A common scenario in installing a wireless LAN (WLAN) at a client site is finding that that wireless access point range isn't quite good enough. For example, you may install an access point in a wing of classrooms, and students and teachers have trouble maintaining association with the access point from one particular classroom. In this type of situation, you could try moving the access point to better cover the area, but then you may disrupt access for users in other areas.
One solution to this problem of wireless access point range is to add more hardware in the problem area. However, this requires your client to authorize you to purchase another access point and install the cabling. In addition, you might need to form a distribution system at the client site that includes an Ethernet switch in order to connect the access points.
Before installing more access points to increase radio frequency (RF) coverage, consider the following methods for extending the wireless access point range:
- Adjust the transmit power. Wireless access points by default usually have their transmit power set to the highest value. In some cases, though, an administrator may have switched the transmit power to a lower level, possibly to avoid spilling radio waves outside the facility. In order to maximize RF coverage, ensure that the transmit power is set to the highest value. It only takes a couple minutes to do this, and it might solve the coverage problem without extra costs for the client. Keep in mind, however, that adjusting the transmit power of the access point only affects the downlink direction of the communications between the access point and the client. You may also need to increase the transmit power of the radio in the client device to realize greater range.
- Relocate the access point. In many cases where the wireless access point range falls short, you can simply move the access point a few feet (possibly more) and fully cover the area. The only cost involved with this approach is your time, assuming there's enough slack in the distribution system cabling. Sometimes you might need to run a longer cable from the switch to the wireless access point -- a good reason to leave some extra length on access point cables when installing them.
- Utilize higher-gain antennas. The factory-default antennas that come with an access point usually have low gain (around 2 dB). If the wireless access point has removable antennas, then replacing the default antennas with higher-gain omnidirectional or even directional patch antennas boosts range significantly. Most of these higher-gain antennas effectively add 6 dB to the system, which equates to a fourfold increase in signal power. Even though that doesn't exactly multiple the range by four, it does make a big difference in range. For example, I've seen range increase by 25% after simply replacing the client's antenna with a higher-gain omnidirectional. For a cost of around $10 each, antenna upgrades are extremely cost-effective. Keep in mind that some wireless access points don't have removable antennas, which of course blocks this approach.
- Consider RF amplifiers. Companies such as RF Linx and Hyperlink Technologies sell RF amplifiers that install between the antenna and the access point. The amplifiers, which cost $100 or more, add gain to the RF signal. This packs quite a punch, which can dramatically extend wireless access point range. Just be sure to comply with effective isotropic radiated power (EIRP) rules, though, when adding amplification (and antennas). In addition, most regulatory agencies, such as the Federal Communications Commission (FCC) in the U.S., require certification beyond what the access point manufacturer receives when the wireless LAN includes additional components such as amplifiers.
One of these approaches should help you successfully extend the range of your client's access point. If not, then you will likely have to install more access points to get the coverage.
About the author
Jim Geier is principal consultant of Wireless-Nets Ltd. and assists companies with the design, implementation and testing of wireless LANs. Jim is author of over a dozen books, including Deploying Voice over Wireless LANs (Cisco Press) and Implementing 802.1X Security Solutions (Wiley).
This was first published in April 2008