Are you talking about channel capacity or analog signal bandwitdh? The latter simply means the frequency band occupied by the radio frequency signal.
There several factors restricting bandwidth in wireless transmission, e.g. regulations, transmitter technology, antennas.
Neither the question is...It is still not clear.
Depends on. For low signal-to-noise ratios, increasing the bandwidth will bring only a small improvement in theoretical channel capacity. With excess SNR, the higher bandwidth translates directly to channel capacity. See Shannon-Hartley theoremI implied that more bandwidth is better, because more bandwidth means more data rates. Right?
... the medium itself is a low pass filter ...
but as I know, the medium is a bandpass filter. right? it has a low pass equivalent representation, but it is in itself is bandpass.
I think it has to do with regularizing the different wireless systems to not to interfere with each others. For example, if the FCC or whatever agency gives a mobile phone company to operate with range of frequencies from 800MHz to 2GHz, then the bandwidth is limited to 1.2 GHz. Am I right?
The best to think about bandwidth is Water flowing through the Pipe. If pipe's diameter is small then at at any given time from one end to another there is less water flowing through it. Even if you have larger bucket of water to pass through the pipe you can only pass at the full capacity of pipe. If you do so you will spill water around and hence water will be wasted.
In order to pass greater quantity of water you need to get bigger pipe (>diameter), it means you have increase the capacity of the system. Now you can pass more water/sec.
In the same way if we want error free transmission then the rate of the transfer R from one end to another based on the Capability of the channel to allow the transfer of information. This capability is the bandwidth of the system.
You can either transmit at R < this Bandwidth or equal to this Bandwidth. When the R is equal to B then this is the max information you can transmit and it is known as Capacity of the system C.
See Figure attached
1st Part of Figure * R≤C can be error free flow or transmission ideally, but other factors are also considered like effect of impairment in the channel. Noise (in communication systems)
2nd Part of Figure * Keeping B constant we can only achieve C capacity even if we increase the R’ bits/sec, and by doing so we get errors in Transmission
3rd Part of Figure * Way to achieve R’ is to increase B to B’. Hence the channel capacity is increase by increasing Bandwidth B (directly proportional)
It seems that we can achieve error free transmission even at higher rate if we increase the Bandwidth of the system
Theoretically we can get Infinite capacity or by Increasing B we can achieve infinite Transmission Rate R
But Unfortunately there is a limiting factor in communication system which is Noise
As bandwidth increases the Noise power also increases
For N = ηB , η/2 is the Noise power spectral density
R=C and at Bandwidth B,
Re-arranging Shannon- Hartley and the plotted curve is shown below.
Some point about figure are as follows:
* No error Free Transmission at -1.59dB regardless of Information rate
* Keeping B Constant (i.e, Numerator of y-axis) and Increasing the R (bits/sec) we can follow this Error free transmission but we have to increase the signal power (energy) if we want to achieve more Data Rate (Spectral Efficiency using various modulation scheme BPSK, QPSK, QAM etc
* Now, Keeping R constant (bits/sec) we can increase/decrease the Bandwidth to move along red curve as desired. It means that for a given rate we can achieve error free transmission at higher Power if B is small. Or we can achieve error free transmission at higher bandwidth and keeping Signal power small
* Hence there is a Trade-off between spectral efficiency and Power
Bandwidth Limited system - Use spectrally efficient modulation scheme (e.g. higher order QAM) & the Transmit power is not a major issue
Power Limited systems - save power at the expense of bandwidth
Hope that might help.
Rgds
Kalim
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