Image Processing Reference
In-Depth Information
Methods to estimate distances
based on
Neighborhood
information
Time period
Signal attenuation
Time of arrival (ToA)
Time difference of
arrival (TDoA)
Round trip
Received signal
strength (RSS)
Connectivity
Hop count
Minimal transmission
power (MTP)
NIDES
The three/two neighbor
Lighthouse
FIGURE .
Classification of distance estimation methods.
Δ
t
2
Δ
t
2
Δ
t
1
S
2
S
2
S
1
S
1
B
1
B
1
t
e
Δ
t
1
t
1
t
2
t
3
t
t
(a)
(b)
Radio signal
Ultrasound signal
Synchronization time
FIGURE .
Distance estimation with time of arrival (ToA) at (a) global synchronization time stamp or (b) local
synchronization time stamp.
c
Air
s. Hence, if material properties as well as propagation speed are known, the dis-
tance can be calculated out of the measured transmission time ∆
t
of the signal between a sender and
its receivers as well as the speed of the signal
d
=
, km
/
∆
t
(Figure .a).
The transmission time ∆
t
is the difference between the time receiving the signal and the start time
the transmission was initiated at the sender (ToA [PJ]). Therefore, each signal contains a time
stamp at which the transmission was started. After receiving the entire signal, the transmission
time (time of flight, ToF) is calculated by the current time subtracted by the start time.
The calculation of the transmission time requires highly synchronized senders and receivers
[Sto]. For example, a small distance (
d
=
c
Air
⋅
=
cm) between two nodes leads in air to a very short
transmission time (∆
t
=
d
/
c
Air
=
. m
/
, km
/
s
=
ns). Hence, the synchronization error
(skew) between these two nodes must be smaller than
t
s
cm.
Further, small distances require high time resolutions and, therefore, high clock rates to determine
the transmission time very precisely.
<
ns to detect distances around
d
=
![](Networked-Embedded-Systems_images/img-gen1299.png)
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