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 ?
Under this scenario, SAS devices can transfer data in both directions simultaneously, with mixed protocol control, to effectively double the useable bandwidth of the link rate to 6.
As the developer tools mature, and as effective bandwidth increases, vendors will be able to significantly expand available features.
ACE will deliver its bandwidth trading/bandwidth-on-demand services through Lucent's CBX 500 Multiservice Wide Area Network (WAN) switches and PacketStar PSAX AC 60 broadband access devices.
History has shown that people will always find new ways to use available bandwidth.
The net result of these issues is very poor bandwidth utilization.
By aggregating bandwidth from a bundle of T1 or fractional T1 circuits, multimegabit access concentrators enable NxT1 service that offers secure and symmetrical transport with low latency.
Total Bandwidth Fees: Internet Radio and Streaming Video Advertising 2005
Founded in 1999, Bandwidth is a nationwide communications provider offering businesses advanced Internet, VoIP, network and wireless services.
General Bandwidth, a leading Voice over IP equipment manufacturer enabling rapid deployment and new service revenue generation over broadband networks, has been selected by Guadalupe Valley Telecommunications Cooperative (GVTC), Texas' largest telecommunication cooperative, to deliver cable telephony services over Guadalupe Valley's hybrid fiber coax (HFC) network.
General Bandwidth, a leading Voice over IP (VoIP) equipment manufacturer enabling rapid deployment and new service revenue generation over broadband networks, announces that it has implemented PseudoWire Emulation End-to-End (PWE3) in its award-winning G6 Universal Media Gateway that allows carriers to migrate legacy services onto new video and data packet networks, such as IPTV/FTTN and GPON.
AUSTIN, Texas -- General Bandwidth, a leading Voice over IP equipment manufacturer enabling rapid deployment and new service revenue generation over broadband networks, announced today that Mpower Communications (AMEX:MPE), a leading provider of broadband Internet access and telephone services to business and wholesale customers, has deployed General Bandwidth's G6 Universal Media Gateway to expand its Voice over IP (VoIP) business services.