Information Technology Reference
In-Depth Information
It must be first created as a radio map of the covered area, that is, a
database of sample places along with the received signal intensity from that
places. A typical record of the radio map may be of the type (x, y, z, ss
i
),
where (x, y, z) are the coordinates of the place where the signal is recorded,
and ss
i
is the signal strength measured by the
i
th base station.
The RADAR approach presents two main advantages: it requires only a
few base stations that have same infrastructure used to provide users with
other kinds of wireless services.
Concerning the drawbacks, the first is that the object to be traced must be
equipped with a W-LAN radio, and this could not be so common especially
in smaller devices. The second disadvantage is that RADAR is not so
expandable: the use of RADAR in multi-storey buildings or for 3D position-
ing is a hard task to be accomplished.
RADAR with scene analysis technique has an accuracy of 3 m with a
precision of 50%. There is a version of RADAR that makes use of the
lateration technique. In this case the accuracy is 4.5 m with the same
precision of 50%.
Although the version that uses the analysis of the scene provides better
accuracy, even little changes in the environment, such as the relocation of a
cabinet, may cause the need to update the previous radio map or to build a
new one.
4.4
MotionStar magnetic tracker
This system uses an electromagnetic-based method for tracing the
position [18]. This type of technology is used by a wide range of products
available for virtual reality and motion capture in the field of computer
animation.
The MotionStar system [19] generates axial magnetic pulses through
an antenna that transmits from a fixed position. The system calculates
the position and orientation of receiving antennas by measuring the pulse
response along three orthogonal axes, taking into account the ongoing effect
of the Earth's magnetic field.
This tracking system allows for almost exact position and compass
estimation. Its accuracy is less than 1 mm for the spatial resolution, 1 ms for
the temporal resolution and 0.1° for compass resolution.
The main drawbacks of MotionStar are the excessive costs of implemen-
tation and the need to connect the object to be traced by a control unit.
In addition, the range is quite short, since magnetic sensors must remain
within 1-3 m from the transmitter. Lastly, the accuracy decreases with the
presence of metallic objects within the environment.
