Global Positioning System Reference
In-Depth Information
interacts with the field. The overall approach may be more reliable than pressure-
sensitive flooring since there are no moving parts to wear but at present the
technology is cumbersome.
A further use of propagating magnetic fields is in underground
communications and positioning. Although something of a niche market, cavers
and those working underground can use specialist magnetic field equipment to
both communicate and navigate. Magnetic fields will propagate well in
environments where normal radio will not penetrate but the disadvantage is that
range and bandwidth are limited and power requirements large. It is, however,
possible to send voice communications between the surface and subterranean
spaces and using directional coils to detect the direction of the signals.
7.7 Sensor Fusion
Multisensor data fusion is a technique used in many areas, including medical
diagnosis, battlefield target recognition, and the control of autonomous vehicles. It
is based on the idea that, although it is useful to process a single source of data
using statistical techniques, the use of multiple data sources “fused” together can
sometimes significantly improve the accuracy of measurements. This is
particularly useful where one inadequate source of data can be compensated by
another. We have already seen several examples in this topic where a multisensing
situation is better than with a single system, including:
GPS and cellular radio;
GPS and wheel sensors;
GPS and WiFi Indoor Positioning;
Personal autonomous navigation (pedometer, compass, accelerometers,
gyros);
Map matching and GPS.
Fusion techniques for general sensors are well documented but often from a
military perspective [9], and it is only recently that fusion is beginning to make an
impact on consumer and business applications. Hightower et al. [10] introduce the
concept of a “location (protocol) stack” that includes sensor fusion for location.
Böhringer [11] describes a novel system that was used accurately to position trains
and is a good example of fusion at work. Data from a radio positioning system
(GPS) is fused with that from a magnetic field sensor attached to the train wheels
(which can pick up characteristic magnetic signatures from track joints and
equipment). Clearly, GPS will not work in rail tunnels but rail joints are always
present and provide complementary information. To extrapolate between readings,
mapping data is used that can be considered to be a third source of information to
be fused. Map matching is an important part of navigational data fusion.
 
Search WWH ::




Custom Search