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The Wireless Data Handbook, ourth Edition. James . DeRose Copyright © 1999 John Wiley & Sons, Inc. ISBNs: 0-471-31651-2 (Hardback); 0-471-22458-8 (Electronic) I GETTING STARTED The Wireless Data Handbook, ourth Edition. James . DeRose Copyright © 1999 John Wiley & Sons, Inc. ISBNs: 0-471-31651-2 (Hardback); 0-471-22458-8 (Electronic) 1 A SHORT HISTORY OF DATA RADIO 1.1 IN THE BEGINNING In 1899, four years after Marconi’sfirst wireless telegraph, theBritish Navy converted to data radio.1 TheCzar’s Navyquickly followed. By 1905 the Japanesehadmastered the key techniques and began to intercept messages from the Russian Vladivostok fleet cruising secretly south of Tokyo Bay. Japan’s victorious Battle of Tsushima followed. Driven by continued military demands, wireless data technology leaped forward. In 1914 the hapless Russians lost the Battle of Tannenburg because of German intercepts of their land-based data radio communications and in 1917 the British successfully employed radio telegraph in tanks at the Battle of Cambrai2; by 1918 these same units were adapted for aircraft. In World War II both the United States and Germany communicated with and controlled their widely scattered submarine fleets via data radio. During this period H. C. A. Van Duuren3 devised the technique still known as ARQ (Automatic Repeat reQuest), one of those disarmingly simple ideas that seems so trivial in retrospect. The idea was to ensure that a block of characters had been successfully transmitted through the use of error detection. A detected error was followed by a signal from the receiver asking the transmitter to repeat the block. In the late 1950s wireless teletype units such as the CY2977LG were in use in high-profile applications like the media pool aboard Air =orce One. The Semi-Automatic Ground Environment (SAGE) air defense system began testing digitized radar information sent by data radio from airborne early warning aircraft. Themorecomplexmessageswereseparatedfromthecontinuously repeatingX andY coordinates. A header identifying the radar address was added to the data. These manageablesegments wereclearforerunners of whatwould later becalled “packets.” 3 4 A SHORT HISTORY OF DATA RADIO Thesepackets traveledfromaircraft to groundstation over dedicatedradio circuits, as in today’s data-over-cellular. In 1957 data radio modems reached speeds of 2000 bits per second (bps), competitive with landlines of the time; by 1967 the General Dynamics ANDET/SC-320 modem achieved 4800 bps.4 In the early 1960s, building on the seminal work of Shannon5 and Hamming,6 commercially practical error correction techniques were available. The stage was set for commercial exploitation of this knowledge base. 1.2 PRIVATE NETWORKS LEAD THE WAY In 1969 IBM began to develop a mobile data radio system for police departments. ueled by block grants from the Law Enforcement Assistance Administration (LEAA), other vendors, including Kustom, Motorola, Sylvania/LTV, and Xerox, offered alternatives. IBM’s 2976 MobileTerminal SystemwasannouncedonMay 12, 1972(seeAppendix B). Apolledsystem, it nonethelessachievedgoodthroughput for its time with a combination of high (∼5400 bps) airlink transmission speeds, forward error correction (which consumed half the bits), and ARQ. The IBM systemwasafailureand was withdrawn in 1974. Competitionfared little better. The failure causes were many: 1. The termination of LEAA funding in 1973 2. The physical inadequacy of the devices: big, heavy, hot, noisy, and unreliable 3. A crushing lack of software support: for example, no dispatch applications 4. Unreadiness of the customers: no data bases or applications in place, inability to cost justify the necessary development activity But the dreamers persisted. In 1970 the successful University of Hawaii’s ALOHA system had established fundamental inbound contention techniques. In 1975 Kleinrock and Tobagi8 codified carrier sense multiple-access (CSMA) methods, permitting greatly improved inbound performance. Mobile Data International (MDI), founded in 1978 to provide a data radio system for the Vancouver (B.C.) police, began to work with ederal Express in 1979. The followingyear the first 12commercial terminals employing CSMAwere delivered to the pioneering package delivery service. Very quickly the ederal Express device count grew to 25,000units, which attracted Motorola’s eye. MDI was purchased, then extinguished. Meanwhile, IBM’s Service Research organization had been privately piloting briefcase-sized “portable” radio terminals, developing a business case for the applications that would yield economic payoff. In November 1981 a contract was signed with Motorola for the Digital Communication System (DCS). Nationwide rollout began in April 1984 and was essentially complete two years later with the installation of more than 1000 base stations. 1.3 RISE OF PUBLIC PACKET SWITCHED NETWORKS 5 DCS was a packet switched, pedestrian (low-target-velocity) oriented system that brokemuchnewtechnicalground.Itusedasingle frequencyonadjacentbase stations, with deliberately overlapping coverage patterns, to achieve better in-building penetration. The end-user device was hand held, incorporating integrated radio modems and internal dual diversity antennas for improved reception at walk speeds. 1.3 RISE OF PUBLIC PACKET SWITCHED NETWORKS Of equal business importance, with the signing of the DCS contract, IBM and Motorola agreed to work together on a shared network approach. The initial opportunity estimateswereenormous: 5 million subscribers werethought possibleby 1987. Within IBM this period later came to be known as the first era of low hanging fruit. But during the period 1983–1985 there were serious business disagreements between the two equally proud companies. IBM better understood the application development barriers that would hinder rapid roll-out of this technology, having struggled to place experimental customers on DCS via the then-extant IBM Information Network. Motorola had a sounder grasp of the infrastructure changes necessary to provide a high-availability system and had begun development of its own, independent network. The proposal to build a public network resting on the shoulders of DCS was rejected by the decision-making elements of both IBM and Motorola for complex (and often emotional) internal business reasons. After the collapse of the joint venture negotiations, Motorola unveiled its own publicpacket switchednetwork, theDigital Radio Network(DRN). This systemused DCS-class base stations but with area controllers sharply modified for both performance and high availability. DRN began in Chicago in 1986 (Ericsson began Mobitex in Sweden the same year). As IBM expected, making a market was an extraordinarily difficult task. It was four years before DRN-Chicago had ∼135 externalusers9; Los Angeles, rolling out second, took 20 months to achieve about the same number; New York, 18 months behind Los Angeles, reached the 135 milestone after one year. Clearly a positive learning curve existed, but the absolute pace was exceedingly slow.10 iveyears after thenegotiations failed,theplan was refurbished,principallyby the incorporation of Motorola’s high-availability DRN switching centers. The venture was agreed to by IBM, surprising since the airtime protocol remained proprietary to Motorola. TheAdvancedRadio Data Information System(ARDIS) wasannouncedin January 1990. The system has been in continuous evolution ever since: new devices, a new higher bit rate protocol, additional frequencies, roaming capability, and extraordinary redundancy added to achieve high availability. The customer base has grown slowlyto ∼40,000 attheend of 1994, reaching ∼80,000at thecloseof thethird quarter of 1998.11 Building a market remains a continuous struggle. On July 6, 1994, protracted disagreements between the two ARDIS partners were resolved when Motorola bought out IBM. There were multiple reasons for this transaction. Paramount was Motorola’s desire, and willingness, to make the required 6 A SHORT HISTORY OF DATA RADIO infrastructure investments necessary to drive horizontal markets12 with their Envoy/Marco devices. Envoy/Marco subsequently failed. At the close of 1997 Motorola, deciding that network management was not its forté and discouraged with the general failure of horizontal market thrusts throughout the industry, sold ARDIS to American Mobile Satellite Corporation (AMSC). AMSC was likely influenced by the fact that ARDIS had won the United Parcel Service (UPS) contract, with devices to be supplied by Motorola. urther, ARDIS had successfully partnered with AMSC on combined terrestrial/satellite devices for trucks. The two companies were not strangers. In October 1990 RAM announced its public data service based upon Ericsson’s newest Mobitex design. Initially plagued by a lack of nearly everything—adequate base stations/coverage, hand-held modems—and a conviction that horizontal applications were the path to success, RAM’s failure to achieve an adequate subscriber base was extraordinarily painful. BellSouth Mobility became an essentially equal RAM partner in 1992 with the investment of $300 million in urgently needed cash. Infrastructure deployment rates jumped. Nationwidecoveragewasachieved in June1993, albeit with alessextensive coverage footprint than ARDIS. By year-end 1994 RAM claimed to have ∼27,000 paying subscribers13 (most in vertical markets) and several intriguing business relationships. As at ARDIS, subscribergrowthcomes slowly: RAM claimed ∼36,000 users atthecloseof thethird quarterof 199514 andprobablyreached∼70,000 atyear-end 1997. BellSouth assumed 100% operational control of RAM on March 18, 1998, 5 renaming the company BellSouth Wireless Data (BSWD). 1.4 CIRCUIT SWITCHED SKIMS THE EARLY CREAM In 1983 thefirst datausers improvised low-speedconnectionsto their host computers using ordinary modems over voice cellular “circuits.” Users treated these dial connections much asthey usedordinary landlines. Theyarenowgreatly helpedby far better modem capability, most cellular ready, and the formation of carrier modem pools in most major metropolitan areas. acsimile transmission alone, usually from a portable computer to a wireline fax, has created thousands of casual public data radio users. In early 1992 UPS made a direct connection of its own leased facilities to cellular mobiletelephoneswitching offices (MTSOs), bypassingthepublicswitched network landlines. This resulted in very advantageous pricing, though there were time connection limits. By ebruary 1993 UPS had approximately 50,00016 operational units with this reduced tariff arrangement, significantly more subscribers than DRN/ARDIS had achieved after seven years of effort. But the struggle to deal with scores of cellular carriers—even though a consortium was created to smooth the path—led UPS to begin the conversion to a nationwide packet switched solution. ARDIS, beginning in late 1998. ... - tailieumienphi.vn