RFID tag identification method and system based on collision recovery

Abstract

The invention provides an RFID tag identification method and system based on collision recovery. Based on different attenuation degrees of the signals, the number of the radio frequency signals and different combination states of the signals can be analyzed and obtained through demodulation, IQ mapping and clustering of the radio frequency signals, and then the amplitude component of each radio frequency signal is obtained through decomposition, so that signal recovery can be performed. In this way, repeated sending of label signals is avoided, and identification timeliness is guaranteed. On the other hand, labels do not need to be identified one by one through a complex tree algorithm label identification method, and the identification efficiency is also guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of radio frequency identification (RFID), and in particular to a collision recovery-based RFID tag identification method and system. Background Art

[0002] In the application of RFID technology, anti-collision is a key technical challenge. When multiple RFID tags enter the reading range of the reader at the same time, they may respond to the reader's query at the same time, resulting in signal conflicts and data confusion, which is the so-called tag collision problem. To solve this problem, researchers have developed a variety of anti-collision algorithms.

[0003] The current anti-collision algorithms are mainly divided into two categories: probabilistic anti-collision algorithms and deterministic anti-collision algorithms. Probabilistic algorithms such as the ALOHA algorithm are random access methods. When a collision occurs, all colliding tags must retransmit data, which will increase the response time to varying degrees. Deterministic algorithms such as the binary search algorithm gradually identify each RFID tag by building a query tree to avoid collisions. However, the query efficiency of the tree algorithm is greatly affected by the number of tags. Therefore, there is a lack of an efficient tag identification method. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides an RFID tag recognition method and system based on collision recovery, which mainly solves the problem that the prior art lacks an efficient tag recognition method.

[0005] The objective of the present invention is achieved through the following solutions:

[0006] In a first aspect, according to an embodiment of the present invention, a method for identifying RFID tags based on collision recovery is provided, comprising the following steps: S1, acquiring radio frequency signals in space, and identifying radio frequency signals emitted by multiple RFID tags and overlapping in time; S2, demodulating the radio frequency signals of the identified RFID tags to baseband to form baseband signals; S3, mapping the formed baseband signals to an IQ plane to obtain IQ sample pairs consisting of an in-phase I component and an orthogonal Q component; S4, using a preset clustering algorithm to group IQ sample pairs with similar characteristics to form a cluster set, wherein each cluster set represents a different amplitude combination of different signals; S5, determining the number of RFID tags based on the number of cluster sets, and then determining the amplitude combination state of each RFID tag in each cluster set based on the number of RFID tags and the relative size of the IQ sample values ​​in different cluster sets, and further obtaining the amplitude of each RFID tag corresponding to each IQ sample pair based on the amplitude combination state of each RFID tag; S6, performing data recovery based on the obtained amplitude of each RFID tag.

[0007] According to an embodiment of the present invention, the radio frequency signal in space includes a reader query signal, an RFID tag response signal and a continuous wave signal.

[0008] According to an embodiment of the present invention, radio frequency signals in the space are all configured based on the same RFID communication standard.

[0009] According to an embodiment of the present invention, the RFID communication standard includes the Gen2 protocol and the ISO 18000-6C air interface protocol.

[0010] According to an embodiment of the present invention, when the RFID communication standard is the Gen2 protocol, the RFID tag response signal is an RN16 signal.

[0011] According to an embodiment of the present invention, the radio frequency signals emitted by multiple RFID tags and overlapping in time are identified as follows: S11, distinguishing the reader query signal and the RFID tag response signal based on the code length and the signal amplitude; S12, identifying the radio frequency signals overlapping in time based on whether they can be resolved.

[0012] According to an embodiment of the present invention, the radio frequency signal emitted by the RFID tag is encoded with a double-phase-space code.

[0013] According to an embodiment of the present invention, the collision recovery-based RFID tag identification method further includes step S13: performing secondary sampling on the radio frequency signal at the lowest data transmission rate.

[0014] According to an embodiment of the present invention, the RFID tag identification method based on collision recovery further includes step S14: using abnormal flag bits for detection and positioning.

[0015] In a second aspect, according to another embodiment of the present invention, a collision recovery-based RFID tag identification system is provided, comprising: an RFID tag, for generating and transmitting a response signal based on a received query signal; an RFID reader, configured to send a query signal and receive a response signal, and identify the RFID tag according to the collision recovery-based RFID tag identification method described in the first aspect.

[0016] Compared with the prior art, the present invention has the following beneficial effects: based on the different attenuation levels of the signal, by demodulating the RF signal, IQ mapping and clustering, the number of RF signals and the different combination states of the signal can be analyzed, and then the amplitude component of each RF signal can be obtained by decomposition, so that the signal can be restored. This avoids repeated transmission of tag signals and ensures the timeliness of identification; secondly, there is no need to use a complex tree algorithm tag identification method to identify tags one by one, which also ensures the efficiency of identification. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The embodiments of the present invention are further described below with reference to the accompanying drawings:

[0018] Figure 1 A schematic diagram of the composition of an existing tag identification system according to an embodiment of the present invention;

[0019] Figure 2 A schematic diagram of a curve of a collision tag signal according to an embodiment of the present invention;

[0020] Figure 3 A schematic diagram of a flow chart of an RFID tag identification method based on collision recovery according to an embodiment of the present invention;

[0021] Figure 4 It is a constellation diagram obtained by IQ mapping in the RFID tag identification method based on collision recovery in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] Before proceeding to the following detailed description, it may be advantageous to set forth the definitions of certain words and phrases used throughout this patent document. The terms "coupling", "connection" and their derivatives refer to any direct or indirect communication or connection between two or more elements, regardless of whether those elements are in physical contact with each other. The terms "transmission", "reception" and "communication" and their derivatives cover direct and indirect communication. The terms "include" and "comprising" and their derivatives refer to including but not limited to. The term "or" is inclusive, meaning and / or. The phrase "associated with..." and its derivatives refer to including, including within, interconnecting, containing, contained within, connecting or connecting with, coupling or coupling with, communicating with, cooperating, interweaving, parallel, close to, binding or binding with, having, having attributes, having a relationship or having a relationship with, etc. The term "controller" refers to any device, system or part thereof that controls at least one operation. Such a controller can be implemented with hardware, or a combination of hardware and software and / or firmware. The functions associated with any particular controller can be centralized or distributed, whether local or remote. The phrase "at least one of", when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one of the items in the list may be required. For example, "at least one of A, B, C" includes any of the following combinations: A, B, C, A and B, A and C, B and C, A and B and C.

[0023] Definitions for other specific words and phrases are provided throughout this patent document. Those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior and future uses of such defined words and phrases.

[0024] In this patent document, the application combination of modules and the division level of sub-modules are only used for illustration, and the application combination of modules and the division level of sub-modules may have different forms without departing from the scope of the present disclosure.

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] In order to better understand the present invention, conventional RFID identification is first reviewed.

[0027] like Figure 1As shown, in the RFID system, the communication process usually starts from the reader (SDR-Reader), which first sends a query command (Query), which contains specific parameters that require the tags (Tag1 and Tag2) to respond, such as the requested tag ID range. The reader broadcasts this query command at a specific frequency through its transmitting antenna (Tx). When the RFID tag enters the signal range of the reader, the tag's antenna (not shown) receives the query signal. After the chip inside the tag detects the query parameters that match it, it will generate a random number (such as RN16 in the EPC Gen2 protocol) according to the protocol requirements, and send this RN16 random number and the Electronic Product Code (EPC) back to the reader through its antenna in a backscatter manner. After receiving these reflected signals, the reader (through Rx) performs demodulation processing and extracts the tag's response data. The reader also sends an acknowledgment signal (ACK) as a response to the tag's response to complete a complete communication interaction process.

[0028] When an RFID system begins communicating, the reader's receiving antenna continues to collect data until the communication stops. The reader receives information from the tag by sending a continuous wave (CW) RF signal to the tag; the tag responds by modulating the reflection coefficient of its antenna, thereby backscattering the information signal to the reader. This means that the tag will only modulate its antenna reflection coefficient with an information signal after being instructed by the reader.

[0029] In addition, in order to complete the above communication process, the reader needs to be properly configured. First, the reader's transceiver frequency needs to be configured to correspond to the working frequency band of the RFID tag, such as 860-960MHz in the UHF band; then set a suitable sampling rate to ensure that the signal can be accurately digitized, while avoiding excessive sampling rates that increase the burden of data processing; connect the transmitter antenna (Tx) and the receiver antenna (Rx) respectively, the former is used to send query instructions, and the latter is used to receive the wireless signal reflected by the RFID tag, which will be captured by the reader's RF front end and converted into a baseband signal; then, filter, demodulate and synchronize the baseband signal to extract useful data segment information.

[0030] It can be seen that, as described in the background technology, the prior art does not involve effective processing for collision signals. Figure 2 As shown, it can be seen that in some time periods, due to the superposition of multiple signals, the signal fluctuations are disordered, and at this time, the reader cannot resolve the signals of each RFID tag.

[0031] Regarding the above issues, Figure 3 As shown, according to an embodiment of the present invention, a method for identifying RFID tags based on collision recovery is provided, comprising the following steps: S1, acquiring radio frequency signals in space, and identifying radio frequency signals emitted by multiple RFID tags and overlapping in time; S2, demodulating the radio frequency signals of the identified RFID tags to baseband to form baseband signals; S3, mapping the formed baseband signals to the IQ plane to obtain IQ sample pairs consisting of in-phase I components and orthogonal Q components; S4, using a preset clustering algorithm to group IQ sample pairs with similar characteristics to form a cluster set, wherein each cluster set represents a different amplitude combination of different signals; S5, determining the number of RFID tags based on the number of cluster sets, and then determining the amplitude combination state of each RFID tag in each cluster set based on the number of RFID tags and the relative size of the IQ sample values ​​in different cluster sets, and further obtaining the amplitude of each RFID tag corresponding to each IQ sample pair based on the amplitude combination state of each RFID tag; S6, performing data recovery based on the obtained amplitude of each RFID tag. Based on the different attenuation levels of the signal, the number of RF signals and the different combination states of the signals can be analyzed through RF signal demodulation, IQ mapping and clustering, and the amplitude component of each RF signal can be decomposed to recover the signal. This avoids repeated transmission and ensures timely identification; secondly, there is no need to use a complex tree algorithm label identification method to identify one by one, which also ensures the efficiency of identification.

[0032] Reference again Figure 1 According to an embodiment of the present invention, the radio frequency signal in the space includes a reader query signal, an RFID tag response signal and a continuous wave signal. Among them, the reader query signal comes from the reader and is used to issue instructions and control signals. The RFID tag response signal comes from a tag in the nearby range and is used to return its stored information. The continuous wave (CW) radio frequency signal is used to receive information from the tag. In addition, in order to ensure the consistency of signal transmission of the entire system, according to an embodiment of the present invention, the radio frequency signals in the space are all configured based on the same RFID communication standard. According to an embodiment of the present invention, the RFID communication standard includes the Gen2 protocol and the ISO 18000-6C air interface protocol. In addition, according to an embodiment of the present invention, when the RFID communication standard is the Gen2 protocol, the RFID tag response signal is an RN16 signal.

[0033] In addition, in order to effectively extract the collision signal, according to the embodiment of the present invention, the radio frequency signals emitted by multiple RFID tags and overlapping in time are identified as follows: S11, distinguishing the reader query signal and the RFID tag response signal based on the code length and signal amplitude; S12, identifying the radio frequency signals overlapping in time based on whether they can be parsed. The reason is that for the reader query signal and the RFID tag response signal, both use binary coding, but the data structure may be different, that is, different encoding methods are used; in addition, in terms of data length, the reader data is usually shorter and only contains the necessary command information, while the tag data may be longer depending on the storage capacity and requirements; in addition, in terms of modulation method, the reader may use modulation techniques such as ASK or FSK, while the tag may use backscattering modulation methods such as PSK or OOK.

[0034] According to an embodiment of the present invention, the radio frequency signal emitted by the RFID tag is encoded with dual phase-space coding. As is well known, dual phase-space coding (FM0) is a coding method for tag data transmission, which represents binary data by changing the phase of the signal. In FM0 coding, binary data "0" is usually represented by a 180-degree phase jump of the signal, while binary data "1" is represented by no phase jump, that is, the signal maintains the current phase. This encoding method ensures that the transmission of each bit is accompanied by a detectable phase change, thereby allowing the receiver to recover the original binary data by detecting the phase change.

[0035] Due to the FM0 coding characteristics and noise interference during the communication process, the points on the constellation diagram will cluster. Using relevant clustering algorithms (such as k-means), a set of similar clusters can be obtained. Each cluster represents a specific combination state of the signal. As we all know, in terms of amplitude, the superposition of signals is generally the superposition of amplitudes. Take two signals as an example, namely, 00, 10, 01 and 11. However, it is generally difficult for the reader to decipher this superimposed amplitude because it is inconsistent with the expected identifier (such as an identification code). The applicant found that after demodulating and IQ mapping the superimposed signal, the points on the constellation diagram will form clusters, and the number of these clusters is related to the superposition of signals. For example, in a single tag reply scenario, two clusters are formed, one cluster may represent binary "0" and the other cluster may represent binary "1". In a multi-tag collision scenario, for example, 2 tags collide, such as Figure 4As shown, compared with the single tag case, there are four cluster symbols in the received signal: [h1+0h2], [0h1+h2], [h1+h2], [0h2+0h1], that is, each cluster symbol represents an amplitude combination. Among them, 0h2 and 0h1 represent low levels, h1 and h2 represent high levels, and the relative size relationship of the IQ sample values ​​in each cluster can also be clearly judged from the figure. For example, the top cluster symbol is related to two high-level combinations, the left cluster symbol and the left cluster symbol are related to a high-low level combination, and the lower cluster symbol is related to two low-level combinations. Therefore, it can be concluded which level combination each cluster corresponds to. Therefore, the level corresponding to the IQ sample of each RFID tag can also be obtained.

[0036] According to an embodiment of the present invention, in order to reduce the impact caused by the environment, a digital filter is used to reduce the high-frequency noise in the baseband signal. Noise interference, such as multipath effect, signal attenuation, environmental noise, etc., will cause the distribution of points on the constellation diagram to change, thereby affecting the formation of clusters. These interferences may cause the diffusion or offset of the cluster, thereby affecting the demodulation and recognition of the signal.

[0037] In addition, according to the Gen2 protocol, the tag adjusts the bit length of its data transmission, including the duration of 0 and 1, by the channel characteristics of the backscatter link. The reader shall add the length of the data 0 symbol to the length of the data 1 symbol (RTcal=0length+1length). The reader shall use the TRcal and division ratio (DR) in the preamble and payload of the query command to specify the tag's backscatter link frequency (its FM0 data rate or the frequency of its Miller subcarrier). BLF (Backscatter Link Frequency) represents the frequency characteristics of the backscatter channel, which affects how the tag adjusts the bit length of its signal to optimize communication performance. The following formula specifies the relationship between the backscatter link frequency (BLF), TRcal and DR:

[0038]

[0039] In addition, the TRcal and RTcal used by the reader in any inventory round should satisfy the following formula:

[0040] 1.1×RTcal≤TRcal≤3×RTcal.

[0041] In order to unify the results of different nominal bit durations of tags, according to an embodiment of the present invention, the RFID tag identification method based on collision recovery further includes step S13: resampling the radio frequency signal at the lowest data transmission rate (40KHz). In detail, in the scenario of multiple tag transmissions, the time when different tag signals arrive at the receiving end is inconsistent. Assume that the data bit durations of tag 1 and tag 2 are TRcal1 and TRcal2 respectively, then T sample =min{TRcal1,TRcal2}.

[0042] In addition, in order to further achieve the synchronization of the collision signal, according to an embodiment of the present invention, the RFID tag identification method based on collision recovery further includes step S14: using the abnormal flag bit for detection and positioning. According to the Gen2 protocol, the preambles of different encoding formats have the characteristics of a fixed format. For example, in the tag data of the FM0 encoding format, the preamble part of the data is fixed to: '1010v1'. Therefore, after the uniform bit duration, the abnormal flag bit ('v') is used for detection and positioning.

[0043] In busy warehouse or air logistics center scenarios, the application of RFID systems is essential for efficiently tracking and managing large quantities of goods. In these environments, goods are often stored on dense shelves or closely arranged during transportation, resulting in very small spacing between RFID tags. This dense layout increases the risk of multi-tag collision problems, that is, when the reader sends a query signal, multiple tags may respond at the same time, causing signal overlap and interference, thereby affecting the accurate reading of data. In order to address this challenge, the present invention implements these collision recovery strategies, and the RFID system can significantly improve the reading efficiency and accuracy in dense storage environments. This not only speeds up the speed of goods in and out of the warehouse, but also improves the accuracy of air baggage handling, ensuring the smooth progress of logistics operations. In addition, the implementation of these strategies also helps to reduce the number of read failures and rereads caused by collisions, thereby reducing overall operating costs.

[0044] According to another embodiment of the present invention, a collision recovery-based RFID tag identification system is provided, comprising: an RFID tag for generating and transmitting a response signal based on a received query signal; an RFID reader configured to send a query signal and receive a response signal, and identify the RFID tag according to a collision recovery-based RFID tag identification method as described above.

[0045] The present invention may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present invention.

[0046] Computer readable storage medium can be a tangible device that holds and stores instructions used by an instruction execution device. Computer readable storage medium can include, for example, but is not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination thereof. More specific examples (non-exhaustive list) of computer readable storage medium include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, for example, a punch card or a protruding structure in a groove on which instructions are stored, and any suitable combination thereof.

[0047] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A RFID tag recognition method based on collision recovery, characterized in that: The following steps are involved: S1, acquiring radio frequency signals in space, and identifying radio frequency signals emitted by multiple RFID tags and overlapping in time; S2, demodulating the radio frequency signal of the identified RFID tag to a baseband to form a baseband signal; S3, mapping the formed baseband signal to an IQ plane to obtain an IQ sample pair consisting of an in-phase I component and an orthogonal Q component; S4. Using a preset clustering algorithm, IQ sample pairs with similar characteristics are grouped into a group to form a cluster set, wherein each cluster set represents a different amplitude combination of different signals; S5. Determine the number of RFID tags based on the number of cluster sets, determine the amplitude combination state of each RFID tag in each cluster set based on the number of RFID tags and the relative size of the IQ sample values ​​in different cluster sets, and further obtain the amplitude of each RFID tag corresponding to each IQ sample pair based on the amplitude combination state of each RFID tag; S6. Perform data recovery based on the obtained amplitude of each RFID tag.

2. The RFID tag recognition method based on collision recovery according to claim 1, characterized in that: The radio frequency signals in space include reader query signals, RFID tag response signals and continuous wave signals.

3. The RFID tag recognition method based on collision recovery according to claim 2 is characterized in that: The radio frequency signals in the space are all configured based on the same RFID communication standards.

4. The RFID tag recognition method based on collision recovery according to claim 3 is characterized in that: RFID communication standards include the Gen2 protocol and the ISO 18000-6C air interface protocol.

5. The RFID tag recognition method based on collision recovery according to claim 4 is characterized in that: When the RFID communication standard is the Gen2 protocol, the RFID tag response signal is an RN16 signal.

6. The RFID tag recognition method based on collision recovery according to claim 2, characterized in that: It is identified that the radio frequency signals emitted by multiple RFID tags and overlap in time are: S11, distinguishing the reader query signal and the RFID tag response signal based on the code length and signal amplitude; S12: Identify the radio frequency signals that overlap in time based on whether they can be resolved.

7. The RFID tag recognition method based on collision recovery according to claim 1, characterized in that: The radio frequency signal emitted by the RFID tag is encoded with a double-phase space number.

8. The RFID tag recognition method based on collision recovery according to claim 7, characterized in that: The method further comprises step S13: performing secondary sampling on the radio frequency signal at the lowest data transmission rate.

9. The RFID tag recognition method based on collision recovery according to claim 8, characterized in that: The method also includes step S14: using an abnormal flag to detect and locate.

10. An RFID tag recognition system based on collision recovery, characterized in that: include: An RFID tag, configured to generate and transmit a response signal based on receiving the query signal; The RFID reader is configured to send an inquiry signal and receive a response signal, and identify the RFID tag according to the RFID tag identification method based on collision recovery according to any one of claims 1-9.

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