科技通信课程教案-2014年10月16日.doc

科技通信课程教案-2014年10月16日
2014年10月16日
Accordingly, we find that telephone circuits that respond well to this latter range of frequencies give quite satisfactory commercial telephone service.
Another important point that we have to keep in mind is the unavoidable presence of noise in a communication system. Noise refers to unwanted waves that tend to disturb the transmission and processing of message signals in a communication system. The source of noise may be internal or external to the system.
A quantitative way to account for the effect of noise is to introduce signal-to-noise ratio (SNR) as a system parameter. For example,
the information. A signal is defined as a single-valued function of time that plays the role of the independent variable; at every instant of time, the function has a unique value. 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. In the sequel, we elaborate on different sources of information.
(1) Speech is the primary method of human communication. Specifically, the speech communication process involves the trans
fer of information from a speaker to a listener, which takes place in three successive stages:
(1) Production. An intended mes