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Deciding where to install the AP

If you’ve ever experienced a dreaded dead zone while talking on a cellular phone, you know how frustrating that can be. Similarly, you should strive to install your wireless network in a way that eliminates dead wireless network zones in your house. Ideally, you determine the best placement of your AP so that no spot in your house is left uncovered; but, if that isn’t possible for some reason, you should at least find out where, if anywhere, the dead zones in your house are to optimize your signal coverage.

To achieve optimum signal coverage, the best place to install an AP is near the center of your home. Think about where you will place the AP when you make your buying decision. All APs can sit on a shelf or table, but some APs can also be mounted to a wall or ceiling. When making your AP selection, ensure that it can be installed where it works best for the configuration of your house as well as keep the AP out of reach of your little ones or curious pets.

The position of the access point is critical because your entire signal footprint emanates from the AP in a known way, centered from on the AP’s antenna(s). Sometimes not enough consideration is given to the positioning of the access point because they so often work pretty well out of the box, just sitting on a table.

Other people install it wrong in the first place. For instance, probably one of the worst manufacturing decisions ever done to access points was to put mounting brackets on them. People get the impression that you should then — duh — mount them on the wall. That’s great except for the fact that,

depending on the antenna you have, you might just kill most of your throughput. You see, when an antenna is flush up against a wall, as is typical in a wall mount situation, the signals of the antenna reflect off the wall back at the antenna, causing interference, and driving down throughput precipitously. Yech. (But you see, customers WANT their wall mount brackets, so product managers at wireless LAN companies decided they had to give it to them.) The best mounting is actually six or more inches off the wall.

The vertical orientation of the mounting point is important as well. Generally, you have more interference lower to the ground. If you did a cross section of your house in one-foot intervals, when you get higher and higher, you’d see less on your map. Thus, signals from an access point located on a shelf low to the ground are going to find more to run into than the ones that are mounted higher. Although this might sound like common sense, consider that most DSL and cable modems are installed by technicians who are used to installing phone and cable TV lines. How many of these are generally located five feet off the floor? They’re not; they tend to be along the floorboards and low to the ground or in the basement. So it’s not surprising that a combined DSL access point router would be plugged in low to the ground, too.

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Factors that affect signal strength

Many variables affect whether you get an adequate signal at any given point in your house, including the following factors:

Distance from the AP: The further away from the AP, the weaker the signal. Wi-Fi 802.11b standards, for instance, promise a maximum operating range of 100 feet at 11 Mbps to 300 feet at 1 Mbps. Indoors, a realistic range at 11 Mbps is about 60 feet. When 802.11a and 802.11g networks become more prevalent, their maximum range may vary. Range differs from vendor to vendor as well.

The power of the transmitter: Wi-Fi APs transmit at a power output of less than 30 dBm (one watt).

The directivity or gain of the antennas attached to the AP and to wireless network adapters: Different antennas are designed to provide different radiation patterns. That’s a fancy way of saying that some are designed to send radio waves in all directions equally, yet others concentrate their strength in certain directions. We talk more about this in Chapter 6, but the thing to keep in mind here is that different brands and models of access points have different kinds of antennas designed for different applications. Check out the specifications of the ones that you’re looking at before you buy them.

The construction materials used in the walls, floors, and ceilings:

Some construction materials are relatively transparent to radio signals, but other materials, such as marble, brick, water, paper, bulletproof glass, concrete, and especially metal, tend to reflect some of the signal, thus reducing signal strength.

Your house plan: The physical layout of your house might determine not only where it’s practical to position an AP, but it also might affect signal strength because the position of walls, the number of floors, brick fireplaces, basements, and so on can partially or even completely block the wireless networks radio signal.

Client locations: Reception is affected by the distance from the AP to the rooms in your house where someone will need wireless network access.

Stationary physical objects: Objects that are permanently installed in your home, such as metal doors, heating ducts, and brick fireplaces can block some or all of the signal to particular spots in your house.

Movable physical objects: Other types of objects, including furniture, appliances, plants, and even people can also block enough of the signal to cause the network to slow down or even to lose a good connection.

APs: Interference can also be caused by the presence of other APs. In other words, if you’ve got a big house (too big for a single AP to cover), you have to keep in mind that in parts of the house — like in the area that’s pretty much directly in between the two APs — you’ll find that the radio waves from each AP can interfere with the other. Check out the following section for more information regarding this phenomenon.

Source: Intel (www.intel.com/network/connectivity/solutions/wireless/ deploy_site.htm); TeleChoice