What are the anti-collision algorithms for RFID systems

1. Pure ALOHA algorithm

This algorithm mainly adopts the way that the tag speaks first, that is, once the RFID electronic tag enters the working range of the UHF reader to obtain energy, it will actively send its own serial number to the reader. In the process of an electronic tag sending data to the reader, if other electronic tags also send data to the reader at the same time, the signals received by the RFID Reader will overlap at this time, resulting in the failure of the reader. Correctly identify and read data. The reader detects and judges whether the received signal collides. Once a collision occurs, the reader sends an instruction to the tag to stop the transmission of data from the electronic tag. After the electronic tag receives the instruction from the reader, it randomly delays Resend the data after a period of time. In the pure ALOHA algorithm, assuming that the electronic tag sends data to the reader at time t, and the communication time with the reader is To, the collision time is 2To. G is the amount of data packet exchange, and S is the throughput rate (the maximum S=18.4% when G=0.5).

2. Slotted ALOHA algorithm

In order to improve the throughput rate of the RFID system, the time can be divided into multiple equal-length time slots. The length of the time slot is determined by the system clock, and it is stipulated that the RFID electronic tag can only send to the RFID reader at the beginning of each time slot. Sending data frames, this is the slotted ALOHA algorithm; according to the above regulations, the data frames are either successfully sent or completely collided, which avoids the occurrence of partial collisions in the pure ALOHA algorithm, and makes the collision period become To; (G=1 Maximum S=36.8%).

3. Dynamic time slot ALOHA algorithm

The dynamic time slot ALOHA algorithm first sends the frame length N to the electronic tag by the RFID reader, and the electronic tag generates a random number between [1, N]. Next, each electronic tag selects the corresponding time slot and reads and writes with the RFID If the current time slot is the same as the number randomly generated by the electronic tag, the electronic tag will respond to the command of the RFID reader, if not, the tag will continue to wait. If there is only one electronic tag responding in the current time slot, the RFID reader will read the data sent by the tag, and make the tag in a "silent" state after reading. If there are multiple tags responding in the current time slot, the data in the time slot will collide. At this time, the RFID reader will notify the tags in the time slot to regenerate random numbers in the next frame cycle. Participate in correspondence. Loop frame by frame until all electronic tags are recognized.

4. Binary search algorithm

After multiple tags enter the reader's workplace, the reader sends an inquiry command with restrictions, and the tag that meets the restrictions answers. If a collision occurs, the restriction is modified according to the bit where the error occurred, and the inquiry command is sent again until Find a correct answer and complete the read and write operations on the tag. Repeat the above operations for the remaining tags until the read and write operations for all tags are completed.