Examples of communication Diagram and elements of Comm.Sys Digital Comm.Sys. Channels and their characteristics UESTC-Introduction Prof李晓峰 2
Elements of Comm.Sys Communication systems are electronic systems designed to transmit information UESTC-Introduction Prof李晓峰 3
Elements of Comm.Sys Communication systems are electronic systems designed to transmit information In general,the infor/msg is Noise TRANSMITTER n(t) RE said to be generated by a information/msg source. Information Transmission r( Info must be something input Signal Carrier s( 1) processing medium circuits unknown and mathematically (channel) described by random signals, also called random processes. m The information or massage may be voic Information/message text,or a file. signal:to represent the .Voice:in telephony,a microphone is us information or message. Transmission signal:to 2.Text:in mobile SMS,a keypad system i go through the channel 3.Video:in network,a video-camera is.. UESTC-Introduction Prof李晓峰 4
Elements of Comm.Sys Communication systems are electronic systems designed to transmit information Noise TRANSMITTER n(t) RECEIVER Information input Transmission Signal Carrier s( r(t Carrier Signal m() medium 11） processing circuits circuits processing (channel) iTo information sink(user) A waveform is basically a time-continuous signal,called analog signal. A seq of data is basically a time-discrete signal with finite values,called digital signal. UESTC-Introduction Prof李晓峰 5
Elements of Comm.Sys Communication systems are electronic systems designed to transmit information Noise TRANSMITTER n(t) RECEIVER Information input Signal Carrier s(I Transmission r() Carrier Signal m() medium 1） processing circuits circuits processing (channel) iTo information sink(user) Channel:the physical media to transmit Say,wire-lines,cables,open space and optical fiber cables Channel is often non-ideal,introducing distortion and noise. UESTC-Introduction Prof李晓峰 6
Elements of Comm.Sys Communication systems are electronic systems designed to transmit information Noise TRANSMITTER n(t) RECEIVER Information input Transmission Signal Carrier s(I r() Carrier Signal m(:) medium 11） processing circuits circuits processing (channel) ITo information sink(user) Transmitter:A device that converts the infor into a signal that matches the channel. 通 Eg.To send an AM radio signal,you have to move the voice into the band at some freq,say 1000kHz. UESTC-Introduction Prof李晓峰 7
Elements of Comm.Sys Communication systems are electronic systems designed to transmit information Noise TRANSMITTER n(t) RECEIVER Information input Transmission Signal Carrier s(I r(t Carrier Signal m() medium 1） processing circuits circuits processing (channel) ITo information sink(user) A basic process of many transmitters is to convert a baseband signal into a bandpass form,call modulation.Say,AM,FM and PM using sinusoid waves,called carriers,of some freqs,often denoted by fc's. UESTC-Introduction Prof李晓峰 8
Elements of Comm.Sys Communication systems are electronic systems designed to transmit information Noise TRANSMITTER n(t) RECEIVER Information input Transmission Signal Carrier s(I r(ty Carrier Signal m() processing medium 1) circuits circuits processing (channel) iTo information sink(user) Receiver:picks up signals in the channel and recovers information;then delivers it to user. The process of extracting information from the modulated signal is called demodulation. signal-correction and noise-suppression are important work in the receiver. UESTC-Introduction Prof李晓峰 9
Elements of Comm.Sys Communication systems are electronic systems designed to transmit information Noise TRANSMITTER n(t) RECEIVER Information input Transmission Signal Carrier r Carrier Signal m(t) processing medium circuits circuits processing 11） (channel) ITo information sink(user) Information->Signals->Channel->Reception ->Restore Theory of Signals and systems UESTC-Introduction Prof李晓峰 10