Jawaharlal Nehru Technological University Hyderabad B.Tech III INDUSTRIAL AUTOMATION Previous Question Paper (February/March - 2022 - R18)

A data communication system consists of five fundamental components that enable the exchange of data between two devices:

1. Message: The information or data to be communicated, which can be in the form of text, numbers, images, audio, or video.
2. Sender: The device that originates the data message, such as a computer, workstation, or telephone.
3. Receiver: The device that receives the message, which can be a computer, printer, or server.
4. Transmission Medium: The physical path by which the message travels from sender to receiver, such as twisted-pair wire, coaxial cable, fiber-optic cable, or wireless radio waves.
5. Protocol: A set of rules that govern data communication. It represents an agreement between the communicating devices regarding how data is formatted, timed, and synchronized.

A digital signal consists of discrete voltage levels (typically square waves) that contain a wide range of frequency components, theoretically extending from zero (DC) to infinity. Most communication channels, such as telephone lines or wireless links, are band-pass channels, meaning they only allow a specific range of frequencies to pass through while attenuating or blocking others.

If a raw digital signal were transmitted through a band-pass channel, the following issues would occur:

1. Signal Distortion: The channel would filter out the low-frequency (DC) components and high-frequency harmonics, causing severe inter-symbol interference and rounding of the pulse edges.
2. Frequency Mismatch: The channel's passband is located at a higher frequency range. To transmit data, the digital information must be shifted from baseband to the channel's passband frequency.

Therefore, digital signals must undergo modulation. Modulation involves using the digital data to alter a characteristic (amplitude, frequency, or phase) of a high-frequency carrier wave. This process shifts the signal spectrum into the channel's passband, ensuring efficient transmission, reduced noise interference, and compatibility with the physical limitations of the medium.