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.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006

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).
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

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.

This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)

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).











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References in periodicals archive ?
Hierarchical token bucket [16] method can avoid idle bandwidth, but it requires tedious manual configurations based on network protocols or ports.
The HTTP clients select the video rates based on the estimated bandwidth; Therefore, bandwidth estimation has a significant effect on the performance of HAS in terms of QoE.
For more information on Bandwidth's 9-1-1 emergency services, visit http://bandwidth.com/9-1-1.
The expansion of VoIP provides a tremendous opportunity for local carriers to grow their user base efficiently and practically, said Steve Leonard, EVP and General Manager at Bandwidth. As communications networks modernize and expand to every corner of the country, carriers will continue to see the value VoIP networks provide to grow their businesses effectively.
ElKhayat said that, though the cost of bandwidth has been
With Bandwidth we access and provision numbers and services in real-time,allowing us to focus our resources on providing more Americans free mobile service, said Stephen Stokols, CEO at FreedomPop.
What I don't understand is why we have schools in both urban and rural areas that lack the bandwidth necessary to effectively use the learning tools of today, and particularly why this isn't the number one priority for each and every school district.
Countries in sub-Saharan Africa especially will contribute to the continent's appetite for international bandwidth. Among those with the fastest-growing demand are Angola, projected to grow 71% annually over the next seven years; Tanzania, projected to grow 68%; and Gabon, expected to rise 67%.
Research reveals that demand for international bandwidth grew 39 per cent last year, and at a compounded annual rate of 53pc between 2007 and 2012.
"There are many schools that do not have the bandwidth to meet current or future needs," Drilling said in the email.
District Administration spoke with four administrators from around the country about what is driving current bandwidth-consumption trends, what impact increased bandwidth has on tight budgets, and what the future of bandwidth looks like for K12 schools.
The main disadvantage of the antenna is that it has a very narrow axial-ratio bandwidth [1,2].