KR20070098958A - Rfid system - Google Patents

Abstract

An RFID(Radio Frequency IDentification) system is provided to generate operation power of an RFID tag in a short time without influence of a modulation condition, and stably perform modulation and demodulation without signal distortion when RFID communication is processed between a reader and a plurality of grouped RFID tags. A signal transceived by the RFID tag and the reader is an OFDM(Orthogonal Frequency Division Multiplexing) signal. The RFID tag transfers an information request signal to the RFID tag through the OFDM signal and interprets tag ID information by generating the tag ID information if the information request signal is reed. The OFDM signal comprises the plurality of synchronized frames forming a time unit. The OFDM signal is an energy supplying signal including the information and comprises the OFDM signals of the predetermined time unit. The RFID tag receives power through the OFDM signal.

Description

RFID system {RFID system}

1 is a block diagram schematically illustrating the components of a tag in a conventional RFID system.

2 is a circuit diagram schematically showing components of a voltage conversion circuit included in a conventional tag.

3 is a circuit diagram schematically showing the components of a modulation circuit included in a conventional tag.

4 is a graph illustrating a form in which a voltage increases according to energy charging when an RF signal is used in the conventional RFID system.

5 is a block diagram schematically illustrating components of an RFID system according to an embodiment of the present invention.

6 is a data structure diagram exemplarily illustrating a data format of an OFDM signal processed in an RFID system according to an embodiment of the present invention.

7 is a graph showing a change in recognition error rate according to the number of tags in the RFID system according to an embodiment of the present invention.

8 is a block diagram schematically illustrating the components of a tag forming an RFID system according to an embodiment of the present invention.

FIG. 9 is a diagram illustrating an OFDM signal standard processed in an RFID system according to an embodiment of the present invention on a spectral region. FIG.

10 is a table for explaining types of parameters of an OFDM signal processed in an RFID system according to an embodiment of the present invention.

11 is a block diagram schematically illustrating components of a reader constituting an RFID system according to an embodiment of the present invention.

<Explanation of symbols for main parts of drawing>

100: RFID system 110: Tag

111: tag antenna 112: reception demodulation unit

113: power supply unit 114: transmission modulator

115: frequency generation unit 116: tag control unit

117: tag memory 120: reader

121: reader antenna 122: demodulator

123: RFID transmitter and receiver 124: modulator

125: reader control unit 126: reader memory

The present invention relates to a radio frequency identification (RFID) system.

Currently, ubiquitous network technology attracts the attention of many people, ubiquitous network technology refers to a technology that allows to connect naturally to various networks regardless of time and place.

Ubiquitous network technology can be implemented in various ways by using communication technologies such as telematics communication, short-range wireless communication, and mobile communication. By using this, a natural connection environment is provided in spaces such as automobiles, homes, and public places. The use of information and technology will increase, and the overall IT industry is expected to develop more rapidly.

As the next generation technology of the ubiquitous network technology, RFID technology may be cited. Among them, RFID technology introduced in commerce is representative.

In general, a commercial RFID system consists of a tag attached to a product and embedded with details, and a reader for receiving and processing information of the tag using RF communication. It passes the area where the leader is located and transmits the information using RF communication, thus providing a foundation for efficiently managing logistics / distribution such as product distribution, assembly, price change, and sales.

FIG. 1 is a block diagram schematically illustrating components of a tag 10 of a conventional RFID system, and FIG. 2 schematically illustrates components of a voltage conversion circuit 13 included in a conventional tag 10. It is a circuit diagram. 3 is a circuit diagram schematically showing the components of the modulation circuit 14 included in the conventional tag 10.

According to FIG. 1, the conventional tag 10 includes an antenna 11, a demodulation circuit 12, a voltage conversion circuit 13, a modulation circuit 14, and a control circuit 15. The passive tag, which is widely used, uses a power supply when a request signal (as RF signal) of tag information is received from a reader.

That is, the voltage conversion circuit 13 converts an RF signal into a DC voltage signal by using an amplitude shift keying (ASK) signal having a constant modulation rate, and provides it to a power source of each component.

As shown in FIG. 2, the voltage conversion circuit 13 has a capacitor 13a and a diode 13b configured in parallel in a multistage configuration, and an “A” connection end is connected to the antenna 11.

The control circuit 15 analyzes the information request signal of the reader, extracts the corresponding tag information (eg, product information) stored in a memory (not shown), and controls each component to transmit the tag information to the reader.

The demodulation circuit 12 decodes the information request signal received through the antenna 11 into a signal that can be interpreted by the control circuit 15, and the modulation circuit 14 is processed by the control circuit 15. The tag information is modulated into an RF signal so that the antenna 11 can transmit it.

As shown in FIG. 3, the modulation circuit 14 includes an envelope detection unit 14a including capacitors and diodes, and a PWM (Pulse Width Modulation) for converting a baseband signal into an intermediate frequency signal and a high frequency signal. It is comprised by the conversion part 14b.

The conventional RFID communication method has some problems as follows.

First, as described above, the voltage conversion circuit 13 takes a certain time to generate a throat voltage because the shottky diodes are connected in multiple stages to charge an RF signal up to a desired DC voltage.

Second, conventionally, since the RF signal is converted into a DC signal using an ASK signal having a constant modulation rate, a constant modulation depth must be secured in order for the tag to operate.

Third, since the modulation depth cannot be divided according to the distance between the tag and the reader and the time until the tag operation is performed, a voltage drop may occur in some cases, and when the voltage drop occurs, the operation power of the tag becomes insufficient. .

Fourth, since the tag processes the modulation and voltage conversion of the signal at the same time, there is a problem that signal distortion may occur in the processing.

4 is a graph illustrating a form in which a voltage increases according to energy charging when an RF signal is used in a conventional RFID system.

As shown in FIG. 4, in the conventional tag, charging and discharging occur sequentially at the peak point of the ASK signal (measuring line shown on the bottom of the graph), and the voltage is gradually rising in the form of sawtooth. Line) is charged / ascended. Therefore, since the energy loss due to the discharge occurs, the operating voltage of the tag gradually rises for a certain time.

If the RF signal of constant energy is introduced, not the ASK signal, only the charging process continuously occurs without the discharge process, so that the operating voltage (eg, 3.3V) of the tag can be generated in a shorter time.

However, if the RF signal is continuously supplied, the existing ASK signal is deteriorated, so the tag cannot demodulate / interpret any signal.

Due to such negative factors, a plurality of tags forming a group (eg, tags attached to goods loaded in a container) are placed in different communication environments, and the plurality of tags are short-lived (eg, a container). More complex communication protocols are required to be recognized for the time it passes through the reader communication area.

In addition, the recognition error rate of the tag is high, and the circuit configuration or DSP incorporating a complex communication protocol raises the production cost of the tag and provides a cause of lengthening the recognition time of the tag.

Accordingly, in the present invention, in processing RFID communication between a plurality of tags constituting a reader and a group, an operating power of a tag is generated in a shorter unit time without the influence of modulation conditions (different amplitude signals), and without modification of the signal. Provides an RFID system in which demodulation is performed stably.

In addition, the present invention simplifies the linear communication protocol with tags having various communication environments, reduces the recognition error rate while increasing the recognition speed, and improves the transmission standard so that the tag information receiving area on the RF signal is efficiently used. Provides an RFID system.

In order to achieve the above object, the RFID system according to the present invention is composed of a tag and a reader, the signal transmitted and received by the tag and the reader is an OFDM (Orthogonal Frequency Division Multiplexing) signal, the tag through the OFDM signal When the information request signal is received from the reader, tag identification information is generated and transmitted to the reader, and the reader transmits the information request signal to the tag through the OFDM signal, and interprets the tag identification information received from the tag. do.

In addition, the OFDM signal processed in the RFID system according to the present invention is an energy supply signal containing information and consists of OFDM symbols of a predetermined time unit, and the tag is supplied with power through the OFDM signal.

Further, in the OFDM signal processed in the RFID system according to the present invention, the number of frames, the number of symbols and the predetermined time unit value are adjusted so that the calculated value of "number of frames x number of symbols x predetermined time unit" becomes a constant.

In addition, the OFDM signal processed in the RFID system according to the present invention,

(여기서, "n"은 태그의 개수를 의미하고, "N"은 상기 기호 개수를 의미하며, "k"는 상기 프레임 개수를 의미함)의 수식에 의하여 인식 에러율이 조정된다.

The recognition error rate is adjusted by the formula of (where "n" means the number of tags, "N" means the number of symbols and "k" means the number of frames).

In addition, the OFDM signal processed in the RFID system according to the present invention is time-divided so that a frequency subchannel is set, and the tag is assigned for each set frequency channel.

In addition, the tag constituting the RFID system according to the present invention is allocated a communication group with the reader for each space divided according to the antenna arrangement of the reader, and contains its own tag identification information one by one in the OFDM signal frame send.

Hereinafter, an RFID system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

5 is a block diagram schematically illustrating the components of an RFID system according to an embodiment of the present invention.

Referring to FIG. 5, the RFID system 100 according to an embodiment of the present invention includes a plurality of tags 110 and a reader 120. In an embodiment of the present invention, the tag 110 includes one group. This is a plurality of tags to move the recognition area of the reader 120, it is assumed that the passive tag (Passive) to obtain power using a signal transmitted from the reader 120.

In addition, the tag 110 and the reader 120 according to an embodiment of the present invention uses a network 200 having an RFID frequency band of about 860 MHz to 960 MHz, and uses an orthogonal frequency division multiplexing (OFDM) modulation scheme. To process the symbolized signal.

Based on the OFDM modulation scheme, a signal specification is defined according to a time division technique, a frequency division technique, a spatial division technique, a symbolization, a data frame configuration, and the like. The RFID system 100 according to the present invention is reliable in recognizing a group unit tag. Can be obtained (recognition error rate can be reduced).

In addition, as the signal standard is newly defined as described above, the reader 120 according to the present invention may recognize about 1000 tags per group, and recognize one tag group for about 1 second.

Before describing the configuration and operation of the tag 110 and the reader 120 according to an embodiment of the present invention, a signal specification according to the OFDM modulation scheme will be described.

6 is a data structure diagram exemplarily illustrating a data format of an OFDM signal processed by the RFID system 100 according to an exemplary embodiment of the present invention.

Referring to FIG. 6, an OFDM signal according to an embodiment of the present invention is composed of k test frames (TF), and the test frame is composed of N time slots (TS).

The k test frames are time-divided signals to form a predetermined unit time. In an embodiment of the present invention, each test frame has a unit time of about 1 second, and each test frame has a start and a clock synchronized so that the tag 110 (or reader ( 120)).

The time slot is composed of a single OFDM symbol. The OFDM unit symbol corresponds to information of one tag 110 and is sized to carry information transmitted and received by the tag 110 and the reader 120. Has

For example, the OFDM unit symbol may have a time period of about 60 μs.

In addition, the OFDM signal is an energy pumping signal (Energy pumping signal) can be converted from the passive tag to the operating power source by the energy supply signal of a constant amplitude is also loaded on the test frame.

The OFDM signal having such a configuration can be represented by the following equation.

k × N × Tsymb ≒ 1 = constant

(In Equation 1,

"k" means the number of test frames,

"N" means the number of time slots,

"Tsymb" means the transmission time of the OFDM unit symbol (about 60μs as described above),

As a constant, "1" means the transmission time (unit "second") of the entire test frame corresponding to the tags 110 forming one group.

According to Equation 1, the reader 120 according to the embodiment of the present invention has a maximum of 1000 tags (60 μs per tag) that form one group for about 1 second by combining the variables “k” and “N”. Can be operated and recognized).

Meanwhile, a probability of identification error is determined according to the three variables "k", "N", and "Tsymb", and the recognition error rate may be determined by the following equation.

(In Equation 2,

“n” means the number of tags 110 forming one group,

"k" means the number of test frames.

"N" means the number of time slots)

According to Equation 2, when "k" has a value of about "18" to "40", the recognition error rate can be known at the minimum value, and when "K" is set to "32" which is the middle of it, " N "is calculated as" 512 ".

FIG. 7 is a graph illustrating a change in a probability of identification error according to the number of tags 110 in the RFID system 100 according to an exemplary embodiment of the present invention.

Thus, by the determined variable, plotted as a curve of the recognition error rate is 7, for example, to the recognition error rate in the ^"10-6" the number (n) of the tag (110) form a single group in the "400 "It should be

At this time, the period of the OFDM unit symbol is about "61μs".

Hereinafter, with reference to the accompanying drawings looks at the configuration and operation of the reader 120 and the tag 110 of the RFID system 100 according to an embodiment of the present invention.

8 is a block diagram schematically illustrating the components of the tag 110 constituting the RFID system 100 according to an embodiment of the present invention.

Referring to FIG. 8, the tag 110 according to the embodiment of the present invention includes a tag antenna 111, a reception demodulation unit 112, a power supply unit 113, a transmission modulator 114, a frequency generator 115, and a tag. It comprises a control unit 116 and the tag memory 117, the tag antenna 111 receives the information request signal (as energy supply signal / OFDM signal) from the reader 120 or processing in the tag 110 The transmitted tag identification information.

The power supply 113 converts the signal received through the tag antenna 111 into the energy of a constant amplitude by OFDM modulation and the received demodulation unit 112, the transmission modulator 114, the frequency generator 115, Provided to the tag control unit 116.

The reception demodulator 112 demodulates the information request signal received from the reader 120 into digital data and transmits the demodulated information request signal to the tag controller 116. The tag controller 116 analyzes the code of the demodulated information request signal. To generate tag identification information.

The tag controller 116 has a communication protocol capable of interpreting an OFDM signal standard to control wireless communication with the reader 120.

The tag memory 117 stores a code system of an information request signal, and the tag controller 116 generates tag identification information using the code system. For example, the code system stores header information, product identification information, error correction information, and the like. It may include.

The header information includes information such as the format of the code, the version of the code system, the length of the code, and the like. The product identification information includes information such as the type, price, expiration date, and country of origin of the product to which the tag 110 is attached. Can be.

The error correction information (CRC: Cyclic Redundancy Checking) is information for correcting an error that may occur in data communication.

In addition, the transmission modulator 114 modulates the tag identification information generated by the tag controller 116 into an RF signal of the OFDM scheme and transmits the tag identification information to the tag antenna 111. The frequency generator 115 transmits an internal clock signal. The low frequency signal is extracted from the energy supply signal, which is transmitted to the transmission modulator 114.

Accordingly, the transmission modulator 114 loads an energy supply signal having a constant amplitude in a test frame of the OFDM signal and transmits the same to the tag antenna 111.

When the transmission modulator 114 modulates the OFDM signal, the period of the OFDM unit symbol may be adjusted, and the period of the OFDM unit symbol has a correlation with the frequency band.

For example, when the period of the OFDM unit symbol is shortened, the frequency band becomes wider, and a frequency division scheme may be introduced to set a frequency subchannel. In this case, the variables are adjusted by Equations 1 and 2 described above.

FIG. 9 is a diagram illustrating an OFDM signal standard processed by the RFID system 100 according to an exemplary embodiment of the present invention on a spectral region, and FIG. 10 is an OFDM signal processed by the RFID system 100 according to an exemplary embodiment of the present invention. Table describing the types of parameters.

9, there is shown a frequency spectrum according to the (phase) angular frequency in OFDM modulation according to the present invention, parameters corresponding to the specifications of the OFDM signal are described in FIG.

FIG. 11 is a block diagram schematically illustrating the components of the reader 120 constituting the RFID system 100 according to an embodiment of the present invention. According to FIG. 11, the reader 120 is a leader antenna 121. And a demodulator 122, an RFID transmitter and receiver 123, a modulator 124, a reader controller 125, and a reader memory 126.

The reader controller 125 includes an OFDM signal protocol to control wireless communication with the tag 110 and periodically transmits an information request signal, which is an energy supply signal / OFDM signal, in order to determine the position of the tag 110.

The reader controller 125 analyzes the code of the tag identification information received from the tag 110 and demodulated by the demodulator 122. At this time, the data is converted and filtered to extract necessary information.

In the reader memory 126, a code analysis system is recorded like the tag memory 117, and the reader control unit 125 uses the code analysis system to store the analyzed tag identification information in the tag memory 117. Can be.

The reader antenna 121 transmits an information request signal through the RFID communication channel or receives tag identification information from the tag 110. The tag antenna 117 and the reader antenna 121 sense each other through the RFID communication channel. It will act as a sensor.

The RFID transmitter / receiver 123 receives the signal identification tag identification information through the reader antenna 121, and the information request signal generated by the reader controller 125 is converted into an OFDM signal through the modulator 124. When modulated, this is transmitted through the reader antenna 121.

In this case, the RFID transmitter / receiver 123 generates an energy supply signal using the oscillation signal and transmits the signal together with the OFDM signal.

The demodulator 122 demodulates the signal identification tag identification information into digital data and transmits the demodulated tag identification information to the reader control unit 125.

The reader antenna 121 may be provided in plural numbers, and the demodulator 122, the modulator 124, and the RFID transmitter / receiver 123 are controlled by the reader controller 125, respectively. An OFDM signal may be processed through an OFDM signal transmitted and received, and an OFDM signal channel may be allocated for each space divided according to the array of the reader antenna 121, and the reader controller 125 may use an "antenna array algorithm. ) To process the OFDM signal channels in parallel.

The present invention has been described above with reference to the preferred embodiments, which are merely examples and are not intended to limit the present invention, and those skilled in the art to which the present invention pertains do not depart from the essential characteristics of the present invention. It will be appreciated that various modifications and applications are not possible that are not illustrated above. For example, each component specifically shown in the embodiment of the present invention can be modified. And differences relating to such modifications and applications will have to be construed as being included in the scope of the invention defined in the appended claims.

According to the RFID system according to the present invention has the following advantages.

First, the tag's operating power can be generated and maintained in a faster time, and signal distortion due to simultaneous processing of signal modulation and voltage conversion can be prevented, thus ensuring high reliability in recognizing tags in group units. It can work.

Second, through a communication protocol of a new standard based on the OFDM modulation scheme, there is an effect that can communicate with a large number of tags in a unit time without having a circuit or algorithm for processing a conventional complex protocol.

Third, since no hardware resources are required to process the communication protocol based on the OFDM modulation scheme, the production cost of tags and readers is reduced, and various RFID systems suitable for the logistics environment are differentiated by adjusting the parameters of the OFDM signal specifications. There is an effect that can be designed.

Claims (12)

In an RFID system consisting of a tag and a reader, The signal transmitted and received by the tag and the reader is an Orthogonal Frequency Division Multiplexing (OFDM) signal, When the tag receives an information request signal from the reader through the OFDM signal, generates a tag identification information and delivers it to the reader, And the reader transmits the information request signal to the tag through the OFDM signal, and interprets the tag identification information received from the tag. The method of claim 1, The OFDM signal comprises a plurality of synchronized frames forming a unit time. The method of claim 1, The OFDM signal is an energy supply signal containing information, and consists of OFDM symbols of a predetermined time unit. The tag system is characterized in that the power is supplied via the OFDM signal. The method of claim 1, wherein the OFDM signal And the number of frames, the number of symbols and the predetermined time unit value are adjusted so that the calculated value of "number of frames x number of symbols x predetermined time unit" becomes a constant. The method of claim 4, wherein the constant is RFID system characterized by a value approaching "1". The method of claim 1, wherein the OFDM signal

RFID is characterized in that the recognition error rate is adjusted by the formula (where "n" means the number of tags, "N" means the number of symbols and "k" means the number of frames). system. The method of claim 1, The OFDM signal is time-divided so that a frequency subchannel is set, and the tag is assigned to each set frequency channel. The method of claim 1, wherein the tag is RFID system, characterized in that the communication group with the reader is allocated for each space divided according to the antenna array of the reader. The method of claim 1, wherein the tag is RFID system, characterized in that for transmitting the tag identification information one by one in the OFDM signal frame. The method of claim 3, wherein the predetermined time unit is RFID system characterized in that the range of 50 μs to 70 μs. The method of claim 1, wherein the tag is An antenna through which the information request signal is received or the signal processed tag identification information is transmitted; A demodulator for demodulating the information request signal into digital data; A control unit having a communication protocol to control wireless communication with the reader, and analyzing the code of the demodulated information request signal to generate the tag identification information; A modulator for modulating the tag identification information into a radio signal and transferring the tag identification information to the antenna; And And a power supply unit for supplying power to the demodulation unit, the control unit and the modulation unit. The method of claim 1, wherein the leader An antenna through which the information request signal is sent or the signal processed tag identification information is received; A demodulator for demodulating the signal processed tag identification information into digital data; A control unit having a communication protocol to control wireless communication with the tag, analyze a code of the demodulated tag identification information, and generate the information request signal; And And a modulator for modulating the information request signal into a wireless signal and transmitting the modulated signal to the antenna.

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