Understanding Bandwidth and Information Capacity

Bandwidth

• The bandwidth of an information signal is the difference between the highest and lowest frequencies contained.
• A communications channel's bandwidth is the difference between the highest and lowest frequencies the channel allows to pass.
• Bandwidth must be large enough to pass significant information frequencies.
• Bandwidth must be equal to or greater than the bandwidth of the information.

Information Capacity

• Information theory is a study of the efficient use of bandwidth to propagate information through electronic communication systems.
• It determines the information capacity of a data communications system.
• Information capacity measures how much information propagates through a communications system.
• This is a function of bandwidth and transmission time
• It represents the number of independent symbols carried through a system in a given time unit.
• A binary digit, or bit, is the most basic digital symbol used to represent information.
• Bit rate refers to the number of bits transmitted in one second, measured in bits per second (bps).

Noise

• Electrical noise is any undesirable electrical energy that falls within the signal's passband.
• Noise is divided into correlated and uncorrelated categories.
• Correlated noise implies a relationship between the signal and the noise, existing only when a signal is present.
• Uncorrelated noise is present whether a signal is present or not.
• Noise results in loudspeakers and hiss.

Types of Noise

• Uncorrelated noise is present regardless of a signal's presence.
• It is divided into external and internal noise.
• External noise is generated outside the system, coming from atmospheric, extraterrestrial, and man-made sources.
• Internal noise is electrical interference generated within a device or circuit. The three kinds of internal noise are shot, transit-timed, and thermal.
• Atmospheric noise is a naturally occurring electrical disturbance originating within Earth's atmosphere and is static electricity.
• It is caused by naturally occurring electrical conditions, like lightning.
• Its magnitude is inversely proportional to frequency, becoming insignificant above 30 MHz.
• Extraterrestrial noise consists of electrical signals originating from outside Earth's atmosphere.
• It originates from the Milky Way, other galaxies, and the sun.
• It is divided into solar and cosmic noise.
• Solar noise is generated directly from the sun and by sunspot activity and solar flare-ups.
• Cosmic noise comes from sources distributed throughout the galaxies and is also called black-body noise.
• Man-made noise, or industrial noise, is noise produced by humans.
• Examples include commutators in motors/generators, automobile ignitions, and fluorescent lights.
• Thermal noise is associated with the rapid and random movement of electrons within a conductor due to thermal agitation.
• It is present in all electronic components and communication systems.
• It is uniformly distributed across the entire electromagnetic spectrum and increases in intensity with the number of devices in a circuit and with the circuit length.
• It is also known as Johnson noise, thermal agitation noise, agitation noise, and white noise.
• Shot noise is caused by the random arrival of carriers at the output element of an electronic device.
• Shot noise is randomly varying and superimposed onto any signal present.
• Sometimes called transistor noise, shot noise is additive with thermal noise.
• Transit time noise is any modification to a stream of carriers as they pass from the input to the output of a device, which produces an irregular, random variation.
• Partition noise occurs whenever current has to divide between two or more electrodes, resulting from the fluctuations in the division.