CN109041203B - Electronic license plate reader-writer and reverse link frequency capturing method of electronic license plate - Google Patents
Electronic license plate reader-writer and reverse link frequency capturing method of electronic license plate Download PDFInfo
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- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04W56/0035—Synchronisation arrangements detecting errors in frequency or phase
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- H—ELECTRICITY
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- H04L27/00—Modulated-carrier systems
- H04L27/0014—Carrier regulation
- H04L2027/0018—Arrangements at the transmitter end
- H04L2027/002—Arrangements at the transmitter end using feedback from a remote receiver
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
- H04W4/80—Services using short range communication, e.g. near-field communication [NFC], radio-frequency identification [RFID] or low energy communication
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Abstract
The invention relates to an electronic license plate reader-writer and a reverse link frequency capturing method of an electronic license plate, wherein the reverse link frequency capturing method comprises the following steps: s10, respectively sending return signals of the electronic tag into at least two correlators, wherein the frequencies of the at least two correlators are different, and the frequency of one correlator is a reference frequency; s20, each path of correlator determines the self correlation of the pilot frequency sequence of the return signal and judges whether a pilot frequency symbol is detected according to the correlation; and S30, the correlator which detects the pilot frequency symbols determines the corrected reverse link frequency according to the determined correlation of the pilot frequency sequence. By implementing the technical scheme of the invention, the synchronization accuracy and the compatibility of the deviation range can be considered at the same time.
Description
Technical Field
The invention relates to the field of Intelligent Transportation (ITS) and particularly relates to an electronic license plate reader-writer and a reverse link frequency capture method of an electronic license plate.
Background
An electronic license plate, namely an automobile electronic identifier, is an electronic identity card which combines a common license plate with an ultrahigh Frequency Radio Frequency Identification (RFID) technology. The automobile electronic identification is used as the basis of intelligent traffic, can help traffic management departments to realize fine management of vehicles, will guide the revolution of the intelligent traffic industry, and drive the upgrading of the comprehensive traffic management system. In addition, the electronic license plate is also one of the entrances of the Internet of vehicles. The traffic big data obtained by the electronic license plate can benefit traffic big data operation services such as bus electronic stop plate operation, real-time traffic road condition information service, pedestrian navigation and the like.
The automobile electronic identification system is characterized in that an RFID passive electronic tag used for storing automobile identity data is arranged on the inner side of a front windshield of an automobile and is communicated with an electronic license plate high-speed reader-writer arranged on the section of an urban road, so that data in the RFID tag can be read and written. The electronic license plate conforms to the national standard of GB/T29768-2013 radio frequency identification 800/900MHz air interface protocol in information technology and the general technical requirement of electronic identification of motor vehicles formulated by the ministry of public Security.
In an automobile electronic identification system, an on-chip clock circuit of an ultrahigh frequency passive tag is influenced by factors such as the process, the temperature and the like, the frequency of a reverse link which is backscattered to a reader-writer has larger deviation, the frequency deviation range is-20% to + 20% within the temperature range of-25 ℃ to 60 ℃ specified by national standards, and in practical application, the frequency deviation of the tag which is put into the market at an early stage exceeds the range when the temperature changes greatly, so that the reader-writer also needs to apply a frequency capture technology which can be compatible with the larger deviation range in order to efficiently analyze tag return data.
In a general wireless communication system, carrier frequency acquisition is often achieved through correlation of preamble sequences, cross-correlation calculation is performed using a local sequence and a received signal, and a frequency-frequency difference of a carrier is estimated through the cross-correlation. In the RFID system, because the frequency deviation of the reverse link of the passive tag is large, the reader-writer adopts a similar technology to realize the frequency capture and the frame synchronization information of the reverse link, the local sequence and the received signal are subjected to cross-correlation calculation, and whether the correlation value reaches the threshold value of synchronization judgment is judged.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide an electronic license plate reader and a method for capturing a reverse link frequency of an electronic license plate, aiming at the defect that the above prior art is difficult to consider the synchronization accuracy and the compatibility of the deviation range.
The technical scheme adopted by the invention for solving the technical problems is as follows: a reverse link frequency capturing method of an electronic license plate is constructed, and the method comprises the following steps:
s10, respectively sending return signals of the electronic tag into at least two correlators, wherein the frequencies of the at least two correlators are different, and the frequency of one correlator is a reference frequency;
s20, each path of correlator determines the self correlation of the pilot frequency sequence of the return signal and judges whether a pilot frequency symbol is detected according to the correlation;
and S30, the correlator which detects the pilot frequency symbols determines the corrected reverse link frequency according to the determined correlation of the pilot frequency sequence.
Preferably, the step S20 includes:
s21, performing autocorrelation calculation on a pilot frequency symbol segment in a first preset pilot frequency symbol group in a pilot frequency sequence of the return signal;
s22, performing cross-correlation calculation on two pilot frequency symbol sections in a second preset pilot frequency symbol group in the pilot frequency sequence of the return signal;
and S23, judging whether the pilot frequency symbol is detected or not by comparing the difference between the cross-correlation calculation result and the autocorrelation calculation result.
Preferably, in step S21, the first pilot symbol segment and the third pilot symbol segment in the first preset pilot symbol set are subjected to autocorrelation calculation according to formula 1:
wherein S1 is the first pilot symbol segment, S3 is the third pilot symbol segment, R0 is the autocorrelation calculation result of the first pilot symbol segment, and R1 is the autocorrelation calculation result of the third pilot symbol segment;
in step S22, performing a cross-correlation calculation on the first pilot symbol segment and the second pilot symbol segment in the second preset pilot symbol group according to formula 2, and performing a cross-correlation calculation on the first pilot symbol segment and the third pilot symbol segment in the second preset pilot symbol group:
wherein S2 is the second pilot symbol segment, R2 is the cross-correlation calculation result of the first pilot symbol segment and the second pilot symbol segment, and R3 is the cross-correlation calculation result of the first pilot symbol segment and the third pilot symbol segment.
Preferably, the step S23 includes:
whether a pilot symbol is detected is determined by determining whether the condition of equation 3 is satisfied:
wherein | R0|, | R1|, | R2|, | R3| are the amplitudes of R0, R1, R2, R3 respectively, angle R2 and angle R3 represent the phase angles of R2, R3 respectively, round (2 × R2-angle R3) represents the nearest integer to the difference between the two phase angles, a is a preset amplitude threshold, and B is a preset phase threshold.
Preferably, in the step S30, the corrected reverse link frequency is determined according to formula 4:
where P1 is the corrected reverse link frequency and P0 is the current correlator frequency.
Preferably, the number of correlators is three, wherein one correlator frequency is higher than the reference frequency and one correlator frequency is lower than the reference frequency;
the step S30 includes:
judging whether the number of correlators for detecting the pilot frequency symbols is two or not, wherein the correlators comprise a path of correlator with frequency as reference frequency;
if yes, a path of correlator with the frequency as the reference frequency is preferentially selected, and the corrected reverse link frequency is determined according to the correlation of the pilot frequency sequence determined by the selected correlator.
Preferably, the number of correlators is three, wherein one correlator frequency is higher than the reference frequency and one correlator frequency is lower than the reference frequency;
the step S30 includes:
judging whether the number of correlators for detecting the pilot frequency symbols is two or not, wherein the correlators do not comprise a path of correlator with the frequency as the reference frequency;
if yes, calculating difference absolute values of the frequency of the corresponding correlator and the corrected reverse link frequency respectively, selecting the correlator corresponding to the smaller difference absolute value, and determining the corrected reverse link frequency according to the correlation of the pilot frequency sequence determined by the selected correlator.
Preferably, before the step S10, the method further includes:
sequentially carrying out noise cancellation, demodulation, intermediate frequency filtering and amplification processing on a return signal of the electronic tag;
performing AD sampling on the amplified signal to acquire a digital signal;
and carrying out sampling rate conversion on the digital signal.
The invention also constructs an electronic license plate reader-writer, which comprises a processor and a memory, and is characterized in that the processor realizes the method of any one of the above items when executing the computer program stored in the memory.
Preferably, the mobile terminal further comprises a receiving processing module, and the receiving processing module comprises:
the analog processing unit is used for sequentially carrying out noise cancellation, demodulation, intermediate frequency filtering and amplification processing on a return signal of the electronic tag;
the AD sampling unit is used for carrying out AD sampling on the amplified signal so as to obtain a digital signal;
and the sampling rate conversion unit is used for carrying out sampling rate conversion on the digital signal.
By implementing the technical scheme of the invention, the return signals of the electronic license plate are simultaneously sent to the multi-channel correlators, and each channel of correlator obtains the synchronization and frequency deviation information of the pilot frequency symbol by analyzing the self-correlation of the pilot frequency sequence in the return signals, thereby being beneficial to accurately obtaining the frame synchronization position through the matching of the lead codes in the follow-up process and improving the reliability of the system. Moreover, the most reliable result is selected after independent calculation by the multi-path parallel correlator, so that a larger frequency difference range can be compatible. Therefore, the synchronization accuracy and the compatibility of the deviation range can be simultaneously considered.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts. In the drawings:
FIG. 1 is a flowchart of a first embodiment of a method for capturing a reverse link frequency of an electronic license plate according to the present invention;
fig. 2 is a format diagram of a preamble when encoded using FM 0;
fig. 3 is a flowchart of a first embodiment of step S20 in fig. 1.
Detailed Description
Fig. 1 is a flowchart of a first embodiment of a reverse link frequency acquisition method for an electronic license plate according to the present invention, the reverse link frequency acquisition method of the embodiment including the steps of:
s10, respectively sending return signals of the electronic tag into at least two correlators, wherein the frequencies of the at least two correlators are different, and the frequency of one correlator is a reference frequency;
s20, each path of correlator determines the self correlation of the pilot frequency sequence of the return signal and judges whether a pilot frequency symbol is detected according to the correlation;
and S30, the correlator which detects the pilot frequency symbols determines the corrected reverse link frequency according to the determined correlation of the pilot frequency sequence.
In this embodiment, it should be noted that the reference frequency refers to the reverse link frequency of the electronic license plate without deviation, and in the case of determining the electronic license plate, the reference frequency is a known value. Specifically, the reverse link frequency that the electronic license plate system specified by the electronic identification national standard needs to support has a total of 8 definite values. Moreover, a plurality of parallel correlators are arranged in the electronic license plate reader-writer, and each correlator corresponds to different reverse link frequency deviation references, namely, the frequency of each correlator is different.
It should also be noted that the reverse link data code used by the tags in the electronic license plates is FM0 code or miller code, as required by the national standard GB/T29768-2013. For example, FM0 encoding uses a preamble with pilots for FM0 encoding (TRext ═ 1), and as shown in fig. 2, all of the 12 pilot symbols of the pilot sequence are 0. After the return signals of the electronic tags are respectively sent to at least two correlators, the basic thought of each correlator is as follows: firstly, the synchronization of the pilot symbols is detected, because 12 pilot symbols are all 0, the correlation of the pilot sequence is very large, whether the pilot symbols are detected or not can be judged by detecting the correlation of a certain sequence and another sequence of the pilot sequence, and the frame synchronization position can be accurately acquired through the matching of the lead codes in the follow-up process; then calculates the reverse link frequency according to the self correlation. In addition, because the multipath parallel correlators perform independent calculation according to the thought and then select reliable results, the method can be compatible with a larger frequency difference range.
Further, before sending the return signal of the electronic license plate to the correlator, the signal is processed, specifically, before step S10, the method further includes:
sequentially carrying out noise cancellation, demodulation, intermediate frequency filtering and amplification processing on a return signal of the electronic tag;
performing AD sampling on the amplified signal to acquire a digital signal;
and carrying out sampling rate conversion on the digital signal.
In an alternative embodiment, in conjunction with fig. 3, step S20 of this embodiment includes the steps of:
s21, performing autocorrelation calculation on a pilot frequency symbol segment in a first preset pilot frequency symbol group in a pilot frequency sequence of the return signal;
s22, performing cross-correlation calculation on two pilot frequency symbol sections in a second preset pilot frequency symbol group in the pilot frequency sequence of the return signal;
and S23, judging whether the pilot frequency symbol is detected or not by comparing the difference between the cross-correlation calculation result and the autocorrelation calculation result.
In this embodiment, it is first explained that the first predetermined pilot symbol group includes at least one pilot symbol segment, and the second predetermined pilot symbol group includes at least two pilot symbol segments. Moreover, the pilot symbol segments included in the first preset pilot symbol group may all exist in the second preset pilot symbol group, or the pilot symbol segments included in the first preset pilot symbol group may only partially exist in the second preset pilot symbol group, or the second preset pilot symbol group and the pilot symbol segments in the first preset pilot symbol group are completely different.
It should be noted that, in a specific application, the lengths of all pilot symbol segments are the same, and the length of the pilot symbol segment may be 2 to 6 pilot symbols, preferably 4, because: if the value is too small, the noise is easy to be used as a useful signal, false detection occurs, but if the value is too large, missed detection occurs easily, and the interference resistance and the reliability of the system are not facilitated. And when judging whether the pilot frequency symbol is detected according to the self-correlation of the pilot frequency sequence, firstly calculating the self-correlation information of the pilot frequency symbol section under the fixed symbol length for the received signal, then carrying out the cross-correlation calculation for the two pilot frequency symbol sections, and finally comparing the difference between the cross-correlation calculation result and the self-correlation calculation result.
Further, the first preset pilot symbol group includes two pilot symbol segments: a first pilot symbol segment S1, a third pilot symbol segment S3; the second preset pilot symbol group comprises three pilot symbol segments: a first pilot symbol segment S1, a second pilot symbol segment S2, and a third pilot symbol segment S3. Preferably, the first pilot symbol segment S1 and the third pilot symbol segment S3 do not contain identical pilot symbols, and the second pilot symbol segment S2 contains partially identical pilot symbols with the first pilot symbol segment S1, and the second pilot symbol segment S2 contains partially identical pilot symbols with the third pilot symbol segment S3. Specifically, at least two pilot symbols should be staggered between different pilot symbol segments. For example, in a specific application, the first pilot symbol segment S1 is a digital signal corresponding to 1 st, 2 nd, 3 rd, 4 th pilot symbols, S2 is a digital signal corresponding to 3 rd, 4 th, 5 th, 6 th pilot symbols, and S3 is a digital signal corresponding to 5 th, 6 th, 7 th, 8 th pilot symbols.
In an alternative embodiment, in step S21, the first pilot symbol segment and the third pilot symbol segment in the first preset pilot symbol set are subjected to autocorrelation calculation according to formula 1:
wherein, R0 is the autocorrelation calculation result of the first pilot symbol segment, and R1 is the autocorrelation calculation result of the third pilot symbol segment;
in step S22, cross-correlation calculation is performed on the first pilot symbol segment and the second pilot symbol segment in the second preset pilot symbol group according to formula 2, and cross-correlation calculation is performed on the first pilot symbol segment and the third pilot symbol segment in the second preset pilot symbol group:
where R2 is the cross-correlation calculation result of the first pilot symbol segment and the second pilot symbol segment, and R3 is the cross-correlation calculation result of the first pilot symbol segment and the third pilot symbol segment.
In step S23, it is determined whether a pilot symbol is detected by determining whether the condition of equation 3 is satisfied:
wherein | R0|, | R1|, | R2|, | R3| are the amplitudes of R0, R1, R2, R3 respectively, angle R2 and angle R3 represent the phase angles of R2, R3 respectively, round (2 × R2-angle R3) represents the nearest integer to the difference between the two phase angles, a is a preset amplitude threshold, and B is a preset phase threshold.
Further, in step S23, if it is judged that the amplitude condition and the phase condition of equation 3 are satisfied, it is determined that the pilot symbol is detected; and if the judgment result does not meet any condition of the formula 3, determining that no pilot frequency symbol is detected.
In this embodiment, first, the 1 st, 2 nd, 3 rd and 4 th pilot symbols are subjected to autocorrelation calculation, and the 5 th, 6 th, 7 th and 8 th symbols are subjected to autocorrelation calculation, so as to obtain the amplitude and phase of the two autocorrelation calculation results. Then, the 1 st, 2 nd, 3 rd and 4 th pilot symbols and the 3 rd, 4 th, 5 th and 6 th pilot symbols are subjected to cross-correlation calculation, and then the 1 st, 2 nd, 3 th and 4 th pilot symbols and the 5 th, 6 th, 7 th and 8 th pilot symbols are subjected to cross-correlation calculation, so that the amplitude and the phase of two cross-correlation calculation results are obtained. And finally, comparing the two cross-correlation amplitudes with the self-correlation amplitude, and if the two ratios are both greater than a set amplitude threshold value and the difference value of the two phases is less than a set phase threshold value, determining that the pilot frequency symbol is detected.
In an alternative embodiment, after pilot synchronization is completed, in step S30, a corrected reverse link frequency is determined according to equation 4:
where P1 is the corrected reverse link frequency and P0 is the current correlator frequency.
Furthermore, the multiple parallel correlators are all processed according to the same pilot frequency symbol length, and each correlator corresponds to different reverse link frequency offset references. Because the number of sampling points corresponding to a fixed number of pilot symbols has a large difference when the frequency deviation is large, in order to improve the precision of frequency acquisition and support a large frequency difference range, each path of correlator is processed by different sampling points respectively, and then a result with high reliability is selected from each path and output. Taking the example of processing according to 8 sampling points of each pilot symbol after sampling rate conversion, when there is no deviation in the reverse link frequency, 4 pilot symbols just correspond to 32 sampling points, and the correlator performs correlation accumulation calculation with 32 data as a unit. However, when the reverse link frequency difference is large, the number of real sampling points corresponding to 4 pilot symbols also changes greatly, and at this time, it is not 4 complete pilot symbols that enter the correlator, and the capture precision will be affected, so each correlator has different frequency offsets relative to the reference frequency, taking a three-way parallel correlator as an example, the frequency offset corresponding to the first way is-25%, the number of sampling points of 4 pilot symbols is 40, the frequency offset corresponding to the second way is 0, i.e., the reference frequency, the number of sampling points of 4 pilot symbols is 32, the frequency offset corresponding to the third way is + 25%, the number of sampling points of 4 pilot symbols is 24, and the three-way correlator performs correlation calculation according to the respective corresponding number of sampling points.
After the three correlators independently perform pilot frequency synchronization and reverse link frequency calculation, if only one correlator detects pilot frequency synchronization information, the calculated reverse link frequency is output to a subsequent module as a result, and if more than two correlators detect synchronization information, the correlator with high reliability needs to be selected as the result for output. The reference frequency offset of the three paths is-25%, 0 and + 25%, when the second path detects synchronization and the calculated reverse link deviation is in the range of-20% to + 20%, the result of the path is selected to be output, and when the deviation exceeds-20% or + 20%, the results of the first path and the third path are respectively selected to be output. The frequency deviation ranges corresponding to the three-way correlator are shown in the following table.
| Serial number | Reference frequency difference | Number of pilot symbols | Number of sampling points | Range of frequency deviation |
| 1 | -25％ | 4 | 40 | <-20％ |
| 2 | 0 | 4 | 32 | -20％～+20％ |
| 3 | +25％ | 4 | 24 | >20％ |
Regarding the selection of the result, if the number of correlators is three, and one of the correlator frequencies is higher than the reference frequency and one of the correlator frequencies is lower than the reference frequency, in one embodiment, step S30 includes:
judging whether the number of correlators for detecting the pilot frequency symbols is two or not, wherein the correlators comprise a path of correlator with frequency as reference frequency;
if yes, a path of correlator with the frequency as the reference frequency is preferentially selected, and the corrected reverse link frequency is determined according to the correlation of the pilot frequency sequence determined by the selected correlator.
In another embodiment, step S30 includes:
judging whether the number of correlators for detecting the pilot frequency symbols is two or not, wherein the correlators do not comprise a path of correlator with the frequency as the reference frequency;
if yes, calculating difference absolute values of the frequency of the corresponding correlator and the corrected reverse link frequency respectively, selecting the correlator corresponding to the smaller difference absolute value, and determining the corrected reverse link frequency according to the correlation of the pilot frequency sequence determined by the selected correlator.
The invention also constructs an electronic license plate reader-writer, which comprises a processor and a memory, and is characterized in that the processor realizes the reverse link frequency capture method of the electronic license plate when executing the computer program stored in the memory.
Further, the electronic license plate reader-writer further comprises a receiving processing module, and the receiving processing module comprises: the device comprises an analog processing unit, an AD sampling unit and a sampling rate conversion unit. The analog processing unit is used for sequentially carrying out noise cancellation, demodulation, intermediate frequency filtering and amplification processing on a return signal of the electronic tag; the AD sampling unit is used for carrying out AD sampling on the amplified signal so as to obtain a digital signal; and the sampling rate conversion unit is used for carrying out sampling rate conversion on the digital signal.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims (6)
1. A reverse link frequency acquisition method of an electronic license plate is characterized by comprising the following steps:
s10, respectively sending return signals of the electronic tag into at least two correlators, wherein the frequencies of the at least two correlators are different, and the frequency of one correlator is a reference frequency;
s20, each path of correlator determines the self correlation of the pilot frequency sequence of the return signal and judges whether a pilot frequency symbol is detected according to the correlation;
s30, determining corrected reverse link frequency by the correlator which detects the pilot frequency symbol according to the correlation of the determined pilot frequency sequence;
wherein the step S20 includes:
s21, performing autocorrelation calculation on a pilot frequency symbol segment in a first preset pilot frequency symbol group in a pilot frequency sequence of the return signal;
s22, performing cross-correlation calculation on two pilot frequency symbol sections in a second preset pilot frequency symbol group in the pilot frequency sequence of the return signal;
s23, judging whether a pilot frequency symbol is detected or not by comparing the difference between the cross-correlation calculation result and the autocorrelation calculation result;
in step S21, an autocorrelation calculation is performed on the first pilot symbol segment and the third pilot symbol segment in the first preset pilot symbol set according to formula 1:
wherein S1 is the first pilot symbol segment, S3 is the third pilot symbol segment, R0 is the autocorrelation calculation result of the first pilot symbol segment, and R1 is the autocorrelation calculation result of the third pilot symbol segment;
in step S22, performing a cross-correlation calculation on the first pilot symbol segment and the second pilot symbol segment in the second preset pilot symbol group according to formula 2, and performing a cross-correlation calculation on the first pilot symbol segment and the third pilot symbol segment in the second preset pilot symbol group:
wherein, S2 is a second pilot symbol segment, R2 is a cross-correlation calculation result of the first pilot symbol segment and the second pilot symbol segment, and R3 is a cross-correlation calculation result of the first pilot symbol segment and the third pilot symbol segment;
the step S23 includes:
whether a pilot symbol is detected is determined by determining whether the condition of equation 3 is satisfied:
the phase angle of R2 and R3 is represented by | R0|, | R1|, | R2|, and | R3|, respectively, the amplitudes of R0, R1, R2, and R3, | R2 and | R3, the phase angle of roundd (2 | -R2-R3) represents that the nearest integer is taken for the difference value of two phase angles, A is a preset amplitude threshold value, and B is a preset phase threshold value;
in step S30, a corrected reverse link frequency is determined according to equation 4:
where P1 is the corrected reverse link frequency and P0 is the current correlator frequency.
2. The method of claim 1, wherein the number of correlators is three, one of the correlators having a frequency higher than a reference frequency and one of the correlators having a frequency lower than the reference frequency;
the step S30 includes:
judging whether the number of correlators for detecting the pilot frequency symbols is two or not, wherein the correlators comprise a path of correlator with frequency as reference frequency;
if yes, a path of correlator with the frequency as the reference frequency is preferentially selected, and the corrected reverse link frequency is determined according to the correlation of the pilot frequency sequence determined by the selected correlator.
3. The method of claim 1, wherein the number of correlators is three, one of the correlators having a frequency higher than a reference frequency and one of the correlators having a frequency lower than the reference frequency;
the step S30 includes:
judging whether the number of correlators for detecting the pilot frequency symbols is two or not, wherein the correlators do not comprise a path of correlator with the frequency as the reference frequency;
if yes, calculating difference absolute values of the frequency of the corresponding correlator and the corrected reverse link frequency respectively, selecting the correlator corresponding to the smaller difference absolute value, and determining the corrected reverse link frequency according to the correlation of the pilot frequency sequence determined by the selected correlator.
4. The method for capturing the reverse link frequency of an electronic license plate of claim 1, further comprising, before the step S10:
sequentially carrying out noise cancellation, demodulation, intermediate frequency filtering and amplification processing on a return signal of the electronic tag;
performing AD sampling on the amplified signal to acquire a digital signal;
and carrying out sampling rate conversion on the digital signal.
5. An electronic license plate reader comprising a processor and a memory, wherein the processor implements the method of any one of claims 1-4 when executing a computer program stored in the memory.
6. The electronic license plate reader of claim 5, further comprising a reception processing module, and wherein the reception processing module comprises:
the analog processing unit is used for sequentially carrying out noise cancellation, demodulation, intermediate frequency filtering and amplification processing on a return signal of the electronic tag;
the AD sampling unit is used for carrying out AD sampling on the amplified signal so as to obtain a digital signal;
and the sampling rate conversion unit is used for carrying out sampling rate conversion on the digital signal.
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