Wireless communication
Handheld wireless radios such as this Maritime VHF radio transceiver use electromagnetic waves to implement a form of wireless communications technology.
Wireless operations permits 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 (e.g., radio transmitters and receivers, remote controls, computer networks, network terminals, etc.) which use some form of energy (e.g. radio frequency (RF), infrared light, laser light, visible light, acoustic energy, etc.) to transfer information without the use of wires.[2] Information is transferred in this manner over both short and long distances.
The term "wireless" has become a generic and all-encompassing word used to describe communications in which electromagnetic waves or RF (rather than some form of wire) carries a signal over part or the entire communication path. Common examples of wireless equipment in use today include:
§ Professional LMR (Land Mobile Radio) and SMR (Specialized Mobile Radio) typically used by business, industrial and Public Safety entities
§ Consumer Two Way Radio including FRS (Family Radio Service), GMRS (General Mobile Radio Service) and Citizens band ("CB") radios
§ The Amateur Radio Service (Ham radio)
§ Consumer and professional Marine VHF radios
§ Cellular telephones and pagers: provide connectivity for portable and mobile applications, both personal and business.
§ Global Positioning System (GPS): 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.
§ Cordless telephone sets: these are limited-range devices, not to be confused with cell phones.
§ Satellite television: allows viewers in almost any location to select from hundreds of channels.
§ Wireless gaming: new gaming consoles allow players to interact and play in the same game regardless of whether they are playing on different consoles. Players can chat, send text messages as well as record sound and send it to their friends. Controllers also use wireless technology. They do not have any cords but they can send the information from what is being pressed on the controller to the main console which then processes this information and makes it happen in the game. All of these steps are completed in milliseconds.
Wireless networking (i.e. the various types of unlicensed 2.4 GHz WiFi devices) 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 avoid obstacles such as physical structures, EMI, or RFI,
§ 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.
Wireless communication can be via:
§ radio frequency communication,
§ microwave communication, for example long-range line-of-sight via highly directional antennas, or short-range communication, or
§ Infrared (IR) short-range communication, for example from remote controls or via IRDA.
Applications may involve point-to-point communication, point-to-multipoint communication, broadcasting, cellular networks and other wireless networks.
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 (e.g. a battery pack) 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.
In the last fifty years, wireless communications industry experienced drastic changes driven by many technology innovations.
History
The term "Wireless" came into public use to refer to a radio receiver or transceiver (a dual purpose receiver and transmitter device), 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 (e.g. radio, infrared, ultrasonic) that is used to accomplish the operation.
Early wireless work
David E. Hughes, eight years before Hertz's experiments, induced electromagnetic waves in a signaling system. Hughes transmitted Morse code by an induction apparatus. In 1878, Hughes's induction transmission method utilized a "clockwork transmitter" to transmit signals. In 1885, T. A. Edison used a vibrator magnet for induction transmission. In 1888, Edison deploys a system of signaling on the Lehigh Valley Railroad. In 1891, Edison attains the wireless patent for this method using inductance (U.S. Patent 465,971 ).
In the history of wireless technology, the demonstration of the theory of electromagnetic waves by Heinrich Rudolf Hertz in 1888 was important.[3][4] The theory of electromagnetic waves were predicted from the research of James Clerk Maxwell and Michael Faraday. Hertz demonstrated that electromagnetic waves could be transmitted and caused to travel through space at straight lines and that they were able to be received by an experimental apparatus.[3][4] The experiments were not followed up by Hertz. The practical applications of the wireless communication and remote control technology were implemented by Nikola Tesla.
The electromagnetic spectrum
Light, colours, AM and FM radio and electronic devices make use of the electromagnetic spectrum. In the US the frequencies that are available for use for communication are treated as a public resource and are regulated by the Federal Communications Commission. 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 was interfering with the pilot's ability to land an airplane. Wireless communication spans the spectrum from 9 kHz to 300 GHz. (Also see Spectrum management)
Applications of wireless technology
Security systems
Wireless technology may supplement or replace hard wired implementations in security systems for homes or office buildings
Television remote control
Modern televisions use wireless (generally infrared) remote control units. Now radio waves are also used.
Cellular telephony (phones and modems)
Perhaps the best known example of wireless technology is the cellular telephone and modems. These instruments use radio waves to enable the operator to make phone calls from many locations world-wide. They can be used anywhere that there is a cellular telephone site to house the equipment that is required to transmit and receive the signal that is used to transfer both voice and data to and from these instruments.
WiFi
Wi-Fi (for wireless fidelity) is a wireless LAN technology that enables laptop PC’s, PDA’s, and other devices to connect easily to the internet. Technically known as IEEE 802.11b, Wi-Fi is faster and less expensive than standard Ethernet and other common wire-based LAN technologies. Several Wi-Fi hot spots have been popular over the past few years. 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. Wi-Fi allows local area networks (LANs) to be deployed without wires for client devices, typically reducing the costs of network deployment and expansion. Spaces where cables cannot be run, such as outdoor areas and historical buildings, can host wireless LANs. Wireless network adapters are now built into most laptops. The price of chipsets for Wi-Fi continues to drop, making it an economical networking option included in even more devices. Wi-Fi has become widespread in corporate infrastructures. Different competitive brands of access points and client network interfaces are inter-operable at a basic level of service. Products designated as "Wi-Fi Certified" by the Wi-Fi Alliance are backwards compatible. Wi-Fi is a global set of standards. Unlike mobile telephones, any standard Wi-Fi device will work anywhere in the world.
Wi-Fi is widely available in more than 220,000 public hotspots and tens of millions of homes and corporate and university campuses worldwide.[7] Wi-Fi Protected Access encryption (WPA and WPA2) is not easily cracked if strong passwords are used. New protocols for Quality of Service (WMM) make Wi-Fi more suitable for latency-sensitive applications (such as voice and video), and power saving mechanisms (WMM Power Save) improve battery operation.
Because of the very limited practical range of Wi-Fi, mobile use is essentially confined to such applications as inventory taking machines in warehouses or retail spaces, barcode reading devices at check-out stands or receiving / shipping stations. Mobile use of Wi-Fi over wider ranges is limited to move, use, move, as for instance in an automobile moving from one hotspot to another (Wardriving). Other wireless technologies are more suitable as illustrated in the graphic.
Standardization is a process driven by market forces. Interoperability issues between non-Wi-Fi brands or proprietary deviations from the standard can still disrupt connections or lower throughput speeds on all user's devices that are within range, to include the non-Wi-Fi or proprietary product. Moreover, the usage of the ISM band in the 2.45 GHz range is also common to Bluetooth, WPAN-CSS, ZigBee and any new system will take its share.
Wi-Fi pollution, or an excessive number of access points in the area, especially on the same or neighboring channel, can prevent access and interfere with the use of other access points by others, caused by overlapping channels in the 802.11g/b spectrum, as well as with decreased signal-to-noise ratio (SNR) between access points. This can be a problem in high-density areas, such as large apartment complexes or office buildings with many Wi-Fi access points. Additionally, other devices use the 2.4 GHz band: microwave ovens, security cameras, Bluetooth devices and (in some countries)Amateur radio, video senders, cordless phones and baby monitors, all of which can cause significant additional interference. General guidance to those who suffer these forms of interference or network crowding is to migrate to a Wi-Fi 5 GHz product, (802.11a, or the newer 802.11n if it has 5 GHz support) because the 5 GHz band is relatively unused, and there are many more channels available. This also requires users to set up the 5 GHz band to be the preferred network in the client and to configure each network band to a different name (SSID). It is also an issue when municipalities,[9] or other large entities such as universities, seek to provide large area coverage. This openness is also important to the success and widespread use of 2.4 GHz Wi-Fi.
Two common, but unproductive, measures to deter unauthorized users include suppressing the AP'sSSID broadcast, allowing only computers with known MAC addresses to join the network, and variousencryption standards. Suppressed SSID and MAC filtering are ineffective security methods as the SSID is broadcast in the open in response to a client SSID query and a MAC address can easily be spoofed. If the eavesdropper has the ability to change his MAC address, then he can potentially join the network byspoofing an authorized address.
Wired Equivalent Privacy (WEP) encryption was designed to protect against casual snooping, but is now considered completely broken. Tools such as AirSnort or aircrack can quickly recover WEP encryption keys. Once it has seen 5-10 million encrypted packets, AirSnort can determine the encryption password in under a second;newer tools such as aircrack-ptw can use Klein's attack to crack a WEP key with a 50% success rate using only 40,000 packets.
To counteract this in 2002, the Wi-Fi Alliance blessed Wi-Fi Protected Access (WPA) which uses TKIPas a stopgap solution for legacy equipment. Though more secure than WEP, it has outlived its designed lifetime, has known attack vectors and is no longer recommended. In 2004 the full IEEE 802.11i (WPA2) encryption standards were released. If used with a 802.1X server or in pre-shared key mode with a strong and uncommon passphrase WPA2 is still considered secure, as of 2009.
Wireless LAN
The notebook is connected to the wireless access point using a PC card wireless card.
A wireless LAN (WLAN) is a wireless local area network that links two or more computers or devices using spread-spectrum or OFDM modulation technology based to enable communication between devices in a limited area. This gives users the mobility to move around within a broad coverage area and still be connected to the network.
For the home user, wireless has become popular due to ease of installation, and location freedom with the gaining popularity of laptops. Public businesses such as coffee shops or malls have begun to offer wireless access to their customers; some are even provided as a free service. Large wireless network projects are being put up in many major cities. Google is even providing a free service to Mountain View, California[1] and has entered a bid to do the same for San Francisco.[2] New York City has also begun a pilot program to cover all five boroughs of the city with wireless Internetaccess.
The popularity of wireless LANs is a testament primarily to their convenience, cost efficiency, and ease of integration with other networks and network components. The majority of computers sold to consumers today come pre-equipped with all necessary wireless LAN technology. Benefits of wireless LANs include:
The wireless nature of such networks allows users to access network resources from nearly any convenient location within their primary networking environment (home or office). With the increasing saturation of laptop-style computers, this is particularly relevant.
With the emergence of public wireless networks, users can access the internet even outside their normal work environment. Most chain coffee shops, for example, offer their customers a wireless connection to the internet at little or no cost.
Initial setup of an infrastructure-based wireless network requires little more than a single access point. Wired networks, on the other hand, have the additional cost and complexity of actual physical cables being run to numerous locations (which can even be impossible for hard-to-reach locations within a building).
Wireless networking hardware is at worst a modest increase from wired counterparts. This potentially increased cost is almost always more than outweighed by the savings in cost and labor associated to running physical cables.
The typical range of a common 802.11g network with standard equipment is on the order of tens of metres. While sufficient for a typical home, it will be insufficient in a larger structure. To obtain additional range, repeaters or additional access points will have to be purchased. Costs for these items can add up quickly. Other technologies are in the development phase, however, which feature increased range, hoping to render this disadvantage irrelevant. (See WiMAX)
The speed on most wireless networks (typically 1-108 Mbit/s) is reasonably slow compared to the slowest common wired networks (100 Mbit/s up to several Gbit/s). There are also performance issues caused by TCP and its built-in congestion avoidance. For most users, however, this observation is irrelevant since the speed bottleneck is not in the wireless routing but rather in the outside network connectivity itself. For example, the maximum ADSL throughput (usually 8 Mbit/s or less) offered by telecommunications companies to general-purpose customers is already far slower than the slowest wireless network to which it is typically connected. That is to say, in most environments, a wireless network running at its slowest speed is still faster than the internet connection serving it in the first place. However, in specialized environments, higher throughput through a wired network might be necessary. Newer standards such as 802.11n are addressing this limitation and will support peak throughput in the range of 100-200 Mbit/s.
§ Radio communication system
§ Broadcasting
§ Amateur radio
§ Land Mobile Radio or Professional Mobile Radio: TETRA, P25, OpenSky, EDACS, DMR,dPMR
§ Communication radio
§ Cordless telephony:DECT (Digital Enhanced Cordless Telecommunications)
§ Cellular systems: 0G, 1G, 2G, 3G, Beyond 3G (4G), Future wireless
§ List of emerging technologies
§ Short-range point-to-point communication : Wireless microphones, Remote controls, IrDA, RFID (Radio Frequency Identification),Wireless USB, DSRC (Dedicated Short Range Communications), EnOcean, Near Field Communication
§ Wireless sensor networks: ZigBee, EnOcean; Personal area networks, Bluetooth, TransferJet, Ultra-wideband (UWB from WiMedia Alliance).
§ Wireless computer networks: Wireless Local Area Networks (WLAN), (IEEE 802.11 branded as WiFi and HiperLAN), Wireless Metropolitan Area Networks (WMAN) and Broadband Fixed Access (BWA) (LMDS, WiMAX, WANKA and HiperMAN)
§ Mobile
§ History of radio, Timeline of radio, Digital radio, Radio resource management (RRM)
§ Hotspot (Wi-Fi), Wireless energy transfer, True wireless, Wireless security, Wireless Access Point
§ Personal area network, comparison of wireless data standards, List of emerging technologies
§
§ References
1. "Wireless Communication". sintef.no. Retrieved on 2008-03-16.
2. "ATIS Telecom Glossary 2007". atis.org. Retrieved on 2008-03-16.
3. “Story, Alfred Thomas (1904). A story of wireless telegraphy. New York, D. Appleton and Co..
4. "Heinrich Rudolf Hertz". chem.ch.huji.ac.il. Retrieved on 2008-03-16.
5. O'Brien, J. & Marakas, G.M.(2008) Managment Information Systems (pp. 239). New York, NY: McGraw-Hill Irwin
6. External links
§ Wikia has a wiki on this subject at wireless
§ U.S. Patent 1,642,420 , S. Loewe, "Wireless Receiving Apparatus"
§ U.S. Patent 1,754,875 , E. E. Clement, "Radiophone desk set"
§ The Colin-Jeance System of Wireless Telephony Scientific American Oct. 31, 1914
§ Wireless Networking Technologies
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