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ch4_digital_baseband_handout - EEN 404 Communication...

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1 1 EEN 404 EEN 404 Communication Systems Communication Systems Ch4 Ch4 Baseband Digital Data Digital Data Transmission Transmission 2 Digital Communications Motivation: • message can be easily stored, regenerated, addressed ? Digital Analog 1 propagation Block diagram of baseband digital communication systems: 3 Pulse-Code Modulation (PCM) CH. 3.6.2 a binary “one’’ a pulse a binary “zero” another pulse Figure 3-65 Generation of PCM. (a) PCM modulator. (b) Quantization and encoding. (c) Transmitted output.
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2 4 •One±sample± n= d log 2 L e bits • If the signal has bandwidth W and sampling rate 2W 2nW bits/second • Each pulse for one bit has width < 1/(2nW) second • Transmission rate in bits/second R =nf s bits/second, f s is the sampling rate • Required bandwidth is inversely proportional to the pulse width B =2knW Hz, k is a constant of proportionality. • the number of levels L ⇑⇒ n ⇑⇒ B Bandwidth analysis 5 A binary channel with bit rate R max = 32 Kbits/second is available for PCM voice transmission. Find appropriate values of the sampling rate f s , the quantizing level L , and the binary digit n, assuming the signal bandwidth f m = 3.2kHz, and at least Nyquist sampling rate is used. Example:
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