铁道供电专业英语 铁道信号Overview of railway signals 1-Overview of Communication.pptx

《Professional Engliah for Railway Elecrical Power Supply》 Overview of CommunicationCao zhongjiaGuangzhou Railway PolytechnicCatalogue1Sampling2QuantizationCoding3 Communication is the act of exchange information from a dispatcher to a receiver. For the remote transmission, it is nessary to build a transmission channel between them.1-SamplingConvertor变换器Channel信道Inverse convertor反变换器Receiver信宿Source信源Noise噪声源Digital signal Analog signalAn analog signal is an continuous signal for which the time-varying feature (variable) of the signal is a representation of some other time varying quantityA digital signal is a signal that is being used to represent data as a sequence of discrete values; at any given time it can only take on one of a finite number of values.The fundamental difference between analog and digital signal is that analog signal is represented by the sine waves whereas, the digital signal is represented by square waves.1-SamplingA/D conversion There are 3 procedures to convert analog signals into digital signals：Sampling 取样：Quantization 量化： Coding 编码：This process is called A/D conversion。1-SamplingSampling is the reduction of a continuous-time signal to a discrete-time signal .The continuous signal is represented with a green colored line while the discrete samples are indicated by the blue vertical lines (Nyquist theory）.1-SamplingQuantization is the process of mapping input values from a large set (often a continuous set) to output values in a (countable) smaller set, often with a finite number of elements (rouding 四舍五入).2-Quantization Coding is the process to use binary sequences to represent the signal after quantization, represented by a binary sequence of digits。1-CodingTransmission mode1-CodingSimplex 单工 Half duplex 半双工Full duplex 全双工Signal switch 交换机AA1-CodingBDBDECECManual switch 人工电话交换机 Automatic telephone switch 自动电话交换机Data Communication 数据通信In the past, communication services generally referred to voice communication. With the development of t