WO2009093815A1

WO2009093815A1 - Data receiving apparatus and receiving method thereof

Info

Publication number: WO2009093815A1
Application number: PCT/KR2008/007772
Authority: WO
Inventors: Yang-Hun Choi
Original assignee: Wicomm Technology Co., Ltd.
Priority date: 2008-01-24
Filing date: 2008-12-30
Publication date: 2009-07-30
Also published as: KR20090081686A; KR100940830B1

Abstract

Disclosed herein are a data receiving apparatus and a data receiving method therefor. The data receiving apparatus includes a reception unit, an Analog/Digital (AfD) conversion unit, and a signal processing unit. The reception unit receives and demodulates signals. The A/D conversion unit samples, digitally converts and then outputs the signals. The signal processing unit compares each digital signal with a preset reference value, changes the input digital signal to digital data according to a comparison result, and decodes the digital data by comparing the changed digital data with previously defined protocol code. If the digital signal is greater than the reference value, the signal processing unit changes the digital signal to corresponding digital data having a positive sign (+). In contrast, if the digital signal is smaller than the reference value, the signal processing unit changes the digital signal to corresponding digital data having a negative sign (-).

Description

DATA RECEIVING APPARATUS AND RECEIVING METHOD

THEREOF

Technical Field

[1] The present invention relates, in general, to a data receiving apparatus used in a

Radio-Frequency IDentification (RFID) system and a data receiving method therefor, and, more particularly, to a data receiving apparatus and a data receiving method therefor which receive and decode communication signals transmitted by a tag. Background Art

[2] An RFID system 10 generally refers to a data recognition system which is capable of reading data stored in the chip of an RFID tag at the request of an RFID reader. The RFID system 10, as shown in FIG. 1, includes an RFID tag 100 for storing unique information, an RFID reader 110 for performing reading and decryption functions, a host computer 120 for processing data read from the RFID tag, application software, and a network.

[3] The RFID tag 100 is also referred to as a transponder which is the compound word of a transmitter and a responder, and is configured to include an IC chip and an antenna circuit. Communication is performed through wireless access by the antenna and an RF module between the RFID tag and the RFID reader. The RFID reader 110 is also referred to as an interrogator, and is configured to include a separate data receiving apparatus and a separate data transmitting apparatus. A direction in which data is transmitted from the data transmitting apparatus of the RFID reader to the RFID tag is called an uplink, and a direction in which data is received from the RFID tag to the data receiving apparatus of the RFID reader is called a downlink.

[4] The data receiving apparatus of the RFID reader must have improved decoding accuracy in order to stably restore data received from the RFID tag.

[5] Furthermore, in the data receiving apparatus of the conventional RFID reader, a sampling frequency and the frequency of a demodulated reception signal must be synchronized with each other. The data receiving apparatus of the RFID system is however problematic in that inconsistency in phase and synchronization occurs due to the distance, reflection, etc. because the data receiving apparatus is based on wireless communication.

[6] Hitherto, in order to solve this problem, the data receiving apparatus of the RFID reader uses an additional sampling correction module before decoding is performed. However, this method produces a delay time depending on sampling correction because decoding is performed after the sampling correction is completed, thereby resulting in the reception apparatus processing slowly.

[7] In order to solve this problem, a method of increasing the sampling frequency of the data receiving apparatus has been proposed. However, if the sampling frequency of the data receiving apparatus is increased as described above, there are problems in that the amount of data that must be processed by the data receiving apparatus is increased and the time taken to restore a large amount of data is long. Furthermore, in order to process and analyze a large amount of received data, the data receiving apparatus of the RFID reader must use a high-speed processor or an additional processor, thereby resulting in increased manufacturing costs. Disclosure of Invention Technical Problem

[8] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a data receiving apparatus and a data receiving method therefor which are capable of increasing the accuracy of decoding and also correcting sampling error without the need to change or use the hardware of a data receiving apparatus in order to increase a sampling frequency. Technical Solution

[9] In order to achieve the above object, according to a first aspect of the present invention, there is provided a data receiving apparatus, including a reception unit for receiving and demodulating signals; an Analog/Digital (A/D) conversion unit for sampling the signals, demodulated by the reception unit, using a preset sampling frequency, converting the sampled signals into digital signals, and outputting the digital signals; and a signal processing unit for comparing each of the digital signals, received from the A/D conversion unit, with a preset reference value, changing the input digital signal to digital data according to a result of the comparison, and decoding the digital data by comparing the changed digital data with previously defined protocol code; wherein, if, as a result of the comparison, the digital signal is greater than the reference value, the signal processing unit changes the digital signal to digital data which has a positive sign (+) and corresponds to the digital signal, and, if, as a result of the comparison, the digital signal is smaller than the reference value, the signal processing unit changes the digital signal to digital data which has a negative sign (-) and corresponds to the digital signal.

[10] Preferably, the reception unit receives and demodulates RFID signals coded using

Miller code.

[11] The signal processing unit may include a change module for changing the input digital signal to the digital data, and the change module may change the input digital signal to the digital data by subtracting the reference value from the input digital signal.

[12] The data receiving further includes a memory unit for storing data, and the signal processing unit sequentially stores the digital data in the memory unit according to data size corresponding to the protocol code.

[13] The signal processing unit includes a decoding module for decoding the stored digital data.

[14] In this case, the decoding module reads digital data which was stored in the memory unit and corresponds to the data size, calculates a comparison value by comparing the read digital data set having the data size with the protocol code, and detects and co rrects sampling error of the digital data set generated during the sampling of the A/D conversion unit using the calculated comparison value and simultaneously outputs a result of decoding.

[15] Here, the decoding module of the signal processing unit may calculate the comparison value by multiplying the read digital data set by the data set of the protocol code in corresponding digit positions and adding values obtained through the multiplication in corresponding digit positions.

[16] Furthermore, the decoding module of the signal processing unit may determine whether sampling error has been generated by determining whether the comparison value falls within a preset error range, and, if, as a result of the determination, the sampling error is determined to have occurred, corrects the sampling error using digital data which was stored before or after the digital data set and belongs to the data stored in the memory unit.

[17] In greater detail, if a frequency of each of the signals demodulated by the reception unit is lower than a predetermined percentage of the sampling frequency and the sampling error is determined to have occurred, the decoding module of the signal processing unit may shift the digital data set to the left by one digital data unit and then fill the lowest digit position of the digital data set with digital data which belongs to the data stored in the memory unit and was stored after the digital data set.

[18] In contrast, if a frequency of each of the signals demodulated by the reception unit is higher than a predetermined percentage of the sampling frequency and the sampling error is determined to have occurred, the decoding module of the signal processing unit may shift the digital data set to the right by one digital data unit and then fill a highest digit position of the digital data set with digital data which belongs to the data stored in the memory unit and was stored before the digital data set.

[19] Furthermore, the reception unit receives and demodulates Radio-Frequency IDen- tification (RFID) communication signals using Miller code having a symbol duration M of 4, the sampling frequency is set to a value four times greater than a frequency of the demodulated signals, the A/D conversion unit converts each of the signals demodulated by the reception unit into a 8 -bit digital signal and outputs the converted 8-bit digital signal, and the decoding module of the signal processing unit sets a size of the digital data set to a value 16 times greater than the size of the digital data.

[20] Meanwhile, according to a second aspect of the present invention, there is provided a data receiving method for a data receiving apparatus, including the steps of (a) demodulating received signals; (b) sampling the demodulated signals using a preset sampling frequency, converting the sampled signals into digital signals, and outputting the digital signals; (c) comparing each of the output digital signals with a preset reference value, and if, as a result of the comparison, the output digital signal is greater than the reference value, changing the digital signal to digital data which has a positive sign (+) and corresponds to the digital signal, and if, as a result of the comparison, the output digital signal is smaller than the reference value, changing the digital signal to digital data which has a negative sign (-) and corresponds to the digital signal; (d) sequentially storing the digital data changed at the step (c) according to data size corresponding to previously defined protocol code; and (e) decoding the digital data by comparing the changed digital data with the protocol code.

[21] Here, the decoding step (e) includes the steps of (el) reading the stored digital data having the data size, and calculating a comparison value by comparing the read digital data set having the data size with a data set of the protocol code; (e2) determining whether the comparison value calculated at the step (el) falls within an error range corresponding to sampling error generated at the step (b); (e3) if, as a result of the determination at the step (e2), the comparison value is determined to fall within the error range, correcting the sampling error for the digital data set and returning to the step (el); and (e4) if, as a result of the determination at the step (e2), the comparison value is determined not to fall within the error range, outputting a result of decoding corresponding to the digital data set based on the comparison value calculated at the step (el).

Advantageous Effects

[22] As described above, in accordance with the data receiving apparatus and the receiving method therefor according to the present invention, input digital signals are changed to signals having a positive sign (+) or a negative sign (-) and are then decoded, so that the accuracy of decoding can be improved.

[23] Furthermore, the operation of the data receiving apparatus and the receiving method therefor according to the present invention are performed through a simple subtraction operation and are performed while digital signals are being input from the A/D conversion unit, so that performance time can be reduced. [24] Furthermore, in accordance with the data receiving apparatus and the receiving method therefor according to the present invention, decoding is not performed after a sampling correction procedure has been completed, but the sampling correction is performed simultaneously with the decoding process, so that performance time can be reduced. [25] Accordingly, the data receiving apparatus and the receiving method therefor according to the present invention can increase a sampling frequency without changing the hardware design, so that the accuracy of decoding can be improved and the performance time of the overall reception procedure can be reduced at low cost.

Brief Description of Drawings

[26] FIG. 1 is a block diagram of a conventional data receiving apparatus;

[27] FIG. 2 is a block diagram of a data receiving apparatus according to a first embodiment of the present invention; [28] FIG. 3 is a diagram showing the waveforms of Miller codes used in embodiments of the present invention; [29] FIG. 4 shows a digital signal obtained through the conversion of an Analog/Digital

(AfD) conversion unit according to the first embodiment of the present invention; [30] FIG. 5 shows digital data obtained through the change of a signal processing unit according to the first embodiment of the present invention; [31] FIG. 6 is a block diagram of a data receiving apparatus according to a second embodiment of the present invention; [32] FIG. 7 is a diagram illustrating a decoding operation according to the second embodiment of the present invention; [33] FIG. 8 is a diagram illustrating the correction module of a signal processing unit according to the second embodiment of the present invention; and [34] FIG. 9 is a flowchart showing the control flow of the signal processing unit according to the second embodiment of the present invention.

Best Mode for Carrying out the Invention

[35] The construction and operation of data receiving apparatuses according to embodiments of the present invention will be described in detail below with reference to the accompanying drawings. [36] <First Embodiment

[37] FIG. 2 is a block diagram of a data receiving apparatus according to a first embodiment of the present invention. [38] The data receiving apparatus 200 according to the first embodiment of the present invention, as shown in FIG. 2, includes a reception unit 210, an A/D conversion unit

220, and a signal processing unit 230. [39] The operation of the data receiving apparatus 200 according to the first embodiment is schematically described below. The reception unit 210 receives and demodulates a communication signal. The A/D conversion unit 220 samples the signal demodulated by the reception unit 210 using a preset sampling frequency, converts the sampled signal into a digital signal, and then outputs the digital signal. The signal processing unit 230 compares the input digital signal, received from the A/D conversion unit 220, with a preset reference value, changes the digital signal to digital data, and decodes the digital data by comparing the digital data with protocol code defined in a protocol.

[40] The protocol code used in the embodiments of the present invention, including the first embodiment, is a Miller code having a symbol duration (M) of 4, as shown in FIG. 3. The protocol code is one of the codes used in RFID wireless communication.

[41] In greater detail, in the case where the Miller code 0 shown in FIG. 3 is represented by data through sampling and quantization using a sampling frequency which is quadruple to the frequency of the Miller code, the Miller code 0 may be represented by 16 data sets {+1,+ 1,-1,-1,+1,+1,-1,-1,+1,+ 1,-1,-1,+1,+1,-1,-1 }, such as MO shown in FIG. 7 (a). The Miller code 1 shown in FIG. 3 may be represented by 16 data sets {+l,+l,-l,-l,+l,+l,-l,-l,-l,-l,+l,+l,-l,-l,+l,+l }, such as Ml shown in FIG. 7 (b).

[42] Other methods used in RFID wireless communication further include Frequency

Modulation 0 (FMO) and Manchester code. The method may be selected depending on the purpose of the RFID system.

[43] Respective elements of the first embodiment will be described in detail below with reference to FIG. 2.

[44] First, the reception unit 210 may include a reception port 211 for receiving communication signals and a demodulation module 212 for demodulating the communication signals received from the reception port 211. Since the construction of the reception unit 210 is known in the art, it will be described in brief.

[45] Here, the reception port 211 may be formed of an antenna or a cable network port for receiving communication signals. The communication signals are defined according to a communication protocol. In the case where the communication signals are electromagnetic signals used in an RFID system, the reception port 211 is formed of an antenna for receiving communication signals in a pertinent frequency band.

[46] The demodulation module 212 restores the original signals (baseband signals) prior to their modulation by demodulating the communication signals received from the reception port 211. In the case where the received communication signals are AM- modulated electromagnetic signals, the demodulation module 212 may demodulate the received communication signals using a heterodyne system. In this case, the demodulated signals are coded baseband signals, such as Miller codes shown in FIG. 3. Although the case where the symbol duration M is 4 has been illustrated here, the symbol duration M may be 2 or 8.

[47] The A/D conversion unit 220 converts the signals demodulated by the demodulation module 212 of the reception unit 210 into digital signals. This conversion is performed through sampling and quantization. A sampling frequency used in the sampling is preferably set to at least a frequency two times greater than the frequency of a normal demodulation signal. The frequency of signals actually received and demodulated by the reception unit 210 may be higher or lower than that of a normal demodulation signal due to disturbance, etc. Accordingly, the sampling frequency is set on the basis of the frequency of a normal demodulation signal.

[48] Here, the sampling frequency is set to a value four times greater than that of a normal demodulation signal. That is, if the frequency of the normal demodulation signal is 100 kHz, the sampling frequency is set to 400 kHz. In the present embodiment, this sampling and quantization process is known in the art, so that a detailed description thereof is omitted.

[49] The A/D conversion unit 220 used in the first embodiment converts the signal demodulated by the demodulation module 212 of the reception unit 210 into 8 -bit digital signals for each sampling.

[50] That is, the digital signal converted by the A/D conversion unit 220 may be represented as shown in FIG. 4. FIG. 4 shows a digital signal corresponding to 16th sampling in the form of a decimal numerical value.

[51] During the normal operation of the A/D conversion unit 220, the A/D conversion unit

220 may convert a demodulation signal having a '0' value into a digital signal '0' and a demodulation signal having a T value into a digital signal '255'.

[52] The signal processing unit 230 compares the digital signal received from the A/D conversion unit 220 with a preset reference value. If, as a result of the comparison, the input digital signal is greater than the reference value, the signal processing unit 230 changes the input digital signal to digital data which has a positive sign (+) and corresponds to the input digital signal. In contrast, if, as a result of the comparison, the input digital signal is smaller than the reference value, the signal processing unit 230 changes the input digital signal to digital data which has a negative sign (-) and corresponds to the input digital signal.

[53] The signal processing unit 230 compares the changed digital data with a protocol code defined according to a protocol, and decodes the digital data. In this case, decoding may be performed using one of various known methods. Here, since the performance of the decoding in the first embodiment is not the essential technical spirit of the present invention, a detailed description thereof is omitted here. However, in a second embodiment, which will be described later, the performance of decoding is related to the essential technical spirit of the present invention. [54] The signal processing unit 230, as shown in FIG. 1, may include a change module

231 for changing the digital signal received from the A/D conversion unit 220 into digital data.

[55] The change module 231 sets a reference value to '127', and subtracts the reference value '127' from an 8-bit digital signal that is received from the A/D conversion unit 220 and is similar to that shown in FIG. 4. In this case, the reference value corresponds to an intermediate value between digital signals '0' and '255' obtained by the A/D conversion unit 220.

[56] Here, the reference value may vary depending on the type of protocol code or the form of a digital signal output from the A/D conversion unit 220. The reference value is set such that a digital signal output from the A/D conversion unit 220 has appropriate negative (-) or positive (+) digital data corresponding to the value of the digital signal.

[57] The digital data changed as described above is shown in FIG. 5.

[58] As described above, the changed digital data shown in FIG. 5 does not include value

'0', such as that shown in FIG. 4, before the change. Accordingly, in the case where the signal processing unit 230 uses the correlation-type decoding method, the result value of a correlation operation for decoding does not become '0'. Accordingly, the inaccuracy in the performance of decoding, which is generated because the result value of a correlation operation for decoding before the performance of the change module 231 becomes '0' can be reduced.

[59] The correction-type decoding method will be described later in connection with a second embodiment.

[60] Furthermore, the change module 231 of the signal processing unit 230 according to the first embodiment can perform its operation through a simple subtraction operation. Since this subtraction operation can be performed while a digital signal is received from the A/D conversion unit 220, the delay of performance time is rarely generated. Mode for the Invention

[61] <Second Embodiment

[62] A data receiving apparatus 300 according to a second embodiment of the present invention includes, as shown in FIG. 6, a reception unit 310, an A/D conversion unit 320, a memory unit 325, and a signal processing unit 330.

[63] The operation of the data receiving apparatus 300 according to the second embodiment will be schematically described. The reception unit 310 receives and demodulates a communication signal. The A/D conversion unit 320 samples the demodulation signal demodulated by the reception unit 310 using a preset sampling frequency, converts the sampled signal into a digital signal, and outputs the digital signal. The signal processing unit 330 compares the digital signal received from the A/ D conversion unit 320 with a preset reference value, and changes the digital signal to digital data. The signal processing unit 330 sequentially stores the changed digital data in the memory unit 325 according to data size corresponding to protocol code defined in a protocol. The signal processing unit 330 detects and corrects sampling error, which is generated when the A/D conversion unit 320 performs sampling, while reading and decoding the digital data stored in the memory unit 325.

[64] Respective elements of the second embodiment will be described in detail below with reference to FIG. 6. The second embodiment is implemented by adding a function of detecting and correcting sampling error to the decoding process of the first embodiment. The description overlapping that of the first embodiment is omitted here. Furthermore, a Miller code having a symbol duration M of 4 shown in FIG. 3 will be described using an example, as in the first embodiment.

[65] The data receiving apparatus 300 of the second embodiment further includes the memory unit 325 for storing data, unlike that of the first embodiment.

[66] The memory unit 325 sequentially stores digital data, changed by a change module

331 to be described later, according to data size corresponding to the protocol code in response to the instruction of the signal processing unit 330.

[67] In this case, the size of data is 16 times greater than the size of digital data in accordance with the Miller code having a symbol duration M of 4 in the protocol code. That is, in the case where the size of the digital data is 8 bits, the size of the data is '8 bits x 16', as shown in FIG. 5. Of course, the size of the data may vary depending on the protocol code. That is, in the case where a Miller code having a symbol duration M of 2 or 8 is used, when the size of digital data is 8 bits, the size of data is '8 bits x 8' or '8 bits x 32'.

[68] The signal processing unit 330 may be divided into the change module 331, a storage module 332, and a decoding module 333, as shown in FIG. 6.

[69] First, the change module 331 compares the digital signal obtained by the A/D conversion unit 320 with a preset reference value. If, as a result of the comparison, the digital signal is greater than the reference value, the change module 331 changes the digital signal to digital data having a positive sign (+). If, as a result of the comparison, the digital signal is smaller than the reference value, the change module 331 changes the digital signal to digital data having a negative sign (-). Since the detailed description thereof has been given in connection with the first embodiment, it is omitted here. That is, the changed digital data is the same as shown in FIG. 5.

[70] The storage module 332 sequentially stores the digital data, changed by the change module 331, in the memory unit 325 according to the data size corresponding to the protocol code defined in the protocol. Here, in the case where the size of data is '8 bits x 16' as shown in FIG. 5, the digital data is sequentially stored in the memory unit 325 from the left side in a fashion similar to that shown in FIG. 5. The leftmost side of FIG. 5 corresponds to the position of the most significant digital data, and the rightmost side of FIG. 5 corresponds to the position of the least significant digital data.

[71] The decoding module 333 reads the digital data which was stored in the memory unit

325 and has a data size corresponding to the protocol code, and performs decoding by comparing the read digital data set having the data size with the data set of the protocol code.

[72] The decoding module 333 will be described in detail below with reference to FIG. 7.

As shown in FIG. 7(a), the decoding module 333 multiplies the digital data set read from the memory unit 325 by the data set MO corresponding to the Miller code 0 in corresponding digit positions and adds the values multiplied in corresponding digit positions, thereby calculating a comparison value. As shown in FIG. 7(b), a comparison value is then calculated using the read digital data set and the data set Ml corresponding to the Miller code 1. In the case where as shown in FIG. 7, the comparison value corresponding to the Miller code 0 is '2040' and the comparison value corresponding to the Miller code 1 is '0', the decoding module 333 outputs decoding result '0' corresponding to the read digital data set according to the correlation-type decoding method.

[73] Furthermore, the decoding module 333 may include a comparison value calculation module 333a for reading the digital data which was stored in the memory unit 325 and has a size corresponding to the protocol code, and calculating a comparison value by comparing the read digital data set with the data set corresponding to the protocol code. The error detection module 333b determines whether sampling error has occurred in the A/D conversion unit 320 based on the calculated comparison value. If, as a result of the determination in the error detection module 333b, sampling error is determined to have occurred, the correction module 333c corrects the sampling error. If, as a result of the determination in the error detection module 333b, sampling error is determined not to have occurred, the result output module 333d outputs the decoding result of the read digital data set based on the calculated comparison value.

[74] First, the comparison value calculation module 333a reads the digital data which was stored in the storage module 332 and has a size corresponding to a protocol code, and calculates a comparison value by comparing the read digital data set with the data set corresponding to the protocol code.

[75] Here, in order to diagrammatically illustrate how the comparison value calculation module 333a calculates the comparison value, a description will be given with reference to FIG. 8.

[76] FIG. 8(a) shows the waveform of the Miller code 0, which is a protocol code and has a symbol duration M of 4, and FIGS. 8(b) and 8(c) show the waveforms of digital data sets read from the memory unit 325. Here, the waveform of FIG. 8(b) lags behind the waveform of FIG. 8 (a) in phase by 45°, and the waveform of FIG. 8(c) leads the waveform of FIG. 8 (a) in phase by 45°.

[77] Here, the waveform shown in FIG. 8(d) is the results of multiplication of the values of FIGS. 8 (a) and 8(b) in corresponding digit positions, and the value of addition of the results obtained through the multiplication in corresponding digit positions corresponds to the comparison value calculated in the comparison value calculation module 333a. In this case, the calculated comparison value is '+135'. FIG. 8(e) shows the results of multiplication of the values of FIGS. 8 (a) and 8(c) in corresponding digit positions, and a comparison value corresponding to the value of addition of the multiplication results is '+135' in the same manner as described above.

[78] If the comparison value calculated as shown in FIG. 7 falls within a set error range, the error detection module 333b determines that sampling error exists in the A/D conversion unit 320 and instructs the correction module 333b to perform its operation. The error range may be set depending on the type of a protocol code, the size of digital data and the size of a digital data set. In a condition, such as that shown in FIG. 7, the error range may be set to a range from '-520' to '+520'.

[79] Here, in the case where the comparison value calculated in the comparison value calculation module 333a is '+135' as shown in FIG. 8, the error detection module 333b determines that the comparison value falls within the set error range, thereby determining that sampling error exists. If the error detection module 333b has determined that there is sampling error, the correction module 333c performs its operation.

[80] In the case where the error detection module 333b has determined that sampling error exists, the correction module 333c corrects the sampling error of the digital data set using digital data stored in the memory unit 325 before or after the digital data set.

[81] The correction module 333c will be described in greater detail with reference to the frequency of the signal demodulated in the reception unit 310. A preset ratio of the sampling frequency

[82] In the case where the frequency of the signal demodulated in the reception unit 310 is lower than the sampling frequency set in the A/D conversion unit 320, by a maximum of 15% and the above-described error detection module 333b has determined that there is sampling error, the correction module 333c shifts the read digital data set to the left by one digital data unit and then fills the lowest digit position of the digital data set with digital data which belongs to the data stored in the memory unit 325 and was stored after the digital data set.

[83] Furthermore, in the case where the frequency of the signal demodulated in the reception unit 310 is higher than the sampling frequency set in the A/D conversion unit 320, by a maximum of 15% and the error detection module 333b has determined that there is sampling error, the correction module 333c shifts the read digital data set to the right by one digital data unit and then fills the highest digit position of the digital data set with digital data which belongs to the data stored in the memory unit 325 and was stored before the digital data set.

[84] Here, the correction module 333c will be described using an example with reference to FIG. 8.

[85] FIG. 8(a) shows the waveform of Miller code 0, which is a protocol code and has a symbol duration M of 4, and FIGS. 8(b) and 8(c) show the waveforms of digital data sets read from the memory unit 325. Here, the waveform of FIG. 8(b) lags behind that of FIG. 8 (a) in phase by 45, and the waveform of FIG. 8(c) leads that of FIG. 8 (a) in phase by 45. Here, the phases of digital data sets, such as those shown in FIGS. 8(b) and 8(c), need correction.

[86] In the case where the error detection module 333b has determined that there is sampling error and the frequency of the signal demodulated in the reception unit 310 is lower than the sampling frequency by a maximum of 15%, the correction module 333c shifts the read digital data set (refers to the waveform of FIG. 8(b)) to the left by one byte, deletes a digital data value in the highest digit position, empties the lowest digit position, and fills the emptied lowest digit position with digital data which was stored in the memory unit 325 after the read digital data set. Accordingly, sampling correction is performed. This approximately corresponds to the case where the waveform of FIG. 8(b) is made to coincide with the waveform of FIG. 8 (a) by shifting the waveform of FIG. 8(b) to the left.

[87] Furthermore, in the case where the error detection module 333b has determined that there is sampling error and the frequency of the signal demodulated in the reception unit 310 is higher than the sampling frequency by a maximum of 15%, the correction module 333c shifts the read digital data set (refer to the waveform of FIG. 8(c)) to the right by one byte, deletes a digital data value in the lowest digit position, empties the highest digit position, and fills the emptied highest digital position with digital data which was stored in the memory unit 325 before the read digital data set. Accordingly, sampling correction is performed. This approximately corresponds to the case where the waveform of FIG. 8(c) is made to coincide with the waveform of FIG. 8 (a) by shifting the waveform of FIG. 8(c) to the right.

[88] As described above, the operation of the correction module 333c can be performed within the decoding process because it is performed while the read digital data is compared with the protocol code. Furthermore, since decoding can be immediately performed when sampling correction is not necessary, the time delay, which is generated because a sampling correction process must be performed before a decoding process as in the conventional data receiving apparatus, is not generated.

[89] The control operation of the signal processing unit 330 will be described below with reference to FIG. 9(a).

[90] The signal processing unit 330 first controls the reception unit 310 so that the reception unit 310 receives and demodulates the communication signals at step S310. Thereafter, the signal processing unit 330 controls the A/D conversion unit 320 so that the A/D conversion unit 320 samples the signals, demodulated at step S310, using a preset sampling frequency, converts the sampled signal into a digital signal, and outputs the digital signal at step S320.

[91] Thereafter, the signal processing unit 330 compares the digital signal output at S320 with a preset reference value. If the digital signal is greater than the reference value, the signal processing unit 330 changes the output digital signal to digital data which has a positive sign (+) and corresponds to the output digital signal. In contrast, if the digital signal is smaller than the reference value, the signal processing unit 330 changes the output digital signal to digital data which has a negative sign (-) and corresponds to the output digital signal at step S330. Here, in the case where the digital signal input at step S320 corresponds to the digital signal shown in FIG. 4, the step S330 is performed by subtracting '127' from a value corresponding to the result of sampling of the digital signal. The changed digital data corresponds to that shown in FIG. 5.

[92] Thereafter, the signal processing unit 330 sequentially stores the digital data changed at step S330 in the memory unit 325 according to the data size corresponding to the protocol code defined in the communication protocol at step S340.

[93] Thereafter, the signal processing unit 330 reads the digital data which was stored at step S340 and has the data size, compares the digital data set with the data set of the protocol code, and performs decoding based on the result of the comparison at step S350. In this case, sampling error generated during the step S320 can be detected and corrected during the performance of decoding at step S350.

[94] The step S350 refers to the decoding step of the signal processing unit 330 according to the second embodiment, and may include four steps as shown in FIG. 9(b).

[95] First, the signal processing unit 330 reads the digital data which was stored at step

S340 and has the data size, and calculates a comparison value corresponding to the sampling error by comparing the read digital data set with the data set of the protocol code at step S351.

[96] In this case, the comparison value is calculated by multiplying the read digital data set by the data set of the protocol code in corresponding digit positions and then adding the results of the multiplication. That is, the results of multiplication of the sets of FIGS. 8 (a) and 8(b) in corresponding digit positions correspond to those shown in FIG. 8(d), and the comparison value is '+135'. The results of multiplication of the sets of FIGS. 8 (a) and 8(c) in corresponding digit positions correspond to those shown in FIG. 8(e), and the sampling error value corresponds to '+135'.

[97] Thereafter, the signal processing unit 330 determines whether the comparison value calculated at step S351 falls within an error range corresponding to the sampling error at step S352.

[98] In the case where the error range is set to a range from '-520' to '+520', the comparison value '+135' calculated in FIGS. 8(d) and 8(e) falls within the error range.

[99] If, as a result of the determination at step S352, the comparison value is determined to fall within the error range, the signal processing unit 330 corrects the sampling error for the digital data set and proceeds to the step S351, at step S353.

[100] In the case where the calculated sampling error value falls within a specific range, the signal processing unit 330 corrects the sampling error for the read digital data using digital data stored before or after the read digital data set.

[101] Furthermore, step S353 may vary depending on the frequency of the signal demodulated at step S310. For example, in the case where the frequency of the demodulated signal is lower than a sampling frequency by a maximum of 15%, step S350 may be performed in such a manner that the waveform of FIG. 8(b) is made to coincide with the waveform of FIG. 8 (a) by shifting the waveform of FIG. 8(b) to the left.

[102] Furthermore, in the case where the frequency of the demodulated signal is higher than the sampling frequency by a maximum of 15%, step S350 may be performed in such a manner that the waveform of FIG. 8(c) is made to coincide with the waveform of FIG. 8 (a) by shifting the waveform of FIG. 8(c) to the right.

[103] However, if, as a result of the determination at step S352, the comparison value is determined not to fall within the error range, the signal processing unit 330 outputs the result of the decoding using the comparison value calculated at step S350, at step S354.

[104] As described above, the signal processing unit 330 according to the second embodiment can perform sampling error, generated in the A/D conversion unit 320, during a decoding process and can also immediately perform decoding without performing a sampling correction procedure when sampling correction is not necessary. Accordingly, the time delay, which is generated because the sampling correction procedure is inevitably performed before the decoding procedure as in a conventional data receiving apparatus, is not generated. Industrial Applicability

[105] The data receiving apparatus according to the present invention can be used in the data receiving apparatus (RFID reader) of an RFID system in which the problem of in- consistency in phase and synchronization frequently occurs due to distance, reflection, etc. because the data receiving apparatus is based on wireless communication.

Claims

[1] A data receiving apparatus, comprising: a reception unit for receiving and demodulating signals; an Analog/Digital (A/D) conversion unit for sampling the signals, demodulated by the reception unit, using a preset sampling frequency, converting the sampled signals into digital signals, and outputting the digital signals; and a signal processing unit for comparing each of the digital signals, received from the A/D conversion unit, with a preset reference value, changing the input digital signal to digital data according to a result of the comparison, and decoding the digital data by comparing the changed digital data with previously defined protocol code; wherein, if, as a result of the comparison, the digital signal is greater than the reference value, the signal processing unit changes the digital signal to digital data which has a positive sign (+) and corresponds to the digital signal, and, if, as a result of the comparison, the digital signal is smaller than the reference value, the signal processing unit changes the digital signal to digital data which has a negative sign (-) and corresponds to the digital signal.

[2] The data receiving apparatus according to claim 1, wherein the reception unit receives and demodulates signals coded using Miller code.

[3] The data receiving apparatus according to claim 1, wherein the signal processing unit comprises a change module for changing the input digital signal to the digital data, and the change module changes the input digital signal to the digital data by subtracting the reference value from the input digital signal.

[4] The data receiving apparatus according to claim 1, further comprising a memory unit for storing data, wherein the signal processing unit sequentially stores the digital data in the memory unit according to data size corresponding to the protocol code.

[5] The data receiving apparatus according to claim 4, wherein: the signal processing unit comprises a decoding module for decoding the stored digital data, and the decoding module reads digital data which was stored in the memory unit and corresponds to the data size, calculates a comparison value by comparing the read digital data set having the data size with the protocol code, and detects and corrects sampling error of the digital data set generated during the sampling of the A/D conversion unit using the calculated comparison value and simultaneously outputs a result of decoding.

[6] The data receiving apparatus according to claim 5, wherein the decoding module of the signal processing unit calculates the comparison value by multiplying the read digital data set by the data set of the protocol code in corresponding digit positions and adding values obtained through the multiplication in corresponding digit positions.

[7] The data receiving apparatus according to claim 5, wherein the decoding module of the signal processing unit determines whether sampling error has been generated by determining whether the comparison value falls within a preset error range, and, if, as a result of the determination, the sampling error is determined to have occurred, corrects the sampling error using digital data which was stored before or after the digital data set and belongs to the data stored in the memory unit.

[8] The data receiving apparatus according to claim 7, wherein, if a frequency of each of the signals demodulated by the reception unit is lower than a predetermined percentage of the sampling frequency and the sampling error is determined to have occurred, the decoding module of the signal processing unit shifts the digital data set to the left by one digital data unit and then fills a lowest digit position of the digital data set with digital data which belongs to the data stored in the memory unit and was stored after the digital data set.

[9] The data receiving apparatus according to claim 7, wherein, if a frequency of each of the signals demodulated by the reception unit is higher than a predetermined percentage of the sampling frequency and the sampling error is determined to have occurred, the decoding module of the signal processing unit shifts the digital data set to the right by one digital data unit and then fills a highest digit position of the digital data set with digital data which belongs to the data stored in the memory unit and was stored before the digital data set.

[10] The data receiving apparatus according to claim 7, wherein: the reception unit receives and demodulates Radio-Frequency IDentification

(RFID) communication signals using Miller code having a symbol duration M of

4, the A/D conversion unit, with the sampling frequency being set to a value four times greater than a frequency of the demodulated siganals, converts each of the signals demodulated by the reception unit into a 8-bit digital signal and outputs the converted 8-bit digital signal, and the decoding module of the signal processing unit sets a size of the digital data set to a value 16 times greater than the size of the digital data.

[11] A data receiving method for a data receiving apparatus, comprising the steps of:

(a) demodulating received signals;

(b) sampling the demodulated signals using a preset sampling frequency, converting the sampled signals into digital signals, and outputting the digital signals;

(c) comparing each of the output digital signals with a preset reference value, and if, as a result of the comparison, the output digital signal is greater than the reference value, changing the digital signal to digital data which has a positive sign (+) and corresponds to the digital signal, and if, as a result of the comparison, the output digital signal is smaller than the reference value, changing the digital signal to digital data which has a negative sign (-) and corresponds to the digital signal;

(d) sequentially storing the digital data changed at the step (c) according to data size corresponding to previously defined protocol code; and

(e) decoding the digital data by comparing the changed digital data with the protocol code.

[12] The receiving method according to claim 11, wherein the decoding step (e) comprises the steps of:

(el) reading the stored digital data having the data size, and calculating a comparison value by comparing the read digital data set having the data size with a data set of the protocol code;

(e2) determining whether the comparison value calculated at the step (el) falls within an error range corresponding to sampling error generated at the step (b); (e3) if, as a result of the determination at the step (e2), the comparison value is determined to fall within the error range, correcting the sampling error for the digital data set and returning to the step (el); and

(e4) if, as a result of the determination at the step (el), the comparison value is determined not to fall within the error range, outputting a result of decoding corresponding to the digital data set based on the comparison value calculated at the step (el).