# Bandwidth and communications channels relationship

Bandwidth is as you say, the difference between the upper frequency and "how much bandwidth does the digital communications channel occupy?" There is no simple relationship between data rate expressed in bits/kilo/mega bits per. Path loss of an underwater acoustic communication channel de- pends not only on the acoustic bandwidth on the communication distance. MAN is a better option for organizations that need high-speed data transmission within a limited The communication channel (once established) is dedicated.

Bandwidth refers to the data throughput capacity of any communication channel. As bandwidth increases, more information per unit of time can pass through the channel.

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A simple analogy compares a communication channel to a water pipe. The larger the pipe, the more water can flow through it at a faster rate, just as a high capacity communication channel allows more data to flow at a higher rate than is possible with a lower capacity channel.

In addition to describing the capacity of a communication channel, the term "bandwidth" is frequently, and somewhat confusingly, applied to information transport requirements. For example, it might be specified that a broadcast signal requires a channel with a bandwidth of six MHz to transmit a television signal without loss or distortion.

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Bandwidth limitations arise from the physical properties of matter and energy. Every physical transmission medium has a finite bandwidth. The bandwidth of any given medium determines its communications efficiency for voice, data, graphics, or full motion video. Widespread use of the Internet has increased public awareness of telecommunications bandwidth because both consumers and service providers are interested in optimizing the speed of Internet access and the speed with which web pages appear on computer screens.

Analog Signals Natural signals such as those associated with voice, music, or vision, are analog in nature. Analog signals are represented by a sine waveand analog channel capacities are measured in hertz Hz or cycles per second.

Analog signals vary in amplitude signal strength or frequency signal pitch or tone. Analog bandwidth is calculated by finding the difference between the minimum and maximum amplitudes or frequencies found on the particular communication channel.

For example, the bandwidth allocation of a telephone voice grade channel, which is classified as narrowbandis normally about 4, Hz, but the voice channel actually uses frequencies from to 3, Hz, yielding a bandwidth that is 3, Hz wide.

The additional space or guardbands on each side of the voice channel serve to prevent signal overlap with adjacent channels and are also used for transmitting call management information. Digital Signals Signals in computing environments are digital.

Digital signals are described as discrete, or discontinuous, because they are transmitted in small, separate units called bits. Digital channel capacities are measured in either bits per second bps or signal changes per second, which is known as the baud rate. Although these terms are frequently used interchangeably, bits per second and baud rate are technically not the same.

Baud rate is an actual measure of the number of signal changes that occur per second rather than the number of bits actually transmitted per second. Prefixes used in the measurement of data transmission speeds include kilo thousandsmega millionsgiga thousands of millionsand tera thousands of giga.

To describe digital transmission capabilities in bits per second, notations such as Kbps, Mbps, Gbps, and Tbps are common. The telephone system has been in a gradual transition from an analog to a digital network. In order to transmit a digital signal over a conventional analog telephone line, a modem is needed to modulate the signal of the sender and demodulate the signal for the receiver.

The term modem is an abbreviation of modulate-demodulate. Although the core capacity of the telephone network has experienced an explosion in available bandwidth, local access to homes and businesses, referred to as the local loop in the telephone network, frequently is limited to analog modem connections. Digital transmission is popular because it is a reliable, high-speed service that eliminates the need for modems. The information is carried through the channel by a signal.

## Communication channel

Channel models[ edit ] A channel can be modelled physically by trying to calculate the physical processes which modify the transmitted signal. For example, in wireless communications the channel can be modelled by calculating the reflection off every object in the environment. Statistically a communication channel is usually modelled as a triple consisting of an input alphabet, an output alphabet, and for each pair i, o of input and output elements a transition probability p i, o.

Semantically, the transition probability is the probability that the symbol o is received given that i was transmitted over the channel. Statistical and physical modelling can be combined.

For example, in wireless communications the channel is often modelled by a random attenuation known as fading of the transmitted signal, followed by additive noise. The attenuation term is a simplification of the underlying physical processes and captures the change in signal power over the course of the transmission. If the attenuation term is complex it also describes the relative time a signal takes to get through the channel. The statistics of the random attenuation are decided by previous measurements or physical simulations.

Channel models may be continuous channel models in that there is no limit to how precisely their values may be defined. Communication channels are also studied in a discrete-alphabet setting. The mathematical model consists of a transition probability that specifies an output distribution for each possible sequence of channel inputs.

In information theoryit is common to start with memoryless channels in which the output probability distribution only depends on the current channel input. A channel model may either be digital quantified, e.

This article may contain too much repetition or redundant language. Please help improve it by merging similar text or removing repeated statements. February Learn how and when to remove this template message Digital channel models[ edit ] In a digital channel model, the transmitted message is modelled as a digital signal at a certain protocol layer.

Bandwidth and data rate of a channel, Data communication fundamentals, Bandwidth and data rate, ma

Underlying protocol layers, such as the physical layer transmission technique, is replaced by a simplified model.