Each - Draper Laboratory

PSI (deg)
m
Node 2, MPATH #1: PSI
150
100
50
0 20 40 60 80
Time (s)
Node 2, MPATH #1: Offset
80
60
40
20
0
0 20 40 60 80
Time (s)
Figure 12. Multipath parameter estimation: Node 2
measurements.
For Node 1, the parameters for the first indirect path (off
the West wall) are estimated with reasonable accuracy after
40 s. The parameters for the second path (off the South
wall) cannot be estimated for the first 27 s since the indirect
path is blocked by the rectangular object. When estimation
commences at 27.5 s, the parameters are almost immediately
estimated with high accuracy, and this accuracy level
continues until the direct path is blocked at 73.5 s.
For Node 2, the parameters for the first indirect path (off
the East wall) are estimated with reasonable accuracy
after 45 s. The direct path becomes blocked at 55.5 s, so
that further updating of the parameter estimates was not
possible. The second indirect path (off the South wall)
was blocked for the first 34 s. At 34.5 s, the indirect path
became unblocked and the indirect path parameters were
estimated. At the next time step (35 s), the direct path
became blocked and remained blocked for the remainder
of the simulation, precluding further estimation of the
indirect path parameters. Thus, in this case, the indirect
parameter estimates are based on a single measurement
pair.
As discussed previously, the variation in the true multipath
parameters was relatively small in this representative
example, so that relatively accurate tag tracking could be
maintained when it was no longer possible to perform
parameter estimation.
12 Innovative Indoor Geolocation Using RF Multipath Diversity
deg
m
Node 2, MPATH #2: PSI
50
0
-50
0 20 40 60 80
Time (s)
Node 2, MPATH #2: Offset
80
60
40
20
0
0 20 40 60 80
Time (s)
x1par2
Conclusion
A new approach is suggested for the problem of indoor
geolocation in the presence of dominating multipath using
RF time-of-arrival measurements. Multipath delays are
modeled using a geometry-based argument. Assuming a
series of specular reflections off planar surfaces, the model
contains a maximum of three unknown multipath parameters
per path, which may be estimated in a nonlinear
filter. Simulation results for a relatively simple representative
example suggest that multipath parameters can be
estimated with sufficient accuracy to maintain geolocation
accuracy when one or more direct paths are undetected.
This approach allows the possibility of building up indoor
map information as the geolocation process commences.
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