JP5487989B2 - Information transmission device using sound - Google Patents

Description

  The present invention relates to an information transmission apparatus that mainly transmits codes using sound.

  When transmitting information using sound, it is conceivable that information is spread-modulated with a spreading code and emitted as sound.

  Such a technique has not been proposed in the past, and there have been those shown in Patent Documents 1 and 2 as code transmission techniques that use sound as a transmission medium. The method of Patent Document 1 is a method in which a carrier wave in the audible sound band is modulated with a baseband signal, and a masker sound is added to the modulated signal to transmit it with difficulty in hearing. The method of Patent Document 2 is a method of embedding a digital watermark in an audio signal using amplitude modulation.

JP 2007-104598 A

JP 2006-251676 A

  In the case of spread modulation of information, in order to improve the transmission efficiency of information, it is conceivable to multiplex spread codes and transmit a plurality of pieces of information in parallel. However, since spread modulation using sound cannot increase the chip rate compared to radio waves, the period of the spread code cannot be increased in order to improve transmission efficiency. A short cycle spread code does not have a high autocorrelation characteristic, and when multiplexed, the correlation characteristic of each spread code deteriorates, making it difficult to ensure the accuracy of demodulation.

  An object of the present invention is to provide an information transmission apparatus capable of performing highly reliable and efficient information transmission using sound.

According to the first aspect of the present invention, a plurality of spreading code generating units that generate a plurality of spreading codes, a data symbol input unit that sequentially inputs data symbols, and the plurality of data symbols that are sequentially input from the data symbol input unit. A spread modulation unit that sequentially selects a spread code from among the spread codes and provides a dummy section at the boundary of the sequentially selected spread code, and an acoustic output unit that outputs the spread code output from the spread modulation unit as sound , Provided.
The invention according to claim 2 is characterized in that the spread modulation section provides the dummy section at the boundary only when the spread code selected immediately before is different from the spread code selected this time.
According to a third aspect of the present invention, in the first and second aspects of the present invention, a blank signal having a continuous zero value is inserted into the dummy section.
According to a fourth aspect of the present invention, in the first and second aspects of the invention, a signal having a waveform obtained by cross-fading the spreading code selected immediately before and the spreading code selected this time is inserted into the dummy section. Features .

  According to the present invention, by selecting a spread code according to a data symbol, a transmission apparatus that spreads the data symbol uses a plurality of spread codes by providing a dummy section or performing window function processing. Therefore, it is possible to transmit highly reliable data symbols by preventing the correlation characteristics from being disturbed.

The figure which shows the structure of the transmitter of an acoustic communication system with which this invention is applied, and a receiver The figure which shows the structure of the data superimposition part of the said transmitter. The figure which shows the structure of the modulation part of a transmitter The figure which shows the structure of the differential encoding part of a transmitter. The figure which shows the example of the spreading code sequence in which the dummy data was inserted The figure which shows the example of the selection rule of the insertion part of dummy data The figure which shows the structure of the demodulation part of the said receiver The figure which illustrates the input signal of the matched filter of a receiver, a filter coefficient, and an output signal Comparison of differences in output signal waveforms when a signal with dummy data inserted and a signal without insertion are input to the matched filter The figure which shows the determination rule of the code | symbol determination part of a receiver The figure explaining the procedure which creates dummy data by crossfading the spreading code before and behind The figure which shows the actual waveform example of the spreading code sequence which inserted the dummy data which cross-fade the spreading code before and behind Diagram showing signal waveform with window function processing applied to spreading code

  An acoustic communication system and an acoustic communication system according to an embodiment of the present invention will be described with reference to the drawings.

≪Acoustic communication system≫
FIG. 1 is a diagram showing a configuration of an acoustic communication system according to an embodiment of the present invention. This acoustic communication system includes a transmission device 1 and a reception device 2.

  The transmission device 1 includes a data superimposing unit 10, an analog circuit unit 11, and a speaker 12. The data superimposing unit 10 is a circuit unit that performs a diffusion process on the data code D and superimposes the data code D on the high frequency range of the acoustic signal S such as music or voice. Details of the configuration and operation of the data superimposing unit 10 will be described later.

  The analog circuit unit 11 includes a D / A converter and an audio amplifier. The analog circuit unit 11 converts the digital composite signal output from the data superimposing unit 10 into an analog signal, amplifies the signal, and supplies the analog signal to the speaker 12. The speaker 12 emits the synthesized signal input from the analog circuit unit 11 as sound. The emitted synthesized signal sound propagates through the space and reaches the microphone 22 of the receiving device 2.

  The receiving device 2 includes a microphone 22, an analog circuit unit 23, and a demodulation unit 21. The analog circuit unit 23 includes an amplifier that amplifies the audio signal picked up by the microphone 22 and an A / D converter that converts the audio signal into a digital signal. The demodulation unit 21 is a circuit unit that detects a spread signal included in the collected audio signal and demodulates the data code D superimposed on the spread signal. Details of the configuration and operation of the demodulator 21 will be described later.

≪Data superimposition part≫
FIG. 2 is a diagram illustrating a configuration example of the data superimposing unit 10 of the transmission device 1. The data superimposing unit 10 performs a spreading process on the data code D by selecting and outputting one spreading code from a plurality of spreading codes according to the input data code D. The data superimposing unit 10 provides a dummy section between these two spread codes when the spread code selected immediately before and the spread code selected this time are different according to the data code D sequentially input. insert. This prevents an error in data demodulation due to a disturbance in correlation characteristics between the two spreading codes.

In FIG. 2, an acoustic signal input unit 31 inputs an acoustic signal S. The input acoustic signal S is cut off at high frequencies by the LPF 32. The cut-off frequency of the LPF 32 is determined based on the audibility and the bandwidth allocated to the modulation signal. If the cut-off frequency is too low, the sound quality of the acoustic signal S deteriorates. At the same time, if the band frequency of the modulation signal is lowered in accordance with the low cut-off frequency, the modulation signal is likely to be attached to the ear for the listener's sense of hearing. Conversely, if the cut-off frequency of the LPF 32 is too high, the modulation signal band cannot be widened, and the transmission quality of the data code is lowered. Therefore, the cutoff frequency of the LPF 32 is determined in consideration of the audibility evaluation of the acoustic signal that has passed through the LPF 32, the required bandwidth of the modulation signal, and the like. Note that the LPF 32 may be omitted when the input acoustic signal has a frequency component only in the mid-low range and no component exists in the high range.
The gain of the acoustic signal S whose high frequency is cut by the LPF 38 is adjusted by the gain adjusting unit 33. The acoustic signal S whose gain has been adjusted is input to the adder 34.

  The data code input unit 35 reads the data code D and inputs it to the modulation unit 37. The spread code generation unit 36 includes a spread code A generation unit 36A and a spread code B generation unit 36B. Two types of spread codes A and B are generated in parallel and in synchronization with each other and input to the modulation unit 37. As the spreading codes A and B, pseudo-random code sequences having a fixed cyclic period such as M series are used. As the two spreading codes A and B, a combination of pseudo-random code sequences with low cross-correlation is selected.

  The modulation unit 37 receives two symbols of the data code from the data code input unit 35 every one cycle of the spread code, and based on the input two-symbol data code D, the positive phase spread code A is inverted ( A spreading process for selecting and outputting one of the spreading code A having the reverse phase, the spreading code B having the normal phase, or the inverted spreading code B having the reverse phase is performed.

  In addition, the modulation unit 37 generates a dummy data insertion signal according to the difference between the spreading code selected corresponding to the immediately preceding 2-symbol data code and the spreading code selected corresponding to the current 2-symbol data code. Output. The dummy data insertion signal is input to a dummy data insertion unit 44 described later. When the dummy data insertion signal is input, the dummy data insertion unit 44 inserts dummy data between the immediately preceding spreading code and the current spreading code. When outputting the dummy data insertion signal, the modulation unit 37 delays the output of the current spreading code by the length of the dummy data.

  FIG. 3A shows a configuration of the modulation unit 37. FIG. 3B is a diagram illustrating a selection rule of the selector 70 of the modulation unit 37. The modulation unit 37 includes an inverter 71A that inverts the phase of the spreading code A, an inverter 71B that inverts the phase of the spreading code B, and a selector 70 that selects the spreading code based on the data code D. Based on the input two-symbol data code, the selector 70 has a positive phase spreading code A (A), an inverted spreading code A (barA), a positive phase spreading code B (B), and an inverted spreading code. Select one of B (barB). A spreading code selection rule based on a 2-bit transmission symbol is as shown in FIG.

  Further, when the spreading code selected immediately before is different from the spreading code selected this time, the selector 70 outputs a dummy data insertion signal, and only the length of the dummy data (one cycle of the spreading code in this embodiment) is output. Delay the output of the currently selected spreading code. If the spreading code selected immediately before is the same as the spreading code selected this time, the spreading code selected this time is output without outputting the dummy data insertion signal. The spread code output from the modulation unit 37 (selector 70) is differentially encoded by the differential encoding unit 38 and then input to the dummy data insertion unit 44. The dummy data insertion unit 44 will be described later.

  The spread code MPN selected and modulated (hereinafter simply referred to as modulation) based on the 2-bit data code D by the modulation unit 37 is converted into a differential code DMPN by the differential encoding unit 38. The differential encoding process 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. By this differential encoding, the symbol can be demodulated with high accuracy using delay detection even if there is no clock that is accurately synchronized with the transmission side on the reception side.

  FIG. 4 is a diagram illustrating an example of the differential encoding unit 38. The differential encoding unit 38 includes an XOR circuit 45 to which the spread code MPN is input to one input terminal, and a one-chip delay circuit that delays the output of the XOR circuit 45 by one chip and returns it to the other input terminal of the XOR circuit 45 46. By feeding back the output of the XOR circuit 45 with a delay of one chip, the XOR circuit 45 outputs the comparison result between the input spread code MPN and the output of the XOR circuit 45 one clock before as a differential code DMPN. That is, in the differential code DMPN, the absolute value of each chip of the spread code MPN is replaced with the presence or absence of a phase change from the chip of the immediately preceding differential code DMPN. As a result, the spread code MPN can be restored on the receiving side by comparing two consecutive chips. The differential code DMPN is converted into a binary signal of -1,1.

  The spread code (DMPN) differentially encoded by the differential encoding unit 38 is input to the dummy data insertion unit 44. When the dummy data insertion signal is input, the dummy data insertion unit 44 is located at the boundary between the immediately preceding spreading code (differential coded spreading code) and the current spreading code (differential coded spreading code). Insert dummy data.

  FIG. 5 shows an example of a spread code string in which dummy data is inserted. In this example, blank data for one cycle is inserted as dummy data. The upper part of the figure shows a spreading code string before dummy data is inserted. The lower part of the figure shows the spreading code string after the dummy data is inserted. In the upper spread code string, dummy data (0 data) is inserted at the boundary point of the spread code period to separate each spread code so that the detection value is not disturbed during correlation detection.

  Insertion of dummy data is performed based on a dummy data insertion signal that is output when two consecutive spreading codes are switched (for example, when switching from spreading code A to spreading code B). Therefore, in this embodiment, dummy data is inserted when two consecutive spreading codes are switched. In the case of simplifying the process, dummy data may be inserted at the boundary of all spreading codes regardless of whether or not there is code switching.

  Further, dummy data may be inserted only when there is a possibility that the correlation characteristic is disturbed, instead of inserting dummy data at all when the spreading code is switched. That is, a combination with low cross-correlation is used for spreading code A and spreading code B. Therefore, as shown in FIG. 6, when the spread code A and the spread code B are switched to each other, and when the spread code barA and the spread code barB are switched to each other, it is considered that the correlation characteristics are not disturbed so much. When switching from spreading code A or spreading code B to spreading code barA or spreading code barB without switching and when switching from spreading code barA or spreading code barB to spreading code A or spreading code B, the correlation characteristics are greatly disturbed. As an alternative, dummy data may be inserted.

  If dummy data is inserted in all the boundaries of the spreading code period, the correlation characteristics can be maintained well and the communication reliability can be improved, but the transmission efficiency is lowered. On the other hand, if the number of places where dummy data is inserted is reduced, the transmission rate can be increased, but the communication reliability is lowered. Where dummy data is inserted may be determined by a trade-off between transmission efficiency and communication reliability.

  The dummy data is not limited to the blank data, and the length is not limited to one spread code period.

  The differential code DMPN in which dummy data is appropriately inserted in the dummy data insertion unit 44 is input to the upsampling unit 39. The upsampling unit 39 upsamples the input code string. Based on the chip rate of the spread code PN generated by the spread code generation unit 36 and the upsampling rate in the upsampling unit 39, the chip rate and bandwidth of the spread code to be transmitted (sound emission) are determined.

  The upsampled signal (differential code DMPN) is input to the LPF 40. The LPF 40 is a filter that limits the band of the baseband signal while suppressing inter-chip interference, and is called a Nyquist filter. The Nyquist filter is a filter having a characteristic that an impulse response rings at a symbol rate (passes through 0), and is configured by an FIR filter generally called a cosine roll-off filter. The order of the filter, the roll-off rate α, etc. are determined according to the conditions to be applied.

  In this embodiment, since filtering is also performed by the LPF 54 (see FIG. 7) on the reception side, each of the root raised cosine roll-off is set so that the LPF 40 and the LPF 54 on the reception side become a complete Nyquist filter. -Consists of filters.

  The signal subjected to band limitation and waveform shaping by the LPF 40 is multiplied by a carrier signal in the multiplier 42 and is frequency-shifted to a high frequency. The frequency of the carrier signal generated by the carrier signal generation unit 41 is arbitrary, but the band of the spread code whose frequency is shifted is equal to or higher than the cutoff frequency of the LPF 32, the movable frequency band of an acoustic device such as a speaker and a microphone, and the signal The digital signal processing unit (CODEC) including compression is set to fall within the range of the coding frequency band.

  The gain adjustment unit 43 adjusts the gain of the modulation signal MDMPN shifted to the high frequency range. The gain-modulated modulation signal MDMPN is added and synthesized by the adder 34 with the acoustic signal S. This synthesized signal is output to the outside. The gain of the gain adjusting unit 43 is determined based on the sound output sound pressure level allowed in the environment to be applied and the system, the required propagation distance, the audibility evaluation, and the like. Note that the gain of the gain adjusting unit 43 may be adaptively controlled according to the level of the acoustic signal S output from the LPF 32. For example, since the masking effect can be expected when the level of the acoustic signal S is high, the level of the modulation signal MDMPN is also increased to increase the gain against noise, and when the level of the acoustic signal S is small, the acoustic signal S is audible. It is also possible to control to lower the level of the modulation signal MDMPN so as not to deteriorate.

≪Demodulation part≫
FIG. 7 is a diagram illustrating a configuration example of the demodulation unit 21 of the reception device 2. The demodulating unit 21 receives a composite signal collected by the microphone 22 and A / D converted by the analog circuit unit 23. The input composite signal is input to the HPF 51. The HPF 51 is a filter for removing the acoustic signal component from the synthesized signal and extracting the spread signal component MDMPN frequency-shifted by the carrier signal. The cutoff frequency of the HPF 51 is set to the lower limit frequency of the modulation signal band. The modulation signal MDMPN extracted by the HPF 51 is input to the delay unit 52 and the multiplier 53. The delay time of the delay unit 52 is set to a time corresponding to one chip of the spread code. When the spreading code is up-sampled N times on the transmission side, the up-sampled N-chip code string is delayed by the delay time of the delay unit 52. The multiplier 53 multiplies the sample for one chip of the HPF 53 by the sample for one chip of the delay unit 52. This process is the above-described delay detection process. By this delay detection processing, the differentially encoded signal MDMPN is converted into a signal including the original spreading code MPN. Thus, by employing differential encoding processing on the transmission side and delay detection on the reception side, it is possible to demodulate the code string on the reception side without reproducing the carrier signal during demodulation.

  The multiplication output of the multiplier 53 is input to the LPF 54. The LPF 54 is a filter for filtering a carrier component to extract a baseband signal and filtering extra noise to improve an S / N ratio, and has the same characteristics as the LPF (Nyquist filter) 40 used on the transmission side. belongs to. As described above, the LPF 40 of the modulation unit and the LPF 54 are combined with each other to have a complete Nyquist filter characteristic.

  The output of the LPF 54 is input to the two matched filters 55A and 55B. The matched filters 55A and 55B are filters having the same length as one period of the spread code generated by the spread code generator 36 on the transmission side. The matched filter 55A is configured by an FIR filter having as a coefficient a code string obtained by up-sampling the spreading code A generated by the spreading code generator 36A on the transmission side by N times. The matched filter 55B is configured by an FIR filter having as a coefficient a code string obtained by up-sampling the spread code B generated by the spread code generation unit 36B on the transmission side by N times. That is, the filter coefficient sequence of the matched filters 55A and B is obtained by repeating each chip of the spread codes A and B N times.

  The matched filters 55A and 55B perform a convolution operation between the output waveform of the LPF 54 and the spread codes A and B, and output a correlation value thereof. Since the interference and noise received on the transmission line have a low correlation with the spread code, the correlation value output from the matched filter is not greatly affected.

  FIG. 8 is a diagram illustrating a waveform example in the matched filter 55A. FIG. 4A shows an example of the input signal waveform of the matched filter 55A. This signal waveform is a waveform in which spreading codes A and barA are alternately continued with dummy data interposed therebetween. FIG. 5B is a diagram showing the filter coefficient of the matched filter 55A as a waveform. FIG. 6C is a diagram showing an example of the output waveform of the matched filter 55A. When the signal waveform of FIG. 5A is sequentially input to the matched filter 55A having the filter coefficient of FIG. 5B, a waveform as shown in FIG. The matched filter 55A outputs positive and negative sharp peaks at the timing synchronized with the spread codes A and barA included in the input signal, and outputs only a low value at other timings.

  FIG. 9 is a diagram comparing the output waveform of FIG. 8C with the output waveform of the waveform in which the spread codes A and barA are alternately continuous without sandwiching dummy data. Among the waveforms shown in the figure, the thick line is the output waveform for the input signal with the dummy data shown in FIG. 8C inserted, and the thin line is the output waveform for the input signal with no dummy data inserted. As for the output waveform for the input signal without inserting dummy data, a correlation peak value is output for each cycle of the spread code, but a relatively large value is output in addition to the peak value (synchronization timing). There is a risk of false detection of peaks due to overlapping signal degradation factors such as. On the other hand, in the output waveform for the input signal with the dummy data inserted as shown in FIG. 8C, the output interval of the correlation peak value is longer than when the dummy data is not inserted. Is kept low, and even if the input signal is degraded, the possibility of erroneously detecting a peak is reduced.

  When the spreading code A or barA is input, the matched filter 55A outputs a strong correlation peak at the timing when the code string is matched. A positive peak appears when the spreading code A is input, and a negative peak appears when the spreading code barA is input. Further, when the spreading code B or barB is input, the matched filter 55B outputs a strong correlation peak at the timing when the code string is matched. A positive peak appears when the spreading code B is input, and a negative peak appears when the spreading code barB is input. Since the spread code A and the spread code B have low cross-correlation, the matched filter 55A does not react to the spread code B, and the matched filter 55B does not react to the spread code A. Further, since the entire waveform value of the dummy data is 0, the corresponding output value is 0 for both the matched filters 55A and 55B.

  Outputs of the matched filters 55A and 55B are input to the code determination unit 56. The sign determination unit 56 detects a large positive / negative peak from the outputs of the matched filters 55A and 55B, and determines a 2-bit data symbol based on which filter has a peak and the positive / negative of the peak. The determination rule is as shown in FIG. That is, “00” is displayed when a positive peak appears in the matched filter 55A, “01” when a negative peak appears in the matched filter 55A, and “01” when a positive peak appears in the matched filter 55B. 10 ”, and“ 11 ”when a negative peak appears in the matched filter 55B. Since the dummy data is 0 data, both matched filters 55A and 55B do not react. As a result, a 2-bit data code can be demodulated in one cycle of the spreading code. The code determination unit 56 outputs the decoded data code D.

  As described above, in this embodiment, a differential code string is generated by differentially encoding a spread code. By performing differential encoding, it is possible to demodulate the original spreading code using the presence or absence of inversion of the code of each chip of the code string even if the receiving side does not have a clock accurately synchronized with the transmitting side. . Further, the differentially encoded spread code is frequency shifted. By shifting the frequency, the band of the differential code is shifted from the baseband to a frequency band that can be emitted and transmitted as sound. Also, by shifting the spreading code to a higher frequency than the audible band, it is possible to mix and emit sound signals such as musical sounds.

  With the above configuration, an acoustic transmission system that has high robustness against frequency fluctuations and disturbances even when spatially transmitted by superimposing a code modulation signal on the acoustic signal with a little sense of incongruity, has a relatively light processing load. And data code can be transmitted at high speed.

<< Modification 1 >>
In the above embodiment, 0 data is inserted as dummy data. By inserting 0 data, it is possible to create a blank section in which the matched filters 55A and 55B do not output a correlation value at all, and to completely separate the preceding and succeeding spreading codes. The waveform (especially the envelope) appearing in may have a colored frequency characteristic of the audible band, which may give the listener a sense of incongruity. Therefore, it is conceivable to use a spreading code different from the spreading codes A and B as the dummy data so as not to have a colored frequency characteristic of the audible band even when the dummy data is inserted.

  FIG. 11 and FIG. 12 are diagrams illustrating an embodiment using a pseudo spreading code obtained by cross-fading the immediately preceding spreading code and the current spreading code as dummy data.

  FIG. 11 is a diagram for explaining the procedure for inserting dummy data in this embodiment. In this figure, the procedure when spreading code A and spreading code B are continuous is illustrated. When the immediately preceding spreading code is spreading code A and the current spreading code is spreading code B (S1), the spreading code A, which is the immediately preceding spreading code, is multiplied by a gradually decreasing window function (S2A) and gradually reduced. A spreading code to be created is created (S3A). Further, the spreading code B, which is the current spreading code, is multiplied by a gradually increasing window function (S2B) to create a gradually increasing spreading code (S3B). Then, a pseudo spreading code is created by adding and synthesizing the spreading code that gradually decreases in S3A and the spreading code that gradually increases in S3B (S4). This pseudo spread code is inserted as dummy data at the boundary between the spread code A and the spread code B (S5).

  In FIG. 11, the spreading code is represented by 1/0 for easy understanding, but in actual processing, the spreading code is a binary signal of 1 / -1. An example of an actual spreading code string in which a pseudo spreading code is inserted as dummy data is shown in FIG. As shown in the figure, since the dummy data section also has a pseudo spread code waveform, it does not have a colored spectrum in the audible frequency band.

  In the block diagram shown in FIG. 2, the dummy data insertion unit 44 creates dummy data for pseudo spreading codes that crossfade based on the preceding and following spreading codes, and this dummy data is placed at the boundary between the preceding and following spreading codes. By inserting, it becomes possible to output the spread code string shown in FIGS.

  Further, in this modification, a third spreading code having a low correlation characteristic with spreading code A and spreading code B may be used as dummy data. By using the third spreading code as the dummy data, it is possible to estimate the received signal level and the transmission path characteristics by using the third spreading code as a pilot signal or a marker signal.

<< Modification 2 >>
In the first modification, a dummy section is provided at the boundary between the preceding and following spreading codes, and a pseudo spreading code obtained by cross-fading the preceding and following spreading codes by applying a window function is inserted as dummy data, but without providing a dummy section. As shown in FIG. 13, deterioration of correlation characteristics may be prevented by multiplying the spread code itself, which is a data symbol, by a window function. In the waveform shown in FIG. 13, all spread codes are multiplied by a window function. However, the window function may be multiplied only when the preceding and succeeding spread codes are switched.

  In order to generate a code string to which a window function is applied as shown in FIG. 13, the dummy data insertion unit 44 shown in FIG. 2 replaces the insertion of dummy data with a window function for a spread code as a transmission symbol. It is sufficient to use a configuration that multiplies.

  The pseudo spreading code as the dummy data shown in FIG. 12 and the spreading code as the symbol multiplied by the window function shown in FIG. 13 are not 1 / −1 binary signals but 1 to − Has an intermediate value between 1. For this reason, if the pseudo spread code of FIG. 12 and the window function of FIG. 13 are multiplied after the upsampling, the number of processing bits of the upsampling unit 39 can be saved.

≪Read more≫
In the above embodiment, addition of an error correction code or the like is not described, but when error correction or interleaving is used on the transmission device side, those processing is added to the received symbol on the reception device side. do it.

  In this embodiment, a 2-bit data code is used as a data symbol to be transmitted, but the data symbol to be transmitted is not limited to bit data.

  In this embodiment, by selecting one from two types of spreading codes and inverting the spreading code, a 2-bit data code is transmitted in one cycle of the spreading code. If a spread code is used, transmission of a data code having a larger number of bits becomes possible.

  Alternatively, a number of spreading codes may be prepared and selected without inverting the spreading code. Furthermore, the phase shift of the spread code is not limited to inversion (180 degrees).

  Further, the lengths of the plurality of spreading codes may not be the same. A plurality of spreading codes having different lengths may be used.

  In the above-described embodiment, multiplication of the carrier signal and the differential code DMPN is performed by arithmetic in the real number domain. However, the carrier signal is converted to a complex number by Hilbert transform, and the differential code DMPN is multiplied by multiplication in the complex domain. Band shifting may be performed.

DESCRIPTION OF SYMBOLS 1 Reception apparatus 2 Transmission apparatus 10 Data superimposition part 21 Demodulation part 36 (36A, 36B) Spreading code generation part 37 Modulation part 44 Dummy data insertion part 55 (55A, 55B) Matched filter 56 Code determination part

Claims (4)

A spreading code generator for generating a plurality of spreading codes;
A data symbol input section for sequentially inputting data symbols;
A spread modulation unit that sequentially selects a spread code from among the plurality of spread codes based on data symbols sequentially input from the data symbol input unit, and provides a dummy section at the boundary of the sequentially selected spread codes;
An acoustic output unit that outputs the spreading code output from the spread modulation unit as sound;
An information transmission device using sound provided with.   The information transmission apparatus using sound according to claim 1, wherein the spread modulation unit provides the dummy section at the boundary only when the spread code selected immediately before is different from the spread code selected this time.   The information transmission apparatus according to claim 1, wherein a blank signal having a continuous zero value is inserted in the dummy section.   The information transmission apparatus according to claim 1 or 2, wherein a signal having a waveform obtained by cross-fading the spreading code selected immediately before and the spreading code selected this time is inserted into the dummy section.

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