Installation guide

18
Wi-Fi Location-Based Services—Design and Deployment Considerations
OL-11612-01
Cisco Location-Based Services Architecture
minimum of three reporting receivers required to be in range of mobile devices at all times. Increased
accuracy and performance (including exceeding 5 meters accuracy) is possible when six to ten receivers
are in range of the mobile device.
Location patterning applications perform well when there are sufficient array entries per location vector
to allow individual locations to be readily distinguishable by the positioning application. However, this
requirement can also contribute to some less-than-desirable deployment characteristics. With location
patterning, achieving high performance levels typically requires not only higher numbers of receivers
(or access points for 802.11) but also much tighter spacing. In large areas where it is possible for clients
to move about almost anywhere, calibration times can take significantly longer than in other approaches.
For this reason, some commercial implementations of location patterning allow the user to segment the
target location environment into areas where client movement is likely and those where client movement
is possible but significantly less likely. The amount of calibration as well as computational resources
allocated to these two classes of areas is adjusted by the positioning application according to the relative
probability of a client being located there.
The radio maps or calibration databases used by pattern recognition positioning engines tend to be very
specific to the campus, building, site, or floor, with little opportunity for re-use. The likelihood is very
low that any two areas, no matter how identical they may seem in construction and layout, will yield
identical calibration data sets. Because of this, it is not possible to use the same calibration data set for
multiple floors of a high-rise office building, for example, because despite their similarity, the location
vectors that are seen at similar positions on each floor will not be identical.
All other variables being equal, location patterning accuracy typically reaches its zenith immediately
after a calibration. At that time, the information is very current and indicative of conditions within the
environment. As time progresses and changes occur that affect RF propagation, accuracy degradation
can be expected to degrade in accordance with the level of environmental change. For example, in an
active logistics shipping and receiving area such as a large scale crossdocking facility, accuracy
degradation of 20 percent can reasonably be expected in a thirty day period. Because calibration data
maps degrade over time, if a high degree of consistent accuracy is necessary, location patterning
solutions require periodic re-verification and possible re-calibration. For example, it is not unreasonable
to expect to re-verify calibration data accuracy quarterly and to plan for a complete re-calibration
semi-annually.
Cisco Location-Based Services Architecture
RF Fingerprinting
Cisco RF Fingerprinting refers to a new and innovative approach that significantly improves the
accuracy and precision of traditional signal strength lateration techniques. Cisco RF Fingerprinting
offers the simplicity of an RSSI-based lateration approach with the customized calibration capabilities
and indoor performance previously available only in location patterning solutions.
RF Fingerprinting significantly enhances RSS lateration by using RF propagation models developed
from radio propagation data gathered directly from the target environment or environments very similar
to it. RF Fingerprinting offers the ability to calibrate an RF model to a particular environment in a
fashion similar to (but more expeditious than) that described for location patterning. However, unlike
location patterning, a unique calibration is not always required, especially in situations where multiple
floors of similar construction, contents, and layout are deployed. In these cases, a common RF model
may apply and is the reason why several known office environment RF models (that is, drywall offices
only and drywall offices combined with cubicles) are pre-packaged with the Cisco LBS solution. These