Q. Digital communication systems?

Today digital communication systems are in common use, carrying the bulk of our daily information transmission through a variety of communication media, such as wire-line telephone channels, microwave radio, fiber-optic channels, and satellite channels. Even the current analog AMand FMradio and television broadcasts will be replaced in the near future by digital transmission systems. High-speed integrated circuits (ICs), programmable digital signal processing chips, microelectronic IC fabrication, and sophisticated digital modulation techniques have certainly helped digital communications as a means of transmitting information.

In spite of the general trend toward digital transmission of analog signals, a significant amount of analog signal transmission still takes place, especially in audio and video broadcasting. Historically, analog communication systems were placed first, and then came digital communication systems.

In any communication system, the communication channel provides the connection between the transmitter and the receiver. The physical channel (medium) may be any of the following:

• A pair of wires, which carry the electric signal

• Optical fiber, which carries the information on a modulated light beam

• An underwater ocean channel, in which the information is transmitted acoustically

• Free space, over which the information-bearing signal is radiated by using an antenna

• Data storage media, such as magnetic tape, magnetic disks, and optical disks.

The available channel bandwidth, as well as the noise and interference, limit the amount of data that can be transmitted reliably over any communication channel.