On Sun, 18 Oct 2020 12:05:43 -0700, Johann Beretta
wrote:

On 10/14/20 7:21 PM, Jeff Liebermann wrote:
On Wed, 14 Oct 2020 00:25:08 -0700, Johann Beretta
wrote:

On 10/6/20 4:35 PM, Jeff Liebermann wrote:

To get some decent speeds, 5GHz
instead of 2.4GHz.

Generally speaking, yes. Practically speaking you can do several
hundred mbps over a 2.4 link. You just need to widen the channel.

While there are 2.4GHz routers available that have a 40MHz channel
bandwidth setting, I prefer not to use it because it reduces the
available bandwidth to other users on 2.4GHz. If one is sufficiently
clueless to use a 40 MHz channel set to CH6, it will effectively
trash most of the 2.4GHz band. Since Wi-Fi pollution can be
symmetrical, it also makes the receiver susceptible to more
interference. Stay with 20MHz channel bandwidth on 2.4GHz.

In dense environments, I agree. In rural areas, interference may not be
a factor. In extremely rural areas, interference PROBABLY won't be a
factor.

Those are fair assumptions. However, I've been surprised a few times.
For example, I couldn't figure out why I was getting miserable 2.4GHz
performance in an isolated farm house that was 2 miles from the
nearest neighbor or potential source of RF interference. I finally
got around to doing a site survey with a spectrum analyzer and
directional dish antenna. I wound that there was a point to point
2.4GHz wireless link between an office building about 5 miles away,
and an isolated pump house about 3 miles away. The farm house was
directly in the line of sight. At first, I simply changed channels
(1, 6, or 11), but the pump house link changed channel every time the
link faded or was obstructed. So much for adaptive channel selection.
So, I switched to 5GHz, and avoided the problem. Yes, interference
can be a problem in the middle of nowhere.

On the other foot, the minimum channel bandwidth on 5GHz is 40MHz
(depending on channel selected) with an option to use 80MHz or 160MHz
for 802.11AC and AX (Wi-Fi 6).
https://en.wikipedia.org/wiki/List_of_WLAN_channels#5_GHz_or_5.9_GHz_(802.11a/h/j/n/ac/ax)
With 1024-QAM, 802.11AX can theoretically do 1.2Gbits/sec in a 160MHz
channel. Your mileage will certainly be less.

No.. The minimum 5GHz channel bandwidth is 5MHz.

Correct. However, 5MHz is not the occupied bandwidth of the signal.
It varies by modulation mode and type. For example, conventional
2.4GHz 802.11b/g is typically about 22MHz wide and occupies four 5MHz
channels. The 2.4GHz band is 83.5MHz wide. Therefore, if it is only
possible to fit 3 non-overlapping 22MHz wide signals in the band
before running out of bandwidth. This is where the recommended CH1,
6, and 11 comes from. Incidentally, picking a channel that lands in
between CH1, 6, or 11 will end up overlapping the two adjacent
channels and interfere with both.

On 5 GHz, it's the same story. You divide the available bandwidth by
the occupied bandwidth of the signal to get the number of available
non-overlapping channels. Diagrams such as these show how it works:
https://www.google.com/search?q=802.11+channel+bandwidth&tbm=isch

Not sure where you are
coming up with 40MHz as a minimum. Out of several dozen transmitters, I
only have two set to 40MHz (backhauls). The rest are set to 20MHz with a
couple at 10Mhz.

You can use 20, 40, 80, or 160 on *PARTS* of the 5GHz band. 10 MHz is
available but I don't know any situation where it might be useful. The
bandwidth situation is a mess on 5GHz. I don't have the time to
explain where all the various protocols, power levels, bandwidth
restrictions, and standards, DFS radar protection, etc, fit together.
Also, things get really strange with 802.11ax. See Fig 9:
https://www.ni.com/en-us/innovations/white-papers/16/introduction-to-802-11ax-high-efficiency-wireless.html

My gear (Ubiquiti) supports 5, 8, 10, 20, 30, 40, 50, 80 Mhz wide channels.

In what country? See:
https://en.wikipedia.org/wiki/List_of_WLAN_channels#5_GHz_or_5.9_GHz_(802.11a/h/j/n/ac/ax)
Go to the column marked United States. Notice that 20 MHz is the
minimum allocated occupied bandwidth. 10 MHz is on the chart, but it
look like no country is using it. 5, 8, 30, and 50 MHz are not on the
chart.

Anyway, the performance limiting factor is usually interference from
co-channel users and noise sources. You could have all the bandwidth
in the world, the most efficient modulation scheme, maximum legal RF
power, and still not be able to communicate very well or far if there
is an interference source nearby. In other words, one needs to do
more than just "widen the channel".

Once again, sometimes. Sometimes ALL you need to do is widen the channel.

Yep. However, if a wide bandwidth is such a great solution, why
doesn't everyone just setup their routers to use as much occupied
bandwidth as possible, or perhaps just use the entire band? Sure,
there are benefits, but compromises must be made to use a larger part
of the band? Hint: Think about how long a radio needs to be
transmitting in order to deliver (for example) 1 MByte of payload
data. If it can deliver the data twice as fast and therefore uses
half the air time, that's that much more air time for other users of
the bandwidth used.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558