0195136047.pdf

15 Communication Systems

15.1 Waves, Transmission Lines, Waveguides, and Antenna Fundamentals

15.2 Analog Communication Systems

15.3 Digital Communication Systems

15.4 Learning Objectives

15.5 Practical Application: A Case Study—Global Positioning Systems

Problems

Even though most modern communication systems have only been invented and developed during

the eighteenth and nineteenth centuries, it is difficult to imagine a world without telephones, radio,

and television. After the invention of the electric battery by Alessandro Volta in 1799, Samuel

Morse developed the electric telegraph and demonstrated it in 1837. Morse devised the variable-

length binary code, in which letters of the English alphabet are represented by a sequence of

dots and dashes (code words). In this code, more frequently occurring letters are represented by

short code words, whereas letters occurring less frequently are represented by larger code words.

Morse code(variable-length binary code), developed in 1837, became the precursor to variable-

length source coding methods.Telegraphy, the earliest form of electrical communication, was a

binary digital communication system in which the letters of the English alphabet were efficiently

encoded into corresponding variable-length code words having binary elements. In thebaudout

code, developed in 1875, the binary code elements were of equal length, and each letter was

encoded into fixed-length binary code words of length 5.

With the invention of the telephone,telephonycame into being and the Bell Telephone

Company was established in 1877. Transcontinental telephone transmission became operational

in 1915. Automatic switching was another important advance, and a digital switch was placed in

service in 1960. Numerous significant advances have taken place in telephone communications

over the past four decades. For example, fiber-optic cables have replaced copper wire, and

electronic switches have come into use in place of electromechanical devices.

Marconi is credited with the development ofwireless telegraphyin the late 1890s, after

Maxwell’s theory of electromagnetic radiation was verified experimentally by Hertz in 1887. The

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