| Abstract |
In wireless positioning system, in addition to channel error, the geometric re-
lationship between sensor nodes and the target may also affect the positioning
accuracy. The effect is called geometric dilution of precision (GDOP). GDOP is
determined as ratio factor between location error and measurement error. A higher
GDOP value indicates a larger location error in location estimation. Accordingly,
the location performance will be poor. The GDOP can therefore be used as an in-
dex of the positioning performance. In this thesis, approaches of tracking a moving
target with extended Kalman filter (EKF) in a time-difference-of-arrival (TDOA)
wireless positioning system are discussed. While the target changes its position with
time, the geometric layout between sensor nodes and the target will become differ-
ent. To maintain the good layout, the positioning system with mobile sensor nodes
is considered. Therefore, the geometric layout can be possibly improved and GDOP
effect can be reduced by the mobility of mobile sensor nodes. In order to find the
positions that mobile sensor nodes should move to, a time-varying function based
on the GDOP distribution is defined for finding the best solutions. Since the simu-
lated annealing is capable of escaping local minima and finding the global minimum
in an objective function, the simulated annealing algorithm is used in finding the
best solutions in the defined function. Thus the best solutions can be determined
as the destinations of mobile sensor nodes. When relocating mobile sensor nodes
from their current positions to the destinations, they may pass through or stay in
high GDOP regions before arriving at the destinations. To avoid the problem, we
establish an objective function for path planning of mobile sensor nodes in order to
minimize the overall positioning accuracy. Simulation results show that the mobile
sensor nodes will accordingly change their positions while the target is moving. All
the sensor nodes will maintain a surrounding region to localize the target and the
GDOP effect can be effectively reduced. |
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