Wireless Site Surveys: The Basics

In order to implement a wireless network with optimal coverage, you have to first have a solid understanding of the radio frequency behavior on site. A wireless site survey is the best way to gain this information, because it will reveal areas of channel interference and identify any dead zones, helping you avoid problems as you build the network and prevent obstacles for network users.

The main goal of performing a wireless site survey is to determine two things. First, you want to determine the feasibility of building a wireless network on your site. Once you have established it's feasible, you’ll need to determine the best place for access points and other equipment such as antennas and cables. A site survey also helps you to determine what type of equipment you will need, where it will go, and how it needs to be installed.

AP placement
WLAN access points can be placed potentially anywhere. What the wireless site survey does is help you to determine where the APs need to be located to avoid overlap or interference.

Many network managers will simply install extra WiFi APs as a quick fix to increase the wireless coverage capability. However, that often does little or nothing to solve the root of the problem. In fact, too many WiFi APs could actually increase the possibility of co-channel interference with other APs already in place. A wireless site survey can help you avoid that problem.

Surveys can also help you know the APs around you. There are three non-overlapping channels you can use to deploy a wireless network in the United States: 1, 6, and 11 for the 2.4 GHz frequency. These rules apply to everyone, not just your site. So if your site is in a building with other organizations that have their own wireless networks, you will have to coordinate with the APs at those other organizations.

You need to know about neighboring APs in order to deploy a wireless network that doesn’t overlap with others in your area. In some cases, using another WiFi frequency like 5 GHz with 802.11 a/n/ac might be a better option.

Channel interference
Channel interference can mean problems for your wireless network and can be caused by a variety of issues. Even the microwave in the lunchroom can cause network interruptions if it is using the same radio frequency.

Human beings can also cause issues. The average human body is made up of mostly water, and since water causes absorption, people’s bodies can actually absorb wireless signals, resulting in problems for your network.

It’s important to keep these things in mind during your site survey. We might do a site survey and figure out where all the APs need to be placed, only to find that when people actually move in and are working (and using the microwave) on site every day, the network fails to work properly.

The best way to avoid these issues is to use the wireless site survey as an opportunity to gain a solid understanding of the RF on your site, which is critical for designing and implementing a wireless network with optimal coverage.

Site survey types
There are three different types of site surveys widely used in the industry: passive site survey, active site survey, and predictive site survey.

A passive site survey tool listens to existing access points and, outside your managed infrastructure, for signal strength, interference, and AP coverage. Passive site surveys, in which surveyed WiFi adapters don't need to associate to the AP or SSID, give a good overall picture of the RF characteristics of existing wireless networks.

During an active site survey, the survey WiFi adapter is associated to the AP(s) and exchanges packets. This allows gathering of very detailed information. Actual network traffic, throughput packet loss, and physical (PHY) rates can be captured. Active surveys are commonly used for new WLAN deployments.

A predictive site survey is performed without any type of field measurements. It uses RF planning software tools that can predict wireless coverage of the APs. To perform this site survey, a floor-plan drawing (AutoCAD, JPEG, PDF) is a must-have. Predictive site surveys are used when the site or building is not yet built and are helpful for budgeting purposes.

The goal of all of these wireless site surveys is to provide detailed information that addresses the site’s radio frequency coverage. Before implementing or attempting to optimize a WLAN, you’ll want to understand all the possible areas of interference, AP placements, power considerations, and wiring requirements that are needed. A wireless site survey can provide all of this information and more, so you have the tools you need to design, implement, and optimize your wireless network.