KR100828897B1 - Rfid system - Google Patents

Abstract

An RFID(Radio Frequency IDentification) system is provided to offer an RFID reader and an RFID tag performing communication with an OFDM(Orthogonal Frequency Division Multiplexing) signal, minimize power consumption of the RFID tag, improve the recognition reliability of the RFID tag, and increase the size of information stored in the RFID tag. An antenna(114) receives an energy pumping signal from an RFID reader and transmits tag ID information stored in a memory(111). A multiplexer(112) multiplexes the tag ID information into an OFDM signal by an information request signal included in the energy pumping signal. A clock generator(116) generates clock by a clock synchronization signal included in the energy pumping signal. A frequency synthesizer(117) generates a frequency by the clock received from the clock generator. A frequency up-converter(113) converts a signal output from the multiplexer into an upper level and transmits the converted signal through the antenna. A PSU(Power Supply Unit)(118) generates internal power by using the received energy pumping signal. The memory stores the tag ID information by converting the tag ID information into a frequency domain.

Description

RF ID System {RFID SYSTEM}

1 illustrates an RFID system according to an embodiment of the invention.

2 is a diagram illustrating a structure of an identification interval.

3 is a diagram illustrating a change in identification error according to the number of tags.

4 is a view showing the structure of a tag according to an embodiment of the present invention.

5 is a diagram illustrating a configuration of a modulator in an embodiment of the present invention.

6 is a view for explaining the structure of a tag according to another embodiment of the present invention.

7 is a diagram illustrating a structure of an OFDM signal according to an embodiment of the present invention.

8 is a diagram illustrating a configuration of an RFID reader according to an embodiment of the present invention.

In the present invention, an RFID reader and an RFID tag are disclosed.

Recently, a Radio Frequency Identification (RFID) system has been widely used.

The RFID system includes a tag in which the detailed information of the product is recorded and attached to the product and a reader for reading the information included in the tag.

Conventional RFID systems follow standards by ISO / IEC and EPCglobal based on an algorithm of either "Slotted Aloha" or "Binary Tree".

Since the standard based on the Slotted Aloha algorithm has a low bit rate, each tag cannot be identified with high recognition if there are multiple tags.

Meanwhile, the standard based on the Binary Tree algorithm has an improved performance of identifying a large number of tags simultaneously at a low bit rate. Theoretically, the standard based on the Binary Tree algorithm can identify 1000 tags per second, but the number of tags that can be identified without an actual error is less than 100.

First of all, the Binary Tree algorithm stipulates to receive replies from a very large number of tags simultaneously according to the reader's inquiry. In this case, the reader receives a not-in-phase response from a very large amount of tags. Thus, the joint reply received by the reader from the tags will have an essential variation in the received power. The change amounts to approximately 40-50 dB. Therefore, even if there is no noise or jams, it is difficult to receive an accurate response.

In addition, since the standard using the Binary Tree algorithm recognizes a tag based on a complicated interactive procedure between a reader and a tag, it shows low reliability in recognition of in-group tags. .

Meanwhile, in an RFID system, a reader transmits a signal using an Amplitude Shift Keying (ASK) signal, and a tag receives an ASK signal of a reader and uses it as a supply power, demodulating the ASK signal to receive information requested from the reader. send.

In general, a passive tag converts the ASK signal through a voltage conversion circuit composed of a plurality of shottky diodes and uses it as a power supply for a response. However, it takes a certain time to generate the supply power from the ASK signal. This makes it impossible to recognize a large number of tags in a short time.

In addition, when there are a large number of tags, and the distance between the tag and the reader is far from the antenna or the beam-width of the antenna, a voltage drop may be induced to prevent the tag from operating.

In addition, since the demodulation of the signal is performed together with the conversion process for generating the supply power from the ASK signal, the signal may be distorted.

The present invention provides an RFID reader and a tag that communicate using an Orthogonal Frequency Division Multiplexing (OFDM) signal.

The present invention provides an RFID reader and tag that can minimize the power consumption of the tag.

The present invention provides an RFID reader and a tag that can improve the identification reliability of the tag.

The present invention provides an RFID reader and tag with a fast identification speed.

The present invention provides an RFID reader and tag that can increase the amount of information stored in a tag.

The present invention provides a tag that can be produced at a low price.

According to an embodiment of the present invention, an RFID tag includes an antenna stage for receiving an energy pumping signal and transmitting tag identification information; A memory in which the tag identification information is stored; A modulator for modulating the tag identification information into an OFDM signal according to the information request signal included in the energy pumping signal; A clock generator for generating a clock according to a clock synchronization signal included in the energy pumping signal; A frequency synthesizer operated according to the clock of the clock generator and generating a frequency; A frequency rising converter configured to up-convert the signal output from the modulator to be transmitted through the antenna terminal; And a power supply unit providing an internal power supply.

According to an embodiment of the present invention, an RFID tag includes an antenna stage for receiving an energy pumping signal and transmitting tag identification information; A memory in which the tag identification information is stored; A D / A converter for converting the tag identification information into an analog signal according to the information request signal included in the energy pumping signal; A clock extractor for extracting a clock signal from the energy pumping signal; A frequency synthesizer operated according to the clock of the clock extractor and generating a frequency; A frequency rising converter configured to up-convert the signal output from the D / A converter to be transmitted through the antenna terminal; And a power supply unit providing an internal power supply.

According to an embodiment of the present invention, an RFID reader includes: a transmitter configured to generate an energy pumping signal for supplying a power supply of an RFID tag and providing a clock synchronization signal and an information request signal; An antenna stage for transmitting the output of the transmitter as a high frequency signal and receiving an OFDM signal from the RFID tag; A receiver which demodulates tag identification information from the OFDM signal received through the antenna terminal; And a microprocessor for controlling the transmitter and processing the demodulated signal at the receiver.

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

The RFID system of the present invention provides reliable identification even when a plurality of tags are concentrated in a predetermined space such as a container. In the present invention, the probability that an identification error of at least one tag is generated may not exceed 10 ⁻⁶ .

The tag of the present invention illustrates a passive tag, which is very simple in structure and can be produced at low cost. The invention can also be applied to an active tag with a pre-charged internal power source.

In the present invention, a new concept RFID system using OFDM technology is provided.

[Time Separation Technique]

The OFDM signal provides a solution to solve the problems of the conventional RFID system.

First, the OFDM technology may transmit all information stored in a tag in one OFDM symbol.

In addition, OFDM symbols can be transmitted in a very short time.

In addition, OFDM signals may be transmitted at very short time intervals. Therefore, ALOHA, which is a statistically anti-collision algorithm, can be effectively applied, and since the information can be read from a plurality of tags during one identification period by using time separation technology, it is possible to avoid error occurrence. Reduce the probability. In addition, it is possible to effectively solve the power consumption problem in the active tag (active tag) as well as the passive tag.

1 is a diagram illustrating an RFID system according to an embodiment of the present invention.

In the RFID system 100 of the present invention, a plurality of tags 110 and a reader 120 are connected through an OFDM signal network 200. In an embodiment of the present invention, the plurality of tags 110 may be illustrated as passive tags, and the plurality of tags 110 pass through an identification area identifiable by the reader 120 in a space such as a container.

The reader 120 transmits an energy pumping signal during the whole identification period. The energy pumping signal is used as a power supply, a clock synchronization signal, and an information request signal of the tag 110.

When the information request signal is received according to the ALOHA algorithm, each tag 110 starts counting a preset pseudo random time interval, respectively.

The time slot is equal to the length of an OFDM symbol.

Thus, each tag 110 responds to the information request signal during its own time slot of the total N time slots. However, in the present invention, a time interval including N time slots is referred to as a test frame.

If two or more tags respond to the same time slot, these tags will not be recognized during the test frame. This collision is associated with an identification error.

It is very likely that an identification error will occur during one test frame. However, the probability of identification error can be reduced if all tags change the time slot number according to their pseudo random way during the k-identification period.

2 is a diagram for explaining the structure of an identification interval.

The identification section includes k test frames TF, and the length of the identification section is illustrated as 1 second. Each test frame has N time slots.

In FIG. 2, T _symb is illustrated as approximately 61 ms, and is a duration including a guard interval (GI) and one OFDM symbol.

The identification section of the OFDM signal having such a configuration can be expressed by the following equation.

k × N × T _symb ≒ 1 = constant

(In Equation 1, k is the number of test frames, N is the number of time slots included in one test frame, and T _symb is the time required to transmit one OFDM symbol.)

As a constant, "1" illustrates one second as a time for receiving information from tags 110 included in one group.

Meanwhile, by varying the variables k and N in Equation 1, an identification error can be minimized while maintaining a total duration of identification period as 1 second.

Equation 2 is a formula for calculating the probability of occurrence of an identification error. The number of test frames k can be 18-40, and k can be selected as 32. In this case, according to Equation 1, N is 512.

At this time, the identification error is changed according to the number n of tags 110 included in one group.

3 is a diagram illustrating a change of an identification error according to the number of tags.

If the number n of tags is 400 or less, the probability of identification error is reduced to 10 ^-6 or less. These results are provided by the time separation technique.

However, the above results are obtained when the OFDM symbol duration is 61 ms, and it is also possible to shorten the OFDM symbol duration. The frequency band then becomes wider, but can increase the number N of time slots and the number k of test frames. Therefore, the number of tags included in one group can be increased and the possibility of identification error can be reduced.

On the other hand, the time separation technique may be extended to the frequency separation technique (Frequency Separation Technique) and the space separation technique (Space Separation Technique).

[Frequency Separation Technique]

Tags may be uniformly distributed over a plurality of frequency sub-channels.

In each frequency channel, the time separation technique is performed in parallel and independently.

Therefore, if four frequency channels are used and there are 250 tags in each frequency channel, the probability of generating an error is 10 ^-10 .

Conversely, if the probability of error occurrence is fixed to 10 ^-6 , the number of tags in each frequency channel can be increased to 1600.

[Space Separation Technique]

The group of tags can be divided into a plurality of subgroups using reader antenna arrays and spatial separation techniques.

At the core of the spatial separation technology are control algorithms for adaptive antenna array systems and multi-element antenna arrays.

Space separation technology allows you to distinguish between narrow local spaces. Thus, subgroups may be selected and identified from the group of all tags. All subgroups are parallel and can be identified separately from other groups.

To this end, scanning may be performed using a single beam antenna array system, or parallel tags may be processed using a multi beam antenna array system.

[Tag Structure]

4 is a diagram showing the structure of a tag according to an embodiment of the present invention, Figure 5 is a diagram showing the configuration of a modulator in an embodiment of the present invention.

Tag 110 of the present invention is an antenna 114, power supply unit 118, memory 111, control logic 115, modulator 112, clock generator 116, frequency synthesizer 117, frequency rising converter 113 is included.

The antenna 114 receives an information request signal received from the reader 120 or transmits tag identification information inside the tag 110 according to the information request signal.

The power supply unit 118 receives the energy pumping signal of the reader 120 transmitted from the antenna 114 to generate internal power. However, in the case of the active tag, the power is charged and stored in advance.

The memory 111 stores tag identification information input from a code source such as a personal computer (PC). The tag identification information is stored by converting a code source into a frequency domain. The tag identification information may include header information, product identification information, and error correction information. The header information may include information such as the format of the code, the version of the code system, the length of the code, etc. The product identification information may include information such as the type of the tagged product, the price, the expiration date, and the country of origin. The error correction information may include information for correcting an error that may occur in a communication process.

The control logic 115 controls the components of the tag 110 to transmit tag identification information according to the information request signal transmitted from the antenna 114. In the present invention, since the tag 110 transmits tag identification information stored in the memory 111 according to the input energy pumping signal, the control logic 115 may be selectively provided.

Meanwhile, the control logic 115 may play a role of counting a random pseudo random time interval of a preset process according to the above-described time separation technique.

The modulator 112 modulates tag identification information stored in the memory 111 and modulates the tag identification information into an OFDM signal.

As shown in FIG. 5, the modulator 112 may include an encoder 1121, an interleaver 1122, an IFFT 1123, a guard interval inserter 1124, and a D / A converter 1125.

The encoder 1121 encodes the tag identification information to output a code symbol. The encoder 1121 outputs a code symbol having a Forward Error Correction (FEC) capability.

The interleaver 1122 interleaves and outputs the code symbols from the encoder 1121 so as to be resistant to burst errors by a given rule.

The inverse fast Fourier transformer (IFFT) 1123 performs inverse fast Fourier transform on the signal output from the interleaver 1122 and modulates the subcarrier to have orthogonality in the frequency domain.

The guard interval inserter 1124 inserts a guard interval to attenuate the effects of multipath interference.

On the other hand, the signal output from the guard interval inserter 1124 is a signal converted into the time domain.

The D / A converter 1125 converts a digital signal into an analog signal and outputs the analog signal.

The clock generator 116 generates a clock based on the signal received at the antenna 114. For example, the clock generator 116 may use TXCO.

The frequency synthesizer 117 generates a predetermined frequency.

The RF up converter 113 up-converts the signal output from the modulator 112 to be transmitted through the antenna 114.

On the other hand, the tag 110 is required to configure the modulation unit 112 in order to generate an OFDM signal, the modulation unit 112 is hindered to produce a tag having a low price and low power consumption. Therefore, it is necessary to simplify the design of the modulator 112.

The tag 110 applied to the RFID system includes digital information that is predefined and stored in the tag 110, unlike other types of wireless communication.

Accordingly, in consideration of such characteristics, the tag 110 having a simpler structure may be provided.

6 is a view for explaining the structure of a tag according to another embodiment of the present invention.

The tag shown in FIG. 6 will only be described with respect to differences from the tags shown in FIGS. 4 and 5.

The tag 110 shown in FIG. 6 has a much simpler structure than the tag 110 shown in FIGS. 4 and 5.

In particular, in the tag 110 shown in FIG. 6, the configuration of the modulator 112 is greatly simplified so that only the D / A converter 1125 exists.

As described above, the tag 110 applied to the RFID system has previously stored information unlike other wireless communication. Therefore, the information converted by converting the code source 130 of the PC into the frequency domain and the time domain is stored in the memory 111.

That is, the tag 110 stores the necessary digital information in the memory 111 by using a software tool in the production line of the tag 110, and converts the required digital information into a frequency domain and a time domain so as to be stored in advance.

Therefore, the tag 110 may have a simpler structure since the configuration of the encoder 1121, the interleaver 1122, the IFFT 1123, and the guard interval inserter 1124 is not required.

In addition, unlike the tag 110 illustrated in FIGS. 4 and 5, the tag 110 illustrated in FIG. 6 does not use a clock generator such as TXCO, and is external from the reader 120 using the clock extractor 119. An internal clock signal is extracted from an external low frequency energy pumping signal.

First of all, if you do not use a clock generator, you can reduce the price and size of the tag. In this case, the tag 110 can be produced in a very small size because it can be composed only of the antenna and the chip.

In addition, when the clock generator is not used, the problem caused by the UHF frequency bands (frequency bands) allowed for the RFID can be solved.

For example, Korea uses a frequency band of 908-914 MHz, and Japan uses a frequency band of 950-956 MHz. And Europe uses a frequency band of 862-870 MHz.

Therefore, if a product produced in Europe and exported to Japan through Korea is attached to a tag suitable for Europe, information cannot be obtained using this in Korea and Japan.

In the present invention, the transmission frequency (Tx frequency) of the tag 110 may be formed by the frequency synthesizer 117 which is the simplest phase locked loop synthesizer. The frequency synthesizer 117 may generate a frequency of 860-960 MHz to cover the RFID frequency band used in each country.

The reference frequency of the frequency synthesizer 117 is determined by the energy pumping signal of the reader 120.

In addition, the frequency of the energy pumping signal may vary according to the RFID frequency range allowed in each country.

In the present invention, the ratio of the transmission frequency and the energy pumping frequency of the tag 110 is fixed by the same frequency divider coefficient in all the countries of the world.

For example, assuming that the frequency division factor for the frequency synthesizer 117 is 100, an energy pumping signal of 8.62-8.7 MHz is used in Europe, an energy pumping signal of 9.08-9.14 MHz is used in Korea, and in Japan. It can be set to use an energy pumped signal of 9.50-9.56 MHz.

In this case, only one difference is the frequency bandwidth and frequency-time scales, which are the duration of the OFDM symbol. However, this difference is less than ± 4%.

The frequency synthesizer 117 synthesizes the frequency by applying the frequency division coefficient to the frequency extracted by the clock extractor 119 from the energy pumping signal. As described above, the frequency synthesizer 117 may generate a frequency of 860-960MHz to cover the RFID frequency band used in each country.

For example, even when the same tag 110 is used in Europe and Japan, a signal that can be read by the reader 120 of the corresponding country may be transmitted according to a frequency extracted from each energy pumping signal.

Thus, one tag 110 may communicate with all the readers 120 of each country.

7 is a diagram illustrating a structure of an OFDM signal according to an embodiment of the present invention.

The parameters of the OFDM signal are shown in Table 1 below.

Parameter Marking Value Frequency band f _o 860-960 MHz Subcarrier spacing ΔF 20 kHz Sampling frequency F _sample 5.12 MHz Symbol length T _symb 50㎲ Guard Interval length T _GI 11㎲ Spectrum width Δf 5.1 MHz Number of pilot subcarriers N _sp 4 Number of data subcarriers N _sd 248 Subcarriers modulation QPSK Forward Error Correction (FEC) 1/2 or 1/4 Tag information capacity Bit 248 or 368

8 is a diagram illustrating a configuration of a reader in an RFID system according to an embodiment of the present invention.

The reader 120 includes a memory 121, a microprocessor 122, a transmitter 123, a receiver 125, and an antenna 124.

The transmitter 123 generates an energy pumping signal for power supply of the tag 110 and for providing a clock synchronization signal and an information request signal.

The antenna 124 transmits a high frequency signal to the tag 110 and transmits a high frequency signal by scanning using a single beam antenna array system for the above-described spatial separation technology, or uses a multi-beam antenna array system. Therefore, high frequency signals can be sent in parallel to the tags separated by space.

The receiver 125 demodulates tag identification information of the OFDM format transmitted from the tag 110. In detail, the receiver 125 may include a guard interval remover, a fast fourier transform (FFT), a deinterleaver, a decoder, and the like.

That is, the receiver 125 demodulates the OFDM signal transmitted from the tag 110.

The microprocessor 122 processes information transmitted and received through the transmitter 123 and the receiver 125.

The memory 121 stores tag identification information received from the tag 110.

The RFID system of the present invention receives tag identification information of an OFDM format from a tag and demodulates it in a reader to accurately and quickly identify a plurality of tags.

The RFID system of the present invention can simplify the structure of the tag and can produce the tag at a low price.

The RFID system of the present invention can provide reliable and fast tag identification by proposing a protocol having a short OFDM symbol and a high information force.

The RFID system of the present invention can store and use sufficient information in a tag.

The RFID system of the present invention can provide a passive tag with a single chip.

The RFID system of the present invention can overcome the difference in RFID frequency in each country of the world.

Claims (20)

An antenna stage for receiving an energy pumping signal and transmitting tag identification information; A memory in which the tag identification information is stored; A modulator for modulating the tag identification information into an OFDM signal according to the information request signal included in the energy pumping signal; A clock generator for generating a clock according to a clock synchronization signal included in the energy pumping signal; A frequency synthesizer operated according to the clock of the clock generator and generating a frequency; A frequency rising converter configured to up-convert the signal output from the modulator to be transmitted through the antenna terminal; And RFID tag, characterized in that configured to include a power supply for providing internal power. The method of claim 1, The power supply unit RFID tag, characterized in that for generating the internal power using the energy pumping signal received through the antenna end. The method of claim 1, The power supply is RFID tag, characterized in that the power is stored in advance. The method of claim 1, The memory tag is characterized in that the tag identification information is converted into the frequency domain and stored. The method of claim 1, The modulator includes an encoder for outputting a code symbol having a forward error correction function, an interleaver for interleaving and outputting the code symbol, and an inverse fast Fourier converter for inverse fast Fourier transforming a signal output from the interleaver to modulate a subcarrier. And a guard interval inserter for inserting a guard interval to attenuate the effects of multipath interference, and a D / A converter for converting a signal output from the guard interval inserter into an analog signal. . The method of claim 1, And a logic circuit for counting a predetermined time interval and controlling the tag identification information to be transmitted with a time delay. The method of claim 1, The tag identification information is included in one OFDM symbol and transmitted. An antenna stage for receiving an energy pumping signal and transmitting tag identification information; A memory in which the tag identification information is stored; A D / A converter for converting the tag identification information into an analog signal according to the information request signal included in the energy pumping signal; A clock extractor for extracting a clock signal from the energy pumping signal; A frequency synthesizer operated according to the clock of the clock extractor and generating a frequency; A frequency rising converter configured to up-convert the signal output from the D / A converter to be transmitted through the antenna terminal; And RFID tag, characterized in that configured to include a power supply for providing internal power. The method of claim 8, The power supply unit RFID tag, characterized in that for generating the internal power using the energy pumping signal received through the antenna end. The method of claim 8, The power supply is RFID tag, characterized in that the power is stored in advance. The method of claim 8, The memory tag is characterized in that the tag identification information modulated by the OFDM signal is converted into the time domain and stored. The method of claim 11, The tag identification information is RFID tag, characterized in that transmitted in one OFDM symbol. The method of claim 8, And a logic circuit for counting a predetermined time interval and controlling the tag identification information to be transmitted with a time delay. The method of claim 8, The frequency synthesizer is an RFID tag, characterized in that to generate all the frequencies of 860-960MHz. The method of claim 8, And the frequency synthesizer generates a different frequency according to the input energy pumping signal. A transmitter configured to generate an energy pumping signal for power supply of the RFID tag and for providing a clock synchronization signal and an information request signal; An antenna stage for transmitting the output of the transmitter as a high frequency signal and receiving an OFDM signal from the RFID tag; A receiver which demodulates tag identification information from the OFDM signal received through the antenna terminal; And And a microprocessor for controlling the transmitter and processing the demodulated signal at the receiver. The method of claim 16, The antenna terminal is a RFID reader, characterized in that for transmitting a high frequency signal by scanning using a single beam antenna array system. The method of claim 16, The antenna terminal is a RFID reader, characterized in that for transmitting a high frequency signal in parallel to the tags separated by space using a multi-beam antenna array system. The method of claim 16, The receiver comprises a guard section remover, a high-speed Fourier transducer, a deinterleaver, and a decoder. The method of claim 16, And a memory in which the demodulated tag identification information is stored.

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