JP2000209122A - Mobile object identification device - Google Patents

Abstract

(57) [Problem] To provide a novel mobile object identification device capable of reducing the bit error rate of data transmission from a transponder to an interrogator. At least a decoding circuit for decoding a signal from a transponder by comparing the level of a signal in an adjacent time slot of pulse position modulation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission technique, and more particularly to a mobile identification apparatus for transmitting data between an interrogator and a transponder wirelessly.

[0002]

2. Description of the Related Art A mobile unit identification system is a system for identifying a mobile unit by bidirectionally communicating information between a transponder attached to the mobile unit and a fixed interrogator in a non-contact manner.
It is rapidly developing in fields such as factory automation such as product entry / exit management and entry / exit management, distribution, and security. The distance between the transponder and the interrogator is at most several meters, and a card is used for the transponder, for example.

[0003] An example of the mobile object identification device is described in "Mobile object identification device standard RCR STD-1" (September 1986) issued by the Radio System Development Center (currently the Radio Industry Association). FIG. 7 shows a basic configuration of the moving object identification device. The mobile object identification device 1 includes an interrogator 2 and at least one transponder 3.

The transponder 3 has an antenna, a detection / control circuit, and a memory, receives data transmitted from the interrogator 2 with a space therebetween, stores the data in the memory, and further stores the data in accordance with an instruction from the interrogator 2. The transmitted data is transmitted to the interrogator 2. The transponders 3 each have a unique ID (identification code). The interrogator 2 reads these IDs, so that even if there are a plurality of transponders 3, the interrogator 2 distinguishes each of the plurality of transponders 3 and extracts data in a specific transponder 3. Can be.

Further, the transponder 3 usually has no battery,
Power is obtained by rectifying the carrier (radio wave, light, etc.) transmitted by the interrogator 2.

[0006] With such a function, when the mobile object identification device 1 is applied to, for example, a system for collecting and delivering luggage, the transponder 3 is used as a tag attached to the moving luggage. With such a configuration, an extremely efficient collection and delivery system is realized.

FIG. 8 shows an example of the configuration of a conventional mobile unit identification device 1. The baseband unit 21 of the interrogator 2 includes a transmission data generation circuit 23 for generating a transmission signal and a data processing circuit 22a for processing data from the transponder 3, and exchanges data with the transponder 3 according to a predetermined procedure. Perform The transmission data generation circuit 23 outputs a binary signal of a command or data accompanying the command to the transmission unit 24 according to an instruction from the data processing circuit 22a.

[0008] The transmission section 24 converts the carrier wave into an ASK (Amplitude Shutter) by the binary signal output from the transmission data generation circuit 23.
Ift Keying) modulates and emits a modulated carrier wave 4 from an antenna 26 via a circulator 25. The circulator 25 simultaneously transmits the transponder 3 received by the antenna 26.
To the receiving unit 27a.

[0009] When the transponder 3 is in a range where it can communicate with the interrogator 2, the transponder 3 receives the radio wave 4 radiated from the antenna 26 of the interrogator 2 by the antenna 31. A part of the received signal is rectified by the rectifier circuit 32, and the obtained power is used as a power source for operating the control circuit 34 and the nonvolatile memory 35.

The other part of the received signal is demodulated by envelope detection in the detection circuit 33. The control circuit 34 receives the command transmitted by the interrogator 2 by inputting the demodulated signal, and operates according to the command. The non-volatile memory 35 stores an ID and information unique to the transponder.
The non-volatile memory 35 includes an EEPROM (ElectricallyEr
(Programmable Read Only Memory) and ferroelectric memory.

The command transmitted by the interrogator 2 includes, for example, a command A for transmitting the n-th bit of the ID of the transponder 3 (n is equal to or less than the number of bits constituting the ID) and a transponder 3
And a command C for specifying the ID of the non-volatile memory 35 and transmitting the contents of the non-volatile memory 35, and a command C for specifying the ID of the transponder 3 and rewriting the contents of the non-volatile memory 35. When, for example, transmission of an ID or transmission of internal data in the non-volatile memory 35 is instructed by these commands, the control circuit 34 reads out the ID and data stored in the non-volatile memory 35 and transmits them to the interrogator 2. I do.

The "transmit the first bit of ID" of the command A is a procedure for specifying the transponder 3 before issuing the commands B and C. When there are a plurality of transponders 3 in a range where communication with the interrogator 2 is possible, when the interrogator 2 transmits the command A, the transponders 3 transmit the first bit of each ID at the same time. There are several commands other than the command A that the plurality of transponders expect to return at the same time.

On the other hand, since the commands B and C specify an ID, only the transponder 3 having that ID returns. Thus, there are several commands that one transponder intends to return in addition to commands B and C.

The procedure for issuing which command and at which time is set in the interrogator 2 in advance. The interrogator 2 operates according to the procedure, and the operation is divided into a mode (transmission state) 1 when a plurality of returns are scheduled and a mode 2 when a single return is scheduled.

Next, the transponder 3 normally uses binary pulse position modulation when transmitting ID and data. FIG. 9 shows an example of binary pulse position modulation. The transmission signal is first divided into frames (100a to 100a).
d) Further, each frame is divided into a plurality of time slots, and data is transmitted using these time slots.

In binary pulse position modulation, binary information is represented by outputting a pulse to one of two time slots. When the binary information is, for example, “0” and “1”, and two time slots for transmitting the binary information are a first slot 102 and a second slot 103 in the frame 100c, respectively, To represent, the slot 102 is set to the low level and the slot 103 is set to the high level (waveform 104). Similarly, when "1" is represented, the slot 102 is set to the high level and the slot 103 is set to the low level (waveform 105). The reason for using such pulse position modulation is that, as a method for transmitting data by the transponder 3, the receiving end impedance of the antenna of the transponder 3 is changed according to the data, whereby the radio wave emitted by the interrogator 2 is reflected by the antenna. This is because a reflected wave intensity modulation method can be employed.

The interrogator 2 receives, at the antenna 26, the radio wave 5 that has been subjected to binary pulse position modulation by the intensity modulation reflected from the transponder 3. The received signal is input to the receiver 27a via the circulator 25. Receiver 27
a includes a detection circuit 28a and a decoding circuit 29. The detection circuit 28a performs synchronous detection on the received signal and outputs an absolute value of the amplitude. The decoding circuit 29 determines the sign of the received data by comparing the detected signal with a predetermined threshold.

Normally, the decoding circuit 29 is specifically configured as shown in FIG.
A threshold value 50 is set as indicated by 0, a determination unit that compares the threshold value 50 with the input signal 53 at the determination timings 51a and 52a, and original "1" and "0" are restored from the determination result. And a decoding unit. FIG. 10 shows a case where the first slot is at a high level and the second slot is at a low level.

[0019]

In the conventional determination method,
The threshold value 50 is usually 1 of the high-level representative voltage value V.
/ 2. Therefore, when the transponder 3 is far away and the high level becomes equal to or lower than the threshold value 50, that is, equal to or lower than V / 2, the judgment becomes impossible. Therefore, the sensitivity of this judgment method corresponds to V / 2.

In other words, an erroneous mistake of a lowered high level as a low level and a mistake of a low level having an increased level due to increased noise at the time of reception as a high level error in data transmission. Therefore, in order to reduce the probability of a code error, the distance must be shortened so as to increase the reception level of the transponder 3.

On the other hand, the responder 3 is used in various ways, such as being attached to a moving luggage, and the position and the distance are largely changed. Therefore, it is desirable to increase the sensitivity to increase the usable range of the transponder 3. However, in the conventional determination method, the use range has to be limited according to the limitation of the sensitivity, that is, the requirement of the required bit error rate.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a novel mobile object identification device capable of reducing the bit error rate of data transmission from a transponder to an interrogator. .

[0023]

In order to achieve the above-mentioned object of the present invention, a moving object identification apparatus according to the present invention comprises a transponder by comparing signal levels of adjacent time slots of pulse position modulation. At least a decoding circuit (hereinafter, referred to as a "first decoding circuit") for decoding a signal from

The determination range of the first decoding circuit is the difference between the low level and the high level of the signal, and if there is a difference, it is possible to make a determination, so that the above-described determination limit corresponds to V / 2. A higher sensitivity than a circuit (hereinafter, referred to as a “second decoding circuit”) is obtained, and therefore, data can be received with a lower bit error rate than before. In addition, the operating distance of the transponder can be extended accordingly.

However, in the mode 1, since a plurality of transponders are expected to respond, the following four types of states may occur when a signal is received.

(1) A pulse exists in slot 102,
No pulse in slot 103 (2) No pulse in slot 102 and slot 103
(3) A state where there is no pulse in both the slot 102 and the slot 103. (4) A state where a pulse exists in both the slot 102 and the slot 103.

When decoding these four methods using the first decoding circuit at a high or low signal level, an error in code determination may occur. In such a case, mode 1
It is desirable that the second decoding circuit be used at the time of (1) and the first decoding circuit be used at the time of mode (2).

An example of a preferred embodiment of the interrogator thus configured is a first decoding circuit, a second decoding circuit, and selecting an output signal of the first decoding circuit in the mode 1, In the case of 2, there is provided a selection circuit for selecting an output signal of the second decoding circuit, and a control unit for generating a control signal for controlling the selection operation of the selection circuit. In the interrogator, the operation procedure of mode 1 and mode 2 is set in advance, and therefore, the control unit can output a signal for distinguishing between mode 1 and mode 2 as a control signal. The control signal is, for example, “1” in the mode 1 and “0” in the mode 2.
The selection circuit is controlled to perform the selection operation according to “0”.

The method of judging using the level of the signal level or the maximum level among a plurality of signals is described in BP Lathi, March 1986, BP Lathi, translated by Sonosuke Yamanaka, “Detailed Explanation Digital-Analog Communication System”, page 496. To 497 and 550 to 551. However, this document merely describes the concept of the determination method and does not mention any specific application such as application to pulse position modulation.

[0030]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a mobile object identification apparatus according to the present invention. 1 to 10
, The same symbol indicates the same or similar.

[0031]

<Embodiment 1> In an interrogator 2 shown on the right side of FIG. 1, reference numeral 41 designates a first unit which makes a judgment by comparing the signal levels of pulses at adjacent positions in pulse position modulation. The decoding circuit 42 uses a threshold level as a criterion, and the second decoding circuit 43a selects and outputs one of the output signal of the first decoding circuit 41 and the output signal of the second decoding circuit 42. The selection circuit 44 includes a control unit that generates a control signal for controlling the selection operation of the selection circuit 43a,
2b is a data processing circuit including the control unit 44, and 27b is
Detection circuit 28, first decoding circuit 41, second decoding circuit 4
2 and a receiving unit including the selection circuit 43a.

The control section 44 outputs a signal which becomes "1" in mode 1 and "0" in mode 2 as the control signal. When the control signal is “1”, the selection circuit 43a closes one contact of the selection switch and extracts the output signal of the second decoding circuit. When the control signal is "0", the other contact is closed and the first decoding circuit 4 is closed.
Extract the output signal of No. 1.

The transmitting section 24, the circulator 25 and the antenna 26 are the same as those of the conventional interrogator 2. The baseband unit 21 includes a transmission data generation circuit 23 for generating a transmission signal and a data processing circuit 22b for processing data transmitted and received between the transponder 3 as in the conventional case.
Consists of

The transmission data generation circuit 23 first transmits a command 101 according to the frame structure 100 shown in FIG. According to this command, the transponder 3 performs transmission. In this case, the pulse 104 or the pulse 105 is transmitted in the slots 102 and 103 whose positions are determined in advance in the frame.

In the mode 1, the interrogator 2 transmits, for example, the command A "transmit the first bit of the ID of the responder 3". In the mode 2, the interrogator 2 transmits, for example, a command B of "specify ID and transmit data in memory". In this case, before transmitting the command B, a procedure for knowing the ID has already been performed between the interrogator 2 and the responder 3 by the command A of the mode 1. Although there is a possibility that the transponder 3 may deviate from the range in which the interrogator 2 can communicate with the interrogator 2 due to a change in the wireless environment or the movement of the transponder 3, the wireless communication environment usually has a sufficiently high data transmission rate for such changes. And the movement of the transponder 3 can be ignored. As a result, after performing a procedure for knowing the ID of the transponder 3 between the interrogator 2 and the transponder 3, for example, the command B "transmitting the data of the memory by designating the ID" to the transponder 3 , The interrogator 2 can receive the response to the command B with a very high probability.

The transponder 3 comprises a rectifier circuit 32, a detection circuit 33, a control circuit 34, and a nonvolatile memory 35, similarly to the conventional transponder 3. The transponder 3 performs data and I / O by binary pulse position modulation according to the command from the interrogator 2.
Send D.

The interrogator 2 receives the radio wave 5 transmitted from the transponder 3 by the antenna 26 and inputs the radio wave 5 to the receiver 27b via the circulator 25. The signal input to the receiving unit 27b is subjected to synchronous detection by the detection circuit 28 to become a pulse signal. The same pulse signal is input to the decoding circuits 41 and 42.

FIG. 2 shows the determination principle of the first decoding circuit 41. The decoding circuit 41 includes a slot 102 and a slot 103
Are configured to make a code determination by comparing the level of each signal level.

FIG. 3 shows a configuration example of the first decoding circuit 41. The decoding circuit 41 includes a sample and hold circuit 58, a timing recovery circuit 59b, a buffer 60,
And 7. The timing reproduction circuit 59b outputs the timings 51b and 52b (see FIG. 2) of the sign determination of the slots 102 and 103. The sample and hold circuit 58 outputs the output timings 51b and 52b
Sample and hold the input signal 53 in accordance with
I do. The hold signal output from the sample and hold circuit 58 is input to the buffer 60. The buffer 60
The hold signal is temporarily stored so that the hold signal of the slot 102 is output at the timing 52b.

The comparator 57 includes a hold signal in the slot 102 from the buffer 60 and the sample-and-hold circuit 5.
8 and the hold signal in the slot 103 are input simultaneously. The comparator 57 compares the levels of the two hold signals, and outputs “1” when the input signal level in the slot 102 is higher than the input signal level in the slot 103. If the signal level is higher than the input signal level in the slot 102, "0" is output.

Then, the second decoding circuit 42
As described above, the signal level of the high level or the low level is determined by comparing the input signal with the threshold value of the determination criterion (determination unit), and the code of the binary data is restored from the result (decoding unit). ).

FIG. 4 shows a configuration example of the second decoding circuit 42. The decoding circuit 42 includes a comparator 57, a sample and hold circuit 58, and a timing recovery circuit 59a. The comparator 57 compares a predetermined threshold value 50 with the input signal 53, and outputs a high level when the input signal 53 is larger, and outputs a low level when the threshold value 50 is larger. The timing recovery circuit 59a outputs timings 51a and 52a (see FIG. 10) for the sign determination of the slot 102 and the subsequent slot 103, and the sample hold circuit 58 outputs the output of the comparator 57 at the timing output by the timing recovery circuit 59a. Sample and hold the high-level and low-level signals.

The sample-and-hold circuit 58 holds the high level first in time, and when the low level is held later, determines that the binary code is "1" and outputs "1". Conversely, when the low level is held first and the high level is held later, it is determined that the binary code is "0" and "0" is output.

As described above, the comparator 57 has the function of the above-described determination section, and the sample-and-hold circuit 58 has the function of the decoding section.

When the mode 1 is set in the control section 44 of the baseband section 21, the selection circuit 43a inputs the output 61a of the second decoding circuit 42 to the data processing section 22b, and sends the mode When 2 is set, the output 61b of the first decoding circuit 41 is input to the data processing unit 22b. With this configuration, the interrogator 2
Can receive the transmission data from the transponder 3 at a low bit error rate.

In this embodiment, the first decoding circuit 41
And the second decoding circuit 42 and the selection circuit 43a are shown as separate circuits. However, these circuits are realized by software using, for example, a microprocessor or a digital signal processor, and the operation is performed according to a mode (transmission state). It is possible to configure to switch.

<Second Embodiment> In the first embodiment, since the signal transmitted by the transponder 3 is binary pulse position modulation, the buffer 60 of the first decoder 41 shown in FIG. Good. In the case of using pulse position modulation of m values (m is 3 or more) that requires m slots larger than two values, a plurality of buffers 60 and a maximum value of a signal level output from the plurality of buffers are set as follows. By using the multi-valued (m-valued) comparator 56 having a function of selecting and thereby assigning a code, an interrogator corresponding to multi-valued pulse position modulation can be realized.

FIG. 5 shows an example of the configuration of a decoder for receiving quaternary pulse position modulation with m = 4. The decoder
Sample hold circuit 58 and timing recovery circuit 59
c, buffers 60a to 60c, and a multi-valued comparator 56. The timing recovery circuit 59c outputs the determination timing of the four slots (first to fourth) determined by the quaternary pulse position modulation, and the sample and hold circuit 58 outputs the input signal 5 according to the output timing.
Sample 3 and hold. Buffers 60a-
The input signal level in the first to third slots output from the sample and hold circuit 58 is input to 60c. The hold signal in the first slot output from the buffer 60a, the hold signal in the second slot output from the buffer 60b, the hold signal in the third slot output from the buffer 60c, and the sample hold circuit 58 The output hold signal in the fourth slot is input to the quaternary comparator 56. The comparator 56 selects the maximum value from these hold signals and assigns a code.

For example, if the first slot has the highest signal level, "11"; if the second slot has the highest signal level, "10"; and if the third slot has the highest signal level, Is "01",
If the fourth slot has the highest signal level, “00” is assigned to each.

<Embodiment 3> An embodiment in which the first decoding circuit 41 is used in a part of the mode 1 is shown in FIG. In the figure, reference numeral 45 denotes a second decoding circuit 42.
The detection unit 43b detects the level of the hold signal, and forcibly turns the control signal from the control unit 44 into a signal for selecting the first decoding circuit 41 in accordance with the detection result. It is a selection circuit.

In this embodiment, the control signal from the control unit 44 is supplied to the selected switch via the detection unit 45. When the detection unit 45 detects in mode 1 that the hold signal of the second decoding circuit 42 is at the high level in the first slot 102 and is also at the high level in the second slot 103, the control unit 45 The control signal from 44 is cut off, and the selection switch is operated to close the contact for extracting the output signal of the first decoding circuit 41. That is, the control signal that has been “1” is changed to “0” and output.

In mode 1, when the hold signal of the second decoding circuit 42 is in any other state, the control signal (set to "1") from the control section 44 is supplied to the selected switch as it is. The output signal of the second decoding circuit 42 is extracted. That is, the selection circuit 43b outputs “0” when the first slot 102 is at the low level and the second slot 103 is at the high level, and outputs the “0” when the first slot 102 is at the high level and When 103 is at the low level, “1” is output. Also, the first slot 102 is at a low level, the second slot 103
Is at the low level, the detecting unit 45 detects that both are at the low level.

First slot 102 and second slot 1
When both 03 are at the high level or both are at the low level, the detection result is sent to the data processing unit 22c (not shown). When both are at the high level, the first decoding circuit 41
Indicates the level of the signal level, so that the accuracy of ID confirmation in the data processing unit 22c is increased. When both are at the low level, the data processing unit 22c determines that there is no signal from the transponder 3.

[0054]

According to the present invention, it is possible to decode the transmission data from the transponder by comparing the level of the signal level. Rate can be reduced. As a result, it is possible to increase the distance between the interrogator and the transponder.

[Brief description of the drawings]

FIG. 1 is a configuration diagram for explaining a first embodiment of a moving object identification device according to the present invention.

FIG. 2 is a waveform chart for explaining the operation of the first decoding circuit of the first embodiment.

FIG. 3 is a configuration diagram for explaining a first decoding circuit of the first embodiment.

FIG. 4 is a configuration diagram for explaining a second decoding circuit of the first embodiment.

FIG. 5 is a configuration diagram for explaining a second embodiment of the present invention.

FIG. 6 is a configuration diagram for explaining a third embodiment of the present invention.

FIG. 7 is a layout diagram for explaining a basic configuration of the moving object identification device.

FIG. 8 is a configuration diagram for explaining a conventional moving object identification device.

FIG. 9 is a diagram illustrating a frame configuration.

FIG. 10 is a waveform chart for explaining the operation of the decoding circuit of the conventional mobile object identification device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Moving body identification device, 2 ... Interrogator, 3 ... Responder, 21 ...
Baseband unit, 22 Data processing unit, 23 Transmission data generation unit, 24 Transmission unit, 25 Circulator, 26
... interrogator antenna, 27 ... receiver, 28 ... detector circuit, 4
3 selection circuit, 44 control unit, 41 first decoding circuit,
42 ... second decoding circuit, 57 ... comparator, 58 ... sample and hold circuit, 59 ... timing reproduction circuit, 60 ... buffer.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeshi Saito 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo F-term in Central Research Laboratory, Hitachi, Ltd. 5J070 AB16 AD01 AE01 AK01 AK14 AK15 BC06 BC08 BC23 BC29 5K012 AB05 AC08 AC09 AC10 AC11 AE13 BA03 BA07

Claims (5)

[Claims] 1. A mobile object identification apparatus comprising an interrogator and a transponder, wirelessly transmitting and receiving data between the interrogator and the transponder, and using pulse position modulation for data transmission from the transponder to the interrogator. Wherein the interrogator comprises at least a first decoding circuit for decoding a signal from the transponder by comparing the level of a signal at a different pulse position. 2. The interrogator decodes a signal from a transponder by comparing a signal at a different pulse position with a predetermined threshold value, and outputs an output signal of the first decoding circuit and a second decoding circuit. A selection circuit for selecting one of the output signals of the second decoding circuit, wherein the selection circuit performs the second decoding when the interrogator issues a command that expects a response to be made from a plurality of transponders. Selecting the output signal of the circuit and operating to select the output signal of the first decoding circuit when the interrogator issues a command that expects a response to be made from one transponder. Claim 1.
3. The moving object identification device according to claim 1. 3. The interrogator decodes a signal from a transponder by comparing a signal at a different pulse position with a predetermined threshold value, and outputs an output signal of the first decoding circuit A selection circuit for selecting any of the output signals of the two decoding circuits, wherein the selection circuit is a case where the interrogator issues a command that expects a response to be made from a plurality of transponders, The output signal of the first decoding circuit is selected only when all of the signals at different pulse positions determined to be at the high level or the low level by the threshold value comparison are at the high level, and at other times the second signal is selected. And operates to select the output signal of the first decoding circuit when the interrogator issues a command that expects a response to be made from one transponder. thing The mobile object identification device according to claim 1, wherein: 4. The decoding circuit according to claim 1, wherein the first decoding circuit performs decoding by setting the maximum value of the level of the signal at different pulse positions to a high level and the other levels to a low level. The moving object identification device according to claim 3. 5. The interrogator has a detection circuit for detecting a reception signal of a signal transmitted wirelessly from a transponder,
The first decoding circuit includes a timing recovery circuit, a sample-and-hold circuit that samples and holds an output signal of the detection circuit at a timing output by the timing recovery circuit, and at least one which stores an output signal of the sample-and-hold circuit. 5. The circuit according to claim 1, further comprising: a plurality of buffer circuits; and a comparison circuit configured to input and compare an output signal of the at least one buffer circuit and an output signal of the sample and hold circuit. Any one of the mobile object identification devices.