JP2014220741A - Communication system, demodulation device, and modulation signal generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve detection accuracy of a peak of a correlation value of a code sequence.SOLUTION: A transmission device 10 modulates the same code sequence by using a data code to generate a modulation signal composed of a dummy symbol A, ranging symbol A, ranging symbol B, and dummy symbol B arranged in order on a time axis, and gives off sound of the modulation signal. When a reception device 20 collects the sound of the modulation signal propagated through a medium, a matching filter sequentially calculates a first correlation value by calculating correlation between the modulation signal and code sequence using a predetermined sampling frequency. The reception device 20 multiplies the first correlation value by a second correlation value obtained by giving time delay equal to a symbol period of the ranging symbol A to the first correlation value, suppresses a level of a peak of a correlation value caused by reflection sound and the like low, and emphasise a peak of the correlation value corresponding to a ranging symbol and detects it. The reception device 20 measures propagation time of the modulation signal in the medium on the basis of a result of the detection of the peak of the correlation value, and calculates a distance between the transmission device 10 and reception device 20.

Description

  The present invention relates to a technique for detecting a correlation between code sequences.

  In a communication system that performs spread spectrum communication, a correlation value between a spread spectrum signal (modulated signal) and a spread code is calculated, and data is demodulated based on a correlation peak detection result. Patent Document 1 discloses that a correlation between a modulation signal and a spread code is detected after performing a filtering process on an acoustic signal including the modulation signal using a high-pass filter (HPF).

JP 2009-115735 A

In the invention described in Patent Document 1, since the spreading code is superimposed on the acoustic signal, for example, in an environment where broadband noise is likely to occur or an environment where there is a lot of reflected sound (reverberation), the influence of disturbance such as broadband noise is affected. As a result, the peak level of the correlation value may decrease.
Accordingly, an object of the present invention is to improve the detection accuracy of the correlation value peak of the code sequence.

In order to solve the above-described problem, the communication system of the present invention generates a modulated signal in which the first symbol and the second symbol generated by modulating the same code sequence are sequentially arranged on the time axis, A sound emission control unit that emits the generated modulation signal; an acquisition unit that acquires the modulation signal emitted by the sound emission control unit; and the modulation signal acquired by the acquisition unit at a predetermined sampling frequency; A correlation detection unit that sequentially calculates a first correlation value by taking a correlation with the code sequence, a first correlation value supplied from the correlation detection unit, and the first correlation value to the first correlation value A multiplier that multiplies a second correlation value that has been given a time delay from the start time of the symbol to the start time of the second symbol, and a peak of the correlation value based on the multiplication result of the multiplier With a peak detector to detect .
In the communication system according to the present invention, the first correlation value, and the second correlation value obtained by adding a time delay corresponding to the time from the first symbol start time to the second symbol start time to the first correlation value, By multiplying, the peak of the correlation value corresponding to the first symbol and the second symbol can be emphasized while suppressing the level of the peak of the correlation value generated due to the influence of the reflected sound or the like.

In the communication system of the present invention, the sound emission control unit is disposed immediately after the third symbol and the third symbol, which are generated by modulating the code sequence, and are disposed immediately before the first symbol. The modulated signal including the fourth symbol rises from the start time of the third symbol for a time longer than the symbol period of the third symbol, and falls from the start time of the fourth symbol. A modulation signal subjected to window function processing by a window function may be generated, and the generated modulation signal may be emitted.
According to the present invention, it is possible to suppress a decrease in detection accuracy of a correlation value peak caused by signals before and after the first symbol and the second symbol.

In the communication system of the present invention, a specific process using a time until the modulation signal emitted by the sound emission control unit is acquired by the acquisition unit based on the detection result of the peak of the correlation value. You may make it provide the process execution part to perform.
ADVANTAGE OF THE INVENTION According to this invention, the precision of the process using the time after a modulation signal is emitted until it is acquired can be improved.

In this communication system, the sound emission control unit generates a modulation signal obtained by frequency-shifting a baseband signal obtained by modulating the code sequence using a plurality of carrier signals having different frequencies, and generates the generated modulation signal. And the said process execution part may perform the said process based on the peak of the said correlation value detected from the said modulation signal corresponding to each carrier signal.
According to the present invention, the processing using the time from when the modulation signal is emitted until it is acquired by preferentially using the peak of the correlation value detected from the modulation signal with less influence of reflected sound or the like. Accuracy can be improved.

  The demodulating device of the present invention includes an acquisition unit that acquires a modulated signal in which a first symbol and a second symbol generated by modulating the same code sequence are sequentially arranged on a time axis, and a predetermined sampling frequency. Taking a correlation between the modulation signal acquired by the acquisition unit and the code sequence, and sequentially calculating a first correlation value; a first correlation value supplied from the correlation detection unit; A multiplier that multiplies a first correlation value by a second correlation value that is a time delay corresponding to a time from the start time of the first symbol to the start time of the second symbol; A peak detection unit that detects a peak of the correlation value based on the multiplication result.

  The modulation signal generation apparatus of the present invention generates a modulation signal in which the first symbol and the second symbol generated by modulating the same code sequence are sequentially arranged on the time axis, and the generated modulation signal is A sound emission control unit that emits sound, sequentially calculating a first correlation value by taking a correlation between the modulation signal and the code sequence at a predetermined sampling frequency, and calculating the first correlation value; Based on the result of multiplying the first correlation value by the second correlation value obtained by giving a time delay corresponding to the time from the start time of the first symbol to the start time of the second symbol, the peak of the correlation value is obtained. A sound emission control unit that emits the modulated signal is provided in a medium in which a demodulator for detection is arranged.

  According to the present invention, it is possible to improve the detection accuracy of the correlation value peak of the code sequence.

1 is a diagram showing an overall configuration of a communication system according to an embodiment of the present invention. The block diagram which shows the detailed structure of the sound emission control part in the communication system. The figure explaining the signal which each part of the sound emission control part supplies. The figure explaining the modulation signal used for the ranging process in the communication system. The graph which shows the waveform of the modulation signal after the window function process which the sound emission control part emits. The block diagram which shows the detailed structure of the demodulation part in the communication system. The figure explaining the delay multiplication process in the demodulation part. The figure explaining the synthetic | combination correlation value after multiplying the correlation values of two symbols. The figure explaining the synthetic | combination correlation value in the environment where influence of reflected sound etc. is especially large. The figure explaining the modulation signal which the sound emission control part which concerns on the modification of this invention emits. The figure which shows the whole imaging | photography system which concerns on the modification of this invention. The figure explaining the other example of a window function process.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an overall configuration of a communication system 1 according to an embodiment of the present invention. As shown in FIG. 1, the communication system 1 is a communication system that includes a transmission device 10 and a reception device 20, and performs spread spectrum communication via sound (sound wave). The transmission apparatus 10 generates and transmits a modulation signal by a direct spread spectrum method. The receiving device 20 receives and demodulates the modulated signal transmitted by the transmitting device 10.

  The transmission device 10 includes a sound emission control unit 11, a transmission circuit unit 12, and a speaker 13. The sound emission control unit 11 functions as a modulation signal generation device that generates a modulation signal in a digital format obtained by modulating a spread code and supplies the modulation signal to the transmission circuit unit 12. The transmission circuit unit 12 converts the digital modulation signal into an analog format, performs amplification processing, and then supplies the signal to the speaker 13. The speaker 13 is a sound emitting unit that emits an analog modulation signal supplied from the transmission circuit unit 12 as sound (sound wave). The modulated signal emitted by the speaker 13 propagates through the medium (here, air) and reaches the microphone 21 of the receiving device 20.

  The receiving device 20 includes a microphone 21, a receiving circuit unit 22, and a demodulating unit 23. The microphone 21 is a sound collection unit that collects a modulation signal that is a sound (sound wave) emitted from the speaker 13 of the transmission device 10 and supplies the analog modulation signal to the reception circuit unit 22. The reception circuit unit 22 converts the modulation signal supplied from the microphone 21 from an analog format to a digital format at a predetermined sampling frequency, and supplies the converted signal to the demodulation unit 23. The demodulator 23 detects a spreading code included in the modulation signal supplied from the receiving circuit unit 22 and demodulates information data (a data code described later) superimposed on the spreading code.

Here, the communication system 1 is realized by a modulation signal transmission / reception device including all the components of the transmission device 10 and the reception device 20. In the communication system 1, for example, components other than the speaker 13 and the microphone 21 are provided in the same casing, the speaker 13 and the transmission circuit unit 12 are connected via, for example, a cable, and the microphone 21 and the reception circuit unit 22. Are connected via a cable, for example.
In the communication system 1 having the above-described configuration, the sound propagation time between the speaker 13 included in the transmission device 10 and the microphone 21 included in the reception device 20 is measured, and the distance between the speaker 13 and the microphone 21 is calculated. Distance measurement processing is executed. Details of the distance measurement processing will be described later.

FIG. 2 is a block diagram illustrating a detailed configuration of the sound emission control unit 11. As shown in FIG. 2, the sound emission control unit 11 includes a spread code generation unit 111, a data code input unit 112, a multiplication unit 113, a differential encoding unit 114, an LPF (Low-pass filter) 115, , A carrier signal generation unit 116, a multiplication unit 117, and a window function processing unit 118. FIG. 3 is a diagram for explaining signals supplied by each unit of the sound emission control unit 11.
The spread code generator 111 generates a spread code and supplies it to the multiplier 113. The spreading code is, for example, an M sequence, but may be another code sequence having a fixed cyclic period such as a Gold sequence. An example of the waveform of the spreading code is shown in FIG.
The data code input unit 112 receives a data code represented by either “0” or “1”. One symbol period of the input data code is adjusted to coincide with one cyclic period of the spread code. An example of the data code waveform is shown in FIG.

  The multiplication unit 113 modulates the data code supplied from the data code input unit 112 by multiplication with the spreading code supplied from the spreading code generation unit 111 and supplies the modulated spreading code to the differential encoding unit 114. To do. An example of the waveform of the spread code after modulation is shown in FIG. Here, the spread code is phase-modulated by the value of the data code, and the frequency spectrum of the data code is spread.

  The differential encoding unit 114 includes, for example, an XOR circuit and a delay unit, converts the spread code supplied from the multiplication unit 113 into a differential code, and supplies this differential code to the LPF 115 as a baseband signal. Differential encoding is a process of replacing the value of each chip of the spread code with a value representing a change from the previous chip from its absolute value. An example of the waveform of the differential code is shown in FIG.

The LPF 115 is, for example, a Nyquist filter, and is a filter that limits the band of the baseband signal from the differential encoding unit 114 and suppresses interference between chips.
An upsampling unit that upsamples the differential code may be provided between the differential encoding unit 114 and the LPF 115 in order to define the chip rate and bandwidth of the spreading code.

  The carrier signal generation unit 116 generates a carrier signal (that is, a carrier wave signal) that is a sine wave signal having a frequency fa, and supplies the carrier signal to the multiplication unit 117. The relationship on the frequency axis between the frequency components of the carrier signal and the spread code is shown in FIG.

The multiplication unit 117 multiplies the baseband signal supplied from the LPF 115 by the carrier signal supplied from the carrier signal generation unit 116 and supplies the modulation signal, which is the multiplication result, to the window function processing unit 118. That is, the multiplication unit 117 generates a modulation signal obtained by frequency shifting the baseband signal to the frequency fa on the high frequency side. The relationship on the frequency axis of the frequency component of the carrier signal after the frequency shift and the spread code is shown in FIG. Due to this frequency shift, the baseband signal is, for example, a relatively high frequency within the audible frequency, a frequency that is difficult to be heard by humans and that has a sense of discomfort or discomfort that is less audible (for example, 18 kHz), and that the audible frequency The frequency is shifted to a frequency within a band including the upper limit value (for example, 20 kHz).
In particular, when the baseband signal is frequency-shifted to a frequency equal to or lower than the upper limit value of the audible frequency, a configuration for reliably transmitting and processing a signal having a high frequency exceeding the audible frequency in the transmission device 10 and the reception device 20. It can be omitted. Note that the upper limit value of the audible frequency as the frequency for modulating the target signal described above may be determined based on the sampling frequency in the transmission device 10 and the reception device 20, for example, 22.05 kHz (the sampling frequency is 44.44 kHz). 1 kHz) or 24.0 kHz (when the sampling frequency is 48.0 kHz).

On the other hand, the reason why the baseband signal is desirably frequency shifted to a frequency of 18 kHz or more is as follows. In the literature (Kenji Kurata, Tazu Mizunami and Kazuma Matsushita, "Percentiles of normal hearing-threshold distribution under free-field listening conditions in numerical form," Acoust. Sci. & Tech. 26, 447-449 (2005).) The sound pressure required to perceive is described for each frequency (especially see the description in Fig. 2). In this document, the sound pressure (P _{5 in} the figure) required for 5% of humans to perceive 18 kHz sound is described as approximately 50 dBSPL. In other words, if the sound pressure level of a sound at 18 kHz is approximately 50 dBSPL, 95% of all humans cannot perceive or hardly perceive that sound. In an environment where humans are placed on a daily basis, background noise of about 40 to 50 dBSPL exists, but in order to use the communication system 1 in this environment, the transmission device 10 has a sound pressure higher than the sound pressure of the background noise. It is necessary to emit sound with sound pressure. For this reason, even when the baseband signal is frequency-shifted to 18 kHz and emitted at approximately 50 dBSPL, the sound having the frequency component of 18 kHz is not perceived by most humans (95%). In addition, a sound having a frequency higher than 18 kHz is more difficult to be perceived by humans. Further, as shown in the figure, for a sound having a frequency lower than 18 kHz, for example, a sound of 17 kHz, the threshold value of P ₅ described above is greatly reduced to about 30 dBSPL. so that the perceived by 25% or more of the human (corresponding to FIG P _25). For the above reasons, it can be said that the baseband signal is desirably frequency-shifted to a frequency of 18 kHz or higher.

  The window function processing unit 118 performs window function processing that multiplies the modulation signal supplied from the multiplication unit 117 by the window function W. The window function processing unit 118 supplies the modulated signal after the window function processing to the speaker 13 via the transmission circuit unit 12. The speaker 13 emits the modulation signal supplied from the window function processing unit 118. A detailed description of the window function processing will be given later.

FIG. 4 is a diagram for explaining a modulation signal generated by the sound emission control unit 11 of the transmission device 10 used for the distance measurement processing. In FIG. 4, the horizontal axis represents the time axis.
FIG. 4A is a diagram for explaining a temporal configuration of a modulation signal used for distance measurement processing. In this modulated signal, four symbols of a dummy symbol A, a distance measurement symbol A, a distance measurement symbol B, and a dummy symbol B are sequentially arranged on the time axis. The signal supplied to each part of the sound emission control part 11 becomes a structure shown to Fig.4 (a). In the following description, in the modulation signal supplied to the window function processing unit 118 of the sound emission control unit 11, the starting time point of the dummy symbol A is t1, the starting time point of the ranging symbol A is t2, and the ranging symbol B The start time is t3, the start time of the dummy symbol B is t4, and the end time of the dummy symbol B is t5. A signal corresponding to each of these four symbols is generated by modulating a spreading code for one period based on a 1-bit data code input to the data code input unit 112. Therefore, the period of each symbol (hereinafter referred to as “symbol period”) T corresponds to the time length of one cycle of the spread code. For example, the signal corresponding to each symbol is generated with a data code value “1”, but may be generated with “0”.

  The modulation signals corresponding to the ranging symbol A and the ranging symbol B are signals for which the correlation value indicating the correlation with the spread code is used for the ranging process. The modulation signal corresponding to the dummy symbol A is a signal used to suppress the influence of the signal before the ranging symbol A on the time axis on the ranging process. The modulation signal corresponding to the dummy symbol B is a signal used to suppress the influence of the signal after the ranging symbol B on the time axis on the ranging process. Details of the action of these dummy symbols will be described later.

FIG. 4B is a diagram for explaining the window function W used for the window function processing in the window function processing unit 118. The value of the window function W changes at the time points t1 to t5 as follows.
The window function W has a value “0” at the start time t1 of the dummy symbol A, rises from the time t1 with a time length longer than the symbol period T of the dummy symbol A, and has a value “1” at the time t2m. Become. The time point t2m is a time point after the start time point t2 of the distance measurement symbol A and before the start time point t3 of the distance measurement symbol B. Therefore, at the start time t2 of the distance measurement symbol A, the value of the window function is larger than “0” and smaller than “1” (for example, 0.7). The value of the window function W is “1” until the end point of the distance measurement symbol B (that is, t4) after the value of the time point t2m becomes “1”. The window function W falls from the start time t4 of the dummy symbol B at the same time length as the symbol period T of the dummy symbol B, and the value of the end time t5 of the dummy symbol B becomes “0”.
As described above, the value of the window function W gradually increases during the period from the time point t1 to t2m, and gradually decreases during the period from the time point t4 to t5.

FIG. 5 is a graph showing the waveform of the modulation signal output from the window function processing unit 118. In FIG. 5, the horizontal axis represents the time axis, and the vertical axis represents the amplitude.
As shown in FIG. 5, in the modulated signal after the window function processing using the window function W, the amplitude gradually changes in the period near the boundary between the distance measuring symbol and the dummy symbol. For this reason, in the modulated signal after the window function processing, it is possible to suppress the signal from becoming discontinuous near the boundary between the distance measuring symbol and the dummy symbol, and to suppress the generation of wideband noise due to the signal discontinuity. . On the other hand, when the modulation signal becomes discontinuous and wideband noise occurs, detection of the correlation for the ranging symbol A and the ranging symbol B may be hindered.

  Further, if the window function processing by the window function W is performed on the modulated signal, it corresponds to the dummy symbol A and the dummy symbol B with respect to the peak level of the correlation value corresponding to the ranging symbol A and the ranging symbol B. The peak level of the correlation value can be suppressed low. As shown in the column “Correlation peak” in FIG. 4B, if the value of the window function W at the start time t2 of the dummy symbol A is set to a small value less than “1”, the correlation value corresponding to the dummy symbol A The peak level is low. Further, since the value of the window function W is “0” at the time point t5, the peak level of the correlation value corresponding to the dummy symbol B becomes zero or almost zero. FIG. 4C is a diagram illustrating an example of a correlation value when a correlation value between the modulation signal emitted from the speaker 13 after the window function processing is performed by the window function processing unit 118 and the spread code is calculated. It is. As shown in FIG. 4C, the peak level of the correlation value of the dummy symbol appearing at time t2 is suppressed to be lower than the peak level of the correlation value of the ranging symbol appearing at time t3 and t4. I understand.

  On the other hand, as shown in FIG. 12A, when the rise of the window function value is completed in the period from time t1 to time t2, the value of the window function becomes “1” at time t2. In this case, as shown in FIG. 12A, the peak level of the correlation value corresponding to the dummy symbol appearing at the time point t2 and the peak level of the correlation value corresponding to the ranging symbol appearing at the time points t3 and t4 are obtained. It will be almost the same. FIG. 12B shows the correlation value when the correlation value between the modulation signal emitted from the speaker 13 after the window function processing is performed with the window function shown in FIG. 12A and the spread code is calculated. It is a figure which shows an example. As shown in the column “Correlation peak” in FIG. 12A and FIG. 12B, when the level of the peak of the correlation value corresponding to the dummy symbol is high, it is particularly affected by reflected sound (reverberation). When a plurality of high-level correlation value peaks appear, it is difficult to accurately determine which is the correlation value peak corresponding to the distance measurement symbol. If the window function processing by the window function W is performed, it is possible to prevent a large number of high-level correlation value peaks from appearing.

FIG. 6 is a block diagram illustrating a detailed configuration of the demodulation unit 23 of the reception device 20. As shown in FIG. 6, the demodulation unit 23 includes a modulation signal acquisition unit 231, a BPF (Band-pass filter) 232, a delay detection unit 233, an LPF 234, a spread code generation unit 235, a matched filter 236, A delay unit 237, a multiplication unit 238, a peak detection unit 239, and a distance measurement unit 240 are provided.
The modulation signal acquisition unit 231 acquires the sound (sound wave) emitted from the speaker 13 and propagated through the space as a modulation signal from the microphone 21. This modulated signal is converted into a digital format by the receiving circuit unit 22. The modulation signal acquisition unit 231 acquires modulation signals corresponding to the dummy symbol A, the ranging symbol A, the ranging symbol B, and the dummy symbol B illustrated in FIG.

  The BPF 232 is a band pass filter for extracting modulated signals corresponding to the dummy symbol A, the ranging symbol A, the ranging symbol B, and the dummy symbol B. The BPF 232 performs a filtering process in which a frequency band including the frequency fa of the carrier signal is set as a pass band, and excess signal components in other frequency bands are not passed. The modulation signal that has passed through the BPF 232 is supplied to the delay detection unit 233.

  The delay detection unit 233 includes, for example, a delay unit and a multiplication unit, and performs delay detection for converting the differentially encoded modulation signal into a modulation signal including the original spreading code. The delay time of the delay unit of the delay detection unit 233 is set to a time corresponding to one chip of the spread code in the transmission device 10. The delay detection unit 233 multiplies the sample for one chip that has passed through the BPF 232 by the sample for one chip of the delay unit.

The LPF 234 is, for example, a Nyquist filter, and removes a carrier component from the modulation signal supplied from the delay detection unit 233 to extract a baseband signal, and further removes an unnecessary noise component to improve an SN ratio. It is a filter.
The spreading code generation unit 235 generates the same spreading code as the spreading code generation unit 111 of the transmission apparatus 10 and supplies it to the matched filter 236.

  The matched filter 236 is a correlation detection unit that calculates a correlation value sequentially by obtaining a correlation between the modulation signal supplied from the LPF 234 and the spread code supplied from the spread code generation unit 235 at a predetermined sampling frequency. Function. The matched filter 236 is configured by an FIR filter using the spreading code supplied from the spreading code generator 235 as a filter coefficient. The matched filter 236 performs a convolution operation between the modulation signal supplied from the LPF 234 and the spreading code to calculate a correlation value. The sampling frequency of the spreading code used for the filter coefficient is, for example, the same as the sampling frequency in the transmission device 10. However, when upsampling of the differential code is performed in the transmission device 10, the sampling frequency after the upsampling is the same.

  The delay unit 237 gives a time delay corresponding to one symbol period T to the correlation value supplied from the matched filter 236 and supplies the correlation value to the multiplication unit 238. One symbol period T corresponds to the time length from the start time t2 of the distance measurement symbol A to the start time t3 of the distance measurement symbol B.

  The multiplication unit 238 performs a delay multiplication process of multiplying the first correlation value supplied from the matched filter 236 and the second correlation value given the time delay by the delay unit 237, and the result of the multiplication. The combined correlation value is supplied to the peak detector 239. That is, the delay unit 237 and the multiplication unit 238 multiply the correlation values calculated corresponding to the ranging symbol A and the ranging symbol B.

FIG. 7 is a diagram for explaining the above-described delay multiplication processing. FIG. 7A is a graph showing the correlation value between the ranging symbol A and the ranging symbol B. FIG. FIG. 7B is a graph showing a combined correlation value between the ranging symbol A and the ranging symbol B. In the graphs of FIGS. 7A and 7B, the horizontal axis represents the time axis, and the vertical axis represents the correlation value. FIG. 8 is a diagram illustrating the combined correlation value after multiplying the correlation values of two symbols that are continuous on the time axis.
As shown in FIG. 7A, before the delay multiplication process is performed, a plurality of correlation value peaks may appear due to the influence of reflected sound or the like. On the other hand, in the combined correlation value after the delay multiplication process shown in FIG. 7B is performed, only one correlation value peak (the maximum peak in the figure) is emphasized. This is because the correlation value peak corresponding to the distance measurement symbol A and the correlation value peak corresponding to the distance measurement symbol B are multiplied, so that these correlation value peaks are more emphasized. It is because of that. As described in FIG. 4, since the peak levels of the correlation values corresponding to the ranging symbol A and the ranging symbol B are high, as shown in FIG. 8, the combined correlation value of the peaks of these two correlation values is Particularly high level. On the other hand, when the peak of the correlation value appears due to the influence of disturbance such as reflected sound, the possibility that the peak of the correlation value appears also at the time after the one symbol period T is low. For this reason, the level other than the peak of the correlation value corresponding to the distance measurement symbol is suppressed to a low level by the delay multiplication process.

  Further, as shown in FIG. 8, the combined correlation value between the dummy symbol A and the ranging symbol A and the combined correlation value between the ranging symbol B and the dummy symbol B are also calculated by the delay multiplication process described above. However, as described with reference to FIG. 4, since the peak level of the correlation value of the dummy symbol A and the dummy symbol B is suppressed to a low level by the window function process, the peak value of the correlation value corresponding to the dummy symbol is not obtained in the combined correlation value. The level will also be suppressed low. That is, the value of the window function W is determined so that the peak of the correlation value corresponding to the dummy symbol is not emphasized by the delay multiplication process.

  The correlation peak detector 239 detects the peak of the correlation value based on the combined correlation value supplied from the multiplier 238. Here, the correlation peak detection unit 239 detects, for example, the peak of the correlation value at the maximum level that is equal to or greater than the threshold value. Here, the correlation peak detector 239 detects the peak of the correlation value labeled “maximum peak” in FIG.

The distance measurement unit 240 functions as a process execution unit that performs a distance measurement process based on the correlation value peak detected by the correlation peak detection unit 239. The distance measuring unit 240 calculates the distance d between the speaker 13 and the microphone 21 by the calculation of the following formula (1).
d = (x−la) × c × 1 / fs (1)

In Expression (1), x is a correlation value delay, and is the number of samples from when the modulation signal is emitted from the speaker 13 until the peak of the correlation value appears. This number of samples corresponds to the time length from when the modulation signal is emitted from the speaker 13 until it is picked up by the microphone 21 (that is, until it is acquired by the modulation signal acquisition unit 231). This corresponds to the time during which the modulated signal has propagated through the emitted space. la is a delay time corresponding to the latency of the entire communication system 1. c is the speed of sound in the space (medium) through which the modulation signal has propagated, and here, the speed of sound in the air may be set to 340 m / s or the like. fs is a sampling frequency. The latency la may be a value set at the design stage or the like, or may be a value measured at the time of execution of the distance measurement process. In the latter case, for example, the distance can be obtained by performing a distance measurement process while the speaker 13 and the microphone 21 are in contact with each other. That is, in this case, since d = 0, the latency la can be uniquely calculated by substituting the correlation value delay x, the sound speed c, and the sampling frequency fs into Equation (1). In other words, the latency la corresponds to the propagation time of the modulated signal in the communication system 1 other than the space (medium) between the speaker 13 and the microphone 21.
As described above, the distance measurement unit 240 performs distance measurement processing using the propagation time of the modulation signal in the medium (in the air). When the distance d is calculated, the distance measuring unit 240 notifies the user of the measurement result of the distance d between the speaker 13 and the microphone 21 using a method such as display output or audio output.

  In the communication system 1 according to the embodiment described above, a delay multiplication process for multiplying correlation values corresponding to two distance measurement symbols is performed to emphasize the peak of the correlation value and to cause an accident due to a disturbance such as a reflected sound. It is possible to suppress the peak of the correlation value generated in (1). At this time, the signals appearing before and after the modulation signal corresponding to the ranging symbol A and the ranging symbol B on the time axis are multiplied by the signal corresponding to the ranging symbol by the above-described delay multiplication processing, whereby the correlation is obtained. In order to avoid an increase in the level of the value, the transmission apparatus 10 gives modulation signals corresponding to the dummy symbol A and the dummy symbol B. Further, the transmission apparatus 10 uses signals corresponding to the dummy symbol A and the dummy symbol B before and after the ranging symbol A and the ranging symbol B on the time axis to correspond to the ranging symbols by the delay multiplication process. In order to avoid an increase in the level of the correlation value, the window function processing using the window function W is performed on the modulated signal before sound emission. With the above operation, according to the communication system 1, the distance measurement between the speaker 13 and the microphone 21 can be performed with high accuracy while suppressing the influence of disturbance of broadband noise or reflected sound (such as reverberation).

The present invention can be implemented in a form different from the above-described embodiment. The present invention can also be implemented in the following forms, for example. Further, the following modifications may be combined as appropriate.
In the embodiment described above, in the communication system 1, the baseband signal is shifted to the high frequency side using one carrier signal having the frequency fa, but a plurality of carrier signals having different frequencies may be used.
FIG. 9 is a graph illustrating a temporal change in the combined correlation value between the ranging symbol A and the ranging symbol B in an environment where the influence of disturbance such as reflected sound is large. The graph shown in FIG. 9 shows a graph showing temporal changes in the composite correlation value, and the value of the composite correlation value (peak value) and the peak location are indicated by line segments extending to the “◯” mark and the “◯” mark. Show.
As shown in FIG. 9, in an environment where the reflected sound or the like is particularly large, a large number of correlation value peaks may appear in the combined correlation value. In the example shown in FIG. 9, since the maximum peak level and the second peak level are very close, it is difficult to accurately determine which is due to the distance measurement symbol. Further, it may be difficult to adjust the position and orientation of the microphone 21 to alleviate the influence of these reflected sounds. In such a case, in the communication system 1, the maximum peak can be easily identified from the plurality of peaks by shifting the frequency of the baseband signal in advance using a plurality of carrier signals. .

  FIG. 10 is a graph illustrating an example of a modulated signal transmitted by the transmission device 10 in this modification. In the graph of FIG. 10, the horizontal axis represents the frequency axis, and the vertical axis represents the amplitude. In this example, the transmission apparatus 10 shifts the frequency of the baseband signal using three different carrier signals whose center frequencies are f01, f02, and f03. Even when these three modulated signals are emitted simultaneously, the transmitting apparatus 10 sets the frequency bands (center frequencies f01, f02, and f03) of the modulated signals on the frequency axis so that the modulated signals do not interfere with each other. Keep away.

Transmitting apparatus 10 emits a modulated signal modulated by each of the three carrier signals through speaker 13. Each unit of the receiving device 20 operates so as to detect the peak of the correlation value from each of the modulated signals modulated by these three carrier signals. Then, the distance measurement unit 240 uses a baseband signal that is frequency-shifted by at least one of the plurality of carrier signals based on the detection result of the peak of the correlation value by the peak detection unit 239. The distance measuring process is executed. At this time, the distance measurement unit 240 performs distance measurement processing based on the peak of the correlation value in which the difference between the maximum peak level and the second peak level is maximized. In addition to this, the distance measurement unit 240 performs measurement based on the peak of the correlation value at the maximum level when the level of the second peak is equal to or less than the threshold, for example, equal to or less than ½ of the maximum peak. Distance processing may be executed. In addition, the distance measurement unit 240 may determine whether the detection accuracy of the peak of the correlation value corresponding to the distance measurement symbol is good or bad with reference to the level of all peaks in the combined correlation value.
Further, the transmitting apparatus 10 does not separate the frequency bands of the plurality of modulation signals on the frequency axis as described above, but shifts the sound emission timing of each modulation signal by separating the plurality of modulation signals on the time axis. In this way, it is possible to prevent interference between the modulation signals.
In addition, although the example which uses 3 types of carrier signals was demonstrated here, 2 types or 4 types or more may be sufficient.

In the communication system 1 of the above-described embodiment, the distance d between the speaker 13 and the microphone 21 is measured using the propagation time of the modulated signal in the space. The process using this propagation time is not limited to the distance measurement process.
For example, if the distance d between the speaker 13 and the microphone 21 is known, the communication system 1 can measure the propagation speed of the modulated signal in space using the propagation time. Further, since the propagation speed of the sound wave in the space changes depending on the temperature, the communication system 1 can also measure the temperature of the space using the propagation time and the distance d. In this case, it is possible to grasp the temperature characteristics of the entire space in which the modulation signal has propagated, not the temperature at a local location in the space. That is, in the communication system 1, a process execution unit that executes a process of measuring a physical quantity that can be calculated using the propagation time may be provided instead of the distance measurement unit 240.

Further, the present invention can be applied to an imaging system having the following configuration.
FIG. 11 is a diagram illustrating an example of the configuration of an imaging system 300 to which the present invention is applied. FIG. 11 illustrates a plan view from above of a space such as a conference room where a telephone conference is held and an acoustic space 400 such as a hall where lectures and concerts are held.
The photographing system 300 includes a controller 200, speakers 13 a and 13 b, a microphone 21, photographing cameras 30 a to 30 c, and a display device 40.
The controller 200 includes a microcomputer having a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), and the sound emission control unit 11 and the demodulation unit 23 described in the above-described embodiment. A function equivalent to is realized. The controller 200 measures the distance d1 between the speaker 13a and the microphone 21 and measures the distance d2 between the speaker 13b and the microphone 21 by the same method as in the above-described embodiment. Here, the distance L between the speaker 13a and the speaker 13b is assumed to be known, and is set in advance in the controller 200, for example.
The photographing cameras 30 a to 30 c are moving image cameras that shoot moving images, and supply image signals indicating captured images to the controller 200. The display device 40 is a monitor, for example, and is a display device that displays images taken by the photographing cameras 30 a to 30 c under the control of the controller 200.

  In this modified example, the controller 200 repeatedly measures the distance d1 between the speaker 13a and the microphone 21 and the distance d2 between the speaker 13b and the microphone 21 (for example, measured at predetermined intervals), and the photographing camera. 30a-30c are controlled. When measuring the distances d1 and d2, the controller 200 specifies the position of the microphone 21, in other words, the position of the person (speaker or singer) having the microphone 21. That is, since the distance L is known, the controller 200 can specify the position of the microphone 21 by the triangulation method. Then, the controller 200 selects the optimum photographing cameras 30a to 30c for photographing the position of the microphone 21, and causes the display device 40 to display an image based on the image signal from the selected photographing camera. According to the photographing system 300, even if there is no person who operates the selection of the photographing cameras 30a to 30c, the photographing cameras 30a to 30c are appropriately selected. Can be continuously displayed on the display device 40.

Further, the controller 200 may control the photographing operation of the photographing cameras 30a to 30c based on the distances d1 and d2. In this case, the controller 200 may control panning and tilting, zoom-up / zoom-back, and the like of the photographing cameras 30a to 30c so that the photographing method is suitable for photographing the position of the microphone 21.
In this modification, the number of the photographing cameras 30a to 30c is three, but may be two or less or four or more.
In this modification, the number of speakers is two (speakers 13a and 13b) and the microphone is one (microphone 21). However, in the photographing system 300, the number of speakers is one and the number of microphones is two. Even in this case, if the distance between the speakers is known, the controller 200 can specify the position of the microphone 21. In the photographing system 300, there may be a plurality of speakers and microphones.

  A distance measuring system that performs a distance measuring process that calculates a distance on a two-dimensional plane by applying a distance measuring process that is executed by the imaging system 300 described above, or a distance measuring system that calculates a distance in a three-dimensional space. It is also possible to configure a distance measuring system that performs distance processing. In the case of the latter ranging system, there are three speakers and one microphone, or three speakers and one microphone, so that the microphone or speaker in a three-dimensional space can be used. The position can be specified.

Furthermore, when the distance measuring system of this modification is applied and the speaker and the microphone are integrated to measure the reflected sound from the object, the distance to the target other than the speaker and the microphone is calculated. A distance measuring system that performs distance processing can be configured. However, in this case, the microphone may collect the modulation signals reflected from the plurality of reflectors. At this time, a plurality of correlation value peaks may be detected. In the ranging system, a plurality of peaks are detected depending on the positional relationship between the target object to be measured and other reflectors (non-target objects). Ranging processing may be performed by selecting an appropriate correlation value peak from the time series of correlation value peaks. In this distance measuring system, for example, when the distance to the target is closer than the distance to the non-target, the distance measuring process may be performed based on the peak of the correlation value detected first.
As described above, according to the present invention, the distance measurement system that measures the distance propagated by the sound represented by the modulation signal from the position of the speaker to the position of the microphone and identifies the position on the path through which the sound has propagated. Can be configured.

  Further, the window function processing performed by the window function processing unit 118 may be anything that can suppress at least the peak level of the correlation value of the dummy symbol A and the dummy symbol B. For example, the fall of the window function W may be completed in a period shorter than one symbol period from the start time t4 of the dummy symbol B or in a period longer than one symbol.

In the communication system 1 of the above-described embodiment, two distance measurement symbols are continuous on the time axis, but three or more distance measurement symbols may be continuous. When n (where n ≧ 3) ranging symbols are consecutive, the receiving device 20 performs correlation multiplication by multiplying the correlation value peaks corresponding to the n ranging symbols by a delay multiplication process. Can be emphasized. At this time, the receiving apparatus 20 delays the k-th (but 1 ≦ k ≦ n) ranging symbol from the beginning by a time length that is (n−k) times the symbol period T, and measures the n-th measurement symbol. What is necessary is just to perform the delay multiplication process which multiplies with the correlation value of a distance symbol. Therefore, the demodulator 23 may include (n−1) delay units 237.
As described above, the transmission apparatus 10 is expected to further improve the accuracy of detection of the correlation value peak by the distance measurement symbol by emitting the modulation signal by continuing three or more distance measurement symbols on the time axis. it can.

  Further, in the communication system 1, even when a plurality of ranging symbols are not consecutive on the time axis, by performing a delay multiplication process that multiplies the correlation value peaks corresponding to the plurality of ranging symbols. The peak of the correlation value corresponding to the ranging symbol can be emphasized.

  The sound emission control unit 11 of the transmission apparatus 10 according to the above-described embodiment modulates the data code with the spread code every time the modulated signal is emitted, and performs window function processing on the modulated signal obtained by this modulation. Thus, a modulation signal to be supplied to the speaker 13 is generated. Instead of this configuration, the sound emission control unit 11 stores in advance a sound emission data serving as a basis for generating a modulation signal to be supplied to the speaker 13, reads out the sound emission data from this memory, A modulation signal to be supplied to the speaker 13 may be generated. In this case, the sound emission control unit 11 does not have to realize the function of modulating the data code with the spread code and the function of performing the window function processing on the modulation signal obtained by modulating the data code with the spread code. Regardless of the configuration, the sound emission control unit 11 generates a modulation signal that generates a modulation signal in which the dummy symbol A, the ranging symbol A, the ranging symbol B, and the dummy symbol B are sequentially arranged on the time axis. Functions as a device.

The communication system 1 may not include a configuration for shifting the baseband signal to the high frequency side. For example, a modulation signal that is a baseband signal may be emitted.
In the communication system 1, for example, in an environment that is not easily affected by disturbance such as reflected sound, the modulation signal corresponding to the dummy symbol may not be added before and after the modulation signal corresponding to the ranging symbol.
The medium that propagates the modulation signal emitted by the transmission device 10 is not limited to a gas such as air, but may be a solid or a liquid. In this case, the transmission device 10 may include a sound emitting device suitable for a medium that propagates a modulation signal, such as using an actuator (vibrator) that vibrates the medium by vibration instead of the speaker 13. The receiving device 20 may be provided with a sound collecting device suitable for a medium through which a modulation signal propagates, such as using a vibration pickup (vibration detector) instead of the microphone 21.

Further, when the communication system 1 is configured to be distributed between the transmission device 10 and the reception device 20, it is necessary for the reception device 20 to specify the timing when the modulation signal is emitted by the transmission device 10. The specific method of specifying the sound emission timing in this case is not particularly limited. For example, the transmission device 10 is connected to the reception device 20 via a communication path such as a cable, and the transmission device 10 communicates with the reception device 20 through this communication. The sound emission time may be notified via the road. Alternatively, the reception device 20 may specify the sound emission time of the transmission device 10 by instructing the sound emission timing to the transmission device 10 via this communication path to emit sound.
In the present invention, a signal obtained by modulating a spread code with a data code may be superimposed on an acoustic signal representing a sound wave such as a musical tone signal or an ultrasonic signal.

  The functions realized by the transmission device 10 or the reception device 20 can be realized by one program or a combination of a plurality of programs, or can be realized by one hardware resource or a combination of a plurality of hardware resources. For example, a modulation signal generation device corresponding to the sound emission control unit 11 or a demodulation device corresponding to the demodulation unit 23 may be realized by executing a program on a dedicated processor or a computer. When the function of the sound emission control unit 11 or the demodulation unit 23 is realized by using a program, the program stores a magnetic recording medium (magnetic tape, magnetic disk (HDD (Hard Disk Drive), FD (Flexible Disk), etc.)). It may be provided in a state stored in a computer-readable recording medium such as an optical recording medium (such as an optical disk), a magneto-optical recording medium, or a semiconductor memory, or may be distributed via a network. The present invention is also implemented as a modulation signal generation method for generating a modulation signal, or a correlation peak detection method (or demodulation method) that emphasizes and detects the peak of the correlation value using the delay multiplication process described above. You can also.

DESCRIPTION OF SYMBOLS 1 ... Communication system, 10 ... Transmission apparatus, 200 ... Controller, 11 ... Sound emission control part, 111 ... Spreading code generation part, 112 ... Data code input part, 113 ... Multiplication part, 114 ... Differential encoding part, 115 ... LPF, 116 ... carrier signal generator, 117 ... multiplier, 118 ... window function processor, 12 ... transmitter circuit, 13, 13a, 13b ... speaker, 20 ... receiver, 21 ... microphone, 22 ... receiver circuit, 23: Demodulation unit, 231 ... Modulation signal acquisition unit, 232 ... BPF, 233 ... Delay detection unit, 234 ... LPF, 235 ... Spread signal generation unit, 236 ... Matched filter, 237 ... Delay unit, 238 ... Multiplication unit, 239 ... Peak detecting unit, 240 ... Distance measuring unit, 30a, 30b, 30c ... Shooting camera, 300 ... Shooting system, 40 ... Display device, 400 ... Acoustic space

Claims (6)

A sound emission control unit that generates a modulation signal in which the first symbol and the second symbol generated by modulating the same code sequence are sequentially arranged on the time axis, and emits the generated modulation signal;
An acquisition unit for acquiring the modulated signal emitted by the sound emission control unit;
A correlation detection unit that sequentially calculates a first correlation value by taking a correlation between the modulation signal acquired by the acquisition unit and the code sequence at a predetermined sampling frequency;
A first correlation value supplied from the correlation detection unit, and a first delay value obtained by giving a time delay corresponding to a time from a start time point of the first symbol to a start time point of the second symbol to the first correlation value. A multiplier for multiplying the correlation value of 2;
A peak detection unit that detects a peak of a correlation value based on a multiplication result by the multiplication unit. The sound emission control unit
A modulated signal generated by modulating the code sequence and including a third symbol arranged immediately before the first symbol and a fourth symbol arranged immediately after the second symbol, A modulated signal is generated from the start time of the third symbol by a window function that rises with a time length longer than the symbol period of the third symbol and falls from the start time of the fourth symbol. The communication system according to claim 1, wherein the generated modulation signal is emitted. Based on the detection result of the peak of the correlation value, a process execution unit that executes a specific process using a time until the modulation signal emitted by the sound emission control unit is acquired by the acquisition unit The communication system according to claim 1 or 2. The sound emission control unit
Generating a modulation signal obtained by frequency-shifting the baseband signal obtained by modulating the code sequence with a plurality of carrier signals having different frequencies, and emitting the generated modulation signal;
The process execution unit
The communication system according to claim 3, wherein the processing is executed based on a peak of the correlation value detected from the modulated signal corresponding to each carrier signal. An acquisition unit that acquires a modulated signal in which a first symbol and a second symbol generated by modulating the same code sequence are sequentially arranged on the time axis;
A correlation detection unit that sequentially calculates a first correlation value by taking a correlation between the modulation signal acquired by the acquisition unit and the code sequence at a predetermined sampling frequency;
A first correlation value supplied from the correlation detection unit, and a first delay value obtained by giving a time delay corresponding to a time from a start time point of the first symbol to a start time point of the second symbol to the first correlation value. A multiplier for multiplying the correlation value of 2;
And a peak detector that detects a peak of a correlation value based on a multiplication result by the multiplier. A sound emission control unit that generates a modulation signal in which a first symbol and a second symbol generated by modulating the same code sequence are sequentially arranged on the time axis, and emits the generated modulation signal. And
A first correlation value is sequentially calculated by taking a correlation between the modulated signal and the code sequence at a predetermined sampling frequency, and the calculated first correlation value and the first correlation value are converted into the first symbol. In a medium in which a demodulator for detecting the peak of the correlation value is arranged based on the result of multiplication with the second correlation value given a time delay of the time from the start time of the second symbol to the start time of the second symbol A modulation signal generation device comprising: a sound emission control unit that emits the modulation signal.