Frequencies and Channels

The frequency spectrum

This diagram ranges anywhere from 50 Hz, which is 50 cycles per second, to 1 megahertz, which is 1 million cycles per second. It has one gigahertz, one billion cycles per second, all the way to 30 exahertz, which is just something crazy. It really shows the wide range of different electromagnetic frequencies that are out there.

There is a band in here that we widely use for communication. That's the low frequencies, the radio frequencies, the microwaves. We use this whole range for different communication. In the radio frequencies there is actual radio. We've got some TV, we've got some broadcast that goes out there, we've got our Wi-Fi in there, we've got our microwave in there. Those are some of the devices that sit within each one of those frequencies.

Licensed and unlicensed bands

What they want to do is limit usage of certain bands of frequencies within here. As an example, they don't want just anybody to be able to broadcast a TV program, so you've got to get a license to broadcast that out. They don't want just anybody to start broadcasting a radio frequency that's already assigned to somebody else, so you have to get a license for that. Pilots in the sky are talking to air traffic control, and they don't want somebody broadcasting on that same frequency, so you've got to get a license for that too. You've got to get licenses to broadcast within these different ranges, although there are some exceptions to it.

They've taken some of these ranges within here — and it's kind of just little slivers within here — and they've created these bands that you can actually do your own thing in, that you don't need a license for. You don't need a license to create certain equipment in it. An example of that is the 9 megahertz range. When phones started going cordless — I'm not talking about cellular, I'm talking about the landline phones, but they had corded or cordless phones — those operated in the 900 megahertz frequencies. And then they came out with the 2.4 gigahertz frequency, because that's another range that they have that's open to people. Same thing with the 5 gigahertz: there's a band within the 5 gigahertz frequency. That's why you see a lot of Wi-Fi operating at the 2.4 GHz frequency and the 5 GHz frequency.

Why lower frequencies travel further

One other thing I mentioned is that these lower frequencies tend to travel further and go through obstacles better. Think of somebody who is driving down the road and they have their speakers blared and it's really loud. What do you hear first? You hear the low frequencies, because they travel further and they go through more obstacles. Versus the higher frequencies — you don't hear the mid-range or the highs until that car is closer, and sometimes you don't even hear the highs until they're really close to you.

So those lower ranges travel further. The upper range, even though we can pack more data into it, doesn't travel as far and gets hindered by certain obstacles, so it doesn't operate as well with transferring data from that perspective — but we can transfer more data. There are some advantages to the low frequency and sending data through the low frequencies, and there are some advantages to the higher frequencies.

Wi-Fi channels

The 2.4 GHz frequency is an actual range, a band that's open that you don't have to have a license to use, and that's one of those Wi-Fi networks that are used out there. Wi-Fi is built into channels. Let's say this is channel one, this is channel 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and then in some countries they have 12 and 13, and one country I think has 14 — maybe a couple of countries have 14. I'm not going to consider those too much in the discussion that follows, but you'll see that we have these channels that we operate in.

This is an access point right here, and it's going to be assigned to a channel. Let's say it's assigned to channel one, and this device then communicates to this access point on channel one. Now we bring in another access point, and when we add this access point we need to choose a different channel. It can't be the same frequency that this radio is communicating off of. So maybe we assign this to channel 2 for other devices to be able to connect to, so that way you can keep your frequencies separate. Although we can't exactly assign one and two next to each other, and I'm going to explain why in a second.

Laying out access points in an office

Let's say I want connectivity in this office, so I'm going to set up an access point in what looks like an office with a conference room in it. Here's another conference room, so I'm going to set up an access point there. Here's a conference room, so I want to set up an access point there. Here's an office, so I want to make sure they have connectivity. Here's another office, so I want to make sure they have connectivity. People who are in the bathroom will probably get a signal from there, but I don't really care too much if it's a strong signal, so I think that's fine.

Then, when we actually do the install of these devices, I'm going to set up the access point, and then we actually see what's called a heat map: the coverage area of these access points for the office. Now this is not a fair representation, because some of these walls are going to cut down on the signal and so it's going to be altered a little bit. But for the most part, let's say I have an access point here right in the office, and this is going to be my coverage area from that access point — like I say, not including how the walls and the different materials are going to interfere with it. Let's just say for now that that is the coverage area, and the access point that I have in here is going to have this coverage right here.

What I need to do is separate these different access points into different channels. I can't have them overlapping. So if this is one right here, then maybe I would assign two right here, and maybe three right here, four, five. No problem — I don't see a problem at this point in time. But there is an issue, and I'm driving home to a point.

Modulation and channel width

When I talked about electromagnetic fields and being able to send data through it, I said that there are two ways we can send data. One of them is through amplitude modulation: we can change the amplitude. One of them is frequency modulation: we can change the frequency. We tend to actually get better data through the frequency modulation. That's one of the reasons why AM stations are better suited for something like talk radio, and FM — frequency modulation — stations are better suited for radio, because we can actually pack a little more data into frequency modulation. That is not the only reason, but for now let's just use that as a framework.

When I'm talking about Wi-Fi, we're doing frequency modulation. We're adjusting the frequency just a little bit to either represent a zero or a one, or whatever data we're trying to represent. So channel one is operating at 2.412 gigahertz — that is a billion hertz per second. We've got that frequency that we're operating at, and then we adjust it one way or another to represent those ones and zeros, to represent the data that is being sent across it.

That means we actually need some of the frequency before it and some of the frequencies after it. We need a band for this channel. We actually need a whole range, a spectrum of frequencies there to adjust, to send this data across. That's what you're seeing in this chart: we have a channel, we've got a frequency, and then we've got the range within it that we need in order to send data across it.

Overlapping channels

What's interesting about this is that this range right here overlaps. It overlaps channel two. It also overlaps channel three. And if we look at channel four, channel 4's range overlaps channel one. And channel 5's range overlaps channel one as well. So it's not until channel six that we can actually use the next channel. And we do the same thing again. The top of this range is 2448, so the next bottom of the range that we can use is channel 11. And channel 12, 13 and 14 aren't even available in some of our regions, in some of our countries. So we really only have three channels to work with.

Here's another visual of that same effect. We have the 2.412 range right here — that's channel one, and it uses up a range here. Channel 6 uses up this range right here. Channel 11 uses up this range right here. So they use up these ranges, and we only really have three available. If you're in certain countries, 12, 13 and 14 don't exist, and in those cases any other combination you have only allows you to have two channels — which is probably why they brought in these extra channels, so that you can actually get a little more usable channels out of these. So we have a problem. There is a problem in the limited number of channels that we have.

Back to the heat map

Now let's take a look at our heat map. If I assign channel one here, then I can't assign two to the next one, because those would be overlapping. So instead, let me assign channel 6 to it. And then I am going to go to this one right here and assign channel 11 to it. I can assign channel one here, because it's not overlapping with this one right here. But right here I now have a problem with this coverage area. I can't assign a one, because it overlaps with this one. I can't assign a six, because it overlaps with this one. I can't assign an 11, because it overlaps with this one. So I'm not able to put the access point there.

This can be problematic on our networks, and that's one of the downfalls of the 2.4 gigahertz range: we're really limited on the bandwidth that we can work with. One way to compensate for this is to lower the power that each one of these access points broadcasts. So there's a lot of adjusting that I have to do to make this all work, and I have to do placements of all of these. We're limited with the amount of channels we have, and it takes quite a bit of changing things around to get this all to work correctly. It's a bit of an artwork to try to get this all to work correctly, especially when you're talking about the 2.4 GHz range.

The 5 gigahertz range has a lot more options, and it's got different ways that we can open up the bands to send more information within each one of these channels. There's a lot more configuration within the standards for 5 gigahertz, and it opens up a lot of possibilities. So typically we want to use 5 gigahertz over 2.4 GHz. The only downside with 5 GHz is that it can transfer more data, but it just doesn't travel as far and it gets interrupted more with different obstacles. It doesn't travel through walls as well, and so it can be more problematic in some cases.

2.4 GHz versus 5 GHz

• 5 GHz has a higher data rate, and it's actually less susceptible to some interference — there are fewer frequencies that will interfere with that frequency. However, it doesn't do as well with obstacles.
• 2.4 GHz has a larger coverage area and is less susceptible to obstructions, things like walls. It's also a very crowded space, which means there are a lot of devices that use that 2.4 GHz frequency.

When you're talking about frequency modulation, you're actually talking about not just a specific frequency that you're sending data across, but a range of frequencies that you modulate within to send that data — and we call that a channel. That is a channel that can get opened up to allow communication to happen. The problem is that the 2.4 gigahertz range has a lot of overlapping channels, making it very limited in what we can use 2.4 GHz Wi-Fi for. So 5 GHz is really the ideal in many situations, although there's still a use case for 2.4 GHz when we're talking about those longer ranges.