JP6498410B2 - Wireless communication system - Google Patents

Description

  The present invention relates to a wireless communication system using a plurality of wireless tags.

In conventional wireless communication, only one transmitter can transmit a signal to one receiver on a certain time series. When a plurality of transmitters simultaneously transmit a signal to one receiver, it causes interference and signal transmission is not performed normally.
Up to now, multiple access such as code division multiple access, time division multiple access, frequency division multiple access, and the like has been used to avoid interference in wireless communication using a large number of transmitters.

  Patent Document 1 discloses the technical contents of a receiving apparatus and a receiving method that can reduce the influence of an interference signal while suppressing an increase in circuit scale and processing time.

JP 2010-16785

  Conventional multiple access is realized by digital signal transmission. In the case of a wireless tag, since it is a light circuit load such as transmitting ID information stored in advance in ROM as it is, multiple access is not possible. It was realized at a low cost. However, when performing power control on the wireless tag side in order to make multiple connections, or when transmitting an output signal such as an acceleration sensor, it is necessary to convert the signal to digital data with an A / D converter A large amount of power is consumed on the wireless tag side. In addition, the occupied bandwidth increases in principle, and the circuit scale also increases. In conventional time division multiple access (TDMA) and frequency division multiple access (FDMA), the circuit scale is large, and in code division multiple access (CDMA), it can be realized without increasing the circuit scale to give a spreading code. A perspective problem in which multiplicity is increased by spreading evenly with respect to the center frequency occurs, and it is necessary to perform power control on the transmission side. Therefore, in order to realize multiple access with low power and low cost using a wireless terminal equipped with a sensor in a wireless tag, it is important to implement multiple access as easily as possible.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a wireless communication system that solves such problems and enables wireless communication by using many low-cost wireless terminals to eliminate interference due to multiple access.

The wireless communication system of the present invention includes an unmodulated wave source, a plurality of sensor terminals, an interrogator, and a receiver. The unmodulated wave source transmits unmodulated waves to the plurality of sensor terminals in order to generate reflected waves from the antennas of the plurality of sensor terminals.
Each sensor terminal includes an antenna for generating a received and reflected wave unmodulated wave from continuous wave sources, and the sub-carrier source that generates a predetermined frequency or subcarrier frequency harmonics of the predetermined frequency, the subcarrier source A switch that switches between an open end and a short-circuit end to connect to the antenna, and a subcarrier frequency of a predetermined frequency or a harmonic thereof from a signal source that is a sensor of each sensor terminal. modulating the signal, a plurality of modulation schemes and a modulation unit capable choice.
The interrogator performs an interactive process with a plurality of sensor terminals to grasp all the sensor terminals existing within a communicable range, creates an inventory of the plurality of sensor terminals capable of communication, and a plurality of sensor terminals Two-way communication is performed in which a predetermined frequency or a subcarrier frequency of a harmonic thereof is assigned. Then, a predetermined frequency or subcarrier frequency of the harmonics of each sensor terminal that is created as a result is, the subcarrier frequency fields that are stored in ascending order of subcarrier frequency, the order of demodulation of the sensor terminals is stored demodulated A sensor terminal list including a forward field and a modulation field storing the modulation scheme of the modulation unit of each sensor terminal of the plurality of sensor terminals is created and transmitted to the receiver.
The receiver comprises an input buffer for storing data received reflected wave transmitted from the sensor terminal once, and have groups Dzu the value of the demodulation order field of each sensor terminal of the sensor terminal list, in the input buffer using auxiliary transport Namishu wave number of each sensor terminal stored from the data in the sub-carrier frequency field comprises a demodulation calculation section for obtaining a demodulated data in ascending order of subcarrier frequency and demodulates sequentially. Further, the receiver uses the subcarrier frequency allocation data and the demodulated data from the data in the input buffer to eliminate interference generated between a predetermined frequency of each sensor terminal or a subcarrier frequency of a harmonic thereof, and sequentially A successive interference canceler that generates interference cancel data is provided. In addition, it includes a demodulation sequence control unit that overwrites and copies the successive interference cancellation data to the input buffer and controls the demodulation order of the demodulation calculation unit with reference to the sensor terminal list .

ADVANTAGE OF THE INVENTION According to this invention, the radio | wireless communications system which enables the radio | wireless communication from which interference by multiple access was removed using many low-cost radio | wireless terminals can be provided.
Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is a block diagram which shows the outline of the experimental installation of a communication system. It is a block diagram of a receiver. A graph comparing the original signal output from the first sensor with the analog signal converted from the demodulated data output from the first demodulation operation unit, the original signal output from the second sensor, and the second demodulation operation unit output A graph comparing the demodulated data converted to analog, the original signal output from the second sensor, the signal converted from the demodulated data output from the second demodulation operation unit, and the successive interference removal unit 6 is a graph comparing the demodulated data output from the second demodulation operation unit with the analog signal. It is the schematic which shows the operation example of the radio | wireless communications system which concerns on this embodiment. It is a schematic block diagram which shows the whole structure of the radio | wireless communications system which concerns on this embodiment. It is a functional block diagram of a sensor terminal. It is a functional block diagram of an interrogator. It is a functional block diagram of a software receiving part. It is an example of the frequency component distribution map which shows the intensity | strength for every frequency component of the subcarrier obtained by FFT. It is a figure which shows an example of a sensor terminal list. It is a sequence diagram which shows the flow of operation | movement of the radio | wireless communications system which concerns on this embodiment. It is a flowchart which shows the flow of the demodulation process by a software receiver.

[Demonstration experiment of basic technology]
Prior to the description of the present embodiment, a demonstration experiment of the technology that is the basis of the present invention and its result will be described.
FIG. 1 is a block diagram showing an outline of an experimental facility 101 of a communication system.
The actual experimental equipment 101 did not use an antenna, but conducted an experiment in the coaxial cable by passing a signal corresponding to a radio wave through the coaxial cable. In consideration of the compatibility with the embodiment described later, FIG. The block diagram supposing the case where is used is shown.
The unmodulated wave source 102 emits a 900 MHz signal. An unmodulated wave antenna 103 is connected to the unmodulated wave source 102, and a 900 MHz unmodulated wave is transmitted from the unmodulated wave antenna 103.
The first transmitter 104 and the second transmitter 105 having the same internal configuration are provided at a distance that allows the unmodulated wave to reach from the unmodulated wave antenna 103 with a strong electric field strength. Hereinafter, the internal configuration of the first transmitter 104 will be described, and only the differences between the second transmitter 105 and the first transmitter 104 will be described.

The first transmitter 104 has a power supply unit 107 that converts the power of the radio wave received from the antenna 106 into circuit drive power instead of having an independent power supply such as a battery.
In addition to the power supply unit 107, the phase modulation unit 108 and the SPDT switch 109 are connected to the antenna 106.
The SPDT switch 109 switches and connects the open end 109a and the short-circuit end 109b to the antenna 106 by a rectangular wave signal (first subcarrier) output from the first subcarrier source 110. The SPDT switch 109 changes the impedance of the antenna 106 with the period of the first subcarrier. Then, the first subcarrier is superimposed on the unmodulated reflected wave obtained from the antenna 106.

A first sensor 111 as a signal source is connected to the phase modulation unit 108. The phase modulation unit 108 performs phase modulation on the first subcarrier with the signal of the first sensor 111.
With the above configuration, the first transmitter 104 performs a well-known backscatter (load modulation) on the unmodulated wave transmitted from the unmodulated wave source 102. Then, a reflected wave in which the first subcarrier is phase-modulated by the signal of the first sensor 111 is transmitted from the antenna 106.

The first subcarrier source 110 of the first transmitter 104 outputs a 9 kHz rectangular wave. The second subcarrier source 112 of the second transmitter 105 outputs a 27 kHz rectangular wave signal (second subcarrier). Then, the phase modulation unit 108 of the second transmitter 105 performs phase modulation on the second subcarrier by the signal of the second sensor 113.
That is, the second subcarrier (27 kHz) has a third harmonic relationship with respect to the first subcarrier (9 kHz), and the modulation scheme is the same phase modulation. Therefore, when the receiver receives the radio waves of the first transmitter 104 and the second transmitter 105 at the same time, the weaker radio wave is drowned out by the radio wave having the stronger antenna power and cannot be received. As is well known, in frequency modulation (FM) and phase modulation (PM), weak signals are masked by strong signals.
That is, in this experiment, the first transmitter 104 and the second transmitter 105 perform interference under extremely unfavorable conditions.

The receiver 114 includes an A / D conversion unit 116 having an antenna 115 and a software reception unit 117.
FIG. 2 is a block diagram of the receiver 114.
The A / D converter 116 extracts the radio wave received from the antenna 115 by the tuning circuit 201 and then amplifies it by the RF amplifier 202. The high frequency signal amplified by the RF amplifier 202 is input to the first mixer 203 and the second mixer 204. The first mixer 203 receives a local oscillation signal having a frequency slightly lower than the frequency of the radio wave output from the local oscillator 205. The second mixer 204 receives a signal whose local signal is shifted by 90 ° by the 90 ° phase shifter 206.

The signal output from the first mixer 203 is passed through a first low-pass filter (hereinafter “LPF”) 207 to output an I signal obtained by subtracting the frequency of the local oscillation signal from the frequency of the radio wave. Similarly, the signal output from the second mixer 204 is output through the second LPF 208 as a Q signal obtained by subtracting the frequency of the local oscillation signal by 90 ° from the frequency of the radio wave. That is, the local oscillator 205, the first mixer 203, the 90 ° phase shifter 206, the second mixer 204, the first LPF 207, and the second LPF 208 constitute a well-known quadrature detection circuit (quadrature mixer).
The I signal and the Q signal are converted into digital data by the A / D converter 209 and output to the software receiving unit 117.
The A / D conversion unit 116 has a down converter using a quadrature detection circuit and an A / D conversion function by the A / D converter 209.

The software receiving unit 117 is a well-known electronic computer such as a personal computer, and an arithmetic function is realized by a program.
The data of the I signal and the Q signal output from the A / D converter 209 of the A / D converter 116 is temporarily stored as received data 210 in a predetermined storage device (not shown).
The received data 210 is first demodulated by the first demodulation calculation unit 211 of the radio wave transmitted by the first transmitter 104. At this time, first subcarrier information 212, that is, information of “9 kHz” is used for the first demodulation calculation unit 211 in the demodulation calculation. Thus, the first demodulation calculation unit 211 outputs the first demodulation data 213. The first demodulated data 213 corresponds to data obtained by A / D converting the analog signal of the first sensor 111.

The first demodulated data 213 and the received data 210 are supplied to the successive interference canceling unit 214. The successive interference removal unit 214 removes interference generated by the first demodulated data 213 from the reception data 210.
The output data of the successive interference canceling unit 214 is demodulated by the second demodulation calculating unit 215 of the radio wave transmitted by the second transmitter 105. At this time, second subcarrier information 216, that is, information of “27 kHz” is used in the second demodulation calculation unit 215 during demodulation calculation. Thus, the second demodulation calculation unit 215 outputs the second demodulated data 217. The second demodulated data 217 corresponds to data obtained by A / D converting the analog signal of the second sensor 113.

FIG. 3A is a graph comparing the original signal output from the first sensor 111 and a signal obtained by converting the demodulated data output from the first demodulation calculation unit 211 into analog. A one-dot chain line is an original signal, and a solid line is a measurement signal.
FIG. 3B is a graph comparing the original signal output from the second sensor 113 and a signal obtained by converting the demodulated data output from the second demodulation calculation unit 215 into analog. A one-dot chain line is an original signal, and a solid line is a measurement signal.
3C shows the original signal output from the second sensor 113, the signal obtained by converting the demodulated data output from the second demodulation calculation unit 215 into analog, and the second demodulation calculation unit 215 without passing through the successive interference removal unit 214. It is the graph which compared the signal which converted the demodulated data output into the analog. The dotted line is the original signal, the alternate long and short dash line is the demodulated signal, and the solid line is the demodulated signal without passing through the successive interference removal unit 214.
In any graph, the vertical axis represents voltage, and the horizontal axis represents time (msec).

Comparing FIG. 3A and FIG. 3B, the waveform of FIG. 3B can partially confirm the disturbance of the signal due to the influence of the first demodulated data 213, but the demodulated signal can obtain a reproduced waveform that is almost similar to the original signal. ing.
Furthermore, when FIG. 3C is seen, it turns out that the effect of the successive interference removal by the successive interference removal unit 214 is extremely large.
As a result of calculating the standard deviation of the error between the demodulated signal that has passed through the successive interference canceling unit 214 and the demodulated signal that has not passed through the successive interference canceling unit 214, the former has a value of 35.82 and the latter has a value of 197.64. . When the former is divided by the latter, it can be seen that the error is reduced to about 18% by the successive interference removing unit 214.

In other words, under conditions that do not require real-time processing, a plurality of analog-modulated radio waves composed of subcarriers of different frequencies are simultaneously received using arithmetic processing by software, interference is removed by successive interference cancellation, and the original is processed. It has been found that it is possible in principle to demodulate the signal.
Based on this experimental result, the wireless communication system according to the present embodiment will be described.

[overall structure]
A vibration test is performed for failure diagnosis on an article or the like that requires a high degree of safety, such as an aircraft or an artificial satellite. First, forced vibration is applied to an object using hammering or a shaker. Next, the output signal of the acceleration sensor attached to a plurality of locations on the object is recorded by a predetermined data recorder, measuring instrument, or the like. Then, the failure is determined by examining the time response and the resonance frequency.
Conventionally, such a vibration test has been performed by wire. That is, a plurality of acceleration sensors are connected to a wire harness (or cable harness), and the wire harness is connected to a measuring device. As the number of acceleration sensors increases, the number of wire harnesses becomes enormous and the installation work of the acceleration sensors becomes extremely complicated.
In order to solve such a problem of the vibration test, the acceleration sensor that has been connected to the measuring device by wire until now is used as a wireless communication terminal.

FIG. 4 is a schematic diagram illustrating an operation example of the wireless communication system 401 according to the present embodiment.
A plurality of sensor terminals 403 are affixed to the body of the aircraft 402 to be measured. In the vicinity of the sensor terminal 403, a plurality of interrogators 404 and an A / D converter 405 are provided. The interrogator 404 and the A / D converter 405 are connected to the software receiver 407 through the network 406.

The sensor terminal 403 is a wireless tag that uses a backscatter and is equipped with an acceleration sensor and an analog modulation circuit.
The interrogator 404, also called a reader / writer, has a function of performing bidirectional wireless data communication with the sensor terminal 403 and a function of transmitting an unmodulated wave similar to the unmodulated wave source 102 of FIG.
The A / D conversion unit 405 has a function equivalent to that of the A / D conversion unit 116 described with reference to FIGS. That is, the A / D conversion unit 405 receives radio waves transmitted from the plurality of sensor terminals 403, down-converts them, and performs A / D conversion.

The software receiving unit 407 has substantially the same function as that of the software receiving unit 117 described with reference to FIGS. 1 and 2, and has an additional function necessary for more general operation. This additional function will be described in detail after FIG.
At the time of measurement, in a state where an unmodulated wave is transmitted from the interrogator 404, vibration such as an impact is applied from the vibration probe 408, and the reflected wave transmitted from the sensor terminal 403 is received by the A / D converter 405. Then, the software receiving unit 407 performs demodulation processing.

FIG. 5 is a schematic block diagram showing the overall configuration of the wireless communication system 401 according to the present embodiment. For ease of explanation, the interrogator 404 and the receiver 501 are described in a single configuration.
The first sensor terminal 403a, the second sensor terminal 403b,..., The nth sensor terminal 403n performs a predetermined communication with the interrogator 404 and then backs up the signal emitted by the sensor with respect to the unmodulated wave transmitted from the interrogator 404. Transmits (reflects) radio waves modulated by the scatter. The receiver 501 receives radio waves transmitted from the plurality of sensor terminals 403 and demodulates the signals of the respective sensors through arithmetic processing.

  The interrogator 404 and the receiver 501 are connected by a network 406. The interrogator 404 performs bidirectional communication for assigning a unique subcarrier frequency to the plurality of sensor terminals 403, and transmits a sensor terminal list created as a result to the receiver 501. The receiver 501 analyzes the received reception data 210 based on the sensor terminal list and performs demodulation processing.

FIG. 6 is a functional block diagram of the sensor terminal 403.
The difference between the first transmitter 104 and the sensor terminal 403 shown in FIG. 1 is that, in the sensor terminal 403, the control unit 601 is connected to the antenna 106, and the control unit 601 variably controls the frequency of the subcarrier source 602. That is, the modulation unit 604 to which the sensor 603 is connected can adopt any analog modulation method. As analog modulation, amplitude modulation (AM), frequency modulation (FM), phase modulation (PM), pulse width modulation (PWM), or the like can be used. Strictly speaking, although pulse width modulation is out of the category of analog modulation, the modulation schemes that can be used in the present embodiment from the viewpoint that an analog signal can be directly modulated without being converted into digital data by an A / D converter. Is included.

FIG. 7 is a functional block diagram of the interrogator 404.
A radio wave received from the antenna 701 is converted into a low-frequency signal through the local oscillator 702, the mixer 703, and the LPF 704. This signal is supplied to the demodulator 705, demodulated, converted into digital data by an A / D converter 706, and supplied to a controller 707 made of a microcomputer.
The control unit 707 interprets information of the sensor terminal 403 included in the digital data, and generates a command or the like for the sensor terminal 403. The digital data constituting this command is converted into an analog signal by the D / A converter 708, and then the carrier wave generated by the carrier wave source 710 is modulated by the modulation unit 709.
The control unit 707 recognizes all the sensor terminals 403 existing within a communicable range by interactive processing with the sensor terminal 403, and then assigns a subcarrier with a unique frequency to the sensor terminals 403. Then, the control unit 707 creates a sensor terminal list 711 that lists the correspondence between the sensor terminal 403 and the subcarrier, and transmits the sensor terminal list 711 to the receiver 501 through the network 406.

Of the receiver 501, the A / D converter 405 is the same as that shown in FIG.
FIG. 8 is a functional block diagram of the software receiving unit 407.
Received data 210 received from A / D conversion section 405 is first obtained by FFT (Fast Fourier Transform) 801 to obtain the intensity for each frequency component of the subcarrier.

  FIG. 9 is an example of a frequency component distribution diagram obtained by FFT 801 and indicating the intensity for each frequency component of the subcarrier. Thus, the intensity for each frequency component of the subcarrier is obtained by the FFT 801. The order of the intensity becomes the order of demodulation.

Returning to FIG.
The intensity data for each frequency component of the subcarrier is supplied to the demodulation sequence control unit 802. The demodulation sequence control unit 802 refers to the sensor terminal list 711 received from the interrogator 404 and determines the demodulation order of the sensor terminals 403. Then, the subcarrier frequency information and the demodulation method information are given to the demodulation arithmetic unit 803.

FIG. 10 is a diagram illustrating an example of the sensor terminal list 711.
The sensor terminal list 711 includes a terminal ID field, a modulation method field, a subcarrier frequency field, and a demodulation order field.
In the terminal ID field, ID information for uniquely identifying the sensor terminal 403 is stored.
In the modulation method field, information indicating the modulation method of the modulation unit 709 provided in the sensor terminal 403 is stored.
In the subcarrier frequency field, information indicating the frequency of the subcarrier assigned by the interrogator 404 is stored.
In the demodulation order field, information indicating the demodulation order of the sensor terminal 403 determined by the demodulation sequence control unit 802 is stored.
The sensor terminal list 711 received from the interrogator 404 has no demodulation order field or is blank, but the value of the demodulation order field is filled by the demodulation sequence control unit 802.
When all the sensor terminals 403 have the same modulation method, the modulation method field is not necessary.

Returning to FIG. 8, the description will be continued.
Received data 210 is stored in input buffer 804. The reception data 210 extracted from the input buffer 804 is supplied to the demodulation arithmetic unit 803. Demodulation calculation section 803 demodulates received data 210 based on subcarrier frequency information and demodulation scheme information given from demodulation sequence control section 802 to create demodulated data 805.
The demodulated data 805 and the data in the input buffer 804 are supplied to the successive interference removal unit 214. The successive interference removal unit 214 removes interference based on the demodulated data 805 from the data in the input buffer 804 and creates successive interference removal data 806. This successive interference cancellation data 806 is overwritten in the input buffer 804. And the process of the demodulation calculating part 803 and the process of the successive interference removal part 214 are repeated.

FIG. 11 is a sequence diagram showing a flow of operations of the wireless communication system 401 according to the present embodiment.
First, in order to grasp all the sensor terminals 403 existing within the communicable range, the interrogator 404 performs a dialogue process with all the sensor terminals 403 and lists all the sensor terminals 403 existing within the communicable range. Is created (S1101).
Next, the interrogator 404 performs dialogue processing with each sensor terminal 403 based on the list created in step S1101, and assigns a unique subcarrier frequency to each sensor terminal 403. When the subcarrier frequency is assigned to all the sensor terminals 403, it is added to the list to create a sensor terminal list 711 (S1102). The interrogator 404 transmits the sensor terminal list 711 to the software receiving unit 407 via the network 406 (S1103).

When receiving the sensor terminal list 711 (S1104), the software reception unit 407 reports to the interrogator 404 that the preparation of reception and demodulation of radio waves from the sensor terminal 403 has been completed (S1105).
When the interrogator 404 receives a report of preparation completion from the software reception unit 407, the interrogator 404 transmits an unmodulated wave (S1106).
The sensor terminal 403 modulates the signal emitted from the sensor with respect to the non-modulated wave by the backscatter, and transmits (reflects) the modulated radio wave (S1107).
The software receiving unit 407 receives radio waves transmitted from the plurality of sensor terminals 403 (S1108), and performs demodulation and successive interference removal (S1109).

FIG. 12 is a flowchart showing the flow of demodulation processing by the software receiving unit 407. This corresponds to step S1109 in FIG.
When the processing is started (S1201), the demodulation sequence control unit 802 applies the received data 210 to the FFT 801, refers to the sensor terminal list 711, and determines the demodulation order of the sensor terminals 403. Then, the demodulation order is written in the demodulation order field (S1202). Next, the demodulation sequence control unit 802 initializes the counter variable i to 1 (S1203). Then, the received data 210 is copied to the input buffer 804 (S1204).

The demodulation sequence control unit 802 causes the demodulation calculation unit 803 to perform demodulation processing of the sensor terminal 403 in the i-th demodulation order (S1205). Specifically, with reference to the record corresponding to the i-th demodulation order in the sensor terminal list 711, the subcarrier frequency information and the demodulation method are passed to the demodulation operation unit 803 to demodulate the data stored in the input buffer 804. Let the process do.
Next, the demodulation sequence control unit 802 gives the i-th demodulated data 805 generated by the demodulation operation unit 803 in step S1205 and the data stored in the input buffer 804 to the sequential interference removal unit 214, and sequentially Interference removal processing is performed (S1206).

When the successive interference removal processing by the successive interference removal unit 214 in step S1206 is completed, the demodulation sequence control unit 802 increments the counter variable i by 1 (S1207), and has the counter variable i exceeded the total number of records in the sensor terminal list 711? It is confirmed whether or not (S1208).
If the counter variable i does not exceed the total number of records in the sensor terminal list 711 (NO in S1208), the demodulation sequence control unit 802 overwrites and copies the successive interference removal data 806 generated by the successive interference removal unit 214 to the input buffer 804. (S1209), and the process is repeated again from step S1205.
If the counter variable i exceeds the total number of records in the sensor terminal list 711 (YES in S1208), the demodulation sequence control unit 802 ends the series of processes (S1210).

In the above embodiment, the following application examples are possible.
(1) As shown in FIG. 4, when a plurality of A / D converters 405 are arranged at different locations in the vicinity of the measurement target, the electric field intensity at which the radio waves of the sensor terminal 403 closest to each A / D converter 405 are maximum. Can be received. That is, by arranging a plurality of A / D conversion units 405 at different locations in the vicinity of the measurement target, it is possible to reliably demodulate the signal of the sensor terminal 403 at a close distance. In this way, the signal of the sensor 603 obtained through each A / D conversion unit 405 is interchanged with the successive interference removal of the other software reception unit 407, so that a more accurate demodulation process can be realized.
(2) In principle, it is possible to equip one sensor terminal 403 with a plurality of sensors 603, a modulator 604, and a subcarrier source 602. However, in this case, it is necessary to consider a combination of frequencies that hardly interfere with the subcarrier frequency.

  (3) In the above-described embodiment, the electric field intensity of the reflected wave emitted from each sensor terminal 403 is determined by the FFT 801, but the FFT 801 is not necessarily required. Prior to the measurement work, the interrogator 404 may control the sensor terminal 403 to measure the electric field strength of the sensor terminal 403 one by one. When measuring the electric field strength of a certain sensor terminal 403, control is performed so that the subcarrier source 602 of the designated sensor terminal 403 is operated and the subcarrier sources 602 of all other sensor terminals 403 are not operated. Then, since the receiver 501 can receive only the subcarrier of the sensor terminal 403, the intensity of the subcarrier emitted from the sensor terminal 403, that is, the electric field strength of the reflected wave can be measured.

(4) In the above-described embodiment, each sensor terminal 403 uses a back scatter, but the transmitter is not necessarily a back scatter. That is, the sensor terminal 403 may be provided with a power source such as a battery and actively emit radio waves. In this case, the interrogator 404 does not need a function as an unmodulated wave source. In addition, the subcarrier source 602 of the sensor terminal 403 functions as a carrier source that emits radio waves independently.
(5) The interrogator 404 has a function of assigning a subcarrier having a unique frequency to the plurality of sensor terminals 403 and a function of transmitting an unmodulated wave. An unmodulated wave transmission function may be provided separately from the interrogator 404.

In the present embodiment, the wireless communication system 401 has been disclosed.
As can be seen from the above description, in the wireless communication system 401 according to the present embodiment, first, the receiver 501 has all the sensor terminals 403, the subcarrier frequency assigned to the sensor terminal 403, and the sensor terminal 403. Know the modulation method. Next, the signal strength of the radio wave transmitted by the sensor terminal 403 that performs analog modulation is determined by FFT 801, and the demodulation order is determined. Then, by repeating demodulation and successive interference removal, the signals of all sensor terminals 403 can be demodulated. Conventionally, almost no technique for removing interference of radio waves modulated with analog signals has been found, but the wireless communication system 401 according to the present embodiment realizes this on the premise that real-time processing is not performed.

The greatest feature of the wireless communication system 401 according to the present embodiment is that the sensor terminal 403 is extremely simple. The sensor terminal 403 that does not even have a battery does not require maintenance work such as battery replacement. Of course, since it is wireless communication, a wire harness is unnecessary. The sensor terminal 403 is affixed to the measurement object as if a ferrite magnet is affixed to the blackboard, the A / D conversion unit 405 and the interrogator 404 are arranged in the vicinity of the measurement object, and the A / D conversion unit 405 and the interrogator 404 are connected to the network 406. And the software receiving unit 407 may be connected.
The analog signal output from the sensor 603 provided in the sensor terminal 403 has already been converted into digital data when demodulated by the receiver 501. Therefore, it can be used as it is for various numerical analyses.
As described above, the wireless communication system 401 according to this embodiment can greatly save the measurement work. In addition, since the cost of the sensor terminal 403 can be reduced, a low-cost measurement environment can be realized.

  If the disadvantages of the wireless communication system 401 according to the present embodiment are forcibly cited, the arithmetic processing of the receiver 501 is enormous. However, since real-time processing is not required, the arithmetic processing only needs time. Also, the arithmetic processing can be easily solved if the computing power of the computer is sufficient. The cloud computing widely used today has extremely high affinity for the arithmetic processing of the receiver 501 of the wireless communication system 401 according to the present embodiment.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and other modifications and application examples are provided without departing from the gist of the present invention described in the claims. including.
For example, in the above-described embodiment, the configuration of the apparatus and the system is described in detail and specifically in order to explain the present invention in an easy-to-understand manner, and is not necessarily limited to one having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Moreover, it is also possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.
Each of the above-described configurations, functions, processing units, and the like may be realized by hardware by designing a part or all of them with, for example, an integrated circuit. Further, each of the above-described configurations, functions, and the like may be realized by software for interpreting and executing a program that realizes each function by the processor. Information such as programs, tables, and files that realize each function must be held in a volatile or non-volatile storage such as a memory, hard disk, or SSD (Solid State Drive), or a recording medium such as an IC card or an optical disk. Can do.
In addition, the control lines and information lines are those that are considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.

  DESCRIPTION OF SYMBOLS 101 ... Experimental equipment, 102 ... Unmodulated wave source, 103 ... Unmodulated wave antenna, 104 ... First transmitter, 105 ... Second transmitter, 106 ... Antenna, 107 ... Power supply unit, 108 ... Phase modulation unit, 109 ... SPDT 110, first subcarrier source, 111, first sensor, 112, second subcarrier source, 113, second sensor, 114, receiver, 115, antenna, 116, A / D converter, 117, software Receiving unit 201 ... tuning circuit 202 ... RF amplifier 203 ... first mixer 204 ... second mixer 205 ... local oscillator 206 ... phase shifter 207 ... first LPF 208 ... second LPF 209 ... A / D converter, 210 ... received data, 211 ... first demodulation operation unit, 212 ... first subcarrier information, 213 ... first demodulation data, 214 ... successive interference removal unit, 215 ... second demodulation Arithmetic unit, 216 ... second subcarrier information, 217 ... second demodulated data, 401 ... wireless communication system, 402 ... aircraft, 403 ... sensor terminal, 404 ... interrogator, 405 ... A / D converter, 406 ... network, 407 ... Software receiver 408 ... Excitation probe, 501 ... Receiver, 601 ... Controller, 602 ... Subcarrier source, 603 ... Sensor, 604 ... Modulator, 701 ... Antenna, 702 ... Local oscillator, 704 ... LPF, 705 ... demodulator, 706 ... A / D converter, 707 ... controller, 708 ... D / A converter, 709 ... modulator, 710 ... carrier wave source, 711 ... sensor terminal list, 801 ... FFT, 802 ... demodulation sequence control 803... Demodulation operation unit 804... Input buffer 805... Demodulated data 806.

Claims (1)

A wireless communication system comprising an unmodulated wave source, a plurality of sensor terminals, an interrogator and a receiver,
The unmodulated wave source is:
In order to generate reflected waves from the antennas of the plurality of sensor terminals, non-modulated waves are transmitted to the plurality of sensor terminals,
Each sensor terminal is
An antenna that receives a non-modulated wave from the non-modulated wave source and generates a reflected wave;
A subcarrier source that generates a subcarrier frequency of the harmonics of the predetermined frequency or predetermined frequency,
A switch that switches between an open end and a short-circuited end for the antenna according to the subcarrier frequency output from the subcarrier source;
A modulation section that modulates the subcarrier frequency of the predetermined frequency or a harmonic thereof with a signal from a signal source that is a sensor of each sensor terminal ;
The interrogator is
In order to grasp all the sensor terminals that exist within a communicable range, perform an interactive process with the plurality of sensor terminals, create an inventory of the plurality of sensor terminals capable of communication,
Two-way communication that assigns the predetermined frequency or a subcarrier frequency of a harmonic thereof to the plurality of sensor terminals,
Wherein said predetermined frequency or subcarrier frequency of the harmonics of each sensor terminal that is created as a result is, the a subcarrier frequency fields that are stored in ascending order of subcarrier frequency, wherein the order of demodulation of each sensor terminal stored Creating a sensor terminal list including a demodulation order field and a modulation field storing a modulation scheme of the modulation unit of each sensor terminal of the plurality of sensor terminals, and transmitting to the receiver,
The receiver
An input buffer for temporarily storing received data received from the reflected wave transmitted from each sensor terminal;
Said have the group Dzu the value of the demodulated sequence field of each sensor terminal of the sensor terminal list, the said sub-carrier Namishu wave number of the sensor nodes from the data in the input buffer is stored the in the sub-carrier frequency field A demodulation operation unit that obtains demodulated data by demodulating in order from the lowest subcarrier frequency ;
By using the subcarrier frequency allocation data and the demodulated data from the data in the input buffer, the interference generated between the predetermined frequency of each sensor terminal or a subcarrier frequency of a harmonic thereof is removed to sequentially interfere. A successive interference canceler for generating cancellation data;
Together copy over the successive interference cancellation data to the input buffer, a wireless communication system and a demodulation sequence control unit for controlling the order of demodulation of the demodulation calculation section with reference to the sensor terminal list.

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