Wireless communication system

Abstract

A wireless communication system is provided with: a transmitter that transmits an unmodulated carrier; a plurality of passive terminals; and a receiver in which each of the plurality of passive terminals receives the carrier wave, a subcarrier having a frequency specified in advance for each of the plurality of passive terminals is superimposed on backscatter of the carrier wave, the subcarrier is modulated by a signal generated by a signal source in a prescribed modulation scheme, and the backscatter is transmitted. The receiver receives a plurality of backscatters transmitted from the plurality of passive terminals, and generates a finite length data string having an I component and a Q component by frequency conversion and orthogonal conversion of the plurality of backscatters, interference components are removed from the finite length data string and signals of the signal sources in each of the plurality of passive terminals are demodulated.

Description

Technical Field

[0001] The present disclosure relates to a method for removing harmonics in a wireless communication system using a plurality of wireless tags. Background Art

[0002] As shown in Patent Document 1, in a wireless communication system, there is a method of using a bandpass filter as a method of removing harmonic components. This method performs regression analysis on a subcarrier data string obtained by bandpass filter processing of a received signal to calculate a carrier phase angle, generates an angle data string based on an analysis data string obtained from the subcarrier data string and the carrier phase angle, harmonically multiplies the angle data string, generates a replica of the harmonic component based on the harmonically multiplied angle data string and the carrier phase angle, and removes the harmonic component from the received signal by subtracting the replica of the harmonic component from a desired subcarrier data string.

[0003] Patent Document 2 discloses a receiving device and a receiving method that can suppress increases in circuit scale and processing time and reduce the influence of interference signals.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2017-200180

[0007] Patent Document 2: Japanese Patent Application Publication No. 2010-16785 Summary of the invention

[0008] Technical Problems to be Solved by the Invention

[0009] The method of Patent Document 1 may increase the amount of calculation in harmonic removal. Specifically, the method of Patent Document 1 samples a signal with a frequency higher than the baseband. Therefore, compared with the case of a baseband signal, the sampling rate is high and the amount of calculation is large.

[0010] The present disclosure provides a wireless communication system capable of suppressing an increase in the amount of calculation in harmonic removal.

[0011] Technical means for solving technical problems

[0012] A wireless communication system according to an embodiment of the present disclosure includes:

[0013] A transmitter that transmits an unmodulated carrier wave;

[0014] Multiple passive terminals; and

[0015] Receiver,

[0016] in,

[0017] The plurality of passive terminals receive the carrier respectively, overlap the backscatter of the carrier with a subcarrier whose frequency is predetermined for the plurality of passive terminals respectively, modulate the subcarrier with a predetermined modulation method by a signal generated by a signal source, and transmit the backscatter,

[0018] The receiver receives a plurality of backscatter signals sent from the plurality of passive terminals, generates a finite length data string having an I component and a Q component by frequency conversion and orthogonal conversion of the plurality of backscatter signals, removes interference components from the finite length data string, and demodulates the signal of the signal source in each of the plurality of passive terminals.

[0019] The receiver further, before demodulating the signal of the signal source,

[0020] Down-converting the finite length data string to baseband and filtering to generate a subcarrier data string,

[0021] performing a harmonic rotation conversion on a first subcarrier data string of an interference channel in the subcarrier data string and obtaining a second subcarrier data string,

[0022] Calculate the covariance matrix and estimate the carrier phase angle according to the third subcarrier data string of the interfered channel in the subcarrier data string and the second subcarrier data string,

[0023] subtracting the carrier phase angle from the second subcarrier data string and obtaining a harmonic data string as the interference component,

[0024] The harmonic data string is subtracted from the third subcarrier data string.

[0025] According to the present disclosure, it is possible to suppress an increase in the amount of calculation in harmonic removal. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic block diagram showing the overall structure of a wireless communication system according to an embodiment of the present disclosure.

[0027] Figure 2 Detailed description of the invention is a block diagram showing a hardware structure of a sensor terminal according to an embodiment of the present disclosure.

[0028] Figure 3 Detailed description of the invention is a block diagram showing a hardware structure of an interrogator according to an embodiment of the present disclosure.

[0029] Figure 4 This is a block diagram of an IQ conversion unit according to one embodiment of the present disclosure.

[0030] Figure 5Detailed description of the invention is a block diagram showing a hardware configuration of a software receiving unit according to an embodiment of the present disclosure.

[0031] Figure 6 Detailed description of the invention is a block diagram showing software functions of a software receiving unit according to an embodiment of the present disclosure.

[0032] Figure 7 This is a diagram schematically showing radio waves received from a sensor terminal according to one embodiment of the present disclosure. DETAILED DESCRIPTION

[0033] An overview of one embodiment of the present disclosure (hereinafter referred to as “this embodiment”) will be described.

[0034] <Overall Configuration of Wireless Communication System 100>

[0035] Figure 1 1 is a schematic block diagram showing the overall structure of the wireless communication system 100 according to the present 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 nth sensor terminal 200n are attached to a measurement target such as a fuselage of an aircraft or a tunnel (not shown) as a large structure. In addition, when the first sensor terminal 200a, the second sensor terminal 200b, ..., the nth sensor terminal 200n are not distinguished, they are simply referred to as sensor terminals 200.

[0036] An interrogator 300 and a receiver 110 are installed near the sensor terminal 200. The receiver 110 includes an IQ converter 400 and a software receiver 500. The interrogator 300 is connected to the software receiver 500 via the network 130.

[0037] The sensor terminal 200 includes a sensor such as a wireless tag using backscatter (i.e., backscattered waves), an acceleration sensor, and an analog modulation circuit. The analog modulation circuit is, for example, a phase modulator in which a varactor diode is connected in parallel with a coil and a capacitor. In the phase modulator, the output voltage of the acceleration sensor is applied to the varactor diode to phase modulate the carrier.

[0038] The interrogator 300 , which is called a reader / writer, has a function of performing bidirectional wireless data communication with the sensor terminal 200 and a function of transmitting an unmodulated wave.

[0039] After the first sensor terminal 200a, the second sensor terminal 200b, ... the nth sensor terminal 200n respectively perform predetermined communication with the interrogator 300, they receive the unmodulated wave transmitted from the interrogator 300. Each sensor terminal 200 superimposes a subcarrier on the backscatter of the unmodulated wave, modulates the subcarrier with the signal generated by the sensor, and transmits the backscatter. That is, each sensor terminal 200 reflects the unmodulated wave. The receiver 110 receives the radio waves transmitted from the plurality of sensor terminals 200, and demodulates the signals of each sensor through calculation processing.

[0040] The interrogator 300 performs two-way communication for assigning a unique subcarrier frequency to each of the plurality of sensor terminals 200. The interrogator 300 transmits the sensor terminal list created as a result 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.

[0041] <Wireless Communication Steps in Wireless Communication System 100>

[0042] The wireless communication system 100 of this embodiment roughly performs two wireless communication steps.

[0043] As a first step, the interrogator 300 performs wireless data communication with each of the plurality of sensor terminals 200 individually before simultaneously receiving measurement signals from the plurality of sensor terminals 200. In the wireless data communication, the interrogator 300 allocates a unique subcarrier frequency to each of the plurality of sensor terminals 200. Furthermore, the interrogator 300 creates a sensor terminal list indicating the relationship between each of the plurality of sensor terminals 200 and the subcarrier frequency, and transmits the sensor terminal list to the receiver 110.

[0044] Next, as a second step, the interrogator 300 transmits an unmodulated carrier wave. Each of the plurality of sensor terminals 200 superimposes a subcarrier wave modulated by a signal of a built-in acceleration sensor on the received unmodulated wave, and causes the backscatter to return to the receiver 110. At this time, the interrogator 300 functions as a carrier wave source (i.e., a transmitter).

[0045] The receiver 110 simultaneously receives multiple backscatter signals from multiple sensor terminals 200 and converts the multiple backscatter signals into a data string of finite length. Since the signals simultaneously received from multiple sensor terminals 200 are mixed in the data string of finite length, the signals of other sensor terminals 200 constitute interference components in demodulation of the signal of a certain sensor terminal 200. Therefore, the software receiving unit 500 to be described later removes the interference components from the data string of finite length and performs demodulation processing of the target received signal.

[0046] Hereinafter, in the present embodiment, the process of removing interference components from a received signal performed by the receiver 110 is referred to as “interference removal”.

[0047] <Sensor terminal list>

[0048] The sensor terminal list indicates the modulation method and subcarrier frequency set for each of the multiple sensor terminals 200, and the demodulation order determined according to the strength of the radio wave received by the receiver 110 and the subcarrier frequency. Specifically, the sensor terminal list includes: a terminal ID field storing a terminal ID (Identifier) ​​that uniquely identifies each of the multiple sensor terminals 200; a modulation method field storing a modulation method set for each of the multiple sensor terminals 200; a subcarrier frequency field storing a subcarrier frequency set for each of the multiple sensor terminals 200; and a demodulation order field storing a demodulation order for each of the multiple sensor terminals 200.

[0049] Any analog modulation method can be set as the modulation method in the sensor terminal 200. As analog modulation, in addition to phase modulation (PM), frequency modulation (FM) and the like can be used. In addition, when all the multiple sensor terminals 200 use the same modulation method, the modulation method field is not included in the sensor terminal list.

[0050] <Sensor Terminal 200>

[0051] Figure 2 2 is a block diagram showing the hardware structure of the sensor terminal 200. The sensor terminal 200 has a power supply unit 202 that converts the power of the radio wave received by the antenna 214 into circuit driving power, and does not have an independent power supply such as a battery. That is, the sensor terminal 200 is a passive terminal. In addition to the power supply unit 202, the antenna 214 is connected to a modulation unit 212, a SPDT (Single Pole Double Throw) switch 204, and a control unit 208.

[0052] The SPDT switch 204 switches the open end 204a and the short-circuit end 204b according to the rectangular wave signal (i.e., subcarrier) outputted from the subcarrier source 206, and is connected to the antenna 214. The impedance of the antenna 214 changes according to the period of the subcarrier by the SPDT switch 204. As a result, the subcarrier overlaps with the reflected wave (i.e., backscatter) of the unmodulated wave obtained from the antenna 214. The frequency of the subcarrier generated by the subcarrier source 206 is determined by controlling the subcarrier source 206 by the control unit 208. The control unit 208 stores the frequency indicated by the interrogator 300 when communicating with the interrogator 300 in the first step. Moreover, the control unit 208 controls the subcarrier source 206 in the second step to generate a subcarrier of the stored frequency.

[0053] The modulation unit 212 is connected to a sensor 210 as a signal source. The sensor 210 is a sensor that outputs an AC signal, such as an acceleration sensor. The modulation unit 212 modulates the subcarrier using the signal from the sensor 210 by phase modulation (PM), frequency modulation (FM), or the like.

[0054] According to the above structure, the sensor terminal 200 overlaps the subcarrier with the reflected wave of the unmodulated wave transmitted from the interrogator 300, which is the unmodulated wave source (i.e., the carrier source). The sensor terminal 200 performs phase modulation, frequency modulation, or pulse width modulation on the subcarrier by the signal of the sensor 210, and transmits the reflected wave overlapped with the subcarrier from the antenna 214.

[0055] <Interrogator 300>

[0056] Figure 3 300 is a block diagram showing the hardware structure of the interrogator 300. The radio wave received by the antenna 302 is converted into 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, and after demodulation, it is converted into digital data by an A / D (Analog / Digital) converter 312 and input to a control unit 314. For example, the control unit 314 is implemented by a microcontroller.

[0057] The control unit 314 interprets the information of the sensor terminal 200 included in the digital data and generates a command to the sensor terminal 200. The digital data constituting the command is converted into an analog signal by the D / A converter 316 and then used by the modulation unit 318 to modulate the carrier generated by the carrier source 320.

[0058] After the control unit 314 grasps all the sensor terminals 200 existing within the communicable range through dialogue processing with the sensor terminals 200, it assigns subcarriers of a unique frequency to all the sensor terminals 200. Moreover, the control unit 314 creates a sensor terminal list 322 listing the correspondence between the sensor terminals 200 and the subcarrier frequencies, and sends the sensor terminal list 322 to the receiver 110 through the network 130. That is, the interrogator 300 has the function of sending control commands for respectively assigning unique subcarriers to a plurality of sensor terminals 200 to the plurality of sensor terminals 200.

[0059] <IQ conversion unit 400>

[0060] Figure 4 is a block diagram of the IQ conversion unit 400. After the IQ conversion unit 400 extracts a signal from the radio wave received by the antenna 402 through the tuning circuit 404, it amplifies the signal through 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 signal with a frequency slightly lower than the frequency of the radio wave output from the local oscillator 412 is input to the first mixer 408. A local signal with a 90° phase shift through the 90° phase shifter 414 is input to the second mixer 410.

[0061] The first mixer 408 adds the RF signal from the RF amplifier 406 and the local signal from the local oscillator 412, and supplies a frequency signal of the frequency difference between the RF signal and the local signal to the first low-pass filter (hereinafter referred to as "LPF") 416. Moreover, an I signal obtained by subtracting the frequency of the local signal output from the local oscillator 412 from the frequency of the radio wave received by the antenna 402 is output from the first LPF 416.

[0062] Similarly, the second mixer 410 adds the RF signal from the RF amplifier 406 and the local signal with a 90° phase shift through the 90° phase shifter 414, and supplies a frequency signal of the frequency difference between the RF signal and the local signal to the second LPF 418. Moreover, a Q signal obtained by subtracting the frequency of the local signal with a 90° phase shift from the frequency of the radio wave received by the antenna 402 is output from the second LPF 418.

[0063] 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 (i.e., a high-speed mixer).

[0064] The I signal and the Q signal are converted into digital data by the A / D converter 420 and output to the software receiving unit 500.

[0065] IQ conversion section 400 has a down converter function using a quadrature detection circuit and an A / D conversion function of A / D converter 420 .

[0066] <Hardware Configuration of Software Receiving Unit 500>

[0067] Figure 5 1 is a block diagram showing the hardware structure of the software receiving unit 500. The software receiving unit 500 is installed 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 memory 514 such as a hard disk device, which are connected to a bus 518. In addition, a NIC (Network Interface Card) 516 for communicating with the interrogator 300 and the IQ conversion unit 400 is connected to the bus 518. The software receiving unit 500 is a general computer, and the functions of the software receiving unit 500 are realized by executing the program stored in the non-volatile memory 514.

[0068] <Software Functions of Software Receiving Unit 500>

[0069] Figure 6 The data received from the IQ conversion unit 400 and composed of I data and Q data are temporarily stored in the RAM 506 (see FIG. 6 ) as a finite length data string 602 to be processed. Figure 5 ). The finite length data string 602 consisting of I data and Q data is first input to a high pass filter (hereinafter referred to as "HPF") 604, and the DC (Direct Current) offset component (ie, the direct current) is removed by the HPF 604. The high pass filter can be provided as required.

[0070] Next, the finite length data sequence 602 output from the HPF 604 is down-converted to the baseband by the down-conversion and filtering processing unit 608 and filtered, and the subcarrier data sequence 610 of each subcarrier component is extracted. As a result, the carrier is removed from the finite length data sequence 602. In addition, down-conversion to the baseband may be performed after filtering, or filtering may be performed after down-conversion.

[0071] Figure 7Schematically shows the radio waves received from the sensor terminal 200. In a real machine, several dozen channels or more are provided for n sensor terminals 200. However, only the channels related to Figure 7 The two channels shown in FIG. 1 are subcarrier 1 (ie, interference channel) at a frequency f1 on which a carrier overlaps, and subcarrier 2 (interfered channel) at a frequency f2 on which a carrier overlaps.

[0072] Here, the frequency fc of the carrier wave is set to 900 MHz, for example. Figure 1 The first sensor terminal 200a in the example is assigned subcarrier 1. The frequency f of subcarrier 1 is s1 The frequency f1 of the subcarrier 1 overlapping with the carrier is fc+f s1 .

[0073] Towards Figure 1 The second sensor terminal 200b in the example is assigned subcarrier 2. The frequency f of subcarrier 2 is s2 is 300KHz. That is, f s2 is the frequency f of subcarrier 1 s1 The frequency f2 of the subcarrier 2 that overlaps with the carrier is fc+f s2 The frequency f of subcarrier 2 can be expressed as s2 .

[0074] f s2 =f s1 ×3

[0075] Here, harmonics are generated at odd-number (3, 5, 7, 9, 11, ...) times of the frequency. Therefore, the harmonics of the interference channel constitute the noise (ie, interference component) of the interfered channel.

[0076] The demodulation processing unit 620 receives a finite length data sequence s1*, s1*=(s 1_1 、s 1_2 、s 1_3 、···s 1_n-1 、s 1_n ), n=number of samples. Then, the subcarrier phase value θ from the first sensor terminal 200a is demodulated using the demodulated data string 622 output from the demodulation processing unit 620. Each s 1_1 、s 1_2 ,...is composed of I data and Q data in each sampling period obtained by sampling subcarrier 1.

[0077] The finite length data sequence s3*, s3*=(s3*) consisting of the I data and Q data of the subcarrier 2 of the interfered channel in the subcarrier data sequence 610 is input to the harmonic order rotation processing unit 612, the carrier phase angle estimation unit 614, and the interference removal processing unit 618. 3_1 、s 3_2 、s 3_3 ···s 3_n-1 、s 3_n ), n = sample size.

[0078] The harmonic order rotation processing unit 612 performs a rotation conversion of the harmonic order on the subcarrier data string of the interference channel. Specifically, the harmonic order rotation processing unit 612 performs a rotation conversion of the subcarrier data string of subcarrier 1 as the interference channel to the harmonic order (here 3) corresponding to subcarrier 2 as the interfered channel.

[0079] The value s obtained by performing the rotation conversion of the harmonic order is expressed as follows γ .

[0080] s γ =|s1|e j3∠s1

[0081]

[0082] Here, θ is the subcarrier phase angle of subcarrier 1, and corresponds to the information from the first sensor terminal 200a. 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 according to the length of the propagation path of the carrier. This phase delay (in other words, phase difference) is the phase difference of subcarrier 1. Phase Difference This is a value determined by the distance between the interrogator 300 and the sensor terminal 200 , and differs for each subcarrier allocated to the sensor terminal 200 .

[0083] Here, the amplitude value of the finite length data string s1* is |s1|, and the finite length data string s1* has The angular component of S γ yes The angle component of is 3 times. For example, the angle on the IQ plane of the finite length data string s1* When it is 60 degrees, the angle becomes 180 degrees by the rotation conversion of the harmonic order.

[0084] The finite length data string s3* is expressed as follows.

[0085]

[0086] Here, s3 is a component originating from subcarrier 2 in the finite-length data string s3*. is the harmonic component originating from subcarrier 1 overlapping with subcarrier 2.

[0087] The carrier phase angle estimation unit 614 calculates the covariance matrix and estimates the carrier phase angle based on the subcarrier data string of the interfered channel and the subcarrier data string that has been subjected to the harmonic order rotation conversion. That is, based on the finite length data string S3* of subcarrier 2 (i.e., the interfered channel) and the subcarrier data string s3* that has been subjected to the harmonic order rotation conversion γ , calculate the covariance matrix. The finite length data string s3* and the subcarrier data string s that has been rotated and converted to the harmonic order γ is an observable known value.

[0088] To s3* T Substitution

[0089] s3* T is the transposed matrix of s3*.

[0090] s3*=(s 3_1 、s 3_2 、s 3_3 ···s 3_n-1 、s 3_n ), n = sample size

[0091]

[0092] As the second term on the right side of the above formula, E(s γ s3 T ) is γ Independent from s3 and in s γ There is no correlation with s3. Specifically, s γ is the parameter caused by the first sensor terminal 200a, and s3 is the parameter caused by the second sensor terminal 200b. Therefore, it can be considered that in s γ There is no correlation between E(s3). γ s3 T ) disappears through the calculation of the covariance matrix. In other words, the carrier phase angle estimation unit 614 does not use E(s) generated during the calculation process. γ s3 T ), calculate E(s γ s3* T ). That is, the calculation is performed as described in the following formula.

[0093]

[0094] When the right side of equation (0) of Set to s γ ′, s γ 、s γ ' represents as follows.

[0095] [Mathematical formula 1]

[0096]

[0097] The right side of equation (0) can also be expressed as the following matrix by substituting it into equation 1.

[0098] [Mathematical formula 2]

[0099]

[0100] The matrix in the lower part of Mathematical Formula 2 is equal to the left side of Formula (0) which is a known value.

[0101] C 11 : Covariance of I signal

[0102] C 22 : Covariance of the Q signal

[0103] C 12 , C 21 : Covariance of I signal and Q signal

[0104] Deriving C through the addition theorem 11 +C 22 and C 12 -C 21 .

[0105] [Mathematical formula 3]

[0106] C11+C22γ cos(2ψ)

[0107] C12-C21-γ sin(2ψ)

[0108]

[0109] According to mathematical formula 3, we can find

[0110] Figure 6 The carrier phase angle subtraction unit 616 shown in FIG. 6 is based on the carrier phase angle obtained by the carrier phase angle estimation unit 614. Based on the calculation of harmonic replicas That is, the carrier phase angle subtraction unit 616 obtains the harmonic data string by subtracting the carrier phase angle from the subcarrier data string that has undergone the rotation conversion of the harmonic order. For example, in the case of harmonic data with a subcarrier frequency of 100KHz and a harmonic order of 3, the angle of the harmonic data on the IQ plane is (carrier phase angle of the subcarrier of 100KHz) + (subcarrier phase angle of the subcarrier of 100KHz × 3). In this embodiment, after the rotation conversion of the harmonic order of the interference channel is performed, a rotation conversion is performed to return the excessively rotated phase angle. The carrier phase angle is subtracted from the subcarrier data string that has undergone the rotation conversion of the harmonic order. This is equivalent to returning the phase angle of the subcarrier data string that has been subjected to the harmonic order rotation conversion to the quantity.

[0111] exist Figure 6 The interference removal processing unit 618 shown in FIG. 5 subtracts the harmonic replica γ from the finite length data string s3* to obtain a subcarrier data string s3 which is equivalent to the subcarrier data string of subcarrier 2 with the harmonic component overlapping with subcarrier 2 removed. That is, the harmonic data string is subtracted from the subcarrier data string of subcarrier 2. Subtracting the harmonic replica This is equivalent to removing the interference component of subcarrier SC2.

[0112] The finite length data string S3 from which the overlapping harmonic components are removed is input to the demodulation processing unit 620. Then, the subcarrier phase value θ2 from the second sensor terminal 200b is demodulated by the demodulation data string 622 output from the demodulation processing unit 620.

[0113] In the above-mentioned embodiment, for the harmonic order 3 and the frequency f s2 In the above description, subcarrier 2 is assigned to 300 Hz, but the present embodiment is not limited thereto. For example, subcarrier 3 is assigned to the third sensor terminal 200c. The frequency f of subcarrier 3 is s3 is the frequency f of subcarrier 1 s1 (ie, 100KHz) by 5 times. In this case, the rotation conversion of the harmonic order is performed as follows.

[0114] The value s obtained by performing the rotation conversion of the harmonic order is expressed as follows γ2 .

[0115] s γ2 =|s1|e j5∠s1

[0116]

[0117] The carrier phase angle estimation unit 614 estimates the carrier phase angle s5* based on the carrier data string s5* of the subcarrier 3 as the interfered channel and the subcarrier data string that has been subjected to the harmonic order rotation conversion. The carrier phase angle subtraction unit 616 calculates the subcarrier data sequence subjected to the harmonic order rotation conversion and the carrier phase angle. The harmonic replica γ2 is calculated. That is, the carrier phase angle subtraction unit 616 returns the phase angle of the subcarrier data sequence that has been subjected to the harmonic order rotation conversion to quantity.

[0118] The interference removal processing unit 618 obtains s5, which is a subcarrier data sequence obtained by removing the harmonic component overlapping with subcarrier 3 from the subcarrier data sequence of subcarrier 3, by subtracting the harmonic replica γ2 from the finite length data sequence s5*. Perform subtraction to remove interference components.

[0119] For example, the subcarrier 4 is allocated to the fourth sensor terminal 200d. The frequency f of the subcarrier 4 is s4 is the frequency f of subcarrier 1 s1 In this case, subcarrier 4 overlaps the harmonic component of subcarrier 1 times 9 and the harmonic component of subcarrier 2 times 3.

[0120] In this case, for subcarrier 4, the harmonic components of subcarrier 4 are removed by sequentially removing the 9th harmonic component of subcarrier 1 and the 3rd harmonic component of subcarrier 2. In addition, the frequency where a plurality of harmonic components overlap may not be allocated to sensor terminal 200 as a subcarrier.

[0121] Thus, the wireless communication system 100 of this embodiment includes:

[0122] The interrogator 300 transmits an unmodulated carrier wave;

[0123] a plurality of sensor terminals 200; and

[0124] Receiver 110,

[0125] The plurality of sensor terminals 200 receive the carrier respectively, overlap the backscatter of the carrier with a subcarrier whose frequency is predetermined for the plurality of sensor terminals 200 respectively, modulate the subcarrier with a predetermined modulation method by a signal generated by the sensor 210, and transmit the backscatter.

[0126] The receiver 110 receives a plurality of backscatter signals transmitted from the plurality of sensor terminals 200, generates a finite length data string 602 having an I component and a Q component by frequency conversion and orthogonal conversion of the plurality of backscatter signals, removes interference components from the finite length data string 602, and demodulates the signal of the sensor 210 in each of the plurality of sensor terminals 200,

[0127] The receiver 110 further, before demodulating the signal of the sensor 210,

[0128] The finite length data string 602 is down-converted to baseband and filtered to generate a subcarrier data string 610,

[0129] Performing a harmonic rotation conversion on the first subcarrier data string of the interference channel in the subcarrier data string 610 and obtaining a second subcarrier data string,

[0130] Calculate the covariance matrix and estimate the carrier phase angle based on the third subcarrier data string of the interfered channel in the subcarrier data string 610 and the second subcarrier data string,

[0131] subtracting the carrier phase angle from the second subcarrier data string and obtaining a harmonic data string as the interference component,

[0132] The harmonic data string is subtracted from the third subcarrier data string.

[0133] In other words, the wireless communication system 100 of the present embodiment distinguishes the carrier phase angle and the subcarrier phase angle of the signal that is filtered and down-converted to the baseband, or the signal that is down-converted to the baseband and filtered. Specifically, the wireless communication system 100 calculates the covariance matrix based on the baseband signal of the interfered channel and the baseband signal that is the baseband signal of the interference channel and has undergone a high-frequency rotation conversion, and uses the independence of the interfered channel signal and the interference channel signal to obtain the carrier phase angle of the interference channel. The wireless communication system 100 generates a harmonic replica by subtracting the carrier phase angle that is redundantly rotated by the harmonic order rotation conversion from the baseband signal of the interference channel that has undergone a high-frequency rotation conversion, and removes the harmonic replica from the baseband signal of the interfered channel.

[0134] Thus, the increase in the amount of calculation in harmonic removal can be suppressed. Specifically, by down-converting the received signal to baseband and performing harmonic removal, the sampling rate of the received signal is reduced. As a result, the amount of calculation in harmonic removal can be reduced. Furthermore, by reducing the amount of calculation in harmonic removal, the increase in the scale of the circuit for harmonic removal can be suppressed. In other words, since harmonics can be removed from the received signal after down-conversion (i.e., baseband signal processing can be performed), the sampling rate is reduced, and communication with more passive terminals (i.e., sensor terminal 200) can be performed at the same circuit scale.

[0135] In the prior art, when the received signal is down-converted to the baseband for harmonic removal, it is difficult to distinguish between the carrier phase angle and the subcarrier phase angle. That is, it is difficult to estimate the carrier phase angle. However, in the wireless communication system 100 of this embodiment, the carrier phase angle is estimated using the covariance matrix calculated based on the second subcarrier data string and the third subcarrier data string. Thus, harmonic removal accompanied by down-conversion can be performed.

[0136] The embodiments of the present disclosure are described above, but the present disclosure is not limited to the above embodiments, and includes other variations and application examples as long as they do not deviate from the purpose of the present disclosure. For example, in the above embodiments, in order to facilitate the description of the present disclosure, the structure of the device and the system is described in detail and specifically, but not all the structures described are necessarily provided. In addition, a part of the structure of a certain embodiment may be replaced with the structure of other embodiments. Furthermore, the structure of other embodiments may be added to the structure of a certain embodiment. In addition, other structures may be added, deleted, or replaced with a part of the structure of each embodiment.

[0137] In addition, the structures, functions, processing units, etc. of the above-mentioned embodiments may also be implemented in part or in whole by hardware, for example, by designing by integrated circuits. In addition, the above-mentioned structures, functions, etc. may also be implemented by programs, i.e., software, for implementing the respective functions by a processor. The information of programs, tables, files, etc. that implement the respective functions may be stored in volatile or non-volatile memories such as memories, hard disks, SSDs (Solid State Drives), or storage media such as IC (Integrated Circuit) cards and optical disks. In addition, the control lines and information lines are shown as those considered necessary for the description, and are not limited to showing all the control lines and information lines. In fact, almost all structures may be connected to each other.

Claims

1. A wireless communication system comprising: A transmitter that transmits an unmodulated carrier wave; Multiple passive terminals; and Receiver, in, The plurality of passive terminals receive the carrier respectively, overlap the backscatter of the carrier with a subcarrier whose frequency is predetermined for the plurality of passive terminals respectively, modulate the subcarrier with a predetermined modulation method by a signal generated by a signal source, and transmit the backscatter, The receiver receives a plurality of backscatter signals sent from the plurality of passive terminals, generates a finite length data string having an I component and a Q component by frequency conversion and orthogonal conversion of the plurality of backscatter signals, removes interference components from the finite length data string, and demodulates the signal of the signal source in each of the plurality of passive terminals. The receiver further, before demodulating the signal of the signal source, Down-converting the finite length data string to baseband and filtering to generate a subcarrier data string, performing a harmonic rotation conversion on a first subcarrier data string of an interference channel in the subcarrier data string and obtaining a second subcarrier data string, Calculate the covariance matrix and estimate the carrier phase angle according to the third subcarrier data string of the interfered channel in the subcarrier data string and the second subcarrier data string, subtracting the carrier phase angle from the second subcarrier data string and obtaining a harmonic data string as the interference component, The harmonic data string is subtracted from the third subcarrier data string.

2. The wireless communication system according to claim 1, wherein: The receiver calculates a covariance matrix based on the third subcarrier data string and the second subcarrier data string, without using the covariance matrix based on the subcarrier data string that does not include the harmonic component of the interfered channel, in the calculation of the covariance matrix in the estimation of the carrier phase angle, and calculates a covariance matrix based on the third subcarrier data string and the second subcarrier data string.

3. The wireless communication system according to claim 1, wherein: The receiver is provided with a high pass filter, The high pass filter is used to remove a DC amount from the finite length data string before down-converting the finite length data string to baseband and filtering to generate the subcarrier data string.

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