Communication System Components

Study Notes

A communication system consists of a source, input transducer, transmitter, channel, receiver, and output transducer.
The source originates a message, which can be human voice, television picture, teletype message, or data.
If the data is non-electrical, it must be converted into an electrical waveform by an input transducer.

The transmitter modifies the baseband signal for efficient transmission.
The channel is a medium through which the transmitter output is sent, such as wire, coaxial cable, or radio link.
The receiver reprocesses the signal received from the channel and undoes the signal modifications made at the transmitter and channel.
The output transducer converts the electrical signal back to its original form.

Messages can be either digital or analog.
Digital messages are constructed with a finite number of symbols, such as printed language.
Analog messages are characterized by data whose values vary over a continuous range, such as temperature or atmospheric pressure.

The task of the receiver is to extract a message from a distorted and noisy signal at the channel output.
Message extraction is often easier from digital signals than from analog signals.
Repeater stations are used in digital systems to detect and retransmit pulses, preventing the accumulation of noise and distortion.

Digital communication is more rugged and can withstand channel noise and distortion.
Regenerative repeaters can be used to improve signal quality.
Digital hardware implementation is flexible and can be coded to yield extremely low error rates.
Digital signals can be multiplexed more efficiently.
Digital communication is inherently more efficient in realizing the exchange of SNR for bandwidth.
Digital signal storage is relatively easy and inexpensive.
Digital messages can be reproduced extremely reliably without deterioration.

The fundamental parameters that control the rate and quality of information transmission are channel bandwidth and signal power.
The bandwidth of a channel is the range of frequencies available for transmission.