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1.1 Historical introduction generate, create code 128 barcode none on .net projects QR Code Safty It is of interest to preced .net vs 2010 barcode standards 128 e our detailed study of mobile wireless communications in this book with a brief historical survey of the eld. Much of the emphasis in the material following is on work at Bell Laboratories, covering developments in the United States.

Further details appear in Frenkiel (2002) and 14 of O Neill (1985). A brief discussion of European activities in mobile wireless communications from 1981 on concludes this section. Details appear in Paetsch (1993).

Ship-to-shore communication was among the rst applications of mobile telephony. Experimental service began on coastal steamers between Boston and Baltimore in the United States in 1919; commercial service using AM technology at 4.2 and 8.

7 MHz began in 1929. This was roughly the same period at which AM radio broadcasting began to capture the public s attention. Note the wavelengths at these frequencies are about 70 and 35 meters, respectively, making ships suitable vehicles for carrying antennas of these lengths.

Ships were also suitable for the size and weight of the radio equipment required to be carried, as well as being able to provide the power required. Police communication was begun at about the same time. In 1928, the Detroit police department introduced land mobile communications using small, rugged radios.

By 1934, 5000 police cars from 194 municipal and 58 police systems in the US had been equipped for, and were using, mobile. Frenkiel, R. 2002. A brief history of mobile communications, IEEE Vehicular Technology Society News, May, 4 7.

O Neill, E. F. 1985.

A History of Engineering and Science in the Bell System: Transmission Technology (1925 1975), ed. E. F.

O Neill, AT&T Bell Laboratories. Paetsch, M. 1993.

Mobile Communications in the US and Europe: Regulation, Technology, and Markets, Boston, MA, Artech House.. Introduction and overview radio communications. These early mobile communications systems used the frequency band at 35 MHz. It soon became apparent, however, that communication to and from automobiles in urban areas was often unsatisfactory because of deleterious propagation effects and high noise levels.

Propagation effects in urban environments were an unknown quantity and studies began at Bell Laboratories and elsewhere. Propagation tests were rst carried out in 1926 at 40 MHz. By 1932, tests were being conducted at a number of other frequencies over a variety of transmission paths with varying distances, and with effects due to such phenomena as signal re ection, refraction, and diffraction noted.

(Such tests are still being conducted today by various investigators for different signal propagation environments, both indoor and outdoor, and at different frequency bands. 2 provides an introduction to propagation effects as well as to models used in representing these effects.) In 1935, further propagation tests were carried out in Boston at frequencies of 35 MHz and 150 MHz.

Multipath effects were particularly noted at this time. The tests also demonstrated that reliable transmission was possible using FM rather than the earlier AM technology. These various tests, as well as many other tests carried out over the years following, led to the understanding that propagation effects could be understood in their simplest form as being the combination of three factors: an inverse distance-dependent average received power variation of the form 1/dn , n an integer greater than the usual free-space factor of 2; a long-term statistical variation about the average received power, which is now referred to as shadow or log-normal fading; a short-term, rapidly varying, fading effect due to vehicle motion.

These three propagation effects are discussed and modeled in detail in 2 following. The advent of World War II interrupted commercial activity on mobile wireless systems, but the post-war period saw a rapid increase in this activity, especially at higher frequencies of operation. These higher frequencies of operation allowed more user channels to be made available.

In 1946, the Federal Communications Commission, FCC, in the USA, granted a license for the operation of the rst commercial land-mobile telephone system in St Louis. By the end of the year, 25 US cities had such systems in operation. The basic system used FM transmission in the 150 MHz band of frequencies, with carrier frequencies or channels spaced 120 kHz apart.

In the 1950s the channel spacing was reduced to 60 kHz, but, because of the inability of receivers to discriminate suf ciently well between adjacent channels, neighboring cities could only use alternate channels spaced 120 kHz apart. A 50-mile separation between systems was required. High towers covering a range of 20 30 miles were erected to provide the radio connections to and from mobile users.

Forty channels or simultaneous calls were made available using this system. The FCC divided these radio channels equally between the local telephone companies (Telcos) and newly established mobile carriers, called Radio Common Carriers (RCCs). These early mobile systems were manual in operation, with calls placed through an operator.

They provided half-duplex transmission, with one side of a connection only being able to communicate at any one time: both parties to a connection used the same frequency channel for the air or radio portion of the connection, and a push-to-talk procedure was required for the non-talking party to take over the channel. With the number of channels available set at 40, the system could accommodate 800 1000 customers in a given area, depending on the length of calls. (Clearly, as user conversations increase in length, on the average, the number of customers that can be accommodated must be reduced.

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