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Wireless CDMA PCS Repeater Optical Fiber

The term wireless refers to telecommunication in which electromagnetic waves (rather than some form of wire) carry the signal over part or all of the communication path. Some monitoring devices, such as intrusion alarms, employ acoustic waves at frequencies above the range of human hearing; these are also sometimes classified as wireless.

The first wireless transmitters went on the air in the early 20th century using radiotelegraphy (Morse code). Later, as modulation made it possible to transmit voices and music via wireless, the medium came to be called "radio." With the advent of television, fax, data communication, and the effective use of a larger portion of the spectrum, the term "wireless" has been resurrected.

Common examples of wireless equipment in use today include:

Cellular phones 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

Home-entertainment-system control boxes -- the VCR control and the TV channel control are the most common examples; some hi-fi sound systems and FM broadcast receivers also use this technology

Remote garage-door openers -- one of the oldest wireless devices in common use by consumers; usually operates at radio frequencies

Two-way radios -- this includes Amateur and Citizens Radio Service, as well as business, marine, and military communications

Baby monitors -- these devices are simplified radio transmitter/receiver units with limited range

Satellite television -- allows viewers in almost any location to select from hundreds of channels

Wireless LANs or local area networks -- provide flexibility and reliability for business computer users

Wirelesss technology is rapidly evolving, and is playing an increasing role in the lives of people throughout the world. In addition, ever-larger numbers of people are relying on the technology directly or indirectly. (It has been suggested that wireless is overused in some situations, creating a social nuisance.) More specialized and exotic examples of wireless communications and control include:

Global System for Mobile Communication (GSM) -- a digital mobile telephone system used in Europe and other parts of the world; the de facto wireless telephone standard in Europe

General Packet Radio Service (GPRS) -- a packet-based wireless communication service that provides continuous connection to the Internet for mobile phone and computer users

Enhanced Data GSM Environment (EDGE -- a faster version of the Global System for Mobile (GSM) wireless service

Universal Mobile Telecommunications System (UTMS) -- a broadband, packet-based system offering a consistent set of services to mobile computer and phone users no matter where they are located in the world

Wireless Application Protocol (WAP) -- a set of communication protocols to standardize the way that wireless devices, such as cellular telephones and radio transceivers, can be used for Internet access

i-Mode -- the world's first "smart phone" for Web browsing, first introduced in Japan; provides color and video over telephone sets

Wireless can be divided into:

Fixed wireless -- the operation of wireless devices or systems in homes and offices, and in particular, equipment connected to the Internet via specialized modems

Mobile wireless -- the use of wireless devices or systems aboard motorized, moving vehicles; examples include the automotive cell phone and PCS (personal communications services)

Portable wireless -- the operation of autonomous, battery-powered wireless devices or systems outside the office, home, or vehicle; examples include handheld cell phones and PCS units

IR wireless -- the use of devices that convey data via IR (infrared) radiation; employed in certain limited-range communications and control systems

Also see CDMA One, CDMA2000, and WCDMA. Compare time-division multiplex (TDM) and frequency-division multiplex (FDM). The term CDMA refers to any of several protocols used in so-called second-generation (2G) and third-generation (3G) wireless communications. As the term implies, CDMA is a form of multiplexing, which allows numerous signals to occupy a single transmission channel, optimizing the use of available bandwidth. The technology is used in ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and 1.9-GHz bands. CDMA employs analog-to-digital conversion (ADC) in combination with spread spectrum technology. Audio input is first digitized into binary elements. The frequency of the transmitted signal is then made to vary according to a defined pattern (code), so it can be intercepted only by a receiver whose frequency response is programmed with the same code, so it follows exactly along with the transmitter frequency. There are trillions of possible frequency-sequencing codes; this enhances privacy and makes cloning difficult. The CDMA channel is nominally 1.23 MHz wide. CDMA networks use a scheme called soft handoff, which minimizes signal breakup as a handset passes from one cell to another. The combination of digital and spread-spectrum modes supports several times as many signals per unit bandwidth as analog modes. CDMA is compatible with other cellular technologies; this allows for nationwide roaming. The original CDMA standard, also known as CDMA One and still common in cellular telephones in the U.S., offers a transmission speed of only up to 14.4 Kbps in its single channel form and up to 115 Kbps in an eight-channel form. CDMA2000 and wideband CDMA deliver data many times faster.

PCS (personal communications services) is a wireless phone service somewhat similar to cellular telephone telephone service but emphasizing personal service and extended mobility. It's sometimes referred to as digital cellular (although cellular systems can also be digital). Like cellular, PCS is for mobile users and requires a number of antennas to blanket an area of coverage. As a user moves around, the user's phone signal is picked up by the nearest antenna and then forwarded to a base station that connects to the wired network. The phone itself is slightly smaller than a cellular phone. PCS is being introduced first in highly urban areas for large numbers of users. The "personal" in PCS distinguishes this service from cellular by emphasizing that, unlike cellular, which was designed for car phone use with transmitters emphazing coverage of highways and roads, PCS is designed for greater user mobility. It generally requires more cell transmitters for coverage, but has the advantage of fewer blind spots. Technically, cellular systems in the United States operate in the 824-849 megahertz (MHz) frequency bands; PCS operates in the1850-1990 MHz bands. Several technologies are used for PCS in the United States, including Cellular Digital Packet Data (Cellular Digital Packet Data) and Global System for Mobile (Global System for Mobile communication) communication. GSM is more commonly used in Europe and elsewhere.

① In telecommunication networks, a repeater is a device that receives a signal on an electromagnetic or optical transmission medium, amplifies the signal, and then retransmits it along the next leg of the medium. Repeaters overcome the attenuation caused by free-space electromagnetic-field divergence or cable loss. A series of repeaters make possible the extension of a signal over a distance. Repeaters are used to interconnect segments in a local area network (). They're also used to amplify and extend wide area network transmission on wire and wireless media. In his Telecom Dictionary, Harry Newton points out that, in addition to strengthening the signal, repeaters also remove the "noise" or unwanted aspects of the signal. According to Newton, repeaters can do this with digital signals because, unlike analog signals, the original signal, even if weak or distorted, can be clearly perceived and restored. With analog transmission, signals are restrengthened with amplifiers which unfortunately also amplify noise as well as information. Because digital signals depend on the presence or absence of voltage, they tend to dissipate more quickly than analog signals and need more frequent repeating. Whereas analog signal amplifiers are spaced at 18,000 meter intervals, digital signal repeaters are typically placed at 2,000 to 6,000 meter intervals. In a cable system, a repeater can be simple, consisting of an amplifier circuit and a couple of signal transformers. The impedance of the cable must be matched to the input and output of the amplifier to optimize the efficiency of the amplifier. Impedance matching also minimizes reflection of signals along the cable. Such reflection can produce undesirable echo effects. In a wireless communications system, a repeater consists of a radio receiver, an amplifier, a transmitter, an isolator, and two antennas. (See repeater illustration.) The transmitter produces a signal on a frequency that differs from the received signal. This so-called frequency offset is necessary to prevent the strong transmitted signal from disabling the receiver. The isolator provides additional protection in this respect. A repeater, when strategically located on top of a high building or a mountain, can greatly enhance the performance of a wireless network by allowing communications over distances much greater than would be possible without it. In a fiber optic network, a repeater consists of a photocell, an amplifier, and a light-emitting diode (LED) or infrared-emitting diode (IRED) for each light or IR signal that requires amplification. (See repeater illustration.) Fiber optic repeaters operate at power levels much lower than wireless repeaters, and are also much simpler and cheaper. However, their design requires careful attention to ensure that internal circuit noise is minimized.

②A bus repeater links one computer bus to a bus in another computer chassis, essentially chaining one computer to another. 3) Repeaters are commonly used by amateur and commercial radio operators to extend signals in the radio frequency range from one receiver to another. These consist of drop repeaters, similar to the cells in cellular radio, and hub repeaters, which receive and retransmit signals from and to a number of directions.

Optical fiber (or "fiber optic") refers to the medium and the technology associated with the transmission of information as light pulses along a glass or plastic wire or fiber. Optical fiber carries much more information than conventional copper wire and is in general not subject to electromagnetic interference and the need to retransmit signals. Most telephone company long-distance lines are now of optical fiber. Transmission on optical fiber wire requires repeater at distance intervals. The glass fiber requires more protection within an outer cable than copper. For these reasons and because the installation of any new wiring is labor-intensive, few communities yet have optical fiber wires or cables from the phone company's branch office to local customers (known as local loop). single mode fiber fiber is used for longer distances; multimode fiber fiber is used for shorter distances.