TRUYỀN THÔNG SỐ DIGITAL COMMUNICATION pptx

TRUYỀN THÔNG SỐ DIGITAL COMMUNICATION    •  –   ! • " #$%&'!( –  !!  ) – * +!'  #()#, /( 0 Encode Transmit "   Sample Quan$ze Demodulate/ Detect Channel Receive Low-pass +lter Decode " ) *   !1 ' 1 2! 1 ' 1 2! 1 !1 source sink 3!  ! 4  1 3!'# !( 1 -!55  01 3!2!6 41  71 " -  81 * -  7  1 3!'# !( 1 -!55  01 3!2!6 41  71 " -  81 * -  8  ! • !  + '!1 • +' ! ! • 91!1266#2   6 6!(59*6 : ;  1 3!'# !( 1 -!55  01 3!2!6 41  71 " -  81 * -  < •   =+> ?> !? • @k+ • /M = 2 k -A – + – += B [...]... Formatting Analog Information 4 Sources of Corruption 5 Pulse Code Modulation 6 Baseband Modulation 13 Format analog signals • To transform an analog waveform into a form that is compatible with a digital communication, the following steps are taken: 1 Sampling 2 Quantization and encoding 3 Baseband transmission 14 Impulse Sampling Time domain xs (t ) = xδ (t ) × x(t ) x(t ) xδ (t ) xs (t ) Frequency... Nyquist rate is called 18 19 Why Oversample? Transform analog signals to digital signals: Without Oversampling: • The signal  high performance analog LPF  sampled at Nyquist rate  ADC With Oversampling: • The signal  low performance (less cost) analog LPF  sampled at (higher) Nyquist rate  ADC  high performance (low cost) digital filter (resample) 20 Quantization • Amplitude quantizing: Mapping... Baseband Modulation 27 Encoding (PCM) • A uniform linear quantizer is called Pulse Code Modulation (PCM) • Pulse code modulation (PCM): Encoding the quantized signals into a digital word (PCM word or codeword) – Each quantized sample is digitally encoded into an l bits codeword where L in the number of quantization levels and 28 Quantization example amplitude x(t) 111 3.1867 Quant levels 110 2.2762 101 . TRUYỀN THÔNG SỐ DIGITAL COMMUNICATION    •  –  .  E=1 !  2! ! "    #"2-(! ; < F)G Transform analog signals to digital signals: F)! • !!!H"