CH1-COM-COMMUNICATION SYSTEM ELEMENTS

COMMUNICATION SYSTEM ELEMENTS
Figure 1.1 shows a commonly used model for a single-link communication system. Although it suggests a system for communication between two remotely located points, this block diagram is also applicable to remote sensing systems, such as radar or sonar, in which the system input and output may be located at the same site. Regardless of the particular application and configuration, all information transmission systems invariably involve three major subsystems-a transmitter, the channel, and a receiver.

Input Transducer: The wide variety of possible sources of information results in many different forms for messages. Regardless of their exact form, however, messages may be categorized as analog or digital. The former may be modeled as functions of a continuous-time variable (e.g., pressure, temperature, speech, music), whereas the latter consists of discrete symbols (e.g., written text). Almost invariably, the message produced by a source must be converted by a transducer to a form suitable for the particular type of communication system employed. For example, in electrical communications, speech waves are converted by a microphone to voltage variations. Such a converted message is referred to as the message signal.