Networking Reference
In-Depth Information
Fig. 6.4 Schematic draw of hardware elements in the parking lot application
entrances and exits of each parking lot row, which is 120m long and 8m wide. Two
sink nodes were placed in the center of the second and third rows of the parking
lot, 60m away from the entrance of the row. The decision to place the sink node
at this location is due to the limitations of radio coverage of the 802.15.4 protocol,
implemented by the Zigbee standard [ 5 ], which allows data transmission up to a
maximum of 100 ft away with direct line-of-sight.
We assume the minimum width of a car as being at least 1.5m. Therefore, any
detected object larger than 1.5m is considered a car by the application. The pair of
sensor nodes at the entrance of each row counts occupied spaces while the par of
sensors at the exit of each row counts the vacancy of a space. The sensors of each
pair of nodes were placed 8m apart from each other. To calculate the size of detected
objects we use the formula:
where OS is the size of the object, DDR is the distance measured by the sensor node
at the right side, and DDL is the distance measured by the sensor node at the left
side. Such formula is applied by the SIM Web service on the measurements sent by
the sensor nodes.
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