3.3 Kinetic Analysis of Physical Anti-Collision …
97
and tag along with the antenna works in the same frequency, so it can be shown
that the channels of the antenna and the tag also have reciprocity. Therefore, the
Eq. (3.56) is introduced into RFID-MIMO system, which represents the number of
antennas. For the RFID-MIO system with channel reciprocity, we can use Eq. (3.56)
to represent the CRB estimator of antenna azimuth in single-antenna multiple tag
system, when M is the number of tags.
3.3.2 Computer Simulation and Analysis
In this section, we imitate the CRB estimator of antenna azimuth in RFID-MIMO
system by computer simulating. We can assume that RFID-MIMO system is
composed of lined-up tag unit, the space between two tags is half a wavelength,
and the centroid is at the origin.
The CRB simulation diagram is shown in Fig. 3.24, where the reader antenna
transmits the orthogonal (β = 0) and coherent (β = 1) signals, the number of tags
are 2, 4, 6, 8, 10, and 100 respectively, and the signal-to-noise ratio is SNR = 20 dB
It is shown that:
(1) When the antenna azimuth angle θ is close to 90°, the CRB is very large.
Regardless of the number of tags or antenna’s transmitted signal is orthogonal
or coherent, the estimation couldn’t be done effectively, which results in a poor
reading performance of tags.
(2) When the reader antennas transmit orthogonal signal, with the changing of
antenna azimuth angle θ, the CRB is relatively stable, and there is no interference between the reflected signal of two tags. Therefore, the estimation
accuracy remains unchanged, and the reading performance of tags is relatively
stable.
(3) When the reader antennas transmit coherent signal, with the increase of the
antenna azimuth θ, interference between two tags’ reflected signal gradually
increases which leads to the decrease of the estimation accuracy and CRB
increases. Therefore, tags’ reading performance declines. And due to the more
concentrated interference in a few degrees, the estimation accuracy decreases
remarkably. Hence, the peak of the CRB appears at a certain angle, and the peak
number increases with the increase of the number of tags. When the number
of tags is 8, the distributions of tags and antenna are shown in Fig. 3.25. At
this case of Fig. 3.25, the CRB is the largest and the RFID-MIMO system has
the worst reading performance.
(4) In addition, the increase of the number of tags decreases the whole system’s
CRB, which improves the estimation accuracy and the reading performance of
tags.
97
and tag along with the antenna works in the same frequency, so it can be shown
that the channels of the antenna and the tag also have reciprocity. Therefore, the
Eq. (3.56) is introduced into RFID-MIMO system, which represents the number of
antennas. For the RFID-MIO system with channel reciprocity, we can use Eq. (3.56)
to represent the CRB estimator of antenna azimuth in single-antenna multiple tag
system, when M is the number of tags.
3.3.2 Computer Simulation and Analysis
In this section, we imitate the CRB estimator of antenna azimuth in RFID-MIMO
system by computer simulating. We can assume that RFID-MIMO system is
composed of lined-up tag unit, the space between two tags is half a wavelength,
and the centroid is at the origin.
The CRB simulation diagram is shown in Fig. 3.24, where the reader antenna
transmits the orthogonal (β = 0) and coherent (β = 1) signals, the number of tags
are 2, 4, 6, 8, 10, and 100 respectively, and the signal-to-noise ratio is SNR = 20 dB
It is shown that:
(1) When the antenna azimuth angle θ is close to 90°, the CRB is very large.
Regardless of the number of tags or antenna’s transmitted signal is orthogonal
or coherent, the estimation couldn’t be done effectively, which results in a poor
reading performance of tags.
(2) When the reader antennas transmit orthogonal signal, with the changing of
antenna azimuth angle θ, the CRB is relatively stable, and there is no interference between the reflected signal of two tags. Therefore, the estimation
accuracy remains unchanged, and the reading performance of tags is relatively
stable.
(3) When the reader antennas transmit coherent signal, with the increase of the
antenna azimuth θ, interference between two tags’ reflected signal gradually
increases which leads to the decrease of the estimation accuracy and CRB
increases. Therefore, tags’ reading performance declines. And due to the more
concentrated interference in a few degrees, the estimation accuracy decreases
remarkably. Hence, the peak of the CRB appears at a certain angle, and the peak
number increases with the increase of the number of tags. When the number
of tags is 8, the distributions of tags and antenna are shown in Fig. 3.25. At
this case of Fig. 3.25, the CRB is the largest and the RFID-MIMO system has
the worst reading performance.
(4) In addition, the increase of the number of tags decreases the whole system’s
CRB, which improves the estimation accuracy and the reading performance of
tags.