JP5532900B2 - 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 efficiently transmitting a variety of information using sound.

According to the first aspect of the present invention, a plurality of spreading codes having low cross-correlation and different cyclic periods are generated in parallel, and the plurality of spreading codes and the plurality of spreading codes obtained by inverting the phases of the plurality of spreading codes, respectively. A spread code generator for outputting codes; a data symbol input for inputting data symbols; and the plurality of spread codes and the plurality of spread codes obtained by inverting the phases based on the data symbols input from the data symbol input A spread modulation unit that selects one spread code from the above, a differential coding unit that differentially codes the selected spread code, and an acoustic output unit that outputs the spread code that has been differentially coded as sound , Provided.

The invention of claim 2, wherein the differential encoding unit and between the sound output unit, up-sampling section that up-samples the previous SL spreading code, frequency shift for frequency shifting said spreading code by multiplying the carrier signal parts, and further comprising a.

According to a third aspect of the present invention, the frequency shift unit shifts the frequency of the spread code to the high frequency part of the acoustic signal, the acoustic output unit inputs another acoustic signal, and the high frequency range of the other acoustic signal is reduced. A low-pass filter for cutting, and an adder that adds and synthesizes another acoustic signal whose high-frequency range has been cut by the low-pass filter and the frequency-shifted spread code are provided.

  In the present invention, a data symbol is transmitted by selecting a spreading code corresponding to the data symbol to be transmitted and outputting it acoustically. By preparing a plurality of spreading codes, various data symbols can be transmitted per cycle of the spreading code. Furthermore, by shifting the phase of the spread code (for example, phase inversion), more various data symbols can be transmitted.

  According to the present invention, when data symbols are transmitted using sound, various data symbols can be transmitted by using a plurality of spreading codes.

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 | alteration part of a transmission apparatus, and a differential encoding part. Diagram showing examples of spreading and differential encoding waveforms The figure which shows the structure of the demodulation part of the said receiver The figure which shows the determination rule of the code | symbol determination part of a receiver

  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 to superimpose the data code D on the high frequency range of the acoustic signal S. 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 acoustic signal S (music, voice, etc.) input from the acoustic signal input unit 31 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.

  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. 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 data code input unit 35 reads the data code D and inputs it to the modulation unit 37. The spread code generating unit 36 generates two types of spread codes in parallel and in synchronization, and inputs them to the modulation unit 37. As the spreading code, a pseudo-random code string having a fixed cyclic period such as an M series is used. A combination having a low cross-correlation is selected for the two pseudo-random code sequences. The data code input unit 35 inputs a 2-symbol data code D to the modulation unit 37 for each cyclic period of the spread code.

  The modulation unit 37 selects one of two spreading codes (spreading code A and spreading code B) based on the input two-symbol data code D, and performs a spreading process for determining the phase of the selected spreading code. Do.

  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) and output. A spreading code selection rule based on a 2-bit transmission symbol is as shown in FIG. As a result, 2-bit data can be expressed by a one-cycle spreading code.

  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. 3C 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.

  FIG. 4 shows waveform examples of the data code D, the spread codes PN, MPN, and DMPN. FIG. 4A shows the spread code PN generated by the spread code generator 36. FIG. 5B shows the data code D input by the data code input unit 35. FIG. 5C shows a spread code MPN that is phase-modulated by the data code D for each cyclic period. Since the data code string D shown in the figure is “10”, the phase is normal in the first period of the spread code MPN, and the phase is inverted in the second period. FIG. 4D shows a code string (differential code) DMPN obtained by differentially encoding the modulated spread code MPN. This code string is a value based on a comparison result (exclusive OR) between the value of each chip of the spreading code MPN and the value of the differential code DMPN of the immediately preceding chip. The differential code DMPN is converted into a binary signal of -1,1.

  The differential code DMPN converted into a binary signal 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.

  Returning to FIG. 2, 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. 5) 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. 5 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.

  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.

  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. 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.

  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.

  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.

≪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 55 (55A, 55B) Matched filter 56 Code determination part

Claims (3)

Spread code generation that generates a plurality of spread codes having low cross-correlation and different cyclic periods in parallel, and outputs the plurality of spread codes and a plurality of spread codes obtained by inverting the phases of the spread codes. And
A data symbol input section for inputting a data symbol;
A spread modulation unit that selects one spread code from the plurality of spread codes and the plurality of spread codes whose phases are inverted based on data symbols input from the data symbol input unit;
A differential encoding unit that differentially encodes the selected spreading code;
An acoustic output unit for outputting the differentially encoded spread code as sound;
An information transmission device using sound provided with. Between the differential encoding unit and the acoustic output unit,
Upsampling unit upsampling prior Symbol spreading code,
A frequency shift unit that multiplies the spreading code by a carrier signal to shift the frequency;
Information transmission apparatus using an acoustic according to claim 1, further comprising a. The frequency shift unit shifts the frequency of the spread code to the treble part of the acoustic signal,
  The acoustic output unit receives another acoustic signal, and a low-pass filter that cuts a high-frequency range of the other acoustic signal; another acoustic signal that has been cut-off by the low-pass filter; and the frequency-shifted The information transmission apparatus using sound according to claim 2, further comprising: an adder that adds and synthesizes the spread code.

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