Wireless technologies
Computers
are very often connected to networks using wireless links
Main
article: Wireless
network
- Terrestrial microwave – Terrestrial microwave communication uses
Earth-based transmitters and receivers resembling satellite dishes.
Terrestrial microwaves are in the low-gigahertz range, which limits all
communications to line-of-sight. Relay stations are spaced approximately
48 km (30 mi) apart.
- Communications satellites – Satellites communicate via microwave
radio waves, which are not deflected by the Earth's atmosphere. The
satellites are stationed in space, typically in geosynchronous orbit
35,400 km (22,000 mi) above the equator. These Earth-orbiting
systems are capable of receiving and relaying voice, data, and TV signals.
- Cellular and
PCS systems use
several radio communications technologies. The systems divide the region
covered into multiple geographic areas. Each area has a low-power
transmitter or radio relay antenna device to relay calls from one area to
the next area.
- Radio and spread
spectrum technologies – Wireless local area networks use a
high-frequency radio technology similar to digital cellular and a
low-frequency radio technology. Wireless LANs use spread spectrum
technology to enable communication between multiple devices in a limited
area. IEEE
802.11 defines a common
flavor of open-standards wireless radio-wave technology known as Wifi.
- Free-space optical communication uses visible or invisible light for
communications. In most cases, line-of-sight propagation is used, which limits the
physical positioning of communicating devices.
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