电子与通信工程硕士专业英语part 4.pptx

;Lesson 1 电子通信简介Introduction to Electronic Communication ;内容大纲 Outline：;内容大纲 Outline：;精读详解 Intensive reading：;精读详解 Intensive reading：;精读详解 Intensive reading：;精读详解 Intensive reading：;精读详解 Intensive reading：;精读详解 Intensive reading：;精读详解 Intensive reading：;精读详解 Intensive reading：;精读详解 Intensive reading：;精读详解 Intensive reading：; Regardless of the particular application , all communications systems involve three main sub-systems: the transmitter, the channel, and the receiver. The message from the source is represented by the information input waveform m(t). The message deliver-ed to the sink is denoted by . The[~] indicates that the message received may not be the same as that transmitted. ; That is the message at the sink may be corrupted by noise in the channel or there may be other impairments in the system, such as undesired filtering or undesired nonlinearities.; The spectra (or frequencies) of m(t) and are concentrated about f=0 ; consequently, they are said to be baseband signals. ; In an analog system, the signal processor may be an analog low-pass filter that is used to restrict the bandwidth of m(t).; In addition, the signal processor may also add parity bits to the digital word to provide channel coding so that error detection and correction can be used by the signal processor in the receiver to reduce or eliminate bit errors that are caused by noise in the channel.; The transmitter carrier circuit converts the processed baseband signal into a frequency band that is appropriate for the transmission medium of the channel.;精读详解 Intensive reading：;精读详解 Intensive reading：;精读详解 Intensive reading：; before1992 CCITT CCIR;Lesson 1 电子通信简介Introduction to Electronic Communication ;Fequency Bands ELF 极低频 extremely ～ ULF 特低频 ultra ～ VLF 甚低频 very ～ LF 低频 low frequency MF 中频 medium frequency HF 高频 high frequency VHF 甚高频 vey ～ UHF 特高频 ultra ～ SHF 超