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 ?
Many applications require a pure IP network and bandwidth speeds that cannot be achieved unless deploying a fiber optic network.
He said: "Until now, broadband has been restricted by technology with existing bandwidth speeds available up to 2Mbps only, but now businesses can take advantage of a phenomenally faster service.
0 platform, delivering the fastest bandwidth speeds - 56Gb/s InfiniBand and 40GbE - that can optimize a data center's ROI.
Also, Internet Colorado/ICConnex's new network, complete with Zhone Active Ethernet OLT and ONT's, along with Ruckus Wireless Mesh wireless access points, will provide an economic boost for the city, establishing necessary bandwidth speeds and ensuring the communications dollars are kept within the City of Gunnison, instead of being sent to other states.
BusinessOne can also be customized to meet a company's growth requirements by increasing the number of phone lines or bandwidth speeds.
With Qwest's Ethernet solution, state and local government and businesses in Utah have access to additional bandwidth speeds to help satisfy increasing public demand for online services.
This agreement includes access to the existing SES network, as well as to upcoming high throughput satellite (HTS) spot beam-based systems, providing significant increases in bandwidth speeds.
The SoC allows consumers to create two wireless networks running at full bandwidth speeds, increasing total network capacity.
In addition, the company upgraded the college's Internet connection and installed the technology to increase bandwidth speeds when needed.
The product allows users to create two wireless networks, both running at full bandwidth speeds, offering an increase in total network capacity.
EarthLink said it has completed the transition from the city's existing network to the company's wireless mesh network architecture, extending service to areas not previously covered and increase network bandwidth speeds and performance.
It expects to reach 100Mbps bandwidth speeds by 2013.