Wireless communication is the transfer of information between two or more points that
are not connected by an electrical conductor. The most common wireless technologies use
radio. With radio waves distances can be short, such as a few meters for television or as
far as thousands or even millions of kilometers for deep-space radio communications. It encompasses
various types of fixed, mobile, and portable applications, including two-way radios, cellular
telephones, personal digital assistants, and wireless networking. Other examples of applications
of radio wireless technology include GPS units, garage door openers, wireless computer mice,
keyboards and headsets, headphones, radio receivers, satellite television, broadcast
television and cordless telephones. Somewhat less common methods of achieving
wireless communications includes the use of other electromagnetic wireless technologies,
such as light, magnetic, or electric fields or the use of sound.
Introduction Wireless operations permit services, such
as long-range communications, that are impossible or impractical to implement with the use of
wires. The term is commonly used in the telecommunications industry to refer to telecommunications systems
which use some form of energy to transfer information without the use of wires. Information
is transferred in this manner over both short and long distances.
History Photophone
The world's first wireless telephone conversation occurred in 1880, when Alexander Graham Bell
and Charles Sumner Tainter invented and patented the photophone, a telephone that conducted
audio conversations wirelessly over modulated light beams. In that distant era, when utilities
did not yet exist to provide electricity and lasers had not even been imagined in science
fiction, there were no practical applications for their invention, which was highly limited
by the availability of both sunlight and good weather. Similar to free-space optical communication,
the photophone also required a clear line of sight between its transmitter and its receiver.
It would be several decades before the photophone's principles found their first practical applications
in military communications and later in fiber-optic communications.
Early wireless work
David E. Hughes transmitted radio signals over a few hundred yards by means of a clockwork
keyed transmitter in 1878. As this was before Maxwell's work was understood, Hughes' contemporaries
dismissed his achievement as mere "Induction". In 1885, Thomas Edison used a vibrator magnet
for induction transmission. In 1888, Edison deployed a system of signaling on the Lehigh
Valley Railroad. In 1891, Edison obtained the wireless patent for this method using
inductance. In 1888, Heinrich Hertz demonstrated the existence
of electromagnetic waves, the underlying basis of most wireless technology. The theory of
electromagnetic waves was predicted from the research of James Clerk Maxwell and Michael
Faraday. Hertz demonstrated that electromagnetic waves traveled through space in straight lines,
could be transmitted, and could be received by an experimental apparatus. Hertz did not
follow up on the experiments. Jagadish Chandra Bose around this time developed an early wireless
detection device and helped increase the knowledge of millimeter-length electromagnetic waves.
Practical applications of wireless radio communication and radio remote control technology were implemented
by later inventors.
Radio
The term "wireless" came into public use to refer to a radio receiver or transceiver,
establishing its usage in the field of wireless telegraphy early on; now the term is used
to describe modern wireless connections such as in cellular networks and wireless broadband
Internet. It is also used in a general sense to refer to any type of operation that is
implemented without the use of wires, such as "wireless remote control" or "wireless
energy transfer", regardless of the specific technology used. Guglielmo Marconi and Karl
Ferdinand Braun were awarded the 1909 Nobel Prize for Physics for their contribution to
wireless telegraphy. Modes
Wireless communications can be via: Radio
radio communication, microwave communication, for example long-range line-of-sight via highly
directional antennas, or short-range communication, Free-space optical
Free-space optical communication is an optical communication technology that uses light propagating
in free space to wirelessly transmit data for telecommunications or computer networking.
"Free space" means air, outer space, vacuum, or something similar. This contrasts with
using solids such as optical fiber cable or an optical transmission line.
The technology is useful where the physical connections are impractical due to high costs
or other considerations. Light, visible and infrared is used in for
example consumer IR devices such as remote controls or via Infrared Data Association.
Sonic Sonic, especially ultrasonic short range communication
involves the transmission and reception of sound.
Electromagnetic induction Electromagnetic induction short range communication
and power. This has been used in biomedical situations such as pacemakers, as well as
for short-range RFid tags. Wireless services
Common examples of wireless equipment include: Telemetry control and traffic control systems
Infrared and ultrasonic remote control devices Professional LMR and SMR typically used by
business, industrial and Public Safety entities. Consumer Two way radio including FRS Family
Radio Service, GMRS and Citizens band radios. The Amateur Radio Service.
Consumer and professional Marine VHF radios. Airband and radio navigation equipment used
by aviators and air traffic control Cellular telephones and pagers: provide connectivity
for portable and mobile applications, both personal and business.
Global Positioning System: allows drivers of cars and trucks, captains of boats and
ships, and pilots of aircraft to ascertain their location anywhere on earth.
Cordless computer peripherals: the cordless mouse is a common example; keyboards and printers
can also be linked to a computer via wireless using technology such as Wireless USB or Bluetooth
Cordless telephone sets: these are limited-range devices, not to be confused with cell phones.
Satellite television: Is broadcast from satellites in geostationary orbit. Typical services use
direct broadcast satellite to provide multiple television channels to viewers.
Wireless networks Wireless networking is used to meet many needs.
Perhaps the most common use is to connect laptop users who travel from location to location.
Another common use is for mobile networks that connect via satellite. A wireless transmission
method is a logical choice to network a LAN segment that must frequently change locations.
The following situations justify the use of wireless technology:
To span a distance beyond the capabilities of typical cabling,
To provide a backup communications link in case of normal network failure,
To link portable or temporary workstations, To overcome situations where normal cabling
is difficult or financially impractical, or To remotely connect mobile users or networks.
Developers need to consider some parameters involving Wireless RF technology for better
developing wireless networks: Sub-GHz versus 2.4 GHz frequency trends
Operating range and battery life Sensitivity and data rate
Network topology and node intelligence Applications may involve point-to-point communication,
point-to-multipoint communication, broadcasting, cellular networks and other wireless networks,
Wi-Fi technology. Cordless
The term "wireless" should not be confused with the term "cordless", which is generally
used to refer to powered electrical or electronic devices that are able to operate from a portable
power source without any cable or cord to limit the mobility of the cordless device
through a connection to the mains power supply. Some cordless devices, such as cordless telephones,
are also wireless in the sense that information is transferred from the cordless telephone
to the telephone's base unit via some type of wireless communications link. This has
caused some disparity in the usage of the term "cordless", for example in Digital Enhanced
Cordless Telecommunications. Electromagnetic spectrum
Light, colors, AM and FM radio, and electronic devices make use of the electromagnetic spectrum.
The frequencies of the radio spectrum that are available for use for communication are
treated as a public resource and are regulated by national organizations such as the Federal
Communications Commission in the USA, or Ofcom in the United Kingdom. This determines which
frequency ranges can be used for what purpose and by whom. In the absence of such control
or alternative arrangements such as a privatized electromagnetic spectrum, chaos might result
if, for example, airlines didn't have specific frequencies to work under and an amateur radio
operator were interfering with the pilot's ability to land an aircraft. Wireless communication
spans the spectrum from 9 kHz to 300 GHz. Applications of wireless technology
Mobile telephones One of the best-known examples of wireless
technology is the mobile phone, also known as a cellular phone, with more than 4.6 billion
mobile cellular subscriptions worldwide as of the end of 2010. These wireless phones
use radio waves to enable their users to make phone calls from many locations worldwide.
They can be used within range of the mobile telephone site used to house the equipment
required to transmit and receive the radio signals from these instruments.
Wireless data communications Wireless data communications are an essential
component of mobile computing. The various available technologies differ in local availability,
coverage range and performance, and in some circumstances, users must be able to employ
multiple connection types and switch between them. To simplify the experience for the user,
connection manager software can be used, or a mobile VPN deployed to handle the multiple
connections as a secure, single virtual network. Supporting technologies include:
Wi-Fi is a wireless local area network that enables portable computing devices to connect
easily to the Internet. Standardized as IEEE 802.11 a,b,g,n, Wi-Fi approaches speeds of
some types of wired Ethernet. Wi-Fi has become the de facto standard for access in private
homes, within offices, and at public hotspots. Some businesses charge customers a monthly
fee for service, while others have begun offering it for free in an effort to increase the sales
of their goods. Cellular data service offers coverage within
a range of 10-15 miles from the nearest cell site. Speeds have increased as technologies
have evolved, from earlier technologies such as GSM, CDMA and GPRS, to 3G networks such
as W-CDMA, EDGE or CDMA2000. Mobile Satellite Communications may be used
where other wireless connections are unavailable, such as in largely rural areas or remote locations.
Satellite communications are especially important for transportation, aviation, maritime and
military use. Wireless Sensor Networks are responsible for
sensing noise, interference, and activity in data collection networks. This allows us
to detect relevant quantities, monitor and collect data, formulate meaningful user displays,
and to perform decision-making functions Wireless energy transfer
Wireless energy transfer is a process whereby electrical energy is transmitted from a power
source to an electrical load that does not have a built-in power source, without the
use of interconnecting wires. There are two different fundamental methods for wireless
energy transfer. They can be transferred using either far-field methods that involve beam
power/lasers, radio or microwave transmissions or near-field using induction. Both methods
utilize electromagnetism and magnetic fields Wireless Medical Technologies
New technologies such as mobile body area networks the capability to monitor blood pressure,
heart rate, oxygen level and body temperature, all with wireless technologies. The MBAN works
by sending low powered wireless signals to receivers that feed into nursing stations
or monitoring sites. This technology helps with the intentional and unintentional risk
of infection or disconnection that arise from wired connections.
Computer interface devices
Answering the call of customers frustrated with cord clutter, many manufacturers of computer
peripherals turned to wireless technology to satisfy their consumer base. Originally
these units used bulky, highly limited transceivers to mediate between a computer and a keyboard
and mouse; however, more recent generations have used small, high-quality devices, some
even incorporating Bluetooth. These systems have become so ubiquitous that some users
have begun complaining about a lack of wired peripherals. Wireless devices tend to have
a slightly slower response time than their wired counterparts; however, the gap is decreasing.
Computer interface devices such as a keyboard or mouse are powered by a battery and send
signals to a receiver through a USB port by way of a radio frequency receiver. The RF
design makes it possible for signals to be transmitted wirelessly and expands the range
of effective use, usually up to 10 feet. Distance, physical obstacles, competing signals, and
even human bodies can all degrade the signal quality.
Concerns about the security of wireless keyboards arose at the end of 2007, when it was revealed
that Microsoft's implementation of encryption in some of its 27 MHz models was highly insecure.
Categories of wireless implementations, devices and standards
Radio communication system Broadcasting
Amateur radio Land Mobile Radio or Professional Mobile Radio:
TETRA, P25, OpenSky, EDACS, DMR, dPMR Cordless telephony:DECT
Cellular networks: 0G, 1G, 2G, 3G, Beyond 3G, Future wireless
List of emerging technologies Short-range point-to-point communication :
Wireless microphones, Remote controls, IrDA, RFID, TransferJet, Wireless USB, DSRC, EnOcean,
Near Field Communication Wireless sensor networks: ZigBee, EnOcean;
Personal area networks, Bluetooth, TransferJet, Ultra-wideband.
Wireless networks: Wireless LAN,, Wireless Metropolitan Area Networks and
See also History of radio, Timeline of radio, Digital
radio, Radio resource management Hotspot, Wireless energy transfer, True wireless,
Wireless security, Wireless access point Li-Fi
Mobile Personal area network, comparison of wireless
data standards, List of emerging technologies Radio antenna
Terrestrial television Tuner
References
Further reading Pahlavan, Kaveh; Levesque, Allen H. Wireless
Information Networks. John Wiley & Sons. ISBN 0471106070. Geier, Jim. Wireless LANs. Sams. ISBN 0-672-32058-4.
Goldsmith, Andrea. Wireless Communications. Cambridge University Press. ISBN 0-521-83716-2.
Molisch, Andreas. Wireless Communications. Wiley-IEEE Press. ISBN 0-470-84888-X.
Pahlavan, Kaveh; Krishnamurthy, Prashant. Principles of Wireless Networks - a Unified
Approach. Prentice Hall. ISBN 0-13-093003-2. Rappaport, Theodore. Wireless Communications:
Principles and Practice. Prentice Hall. ISBN 0-13-042232-0. Rhoton, John. The Wireless Internet Explained.
Digital Press. ISBN 1-55558-257-5. Tse, David; Viswanath, Pramod. Fundamentals
of Wireless Communication. Cambridge University Press. ISBN 0-521-84527-0.
Larsson, Erik; Stoica, Petre. Space-Time Block Coding For Wireless Communications. Cambridge
University Press. External links
Nets, Webs and the Information Infrastructure at Wikibooks
"Wireless Telegraphy and Telephony". Collier's New Encyclopedia. 1921.
Wireless at DMOZ