bandwidth

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bandwidth

1. The range of frequencies over which an instrument, such as a radio telescope, is sensitive. A wide bandwidth gives good sensitivity to sources that emit over a wide range of frequencies (e.g. by synchrotron emission), whereas a narrow bandwidth gives good sensitivity to spectral lines.
2. (coherence bandwidth) The range of frequencies over which electromagnetic or other emissions from a source maintain coherence.

bandwidth

[′band‚width]
(communications)
The difference between the frequency limits of a band containing the useful frequency components of a signal.
A measure of the amount of data that can travel a communications path in a given time, usually expressed as thousands of bits per second (kbps) or millions of bits per second (Mbps).

bandwidth

(communications)
The difference between the highest and lowest frequencies of a transmission channel (the width of its allocated band of frequencies).

The term is often used erroneously to mean data rate or capacity - the amount of data that is, or can be, sent through a given communications circuit per second.

bandwidth

(1) Computer people may use the term for capability and time. For example, "not enough bandwidth to get the job done" means not enough staff or time to do it. Its true meaning follows.

(2) The transmission capacity of an electronic pathway such as a communications line, computer bus or computer channel. Digital bandwidth is the number of pulses per second measured in bits per second (bps). For example, Ethernet transmits at different speeds, including 10 Mbps, 100 Mbps and 1000 Mbps (see Mbps and baseband).

When transmitting alternating frequencies, as with all wired analog, many wired digital and most wireless communications, the bandwidth is the difference between the highest and lowest frequencies, measured in cycles per second, or Hertz (Hz). For example, 802.11n Wi-Fi transmits in 20 MHz and 40 MHz channels within the 2.4 GHz and 5 GHz bands. The 20 and 40 MHz channel frequencies are the bandwidths, and each channel is divided into subchannels.

From Hertz to Bits - A Complicated Process
When using alternating frequencies for digital transmission, the frequencies are modified (modulated) by the digital input. Using the 802.11n Wi-Fi example, the resulting bit rate can range from 6.5 Mbps to 600 Mbps. This extremely wide range is determined by the signal strength and interference in the environment at any given moment. Any one of more than 30 combinations of channel bandwidth (20, 40 MHz), modulation scheme, error correction rate, channel spacing and number of antennas may be selected, on a packet-by-packet basis. See modulation, video bandwidth, space/time and bandwidth junkie.


Bandwidth in Hertz to Bandwidth in Bits
This quadrature PSK (QPSK) example is one of the simplest modulation schemes. Each set of two input bits modifies the carrier into four phase angles. The amplitude remains constant, unlike QAM modulation, in which the amplitude is varied (see QAM).











References in periodicals archive ?
Avaya Network Bandwidth Optimization has the potential to create instant improvements in network traffic," said Thomas Dunkerley, IT communications chief for The Seattle Times.
The Avaya Network Bandwidth Optimization solution is based on patent- pending technology from Artera Group, Inc.
Avaya Network Bandwidth Optimization helps companies extend the capacity of existing networks while creating application headroom for running IP telephony and other advanced applications," said Mehrdad Nadooshan, chief technology officer, Avaya Global Services.
Avaya Network Bandwidth Optimization is part of a suite of Avaya services that help companies successfully plan, design, implement and manage IP communications networks.
Project video server and client network bandwidth requirements easily and maintain on-demand servers in an eloquent way.
Maximize Bandwidth - Improves network utilization of digital services by dynamically allocating service-to-network capacity; validates available network bandwidth allowed to subscribers and allows online activation of additional resources to meet session demand spikes.
SeaChange Axiom Open Suite software simplifies content acquisition and management, optimizes network bandwidth and easily integrates new applications and connections beyond television settops.
0, Webroot will also start releasing incremental definitions that allow client workstations to download only the new or updated definitions from their administration console, thereby significantly reducing impact on desktop resources and vastly improving network bandwidth consumption.
com), an industry leader in affordable video over IP network solutions, today announced that VBrick is enabling employees to view NCAA Men's College Basketball tournament games at work without monopolizing corporate network bandwidth or crippling IT performance.

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