信息通信Chapter 04.pptVIP

* * Chapter 4 Signals Chapter 4 Signals  4.1 Analog and Digital 4.2 Aperiodic and Periodic Signals 4.3 Analog Signals 4.4 Digital Signals 4.5 Summary 4.1 Analog and Digital Information can be in the form of data, voice, picture and so on. To be transmitted, information must be transformed into electromagnetic signals . Information can be analog or digital. Analog information is continuous. Digital information is discrete. Fig 4.1 Analog and Digital Clocks 4.1 Analog and Digital Signals can be analog or digital. Analog signals can have any value in a range. Digital signals can have only a limited number of values. Fig 4.3 comparison of analog and digital signals 4.1 Analog and Digital 4.2 Aperiodic and Periodic Signals 4.3 Analog Signals 4.4 Digital Signals 4.5 Summary 4.2 Aperiodic and Periodic Signals Both analog and digital signals can be of two forms: periodic and aperiodic (nonperiodic) . 4.2.1 Periodic Signals A periodic signal consists of a continuously repeated pattern. T——(s). Fig 4.4 4.2 Aperiodic and Periodic Signals 4.2.2 Aperiodic Signals An aperiodic signal has no repetitive pattern. An aperiodic signal can be decomposed into an infinite signals. A sine wave is the simplest periodic signal. Fourier transform Fig 4.5 Examples of aperiodic Signals 4.1 Analog and Digital 4.2 Aperiodic and Periodic Signals 4.3 Analog Signals 4.4 Digital Signals 4.5 Summary 4.3 Analog Signals Analog signals can be simple or complex(复合). A simple analog signal, or a sine wave cannot be decomposed into simpler signals. A complex analog signal is composed of multiple sine waves. 4.3.1 Simple Analog Signals 4.3.1.1 Amplitude Amplitude refers to the height of the signal. For electric signal, the unit is volts, amperes, or watts. minimum Fig 4.6 A sine wave maximum 4.3.1.2 Period and Frequency Period refers to the amount of time, in seconds, a signal needs to complete