问题
According to the definition of the bandwidth, it is the width of the frequency spectrum. Hence bandwidth should be measured in Hz. But bps, Mbps, kbps have been used as the measurement of bandwidth almost everywhere. What I need to know is, why bps, kbps kind of measurements of data transmission rate are used to measure the bandwidth of a signal.
回答1:
Throughput, measured in bps, Mbps, Kbps, is mistakenly referred to as bandwidth because of a mis-conception of the Shannon-Hartley law.
The Shannon-Hartley law states that a given frequency bandwidth is proportional to the channel capacity. Channel capacity is the theoretical upper limit of the throughput for a channel. A channel could be a single fiber optic cable, or a FDMA or ADMA channel.
Bandwidth is not the same thing as throughput. Not long ago radio stations in the United States switched from analog to digital. Stations had (under the analog system) been allocated a frequency separated from the adjacent frequencies by 200 KHz. So their station's bandwidth was 200 KHz, from 100 KHz below to 100 KHz above their assigned center frequency. (In practice some of a stations power might leak outside their assigned frequency band.)
With the digital standard, stations could transmit clearly in a 40 KHz band. So stations could use their allocated band to set up as many as five channels.
For example, a local radio station is assigned 88.1 MHz. Under the analog assignment, the could transmit in the 88.0 MHz to 88.2 MHz band. After switching to digital, they used this band for three channels, 88.0 to 88.04, 88.08 to 88.12, and 88.16 to 88.2 MHz. So they tripled their throughput but their bandwidth (used) was reduced from 200 KHz, to 120 KHz.
Bandwidth and throughput are not the same thing, so calling throughput, which is measured in bps, by the name bandwidth is mistaken.
回答2:
Well, in data communications, bits per second (abbreviated bps or bit/sec) is a common measure of data speed for computer modems and transmission carriers. As the term implies, the speed in bps is equal to the number of bits transmitted or received each second.
It is important to distinguish between bits per second (bps) and bytes per second (Bps). One byte is equal to 8 bits.
回答3:
First place to start is the Spectrum. Here the whole thing, from 0 Hz to Gazillion Hz has been mapped out in highway-like lanes. Just as in a highway, you measure the width of the lane by meters, here too, the width is measured in Hz. This is an analog concept. However note, that Hz, is actually a two dimensional concept, not one. It tells you how many cycles are taking place per time. (Hz -> cycles/time) So Hz is not a linear measure like distance. It is a more complex idea, but we tend to forget the time part and plot it as if it were a scalar.
Then we come to digital communications. Here we have two ways of judging how many bits we can transmit per time. This also has a time dimension. Nyquist gave us the first way of estimating how many bits/time we can transmit given a bandwidth, B Hz. He says it is 2 times B, max. But by taking into account signal levels, a completely independent parameter, the number is actually 2 B log2(M). This Nyquist limit is in terms of bits per second. As you see in this equation the term B in Hz has been converted to bps by merely multiplication with a scalar number, M. So they are really the same thing.
Then we have Shannon, who developed an expression that takes into account the noise in the channel and and came up with C = B log2(1+SNR) irrespective of M. This too is in bits/second.
Both of these are way to represent the frequency measure of a signal, which is Hz, into bits per second. Note that both Hz and bit per second are time related concepts and so nothing strange has happened here. Hz and bps are essentially the same concept and directly related.
Bit efficiency is often given in just bits. (bit efficiency = rate/bandwidth) When you divide rate by bandwidth in Hz, the time units cancel and you are left with just bits. Such as 200 bps/100 Hz -> 2 bps per cycle. But this is often written just as bits.
来源：https://stackoverflow.com/questions/23389972/why-bandwidth-is-measured-in-bits-per-second