# Reconciling multiple definitions of Bandwidth

I am confused about the meaning of the term 'Bandwidth' in a wireless transmission environment. The two most common definitions I could find are:

• difference between the upper and lower frequencies in a continuous band of frequencies
• the maximum rate of information transfer (bps) across a given path

How do I reconcile these (assuming they are reconcilable)? In other words, why does the difference between the upper and lower frequencies in a frequency band equal the maximum rate of information transfer across the path transmitted? Can someone kindly explain the connection in a clear, visual way if possible?

• Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer. – Ron Maupin Dec 17 '20 at 17:56

This is the same term used in two different contexts and it has quite different meanings. (it could also have other different meanings in other domains)

In the context of radio frequency, yes it is literally a range of frequency. For example WiFi 802.11 (legacy/b/g) use the 2.4 - 2.5 Ghz range and so has a 0.1Ghz bandwidth.

In the context of network it usually refer to the maximum amount of information that can be transferred by second on a specific medium with a specific protocol.

The two are (very) loosely connected because when using radio technology (like WiFi) the more radio bandwidth you have the more data you can potentially push by second.

But you can also improve the network bandwidth without increasing the radio bandwidth by improving the protocol. This is exactly what WiFi did, going from 2Mbs for the original spec to 11Mbs for 802.11b and 54Mbs for 802.11g still with the same radio bandwidth.

• The two are (very) loosely connected because when using radio technology (like WiFi) the more radio bandwidth you have the more data you can potentially push by second. You've got it backwards. The higher the frequency (data rate) that you modulate, the higher the resultant bandwidth. – Ron Trunk Jun 8 '20 at 17:13
• @RonTrunk I was really speaking about radio bandwidth like: 2,4 to 2,6Ghz = 200Mhz bandwidth vs 2,4 to 2,5GH = 100Mhz bandwidth). Admittedly, using the same modulation (ignoring the impact of the frequency itself) you can push twice as much data. – JFL Jun 8 '20 at 17:32
• It's the modulation that causes the range of frequencies. – Ron Trunk Jun 8 '20 at 17:39

I am confused about the meaning of the term 'Bandwidth' in a wireless transmission environment.

The two are more closely related than you might think.

The two most common definitions I could find are:

difference between the upper and lower frequencies in a continuous band of frequencies

This isn't quite right. A better definition is "a range of frequencies occupied by a modulated carrier." The word modulated is the key. When you modulate a carrier wave to add information (like sending data over Wi-fi), the high the modulating frequency (i.e., the data rate), the higher the bandwidth the signal occupies. So as you increase your data rate, the bandwidth also increases.

(There are tricks to minimize the increase, such as using coding algorithms or multiple sub-carriers, but that is a different discussion)

the maximum rate of information transfer (bps) across a given path

Conversely, for a given bandwidth (and modulation technique), there is a maximum data rate. So the two definitions are closely related. Informally, when we talk about the bandwidth of a data circuit, We are talking about the maximum data rate that we can use, given the actual signal bandwidth available (electrical or optical).