Bandwidth requirements

Bandwidth requirements (communications)

The channel bandwidths needed to transmit various types of signals, using various processing schemes. Every signal observed in practice can be expressed as a sum (discrete or over a frequency continuum) of sinusoidal components of various frequencies. The plot of the amplitude versus frequency constitutes one feature of the frequency spectrum (the other being the phase versus frequency). The difference between the highest and the lowest frequencies of the frequency components of significant amplitudes in the spectrum is called the bandwidth of the signal, expressed in the unit of frequency, hertz. Every communication medium (also called channel) is capable of transmitting a frequency band (spectrum of frequencies) with reasonable fidelity. Qualitatively speaking, the difference between the highest and the lowest frequencies of components in the band over which the channel gain remains reasonably constant (or within a specified variation) is called the channel bandwidth.

Clearly, to transmit a signal with reasonable fidelity over a communication channel, the channel bandwidth must match and be at least equal to the signal bandwidth. Proper conditioning of a signal, such as modulation or coding, however, can increase or decrease the bandwidth of the processed signal. Thus, it is possible to transmit the information of a signal over a channel of bandwidth larger or smaller than that of the original signal.

Amplitude modulation (AM) with double sidebands (DSB), for example, doubles the signal bandwidth. If the audio signal to be transmitted has a bandwidth of 5 kHz, the resulting AM signal bandwidth using DSB is 10 kHz. Amplitude modulation with a single sideband (SSB), on the other hand, requires exactly the same bandwidth as that of the original signal. In broadcast frequency modulation (FM), on the other hand, audio signal bandwidth is 15 kHz (for high fidelity), but the corresponding frequency-modulated signal bandwidth is 200 kHz.

C. E. Shannon proved that over a channel of bandwith B the rate of information transmission, C, in bits/s (binary digits per second) is given by the

equation below, where SNR is the signal-to-noise power ratio. This result assumes a white gaussian noise, which is the worst kind of noise from the point of view of interference. See Information theory, Signal-to-noise ratio

It follows from Shannon's equation that a given information transmission rate C can be achieved by various combinations of B and SNR. It is thus possible to trade B for SNR, and vice versa.

A corollary of Shannon's equation is that, if a signal is properly processed to increase its bandwidth, the processed signal becomes more immune to interference or noise over the channel. This means that an increase in transmission bandwidth (broadbanding) can suppress the noise in the received signal, resulting in a better-quality signal (increased SNR) at the receiver. Frequency modulation and pulse-code modulation are two examples of broadband schemes where the transmission bandwidth can be increased as desired to suppress noise.

Broadbanding is also used to make communication less vulnerable to jamming and illicit reception by using the so-called spread spectrum signal. See Electrical communications

References in periodicals archive ?
Given those reports, it's more important than ever for IT consider a number of different issues that impact bandwidth requirements, including the type of digital learning applications being used, such as video, as well as on-line assessments, and administrative functions.
Performance of the PCI bus has been continually improved to keep pace with increased bandwidth requirements by increasing clock speeds and widening buses.
If we are called to action in the Middle East in the next few weeks, with the large numbers of troops likely to be engaged and operations likely to be executed, I'm certain the bandwidth requirements will be off all previous charts.
Steelcape Gateway(tm) doesn't open ports in a TCP/IP-based network that are vulnerable to hacking opportunities and minimizes bandwidth requirements for sending digital content.
SONET/SDH connectivity is readily available to enterprises worldwide and well suited to support data replication for low to moderate bandwidth requirements both within metropolitan areas and beyond.
DALLAS -- Today, on-demand hosting provider, SoftLayer Technologies, announced a multi-million dollar Cisco upgrade to its core network designed at meeting the future bandwidth requirements of the Internet.
The debate over 4Gb or 10Gb as the next server to storage speed target has been largely argued as an "either/or" case based on the assumption that every application has similar bandwidth requirements and is of equal value to an organization.
Steelcape actually delivers fast and secure online transactions by what it doesn't do - Steelcape Gateway doesn't open ports in the network that are vulnerable to hacking opportunities and minimizes bandwidth requirements for eCommerce.
The unique combination of complex objects, along with different availability and bandwidth requirements for archival data pose several new challenges for the storage management industry.
The PostPath Server Remote Office Edition's on-site server deployment minimizes bandwidth requirements by eliminating WAN usage when local users access their data.
This approach provides a low-cost solution for connecting storage systems that have low bandwidth requirements.
We're thrilled that Switchpod has offered not only to provide E-1 with the storage it needs this term but also to keep up with its ever-increasing bandwidth requirements.

Full browser ?