WiFi Signals and Hardware Table of Contents Wi-Fi Signaling -1............................................................................................................................. 2 Wi-Fi Signaling -2............................................................................................................................. 4 Wi-Fi Signaling -3............................................................................................................................. 6 Wireless Network Hardware -1....................................................................................................... 8 Wireless Network Hardware -2..................................................................................................... 10 Wireless Network Antennas ......................................................................................................... 11 Wi-Fi Summary .............................................................................................................................. 13 Notices .......................................................................................................................................... 14 Page 1 of 14 Wi-Fi Signaling -1 Wi-Fi Signaling -1 Special techniques are used to transmit digital data through radio waves and de-conflict multiple signals. • Modulation – encoding a data signal in a transmitted wave • Carrier wave – reference signal that data is modulated onto Carrier Wave + Data 1 0 1 Signal = Transmitted Signal 30 **030 So Wi-Fi Signaling. Techniques are used to transmit digital data through radio waves, and to deconflict multiple signals. So modulation is the encoding a data signal in a transmitted wave; and a carrier wave is a reference signal that data is modulated on to. So the Wi-Fi access point has this carrier wave that it's always transmitting; over and over and over again. Well to get data across that data signal, what it does is it has hard stops. Page 2 of 14 So as you can see here with the transmitted signal, this right here would be equivalent to a 1. And this is just an example. This isn't exactly what the carrier wave necessarily looks like. But it gets the point across. Then when a 0-bit needs to be transmitted, we get a hard stop where the signal isn't sent anymore; and then we get the next 1 where the signal continues to transmit. And that's how digital data is sent over an analog signal; because that's what these are. We're sending it over a radio wave, which is just an analog signal. Page 3 of 14 Wi-Fi Signaling -2 Wi-Fi Signaling -2 Special techniques are used to transmit digital data through radio waves and de-conflict multiple signals. • Direct Sequence Spread Spectrum (DSSS) – Data signals are modulated over a band of frequencies; 802.11b • Orthogonal frequency division multiplexing (OFDM) – Encodes data signals on multiple carrier waves; 802.11a / g • Spatial division multiplexing (SDM) – Encodes data on multiple signals transmitted by multiple antennas; 802.11n 802.11a 802.11b Channel Channel Power Power 802.11b Frequency DSSS 802.11a Frequency Chan #6 OFDM Freq1 31 **031 Special techniques are used to transmit digital data through radio-- oh we already that. Direct Sequence Spread Spectrum-- DSSS-- are used in 802.11b routers to modulate over a band of frequencies. So here we have an 802.11b; channel number 6. This is one channel. I'm not going to go in- depth on this; it's not necessarily really pertinent to your understanding of exactly what the wave looks like for a b router. But just know that it uses a specific data signal to transmit the data. Page 4 of 14 Orthogonal frequency division multiplexing, or OFDM, is used by a and g routers. It encodes data on multiple carrier waves. So here's an example of an 802.11a channel where you can see there's multiple carrier waves that are sending the data. 802.11n encodes multiple signals on to- transmitted by multiple antennas. So now we have more than one antenna working at the same time; which is why we get higher throughput with n than we do with a, b or g. Page 5 of 14 Wi-Fi Signaling -3 Wi-Fi Signaling -3 The distance a Wi-Fi signal can travel is affected by: • Power • Object density • Transmit and receive antenna location • Interference Source of Interference Microwave ovens Distance Cordless phones Bluetooth devices Transmit Power Fluorescent lights Radar Wireless security devices 32 **032 The distance a Wi-Fi signal can travel is affected by four main factors: How much power is the signal- is the wireless access point pushing; or whatever is sending the signal pushing? How strong is the antenna for both the transmission and the receive side? The density of objects such as walls; the external walls of the house; the floors for the building; what kind of material they're made out of; how much space is there for the signal to actually make it through those surfaces; and any interference. So if there's any other signals on the same frequency. Page 6 of 14 And you can see here different devices that may run on the same frequency. With an older router, I used to notice that when I used the microwave my streaming would stop. And it took me about a month to figure out what was going on. And then I realized wait, the microwave is interfering with the use of this router. Once I moved the router farther away from the microwave, I stopped having that issue. Just as a raise of hands, who has- who still has a corded phone at home? One person. Yes, cordless phones were- used to be a really big device that caused interference. Nowadays it's not as much of a problem. Because most people don't have corded- cordless phones anymore. Most of the people I know just use their cellular devices for communication. Page 7 of 14 Wireless Network Hardware -1 Wireless Network Hardware -1 Wireless networks use the ubiquitous “access point,” which is simply a device that bridges or routes between networks. Clients require a wireless network interface card to connect to a wireless network. Most laptops have these built into the case and are not externally visible. • These can also be expansion cards, USB dongles, or USB devices. Antennas send/receive wireless radio signals and are located on both the access point and the wireless cards. Laptop “mini” card USB “Dongle” PCI Expansion Card USB Device 33 **033 Wireless network hardware. So wireless networks use the ubiquitous access point. All it is is a device that either bridges or routes between networks. Clients require some sort of way to receive the signal. So you can see different options down here. You could have a PCI expansion card. You can have a laptop mini card. You can have a USB dongle. You could have an antenna that's internal to your laptop. You can have an antenna that's internal to your cell phone. Page 8 of 14 So you don't necessarily need to see antenna external to the device if the device itself has an antenna internal to it. Most of them are built in. When they first- when wireless was first coming out, almost everybody had some sort of either expansion card or mini card that they had to plug in, in order to get the wireless signal. I personally don't know of a single laptop released in the last two years that doesn't have wireless built into the laptop. Again, users expect it. The Dells and the HPs of the world are not going to create a laptop that doesn't have the functionality built in. The antennas send and receive the radio signals. And they're located at both ends; because well one side has to transmit and the other side has to receive. So yes, you have to have antennas at both ends. Page 9 of 14 Wireless Network Hardware -2 Wireless Network Hardware -2 Access points come in all shapes and sizes. • Multiple antennas indicate 802.11n or 802.11a/b/g support. — Recall, 802.11a is 5.0 GHz, 802.11 b/g is 2.4GHz — 802.11n supports MIMO • Some antennas are inside the case. 34 **034 They come in all shapes and sizes. So we can see here-- the funny thing is I actually have this router at home. I think the person that created this just got a picture on the internet; but that's my router at home. So please don't do any research on to what router it is. I don't want you to find any vulnerabilities to get onto my network. Multiple antennas usually indicate an 802.11n or 802.11a, b, g support. However, as you can see with this device, I don't see any external antennas on it. Again, the antennas are internal. It doesn't necessarily have to have external antennas. Page 10 of 14 Wireless Network Antennas Wireless Network Antennas Omnidirectional antennas radiate signals in all (( ( ) ) ) directions; typically in laptops and access points Directional antennas radiate signals in a more constrained path. These antennas provide higher gain (send / receive stronger signals), but only to clients in the direction they are pointing. ) ) ) http://www.turnpoint.net/wireless/has.html A homebrew directional Wi-Fi antenna 35 **035 Wireless Network Antennas. One of two type of antennas: omni- directional, which radiates signals in all directions. These are typically what laptops and access points have. So it's just transmitting in every direction from it. Now directional antennas can be used to force the signal to either a very specific path; or you can have a wider directional antenna that can focus; but just not as widespread as an omni-directional. If you're worried about security, omni- or directional antennas are the easiest way to make sure that the signal doesn't reach areas you don't want it to reach. Page 11 of 14 So if you have a cone-shaped antenna, in a corner of the house, you probably can cover just the confines of the house, without much bleed over; at least not on the other sides of the antenna. Most routers don't have that. You'll be more likely to see that in a business.