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Wireless Basics


Updated 8/11/2008: Link to wireless card article

This is supposed to illustrate  "whole house" wireless coverage

Part 1 of this series provided an explanation of WLAN basics and described common wireless problem symptoms and their probable causes. And Part 2 showed you how to perform a site survey to get information about your wireless environment. In this installment, I'll show you how to increase the effective coverage of your wireless network. Note that I didn't say "range", and it's important to understand the difference.

NoteNOTE: Please read references to access points (AP) or wireless routers as applicable to both kinds of products unless otherwise noted.

When manufacturers spec range, they mean how far a wireless router and card will stay connected—regardless of speed in an open-field (no obstacles), interference-free, outdoor environment. While this may make for enticing advertising copy, it bears little relation to what you'll experience in your home or office.

The effective coverage of a wireless network is a combination of enough throughput for the desired applications at the desired locations. In other words, effective coverage is a combination of throughput, distance and application.

For example, if you are primarily using your wireless network to connect a notebook for email, chat and casual web-browsing, a connection speed of around 1 Mbps or even less will probably be just fine. Those applications don't require much bandwidth and chances are your "broadband" connection might be running only around 1.5 Mbps anyway for download and a quarter of that for upload.

If, on the other hand, you want to connect three or four computers running a combination of gaming, heavy downloading and YouTube viewing, you could easily multiply the effective bandwidth needed by 5. Add in local backup of large media files and multiple local video streams and you could easily exceed the available bandwidth in some locations.

NoteNOTE: For more on the effect of bandwidth on video streaming, see Video Streaming Need To Know: Part 2

As I've said many times before, the best solution is the one that meets your needs. So it's important to understand what those needs are before you devise a solution.

Radio Basics...Again

We covered RF basics back in Part 1. But it's helpful to again picture your wireless router as a tiny, faint light bulb and your home's walls and ceilings not as solid objects, but more like translucent panels with varying opacity, to get into the right frame of mind. The more panels between the bulb and your eye, the tougher it will be to see the light. The number and location of other "light" sources - 2.4GHz cordless phones, microwave ovens, etc. - will make it difficult, or even impossible to see the flashlight bulb instead of the interfering sources.

It's also helpful to visualize how the radio signal radiates from your access point or wireless router's antenna(s).

Simple dipole antenna radiation pattern

Figure 1: Simple dipole antenna radiation pattern
(click on image for a larger view)
From Antennas Enhance WLAN Security by Trevor Marshall
Used by permission

Figure 1 shows the radiation pattern for the dipole antenna that comes with most access points and wireless routers. The red "donut" at the top is a 3D representation of the energy radiating from the antenna, which you should picture as sticking up through the "donut"'s hole.

The circular plot at the lower left is an Azimuth plot which shows the energy pattern from a top (or bottom) view, while the right-hand plot is an Elevation (side) view. You should look for Azimuth and Elevation plots for any antenna that you are considering buying, since they give you essential information for determining whether an antenna will work in your intended application.

You can see that a dipole is an omni-directional antenna, since its energy pattern is equally strong over all 360 degrees around it. Note also that the pattern is not a perfect sphere, but is flattened slightly on the bottom and top. If the radiation pattern were a perfect sphere, i.e. spread out equally in all directions, the antenna would be a perfect isotropic radiator.

But since every antenna type concentrates radiated (or received) energy in some way, that concentration increases the radiated signal output or sensitivity to received signals. The energy concentration is referred to as gain, and is expressed in units of dBi (decibels relative to isotropic radiator). Given that the dipole is the simplest antenna type, it also has the lowest gain - about 2.15dBi (usually rounded up to 2.2dBi).

I'll have more on antennas later, but with these basics under our belt, let's move on to some wireless improvement!

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