WEBVTT 0:00:02.920000 --> 0:00:06.960000 Hello and welcome to this video titled RF Channels. 0:00:06.960000 --> 0:00:10.280000 In this video I'm going to talk about what is this concept of this thing 0:00:10.280000 --> 0:00:12.220000 called a Wi-Fi channel. 0:00:12.220000 --> 0:00:15.940000 I'll talk about channel bandwidth and we'll take a look at an example 0:00:15.940000 --> 0:00:19.880000 of Wi-Fi bandwidth and how that relates to Wi-Fi channels. 0:00:19.880000 --> 0:00:24.900000 So let's start with what is a Wi-Fi channel. 0:00:24.900000 --> 0:00:30.620000 So if you're just a common user of a Wi-Fi network, you bring in your 0:00:30.620000 --> 0:00:34.340000 smartphone or tablet into a coffee shop or business and you connect to 0:00:34.340000 --> 0:00:39.280000 the Wi-Fi, this concept of a channel number is probably meaningless or 0:00:39.280000 --> 0:00:40.880000 irrelevant to you. 0:00:40.880000 --> 0:00:44.980000 You have no idea what channel number you are connecting to. 0:00:44.980000 --> 0:00:50.340000 But every access point when it's advertising its availability, when it's 0:00:50.340000 --> 0:00:57.400000 advertising its which is its range of coverage and advertising its name 0:00:57.400000 --> 0:01:04.120000 like corporate, payroll, Starbucks, I &E, whatever it is, that BSS is being 0:01:04.120000 --> 0:01:09.180000 advertised within a certain radio frequency space and that radio frequency 0:01:09.180000 --> 0:01:11.620000 space is called a channel. 0:01:11.620000 --> 0:01:15.920000 And so in order for your laptop or smartphone or tablet to even hear that, 0:01:15.920000 --> 0:01:18.560000 you have to be tuned in to that channel. 0:01:18.560000 --> 0:01:21.700000 So the channel is really more relevant from the perspective of a network 0:01:21.700000 --> 0:01:27.260000 administrator or network engineer who is setting up a wireless LAN topology 0:01:27.260000 --> 0:01:31.340000 because part of what you have to decide upon is not only the name of your 0:01:31.340000 --> 0:01:36.240000 SSID and where you want your access points to be physically located, you 0:01:36.240000 --> 0:01:40.660000 have to decide what channel you want your radio to be transmitting on 0:01:40.660000 --> 0:01:42.720000 so other people can hear you. 0:01:42.720000 --> 0:01:46.340000 So as this says right here, Wi-Fi channel is really a collection of different 0:01:46.340000 --> 0:01:49.260000 frequencies working together. 0:01:49.260000 --> 0:01:53.180000 For example, if you're setting up an access point, you might see that 0:01:53.180000 --> 0:01:57.800000 channel one is available, that you can advertise on channel one that will 0:01:57.800000 --> 0:01:59.520000 consist of your BSS. 0:01:59.520000 --> 0:02:07.640000 Well in the 2.4 gigahertz space, channel one actually consists of modulating 0:02:07.640000 --> 0:02:14.100000 or oscillating your radio frequencies from 2.401 billions of times per 0:02:14.100000 --> 0:02:21.420000 second, we call that gigahertz, 3 billions of times per second. 0:02:21.420000 --> 0:02:26.180000 So within that range, you can modulate your frequency within that range, 0:02:26.180000 --> 0:02:29.940000 that is all considered to be channel one. 0:02:29.940000 --> 0:02:33.640000 And all these frequencies can be modulated differently at the same time 0:02:33.640000 --> 0:02:40.540000 to encode data. So as an example, a radio could be depending on him, for 0:02:40.540000 --> 0:02:44.380000 example, if you have an access point that has, let's just make it simple, 0:02:44.380000 --> 0:02:49.200000 two transceivers, you've got two antennas connected to two different transceivers. 0:02:49.200000 --> 0:02:53.220000 Well what that access point could do is on one transceiver, it could be 0:02:53.220000 --> 0:02:58.680000 modulating at 2.401 billions of times per second right now, at the exact 0:02:58.680000 --> 0:03:07.020000 same time on the second transceiver, it could be modulating at 2.415 gigahertz 0:03:07.020000 --> 0:03:08.640000 per second, at the same time. 0:03:08.640000 --> 0:03:12.060000 So if it's trying to lock in on the phase, if it's trying to say, hey, 0:03:12.060000 --> 0:03:15.200000 look at these two signals, compare the phase of these two signals, are 0:03:15.200000 --> 0:03:19.280000 they both the same, are they out of phase, or just the different frequencies, 0:03:19.280000 --> 0:03:21.400000 it can be used to encode the data. 0:03:21.400000 --> 0:03:25.660000 Or a single radio could say, alright, for this tiny slice of time, right 0:03:25.660000 --> 0:03:28.820000 now, because I'm on channel one, I'm going to oscillate my frequency at 0:03:28.820000 --> 0:03:31.320000 2.401 gigahertz per second. 0:03:31.320000 --> 0:03:34.760000 Now in the next tiny slice of time, I'm going to ramp that up a little 0:03:34.760000 --> 0:03:38.980000 bit, and I'm going to oscillate at 2.421 gigahertz per second. 0:03:38.980000 --> 0:03:43.140000 I'm going to go back down to 2.419 gigahertz per second, so it can go 0:03:43.140000 --> 0:03:48.100000 all over in this range to encode data, and that still considered to be 0:03:48.100000 --> 0:03:55.980000 channel one. Now if you recall, Wi-Fi operates in these unlicensed frequency 0:03:55.980000 --> 0:04:00.080000 bands, called the Industrial Scientific and Medical bands. 0:04:00.080000 --> 0:04:02.840000 So we can see here, there's three of them, there's the lower bands and 0:04:02.840000 --> 0:04:05.000000 the 900 megahertz range. 0:04:05.000000 --> 0:04:09.020000 Wi-Fi doesn't really operate there, it operates in the next two, in the 0:04:09.020000 --> 0:04:12.720000 2.4 gigahertz range and in the 5 gigahertz range. 0:04:12.720000 --> 0:04:16.320000 And within each one of those, let's just take a look at the 2.4 and the 0:04:16.320000 --> 0:04:20.060000 5 gigahertz, within each one of those, we have different channels available 0:04:20.060000 --> 0:04:23.320000 that you can select for your access point. 0:04:23.320000 --> 0:04:30.840000 Now one of the things you have to select is when you tell your access 0:04:30.840000 --> 0:04:34.360000 point, okay, I want you to start advertising your availability, I want 0:04:34.360000 --> 0:04:37.860000 you to start broadcasting out onto the radio waves, I'm here, you can 0:04:37.860000 --> 0:04:40.880000 connect to me, and here's the range of frequencies that I use. 0:04:40.880000 --> 0:04:43.560000 You have some choices with that as well. 0:04:43.560000 --> 0:04:47.800000 Originally, when Wi-Fi first came out and for several years after it came 0:04:47.800000 --> 0:04:52.300000 out, a single channel, if you thought about the lowest frequency it could 0:04:52.300000 --> 0:04:55.940000 advertise on, and then the highest frequency it could advertise on, if 0:04:55.940000 --> 0:04:58.960000 you subtracted those two and you looked at what's the total in the middle, 0:04:58.960000 --> 0:05:02.200000 a single channel was 20 megahertz wide. 0:05:02.200000 --> 0:05:06.800000 Now in reality, it's more like 22 megahertz wide, but in documentation 0:05:06.800000 --> 0:05:14.720000 and papers and so Wi-Fi for the longest time operated on 20 megahertz 0:05:14.720000 --> 0:05:22.100000 channels. So channel one was a range of 20 megahertz and then channel 0:05:22.100000 --> 0:05:25.860000 two was another range of 20 megahertz and so on and so forth. 0:05:25.860000 --> 0:05:29.840000 When newer Wi-Fi standards came out and they started trying to make Wi 0:05:29.840000 --> 0:05:35.340000 -Fi faster, one of the ways to make it faster was to increase the range 0:05:35.340000 --> 0:05:40.880000 of that size. Because if I have more frequencies I can modulate and change, 0:05:40.880000 --> 0:05:44.240000 that gives me more variations that I can encode my data on. 0:05:44.240000 --> 0:05:48.240000 So within, so I can actually transmit, transmit at a faster rate by using 0:05:48.240000 --> 0:05:49.560000 a wider channel. 0:05:49.560000 --> 0:05:55.680000 So for example, 802.11n was the first time we could use 40 megahertz channels. 0:05:55.680000 --> 0:06:00.620000 When 802.11ac came out, they said, hey, let's make that even wider to 0:06:00.620000 --> 0:06:03.280000 an 80 megahertz channel. 0:06:03.280000 --> 0:06:09.000000 And then with 802.11ax, which is scheduled to be formalized and standardized 0:06:09.000000 --> 0:06:14.780000 sometime in 2020, technically to get the absolute fastest speeds, you 0:06:14.780000 --> 0:06:20.100000 would have to use 160 megahertz of a channel, which is a super wide channel. 0:06:20.100000 --> 0:06:22.340000 So let's see how all this plays out here. 0:06:22.340000 --> 0:06:26.260000 So here we're looking at the industrial and scientific medical band that's 0:06:26.260000 --> 0:06:28.440000 in the 2.4 gigahertz space. 0:06:28.440000 --> 0:06:34.040000 And if we're focusing just on channel 1, channel 1, so you might remember 0:06:34.040000 --> 0:06:39.940000 it was something like 2.4 1 gigahertz or something like that. 0:06:39.940000 --> 0:06:43.020000 And I don't remember what the upper layer was. 0:06:43.020000 --> 0:06:47.740000 It looks like it was about 2.42 gigahertz. 0:06:47.740000 --> 0:06:49.520000 So that's this right here. 0:06:49.520000 --> 0:06:55.780000 So this is all the frequency space that channel 1 can operate in. 0:06:55.780000 --> 0:06:59.400000 From the lowest frequency range, which is right there, to the highest 0:06:59.400000 --> 0:07:01.740000 frequency range, which is right there. 0:07:01.740000 --> 0:07:05.740000 And so the frequency right in the middle, that's technically what we call 0:07:05.740000 --> 0:07:12.100000 channel 1. So channel 1 is, we say it operates in the 2.4 1 2 gigahertz 0:07:12.100000 --> 0:07:14.220000 space, but that's the middle channel. 0:07:14.220000 --> 0:07:17.260000 That's the middle frequency right in the middle between the lowest and 0:07:17.260000 --> 0:07:24.060000 the highest. And the size of this, the size of all of these half circles, 0:07:24.060000 --> 0:07:28.800000 is what we would call a 20 megahertz channel. 0:07:28.800000 --> 0:07:33.400000 Because if we take a look at the lowest transmission point and the highest 0:07:33.400000 --> 0:07:37.880000 transmission point and we subtracted them, we would get about 22 megahertz. 0:07:37.880000 --> 0:07:42.820000 So you can see in the 2.4 gigahertz space, which is what Wi-Fi originally 0:07:42.820000 --> 0:07:49.200000 started on, and still operates on to this day, you have up to 14 channels, 0:07:49.200000 --> 0:07:53.840000 each of which is 22 megahertz wide. 0:07:53.840000 --> 0:07:58.180000 Now, depending on the country you're in, sometimes you don't have access 0:07:58.180000 --> 0:07:59.180000 to all of these. 0:07:59.180000 --> 0:08:03.040000 For example, here in the US, where I'm recording this video, channel 14 0:08:03.040000 --> 0:08:08.820000 is off limits. The FCC has determined that it's actually, I think they 0:08:08.820000 --> 0:08:12.040000 actually called a felony, believe of all things, but they have said, no, 0:08:12.040000 --> 0:08:13.380000 you can't use this. 0:08:13.380000 --> 0:08:16.900000 The highest channel number you can go up to is channel 13. 0:08:16.900000 --> 0:08:19.880000 Other countries like Japan and other places, they have no problem with 0:08:19.880000 --> 0:08:24.300000 channel 14. The last thing I want to point out here about these channels 0:08:24.300000 --> 0:08:30.380000 is notice that there's actually quite a lot of overlap between them. 0:08:30.380000 --> 0:08:35.580000 For example, the frequency is used by channel 1 and the frequency is used 0:08:35.580000 --> 0:08:39.720000 by channel 2, almost completely cover each other. 0:08:39.720000 --> 0:08:44.140000 Channel 2 is right here, channel 1 is right here, and there's a lot of 0:08:44.140000 --> 0:08:46.660000 overlap. Why do we care? 0:08:46.660000 --> 0:08:50.320000 Well, because when channels overlap like this, we might end up getting 0:08:50.320000 --> 0:08:54.940000 a lot of interference from an access point on one channel, if it's closely 0:08:54.940000 --> 0:08:58.600000 physically located to an access point on an adjacent channel. 0:08:58.600000 --> 0:09:02.300000 But the main takeaway I want you to get from this is what is a channel, 0:09:02.300000 --> 0:09:06.680000 so a channel is a range of frequencies, starting with some defined lower 0:09:06.680000 --> 0:09:10.260000 frequency and ending with some upper frequency. 0:09:10.260000 --> 0:09:14.580000 How big that range of frequencies is is going to be either 20 megahertz, 0:09:14.580000 --> 0:09:21.620000 40 megahertz, 80 megahertz, or in some cases 160 megahertz. 0:09:21.620000 --> 0:09:25.140000 And the frequency that's assigned to that channel number is the frequency 0:09:25.140000 --> 0:09:28.240000 that's right in the middle. 0:09:28.240000 --> 0:09:31.680000 So that concludes this video. 0:09:31.680000 --> 0:09:34.160000 Thank you for watching, and I hope you found it useful.