JP2003298463A - Mobile body identification system, operating method for mobile body identification system, and interrogator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an interrogator with a simpler structure, a mobile body identification system employing the same, and an operating method of the mobile body identification system. <P>SOLUTION: After emitting a high frequency signal modulated by data to be transmitted within a first period, an antenna 31 of the interrogator 30a emits the high frequency signal not modulated within a second period in the case of transceiving data. A responder receives and demodulates the modulated high frequency signal within the first period and repeats absorption and reflection of the energy of a carrier signal in a non modulation state from the interrogator according to data to be returned within the second period. The interrogator uses a local oscillation signal with a first phase as a local oscillation signal to be used by a mixer 310 for the second period to receive and demodulate the data and repeats the operations for the first and second periods again when the result of reception indicates occurrence of error. However, the interrogator uses a local oscillation signal with a second phase for the operation within the second period. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio frequency identification (RFID) system including an interrogator and a responder, and more particularly to a novel structure of the interrogator.

[0002]

2. Description of the Related Art An RFID system is a mobile body identification system generally used for physical distribution and non-contact IC cards, and is also called a wireless tag system for identification of tags in physical distribution.

FIG. 5 shows a typical configuration example of an RFID system. This system includes an interrogator 30 and a transponder 1.
It is composed of 0.

The interrogator 30 itself generates high frequency energy and radiates this energy from the antenna 31 to the space. At this time, it is common to superimpose information on the high-frequency energy using changes in amplitude, frequency, phase, etc., and radiate the information. At the same time, the interrogator receives a signal propagated from the transponder 10 to the interrogator 30 by the same distance d as a result of the high-frequency energy emitted by the interrogator being reflected by the transponder 10 separated from the antenna 31 by the distance d. Is possible. At this time, the interrogator 30
Since the responder 10 superimposes information on a part of the high-frequency energy emitted from the device using changes in amplitude, frequency, phase, etc., the interrogator 30 can detect the information.

The antenna 31 radiates the high frequency energy emitted from the interrogator 30 to the space, and at the same time, receives the high frequency energy from the response from the responder 10 and sends it to the interrogator 30.

The transponder 10 roughly performs the following three operations. First, the high frequency energy emitted from the interrogator 30 is received and rectified and used as the power source for the interrogator itself. Secondly, the superposed information is detected for the high frequency energy emitted from the interrogator by using changes in amplitude, frequency, phase, etc., and it is sent out as its own action or response according to the instruction of the signal. Change the data. Thirdly, the antenna impedance of the transponder is changed corresponding to the information to be transmitted by the transponder within the time when the interrogator is transmitting high-frequency energy. This change reflects or absorbs a part of the high-frequency energy sent from the interrogator on the transponder side, and as a result, the reflected wave from the transponder received on the interrogator side changes. Becomes The interrogator can obtain the information transmitted from the responder by detecting the change in the reflected wave from the steady state.

[0007]

SUMMARY OF THE INVENTION Such a conventional RF
The ID system still has room for improvement as described below. 1. Due to its characteristics, in order to avoid reception deterioration at the reception null point, the interrogator has a structure capable of simultaneously receiving signals with a plurality of phase differences, and the structure is complicated.
2. The interrogator uses multiple receivers (reception systems), but only one output uses the reception result, and it is uneconomical to have two reception systems just to avoid null points. Is. 3. The two receiving systems of the interrogator are exactly the same circuit and provide only the same function. Further, only the phase shifter is essentially necessary to avoid the null point, and the subsequent reception system exists only to obtain the same reception result within the same time axis.

Accordingly, an object of the present invention is to provide an interrogator having a simpler structure, a mobile body identification system using the interrogator, and an operation method of the mobile body identification system.

[0009]

A mobile object identification system according to the present invention is a mobile object identification system in which an interrogator emits a predetermined high-frequency energy into space and receives a reflected signal from a transponder, wherein the interrogator comprises: Having only one system for receiving the reflected signal from the transponder, and having means for generating local oscillation signals of different phases, and using one of the local oscillation signals of different phases when receiving the reflected signal. It is characterized in that when the signal is received and the result is an error, another local oscillation signal is selected and the signal is received again.

In this system, instead of reducing the reception system to one system, local oscillation signals of a plurality of phases are selectively available, and the local oscillation signals are switched and used when the reception result is an error. As a result, if the reception is successful, the data from the transponder can be received by one receiving operation. Even if the reception is an error, it can be expected that the same data will be correctly received by the retry by switching the local oscillation signal. This is because this processing is performed within an extremely short time, and it is considered that the radio wave condition during that time is unchanged.

The operation method of this mobile body identification system is as follows. (A) When transmitting and receiving data, the interrogator emits a high-frequency signal modulated with data to be transmitted within a first period, and then emits an unmodulated high-frequency signal within a second period, (B) The transponder receives and demodulates the modulated high-frequency signal within the first period, and within the second period, according to the data to be returned, the carrier wave in an unmodulated state from the interrogator. Repeating absorption and reflection of signal energy, (c) the interrogator performs data reception and demodulation using the first local oscillation signal within the second period, and (d) the reception result is an error. In this case, steps (a) and (b) are executed again, and in the subsequent step (c), the second local oscillation signal is used.

In this method, when the reception is successful in the step (c), it is preferable to maintain the local oscillation signal used at that time and use the same local oscillation signal when receiving the subsequent data. This is because it is considered that there is little change in the radio wave condition during reception of a series of data, and it is expected that normal reception can be performed with local oscillation signals of the same phase.

An interrogator according to the present invention is an interrogator in a mobile body identification system that radiates a predetermined high frequency energy into a space and receives a reflected signal from a responder, and a high frequency oscillating means for generating a high frequency signal, Modulating means for modulating a high frequency signal based on transmission data, high frequency amplifying means for amplifying the output of the modulator, and radiation for emitting modulated high frequency energy and non-modulated high frequency energy from an antenna based on the output of the high frequency amplifier. Means, a single receiving system for receiving the reflected signal from the responder, and a control means for controlling the operation of the interrogator, wherein the single receiving system has different phases based on the high frequency signal. Generating means for generating a plurality of local oscillation signals, selecting means for selecting one of the plurality of local oscillation signals having different phases, and the unmodulated high frequency energy When a gee is radiated, the mixer has a mixer for inputting the reflected signal from the transponder received by the antenna and the selected local oscillation signal, and demodulation means for demodulating the received signal based on the output of the mixer. When the reflected signal from the transponder is received by the single receiving system, the control means receives using one of the local oscillation signals having different phases, and if the result is an error, the other local signal is received. A feature is that an oscillating signal is selected and reception is performed again.

When the reflected signal from the responder is received, the control means of the interrogator first tries the reception by using the local oscillation signal of the first phase, and if this results in an error, then the local means of the second phase is successively received. Attempt reception using the oscillating signal.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings.

As shown in FIG. 5, the overall configuration of the RFID system according to this embodiment comprises an interrogator 30 having an antenna 31 and a responder 10. This transponder functions as a tag, a label, an IC card, or the like.

In order to better understand this embodiment,
First, the configuration and operation of a general interrogator and transponder will be described, and then the configuration and operation of the present embodiment will be described.

FIG. 1 shows a transponder 10 used in this embodiment.
A configuration example of is shown.

The signal radiated from the interrogator 30 is received by the antenna 101. This received signal is
The signal is distributed to the ASK (Amplitude Shift Keying) demodulator 102 and the rectifier circuit 111. The rectifier circuit 111 rectifies the signal received from the antenna 101 to generate a direct current voltage (DC).
Then, after stabilizing the voltage in the stabilizing circuit 112, the voltage is supplied to each circuit inside the responder 10 as an operating power supply. In addition, a reset signal is generated by the reset circuit 113 when necessary to prevent unstable operation due to voltage fluctuations.

On the other hand, the signal input to the ASK demodulator 102 is converted into digital data by ASK demodulation,
It is converted into an information bit string by the decoder 103. Then, the command interpreting unit 104 interprets the command portion in the information bit string, and the memory address converting unit 105 determines which storage position in the memory 110 to read. In addition,
The memory 110 is a non-volatile memory.

Subsequently, the data string stored at the designated position in the memory 110 is read out from the memory, converted into a bit string by the parallel / serial conversion unit 109, and predetermined by the encoder 108. Modulator 1 after the encoding of
The signal is modulated at 07 and input to the load change switch (SW) 106. This load change switch 106 is used for the modulator 1
It works so as to change the load of the antenna 101 according to the input from 07. The antenna 101 functions to repeat absorption and reflection of the energy of the carrier signal in the non-modulated state transmitted from the interrogator at this time.

This system is established by the interrogator that emits high-frequency energy and the responder that absorbs and reflects the energy as described above, but there is a major problem in using this reflected wave. know. That is, a standing wave formed by a traveling wave and a reflected wave is generated between the antenna connected to the interrogator and the responder. This standing wave has a point at which the amplitude becomes 0 at every 1/4 of the propagation wavelength of the high frequency energy generated from the interrogator. As shown in FIG. 5, when the distance d between the antenna 31 and the transponder 10 becomes the length of “an integer multiple of ¼ of the wavelength”, the amplitude of the reflected wave from the transponder 10 is changed to the interrogator 30. There is a phenomenon that the reflected wave is not detected at all on the interrogator 30 side even though the responder 10 responds to 0 at the antenna end face on the side. The problem of such a null point is also described in detail in Japanese Patent Laid-Open No. 10-209912.

FIG. 2 is an explanatory view of the principle of generation of null points in the RFID system. In this figure,
The high frequency energy generated by the interrogator is Ei and is shown by the following equation. Ei = A sin (2πft) (1)

On the other hand, when the distance from the interrogator to the responder is d, the phase difference φ between the interrogator and the responder is:
It is expressed as follows. φ = (4πdf / c) = (4πd
/ Λ) (2) where c is the speed of light and λ is the wavelength.

Therefore, the reflected wave of the transponder received by the interrogator is expressed as follows. Er = A ・ b ・ sin (2
πft + φ) (3)

The interrogator demodulates the reflected wave using the transmitted high frequency energy. The demodulated signal is represented as follows. Em = Ei ・ Er = A ²・ b ・ (1/2) {cos (4πft +
φ) −cos (φ)} (4) Here, since the first term in {} is a component of the second harmonic, it is suppressed by a filter or the like, and only the second item remains. Therefore, as can be seen from this equation (4) and the above equation (2), Em becomes 0 every time d changes by 1/4 of the wavelength.

For example, the frequency of the high frequency energy is 2.
When it is 45 [GHz], 1/4 of the wavelength is about 3.1.
Since it is cm, the distance between the transponder and the antenna is 3.1c.
A point at which the received signal is not received occurs every m. In general, the distance between the transponder and the antenna is arbitrary, and if unfortunately it falls to such a point, there arises a problem that the transponder cannot receive even if it is in the immediate vicinity of the antenna.

In order to avoid this problem, a typical conventional interrogator is often constructed as shown in FIG. The configuration and operation of this interrogator will be described below.

High frequency oscillator (high frequency signal generator) 208
Is controlled by the CPU 220, and this CPU generates a signal having a frequency specified by the CPU. The high frequency signal generated by the high frequency oscillator 208 is modulated by the modulation signal from the CPU 220 in the ASK modulator 207 and becomes an amplitude modulation signal. This amplitude modulation signal is supplied to the high frequency amplifier 20.
After being amplified by 6, the power divider 205
It is divided into two lines. One of them is amplified to a large signal by the power amplifier 204, then passes through the circulator 203, the unnecessary signal is removed by the filter 202, and the antenna 31 radiates it into the air.

On the other hand, the other signal distributed by the power distributor 205 is further divided into two signals having a 90 ° phase difference in the 90 ° phase shift generator (phase shifter) 212,
The local oscillation signal (local signal) is input to each of the two receiving mixers 210 and 211.

A part of the high-frequency energy emitted into the air by the antenna 31 is reflected by the transponder and is again input from the antenna 31. The signal input from the antenna 31 passes through the filter 202 and passes through the circulator 20.
Input to 3. The signal input from the filter side is distributed to the power distributor 209 side by the circulator 203, and is further equally divided here to become RF signals input to the reception mixers 210 and 211, respectively.

Here, in the receiving mixers 210 and 211, the frequencies of the local signal and the RF signal are exactly the same, and the phase relationship is almost constant, so most of the output signals of the receiving mixers are DC components. However, since only the reflected signal from the interrogator is a changing component, I
Only the variation is taken out by the (in-phase) filter 213 and the Q (quadrature phase) filter 216, and high-gain amplified by the multistage amplifiers 214, 215, 217, and 218.
The demodulator 219 demodulates the signal data. The demodulated signal is subjected to signal processing by the CPU 220 and can be displayed on an arbitrary display device by the display unit 224 via the input / output interface 221. Also,
A user's instruction and necessary data can be input from the operation unit 225 including operation keys and buttons. The external interface 222 enables connection with an arbitrary external device such as an arbitrary wired or wireless network, an external storage device, and a printer. Memory 223
Is a storage device such as a ROM or a RAM that provides a storage area for the operation program of the CPU 220, a work area, a temporary storage area, and the like. The operating power of each part of the interrogator 30 is the power supply 2
Supplied from 28.

In the configuration shown in FIG. 3, in order to avoid the influence of the null point described above, two local signals having a phase difference of 90 degrees are prepared in the receiving system, and the normal output and as if the interrogator is used. It is possible to simultaneously obtain an output such that the distance between the transponder and the transponder is shifted by ⅛ wavelength from the actual position. Therefore, it is possible to obtain a state where the output does not become 0 in either of the two systems of receivers, and a stable reception operation can be expected.

However, in the configuration shown in FIG. 3, it is necessary to prepare two identical receiving circuits in order to simultaneously obtain results from the two receiving systems. Generally, one of the results of the two systems that has a good reception state is generally acquired as data, and the other result is discarded without being used.

On the other hand, in one type of RFID system,
It supports time-division transmission, and has the feature of receiving responses to short transmission words within a narrow window. In such a system, if the received data does not come after the transmission of the transmission word, the transmission word can be immediately retransmitted, and the change in the reception state can be flexibly dealt with.

In the present embodiment, R of such time division is used.
In the FID system, assuming that the retransmitting operation of reception is possible, the number of the two receiving circuits is reduced to one, and a new phase change switch is introduced. Is to achieve.

FIG. 4 shows an interrogator 30 according to this embodiment.
The structural example of a is shown. The structure of the transponder used may be the same as that shown in FIG. In FIG. 4, an antenna 31, a filter 302, a circulator 303, a power amplifier 304, a power distributor 305, a high frequency amplifier 306, a modulator 307, a high frequency oscillator 308, a CPU 317, an input / output interface 318, and an external interface 31.
9, the memory 320, the display unit 321, the operation unit 322, and the power source 323 are the same as the corresponding parts in FIG. 3, and detailed description thereof will be omitted.

The signal distributed from the circulator 303 is directly input to the single mixer 310. on the other hand,
The signal distributed by the power distributor 305 is input to the 90 ° phase shifter 312. This phase shifter outputs two outputs that are 90 ° out of phase with each other.
11, and one of them is selectively input to the mixer 310. The switch 311 is the CPU 3
It is controlled by 17 and receives an instruction of which phase signal should be input to the mixer. The output signal of the mixer 310, like one of the two reception systems in the interrogator of FIG. 3, takes out only the change of the signal in the filter 313, is subjected to high gain amplification in the multistage amplifiers 314 and 315, and is demodulated by the demodulator 316. At, the signal data is demodulated. The demodulated signal is processed by the CPU 317.
The subsequent operation and other operations are similar to those of the interrogator of FIG.

The 90 ° phase shifter 312 and the switch 311 are 2
Although the phase local oscillation signal generator 330 is configured, the present invention is not limited to the illustrated configuration as long as it is a configuration capable of generating a plurality of local oscillation signals having different phases.

Next, a detailed flow of how the reception operation and the antenna switching are performed in the configuration of the interrogator of FIG. 4 will be described with reference to FIGS. 6 and 7.

FIG. 7 is a flow chart showing the general flow of the processing procedure executed by the CPU 317 of the interrogator 30a. FIG. 6 is a timing chart used for the explanation. Although this flow may change depending on the application to which the present invention is applied, it will be described here as a typical processing example.

In FIG. 7, the interrogator first confirms whether or not there is data to be transmitted / received after the power is turned on or after receiving a predetermined instruction from the user or the system (S11).
If not, the process ends (S26). If there is data to be transmitted / received, first, the switch 311 is set to either side (for example, 0 ° side) (S12), and the transmission-reception operation is performed once (S13).

As shown in FIG. 6, this operation is executed in a predetermined transmission section (for example, about 1 to several milliseconds) and a reception section of the same time following this section. The signal radiated into the air from the antenna 31 is the high frequency signal generated by the high frequency oscillator 308 modulated by the modulation signal from the CPU 220 during the transmission section, but is not modulated during the reception section. It is a signal.

While no error occurs in the received data (S14, No), the switch 311 remains in the same state,
The transmission-reception operation is repeated for the data to be transmitted / received (S12, S13).

However, when the signal obtained by the receiving operation causes a receiving error due to an excessively low receiving level or a code error (S14, Yes), the retransmission operation is immediately started (S15). If this retransmission exceeds the specified number of times,
An error is displayed and the process is temporarily terminated (S17).

If the specified number of times is not exceeded, the switch 311 is switched to the opposite side (for example, 90 ° side) before the start of the next transmission (“transmission (retransmission)” in FIG. 6) (S1).
8) Then, the same transmission-reception operation as above is performed once again (S).
19). If the data can be received and the data can be properly decoded (S20, No), the transmission / reception operation is repeated for a series of data (S24, Yes, S19). When one transmission / reception operation of a series of data is completed, this processing is completed (S25).

If a reception error occurs again in step S20, the retransmission operation is immediately started (S21). If this retransmission exceeds the specified number of times (S22, Yes
s), an error is displayed and this processing is terminated (S2).
3). If it has not exceeded the specified number of times, the switch is returned to the opposite side (original side) again (S12), and the transmission / reception operation similar to the above is performed.

In this way, the operation of transmission-reception is repeated while alternately switching the switches, and if the error is not resolved even after repeating a predetermined number of times, it is judged as a final reception error and the upper layer is notified ( S17 or S2
3).

As described above, the conventional interrogator has a configuration of 1
While two reception results of 0 ° and 90 ° can be obtained at the same time by the transmission-reception operation once, the configuration of the present invention may require a plurality of transmission-reception operations (of course, 1 If there is no error in the operation of transmitting and receiving once, it is the same as the conventional one). However, there is an advantage that the circuit configuration of the receiving portion is greatly simplified. In addition, the radio wave condition may slightly change due to a time difference between the first and second transmission-reception operations, but the transmission-reception cycle is sufficiently short (for example, about 10 ms or several ms). It is considered that there is not much change in the radio wave condition in the system. Therefore,
By the software operation as shown in FIG. 7, the RFID
Even if the structure of the interrogator is simplified, the null point can be avoided, and the size and cost of the interrogator can be reduced.

Although the preferred embodiment of the present invention has been described above, various modifications and changes other than those mentioned above can be made. For example, as a digital modulation / demodulation system, A
The SK method has been taken as an example, but FSK (Frequency Shift)
Keying) and PSK (Phase Shift Keying) methods may be used.

[0051]

According to the present invention, the hardware configuration of the interrogator of the mobile body identification system can be simplified, and it can contribute to downsizing, cost reduction, and power consumption reduction of the interrogator. .

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of a transponder used in an embodiment according to the present invention.

FIG. 2 is an explanatory diagram of a principle of generation of a null point in an RFID system.

FIG. 3 is a block diagram showing a configuration of a typical conventional interrogator.

FIG. 4 is a block diagram showing a configuration example of an interrogator in the embodiment of the present invention.

FIG. 5 is a diagram showing a typical configuration example of an RFID system.

FIG. 6 is a timing diagram for explaining a receiving operation and switching of antennas according to the embodiment of the present invention.

FIG. 7 is a flowchart showing a schematic flow of a processing procedure executed by the CPU of the interrogator according to the embodiment of the present invention.

[Explanation of symbols]

10 ... Responder, 30, 30a ... Interrogator, 31 ... Antenna, 101 ... Antenna, 102 ... Demodulator, 103 ... Decoder, 104 ... Command interpreting unit, 105 ... Memory address converting unit, 106 ... Load change switch, 107 … Modulators,
108 ... Encoder, 109 ... Parallel-to-serial converter, 110 ...
Memory, 111 ... Rectifier circuit, 112 ... Stabilization circuit, 11
3 ... Reset circuit, 302 ... Filter, 303 ... Circulator, 304 ... Power amplifier, 305 ... Power distributor,
306 ... High frequency amplifier, 307 ... Modulator, 308 ... High frequency oscillator, 310 ... Mixer, 311 ... Switch, 312
... Phase shifter, 313 ... Filter, 314 ... Amplifier, 316
... Demodulator, 318 ... Input / output interface, 319 ...
External interface, 320 ... Memory, 321 ... Display section, 322 ... Operation section, 323 ... Power supply, 330 ... Two-phase local oscillation signal generator

Claims (6)

[Claims] 1. A mobile body identification system in which an interrogator radiates a predetermined high-frequency energy to space and receives a reflected signal from a responder, wherein the interrogator has one system for receiving a reflected signal from the responder. And having means for generating local oscillation signals of different phases, and receiving by using one of the local oscillation signals of different phases when receiving the reflected signal, the other if the result is an error. A mobile body identification system characterized by selecting a local oscillation signal and performing reception again. 2. The moving body identification system according to claim 1, wherein the transponder obtains its own operating power from the high frequency energy. 3. A method of operating a mobile body identification system, wherein an interrogator emits a predetermined high-frequency energy into space and receives a reflected signal from a transponder, the method comprising: (a) the interrogator transmitting and receiving data. Radiating a high frequency signal modulated with data to be transmitted within a first period, and then radiating a non-modulated high frequency signal within a second period, and (b) the responder within the first period. In the second period, according to the data to be returned, absorption and reflection of the energy of the carrier signal in the non-modulated state from the interrogator are repeated, and the modulated high frequency signal is received and demodulated, (c) The interrogator performs data reception and demodulation using the first local oscillation signal within the second period, and (d) executes steps (a) and (b) again when the reception result is an error. And subsequent step (c)
Then, a method of operating a mobile body identification system, characterized by using a second local oscillation signal. 4. If the reception is successful in step (c), the local oscillation signal used at that time is maintained,
4. The method of operating a mobile body identification system according to claim 3, wherein the same local oscillation signal is used when receiving subsequent data. 5. Radiating predetermined high frequency energy into space,
An interrogator in a moving body identification system that receives a reflected signal from a transponder, including a high-frequency oscillating means for generating a high-frequency signal, a modulating means for modulating the high-frequency signal based on transmission data, and an output of the modulator. High-frequency amplifying means for amplifying, based on the output of the high-frequency amplifier, radiating means for radiating modulated high-frequency energy and non-modulated high-frequency energy from the antenna, a single receiving system for receiving the reflected signal from the responder, And a control means for controlling the operation of the interrogator, wherein the single reception system generates a plurality of local oscillation signals having different phases based on the high frequency signal, and a plurality of local oscillations having different phases. Selecting means for selecting one of the signals, the reflected signal from the transponder received by the antenna when the unmodulated high frequency energy is emitted, and the selecting And a demodulation means for demodulating a reception signal based on the output of the mixer, wherein the control means is a reflection signal from the responder by the single reception system. An interrogator which receives at the time of reception using one of the local oscillation signals having different phases, and when the result is an error, selects another local oscillation signal and performs reception again. 6. The interrogator according to claim 5, wherein the generating means is a 90 ° phase shifter.