Chapter 4 Information source and source coding by Prof.XIAOFENG LI SICE,UESTC UESTC-Digital transmission through the AWGN channel Prof李晓峰 1
ADC and PCM Modeling of digital source UESTC-Introduction Prof李晓峰 3
A analog communication system transfers analog msg signals. A digital communication system transfers digital msg signals. Digital transmission has important advantages over analog one. UESTC-Introduction Prof李晓峰 4
Introduction Many info signals are naturally in the forms of sequence,such as 1.A digital picture in JPEG file; 2.A video file in H.264 format; 3.A music file in MP3 format; 4. An email 00000120h:31393B36383B34323B3132323B32313B:19:68:42:122:21: 00000130h:31333B3130383B3137313B33393B3139:13:108:171:39:19 00000140h:363B3135335D2A343B0D0A0D0A726762:6:153]*4:,.,.rgb 00000150h:203D205B7267625F722C7267625F672C;=[xgbr,rgb_g, 00000160h:7267625F625D3B20256C6566742D3E72:xgbb]:1eft->x 00000170h:696768742052204720422E2075702D3E:1 ght R G B.up-> 00000180h:646F776E20626C61636B206669727379:down b1ackf1r3t 00000190h:2E0D0A0D0A25203234636F6C6F72204a:.···.号24co1orJ 000001a0h:50473F3F0D0A726762203D20205B0D0A:PG??..rgb=【.· This type of info signals is called digital signal and They are time- discrete and has finite values. UESTC-Digital transmission through the AWGN channel Prof李晓峰 5
Introduction Many info signals are naturally in the forms of sequence,such as 1.A digital picture in JPEG file; 2.A video file in H.264 format; 3. A music file in MP3 format; 4.An email However,there are also many analog msgs, Analog msgs are often converted to digital form to take the advantages of digital transmission. PCM is a typical technique of this process. UESTC-Digital transmission through the AWGN channel Prof李晓峰 6
1.ADC PCM The unit doing the conversion is called ADC. UESTC-Digital transmission through the AWGN channel Prof李晓峰 7
1.ADC PCM The unit doing the conversion is called ADC. There are 2 important operations, 1. discrete in TIME; 0→[ 2. discrete in Value; xn川]→x[n Analog waveform Discrete sequence Digital sequence Sampling Quantizing t1:-04.88y -5 t2:+21.43V 21 UESTC-Digital transmission through the AWGN channel Prof李晓峰 8
1.ADC PCM The unit doing the conversion is called ADC. There are 2 important operations, 1. discrete in TIME; 0→[ 2. discrete in Value; xn川]→x[n Analog waveform Discrete sequence Digital sequence Sampling Quantizing t1:-04.88V t2:+21.43v 21 Sampling:to sample the analog waveform every Ts and outputs a sequence of samples. Quantizing:to approximating the continuous value by using finite numbers of levels UESTC-Digital transmission through the AWGN channel Prof李晓峰 9
1.ADC PCM The procedure of ADC consists of 3 steps,sampling,quantizing and encoding. 0 0011010100110010010101100100 mnnmnnmn 0123456 UESTC-Digital transmission through the AWGN channel Prof李晓峰 10
1.ADC PCM The procedure of ADC consists of 3 steps,sampling,quantizing and encoding. Sampling:to sample the analog waveform every Ts and outputs a sequence of samples. 0011010100110010010101100100 mnnmnnnmn 0123456 UESTC-Digital transmission through the AWGN channel Prof李晓峰 11