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1、东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Communication Systems)”课件课件OutlineOutlineThe communication process Basic elements of communication systems (p.2) Primary communication resources (p.3) Source of information Communication channel The mobile radio channel (p.18) Block diagram of digit
2、al communication system (p.22) Shannons information capacity theorem (p.23- 24) 1东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Communication Systems)”课件课件The Communication process The generation of a message signal: Voice,Music,Picture,Computer data Describing the message signal with a certain
3、measure of precision,by a set of symbols: Electrical, Aural, Visual The encoding of these symbols in a form that is suitable for transmission over a physical medium of interest. The transmission of the encoded symbols to the desired destination The decoding and reproduction of the original symbols.2
4、东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Communication Systems)”课件课件The Communication process The re-creation of the original message signal, with a definable degradation in quality; the degradation is caused by imperfections in the system.informationdatasignalTransnitsignaldatainformation
5、Task of CommunicationNOTE: Information or data “0,1” cant be transmitted directly through channel.3东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Communication Systems)”课件课件 Basic elements of communication systems Transmitter Channel Receiver4东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Co
6、mmunication Systems)”课件课件 Primary Communication Resources Transmitted Power the average power of the transmitted signal Bandwidth the band of frequencies allocated for the transmission of the message signal.5东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Communication Systems)”课件课件Source of Info
7、rmation Telecommunication channel is dominated by four important source of information. Speech, music, pictures and computer data Source of information : signal Signal : single valued function of time. One dimensional : speech, music, data Two dimensional : pictures Three dimensional : video, volume
8、 data Four dimensional : volume data over time6东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Communication Systems)”课件课件Communication channels Guided propagation Telephone, coaxial, optical fiber Free propagation Wireless, mobile, satellite. Linear or nonlinear a wireless radio channel (Linear)
9、 a satellite channel usually nonlinear. Bandwidth limited or power limited a telephone channel is bandwidth limited a satellite channel are power limited7东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Communication Systems)”课件课件无线电 固定终端点（基站）和 终端之间是无线链路BS基站用户计算机和终端BS基站覆盖的无线电区域基站覆盖的无线电区域F F2 2F F3
10、 3F F1 1F F2 2F F3 3F F1 1F F2 2F F3 3F F1 1F F2 2F F2 2F F3 3F F1 1F1, F2, F3 = 使用的频率8东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Communication Systems)”课件课件 Block diagram of digital communication system.9东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Communication Systems)”课件课件 Shannons
11、 Information Capacity Theorem Shannons theorem in Gaussian channel B : channel bandwidth (Hz) SNR : received signal to noise ratio C: information capacity of the channel.b/sS/NdB = 10 log10 S/N10东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Communication Systems)”课件课件Chapter 1 Random Process No
12、tion of random process Partial description of random process Stationary process, ergodic process Random process transmitted through a linear time invariant system Frequency domain description of a random process Gaussian process Sources of noise and their narrowband form Rayleigh and Rician distribu
13、tion11东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Communication Systems)”课件课件This Contents Chapter1 Random Process - 1.1 Introduction - 1.2 Mathematical Definition of a random Process 1.3 Stationary Process 1.4 Mean, Correlation, and Covariance function 1.5 Ergodic Process 1.6 Transmission of
14、 a Random Process Through a Linear Time-Invariant 12东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Communication Systems)”课件课件概率基本知识 随机变量及其分布 随机变量的定义 随机变量的分布函数及概率密度函数 常见的随机变量 随机变量的数字特征 数学期望、方差、矩13东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Communication Systems)”课件课件若某种试验A每一次取值都是随机的、不确 定的
15、，则称这一次试验为随机事件，若其随机 结果用X表示，则称此X为一个随机变量，并设 它的取值为x。例如，在一定时间内电话交换台收到的呼叫 次数是一个随机变量。随机变量的概念14东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Communication Systems)”课件课件随机变量的分布函数 定义 随机变量X取值不超过某个数x的概率P(X x) 是 取值x的函数，记为FX(x) = P(X x)函数FX(x) 即为随机变量X的分布函数。 已知分布函数就知道了随机变量X在任何区间 （a, b上取值的概率。 P(a 0, a = 常数bax0
16、pA(x)a，b为常数18东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Communication Systems)”课件课件常见随机变量举例 瑞利(Rayleigh)分布随机变量a 0，为常数。19东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Systems)”(Communication Systems)”课件课件随机变量的数字特征 数学期望定义：对于连续随机变量，其数学期望可以定义为：对于离散随机变量，其数学期望为式中，pX(x)为随机变量X 的概率密度。l 数学期望又称为统计平均值。20东南大学移动通信国家重点实验室“ “通信系统通信系统(Communication Sy
