Wi-Fi Surveys can be performed in one of three modes. It can be operated in
Planner mode (also known as Virtual Predictive Survey), or the default Passive Survey
mode and lastly an optional Active Survey mode. Each of the specific modes are
used for different purposes. The two most popular software brand packages for surveying are Ekahau or AirMagnet.
PREDICTIVE VIRTUAL SURVEYS
The
Planner mode involves the process of creating and adjusting a virtual
environment model, utilizing a selection and placement of simulated APs. To
create a virtual model of the environment, the physical objects that affect
radio wave propagation are input into the application and using the tools to
draw the position, size, and type of building materials. Planner mode uses
built-in or custom-designed walls, floors, attenuation areas, simulated access
points, and a large selection of antenna patterns. The resulting WLAN model can
then simulate coverage and output heatmap examples that can be analyzed for
theoretical AP placements.
PASSIVE SITE SURVEYS
In
a Passive Survey mode, the wireless network card does not associate itself with
any particular AP or SSID (Service Set Identifier). Instead, it simply listens
to the RF data moving through the site, detecting and recording all RF signals and
noises in the environment. Passive Surveys do not have to be performed as AP on
a Stick method. Passive Surveys are normally performed either during the
pre-planning stage or post-installation stage. During the pre-planning stage Passive
Surveys help to determine design around problem areas and working with rogue AP’s.
Passive Surveys in the post-installation stage help to validate performance and
detect actual coverage of all broadcasting AP’s in designated areas. By
default, AirMagnet Survey opens in the Passive Survey mode and can be toggled
to Active if needed. Passive Surveys are able to collect both 2.4 GHz and 5.0 GHz
data at the same time. Passive Surveys should be used to test multiple AP
performance and to detect Rogues.
ACTIVE SITE SURVEYS
In
Active Survey mode the wireless network card actively associates itself with just
a single selected AP (Wireless Access Point), sending and receiving RF (Radio
Frequency) packets to and from the target AP. Active Surveys are normally
performed as an AP-on-a-Stick survey. Active surveys are useful for scientific
research, lab tests, and finding specific metrics of AP performance, and RF propagation
through various types of building materials.
However, In Active Survey mode, surveys
are strongly recommended to be conducted separately for 2.4 GHz and 5.0 GHz results.
While using Active mode for AP-on-a-stick surveys, it is possible to choose Dual-band
which in theory scans both 2.4GHz and 5.0 GHz bands but results from such
surveys are at the mercy of the end-client network interface card and its Wi-Fi
choices. The NIC on the end-user device is what decides how to connect to
either 2.4 GHz or 5.0 GHz which can leave gaps in survey data collection if
Dual-band is selected. The NIC can swap between 2.4 GHz and 5.0 GHz depending on
signal integrity using its own internal device computations without the
surveyor or user being able to control it. That is why it is better to select
one bandwidth at a time for more consistent and reliable results.
Additionally
with Active Surveys, inconsistencies in results can arise if the environment is
not controlled.
During active association, beamforming is created between the AP and end-client
NIC and can cause some skewing of results.
Active surveys should only be used to test singular AP with singular end-client
performance. Results will vary if there are multiple clients connected or
multiple APs involved (roaming).
Using Passive mode for AP-on-a-stick surveys can collect data for both 2.4 GHz
and 5.0 GHz at the same time without gaps in data collection. Results from Passive
mode AP-on-a-stick surveys can be more consistent and is far more time-saving.
AP ON A STICK SURVEYS
AP-on-a-Stick
(APoaS) methods are most often performed to test a specific predetermined AP
model in an environment. This can be a long and tedious task if there are
several planned AP placements. AP on a Stick surveys can be performed in either
Passive or Active modes but usually have different purposes. AP on a Stick
Surveys are typically conducted in the pre-planning stage to test the performance
of the predetermined specified AP, and helps to identify the best locations for
installation and deployment of wireless access points.
During an AP-on-a-stick Survey, the test wireless access point is usually suspended approximately three meters from the floor and placed on or near the ceiling. Typical installation locations of APs should be placed no higher than four meters and near ceiling height in a spot where it is most likely to give the best wireless availability. In most instances where the ceiling or rafters are unreachable or inaccessible, the AP’s are simply secured to the top rung of a step-ladder for testing purposes.
In
situations where there are very high vaulted ceilings more than four meters, AP
installations should consider wall-mounting as a primary locations while the AP’s
are using their default Omni antennas. The distance from AP to end client will affect
connection quality and stability. If proceeding with vaulted ceiling
installations, please consider using APs with diversity antennas that can be
swapped. Certain types of directional or higher dBi output powered antennas can
be used for focusing signals downward or in the proper direction.
The information gathered from multiple readings and surveys can assist in
determining the optimal positions for each AP.
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