Figure 10.4 shows an example of a 90% read
accuracy powering region when the radio frequency is 915 MHz, transmitter power is
0.5 W, and the minimum operational power of an RFID tag is 50 mW.
10.3 100a% Read Accuracy Powering Region with Multiple
Reader Antennas
In Section 10.2, an ef?¬?cient algorithm was presented to calculate the 100a% read accuracy
powering region of a single reader antenna. From Corollary 1, such a region is bounded by
a surface on which each point has exactly 100a% read accuracy. However, when the
number of reader antennas placed at a portal is more than one, such a region cannot be
obtained by simply merging the 100a% read accuracy powering region from each individual
antenna. In this section, we ?¬?rst discuss why merging such regions does not work.
After providing a mathematical representation of the problem, we then discuss a methodology
for locating readers and related implementation issues.
0 50 100 150 200
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
qR
GR
FIGURE 10.3
Half-wave dipole antenna??™s gain versus uR.
Maximizing Read Accuracy by Optimally Locating RFID Interrogators 187
10.3.1 Merging 100a% Read Accuracy Powering Regions
Given the location of a tag along with its orientation, the tag can be regarded as readable as
long as there is at least one reader antenna that provides enough power to activate the tag.
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