Disclosure of Invention
The invention provides a self-adaptive range control method and a self-adaptive range control system for combined reading of RFID and bar codes, and aims to solve the problems of high energy consumption, dynamic adaptability, cooperative efficiency, insufficient robustness of complex environments and the like in the prior art.
In order to solve the technical problems, the self-adaptive range control method for combined reading of RFID and bar code provided by the invention comprises the following steps:
capturing a back scattering signal of the tag in real time through the RFID reader-writer, extracting carrier frequency offset, and calculating real-time motion speed and real-time motion direction of the tag based on Doppler effect;
According to the real-time movement speed and the real-time movement direction, the fixed space coordinates of the RFID reader-writer and the bar code scanner are combined, and the first distance between the tag and the RFID reader-writer and the second distance between the tag and the bar code scanner at the next moment are predicted;
Acquiring an RFID effective reading radius and a bar code effective reading distance;
And setting an adjustment strategy to adjust the reading mode according to the relation among the first distance, the second distance, the RFID effective reading radius and the bar code effective reading distance.
Preferably, the specific method for extracting the carrier frequency offset is as follows:
Down-converting the received backscatter signal to baseband or intermediate frequency;
Phase demodulating the down-converted signal to extract instantaneous phase information of the signal;
Calculating at successive time intervalsPhase variation in;
Carrier frequency offsetApproximated as an average of the phase change rates:。
Preferably, the calculation formula of the real-time movement speed is as follows:
In the formula,For the real-time speed of movement of the tag,As the amount of carrier frequency offset,In order to achieve the light velocity, the light beam is,Is the carrier frequency of the RFID reader,An included angle between the movement direction of the tag and the main lobe of the RFID antenna;
Wherein the included angle isThe method comprises obtaining real-time azimuth angle of the tag by using phase difference direction finding method of RFID antenna array, and calculating by combining geometric relationship of tag motion direction and azimuth angleCosine values of (a) are provided.
Preferably, the method for acquiring the effective reading radius of the RFID comprises the following steps:
In the formula,For the RFID to effectively read the radius,For a preset RFID maximum read radius,For the preset attenuation coefficient, the damping coefficient is set,Is the intensity of the ambient electromagnetic noise obtained in real time by the spectrum analyzer.
Preferably, the method for acquiring the effective reading distance of the bar code comprises the following steps:
In the formula,For the effective reading distance of the bar code,For a preset minimum barcode reading distance,As a scale factor, the number of the elements is,For the intensity of the ambient light,Is the minimum effective illumination intensity threshold.
Preferably, the adjustment strategy includes:
if the first distance is less than or equal to the RFID effective reading radius and the second distance is greater than the bar code effective reading distance, activating RFID single mode reading;
If the first distance is greater than the RFID effective reading radius and the second distance is less than or equal to the bar code effective reading distance, activating bar code single mode reading;
if the first distance is smaller than or equal to the effective reading radius of the RFID and the second distance is smaller than or equal to the effective reading distance of the bar code, activating the combined reading of the RFID and the bar code.
Preferably, the calculating method of the first distance and the second distance includes:
Predicting the position of the tag at the next moment:
In the formula,For the current momentPassing by time intervalThe position of the tag at the back is determined,For the current momentIs used for the position of the tag,For the real-time speed of movement of the tag,The real-time motion direction unit vector of the label;
according to the position of the tag at the next momentFixed space coordinates with RFID readerCalculating a first Euclidean distance as a first distance;
according to the position of the tag at the next momentFixed spatial coordinates with a bar code scannerThe second Euclidean distance is calculated as the second distance.
Preferably, the calculating of the first distance and the second distance further includes a dynamic confidence correction for the first euclidean distance and the second euclidean distance:
confidence of motion direction prediction by signal-to-noise ratio of RFID signal,;
The corrected first distance and second distance are:
In the formula,The corrected first Euclidean distance and the corrected second Euclidean distance are respectively used as a first distance and a second distance,The first Euclidean distance and the second Euclidean distance are respectively,As the measured distance corresponding to the current first distance,And the measured distance corresponding to the current second distance.
Preferably, the method further adjusts the reading mode according to a tag movement speed setting adjustment strategy, and the specific adjustment method is as follows:
and if the movement speed of the tag exceeds the threshold value, the RFID batch reading mode is forcedly started.
Correspondingly, the invention also provides a self-adaptive range control system for combined reading of RFID and bar codes, which is used for implementing the self-adaptive range control method and comprises the following steps:
the RFID reader-writer is used for transmitting continuous waves, receiving tag backscattering signals and recognizing and reading the RFID tags;
a bar code scanner for scanning a bar code on the label to perform bar code reading;
The signal processing module is used for carrying out down-conversion and phase demodulation on the back scattering signal, extracting carrier frequency offset and calculating real-time movement speed and direction of the tag based on Doppler effect;
The coordinate prediction module is used for predicting the position of the label at the next moment by combining the speed, the direction and the current position of the label;
The distance calculation module is used for calculating a first distance and a second distance according to the predicted position of the tag and fixed space coordinates of the RFID reader-writer and the bar code scanner;
the reading range acquisition module is used for acquiring the RFID effective reading radius and the bar code effective reading distance;
and the control decision module is used for setting an adjustment strategy and dynamically controlling the reading mode according to the relation among the first distance, the second distance, the reading radius and the reading distance and the label speed threshold.
Compared with the prior art, the invention has the following technical effects:
1. The self-adaptive range control method provided by the invention calculates the movement speed and direction of the tag in real time through carrier frequency shift of the RFID backscattering signal, predicts the future distance by combining with the space coordinate, solves the problem of mode switching delay in a high-speed scene, adjusts the RFID effective reading radius and the barcode scanning distance according to the real-time noise intensity, improves the robustness in a complex environment, and solves the problems of overhigh energy consumption caused by continuously running dual-mode hardware, and particularly limited endurance in mobile equipment.
2. The self-adaptive range control method provided by the invention can automatically select the RFID reading mode, the bar code reading mode or the combined reading mode according to the predicted first distance and the second distance and combining the respective effective reading range, effectively avoids the blind triggering of the scanning code or the reading and writing failure caused by the blind area of the RFID reading signal when the bar code does not enter the visible range, and greatly improves the reading efficiency and the reading success rate.
3. The self-adaptive range control method provided by the invention can switch the reading modes in real time according to the actual scene, combines the advantages of the two modes, avoids respective limitations, and is particularly suitable for complex recognition tasks in the scenes of logistics, storage, retail and the like.
4. The self-adaptive range control method provided by the invention dynamically adjusts the effective reading range model through external parameters such as the environmental noise intensity, the illumination intensity and the like, can effectively adapt to the reading interference under different environments, such as high electromagnetic noise or low illumination scenes, ensures that the system is always in an optimal reading state, and enhances the robustness of the system.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the technical solutions of the present application will be clearly and completely described below with reference to the accompanying drawings in conjunction with specific embodiments of the present application.
Example 1
The embodiment is a self-adaptive range control method for combined reading of RFID and bar code, as shown in FIG. 1, comprising the following steps:
step one, capturing a back scattering signal of a tag in real time through an RFID reader-writer, extracting carrier frequency offset, and calculating real-time motion speed and real-time motion direction of the tag based on Doppler effect.
The doppler shift appears as a linear change in the phase of the received signal over time in the time domain, and thus the doppler shift can be estimated by measuring the rate of change in the phase of the received signal over time. In one embodiment of the present invention, the specific method for extracting the carrier frequency offset is as follows:
Down-converting the received backscatter signal to baseband or intermediate frequency;
Phase demodulating the down-converted signal to extract instantaneous phase information of the signal;
Calculating at successive time intervalsPhase variation in;
Carrier frequency offsetApproximated as an average of the phase change rates:。
by acquiring the carrier frequency offset by the method, more real-time frequency offset estimation can be provided.
In addition, the backscatter signal of a passive tag is affected by the doppler effect and its spectrum is shifted relative to the original carrier frequency. By performing a spectral analysis of the received backscattered signal, it can be observed that the spectral peaks of the signal are no longer located at the original carrier frequency, but are shifted. Thus, in other embodiments of the present invention, obtaining the carrier frequency offset based on the spectrum analysis method is further included。
The RFID reader-writer receives a back-scattered signal from a passive tag, samples and Analog-to-Digital Converter (ADC) the received Analog signal to obtain a digital signal, performs windowing (such as Hamming window, blackman window and the like) on the acquired digital signal to reduce spectrum leakage and improve frequency resolution, and performs fast Fourier transform (Fast Fourier Transform, FFT) on the windowed signal to obtain a spectrum of the signal. Searching the peak value with the largest energy in the frequency spectrum, wherein the difference value between the frequency corresponding to the peak value and the original carrier frequency is Doppler frequency shift, namely carrier frequency offset.
After the carrier frequency offset is obtained, the real-time motion speed can be calculated according to the carrier frequency offset, and a calculation formula is as follows:
In the formula,For the real-time speed of movement of the tag,As the amount of carrier frequency offset,In order to achieve the light velocity, the light beam is,Is the carrier frequency of the RFID reader,An included angle between the movement direction of the tag and the main lobe of the RFID antenna;
Wherein the included angle isThe method comprises obtaining real-time azimuth angle of the tag by using phase difference direction finding method of RFID antenna array, and calculating by combining geometric relationship of tag motion direction and azimuth angleCosine value of (2) to obtain final included angleIs a numerical value of (2).
In one embodiment of the invention, the angle based on the phase difference direction finding methodThe calculation adopts a 4-unit uniform linear array, the antenna spacing is half of the carrier wavelength of the RFID reader-writer, and the FPGA is equipped to realize real-time phase difference measurement. The tag backscatter signals are received by 4 units of the antenna array to form 4 channel signals, cross-correlation operation is carried out on adjacent antenna signals, 3 groups of phase differences are extracted, and the horizontal azimuth angle is calculated through average phase differences. By applying labels in continuous timeAndCalculating the predicted positions at two moments to obtain a unit vector of the motion direction of the tagSince the azimuth angle can be converted into a unit direction vector pointing to the tag from the main lobe direction of the reader-writer antennaThus an included angleThe cosine value can be calculated through the dot product between the two vectors, and finally the included angle is obtained。
In other embodiments of the invention, tag direction of motion unit vectors may also be obtained by historical position fitting。
And secondly, predicting a first distance between the tag and the RFID reader-writer and a second distance between the tag and the bar code scanner at the next moment according to the real-time movement speed and the real-time movement direction and by combining fixed space coordinates of the RFID reader-writer and the bar code scanner.
The following known quantities have been obtained so far:
Device fixed spatial coordinates including the location of an RFID reader(I.e., fixed spatial coordinates of the RFID reader-writer)) Position of bar code scanner(I.e., fixed spatial coordinates of the barcode scanner)) Wherein, the method comprises the steps of,,;
The current state of the tag comprises the current space coordinates of the tagCurrent speed of movement of the tagUnit vector of current motion direction of labelWherein, the method comprises the steps of,,;
Time interval from current time to next time。
In one embodiment of the present invention, the method for calculating the first distance and the second distance includes:
Tag motion is continuous and the position of the tag at the next time can be predicted:
In the formula,For the current momentPassing by time intervalThe position of the tag at the back is determined,For the current momentIs used for the position of the tag,For the real-time speed of movement of the tag,The real-time motion direction unit vector of the label;
Namely:
representing the predicted tag at the next timeIs the predicted position。
According to the position of the tag at the next momentFixed space coordinates with RFID readerCalculating a first Euclidean distance as a first distance;
according to the position of the tag at the next momentFixed spatial coordinates with a bar code scannerThe second Euclidean distance is calculated as the second distance.
In other embodiments of the present invention, the calculating of the first distance and the second distance further includes a dynamic confidence correction for the first euclidean distance and the second euclidean distance:
confidence of motion direction prediction by signal-to-noise ratio of RFID signal,;
The corrected first distance and second distance are:
In the formula,The corrected first Euclidean distance and the corrected second Euclidean distance are respectively used as a first distance and a second distance,The first Euclidean distance and the second Euclidean distance are respectively,As the measured distance corresponding to the current first distance,And the measured distance corresponding to the current second distance.
In other embodiments of the invention, the first and second distances after correction further comprise obstacle detection compensation, and the compensated value is taken as the final first and second distances. Specifically, if an obstacle exists, for example, a Time of Flight (TOF) sensor detects an obstruction between the tag and the device, and RFID distance compensation is expressed asWhereinIs the attenuation coefficient of the obstacle material, and the bar code distance compensation is expressed as(Indicating that the optical barrier is not penetrable). Will be compensated forAndAs a final first distance and second distance.
In other embodiments of the present invention, the obstacle detection compensation directly acts on the first euclidean distance and the second euclidean distance. I.e. RFID distance compensation is denoted asWhereinIs the attenuation coefficient of the obstacle material, and the bar code distance compensation is expressed as(Indicating that the optical barrier is not penetrable). Will be compensated forAndAs a final first distance and second distance.
And thirdly, acquiring the effective RFID reading radius and the effective barcode reading distance.
The RFID effective reading radius acquisition method comprises the following steps:
In the formula,For the RFID to effectively read the radius,For a preset RFID maximum read radius,For the preset attenuation coefficient, the damping coefficient is set,Is the intensity of the ambient electromagnetic noise obtained in real time by the spectrum analyzer.
In one embodiment of the invention, the preset RFID maximum read radius and attenuation coefficient are determined experimentally. The method comprises the steps of firstly configuring a UHF RFID module supporting adjustable power, a spectrum analyzer for scanning carrier frequency band noise in real time, and a passive tag (for calibrating the RFID maximum reading radius) at a fixed position. Then the reader-writer power is gradually increased in the shielding room, and the farthest readable distance of the tag, namely the RFID maximum reading radius, is measured. Injecting controllable noise, measuring noise power and effective radius to obtain attenuation coefficient。
The method for acquiring the effective reading distance of the bar code comprises the following steps:
In the formula,For the effective reading distance of the bar code,For a preset minimum barcode reading distance,As a scale factor, the number of the elements is,For the intensity of the ambient light,Is the minimum effective illumination intensity threshold.
Similar to the method for acquiring the RFID maximum reading radius, the preset minimum reading distance and the scale factor of the bar code in the embodiment are also determined through experiments. A bar code scanner integrating an ambient light sensor, an illumination sensor, and a bar code print sample with a standard reflectivity of 20% were first configured. Gradually increasing illumination in darkroom, and measuring minimum illumination capable of identifying bar code. Continuously increasing illumination to obtain the optimal reading distance and the current illumination, and solving to obtain a scale factor。
The effective reading range model is dynamically adjusted through external parameters such as the environmental noise intensity, the illumination intensity and the like, so that the system can be effectively adapted to reading interference under different environments, such as high electromagnetic noise or low illumination scenes, the system is ensured to be always in an optimal reading state, and the system robustness is enhanced.
And step four, setting an adjustment strategy to adjust the reading mode according to the relation among the first distance, the second distance, the RFID effective reading radius and the bar code effective reading distance.
The adjustment strategy comprises the following steps:
if the first distance is less than or equal to the RFID effective reading radius and the second distance is greater than the bar code effective reading distance, activating RFID single mode reading;
If the first distance is greater than the RFID effective reading radius and the second distance is less than or equal to the bar code effective reading distance, activating bar code single mode reading;
if the first distance is smaller than or equal to the effective reading radius of the RFID and the second distance is smaller than or equal to the effective reading distance of the bar code, activating the combined reading of the RFID and the bar code.
Besides the adjustment according to the first distance and the second distance, the adjustment strategy can be set according to the movement speed of the tag to adjust the reading mode, and the specific adjustment method is that if the movement speed of the tag exceeds a threshold value, the RFID batch reading mode is forcedly started.
Further, other embodiments of the present invention provide a priority dynamic selection dominant mode for cases where the first distance is less than or equal to the RFID effective reading radius and the second distance is less than or equal to the barcode effective reading distance;
calculating priority weights:
In the formula,The weight of the RFID is represented as,The weight of the bar code is represented,For a signal-to-noise ratio based RFID current signal quality score,For a contrast-based bar code current signal quality score,The first distance to participate in the calculation for this step,The first distance participated in the calculation of the step for the second distance participated in the calculation of the step can be the original first Euclidean distanceCorrected first distanceFirst distance after compensationThe second distance involved in the calculation in this step may be the original second Euclidean distanceCorrected first distanceFirst distance after compensationOne of them. If it isThe RFID mode is preferably activated or the RFID mode will be activatedMultiplying with a preset coefficient, and then withAnd (5) comparing.
Example two
The embodiment is an adaptive range control system for combined reading of RFID and barcode, where the system is configured to implement the adaptive range control method according to the first embodiment, and includes:
the RFID reader-writer is used for transmitting continuous waves, receiving tag backscattering signals and recognizing and reading the RFID tags;
a bar code scanner for scanning a bar code on the label to perform bar code reading;
The signal processing module is used for carrying out down-conversion and phase demodulation on the back scattering signal, extracting carrier frequency offset and calculating real-time movement speed and direction of the tag based on Doppler effect;
The coordinate prediction module is used for predicting the position of the label at the next moment by combining the speed, the direction and the current position of the label;
The distance calculation module is used for calculating a first distance and a second distance according to the predicted position of the tag and fixed space coordinates of the RFID reader-writer and the bar code scanner;
the reading range acquisition module is used for acquiring the RFID effective reading radius and the bar code effective reading distance;
and the control decision module is used for setting an adjustment strategy and dynamically controlling the reading mode according to the relation among the first distance, the second distance, the reading radius and the reading distance and the label speed threshold.
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that modifications and improvements could be made by those skilled in the art without departing from the inventive concept, which falls within the scope of the present invention.