The Evolution of Untethered Communications (1997) / Chapter Skim
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1 PAST, PRESENT, AND FUTURE
1 PAST, PRESENT, AND FUTURE
Pages 10-55
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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.
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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.
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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.
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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.
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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.
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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.
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communications satellite, Echo-l, in a low Earth orbit. The first satellite-based voice message was sent by President Dwight Eisenhower using passive transmission techniques.
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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.
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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)
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, 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.
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Combat net radios, for example, are designed for communications within a battle group. 1.3 MILITARY WIRELESS SYSTEMS AND RESEARCH 1.3.1 Terrestrial Systems Radio communications technology is widely used by U.S.
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net ground and airborne radio system (SINCGARS) has been updated with recent technology, including programmable microprocessors, application-specific integrated circuits (ASICs)
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The U.S. Department of Defense established IP as the underlying "building code" for the Army, making a commitment to migrate all communications networks to the same basic structure as the Internet to position the military to integrate and leverage the advances in commercial information technologies.
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is designed using modern radio technology, perhaps even including software-defined radios (see Section 1.3.3.2~. High data rates sufficient for multimedia transmissions can be achieved only with the most advanced technology.
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Although launching and upkeep of the entire fleet of satellites are paid for by the United States, commercial GPS receivers were used by both sides in the Gulf War. 1.3.3 Research Initiatives in Untethered Communications The DOD's vision for future communications systems is typically expressed in general terms, such as "multimedia to the foxhole" (see Box 1-3~.
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As an alternative, some general DOD requirements can be inferred from military plans and the known technical capabilities of existing and emerging communications technologies. For example, future military wireless systems will require high data rates the long-range goal is at least 10 Mbps and the capability to transmit over broad and variable frequency bands (some experimental radios are designed to span frequencies from 2 MHz to 2 GHz)
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This effort addresses how best to operate across a heterogeneous mix of underlying networks, both wireless and wired. Research areas include extensions to TCP/IP that will enable mobile users to access the Internet, satellite extensions to the Internet, and overlay wireless networking that supports mobility across diverse wireless subnetworks inside buildings and in the wider area.
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The most prominent of these initiatives is the SpeakEASY program sponsored by DARPA, the Air Force Rome Laboratory, and the Army Communication Electronics Command. The key objective of SpeakEASY is to change the paradigm for military radios.
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capabilities including those of combat net radios SINCGARS and Have Quick (a UHF system designed to provide secure air-to-air and air-to-ground communications with AT capabilities) and commercial avionics radios such as GPS, VHF air to ground, and the aircraft communications addressing and reporting system.
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This program includes projects that create models and a library of computer programs for simulating mobility, radio propagation, and teletraffic patterns in large-scale wireless networks. 1.4 COMMERCIAL TERRESTRIAL MOBILE TELEPHONE SYSTEMS AND SERVICES Commercial wireless communications systems have exhibited remarkable growth over the past decade (see Figure 1-2~.
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In addition to terrestrial mobile telephone systems, other commercial wireless systems include satellite communications, mobile data systems, and wireless local area networks (LANs)
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This standard supports clear communication and inexpensive mobile telephones, but the transmissions are easy to intercept on a standard radio receiver and therefore are susceptible to eavesdropping. As of late 1996, 88 percent of all cellular telephones in the United States used the AMPS standard (digi
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technique.5 The GSM standard, which has been adopted in more than 100 countries, specifies a complete wide-area communications system. The other two standards specify only the communications between mobile telephones and base stations.
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Commercial products based on DECT, PHS, and a modified version of PACS (designated PACS-UB, for unlicensed band) are under consideration for deployment in the 19101930 MHz band.
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The competing radio interfaces would provide minimum outdoor data rates of 384 kpbs and an indoor rate of 2 Mbps. Other than providing a forum for discussion of
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The bands are 1920-1980 MHz and 2110-2170 MHz for terrestrial communications and 1980-2010 MHz and 2170-2200 MHz for satellites. As noted in Table 1-4 and Table 1-5, the United States has already allocated spectrum bands to personal communications that include part of the lower IMT-2000 band, making it unlikely
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Meanwhile, the European telecommunications industry established a framework for developing third-generation mobile wireless technology. The universal mobile telephone system (UMTS)
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It is possible that advances in second-generation systems will meet future demand for mobile telephone services and that a demonstrated demand for high-bit-rate data services will be necessary to stimulate the commercial deployment of third-generation technology. 1.5 COMMERCIAL SATELLITE SYSTEMS Satellite systems can be classified by frequency and orbit.
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Recently introduced GEO systems for data communications include Mobilesat in Australia and MSAT in North America (see Table 1-6~. Innovations in GEO systems include spot beams for custom broadcast coverage and improved on-board processing.
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Communications systems using non-GEO satellites are emerging as major players in commercial wireless applications. These satellites are characterized as either medium Earth orbit (MEO)
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1.6 MOBILE DATA SERVICES Commercial packet-switched mobile data services emerged after the success of short-message, alphanumeric one-way paging systems. Mobile data networks provide two-way, low-speed, packet-switched data communication links with some restrictions on the size of the message (10 to 20 kilobytes)
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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.
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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.
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To maintain mobile telephone service, an international traveler in Europe needed up to five different telephones. The situation was reversed by secondgeneration systems.
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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.
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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.
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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.
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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.
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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)
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