A high-frequency RFID system decoding method based on synchronous index dynamic adjustment

Abstract

The application relates to a high-frequency RFID system decoding method based on synchronous index dynamic adjustment and belongs to the field of radio frequency identification. The application calibrates the starting point of a start of frame (SOF) pulse propagation time delay; under the condition of SOF time delay precision, the high-frequency RFID system decoding method based on synchronous index dynamic adjustment; under the condition of SOF time delay deviation, the high-frequency RFID system decoding method based on synchronous index dynamic adjustment. The method disclosed by the application realizes the decoding of a high-frequency RFID system, through 8 times bit over-sampling, the introduction of synchronous index dynamic adjustment and a dynamic window judgment mechanism, the stable extraction and analysis of tag data under non-ideal conditions such as noise, multi-tag conflict and signal distortion can be realized, the reliability problem of tag information decoding of a reader under a complex environment is effectively solved, and the reading accuracy and anti-interference ability of the system are obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of radio frequency identification, specifically relating to a decoding method for a high-frequency RFID system based on dynamic adjustment of synchronous index. Background Technology

[0002] High-frequency RFID systems have advantages over other frequency band RFID systems due to their operating frequency band and magnetic field coupling principle, such as being insensitive to liquids; having a controllable reading range and being less prone to misreading; and being able to accurately read densely stacked RFID tags. Therefore, they are widely used in industries such as document management and smart warehousing.

[0003] However, in the hardware design of the reader, the RF front-end uses an envelope detector to extract the envelope signal from the high-frequency signal. However, due to factors such as nonlinear distortion, bandwidth limitations, and component parameter deviations, the waveform of the resulting envelope may be distorted after the non-ideal processing of the RF circuit. It no longer presents a standard pulse waveform, but rather phenomena such as blurred rising / falling edges, amplitude fluctuations, or bottom clipping distortion, instead of a standard Manchester encoded waveform. This waveform distortion will significantly increase the frame synchronization error and seriously interfere with the decoding circuit's accurate judgment of bit boundaries, thus introducing bit errors. For example, when sampling in a noisy environment, if the sampling time is not accurately aligned with the effective range of the signal, but is in the rising edge stage of the distorted waveform, it will introduce incorrect level judgment. If the system timing control is inaccurate and the delay estimation is biased, it will further aggravate the offset of SOF (Start of Frame) detection. As a key marker for the start of a frame, the detection deviation of SOF will directly lead to frame synchronization failure. Ultimately, due to the incorrect synchronization position, the decoder cannot correctly parse the data format, and subsequent checks (such as CRC) will also fail due to data misalignment, causing the entire communication process to be interrupted. Therefore, decoding tag information by a reader is a fragile process, susceptible to signal attenuation, waveform distortion, environmental interference noise, multi-tag collisions, and encoding verification challenges. These factors often intertwine and work together to lead to decoding errors.

[0004] Therefore, there is an urgent need for a highly reliable decoding method for high-frequency RFID systems to improve data decoding accuracy and anti-interference capabilities under non-ideal channel conditions, thus meeting the needs of practical RFID applications. This invention is precisely designed to meet this practical need. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] The technical problem to be solved by this invention is how to provide a high-frequency RFID system decoding method based on dynamic adjustment of synchronization index, so as to solve the problems of signal synchronization difficulties and reduced data decoding reliability caused by non-ideal conditions such as waveform distortion, environmental interference noise, and multi-tag conflict.

[0007] (II) Technical Solution

[0008] To address the aforementioned technical problems, this invention proposes a decoding method for a high-frequency RFID system based on dynamic adjustment of synchronization index. This method includes:

[0009] (1) Determine the starting point of the SOF pulse propagation delay in the initial frame;

[0010] (2) Under the condition of accurate SOF delay, high-frequency RFID system decoding is performed based on the synchronization index;

[0011] Ideally, the maximum amplitude index SycIndex is calculated using the logical "1" bits in the 8x oversampled SOF, where SycIndex ≤ 3. Based on this, the two comparison points for each subsequent data bit are dynamically located in a 16-bit circular buffer: MaxFront = (SycIndex + 4n) % 16, MaxRear = (SycIndex + 4 + 4n) % 16, where n = 0 corresponds to an SOF logic "1", n = 2, 4, ..., N, where N is an even number, corresponding to n / 2 data bits. According to the Manchester encoding rules, stable decoding is achieved by comparing the magnitudes of the two points to determine the bit.

[0012] (3) Under the condition of SOF delay deviation, high frequency RFID system decoding is performed based on dynamically adjusted synchronization index;

[0013] Under non-ideal conditions, when the synchronization index SycIndex > 3, the sampled data is stored in a 16-bit circular buffer via DMA and updated using a sliding window. During decoding, the comparison point positions MaxFront = (SycIndex + 8n) % 16 and MaxRear = (SycIndex + 4 + 8n) % 16 are dynamically calculated, where n = 0 corresponds to SOF logic "1", and n = 1, 2, ..., N corresponds to the nth data bit. Bit decision is achieved by comparing amplitudes according to Manchester coding rules.

[0014] (III) Beneficial Effects

[0015] This invention proposes a decoding method for high-frequency RFID systems based on dynamic adjustment of the synchronization index. The proposed method realizes the decoding of high-frequency RFID systems. By oversampling the bits by 8 times, introducing dynamic adjustment of the synchronization index and a dynamic window decision mechanism, it can achieve stable extraction and parsing of tag data under non-ideal conditions such as noise, multi-tag collisions and signal distortion. It effectively solves the reliability problem of reader decoding tag information in complex environments and significantly improves the system's reading accuracy and anti-interference ability. Attached Figure Description

[0016] Figure 1 This invention provides a high-frequency RFID system decoding method based on dynamic adjustment of synchronization index under precise delay conditions.

[0017] Figure 2 A decoding method for high-frequency RFID systems based on dynamic adjustment of synchronization index under the condition of time delay deviation. Detailed Implementation

[0018] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0019] This invention discloses a high-frequency RFID system decoding method based on dynamic adjustment of synchronization index, applicable to decoding from tag to reader in a high-frequency RFID system based on 18000-3M. The method mainly includes: (1) calibrating the starting point of the propagation delay of the Start of Frame (SOF) pulse; (2) a high-frequency RFID system decoding method based on dynamic adjustment of synchronization index under the condition of accurate SOF delay. Under ideal conditions, the SOF delay is accurate. By oversampling the logical "1" bit in the SOF by 8 times, the index of the maximum amplitude point, i.e., the synchronization index SycIndex, is calculated. Based on this, the two comparison points of each subsequent bit data are dynamically located in a 16-bit circular buffer: MaxFront = (SycIndex + 4n) % 16, MaxRear = (SycIndex + 4 + 4n) % 16. According to the Manchester coding rules, stable decoding is achieved by comparing the magnitude of the two points to determine the bit; (3) a high-frequency RFID system decoding method based on dynamic adjustment of synchronization index under the condition of SOF delay deviation. Under non-ideal conditions, with SOF delay deviation and a synchronization index SycIndex > 3, sampled data is stored in a 16-bit circular buffer via DMA (Direct Memory Access) and updated using a sliding window. During decoding, the comparison point positions MaxFront = (SycIndex + 8n) % 16 and MaxRear = (SycIndex + 4 + 8n) % 16 are dynamically calculated. Bit decision is achieved by comparing amplitudes according to Manchester encoding rules, effectively overcoming synchronization deviation and ensuring reliable decoding.

[0020] The problem this invention aims to solve is how to provide an RFID system decoding method to address the difficulties in signal synchronization and the decrease in data decoding reliability caused by non-ideal conditions such as waveform distortion, environmental interference noise, and multi-tag conflicts.

[0021] To address the above technical challenges, this invention proposes a decoding method for an RFID system based on dynamic adjustment of a synchronization index. This method includes the following steps:

[0022] (1) SOF pulse delay start point calibration

[0023] To accurately detect SOF (Signal of Frame) and determine its precise start time during frame synchronization in an RFID system, background noise is first sampled during the unmodulated period before the tag responds to SOF. The maximum value among these samples is taken, and a predetermined correction value is added to this value to overcome random interference and ensure robustness, together forming a noise threshold. Subsequently, the system compares subsequent signal sampling points with this noise threshold. When the level of consecutively detected sampling points exceeds this threshold, it is determined as the edge trigger point of SOF, and this instant is marked as the start time of SOF pulse delay. From this moment, the system activates a high-precision timer to perform precise delays according to the strict time intervals specified by the communication protocol, in order to accurately align and parse subsequent data frames.

[0024] (2) In the ideal case of accurate SOF delay, high-frequency RFID system decoding is based on synchronization index.

[0025] Ideally, the system timing control is precise. After accurately delaying the SOF, the logical "1" encoded bits of the SOF field in the tag response signal are oversampled by 8 times. The position index of the point with the largest amplitude among the 8 sampled points is denoted as SycIndex. According to the Manchester coding characteristics and the coding rule that the end of the SOF is fixed as a bit "1", this maximum value point should be located within the first half of the bit window. Therefore, the ideal value range of SycIndex is [0,3], and it can be further deduced that the position index of the minimum value point in the same bit window is SycIndex+4.

[0026] In the subsequent data storage and decision decoding stages, the system samples each bit of the tag response eight times. During data storage, the system configures the ADC (Analog-to-Digital Converter) to operate in cyclic scanning mode, using DMA to store the sampled data in a 16-bit circular buffer (ADCbuffer) to achieve sliding window data updates. After the sampled data storage is complete, the system dynamically determines the positions of the two comparison points in the circular buffer based on the previously calculated SycIndex.

[0027] MaxFront=(SycIndex+4n)%16;

[0028] MaxRear=(SycIndex+4+4n)%16;

[0029] When n = 0, it corresponds to the SOF logic value of "1". When n = 2, 4, ..., N, N is an even number, which corresponds to n / 2 data bits.

[0030] According to the Manchester encoding rules, bit decisions are made for the two comparison points: if MaxFront is less than MaxRear, it is judged as "0"; if it is greater, it is judged as "1"; if they are equal, a decoding error is marked. Stable decoding is achieved by comparing the maximum values ​​of the first and second halves of the bit window, as shown in Table 1. Finally, the sampled point sequence is mapped back to the original data bit stream to complete the entire decoding process.

[0031] (3) Under non-ideal conditions of SOF delay deviation, high-frequency RFID system decoding is based on dynamically adjusted synchronization index.

[0032] Under non-ideal conditions such as clock deviation, signal distortion, or noise interference, when sampling the logical "1" bit code of the tag response SOF, due to delay error, the first sampling may capture the low-level segment of the SOF modulation pulse, causing the calculated synchronization index SycIndex to exceed the theoretical value range [0,3], i.e. SycIndex>3, which is considered a non-ideal situation.

[0033] In non-ideal cases, sampled data is stored in a 16-bit circular buffer via DMA. If the number of sample points exceeds 16 bits, new data overwrites the first 8 bits of the buffer, implementing a sliding window data update. During decoding, the positions of the two comparison points in the circular buffer are dynamically determined.

[0034] MaxFront = (SycIndex + 8n) % 16

[0035] MaxRear=(SycIndex+4+8n)%16

[0036] When n is 0, it corresponds to the SOF logic "1"; when n = 1, 2, ..., N, it corresponds to the nth data bit.

[0037] Decoding is performed according to Manchester encoding, as shown in Table 1. This offset calculation based on the abnormal SycIndex essentially dynamically adjusts the sampling window, attempting to realign or compensate in the event of synchronization misalignment, in order to find sampling points that reliably reflect bit values, effectively overcoming the impact of synchronization deviation and ensuring reliable decoding under non-ideal channel conditions.

[0038] Table 1. Decoding Methods for High-Frequency RFID Systems Based on Dynamic Adjustment of Synchronization Index

[0039]

[0040]

[0041] Example 1:

[0042] This invention proposes a method based on synchronous index dynamic adjustment, utilizing oversampling and dynamic window decision-making, and simultaneously considering both SOF standard sampling and delayed sampling, to effectively improve the accuracy of high-frequency RFID systems while ensuring inventory efficiency.

[0043] The process of this method is as follows:

[0044] (1) SOF pulse delay start time calibration

[0045] To accurately detect SOF (Signal of Frame) and determine its precise start time during frame synchronization in an RFID system, background noise is first sampled during the unmodulated period before the tag responds to SOF. The maximum value among these samples is taken, and a predetermined correction value is added to this value to overcome random interference and ensure robustness, together forming a noise threshold. Subsequently, the system compares subsequent signal sampling points with this noise threshold. When the level of consecutively detected sampling points exceeds this threshold, it is determined as the edge trigger point of SOF, and this instant is marked as the start time of SOF pulse delay. From this moment, the system activates a high-precision timer to perform precise delays according to the strict time intervals specified by the communication protocol, in order to accurately align and parse subsequent data frames.

[0046] In practice, the noise floor sampling and threshold calculation are performed first. Before the expected tag response time window, the reader initiates background noise sampling during an unmodulated period, continuously collecting the amplitude of at least five noise points. The maximum value among these samples is denoted as Noisemax, representing the worst-case instantaneous noise level. A predetermined correction value Δ is added to this maximum value. This correction value needs to be set based on the system noise characteristics and experimental experience to overcome random interference and provide a safety margin. The sum of the two is the final noise threshold Noisemax + Δ.

[0047] Then, signal monitoring and trigger determination are performed. The reader begins to continuously sample the tag response signal and compares the level of each sample point with the calculated noise threshold (Noisemax + Δ). In order to filter out occasional spike noise interference, when the average level of multiple consecutive sample points, such as 2-3 points, exceeds the noise threshold, the system determines that a valid signal has been detected.

[0048] Finally, the precise start time is marked and the precise delay is specified by the protocol. The time corresponding to the first sampling point exceeding the threshold is marked as the start time t0 of the SOF pulse delay, such as... Figure 1As shown in the diagram. Starting from the marked start time t0, the system starts a high-precision timer. For example, a precise delay of 23.6μs is performed according to the strict time interval specified in the communication protocol ISO / IEC 18000-3 Mode 3. This delay corresponds to the standard duration of the SOF pulse. After the delay ends, it marks the end of the SOF segment and the beginning of subsequent data bits. The system then starts the sampling and decoding process for the data bits.

[0049] (2) In the ideal case of accurate SOF delay, high-frequency RFID system decoding is based on synchronization index.

[0050] Ideally, the system timing control is precise. After accurately delaying the SOF, the logical "1" encoded bits of the SOF field in the tag response signal are oversampled by 8 times. The position index of the point with the largest amplitude among the 8 sampled points is denoted as SycIndex. According to the Manchester coding characteristics and the coding rule that the end of the SOF is fixed as a bit "1", this maximum value point should be located within the first half of the bit window. Therefore, the ideal value range of SycIndex is [0,3], and it can be further deduced that the position index of the minimum value point in the same bit window is SycIndex+4.

[0051] In the subsequent data storage and decision decoding stages, the system samples each bit of the tag response eight times. During data storage, the system configures the ADC to operate in cyclic scanning mode, using DMA to store the sampled data in a 16-bit circular buffer (ADCbuffer) to achieve sliding window data updates. After the sampled data storage is complete, the system dynamically determines the positions of the two comparison points in the circular buffer based on the previously calculated SycIndex.

[0052] MaxFront=(SycIndex+4n)%16;

[0053] MaxRear=(SycIndex+4+4n)%16;

[0054] When n = 0, it corresponds to the SOF logic value of "1". When n = 2, 4, ..., N, N is an even number, which corresponds to n / 2 data bits.

[0055] According to the Manchester encoding rules, bit decisions are made on two comparison points: if MaxFront is less than MaxRear, it is judged as "0"; if it is greater, it is judged as "1"; if they are equal, a decoding error is marked. Stable decoding is achieved by comparing the maximum values ​​of the first and second halves of the bit window. This maps the sampled point sequence back to the original data bit stream, completing the entire decoding process.

[0056] In practice, the first step is to accurately delay the SOF and locate the key index. After the system accurately delays the SOF, the logical "1" encoded bits of the SOF field in the tag response signal are oversampled by 8 times. This means that within one bit window, eight equally spaced sampling points will be collected, such as... Figure 1 As shown. A bubble sort algorithm is performed on the amplitudes of these 8 oversampled points to find the sampling point with the largest amplitude, and its position index among the 8 points is recorded, denoted as SycIndex. Since the SOF ends with a fixed coded bit "1", its energy or amplitude characteristics will cause the maximum value point to appear in the first half of the bit window; therefore, the ideal range of SycIndex is [0,3]. Considering the waveform symmetry within a single coded window, the position index of the minimum value point within the same bit window can be derived from SycIndex. Under 8x sampling, the formula for calculating the position index of the minimum value point is SycIndex + 4. To determine the optimal sampling point for subsequent data bits, the system dynamically determines the positions of the two comparison points in the circular buffer based on the previously calculated SycIndex:

[0057] MaxFront = (SycIndex + 4n) % 16

[0058] MaxRear=(SycIndex+4+4n)%16;

[0059] When n is 0, it corresponds to the SOF logic "1". When n = 1, 2, ..., N, it corresponds to the nth data bit. For example, n = 2 represents the two half-bit windows before and after the first data bit, and so on.

[0060] Then, data bit sampling and storage are performed. All data bits after SOF are oversampled 8 times, with 8 points sampled from each data bit. The system is configured to operate the ADC in cyclic scanning mode, and DMA is used to automatically store the 16 sampled data points into a 16-bit circular buffer. After the DMA finishes filling the 16 sampled points, the ADC continues to acquire the next 8 points. Because the ADC operates in cyclic mode, these newly acquired 8 points will be written from the beginning of the ADC buffer, i.e., the first 8 elements of the array, thus achieving a sliding window effect and ensuring that the buffer always retains the latest sampled data. Figure 2 As shown.

[0061] Finally, data bit decision and decoding are performed. During decoding, the system dynamically determines the positions of the two comparison points of a data bit in the circular buffer based on the previously calculated BestIndex. Comparison point MaxFront: index position (SycIndex+4n)%16; Comparison point MaxRear: index position (SycIndex+4+4n)%16; where n=0 corresponds to SOF logic "1", n=2,4,...,N, where N is an even number, corresponding to n / 2 data bits.

[0062] According to the rules of Manchester encoding, the decoding logic is as follows: if MaxFront is less than MaxRear, the bit is determined to be logic "0"; if MaxFront is greater than MaxRear, the bit is determined to be logic "1"; if MaxFront equals MaxRear, it means that the level transition characteristic is not obvious and cannot be reliably determined, usually marked as a decoding error, and the system may need to request retransmission or adopt an error correction mechanism. This method combines the efficient data transfer of hardware DMA with the inherent characteristics of Manchester encoding, and resists noise interference by comparing the maximum values ​​of the first and second halves of the bit window, thereby achieving stable decoding.

[0063] (3) Under non-ideal conditions of SOF delay deviation, high-frequency RFID system decoding is based on dynamically adjusted synchronization index.

[0064] Under non-ideal conditions such as clock deviation, signal distortion, or noise interference, when this patent samples the logical "1" bit encoding of the tag response SOF based on the double buffer mechanism, due to delay error, the first sampling may capture the low-level segment of the SOF modulation pulse, causing the calculated synchronization index SycIndex to exceed the theoretical value range [0,3], i.e. SycIndex>3, which is determined to be a non-ideal situation.

[0065] In non-ideal cases, sampled data is stored in a 16-bit circular buffer via DMA. If the number of sample points exceeds 16 bits, new data overwrites the first 8 bits of the buffer, implementing a sliding window data update. During decoding, the positions of the two comparison points in the circular buffer are dynamically determined.

[0066] MaxFront = (SycIndex + 8n) % 16

[0067] MaxRear=(SycIndex+4+8n)%16

[0068] When n is 0, it corresponds to the SOF logic "1"; when n = 1, 2...n, it corresponds to the data bit index.

[0069] According to Manchester encoding, if the former is less than the latter, the current bit is determined to be "0"; otherwise, it is "1". This offset calculation based on the abnormal SycIndex essentially dynamically adjusts the sampling window, attempting to realign or compensate in the event of synchronization misalignment, in order to find a sampling point that can reliably reflect the bit value, effectively overcoming the impact of synchronization deviation and ensuring reliable decoding under non-ideal channel conditions.

[0070] In practice, the synchronization index threshold is first set. The ideal range of the synchronization index SycIndex is defined as [0,3]. Any case where SycIndex>3 will be identified by the system as a non-ideal condition such as clock deviation, signal distortion, or noise interference causing synchronization offset, and the subsequent redundant sampling and dynamic decoding decision mechanism will be activated.

[0071] Then, data bit sampling and storage are performed. Data bit sampling is performed on all data bits after SOF. Each data bit is also oversampled by 8 times, resulting in 8 points per data bit, which are stored in a 16-bit circular buffer (ADCbuffer). After the DMA completes filling the 16 sampling points, the ADC continues to acquire the next 8 points. These newly acquired 8 points are written over the previous 8 elements of the ADCbuffer array, thus achieving a sliding window effect. For each bit that needs to be decoded, the system extracts the corresponding 8 oversampled points from the buffer, i.e., a complete bit window data, such as... Figure 2 As shown.

[0072] Finally, a decoding decision mechanism is implemented. During decoding, the system dynamically determines the positions of the two comparison points in the circular buffer based on the previously calculated SycIndex. The comparison point MaxFront is the value of index position (SycIndex+8n)%16, and the comparison point MaxRear is the value of index position (SycIndex+4+8n)%16. When n is 0, it corresponds to SOF logic "1", and when n = 1, 2, ..., N, it corresponds to the data bit index. This offset calculation based on abnormal SycIndex essentially dynamically adjusts the sampling window, attempting to realign or compensate in the event of synchronization misalignment to find a sampling point that reliably reflects the bit value. According to the Manchester encoding rules, the decoding rules are consistent with the decoding approach under ideal conditions.

[0073] Example 2:

[0074] A decoding method for a high-frequency RFID system based on dynamic adjustment of synchronization index: The method includes the following steps:

[0075] (1) Determine the starting point of the start of the start of frame (SOF) pulse propagation delay;

[0076] (2) Under precise SOF delay conditions, high-frequency RFID system decoding is performed based on the synchronization index. Ideally, the maximum amplitude point index SycIndex is calculated using the logical "1" bit in the 8x oversampled SOF. Based on this, the two comparison points for each subsequent data bit are dynamically located in a 16-bit circular buffer: MaxFront = (SycIndex + 4n) % 16, MaxRear = (SycIndex + 4 + 4n) % 16, where n = 0 corresponds to SOF logic "1", n = 2, 4, ..., N, where N is an even number, corresponding to n / 2 data bits. According to Manchester coding rules, stable decoding is achieved by comparing the amplitude values ​​of the two points to determine the bit position.

[0077] (3) Under SOF delay deviation, high-frequency RFID system decoding is based on dynamically adjusted synchronization index. Under non-ideal conditions, the synchronization index SycIndex>3. The sampled data is stored in a 16-bit circular buffer via DMA and updated using a sliding window. During decoding, the comparison point position MaxFront=(SycIndex+8n)%16 and MaxRear=(SycIndex+4+8n)%16 are dynamically calculated, where n=0 corresponds to SOF logic "1", and n=1,2,…,N corresponds to the nth data bit. The amplitude is compared according to the Manchester coding rule to realize bit decision, effectively overcoming synchronization deviation and ensuring reliable decoding.

[0078] In step (1), the starting point of the start of the propagation delay of the start of frame (SOF) pulse is determined:

[0079] To accurately detect SOF (Signal of Frame) and determine its precise start time during frame synchronization in an RFID system, background noise is first sampled during the unmodulated period before the tag responds to SOF. The maximum value among these samples is taken, and a predetermined correction value is added to this value to overcome random interference and ensure robustness, together forming a noise threshold. Subsequently, the system compares subsequent signal sampling points with this noise threshold. When the level of consecutively detected sampling points exceeds this threshold, it is determined as the edge trigger point of SOF, and this instant is marked as the start time of SOF pulse delay. From this moment, the system activates a high-precision timer to perform precise delays according to the strict time intervals specified by the communication protocol, in order to accurately align and parse subsequent data frames.

[0080] The predetermined correction value can be dynamically adjusted according to the actual channel environment and interference level to adapt to noise backgrounds of different intensities.

[0081] The specific number of consecutive sampling points in the phrase "multiple sampling point levels exceeding the threshold are continuously detected" can be configured according to the fault tolerance requirements of the communication protocol and channel conditions.

[0082] In step (2): Under ideal conditions, the RFID system decodes:

[0083] Ideally, the system timing control is precise. After accurately delaying the SOF, the logical "1" encoded bits of the SOF field in the tag response signal are oversampled by 8 times. The position index of the point with the largest amplitude among the 8 sampled points is denoted as SycIndex. According to the Manchester coding characteristics and the coding rule that the end of the SOF is fixed as a bit "1", this maximum value point should be located within the first half of the bit window. Therefore, the ideal value range of SycIndex is [0,3], and it can be further deduced that the position index of the minimum value point in the same bit window is SycIndex+4.

[0084] In the subsequent data storage and decision decoding stages, the system samples each bit of the tag response eight times. During data storage, the system configures the ADC to operate in cyclic scanning mode, using DMA to store the sampled data in a 16-bit circular buffer (ADCbuffer) to achieve sliding window data updates. After the sampled data storage is complete, the system dynamically determines the positions of the two comparison points in the circular buffer based on the previously calculated SycIndex.

[0085] MaxFront=(SycIndex+4n)%16;

[0086] MaxRear=(SycIndex+4+4n)%16;

[0087] When n = 0, it corresponds to the SOF logic value of "1". When n = 2, 4, ..., N, N is an even number, which corresponds to n / 2 data bits.

[0088] According to the Manchester encoding rules, bit decisions are made on two comparison points: if MaxFront is less than MaxRear, it is judged as "0"; if it is greater, it is judged as "1"; if they are equal, a decoding error is marked. Stable decoding is achieved by comparing the maximum values ​​of the first and second halves of the bit window. This maps the sampled point sequence back to the original data bit stream, completing the entire decoding process.

[0089] Under ideal synchronization conditions, the theoretical range of SycIndex is [0,3], and the positions of the two comparison points are dynamically determined by the following formula:

[0090] MaxFront = (SycIndex + 4n) % 16

[0091] MaxRear=(SycIndex+4+4n)%16

[0092] When n = 0, it corresponds to the SOF logic value of "1". When n = 2, 4, ..., N, N is an even number, which corresponds to n / 2 data bits.

[0093] The sampled data is stored in a 16-bit circular buffer ADCbuffer via DMA. When the sampled data exceeds the buffer capacity, the new data overwrites the old data, realizing sliding window updates and maintaining data continuity.

[0094] In step (3): Under non-ideal conditions, the RFID system decodes:

[0095] Under non-ideal conditions such as clock deviation, signal distortion, or noise interference, when sampling the logical "1" bit encoding of the tag response SOF based on the double buffer mechanism, due to delay error, the first sampling may capture the low-level segment of the SOF modulation pulse, causing the calculated synchronization index SycIndex to exceed the theoretical value range [0,3], i.e. SycIndex>3, which is determined to be a non-ideal situation.

[0096] In non-ideal cases, sampled data is stored in a 16-bit circular buffer via DMA. If the number of sample points exceeds 16 bits, new data overwrites the first 8 bits of the buffer, implementing a sliding window data update. During decoding, the positions of the two comparison points in the circular buffer are dynamically determined.

[0097] MaxFront = (SycIndex + 8n) % 16

[0098] MaxRear=(SycIndex+4+8n)%16

[0099] When n is 0, it corresponds to the SOF logic "1"; when n = 1, 2, ..., N, it corresponds to the nth data bit.

[0100] According to Manchester encoding, if the former is less than the latter, the current bit is determined to be "0"; otherwise, it is "1". This offset calculation based on the abnormal SycIndex essentially dynamically adjusts the sampling window, attempting to realign or compensate in the event of synchronization misalignment, in order to find a sampling point that can reliably reflect the bit value, effectively overcoming the impact of synchronization deviation and ensuring reliable decoding under non-ideal channel conditions.

[0101] Under non-ideal synchronization conditions, when SycIndex > 3, the positions of the two comparison points are dynamically determined by the following formula:

[0102] MaxFront = (SycIndex + 8n) % 16

[0103] MaxRear=(SycIndex+4+8n)%16

[0104] When n is 0, it corresponds to the SOF logic being "1". When n = 1, 2, ..., N, it corresponds to the nth data bit. This method compensates for synchronization deviation by adjusting the position of the comparison point.

[0105] The method proposed in this invention realizes the decoding of high-frequency RFID systems. By oversampling the bits by 8 times, introducing dynamic adjustment of the synchronous index and dynamic window decision mechanism, it can achieve stable extraction and parsing of tag data under non-ideal conditions such as noise, multi-tag conflict and signal distortion. It effectively solves the reliability problem of the reader decoding tag information in complex environments and significantly improves the reading accuracy and anti-interference ability of the system.

[0106] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A decoding method for a high-frequency RFID system based on dynamic adjustment of synchronization index, characterized in that, The method includes: (1) Determine the starting point of the SOF pulse propagation delay in the initial frame; (2) Under the condition of accurate SOF delay, high-frequency RFID system decoding is performed based on the synchronization index; Under ideal conditions, the maximum amplitude point index SycIndex is calculated using the logic "1" bits in the 8x oversampled SOF, where SycIndex ≤ 3. Based on this, the two comparison points for each subsequent data bit are dynamically located in the 16-bit circular buffer: MaxFront = (SycIndex + 4) n )%16, MaxRear=(SycIndex+4+4 n )%16, where n=0 corresponds to SOF logic "1", n=2,4,...,N, where N is an even number, corresponding to n / 2 data bits; according to the Manchester encoding rules, the bits are determined by comparing the magnitudes of two points, thus achieving stable decoding; (3) Under the condition of SOF delay deviation, high frequency RFID system decoding is performed based on dynamically adjusted synchronization index; Under non-ideal conditions, when the synchronization index SycIndex > 3, the sampled data is stored in a 16-bit circular buffer via DMA and updated using a sliding window. During decoding, the comparison point position MaxFront = (SycIndex + 8n)%16 and MaxRear = (SycIndex + 4 + 8n)%16 are dynamically calculated, where n = 0 corresponds to SOF logic "1", and n = 1, 2, ..., N corresponds to the nth data bit. The bit decision is achieved by comparing the amplitude according to the Manchester encoding rule.

2. The high-frequency RFID system decoding method based on dynamic adjustment of synchronization index as described in claim 1, characterized in that, The starting point for determining the SOF pulse propagation delay of the initial calibration frame includes: First, background noise is sampled during the unmodulated period before the tag response SOF. The maximum value among these samples is taken, and a predetermined correction value is added to it to overcome random interference and ensure robustness, together forming the noise threshold. Then, the system compares subsequent signal sampling points with this noise threshold. When the level of a sampling point is continuously detected to exceed the threshold, it is determined as the edge trigger point of SOF start, and this moment is marked as the start time of SOF pulse delay. From this moment, the system starts a high-precision timer to perform precise delay according to the strict time interval specified by the communication protocol, so as to accurately align and parse subsequent data frames.

3. The high-frequency RFID system decoding method based on dynamic adjustment of synchronization index as described in claim 2, characterized in that, Before the expected tag response time window, the reader will start background noise sampling during an unmodulated period, continuously collecting the amplitude of at least 5 noise points. The maximum value among these samples is denoted as Noisemax, which represents the worst-case instantaneous noise level. A predetermined correction value Δ is added to this maximum value. The correction value needs to be set according to the system noise characteristics and experimental experience to overcome random interference and provide a safety margin. The sum of the two is the final noise threshold Noisemax+Δ.

4. The high-frequency RFID system decoding method based on dynamic adjustment of synchronization index as described in claim 2, characterized in that, The time corresponding to the first sampling point that exceeds the threshold is marked as the start time of the SOF pulse delay. t 0; from the start time of the marker t Starting from 0, the system starts a high-precision timer; it performs a precise delay of 23.6μs according to the strict time interval specified by the communication protocol ISO / IEC 18000-3Mode3; this delay corresponds to the standard duration of the SOF pulse. After the delay ends, it marks the end of the SOF segment and the beginning of the subsequent data bits. The system then starts the sampling and decoding process for the data bits.

5. The high-frequency RFID system decoding method based on dynamic adjustment of synchronization index as described in claim 2, characterized in that, The predetermined correction value is dynamically adjusted according to the actual channel environment and interference level to adapt to noise backgrounds of different intensities.

6. The high-frequency RFID system decoding method based on dynamic adjustment of synchronization index as described in claim 1, characterized in that, Ideally, the system timing control is precise. After completing the precise delay of SOF, the logical "1" encoded bits of the SOF field in the tag response signal are oversampled by 8 times. The position index of the point with the largest amplitude among the 8 sampled points is the synchronization index, denoted as SycIndex. According to the Manchester coding characteristics and the coding rule that the end of SOF is fixed as a bit "1", this maximum value point should be located within the first half of the bit window. Therefore, the ideal value range of SycIndex is [0, 3]. Furthermore, the position index of the minimum value point in the same bit window is derived as SycIndex + 4.

7. The high-frequency RFID system decoding method based on dynamic adjustment of synchronization index as described in claim 6, characterized in that, In the ideal scenario of subsequent data storage and decision decoding stages, the system samples each bit of the tag response 8 times. During data storage, the system configures the ADC to operate in cyclic scanning mode and uses DMA to store the sampled data in a 16-bit circular buffer (ADCbuffer) to achieve sliding window data updates. After the sampled data storage is completed, the system dynamically determines the positions of the two comparison points in the circular buffer based on the previously calculated SycIndex. MaxFront=(SycIndex+4 n )%16; MaxRear=(SycIndex+4+4 n )%16; in n =0 corresponds to SOF logic value "1". n =2,4,….,N, where N is an even number, corresponding to n / 2 data bits; According to the Manchester encoding rules, bit decisions are made on the two comparison points: if MaxFront is less than MaxRear, it is judged as "0"; if it is greater than MaxRear, it is judged as "1"; if they are equal, a decoding error is marked. Stable decoding is achieved by comparing the maximum values ​​of the front and back halves of the bit window. Finally, the sampling point sequence is mapped back to the original data bit stream to complete the entire decoding process.

8. The high-frequency RFID system decoding method based on dynamic adjustment of synchronization index as described in claim 1, characterized in that, The non-ideal conditions include: clock skew, signal distortion, or noise interference.

9. The high-frequency RFID system decoding method based on dynamic adjustment of synchronization index as described in claim 1, characterized in that, Under non-ideal conditions, when sampling the logical "1" bit encoding of the tag response SOF, due to delay error, the first sampling may capture the low-level segment of the SOF modulation pulse, causing the calculated synchronization index SycIndex to exceed the theoretical value range [0,3], i.e. SycIndex>3, which is considered a non-ideal situation.

10. The high-frequency RFID system decoding method based on dynamic adjustment of synchronization index as described in claim 9, characterized in that, In non-ideal cases, sampled data is stored in a 16-bit circular buffer via DMA; if the number of sample points exceeds 16 bits, new data overwrites the first 8 bits of the circular buffer, implementing a sliding window data update; during decoding, the positions of the two comparison points in the circular buffer are dynamically determined. MaxFront=(SycIndex+8 n )%16 MaxRear=(SycIndex+4+8 n )%16 in n When the value is 0, the corresponding SOF logic is "1". n When the value is 1, 2, ..., N, it corresponds to the nth data bit; Decoding is performed according to Manchester encoding. If MaxFront is less than MaxRear, the bit is determined to be logic "0"; if MaxFront is greater than MaxRear, the bit is determined to be logic "1"; if MaxFront is equal to MaxRear, it means that the level transition characteristic is not obvious and cannot be reliably determined. It is marked as a decoding error, and the system requests retransmission or adopts error correction mechanism as needed.

Images