CN112149435B - RFID reader-writer sensitivity testing device and method based on multipath fading channel scene - Google Patents

RFID reader-writer sensitivity testing device and method based on multipath fading channel scene Download PDF

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CN112149435B
CN112149435B CN202011016709.2A CN202011016709A CN112149435B CN 112149435 B CN112149435 B CN 112149435B CN 202011016709 A CN202011016709 A CN 202011016709A CN 112149435 B CN112149435 B CN 112149435B
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signal
rfid reader
rfid
writer
multipath fading
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CN112149435A (en
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黄钰
王瑜
章学周
俞晓磊
李翔
胡冶
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Jiangsu Institute Of Quality And Standardization
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
    • G06K7/0095—Testing the sensing arrangement, e.g. testing if a magnetic card reader, bar code reader, RFID interrogator or smart card reader functions properly

Abstract

The invention discloses a device and a method for testing the sensitivity of an RFID reader-writer based on a multipath fading channel scene, wherein the method comprises the following steps: processing a direct path signal sent by the RFID reader-writer to be detected to generate an RFID multipath fading signal, adjusting a forward attenuation value of the RFID multipath fading signal until the forward attenuation value reaches a critical state that the RFID reader-writer to be detected can just read the reference label, and recording a power value of a reflected signal at the moment; adjusting the reverse attenuation value of the reflected signal until the measured RFID reader-writer just cannot read the reference label to reach a critical state, and recording the reverse attenuation value at the moment; and subtracting the reverse attenuation value from the power value of the reflected signal to obtain the minimum receiving sensitivity of the tested RFID reader-writer. The invention simulates an actual application scene by using a multipath fading channel scene, and measures and obtains the sensitivity of the RFID reader-writer in the actual application scene.

Description

RFID reader-writer sensitivity testing device and method based on multipath fading channel scene
Technical Field
The invention relates to the technical field of RFID (radio frequency identification) readers, in particular to a device for testing the sensitivity of an RFID reader based on a multipath fading channel scene, and also relates to a method for measuring the sensitivity of the RFID reader based on the multipath fading channel scene.
Background
In an actual environment, signals in the RFID communication link include not only direct wave signals, but also non-direct wave signals such as specular reflection signals and diffuse scattering signals generated by reflection of surrounding objects. The indirect wave signal interferes with the indirect wave signal, so that the observation value of the RFID reader deviates from the true value, resulting in a so-called "multipath error". The complex and various actual radio-magnetic environment factors present great challenges to the testing work of the RFID products.
The analysis shows that the prior RFID reader-writer testing technology has the following problems: the existing electromagnetic shielding environment based on no external interference tests signals in an RFID communication link, and the actual communication performance of an RFID reader-writer in a multipath fading scene cannot be comprehensively evaluated. Therefore, the sensitivity test of the RFID reader-writer under the condition of simulating the multipath fading channel has important significance for comprehensively analyzing the actual performance of the RFID reader-writer.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a method for testing the sensitivity of an RFID reader-writer based on a multipath fading channel scene.
In order to solve the above technical problem, the present invention provides a device for testing the sensitivity of an RFID reader based on a multipath fading channel scenario, comprising: the system comprises a multipath fading channel simulation module, an RFID reader-writer sensitivity test module, two circulators and a power amplifier;
the radio frequency input port of the multipath fading channel simulation module is connected with the tested RFID reader-writer through a first circulator; a radio frequency output port of the multipath fading channel simulation module is connected with a first radio frequency connection port of the RFID reader sensitivity test module after passing through the power amplifier and the second circulator; the RFID reader-writer sensitivity testing module is connected with the reference label through a second radio frequency connection port; the two circulators are directly connected;
a direct path signal sent by a tested RFID reader-writer is input into a multipath fading channel simulation module after passing through a first circulator, the multipath fading channel simulation module processes the direct path signal to generate an RFID multipath fading signal, the RFID multipath fading signal is amplified by a power amplifier and then is sent into an RFID reader-writer sensitivity testing module, and the RFID reader-writer sensitivity testing module is used for adjusting an RFID multipath fading signal attenuation value and then outputting the RFID multipath fading signal to a reference label to activate the reference label;
and the reflected signal returned by the reference label is input into the sensitivity testing module of the RFID reader-writer to adjust the attenuation value of the RFID reader-writer, and the adjusted reflected signal returns to the tested RFID reader-writer after passing through the second circulator and the first circulator.
Further, the multipath fading channel simulation module includes: the device comprises a time delay processing unit, a fading factor superposition unit, a phase shifter, an adder, an interference signal generator, an attenuator, a D/A digital-to-analog converter and an A/D analog-to-digital converter;
the direct path signal is input into an A/D analog-to-digital converter for analog-to-digital conversion and then is output in two paths, one path is directly connected with an adder, and the other path is connected with an input port of a time delay processing unit; the time delay processing unit performs corresponding time delay processing on the input direct path signal and outputs a plurality of delay signal components; a plurality of delayed signal components are respectively input into a fading factor superposition unit and a phase shifter, and after corresponding attenuation and phase shift are superposed on each delayed signal component, a plurality of indirect path signals are generated; superposing one direct path signal and a plurality of indirect path signals in an adder to synthesize a multipath signal;
the interference signal generator and the attenuator are connected in series to generate interference signals, and the interference signals and the synthesized multipath signals are superposed in the adder to generate RFID multipath fading signals; and the RFID multipath fading signals are output after being subjected to digital-to-analog conversion by a D/A analog-to-digital converter.
Further, the sensitivity testing module of the RFID reader includes: the power meter, the forward attenuator, the reverse coupler and the two circulators;
the RFID multipath fading signal is input into the forward attenuator through the third circulator, the forward attenuator adjusts the RFID multipath fading signal and then inputs the adjusted RFID multipath fading signal into the fourth circulator, and the adjusted RFID multipath fading signal is output to the reference label through the fourth circulator to activate the reference label;
the reference tag returns a reflection signal after being activated, the reflection signal passes through the fourth circulator and then is output through the reverse coupler, the reverse attenuator and the third circulator in sequence, and the output end of the reverse coupler is further connected with a power meter for measuring power.
Correspondingly, the invention also provides a method for testing the sensitivity of the RFID reader-writer based on the multipath fading channel scene based on the device, which comprises the following steps:
processing a direct path signal sent by a tested RFID reader-writer to generate an RFID multi-path fading signal, wherein the RFID multi-path fading signal is used for activating a reference label, and the reference label returns a reflected signal to the tested RFID reader-writer after being activated;
adjusting the forward attenuation value of the RFID multipath fading signal until the critical state that the RFID reader-writer to be tested can just read the reference label is reached, and recording the power value of the reflected signal at the moment;
adjusting the reverse attenuation value of the reflected signal until the measured RFID reader-writer just cannot read the reference label to reach a critical state, and recording the reverse attenuation value at the moment;
and subtracting the reverse attenuation value from the power value of the reflected signal to obtain the minimum receiving sensitivity of the tested RFID reader-writer.
Further, the processing the direct path signal sent by the detected RFID reader to generate an RFID multipath fading signal includes:
dividing the direct path signals into multiple paths, and sequentially performing time delay, amplitude attenuation and phase shift processing to obtain multiple indirect path signals;
and adding and synthesizing the direct path signal and the plurality of indirect path signals, and then superposing the interference signals to finally generate the RFID multi-path fading signal.
Further, the dividing the direct path signal into multiple paths and sequentially performing time delay, amplitude attenuation and phase shift processing to obtain multiple indirect path signals includes:
determining parameters of a multipath fading channel model according to different application scenes, wherein the parameters comprise the number of indirect paths, time delay, phase shift and fading factors;
and dividing the direct path signal into multiple paths according to the parameters, and sequentially performing time delay, amplitude attenuation and phase shift processing to obtain multiple indirect path signals.
Further, the number of the indirect paths is 5.
Further, the RFID multipath fading signal is generated according to the following calculation formula:
Figure BDA0002699308600000041
wherein s is0.lRepresenting the components of the direct path signal,
Figure BDA0002699308600000042
representing multiple indirect
A superposition of the path signal components, n (t) representing a superimposed interference signal; f. oflFor the l-th sub-carrier, the number of sub-carriers,
wherein K is [1, K ]]K is the number of indirect path signals in the RFID signals; alpha is alphak,lRepresenting the amplitude attenuation coefficient of the kth path of non-direct path component of the l subcarrier; tau isk,lRepresenting the relative time delay of the component of the k path of the first subcarrier in the indirect path relative to the direct path; thetak,lRepresenting the relative phase shift of the kth path non-direct path component of the l subcarrier relative to the direct path.
Further, the interference signal is of a continuous wave type.
Further, the specific calculation formula of the interference signal is as follows:
Figure BDA0002699308600000051
wherein B represents the amplitude of the continuous sine wave,
Figure BDA0002699308600000052
representing the phase of the direct path signal.
Further, the different application scenarios include an urban model, a rural model, an indoor model, a mountain model, and a tunnel model.
Compared with the prior art, the invention has the following beneficial effects: the invention realizes the method for testing the sensitivity of the RFID reader-writer in the practical application scene, and realizes a unified and reproducible third-party detection means in the aspect of testing the sensitivity of the RFID reader-writer in the multipath fading channel scene; the installation of the distance and the angle between the RFID reader-writer and the label can be adjusted according to different application scenes in practical application; the method is beneficial to comprehensively evaluating the actual performance of the sensitivity of the RFID reader-writer, and a sensitivity test system and an evaluation system of the RFID reader-writer in an application scene are established; the RFID reader-writer has an important technical support effect on independent research and development of RFID product production enterprises, and the RFID reader-writer accords with more practical application, so that the development of RFID related industries can be further driven.
Drawings
FIG. 1 is a schematic diagram of a test system according to the present invention;
FIG. 2 is a schematic diagram of a simulation module of a multipath fading channel;
FIG. 3 is a schematic diagram of a sensitivity testing module of the RFID reader;
FIG. 4 is a graph showing the results of the test according to the method of the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
The invention discloses a method for testing the sensitivity of an RFID reader-writer based on a multipath fading channel scene, which comprises the following steps:
step 1, actually building an RFID reader-writer sensitivity test system in a multipath fading channel scene.
And (3) constructing a sensitivity test system of the RFID reader-writer of the multipath fading channel scene. The schematic structural diagram is shown in fig. 1, which includes: the device comprises a multipath fading channel simulation module, an RFID reader-writer sensitivity test module, two circulators and a power amplifier. The circulator is used for controlling the input RFID signal to be transmitted to the next processing unit along a certain circulating direction. The power amplifier is used for amplifying the low-power RFID multipath fading signals so as to improve the output power and efficiency and meet the requirement of the system test range.
The forward link of the RFID signal is shown with solid arrows in fig. 1 and the reverse link is shown with dashed arrows in fig. 1. And after the RFID multipath fading signal activates the reference label, the reference label reflected signal returns to the RFID reader-writer to be tested.
The radio frequency input port 1 of the multipath fading channel simulation module is connected with the tested RFID reader-writer through a first circulator; a radio frequency output port 2 of the multipath fading channel simulation module is connected with a radio frequency connection port 1 of the RFID reader sensitivity test module through a power amplifier and a second circulator; the RFID reader sensitivity testing module is connected with the reference label through a radio frequency connection port 2; the two circulators are connected to transmit the reverse link signal returned by the reference tag.
Step 2, setting the sub-carrier frequency as a fixed single frequency f in the tested RFID reader-writerl(ii) a The sending mode is set to be continuous sending, and the sending command is set to be a QUERY command, so that an RFID direct path signal can be generated and sent to the multipath fading channel simulation module.
First, in the range of 860MHz to 960MHz, two frequency bands are selected, i.e., (f)1～f2) And (f)3～f4) Set to the operating frequency of the RFID reader to be tested, where f1，f2，f3，f4Needs to satisfy 860MHz < f1＜f2＜f3＜f4＜960MHz，
Figure BDA0002699308600000071
In (f)1～f2) In a frequency band of
Figure BDA0002699308600000072
Sub-channels, similarly at (f)3～f4) Also has one in the frequency band
Figure BDA0002699308600000073
A subchannel, and thus L subchannels in total in two frequency bands, one subchannel for each.
Secondly, setting a fixed single frequency f for the subcarrier frequency of the tested RFID reader-writerlRather than the default hopping. And ignoring Doppler effect in a low-speed scene, wherein the frequency of direct path signal components and non-direct path signal components on the same subcarrier is the same. Due to the fact that the ultrahigh frequency RFID reader-writer is specified in the international ISO standardThe bandwidth of each sub-channel is fixed to 0.25MHz, so the frequency f of the ith sub-carrierlMay be configured to:
when in use
Figure BDA0002699308600000074
When f is presentl＝f1+0.25×(l-1)
When in use
Figure BDA0002699308600000075
When the temperature of the water is higher than the set temperature,
Figure BDA0002699308600000076
wherein L is ∈ [1, L ∈]，
Figure BDA0002699308600000077
And 860MHz < f1＜f2＜f3＜f4＜960MHz。
The direct path signal sent by the tested RFID reader-writer is a direct path component s in the ith subcarrier0.lSpecifically, the formula is shown as follows:
s0.l＝exp(i2πflt)
and 3, setting parameters of the multipath fading channel model in a multipath fading channel simulation module according to different application scene models, and generating the RFID multipath fading signal.
The multipath fading channel simulation module has a schematic structure as shown in fig. 2. The device comprises a time delay processing unit, a fading factor superposition unit, a phase shifter, an adder, an interference signal generator, an attenuator, a D/A digital-to-analog converter and an A/D analog-to-digital converter.
A direct path signal is input into an A/D (analog-to-digital) converter from a radio frequency input port 1, the A/D converter performs analog-to-digital conversion on the direct path signal and outputs the direct path signal in two paths, one path is directly connected with an adder, and the other path is connected with an input port of a time delay processing unit; the time delay processing unit performs corresponding time delay processing on the input RFID direct path signal and outputs a plurality of delay signal components; a plurality of delayed signal components are respectively input into a fading factor superposition unit and a phase shifter, and after corresponding attenuation and phase shift are superposed on each delayed signal component, a plurality of indirect path signals are generated; superposing one direct path signal and a plurality of indirect path signals in an adder to synthesize a multipath signal; generating an interference signal by connecting an interference signal generator and an attenuator in series, and superposing the interference signal and the synthesized multipath signal in an adder to generate an RFID multipath fading signal; the RFID multipath fading signal is output from the radio frequency output port 2 after being subjected to digital-to-analog conversion by the D/A analog-to-digital converter.
In the multipath fading channel simulation module, processing a direct path signal sent by a tested RFID reader-writer to generate an RFID multipath fading signal, comprising the following steps:
(1) a direct path signal (analog signal) sent by the RFID reader-writer to be tested and received from the radio frequency input port 1 is converted into a digital signal through an A/D analog-to-digital converter.
(2) Setting a multipath fading channel scene model according to different application scenes, wherein the scene model comprises an urban area model, a rural area model, an indoor model, a mountain land model and a tunnel model. The parameters of the multipath fading channel model are set as one or any combination of the following: number of non-direct paths K, relative time delay tauk,lRelative phase shift θk,lFading factor alphak,l。
Wherein K is [1, K ]]K is the number of indirect path signals in the RFID signals; alpha is alphak,lRepresenting the amplitude attenuation coefficient of the kth path of non-direct path component of the l subcarrier; tau isk,lRepresenting the relative time delay of the component of the k path of the first subcarrier in the indirect path relative to the direct path; thetak,lRepresenting the relative phase shift of the kth path non-direct path component of the l subcarrier relative to the direct path.
(3) And the digital direct path signal sequentially passes through the time delay processing unit, the fading factor superposition unit and the phase shifter to perform time delay, amplitude attenuation and phase shift processing to obtain a non-direct path signal.
(4) And adding and synthesizing the direct path signal and the plurality of indirect path signals, and then superposing the interference signals to finally generate the RFID multi-path fading signal.
Specifically, the RFID multipath fading signal is generated according to the following calculation formula.
Figure BDA0002699308600000091
Wherein s is0.lRepresenting the components of the direct path signal,
Figure BDA0002699308600000092
representing the superposition of a plurality of indirect path signal components, n (t) representing the superposed interference signals, and the Continuous Wave (CW) type interference is specifically calculated by the following formula:
Figure BDA0002699308600000093
wherein B represents the amplitude of the continuous sine wave,
Figure BDA0002699308600000094
representing the phase of the direct path signal.
(5) The digital RFID multipath fading signals are converted into analog signals through a D/A digital-to-analog converter, and the analog signals are output from a radio frequency output port 2.
And 4, adjusting the forward attenuator and the reverse attenuator in the sensitivity test module of the RFID reader-writer to reach a critical state that the RFID reader-writer to be tested can not read the reference label, so as to realize the sensitivity test of the RFID reader-writer to be tested.
The structural schematic diagram of the sensitivity testing module of the RFID reader is shown in fig. 3. The power meter comprises a power meter, a forward attenuator, a reverse coupler and two circulators. The reverse coupler enables signals of a reverse link to be transmitted in a single direction, and divides input signals into 2 paths according to power proportion, wherein one path is used for transmitting the reverse signals, and the other path is used for being connected with a power meter. The power meter is connected with the reverse coupler and used for testing the power value of the return signal of the reference label. The measured RFID reader-writer can just read the reference label to reach the critical state by adjusting the forward attenuator, and the measured RFID reader-writer can just not read the reference label to reach the critical state by adjusting the reverse attenuator. The circulator is used for controlling the input signal to be transmitted to the next processing unit along a certain circulating direction.
In the forward link: the radio frequency connection port 1 receives the RFID multipath fading signals, the RFID multipath fading signals are input into the forward attenuator through the third circulator, the forward attenuator adjusts the RFID multipath fading signals and then inputs the RFID multipath fading signals into the fourth circulator, and the RFID multipath fading signals are output to the reference tag from the radio frequency connection port 2 through the fourth circulator. The RFID multi-path fading signal activates the reference tag.
In the reverse link: the reference tag returns a reflection signal after being activated, the reflection signal is input from the radio frequency connection port 2, passes through the fourth circulator and then sequentially passes through the reverse coupler and the reverse attenuator and is output from the radio frequency connection port 1. And the reflected signal after subsequent output returns to the tested RFID reader-writer through the second circulator and the first circulator.
In the RFID reader sensitivity test module, the method for measuring the receiving sensitivity of the tested RFID reader comprises the following steps:
(1) setting a test frequency, and sequentially setting the test frequency as a subcarrier frequency f of the work of the RFID reader-writer to be tested in a power meterl(ii) a The receiving frequency of the power meter is equal to the sending frequency of the tested RFID reader-writer, so that the signals can be normally received and the power can be tested.
(2) And adjusting a forward attenuator on a forward link, wherein the step length of forward attenuation adjustment is not too small in order to shorten the test duration, the forward attenuation value is increased from zero according to the step length of 0.5dB according to an empirical value until the reference tag cannot be read by the RFID reader-writer to be tested, and then the forward attenuation value is gradually reduced according to the step length of 0.1dB, wherein the step length of 0.1dB is selected in order to more accurately find the critical state until the critical state that the RFID reader-writer to be tested can just read the reference tag is reached. At this time, the power value P of the reflected signal returned by the reference tag at this time can be obtained through the measurement of the power meterfl；
(3) Adjusting a reverse attenuator on a reverse link, increasing a reverse attenuation value from zero according to a step length of 0.1dB, wherein the step length of 0.1dB is selected to ensure that a sensitivity measurement result is accurate to 0.1dB until a tested RFID reader-writer can not read a reference label to reach a critical state, and recording the step length at the momentReverse attenuation value Afl；
(4) Calculating power value P of return signal of reference labelflSubtracting the reverse attenuation value A on the added reverse linkflEqual to the minimum reverse power that the RFID reader-writer to be tested can receive, i.e. the minimum receiving sensitivity J of the RFID reader-writer to be testedflThe calculation method is expressed by the following formula:
Figure BDA0002699308600000111
the sensitivity of the RFID reader-writer in the multipath fading channel scene obtained by calculation is generally poorer than the nominal sensitivity of the RFID reader-writer, but better accords with the actual sensitivity of the RFID reader-writer. The sensitivity detection instrument of the existing RFID reader-writer can only carry out testing in an interference-free environment of a laboratory, so that the measured nominal sensitivity value is good. But when it is applied in the actual multipath fading channel scenario, its nominal sensitivity can not be achieved due to the existence of interference. In practical application, the use effect is poor because the application scene of the RFID reader-writer is not overlapped with the original design.
Therefore, the invention realizes the method for testing the sensitivity of the RFID reader-writer in the practical application scene, and realizes a uniform and reproducible third-party detection means in the aspect of testing the sensitivity of the RFID reader-writer in the multipath fading channel scene; the installation of the distance and the angle between the RFID reader-writer and the label can be adjusted according to different application scenes in practical application; the method is beneficial to comprehensively evaluating the actual performance of the sensitivity of the RFID reader-writer, and a sensitivity test system and an evaluation system of the RFID reader-writer in an application scene are established; the RFID reader-writer has an important technical support effect on independent research and development of RFID product production enterprises, and the RFID reader-writer accords with more practical application, so that the development of RFID related industries can be further driven.
Examples
Step 1, constructing a sensitivity test system of an RFID reader-writer in a multipath fading channel scene according to the figures 1-3, wherein the radio frequency working frequency of a power amplifier is 50-1000 MHz, and the power gain is 35 dB. The power capacity of the forward attenuator and the reverse attenuator is 40W, and the nominal attenuation is 35 dB; the reference tag is an ultrahigh frequency RFID tag with the working frequency range of 800-1000 MHz. The time delay processing unit in the multipath fading channel simulation module can simultaneously obtain 5 time delays of non-direct paths in a shift register mode. Nominal attenuation of a forward attenuator and a reverse attenuator in the RFID reader-writer sensitivity test module is adjustable within the range of 0-35 dB.
Step 2, configuring subcarrier frequency f in tested RFID reader-writerlAnd generating a direct path signal and sending the direct path signal to a multipath fading channel simulation module.
The working frequency of the RFID reader-writer is specifically set to 860.125 MHz-864.875 MHz and 920.125 MHz-924.875 MHz, the two frequency bands comprise 40 sub-channels, and each sub-channel corresponds to one sub-carrier. Under the condition of neglecting Doppler frequency shift in low-speed short distance, the frequency of all signal path components in the same sub-carrier is the same, and since the bandwidth of each sub-channel is 0.25MHz, the frequency f of the ith sub-carrierlMay be configured to:
when l is equal to [1,20 ]]When f is presentl＝860.125+0.25×(l-1)；
When l ∈ [21,40 ]]When f is presentl＝920.125+0.25×(l-21)
And L belongs to [1, L ], wherein L is the number of the subcarriers of the RFID signal, and L is 40.
I.e. configuring the subcarrier frequency f in the tested RFID reader-writerl860.125MHz,860.375MHz,860.625MHz,860.875MHz,861.125MHz,861.375MHz, 861.625MHz,861.875MHz,862.125MHz,862.375MHz,862.625MHz,862.875MHz,863.125MHz,863.375MHz,863.625MHz,863.875MHz,864.125MHz,864.375MHz,864.625MHz,864.875MHz,920.125MHz,920.375MHz,920.625MHz,920.875MHz,921.125MHz,921.375MHz, 921.625MHz,921.875MHz,922.125MHz,922.375MHz,922.625MHz,922.875MHz,923.125MHz,923.375MHz,923.625MHz,923.875MHz,924.125MHz,924.375MHz,924.625MHz,924.875MHz in sequence.
And setting the transmission signal of the tested RFID reader-writer as a QUERY signal.
And 3, setting parameters of a multipath fading channel model in a multipath fading channel simulation module according to different application scene models, and generating the RFID multipath fading signal.
In this embodiment, a mountain model version is selected as an example, and parameters of a multipath fading channel scene model are set, as shown in table 1. The parameters of the multipath fading channel model are set as one or any combination of the following: the number K of indirect paths is 5, relative time delay tauk,lRelative phase shift θk,lFading factor alphak,lInterference signal n (t). And 6 paths are set, wherein the 0 th path is a direct path, and the following 5 paths are indirect paths.
The K is equal to [1, K ∈ >]，αk,lThe value range is as follows: -20dB ≦ alphak,l≤0dB；τk,lThe value range is as follows: tau is less than or equal to 0 mu sk,l≤20μs；θk,lThe value range is as follows: -pi ≦ θk,l≤π；
TABLE 1 multipath fading channel model parameters
Route of travel Fading factor (dB) Relative time delay (mu s) Relative phase shift (°)
0 0 0 0
1 -2.0 1.56μs 0
2 -4.0 3.12μs 0
3 -7.0 4.68μs 0
4 -6.0 11.70μs 0
5 -12.0 13.26μs 0
The 1 st non-direct path fading factor is-2.0 dB, the relative delay is 1.56 mu s, and the relative phase shift is 0 degree; the 2 nd non-direct path fading factor is-4.0 dB, the relative delay is 3.12 mu s, and the relative phase shift is 0 degree; the 3 rd non-direct path fading factor is-7.0 dB, the relative delay is 4.68 mu s, and the relative phase shift is 0 degree; the 4 th non-direct path fading factor is-6.0 dB, the relative delay is 11.70 mu s, and the relative phase shift is 0 degree; the fading factor of the 5 th non-direct path is-12.0 dB, relative delay is 13.26 mu s, and relative phase shift is 0 degree.
The interference signal n (t) superimposed by all paths is of Continuous Wave (CW) type interference.
N (t) represents a superimposed interference signal, and the frequency is set to flWith amplitude B equal to 1 and phase
Figure BDA0002699308600000131
The interference of CW is generated, and the specific calculation formula is as follows.
Figure BDA0002699308600000132
And 4, adjusting the forward attenuator and the reverse attenuator in the sensitivity test module of the RFID reader-writer to reach a critical state that the RFID reader-writer to be tested can not read the reference label, and then realizing the sensitivity test of the RFID reader-writer to be tested.
(1) Setting a test frequency, and sequentially setting the test frequency as a subcarrier frequency f of the work of the RFID reader-writer to be tested in a power meterl；
(2) Adjusting a forward attenuator on a forward link, increasing a forward attenuation value from zero according to the step length of 0.5dB until the RFID reader-writer to be tested can not read the reference label, and then gradually reducing the forward attenuation value according to the step length of 0.1dB until the RFID reader-writer to be tested can just read the reference label; at this time, the power value of the return signal of the reference label at this time can be obtained by the measurement of the power meter
Figure BDA0002699308600000141
(3) Adjusting a reverse attenuator on the reverse link, the reverse attenuation value increasing from zero in steps of 0.1dB until the reverse attenuation value increases
Figure BDA0002699308600000142
When the RFID reader-writer to be tested can not read the reference label to reach the critical state;
(4) calculating power value of reference label return signal
Figure BDA0002699308600000143
Subtracting the reverse attenuation value on the added reverse link
Figure BDA0002699308600000144
Equal to the minimum reverse power which can be received by the tested RFID reader-writer, namely the minimum receiving sensitivity of the tested RFID reader-writer
Figure BDA0002699308600000145
The calculation method is expressed by the following formula
Figure BDA0002699308600000146
In this embodiment, a fitted curve of the measured value of the minimum receiving sensitivity of the RFID reader/writer to be measured at the operating frequency of the subcarrier of 920.125MHz to 924.875MHz is shown in detail in fig. 4. Wherein, the result curve of the minimum receiving sensitivity of the RFID reader-writer under the multipath fading scene is positioned at the upper part of the figure 4, and the test result is-40.5 dB to-38.8 dB. In the prior art, the minimum receiving sensitivity result curve of the RFID reader-writer under the non-interference environment is positioned at the lower part of a graph 4, and the test result is-46.6 dB to-44.4 dB. The smaller the minimum receiving sensitivity is, the stronger the representative receiving capability is, and the better the performance of the RFID reader-writer is, so that the minimum receiving sensitivity performance of the RFID reader-writer under the multipath fading scene is inferior to the sensitivity test result under the interference-free environment. Therefore, the reader-writer sensitivity test is developed in the application scene simulating the multipath fading, so that the actual performance of the reader-writer sensitivity can be better evaluated, the production requirement of enterprise products is met, and the product quality of RFID products in actual application is ensured.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.

Claims (7)

1. A RFID reader-writer sensitivity testing device based on a multipath fading channel scene is characterized by comprising: the system comprises a multipath fading channel simulation module, an RFID reader-writer sensitivity test module, two circulators and a power amplifier;
a direct path signal sent by a tested RFID reader-writer is input into a multipath fading channel simulation module after passing through a first circulator, the multipath fading channel simulation module processes the direct path signal to generate an RFID multipath fading signal, the RFID multipath fading signal is amplified by a power amplifier and then is sent into an RFID reader-writer sensitivity testing module, and the RFID reader-writer sensitivity testing module is used for adjusting an RFID multipath fading signal attenuation value and then outputting the RFID multipath fading signal to a reference label to activate the reference label;
the reflected signal returned by the reference label is input into the sensitivity testing module of the RFID reader to adjust the attenuation value of the RFID reader, and the adjusted reflected signal returns to the tested RFID reader after passing through the second circulator and the first circulator;
the multipath fading channel simulation module comprises: the device comprises a time delay processing unit, a fading factor superposition unit, a phase shifter, an adder, an interference signal generator, an attenuator, a D/A digital-to-analog converter and an A/D analog-to-digital converter;
the direct path signal is input into an A/D analog-to-digital converter for analog-to-digital conversion and then is output in two paths, one path is directly connected with an adder, and the other path is connected with an input port of a time delay processing unit; the time delay processing unit performs corresponding time delay processing on the input direct path signal and outputs a plurality of delay signal components; a plurality of delayed signal components are respectively input into a fading factor superposition unit and a phase shifter, and after corresponding attenuation and phase shift are superposed on each delayed signal component, a plurality of indirect path signals are generated; superposing one direct path signal and a plurality of indirect path signals in an adder to synthesize a multipath signal;
the interference signal generator and the attenuator are connected in series to generate interference signals, and the interference signals and the synthesized multipath signals are superposed in the adder to generate RFID multipath fading signals; the RFID multipath fading signal is output after being subjected to digital-to-analog conversion by a D/A analog-to-digital converter;
the RFID reader sensitivity test module comprises: the power meter, the forward attenuator, the reverse coupler and the two circulators;
the RFID multipath fading signal is input into the forward attenuator through the third circulator, the forward attenuator adjusts the RFID multipath fading signal and then inputs the adjusted RFID multipath fading signal into the fourth circulator, and the adjusted RFID multipath fading signal is output to the reference label through the fourth circulator to activate the reference label;
the reference tag returns a reflection signal after being activated, the reflection signal passes through the fourth circulator and then is output through the reverse coupler, the reverse attenuator and the third circulator in sequence, and the output end of the reverse coupler is further connected with a power meter for measuring power.
2. A method for testing the sensitivity of an RFID reader-writer based on a multipath fading channel scene is characterized by comprising the following steps:
processing a direct path signal sent by a tested RFID reader-writer to generate an RFID multi-path fading signal, wherein the RFID multi-path fading signal is used for activating a reference label, and the reference label returns a reflected signal to the tested RFID reader-writer after being activated;
adjusting the forward attenuation value of the RFID multipath fading signal until the critical state that the RFID reader-writer to be tested can just read the reference label is reached, and recording the power value of the reflected signal at the moment;
adjusting the reverse attenuation value of the reflected signal until the measured RFID reader-writer just cannot read the reference label to reach a critical state, and recording the reverse attenuation value at the moment;
subtracting the reverse attenuation value from the power value of the reflected signal to obtain the minimum receiving sensitivity of the tested RFID reader-writer;
the step of processing the direct path signal sent by the tested RFID reader to generate an RFID multipath fading signal comprises the following steps:
dividing the direct path signals into multiple paths, and sequentially performing time delay, amplitude attenuation and phase shift processing to obtain multiple indirect path signals;
and adding and synthesizing the direct path signal and the plurality of indirect path signals, and then superposing the interference signals to finally generate the RFID multi-path fading signal.
3. The method for testing the sensitivity of the RFID reader-writer based on the multipath fading channel scene as claimed in claim 2, wherein the step of dividing the direct path signal into multiple paths and sequentially performing time delay, amplitude attenuation and phase shift processing to obtain a plurality of indirect path signals comprises the following steps:
determining parameters of a multipath fading channel model according to different application scenes, wherein the parameters comprise the number of indirect paths, time delay, phase shift and fading factors;
and dividing the direct path signal into multiple paths according to the parameters, and sequentially performing time delay, amplitude attenuation and phase shift processing to obtain multiple indirect path signals.
4. The method as claimed in claim 3, wherein the different application scenarios include urban model, rural model, indoor model, mountain model, and tunnel model.
5. The method as claimed in claim 2, wherein the number of said indirect paths is 5.
6. The method for testing the sensitivity of the RFID reader-writer based on the multipath fading channel scene as claimed in claim 2, wherein the RFID multipath fading signal is generated according to the following calculation formula:
Figure FDA0002963514050000031
wherein s is0.lRepresenting the components of the direct path signal,
Figure FDA0002963514050000032
representing a superposition of a plurality of non-direct path signal components, n (t) representing a superposed interference signal; f. oflFor the l-th sub-carrier, the number of sub-carriers,
wherein K is [1, K ]]K is the number of indirect path signals in the RFID signals; alpha is alphak,lRepresenting the amplitude attenuation coefficient of the kth path of non-direct path component of the l subcarrier; tau isk,lRepresenting the relative time delay of the component of the k path of the first subcarrier in the indirect path relative to the direct path; thetak,lRepresenting the relative phase shift of the kth path non-direct path component of the l subcarrier relative to the direct path.
7. The method for testing the sensitivity of the RFID reader-writer based on the multipath fading channel scene as claimed in claim 2, wherein the interference signal is of a continuous wave type, and the specific calculation formula of the interference signal is as follows:
Figure FDA0002963514050000041
wherein B represents the amplitude of a continuous sine wave, flFor the l-th sub-carrier, the number of sub-carriers,
Figure FDA0002963514050000042
representing the phase of the direct path signal.
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