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1 Overview of RFID System Anti-Collision Technology
two ways. One is to realize tag collision prevention by software algorithm according
to existing resources. The other is to optimize the hardware environment, including
the tag according to a specific geometric distribution, reduce space electromagnetic
interference, design of a novel antenna, build a multi-in-multi-out system, and other
physical methods to achieve tag collision prevention.
1.2.2 Software Anti-Collision
At present, the most commonly used software anti-collision algorithms can be divided
into two categories. One is a probabilistic algorithm represented by the ALOHA
algorithm(ISO/IEC 18,000–6 Type A Tags as defined by the standard). The other is
a deterministic algorithm represented by a binary tree algorithm(ISO/IEC 18,000–6
Type B Tags as defined by the standard) [22].
The basic idea of the ALOHA algorithm is time-division multiple access. ALOHA
algorithm is simple, easy to implement, and suitable for low-cost RFID systems.
However, due to the randomness of this kind of algorithm, that is, the possibility that
a tag cannot be recognized in a considerable period of time, this kind of method is
called the probabilistic method.
(1) Pure ALOHA algorithm
Pure ALOHA algorithm is a simple time-division multiple access method. ALOHA
was originally a greeting used by Hawaiians. In the 1970s, the ALOHA system at
the University of Hawaii was the first computer system to use radio broadcasting as a
communication facility. The system is applied to the ground network using ALOHA
protocol, or pure ALOHA. Pure ALOHA is a simple idea, with tags sending data
to readers in real time, which creates collisions. However, based on the feedback
of the broadcast channel, the sender can carry out collision detection. Once the
sender detects a collision, it will wait for a random time to resend the ton until it is
successfully sent. The basic process is shown in Fig. 1.3.
This algorithm is suitable for occasions where the real-time requirement is not
high. As long as the communication identification process is long enough, the reader
can identify all the tags within its reading and writing range. However, this algorithm
is only used when a small amount of information is transmitted to the read-only tag
of the reader, and there will be a collision of data parts.
(2) Slotted ALOHA algorithm
The time slot ALOHA algorithm was proposed in 1972. Its basic idea is to divide
the channel into discrete time slots, and the size of the time slots is determined by
the system, but the time slots are at least greater than the time required to send data.
It is stipulated that only at the critical point of each time slot, the tag will actively
send data to the reader, and the time of sending data is fixed within each time slot,
1 Overview of RFID System Anti-Collision Technology
two ways. One is to realize tag collision prevention by software algorithm according
to existing resources. The other is to optimize the hardware environment, including
the tag according to a specific geometric distribution, reduce space electromagnetic
interference, design of a novel antenna, build a multi-in-multi-out system, and other
physical methods to achieve tag collision prevention.
1.2.2 Software Anti-Collision
At present, the most commonly used software anti-collision algorithms can be divided
into two categories. One is a probabilistic algorithm represented by the ALOHA
algorithm(ISO/IEC 18,000–6 Type A Tags as defined by the standard). The other is
a deterministic algorithm represented by a binary tree algorithm(ISO/IEC 18,000–6
Type B Tags as defined by the standard) [22].
The basic idea of the ALOHA algorithm is time-division multiple access. ALOHA
algorithm is simple, easy to implement, and suitable for low-cost RFID systems.
However, due to the randomness of this kind of algorithm, that is, the possibility that
a tag cannot be recognized in a considerable period of time, this kind of method is
called the probabilistic method.
(1) Pure ALOHA algorithm
Pure ALOHA algorithm is a simple time-division multiple access method. ALOHA
was originally a greeting used by Hawaiians. In the 1970s, the ALOHA system at
the University of Hawaii was the first computer system to use radio broadcasting as a
communication facility. The system is applied to the ground network using ALOHA
protocol, or pure ALOHA. Pure ALOHA is a simple idea, with tags sending data
to readers in real time, which creates collisions. However, based on the feedback
of the broadcast channel, the sender can carry out collision detection. Once the
sender detects a collision, it will wait for a random time to resend the ton until it is
successfully sent. The basic process is shown in Fig. 1.3.
This algorithm is suitable for occasions where the real-time requirement is not
high. As long as the communication identification process is long enough, the reader
can identify all the tags within its reading and writing range. However, this algorithm
is only used when a small amount of information is transmitted to the read-only tag
of the reader, and there will be a collision of data parts.
(2) Slotted ALOHA algorithm
The time slot ALOHA algorithm was proposed in 1972. Its basic idea is to divide
the channel into discrete time slots, and the size of the time slots is determined by
the system, but the time slots are at least greater than the time required to send data.
It is stipulated that only at the critical point of each time slot, the tag will actively
send data to the reader, and the time of sending data is fixed within each time slot,