Anti-collision method for multi-RFID tag reading

Abstract

The invention discloses an anti-collision method for reading multiple RFID (Radio Frequency Identification) tags. The anti-collision method comprises the following steps of: 1) sending an inquiry instruction containing an initial frame length N; 2) judging whether the proportion of the collision time slot of the current frame exceeds b% or not, and if so, entering step 3); otherwise, judging whether the proportion of the current frame space time slot exceeds c%, if so, entering the step 4), and otherwise, entering the step 5); (3) entering interruption, increasing the frame length, resending the inquiry instruction, and then returning to the step (2); (4) entering interruption, reducing the frame length, resending the inquiry instruction, and then returning to the step (2); and 5) identifying the RFID tag. According to the anti-collision method, the length of the data frame is adjusted according to the number of the collided labels, the frame length most suitable for the number of the current labels is selected by dynamically adjusting the frame length so as to meet the anti-collision requirement of a reader, and the label reading efficiency is effectively improved.

Description

Technical Field

[0001] The present invention relates to, and in particular to, an anti-collision method for reading multiple RFID tags. Background Art

[0002] The anti-collision protocol in RFID tags is a communication mechanism used to avoid data conflicts and collisions when multiple RFID tags are simultaneously read by a reader. Since an RFID system usually needs to read the information of multiple tags in a short time, an effective anti-collision mechanism is required to ensure the accuracy and efficiency of communication.

[0003] Currently, the most widely used anti-collision algorithm in RFID systems is the ALOHA method. When multiple tags simultaneously send data information to the reader, it will cause information conflicts in the wireless channel, and the reader will not be able to read the tag data information. Once a tag data information transmission conflict occurs, the reader will send an instruction to terminate all tags from sending their own data information, and each tag will randomly delay for a period of time and then resend. Since the data frame of the ALOHA algorithm is fixed and cannot be adjusted according to the number of tags in the actual application environment, the system throughput varies greatly, the system performance is unstable, and the tag reading efficiency needs to be further improved. Summary of the Invention

[0004] In view of the above-mentioned defects or deficiencies in the prior art, it is desired to provide an anti-collision method for reading multiple RFID tags, which adjusts the length of the data frame according to the number of collided tags, selects the most suitable frame length for the current number of tags by dynamically adjusting the frame length to meet the anti-collision requirements of the reader, and effectively improves the tag reading efficiency.

[0005] An anti-collision method for reading multiple RFID tags provided by the present invention includes the following steps:

[0006] 1) The reader sends an interrogation instruction containing an initial frame length of N to the RFID tags to be identified in the identification area;

[0007] 2) Determine whether the proportion of collision time slots in the first a% time slots of the current frame exceeds b%. If so, go to step 3); otherwise, determine whether the proportion of empty time slots in the first a% time slots of the current frame exceeds c%. If so, go to step 4); otherwise, go to step 5);

[0008] 3) Enter an interruption, the reader increases the frame length and resends the interrogation instruction to the RFID tags to be identified in the identification area, and then returns to step 2);

[0009] 4) Enter an interruption, the reader decreases the frame length and resends the interrogation instruction to the RFID tags to be identified in the identification area, and then returns to step 2);

[0010] 5) Identify the RFID tags to be identified within the identification area.

[0011] Further, the frame length includes collision time slots, empty time slots, and successful time slots; the collision time slot indicates that multiple RFID tags send data simultaneously within this time slot; the empty time slot indicates that no RFID tag sends data within this time slot; the successful time slot indicates that only one RFID tag sends data within this time slot.

[0012] Further, in step 2), a is 20 - 40; b is 60 - 80; c is 60 - 80.

[0013] Further, in step 3), the reader increases the frame length to the integer value of 1.5 - 2 times the frame length of the previous frame.

[0014] Further, in step 4), the reader decreases the frame length to the integer value of 0.5 - 0.6 times the frame length of the previous frame.

[0015] Further, in step 5), the identification of the RFID tags includes the following steps:

[0016] 51) After the RFID tags to be identified within the identification area receive the interrogation command, initialize the value of their time slot counters to the number of frame lengths.

[0017] 52) Determine whether the value of the time slot counter of the RFID tags to be identified within the identification area is 1. If so, proceed to the next step; otherwise, perform the following operations:

[0018] If the current time slot is an empty time slot, send a time slot end command to the RFID tags within the reader identification area. The value of the time slot counter of the RFID tags in the to-be-identified state is decremented by 1, and then step 52) is executed again.

[0019] If the current time slot is a collision time slot, the RFID tags in this time slot will no longer participate in the identification process of the remaining time slots of this frame, and the value of their time slot counters is decremented to 0; the value of the time slot counters of the remaining RFID tags in the to-be-identified state is decremented by 1, and then step 52) is executed again; among them, the RFID tags with the value of the time slot counter being 0 will restart the identification process at the beginning of the next frame.

[0020] If the current time slot is a successful time slot, the RFID tags in this time slot receive the sleep command from the reader before the current time slot end command and will no longer participate in the subsequent identification process; the value of the time slot counter of the RFID tags in the to-be-identified state is decremented by 1, and then step 52) is executed again.

[0021] 53) When there are still RFID tags to be identified in the identification area, the reader sends an interrogation command to the RFID tags to be identified in the identification area, and then returns to step 51); when there are no RFID tags to be identified in the identification area, the identification is completed and the identification process stops.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The anti-collision method of the present invention adjusts the length of the data frame according to the number of collided tags, and appropriately increases the number of time slots of the data frame according to the number of collided tags; when the number of tags is less than the number of time slots of the data frame, the number of time slots of the data frame is appropriately reduced. It can ensure that the number of time slots of the data frame is basically the same as the number of tags, making the system efficiency reach the best, and the channel utilization rate is high. It effectively improves the tag reading efficiency and the stability of the system.

[0024] It should be understood that the content described in the section of the invention content is not intended to limit the key or important features of the embodiments of the present invention, nor is it used to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objects, and advantages of the present invention will become more apparent:

[0026] Figure 1 is a flowchart of an anti-collision method for multi-RFID tag reading;

[0027] Figure 2 is a schematic diagram of the dynamic frame time slot algorithm. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The present invention will be further described in detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related invention, rather than limiting the invention. Additionally, it should be noted that for the sake of description, only the parts related to the invention are shown in the drawings.

[0029] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and embodiments.

[0030] Please refer to Figures 1 to 2 , the embodiments of the present invention provide an anti-collision method for multi-RFID tag reading, including the following steps:

[0031] 1) The reader sends an interrogation command including an initial frame length of N to the RFID tags to be identified in the identification area;

[0032] 2) Determine whether the proportion of collision time slots within the first 30% of the time slots in the current frame exceeds 80%. If so, proceed to step 3); otherwise, determine whether the proportion of empty time slots within the first 30% of the time slots in the current frame exceeds 80%. If so, proceed to step 4); otherwise, proceed to step 5).

[0033] Among them, the frame length includes collision time slots, empty time slots, and successful time slots.

[0034] A collision time slot indicates that multiple RFID tags send data simultaneously within this time slot.

[0035] An empty time slot indicates that no RFID tag sends data within this time slot.

[0036] A successful time slot means that only one RFID tag sends data within this time slot.

[0037] 3) Enter the interrupt. The reader increases the frame length to twice the length of the previous frame and resends the interrogation command to the RFID tags to be identified within the identification area, and then returns to step 2).

[0038] 4) Enter the interrupt. The reader decreases the frame length to 0.5 times the length of the previous frame and resends the interrogation command to the RFID tags to be identified within the identification area, and then returns to step 2).

[0039] 5) Identify the RFID tags to be identified within the identification area, including the following steps:

[0040] 51) After the RFID tags to be identified within the identification area receive the interrogation command, initialize the value of their time slot counters to the frame length number.

[0041] 52) Determine whether the value of the time slot counter of the RFID tags to be identified within the identification area is 1. If so, proceed to the next step; otherwise, perform the following operations:

[0042] If the current time slot is an empty time slot, send a time slot end command to the RFID tags within the reader's identification area. The value of the time slot counter of the RFID tags in the to-be-identified state is decremented by 1, and then step 52) is executed again.

[0043] If the current time slot is a collision time slot, the RFID tags in this time slot will no longer participate in the identification process of the remaining time slots in this frame, and the value of their time slot counters is decremented to 0; the value of the time slot counters of the remaining RFID tags in the to-be-identified state is decremented by 1, and then step 52) is executed again; among them, the RFID tags with a time slot counter value of 0 will restart the identification process at the beginning of the next frame.

[0044] If the current time slot is a successful time slot, the RFID tags in this time slot receive the sleep command from the reader before the current time slot end command and will no longer participate in the subsequent identification process; the value of the time slot counter of the RFID tags in the to-be-identified state is decremented by 1, and then step 52) is executed again;

[0045] 53) When there are still RFID tags to be identified in the identification area, the reader sends an interrogation command to the RFID tags to be identified in the identification area, and then returns to step 51); when there are no RFID tags to be identified in the identification area, the identification is completed and the identification process stops.

[0046] In this embodiment, in order to reduce the waste of a large amount of judgment time caused by the mismatch between the dynamic frame time slots and the number of RFID tags to be identified, an interruption is added to sample and judge the state of the first 30% of the time slots in a frame. If a large number of collision time slots appear, reaching more than 80%, an interruption is generated, and it is judged that there are a large number of RFID tags in the current environment and there will be a large number of collision phenomena in the frame length; therefore, in order to reduce the waste of a large amount of time caused by continuing to judge the remaining part, the interruption mode is directly entered, and the frame length is doubled. Then, the identification process of the next frame is carried out. The same principle applies to the identification process of the next frame. Sampling judgment is still carried out from it. If the collision time slots exceed 80%, enter the interruption and double the frame length to the current 2 times. Otherwise, judge the proportion of empty time slots. If the empty time slots reach more than 80%, enter the interruption and set the frame length to 1 / 2 of the original. If neither of the two situations is satisfied, it means that the current frame length is the appropriate length, and the RFID tag identification is completed.

[0047] This application can efficiently identify each RFID tag in an environment with a large number of RFID tags, avoid conflicts when RFID tags respond, improve the identification efficiency, and support the identification requirements of RFID tags from a small number to a large number. By dynamically adjusting the frame length, the conflict between RFID tags is reduced, and the frame length most suitable for the number of RFID tags in the current environment is selected, ensuring that the number of time slots in the data frame is basically the same as the number of tags, making the system efficiency reach the best, and having a high channel utilization rate. The tag reading efficiency is effectively improved, and the stability of the system is improved.

[0048] In the description of this specification, the descriptions of terms such as "one embodiment" and "some embodiments" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or instance. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0049] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for anti-collision of multiple RFID tags, characterized in that: The steps include: 1) The reader sends an inquiry instruction containing an initial frame length of N to the RFID tag to be identified in the identification area; 2) Determine whether the proportion of collision time slots in the first a% of time slots of the current frame exceeds b%, if so, proceed to step 3); otherwise, determine whether the proportion of empty time slots in the first a% of time slots of the current frame exceeds c%, if so, proceed to step 4), otherwise proceed to step 5); 3) Entering an interrupt, the reader increases the frame length and resends an inquiry command to the RFID tag to be identified in the identification area, and then returns to step 2); 4) Entering an interrupt, the reader reduces the frame length and resends an inquiry command to the RFID tag to be identified in the identification area, and then returns to step 2); 5) Identify the RFID tags to be identified in the identification area.

2. The anti-collision method for reading multiple RFID tags according to claim 1, characterized in that: The frame length includes collision time slot, empty time slot and success time slot; the collision time slot means that multiple RFID tags send data simultaneously in the time slot; the empty time slot means that no RFID tag sends data in the time slot; and the success time slot means that only one RFID tag sends data in the time slot.

3. The anti-collision method for reading multiple RFID tags according to claim 1, characterized in that: In the step 2), a is 20-40; b is 60-80; and c is 60-80.

4. The anti-collision method for reading multiple RFID tags according to claim 3, characterized in that: In the step 3), the reader increases the frame length to 1.5-2 times the previous frame length and rounds it up.

5. The anti-collision method for reading multiple RFID tags according to claim 3, characterized in that: In the step 4), the reader reduces the frame length to 0.5-0.6 times the previous frame length and rounds it up.

6. The anti-collision method for reading multiple RFID tags according to claim 2, characterized in that: In step 5), the identification of the RFID tag includes the following steps: 51) After receiving the inquiry command, the RFID tag to be identified in the identification area initializes the value of its time slot counter to the frame length; 52) Determine whether the value of the time slot counter of the RFID tag to be identified in the identification area is 1, if so, proceed to the next step; otherwise, perform the following operations: If the current time slot is an empty time slot, a time slot end command is sent to the RFID tags in the reader identification area, the value of the time slot counter of the RFID tags in the to-be-identified state is reduced by 1, and then step 52 is re-executed; If the current time slot is a collision time slot, the RFID tag in this time slot no longer participates in the identification process of the remaining time slots of this frame, and the value of its time slot counter is reduced to 0; the value of the time slot counter of the remaining RFID tags in the to-be-identified state is reduced by 1, and then step 52 is re-executed); wherein, the RFID tag whose time slot counter value is 0 restarts the identification process at the beginning of the next frame; If the current time slot is a successful time slot, the RFID tag in this time slot receives the sleep command of the reader before the current time slot end command and no longer participates in the subsequent identification process; the value of the time slot counter of the RFID tag in the to-be-identified state is reduced by 1, and then step 52 is re-executed; 53) When there are still RFID tags to be identified in the identification area, the reader sends an inquiry instruction to the RFID tags to be identified in the identification area, and then returns to step 51); when there are no RFID tags to be identified in the identification area, the identification is completed and the identification process is stopped.

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