It's easy to focus on the concept of interference, and in the wireless world we
actually refer
to this as co-channel interference, or CCI, to make sure that we're talking
about interference
that's happening with the same frequencies.
But if we are talking about co-channel interference, then yes, that is a big
problem.
But what we're going to find is that when it's special when it comes to our
wireless
designs, co-channel interference usually isn't as big of a deal as another
mechanism.
And we'll get into here in a moment. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And we'll get into here in a moment.
But for now, let's go ahead and talk about co-channel interference since CCI.
I mean, what exactly causes it?
So remember, we might have that hidden node problem where we are causing
interference
with our fellow Wi-Fi devices.
I'm transmitting from here, I'm transmitting from here, and this device here,
usually
the axis point, is kind of caught in the middle.
And so we might have that issue, that usually happens if we have very large WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And so we might have that issue, that usually happens if we have very large
cells, because
these two devices have to be really far apart to not be able to hear one
another, or maybe
we have like a really thick wall on one side or the other.
And so it's all things to consider.
But fortunately, we can usually shrink ourselves and kind of get around this
hidden node issue.
For the most part, because of that, when we're talking about interference, we
usually are
referring to non-Wi-Fi devices.
For example, a common culprit with this is Bluetooth. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
For example, a common culprit with this is Bluetooth.
Bluetooth is another means of data communication.
It uses the 2.4 gigahertz band.
And it causes interference because it uses frequencies all over this band.
It doesn't just lock down to, let's say, channel 1 or something along those
lines.
So remember, when our Wi-Fi devices are communicating, they're supposed to wait
.
They're supposed to listen. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
They're supposed to listen.
They wait.
And here's what's important.
They follow a set of rules for communication.
This set of rules makes it so Wi-Fi devices very rarely communicate over the
top of one
another.
If they do, then they do cause interference.
But for the most part, because of these rules, the Wi-Fi devices don't speak on
top of one
another.
Bluetooth, and anything else we're talking about here, so maybe we're just
talking about
a, something that's causing noise.
Maybe it's another type of communicator. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Maybe it's another type of communicator.
Maybe it's a wireless phone that's using 2.4 gigahertz.
All of these follow a different set of rules.
And even though they will usually wait to communicate, their rules for when to
start communicating, how
long to communicate, those are all very different.
And so this creates a lot more overlap and overlapping, as we know, does create
interference.
So this is where co-channel interference can come from. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So this is where co-channel interference can come from.
I was once playing a video game system, and it's still crazy to me to this day
that this
happened.
This was back in the late 2000s or so.
And this video game system was speaking Wi-Fi to communicate out to the
internet, and it
was playing online with somebody.
And I'm sitting over here, not thinking anything of it.
I've got this controller that I'm using that is wireless.
And it was wireless communicating to this game system as well.
And what I came to realize eventually was that this is all using 2.4 gigahertz. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And what I came to realize eventually was that this is all using 2.4 gigahertz.
And so every time I'd start to move on the controller, the game would lag out.
And everything would stop moving and grind to a halt.
And then I'd stop because the game had stopped.
Because I stopped, there was no more interference.
The game would communicate.
I said, oh, the game started again.
Great.
I'd start moving again.
I'd cause the interference and the game would stop again.
And it's one of the most blatant experiences I've had with direct wireless
interference.
But again, because the game controller and the Wi-Fi space, they were following WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
But again, because the game controller and the Wi-Fi space, they were following
very different
rules, although be it with the same frequencies, that was causing a bunch of
interference to
the point that it wasn't possible, even though the game system supported it, it
wasn't
possible to use wireless controller and be on the Wi-Fi at the same time.
So that is the concept of co-channel interference.
Now again, in a pure Wi-Fi space, we don't usually worry as much about co-ch
annel interference.
But there is another big issue that can happen with our Wi-Fi world, and that WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
But there is another big issue that can happen with our Wi-Fi world, and that
is known as
co-channel contention, which is abbreviated CC-C.
So what is co-channel contention about?
Co-channel contention has to do with the fact that we are indeed waiting.
Remember, we take turns in the wireless space.
But what happens if we have a lot of stations all together?
So if I've got an access point here, and I've got let's say, I don't know, five WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So if I've got an access point here, and I've got let's say, I don't know, five
stations
all communicating, yeah, they can all take turns, no problem.
But what happens if I have 30 devices all in here, and they're all trying to
take turns?
Well the more devices that are communicating, the more likely we are to step on
each other's
flows, the more waiting we have to do, we all have to kind of get in line and
wait to speak,
and this creates contention, which is where we get this phrase from. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and this creates contention, which is where we get this phrase from.
Contention for channel access.
I want to access this channel, I'm listening and waiting my turn, and
eventually I will get
to speak, and hopefully my communication goes through, but as soon as I'm ready
to make
my next transmission, I'm right back into the line.
And so that's really not ideal.
But here's where things can take an even worse turn.
What happens if I have two access points that are on the same channel, let's
say this is
five gigahertz space, I'm on channel 40 here, and then I do my cell design, I WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
five gigahertz space, I'm on channel 40 here, and then I do my cell design, I
've got another
cell in here, and so we'll leave this one out for a moment.
And then all the way over here, I've got another channel 40 cell.
Well on paper, this is great, I've got this wonderful gap here, and we don't
need to
worry about things.
But what happens if I have a device that's here like a laptop?
And when wireless communicates, we like to draw it as if it's going in a
straight line.
Wireless usually goes through dimensionally like the sphere that we commented WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Wireless usually goes through dimensionally like the sphere that we commented
on earlier.
So now I've got this device and look what it's doing.
It's sending channel 40 signals into this space over here, the other cell,
meaning that
this device here actually has to wait to communicate.
Now we might have a hidden node issue so to speak where this device all the way
on the right
can't see it.
But again, our devices are really good at picking up signals.
And so maybe it's still enough so that now these two cells aren't creating WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And so maybe it's still enough so that now these two cells aren't creating
interference
with one another, but they are creating contention with one another.
This is a big problem when it comes to high density deployments.
We need to make sure that we understand that not only the access points form
cells, but
so do the clients a little bit.
And furthermore, we might make the cells smaller, say hey, access point
transmit with less power,
but it's a little harder to get the laptop to not communicate it full blast. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
but it's a little harder to get the laptop to not communicate it full blast.
And now it's sending signals out everywhere that's causing problems in other
cells.
Because I say within the world of Wi-Fi, we typically are more concerned with
co-channel
contention when we have non-Wi-Fi devices, especially thinking about Bluetooth,
phones, wireless
gaming controllers, for example, that's where we can start to hit problems with
interference.