CN116415601A - Improved RFID reader frequency estimation method and estimation module - Google Patents
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- G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
- G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
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- G06K7/10198—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves setting parameters for the interrogator, e.g. programming parameters and operating modes
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- 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
- G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
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- 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
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- G06K7/10217—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves setting parameters for the interrogator, e.g. programming parameters and operating modes parameter settings controlling the transmission power of the interrogator
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Abstract
The invention discloses an improved RFID reader frequency estimation method and an estimation module. The method comprises the following steps: performing correlation processing on I, Q signals by adopting a first correlator group with a plurality of first parallel correlators, wherein the frequency offset of the correlator corresponding to the correlation maximum value is used as a rough estimated frequency offset; performing correlation processing on the I, Q signal by using a second correlator set; and respectively carrying out power calculation on the correlation values output by the correlators, adding and combining I, Q paths of power, then carrying out serial peak detection, obtaining the frequency offset of the correlators corresponding to the peak value, and further calculating to obtain the nearest estimated value of the frequency of the received signal. The invention provides a method for frequency estimation by correlation operation, which is different from the traditional method for frequency estimation by a correlator array.
Description
Technical Field
The invention relates to the technical field of electronics, in particular to an improved RFID reader frequency estimation method and a corresponding estimation module.
Background
RFID is a contactless radio frequency identification technology that performs contactless communication using electromagnetic wave induction, radio waves, and performs data exchange to achieve a technology of identifying an object. At present, the RFID technology is widely applied to various fields such as logistics, tracking, monitoring, entrance guard and the like. And the passive tag has the advantages of low cost, small size, long service life, easy production and the like, and becomes the mainstream of RFID system application, however, the passive tag has the problems of difficult guarantee of tag power supply energy, weak return signal, easy space environment interference and the like, and higher requirements are put forward on the reader-writer.
Because the passive tag has no clock calibration circuitry inside, the link frequency returned by the tag may deviate from the data frequency set by the reader by-22% to +22%. Meanwhile, in the received signal, the data frame header used for synchronization is very short, and the synchronization frame header in each received data frame only appears once, if the frame header cannot be analyzed, the communication will fail.
In view of the above-described analysis disadvantages, further improvements and refinements are needed for RFID systems to be better utilized.
Disclosure of Invention
The invention mainly aims at solving the problem of frequency deviation of a received signal and provides an effective solution.
Specifically, the invention provides an improved RFID reader frequency estimation method, which is characterized by comprising the following steps:
step 1, receiving an RFID radio frequency signal and converting the RFID radio frequency signal into a I, Q signal;
step 3, comparing the correlation results obtained by the correlators, wherein the frequency offset of the correlator corresponding to the correlation maximum value is used as a rough estimated frequency offset;
step 4, performing correlation processing on the I, Q signal by using a second correlator set with a plurality of second parallel correlators, wherein the second parallel correlators have second frequency offset between each other, and the frequency offset of the second correlator set is set to cover the roughly estimated frequency offset;
and 5, respectively carrying out power calculation on the correlation values output by the second parallel correlators, adding and combining I, Q paths of power, carrying out serial peak detection, obtaining the frequency offset of the correlators corresponding to the peak value, and further calculating to obtain the nearest estimated value of the frequency of the received signal.
In a preferred implementation, the first correlator set covers a frequency offset of at least-22% to 22% of the target RFID tag transmit frequency.
In another preferred implementation, the first correlator set includes 8-14 correlators; the second correlator group comprises 3-6 correlators.
In another preferred implementation, the method further includes sequentially counting each symbol in the received data, and when the serial peak value output by the correlator is retrieved in the step 5, the received corresponding data count value is used as the position of the synchronous frame header, and the position information is used as the initial position of the data read by the storage unit.
In another aspect, the present invention provides an improved RFID reader frequency estimation module, wherein the RFID reader frequency estimation module comprises: a first correlator set having a plurality of first correlators, a second correlator set having a plurality of second correlators, a comparison module, a power calculation module, and a peak detection module,
the first correlators are used for respectively carrying out correlation processing on I, Q signals received by the RFID reader-writer, the first parallel correlators have preset frequency offset, and the first parallel correlators have the same local code element;
the comparison module is used for comparing the correlation results obtained by the correlators, and the frequency offset of the correlator corresponding to the correlation maximum value is used as a rough estimated frequency offset;
the plurality of second parallel correlators are used for carrying out correlation processing on the I, Q signals, the second parallel correlators are provided with second frequency offset between each other, and the frequency offset of the second correlator group is set to cover the roughly estimated frequency offset;
the power calculation module is used for carrying out power calculation on the correlation value output by each second parallel correlator and adding and combining I, Q paths of power;
the peak detection module is used for carrying out serial peak detection and obtaining the frequency offset of the correlator corresponding to the peak so as to obtain the nearest estimated value of the frequency of the received signal.
In another preferred implementation, the first correlator set covers a frequency offset of at least-22% to 22% of the target RFID tag transmit frequency.
In another preferred implementation, the first correlator set includes 8-14 correlators; the second correlator group comprises 3-6 correlators.
In another preferred implementation, the method further includes a bias counter for sequentially counting each symbol in the received data, and when the serial peak value output by the correlator is retrieved, the received corresponding data count value is used as the position of the synchronous frame header, and the position information is used as the initial position of the data read by the storage unit.
In another preferred implementation, the device further comprises a storage unit for storing the received data.
Technical effects
The invention provides a method for frequency estimation by correlation operation, which is different from the traditional method for frequency estimation by a correlator array, wherein a secondary correlator group is adopted to respectively perform correlation operation on a preamble and a synchronous frame head to obtain a frequency offset, and then an accurate frequency estimation value is obtained by calculation.
Firstly, the invention adopts a plurality of (12) parallel correlators as a first-stage correlator group to carry out frequency coarse estimation, each local code element of the correlators is 2 symbol leading code elements, the estimation precision of the frequency offset is 4%, and the frequency offset is obtained after the maximum value of the correlation is taken. Then, based on the frequency offset, 4 paths of parallel correlators are adopted as a second-stage correlator set to perform approximate frequency estimation on the received signal, the local code element of each correlator is 6 symbol synchronization frame head code elements, the estimation precision of the frequency offset reaches 1% of the fundamental frequency (preset RFID signal frequency), and an approximate frequency estimation value is calculated according to the frequency offset. Meanwhile, in the process of carrying out correlation power peak detection on the synchronous frame head at the second stage, the position information of the synchronous frame head in the received data is extracted, so that the data starting position of the received data after the synchronous frame head is removed can be obtained. The method provides accurate frequency estimation value and received data initial identification information for subsequent data demodulation, and improves demodulation accuracy more effectively under the condition of the same signal-to-noise ratio, so as to optimize the receiving performance of the reader-writer.
Drawings
FIG. 1 is a block diagram of an improved frequency estimation architecture based on the method of the present invention;
FIG. 2 is a schematic diagram of a frequency coarse estimation module according to the method of the present invention;
FIG. 3 is a schematic diagram of a frequency approximation estimation module according to the method of the present invention;
FIG. 4 is a waveform diagram of test received data (time domain signal characteristics of test received symbol data frames at 6dB signal-to-noise ratio, with frequency offset);
fig. 5 is a diagram of a test map symbol data waveform (time domain signal characteristics of a test received symbol data frame at a 6dB signal-to-noise ratio).
Fig. 6 is a power peak detection time domain waveform.
Detailed Description
The RFID reader synchronization method of the present invention is described in detail below with reference to the accompanying drawings.
The improved frequency estimation method of the RFID reader of the present embodiment adopts an architecture design as shown in fig. 1. The frequency estimation design comprises two parts, namely a frequency coarse estimation and a frequency approximate estimation.
1. Frequency coarse estimation module
The frequency coarse estimation module samples 12 groups of correlators to perform coarse frequency estimation on a received signal (including a synchronous frame header and data information), and as shown in fig. 2, the module architecture consists of a preamble correlator group module, a maximum value taking module and a frequency coarse estimation value acquisition module.
Defined by a correlation function, the correlation calculation may be expressed as a sum of products of two correlation functions over a given time interval, as follows:
equation (1) is a cross-correlation function of signals x (n) and y (n). The expression r xy (m) the correlation calculation at time m is equal to the result of corresponding multiplication and addition of two sequences after x (n) is kept stationary and y (n) is shifted left by m sample points. In the present invention, the local symbol inside the correlation is denoted by x (n), and y (n) is the input signal, i.e., the received signal.
In order to obtain better frequency estimation accuracy, in this embodiment, 12 parallel correlators are used to perform correlation processing on the received signal to achieve the capturing operation of the preamble of the received signal, where the frequency offset covered by the correlator set ranges from-22% to 22%, and between any two correlators in the 12 correlators, there is a frequency difference of 4% relative to the fundamental frequency. Each correlator in this embodiment uses the same local symbol, i.e. the preamble of the input signal, but each correlator uses a different frequency. Miller2 was chosen as an example, the Miller2 subcarrier preamble meaning 2 fundamental waves per symbol, each employing 20-fold oversampling. When the fundamental frequency offset is-22%, the number of sampling points of the correlator is as follows:
when the frequency offset of the fundamental wave is 22%, the number of sampling points of the correlator is as follows:
according to the calculation, the number of sampling points of the correlators corresponding to different frequency offsets can be obtained. The frequency offset corresponding to each correlator in the correlator set and the number of samples per fundamental wave are shown in table 1. This embodiment uses 2 symbols as correlator local symbols. Taking the minimum number of samples as an example, miller2 corresponds to a correlator local symbol with a frequency offset of 22% as follows: mille2_preamble= 66' b 01_0101_0101_0101_1111_1111_1111_1111_1101_1101_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111 of 1_0111_1111_1111_1111 a. The invention relates to a method for producing a fibre-reinforced plastic composite a. The invention relates to a method for producing a fibre-reinforced plastic composite.
In this embodiment, each correlator is designed as a complex correlator, that is, each correlator performs correlation operation on data of two paths I, Q at the same time, inputs correlation results obtained by calculation of each correlator into a maximum value taking module, compares each correlation result, selects a maximum value, and uses a frequency offset of the correlator corresponding to the maximum value as a frequency offset output by a frequency coarse estimation module.
2. Frequency approximation estimation module
Since the data frame header (synchronization frame header data) available for synchronization in the received signal is very short, only 6 symbols are available, in order to increase the success rate of capturing the synchronization frame header, the embodiment uses a 4-way parallel correlator as the second-stage correlator set to perform approximate frequency offset estimation, as shown in fig. 3.
The module adopts a correlator group consisting of 4 approximate correlators, and also correlates I, Q two paths of received data. The reference baseband frequency of the approximate correlator set is the frequency offset output by the above-mentioned frequency coarse estimation (for example, assuming that the frequency offset obtained by the frequency coarse estimation is 22%, the second set of correlators are set to offset, for example, 22%, 21%, 20% and 19% relative to the baseband frequency, that is, the coverage range covered by the corresponding correlators in the first correlator set is covered, and the difference is finer), and 4 sets of correlators are used to set the frequency offset on the basis of the offset, and each correlator frequency offset value is set in the same manner as the frequency coarse estimation set described above, and it can be known from table 2 that the frequency offset of the frequency estimated value relative to the baseband frequency can reach 1%, so as to further improve the frequency estimation accuracy. In this embodiment, miller2 is taken as a reference example, the synchronization frame header symbol is 010111, and each correlator uses 6 symbol synchronization frame headers as local symbols. Assuming that the frequency offset of the frequency coarse estimation value is 18%, the number of fundamental wave sampling points corresponding to the approximate correlator 2 is 17.09, the number of local symbols of the correlator is 6×2×17.09=205.8, and the number of local symbols of each correlator can be calculated by the same method, and the local symbols are converted into local symbol information by referring to the synchronous frame header symbols.
In order to increase the accuracy of synchronous frame header detection, power calculation (squaring of the correlation value) is performed on the correlation values output by the correlators in the second group of correlators, I, Q paths of power are added and combined, serial peak detection is performed, the frequency offset of the correlators corresponding to the peak is obtained, and then the nearest estimated value of the frequency of the received signal is calculated.
Meanwhile, a deviation counter (offset) is set in the frequency approximation estimation module to record the deviation between the received data (including the preamble and the data information) and the peak point of the correlation result, and when the receiving end starts to receive the data frame, the deviation counter starts to count for each received symbol. When the correlation power peak value of the correlator group is searched, the accumulated value of the corresponding received data accumulated count value, namely the accumulated value of the offset counter (offset), is the position information of the synchronization frame header (only when six symbols are all synchronized, the correlation peak value is the largest, and the six symbols are determined to be the synchronization frame header), the next position information of the position information (six symbols) is used as the initial position of the data read by the storage unit, and the data in the data receiving buffer unit is the received data after the synchronization frame header is removed from the moment. The next position of the offset counter (offset) at this time is the actual data start point. Therefore, the improved synchronization method in this embodiment can obtain more accurate frequency estimation value and position information of the synchronization frame header, and provide frequency and effective data information for the subsequent data decoding module.
Through simulation test, the improved frequency estimation method based on the two-stage correlator group can be applied to a channel environment with a signal-to-noise ratio greater than 6Db, in an embodiment, test received data with a signal-to-noise ratio of 6Db is introduced, the test data consists of a preamble, a synchronous frame head and random data in a protocol, and the oversampling rate is 20 times as high as that of the sample, as shown in figure 4. Because the test received data is sampled data after ADC sampling and down-conversion processing, mapping processing is carried out on the received signal before symbol data processing, and when the received data is greater than 0, the sampled data is mapped to be 01; when the received data is smaller than 0, the sample point data is mapped to 11, and the symbol data waveform after the mapping process is shown in fig. 5. The received symbol data is subjected to a two-level frequency estimation, wherein fig. 6 is a time domain waveform diagram of power peak detection at the time of frequency approximation estimation.
Table 1 correlator bank parameters
| Correlator numbering | Frequency offset | Fundamental wave sampling point number | Remarks |
| 1 | 22％ | 16.39 | |
| 2 | 18％ | 16.94 | |
| 3 | 14％ | 17.54 | |
| 4 | 10％ | 18.18 | |
| 5 | 6％ | 18.86 | |
| 6 | 2％ | 19.6 | |
| 7 | -2％ | 20.4 | |
| 8 | -6％ | 21.27 | |
| 9 | -10％ | 22.22 | |
| 10 | -14％ | 23.25 | |
| 11 | -18％ | 24.3 | |
| 12 | -22％ | 25.64 |
Table 2 approximate correlator bank parameters
While the principles of the invention have been described in detail in connection with the preferred embodiments thereof, it should be understood by those skilled in the art that the foregoing embodiments are merely illustrative of the implementations of the invention and are not intended to limit the scope of the invention. The details of the embodiments are not to be taken as limiting the scope of the invention, and any obvious modifications based on equivalent changes, simple substitutions, etc. of the technical solution of the invention fall within the scope of the invention without departing from the spirit and scope of the invention.
Claims (9)
1. An improved method of estimating frequency of an RFID reader, the method comprising:
step 1, receiving an RFID radio frequency signal and converting the RFID radio frequency signal into a I, Q signal;
step 2, performing correlation processing on the I, Q signal by adopting a first correlator with a plurality of first parallel correlators respectively, wherein the first parallel correlators have preset frequency offset, and the first parallel correlators have the same local code element;
step 3, comparing the correlation results obtained by the correlators, wherein the frequency offset of the correlator corresponding to the correlation maximum value is used as a rough estimated frequency offset;
step 4, performing correlation processing on the I, Q signal by using a second correlator set with a plurality of second parallel correlators, wherein the second parallel correlators have second frequency offset between each other, and the frequency offset of the second correlator set is set to cover the roughly estimated frequency offset;
and 5, respectively carrying out power calculation on the correlation values output by the second parallel correlators, adding and combining I, Q paths of power, carrying out serial peak detection, obtaining the frequency offset of the correlators corresponding to the peak value, and further calculating to obtain the nearest estimated value of the frequency of the received signal.
2. The method of claim 1, wherein the first correlator bank covers a frequency offset of at least-22% to 22% of the transmit frequency of the target RFID tag.
3. The RFID reader frequency estimation method of claim 1, wherein the first correlator set includes 8-14 correlators; the second correlator group comprises 3-6 correlators.
4. The RFID reader frequency estimation method according to claim 1, further comprising sequentially counting each symbol in the received data, and when the serial peak value outputted from the second parallel correlator is retrieved in the step 5, taking the received corresponding data count value as the position of the synchronization frame header, and taking the next position of the position information as the initial position of the data read by the storage unit.
5. An improved RFID reader frequency estimation module, the RFID reader frequency estimation module comprising: a first correlator set having a plurality of first correlators, a second correlator set having a plurality of second correlators, a comparison module, a power calculation module, and a peak detection module,
the first correlators are used for respectively carrying out correlation processing on I, Q signals received by the RFID reader-writer, the first parallel correlators have preset frequency offset, and the first parallel correlators have the same local code element;
the comparison module is used for comparing the correlation results obtained by the correlators, and the frequency offset of the correlator corresponding to the correlation maximum value is used as a rough estimated frequency offset;
the plurality of second parallel correlators are used for carrying out correlation processing on the I, Q signals, the second parallel correlators are provided with second frequency offset between each other, and the frequency offset of the second correlator group is set to cover the roughly estimated frequency offset;
the power calculation module is used for carrying out power calculation on the correlation value output by each second parallel correlator and adding and combining I, Q paths of power;
the peak detection module is used for carrying out serial peak detection and obtaining the frequency offset of the correlator corresponding to the peak so as to obtain the nearest estimated value of the frequency of the received signal.
6. The RFID reader frequency estimation module of claim 5, wherein the first correlator bank covers a frequency offset of at least-22% to 22% of the target RFID tag transmit frequency.
7. The RFID reader frequency estimation module of claim 5, wherein the first correlator bank comprises 8-14 correlators; the second correlator group comprises 3-6 correlators.
8. The RFID reader frequency estimation module of claim 5, further comprising a bias counter for sequentially counting each symbol in the received data, wherein when the serial peak value of the correlator output is retrieved, the received corresponding data count value is used as a position of the synchronization frame header, and a next position of the position information is used as an initial position of the storage unit read data.
9. The RFID reader frequency estimation module of claim 5, further comprising a storage unit for storing the received data.
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