KR20110027421A - Apparatus and method for decoding signal of radio frequency identification tag - Google Patents

Abstract

The present invention relates to an RFID tag signal decoding apparatus and method for accurately decoding a signal received from an RFID tag including signal distortion and frequency variation. In an RFID system, an RFID tag signal decoding apparatus calculates a distortion compensation value and a frequency variation value from a signal received from a tag, detects a length of a symbol, and determines a decoding value of the received signal according to the detected symbol length. Decoding means.

Description

Apparatus and method for decoding signal of radio frequency identification tag

The present invention relates to an RFID tag signal decoding apparatus and method for accurately decoding a signal received from an RFID tag including signal distortion and frequency variation.

RFID (radio frequency identification) system consists of a tag and a reader. In the communication between the tag and the reader, when the reader transmits a command requesting information stored in the tag, the tag responds to the command.

1A is a normal data pattern that a reader receives from a tag. This pattern must be correctly decoded for a unit of time in order for smooth communication between the reader and the tag. The unit time shown in FIG. 1A is a time varying by the communication mode (FM0 / Miller- / Miller-4 / Miller-8) or a predetermined link frequency between the reader and the tag. Defined as a symbol. In other words, a symbol is a protocol for delivering a message by the number of cycles of a signal transmitted for a certain time. When transmitting a signal from the tag to the reader in the RFID system, the data pattern shown in FIG. 1A is used. That is, 1 is transmitted when maintaining +1 or -1 during 1 symbol period, and 0 is transmitted when +1, -1 or -1, +1 is maintained during 1 symbol. do.

Under the wireless environment, communication has a lot of potential for error compared to the wired environment. For example, as shown in FIG. 1B, a signal is distorted on a communication channel between a reader and a tag due to interference with radio signals transmitted from other wireless communication devices. The distorted signal prevents the reader from correctly decoding the received signal.

Although communication is performed with a predetermined link frequency of a tag transmitted from a tag to a reader, a frequency tolerance can be generated as shown in FIG. 1C because the signal speed cannot be set due to the characteristics of a wireless environment. This frequency tolerance is a cause of frequency variation. Signals with frequency tolerances also have problems when distinguishing whether the current input signal is data 0 or data 1, but it affects the distinction between the signals that follow and cannot be decoded correctly.

As described above, there is a problem in that a large number of errors are generated when decoding a signal due to predictable noise, distortion, and frequency variation due to frequency tolerance during communication between the reader and the tag.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide an RFID tag signal decoding apparatus and method for accurately decoding a signal received from an RFID tag including signal distortion and frequency variation.

The RFID tag signal decoding apparatus for solving the technical problem to be achieved by the present invention, in the RFID system, calculates the distortion compensation and the frequency variation value from the signal received from the tag to detect the length of the symbol, the detected symbol length Preferably comprises decoding means for determining a decoding value of the received signal.

In the present invention, the decoding means includes: a frequency estimator for calculating an average symbol length of an initial pilot signal of a preamble among the received signals; A filter for filtering a signal based on the average symbol length; A frequency variation detector detecting a correlation value of the filtered signal and detecting a symbol length from the detected correlation value; And a determining unit to determine a decoding value of the received signal according to the symbol length.

In an embodiment of the present invention, the filter unit may be a matched filter that outputs a maximum output value for the received signal using the average symbol length as a bandwidth.

In the present invention, the frequency variation detection unit comprises: correlators for generating a plurality of correlation values from the filtered signal; A correlation value detector configured to detect a maximum correlation value among correlation values generated by the correlators; And a symbol length detector for detecting the number of samples included in the symbol from the maximum correlation value.

The RFID tag signal decoding method is an operation method of an RFID system, which includes: (a) a symbol of an initial pilot signal of the preamble signal with respect to a tag signal including a preamble and a data signal; Calculating a length average; (b) filtering a signal by the average symbol length; (c) detecting a correlation value of the filtered signal and detecting a symbol length from the detected correlation value; And (d) determining a decoding value of the received signal according to the symbol length.

In the present invention, the maximum output value may be output for the received signal using the average symbol length as the bandwidth during the filtering in the step (b).

In the present invention, step (c) comprises: (c-1) generating a plurality of correlation values from the filtered signal; (c-2) detecting a maximum correlation value among correlation values generated by the correlators; And (c-3) calculating the symbol length by detecting the number of samples included in the symbol from the maximum correlation value.

As described above, according to the present invention, it is possible to accurately decode a signal received from an RFID tag including signal distortion and frequency variation.

The performance of the reader is evaluated by the number of tags recognized per unit time and the recognition distance. Through accurate decoding, the performance of the reader can be improved by increasing the number of tag recognition and the tag recognition distance.

Hereinafter, with reference to the accompanying drawings, the configuration and operation of the embodiment of the present invention will be described in detail. The drawings and the description of the drawings are examples of the present invention, which does not limit the scope of the present invention.

The communication between the tag and the reader sends a preamble pattern as shown in FIG. 2, and then sends a data signal as shown in FIG. 3. FIG. 2A shows a preamble pattern in the FM0 communication mode, and FIG. 2B shows a preamble pattern in the Miller-2 / Miller-4 / Miller-8 communication mode. 3A shows a data signal in the FM0 communication mode, and FIG. 3B shows a preamble pattern in the Miller-2 / Miller-4 / Miller-8 communication mode.

4 is a diagram illustrating a baseband receiver of a reader including a decoder in an RFID system according to the present invention. The receiving antenna 100, the demodulator 200, the ADC 300, the digital filter 400, and the decoder 500 are shown in FIG. It includes.

Receive antenna 100 receives a signal from a tag.

The demodulator 200 demodulates and outputs a tag signal received through the receiving antenna 100. The demodulated signal is shown as a preamble and a data signal in FIGS. 2 and 3. The demodulator 200 then down converts the demodulated preamble and data signals to baseband. Subsequently, the down-converted signal to baseband is signaled through a band pass filter, a balun, a mixer, and a low pass filter, although not shown in the figure. Rental pass filters and low pass filters can remove noise from the signal at each stage. The received signal is input to the mixer after passing through the band pass filter and the balun. The mixer may convert the noise canceled and converted received signal and output it as an I channel baseband signal and a Q channel baseband signal. In this case, the mixer may include a quaternary phase mixer having a phase difference between an in-phase mixer and a 1 / 2π radian therein. The channel signal generated by the mixer may include an I channel signal and a Q channel signal. The I channel signal may correspond to the cosine component of the received signal, and the Q channel signal may correspond to the sine component of the received signal. The I / Q channel signal is input to the ADC 300 via a low pass filter.

The ADC 300 converts the demodulated analog signal into a digital signal.

The digital filter 400 filters the converted digital signal to remove noise.

The decoder 500 detects a length of a symbol by calculating a distortion compensation value and a frequency variation value from a signal received from a tag, and determines a decoding value of the received signal according to the detected symbol length.

FIG. 5 is a detailed block diagram of the decoder of FIG. 4, and includes a frequency estimator 510, a matched filter 520, a frequency variation detector 530, and a determiner 540.

The frequency estimator 510 calculates an average symbol length of the initial pilot signal of the preamble shown in FIG. 2 among the received signals of the tag. FIG. 6A shows a preamble signal and a pilot signal in Miller-4 communication mode, and FIG. 6B shows a preamble example of the received signal. FIG. 6C is an enlarged view of a pilot portion of the preamble signal in FIG. 6B. The frequency estimator 510 calculates a symbol length average of the pilot part in FIG. 6C, and counts the number of samples in one symbol to calculate a symbol length average of all pilot signals.

The matched filter 520 filters the signal based on the average symbol length. In order to minimize loss of information when the signal is transmitted through a medium having a limited bandwidth, the matched filter 520 transmits after limiting the band of the signal in advance. The band of the signal is an average symbol length calculated by the frequency estimator 510. The matched filter 520 is a filter used when the transmitter limits the band of the signal in order to maximize the signal-to-noise ratio at the receiver. That is, as a filter which shows the maximum output value with respect to the specific input signal of a certain shape, it is a filter whose filter is the reverse of an input signal factor. Filtering with the matched filter 520 is the same as autocorrelation of the input signal. This is used when the shape of the input wave is known, such as a Vibroceus signal. The amplitude and phase spectrum of matched filter 520 is the same as that of the signal but only opposite in sign. Matched filters are used to identify specific signals in noisy signals.

7A is a diagram illustrating an impulse frequency response of the matched filter 520, and it can be seen that the bandwidth is an average symbol length. 7B-1 illustrates an example of the impulse frequency response of the matched filter 520, FIG. 7B-2 illustrates a sample of the received signal, and FIG. 7B-3 illustrates the matched filtering result. It can be seen from FIG. 7B-3 that the matched filter 520 shows the maximum output value with respect to the signal of FIG. 7B-2.

8A illustrates signals that are distorted as signals input to the matched filter 520. 8B is an output signal of the matched filter 520, and it can be seen that distorted signals are compensated. FIG. 8C shows the effect of the matched filter 520 on the SNR increase observed in the frequency domain, FIG. 8C-1 shows the SNR of the signal input to the matched filter 520, and FIG. 8C-2 shows the matched filter 520. It shows the SNR of the signal output from, and it can be seen that the SNR increased after the matched filtering.

The frequency variation detection unit 530 calculates a correlation value from the matched filtered signal, detects a maximum correlation value, and detects a symbol length from the maximum correlation value.

9 is a detailed diagram of the frequency variation detector 530, and includes a first-Nth correlator 531-534, a correlation value detector 535, and a symbol length detector 536.

The first-Nth correlators 531-534 generate correlation values from the matched filtered signal. The frequency tolerance deviation causing the frequency variation is detected by the correlation bank (first-Nth correlators 531-534). Each correlator 531, 532, 533, 534 represents one symbol having a frequency tolerance, and frequency frequency tolerance deviation detection by each correlator 531, 532, 533, 534 is performed in units of symbols.

FIG. 10A shows a Miller-4 code input to a first-Nth correlator 531-534 for frequency tolerance deviation estimation and symbol detection, and FIG. 10B shows a symbol sample and data 1 representing data 0 of which Figure shows a symbol sample.

The correlation values generated by the first to Nth correlators 531 to 534 are input to the correlation value detector 535, and the correlation value detector 535 outputs a symbol having the maximum correlation value.

The symbol having the maximum correlation value is input to the symbol length detection unit 536, and the symbol length detection unit 536 counts the number of samples included in the symbol to detect the symbol length. 10C shows symbol detection by the first-Nth correlators 531-534 and the correlation value detector 535. FIG. 11A shows a matched filtering signal in which a frequency variation has occurred within a frequency tolerance, and FIG. 11B shows the detection of a symbol length in the frequency variation portion.

The determination unit 540 determines 0 and 1 of the input sample according to the detected symbol length. For example, in the case of Miller-2, when the input symbol is 01_01, the determination unit 540 may output 00 as a decoding result. When the input symbol is 10_01, the determination unit 540 outputs 11 as the decoding result. can do. In the case of Miller-4, when the input symbol is 0001_0001, the determination unit 540 may output 00 as a decoding result, and when the input symbol is 0100_0100, the determination unit 540 may output 11 as the decoding result. . In case of Miller-8, when the input symbol is 00000001_00000001, the determination unit 540 may output 00 as the decoding result, and when the input symbol is 00010000_00010000, the determination unit 540 may output 11 as the decoding result. .

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

FIG. 1 is a diagram illustrating definition of a basic symbol and signal distortion and frequency variation included in a signal received from a tag.

2 is a diagram illustrating a demodulated preamble signal received from a tag according to a communication mode FM0 / Mille.

3 is a diagram showing a demodulated data signal received from a tag according to a communication mode FM0 / Miller.

4 is a view showing a baseband receiver of the RFID tag signal decoding apparatus according to the present invention.

FIG. 5 is a detailed view of the decoder of FIG. 4.

FIG. 6 is a diagram illustrating a signal for explaining a frequency estimator in FIG. 5.

FIG. 7 is a diagram illustrating a signal for describing a matched filter in FIG. 5.

FIG. 8 is a diagram illustrating the effect of a matched filter on the result of simulating a distorted signal in the time domain according to the matched filter and an increase in the SNR observed in the frequency domain.

9 is a detailed view of the frequency variation detector of FIG. 5.

FIG. 10 is a diagram illustrating a signal for explaining the frequency variation detector of FIG. 9.

FIG. 11 is a diagram illustrating a signal for explaining a symbol length detection unit in FIG. 9.

Claims (7)

A reader for receiving an RFID tag signal, Decoding means for calculating a distortion compensation and frequency variation value from a signal received from a tag, detecting a length of a symbol, and determining a decoding value of the received signal according to the detected symbol length. The method of claim 1 wherein said decoding means A frequency estimator configured to calculate a symbol length average of an initial pilot signal of a preamble among the received signals; A filter for filtering a signal based on the average symbol length; A frequency variation detector detecting a correlation value of the filtered signal and detecting a symbol length from the detected correlation value; And And a determining unit to determine a decoding value of the received signal according to the symbol length. The method of claim 2, wherein the filter unit And a matched filter for outputting a maximum output value for the received signal using the average symbol length as a bandwidth. The method of claim 2, wherein the frequency variation detection unit Correlators for generating a plurality of correlation values from the filtered signal; A correlation value detector for detecting a maximum correlation value among the correlation values generated by the correlators; And And a symbol length detector for detecting the number of samples included in the symbol from the maximum correlation value. In the signal processing method of the reader for receiving the RFID tag signal, (a) calculating a symbol length average of an initial pilot signal of the preamble signal with respect to a tag signal including a preamble and a data signal; (b) filtering a signal by the average symbol length; (c) detecting a correlation value of the filtered signal and detecting a symbol length from the detected correlation value; And (d) determining a decoding value of the received signal according to the symbol length. The method of claim 5, wherein in step (b) And outputting a maximum output value for the received signal using the average symbol length as a bandwidth during the filtering. The method of claim 5, wherein step (c) (c-1) generating a plurality of correlation values from the filtered signal; (c-2) detecting a maximum correlation value among correlation values generated by the correlators; And (c-3) calculating the symbol length by detecting the number of samples included in the symbol from the maximum correlation value.

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