KR101728968B1 - Method for detecting transmit signal in audio frequency based short-range sound communication, and transmit signal detection system - Google Patents

Method for detecting transmit signal in audio frequency based short-range sound communication, and transmit signal detection system Download PDF

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KR101728968B1
KR101728968B1 KR1020150173041A KR20150173041A KR101728968B1 KR 101728968 B1 KR101728968 B1 KR 101728968B1 KR 1020150173041 A KR1020150173041 A KR 1020150173041A KR 20150173041 A KR20150173041 A KR 20150173041A KR 101728968 B1 KR101728968 B1 KR 101728968B1
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frequency
signal
symbol
fft
transmission signal
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Korean (ko)
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박세권
조국래
손종욱
성혜민
장보규
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재단법인대구경북과학기술원
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/10—Frequency-modulated carrier systems, i.e. using frequency-shift keying
    • H04L27/14—Demodulator circuits; Receiver circuits
    • H04L27/144—Demodulator circuits; Receiver circuits with demodulation using spectral properties of the received signal, e.g. by using frequency selective- or frequency sensitive elements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B11/00—Transmission systems employing sonic, ultrasonic or infrasonic waves
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/10—Frequency-modulated carrier systems, i.e. using frequency-shift keying
    • H04L27/14—Demodulator circuits; Receiver circuits
    • H04L27/156—Demodulator circuits; Receiver circuits with demodulation using temporal properties of the received signal, e.g. detecting pulse width
    • H04L27/1566—Demodulator circuits; Receiver circuits with demodulation using temporal properties of the received signal, e.g. detecting pulse width using synchronous sampling

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)

Abstract

Disclosed are a method for detecting a transmission signal in an audio frequency-based short-range sound communication system, and an apparatus for detecting the transmission signal. According to an embodiment of the present invention, a method for detecting a transmission signal in an audio frequency-based sound communication system comprises the following steps: converting a received signal to a symbol signal by performing a primarily fast Fourier transformation (FFT); when n symbol signals overlapping a frequency band after the conversion are present, wherein n is a natural number equal to or greater than two, calculating a frequency range including at least respective maximum frequencies of the n symbol signals; and separating each of the n symbol signals by increasing a frequency resolution for the frequency range.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for detecting a transmitted signal in a near-field communication system using an audible frequency and a method for detecting a transmitted signal,

The present invention relates to a near-field acoustic communication technique using an audible frequency, which increases the frequency resolution of a signal received on the basis of an audible frequency band, thereby enhancing detection performance of a transmission signal at a receiving end and improving transmission efficiency of a transmission signal And a transmission signal detection apparatus.

With the spread of smart devices such as smart phones and tablet PCs, demand for services related to short-range wireless communication technology is increasing. However, short-range wireless communication technologies such as Bluetooth (Bluetooth) and Near Field Communication (NFC) have a hardware limitation.

Accordingly, research and application of a sound-based communication technology capable of providing a short-range communication function without depending on hardware are being actively pursued. Generally, sonic communication technology does not require any additional hardware, so it has features that can be used in general-purpose sound equipment (e.g., TV, smart phone, etc.).

Unlike a specialized sonar signal processing device such as an underwater probe (Sonar) for the purpose of signal processing of an invisible frequency band such as an ultrasonic wave, the general purpose acoustic device is intended to transmit a sound signal to a person, It is difficult to guarantee the response performance to the sound wave signal in the non-audible frequency band, although the response performance to the sound wave signal of the frequency band (20 Hz to 20 KHz) is excellent.

That is, when data is transmitted using a non-audible frequency in a general-purpose sound apparatus, it may be difficult to accurately transmit signals due to a distortion of a signal due to the sound apparatus itself. For this reason, a sound wave communication technique aiming at near field communication in a general purpose acoustic device is generally used for signal (data) transmission based on an audible frequency band.

Generally, a frequency shift keying (FSK) modulation method is widely used for signal transmission using an audible frequency, because it is easy to generate and detect a signal without being affected by amplitude distortion due to noise or the like. Quadrature receivers and FFT (Fast Fourier Transform) receivers are used to detect such signals.

Assuming that one symbol is transmitted at frequency f i (i = 1, ..., M), the signal transmitted at the transmitter is

Figure 112015119379437-pat00001
As shown in FIG.

In the orthogonal receiver, the frequency signal f i is multiplied by the received signal r (t)

Figure 112015119379437-pat00002
And a signal having the largest value among the M R i can be selected to recover (restore) the transmission signal transmitted by the transmitter.

At this time, in order to recover one symbol signal in the orthogonal receiver, M

Figure 112015119379437-pat00003
It is necessary to calculate R i with respect to the signal, so that it can have a disadvantage that the amount of calculation greatly increases as M increases.

On the other hand, an FFT-based receiver (FFT detector) can obtain a discrete spectrum of a transmission signal through A / D conversion and FFT on a received signal, and then select a maximum frequency. Since the FFT detector requires only one FFT detector regardless of M, it does not have the same disadvantages as the orthogonal receiver.

The frequency resolution in the FFT detector with the sampling frequency f s and the number of sampling data N can be expressed as? F = f s / N. Therefore, in order to improve the frequency resolution of the FFT detector, there may be a method of lowering the sampling frequency or increasing the number of sampling data.

However, because the sampling frequency should be at least twice the maximum frequency of the signal, and typically 3 to 5 times the sampling frequency, according to the Nyquist sampling theory limit, the lowest available sampling frequency Is limited. In addition, frequency resolution can be improved by increasing the number of samples, but an infinitely large value can not be used due to the increase in computational complexity.

As described above, the transmission rate of data that can be transmitted and received using a conventional FFT detector is limited to a low transmission rate of several tens of bps to several hundreds of bps. Thus, in the near-field communication using the audio frequency, There is a demand for a transmission / reception technique that can be improved.

In an embodiment of the present invention, in a near-field acoustic communication system using an audible frequency, a signal subjected to a first-order FFT processing (a sound wave signal) modulated according to an MFSK (Multi Frequency Shift Keying) A frequency range including the maximum frequency is calculated and the frequency resolution with respect to the frequency interval is increased to perform secondary FFT to recover the transmission signal at the receiving end and improve the transmission efficiency of the transmission signal do.

In the embodiment of the present invention, the frequency section including the maximum frequency calculated through the first-order FFT is shifted to the low frequency band, the interest symbol signal is separated through the low band pass filter, and the separated interest symbol signal is resampled (FFT) receiver by performing a secondary FFT and then restoring the signal to a signal in a high frequency band to detect a transmission signal (transmission frequency).

A method of detecting a transmitted signal in a near-field communication system using an audible frequency according to an embodiment of the present invention includes a step of converting a received signal into a symbol signal by performing a first FFT (Fast Fourier Transform) Calculating a frequency interval including at least a maximum frequency of each of the n symbol signals when there are n (n is a natural number equal to or greater than 2) symbol signals overlapping the frequency interval, And separating each of the n symbol signals.

Also, an apparatus for detecting a transmitted signal in a near-field communication system using an audible frequency according to an embodiment of the present invention includes a first converter for performing a first-order FFT on a received signal to convert the received signal into a symbol signal, (N is a natural number equal to or greater than 2) overlapping n number of symbol signals, a calculation section for calculating a frequency section including at least a maximum frequency of each of the n symbol signals, And a separator for separating each of the n symbol signals by increasing the resolution.

According to an embodiment of the present invention, in a near-field acoustic communication system using an audible frequency, a signal (sound wave signal) modulated and received according to an MFSK (Multi Frequency Shift Keying) The FFT is performed to calculate the frequency interval including the maximum frequency and the frequency resolution for the frequency interval is increased to perform the secondary FFT to improve the detection performance of the transmission signal at the receiving end and improve the transmission efficiency of the transmission signal .

According to an embodiment of the present invention, a frequency interval including a maximum frequency calculated through a first-order FFT is shifted to a low frequency band, a desired symbol signal is separated through a low-pass filter, The transmission efficiency can be improved as compared with the conventional orthogonal receiver or FFT receiver by performing the secondary FFT by resampling and then restoring the signal to a signal in the high frequency band to detect a transmission signal (transmission frequency).

According to an embodiment of the present invention, a frequency position interval is determined in a first stage, and a frequency resolution is improved through a process of frequency movement, resampling, and frequency re-movement in a second stage, It is possible to improve the detection performance.

According to an embodiment of the present invention, the number of frequencies that can be transmitted through the MFSK modulation in the transmitter can be increased by improving the frequency resolution at the receiving end of the near-field acoustic communication system using the audio frequency, It is possible to improve the transmission efficiency.

1 is a block diagram illustrating an internal configuration of a transmission signal detecting apparatus in a near acoustic wave communication system using an audible frequency according to an embodiment of the present invention.
2 is a diagram for explaining a process in which a symbol signal transmitted by a transmitter is modulated by an MFSK modulation method.
FIG. 3 is a diagram illustrating an example of a sound signal that is MFSK-modulated and transmitted by a transmitter in an apparatus for detecting a transmitted signal in a near-field acoustic communication system using an audible frequency according to an embodiment of the present invention.
4 is a diagram illustrating an example of moving a band belonging to a frequency band including a maximum frequency to a low frequency band in an apparatus for detecting a transmitted signal in a near acoustic wave communication system using an audible frequency according to an embodiment of the present invention .
5 is a flowchart illustrating a procedure of a method of detecting a transmitted signal in a near-field acoustic communication system using an audible frequency according to an embodiment of the present invention.
6 is a flowchart illustrating a method of detecting a transmission signal in a near-field communication system using an audible frequency according to another embodiment of the present invention.

Hereinafter, an apparatus and method for updating an application program according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to or limited by the embodiments. Like reference symbols in the drawings denote like elements.

For example, in the present invention, a near-field acoustic communication system using an audible frequency may be composed of a transmitter and a receiver, and other modules may be added or deleted as needed.

The transmission signal (data) transmitted from the transmitter can be transmitted through a speaker after being subjected to source coding, encryption and channel coding, and then converted into an audible sound signal through a modulation process.

The receiver may receive the sound wave signal through the microphone, and then recover the transmitted signal through processes such as demodulation, channel decoding, decoding, and source decoding.

The apparatus for detecting a transmitted signal in a near-field acoustic communication system using an audible frequency according to an embodiment of the present invention can be implemented by the above-described receiver.

1 is a block diagram illustrating an internal configuration of a transmission signal detecting apparatus in a near acoustic wave communication system using an audible frequency according to an embodiment of the present invention.

Referring to FIG. 1, an apparatus 100 for detecting a transmitted signal in a near-field acoustic communication system using an audible frequency according to an embodiment of the present invention includes a first conversion unit 110, a calculation unit 120, 130). In addition, according to the embodiment, the transmission signal detecting apparatus 100 can be configured by adding the second converting unit 140 and the restoring unit 150, respectively.

The first converter 110 performs a first FFT (Fast Fourier Transform) on a received signal to convert the received signal into a symbol signal.

Here, the received signal may be a sinusoid modulated by a transmitter so as to have different frequencies for each symbol period according to an MFSK (Multi Frequency Shift Keying) modulation scheme in an audio frequency band, .

Hereinafter, a process of transmitting a sound wave signal in a transmitter of a near-field acoustic communication system using an audible frequency will be described with reference to FIG. 2 to FIG.

2 is a diagram for explaining a process in which a symbol signal transmitted by a transmitter is modulated by an MFSK modulation method.

Referring to FIG. 2, in the transmitter, a symbol signal composed of M bits can be converted into an audio signal in an audible frequency band (20 Hz to 20 KHz) through MFSK modulation and transmitted to a transmission signal detecting apparatus (receiver) of the present invention.

For example, the transmitter may MFSK modulate each symbol signal (symbol 1 through symbol M) into a sound wave signal by mapping the frequency of the audio frequency band (20 Hz to 20 KHz) with reference to the mapping information shown in FIG. 2 .

Here, 'Δf' is the frequency resolution and can be expressed as 'f s / N' (f s : sampling frequency, N: number of sampling data).

FIG. 3 is a diagram illustrating an example of a sound signal that is MFSK-modulated and transmitted by a transmitter in an apparatus for detecting a transmitted signal in a near-field acoustic communication system using an audible frequency according to an embodiment of the present invention.

Referring to FIG. 3, the transmitter can convert (modulate) the symbol signals into MFSK-modulated sound signals having different frequencies for each symbol period T s in the time domain.

The transmission signal detecting apparatus 100 of the present invention may be implemented as a receiver that receives a signal including at least an acoustic wave signal transmitted by the transmitter. The first converter 110 may perform a first-order FFT on a received signal (sound wave signal) to convert the signal into a symbol signal.

Referring back to FIG. 1, when there are n (n is a natural number equal to or larger than 2) symbol signals in which the frequency bands after the conversion are overlapped, the calculating unit 120 sets each maximum frequency possessed by the n symbol signals at least And calculates the included frequency section. Here, the maximum frequency may refer to a frequency at which the amplitude is maximum.

In one example, the calculating unit 120 is between the highest frequency (f H) and the lowest frequency (f L) in which the n symbol signal occupy the frequency range - can be calculated as ( 'f H f L') .

For example, referring to FIG. 4, when a sound signal of f MFSK -1 = 10000 Hz, f MFSK -2 = 10070 Hz, and f MFSK -3 = 10140 Hz is received from the transmitter, Each received signal can be recovered by first-order FFT as shown in (i) of FIG.

Here, since the frequency resolution used in the first-order FFT is low, the restoration values (maximum frequencies) of the three symbol signals are all about 9991 Hz, so that it is impossible to separate each symbol signal by the separator 130 have.

In this case, the calculation unit 120 can not accurately detect the transmission signal (transmission frequency) transmitted from the transmitter. However, in the discrete spectral signal of the signal received in the frequency band through the primary FFT, It is possible to determine the section 410.

For example, in the case where three 8-bit symbols are transmitted by a sinusoidal sound wave signal at the transmitter, the calculating unit 120 calculates the following equation ( 1) : f MFSK -1 = 10000 Hz, f MFSK -2 = 10070 Hz, f MFSK -3 = It can be seen that the maximum amplitude (Amplitude) is located at the thirtieth point in the discrete spectrum signal obtained by the first-order FFT of each received sinusoidal sound signal with f s = 44.1 KHz and N = 128, '9991 Hz' can be calculated.

Since the maximum frequency (about '9991 Hz') is located at the 29th point and the 31st point of the result of performing the first FFT, the calculating unit 120 calculates the frequency interval f L - f H ') And its center frequency f c ( ' 9990 Hz ').

The separator 130 separates the n symbol signals by increasing the frequency resolution for the frequency interval.

In one example, the separation unit 130 is the frequency area ( 'f H - f L' ) of the band belonging to, go to the low frequency band, and to increase the frequency resolution, the n symbol signal is spread in the low frequency band Through the low pass filter, the desired symbol signal can be separated.

At this time, the separating unit 130

Figure 112015119379437-pat00004
The frequency resolution can be increased by shifting each of the n symbol signals within the frequency interval by a center frequency f c .

Specifically, when the frequency section ('f H- f L ') having the center frequency f c is calculated through the first-order FFT, the separating section 130 extracts, from the characteristic of the Fourier transform equation,

Figure 112015119379437-pat00005
Performing a multiplication operation in the frequency area in the frequency domain, - the ( 'f H f L') , the center frequency f c Frequency band, and thus the frequency resolution can be increased.

In addition, the separator 130 can leave only the interest symbol signal of the -350 Hz to 350 Hz band among the signals received from the transmitter through the low-pass filter.

In this way, the separation unit 130 increases the frequency resolution by moving the frequency interval to the low frequency band and using the low-pass filter using f L , f H , and f c calculated through the first-order FFT, It is possible to obtain an accurate transmission signal (transmission signal frequency) by separating frequency signals that can not be distinguished by the general FFT process of FIG.

The transmission signal detecting apparatus 100 may further include a second converting unit 140 and a restoring unit 150. [

The second transform unit 140 resamplifies the interest symbol signal in consideration of a sampling frequency used in the first FFT, and performs a second-order FFT.

For example, the second transform unit 140 may set the maximum frequency of the interest symbol signal to twice the sampling frequency at the re-sampling.

For example, the second conversion unit 140 sets the sampling frequency to twice the maximum frequency '350 Hz' after passing through the low-pass filter by Nyquist theorem, that is, a sampling frequency of about '700 Hz' , And performs the second-order FFT by resampling the interest symbol signal.

In addition, the second converter 140 may perform the resampling by setting the sampling frequency at the resampling to be lower than the sampling frequency used at the first FFT.

The sampling frequency f s 'at the resampling can be designed or obtained by the design of the system. For example, according to f s ' = f s / D, the sampling frequency f s at the time of the first FFT is D times If the re-sampled at a low sampling frequency, frequency resolution Δf 'is, Δf', it can be seen that D-fold improvement according to = f s' / N = ( f s / D) / N = Δf / D.

In addition, the second conversion unit 140 may perform zero padding in order to maintain the number N of sampling data to be reduced as the re-sampling is performed.

, (N) number of sampling data (sampling point FFT) according to the sampling frequency f s' at the time of the re-sampling of the first sampling frequency f s D time becomes lower than at the time of FFT in the above example can also be lowered. Accordingly, the second conversion unit 140 may perform zero padding to maintain the N value.

The restoring unit 150 moves the band backward and restores the interest symbol signal of the secondary FFT into a signal in the high frequency band.

Here, the degree of backward movement may be determined according to a value shifted to the low frequency band when the frequency resolution is increased.

That is, the reconstructing unit 150 can detect the transmission signal (the precise frequency transmitted) by shifting the frequency band of the precise frequency interval obtained through the second-order FFT to the high frequency band as the frequency band moves to the low frequency band.

Thus, according to one embodiment of the invention, the maximum frequency is in the frequency range 410 to move to the low band (base band), a relatively lower sampling frequency than the sampling frequency f s used in primary FFT f s (Frequency band) of the frequency band obtained by resampling the frequency-converted result to the high-frequency band as high as the moving frequency, the frequency resolution is improved as shown in FIG. 4 (ii) Thus, it is possible to enhance the detection performance of the transmission signal at the receiving end and improve the transmission efficiency of the transmission signal.

4 is a diagram illustrating an example of moving a band belonging to a frequency band including a maximum frequency to a low frequency band in an apparatus for detecting a transmitted signal in a near acoustic wave communication system using an audible frequency according to an embodiment of the present invention .

Referring to FIG. 4, when a general FFT detection technique is used in the transmission signal detecting apparatus (receiver) of the present invention, the frequency resolution of an FFT having a sampling frequency f s and an FFT pointer number (sampling data number) N is Δf = f s / N.

For example, a sampling frequency f s, "The use of a point FFT, frequency resolution Δf are 'commonly used sampling frequency '44 .1KHz that the" use and, as FFT point N' 128 in the acoustic signal to 345Hz ' . In this case, the maximum number of frequencies that can be decomposed by the FFT in the audio frequency range of 20 Hz to 20 KHz is about 58, and the transmitter can transmit only a maximum of 4 bits symbols at a time.

In this case, when the transmitter transmits symbols of 8 bits at a time using 256 MFSK, the maximum interval between the frequencies becomes about 78 Hz. For example, in the transmitter, f MFSK -1 = 10000 Hz, f MFSK -2 = 10070 Hz, f MFSK -3 = 10140 Hz When three 8-bit symbols are transmitted by a sinusoidal sound wave signal, the transmission signal detecting apparatus of the present invention transmits each signal received from the transmitter as a first Can be restored by FFT.

However, as shown in (i) of FIG. 4, since the recovery values of all three symbol signals are all about 9991 Hz, the transmission signal detecting apparatus of the present invention can not perform separation of each symbol signal. As described above, when the transmission signal detecting apparatus of the present invention performs FFT using a low frequency resolution, it can not accurately detect the transmission frequency transmitted from the transmitter.

Therefore, the transmission signal detecting apparatus of the present invention can maximize the signal transmission efficiency by further performing the second-order FFT to improve the frequency resolution of the received signal.

4 (i), in the discrete spectrum signal for the received signal obtained through the first-order FFT, the transmission signal detecting apparatus of the present invention detects a frequency interval 410 in which the maximum frequency is located, (A frequency interval determination interval algorithm).

4, the transmission signal detecting apparatus of the present invention shifts the frequency interval 410 in which the maximum frequency is located to a low band (baseband) and outputs a sampling frequency f s more relatively low sampling frequency f s' to the material by the frequency, the resulting values obtained after sampling, improves the frequency resolution through a process of high-frequency re-moved to the band as much as the moving, accurate transmission signal (transmission signal frequency) (Accurate frequency acquisition algorithm).

In other words, the transmission signal detecting apparatus of the present invention can not accurately detect the transmission frequency transmitted from the transmitter because the frequency resolution used in the first-order FFT is low, but the transmission frequency of the 29th point and the 31st point It can be seen that the maximum frequency is located. That is, the transmission signal detecting apparatus of the present invention can calculate that the maximum frequency is located between f L = '9640 Hz' and f H = '10340 Hz' through the primary FFT and the center frequency f c is '9990' .

Then, the transmission signal detecting apparatus of the present invention increases frequency resolution by using f L , f H , and f c calculated through the primary FFT, thereby separating frequency signals that can not be distinguished by the conventional FFT process .

If the transmission signal detecting device according to the present invention is that the calculating the first FFT on the center frequency f c of the frequency interval ( 'f H- f L') through, from a characteristic of the Fourier transformation, a signal in the time domain

Figure 112015119379437-pat00006
And multiplies the frequency interval in the frequency domain by the center frequency f c Frequency band, the band of the frequency band may be shifted to the low-frequency band, and then may be passed through the low-pass filter to leave only the signal of interest (interest symbol signal).

The transmission signal detecting apparatus of the present invention can leave only the interest symbol signal of, for example, a frequency band of -350 Hz to 350 Hz among the signals received from the transmitter through the low-pass filter. By the Nyquist theorem, It can be resampled at a sampling frequency of twice the frequency of 350 Hz, which is the maximum frequency after passing through the pass filter, that is, about 700 Hz. At this time, the sampling frequency at the resampling may be designed or obtained by the design of the system.

In the transmission signal detecting device according to the present invention, the sampling frequency f s' (= f s / D) during the resampling in (f s is the first sampling frequency at the time of FFT), the sampling frequency is D times less so after resampling frequency resolution Δf 'is, Δf' = f s' / N = D can be improved in accordance with the times (f s / D) / N = Δf / D.

At this time, as the sampling frequency is lowered, the transmission signal detecting apparatus of the present invention lowers the sampled FFT point (the number of sampling data) and can perform zero padding to maintain the N value.

Thereafter, the transmission signal detecting apparatus of the present invention can detect the transmission signal (the transmitted accurate frequency) by shifting the frequency band of the precise frequency interval obtained through the second-order FFT to the high frequency band by moving to the low frequency band .

5 to 6, the operation flow of the transmission signal detecting apparatus 100 according to the embodiments of the present invention will be described in detail.

5 is a flowchart illustrating a procedure of a method of detecting a transmitted signal in a near-field acoustic communication system using an audible frequency according to an embodiment of the present invention.

The transmission signal detection method according to the present embodiment can be performed by the transmission signal detection apparatus 100 described above.

Referring to FIG. 5, in step 510, the transmission signal detecting apparatus 100 performs a first-order FFT on a received signal to convert the received signal into a symbol signal.

Here, the received signal may include a sound wave signal which is modulated and transmitted by the transmitter so as to have different frequencies for each symbol period according to the MFSK modulation scheme in the audio frequency band.

In step 520, when there are n (n is a natural number equal to or larger than 2) symbol signals in which the frequency bands after the conversion are overlapped, the transmission signal detecting apparatus 100 determines the maximum frequency Is calculated.

For example, referring to FIG. 4 (i), the transmitter transmits three 8-bit symbols as a sinusoidal sound signal, f MFSK -1 = 10000 Hz, f MFSK-2 = 10070 Hz, f MFSK -3 = 10140 Hz, In transmission, the transmission signal detecting apparatus 100 detects a discrete spectrum signal obtained by first-order FFT of each received sinusoidal sound signal with f s = 44.1 KHz, N = 128, (About 9991 Hz) is located at the 29th point and the 31st point of the result of the first FFT, so that the maximum frequency can be obtained. ('F L - f H ') and its center frequency f c ( '9990 Hz') can be calculated.

In step 530, the transmission signal detection apparatus 100 increases the frequency resolution for the frequency interval and separates each of the n symbol signals.

Specifically, the transmission signal detecting device 100 includes a center frequency on the primary FFT f c the frequency area - if ( 'f f H L') is calculated from the characteristic of the Fourier transformation, a signal in the time domain

Figure 112015119379437-pat00007
By performing a multiplication operation for the frequency area ( 'f H- f L') in the frequency domain, the center frequency f c Frequency band, and thus the frequency resolution can be increased.

Further, the transmission signal detecting apparatus 100 can leave only the interest symbol signal in the -350 Hz to 350 Hz band among the signals received from the transmitter through the low-pass filter.

As described above, the transmission signal detecting apparatus 100 increases the frequency resolution through the low frequency band shift and the low frequency band pass by using f L , f H , and f c calculated through the primary FFT. , It is possible to obtain an accurate transmission signal (transmission signal frequency) by separating frequency signals that can not be distinguished by the conventional general FFT process.

In step 540, the transmission signal detection apparatus 100 resamplifies the interest symbol signal in consideration of a sampling frequency used in the primary FFT, and performs a second-order FFT.

For example, the transmission signal detecting apparatus 100 can perform the resampling by setting the sampling frequency at the resampling to be lower than the sampling frequency used at the time of the first FFT.

The sampling frequency f s 'at the resampling can be designed or obtained by the design of the system. For example, according to f s ' = f s / D, the sampling frequency f s at the time of the first FFT is D times If the re-sampled at a low sampling frequency, frequency resolution Δf 'is, Δf', it can be seen that D-fold improvement according to = f s' / N = ( f s / D) / N = Δf / D.

At this time, according to the transmission signal detecting device 100 includes a sampling frequency f s' is D time becomes lower than 1 f the sampling frequency at the time of car FFT s at the time of the re-sampling, the number of the sampling data (sampling FFT points) (N) So that zero padding can be performed to maintain the N value.

In step 550, the transmission signal detecting apparatus 100 moves the band backward and restores the second-order FFT-processed interest symbol signal into a signal in the high-frequency band. Here, the degree of backward movement may be determined according to a value shifted to the low frequency band when the frequency resolution is increased.

That is, the transmission signal detecting apparatus 100 can detect a transmission signal (an accurate frequency transmitted) by shifting the frequency band of the precise frequency interval obtained through the secondary FFT to the high frequency band by moving to the low frequency band .

Thus, according to one embodiment of the invention, the maximum frequency is in the frequency range 410 to move to the low band (base band), a relatively lower sampling frequency than the sampling frequency f s used in primary FFT f s (Frequency of the transmitted signal) by improving the frequency resolution through the process of frequency re-sampling the obtained frequency result value to the high band as high as the movement, It is possible to enhance the detection performance of the transmission signal at the receiving end and improve the transmission efficiency of the transmission signal.

6 is a flowchart illustrating a method of detecting a transmission signal in a near-field communication system using an audible frequency according to another embodiment of the present invention.

The transmission signal detection method according to the present embodiment can be performed by the transmission signal detection apparatus 100 described above.

6, the step (601 to 604) is the maximum frequency is located frequency area ( 'H- f f L') to indicate an algorithm for determining, the step (605 to 610) is the correct transmission frequency (transmission frequency , A transmitted signal).

First, the transmission signal detecting apparatus 100 receives a sound wave signal modulated by MFSK transmitted by a transmitter, A / D-converts the signal, firstly performs a first-order FFT with a sampling frequency f s to obtain a frequency interval including at least a maximum frequency And calculates the center frequency (steps 601 to 604).

That is, the transmission signal detecting apparatus 100 calculates a frequency at a point where the amplitude is the maximum, that is, the maximum frequency, in the discrete spectral signal of the signal received in the frequency band through the primary FFT, The frequency interval between the frequency f H and the minimum frequency f L ('f H - f L ') can be calculated.

In addition, the transmission signal detecting apparatus 100 moves the frequency band belonging to the frequency band to a low frequency band (step 605), increases the frequency resolution, and among the n symbol signals spread in the low frequency band, Through the pass filter, the signal symbol of interest is separated (step 606).

That is, the transmission signal detecting apparatus 100 increases the frequency resolution through the movement of the frequency interval to the low frequency band and the low-pass filter using f L , f H , and f c calculated through the first-order FFT It is possible to obtain an accurate transmission signal (transmission signal frequency) by separating a frequency signal that can not be distinguished by the conventional general FFT process.

Also, the transmission signal detecting apparatus 100 resamplifies the interest symbol signal in consideration of a sampling frequency used in the first FFT, and performs a second-order FFT (steps 607 to 608).

For example, the transmission signal detecting apparatus 100 resets the sampling frequency at the resampling by D times lower than the sampling frequency used at the first FFT to resample the frequency resolution Δf ' it is possible to improve D times according to f s ' / N = (f s / D) / N = f / D.

In addition, the transmission signal detecting apparatus 100 obtains a transmission signal (transmission frequency) by shifting the frequency band of the precise frequency interval obtained through the second FFT back to the high frequency band by moving to the low frequency band (step 609 610).

As described above, according to the embodiment of the present invention, in the near-field communication system using the audio frequency, the signal (sound wave signal) modulated according to the MFSK frequency modulation scheme based on the audio frequency band is subjected to first-order FFT It is possible to improve the detection performance of the transmission signal at the receiving end and improve the transmission efficiency of the transmission signal by calculating the frequency interval including the maximum frequency and increasing the frequency resolution with respect to the frequency interval and performing the secondary FFT.

The method according to an embodiment of the present invention may be implemented in the form of a program command that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions to be recorded on the medium may be those specially designed and configured for the embodiments or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Lt; / RTI > or equivalents, even if it is replaced or replaced.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

100: Transmission signal detecting device
110: first conversion unit 120: calculation unit
130: separator 140:
150:

Claims (20)

Converting a received signal into a symbol signal by performing a first FFT (Fast Fourier Transform) on the received signal;
Calculating a frequency interval including at least a maximum frequency of n (n is a natural number equal to or greater than 2) symbol signals whose frequency bands after the conversion overlap;
Moving a band belonging to the frequency band to a low frequency band;
Separating the symbol signal of interest through the low pass filter among the n symbol signals spread in the low frequency band;
And performing second-order FFT by resampling the interest symbol signal, wherein the step of performing the resampling at a sampling frequency that is lower than a sampling frequency used for the first-order FFT by a multiple that is intended to improve the frequency resolution for the frequency interval ; And
Restoring the band-of-interest signal symbol into a signal in a high-frequency band,
Wherein the frequency of the at least one of the first and second signals is at least one of a first frequency and a second frequency. delete The method according to claim 1,
Wherein the step of moving to the low-
Figure 112017019836425-pat00016
, Multiplying each of the n symbol signals within the frequency interval by a center frequency (f c ) to increase the frequency resolution
And transmitting the transmission signal. delete The method according to claim 1,
The degree of the backward movement,
And is determined according to a value shifted to the low-frequency band
A method of detecting a transmitted signal. The method according to claim 1,
Wherein the step of performing the second FFT includes:
Setting the sampling frequency at the resampling to be twice the maximum frequency of the symbol signal of interest
Further comprising the steps of: The method according to claim 1,
Wherein the step of performing the second FFT includes:
And performing the resampling by setting the sampling frequency to be lower than a sampling frequency used in the primary FFT
Further comprising the steps of: The method according to claim 1,
Performing zero padding to maintain the number of sampling data to be reduced as the re-sampling occurs;
Further comprising the steps of: The method according to claim 1,
Wherein the calculating the frequency interval comprises:
Calculating a frequency interval between the highest frequency f H and the lowest frequency f L occupied by the n symbol signals,
And transmitting the transmission signal. The method according to claim 1,
Wherein the received signal comprises:
(Sinusoid) modulated and transmitted so as to have different frequencies in each symbol period according to a MFSK (Multi Frequency Shift Keying) modulation scheme in an audio frequency band by a transmitter
A method of detecting a transmitted signal. A first converter for performing a first order FFT on a received signal to convert the signal into a symbol signal;
A calculating section for calculating a frequency interval including at least a maximum frequency of n (n is a natural number equal to or greater than 2) symbol signals whose frequency bands after the conversion overlap;
A demultiplexer for demultiplexing a band belonging to the frequency band into a low frequency band and separating a symbol signal of interest through the low band pass filter among the n symbol signals spread in the low frequency band;
A second transformer for performing a second-order FFT by resampling the interest symbol signal to a sampling frequency that is lower than a sampling frequency used for the first FFT to a frequency lower than a sampling frequency for improving the frequency resolution for the frequency interval; And
A restoring unit for restoring the interest symbol signal subjected to the second FFT to a signal within a high frequency band,
And a receiver for detecting the transmission signal in the near-field communication system using the audio frequency. delete 12. The method of claim 11,
The separator may include:
Figure 112017019836425-pat00017
, Thereby shifting each of the n symbol signals in the frequency interval by the center frequency f c to increase the frequency resolution
A transmission signal detection device. delete 12. The method of claim 11,
The degree of the backward movement,
And is determined according to a value shifted to the low-frequency band
A transmission signal detection device. 12. The method of claim 11,
Wherein the second conversion unit comprises:
And sets the sampling frequency at the resampling to be twice the maximum frequency of the symbol signal of interest
A transmission signal detection device. 12. The method of claim 11,
Wherein the second conversion unit comprises:
Is set to be lower than a sampling frequency used at the time of the first FFT,
A transmission signal detection device. 12. The method of claim 11,
Wherein the second conversion unit comprises:
As the resampling is performed, zero padding is performed to maintain the number of sampling data to be reduced
A transmission signal detection device. 12. The method of claim 11,
The calculating unit calculates,
Calculates between the highest frequency (f H ) and the lowest frequency (f L ) occupied by the n symbol signals as the frequency interval
A transmission signal detection device. 12. The method of claim 11,
Wherein the received signal comprises:
A signal including a sound wave signal which is modulated and transmitted so as to have a different frequency per symbol period in the audio frequency band, according to the MFSK modulation method, by the transmitter
A transmission signal detection device.
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KR20230127773A (en) 2022-02-25 2023-09-01 고려대학교 산학협력단 Device and method for communication using ultrasonics wave

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Publication number Priority date Publication date Assignee Title
US20140153614A1 (en) * 2006-12-20 2014-06-05 Kabushiki Kaisha Toshiba Wireless communications apparatus
KR101454621B1 (en) * 2013-04-03 2014-10-28 주식회사화신 Apparatus for detecting range and velocity of target by using radar and method thereof

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109217945A (en) * 2018-09-14 2019-01-15 深圳市琦志航智能科技有限公司 A kind of sound wave communication method
KR20230127773A (en) 2022-02-25 2023-09-01 고려대학교 산학협력단 Device and method for communication using ultrasonics wave

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