JP7645663B2 - Receiver and receiving method - Google Patents

Description

This invention relates to a receiver and a receiving method for measuring the propagation time of a signal (wave).

Conventionally, a method for measuring propagation time using waves such as ultrasonic waves is known (see, for example, Patent Document 1). This propagation time measurement is realized by modulating a carrier wave with Phase Shift Keying (PSK) and calculating the cross-correlation between a transmitted signal and a received signal when the modulated signal is transmitted and received.
Measurement of this propagation time is used, for example, in distance measurement (see, for example, Non-Patent Document 1). In general, when demodulating phase shift keying, it is necessary to align the phase of a local oscillator (LO) signal in the receiver with the phase of a carrier wave in the received signal. In the technology disclosed in Non-Patent Document 1, the same clock is used on the transmitter side and the receiver side to align the phases. However, this is possible because the transmitter and receiver are in the same place, and since the receiver is usually located away from the transmitter, it was thought that it was necessary to generate a local oscillation signal in the receiver so that the phase would match the carrier wave using a circuit such as a phase-locked loop (PLL).

JP 2006-246476 A

Yamane et al., Application of pseudorandom M-sequence spread spectrum sound waves to distance measurement, https://www.jstage.jst.go.jp/article/sicetr1965/39/10/39_10_879/_pdf/-char/ja

As mentioned above, when measuring propagation time using a phase-shift keyed signal, it was thought that when demodulating the phase-shift keyed signal, it was necessary to align the phase of the local oscillator signal with the phase of the carrier wave. This required a circuit such as phase synchronous detection in the receiver, which made the circuitry complicated.

This invention has been made to solve the above problems, and aims to provide a receiver that can demodulate a phase-shift-keyed signal when measuring propagation time using the signal, without aligning the phase of the local oscillator signal with the phase of the carrier wave.

The receiver according to the present invention includes a transmission information holding unit that holds a signal of a pseudo-random number sequence used in phase shift keying for a carrier wave in the transmitter, a reception information acquisition unit that acquires a reception signal which is a signal after phase shift keying transmitted by the transmitter, a demodulation unit that demodulates the reception signal acquired by the reception information acquisition unit by performing quadrature detection, a cross-correlation calculation unit that regards the signal after demodulation by the demodulation unit as a complex number and calculates a correlation function between the signal of the pseudo-random number sequence held by the transmission information acquisition unit, an absolute value calculation unit that calculates the absolute value of the correlation function of the complex number calculated by the cross-correlation calculation unit, and a propagation time calculation unit that calculates a propagation time by calculating the position of the peak of the absolute value calculated by the absolute value calculation unit. The demodulation unit includes a first sine wave generation unit that generates a first sine wave signal as a local oscillation signal, the first sine wave signal having a frequency different from that of the carrier wave in the reception signal acquired by the reception information acquisition unit, and a first sine wave generation unit that generates a first sine wave signal having a frequency different from that of the carrier wave in the reception signal acquired by the reception information acquisition unit. the first LPF obtaining an I signal by removing high frequency components from a result of the multiplication by the first multiplier; a second sine wave generation unit generating a second sine wave signal as a local oscillation signal, the second sine wave signal having the same frequency as the first sine wave signal generated by the first sine wave generation unit and a phase advanced by 90° from the first sine wave signal generated by the first sine wave generation unit; a second multiplier multiplying the received signal obtained by the reception information acquisition unit by the second sine wave signal generated by the second sine wave generation unit; and a second LPF obtaining a Q signal by removing high frequency components from the result of the multiplication by the second multiplier, wherein the transmitter transmits a signal after phase shift keying using a signal of only one period of a pseudo-random number sequence, and suppresses an amount of rotation of the position of the demodulated signal in IQ space to 180° or less during a time required for the transmitter to transmit the signal, without aligning the phase of the local oscillation signal with the phase of the carrier wave .

According to this invention, as configured as above, when measuring the propagation time using a phase-shift-keyed signal, the phase-shift-keyed signal can be demodulated without aligning the phase of the local oscillation signal with the phase of the carrier wave.

1 is a diagram illustrating a configuration example of a propagation time measuring device according to a first embodiment; FIG. 2 is a diagram illustrating a configuration example of a transmitter according to a first embodiment. FIG. 2 is a diagram illustrating a configuration example of a receiver according to a first embodiment. FIG. 2 is a diagram illustrating a configuration example of a demodulation unit in the first embodiment. FIG. 4 is a diagram illustrating a configuration example of a correlation calculation unit in the first embodiment. 5 is a flowchart showing an example of the operation of the receiver according to the first embodiment; 1 is a diagram showing an example of a demodulation result of a BPSK signal when the phases of a carrier wave and a local oscillation signal are aligned; 11 is a diagram showing an example of a demodulation result of a BPSK signal when the phase of a carrier wave leads the phase of a local oscillation signal by φ. FIG. 11 is a diagram showing an example of a demodulation result of a PSK signal when the phase of a carrier wave leads the phase of a local oscillation signal by φ. FIG. 1 is a diagram illustrating a specific configuration example of a propagation time measuring device according to a first embodiment; 11 is a diagram showing a signal for one period of a pseudorandom number sequence (M sequence) used in the propagation time measuring device shown in FIG. 10. 11 is a diagram showing a received signal obtained by the propagation time measuring device shown in FIG. 10 . 13A is a diagram showing an I signal obtained by the demodulator shown in FIG. 10, and FIG. 13B is a diagram showing a Q signal obtained by the demodulator shown in FIG. 11 is a diagram showing the absolute value of a correlation function obtained by the correlation calculation unit shown in FIG. 10 .

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
Embodiment 1.
FIG. 1 is a diagram showing an example of the configuration of a propagation time measuring device according to the first embodiment.
The propagation time measuring device measures the propagation time of a signal (wave). As shown in FIG.

FIG. 2 is a diagram showing an example of the configuration of the transmitter 1 according to the first embodiment.
The transmitter 1 includes a modulation section 11 and a transmission section 12 .
The modulation unit 11 generates a modulated signal by performing phase shift keying on a carrier wave using a signal of a pseudorandom number sequence. The modulation unit 11 performs the above generation in accordance with a transmission timing indicated by a transmission timing signal input from the outside.
The transmitter 12 transmits the modulated signal (the signal after phase shift keying) generated by the modulator 11 .

FIG. 3 is a diagram showing an example of the configuration of the receiver 2 according to the first embodiment.
The receiver 2 acquires the modulated signal transmitted by the transmitter 1 using a reception information acquisition unit 22 (reception unit) described later. Furthermore, the receiver 2 calculates the propagation time of the signal from the transmitter 1 to the receiver 2 based on the pseudorandom number sequence signal used in the transmitter 1 and the modulated signal (reception signal) acquired by the reception information acquisition unit 22 using a demodulation unit 23 and a correlation calculation unit 24 described later. Furthermore, the receiver 2 can calculate the distance from the transmitter 1 to the receiver 2 by multiplying the propagation time by the speed of sound, as shown in Fig. 3.

As shown in FIG. 3, the receiver 2 includes a transmission information storage unit 21, a reception information acquisition unit 22, a demodulation unit 23, and a correlation calculation unit 24.

The receiver 2 may be realized by discrete components, a processing circuit such as a system LSI (Large Scale Integration), a CPU (Central Processing Unit) that executes a program stored in a memory, or an FPGA (Field Programmable Gate Array) that executes logic stored in a memory.

The transmission information storage unit 21 stores the pseudorandom number sequence signal used by the transmitter 1.

The reception information acquisition unit 22 receives and acquires the modulated signal (received signal) transmitted as a wave such as an ultrasonic wave by the transmitter 1.

The demodulation unit 23 demodulates the received signal acquired by the reception information acquisition unit 22 by performing quadrature detection. As shown in FIG. 4, the demodulation unit 23 has a quadrature detection unit 231, a sine wave generation unit (first sine wave generation unit) 232, a sine wave generation unit (second sine wave generation unit) 233, a multiplier 234, and an adder 235. The quadrature detection unit 231 shown in FIG. 4 also has a multiplier (first multiplier) 2311, an LPF (Low Pass Filter) (first LPF) 2312, a multiplier (second multiplier) 2313, and an LPF (second LPF) 2314.

The sine wave generating unit 232 generates a sine wave signal (first sine wave signal) as a local oscillation signal, the first sine wave signal having the same frequency as the carrier wave in the received signal acquired by the reception information acquiring unit 22.

The sine wave generating unit 233 generates a sine wave signal (second sine wave signal) as a local oscillation signal, which has the same frequency as the first sine wave signal generated by the sine wave generating unit 232 and is 90° ahead in phase.

The multiplier 2311 multiplies the received signal acquired by the reception information acquisition unit 22 by the first sine wave signal generated by the sine wave generation unit 232.

The LPF 2312 obtains an I signal by removing high-frequency components from the multiplication result by the multiplier 2311. This LPF 2312 is a filter that does not allow frequencies twice the carrier wave in the received signal acquired by the reception information acquisition unit 22 to pass through.

The multiplier 2313 multiplies the received signal acquired by the reception information acquisition unit 22 by the second sine wave signal generated by the sine wave generation unit 233.

The LPF 2314 obtains a Q signal by removing high-frequency components from the multiplication result by the multiplier 2313. This LPF 2314 is a filter that does not allow frequencies twice the carrier wave in the received signal acquired by the reception information acquisition unit 22 to pass through.

The multiplier 234 multiplies the Q signal obtained by the LPF 2314 by the imaginary unit j.

The adder 235 adds the I signal obtained by the LPF 2312 to the signal multiplied by the multiplier 234 to obtain a demodulated signal (complex number).

The correlation calculation unit 24 calculates the propagation time based on the pseudorandom number sequence signal held by the transmission information holding unit 21 and the signal (demodulated signal) demodulated by the demodulation unit 23 in response to the transmission timing indicated by the externally input transmission timing signal. As shown in FIG. 5, the correlation calculation unit 24 has a cross-correlation calculation unit 241, an absolute value calculation unit 242, and a propagation time calculation unit 243.

The cross-correlation calculation unit 241 regards the signal demodulated by the demodulation unit 23 (demodulated signal) as a complex number according to the transmission timing indicated by the externally input transmission timing signal, and calculates the correlation function (complex correlation function) between the signal and the pseudo-random number sequence held by the transmission information holding unit 21.

The absolute value calculation unit 242 calculates the absolute value of the complex correlation function calculated by the cross-correlation calculation unit 241.

The propagation time calculation unit 243 calculates the propagation time by calculating the position of the peak of the absolute value calculated by the absolute value calculation unit 242.

Next, an example of the operation of the receiver 2 according to the first embodiment shown in FIGS. 1 to 5 will be described with reference to FIG.
The transmitter 1 generates a modulated signal by phase shift keying a pseudorandom number sequence signal onto a carrier wave and transmits the generated modulated signal as a wave such as an ultrasonic wave, and the receiver 2 receives this modulated signal.

Here, the modulation method used in the transmitter 1 is limited to phase shift keying (PSK).
PSK is a modulation method that changes the phase of a carrier wave with respect to an original signal. Examples of PSK include binary PSK (BPSK) and quadrature PSK (QPSK). Binary PSK is a modulation method that assigns phases of 0° and 180° to two values of the original signal, 0 and 1. Quadrature PSK is a modulation method that assigns phases in increments of 90°, such as 45°, 135°, 225°, and 315°, to four values of the original signal, 00, 01, 10, and 11 (binary). In addition, PSK also includes a method such as quadrature amplitude modulation (QAM) that modulates not only the phase but also the amplitude. In the following, BPSK will be mainly used for simplicity, but other modulation methods such as QPSK or QAM can be similarly applied.

The signal used by the transmitter 1 to apply modulation is a pseudorandom number sequence signal. As the pseudorandom number sequence signal, a signal such as an M sequence or Gold code may be used.

It should be noted that the pseudorandom number sequence has a period. It is desirable for the transmitter 1 to use only one period as the signal that is the source of modulation and to stop transmitting the modulated signal at other times, but it is also possible to transmit the signal continuously for multiple periods. However, when the transmitter 1 transmits the pseudorandom number sequence signal continuously for multiple periods, there is a possibility that multiple correlation peaks will appear for each period of the pseudorandom number sequence, so measures such as restricting the peak search range in order to find the true peak are necessary. If the pseudorandom number sequence signal is transmitted for only one period, such measures are not necessary. It is also possible for the transmitter 1 to transmit only two periods and combine the data for the two periods by post-processing to reduce noise (see, for example, non-patent document 2).
Otsuki et al., M-sequence two-period signal method for observing ultrasonic propagation conditions in the ocean, https://www.jstage.jst.go.jp/article/jasj/38/10/38_KJ00001453293/_pdf/-char/ja

Then, the receiver 2 calculates the propagation time of the modulated signal propagated as a wave such as an ultrasonic wave from the transmitter 1 to the receiver 2 based on the pseudorandom number sequence signal used by the transmitter 1 and the modulated signal (received signal) acquired by the reception information acquisition unit 22.

In an example of operation of the receiver 2 according to embodiment 1 shown in Figures 1 to 5, as shown in Figure 6, first, the reception information acquisition unit 22 acquires, as a reception signal, a modulated signal transmitted by the transmitter 1 and propagated as a wave such as an ultrasonic wave (step ST601).
Next, the demodulation unit 23 demodulates the reception signal acquired by the reception information acquisition unit 22 by performing quadrature detection (step ST602).
Next, receiver 2 stores the time-series data of the signal (demodulated signal) demodulated by demodulation section 23 (step ST603).

Furthermore, the transmission information holding section 21 acquires and holds a signal of a pseudo-random number sequence used in the transmitter 1 (step ST604).
Next, cross-correlation calculation section 241 regards the demodulated signal by demodulation section 23 as a complex number, and calculates a correlation function between the signal and the pseudo-random number sequence held by transmission information holding section 21 (step ST605).

Here, when the cross-correlation calculation unit 241 calculates the correlation, it is possible to consider a method of calculating the correlation in a modulated state. However, this method is not suitable because it has been pointed out that multiple peaks occur in the correlation result due to the influence of the carrier wave. In addition, if the correlation is calculated in a modulated state, the number of data for the correlation calculation increases, which increases the required memory amount and the amount of calculation.
Therefore, when calculating the correlation, the cross-correlation calculation unit 241 calculates the correlation between the demodulated signal and the pseudo-random number sequence signal. In this way, multiple peaks do not appear in the cross-correlation result, the sampling frequency can be lowered, and less memory is required.

Furthermore, when the modulation method is PSK or QAM, the demodulator 23 performs demodulation by performing quadrature detection on the received signal.
That is, the demodulator 23 generates an I signal and a Q signal by multiplying the modulated received signal by a first sine wave signal and a second sine wave signal, respectively, and passing the multiplied signals through an LPF. The first sine wave signal is a locally oscillating signal having the same frequency as the carrier wave in the received signal. The second sine wave signal is a locally oscillating signal having the same frequency as the first sine wave signal but with a phase lead of 90°.

On the other hand, when the modulation method is BPSK, the modulated phase is simple, only 0° and 180°, so quadrature detection is not necessary in principle. However, the demodulation unit 23 assumes that the carrier wave and the locally oscillating signal have different phases, so it also performs quadrature detection on the BPSK signal. Note that although the two locally oscillating signals (the first sine wave generated by the sine wave generating unit 232 and the second sine wave generated by the sine wave generating unit 233) are not phase-synchronized with the carrier wave, they have the same frequency. Cases where there is a difference in frequency will be discussed later.

When a PSK signal is subjected to quadrature detection, a demodulated result is obtained in the IQ space.
When a BPSK signal is demodulated, if the phases of the carrier wave and the local oscillation signal are aligned, the state changes on the I axis in the IQ space, as shown in Fig. 7. Also, if the phase of the carrier wave leads the phase of the local oscillation signal by φ, as shown in Fig. 8, the state changes along a straight line rotated by φ around the I axis with the origin as the center.

In general, PSK or QAM modulated in the amplitude direction is demodulated in IQ space when quadrature detection is performed, but as shown in Figure 9, if the phase of the carrier wave advances by φ relative to the phase of the local oscillator signal, the state will change to a position rotated by φ from the original point in IQ space with the origin as the center.

In this state, the signal is not in the correct position in IQ space, so if it were digital communication, the original signal could not be demodulated, but if the purpose is to measure the propagation time, there is no problem. This point will be explained below.

Points in IQ space can be expressed as complex numbers with the I axis as the real axis and the Q axis as the imaginary axis. For example, the point (I,Q) = (1,-1) is expressed as 1-j as a complex number.

If the phases of the carrier wave and the local oscillation signal are aligned, the point in the IQ space at the time of transmission will be the same as the point in the IQ space at the time of reception. On the other hand, if the phase of the carrier wave leads the phase of the local oscillation signal by φ, the point in the IQ space at the time of reception will be a point rotated by φ around the origin with respect to the point in the IQ space at the time of transmission. Expressing this as a complex number, if the point at the time of transmission is x, then the point at the time of reception is y = xe ^jφ .

Here, the transmitted signal and the received signal are considered as complex IQ signals.
The transmission signal is a pseudorandom number sequence arranged in an IQ space according to the modulation method. Because a pseudorandom number sequence is used, when the autocorrelation of the transmission signal is calculated, the correlation function peaks when there is no time lag and has small values elsewhere. In other words, the autocorrelation function (equation (1) below) of the transmission signal x(t) has a maximum value when there is no time lag (τ=0). In equation (1), C(τ) represents the autocorrelation function.

Here, if the phases of the carrier wave and the local oscillation signal are aligned, the transmitted signal x(t) and the received signal y(t) are similar signals that are shifted in time by the propagation time (y(t)=x(t- _t0 ), ( _t0 represents the propagation time)), and the cross-correlation function between the transmitted signal and the received signal (equation (2) below) is maximized when the time shift matches the propagation time (τ= _t0 ). Therefore, the propagation time can be found by searching for the peak of the cross-correlation function. In equation (2), C'(τ) represents the cross-correlation function between the transmitted signal and the received signal.

On the other hand, if the phase of the carrier leads by φ with respect to the phase of the local oscillation signal, the received signal is multiplied by ^ejφ (y(t)=x(t- _t0 ) ^ejφ ), and the cross-correlation function is also multiplied by ^ejφ (equation (3) below). In equation (3), C''(τ) represents the cross-correlation function when the phase of the carrier leads by φ with respect to the phase of the local oscillation signal.

Therefore, absolute value calculation section 242 calculates the absolute value of the correlation function calculated by cross-correlation calculation section 241 (step ST606).
Next, the propagation time calculation section 243 calculates the position of the peak of the absolute value calculated by the absolute value calculation section 242, thereby calculating the propagation time (step ST607).

That is, when the absolute value of the cross-correlation function is taken, it becomes the product of the absolute value of the cross-correlation when there is no phase shift and the absolute value of e ^jφ . Since the absolute value of e ^jφ is 1, it becomes as shown in the following equation (4).

Here, the cross-correlation is calculated as a complex number taking into account the phase shift, assuming that there is a phase shift between the local oscillation signal and the carrier wave, but compared with the correlation function calculated as a real number when there is no phase shift, the position where the absolute value of the correlation function is maximum is the same as the position where the correlation function is maximum when calculated as a real number. Therefore, by calculating the cross-correlation between the demodulated signal as a complex IQ signal and the pseudorandom number sequence signal to obtain the absolute value, the propagation time can be calculated from the position where the absolute value of the correlation function is maximum, even if the phase of the local oscillation signal is not aligned with the phase of the carrier wave.
This makes it possible to obtain the propagation time without matching the phase of the local oscillation signal to the phase of the carrier wave.

Note that in FIG. 6, if there are multiple pseudo-random number sequences, receiver 2 repeats the process of steps ST604 to ST607. Also, in FIG. 6, if there is only one pseudo-random number sequence, receiver 2 can omit the process of step ST603.

The demodulation unit 23 may use an existing method for quadrature detection, such as a method using a commonly used multiplication circuit and LPF as shown in FIG. 4, or a quadruple frequency sampling method (see, for example, non-patent document 3).
Furthermore, the cross-correlation calculation unit 241 may perform multiplication in frequency space by performing Fourier transform instead of the above-described method of calculating cross-correlation by convolution in time space. When the range in which correlation peaks appear is wide, the amount of calculation required is reduced by performing Fourier transform by FFT (Fast Fourier Transform) and multiplication in frequency space compared to convolution in time space.
Onioi et al., A Method for Constructing a Digital Quadrature Detector, Hiroshima Institute of Technology Research Bulletin Vol. 45 (2011), pp. 213-217, http://www.it-hiroshima.ac.jp/institution/library/pdf/research45_213.pdf

In addition, a case where the local oscillation signal and the carrier wave have different frequencies will be described below.
If the local oscillator signal and the carrier wave have different frequencies, the phase changes over time, and the demodulated signal rotates in the IQ space. If one period of a pseudorandom number sequence is used to calculate the propagation time, the problem is how much the position in the IQ space rotates during the time required to send out one period (= the time required to receive it). For example, if the position in the IQ space rotates 360° while sending out one period of a pseudorandom number sequence, the correlation calculation will work in a direction that strengthens the transmitted signal and the received signal at one time, and in a direction that weakens the transmitted signal and the received signal at another time, and the correlation results will cancel each other out, resulting in a small correlation result. In order to ensure a certain degree of correlation result, it is better to keep the amount of rotation of the position in the IQ space during the sending out of one period of the pseudorandom number to 180° or less. It is preferable to keep it to 90° or less. If the time it takes to send out one period of the pseudorandom number sequence is _Tn and the frequency difference between the carrier wave and the local oscillation signal is Δf, the amount of rotation in the IQ space is given by the following formula (5). In formula (5), Δθ represents the amount of rotation in the IQ space. This amount of rotation is suppressed to 180° (π), and preferably to 90° (π/2) or less.

The propagation time calculated by the propagation time calculation unit 243 can be converted to distance by multiplying it by the speed of the wave used for propagation (the speed of sound in the case of ultrasound). In other words, distance measurement can be performed by configuring a distance measurement device that adds a distance calculation unit that performs the above calculation to the propagation time measurement device according to embodiment 1.

Furthermore, the distance measurement device can perform positioning (position measurement) by measuring multiple distances. In this case, a different pseudo-random number sequence is used for each transmitter 1, and the receiver 2 stores a pseudo-random number sequence for each transmitter 1, so that the distance to each transmitter 1 can be measured. There may be multiple receivers 2, and each receiver 2 can measure the distance to each transmitter 1. This distance measurement device is particularly effective for indoor positioning (indoor positioning) where GPS cannot be used.
In Fig. 10 described later, only one correlation calculation unit 24 is provided and the pseudo-random number sequence is switched in sequence, but a separate correlation calculation unit 24 may be provided for each pseudo-random number sequence. In this case, it is possible to simultaneously measure the propagation time or distance from each transmitter 1 for the demodulated signal. Alternatively, the signal may be stored in memory in the portion of the demodulated signal between the demodulation unit 23 and the correlation calculation unit 24. In this case, it is possible to measure multiple propagation times or distances for the same reception by performing correlation calculations between different pseudo-random number sequences in sequence for the same demodulated signal stored in the memory.

It is also possible to obtain the flow velocity or flow rate from the propagation time calculated by the propagation time calculation unit 243. In other words, a flow velocity meter or flow rate meter may be configured by adding a flow velocity calculation unit or flow rate calculation unit that performs the above calculation to the propagation time measuring device according to embodiment 1.

In addition, as the wave transmitted and received between the transmitter 1 and the receiver 2, in addition to ultrasonic waves or sound waves, radio waves can also be used. When radio waves are used in the propagation time measuring device according to the first embodiment, the transmission timing cannot be electrically obtained, so it is appropriate to use them for positioning by the propagation time difference (TDOA) (similar to GPS). Since the difference in distance can be obtained by multiplying the propagation time difference by the wave speed, positioning can be performed using the principle of radio navigation. The method using TDOA can be used not only when radio waves but also when ultrasonic waves are used. In the TDOA method, it is not necessary to use the transmission timing to obtain the timing of transmission and reception. However, when using the TDOA method, it is necessary to obtain the difference in propagation time from each transmitter 1 for the same received signal. To this end, as described above, it is necessary to prepare a separate correlation calculation unit 24 for each pseudorandom number sequence and measure the propagation time simultaneously, or to store the demodulated signal in memory and then correlate the same demodulated signal with different pseudorandom number sequences to measure the propagation time between each transmitter 1. The propagation time calculated in this way is relative and includes an offset because the transmission timing is unknown, but the TDOA, which is the difference in propagation time between transmitters 1, can be calculated accurately because the offset is cancelled out by subtraction.

Next, a specific example of the propagation time measurement device shown in Figures 1 to 5 will be described with reference to Figure 10. The propagation time measurement device shown in Figure 10 uses ultrasonic waves as a wave motion and performs multiple distance measurements in the air at the same time.
In Fig. 10, an ultrasonic transmitter 1b that transmits ultrasonic waves of 40 kHz is used as the transmitter 1. Also in Fig. 10, an ultrasonic receiver 2b (MEMS microphone) that has sensitivity to and can receive ultrasonic waves of 40 kHz is used as the receiver 2. Hereinafter, the ultrasonic transmitter 1b and the ultrasonic receiver 2b are also referred to as ultrasonic sensors.

In addition, in FIG. 10, N ultrasonic transmitters 1b are provided. In FIG. 10, the first ultrasonic transmitter 1b and ultrasonic receiver 2b are placed a distance (1) apart and transmit and receive ultrasonic waves, the second ultrasonic transmitter 1b and ultrasonic receiver 2b are placed a distance (2) apart and transmit and receive ultrasonic waves, and the Nth ultrasonic transmitter 1b and ultrasonic receiver 2b are placed a distance (N) apart and transmit and receive ultrasonic waves. In addition, since the ultrasonic frequencies are the same in each ultrasonic transmitter 1b, the ultrasonic waves interfere with each other. Methods for preventing this interference include time division, frequency division, and code division.

Although time division is a reliable method, there are cases where it is not possible to shift the time due to time constraints.
Furthermore, frequency division cannot be supported by commercially available ultrasonic sensors since there are almost no frequency variations.
Therefore, in the following, the code division method will be used.

Code division uses pseudorandom number sequences and correlation to enable transmission and reception without interfering with transmissions using different pseudorandom number sequences.
Pseudo-random number sequences cannot be sent directly by ultrasonic sensors. Ultrasonic waves modulated with the pseudo-random number sequence as a signal using a 40 kHz carrier wave are transmitted and received. BPSK was used as the modulation method. Two types of 7-bit M-sequences were used for the pseudo-random numbers. Different types of M-sequences are uncorrelated, and will not interfere with each other even if used simultaneously. The period of the 7-bit M-sequence is 2 ⁷ -1=127.

Ultrasonic sensors have a narrow frequency band and cannot be deeply modulated. Experiments showed that the ultrasonic sensor used can perform phase shift keying every 20 carrier cycles (chip length = 20). One carrier cycle is 25 μs, so 20 carrier cycles are equivalent to 0.5 ms. The M-sequence has a period of 127, so it takes 63.5 ms to transmit one M-sequence period. The ultrasonic transmitter 1b starts transmitting ultrasonic waves from the transmission start timing, and ends transmitting ultrasonic waves when one M-sequence period has been transmitted. The graph in Figure 11 shows an example of a transmission signal. The signal is 0 before time 0 and after time 63.5 ms (0.635 s), and between those periods, 1 is assigned to the M-sequence 0, and -1 is assigned to the M-sequence 1, in order, at 0.5 ms intervals.

The ultrasonic receiver 2b is also provided with a demodulation unit 23. Here, the demodulation unit 23 obtains the I signal and the Q signal by using a quadruple frequency sampling method. With the quadruple frequency sampling method, it is necessary to correct the time difference between the I signal and the Q signal, but since the modulation frequency is low, once every 20 carrier wave periods, the time difference is not corrected here, but may be corrected. Also, although the quadruple frequency method is used here, normal quadrature detection may also be used.

In the quadruple frequency sampling method, an I signal and a Q signal are obtained every carrier wave period (25 μs).
The maximum distance to be measured is 10 m. If the speed of sound in air is 340 m/s, the maximum propagation time is 29.4 ms. Since it takes 63.5 ms to send one period of the M sequence, the maximum time required from the start of transmission to the end of reception is 29.4 ms + 63.5 ms = 92.9 ms. This is 3716 points for the I signal and Q signal. Considering that FFT is used to calculate correlation, a power of 2 is convenient for the number of data. Therefore, 4096 points are used for the I signal and Q signal. Since each point is 25 μs, 4096 points are equivalent to 102.4 ms (0.1024 seconds).

Figure 12 shows the waveform of the received signal when ultrasonic transmitter 1b and ultrasonic receiver 2b are installed 5 m apart and a signal modulated by BPSK of a 7-bit M sequence is sent from ultrasonic transmitter 1b. 0 on the time axis is the start of transmission, and the plot is up to 0.1024 seconds, when the I and Q signals should be extracted. Since the I and Q signals are extracted using the quadruple frequency sampling method, sampling is performed at 160 kHz at this stage. Since the propagation time at 5 m is 14.7 ms, the range from 14.7 ms to 78.2 ms (= 14.7 ms + 63.5 ms) contains the BPSK signal.

The demodulator 23 extracts the I and Q signals from the received signal using a quadruple frequency sampling method (see FIG. 13).
Then, the correlation calculation unit 24 regards these I and Q signals as complex received signals, calculates the cross-correlation between them and the M-sequence signal used during transmission, and obtains the absolute value of the correlation function, thereby making it possible to obtain the propagation time from the peak position (see FIG. 14).
In FIG. 14, the peak position is 15 ms, and multiplying this by the speed of sound of 340 m/s gives a distance of 5.1 m.

As described above, according to this embodiment 1, the receiver 2 includes a transmission information storage unit 21 that stores a pseudorandom number sequence signal used in phase shift keying for a carrier wave in the transmitter 1, a reception information acquisition unit 22 that acquires a reception signal that is a signal after phase shift keying transmitted by the transmitter 1, a demodulation unit 23 that demodulates the reception signal acquired by the reception information acquisition unit 22 by performing quadrature detection, a cross-correlation calculation unit 241 that regards the signal after demodulation by the demodulation unit 23 as a complex number and calculates a correlation function between the signal of the pseudorandom number sequence stored by the transmission information storage unit 21, an absolute value calculation unit 242 that calculates the absolute value of the correlation function of the complex number calculated by the cross-correlation calculation unit 241, and a propagation time calculation unit 243 that calculates the propagation time by calculating the position of the peak of the absolute value calculated by the absolute value calculation unit 242. As a result, the propagation time measurement device according to embodiment 1 can measure the propagation time without aligning the phase of the local oscillation signal with the phase of the carrier wave.

In addition, any of the components of the embodiments of the present invention may be modified or omitted within the scope of the invention.

1 Transmitter 2 Receiver 21 Transmission information storage unit 22 Reception information acquisition unit 23 Demodulation unit 24 Correlation calculation unit 231 Quadrature detection unit 232 Sine wave generation unit (first sine wave generation unit)
233 Sine wave generation section (second sine wave generation section)
234 Multiplier 235 Adder 241 Cross-correlation calculator 242 Absolute value calculator 243 Propagation time calculator 2311 Multiplier (first multiplier)
2312 LPF (1st LPF)
2313 Multiplier (second multiplier)
2314 LPF (2nd LPF)

Claims (3)

a transmission information storage unit for storing a pseudorandom number sequence signal used in phase shift keying for a carrier wave in the transmitter;
a reception information acquisition unit that acquires a reception signal that is a signal that has been subjected to phase shift keying and that is transmitted by the transmitter;
a demodulation unit that demodulates the reception signal acquired by the reception information acquisition unit by performing quadrature detection;
a cross-correlation calculation unit that regards the signal demodulated by the demodulation unit as a complex number and calculates a correlation function between the signal and the pseudo-random number sequence signal stored in the transmission information storage unit;
an absolute value calculation unit that calculates an absolute value of a correlation function of complex numbers calculated by the cross-correlation calculation unit;
a propagation time calculation unit that calculates a propagation time by calculating a peak position of the absolute value calculated by the absolute value calculation unit,
The demodulation unit is
a first sine wave generating unit that generates, as a local oscillation signal, a first sine wave signal having a frequency different from that of a carrier wave in the reception signal acquired by the reception information acquiring unit;
a first multiplier that multiplies the reception signal acquired by the reception information acquisition unit by a first sine wave signal generated by the first sine wave generation unit;
a first LPF that removes high frequency components from a multiplication result by the first multiplier to obtain an I signal;
a second sine wave generating unit that generates, as a local oscillation signal, a second sine wave signal having the same frequency as the first sine wave signal generated by the first sine wave generating unit and a phase that is advanced by 90°;
a second multiplier that multiplies the reception signal acquired by the reception information acquisition unit by a second sine wave signal generated by the second sine wave generation unit;
a second LPF that removes high frequency components from a multiplication result by the second multiplier to obtain a Q signal;
The transmitter transmits a signal that has been subjected to phase shift keying using a pseudorandom number sequence signal for only one period,
A receiver characterized in that the amount of rotation of the position of a demodulated signal in an IQ space during the time required for the transmitter to transmit the signal is kept to 180° or less without aligning the phase of a local oscillation signal with the phase of a carrier wave. 2. The receiver according to claim 1, wherein the waves transmitted and received between the transmitter and the receiver are ultrasonic waves. A transmission information storage unit stores a signal of a pseudorandom number sequence used in phase shift keying for a carrier wave in a transmitter;
A reception information acquisition unit acquires a reception signal which is a phase shift keying-modulated signal transmitted by the transmitter;
A demodulation unit demodulates the reception signal acquired by the reception information acquisition unit by performing quadrature detection;
a cross-correlation calculation unit that regards the signal demodulated by the demodulation unit as a complex number and calculates a correlation function between the signal and the pseudo-random number sequence signal stored in the transmission information storage unit;
An absolute value calculation unit calculates an absolute value of a correlation function of complex numbers calculated by the cross-correlation calculation unit;
A propagation time calculation unit calculates a position of a peak of the absolute value calculated by the absolute value calculation unit to calculate a propagation time,
The demodulation unit is
A step in which a first sine wave generating unit generates, as a local oscillation signal, a first sine wave signal having the same frequency as a carrier wave in the reception signal acquired by the reception information acquiring unit;
A first multiplier multiplying the reception signal acquired by the reception information acquisition unit by a first sine wave signal generated by the first sine wave generation unit;
A step of obtaining an I signal by removing high frequency components from a multiplication result by the first multiplier using a first LPF;
A step in which a second sine wave generating unit generates, as a local oscillation signal, a second sine wave signal having the same frequency as the first sine wave signal generated by the first sine wave generating unit and a phase that is advanced by 90°;
A second multiplier multiplying the reception signal acquired by the reception information acquisition unit by a second sine wave signal generated by the second sine wave generation unit;
A second LPF removes high frequency components from the multiplication result by the second multiplier to obtain a Q signal;
The transmitter transmits a signal that has been subjected to phase shift keying using a pseudorandom number sequence signal for only one period,
A receiving method characterized in that the amount of rotation of the position of a demodulated signal in an IQ space during the time required for the transmitter to transmit the signal is suppressed to 180° or less without aligning the phase of a local oscillation signal with the phase of a carrier wave.

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