WLAN Site Survey Best Practices

Article ID: 19041578

Question

What are WLAN Site Survey Best Practices? Determining the SNR Cutoff and Access Point Range Boundaries

Facts

When measuring the SNR levels, be sure to use the same radio card and antenna that will be used in the environment you are testing. A variance in antenna gain between the survey equipment and user device will likely result in the users having different performance than what you measured during the survey. Changes made in the facility, such as the addition of walls and movement of large boxes/crates will affect SNR as well and must be considered. A good idea would be to either recheck the SNR from time-to-time, even after the network is operational or perform the survey under the worst conditions with respect to warehouse stock levels being at their highest.

Answer

When performing an RF site survey, it is important to define the range boundary of an access point based on signal-to-noise (SNR) ratio. The SNR is measured as the signal level (in dBm) minus the noise level (in dBm). SNR directly impacts the performance of a wireless LAN connection. A higher SNR value means that the signal strength is stronger in relation to the noise levels, which allows higher data rates and fewer retransmissions. A lower SNR requires wireless LAN devices to operate at lower data rates, which decreases throughput.

The following data should be used as a guide for determining the access point’s range boundary:
40dB SNR = Excellent signal (closest to AP)
  • 25dB to 40dB SNR = Very good signal
  • 15dB to 25dB SNR = Low signal (furthest from AP)