1.2 RFID System Anti-Collision Technology
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(2) Frequency-division multiple access, FDMA
Frequency-division multiple access means that the transmission channel is divided
into several different carrier frequency channels, each channel between isolated areas
in order to prevent interference between the channel. In RFID systems, reader-totag communication, known as downlink, is fixed in frequency. If frequency-division
multiple access is applied, the signal input from the tag to the reader, i. e., the uplink,
must be transmitted at a variable frequency so that the reader can pass through
different tags in the frequency zone. In the RFID system using frequency-division
multiple access technology has obvious drawbacks, each tag must have a receiving
module, working frequency of the read and write also need to widen, so it will
improve the cost.
(3) Time-division multiple access, TDMA
Time-division multiple access (TDMA) is the division of the whole channel transmission information into thousands of time slots, allocated to multiple users. It is
characterized by fixed time slot distribution and suitable for transmitting digital
information. The application of time-division multiple access is very extensive, the
promotion and application of telephone is a classic application example. For RFID
systems, time division multiple access is the most widely used basic principle in
collision avoidance algorithms, such as the ALOHA method, binary tree method,
etc.
(4) Code-division multiple access, CDMA
Code-division multiple access (CDMA) technology has been applied to civil
communication as the quality of wireless communication becomes more and more
demanding. Code-division multiple access technology can be traced back to spread
spectrum communication technology for military use during World War II. When
code division multiple access communication is applied, the sender first modulates
the information to be transmitted with pseudo-random code, and then sends it with the
carrier. The receiver needs the same pseudo-random code to unexpand the received
signal. Code-division multiple access (CDMA) is not separated from frequency band
transmission, so it can distinguish multi-channel information transmitted at the same
time by coding, and discard unwanted signals as noise. Code-division multiple access
technology channel capacity is not large, frequency band utilization is not high,
address code selection also needs strong computing power, the receiver needs a long
time to capture address code. This makes code-division multiple access difficult to
apply to RFID systems.
Traditional multiplexing methods in the field of communication are difficult to be
directly applied to the problem of RFID multi-tag reading, but with the development
of RFID, these methods contain the possibility of solving the problem. In terms of
tag collision prevention, considering the complexity and cost of tags, most RFID
tags used in practice are passive tags. Therefore, this chapter focuses on the problem
of passive tag collision prevention. Collision prevention methods are divided into
15
(2) Frequency-division multiple access, FDMA
Frequency-division multiple access means that the transmission channel is divided
into several different carrier frequency channels, each channel between isolated areas
in order to prevent interference between the channel. In RFID systems, reader-totag communication, known as downlink, is fixed in frequency. If frequency-division
multiple access is applied, the signal input from the tag to the reader, i. e., the uplink,
must be transmitted at a variable frequency so that the reader can pass through
different tags in the frequency zone. In the RFID system using frequency-division
multiple access technology has obvious drawbacks, each tag must have a receiving
module, working frequency of the read and write also need to widen, so it will
improve the cost.
(3) Time-division multiple access, TDMA
Time-division multiple access (TDMA) is the division of the whole channel transmission information into thousands of time slots, allocated to multiple users. It is
characterized by fixed time slot distribution and suitable for transmitting digital
information. The application of time-division multiple access is very extensive, the
promotion and application of telephone is a classic application example. For RFID
systems, time division multiple access is the most widely used basic principle in
collision avoidance algorithms, such as the ALOHA method, binary tree method,
etc.
(4) Code-division multiple access, CDMA
Code-division multiple access (CDMA) technology has been applied to civil
communication as the quality of wireless communication becomes more and more
demanding. Code-division multiple access technology can be traced back to spread
spectrum communication technology for military use during World War II. When
code division multiple access communication is applied, the sender first modulates
the information to be transmitted with pseudo-random code, and then sends it with the
carrier. The receiver needs the same pseudo-random code to unexpand the received
signal. Code-division multiple access (CDMA) is not separated from frequency band
transmission, so it can distinguish multi-channel information transmitted at the same
time by coding, and discard unwanted signals as noise. Code-division multiple access
technology channel capacity is not large, frequency band utilization is not high,
address code selection also needs strong computing power, the receiver needs a long
time to capture address code. This makes code-division multiple access difficult to
apply to RFID systems.
Traditional multiplexing methods in the field of communication are difficult to be
directly applied to the problem of RFID multi-tag reading, but with the development
of RFID, these methods contain the possibility of solving the problem. In terms of
tag collision prevention, considering the complexity and cost of tags, most RFID
tags used in practice are passive tags. Therefore, this chapter focuses on the problem
of passive tag collision prevention. Collision prevention methods are divided into