电子科技大学：《数字通信基础 Digital Communications》课程教学资源（课件讲稿，图片版）Chapter 01 Introduction 1.3 Digital Comm.Sys

Examples of communication Diagram and elements of Comm.Sys Digital Comm.Sys. Channels and their characteristics UESTC-Introduction Prof李晓峰 2

Digital Comm.Sys. A waveform is basically a time-continuous signal,called analog signal. A seg of data is basically a time-discrete signal with finite values, called digital signal. 100-1111-100-1111-100-1111 UESTC-Introduction Prof李晓峰 3

Digital Comm.Sys. A analog communication system transfers analog msg signals. A digital communication system transfers digital msg signals. WH ATH AT 100-1111-100-1111-100-1111 UESTC-Introduction Prof李晓峰 4

Digital Comm.Sys. A analog communication system transfers analog msg signals. For analog info,we measure the difference of the restored signal and the src signal,or the SNR(ratio of the signal pwr to the pwr of the difference). A digital communication system transfers digital msg signals. The performance is often evaluated in term of rate of error in bits(BER),equivalent to the probability of the bit error,Pb. 100-1111-100-1111-100-1111 UESTC-Introduction Prof李晓峰 5

Digital Comm.Sys. A analog communication system transfers analog msg signals. A digital communication system transfers digital msg signals. Advantages of digital comm. 1.In long-distance transmission,we may regenerate the signal to clear the noise periodically 2. It is very easy to compress the digital msg signal. 3. It works well for different msg and support networking. 4. Digital system are cheap and easy to implement with the development of VLSI and DSP So,analog msgs are often converted to digital form,then transferred by a digital sys. UESTC-Introduction Prof李晓峰 6

Digital Comm.Sys. 3 inherent advantages: √Noise immunity √Unified format √Easy to implement Unable to clr the noise Able to clr the noise A perfect copy :Src re-generator re-generator receiver UESTC-Introduction Prof李晓峰 7

Digital Comm.Sys. 3 inherent advantages: √Noise immunity √Unified in format (all are in bits or bytes) √Easy to implement Like standard-containers,text,voice,video,data,...all can be packed in one,so that be handled and dispatched simply ---multimedia,packet switching,internet,all becomes possible UESTC-Introduction Prof李晓峰 8

Digital Comm.Sys. 3 inherent advantages: √Noise immunity √Unified in format (all are in bits or bytes) √Easy to implement UESTC-Introduction Prof李晓峰 9

Digital Comm.Sys. 3 inherent advantages: √Noise immunity √Unified format √Easy to implement Simply,handling integers are much more easer than handling real numbers. So,digital circuits and algorithms are prevalent. UESTC-Introduction Prof李晓峰 10

Digital Comm.Sys. Transmitter src encoder,channel encoder and digital mod. Receiver is expanded accordingly. UESTC-Introduction Prof李晓峰 11