Editing Communications system (section)

=== By media===
An [[optical communication]] system is any form of communications system that uses [[light]] as the transmission medium. Equipment consists of a [[transmitter]], which encodes a ''[[message]]'' into an optical ''[[signal]]'', a ''[[communication channel]]'', which carries the signal to its destination, and a [[Radio receiver|receiver]], which reproduces the message from the received optical signal. [[Fiber-optic communication]] systems transmit information from one place to another by sending light through an [[optical fiber]]. The light forms a [[carrier signal]] that is [[Modulation|modulated]] to carry information.

A [[radio communication system]] is composed of several communications [[subsystem]]s that give exterior communications capabilities.<ref>Schwartz, M., Bennett, W. R., & Stein, S. (1996). ''Communication systems and techniques''. New York: IEEE Press.</ref>{{page needed|date=May 2023}}<ref>Rappaport, T. S. (1996). ''Wireless communications: principles and practice''. Upper Saddle River, N.J.: Prentice Hall PTR.</ref>{{page needed|date=May 2023}}<ref name=":0">{{cite web |url=http://www.fas.org/man/dod-101/sys/ship/weaps/radio.htm |title=Radio Communications System |access-date=2021-02-09}}</ref> A radio communication system comprises a transmitting [[Electrical conductor|conductor]]<ref name="JSS717512" /> in which electrical  [[oscillation]]s<ref>[[John Stone Stone]], {{US patent|726476}}</ref><ref>John Stone Stone, {{US patent|726368}}</ref><ref>John Stone Stone, {{US patent|577214}}</ref> or [[Electric current|currents]] are produced and which is arranged to cause such currents or oscillations to be propagated through the [[free space]] medium from one point to another remote therefrom and a receiving conductor<ref name="JSS717512">John Stone Stone, {{US patent|717512}}</ref> at such distant point adapted to be excited by the oscillations or currents propagated from the transmitter.<ref>[[Nikola Tesla]], {{US patent|649621}}</ref><ref>Nikola Tesla, {{US patent|787412}}</ref><ref>John Stone Stone, {{US patent|714756}}</ref><ref>John Stone Stone, {{US patent|716955}}</ref>

[[Power-line communication]] systems operate by impressing a modulated carrier signal on power wires. Different types of power-line communications use different frequency bands, depending on the signal transmission characteristics of the power wiring used. Since the power wiring system was originally intended for transmission of [[AC power]], the power wire circuits have only a limited ability to carry higher frequencies. The propagation problem is a limiting factor for each type of power line communications.