Digitizing Analog Data: Understanding Pulse Code Modulation (PCM) and Delta Modulation, Slides of Data Communication Systems and Computer Networks

Download Digitizing Analog Data: Understanding Pulse Code Modulation (PCM) and Delta Modulation and more Slides Data Communication Systems and Computer Networks in PDF only on Docsity! Digitizing Analog Data Modulator Analog data (voice) Analog data (ASK) Pulse Code Modulation (PCM)  sampling theorem:  “If a signal is sampled at regular intervals at a rate higher than twice the highest signal frequency, the samples contain all information in original signal”  eg. 4000Hz voice data, requires 8000 sample per sec  strictly have analog samples  Pulse Amplitude Modulation (PAM)  so assign each a digital value Docsity.com Non-Linear Coding Quantizing levels Strong signal Weak signal (a) Without nonlinear encoding (b) With nonlinear encoding Companding --- Strong companding a oJ =| = a eh EI & gd a ep # =| = S| a Input signal magnitude Delta Modulation  analog input is approximated by a staircase function  can move up or down one level () at each sample interval  has binary behavior  since function only moves up or down at each sample interval  hence can encode each sample as single bit  1 for up or 0 for down Docsity.com PCM verses Delta Modulation DM has simplicity compared to PCM  but has worse SNR  issue of bandwidth used  eg. for good voice reproduction with PCM • want 128 levels (7 bit) & voice bandwidth 4khz • need 8000 x 7 = 56kbps  data compression can improve on this  still growing demand for digital signals  use of repeaters, TDM, efficient switching  PCM preferred to DM for analog signals Docsity.com Signal Encoding Techniques Digital Data, Digital Signals Digital Data, Analog Signals  Analog Data, Digital Signals  Analog Data, Analog Signals Docsity.com Analog Data, Analog Signals  modulate carrier frequency with analog data  why modulate analog signals?  higher frequency can give more efficient transmission  permits frequency division multiplexing (chapter 8)  types of modulation  Amplitude  Frequency  Phase Docsity.com