SAFETY & SECURITY
The characteristics of radio waves and sound waves were actually confirmed using the following method: In order to examine the characteristics of radio waves, a radio wave transmitter was installed at one location in a hallway, and the relationship between the position of a person carrying a smartphone and the strength of the radio waves was examined. Also, because the position detection area can be restricted by the strength of radio waves received by a computer of the location management system (the position detection sensitivity can be adjusted), the relationship between the position detection sensitivity and the position detection area was also examined. More specifically, a radio wave transmitter was attached to the ceiling at the position shown by the yellow square in Figure 3a. A person carrying a smartphone stood at each of the 175 points shown in Figure 3a and measured the strength of the radio waves at each location. For the sound waves, a sound wave transmitter was installed at the position shown by the yellow square in Figure 3b (each at the doorway of the targeted room), and sound wave reception status of a smartphone was confirmed with the door opened and with the door closed at the locations indicated by the red points (inside an adjacent room, hallway outside of the room, and in the room where the sound wave transmitter was installed). The results are shown in Figure 4a and
Figure 5. Based on Figure 4a the area where reception was possible with a position detection sensitivity of –70 dbm or greater is shown in Figure 4b and the area where reception was possible with a position detection sensitivity of –80 dbm or greater is shown in Figure 4c. The frequency of the radio wave transmitter was set to one transmission per second, and therefore when the reception area is narrow, it is possible that the radio waves of the transmitter could pass without being received by the smartphone. At a position detection sensitivity of
–70 dbm or greater, when the person walked from point (a) to point (b) shown in Figure 4b, the distance at which reception was possible was approximately 1.7 m, and if the person walks quickly, it is possible that the radio waves will not be received. With a position detection sensitivity of –80 dbm or greater, when the person walked from point (a) to point (b) shown in Figure 4c the distance at which reception was possible was approximately 7.6 m, and a sufficient distance for radio wave reception was obtained. The sound wave results are shown in Figure 5 (both a and b) showing a diagram of the room when the door was closed. The sound waves were not received at the room adjoining the room where the sound wave transmitter was installed. Moreover, it was also confirmed
IFHE DIGEST 2017
a
Radio wave transmitters (beacon)
b
Sound wave transmitters
Sound wave transmitters
Figure 2: Characteristics of sound waves and radio waves used in location management systems.
a
Radio wave transmitters (beacon)
b Room 3 Room 2
Sound wave transmitter
Room 1
12.0 m
0.5 m
0.5 m
Door open and close Figure 3: Transmitter attachment positions and measurement points. 0 500
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0 0 500
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0 0 500
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Point (b)
7.6 m
Radio wave transmitter
0 2000 4000
6000 mm
8000 Figure 4: Radio wave strength at each measurement point. 39 10000
Point (a)
c 2000 4000 2000 4000
Radio wave transmitter
6000 mm
b Sensitivity of –70 dbm or greater
Point (b)
Radio wave transmitter
6000 mm
1.7 m 8000 10000 12000
Point (a)
0 500 1000 1500 2000 2500 3000
8000 Sensitivity of –80 dbm or greater 10000 12000
0 500 1000 1500 2000 2500 3000
12000 a
–60 –65 –70 –75 –80 –85 –90
dbm
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3.0 m 0.5 m
Wall
0.5 m
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