Saturday, November 7, 2009
Sunday, September 27, 2009
technical introducion to wireless
1 A Technical Introduction to Wireless: 1.1History of Radio and Wireless Telephony Days before radio 1680 Newton first suggested concept of spectrum, but for visible light only 1831 Faraday demonstrated that light, electricity, and magnetism are related 1864 Maxwell’s Equations: spectrum includes more than light 1890’s First successful demos of radio transmission Telegraphy Samuel F.B. Morse had the idea of the telegraph on a sea cruise in the 1833. He studied physics for two years, and In 1835 demonstrated a working prototype, which he patented in 1837. Derivatives of Morse’ binary code are still in use today The US Congress funded a demonstration line from Washington to Baltimore, completed in 1844. 1844: the first commercial telegraph circuits were coming into use. The railroads soon were using them for train dispatching, and the Western Union company resold idle time on railroad circuits for public telegrams, nationwide 1857: first trans-Atlantic submarine cable was installed Telephony By the 1870’s, the telegraph was in use all over the world and largely taken for granted by the public, government, and business. In 1876, Alexander Graham Bell patented his telephone, a device for carrying actual voices over wires. Initial telephone demonstrations sparked intense public interest and by the late 1890’s, telephone service was available in most towns and cities across the USA Radio Milestones 1888: Heinrich Hertz, German physicist, gives lab demo of existance of electromagnetic waves at radio frequencies 1895: Guglielmo Marconi demonstrates a wireless radio telegraph over a 3-km path near his home it Italy 1897: the British fund Marconi’s development of reliable radio telegraphy over ranges of 100 kM 1902: Marconi’s successful trans-Atlantic demonstration 1902: Nathan Stubblefield demonstrates voice over radio Guglielmo Marconi 1906: Lee De Forest invents “audion”, triode vacuum tube radio pioneer, 1895 feasible now to make steady carriers, and to amplify signals 1914: Radio became valuable military tool in World War I 1920s: Radio used for commercial broadcasting 1940s: first application of RADAR - English detection of incoming German planes during WW II MTS, 1950s: first public marriage of radio and telephony - MTS, IMTS Mobile Telephone System 1961: transistor developed: portable radio now practical 1961: IMTS - Improved Mobile Telephone Service Lee De Forest 1970s: Integrated circuit progress: MSI, LSI, VLSI, ASICs vacuum tube inventor 1979, 1983: AMPS cellular demo, commercial deployment Frequencies Used by Wireless Systems Overview of the Radio Modulation Schemes and Bandwidth Characteristics of a Radio Signal The purpose of telecommunications is to send information from one place to another Our civilization exploits the transmissible nature of radio signals, using them in a sense as our “carrier pigeons” To convey information, some characteristic of the radio signal must be altered (I.e., ‘modulated’) to represent the information The sender and receiver must have a consistent understanding of what the variations mean to each other RF signal characteristics which can be varied for information transmission: Amplitude Frequency Phase \
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