1、 Introduction

Radio frequency identification (RFID) system uses radio frequency technology to identify objects in an open system environment. The advantages of the recognition include no physical contact or other contact, and can be recognized in high-speed movement. It is of great significance to improve the speed of inventory, identity authentication and location determination, and is the basis of building a smart city.

By placing an electronic identity tag in the front of the owner’s vehicle, the access control of the campus garage can be completed, or the RFID reader can be installed in the garage to monitor the parking status and complete the parking guidance. In e-commerce enterprises, RFID technology is used to systematically plan the in and out management, location allocation and commodity retrieval of a large number of commodities.

2、 Application of FIFO in RFID

FIFO is one of the most basic scheduling algorithms in computer operating system. When a process applies for limited system resources, the system generates a waiting queue according to the order of process application, allocates resources to the process from the head of the queue, and when a new process arrives, it is added to the tail of the queue, so that the process processing can proceed orderly.

When working in RFID system, due to the limited hardware resources of the reader, only a small number of tags can be identified and processed at the same time. When a large number of tags come in one after another, there will be a blocking phenomenon due to too late processing, which is called multi tag collision.

Alt4518529791214592 how to realize anti-collision based on FIFO RFID

The RFID anti-collision algorithm based on FIFO adds FIFO to the deterministic anti-collision algorithm. By generating the waiting queue of tags to be processed, the conflict of tag identification can be reduced. The algorithm has a significant effect on the improvement of the overall label recognition efficiency and the reduction of the waiting time of a single label.

In the RFID system using this algorithm, when the tag enters into the range of the inquiry signal transmitted by the reader, it immediately sends its own ID to the reader. After receiving the ID information, the reader feeds back the response signal to the tag and asks the reader to enter the waiting state. And the ID information is added in the tag processing waiting queue of the reader writer. The processing module reads the waiting tag information from the tag waiting queue in turn, sends the read broadcast containing the tag ID, and responds to the reader writer after receiving the read application for identity authentication and data exchange

① Tag 01 sends an authentication request “request (01)” containing identity information;

② Reader a receives the “request” signal and adds “request (01)” to the waiting queue;

③ Reader a sends feedback “get (01), wait” and receives 01 message. Please wait for verification;

④ Tag 01 receives the message “get (01), wait” and randomly enters the state of waiting for authentication;

⑤ Tag 0x requests authentication and enters the waiting queue in the same way;

⑥ The system reads the waiting queue and sends “identity (01)” when “request (01)” is read;

⑦ If “identity (01)” is sent three times without feedback, skip this tag;

⑧ Tag 01 receives “identity (01)”, and the feedback response information is “wait (01)”;

⑨ After completing the identity authentication and data processing exchange with tag 01, reader a sends the tag removal information “remove (01)”.

In the RFID system using this algorithm, the reader must have at least two independent signal processing modules, one for processing “request” authentication request signal and sending “get, wait” feedback waiting signal, the other for processing “identity” and data exchange module. It is better to have two signal antennas with different frequencies, so that the two functions of authentication and data interaction can be separated independently, and the tag recognition and data processing can be completed better and faster.

Compared with wired signal, wireless signal is easy to be interfered or even shielded. In this algorithm, if the tag can not receive the “identity” signal or the signal is wrong due to special reasons, it will only be in the “wait” state, unless it is powered off due to leaving the signal range. The specific solution is to add a counter module in the tag, and add 1 every time the “identity” signal of other tags is detected, When it is added to a certain value (determined according to the total number of tags of a specific item), the authentication request is sent again, which increases the cost of tags.

3、 Summary

RFID deterministic tag anti-collision algorithm based on first in first out (FIFO) algorithm is a method to reduce the identification conflict by separating the signal docking and data exchange between reader and tag into two independent parts. Its core algorithm (FIFO) is the premise to ensure that the tag can complete the data exchange as soon as possible under equal conditions.

This algorithm can improve the tag recognition and processing speed to a certain extent, but it has higher requirements for the reader in terms of antenna, processor and memory, especially in terms of antenna. It even requires two antennas, which undoubtedly increases the hardware cost. A small increase in the cost of the reader does not have much impact on the whole system.

Editor in charge: CT

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