Lecture2-SignalsAndSignalAnalysis.ppt

Any composite signal can be represented as a sum of simple sine waves Bandwidth Important property of a medium Difference between highest and lowest frequency that can pass through the medium Measured in Hertz [Hz] Limits the channel’s capacity Undesired signal added to the transmitted signal Thermal noise Random motion of electrons Independent of frequency (”white noise”) and amplitude Added to the signal Data communications and networking Data Communications and Networking 数据通信与计算机网络 授课教师： 刘振盛 武汉大学 电气工程学院 School of Electrical Engineering, Wuhan University. By Liu Zhensheng Email: zsliu@whu.edu.cn Lecture 2. Signals and signal Analysis 2.5 Noise 2.4 Periodic and Aperiodic Signals 2.3 Analog and Digital Signals 2.2 Time-domain and Frequency-domain Analysis 2.1 Information and Signals Lecture 2. Signals and signal Analysis 2.1 Information and Signals Information reduction of uncertainty, that is , reduction of entropy（熵） Assume： probability of a message is p, then Information Capacity of the message is I = log 2 1/p （bit） Signals representation form of information In data communication, signals are electromagnetic signals or optical signals corresponding with the data generally. To be transmitted, information must be transformed into signals. Signals must match with the transmission medium. Type of Signals Continuous and discrete signals Continuous signals--- continuous ,it can be all possible values and be called analog signals. Discrete signals---discrete and discontinuous impulses, and it be called digital signals. Random and certain signals All signals are random signals except regular signals that are produced in lab. Only random signals include information. Periodic and aperiodic signals Periodic signals are certain signals and have no information. 2.2 Time-domain and Frequency-domain Analysis 2 analysis methods for continuous signals: Time-domain anal