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band. The sender unit was equipped with a simple
omnidirectional stick antenna and the receiver unit
was equipped with a 9 dBm PCB Yagi antenna. By
turning around the Yagi antenna, the angle range (0
degree being the direction of the sender) was iden-
tified where the sender’s data can be received. Un-
fortunately the nRF24L01P module has no Received
Signal Strength Indicator (RSSI) feature, the signal is
either present or not. This means that there is a min-
imum distance to the sender because if the receiver
is closer to the sender than the minimal distance, the
signal can be received independently of the angle of
the receiver’s antenna. This restriction can be miti-
gated by a receiver that provides RSSI along with the
received data packets.
The measurements were made on an agricultural
field that serves as a pasture. The sender’s trans-
mission power was set to one of the 3 levels the
nRF24L01P supports. The receiver was located at
a specified distance from the sender and the antenna
was rotated. The angle when the signal appeared and
when the signal disappeared was recorded. With this
simple method the direction of the sender was iden-
tifiable with 1 degree precision. The minimum and
maximum distances with different power levels were
the following: PA MIN: 4-20 meters, PA LOW: 22-
41 meters, PA HIGH: 31-70 meters.
7 CONCLUSIONS
Low-cost, accurate localisation is often required in
agricultural applications. We found that low-cost GPS
modules are inadequate but in differential setup cer-
tain low-cost modules are able to produce the required
accuracy if the target is stationary for at least 8-10
minutes. Certain cows (but not all of them) were
found to satisfy the criteria for being stationary for
40-80 % of their grazing time. Movements have to
be tracked by an auxiliary technology. We made sim-
ulations for two of such technologies: distance- and
angle-based short-range localisation technology. In
case of distance-based, the effect of distance mea-
surement error results in worse position estimation
than the effect of reference point measurement error.
Angle-based short-range localisation turned out to be
more cost-efficient but also more problematic, due to
the rapidly growing localisation error as the distance
between the mobile and the fixed station grows.
ACKNOWLEDGEMENTS
The Hungarian side of the research is supported by
the AgroDat.hu project (project code: VKSZ 12-1-
2013-0024), financed by the Government of Hungary.
I thank ESEO for co-financing my research stay in
Angers, France where part of the research was done.
The French side of the research is financed by the re-
gion of ”Pays de la Loire” (Vagabond project).
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