve ship-to-shore communications, which at the time was still dependent on ionospheric reflection at high frequency. The first shipboard Marisat terminals still needed a dish type of antenna to provide adequate link performance for SCPC telephone and telex service. At the other end of the link is a land station acting as a gateway to the telephone network in the respective country. This service was so successful that COMSAT created Inmarsat, another alliance to promote the proliferation of earth stations in the global mobile ground segment. We will discuss again how Mobile Satellite Servicesgrew to extend to the air and land, providing communications to a wide varieter terminals.

First Satellite Earth Stations

Satellite earth stations are different from previous ground-based installations in that they are intended to transmit to and receive from spacecraft. The first of these were used to track the early vehicles that were launched into orbit and deep space. The function is called tracking, telemetry, and command (TT&C) and often includes a requirement to receive various types of sensor information. Such stations could also be equipped for communication with manned spacecraft and orbiting repeaters (e.g., communication satellites).

Both the United States and the former Soviet Union introduced these capabilities as part of their respective space programs, which began in the mid-1950s. The first TT&C ground stations were, in fact, radio telescopes that had been modified for bidirectional transmission. An example is the 90-m Goldstone, California, tracking station antenna, which was installed in the late 1950s to track Explorer 1 by Jet Propulsion Laboratories (JPL), which at the time was under contract to the U.S. Army. In 1959, JPL was transferred to the National Aeronautics and Space Administration (NASA) as part of the still-operating Deep Space Network (DSN).

Also installed at Goldstone was the 30.5-m earth station for use with the Project Echo passive balloon reflector satellite. Bell Labs in Holmdale, New Jersey, provided the other end of the link with their reflector horn antenna. Horn antennas of this type have the added feature of very low side and back lobe radiation and reception, something that helps reduce noise pickup from extraneous sources. Later, this antenna was the instrument used by Bell Labs’ scientists A. A. Penzias and R. W. Wilson to make the discovery of the cosmic background noise level, produced by the Big Bang.

While experimenting with noise measurements, they were trying to find where about three degrees of excess noise was coming from.
The first active repeater satellite was Bell Laboratories Telstar 1, which allowed the United States and the United Kingdom to communicate realtime TV and voice. As the first true earth stations, these facilities were as large and elaborate as the TT&C stations and large radio telescopes that they emulated. Size did matter because of the low power and antenna gain provided by the little Telstar satellite. Because Telstar 1 was in low earth orbit (LEO), the earth stations required tracking systems; also, the service was interrupted whenever the satellite was not in simultaneous view of the end points.

All of these earth stations were highly customized and experimental in nature. They were not constructed to provide a service to subscribers and certainly were not operated as a business. In the next section, we consider how earth stations evolved into commercial ground segments installed to provide profitable communications services.

Microwave and Radar Development

Earth stations use microwave frequencies, which lie between approximately 1 and 30 GHz, and therefore owe much to the development of Radio Detecting and Ranging (RADAR) systems. Many readers are aware that a radar antenna in the Hawaiian Islands detected imperial Japanese aircraft that bombed Pearl Harbor on December 7, 1941 [3]. However, much earlier, in 1929, G. Ross Kilgore, an engineer at Westinghouse, generated 18 GHz of microwave energy with an experimental split-anode magnetronvacuum tube. This particular device could measure Doppler reflections from moving automobiles and railroad cars. Radar improved in RF power output and sophistication during World War II and shortly thereafter, providing a technology base for terrestrial and satellite microwave communications.

Professor Wilmer Barrow of the pioneering Radiation Laboratory at MIT experimented with electromagnetic horn antennas for static-less ultrahigh-frequency wave transmission. The system consisted of a conducting tube, a transmitting terminal device, and either a receiving terminal unit or the radiating horn. Other developments at the Rad Lab include a multitude of microwave components like the klystron, numerous waveguide devices like diplexers, and antenna systems for radar and communication applications. An early horn reflector antenna was developed at Bell Laboratories in 1942, a precursor to antennas used in terrestrial and satellite microwave communications. After the war, Raytheon used microwave technology in an innovative (and noncommunication) manner with their invention of the microwave oven. Not surprisingly, the first food item to be cooked was popcorn.

AT&T recognized that microwave technology could increase the capacity and reliability of long-haul communication lines. Line-of-sight microwave links were established across the developed regions of the world during the 1950s and 1960s. The terminal ends and intermediate connection points were very much like earth stations in their design and use, namely to interface the long-distance link with local users. The overall microwave network offers much that a modern ground segment can, although it is tied to the specific routing and associated real estate.
Radio astronomy, while not able to command the investment and revenues of commercial telephone and television services, still benefited from the availability of microwave technology. Here, the challenge is to receive very weak signals (effectively noise within the noise). The parabolic dish antennas grew in size to provide greater ability to discriminate distant radio emitters.

The principle behind this is that the width of the narrow antenna beam is inversely proportional to the diameter of the reflector. Thus, radio telescopes in the 30-to-100-m range soon appeared, topped by the giant 305-m Arecibo dish antenna in Puerto Rico (this antenna is actually constructed in a small lake basin and was featured in the James Bond movie Golden Eye). Constructed in 1960, and operated by Cornell University under a cooperative agreement with the National Science Foundation (NSF), the Arecibo radio telescope not only receives celestial noise, it can also transmit radar signals to map the planets of our solar system.

Radio telescopes more along the lines of earth stations were constructed at several locations in the United States and around the world. The 91-m (300-ft) Green Bank Telescope was constructed in the 1960s but experienced mechanical failure in 1988. At the time of this writing, another 100-m radio telescope was under construction, this time using the offset parabolic reflector design popular for home DBS installations (and many spacecraft reflector antennas as well). Another type of terrestrial radio communications system is the tropospheric scatter communication link, which employs microwave signals that can be propagated over the horizon (OTH).

The tropo installation shown in Figure 1.4 was installed in 1967 by the U.S. Army Signal Corps at Pleiku, Vietnam, where it provided a single-hop link of about 230 km to Nha Trang (four times line-of-sight range). As can be seen, this 15-m antenna points nearly at the horizon to acquire the relatively weak but reasonably stable) signals that have been dispersed by the troposphere.

First Space Application of Radio

While HF signals (which lie between 3 and 30 MHz) are much lower in frequency than today’s modern satellite links, the principle is nevertheless the same as for the ground segment. Private individuals and experienced radio hobbyists (called radio amateurs or hams) helped develop radio communications through the medium of amateur radio communication (also called ham radio) and radio astronomy. This author spent many hours as a teenager, college student, and young engineer using the international Morse code to meet fellow amateurs around the world. (International Morse code differs from the original American Morse code because it composes letters with long and short on radio transmissions rather than sequences of clicks of DC current over telegraph wires.) Starting in the 1920s, amateurs were granted key
status in the U.S. domestic regulations and later international regulations as well.

They developed their own equipment and antenna systems, and moved the technology from the low frequencies up to the bands close to those of modern satellites.

The first indication of a connection between radio and space came in 1922 when Karl Jansky, a young electrical engineer at Bell Laboratories, was investigating the various sources of noise that hinder long-distance radio communication. While most of the emitters he identified were due to terrestrial sources such as electrical machinery and thunderstorms, there was one unidentified source that appeared and disappeared on a daily basis. The clue as to the celestial nature of this source was the fact that it appeared four minutes earlier every day. From the standpoint of an astronomer, this indicated that the source was extraterrestrial. Karl Janskys announcement of the source as in the direction of the center of the Milky Way Galaxy was reported on May 5, 1933, on the front page of the New York Times.

Most early radio installations looked more like broadcasting sites than earth stations. However, it was an amateur radio operator by the name of Grote Reber who built the first operating parabolic reflector antenna. (The reflector is parabolic in cross section, producing a surface called a paraboloid.

However, the term parabola is more popular, probably because it is easier to say.) Shown in Figure 1.3 is the 10m (32 ft) wonder he created to explore the radio sky. Reber built this first model himself literally in his own backyard, and made his first discoveries of cosmic radio emissions in 1939. After continued measurement and exploration of celestial radio sources, he published the first survey of the sky at radio wavelengths in 1942 in the Proceedings of the Institute of Radio Engineers.

Earth Station

Introduction to the Satellite Communication Ground Segment
Ground segments of satellite communication systems employ a variety of node designs and network configurations in order to provide and manage services delivered to end users. The nodes in these networks range from the large earth stations used as gateways in a telephone network to very small aperture terminals (VSATs) that deliver data communication applications to remote business locations. Small aperture in this context refers to a reflector diameter in the range of 60 cm to 2.8m. We must also include low-cost end-user communication devices like desktop and handheld mobile telephones and direct broadcast satellite (DBS) home receivers.

This broad range of ground systems and devices employs many of the same hardware and software technologies found in other modern telecommunications and broadcastingnetworks that are the core of terrestrial wireless and Internet services.
As illustrated in Figure 1.1, the ground segment is that half of a satellite communication system which, quite naturally, resides on the ground. The space segment, consisting of orbiting communication satellites and a satellite control system used to operate and maintain the satellites, is that vital component which relays information between and among the various types of earth stations that make up the ground segment. In a previous work, we discuss in detail the design, operation, and management of the space segment, considering the technologies and physical principles that are key to its success.
In essence, the ground segment is useless without a properly operatingspace segment. Implementation of the space segment of geostationaryearth orbit (GEO) satellites represents many hundreds of millions of dollars;
a global nongeostationary (non-GEO) satellite system increases this levelto billions. Operators of GEO space segments include INTELSAT, SociétéEuropéene des Satéllites (SES), PanAmSat, GE American Communications(Americom), EUTELSAT, Japan Satellite Telecommunications (Jsat), andothers. Companies such as Globalstar LLC, ICO Teledesic, and OrbCommoperate non-GEO satellite constellations and systems. We will not discussthe space segment in detail in this book, but we will at times need to considerthe capabilities and constraints that it imposes as we work to provide theservice element of the overall system.

We use the term earth station to include classic fixed earth station facilitiesas well as mobile aeronautical, maritime, and handheld devices. In somecases, earth stations are individually owned and managed (e.g., the teleportoperated as a business), but this approach is being overtaken by the integratedtotal system that provides services to end users. Many readers alreadyown their own user terminals, which are technically small self-containedearth stations. But these terminals cannot operate without the ground segmentof the network operator. Examples of the latter include DIRECTV,British Sky Broadcasting (BSB), Measat Broadcasting Network Services(MBNS), operator of the Astra DBS service in Malaysia, COMSAT MobileServices, Telia of Sweden, Hong Kong Telecom, PT Indosat, and others.

The first two chapters of this text will lay the groundwork for thedetailed discussion of design and operating principles that follows. Theintention is to permit readers to devise their own approach to implementingand managing the earth stations and the overall ground segment. The materialpresented in this book should give readers a head start in the process,allowing them to prepare requirements, perform preliminary analyses, reviewdesigns provided by hardware suppliers, and manage the introduction of theoverall ground segment. We assume that readers have some level of familiaritywith the overall satellite system and the principles of RF engineering andtelecommunications networks, particularly those using satellites. We start with a chronological review of earth station technology, beginning in theearly twentieth century with the first introduction of radio (synonymouswith wireless at that point in time).

The long history of ground segment and earth station development andapplication dates back to the early 1900s, to the very beginnings of radiocommunications. Guglielmo Marconi successfully conducted the first transatlanticmessage transmission in 1901. The transmitters of the day produced aradio signal of around 1 MHz generated from a continuous spark. Radio wavesfrom this frequency and up to about 30 MHz can travel long distances on theground, since they can be reflected by the ionosphere (instead of an orbitingplatform). Later, commercial ships were equipped with these radios so thatland-based stations could handle messages sent with the international Morsecode. The 1997 movie Titanic dramatized how these simple mobile radio stationswere the lifelines of communication afforded the greatest ships at sea.

An overall timeline for the evolution of modern ground segments andearth stations is presented in Figure 1.2. It is impossible to present here everysignificant class of facility and application, since to do so would require anarea the size of a movie screen. However, we aim to show each major introductionof ground-based radio technology that contributed to how we usecommunication satellites in orbit. Other aspects of this history, particularlyfrom the space segment standpoint, can be found in our previous work.