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1 Overview of RFID System Anti-Collision Technology
According to Shannon calculation, under typical circumstances, that is, under the
interference of Gaussian white noise, channel capacity is written as
C = BW log 2
1 +
S
N
(1.4)
where the unit of BW is Hertz, S is signal power, and N is noise power, both in
watts. Channel capacity is proportional to channel bandwidth, which determines the
maximum information transfer rate in the current channel.
It can be seen from the channel definition and channel capacity calculation formula
that, in a certain RFID tag reading and writing scene, the background noise is relatively stable, the transmitting power is certain, and the medium condition is certain,
so the channel capacity has a fixed upper limit. Therefore, the anti-collision algorithm is to improve the utilization of the channel under the condition of fixed channel
capacity.
According to Eq. (1.4), channel capacity is known. The transmitter of the singleinput single-output (SISO) system is a single reader and the receiver is a single tag.
Thus, the channel matrix H is the identity matrix, and the SNR is ξ . According to
Eq. (1.4), normalized channel capacity is
C = log 2 (1 + ξ )
(1.5)
The receiver of the single-input multi-output (SIMO) system is equipped with
M tags, and the transmitter has only N = 1 reader antenna. Channel matrix
H = [h 1 h 2 . . . h M ], where h i represents the channel coefficient of the ith root reader
antenna from the transmitter to the receiver, then the channel capacity is
C = log 2
1 + H H
T
ξ
= log 2
1 +
M
i=1
|h i |
2
ξ
= log 2 (1 + Mξ )
(1.6)
The transmitter of the multiple-input single-output (MISO) system is equipped
with N reader antennas, while the receiver has only M = 1 tag. Channel matrix
H = [h 1 h 2 . . . h N ], where h j represents the channel coefficient from the jth reader
antenna at the transmitting end to the receiving end, then the channel capacity
C = log 2
1 + H H
T
ξ
= log 2
⎛
⎝ 1 +
N
j=1
h j
2 ξ
⎞
⎠ = log 2 (1 + N ξ )
(1.7)
The transmitting end of the MIMO system is equipped with multiple reader
antennas, and the receiving end is equipped with multiple tags, that is, M and N
are larger than 1, and the channel capacity is as Eq. (1.8).
C = log 2 (1 + M N ξ )
(1.8)
1 Overview of RFID System Anti-Collision Technology
According to Shannon calculation, under typical circumstances, that is, under the
interference of Gaussian white noise, channel capacity is written as
C = BW log 2
1 +
S
N
(1.4)
where the unit of BW is Hertz, S is signal power, and N is noise power, both in
watts. Channel capacity is proportional to channel bandwidth, which determines the
maximum information transfer rate in the current channel.
It can be seen from the channel definition and channel capacity calculation formula
that, in a certain RFID tag reading and writing scene, the background noise is relatively stable, the transmitting power is certain, and the medium condition is certain,
so the channel capacity has a fixed upper limit. Therefore, the anti-collision algorithm is to improve the utilization of the channel under the condition of fixed channel
capacity.
According to Eq. (1.4), channel capacity is known. The transmitter of the singleinput single-output (SISO) system is a single reader and the receiver is a single tag.
Thus, the channel matrix H is the identity matrix, and the SNR is ξ . According to
Eq. (1.4), normalized channel capacity is
C = log 2 (1 + ξ )
(1.5)
The receiver of the single-input multi-output (SIMO) system is equipped with
M tags, and the transmitter has only N = 1 reader antenna. Channel matrix
H = [h 1 h 2 . . . h M ], where h i represents the channel coefficient of the ith root reader
antenna from the transmitter to the receiver, then the channel capacity is
C = log 2
1 + H H
T
ξ
= log 2
1 +
M
i=1
|h i |
2
ξ
= log 2 (1 + Mξ )
(1.6)
The transmitter of the multiple-input single-output (MISO) system is equipped
with N reader antennas, while the receiver has only M = 1 tag. Channel matrix
H = [h 1 h 2 . . . h N ], where h j represents the channel coefficient from the jth reader
antenna at the transmitting end to the receiving end, then the channel capacity
C = log 2
1 + H H
T
ξ
= log 2
⎛
⎝ 1 +
N
j=1
h j
2 ξ
⎞
⎠ = log 2 (1 + N ξ )
(1.7)
The transmitting end of the MIMO system is equipped with multiple reader
antennas, and the receiving end is equipped with multiple tags, that is, M and N
are larger than 1, and the channel capacity is as Eq. (1.8).
C = log 2 (1 + M N ξ )
(1.8)