wireless communication system

Abstract

A wireless communication system comprising a transmitter that transmits an unmodulated carrier wave, a plurality of passive terminals, and a receiver. Each of the plurality of passive terminals receives the carrier wave, superimposes a subcarrier with a predetermined frequency for each of the plurality of passive terminals on the backscatter of the carrier wave, modulates the subcarrier with a signal generated by a signal source using a predetermined modulation scheme, and transmits the backscatter. The receiver receives the plurality of backscatters transmitted from the plurality of passive terminals, generates a finite-length data string having an I component and a Q component, by performing frequency conversion and orthogonal transformation on the plurality of backscatters, and demodulates the signal of the signal source at each of the plurality of passive terminals by removing interference components from the finite-length data string.

Description

[Technical Field]

[0001] The present disclosure relates to a harmonic elimination method in a wireless communication system that uses multiple wireless tags. [Background technology]

[0002] As shown in Patent Document 1, a method using a bandpass filter is one method for removing harmonic components in a wireless communication system. This method calculates a carrier phase angle by performing regression analysis or the like on a subcarrier data sequence obtained by bandpass filtering a received signal, generates an angle data sequence from an analysis data sequence obtained from the subcarrier data sequence and the carrier phase angle, harmonically multiplies the angle data sequence, generates replicas of the harmonic components from the harmonically multiplied angle data sequence and the carrier phase angle, and subtracts the replica of the harmonic components from a desired subcarrier data sequence, thereby removing the harmonic components from the received signal.

[0003] Patent Document 2 discloses a receiving device and a receiving method that can reduce the influence of an interference signal while suppressing an increase in circuit size and processing time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-200180 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-16785 Summary of the Invention

[0005] The method of Patent Document 1 may increase the amount of calculation required for harmonic removal. Specifically, the method of Patent Document 1 samples signals with frequencies higher than the baseband. Therefore, compared to baseband signals, the sampling rate is higher, and the amount of calculation may increase.

[0006] The present disclosure provides a wireless communication system that makes it possible to suppress an increase in the amount of calculation required for harmonic removal.

[0007] A wireless communication system according to an embodiment of the present disclosure includes: a transmitter that transmits an unmodulated carrier wave; a plurality of passive terminals; a receiver; A wireless communication system comprising: Each of the plurality of passive terminals receives the carrier wave, superimposes a subcarrier wave having a frequency predetermined for each of the plurality of passive terminals onto backscatter of the carrier wave, modulates the subcarrier wave with a signal generated by a signal source using a predetermined modulation method, and transmits the backscatter; the receiver receives a plurality of backscatters transmitted from the plurality of passive terminals, performs frequency conversion and orthogonal conversion on the plurality of backscatters to generate a finite-length data sequence having I components and Q components, removes interference components from the finite-length data sequence, and demodulates the signal of the signal source in each of the plurality of passive terminals; The receiver further comprises, before demodulating the signal of the signal source, down-converting the finite length data sequence to baseband and filtering to generate a subcarrier data sequence; performing a harmonic order rotation transform on a first subcarrier data sequence of an interference channel among the subcarrier data sequences to obtain a second subcarrier data sequence; calculating a covariance matrix based on a third subcarrier data sequence of an interfered channel among the subcarrier data sequences and the second subcarrier data sequence to estimate a carrier phase angle; subtracting the carrier phase angle from the second subcarrier data sequence to obtain a harmonic data sequence as the interference component; The harmonic data sequence is subtracted from the third subcarrier data sequence.

[0008] The present disclosure makes it possible to suppress an increase in the amount of calculation required for harmonic removal. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic block diagram illustrating an overall configuration of a wireless communication system according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a block diagram illustrating a hardware configuration of a sensor terminal according to an embodiment of the present disclosure. [Figure 3] FIG. 2 is a block diagram illustrating a hardware configuration of an interrogator according to an embodiment of the present disclosure. [Figure 4] FIG. 2 is a block diagram of an IQ conversion unit according to an embodiment of the present disclosure. [Figure 5] FIG. 2 is a block diagram illustrating a hardware configuration of a software receiving unit according to an embodiment of the present disclosure. [Figure 6] FIG. 2 is a block diagram illustrating software functions of a software receiving unit according to an embodiment of the present disclosure. [Figure 7] FIG. 10 is a diagram schematically illustrating radio waves received from a sensor terminal according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] An outline of one embodiment of the present disclosure (hereinafter referred to as "the present embodiment") will be described.

[0011] <Overall Configuration of Wireless Communication System 100> 1 is a schematic block diagram showing the overall configuration of a wireless communication system 100 according to this embodiment. The wireless communication system 100 includes a receiver 110, a sensor terminal 200, and an interrogator 300. A first sensor terminal 200a, a second sensor terminal 200b, ... an n-th sensor terminal 200n are attached to a measurement target, which is a large structure such as the fuselage of an aircraft or a tunnel (not shown). Note that when there is no need to distinguish between the first sensor terminal 200a, the second sensor terminal 200b, ... the n-th sensor terminal 200n, they will be simply referred to as sensor terminals 200.

[0012] An interrogator 300 and a receiver 110 are provided near the sensor terminal 200. The receiver 110 includes an IQ conversion unit 400 and a software receiving unit 500. The interrogator 300 is connected to the software receiving unit 500 via a network 130.

[0013] The sensor terminal 200 includes a wireless tag that uses backscatter (i.e., backward scattered waves), a sensor such as an acceleration sensor, and an analog modulation circuit. The analog modulation circuit is, for example, a phase modulator in which a varicap is connected in parallel to a coil and a capacitor. In this phase modulator, the output voltage of the acceleration sensor is applied to the varicap, thereby performing phase modulation on the carrier wave.

[0014] The interrogator 300, also called a reader / writer, has a function of performing two-way wireless data communication with the sensor terminal 200 and a function of transmitting unmodulated waves.

[0015] The first sensor terminal 200a, the second sensor terminal 200b, ..., the n-th sensor terminal 200n each perform predetermined communications with the interrogator 300 and then receive unmodulated radio waves transmitted from the interrogator 300. Each sensor terminal 200 superimposes a subcarrier on the backscatter of the unmodulated radio waves, modulates the subcarrier with a signal generated by the sensor, and transmits the backscatter. In other words, each sensor terminal 200 reflects the unmodulated radio waves. The receiver 110 receives radio waves transmitted from each of the multiple sensor terminals 200 and demodulates the signals of each sensor through computational processing.

[0016] The interrogator 300 performs bidirectional communication to assign a unique subcarrier frequency to each of the multiple sensor terminals 200. The interrogator 300 transmits the resulting sensor terminal list to the receiver 110 via the network 130. The receiver 110 analyzes the received data based on the sensor terminal list and performs demodulation processing.

[0017] <Wireless communication procedure in wireless communication system 100> The wireless communication system 100 according to this embodiment performs two main wireless communication procedures.

[0018] As a first step, before simultaneously receiving measurement signals from the multiple sensor terminals 200, the interrogator 300 performs wireless data communication with each of the multiple sensor terminals 200. In this wireless data communication, the interrogator 300 assigns a unique subcarrier frequency to each of the multiple sensor terminals 200. Then, the interrogator 300 creates a sensor terminal list indicating the relationship between each of the multiple sensor terminals 200 and the subcarrier frequency, and transmits the sensor terminal list to the receiver 110.

[0019] Next, in the second step, the interrogator 300 transmits an unmodulated carrier wave. Each of the sensor terminals 200 superimposes a subcarrier modulated with the signal from its built-in acceleration sensor onto the received unmodulated wave, and transmits the backscatter back to the receiver 110. At this time, the interrogator 300 functions as a carrier wave source (i.e., a transmitter).

[0020] The receiver 110 simultaneously receives multiple backscatters from multiple sensor terminals 200 and converts the multiple backscatters into a finite-length data string. Since this finite-length data string contains a mixture of signals simultaneously received from the multiple sensor terminals 200, when demodulating the signal of a certain sensor terminal 200, the signals of the other sensor terminals 200 become interference components. Therefore, the software receiving unit 500, which will be described later, removes the interference components from the finite-length data string and performs demodulation processing on the target received signal.

[0021] Hereinafter, in this embodiment, the process performed by the receiver 110 to remove interference components from the received signal will be referred to as "interference removal."

[0022] <Sensor terminal list> The sensor terminal list indicates the modulation method and subcarrier frequency set in each of the multiple sensor terminals 200, and the demodulation order determined based on the subcarrier frequency and intensity of the radio waves received by the receiver 110. Specifically, the sensor terminal list includes a terminal ID field in which a terminal ID (Identifier) that uniquely identifies each of the multiple sensor terminals 200 is stored, a modulation method field in which the modulation method set in each of the multiple sensor terminals 200 is stored, a subcarrier frequency field in which the subcarrier frequency set in each of the multiple sensor terminals 200 is stored, and a demodulation order field in which the demodulation order of each of the multiple sensor terminals 200 is stored.

[0023] Any analog modulation method may be set as the modulation method in the sensor node 200. As the analog modulation, frequency modulation (FM) and the like can be used in addition to phase modulation (PM). Note that if multiple sensor nodes 200 all use the same modulation method, the modulation method field is not included in the sensor node list.

[0024] <Sensor terminal 200> 2 is a block diagram showing the hardware configuration of the sensor terminal 200. The sensor terminal 200 does not have an independent power source such as a battery, but instead has a power supply unit 202 that converts the power of radio waves received by an antenna 214 into circuit driving power. In other words, the sensor terminal 200 is a passive terminal. In addition to the power supply unit 202, a modulation unit 212, an SPDT (Single Pole Double Throw) switch 204, and a control unit 208 are connected to the antenna 214.

[0025] The SPDT switch 204 switches between the open end 204a and the short end 204b in response to the square wave signal (i.e., the subcarrier) output by the subcarrier source 206, and connects to the antenna 214. The impedance of the antenna 214 is changed by the SPDT switch 204 with the period of the subcarrier. As a result, the subcarrier is superimposed on the unmodulated reflected wave (i.e., backscatter) obtained from the antenna 214. The frequency of the subcarrier generated by the subcarrier source 206 is determined by the control unit 208 controlling the subcarrier source 206. The control unit 208 stores the frequency specified by the interrogator 300 during communication with the interrogator 300 in the first procedure. Then, in the second procedure, the control unit 208 controls the subcarrier source 206 so that a subcarrier of the stored frequency is generated.

[0026] The modulation unit 212 is connected to a sensor 210, which is a signal source. The sensor 210 is a sensor that outputs an AC signal, such as an acceleration sensor. The modulation unit 212 performs modulation such as phase modulation (PM) or frequency modulation (FM) on the subcarrier wave using the signal from the sensor 210.

[0027] With the above configuration, the sensor terminal 200 superimposes a subcarrier on the reflected wave of the unmodulated wave transmitted from the interrogator 300, which is an unmodulated wave source (i.e., a carrier wave source). The sensor terminal 200 performs phase modulation, frequency modulation, or pulse width modulation on the subcarrier using the signal from the sensor 210, and transmits the reflected wave on which the subcarrier has been superimposed from the antenna 214.

[0028] <Interrogator 300> 3 is a block diagram showing the hardware configuration of the interrogator 300. Radio waves received by the antenna 302 are converted to a low-frequency signal using a local oscillator 304, a mixer 306, and an LPF 308. The converted signal is input to a demodulator 310, demodulated, and then converted to digital data by an A / D (Analog / Digital) converter 312 and input to a controller 314. The controller 314 is implemented, for example, by a microcontroller.

[0029] The control unit 314 interprets the information of the sensor terminal 200 included in the digital data and generates an instruction for the sensor terminal 200. The digital data constituting the instruction is converted into an analog signal by the D / A converter 316 and then used for modulation by the modulation unit 318 of the carrier wave generated by the carrier wave source 320.

[0030] After grasping all the sensor terminals 200 existing within the communicable range through the interactive processing with the sensor terminal 200, the control unit 314 assigns sub-carriers of unique frequencies to all the sensor terminals 200. Then, the control unit 314 creates a sensor terminal list 322 listing the correspondence between the sensor terminal 200 and the sub-carrier frequency, and transmits the sensor terminal list 322 to the receiver 110 via the network 130. That is, the interrogator 300 has a function of transmitting a control instruction for assigning a unique sub-carrier to each of the plurality of sensor terminals 200 to each of the plurality of sensor terminals 200.

[0031] <IQ conversion unit 400> FIG. 4 is a block diagram of the IQ conversion unit 400. After extracting a signal from the radio wave received by the antenna 402 with the tuning circuit 404, the IQ conversion unit 400 amplifies the signal with the RF (Radio Frequency) amplifier 406. The signal amplified by the RF amplifier 406 (for example, a high-frequency signal) is input to the first mixer 408 and the second mixer 410. A local oscillation signal having a frequency slightly lower than the frequency of the radio wave is input to the first mixer 408 from the local oscillator 412. A local oscillation signal whose phase is shifted by 90° by the 90° phase shifter 414 is input to the second mixer 410.

[0032] The first mixer 408 multiplies the RF signal from the RF amplifier 406 and the local oscillation signal from the local oscillator 412, and supplies a frequency signal of the frequency difference between the RF signal and the local oscillation signal to the first low-pass filter (hereinafter referred to as "LPF") 416. Then, an I signal obtained by subtracting the frequency of the local oscillation signal output from the local oscillator 4,12 from the frequency of the radio wave received by the antenna 402 is output from the first LPF 416.

[0033] Similarly, the second mixer 410 multiplies the RF signal from the RF amplifier 406 by the local oscillator signal whose phase has been shifted by 90° by the 90° phase shifter 414, and supplies a signal having a frequency corresponding to the difference in frequency between the RF signal and the local oscillator signal to the second LPF 418. The second LPF 418 then outputs a Q signal in which the frequency of the radio wave received by the antenna 402 has been subtracted by the frequency of the local oscillator signal whose phase has been shifted by 90°.

[0034] The local oscillator 412, the first mixer 408, the 90° phase shifter 414, the second mixer 410, the first LPF 416, and the second LPF 418 constitute a quadrature detection circuit (ie, a quadrature mixer).

[0035] The I and Q signals are converted into digital data by the A / D converter 420 and output to the software receiving unit 500 .

[0036] The IQ conversion unit 400 has a function of a down-converter using a quadrature detection circuit, and an A / D conversion function by the A / D converter 420 .

[0037] <Hardware Configuration of Software Receiving Unit 500> 5 is a block diagram showing the hardware configuration of the software receiving unit 500. The software receiving unit 500 is implemented by a computer such as a personal computer. The software receiving unit 500 includes a CPU (Central Processing Unit) 502, a ROM (Read Only Memory) 504, a RAM (Random Access Memory) 506, a display unit 510 such as a liquid crystal display, an operation unit 512 such as a keyboard and a mouse, and a non-volatile storage 514 such as a hard disk drive, all connected to a bus 518. In addition, a NIC (Network Interface Card) 516 is connected to the bus 518 for communicating with the interrogator 300 and the IQ conversion unit 400. The software receiving unit 500 is a general-purpose computer, and realizes its functions by executing a program stored in the non-volatile storage 514.

[0038] <Software Functions of Software Receiving Unit 500> 6 is a block diagram showing the software functions of the software receiving unit 500. Data consisting of I data and Q data received from the IQ conversion unit 400 is temporarily stored in the RAM 506 (see FIG. 5) as a finite-length data sequence 602 to be processed. The finite-length data sequence 602 consisting of I data and Q data is first input to a high-pass filter (hereinafter referred to as "HPF") 604, which removes a DC (Direct Current) offset component (i.e., a direct current component). A high-pass filter may be provided as needed.

[0039] The finite length data sequence 602 output from the HPF 604 is then down-converted to baseband and filtered in a down-conversion and filtering processor 608, whereby a subcarrier data sequence 610 of each subcarrier component is extracted. As a result, carrier removal is performed on the finite length data sequence 602. Note that down-conversion to baseband may be performed after filtering, or filtering may be performed after down-conversion.

[0040] Fig. 7 is a diagram showing a schematic diagram of radio waves received from a sensor terminal 200. In an actual device, several tens of channels or more are provided for n sensor terminals 200. However, here, only two channels will be explained: subcarrier 1 (i.e., interference channel) with frequency f1 superimposed on the carrier shown in Fig. 7, and subcarrier 2 (interfered channel) with frequency f2 superimposed on the carrier.

[0041] Here, the carrier frequency fc is set to, for example, 900 MHz. Subcarrier 1 is assigned to the first sensor terminal 200a in FIG. 1. The frequency f s1 is 100KHz. The frequency f1 of subcarrier 1 superimposed on the carrier is fc+f s1 is.

[0042] Subcarrier 2 is assigned to the second sensor node 200b in FIG. 1. The frequency f s2 is 300KHz. That is, f s2 is the frequency of subcarrier 1, f s1 (i.e., 100KHz). The frequency f2 of subcarrier 2 superimposed on the carrier is fc+f s2 The frequency of subcarrier 2 is f s2 can be expressed as follows: f s2 =f s1 ×3 Here, harmonics are generated at odd multiples of the frequency (3, 5, 7, 9, 11, . . . ), and therefore the harmonics of the interfering channel become noise (i.e., interference components) in the interfered channel.

[0043] Among the subcarrier data sequence 610, a finite length data sequence s1 consisting of I data and Q data of subcarrier 1 of the interference channel * , s1 * =(s 1_1 , s 1_2 , s 1_3 , ··· s1_n-1 , s 1_n ), n = number of samples is input to the demodulation processing unit 620. Then, the subcarrier phase value θ from the first sensor terminal 200a is demodulated via the demodulated data sequence 622 output from the demodulation processing unit 620. 1_1 , s 1_2 , ··· consist of I data and Q data for each sampling period obtained by sampling subcarrier 1.

[0044] Among the subcarrier data sequence 610, a finite length data sequence s3 consisting of I data and Q data of subcarrier 2 of the interfered channel * , s3 * =(s 3_1 , s 3_2、 s 3_3··· s 3_n-1、 s 3_n ), n = number of samples is input to the harmonic order rotation processing unit 612, the carrier phase angle estimation unit 614, and the interference removal processing unit 618.

[0045] The harmonic order rotation processor 612 performs a rotation transformation of the harmonic order on the subcarrier data sequence of the interfering channel. Specifically, the harmonic order rotation processor 612 performs a rotation transformation of the harmonic order (3 in this case) corresponding to the subcarrier 2, which is the interfered channel, on the subcarrier data sequence of the subcarrier 1, which is the interfering channel. The value s obtained by rotational transformation of the harmonic order γ is expressed by the following equation: s γ =|s1|e j3∠s1 3∠s1=3θ+3ψ

[0046] Here, θ is the subcarrier phase angle of subcarrier 1, which corresponds to the information from the first sensor terminal 200a. ψ is the carrier phase angle of subcarrier 1. When the carrier transmitted from the interrogator 300 is reflected by the first sensor terminal 200a and reaches the receiver 110, a phase delay of the carrier occurs depending on the length of the carrier propagation path. This phase delay (in other words, phase difference) is the phase difference ψ of subcarrier 1. The phase difference ψ is a value determined by the distance between the interrogator 300 and the sensor terminal 200, and differs for each subcarrier assigned to the sensor terminal 200.

[0047] Here, the finite length data string s1 * The amplitude value of is |s1|, and the finite length data sequence s1 * has an angular component of θ+ψ. s γ is the angle component of θ+ψ multiplied by three. For example, the finite length data sequence s1 * If the angle (θ+ψ) on the IQ plane is 60 degrees, the angle becomes 180 degrees due to the rotational transformation of the harmonic order.

[0048] Finite length data sequence s3 * is expressed by the following equation: s3 * =s3+βs γ e -j2ψ Here, s3 is a finite length data string s3 * This is the component originating from subcarrier 2 in βs γ e -j2ψ is the harmonic component originating from subcarrier 1 superimposed on subcarrier 2.

[0049] The carrier phase angle estimator 614 calculates a covariance matrix based on the subcarrier data sequence of the interfered channel and the subcarrier data sequence that has undergone rotational transformation of the harmonic order, and estimates the carrier phase angle. * and the subcarrier data sequence s after the rotation transformation of the harmonic order γ The covariance matrix is calculated based on the finite length data sequence s3.* and the subcarrier data sequence s after the rotational transformation of the harmonic order γ is a known observable value.

[0050] s3 *T to s3 * =s3+βs γ e -j2ψ is assigned. s3 *T is s3 * is the transpose of s3 * =(s 3_1 , s 3_2、 s 3_3··· s 3_n-1、 s 3_n ), n = number of samples C=E(s γ s3 *T )=E(s γ (βs γ T e -j2ψT +s3 T )) =βE(s γ s γ T e -j2ψT )+E(s γ s3 T ) The second term on the right side of the above equation is E(s γ s3 T ) is s γ and s3 are independent and s γ There is no correlation between s and s3. Specifically, s γ is a parameter caused by the first sensor terminal 200a, and s3 is a parameter caused by the second sensor terminal 200b. γ It can be said that there is no correlation between E(s γ s3 T ) disappears due to the calculation of the covariance matrix. In other words, the carrier phase angle estimator 614 calculates E(s γ s3 T ) without using E(s γ s3 *T ) is calculated. That is, the calculation is performed as follows: E(s γs3 *T )=βE(s γ s γ T e -j2ψT ) (0)

[0051] s on the right side of equation (0) γ s γ T e -j2ψT s γ T e -j2ψT s γ ´ and s γ、 s γ ´ is expressed as follows:

number

number

[0052] C 11 +C 22 and C 12 -C 21 is derived using the addition theorem.

number

[0053] The carrier phase angle subtractor 616 shown in FIG. 6 subtracts the harmonic replica γ=e -j2ψ s γThat is, the carrier phase angle subtraction unit 616 subtracts the carrier phase angle from the subcarrier data sequence that has been subjected to harmonic order rotational transformation to obtain a harmonic data sequence. For example, in the case of harmonic data where the subcarrier frequency is 100 kHz and the harmonic order is 3, the angle of the harmonic data on the IQ plane is (carrier phase angle of the 100 kHz subcarrier) + (subcarrier phase angle of the 100 kHz subcarrier × 3). In this embodiment, after the harmonic order rotational transformation of the interference channel is performed, a rotational transformation is performed to return the over-rotated phase angle. Subtracting the carrier phase angle 2ψ from the subcarrier data sequence that has been subjected to harmonic order rotational transformation is equivalent to returning the phase angle by 2ψ for the subcarrier data sequence that has been subjected to harmonic order rotational transformation.

[0054] The interference removal processing unit 618 shown in FIG. 6 is a finite length data sequence s3 * By subtracting the harmonic replica γ from the subcarrier data sequence of subcarrier 2, s3 is obtained, which corresponds to the subcarrier data sequence from which the harmonic components superimposed on subcarrier 2 have been removed. In other words, the harmonic data sequence is subtracted from the subcarrier data sequence of subcarrier 2. Harmonic replica γ=e -j2ψ s γ Subtracting ω corresponds to removing the interference component of subcarrier SC2.

[0055] The finite-length data sequence S3 from which the superimposed harmonic components have been removed is input to the demodulation processing unit 620. Then, the subcarrier phase value θ2 from the second sensor terminal 200b is demodulated via the demodulated data sequence 622 output from the demodulation processing unit 620.

[0056] In the above embodiment, the harmonic order is 3 and the frequency is f s2 Although the subcarrier 2 having a frequency of 300 Hz has been described, this embodiment is not limited to this. For example, the subcarrier 3 is assigned to the third sensor terminal 200c. The frequency f s3 is the frequency of subcarrier 1, f s1 (i.e. 100KHz) times 5. In this case, the rotational transformation of the harmonic order is performed as follows: The value s obtained by rotational transformation of the harmonic order γ2 is expressed by the following equation: s γ2 =|s1|e j5∠s1 5∠s1=5θ3+5ψ3

[0057] The carrier phase angle estimation unit 614 estimates the carrier data sequence s5 of the subcarrier 3, which is the interfered channel. * and the subcarrier data sequence that has been subjected to harmonic order rotational transformation. The carrier phase angle subtraction unit 616 calculates a harmonic replica γ2 based on the subcarrier data sequence that has been subjected to harmonic order rotational transformation and the carrier phase angle ψ3. In other words, the carrier phase angle subtraction unit 616 returns the phase angle of the subcarrier data sequence that has been subjected to harmonic order rotational transformation by 4ψ.

[0058] The interference removal processing unit 618 extracts the finite length data sequence s5 * By subtracting the harmonic replica γ2 from the subcarrier data sequence of subcarrier 3, s5 corresponding to the subcarrier data sequence in which the harmonic components superimposed on subcarrier 3 have been removed is obtained. That is, the interference removal processing unit 618 calculates the harmonic replica γ=e -j4ψ3 s γ2 is subtracted to remove the interference component.

[0059] For example, the fourth sensor terminal 200d is assigned subcarrier 4. The frequency f s4 is the frequency of subcarrier 1, f s1 (i.e., 100 KHz). In this case, subcarrier 4 is superimposed with a harmonic component that is 9 times that of subcarrier 1 and a harmonic component that is 3 times that of subcarrier 2.

[0060] In this case, for subcarrier 4, the harmonic components of subcarrier 4 are removed by successively removing the harmonic components that are nine times that of subcarrier 1 and the harmonic components that are three times that of subcarrier 2. Note that a frequency on which multiple harmonic components are superimposed may not be assigned as a subcarrier to the sensor terminal 200.

[0061] In this way, the wireless communication system 100 according to this embodiment: an interrogator 300 transmitting an unmodulated carrier wave; a plurality of sensor terminals 200; a receiver 110; Equipped with Each of the plurality of sensor terminals 200 receives the carrier wave, superimposes a subcarrier wave having a frequency predetermined for each of the plurality of sensor terminals 200 onto the backscatter of the carrier wave, modulates the subcarrier wave with a signal generated by a sensor 210 using a predetermined modulation method, and transmits the backscatter; The receiver 110 receives a plurality of backscatters transmitted from the plurality of sensor terminals 200, performs frequency conversion and orthogonal conversion on the plurality of backscatters to generate a finite length data sequence 602 having I components and Q components, removes interference components from the finite length data sequence 602, and demodulates the signal of the sensor 210 in each of the plurality of sensor terminals 200, The receiver 110 further includes, before demodulating the sensor 210 signal: downconverting the finite length data sequence 602 to baseband and filtering to generate a subcarrier data sequence 610; performing a harmonic order rotation transformation on a first subcarrier data sequence of an interference channel among the subcarrier data sequences 610 to obtain a second subcarrier data sequence; calculating a covariance matrix based on the third subcarrier data sequence of the interfered channel and the second subcarrier data sequence of the subcarrier data sequence 610 to estimate a carrier phase angle; subtracting the carrier phase angle from the second subcarrier data sequence to obtain a harmonic data sequence as the interference component; The harmonic data sequence is subtracted from the third subcarrier data sequence.

[0062] In other words, the wireless communication system 100 according to this embodiment distinguishes between the carrier phase angle and the subcarrier phase angle of a signal that has been filtered and downconverted to baseband, and a signal that has been downconverted to baseband and filtered. Specifically, the wireless communication system 100 calculates a covariance matrix based on the baseband signal of the interfered channel and the baseband signal of the interfering channel that has been subjected to a rotational transformation of a higher order, and determines the carrier phase angle of the interfering channel by utilizing the independence of the interfered channel signal and the interfering channel signal. The wireless communication system 100 generates a harmonic replica by subtracting the carrier phase angle that has been excessively rotated by the rotational transformation of the harmonic order from the baseband signal of the interfering channel that has been subjected to a rotational transformation of a higher order, and then removes the harmonic replica from the baseband signal of the interfered channel.

[0063] This makes it possible to suppress an increase in the amount of calculation required for harmonic removal. Specifically, by down-converting the received signal to baseband and then performing harmonic removal, the sampling rate of the received signal is reduced. As a result, the amount of calculation required for harmonic removal can be reduced. Furthermore, by reducing the amount of calculation required for harmonic removal, it is possible to suppress an increase in the scale of the circuit that performs harmonic removal. In other words, because harmonics can be removed using the down-converted received signal (i.e., baseband signal processing can be performed), the sampling rate is reduced, and it becomes possible to communicate with more passive terminals (i.e., sensor terminals 200) with the same circuit scale.

[0064] In conventional technology, when downconverting a received signal to baseband and performing harmonic removal, it is difficult to distinguish between the carrier phase angle and the subcarrier phase angle. In other words, it is difficult to estimate the carrier phase angle. However, in the wireless communication system 100 according to this embodiment, the carrier phase angle is estimated using a covariance matrix calculated based on the second subcarrier data sequence and the third subcarrier data sequence. This enables harmonic removal accompanied by downconversion.

[0065] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments and includes other modifications and applications without departing from the spirit of the present disclosure. For example, in the above embodiments, the configurations of the devices and systems are described in detail and specifically to clearly explain the present disclosure, but all of the described configurations do not necessarily need to be included. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment. Furthermore, it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is also possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0066] Furthermore, the configurations, functions, processing units, etc. of the above-described embodiments may be partially or entirely implemented in hardware, for example, by designing them as integrated circuits. Furthermore, the above-described configurations, functions, etc. may be implemented by programs, i.e., software, that cause a processor to implement the respective functions. Information such as programs, tables, and files that implement the respective functions may be stored in volatile or non-volatile storage, such as memory, a hard disk, or a solid-state drive (SSD), or in recording media, such as an integrated circuit (IC) card or an optical disk. Furthermore, the control lines and information lines shown are those considered necessary for the explanation, and not all control lines and information lines are necessarily shown. In reality, almost all of the configurations may be interconnected.

Claims

1. a transmitter that transmits an unmodulated carrier wave; a plurality of passive terminals; A receiver; A wireless communication system comprising: Each of the plurality of passive terminals receives the carrier wave, superimposes a subcarrier wave having a frequency predetermined for each of the plurality of passive terminals onto backscatter of the carrier wave, modulates the subcarrier wave with a signal generated by a signal source using a predetermined modulation method, and transmits the backscatter; the receiver receives a plurality of backscatters transmitted from the plurality of passive terminals, performs frequency conversion and orthogonal conversion on the plurality of backscatters to generate a finite-length data sequence having I components and Q components, removes interference components from the finite-length data sequence, and demodulates the signal of the signal source in each of the plurality of passive terminals; The receiver further comprises, before demodulating the signal of the signal source, down-converting the finite length data sequence to baseband and filtering to generate a subcarrier data sequence; performing a harmonic order rotational transform on a first subcarrier data sequence of an interference channel among the subcarrier data sequences to obtain a second subcarrier data sequence; calculating a covariance matrix based on a third subcarrier data sequence of an interfered channel among the subcarrier data sequences and the second subcarrier data sequence to estimate a carrier phase angle; subtracting the carrier phase angle from the second subcarrier data sequence to obtain a harmonic data sequence as the interference component; subtracting the harmonic data sequence from the third subcarrier data sequence; Wireless communication system.

2. The receiver of the wireless communication system of claim 1 comprises: In calculating the covariance matrix in the estimation of the carrier phase angle, A covariance matrix based on the third subcarrier data sequence and the second subcarrier data sequence is calculated without using a covariance matrix based on the second subcarrier data sequence and a subcarrier data sequence that does not include harmonic components of the interfered channel.

3. 2. The wireless communication system of claim 1, the receiver comprises a high-pass filter; The high pass filter is used to remove DC from the finite length data sequence before downconverting it to baseband and filtering it to generate the subcarrier data sequence.

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