Performing Wireless Site Surveys

On-Site Surveys are essential for optimal WLAN performance. Here's how it goes.

Pre-Deployment Wireless Site Survey 

Before deploying a new wireless network, a site survey must be conducted prior to deployment to begin developing a wireless network project based on requirements collected by corporate stakeholders. You can perform a pre-deployment site survey in two ways: AP-on-a-stick or predictive modeling.

AP-on-a-stick that consumes more time. This involves setting up a WLAN and WLAN access to associate with a laptop. The laptop is equipped with Wireless Site Survey software and is used to collect information such as signal strength, data rate, and overlapping channels. It's called AP-on-a-stick simply because an access point is mounted on a pole and raised to where the access point will be installed. The wireless engineer then analyzes the access point, collecting the data needed to determine cell size, signal propagation, and other information.

In the site survey software, the engineer freezes the access point on the floor plan so that he can move the access point to another location and inspect a new area. In this way, an engineer can find the edge of each cell and plan the appropriate cell overlay for roaming and secondary coverage and other requirements.

Although still used by wireless engineers, the AP-on-a-stick method isn't used very often today. It takes too long for an engineer to run, and for some companies, this cost is a high hourly rate. However, some scenarios, such as external distributions, lend themselves well to the method.

A faster and more efficient way to design a wireless network using site detection software is to create a predictive model. The result is a floor plan with strategically simulated access points positioned with an appropriate channel plan based on coverage and capacity requirements.

The site detection of the software performs all these calculations with special formulas based on the provider's access point and on the antenna chosen for the predictive model. The engineer imports a floor plan into the software and tracks the wall materials through the floor plan based on the expected dB loss.

To return to coverage requirements, the software will take into account the minimum configured requirements such as:

• Interference in the same channel or overlapping channels
• Signal strength
• Data rate
• Packet loss

The software can also take capacity needs into account by configuring the number of devices and their types expected on the wireless network. Devices are determined during the requirements collection phase and added to the site detection software.

As a reminder, this method is exactly what we call it: predictive. It is the process of predicting signal propagation, data rates, channels, access point transmission power and other mathematical and attenuation data.

Post-Deployment Wireless Site Survey

Post-distribution surveys are also often called validation surveys. The purpose of a validation survey is to ensure that the distributed wireless network meets the customer or customer's requirements. The validation survey must be compared with the predictive model previously performed. In some scenarios, a pre-deployment detection may not have been performed prior to installation. A post-distribution survey can be conducted at any time and is also part of the iterative process of a wireless distribution.

The process of conducting a validation survey begins with importing a floor plan. The next step is to measure a long wall, which is needed to crumble the numbers used to calculate the RF characteristics. One of the benefits of validation surveys is to skip the layout of the walls on the floor plan.

With the validation survey ready, it's time to take the laptop, start the survey, and walk slowly and steadily. It is important to walk slowly and steadily so that the external adapter passively collects wireless information from all the necessary channels. The adapter scans all frequencies in the 2.4 GHz spectrum and all channels in the 5 GHz spectrum. To maintain performance, you can select which channels to scan.

After exploring and collecting this data, it is time to analyze and validate. At a minimum, determine if the cell size of an access point is within specification. Identify if the transmit power level is configured correctly. Secondary coverage from other access points will be essential to validate compliance with roaming requirements, if necessary. This can be viewed with site survey software, such as Ekahau Site Survey. The secondary cover will display the overlapping cells.

Verify that the channel widths are appropriate. In most environments, the 20 MHz change width will provide maximum efficiency. Anything bigger will result in improper reuse of channels and could cause channels to overlap. If the validation survey indicates that 40 MHz channel widths are usable, do so. But I strongly advise against using channel widths of 80 MHz or 160 MHz.

Speaking of overlap, another fundamental measure is the overlap of channels. Although secondary coverage is crucial, channel overlap should be kept to a minimum. Having two or more access points operating on the same channel in the same area will create the capacity of an access point. Not only will the devices share the same conflicting domain, but the access points will also compete for the airtime.

Go through the validation survey and determine if optimization is needed. If so, revalidate the project with another survey and compare it to the customer or customer requirements. It is only when these requirements are met that distribution can be considered complete. Keep in mind that wireless environments and requirements are changing, which can trigger the entire Wireless Survey cycle again.

Wireless Site Survey Software

You may be wondering what software is available to conduct predictive and validation surveys. Fortunately, there are a few options available; the list below is not exhaustive. Do your due diligence and request a demo to find out which works best with your workflow.

• Investigation on the Ekahau website
• iBwave
• AirMagnet of Fluke Networks
• WiFi acrylic
• TamoGraph
• VisiWave