utilizing physical layer information to improve rfid tag

6.1 Tag estimation from collision
CHAPTER 6
EXPERIMENTS AND RESULTS
As explained in the previous chapter, I-Q plot of the collision waveform shows
the RCS states of the colliding tags. I-Q plot of a single tag has only 2 RCS states as
shown in Fig. 6.1 below. If more tags are involved in a collision more RCS states
Figure 6.1. RN16 signal I-Q plot.
are observed. N tags will have 2 N states in the I-Q plot. Fig. 6.2 shows the I-Q plot
for a 3 tag collision and Fig. 6.3 shows the I-Q plot for a 4 tag collision. As
expected, the 3 tag case has 2 3 = 8 RCS states and the 4 tag case has 2 4 = 16 states.
Thus the I-Q plot of the collided RN16 waveform can be used to detect the number of
tags involved in the collision by counting the number of RCS states in it. Depending
upon the number of tags, their orientation with respect to the reader antenna and
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