1.1 RFID Collision Problem and Research Progress of Anti-Collision
3
closely. When multiple tags overlap closely, the resonant frequency shift caused
by tag coupling and the loss of coupling energy makes the tag unable to read and
write normally. This phenomenon is more obvious under the interference of transient
electromagnetic waves, which seriously affects the working efficiency of the RFID
system. Therefore, the read–write barrier of overlapping tags is a technical bottleneck in RFID industrial applications. Studies have shown that when multiple tags
are distributed according to a certain geometric shape, different conditions such as
electromagnetic fields, media, and RFID tags’ speed, angle, and distance relative to
reader antenna in different spaces are all key factors affecting the communication
performance between readers and tags [8–11]. In some areas involving public safety,
electromagnetic interference with RFID systems has been listed as a “serious and
dangerous source of interference”. According to a recent study published in The
Journal of the American Medical Association (JAMA), electromagnetic interference
will seriously damage the RFID-centered medical Internet of Things system in the
in-depth treatment test, which was conducted by the Academic Medical Center of the
University of Amsterdam in the Netherlands [12]. Pacemakers, defibrillators, dialysis
machines, infusion/syringe pumps, and ventilator fans are all medical devices that
are susceptible to interference. The interference of electromagnetic waves, especially
transient electromagnetic waves, on RFID systems will have a direct physical impact
on patients, such as patients. The IV pump or pacemaker in use is stopped and the
device issues an incorrect alarm and so on. Therefore, in the intensive care unit and
other similar medical environments, the implementation of RFID technology must
carry out on-site electromagnetic interference tests in accordance with the latest
international standards. Researchers at the RFID laboratory of the University of
Wisconsin-Madison have been studying and evaluating the suitability of using RFID
technology to track blood products and expensive medical supplies. The Chinese
government also attaches great importance to the intelligence of medical production,
manufacturing, and transportation. Premier Keqiang Li proposed at the executive
meeting of the State Council held in February 2016 that “promoting the intelligent
transformation of pharmaceutical production as an important measure for the innovation and upgrading of the pharmaceutical industry” was proposed. In the process
of intelligent transformation, safety and reliability are the keys to the application of
RFID technology [13, 14]. In addition, in the field of mass production and logistics, in order to improve the degree of automation, many UHF RFID tags are used.
When there are multiple RFID tags in the effective range of a reader, because all tags
use the same working frequency, the communication between the reader and the tag
shares the wireless channel, and sending data at the same time may cause channel
contention, data conflict, and transmission issues such as signal interference, leading
to information loss, so that the reader cannot correctly identify all tags, this is the
collision problem of the RFID multi-tag system. At present, it is the most concerned
and the hottest research in the field of RFID technology research and application at
home and abroad [15, 16].
There are many factors that cause the collision phenomenon, but electromagnetic
interference, static electricity, and environmental factors (such as metals, liquids)
are the main reasons. A study found that when the goods with RFID tags pass
3
closely. When multiple tags overlap closely, the resonant frequency shift caused
by tag coupling and the loss of coupling energy makes the tag unable to read and
write normally. This phenomenon is more obvious under the interference of transient
electromagnetic waves, which seriously affects the working efficiency of the RFID
system. Therefore, the read–write barrier of overlapping tags is a technical bottleneck in RFID industrial applications. Studies have shown that when multiple tags
are distributed according to a certain geometric shape, different conditions such as
electromagnetic fields, media, and RFID tags’ speed, angle, and distance relative to
reader antenna in different spaces are all key factors affecting the communication
performance between readers and tags [8–11]. In some areas involving public safety,
electromagnetic interference with RFID systems has been listed as a “serious and
dangerous source of interference”. According to a recent study published in The
Journal of the American Medical Association (JAMA), electromagnetic interference
will seriously damage the RFID-centered medical Internet of Things system in the
in-depth treatment test, which was conducted by the Academic Medical Center of the
University of Amsterdam in the Netherlands [12]. Pacemakers, defibrillators, dialysis
machines, infusion/syringe pumps, and ventilator fans are all medical devices that
are susceptible to interference. The interference of electromagnetic waves, especially
transient electromagnetic waves, on RFID systems will have a direct physical impact
on patients, such as patients. The IV pump or pacemaker in use is stopped and the
device issues an incorrect alarm and so on. Therefore, in the intensive care unit and
other similar medical environments, the implementation of RFID technology must
carry out on-site electromagnetic interference tests in accordance with the latest
international standards. Researchers at the RFID laboratory of the University of
Wisconsin-Madison have been studying and evaluating the suitability of using RFID
technology to track blood products and expensive medical supplies. The Chinese
government also attaches great importance to the intelligence of medical production,
manufacturing, and transportation. Premier Keqiang Li proposed at the executive
meeting of the State Council held in February 2016 that “promoting the intelligent
transformation of pharmaceutical production as an important measure for the innovation and upgrading of the pharmaceutical industry” was proposed. In the process
of intelligent transformation, safety and reliability are the keys to the application of
RFID technology [13, 14]. In addition, in the field of mass production and logistics, in order to improve the degree of automation, many UHF RFID tags are used.
When there are multiple RFID tags in the effective range of a reader, because all tags
use the same working frequency, the communication between the reader and the tag
shares the wireless channel, and sending data at the same time may cause channel
contention, data conflict, and transmission issues such as signal interference, leading
to information loss, so that the reader cannot correctly identify all tags, this is the
collision problem of the RFID multi-tag system. At present, it is the most concerned
and the hottest research in the field of RFID technology research and application at
home and abroad [15, 16].
There are many factors that cause the collision phenomenon, but electromagnetic
interference, static electricity, and environmental factors (such as metals, liquids)
are the main reasons. A study found that when the goods with RFID tags pass