Communication Systems: Basic Concepts

Communication Basics

• Communication is the exchange of information between two points.
• From an electronics perspective, communication involves using electronic devices to exchange information between distant points.
• Information exchange can occur through wired or wireless means.
• Types of communication include point-to-point, point-to-multipoint, network, and broadcast.
• FM transmission is an example of broadcasting where a radio station transmits information at a specific frequency for anyone to tune into.

Basic Block Diagram of a Communication System

• The communication system consists of several key components that facilitate the transmission of information from a source to a destination.
• The source generates the message signal, which can be voice, email, television signal, or data.
• If the message is in a non-electrical form, a transducer converts it into an electrical signal.
• Examples of transducers include microphones, CCD cameras, and computer keyboards.
• The electrical signal produced after the transducer is the input signal.
• The transmitter modifies the input signal for efficient transmission, containing subsystems like modulators, analog-to-digital converters, and encoders.
• The transmitter may also contain an amplifier system.
• If the signal is analog, it is sampled at regular intervals, quantized, and then converted into digital form using an analog-to-digital converter.
• The signal can be encoded into a specific format using an encoder.
• Modulation involves altering the amplitude, phase, or frequency of a periodic signal based on the input signal.

Characteristics of the Transmitted Signal

• Key characteristics include whether the signal is analog or digital.
• The frequency of the signal needs to be known.
• The range of frequencies in the transmitted signal, or the bandwidth, needs to be determined.
• For digital signals, the data rate or bit-rate of transmission is essential.
• The power level of the signal determines how far it can be transmitted faithfully over a medium.
• The signal after the transmitter is the transmitted signal.

Channel

• A channel is a medium through which the signal is transmitted over a distance and can be physical (optical fiber, coaxial cable) or wireless (radio link).
• The channel can act as a filter, attenuating different frequencies of the transmitted signal differently.
• The transmitted signal becomes attenuated and distorted, with superimposed noise, after passing through the channel.
• The amount of attenuation and distortion depends on the channel's length.
• A detector or receiver should recover the message signal from the distorted signal.
• Signal-to-noise ratio, the ratio of signal power to noise power, is a critical parameter where increasing signal power improves the signal-to-noise ratio.
• Regenerative repeaters detect and regenerate a fresh copy of the transmitted signal for long-distance transmission cases where the signal power cannot be infinitely increased.
• Error correction mechanisms and redundancy help reduce errors in digital signals.

Channel Specifications

• The length of the channel or the maximum transmission distance is important.
• The bandwidth of the channel, is the range of frequencies supported by the channel with reasonable fidelity.
• The maximum supported data rate is relevant for digital signals.

Receiver

• At the receiver, the received signal is demodulated.
• Digital signals are first decoded.
• Digital signals are converted into analog signals using a digital-to-analog converter.
• After amplification, the signal is sent to the output transducer, such as a speaker or display screen.