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