802.11 wireless network technologies are many and varied. In this video, you’ll learn about 802.11 frequency use, MIMO, MU-MIMO, power levels, antenna types, and more.
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There are a number of different technologies used to communicate over 802.11 networks. One big difference between different standards of 802.11 networks are the frequencies used to communicate. Some 802.11 networks use the 2.4 gigahertz frequency range. Other 802.11 technologies will use the 5 gigahertz frequency range.
Instead of us having to remember the exact frequency in the 2.4 gigahertz or 5 gigahertz frequency range, the IEEE standards have grouped together these frequencies into channels. It makes it very easy to reference when you’re configuring a wireless access point. If you’re trying to make sure that multiple access points can communicate, you may want to choose channels that don’t overlap with each other.
Different 802.11 standards will use different bandwidths in these 2.4 and 5 gigahertz frequency ranges. This is the amount of frequency you’re using at any particular time. And I’ll show you a graph that breaks out for you the differences in the standards and the different frequency ranges that are available with 2.4 gigahertz and 5 gigahertz.
802.11a and 802.11b were introduced at effectively the same time, and they used very similar bandwidths. You could see that 802.11a uses 20 megahertz and 802.11b uses 22 megahertz. The modulation used for these two standards was slightly different, but the overall amount of bandwidth being used was very similar between both of them. The introduction of 802.11g also used the same frequencies as 802.11b, but you can see that a change in the modulation also changed the bandwidth that that particular standard would use in the 2.4 gigahertz range.
We realized that if we wanted to increase the amount of data that we could send over these wireless networks that we would need to use more of these frequency ranges. And with 802.11n, we have the choice of either 20 megahertz or doubling it to a 40 megahertz channel bandwidth. That means with 802.11n running at 2.4 gigahertz, a 40 megahertz channel would use 80% of the available frequencies in the 2.4 gigahertz range.
To avoid some of those bandwidth shortcomings with 2.4 gigahertz, the 802.11ac standard uses 5 gigahertz. And it will use, at a minimum, 40 megahertz of a channel bandwidth. It can also increase that to 80 megahertz channel bandwidth, and that’s required for 802.11ac, and if you even wanted to increase it to 160 megahertz bandwidth, you would be able to move that much more data through your 802.11ac network.
Here’s a chart that shows the differences in the available frequencies in the 2.4 gigahertz range and the available frequencies in the 5 gigahertz range. This also shows you how you’re able to increase the different channel widths to use more frequencies at the same time.
If we first look at the 2.4 gigahertz range, we see the different channels that have been assigned by the IEEE and these are three channels that don’t overlap with each other– channels 1, channel 6, and channel 11– and you can see they range with these 20 megahertz blocks for each one of these.
For 5 gigahertz, you can see that we have many more blocks of 20 megahertz channel bandwidths available. Anything that is not red is available bandwidths that you can use in 5 gigahertz. So you can see a large difference in available bandwidth when you move up to the 5 gigahertz ranges. But of course, some of these 5 gigahertz standards allow you to have larger channel bandwidths. So you can group together and have 40 megahertz channel bandwidths, 80 megahertz, or in the case of 802.11ac you can use a 160 megahertz channels to be able to move data over that wireless network.
Not only did we change the amount of frequencies that we were using with these channel bandwidths, we also changed the way that we were sending data over these wireless networks. Prior to 802.11n, we would simply send a single stream of information between point A and point B.
But 802.11n introduced a new way to send data called MIMO. That stands for multiple-input and multiple-output. That allows us to send multiple streams of information over exactly the same frequencies at the same time. Prior to this, we weren’t able to accomplish that.
With 802.11ac, we improved on MIMO by introducing multi-user MIMO where we could send data to multiple users simultaneously over the same frequencies.
The ability to provide this multiple-input multiple-output was very dependent on the number of antennas that you might have available on a particular device. So for 802.11n and 802.11ac, you may see this number of antennas on an access point, number of antennas on a client, and the number of streams available documented somewhere on that particular device.
For example, if you see 2×2 and a colon and 2, that means there’s two antennas on the access point, two antennas on the client, and it can support two total streams. A device that specifies three by three with a two means that it has three antennas on an access point and three antennas on a client– can support a maximum number of two streams. And on higher-end equipment, you may see that there are four antennas on the access point and four antennas on the client that can support up to four simultaneous streams.
On 802.11a, b, and g, there was one antenna on the access point and one antenna on the client. The communication occurred over a single frequency from one device to the other.
When we introduced MIMO with 802.11n, this introduced a completely new way to communicate. With MIMO, we need signal diversity. We need a way for some signals to bounce off of other devices and make their way to the device on the other side.
There’s something in the middle and it’s bouncing the signal off and the data on the other end is reconstructed using digital signal processing. This allows you to send multiple streams of information between devices and you’re able to do it over exactly the same frequency.
With MIMO, we could really increase the amount of throughput between devices because if both devices supported multiple streams, you could begin to send lots of data between those. The MIMO that was included with 802.11n could only send one grouping at a time. So it could send data down to this laptop, it could then change and send data to a mobile device, and then send data to a television. But it could not do all three of these simultaneously.
In 802.11ac, we were provided with multi-user MIMO, which meant that we could use multiple streams to send data over the same frequency. But we could do it to multiple clients simultaneously. So you could have a couple of streams of data going to a laptop, you could have a stream of information going to your mobile device, and another stream going to this television, all using the same frequencies simultaneously on this 802.11ac network.
If you live in an apartment building or you work in an office building with many different companies, you’ve probably seen a number of different wireless access points show up on a list of available networks. Because of this you may want to consider how much signal you’re sending out for your access points.
This is usually a configuration change that you could make inside the software configuration of a wireless access point or wireless router. This may take a little bit of survey work while you walk around with a mobile device and determine how much of the wireless signal you’re able to hear between the access point and your mobile device.
With some devices, you may even have an option as to the type of antenna you use, especially with the desktop computer. And by changing the type of antenna, you may be able to turn down the amount of power on your access point, but still maintain a good level of communication between those two devices.
If you’ve ever purchased a wireless access point or a wireless router, it probably came with antennas that look a lot like these. These are omnidirectional antennas and they are some of the most common that you’ll find on these devices. We call these antennas omnidirectional because they distribute the wireless signal evenly on all sides of that antenna. This would allow you to put the wireless access point in a central location and you’d have effectively the same signal strength on all sides of that access point.
You may run into a challenge, however, if your access point is on one side or the other of where you need the signal to go. In those cases, you may want to use a more directional antenna.
A directional antenna would allow you to focus the signal to go into a particular direction. So if you’re needed to send information between buildings or you had an access point at one end of the hall and you needed to provide signal across the rest of the hallway, you may want to use a directional antenna. We usually measure the performance of these antennas in decibels. So if you have an antenna that doubles the amount of effective power, then we say that you’re doubling this by three db.
One type of high-gain directional antenna is the Yagi antenna where you have the single antenna and multiple reflectors along the side that allow you to focus the signal. Another type of directional antenna is the parabolic antenna. This allows you to reflect a signal off of a curved surface and reflect it into a single feed horn, allowing you a very good way to have a directional signal between two devices.
If you’re doing any type of wireless communication on your network, you may need some way to provide a survey. You may need to walk around with a mobile device and be able to understand the wireless characteristics in your area– would not only be able to show you the coverage of signal as you walk around, but you may be able to find certain spots of interference that may be coming from other access points or other wireless devices. You may find a number of built-in tools in the operating system that you’re using, but a number of third-party products may provide you with some additional insight into exactly what’s happening on your wireless network.
And if you’re doing a lot of wireless installations and you need a very precise view of exactly what’s going on at every frequency of the 802.11 wireless range, you may want to invest in a spectrum analyzer that can show you details of exactly what’s happening at every frequency.
Category: CompTIA Network+ N10-007