Global Positioning System Reference
In-Depth Information
initially, at providing location information for an internal telephone switchboard
operator to locate people within a corporate environment. Subsequently the same
technology supported many other experiments in ubiquitous computing. The
Active Badge was a small battery-powered badge worn by people and contained
an IR transmitter that transmitted a code unique to each badge. The rooms of the
building were fitted with IR receivers attached to a fixed communications network
so that any badges detected within range would be reported to the central control
computer that tracked movements. Figure 7.1 shows a simplified block diagram of
an IR tag system for tracking people. This approach is the mirror image of the ITS
experiment since it is the moving objects that transmit signals and that positioning
is centralized rather than autonomous. Section 1.4.4 highlights the advantages of
each approach.
Figure 7.1
Infrared tag personal location system.
The weakness of the IR badge system is that the IR transmitters must always
be visible, which is not always easy to manage. A movement sensor was included
to detect when badges were not being used (e.g., after office hours) so that battery
life could be conserved by disabling the transmitter, but like any active mobile
device, battery management is necessary. The great advantage is the very low
potential cost of the badges, but on the other hand a dedicated network of room
