Setting up wireless devices that belong to the 802.11 family is relatively simple, but you do have to pay attention to a few simple factors.
Ad-hoc or infrastructure... more/see it nowmode?
The 802.11 wireless standards support two basic configurations: ad-hoc mode and infrastructure mode.
In ad-hoc mode, wireless user devices such as laptop computers and PDAs communicate directly with each other in a peer-to-peer manner without the benefit of access points.
Ad-hoc mode is generally used to form very small spontaneous networks. For instance, with ad-hoc mode, laptop users in a meeting can quickly establish a small network to share files.
Infrastructure mode uses wireless access points to enable wireless devices to communicate with each other and with your wired network. Most networks use infrastructure mode.
The basic components of infrastructure mode networks include:
One or many access points?
- The radios embedded or installed within the wireless devices themselves. Many notebook computers and other Wi-Fi-compliant mobile devices, such as PDAs, come with the transmitters built in. But for others, you need to install a card-type device to enable wireless communications. Desktop PCs may also need an ISA or a PCI bus adapter to enable the cards to work.
- The access point, which acts as a base station that relays signals between the 802.11 devices.
Access points are standalone hardware devices that provide a central point of communication for your wireless users. How many you need in your application depends on the number of users and the amount of bandwidth required by each user. Bandwidth is shared, so if your network has many users who routinely send data-heavy multimedia files, additional access points may be required to accommodate the demand.
A small-office network with fewer than 15 users may need just 1 access point. Larger networks require multiple points. If the hardware supports it, you can overlap coverage areas to allow users to roam between cells without any break in network coverage. A user’s wireless device picks up a signal beacon from the strongest access point to maintain seamless coverage.
How many access points to use also depends on your operating environment and the required range. Radio propagation can be affected by walls and electrical interference that can cause signal reflection and fading. If you’re linking mobile users indoors-where walls and other obstructions impede the radiated signal-the typical maximum range is 150 feet. Outdoors, you can get greater WLAN range-up to 2000 feet (depending on your antenna type) where there’s a clear line of sight!
For optimal speed and range, install your wireless access point several feet above the floor or ground and away from metal equipment or large appliances that may emit interference.
Battle of the bands.
In addition to sharing bandwidth, users also share a band. Most IEEE 802.11 or 802.11b devices function in the 2.4-2.4835-GHz band. But these frequencies are often congested, so you may want to use devices that take advantage of the IEEE 802.11a 5.725-5.825-GHz band.
No matter what frequency you use, you’ll want to isolate your users from outsiders using the same frequency. To do this, assign your users a network identifier, such as an Extended Service Set Identifier (ESSID), as well as distinct channels.
Web and wired network links.
The access point links your wireless network to your wired network, enabling your wireless users to access shared data resources and devices across your LAN enterprise. Some access points even feature capabilities for routing traffic in one or both directions between a wired and wireless network.
For Internet access, connect a broadband router with an access point to an Internet connection over a broadband service such as DSL, cable modem, or satellite.
For connecting network printers, you can dedicate a computer to act as a print server or add a wireless print server device; this enables those on your wireless network to share printers.
When to use external antennas.
If you plan to install access points, you can boost your signal considerably by adding external antennas. Various mounting configurations and high- and low-gain options are available.
You can also use add-on antennas to connect nodes where the topology doesn’t allow for a clear signal between access points. Or use them to link multiple LANs located far apart.
Additional external antennas are also useful to help overcome the effects of multipath propagation in which a signal takes different paths and confuses the receiver. It’s also helpful to deploy antennas that propagate the signal in a way that fits the environment. For instance, for a long, narrow corridor, use an antenna that focuses the RF pattern in one direction instead of one that radiates the signal in all directions.
Plan ahead with a site survey.
A site survey done ahead of time to plot where the signal is the strongest can help you identify problem areas and avoid dead spots where coverage isn’t up to par or is unreliable. For this, building blueprints are helpful in revealing potential obstructions that you might not see in your physical site walkthrough.
To field test for a clear signal path, attach an antenna to an access point or laptop acting as the transmitter at one end. Attach another antenna to a wireless device acting as a receiver at the other end. Then check for interference using RF test equipment (such as a wireless spectrum analyzer) and determine whether vertical or horizontal polarization will work best.
Need help doing this? Call us. We even offer a Site Survey Kit that has a variety of antennas included. Great for installers, the kit enables you to test a variety of antennas in the field before placing a larger antenna order. collapse