L19-cellphones-2009 - Information Transmission Trac D. Tran...

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1 Information Transmission Information Transmission Trac D. Tran ECE Department The Johns Hopkins University Baltimore, MD 21218 Outline Outline ± M-ary transmission and data rate ± Channel capacity ± Modulation ² Pulse modulation ² Amplitude modulation ² Frequency modulation ± Radio waves and radio frequencies ± Two-way data transmission with modems ± Cellular phone ² Inside a cell phone ² The cell approach ² From cell to cell ² Cell tower and antenna ² Digital cellular technologies
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2 M -ary ary Transmission & Data Rate Transmission & Data Rate 0 00 V 1 01 V 2 10 V 3 11 V time amplitude threshold levels ± M -ary transmission ² M different signals in the transmission scheme ² Faster data transmission when M increases ² Problem: how to differentiate different signals with noise? ± Data rate bps M R D log 2 = signals transmitted or received per second Channel Capacity Channel Capacity bps B C n s 1 log 2 2 2 + = σ ± Channel capacity C channel bandwidth (bps) signal-to-noise ratio = = + = 2 2 2 2 log 0 1 log 0 B B C s n Noiseless channel: Noisy channel: ( ) 0 1 log 0 1 log 2 2 2 2 = = + = >> B B C s n ± Example ² Telephone channel (3000Hz) with SNR=1,000 () bps B C n s 900 , 29 1000 1 log 3000 1 log 2 2 2 2 + × = + =
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3 ± Modulation ² Using higher-frequency sinusoids to carry signals ² More efficient transmission & allow multi-user sharing ± Pulse modulation ± Amplitude modulation ± Frequency modulation Modulation Modulation Morse code, infrared remote control… AM radio stations, video part of TV signals…
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L19-cellphones-2009 - Information Transmission Trac D. Tran...

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