Tuesday, May 10, 2005

Stretch Your Signal

Having a wireless network in your home or office is great, right? You can check your e-mail in bed and work from the living room with the ball game on TV (but don't make it a habit). You're also no longer chained to your desk at work. You can take your laptop to a meeting and stay connected to your network and the Internet. What happens, however, when your signal doesn't extend to the kitchen, or to the last few offices in your corridor?

In one of our informal tests, we lost the connection less than 50 linear feet from the access point in a wood-frame house. Many wireless users have similar complaints. Wi-Fi, officially known as the 802.11b standard, is supposed to be better than that. But vendors invoke very broad caveats because of the many causes of dead zones in a Wi-Fi network. Many buildings have structural elements that can block radio transmissions, including Wi-Fi. Even passing through wood and drywall may limit the power of your access point's signal.

Networking Bridges
In addition, Wi-Fi uses the same basic radio technology as 2.4-GHz cordless phones. Such phones, and especially their base stations, can cause interference. If you have a phone base and a wireless AP, keep them as far apart as you can.

Microwave ovens are another major source of Wi-Fi interference. These devices throw out enough radio waves in the Wi-Fi range to make communications unreliable within a few feet of a microwave. But interference occurs only when the microwave is in use, and it usually extends no farther than 10 feet from the oven.

Find Your Center

The best thing you can do to maximize the signal from a simple access point is to place it in the middle of the building, or at least at the physical center of the area in which you use the signal. Most access point antennas are omnidirectional, meaning they attempt to broadcast to a spherical area. So placing an access point in the center of your building maximizes the signal strength within the area you want to cover. Also, by maximizing the signal strength inside, you minimize the signal strength outside the building. This way, people outside have a harder time latching onto your signal to crack your network or use your Internet connection.

Placing an access point in the center of your building is often easier said than done. A simple AP must be connected to a hub that goes to your existing network infrastructure, which means you must be able to run an Ethernet cable from the AP to your hub. Usually a consumer access point comes integrated with a broadband router, so you must connect it to your cable modem or DSL. This may be hard when your networking equipment is in an attic or an office, which means drilling through walls to run a cable to an AP at the physical center.

But if you can't (or don't want to) make a better Wi-Fi network by moving your antenna or ripping the metal out of your walls, you can purchase a product to fill in the dead zones and extend your coverage.

Stronger Signals

Generally speaking, there are three ways to fix the problem. The first is to get a more powerful antenna, or perhaps one more suited to the environment. The second is to use some other networking method as a bridge, so you can move the AP without an Ethernet connection to the network. We discussed this option briefly in "Home Networking 101" (April 22), but we'll provide more detail here. The third and perhaps simplest and cheapest approach is to use a Wi-Fi repeater.

Repeaters receive a signal from one AP and boost it locally. The D-Link DWL-800AP+ (www.d-link.com/products/wireless/dwl800ap+) and DWL-900AP+ (www.dlink.com/products/digitalHome/wireless/11b+/dwl900ap+) operate as standalone access points or as repeaters. Another repeater option is the Buffalo AirStation Pro WLA-AWCG (www.buffalotech.com/wireless/products/airstationpro/index.php). This model works as a repeater and can be connected to a directional antenna as well. Simply point the antenna toward another access point or repeater and you can extend a wireless network to cover nearby buildings.

Repeaters can decrease wireless performance, because they must receive and retransmit every packet of data through the same transceiver. But unless you have a lot of traffic or very large gaps in your signal, the performance is still likely to be acceptable, especially for the price.

Straight Shooting

The broadest segment of the market is best served by omnidirectional antennas, but directional antennas, which focus the signal on a particular area, are readily available. At the high end, you can find parabolic dishes, which have a very narrow energy path and must be aimed precisely. A simpler directional antenna throws the signal along a relatively narrow angular path. The reflectors in a directional antenna direct the signal.

A directional antenna with a 45-degree sweep placed in the corner of a building could cover the interior of the building with minimal signal thrown outside. Directional antennas are also useful for connecting two points, such as two buildings in an office park. Cisco Systems (www.cisco.com) carries a wide variety of sophisticated antennas.

You may have read stories about homemade directional antennas (you can find an interesting recipe at www.oreillynet.com/~rob/pringles). Such antennas produce tightly focused signals that are not useful for mobile devices in general. Another problem with home-brewed solutions is that they may not be FCC-compliant. The 2.5-GHz space is unlicensed, but there are regulations for using it. Most likely, you won't comply with those rules if you build your antenna out of household items. Lastly, if the connectors on your jury-rigged antenna don't fit your equipment out of the box, you'll have to open the cases, and doing so not only affects the shielding but voids your warranty.

A good off-the-shelf approach for most users is a signal-boosting antenna, available from many vendors. According to its maker, the Linksys WSB24 Wireless Signal Booster works only with the Linksys WAP11 Wireless Access Point or the Etherfast BEFW11S4. But we found that the antenna connectors on many access points (even those from other companies) are compatible with the Linksys booster. The problem with this solution, apart from potential FCC-compliance issues, is that Linksys doesn't guarantee its product will work in any unintended configuration.

The Power-Line Alternative

As we've stated, the ideal place for your AP is the physical center of a building, and vendors are starting to come up with other solutions to make that placement easier without network wiring. One example is the Siemens SpeedStream 2521 Powerline 802.11b Wireless Access Point (www.speedstream.com), which is a power-line network adapter and wireless access point built into one little box.

The idea behind this approach is that you may not have Ethernet cable running to the physical center of your building, but you probably have an electrical power outlet somewhere nearby. Power-line networking is a standard defined by the HomePlug Powerline Alliance (www.homeplug.org) for networking over home power lines. If you investigated power-line networking before and were turned off by the low speeds and unreliability, give it another look. Products based on the HomePlug 1.0 specification began to appear in late 2001, and theoretically they can run at 14 Mbps, although a realistic sustained speed is probably closer to 8 Mbps.

With this simple solution, you just plug a standard power-line network adapter into a computer via a USB or Ethernet connection on one end and the electrical socket on the other, and you're on the network. HomePlug requires a password, which is then used to encrypt data, so make sure to set a password that is different from the vendor's default. Everyone on your street or in your building out to the transformer is on the same physical network.

With power-line networking for your wireless devices, you can use a device like the SpeedStream 2502 Powerline Ethernet Adapter to connect your computer or Ethernet network to the power lines. Plug in the SpeedStream 2521 unit where you want the wireless antenna to be and you're in business. You will need to use the SpeedStream software to configure the network, but that's all there is to it. You can easily extend the network by adding a second access point.

Even without a combination device like the SpeedStream 2521, you can use two power-line–to–Ethernet bridge adapters, such as the SpeedStream 2502 or the Netgear XE602 Powerline Ethernet Adapter, and connect one to a computer or hub and the other to a conventional wireless AP. This approach lets you work with other wireless technologies, such as 802.11a (up to 54 Mbps in the 5-GHz range) and 802.11g (up to 54 Mbps in the 2.4-GHz range).

Home phone-line networking is yet another option for bridging, although it's probably not as good a solution as the others. Phone-line networking provides 10-Mbps throughput on the same two-pair telephone lines as your voice and fax devices without interfering with them. Phone-line devices require power, so you will need electrical outlets anyway.

When a wireless network is working correctly, it's like magic—especially if you have a notebook PC or wireless PDA. Once your wireless network is operating at its peak, you'll be glad you put in the extra work and investment.

No comments: