Types of Wireless Site Surveys
There are three main types of wireless site surveys: passive, active, and predictive.
During a passive survey, a site survey application passively listens to WLAN traffic to detect active access points, measure signal strength and noise level. However, the wireless adapter being used for a survey is not associated to any WLANs. For system design purposes, one or more temporary access points are deployed to identify and qualify access point locations. This used to be the most common method of pre-deployment wifi survey.
During an active survey, the wireless adapter is associated with one or several access points to measure round-trip time, throughput rates, packet loss, and retransmissions. Active surveys are used to troubleshoot wifi networks or to verify performance post-deployment.
During a predictive survey, a model of the RF environment is created using simulation tools. It is essential that the correct information on the environment is entered into the RF modeling tool, including location and RF characteristics of barriers like walls or large objects. Therefore, temporary access points or signal sources can be used to gather information on propagation in the environment. Virtual access points are then placed on the floor plan to estimate expected coverage and adjust their number and location. The value of a predictive survey as a design tool versus a passive survey done with only a few access point is that modeled interference can be taken into account in the design.
Additionally, some survey application allow the user to collect RF spectrum data using portable hardware spectrum analyzers, which is beneficial in case of high RF interference from non-802.11 sources, such as microwave ovens or cordless phones.
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