WEBVTT 1 00:00.000 --> 00:04.880 It's easy to focus on the concept of interference, and in the wireless world we 2 00:04.880 --> 00:05.500 actually refer 3 00:05.500 --> 00:10.660 to this as co-channel interference, or CCI, to make sure that we're talking 4 00:10.660 --> 00:11.460 about interference 5 00:11.460 --> 00:13.940 that's happening with the same frequencies. 6 00:13.940 --> 00:19.070 But if we are talking about co-channel interference, then yes, that is a big 7 00:19.070 --> 00:19.940 problem. 8 00:19.940 --> 00:22.940 But what we're going to find is that when it's special when it comes to our 9 00:22.940 --> 00:23.420 wireless 10 00:23.420 --> 00:28.180 designs, co-channel interference usually isn't as big of a deal as another 11 00:28.180 --> 00:29.020 mechanism. 12 00:29.020 --> 00:30.980 And we'll get into here in a moment. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 12 00:29.020 --> 00:30.980 And we'll get into here in a moment. 13 00:30.980 --> 00:34.380 But for now, let's go ahead and talk about co-channel interference since CCI. 14 00:34.380 --> 00:36.700 I mean, what exactly causes it? 15 00:36.700 --> 00:44.510 So remember, we might have that hidden node problem where we are causing 16 00:44.510 --> 00:45.820 interference 17 00:45.820 --> 00:47.380 with our fellow Wi-Fi devices. 18 00:47.380 --> 00:52.320 I'm transmitting from here, I'm transmitting from here, and this device here, 19 00:52.320 --> 00:52.900 usually 20 00:52.900 --> 00:55.620 the axis point, is kind of caught in the middle. 21 00:55.620 --> 01:00.450 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 21 00:55.620 --> 01:00.450 And so we might have that issue, that usually happens if we have very large 22 01:00.450 --> 01:01.840 cells, because 23 01:01.840 --> 01:05.330 these two devices have to be really far apart to not be able to hear one 24 01:05.330 --> 01:06.360 another, or maybe 25 01:06.360 --> 01:10.340 we have like a really thick wall on one side or the other. 26 01:10.340 --> 01:13.180 And so it's all things to consider. 27 01:13.180 --> 01:17.490 But fortunately, we can usually shrink ourselves and kind of get around this 28 01:17.490 --> 01:20.020 hidden node issue. 29 01:20.020 --> 01:23.490 For the most part, because of that, when we're talking about interference, we 30 01:23.490 --> 01:23.940 usually are 31 01:23.940 --> 01:27.500 referring to non-Wi-Fi devices. 32 01:27.500 --> 01:35.540 For example, a common culprit with this is Bluetooth. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 32 01:27.500 --> 01:35.540 For example, a common culprit with this is Bluetooth. 33 01:35.540 --> 01:39.660 Bluetooth is another means of data communication. 34 01:39.660 --> 01:43.500 It uses the 2.4 gigahertz band. 35 01:43.500 --> 01:49.260 And it causes interference because it uses frequencies all over this band. 36 01:49.260 --> 01:54.340 It doesn't just lock down to, let's say, channel 1 or something along those 37 01:54.340 --> 01:55.060 lines. 38 01:55.060 --> 01:59.060 So remember, when our Wi-Fi devices are communicating, they're supposed to wait 39 01:59.060 --> 01:59.340 . 40 01:59.340 --> 02:00.660 They're supposed to listen. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 40 01:59.340 --> 02:00.660 They're supposed to listen. 41 02:00.660 --> 02:01.660 They wait. 42 02:01.660 --> 02:02.660 And here's what's important. 43 02:02.660 --> 02:06.460 They follow a set of rules for communication. 44 02:06.460 --> 02:10.650 This set of rules makes it so Wi-Fi devices very rarely communicate over the 45 02:10.650 --> 02:11.260 top of one 46 02:11.260 --> 02:12.260 another. 47 02:12.260 --> 02:14.060 If they do, then they do cause interference. 48 02:14.060 --> 02:18.750 But for the most part, because of these rules, the Wi-Fi devices don't speak on 49 02:18.750 --> 02:19.260 top of one 50 02:19.260 --> 02:20.260 another. 51 02:20.260 --> 02:25.550 Bluetooth, and anything else we're talking about here, so maybe we're just 52 02:25.550 --> 02:26.620 talking about 53 02:26.620 --> 02:29.700 a, something that's causing noise. 54 02:29.700 --> 02:32.100 Maybe it's another type of communicator. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 54 02:29.700 --> 02:32.100 Maybe it's another type of communicator. 55 02:32.100 --> 02:35.500 Maybe it's a wireless phone that's using 2.4 gigahertz. 56 02:35.500 --> 02:40.100 All of these follow a different set of rules. 57 02:40.100 --> 02:44.920 And even though they will usually wait to communicate, their rules for when to 58 02:44.920 --> 02:46.220 start communicating, how 59 02:46.220 --> 02:49.500 long to communicate, those are all very different. 60 02:49.500 --> 02:55.990 And so this creates a lot more overlap and overlapping, as we know, does create 61 02:55.990 --> 02:57.580 interference. 62 02:57.580 --> 03:01.580 So this is where co-channel interference can come from. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 62 02:57.580 --> 03:01.580 So this is where co-channel interference can come from. 63 03:01.580 --> 03:06.050 I was once playing a video game system, and it's still crazy to me to this day 64 03:06.050 --> 03:06.460 that this 65 03:06.460 --> 03:07.460 happened. 66 03:07.460 --> 03:09.380 This was back in the late 2000s or so. 67 03:09.380 --> 03:13.520 And this video game system was speaking Wi-Fi to communicate out to the 68 03:13.520 --> 03:14.580 internet, and it 69 03:14.580 --> 03:16.380 was playing online with somebody. 70 03:16.380 --> 03:19.700 And I'm sitting over here, not thinking anything of it. 71 03:19.700 --> 03:23.980 I've got this controller that I'm using that is wireless. 72 03:23.980 --> 03:28.140 And it was wireless communicating to this game system as well. 73 03:28.140 --> 03:34.020 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 73 03:28.140 --> 03:34.020 And what I came to realize eventually was that this is all using 2.4 gigahertz. 74 03:34.020 --> 03:38.500 And so every time I'd start to move on the controller, the game would lag out. 75 03:38.500 --> 03:40.620 And everything would stop moving and grind to a halt. 76 03:40.620 --> 03:43.260 And then I'd stop because the game had stopped. 77 03:43.260 --> 03:46.380 Because I stopped, there was no more interference. 78 03:46.380 --> 03:47.380 The game would communicate. 79 03:47.380 --> 03:48.780 I said, oh, the game started again. 80 03:48.780 --> 03:49.780 Great. 81 03:49.780 --> 03:50.780 I'd start moving again. 82 03:50.780 --> 03:53.740 I'd cause the interference and the game would stop again. 83 03:53.740 --> 03:58.280 And it's one of the most blatant experiences I've had with direct wireless 84 03:58.280 --> 03:59.420 interference. 85 03:59.420 --> 04:02.670 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 85 03:59.420 --> 04:02.670 But again, because the game controller and the Wi-Fi space, they were following 86 04:02.670 --> 04:03.340 very different 87 04:03.340 --> 04:09.190 rules, although be it with the same frequencies, that was causing a bunch of 88 04:09.190 --> 04:10.420 interference to 89 04:10.420 --> 04:14.770 the point that it wasn't possible, even though the game system supported it, it 90 04:14.770 --> 04:15.020 wasn't 91 04:15.020 --> 04:19.900 possible to use wireless controller and be on the Wi-Fi at the same time. 92 04:19.900 --> 04:23.100 So that is the concept of co-channel interference. 93 04:23.100 --> 04:27.370 Now again, in a pure Wi-Fi space, we don't usually worry as much about co-ch 94 04:27.370 --> 04:28.740 annel interference. 95 04:28.740 --> 04:33.120 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 95 04:28.740 --> 04:33.120 But there is another big issue that can happen with our Wi-Fi world, and that 96 04:33.120 --> 04:33.800 is known as 97 04:33.800 --> 04:41.460 co-channel contention, which is abbreviated CC-C. 98 04:41.460 --> 04:44.700 So what is co-channel contention about? 99 04:44.700 --> 04:49.820 Co-channel contention has to do with the fact that we are indeed waiting. 100 04:49.820 --> 04:54.700 Remember, we take turns in the wireless space. 101 04:54.700 --> 04:59.220 But what happens if we have a lot of stations all together? 102 04:59.220 --> 05:03.360 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 102 04:59.220 --> 05:03.360 So if I've got an access point here, and I've got let's say, I don't know, five 103 05:03.360 --> 05:04.020 stations 104 05:04.020 --> 05:08.180 all communicating, yeah, they can all take turns, no problem. 105 05:08.180 --> 05:13.110 But what happens if I have 30 devices all in here, and they're all trying to 106 05:13.110 --> 05:14.740 take turns? 107 05:14.740 --> 05:18.870 Well the more devices that are communicating, the more likely we are to step on 108 05:18.870 --> 05:19.660 each other's 109 05:19.660 --> 05:24.750 flows, the more waiting we have to do, we all have to kind of get in line and 110 05:24.750 --> 05:26.460 wait to speak, 111 05:26.460 --> 05:32.740 and this creates contention, which is where we get this phrase from. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 111 05:26.460 --> 05:32.740 and this creates contention, which is where we get this phrase from. 112 05:32.740 --> 05:35.100 Contention for channel access. 113 05:35.100 --> 05:39.260 I want to access this channel, I'm listening and waiting my turn, and 114 05:39.260 --> 05:40.540 eventually I will get 115 05:40.540 --> 05:43.980 to speak, and hopefully my communication goes through, but as soon as I'm ready 116 05:43.980 --> 05:44.340 to make 117 05:44.340 --> 05:47.580 my next transmission, I'm right back into the line. 118 05:47.580 --> 05:50.380 And so that's really not ideal. 119 05:50.380 --> 05:53.100 But here's where things can take an even worse turn. 120 05:53.100 --> 05:56.880 What happens if I have two access points that are on the same channel, let's 121 05:56.880 --> 05:57.980 say this is 122 05:57.980 --> 06:01.920 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 122 05:57.980 --> 06:01.920 five gigahertz space, I'm on channel 40 here, and then I do my cell design, I 123 06:01.920 --> 06:02.700 've got another 124 06:02.700 --> 06:07.540 cell in here, and so we'll leave this one out for a moment. 125 06:07.540 --> 06:11.020 And then all the way over here, I've got another channel 40 cell. 126 06:11.020 --> 06:14.390 Well on paper, this is great, I've got this wonderful gap here, and we don't 127 06:14.390 --> 06:14.780 need to 128 06:14.780 --> 06:16.660 worry about things. 129 06:16.660 --> 06:20.980 But what happens if I have a device that's here like a laptop? 130 06:20.980 --> 06:25.240 And when wireless communicates, we like to draw it as if it's going in a 131 06:25.240 --> 06:26.500 straight line. 132 06:26.500 --> 06:30.870 Wireless usually goes through dimensionally like the sphere that we commented WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 132 06:26.500 --> 06:30.870 Wireless usually goes through dimensionally like the sphere that we commented 133 06:30.870 --> 06:31.700 on earlier. 134 06:31.700 --> 06:34.540 So now I've got this device and look what it's doing. 135 06:34.540 --> 06:40.040 It's sending channel 40 signals into this space over here, the other cell, 136 06:40.040 --> 06:41.020 meaning that 137 06:41.020 --> 06:47.140 this device here actually has to wait to communicate. 138 06:47.140 --> 06:50.350 Now we might have a hidden node issue so to speak where this device all the way 139 06:50.350 --> 06:50.900 on the right 140 06:50.900 --> 06:52.220 can't see it. 141 06:52.220 --> 06:55.220 But again, our devices are really good at picking up signals. 142 06:55.220 --> 07:00.330 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 142 06:55.220 --> 07:00.330 And so maybe it's still enough so that now these two cells aren't creating 143 07:00.330 --> 07:01.380 interference 144 07:01.380 --> 07:06.380 with one another, but they are creating contention with one another. 145 07:06.380 --> 07:11.180 This is a big problem when it comes to high density deployments. 146 07:11.180 --> 07:15.870 We need to make sure that we understand that not only the access points form 147 07:15.870 --> 07:16.540 cells, but 148 07:16.540 --> 07:19.300 so do the clients a little bit. 149 07:19.300 --> 07:22.830 And furthermore, we might make the cells smaller, say hey, access point 150 07:22.830 --> 07:25.140 transmit with less power, 151 07:25.140 --> 07:30.500 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 151 07:25.140 --> 07:30.500 but it's a little harder to get the laptop to not communicate it full blast. 152 07:30.500 --> 07:34.830 And now it's sending signals out everywhere that's causing problems in other 153 07:34.830 --> 07:35.460 cells. 154 07:35.460 --> 07:39.680 Because I say within the world of Wi-Fi, we typically are more concerned with 155 07:39.680 --> 07:40.420 co-channel 156 07:40.420 --> 07:45.970 contention when we have non-Wi-Fi devices, especially thinking about Bluetooth, 157 07:45.970 --> 07:47.500 phones, wireless 158 07:47.500 --> 07:51.480 gaming controllers, for example, that's where we can start to hit problems with 159 07:51.480 --> 07:52.380 interference.