CWNP CWNA – Spread Spectrum Technologies

1. Spread Spectrum Technologies

This module is on the spread spectrum technologies that we’re going to look at. And that means we’re going to talk about things like the Ism bands, the ones that are unlicensed, calling them the industrial, scientific and medical. We’ll talk about the uni bands that exist within those unlicensed portions. Then we’ll look at concepts like narrow band, spread spectrum. Then we’ll look at some of the encoding methods that we use, like the FHSS, the DSS, the OFDM, and how those apply to the different channels that we have with wireless at 2. 4. Then we’ll understand why we have so many limited channels when we talk about adjacent nonajns and overlapping channels and then make sure we understand the difference between throughput and bandwidth. Bye.

2. Industrial, Scientific, and Medical Bands

When it comes to the Ism, part of the standard that we see with the eight or 211 and all of the other standards we saw there like eight or 211, b, G and N, and A, the amendments that were put in there all define the communications in our frequency range between 2. 4. Again. An ism band. And that actually has more than just 2. 4 from 2. 4, it actually, it goes from 2. 4 to 2. 4835 GHz. Not like you want to remember that because you really don’t have to. But those are a range of frequencies that are unlicensed, that we can use not only just for wireless communications, but for things like the kids with the remote control cars, and if people still have cordless phones and those types of things. So the ranges, by the way, of the unlicensed bands, back when we talk almost 15 years ago, many things were operating at the 900 MHz range, which was at that time considered to be very good for cordless phones and for remote control cars and those type of things.

But we also had the 2. 4, well, we call it 5. 0 GHz, but technically the 5. 725 gigahertz range. Now, the purpose of that is to say that there are companies, vendors that can create equipment that can run on that range without having to get a license. Unlike an Am or FM radio station, we have to get a license and do all that paperwork to be able to use that. These were free for any vendor to be able to use. The only restriction was about how powerful the gain would be from the antennas. So when we look at the Ism, the 900 MHz was considered the industrial band, the 2. 4 GHz band was known as scientific, and the 5. 8 GHz band was known as the medical band. Now we call it Ism because we can do any of those things at any of those bands. It’s not just that kind of equipment. Some people even call it the junk band, meaning that all of the other junk that’s out there that’s not licensed will run in that band.

3. 900 MHz

Alright, so when we look at the 900 MHz that ism band had many channels that we could use and each channel was 26 MHz wide and it spanned basically from 2. Obviously we just rendered it down to say 900. Factor that limited the use of that band is that in many parts of the world that band was actually being used for cellular communications. Something that they called the GSM or the Global System for mobile communications. Most of that was in Europe. We really didn’t have that problem in the United States. In the United States we used that band back in those days for things like I said, the cordless telephone or the kids toys that remote controlled.

4. 2.4 GHz

The 2. 4 GHz band is the most common band that is used in wireless networking. At least it was until the advent of 8211 N and 8211 AC. I mean, AC will only work at 5 GHz, but the end could have been at either 2. 4 or five. It was your choice. Now, those bands, each one of those had channels that were 100 MHz wide and it actually expanded, like I said, from 2. 4 to almost 2. 5. Following types of wireless radios would use the span for different types of encoding of the information.

So like the original standard of 811 was the frequency hopping spread spectrum. And that again was a very old technology. It was certainly changed by the advent of 800 and 211 B, G and N, where we see the direct sequence or the rest of those the high throughput different types of technologies, which by the way, was all about how we would encode the ones and zeros in the radio frequency that we were sending. Now, unfortunately, that band is also used by things like microwave ovens.

The big difference is the amplitude or the power of that signal. So in a microwave oven, of course, it was high enough to be able to cook food. But if we were to use that same type of amplitude in the real world, we would be causing a lot of injuries to people that are out there. Your cordless home telephones again, can use that. Still, a lot of people have moved away from 900 MHz. Your baby monitor monitors, your wireless video cameras, so they all compete on that same frequency, which makes for the possibility of having a lot of interference.

5. 5.0 GHz

The 5 GHz band, which really is the 5. 8 GHz band had 150 MHz wide channels. So if you think about it, it started at 5. 75 GHz, went to 5. 85 GHz, but within those gigahertz range, we had a bunch of 150 MHz wide channels. That gave us more channels. Actually, that gave us twelve channels to use.

In the United States, we can only use eleven. In countries like Japan, they can have number twelve, but they’re also being used for the same type of equipment your cordless phones, your cameras and your baby monitors. So that’s why we called it the junk band. Everybody is using those bands. And it might not be great for you in wireless communications, but you should be aware of it.

6. Unlicensed National Information Infrastructure Bands

So all of these bands that I mentioned are unlicensed, at least inside of the United States, and we call them the Unes, the Unlicensed national Information Infrastructure Bands. And that was part of what we worked with, with the IEEE to come up with the amendments to be able to use those frequencies for wireless communications. Now these frequencies and the ranges are known as Unlicensed or Unis. And believe it or not, they actually break them up. If you look at 5 GHz with twelve channels, they break them up into groups of three channels for what they basically were planning for different kinds of wireless communications.

So the way they broke them up is they just basically said, hey, look, the lower band channels are called the lower channels one through four, the middle channels five through eight, the upper channels from nine through twelve. Now they gave them numbers for those like une one for the lower, une two for the middle, une three for the upper. And then for the different types of protocols that we use for wireless, the 800 and 211 A, the N and the Ace would use those groups of channels to be able to do their transmissions of the data. And again, remember, N is called high throughput, the AC is considered very high throughput.