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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 Pulse modulation Amplitude modulation Frequency modulation Radio waves and radio frequencies Two-way data transmission with modems Cellular phone Inside a cell phone The cell approach From cell to cell Cell tower and antenna 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 M different signals in the transmission scheme Faster data transmission when M increases 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 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 σ σ Noiseless channel: Noisy channel: ( ) 0 1 log 0 1 log 2 2 2 2 = = + = >> B B C s n σ σ Example Telephone channel (3000Hz) with SNR=1,000 ( ) bps B C n s 900 , 29 1000 1 log 3000 1 log 2 2 2 2 + × = + = σ σ
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