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1
Past, Present, and Future

Humans have long dreamed of possessing the capability to communicate with each other anytime, anywhere. Kings, nation-states, military forces, and business cartels have sought more and better ways to acquire timely information of strategic or economic value from across the globe. Travelers have often been willing to pay premiums to communicate with family and friends back home. As the twenty-first century approaches, technical capabilities have become so sophisticated that stationary telephones, facsimile (fax) machines, computers, and other communications devices—connected by wires to power sources and telecommunications networks—are almost ubiquitous in many industrialized countries. The dream is close to becoming reality. The last major challenge is to develop affordable, reliable, widespread capabilities for "untethered" communications, a term coined by the U.S. military and referring to the union of wireless and mobile technologies. Because "untethered" is not a widely used term, this report concentrates on "wireless" communications systems that use the radio frequency (RF) part of the electromagnetic spectrum. These systems and their component technologies are widely deployed to serve mobile users.

Mobile wireless communications is a shared goal of both the U.S. military and civilian sectors, which traditionally have enjoyed a synergistic relationship in the development and deployment of communications technology. The balance of that long-standing interdependence is changing now as a result of trends in the marketplace and defense operations and budgets. These trends suggest that market forces will propel advances



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Page 10 1 Past, Present, and Future Humans have long dreamed of possessing the capability to communicate with each other anytime, anywhere. Kings, nation-states, military forces, and business cartels have sought more and better ways to acquire timely information of strategic or economic value from across the globe. Travelers have often been willing to pay premiums to communicate with family and friends back home. As the twenty-first century approaches, technical capabilities have become so sophisticated that stationary telephones, facsimile (fax) machines, computers, and other communications devices—connected by wires to power sources and telecommunications networks—are almost ubiquitous in many industrialized countries. The dream is close to becoming reality. The last major challenge is to develop affordable, reliable, widespread capabilities for "untethered" communications, a term coined by the U.S. military and referring to the union of wireless and mobile technologies. Because "untethered" is not a widely used term, this report concentrates on "wireless" communications systems that use the radio frequency (RF) part of the electromagnetic spectrum. These systems and their component technologies are widely deployed to serve mobile users. Mobile wireless communications is a shared goal of both the U.S. military and civilian sectors, which traditionally have enjoyed a synergistic relationship in the development and deployment of communications technology. The balance of that long-standing interdependence is changing now as a result of trends in the marketplace and defense operations and budgets. These trends suggest that market forces will propel advances

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Page 11 in technology to meet rising consumer expectations. However, the military may need to take special measures to field cost-effective, state-of-the-art untethered communications systems that meet defense requirements. This chapter lays the foundation for an analysis of military needs in this area by chronicling the evolution of military and civilian applications of communications technology, from ancient times leading up to the horizon of 2010. Section 1.1 is an overview of the challenge facing the U.S. military. Section 1.2 provides an historical perspective on the development of communications infrastructures. Section 1.3 outlines the wireless systems currently used by the U.S. military and the related research and development (R&D) activities. Sections 1.4 through 1.7 recount the evolution and current status of commercial wireless systems. Section 1.8 compares the development paths for wireless technologies in the United States, Europe, and Japan. 1.1 Overview In the final years of the twentieth century, all aspects of wireless communications are subject to rapid change throughout the world. Dimensions of change include the following: • Vigorously expanding public demand for products and services; • Dramatic changes worldwide in government policies regarding industry structure and spectrum management; • Rapidly advancing technologies in an atmosphere of uncertainty about the relative merits of competing approaches; • Emergence of a wide variety of new systems for delivering communications services to wireless terminals; and • Profound changes in communications industries as evidenced by an array of mergers, alliances, and spin-offs involving some of the world's largest corporations. These changes are fueled by opportunities for profit and public benefit as perceived by executives, investors, and governments. Although the patterns are global, the details differ significantly from country to country. Each dimension of change is complex and all of them interact. Overall, the dynamic nature of wireless communications creates a mixture of confusion and opportunity for stakeholders throughout the world. A principal attraction of wireless communications is its capability to serve mobile users. Because mobility is an important feature of military operations, the U.S. armed forces have always played a leading role in the development and deployment of wireless communications technology.

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Page 12 In the coming years, however, it appears that the commercial sector will have sufficient incentives and momentum to push the technical envelope on its own. At the same time, flat or declining defense budgets are motivating the military to adopt commercial products and services to an increasing extent. Yet there are significant differences between military and commercial requirements. Thus, it is important to examine carefully the opportunities for, and limitations to, military use of commercial wireless communications products and services. In contrast to other areas of information technology, wireless communications has yet to converge toward a single technical standard or even a very small number of them. Instead it appears that diversity will endure for the foreseeable future. In this environment, the management and coordination of complex, diverse systems will be an ongoing challenge, particularly for the U.S. military, which coincidentally has to adapt to new threats and responsibilities after more than half a century of following the paradigm set by World War II and the Cold War. Information is now assuming greater strategic importance than ever before in warfare and other military operations, and so the wide deployment of cost-effective, state-of-the-art wireless communications systems has become particularly critical. The present situation recalls previous epochs in which breakthroughs in hardware—aircraft carriers, jet aircraft, tactical missiles, nuclear weapons—have led to radical revisions of military doctrine. The next great revolution in military affairs could be shaped by information technology: global communications, ubiquitous sensors, precision location, and pervasive information processing. Advanced command, control, communications, computing, and intelligence (C4I) systems could make it possible to monitor an adversary, target specific threats, and neutralize them with the best available weapon. Admiral William Owens, former vice chairman of the Joint Chiefs of Staff, has called such an integrated capability a ''system of systems." Using such a system, a commander could observe the battle from a computer screen, select the most threatening targets, and destroy them with the press of a button. Battles would be won by the side with the best information, not necessarily the one with the largest battalions. But unlike the military hardware of the past, information technology is advancing at a breakneck pace in a worldwide marketplace, driven not by military requirements but by the industrial and consumer sectors. Increasingly these technologies are available worldwide, and the best technology is no longer limited to U.S. manufacture and control. Highly accurate position data transmitted by satellite are now available to any yachtsman. High-resolution satellite photographs are for sale around the

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Page 13 world. Any nation can purchase the latest communications gadgets from the electronics stores of Tokyo. Therein lies the challenge for the U.S. military: how to exploit the advances in affordable technology fueled by worldwide consumer demand while also maintaining technical capabilities that significantly exceed those of any potential adversary. 1.2 Historical Perspective Throughout most of history, the evolution of communications technologies has been intimately intertwined with military needs and applications. Some of the earliest government-sponsored R&D projects focused on communications technologies that enabled command and control. A synergistic relationship then evolved between the military and commercial sectors that accelerated the technology development process. Now large corporations develop the latest communications technologies for international industrial and consumer markets shaped by government regulation and international agreements. World trade in telecommunications equipment and services was valued at $115 billion in 1996 (The Economist, 1997). Modern wireless communication systems are rooted in telephony and radio technologies dating back to the end of the nineteenth century and the older telegraphy systems dating back to the eighteenth century. Wireless systems are also influenced by and increasingly linked to much newer communications capabilities, such as the Internet, which originated in the 1960s. All wireless systems transmit signals over the air using different frequency transmission bands designated by government regulation. Table 1-1 provides an overview of wireless RF communications systems and services and the frequency bands they use.1Each frequency band has both advantages and disadvantages. At low frequencies the signal propagates along the ground; attenuation is low but atmospheric noise levels are high. Low frequencies cannot carry enough information for video services. At higher frequencies there is less atmospheric noise but more attenuation, and a clear line of sight is needed between the transmitter and receiver because the signals cannot penetrate objects. These frequencies offer greater bandwidth, or channel capacity. 1.2.1 Communications Before the Industrial Age The annals of antiquity offer examples of muscle-powered communications: human runners, homing pigeons, and horse relays. Perhaps the earliest communications infrastructure was the road network of Rome, which carried not only the legions needed to enforce the emperor's will

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Page 14 TABLE 1-1 Overview of Wireless Radio Frequency Communications Systems and Services Frequency Banda Communications Applications Characteristics 3–30 kHz (very low, or VLF); 30–300 kHz (low, or LF) Long-range navigation, marine radio beacons Low attenuation, high atmospheric noise 300–3000 kHz (medium, or MF); 3–30 MHz (high, or HF) Maritime radio, AM radio, telephone, telegraph, facsimile Attenuation varies, noise drops at 30 MHz 30–300 MHz (very high, or VHF); 0.3–3 GHz (ultrahigh, or UHF) VHF television, FM two-way radio, UHF television, radar Cosmic noise, line-of-sight propagation 3–30 GHz (superhigh, or SHF) Satellite, radar, microwave Atmospheric attenuation 30–300 GHz (extremely high, or EHF) Experimental satellite, radar Line-of-sight propagation aFrequencies are in kilohertz (kHz), megahertz (MHz), and gigahertz (GHz). SOURCE: Adapted from Couch (1995).

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Page 15 but also messengers to direct forces far from the capital. Ancient societies also developed systems that obviated the need for physical delivery of information. These systems operated within line-of-sight distances (later extended by telescope): smoke signals, torch signaling, flashing mirrors, signal flares, and semaphore flags (Holzman and Pehrson, 1995). Observation stations were established along hilltops or roads to relay messages across great distances. 1.2.2 Telegraphy The first comprehensive infrastructure for transmitting messages faster than the fastest form of transportation was the optical telegraph, developed in 1793. Napoleon considered this his secret weapon because it brought him news in Paris and allowed him to control his armies beyond the borders of France. The optical telegraph consisted of a set of articulated arms that encoded hundreds of symbols in defined positions. Under a military contract, the signaling stations were deployed on strategic hilltops throughout France, linking Paris to its frontiers. By the mid-1800s, 556 stations enabled transmissions across more than 5,000 kilometers (km). The optical telegraph was superseded by the electrical telegraph in 1838, when Samuel Morse developed his dot-and-dash code. Now information could be transmitted beyond visible distances without significant delay. In an 1844 demonstration on a government-funded research testbed, Morse sent the message "What Hath God Wrought?" from Baltimore to the U.S. Capitol (Bray, 1995). The rapid deployment of telegraphic lines around the world was driven by the need of nineteenth-century European powers to communicate with their colonial possessions. High-risk technology investments were required. After the use of rubber coating was demonstrated on cables deployed across the Rhine River, the first transatlantic cable was laid in 1858, but it failed within months. A new cable designed by Lord Kelvin was laid in 1866 and operated successfully on a continuous basis. The result was a rapidly expanding telegraphic network that reached every corner of the globe. By 1870, Great Britain communicated directly with North America, Europe, the Middle East, and India. Other nations scrambled to duplicate that system's global reach, for no nation could trust its critical command messages to the telegraphic lines of a foreign power. 1.2.3 Early Wireless Within a few decades of its widespread deployment, telegraphy began to lose customers to a new technology—radio. In 1895 Guglielmo

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Page 16 Marconi demonstrated that electromagnetic radiation could be detected at a distance. Great Britain's Royal Navy was an early and enthusiastic customer of the company that Marconi created to develop radio communications. In 1901 Marconi bridged the Atlantic Ocean by radio, and regular commercial service was initiated in 1907 (Masini, 1996). The importance of this new technology became evident with the onset of World War I. Soon after hostilities began, the British cut Germany's overseas telegraphic cables and destroyed its radio stations. Then Germany cut Britain's overland cables to India and those crossing the Baltic to Russia. Britain enlisted Marconi to put together a string of radio stations quickly to reestablish communications with its overseas possessions. The original Marconi radios were soon replaced by more advanced equipment that exploited the vacuum tube's capability to amplify signals and operate at higher frequencies than did older systems. In 1915 the first wireless voice transmission between New York and San Francisco signaled the beginning of the convergence of radio and telephony. The first commercial radio broadcast followed in 1920 (Lewis, 1993). The use of higher frequencies (called shortwaves) exploited the ionosphere as a reflector, greatly increasing the range of communications. By World War II, shortwave radio had developed to the point where small radio sets could be installed in trucks or jeeps or carried by a single soldier. The first portable two-way radio, the Handie-Talkie, appeared in 1940. Two-way mobile communications on a large scale revolutionized warfare, allowing for mobile operations coordinated over large areas. 1.2.4 Telephony The telephone was first demonstrated in 1876. A telephone network based on mechanical switches and copper wires then grew rapidly. The high cost of the cables limited the number of conversations possible at any one time; as demand increased, multiplexing techniques, such as time division and frequency division, were developed. A mix of independent operators ran telephone services in the early days. Subscribers to different services could not call each other even when in the same town. In 1913 the U.S. government allowed American Telephone and Telegraph (AT&T) to assume control of the national telephone network in return for becoming a regulated monopoly delivering "universal" service. Yet it was not until the 1950s that unified network signaling was offered to subscribers, allowing them to make direct-dial long-distance telephone calls (Calhoun, 1992). Since then, the rapid extension of the long-distance telephone network has been made possible by advances in photonic communications and network control technologies.

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Page 17 1.2.5 Communications Satellites The concept of using geosynchronous satellites for communications purposes was first suggested in 1945 by the science fiction writer Arthur C. Clarke, then employed at Britain's Royal Aircraft Establishment, part of the Ministry of Defence. Satellites of this type are positioned above the equator and move in synch with Earth's rotation. In 1954 J.R. Pierce at AT&T's Bell Telephone Laboratories developed the concept of orbital radio relays and identified the key design issues for satellites: passive versus active transmission, station keeping, attitude control, and remote vehicle control (Bray, 1995). Pierce advocated an approach of reaching geostationary orbit in successive stages of technology development, starting with nonsynchronous, low-orbit satellites. Hughes Aircraft Company advocated a geostationary concept based on the company's patented station-keeping techniques. In 1957 the Soviet Union launched Sputnik, the first satellite to be placed in orbit. Amateur radio operators were able to pick up its low-power transmissions all over the world. In 1960 the National Aeronautics and Space Administration (NASA) and Bell Laboratories launched the first U.S. communications satellite, Echo-1, in a low Earth orbit. The first satellite-based voice message was sent by President Dwight Eisenhower using passive transmission techniques. The next advance in satellite technology was the successful launch of the TELSTAR system by NASA and Bell Laboratories. Using active transmission technology TELSTAR delivered the first television transmission across the Atlantic in 1962. Because it was placed in an elliptical orbit that varied from low to medium altitudes, the satellite was visible contemporaneously to Earth stations on both sides of the Atlantic for only about 30 minutes at a time. Clearly geostationary orbits were desirable if satellites were to be used for continuous telephone and television communications across long distances. In 1963 Hughes Aircraft and NASA achieved geosynchronous orbit (known as GEO today) with the successful launch of the SYNCOM satellite. The satellite was placed in an orbit of approximately 36,210 km, a distance that allowed it to remain stationary over a given point on Earth's surface. SYNCOM led the way for the next several decades of satellite systems by demonstrating that synchronous orbit was achievable, and that station keeping and attitude control were feasible. Today most satellites, both military and commercial, are of the GEO variety. COMSAT was formed by an act of Congress in 1962 and represented U.S. commercial interests in satellite technology development at Intelsat, established in 1964 as an international, government-chartered organization to coordinate worldwide satellite communications issues. INTELSAT-II (Early Bird) was launched into a geosynchronous orbit in

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Page 18 1965 and supported 240 telephone links or one television channel. Channel capacities are now measured in the tens of thousands of voice channels (the INTELSAT-VI, launched in 1987, supports 80,000 voice channels). The first military satellites, the DSCS-I group, were launched by the U.S. Air Force in 1966. Three launches placed 26 lightweight (100-pound) satellites in near-geosynchronous orbit. These systems supported digital voice and data communications using spread-spectrum technology (an important signal-processing approach discussed extensively in Chapter 2). The satellites were replaced in the 1970s by the DSCS-II group, which increased channel capacity by using spot-beam antennas with high gain to boost the received power. The first cross-linked military satellites, the LES 8/9, were launched in 1976. This demonstration fostered a vision of space-based architectures—without vulnerable ground relays—for communication, navigation, surveillance, and reconnaissance. Satellites offer several advantages over land-based communications systems. Rapid, two-way communications can be established over wide areas with only a single relay in space, and global coverage with only a few relay hops. Earth stations can now be set up and moved quickly. Furthermore, satellite systems are virtually immune to impairments such as multipath fading (channel impairments are discussed in Chapter 2). But with the rapid deployment of undersea fiber-optic links, the use of satellite channels for telephony has been on the decline. The high capacity of fiber provides for competitive costs, which, combined with low latency, have attracted consumers. The future of the satellite industry depends on the emergence of applications other than fixed telephony channels. A new generation of satellite systems is being deployed to provide mobile telephone services (see Section 1.5). 1.2.6 Mobile Radio and the Origins of Cellular Telephony The early development of mobile radio was driven by public safety needs. In 1921 Detroit became the first city to experiment with radio-dispatched police cars. However, transmission from vehicles was limited by the difficulty of producing small, low-power transmitters suitable for use in automobiles. Two-way systems were first deployed in Bayonne, New Jersey, in the 1930s. The system operated in "push-to-talk" (i.e., half-duplex) mode; simultaneous transmission and reception, or full-duplex mode, was not possible at the time (Calhoun, 1988). Frequency modulation (FM), invented in 1935, virtually eliminated background static while reducing the need for high transmission power, thus enabling the development of low-power transmitters and receivers for use in vehicles. World War II stimulated commercial FM manufacturing capacity and the rapid development of mobile radio technology. The

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Page 19 need for thousands of portable communicators accelerated advances in system packaging and reliability and reduced costs. In 1946 public mobile telephone service was introduced in 25 cities across the United States. The initial systems used a central transmitter to cover a metropolitan area. The inefficient use of spectrum and the coarseness of the electronic filters severely limited capacity: Thirty years after the introduction of mobile telephone service the New York system could support only 543 users. A solution to this problem emerged in the 1970s when researchers at Bell Laboratories developed the concept of the cellular telephone system, in which a geographical area is divided into adjacent, non-overlapping, hexagonal-shaped "cells." Each cell has its own transmitter and receiver (called a base station) to communicate with the mobile units in that cell; a mobile switching station coordinates the handoff of mobile units crossing cell boundaries. Throughout the geographical area, portions of the radio spectrum are reused, greatly expanding system capacity but also increasing infrastructure complexity and cost. In the years following the establishment of the mobile telephone service, AT&T submitted numerous proposals to the Federal Communications Commission (FCC) for a dedicated block of spectrum for mobile communications. Other than allowing experimental systems in Chicago and Washington, D.C., the FCC made no allocations for mobile systems until 1983, when the first commercial cellular system—the advanced mobile phone system (AMPS)—was established in Chicago. Cellular technology became highly successful commercially with the miniaturization of subscriber handsets. 1.2.7 The Internet and Packet Radio The original concepts underlying the Internet were developed in the mid-1960s at what is now the Defense Advanced Research Projects Agency (DARPA), then known as ARPA. The original application was the ARPANET, which was established in 1969 to provide survivable computer communications networks. The ARPANET relied heavily on packet switching concepts developed in the 1960s at the Massachusetts Institute of Technology, the RAND Corporation, and Great Britain's National Physical Laboratory (Kahn et al., 1978; Hafner and Lyon, 1996; Leiner et al., 1997). This approach was a departure from the circuit-switching systems used in telephone networks (see Box 1-1). The first ARPANET node was located at the University of California at Los Angeles. Additional nodes were soon established at Stanford Research Institute (now SRI International), the University of California at Santa Barbara, and the University of Utah. The development of a host-to-host protocol,
2the network control protocol (NCP), followed in 1970,

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BOX 1-1 Circuit Switching Versus Packet Switching Telephone systems are based on a connection-oriented or circuit-switched model in which connections are fixed for the duration of a call. Such systems are inefficient when transmission occurs in short bursts separated by long pauses. Packet switching replaces the centralized switches with distributed routers, each with multiple connections to adjacent routers. Messages are divided into "packets" that are independently routed on a hop-by-hop ba is. Such an approach allows messages to be multiplexed over the available paths on a statistically determined basis, gracefully adapting the transmissions to traffic level, and optimizing the use of existing link capacity without pre-allocating link bandwidth. enabling network users to develop applications. At the same time, the ALOHA Project at the University of Hawaii was investigating packet-switched networks over fixed-site radio links. The ALOHANET began operating in 1970, providing the first demonstration of packet radio access in a data network (Abramson, 1985). The contention protocols used in ALOHANET served as the basis for the "carrier-sense multiple access with collision detection" (CSMA/CD) protocols used in the Ethernet local area network (LAN) developed at Xerox Palo Alto Research Center in 1973. The widespread use of Ethernet LANs to connect personal computers (PCs) and workstations allowed broad access to the Internet, a term that emerged in the late 1970s with the design of the Internet protocol (IP). The need to link wired, packet radio, and satellite networks led to the specifications for the transmission control protocol (TCP), which replaced NCP and shifted the responsibility for transmission from the network to the end hosts, thereby enabling the protocol to operate no matter how unreliable the underlying links.3 The development of microprocessors, surface acoustic wave filters, and communications protocols for intelligent management of the shared radio channel contributed to the advancement of packet radio technology in the 1970s. In 1972 ARPA launched the Packet Radio Program, aimed at developing techniques for the mobile battlefield, and SATNet, an experimental satellite network. In 1983 ARPA launched a second-generation packet radio program, Survivable Adaptive Networks, to demonstrate how packet radio networks could be scaled up to encompass much larger numbers of nodes and operate in the harsh environment likely to be encountered on the mobile battlefield.

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Page 45 TABLE 1-7 Selected Big Low Earth Orbit (LEO)/Medium Earth Orbit (MEO) Systems System Organization Number of Satellites Orbit Coverage Data Rate (kbps)a Year Operational Globalstar Loral/QUALCOMM 48 LEO Global 9.6 1998 Iridium Motorola 66 LEO Global 2.4 1998 Odyssey TRW 12 MEO Global 9.6 1998 Teledesic Teledesic 240 LEO Global 20–2,000 2002 ICO ICO Global Communications 10 MEO Global 2.4 1999 Archimedes European Space Agency 5–6 MEO Europe, Asia, Canada 256 After 2000 a Kilobits per second. SOURCE: Reprinted from Abrishamkar and Siveski (1996) with permission. Copyright © 1996 by IEEE.

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Page 46 • Interactive services (terminal access to host, remote LAN access, games); and • Multicast service (subscription information services, law enforcement, private bulletin boards). The first commercial mobile data network was Ardis, a private network developed in 1983 by IBM Corporation and Motorola to enable IBM to provide computing facilities in the field. By 1990 Ardis was deployed in more than 400 metropolitan areas and 10,700 cities and towns using 1,300 base stations. By 1994 Ardis (since then owned by Motorola) provided nationwide roaming for approximately 35,000 users, at a rate of 45 million messages per month, and a data rate of 19.2 kbps. In 1986, Swedish Telecomm and Ericsson Radio Systems AB introduced Mobitex and deployed it in Sweden. This system is available in the United States, Norway, Finland, Great Britain, the Netherlands, and France. The system supports a data rate of 8 Mbps and nationwide roaming (international roaming is planned). This service is distributed by RAM Mobile Data in the United States, where by 1994 it had 12,000 subscribers. A total of 840 base stations are connected to 40 switching centers to cover 100 metropolitan areas and 6,300 cities and towns. Cellular digital packet data (CDPD) technology was developed by IBM, which together with nine operating companies formed the CDPD Forum to develop an open standard and multivendor environment for a packet-switched network using the physical infrastructure and frequency bands of the AMPS systems. The CDPD specification was completed in 1993 with key contributions from IBM, McCaw Cellular Communications, Inc., and Pacific Communications Sciences, Inc. Deployment of the 19.2-kbps CDPD infrastructure, designed to make use of idle channels in analog cellular systems, commenced in 1995. In the 1990s Metricom, Inc., developed a metropolitan-area network that was deployed first in the San Francisco Bay area and then in Washington, D.C. The signaling rate of this system is advertised at 100 kbps but the actual data rate is substantially slower. The Metricom system uses ''frequency hopping" spread-spectrum (FHSS) technology in the lower frequencies (around 900 MHz) of the unlicensed industrial, scientific, and medical (ISM) bands.11 In 1996 the European Telecommunications Standards Institute (ETSI) standard for mobile data services, trans-European trunked radio (TETRA), was completed. It is currently being used primarily for public safety purposes. Work is in progress to enhance the digital cellular and personal communications technologies. More recently, the digital cellular standards (GSM, IS-95, PHS, PACS, and IS-136) have been updated to support packet-switched mobile data services at a variety of data rates. Key features

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Page 47 of existing mobile data services are shown in Table 1-8. Although many services are available, the mobile data market has grown more slowly than have voice services. 1.7 Wireless Local Area Networks Wireless LANs provide data rates exceeding 1 Mbps in coverage areas with dimensions on the order of tens of meters. They are used for a variety of applications, including the following: • LAN extensions in hospitals, factory floors, branch offices, and offices with wiring difficulties; • Cross-building inter-LAN bridges that serve as point-to-point, high-speed links connecting separate LANs located within a few miles of each other; • Temporary ad hoc networks used in conference registration, campaign headquarters, and military camps; • Temporary wireless access to a wired LAN from a portable device such as a laptop computer; and • Access to centralized computing facilities of a shipboard or research facility through a wireless device such as a notepad computer. In 1990 the Institute of Electrical and Electronics Engineers (IEEE) formed a committee to develop a standard for wireless LANs operating at 1 and 2 Mbps. In 1992 the ETSI chartered a committee to develop a standard for high-performance radio LANs (HIPERLAN) operating at 20 Mbps. Table 1-9 indicates the technical features of various LAN products (including some that use the infrared portion of the spectrum and are therefore not examined in detail in this report). The market for wireless LAN products is growing rapidly but not nearly as fast as the market for wireless voice applications. The $200 million market for wireless LANs is tiny compared to the cellular industry, which is worth billions (Wickelgren, 1996). 1.8 Comparison Of International Research, Development, And Deployment Strategies Commercial wireless technologies have followed divergent evolutionary paths in different parts of the world. For example, strong contrasts are evident in the transition from first-generation cellular systems to second-generation systems in the United States and Europe. At first a single U.S. system was used for analog cellular communications, AMPS, and every cellular telephone in the United States and Canada could communicate

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Page 48 TABLE 1-8 Mobile Data Services System Ardis Mobitex CDPDa TETRAb Metricom Frequency band (MHz)c 800 bands; 45 kHzd sep. 935–940, 896–961 869–894, 824–849 380–383, 390–393 902–928 (ISMe bands) Channel bit rate (kbps)f 19.2 8.0 19.2 36 100 RFg channel spacing (kHz) 25 12.5 30 25 160 Channel access/ multiuser access FDMAh/ALOHA Slotted ALOHA FDMA/ALOHA ALOHA FHSSi/BTMAj aCellular digital packet data. bTrans-European trunked radio. cMegahertz. dKilohertz. eIndustrial, scientific, and medical. fKilobits per second. gRadio frequency. hFrequency division multiple access. iFrequency hopping spread spectrum. jBusy tone multiple access. SOURCE: Reprinted from Cox (1995) with permission. Copyright © 1995 by IEEE.

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Page 49 TABLE 1-9 Wireless Local Area Network Technologies Technology DFIRa DBIRb RFc DSSSd FHSSe Channel bit rate (Mbps)f 1–4 10–155 5–10 2–20 1–3 Mobility Stationary / portable Stationary with LOSg Stationary Stationary / portable Portable Range (meters) 15–60 30 10–40 30–200 30–100 Frequency bands Infrared Infrared 18 GHzh, ISMi ISM ISM Systems (companies) Spectrixlite (Spectrix Corp.); Photolink (Photonics) Infralan (InfraLAN); UWIN (Jolt Ltd.) Altair (Motorola, Inc.); Fast Wave (Southwest Microwave, Inc.); RediCARDrf (Data Race, Inc.) Roamabout (Digital Equipment Corp.); ARLAN (AiroNet Wireless Communications); WaveLAN (Lucent Technologies); INTERSECT (Persoft, Inc.); AIRLAN (Solectek Corp.); RangeLAN (Proxim); FreePort (WinData); PRISM (Harris Corp.) Range-LAN2 (Proxim); PortLAN (RDC Networks); Netwave (Xircom) aDiffused infrared. bDirected-beam infrared. cRadio frequency. dDirect sequence spread spectrum. eFrequency hopping spread spectrum. fMegabits per second. gLine of sight. hGigahertz. iIndustrial, scientific, and medical. SOURCES: Reproduced from material in Cox (1995) and Pahlavan et al. (1995).

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Page 50 with every base station. By contrast, European users were faced with a complex mixture of incompatible analog systems. To maintain mobile telephone service, an international traveler in Europe needed up to five different telephones. The situation was reversed by second-generation systems. Now there is a single digital technology, GSM, deployed throughout Europe (and in more than 100 countries worldwide), whereas the United States has become a technology battleground for three competitors: GSM (DSC-1900), TDMA (IS-136), and CDMA (IS-95). The differences in technology evolution are due in large measure to different government policies in Europe, the United States, and Japan, the world's principal sources of wireless technologies. Three types of government policies influence developments in wireless systems: policies on radio spectrum regulation, approaches to R&D, and telecommunications industry structure. The reasons for the shifts in the above example can be found primarily in changes in spectrum regulation policies adopted in the 1980s. In establishing first-generation systems in the United States in the late 1970s, the FCC regulated four properties of a radio system: noninterference, quality, efficiency, and interoperability. In the 1980s, deregulation was in vogue and the scope of the FCC's authority was restricted to noninterference; the other properties were deemed commercial issues to be settled in the marketplace. Although this policy stimulated innovation in the U.S. manufacturing industry, it also meant that operating companies had to choose among various competing technologies. In Europe, the main trend in government regulation in the 1980s was a move from national authority to multinational regulation under the aegis of the European Community (EC; now the European Union [EU]). The EC had a strong interest in establishing continental standards for common products and services, including electric plugs and telephone dialing conventions. In this context the notion of a telephone that could be used throughout Europe had a strong appeal. To advance this notion, the EC offered new spectrum for cellular service on the condition that the operating industries of participating countries agree on a single standard. Attracted by the availability of free spectrum, operating companies (many of them government-owned) in 15 countries put aside national rivalries and adopted the GSM standard. Thus, a new pattern of technical cooperation was established in Europe. This cooperation was reinforced by the European Commission (the administrative unit of the EU), which funded cooperative precompetitive research focusing on advanced communications systems, first in the Research for Advanced Communications in Europe (RACE) program and then in the Advanced Communications Technologies and Services (ACTS) program. In both programs a consortium of companies and universities

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Page 51 performs the research. Spectrum management rules continue to prescribe a single standard for each service, meaning that an industry consensus is required before a standard is introduced. Once a technology is established, companies enter the competitive phase of product development and marketing. This process promotes a thorough investigation of technologies prior to standardization and assures economies of scale when commercial service begins. In preparation for UMTS, scheduled for initial deployment in 2002, extensive R&D and evaluation of competing prototypes have been under way since 1994. All of this activity will provide European industry with a strong technical base for realizing the goals for mobile communications in the first decade of the next century. The U.S. approach to communications technology R&D is much more competitive. Individual companies perform much of this research in the context of their product marketing plans. Coordination takes place within diverse standards organizations such as the Telecommunications Industry Association, IEEE, and American National Standards Institute. Some interaction also takes place in the GloMo program, which brings together universities and industry to fill specific technology gaps identified by DARPA program managers. But for the most part standards setting is a competitive rather than cooperative process, with each company or group of companies striving to protect commercial interests. The FCC rules for spectrum management allow license holders to transmit any signals, subject only to constraints on interference with the signals of other license holders. Similar flexibility is extended to unlicensed transmissions. As a consequence, there are multiple competing standards (seven in the case of wideband personal communications) for wireless service in the United States. Government policies on industry structure also strongly influence technology development. After the FCC issued cellular operating licenses, most of the companies that began offering cellular service had limited technical resources and relied almost entirely on vendors and consultants for technical expertise. Even the cellular subsidiaries of the regional Bell operating companies had to build a new base of expertise: Under the terms of the consent decree that broke up AT&T in 1984, these cellular companies had no access to the abundant technical resources of Bellcore, the research unit of the regional Bell companies. In this environment, much of the new wireless communications technology in the United States has come from the manufacturing industry, with the result that proprietary rather than open network-interface standards have proliferated. The published technical standards for wireless communications were at first confined to the air interface between terminals and base stations. Eventually the industry adopted a standard for intersystem operation to facilitate roaming. Many other interfaces, especially those between switching

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Page 52 centers and base stations, remain proprietary but the situation is changing to allow fully open systems. By contrast, the European cellular operating industry has been dominated by national telephone monopolies. These companies have strong research laboratories that participate fully in technology creation and standards setting. To gain the advantage of flexibility in equipment procurement, operating companies favor mandatory open interfaces, a preference reflected in the GSM standard. Little has been published concerning the factors that influence the evolution of wireless communications technology in Japan. In recent years NTT, the dominant telecommunications operating company, has provided a strong coordinating mechanism for creating and standardizing new technology. The biggest success has been PHS, which entered commercial service in 1995 and attracted 4 million subscribers in its first year of operation. The initial R&D for PHS was conducted by NTT, but it licenses many manufacturers to offer PHS equipment. Now many Japanese companies are cooperating in a study of wideband CDMA technology for third-generation systems. A joint experimental trial of one system is scheduled for the end of 1997. In addition to corporate R&D, a government organization, Research and Development Center for Radio Systems, is a significant source of wireless communications technology in Japan. Worldwide efforts to guide the evolution of wireless communications technology come together in the IMT-2000 project. National delegations to IMT-2000 reflect their country's policies: The U.S. delegation pushes for diversity,
12the Europeans advocate a structure favorable to UMTS and its descendants, and the Japanese delegation favors convergence to a small number of worldwide standards. Other countries assert their own service needs, which in some cases can be met by mobile communications satellites and in other cases by wireless local loops. 1.9 Summary And Report Organization The history of wireless communications suggests a number of key points to be considered in evaluating potential future strategies for the DOD and DARPA. Wireless technology has now evolved to a point where the goal of "anytime, anywhere" communications is within reach. Since 1980 consumer demand for cordless and cellular telephones has driven rapid growth in wireless services, especially for voice communications. Wireless data services have not taken off as yet although expectations are high, given the growth of Internet applications. Extensive research is under way to develop third-generation commercial wireless systems, which are expected to be in place before 2010. These trends suggest that

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Page 53 the DOD will continue to have an ample selection of advanced commercial wireless technologies from which to choose. The DOD, which currently uses a variety of wireless systems based on 1970s and 1980s technology, is relying increasingly on commercial wireless products to cope with reductions in defense budgets and the growing need for flexible systems that can be deployed rapidly. In the Gulf War, the DOD used commercial equipment such as GPS receivers and INMARSAT links and found that performance was comparable to that of technologies designed explicitly to meet military needs. However, the DOD will continue to have unique needs for security, interoperability, and other features that might not be met by commercial products. The gaps between commercial technologies and military needs are difficult to identify precisely because, although the DOD has defined its vision for future untethered systems in general terms, projected operational needs have apparently not been translated into technical specifications that conform to the capabilities of commercial products. The GloMo program and other military R&D efforts are attempting to meet DOD's future communications needs and have produced some useful results. However, none of these programs has adopted a systems approach to the problem, most notably with respect to the design of a network architecture. There may be other unmet needs as well; however, the committee based its work on first principles rather than an assessment of GloMo. A new strategy may be needed to identify the needs more specifically as a basis for determining where to focus DARPA's R&D efforts and where commercial products will suffice. The effort to evaluate commercial technologies in light of defense needs will be complicated by the characteristics of the U.S. marketplace. In Europe there is a single standard (GSM) for digital wireless communications, and precompetitive research on new wireless technologies is carried out in cooperative, government-funded programs. The U.S. wireless market features a mixture of competing standards, and most technology R&D is conducted by individual companies. This environment forces operators to choose from an assortment of competing technologies. The remainder of this report is an attempt to help the DOD devise strategies for making those choices. Chapter 2 provides technical background on the many issues that need to be addressed in designing wireless communications systems, which are extremely complex. The highly technical discussion may not interest all readers but is fundamental to any informed analysis of wireless systems. Chapter 3 explores the opportunities for and barriers to synergy between the military and commercial sectors in the development of wireless technologies. Chapter 4 integrates all the information presented in this report to provide a set of recommendations for the DOD and DARPA.

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Page 54 Notes 1. This report does not address unguided optical communications systems, which use the 103–107 gigahertz frequency band (infrared, visible, and ultraviolet light), because the commercial products that operate in these bands are designed for indoor applications and therefore would not be of great use in military applications. 2. A protocol is a set of rules, encoded in software, for performing specific functions. 3. The developments since the mid-1970s, when the use of computer networks moved beyond the ARPA research community, paved the way for commercial services. The CSNet project, funded by the National Science Foundation (NSF) for the computer science community, eventually led to the NSFNET and a dramatic increase in the number of interconnected nodes. The commercialization of Internet service was symbolized by the decommissioning of the ARPANET in 1990 and privatization of the NSFNET in 1995. 4. Two types of codes are used to spread the signal. A long code is reserved for use by the military to obtain location information within a few meters of accuracy and timing information within 100 nanoseconds. A shorter code is used by commercial systems to obtain location information accurate to within 100 meters. 5. A fourth digital modulation technique, based on Motorola's iDEN technology, is used by some specialized U.S. mobile radio services in the lower 800-MHz band to provide cellular-like voice, trunked radio, paging, and messaging services. 6. One integrated solution not addressed in detail in this report is the new generation of public safety radio networks. These systems are used in both the military and commercial sectors for applications such as law enforcement and fire fighting. Until recently these systems were characterized simply as 25-kilohertz FM voice radios and 9.6-kbps modems. In the past a municipal law enforcement radio system typically was deployed as a redundant overlay of towers and repeaters separate from the radio systems operated by fire, health, highway, and other municipal departments. Today's tight budgets often force municipalities to pool departmental funds to upgrade public safety radios and establish a single system with enough capacity to meet every user's needs. To assist in this process the Association of Public Safety Communication Officers (APCO), which includes law enforcement, highway, forestry, health, and many other municipal and federal users, recently initiated an ambitious program called Project-25 to reduce the cost of next-generation radios. APCO Project-25 seeks to reduce user dependence on proprietary radios from a single manufacturer (generally the system installer) and introduce cost competition in the upgrading and replacement market at the municipality level. The strategy is to standardize a digital-modulation radio, which would be described as APCO Project-25 compliant, thus opening up public radio purchasing to a variety of competing manufacturers. Some radios that are APCO Project-25 compliant are now available and are being adopted by the Federal Law Enforcement Radio Users Group (representing radio users in the Federal Bureau of Investigation, Drug Enforcement Agency, Secret

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Page 55 Service, Department of the Treasury, and other civilian agencies). The APCO Project-25 process has encouraged an unprecedented level of cooperation among municipal radio users. 7. These activities are carried out by the ITU Radiocommunication Sector (ITU-R) Working Party 8/13, later renamed ITU-R Task Group 8/1. 8. The implementation of standards based on IMT-2000 in Japan clearly would give Japanese companies early experience with the technology and perhaps position them to dominate future world markets for IMT-2000 products. 9. Although optical communications systems are not addressed in detail in this report, in large part because the commercial research focuses on indoor applications, the advantages of laser systems need to be mentioned. A laser produces optical radiation by stimulating emissions from an electronic or chemical material. Unlike light produced by incandescent or fluorescent sources, the resultant beam is coherent and exhibits extremely low angular divergence, properties that enable transmissions spanning great distances (i.e., thousands of miles). The data, voice, images, or other signals are modulated on a beam of light, which is detected by an optical receiver and decoded. The transmitter and receiver need to be in direct visual contact, and so the laser beam is steered in the appropriate direction using mirrors or other optical elements. Laser communications systems offer several advantages over RF systems. The main advantage is high capacity: Systems now under development will support transmissions in the range of hundreds of megabits per second, with systems under consideration attaining the gigabits-per-second range. Another advantage is the low power requirement for point-to-point communications (orders of magnitude lower than RF systems). All the energy is focused into a very narrow beam because the physical dispersion of a laser beam in space is minimal. Furthermore, laser communications systems offer security benefits because almost no energy is diffused outside the laser beam, which is therefore not easily detected by an adversary. This combination of features makes laser communications systems attractive for secure transmissions between hub points in mobile, dynamically changing environments (e.g., between base stations on vehicle-mounted switching facilities). However, laser systems are sensitive to interference from other light sources, such as the sun, and any obstructions of the visual link by dust, rain, or fog. There is also a risk of damage to the eyes of unprotected observers. Finally, components for laser-based systems are much more expensive than those for RF systems and therefore are unlikely to penetrate the commercial market for some time. 10. These activities are carried out by the ITU Telecommunications Sector, Study Group 11. 11. The ISM bands (at 902–928 MHz, 2400–2483 MHz, and 5700–5850 MHz) are available for any wireless device that uses less than 1 watt of transmit power. 12. The United States participates in the IMT-2000 process in Task Group 8/1 through a delegation led by the FCC.