Hello David
With a wired connection, the bandwidth stated is quite straightforward. You will typically be able to reach very close to the stated bandwidth (i.e. 100 Mbps, 1000 Mbps, 10 Gbps etc) on such a link if there’s no congestion or if the resources of the router or switch are not reaching their limits. However, for a wireless link, there are many more factors involved.
Strictly speaking, if you have only one transmitter and one receiver, and you have no other wireless interference in the area, the bandwidth available between the sender and receiver is dependent only on the standard being used. For example, IEEE 802.11g gives you up to 54 Mbps, 802.11ac gives you up to 6.933 Gbps and so on. Now these as you know are theoretical, but they’re based on the specific parameters of the standard being used (encoding, frequencies, channel widths, modulation and others). So it’s not a matter of the “air” but of the transmitter’s and receiver’s capabilities.
Other factors that will affect the real achievable bandwidth include interference, obstacles, client density, AP capabilities and many more, as you have already seen from this and other lessons.
In wireless networks like Wi-Fi, various modulation mechanisms are used to encode data onto wireless waveforms. One that is used in many Wi-Fi standards is Orthogonal Frequency Division Multiplexing or OFDM. On a wireless channel with a channel width of 20 MHz OFDM creates what are known as subcarriers. A subcarrier in OFDM is a smaller frequency slice within the main channel bandwidth, individually modulated to carry part of the overall data, and precisely spaced to avoid interference with neighboring subcarriers.
A 20 MHz channel width using OFDM has a total of 64 subcarriers, 52 of which are used to carry data. The other 12 are used for control and as “guards” on either end of the channel to avoid interference with neighboring frequencies. Theoretically, by doubling the channel width, you can double the number of subcarriers. Actually, you get a larger number of data-carrying subcarriers because for a 40MHz channel width, you still only need 12 subcarriers as non-data-carrying subchannels, so you get more than double the number of data carrying subchannels, i.e. 114.
BUT, there is a tradeoff that doesn’t allow you to get twice as much throughput. Wider channels mean:
- they are prone to more interference noise and congestion, meaning in practice, they may actually be slower in a “crowded” wireless environment
- fewer non overlapping channels reduces the number of non interfering communications
- in a particularly crowded environment, you may find that using smaller channel widths actually allows a deployment to perform better than having channels bonded.
You could, if you have only a single client and a single AP. But this is rarely the case. Even if it is, you will definitely have interference from nearby sources. And you also must ensure that your client and AP both support the level of channel bonding you want to achieve.
So there is a tradeoff, and you must examine each case independently.
I hope this has been helpful!
Laz