专业英语测验复习总结.docVIP

专业英语测验复习总结 ———————————————————————————————— 作者： ———————————————————————————————— 日期： 1.1 Electronic communication can be summarized as the transmission , reception , and processing of information between two or more locations using electronic circuits . 电子通信就是利用电路在两地或多地之间进行信息的发送、接收和处理。 1.2 Regardless of the particular application, all communications systems involve three main subsystems: the transmitter, the channel, and the receiver. 无论何种具体应用，通信系统都包括三个主要的子系统：发送机、信道和接收机。 1.4 The bandwidth of a communications channel must be large (wide) enough to pass all significant information frequencies. In other word, the bandwidth of the communications channel must be equal to or greater than the bandwidth of information. For example, voice frequencies contain signals between 300Hz and 3000Hz. Therefore, a voice-frequency channel must have a bandwidth equal to or greater than 2700Hz. 信道的带宽必须足够大(宽),以便所有重要的信息频率都能通过。换句话说,信道的带宽必须等于或大于信息的带宽。例如,话音频率包含300Hz到3000Hz的信号。因此,话音频率的信道必须具有等于或大于2700Hz的带宽。 Information capacity is a measure of how much information can be transferred through a communications system in a given period of time 信息容量是在给定时间内,能通过通信系统传送多少信息的量度。 2.1 The signal can be one-dimensional, as in the case of speech, music, or computer data; two-dimensional, as in the case of pictures; three dimensional, as in the case of video data; and four-dimensional, as in the case of volume data over time. 信息可以是一维的，例如语音、音乐和计算机数据；也可以是二维的，例如图像；也可以是三维的，例如视频数据；还可以是四维的，例如随时间变化的立体空间数据 2.2 The type of scanning used in television is a form of a spatial sampling called raster scanning, which converts a two-dimensional image intensity into one-dimensional waveform; it is somewhat analogous to the manner in which we read a printed paper in that the scanning is preformed form left to right on a line-by-line basis. 电视用的扫描是一种称为栅格扫描的空间取样形式，它把二维的图像亮度转换为一维波形，类似于我们阅读印刷品时的逐行从左到右的扫描。 2.3 Suppose, for example, the communications agree to use even parity ; then the parity bit will be a 0 when the number of 1s