Radio Positioning - Ubiquitous Positioning - page 109

pulse generator (similar to the idea behind radar). A pulse of energy very narrow
in time has a radio spectrum that is very wide. At the transmitter, the energy can
be thought of as being transformed from a time domain nanosecond wide pulse
signal into a very, very low-level frequency domain signal that spreads across a
significant part of the radio spectrum. If care is taken, the level is lower than the
ambient noise (and confusingly below the level to actually be regarded as
interference). At a UWB receiver the received spectral components are “despread”
using correlation techniques (along the same lines as for a GPS receiver) and the
pulse is recovered. Information is encoded by the presence or absence of pulses
with respect to time but the actual epoch of the pulses, if synchronized and
transmitted from multiple base stations, can operate in a similar way to a GPS
system. UWB tags can thus be positioned in the overlap area between a set of
transmitters or receivers and positioning performances of centimeter accuracy in
three dimensions is expected.
Currently commercial units are emerging [17] and in time will probably be
combined with more conventional hotspot base stations. Applications are being
used in environments such as hospitals, where there are scarce high-value assets
and specialist workers, where good logistics can be lifesaving.
6.2.11 Low-Range Radio Systems (Bluetooth and ZigBee)
A number of useful radio standards have been developed for applications where
range is less than the 100m normal with WiFi. These systems can also be used for
positioning using the same approaches as for other hotspots mentioned above. For
applications such as remote earphones and other communications about the
person, the cell phone manufacturers pioneered the development of Bluetooth. For
lowrange telemetry (i.e., machine-to-machine communications), a different
protocol called ZigBee has emerged. All can share the same unlicensed spectrum.
A future building could thus have several useful infrastructures that could
support Whereness applications. WiFi would be available for general wireless
broadband Internet access ZigBee for the control of the building lighting, heating,
fire and intruder alarms, and energy management; and islands of Bluetooth
associated with personal equipment. The very low ranges (3-10m is typical) result
in quite accurate positioning by simple proximity.
6.2.12 Dedicated Short-Range Communications (DSRC) Systems and Active
RFID
DSCR systems are used at the roadside for vehicle applications such as tolling,
parking payments, and between vehicles for more advanced concepts such as
adaptive cruise control. The radio band allocated is in the microwave region (5.8
GHz) and as such uses conveniently small antennae suitable for easy integration
into physical tags. The technology is part of what can be considered to be a radio
frequency identification (RFID) system, since a principal function of a tag is