WO2010074376A1

WO2010074376A1 - Device and method for transmitting audio signal based on frequency modulation

Info

Publication number: WO2010074376A1
Application number: PCT/KR2009/002873
Authority: WO
Inventors: Jung-Hwan Hwang; Kyung-Soo Kim; Jung-Bum Kim; In-Gi Lim; Chang-Hee Hyoung; Hyung-Il Park; Sung-Eun Kim; Tae-Wook Kang; Hey-Jin Myoung; Kyung-Hwan Park; Seok-Bong Hyun; Byoung-Gun Choi; Tae-Young Kang; Sung-Weon Kang
Original assignee: Electronics And Telecommunications Research Institute
Priority date: 2008-12-22
Filing date: 2009-05-29
Publication date: 2010-07-01
Also published as: KR101210276B1; KR20100073037A

Abstract

Device (100) and method for transmitting an audio signal using a human body as a communication channel (170). The method comprises modulating an audio signal by using the frequency modulation scheme, applying the modulated audio signal to a human body, and generating a sound by using a nonlinear operation generated by the human body without using a transmission device. The device (100) includes: a first modulation unit (10) that performs frequency modulation on a signal transferred from a sound source, and shifts the phase of the signal; a second modulation unit (20) that delays time of the signal transferred from the sound source, and performs frequency modulation on the corresponding signal; and a ultrasonic converter (160) that receives the signals from the first (10) and second (20) modulation units, converts the received signals into ultrasonic signals, and transmits the converted ultrasonic signals via a human body (170).

Description

DEVICE AND METHOD FOR TRANSMITTING AUDIO SIGNAL BASED ON FREQUENCY MODULATION

The present invention relates to a device and method for transmitting a human body audio signal using a human body as a communication channel, and more particularly, to a device and method for transmitting an audio signal (i.e., sound signal) based on a frequency modulation scheme capable of modulating an audio signal by using the frequency modulation scheme, applying the modulated audio signal to a human body, and generating a sound by using a nonlinear operation (i.e., action, working, effect, etc.) generated by the human body without using a transmission device.

Human body communication is a technique that uses a human body as a communication channel to transmit a signal based on the principle that electricity is able to flow through the human body.

Among human body communications, a technique that transmits an audio signal to a human body (i.e., user) and then allows the user to directly hear a corresponding sound with his ears is called a human body sound transmission/reception technique. According to the related art human body sound transmission/reception technique, an audio signal desired to be transmitted is modulated into a signal that can be transmitted in the human body, and outputted such that it can be transmitted via the human body. Then, a receiving device positioned to be in contact with the vicinity of the user's ear demodulates it into an audio signal of an audible frequency band to allow the user to hear it.

In addition, a human body audio signal transmitting device and method using the nonlinear operation of a human body has been also proposed to remove the necessity of a cumbersome receiving device to receive an audio signal transmitted via the human body.

In the related art human body audio signal transmitting device and method of using the nonlinear operation of a human body, an audio signal desired to be transmitted is mixed with an RF signal, namely, the audio signal is amplitude-modulated, so as to be converted (i.e., transformed) into an ultrasonic band signal of about 20kHz or higher. The signal converted thusly is then converted into an ultrasonic signal via a single or two or more ultrasonic conversion elements along with the RF signal which has been used for mixing, and these are then applied to the human body. Over the ultrasonic band signal, the human body performs a nonlinear operation as well as a linear operation, namely, an operation in proportion to the size of the input signal. The nonlinear operation on the two or more signals may be modeled into the product of the two signals. If an audio signal to be transmitted is m(t) and the amplitude and frequency of the RF signal is A_c and f_c, the signal mixed with the RF signal, i.e., the amplitude-modulated signal, and the RF signal can be represented by Equations 1 and 2 shown below:

[Equation 1]

[Equation 2]

When the two signals are converted into the ultrasonic signals via the ultrasonic conversion element and then applied to the human body, the ultrasonic signals are transmitted via the user's body, respectively, and at this time, a signal represented by Equation 3 is generated from the vicinity of the user's ear due to the nonlinear operation of the human body.

[Equation 3]

Equation 3 may be developed by using a sine formula into Equation 4 shown below:

[Equation 4]

A first term of the above Equation 4 is the ultrasonic band signal which cannot be heard in the user's normal range of hearing, while the second term thereof is a signal of an acoustic band which can be heard. Thus, the user can hear a desired audio signal without using a receiving device.

However, although the related art human body audio signal transmitting method is advantageous, in that the system can be simply implemented, there is a problem, in that a utilized frequency bandwidth cannot be adjusted.

In addition, the signal mixed with the RF signal has the same frequency bandwidth as that of the audio signal. In considering the fact that a general audio signal has a bandwidth of about 10 kHz, very broad bandwidth characteristics of 10 kHz or larger are required for an ultrasonic element, in order to convert the mixed signal into the ultrasonic signal.

Thus, in order to cover the broad bandwidth characteristics, the power consumption of the element would be necessarily increased, and the element would have a complicated structure. In addition, a signal modulated according to the amplitude modulation is quite vulnerable to noise, resulting in degradation of sound quality.

An aspect of the present invention provides a device and method for transmitting an audio signal based on frequency modulation capable of adjusting a frequency bandwidth of a transmission signal and improving noise characteristics by applying the frequency modulation scheme to a human body audio signal communication method.

According to an aspect of the present invention, there is provided a device for transmitting an audio signal based on frequency modulation, including: a first modulation unit that performs frequency modulation on a signal transferred from a sound source, and shifts the phase of the signal; a second modulation unit that delays the signal transferred from the sound source, and performs frequency modulation on the corresponding signal; and a ultrasonic converter (i.e., ultrasonic transformer) that receives the signals from the first and second modulation units, converts the received signals into ultrasonic signals, and transmits the converted ultrasonic signals via a human body.

The first modulation unit may include a first frequency modulator that modulates the signal transferred from the sound source according to the frequency modulation scheme, and a phase shifter that shifts the phase of the signal whose frequency has been modulated by the first frequency modulator, and transfers the phase-shifted signal to the ultrasonic converter.

The phase shifter may shift the phase of the signal received from the first frequency modulator by 90˚.

The second modulation unit may include a time delay part that delays the signal transferred from the sound source, and a second frequency modulator that modulates the delayed signal according to the frequency modulation scheme.

The ultrasonic converter may process the signal received from the first modulation unit and the signal received from the second modulation unit through separate devices.

According to another aspect of the present invention, there is provided a method for transmitting an audio signal based on a frequency modulation scheme, including: a first step of generating an audio signal from a sound source; a second step of modulating the frequency of the signal generated from the sound source and shifting the phase of the frequency-modulated signal; a third step of delaying the signal generated from the sound source and modulating the frequency of the delayed signal; a fourth step of receiving the phase-shifted signal and the frequency-modulated delayed signal and converting them into ultrasonic signals; and a fifth step of transmitting the converted signals via a human body.

The second step may include: modulating the signal transferred from the sound source according to the frequency modulation scheme; and shifting the phase of the frequency-modulated signal.

The third step may include: delaying the signal transferred from the sound source; and modulating the delayed signal according to the frequency modulation scheme.

In the fourth step, the phase-shifted signal and the frequency-modulated signal may be sequentially converted, respectively, or simultaneously converted.

As set forth above, the device for transmitting an audio signal based on frequency modulation according to exemplary embodiments of the invention has the advantages that because it uses the nonlinear operation of a human body, it does not need to use a receiving device. Also, a frequency bandwidth can be variably adjusted by using the frequency modulation scheme, and audio communication can be performed by using the human body which is resistant (i.e., strong) to noise.

The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic block diagram illustrating the configuration of a device for transmitting an audio signal based on a frequency modulation scheme according to an exemplary embodiment of the present invention; and

FIG. 2 is a flow chart illustrating the process of changing an audio signal in each element of the device for transmitting an audio signal based on a frequency modulation scheme according to an exemplary embodiment of the present invention.

Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The invention may however be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the shapes and dimensions may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like components.

FIG. 1 is a schematic block diagram illustrating the configuration of a device for transmitting an audio signal based on a frequency modulation scheme according to an exemplary embodiment of the present invention.

The device for transmitting an audio signal based on a frequency modulation scheme according to an exemplary embodiment of the present invention includes a sound source 110, a first frequency modulator 120, a phase shifter 130, a time delay part 140, a second frequency modulator 150, and an ultrasonic converter 160.

The sound source 110 generates a sound (i.e., audio signal) to be heard by the user's ear. The audio signal generated from the sound source 110 is transmitted to the first frequency modulator 120 by which the audio signal is frequency-modulated and then phase-shifted by 90˚.

The audio signal generated from the sound source 110 is transmitted to the time delay part 140 by which the audio signal is delayed and then frequency-modulated.

The first frequency modulator 120 modulates the audio signal transferred from the sound source 110. In the frequency modulation scheme, the frequency of an RF signal is proportional to the amplitude of the audio signal, whereby the frequency range of a modulated signal can be adjusted.

The audio signal modulated by the first frequency modulator 120 is phase-shifted by 90˚ by the phase shifter 130, which is then transferred to the ultrasonic converter 160.

The time delay part 140 delays the audio signal transferred from the sound source 110 by a predetermined delay time (t_d) and transfers the delayed audio signal to the second frequency modulator 150.

Like the first frequency modulator 120, the second frequency modulator 150 frequency-modulates the td-delayed audio signal and transfers the modulated audio signal to the ultrasonic converter 160.

The ultrasonic converter 160 converts the signals respectively received from the phase shifter 130 and the second frequency modulator 150 into ultrasonic signals and transfers them via a human body channel 170. Here, the respective signals from the phase shifter 130 and the second frequency modulator 150 may be converted into the ultrasonic signals by the single ultrasonic converter 160, or may be converted into ultrasonic signals by separate ultrasonic converters.

The two signals transferred via the human body (i.e., the user) are transmitted to the vicinity of the user's ear, and at this time, an audio signal that can be heard according to a nonlinear operation of the human body is generated, and accordingly, the user can hear the audio signal generated from the sound source 110 without using a receiving device.

FIG. 2 is a flow chart illustrating the process of changing the audio signals in each element of the device for transmitting an audio signal based on a frequency modulation scheme according to an exemplary embodiment of the present invention.

Specifically, FIG. 2 illustrates a method for transmitting an audio signal based on the frequency modulation scheme through the process of changing the audio signals generated from the sound source 110 by the device for transmitting an audio signal based on a frequency modulation scheme before their transmission to the human body.

First, an audio signal with respect to a sound desired to be heard is generated from the sound source 110 (S210).

The generated audio signal is transferred to both the first frequency modulator 120 and the time delay part 140.

The first frequency modulator 120 performs frequency modulation on the received audio signal to generate a signal represented by Equation 5 shown below (S220):

[Equation 5]

In Equation 5, m(τ) is the audio signal, A_c is the amplitude of radio frequency, f_c is the modulated frequency, k_f is frequency sensitivity, and 't' is a current time. These factors may be defined with the same meaning in other equations. The frequency modulation is the modulation scheme in which the frequency of an RF signal is proportional to the amplitude of the audio signal. The frequency range of a modulated signal is adjusted by controlling the frequency sensitivity k_f. The modulated signal has the characteristics that it is resistant to noise, so the sound quality of the audio signal is superior compared with amplitude modulation.

The signal represented by Equation 5 which has been converted by the first frequency modulator 120 is phase-shifted by 90˚ by the phase shifter 130 into a signal represented by Equation 6 shown below (S230):

[Equation 6]

The signal generated thusly, represented by Equation 6, is ultrasonic-converted by the ultrasonic converter 160 (S260).

The audio signal m(τ) transferred to the time delay part 140 is delayed by time t_d (S240).

The delayed signal is transferred to the second frequency modulator 150 so as to be frequency-modulated into a signal represented by Equation shown below (S250). In Equation 7, t_d is a pre-set delay time, and m(τ-t_d) is the delayed signal.

[Equation 7]

The signal which has been modulated by the second frequency modulator 150 is transferred to the ultrasonic converter 160 so as to be ultrasonic-converted (S260) and then transferred via the human body (S270).

When the signals which have been ultrasonic-converted by the ultrasonic converter 160 are applied to the human body and then converted according to the nonlinear operation of the human body in the vicinity of the user's ear as represented by Equation 8 shown below:

[Equation 8]

Equation 8 can be developed into Equation 9 shown below by using a trigonometric function formula.

[Equation 9]

The first term of Equation 9 is a signal in the ultrasonic band which cannot be heard by the user. Meanwhile, if t_d is too small, the second term of Equation 9 may be approximated as represented by Equation 11, using Equation 10 below:

[Equation 10]

[Equation 11]

This can be further approximated into Equation 12 by the development of Taylor series of sine function shown below:

[Equation 12]

Accordingly, when Equation 13 is satisfied, Equation 11 may be approximated into Equation 14.

[Equation 13]

[Equation 14]

In this manner, the two signals applied to the human body are converted into the audio signals (m(t)) by the nonlinear operation of the human body, and accordingly, the user can hear the audio signal (m(t)).

While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

A device for transmitting an audio signal based on frequency modulation, the device comprising:

a first modulation unit that performs frequency modulation on a signal transferred from a sound source, and shifts the phase of the signal;

a second modulation unit that delays the signal transferred from the sound source, and performs frequency modulation on the corresponding signal; and

a ultrasonic converter that receives the signals from the first and second modulation units, converts the received signals into ultrasonic signals, and transmits the converted ultrasonic signals via a human body.
The device of claim 1, wherein the first modulation unit comprises:

a first frequency modulator that modulates the signal transferred from the sound source according to the frequency modulation scheme; and

a phase shifter that shifts the phase of the signal whose frequency has been modulated by the first frequency modulator, and transfers the phase-shifted signal to the ultrasonic converter.
The device of claim 2, wherein the phase shifter shifts the phase of the signal which has been received from the first frequency modulator, by 90˚.
The device of claim 1, wherein the second modulation unit comprises:

a time delay part that delays the signal transferred from the sound source; and

a second frequency modulator that modulates the delayed signal according to the frequency modulation scheme.
A method for transmitting an audio signal based on frequency modulation, the method comprising:

generating an audio signal from a sound source;

modulating the frequency of the signal generated from the sound source according to the frequency modulation scheme and shifting the phase of the frequency-modulated signal;

delaying the signal generated from the sound source and modulating the frequency of the delayed signal according to the frequency modulation scheme;

receiving the phase-shifted signal and the frequency-modulated delayed signal and converting them into ultrasonic signals; and

transmitting the converted signals via a human body, respectively.
The method of claim 5, wherein the phase-shifted signal is a signal obtained by shifting the phase of the modulated signal by 90˚ as represented by Equation shown below:

[Equation 6]

wherein m(τ) is the audio signal, A_c is the amplitude of radio frequency, f_c is the frequency of the RF signal, 't' is a current time, and k_f is frequency sensitivity.
The method of claim 5, wherein the frequency-modulated signal after being delayed is a signal which has been delayed and then frequency-modulated, as represented by Equation 7 shown below:

[Equation 7]

wherein t is a current time, m(τ-t_d) is the delayed signal, A_c is the RF amplitude, f_c is the frequency of the RF signal, and k_f is the frequency sensitivity.
The method of claim 5, wherein, in converting the phase-shifted signal and the time-delayed and then frequency-modulated signal into the ultrasonic signals, the phase-shifted signal and the frequency-modulated signals are sequentially converted, respectively, or simultaneously converted.
The method of claim 5, wherein when the respective ultrasonic signals are applied to a human body, they are converted into audio signals according to a nonlinear operation of the human body.