Installation guide

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Wi-Fi Location-Based Services—Design and Deployment Considerations
OL-11612-01
Deployment Best Practices
Calibrating Under Representative Conditions
As mentioned previously, the location appliance and the Cisco WCS use the information gathered during
a site calibration to better understand the propagation characteristics present within the environment.
This information is culled from the aggregate of all data collection performed during the calibration. To
facilitate an accurate calibration, Cisco recommends that the environment in which the calibration is
performed be representative of the daily production environment to the greatest extent possible.
For example, the calibration should be performed during business hours when the facility contains a
representative population of people (human attenuation) as well as material on shelves (material
attenuation). If carts, racks, beds, or other large metallic objects are normally used in this environment,
these should also be present during calibration. If large doors are present in the environment, they should
be positioned as they would normally be during business hours. In many (but certainly not all) cases,
calibration done during the normal business hours are more representative of the actual daily
environment than off-hours calibration.
In some cases, the most convenient time to perform a calibration might be before people and contents
are moved in. Cisco recommends that the temptation to perform a site calibration of such “empty rooms”
be avoided to not create a path loss model that has little relation to the actual production environment.
Such cases are typical of facilities after they are first built but before personnel and material have been
fully moved in.
If it cannot be determined from prior conversations with site personnel, one way to determine a good
time to perform a calibration is to visit the site beforehand and observe the activity pattern of both the
facility and the personnel present. Observing the activity patterns beforehand in many cases allows the
designer to plan for the optimum time to perform the calibration, so as to yield the most representative
results and also to not excessively inconvenience the personnel employed at the facility.
Keep in mind that when faced with a site that possesses constantly changing environmental conditions,
results are typically better when the calibration is performed in an environment that contains more
attenuation and path loss than is seen during normal use rather than less path loss.
Recommended Calibration Clients and Transmit Power
Cisco recommends using the Cisco Aironet 802.11 a/b/g Wireless Cardbus Adapter Client
(AIR-CB21AG) with recent drivers and firmware (CCX version 2 or better) as a calibration data
collection client. Versions of CCX earlier than version 2 are not ideal for calibration usage.
When performing the calibration data collection, ensure that your calibration client is being detected by
access points on the floor where you wish to perform the calibration. For best results during calibration,
perform one of the following:
• Disable automatic power assignment on all applicable access point radios within the calibration
environment
• Ensure that TX Power assignment mode for each access point radio is set to a “custom” value
For best results with either of these alternatives, set the transmit power of each access point to a known
fixed level that is as close as possible to the default transmit power of the calibration client. At the
completion of calibration, all these values can be returned to their original settings.
As mentioned in Minimum Signal Level Thresholds, page 51 and Access Point Density Considerations,
page 55, Cisco highly recommends that at least three (and preferably four or more) access points be able
to detect mobile client devices and asset tags at signal levels that are at the RSSI cutoff value (typically
-75 dB) or better. When verifying this, it is important to ensure not only that all installed access points
and antennas are representative of the final installation but to be mindful as well of maximum transmitter
power output of the mobile device being used to verify signal thresholds. Remember, you are interested
in the signal level of the client as it is detected by the access points, not vice-versa.