Global Positioning System Reference
In-Depth Information
Figure 7.2
Multilateration positioning of ultrasonic tag within a room.
Since many more combinations of readings may be available than just three,
statistical positioning algorithms have been developed to produce the best fit of
location to all the physical measurements that are available. Repeated
measurements will further increase the accuracy of the location. If three tags are
attached to an object, it is possible to determine object orientation as well as its
location.
Until the invention of UWB radio positioning, the Bat approach has been the
best indoor positioning system available. A number of commercial products have
been developed and numerous ubiquitous computing experiments performed.
Unfortunately, like the more basic IR tag, the system has a number of
disadvantages. The centralized approach places a limit to the number of tags that
can be used in one environment. While adequate for normal office environments,
it would not perform well, for example, in a crowded mass transit situation during
an emergency since there would be too many tags needing servicing and a
crowded train or station would not allow enough clear paths from passengers
using tags to the ceiling detectors. It might be better to work the system in reverse
(rather like an indoor version of GPS).
Research work on ultrasonic position is continuing with the current focus
being on ad hoc peer-to-peer systems with moving objects being tagged that
laterate between each other. Significant progress with the technology could come
