This topic is to discuss the following lesson:
Hello Rene,
a question regarding the channel re-use thing: Is WiFi 6 also considered a valid solution for high density WiFi? I at least think so, since WiFi 6 should have more non-overlapping channels, right?
Thanks in advance!
Kind regards,
Mirko
Hello Mirko
WiFi 6 is also considered a valid solution for high density WiFi. WiFi 6 has two specific features that aid in increasing capacity: Spectral efficiency, as well as an extension of the available frequencies and channels.
Spectral efficiency refes to the methoology by which multiple clients are managed and how efficiently the available spectrum is leveraged. WiFi6 uses what is known as orthgonal frequency division multiple access (OFDMA) which brings better spectrum use, improved power control to avoid interference, and enhancements like 1024‑QAM, MIMO and MU-MIMO for faster speeds.
WiFi6E, where “E” stands for “Extended”, is the version of WiFi6 that includes the extension of the WiFi 6 standard into the 6 GHz band. This new band opens up more than 1,200 MHz of spectrum for WiFi which means we have more channels available to us than those provided by the 2.4 and 5GHz bands alone. This does indeed provide us with an additional set of non overlapping channels, but only for clients that support this extended frequency range.
I hope this has been helpful!
Laz
Hello.
I don’t think I quite understand what bandwidth means in the context of wireless networks. Like the air has a certain amount of data that it can transmit per second?
With channel bonding, if you combine two 20 MHz channels into one 40 MHz one, does the bandwidth simply increase because the device has more frequences that it can use to transmit that data without any interference?
What if I have just one BSS? Couldn’t I combine every single 5 GHz channel into one? 
Thank you.
David
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