A lost tag detection method for multi-packet RFID system

Abstract

A method for detecting lost tags in a multi-group RFID system, comprising: step 1, a reader maps each group of tags to a f using a hash function using the tag IDs of known tags stored in a backend server; g Build a desired frame vector v from an array of length g ; Step 2, the reader forms a request command with the group ID, frame length and random seed of the hash function of each group of tags, and polls and broadcasts all request commands; Step 3, if the tag receives the broadcast containing the group ID, it sends a 96-bit response information to the reader through the hash function according to the request command broadcast by the reader; Step 4, after the reader receives the response information of all tags in a time slot, the reader performs an OR operation on all the response information and adds it to the expected frame vector v g Perform a comparison and detect whether a label is missing based on the comparison results.

Description

Technical Field

[0001] The present invention relates to the technical field of radio frequency identification and the Internet of Things, and in particular to a lost tag detection method for a multi-group RFID system. Background Art

[0002] As more and more devices are connected to the internet, the Internet of Things (IoT) has experienced rapid development. Radio Frequency Identification (RFID), a key technology in the IoT, has achieved remarkable success over the past decade. A typical RFID system typically consists of a backend server, one or more readers, and a large number of tags. The backend server provides powerful computing and storage capabilities, while each reader is equipped with one or more antennas to collect responses from tags within its communication range. Tags can be categorized as active, semi-active, and passive based on their communication mode. Active tags have an internal power supply and offer long communication ranges, but are larger in size. Semi-active tags operate only when activated, while passive tags lack an internal power supply and rely on radio frequency signals from the reader for power. The backend server stores the ID information of all known tags for real-time tag monitoring and provides real-time instructions to readers to coordinate the tags in the system. In some large-scale, multi-group RFID systems, such as those in large warehouses, all goods are tagged with RFID tags. Due to various factors, such as theft and employee error, goods in the system can be lost, resulting in significant economic losses. Rapid detection of lost tags in the system can quickly detect lost goods and prevent economic losses. In large-scale RFID systems, tags can be divided into multiple groups based on their attributes and characteristics, with each group of tags having the same group ID. The most direct method for detecting lost tags is to collect the IDs of all tags in the system and then compare them with the IDs stored in a server. If the ID is not collected on the server, the tag is considered lost. This method has the advantage of high accuracy, but also has significant disadvantages. Since this method requires frequent ID transmission between the reader and the tag, it is time-consuming, resulting in extremely low detection efficiency and posing significant security risks. Summary of the Invention

[0003] In view of the technical defects and drawbacks in the prior art, the embodiments of the present invention provide a method for detecting lost tags in a multi-group RFID system that overcomes or at least partially solves the above problems. The specific solution is as follows:

[0004] A method for detecting lost tags in a multi-group RFID system. All known tags in the system are divided into G groups. Let the gth group contain N g , N g ≤ preset value z, 1≤g≤G labels, of which the number of lost labels is m g Each tag has a unique z-bit tag ID and a group ID for tag identity verification, the method comprising:

[0005] Step 1: The reader uses the hash function to map each group of tags to an f g Build a desired frame vector V from an array of arrays of length g ;

[0006] Step 2: The reader combines the group ID, frame length, and random seed of the hash function of each group of tags into a request command, and then polls and broadcasts all request commands;

[0007] Step 3: If the tag receives the broadcast containing the group ID, it sends a 96-bit response message to the reader through the hash function according to the request command broadcast by the reader;

[0008] Step 4: After the reader receives all the tag response information in a time slot, it performs an OR operation on all the response information and adds it to the expected frame vector V. g Perform a comparison and detect whether a label is missing based on the comparison results.

[0009] Furthermore, step 1 includes:

[0010] The reader performs a hash operation on the tag IDs in a group of tags through a hash function with a random seed R, and the hash result is f g After taking the remainder, it is mapped to a length of f g In the array, if a bit in the array is mapped by only one label, the bit in the array is set to "1", otherwise it is set to "0". When all the label mappings of this group are completed, the expected frame vector V g The construction is completed, and the desired frame vector V g In , “1” represents the desired single time slot and “0” represents the desired non-single time slot.

[0011] Furthermore, in step 3,

[0012] If the tag receives a broadcast containing the group ID to which it belongs, it performs a hash operation H(tag ID, R) on the tag ID using the random seed in the broadcast request command and calculates the frame length f g Take the remainder and record the result as Y i , where H() is a hash function, and each label is based on The value of selects a tag time slot to reply a 96-bit message to the reader. The response message contains 95 bits of "0" and 1 bit of "1", where the index value of "1" in the response message is Y i Divide by 96 and take the remainder.

[0013] Furthermore, step 4 includes:

[0014] When a tag time slot is completed, the reader performs an OR operation on all 96-bit tag response information received in the tag time slot to form a composite 96-bit vector. When a bit in the composite vector is "0" but the expected frame vector V g When the corresponding bit in is "1", it is determined that there is a lost tag event in the g-th group. The reader stops detecting the g-th group of tags and starts the lost tag detection of the next group of tags by broadcasting a request command consisting of the group ID, frame length and random seed of the next group of tags.

[0015] Furthermore, when it is determined that there is a lost tag event in the g-th group, the reader stops detecting the g-group tags and starts the lost tag detection of the next group of tags by broadcasting a request command consisting of the group ID, frame length and random seed of the next group of tags.

[0016] Furthermore, during the detection of a group of lost tags, the reader performs r g The group of missing tag events is detected in rounds to achieve the required detection accuracy, wherein the number of rounds is determined by the given detection accuracy and the number of missing tags in the group.

[0017] Furthermore, the method further comprises:

[0018] Calculate the expected frame vector V g The expected single time slot ratio P s for:

[0019]

[0020] When the above formula is derived, it can be found that when N g =f g When P s Get the maximum value of That is N g The value of f g To maximize the proportion of expected single time slots, to improve the utilization of expected single time slots, where is the probability of expecting a single time slot.

[0021] Furthermore, in step 4, for any round in any group g, the probability that a lost tag is mapped to a desired single time slot is Then the probability that a lost tag cannot be detected by the expected single time slot in the current round is The probability that a time slot in the current round is an isomorphic time slot is:

[0022]

[0023] Therefore, a missing label passes through r g The probability that the wheel still cannot be detected is:

[0024]

[0025] According to the given detection reliability α g ,have:

[0026] 1-P u ≥α g . (4)

[0027] Right now:

[0028]

[0029] According to the above formula (5), we can get:

[0030]

[0031] but is the optimal value to meet the reliability requirements.

[0032] The present invention has the following beneficial effects:

[0033] (1) The present invention can realize accurate and efficient lost tag detection in a multi-group large-scale RFID system by simultaneously processing the responses of multiple tags, quickly and accurately detecting lost tags in each group of tags, and the reliability of the detection can meet the requirements of the system.

[0034] (2) The present invention arranges multiple tags to respond simultaneously in each tag time slot and performs OR operation on the responses of multiple tags, which greatly reduces the response time of the tags and improves the detection efficiency of lost tags. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 An embodiment of the present invention provides a method for detecting lost tags in a multi-group RFID system.

[0036] Figure 2 This is the structural diagram of the large-scale multi-group RFID system.

[0037] Figure 3 Schematic diagram of a lost tag detection method based on a multi-group RFID system according to an embodiment of the present invention.

[0038] Figure 4Schematic diagram comparing the execution time of the lost tag detection method based on the multi-group RFID system according to the embodiment of the present invention and the existing method with the total number of tags in the system when α=0.9.

[0039] Figure 5 Schematic diagram comparing the execution time of the lost tag detection method based on the multi-group RFID system according to the embodiment of the present invention and the existing method with the total number of tags in the system when α=0.99.

[0040] Figure 6 Schematic diagram comparing the execution time of the lost tag detection method based on a multi-group RFID system according to an embodiment of the present invention and the existing method with the change of the detection reliability of each group when M=1.

[0041] Figure 7 A schematic diagram comparing the execution time of the lost tag detection method based on a multi-group RFID system according to an embodiment of the present invention and the existing method with the change of the detection reliability of each group when M=5.

[0042] Figure 8 Schematic diagram comparing the execution time of the lost tag detection method based on a multi-group RFID system according to an embodiment of the present invention and the existing method with the number of lost tags in each group when α=0.9.

[0043] Figure 9 Schematic diagram comparing the execution time of the lost tag detection method based on a multi-group RFID system according to an embodiment of the present invention and the existing method with the number of lost tags in each group when α=0.99.

[0044] Figure 10 A schematic diagram comparing the actual detection reliability of the lost tag detection method based on a multi-group RFID system according to an embodiment of the present invention and the existing method as the number of tags in each group changes when α is 0.9.

[0045] Figure 11 Schematic diagram comparing the actual detection reliability of the lost tag detection method based on the multi-group RFID system according to the embodiment of the present invention and the existing method as the number of tags in each group changes when α=0.99.

[0046] Figure 12 Schematic diagram comparing the detection reliability of each group between the lost tag detection method based on a multi-group RFID system according to an embodiment of the present invention and the existing method when M=1.

[0047] Figure 13 Schematic diagram comparing the detection reliability of each group between the lost tag detection method based on a multi-group RFID system according to an embodiment of the present invention and the existing method when M=5. DETAILED DESCRIPTION

[0048] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0049] See also Figure 2 A large-scale multi-group RFID system includes a back-end server, a reader, and n known tags divided into G groups. The i-th group of tags contains g i tags, which contain m i Tags are considered lost, with 1 ≤ i ≤ G, and the remaining tags are considered present. Each tag in the system has a unique 96-bit ID, which accurately identifies its identity, attributes, and other information. The reader communicates with tags within its communication range via radio frequency signals emitted by its antenna. All tag IDs are stored on a backend server, and the reader can access these IDs at any time for real-time tag monitoring. To improve communication efficiency and reduce information conflicts between the reader and tags, communication between the reader and tags is based on the frame-slotted Aloha protocol.

[0050] like Figure 1 The method for detecting lost tags in a multi-group RFID system is described, and includes the following steps:

[0051] Step 1: The reader uses the hash function to map each group of tags to an f g Construct a desired frame vector V from an array of length g ;

[0052] Step 2: The reader combines the group ID, frame length, and random seed of the hash function of each group of tags into a request command, and then polls and broadcasts all request commands;

[0053] Step 3: If the tag receives the broadcast containing the group ID, it sends a 96-bit response message to the reader through the hash function according to the request command broadcast by the reader;

[0054] Step 4: After the reader receives all the tag response information in a time slot, it performs an OR operation on all the response information and adds it to the expected frame vector V. g Perform a comparison and detect whether a label is missing based on the comparison results.

[0055] In a specific embodiment, step 1 includes: the reader performs a hash operation on the IDs of all tags in a group, and the obtained hash result is used to calculate the length of the array f. g The reader uses the remainder as the index value to map the tag to the array. If there is only one tag mapped to a certain position in the array, the position is set to "1", otherwise it is set to "0", that is, "1" indicates that a single time slot is expected, and "0" indicates that an empty time slot and a conflicting time slot are expected. Therefore, the expected frame vector V g The expected single time slot ratio P s for:

[0056]

[0057] When the above formula is derived, it can be found that when N g =f g When P s The maximum value that can be obtained is Therefore, in the method of the present invention, N g The value of f g To maximize the proportion of expected single time slots and improve the utilization of expected single time slots.

[0058] In a specific embodiment, step 3 includes, when the tag receives the group ID to which it belongs, performing a hash operation H(tag ID, R) on the ID using a random seed and performing a frame length f g Take the remainder and record the result as Y i Each tag is based on The value of selects a tag time slot to reply a 96-bit message to the reader. The response message contains 96 bits of "0" and 1 bit of "1", where the index value of "1" in the response is Y i Divide by 96 and take the remainder. When a tag time slot completes, the reader combines all 96 bits of tag response information received into a composite 96-bit vector using an OR operation. If a bit in the composite vector is "0" but the corresponding bit in the expected frame vector is "1", it can be determined that a tag in group g has been lost. The reader immediately stops detecting group g and begins detecting lost tags in the next group by broadcasting parameters such as the group ID, frame length, and random seed of the next group of tags.

[0059] The above detection process is repeated in each group until a group detects a missing label event or r g When all rounds are completed, the reader stops detecting the group and turns to the next group. For any round in any group g, the probability that a lost tag is mapped to an expected single time slot is Then the probability that a lost tag cannot be detected by the expected single time slot in the current round is The probability that a time slot in the current round is an isomorphic time slot is:

[0060]

[0061] Therefore, a missing label passes through r g The probability that the wheel still cannot be detected is:

[0062]

[0063] According to the given detection reliability α g , we have:

[0064] 1-P u ≥α g . (4)

[0065] Right now:

[0066]

[0067] Available from the listing:

[0068]

[0069] but

[0070] is the optimal value to meet the reliability requirements.

[0071] The definition of a homogeneous time slot is: when a time slot is simultaneously mapped by multiple lost labels, the lost label event can still be detected, and such a time slot is defined as a homogeneous time slot.

[0072] Based on the above definition, when a lost tag is mapped into an expected single time slot or a homogeneous time slot, the tag can be detected by the reader as a lost tag.

[0073] In order to further illustrate the advantages of the above method of the present invention, the present invention is further described below with reference to the accompanying drawings and embodiments.

[0074] See also Figure 3 , assuming that the number of tags in a group in the RFID system is 8, tag 8 is the lost tag, and the frame length is assumed to be 10. The reader maps all tags to the expected frame vector V through the hash function g Then the group ID, frame length and random seed R are broadcast to all tags on site. When the tag receives the vector request, it calculates the index value of its selected bit through the random seed, frame length and hash function, and then replies with a 10-bit response vector. Each tag responds to the reader with a 10-bit response message in a tag time slot based on the result of the hash operation. After receiving the responses from all tags in the tag time slot, the reader performs an OR operation on them to generate a new vector 1011010100, and then adds the resultant vector to the expected frame vector V.g Compare, if V g If the bit expected to be "1" is actually "0", the corresponding tag can be determined to be a lost tag. Figure 2 , the reader can find that the bit corresponding to tag 8 is actually "0", so the reader can conclude that tag 8 is a lost tag.

[0075] When the reliability required by the multi-group RFID system is α=0.9 and α=0.99 respectively, the lost tag detection method based on the multi-group RFID system with operable multiple responses (hereinafter referred to as the EMD method) of the present invention is used together with the existing GAB-detect method and SMTD+CC method for lost tag detection. Figure 4 and Figure 5 ,It can be found that the time cost of the three ,methods increases as the number of tags in the system increases, but the time ,efficiency of the EMD method described in the present ,presentation is much higher than the other two methods.

[0076] When the thresholds of lost tags in each group of the multi-group RFID system are M=1 and M=5 respectively, the EMD method of the present invention is used together with the existing GAB-detect method and SMTD+CC method to detect lost tags. Figure 6 and Figure 7 It can be found that as the number of tags in the system increases, the time cost of the three methods also increases, and the higher the required reliability, the more obvious the increase in detection time. However, the time efficiency of the EMD method described in the present invention is still higher than that of the other two methods.

[0077] When the reliability required by the multi-packet RFID system is α=0.9 and α=0.99 respectively, the EMD method of the present invention is used together with the existing GAB-detect method and SMTD+CC method to detect lost tags. Figure 8 and Figure 9 ,As the number of missing labels in each group increases, the ,detection time of the three methods does not change at all, while the time taken by the ,EMD method is less than the other two methods.

[0078] When the reliability required by the multi-packet RFID system is α=0.9 and α=0.99 respectively, the EMD method of the present invention is used together with the existing GAB-detect method and SMTD+CC method to detect lost tags. Figure 10 and Figure 11 , all three methods can meet the given reliability requirements of the system.

[0079] When the thresholds of lost tags in each group of the multi-group RFID system are M=1 and M=5 respectively, the EMD method of the present invention is used together with the existing GAB-detect method and SMTD+CC method to detect lost tags. Figure 12 and Figure 13 ,All three methods can meet the given reliability requirements of the system, but the ,reliability of the EMD method is much higher than the other two ,methods.

[0080] From the above, it can be seen that the lost tag detection method based on the multi-group RFID system with operable multi-response provided by the present invention can efficiently detect the lost tags in the multi-group RFID system, and the reliability fully meets the requirements of the system.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for detecting lost tags in a multi-packet RFID system, characterized in that: All known tags in the system are divided into G groups, and the gth group contains N g , N g ≤ preset value z, 1≤g≤G labels, of which the number of lost labels is m g Each tag has a unique z-bit tag ID and a group ID for tag identity verification, the method comprising: Step 1: The reader maps each set of tags to an f based on the tag ID of the known tag through a hash function. g Construct a desired frame vector V from an array of length g ; Step 2: The reader combines the group ID, frame length, and random seed of the hash function of each group of tags into a request command, and then polls and broadcasts all request commands; Step 3: If the tag receives the broadcast containing the group ID, it sends a 96-bit response message to the reader through the hash function according to the request command broadcast by the reader; Step 4: After the reader receives all the tag response information in a time slot, it performs an OR operation on all the response information and adds it to the expected frame vector V. g Perform a comparison and detect whether a label is missing based on the comparison results; During the detection of a group of lost tags, the reader performs r g Rounds are performed to detect the missing tag events of the group to achieve the required detection accuracy, wherein the number of rounds is determined by the given detection accuracy and the number of missing tags in the group; In step 4, for any round in any group g, the probability that a missing tag is mapped to a desired single time slot is Then the probability that a lost tag cannot be detected by the expected single time slot in the current round is The probability that a time slot in the current round is an isomorphic time slot is: Therefore, a missing label passes through r g The probability that the wheel still cannot be detected is: According to the given detection reliability α g ,have: 1-P u ≥α g (4) That is: According to the above formula (5), we can get: but is the optimal value to meet the reliability requirements.

2. The method for detecting lost tags in a multi-group RFID system according to claim 1, wherein: Step 1 includes: The reader performs a hash operation on the tag IDs in a group of tags through a hash function with a random seed R, and the hash result is f g After taking the remainder, it is mapped to a length of f g In the array, if a bit in the array is mapped by only one label, the bit in the array is set to "1", otherwise it is set to "0". When all label mappings of the group are completed, the expected frame vector V g The construction is completed, and the desired frame vector V g In the example, "1" indicates that a single time slot is desired, and "0" indicates that a non-single time slot is desired.

3. The method for detecting lost tags in a multi-group RFID system according to claim 2, wherein: In step 3, If the tag receives a broadcast containing the group ID to which it belongs, it performs a hash operation H(tag ID, R) on the tag ID using the random seed in the broadcast request command and calculates the frame length f g Take the remainder and record the result as Y i , where H() is a hash function, and each label is based on The value of selects a tag time slot to reply a 96-bit message to the reader. The response message contains 95 bits of "0" and 1 bit of "1", where the index value of "1" in the response message is Y i Divide by 96 and take the remainder.

4. The method for detecting lost tags in a multi-group RFID system according to claim 3, wherein: Step 4 includes: When a tag time slot is completed, the reader performs an OR operation on all 96-bit tag response information received in the tag time slot to form a composite 96-bit vector. When a bit in the composite vector is "0" but the expected frame vector V g When the corresponding bit in is "1", it is determined that there is a lost tag event in the g-th group. The reader stops detecting the g-th group of tags and starts the lost tag detection of the next group of tags by broadcasting a request command consisting of the group ID, frame length and random seed of the next group of tags.

5. The method for detecting lost tags in a multi-group RFID system according to claim 3, wherein: When it is determined that there is a lost tag event in the g-th group, the reader stops detecting the g-group tags and starts the lost tag detection of the next group of tags by broadcasting a request command consisting of the group ID, frame length and random seed of the next group of tags.

6. The method for detecting lost tags in a multi-group RFID system according to claim 1, further comprising: Calculate the expected frame vector V g The expected single time slot ratio P s for: When the above formula is derived, it can be found that when N g =f g When P s Get the maximum value of That is N g The value of f g To maximize the proportion of expected single time slots, to improve the utilization of expected single time slots, where is the probability of expecting a single time slot.

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