Let's Make Some Noise

In The Bell System Technical Journal, Vol. 27, pp. 379–423, 623–656, July, October, 1948, Claude Shannon a mathematician and engineer wrote a simple and foundational paper called “A Mathematical Theory of Communication," [http://cm.belllabs.com/cm/ms/what/shannonday/shannon1948.pdf ]. The article is prefaced by Warren Weaver's introduction, ``Recent contributions to the mathematical theory of communication”. Together the contributions were called the “Shannon-Weaver model of communication”.

Claude Elwood Shannon is famous for having founded an entire new field called information theory with this one landmark paper. He also has numerous contributions to digital computer and digital circuit design, when, as a 21-year-old master's student at MIT, he wrote a thesis demonstrating that electrical application of Boolean algebra could construct and resolve any logical, numerical relationship. It has been noted in Wikipedia that this was the most important master's thesis of all time.

The Shannon-Weaver model is simply and elegantly designed to define the effective communication between a sender and receiver. Also defined are variables which affect the communication process and labeled “Noise”. The model simplifies the definition of key communication channel components like Information source, transmitter, Noise, channel, message, receiver, channel, information destination, encode and decode.

The noise classifications common to the communication channels (wired and wireless) include Thermal Noise, Intermodulation noise, Crosstalk and Impulse Noise. The definitions in the book (Fundamentals of Telecommunications, Second Edition 2005, Roger L. Freeman) describe each of these types.

Thermal Noise is a function of temperature that excites electrons and is a noise source that cannot be eliminated. The noise is quantitatively expressed as amount of thermal noise to be found in a bandwidth of 1Hz in any device or conductor is:

N0=noise power density in watts per 1 Hz of bandwidth

k=Boltzmann's constant=1.3803 x 10-23J/K

T=temperature (in Kelvin)/absolute temperature

Intermodulation noise is variant that is created when signals with different frequencies share the same medium. Interference is caused by a signal produced at a frequency that is the sum or difference of original frequencies. This is a noise type that can be estimated if the variables are known and can be removed.

Crosstalk noise is an undesired capacitive, inductive, or conductive coupling from one circuit, part of a circuit, or channel, to another. It is a phenomenon by which a signal transmitted on one channel creates an undesired effect in another channel. This is also a noise type that can estimated if the coupling and variables are precisely known. In real world these are typically not known. Crosstalk can be minimized and there are many optimal transmission techniques used to cancel crosstalk.

Impulse noise is an irregular, non-deterministic spike of noise pulses. These are defined as function of duration and high amplitude. They are Generally caused by external electromagnetic interference sources in the communications system such as power surges etc. They are common and if characterized accurately the impacts of impulse noise on data transmission or communication can be minimized by various forward error correction (FEC) coding techniques.