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1 Overview of RFID System Anti-Collision Technology
Fig. 1.2 The comparison of the MIMO channel capacities for different tag combinations
It can also 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 study how to improve the utilization of channels under the condition
of fixed channel capacity.
As a matter of fact, scholars from all over the world have already begun to explore
the methods to improve channel utilization and realize multiple access in a communication system to overcome the problem of signal collision [21]. Therefore, it is
necessary to make a simple analysis of these methods.
(1) Space-division multiple access, SDMA
The space-division multiple access method is used to identify multiple objects by
dividing the space scope. One application for RFID systems is to divide tags and
readers by distance, at the expense of having more readers in the space; Another
application is to add a phased array antenna to the reader space. Readers use different
angles and positions to distinguish different spatial tags. Phased array antennas used
for air separation multiple access are complex and costly, and are used only for
special occasions such as mass marathons.
1 Overview of RFID System Anti-Collision Technology
Fig. 1.2 The comparison of the MIMO channel capacities for different tag combinations
It can also 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 study how to improve the utilization of channels under the condition
of fixed channel capacity.
As a matter of fact, scholars from all over the world have already begun to explore
the methods to improve channel utilization and realize multiple access in a communication system to overcome the problem of signal collision [21]. Therefore, it is
necessary to make a simple analysis of these methods.
(1) Space-division multiple access, SDMA
The space-division multiple access method is used to identify multiple objects by
dividing the space scope. One application for RFID systems is to divide tags and
readers by distance, at the expense of having more readers in the space; Another
application is to add a phased array antenna to the reader space. Readers use different
angles and positions to distinguish different spatial tags. Phased array antennas used
for air separation multiple access are complex and costly, and are used only for
special occasions such as mass marathons.