Installation guide

80
Wi-Fi Location-Based Services—Design and Deployment Considerations
OL-11612-01
Deployment Best Practices
concern. Although the overall path loss model may not be generally optimized, performance may still
be acceptable, depending on the application requirements. Both these two options are fairly
straightforward and follow the standard procedure for calibration and deployment.
The third option offers the ability to calibrate for separate path loss models, each attuned to the
individual floor areas and with that, the potential for improved location performance in each sub-floor
area. However, this requires additional management on the part of the WCS administrator to assign a
naming convention to floors and sub-floors such that they are easily recognizable by users of the system
and able to be considered as a group. Each floor should be considered as an independent location area
subject to the location-aware design recommendations in “Location-Aware” WLAN Design
Considerations, page 51. This is especially important given the fact that when performing localization
for a device on any given floor, the location appliance positioning engine does not consider signal
strength readings from access points that are resident on a different floor. Thus, as devices approach the
edges of the “sub-floors”, location accuracy may be less.
Small Sites
Access Point Density Considerations, page 55 described recommended practices for deploying access
points in a location-aware design in terms of both access point density and inter-access point spacing. In
some cases, the designer may be faced with a small environment that allows for the recommended
inter-access point spacing but still does not provide satisfactory performance. This type of situation may
be found in the suburban branch offices of some corporations or in some suburban healthcare clinics,
where monitoring the location of key assets may be desirable across a number of smaller enterprise
locations.
In lab testing for this white paper, this behavior has been confirmed, and it has been observed that
attempting to deploy a location-aware design in small areas may result in less than optimal performance.
Further testing and investigation indicates that the use of low-gain external antennas (such as
AIR-ANT4941 and AIR-ANT5135) has a positive effect in such cases by mitigating this situation to
some degree and restoring at least a portion of lost location fidelity. This was especially evident when
testing in small environments. Location-aware designs in small-scale environments using s access points
equipped with low-gain external antennas consistently outperformed designs using access points with
the higher gain internal antennas in terms of delivered location accuracy and precision.
Antenna Installation Height
The positioning algorithms used within the location appliance assume that all antennae are situated at
heights where the apparent gain is mainly because of the azimuth and not the elevation pattern of the
antenna. Laboratory testing performed with the AP-1000 and AIR-ANT1000 antennae confirms that
when located at heights above floor level of 10 feet or less, a very steep and monotonic relationship is
present between measured signal strength and distance.
Except at very close horizontal distances of 12–15 feet or less from the access point, the curve
representing this relationship tends to be single-valued with a steep slope, which is very conducive to
good location performance because a high degree of differentiation in signal strength is apparent as
horizontal distance varies. When antennas are mounted at heights of 20 feet or beyond, the steep slope
degrades and the curve tends to be multi-valued at horizontal distances out to about 40 feet from the
access point.
To be conducive to good location fidelity, the location-aware design must do the following:
• Minimize the amount of exposure to those areas of the signal strength versus distance curve
exhibiting a lack of monotonicity