An Adaptive Frequency Hopping Pattern Design Method for Passive UHF RFID Systems Based on Power Self-Test

Abstract

The application discloses a passive UHF RFID system adaptive frequency hopping pattern design method based on power self-checking, a signal transmission model is established according to the interference fading characteristics of the passive UHF RFID system, and the next frequency point is derived from the current channel transmission signal fading depth, so that the communication between the reader and the tag is implemented at the new frequency point, the channel fading range is jumped out, the system communication quality is improved, and the adaptive frequency hopping communication of the reader and the tag is completed. The method can make the current communication quickly jump out of the channel fading area, effectively resist the frequency selective fading, improve the system communication quality, solve the phenomena that the current passive UHF RFID system is prone to identification blind area, random narrowband interference, and the like during reading tags, and further cause the problems that the tags cannot be successfully read and the like.

Description

Technical Field

[0001] This invention belongs to the field of radio frequency identification technology, specifically relating to an adaptive frequency hopping pattern design method for a passive UHF RFID system based on power self-testing. Background Technology

[0002] Radio Frequency Identification (RFID) is a non-contact automatic identification technology that uses radio frequency signals to acquire and identify data about objects. Since its inception in the 1940s, RFID technology has gradually spread to various sectors of production and daily life, including public safety, warehousing and logistics, manufacturing, and retail, becoming a cornerstone of the Internet of Things (IoT). Among these, passive ultra-high frequency (UHF) RFID has become a primary method for realizing the IoT due to its advantages such as long reading distance, fast reading speed, and low equipment cost. However, most UHF readers are based on a single frequency point or have a narrow bandwidth, which can easily lead to problems such as blind spots and strong random narrowband interference in practical applications, resulting in the inability to successfully read tags.

[0003] Typical solutions often employ digital frequency hopping and spread spectrum technologies. By setting the center frequency and hopping step on a host computer, frequency hopping can be used to read tags, or pseudo-random codes can be used to spread the transmitted information to alleviate identification failures caused by blind spots and strong interference. However, in the field of passive UHF RFID, spread spectrum technology is not suitable due to the structure and computing power of passive tags. The application of frequency hopping technology focuses more on avoiding reader collisions. In densely deployed environments, multiple readers each maintain a grid of available channels. Combined with channel sensing technology, a carrier hopping occurs when a collision occurs, enabling communication with the tag. This method mitigates identification failures caused by collision interference to some extent, but malicious interference and channel fading may still exist after frequency hopping. Therefore, the design of the frequency hopping pattern is crucial. Numerous research results on frequency hopping pattern design exist in the mobile communication field, such as constructing frequency hopping patterns based on pseudo-random sequences, algebraic construction principles, and interleaving techniques. Parameters such as the basic sequence, the number of available frequency points, and the channel spacing all significantly affect the overall performance of the frequency hopping pattern.

[0004] Among these methods, one approach involves constructing frequency hopping patterns based on pseudo-random sequences. First, a pseudo-random sequence is generated, and each sequence value is mapped one-to-one with available frequency points to form a frequency hopping pattern. Another approach is based on algebraic construction principles. Using polynomial congruence theory, any prime number is selected based on the number of available frequency points, and the congruence equation of the high-order polynomial of the unknowns is solved to establish the frequency hopping pattern. A third approach uses interleaving technology. First, an initial frequency hopping pattern is generated, then an interleaver is constructed, and the initial pattern is fed into the interleaver, undergoing multiple interleaving transformations to produce the final frequency hopping pattern. However, for passive UHF RFID systems with a limited number of available frequency points, existing methods may suffer from short-period phenomena, poor randomness, weak anti-interference capabilities, poor adaptability to dynamic environments, limited frequency hopping pattern capacity, numerous design parameters, difficulty in guaranteeing fading countermeasures, and an inability to fully realize the advantages of frequency hopping communication.

[0005] According to the new regulations of the National Standardization Management Committee on radio management of RFID equipment, the application for type approval of RFID radio transmitting equipment in the 840-845MHz frequency band will no longer be accepted or approved. The frequency band that UHF RFID radio transmitting equipment can use is limited to 920-925MHz, and the channel bandwidth occupied is less than 250KHz. As a result, the number of available frequency points of UHF RFID system is reduced to 20. Under this number of available frequency points, the existing frequency hopping pattern design method is difficult to demonstrate its performance advantages such as randomness, capacity, and wide spacing, that is, it cannot guarantee the fading countermeasure effect. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides an adaptive frequency hopping pattern design method for a passive UHF RFID system based on power self-testing. A signal transmission model is established based on the interference fading characteristics of the passive UHF RFID system, and the next frequency point sufficient to improve the current signal fading is derived from the fading depth of the current channel transmission signal. Communication between the reader and the tag is implemented at the new frequency point, thereby improving the system's communication quality.

[0007] The technical solution adopted in this invention is: an adaptive frequency hopping pattern design method for a passive UHF RFID system based on power self-testing, the specific steps of which are as follows:

[0008] S1. The passive UHF RFID system initializes the configuration of each parameter according to the settings, and then determines whether it is the initial communication. If it is, the first round of identification is performed at the initial working frequency; otherwise, identification continues at the current working frequency.

[0009] S2. Based on step S1, the reader detects the power of the received synthesized signal;

[0010] S3. Determine whether the power of the received composite signal under the current working channel meets the threshold requirement of the number of frequency hopping and the corresponding signal power. If yes, it is considered that the channel supports the current environment transmission and the current working frequency can continue to be used. Proceed to step S6. Otherwise, proceed to step S4.

[0011] S4. Enter the frequency hopping communication stage, perform adaptive frequency hopping design, update the system operating frequency, and record the number of frequency hopping times.

[0012] S5. Determine whether the current frequency hopping has reached the limit of the number of frequency hopping. If so, retain the last working channel identification result, end the current identification, and randomly change the frequency point to return to step S2 for a new round of identification. Otherwise, update the received synthesized signal power value and return to step S3.

[0013] S6. Determine whether all tags have been identified. If not, return to step S1 and continue identifying at the current working frequency. If yes, complete the inventory of all tags.

[0014] Furthermore, in step S1, the passive UHF RFID system includes: a reader, an electronic tag, and corresponding higher-level components.

[0015] The interaction between the reader and the tag is strictly in accordance with the ISO 18000-6C protocol specification. When the reader receives the tag's return signal, it starts to send and execute a power self-test command. The tag does not need to respond to the command. The reader determines the next command based on the self-test result: whether to reply to the tag on the current channel or to change the channel and repeat the query.

[0016] Furthermore, step S3 is specifically as follows:

[0017] Set a threshold set T for determining the number of frequency hopping events. th ={t th1 ,t th2 ,…,t thm}, and the corresponding signal power judgment threshold set Q th ={q th1 ,q th2 ,…,q thm Furthermore, the signal power judgment threshold decreases as the number of frequency hopping increases. When the number of frequency hopping is detected to be within t... thi When the received synthesized signal power is greater than the corresponding power judgment threshold q, thi If the frequency hopping signal indicates that the communication quality of the working channel is better than that of the previous working channel, it can continue to be used, and proceed to step S6; otherwise, proceed to step S4.

[0018] Furthermore, in step S4, the adaptive frequency hopping design is specifically as follows:

[0019] First, a transmission model for the signal in a multipath propagation environment is established, with the following expression:

[0020]

[0021] Where t represents time, f represents the current operating frequency of the system, and a0 represents the effective reflected signal amplitude of the tag. The delay caused by the tag-to-reader deployment distance r0 is represented by c, the propagation speed of electromagnetic waves in free space is represented by n, and the number of multipath propagation paths in the current environment is represented by a. i Indicates the amplitude of each multipath reflection signal. The distance d represents the propagation distance of each multipath path. i The resulting delay, Rx, represents the synthesized signal at the receiving antenna.

[0022] Then the phase of the tag's reflected signal can be obtained. The expression is as follows:

[0023]

[0024] Where k represents the number of periods, and N represents the set of non-negative integers. This indicates the phase within the unit circle.

[0025] Similarly, the phase of the multipath composite reflected signal The delay can be approximated by multipath synthesis. The expression is as follows:

[0026]

[0027] Where d represents the approximate distance of multipath synthesis, and k′ represents the number of periods. This indicates the phase within the unit circle.

[0028] Then, based on the direct proportionality between distance and signal power, the expression for the phase period difference Δk between the tag's reflected signal and the multipath composite reflected signal can be obtained as follows:

[0029]

[0030] Where Δd represents the distance difference between the two. This represents the single-cycle phase difference between the two, where P0 represents the power of the tag-reflected signal, and P... d denoted by , where α represents the power of the multipath synthesized reflected signal, and α represents the loss coefficient.

[0031] When the synthesized signal is attenuating, the phase difference between the tag reflection signal and the multipath synthesized reflection signal... Exceeding a certain phase angle threshold This threshold can be adjusted according to the specific environment and improvement needs, and Then we have:

[0032]

[0033] When deriving the next frequency point, the phase difference between the tag reflection signal and the multipath synthesized reflection signal is used. The reduction is used to enhance the synthesized signal, that is, to design the phase of the multipath synthesized reflection signal after frequency hopping. The expression is as follows:

[0034]

[0035] Based on the relationship between signal phase and frequency, the corresponding frequency point f is... new It is given by the following formula:

[0036]

[0037] The expression for the frequency hopping interval Δf can then be obtained as follows:

[0038]

[0039] The design frequency can then be obtained as follows:

[0040]

[0041] Using the midpoint of the available frequency band as the boundary, if the current operating frequency is located in the first half of the available frequency band, the default design frequency is the current operating frequency plus the frequency hopping interval; otherwise, the design frequency is the current operating frequency minus the frequency hopping interval. The channel center frequency closest to the design frequency is selected from the set of channel center frequencies specified in the protocol as the frequency hopping point for this operation. If the designed frequency hopping interval exceeds the range of available frequency points, the channel center frequency furthest from the current operating frequency is selected from the available frequency range as the frequency hopping point for this operation.

[0042] The beneficial effects of this invention are as follows: The method of this invention establishes a signal transmission model based on the interference fading characteristics of passive UHF RFID systems, and derives the next frequency point from the fading depth of the current channel transmission signal. Communication between the reader and the tag is then implemented at the new frequency point, thus escaping the channel fading range, improving system communication quality, and completing adaptive frequency hopping communication between the reader and the tag. This method enables the current communication to quickly escape the channel fading region, effectively combating frequency-selective fading, improving system communication quality, and solving problems such as blind spots and strong random narrowband interference that easily occur in current passive UHF RFID systems during tag reading, leading to unsuccessful tag reading. Attached Figure Description

[0043] Figure 1 This is a flowchart of an adaptive frequency hopping pattern design method for a passive UHF RFID system based on power self-testing, according to the present invention.

[0044] Figure 2 This is a structural diagram of a passive UHF RFID system in an embodiment of the present invention.

[0045] Figure 3 This is a schematic diagram of the working timing of the passive UHF RFID system in an embodiment of the present invention.

[0046] Figure 4 This is a schematic diagram illustrating the principle of multipath transmission effect in an embodiment of the present invention.

[0047] Figure 5 This is a schematic diagram illustrating the principle of frequency conversion against multipath propagation in an embodiment of the present invention.

[0048] Figure 6 This is a schematic diagram of frequency conversion continuous transmission in an embodiment of the present invention. Detailed Implementation

[0049] The method of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0050] like Figure 1 The flowchart shown is a method for adaptive frequency hopping pattern design in a passive UHF RFID system based on power self-testing according to the present invention. The specific steps are as follows:

[0051] S1. The passive UHF RFID system initializes the configuration of each parameter according to the settings, and then determines whether it is the initial communication. If it is, the first round of identification is performed at the initial working frequency; otherwise, identification continues at the current working frequency.

[0052] S2. Based on step S1, the reader detects the power of the received synthesized signal;

[0053] S3. Determine whether the power of the received composite signal under the current working channel meets the threshold requirement of the number of frequency hopping and the corresponding signal power. If yes, it is considered that the channel supports the current environment transmission and the current working frequency can continue to be used. Proceed to step S6. Otherwise, proceed to step S4.

[0054] S4. Enter the frequency hopping communication stage, perform adaptive frequency hopping design, update the system operating frequency, and record the number of frequency hopping times.

[0055] S5. Determine whether the current frequency hopping has reached the limit of the number of frequency hopping. If so, retain the last working channel identification result, end the current identification, and randomly change the frequency point to return to step S2 for a new round of identification. Otherwise, update the received synthesized signal power value and return to step S3.

[0056] S6. Determine whether all tags have been identified. If not, return to step S1 and continue identifying at the current working frequency. If yes, complete the inventory of all tags.

[0057] like Figure 2 As shown, in this embodiment, in step S1, the passive UHF RFID system includes: a reader, an electronic tag, and corresponding higher-level system components. The passive UHF RFID system utilizes radio frequency to achieve contactless bidirectional data transmission between the reader and the electronic tag, and the higher-level system processes the data to achieve target identification and control. Specifically, the passive UHF RFID system works as follows: the reader radiates a continuous radio frequency signal of a certain frequency through its antenna to activate the system. When a tag within the radiation range receives sufficient energy, it is activated and modulates its stored information onto the received radio frequency carrier. This information is then backscattered through the built-in antenna. The reader receives the reflected signal from the tag, demodulates and decodes it, and sends it to the higher-level system for further processing.

[0058] The operating timing of the passive UHF RFID system is as follows: Figure 3 As shown, the interaction between the reader and the tag is strictly in accordance with the ISO 18000-6C protocol specification. When the reader receives the tag's return signal, it starts to send and execute the power self-test command. The tag does not need to respond to the command. The reader determines the next command based on the self-test result: whether to reply to the tag on the current channel or to change the channel and repeat the query.

[0059] In the actual operation of the passive UHF RFID system, due to different propagation conditions, the transmission of electromagnetic waves involves various situations such as direct transmission, reflection, scattering, and diffraction. The field strength at the receiving antenna is the superposition of all electric fields. Therefore, the accurate identification of a passive UHF RFID system relies on the reliable transmission of electromagnetic waves in the 900MHz band. With the increasing diversity of system application environments and the rapid increase in equipment deployment density, the environments in which readers and tags are located are becoming more complex. Although electromagnetic waves in this band have strong diffraction capabilities and obstacles have a relatively small impact on electromagnetic wave transmission, attenuation and fading inevitably occur during electromagnetic wave transmission.

[0060] Attenuation refers to the reduction in the amplitude of an electromagnetic signal as it travels from the transmitting antenna to the receiving antenna. The attenuation component mainly originates from propagation loss in free space, which is the loss caused by the natural diffusion of energy as the propagation distance increases. This loss L... bf It is related to the system's operating frequency, the deployment location of the reader and the tag, as shown in equation (10):

[0061]

[0062] Where d represents the electromagnetic wave transmission distance and λ represents the operating wavelength.

[0063] Fading refers to the random fluctuations in signal strength at the receiving point over time. Based on different mechanisms, fading can be divided into two types: absorption fading, mainly caused by changes in the electrical parameters of the transmission medium, and interference fading, mainly caused by random multipath propagation. In passive UHF RFID systems, interference fading is the most common type. The signal radiates into free space according to the characteristics of the transmitting antenna beam. When the signal propagates to an obstacle with a geometric size much larger than the operating wavelength, the electromagnetic wave cannot bypass the obstacle and is reflected at the object's surface. When the obstacle's geometric size is smaller than the operating wavelength, or when the obstacle's surface is rough, irregularly shaped, and has little undulation, the electromagnetic wave is scattered at the object's surface.

[0064] Therefore, as Figure 4 As shown, a schematic diagram of the multipath transmission effect principle is presented, in which, Figure 4 (a) is a schematic diagram of a multipath transmission path. Figure 4 (b) is a schematic diagram of multipath superposition transmission. Figure 4 (a) In the operation of the passive UHF RFID system, electromagnetic waves travel through several transmission paths of different lengths to reach the receiving antenna. The receiving antenna captures the composite signal formed by the superposition of all arriving waveforms at that moment. Figure 4 (b) The dashed and double solid lines represent electromagnetic waves propagating along two different paths, while the receiver actually collects the solid line waveform formed by the superposition of the two. It can be seen that as long as the signal propagation delay of either path changes slightly, the intensity of the actual received composite signal will fluctuate significantly.

[0065] In this embodiment, step S3 is specifically as follows:

[0066] Set a threshold set T for determining the number of frequency hopping events. th ={t th1 ,t th2 ,…,t thm}, and the corresponding signal power judgment threshold set Q th ={q th1 ,q th2 ,…,q thm To avoid getting trapped in a frequency hopping loop, the judgment criterion should be appropriately relaxed as the number of frequency hoppings increases; that is, the signal power judgment threshold should decrease as the number of frequency hoppings increases. When the number of frequency hoppings detected is within t... thi When the received synthesized signal power is greater than the corresponding power judgment threshold q, thi If the frequency hopping signal indicates that the communication quality of the working channel is better than that of the previous working channel, it can continue to be used, and proceed to step S6; otherwise, proceed to step S4.

[0067] This embodiment adopts an adaptive frequency hopping pattern synchronization design based on power self-test. The frequency hopping point is derived based on the power detection value of the received synthetic signal during real-time communication. This design can effectively combat time-varying channel narrowband interference and save unnecessary frequency hopping steps.

[0068] In this embodiment, the adaptive frequency hopping design in step S4 is as follows:

[0069] Signal propagation delay is affected not only by the path distance but also by the operating wavelength, such as... Figure 5 As shown, the dashed and double solid lines still represent signals propagating along two different paths, respectively. Their superposition forms the solid line waveform, representing the synthesized signal actually received by the receiver. When the system operating frequency is f1 and the operating wavelength is λ1, multipath superposition weakens the amplitude of the synthesized signal at the receiver. However, changing the system operating frequency to f0 and the operating wavelength to λ0 causes a change in the phase of the signal when it reaches a certain spatial location. In this case, the amplitude of the synthesized signal at the receiver formed by the superposition of multipath signals is enhanced.

[0070] In a variable frequency continuous transmission scenario, a weakened composite signal amplitude indicates that the signal is near a trough, and vice versa, it indicates that the signal is near a peak. Figure 6 As shown. This means that in the operation of a passive UHF RFID system, changing the operating frequency can mitigate the negative impact of the multipath environment, and by making reasonable use of this transmission environment, it is more likely to play a positive role in the communication process.

[0071] Since signal fading is random, we can only grasp the statistical laws governing signal changes over time. When pre-setting frequency hopping patterns to reduce the probability of interference, the focus is usually on the uniformity of frequency hopping points within the bandwidth. However, due to the limited number of available frequencies in current systems, it is difficult to avoid falling into fading channels in applications, and even more difficult to adapt to dynamic environments. Therefore, this embodiment proposes for the first time an adaptive frequency hopping pattern design method for passive UHF RFID systems based on power self-testing. It establishes a signal transmission model based on the interference fading characteristics of UHF RFID systems, derives the next frequency point from the fading depth of the current channel signal, escapes the channel fading range, improves system communication quality, and completes adaptive frequency hopping communication between the reader and the tag.

[0072] First, a transmission model for the signal in a multipath propagation environment is established, with the following expression:

[0073]

[0074] Where t represents time, f represents the current operating frequency of the system, and a0 represents the effective reflected signal amplitude of the tag. The delay caused by the tag-to-reader deployment distance r0 is represented by c, the propagation speed of electromagnetic waves in free space is represented by n, and the number of multipath propagation paths in the current environment is represented by a. i Indicates the amplitude of each multipath reflection signal. The distance d represents the propagation distance of each multipath path. i The resulting delay, Rx, represents the synthesized signal at the receiving antenna.

[0075] Then the phase of the tag's reflected signal can be obtained. The expression is as follows:

[0076]

[0077] Where k represents the number of periods, and N represents the set of non-negative integers. This indicates the phase within the unit circle.

[0078] Similarly, the phase of the multipath composite reflected signal The delay can be approximated by multipath synthesis. The expression is as follows:

[0079]

[0080] Where d represents the approximate distance of multipath synthesis, and k′ represents the number of periods. This indicates the phase within the unit circle.

[0081] Then, based on the direct proportionality between distance and signal power, the expression for the phase period difference Δk between the tag's reflected signal and the multipath composite reflected signal can be obtained as follows:

[0082]

[0083] Where Δd represents the distance difference between the two. This represents the single-cycle phase difference between the two, where P0 represents the power of the tag-reflected signal, and P... d denoted by , where α represents the power of the multipath synthesized reflected signal, and α represents the loss coefficient.

[0084] When the synthesized signal is attenuating, the phase difference between the tag reflection signal and the multipath synthesized reflection signal... Exceeding a certain phase angle threshold This threshold can be adjusted according to the specific environment and improvement needs. For ease of calculation, it is denoted here as [insert threshold here]. Then we have:

[0085]

[0086] The main idea of ​​the adaptive frequency hopping pattern design method is to change the system's operating frequency in the current multipath environment. Since different operating frequencies may introduce new multipath transmissions, the goal is to make the synthesized signal jump out of the trough. The threshold for the trough and intensity improvement can be defined according to environmental needs. When deriving the next frequency point, it is mainly based on the phase difference between the tag's reflected signal and the multipath synthesized reflected signal. The reduction is used to enhance the synthesized signal, that is, to design the phase of the multipath synthesized reflection signal after frequency hopping. The expression is as follows:

[0087]

[0088] Based on the relationship between signal phase and frequency, the corresponding frequency point f is... new It is given by the following formula:

[0089]

[0090] The expression for the frequency hopping interval Δf can then be obtained as follows:

[0091]

[0092] The design frequency can then be obtained as follows:

[0093]

[0094] Using the midpoint of the available frequency band as the boundary, if the current operating frequency is located in the first half of the available frequency band, the default design frequency is the current operating frequency plus the frequency hopping interval; otherwise, the design frequency is the current operating frequency minus the frequency hopping interval. The channel center frequency closest to the design frequency is selected from the set of channel center frequencies specified in the protocol as the frequency hopping point for this operation. If the designed frequency hopping interval exceeds the range of available frequency points, the channel center frequency furthest from the current operating frequency is selected from the available frequency range as the frequency hopping point for this operation.

[0095] In summary, the method of this invention establishes a multipath transmission model for UHF passive RFID signals, analyzes the impact of multipath reflection signal characteristics on the communication process, and employs a frequency hopping pattern design method based on power self-testing to design frequency hopping points that keep the synthesized signal away from the trough. Simultaneously, the workflow and timing of the passive UHF RFID frequency hopping communication system are designed accordingly. Using the method of this invention, current communication can quickly escape the channel fading region, effectively combat frequency-selective fading, and improve system communication quality.

[0096] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A method for designing adaptive frequency hopping patterns for a passive UHF RFID system based on power self-testing, the specific steps of which are as follows: S1. The passive UHF RFID system initializes the configuration of each parameter according to the settings, and then determines whether it is the initial communication. If it is, the first round of identification is performed at the initial working frequency; otherwise, identification continues at the current working frequency. S2. Based on step S1, the reader detects the power of the received synthesized signal; S3. Determine whether the power of the received composite signal under the current working channel meets the threshold requirement for the frequency hopping number and its corresponding signal power. If so, the channel is considered to support the current environment for transmission, and the current operating frequency can continue to be used, proceeding to step S6; otherwise, proceeding to step S4. S4. Enter the frequency hopping communication stage, perform adaptive frequency hopping design, update the system operating frequency, and record the number of frequency hopping times. In step S4, the adaptive frequency hopping point design is as follows: First, a transmission model for the signal in a multipath propagation environment is established, with the following expression: （1）； in, Indicates time, Indicates the current operating frequency of the system. Indicates the effective reflected signal amplitude of the tag. Indicates the distance between the tag and the reader deployment. The resulting delay This represents the speed at which electromagnetic waves propagate in free space. This indicates the number of multipaths in the current environment. Indicates the amplitude of each multipath reflection signal. Indicates the propagation distance of each multipath. The resulting delay This represents the synthesized signal at the receiving antenna; Then the phase of the tag's reflected signal can be obtained. The expression is as follows: （2）； in, Indicates the number of periods. Represents the set of non-negative integers. Indicates the phase within the unit circle; Similarly, the phase of the multipath composite reflected signal The delay can be approximated by multipath synthesis. The expression is as follows: （3）； in, This represents the approximate distance of the multipath synthesis. Indicates the number of periods. Indicates the phase within the unit circle; Then, based on the direct proportionality between distance and signal power, the phase period difference between the tag-reflected signal and the multipath composite reflected signal can be obtained. The expression is as follows: （4）； in, This represents the difference in distance between the two. This represents the single-cycle phase difference between the two. Indicates the power of the tag's reflected signal. This represents the power of the multipath composite reflected signal. Indicates the loss coefficient; When the synthesized signal is attenuating, the phase difference between the tag reflection signal and the multipath synthesized reflection signal... Exceeding a certain phase angle threshold This threshold can be adjusted according to the specific environment and improvement needs, and Then we have: （5）； When deriving the next frequency point, the phase difference between the tag reflection signal and the multipath synthesized reflection signal is used. The reduction is used to enhance the synthesized signal, that is, to design the phase of the multipath synthesized reflection signal after frequency hopping. The expression is as follows: （6）； Based on the relationship between signal phase and frequency, the corresponding frequency hopping point It is given by the following formula: （7）； The frequency hopping interval can then be obtained. The expression is as follows: （8）； The design frequency can then be obtained as follows: （9）； Using the midpoint of the available frequency band as the boundary, if the current operating frequency is located in the first half of the available frequency band, the default design frequency is the current operating frequency plus the frequency hopping interval; otherwise, the design frequency is the current operating frequency minus the frequency hopping interval. The channel center frequency closest to the design frequency is selected from the set of channel center frequencies specified in the protocol as the frequency hopping frequency for this operation. If the designed frequency hopping interval exceeds the range of available frequency points, the channel center frequency farthest from the current operating frequency is selected from the range of available frequency points as the frequency hopping frequency for this operation. S5. Determine whether the current frequency hopping has reached the limit of the number of frequency hopping. If so, retain the last working channel identification result, end the current identification, and randomly change the frequency point to return to step S2 for a new round of identification. Otherwise, update the received synthesized signal power value and return to step S3. S6. Determine whether all tags have been identified. If not, return to step S1 and continue identifying at the current working frequency. If yes, complete the inventory of all tags.

2. The adaptive frequency hopping pattern design method for a passive UHF RFID system based on power self-testing according to claim 1, characterized in that, In step S1, the passive UHF RFID system includes: a reader, an electronic tag, and corresponding higher-level system components; The interaction between the reader and the tag is strictly in accordance with the ISO 18000-6C protocol specification. When the reader receives the tag's return signal, it starts to send and execute a power self-test command. The tag does not need to respond to the command. The reader determines the next command based on the self-test result: whether to reply to the tag on the current channel or to change the channel and repeat the query.

3. The adaptive frequency hopping pattern design method for a passive UHF RFID system based on power self-testing according to claim 1, characterized in that, Step S3 is as follows: Set a set of thresholds for determining the number of frequency hopping events. and the corresponding set of signal power judgment thresholds. Furthermore, the signal power judgment threshold decreases as the number of frequency hopping increases; when the number of frequency hopping is detected to be within a certain range... When the received synthesized signal power is greater than the corresponding power judgment threshold, the signal power is within the threshold value. If the frequency hopping signal indicates that the communication quality of the working channel is better than that of the previous working channel, it can continue to be used, and proceed to step S6; otherwise, proceed to step S4.

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