CSE5345_Lecture5 - Last Class Propagation CSE 5345...

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1 CSE 5345 – Fundamentals of Wireless Networks Yonghe Liu [email protected] 1/31/12 Last Class Propagation Free Space Loss Free space loss accounting for gain of other antennas G t = gain of transmitting antenna G r = gain of receiving antenna A t = effective area of transmitting antenna A r = effective area of receiving antenna    t r t r t r r t A A f cd A A d G G d P P 2 2 2 2 2 2 4 Expression E b / N 0 Ratio of signal energy per bit to noise power density per Hertz The bit error rate for digital data is a function of E b / N 0 Given a value for E b / N 0 to achieve a desired error rate, parameters of this formula can be selected As bit rate R increases, transmitted signal power must increase to maintain required E b / N 0 TR S N R S N E b k / 0 0
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2 Spectral Efficiency B N N R B N S R N S N R S N E b 0 0 0 0 Notice / S/N 1 log SNR 1 log S/N 1 log SNR 1 log 2 2 2 2 B C B B C ) 1 2 ( / 0 B C b C B N E Shannon’s Capacity: Spectral Efficiency Today Modulation/Signal Encoding Technique Digitization Reasons for Choosing Encoding Techniques Digital data, digital signal Equipment less complex and expensive than digital-to- analog modulation equipment Analog data, digital signal Permits use of modern digital transmission and switching equipment Reasons for Choosing Encoding Techniques Digital data, analog signal Some transmission media will only propagate analog signals E.g., optical fiber and unguided media Analog data, analog signal Analog data in electrical form can be transmitted easily and cheaply Done with voice transmission over voice-grade lines
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