KR100941853B1 - An apparatus and a method for transmitting a digital signal under water channel - Google Patents

Abstract

The present invention includes receiving a pilot signal from a receiver for a predetermined time, generating a reverse impulse response of an underwater channel, generating a signal to be transmitted to a receiver, precoding the transmitted signal with the generated reverse impulse response, And transmitting the precoded signal through the underwater channel to the receiving end.

According to the present invention, in the underwater channel, when transmitting a digital signal by precoding, it is possible for the receiver to receive data to be transmitted by the transmitter with minimal equalization.

Underwater channel

Description

An apparatus and method for transmitting a digital signal in an underwater channel {An apparatus and a method for transmitting a digital signal under water channel}

The present invention relates to an apparatus and method for transmitting digital signals underwater, and more particularly, to an apparatus and method for transmitting digital signals without distortion, in consideration of the specificity of the underwater channel environment.

Digital signals transmitted underwater generate reflections and refractions at the bottom and sea level, and are propagated in multiple paths and received at the receiving end. Because of this characteristic, it is difficult to detect accurate phase synchronization when communicating underwater. In order to overcome the limitation of multi propagation path phenomenon, underwater communication uses non-coherent which is not affected by multi propagation path phenomenon, or multipath in coherent using equalizer. The effects can be corrected. However, the non-phase synchronization method has a lower data rate than the synchronous phase method. In case of using synchronous digital communication technique underwater, intersymbol interference (ISI) occurs due to multiple propagation path phenomena, making it difficult to match phase synchronization. To solve this problem, the equalizer is used in underwater communication system. . However, for underwater communication systems that require the use of a built-in power source, the use of an equalizer is a detrimental factor to the performance of the system.

When using the synchronous phase method in such an underwater communication system, there is a need for a digital communication technique capable of minimizing signal distortion in an underwater channel while simplifying or eliminating equalization at a receiving end.

The present invention is to solve the signal distortion in the underwater channel as described above, to provide a digital communication technique that can improve the signal performance while eliminating or simplifying the equalization in the receiving system.

The present invention is to propose a digital communication technique that can improve the communication performance in a special environment called an underwater channel environment.

In order to achieve the above object, the present invention receives a pilot signal from the receiving end for a predetermined time, generating a reverse impulse response of the underwater channel, generating a signal to be transmitted to the receiving end, the transmission in the generated reverse impulse response A method of transmitting a digital signal in an underwater channel, the method comprising precoding a signal, and transmitting the precoded signal through the underwater channel to the receiving end.

In this case, the pilot signal is characterized by using a Ricker wave (Ricker Wave) of the frequency band (bandlimited).

At this time, the Ricker wave (Ricker Wave) is the following formula

을 만족하는 것을 특징으로 한다.

It is characterized by satisfying.

Where t is greater than 0, less than 3 / fc (0 <t <3 / fc), and fc is the center frequency.

In this case, the pilot signal is characterized by using a Gaussian pulse, which is a pulse having a Gaussian distribution function in the pulse waveform in the time domain.

In this case, the step of precoding the signal to be transmitted is a step of pre-distorting the signal to be transmitted at the transmitting end, characterized in that the convolution of the inverse impulse response to the signal to be transmitted.

At this time, the precoded signal is the following equation

을 만족하는 것을 특징으로 한다.

It is characterized by satisfying.

Where s' (t) is a precoded signal, s (t) is a signal to be transmitted, S (f) is a Fourier transformed signal of s (t), h (t) is an impulse response of an underwater channel, and H (f Is a signal obtained by Fourier transforming h (t), r (t) is a received signal of the receiving end, and R (f) is a signal obtained by Fourier transforming r (t).

At this time, the predetermined time is characterized in that the time is more than the time that the pilot signal is transmitted from the receiving end to the transmitting end, the transmitted pilot signal is completely attenuated so that there is no reverberation sound.

According to another embodiment of the present invention, the present invention provides a receiver for receiving a pilot signal from a receiver for a predetermined time, a data encoder for encoding a data to be transmitted to the receiver, and generating a signal to be transmitted, and analyzing a pilot signal received by the receiver. A control unit for generating an inverse impulse response of the underwater channel, a precoding unit for precoding the signal to be transmitted with the inverse impulse response generated by the control unit, and a transmitter for transmitting the signal precoded by the precoding unit through the underwater channel It provides a digital signal transmission apparatus in an underwater channel comprising a.

The control unit transmits a pilot signal from a receiving end to a transmitting end, and controls the receiving unit to receive the pilot signal for more than a time when the transmitted pilot signal is completely attenuated and there is no reverberation sound.

The precoded signal is expressed by the following equation

을 만족하는 것을 특징으로 한다.

It is characterized by satisfying.

Where s' (t) is a precoded signal, s (t) is a signal to be transmitted, S (f) is a Fourier transformed signal of s (t), h (t) is an impulse response of an underwater channel, and H (f Is a signal obtained by Fourier transforming h (t), r (t) is a received signal of the receiving end, and R (f) is a signal obtained by Fourier transforming r (t).

The effects of the digital signal transmission apparatus and method in the water according to the present invention described above are as follows.

According to the present invention, in the underwater channel, when transmitting a digital signal by precoding processing, the receiver can receive the data to be transmitted from the transmitting end with minimal equalization.

According to the present invention, since the equalizer is not used at the receiving end or the equalization can be minimized, the burden of power and equipment loading of the system can be reduced, and thus the signal receiving performance of the receiving side can be improved.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention that can specifically realize the above object will be described. At this time, the configuration and operation of the present invention shown in the drawings and described by it will be described as at least one embodiment, by which the technical spirit of the present invention and its core configuration and operation is not limited.

1 is a flowchart illustrating a digital signal transmission method according to an embodiment of the present invention.

1, in the digital signal transmission method according to the present invention, receiving a pilot signal from a receiver for a predetermined time, generating a reverse impulse response of an underwater channel, generating a signal to be transmitted to a receiver, and the generated station. Precoding the signal to be transmitted in a pulse response, and transmitting the precoded signal to the receiving end.

Receiving a pilot signal from the receiving end for a predetermined time (S10) is received for a predetermined time (Pulse Response Duration: hereinafter referred to as PRD) after transmitting the pilot signal at the receiving end, the status of the channel and / or channel at the transmitting end The characteristics will be judged.

A pilot signal transmitted by the receiver, received by the transmitter, and informing the characteristics of the channel will be described with reference to FIGS. 2 to 4.

Using the received pilot signal, a reverse impulse response of the underwater channel is generated (S20).

Let's look at how to generate a reverse impulse response.

If the impulse response of the underwater channel environment is h (t), the transmitter sends s (t), and the receiver receives r (t), the response r (t) received by the receiver is expressed as Satisfies.

r (t) = s (t) * h (t)

In addition, the impulse response h (t) and the inverse impulse response ih (t) satisfy the following equation (2).

h (t) * ih (t) = δ (t)

The Fourier transform of Equation 2 satisfies Equation 3 below in the frequency domain.

H (f) IH (f) = 1

Before transmitting the signal s (t) to be transmitted, convolution with ih (t) (*), the received signal r (t) becomes the transmission signal s (t), and satisfies Equation 4 below. do.

r (t) = {s (t) * ih (t)} * h (t)

    = s (t) * {ih (t) * h (t)} = s (t)

Using Equation 3, the inverse impulse response can be obtained by Equation 5 as follows.

In order to know the impulse response of the channel, the channel response is obtained by transmitting a suitable pulse and comparing the signal measured at the receiver with the original pulse. A pilot signal transmitted by the receiver, received by the transmitter, and informing the characteristics of the channel will be described with reference to FIGS. 2 to 4.

When Fourier transforms Equation 1, R (f) = S (f) H (f), so that the channel response can be obtained by Equation 6.

H (f) = R (f) / S (f)

In addition, the inverse impulse response required for pre-coding of a signal to be transmitted according to the present invention can be obtained by Equation 7 below.

If a convolution (*) is transmitted in convolution with a signal to transmit the inverse impulse response obtained by Equation 7, the receiver can receive the reconstructed signal. In this specification, the frequency response H (w) was calculated using the Discrete Fourier Transform, and the inverse Fourier transform was also obtained using the Discrete Fourier Transform. This is merely an embodiment, and can be obtained using other operations and using frequency response and inverse Fourier transform, and such a calculation method does not limit the scope of the present invention.

Generating a signal to be transmitted to the receiver (S30) is a process of encoding data to be transmitted. In the present specification, a signal to be transmitted will be referred to as s (t).

The step S40 of precoding the signal s (t) to be transmitted is a step of distorting the signal to be transmitted in advance at the transmitter, thereby convolving a de-impulse response to the signal to be transmitted.

If a transmission signal obtained by pre-coding the signal to be transmitted to the receiver is s '(t), the transmission signal s' (t) can be generated by Equation 8 as follows.

s' (t) = ih (t) * s (t)

If s (t) is equal to the signal to be used for channel impulse estimation, the following equation (9) holds.

Where R (f) is the Fourier transform of the signal r (t) received by the receiver.

In step S50, the signal s' (t), which is a precoded signal, is transmitted to the receiver.

When s' (t), which is a precoded signal, is transmitted, the receiving side receives s (t).

Since the frequency component of the signal to be transmitted is in the 0 ~ 200kHz band, passing through a bandpass filter that accepts only signals in the 0 ~ 200kHz band, it is possible to remove the ambient noise existing in the unnecessary band. In addition, a sufficient sampling rate of the transmission and reception signals can be provided to prevent signal aliasing.

2 to 4 show waveforms according to types of signals.

2A to 2E show waveform diagrams in the case of transmitting a sine wave.

FIG. 2A is a sine wave which is a signal to be transmitted, and FIG. 2B shows S (f) by Fourier transforming a transmission signal s (t) into a frequency domain. 2C shows s '(t) with inverse Fourier transform of precoded S' (f). FIG. 2D shows a waveform after passing the s' (t) through the underwater channel, and FIG. 2E is an enlarged waveform diagram of a predetermined portion (dashed box portion) of FIG. 2D. This waveform becomes the signal finally received at the receiving end.

Looking at Figure 2e, it can be seen that the sine wave is finally restored, but slightly distorted.

3A to 3E show waveform diagrams in the case of transmitting a square wave.

FIG. 3A shows a square wave as a signal to be transmitted, and FIG. 3B shows S (f) by Fourier transforming the transmission signal s (t) into a frequency domain. 3C shows s '(t) with inverse Fourier transform of precoded S' (f). FIG. 3D shows a waveform after passing the s' (t) through the underwater channel, and FIG. 3E is an enlarged waveform diagram of a predetermined portion (dashed box portion) of FIG. 3D. This waveform becomes the signal finally received at the receiving end.

Referring to FIG. 3E, it can be seen that the square wave is finally restored, but distorted to some extent as in the case of the sine wave.

4A to 4E show waveform diagrams in the case of transmitting a leaker wave.

4A is a recursive signal which is a signal to be transmitted, and FIG. 4B shows a S (f) obtained by Fourier transforming a transmission signal s (t) into a frequency domain. Referring to FIG. 4B, the liquor wave is a waveform in which the frequency band is limited.

The Ricker wave satisfies Equation 10 below.

Where t is greater than 0, less than 3 / fc (0 <t <3 / fc), and fc is the center frequency.

4C shows s '(t) with inverse Fourier transform of precoded S' (f). FIG. 4D shows a waveform after passing s' (t) through the underwater channel, and FIG. 4E is an enlarged waveform diagram of a predetermined portion (dashed box portion) of FIG. 4D. This waveform becomes the signal finally received at the receiving end.

Referring to FIG. 4E, unlike the result of a sine wave or a square wave, it can be seen that the liquor wave is restored with almost no distortion. This difference is considered to be an effect of the bandpass filter. That is, since the waver wave has a large amount of energy of a wave in a predetermined frequency band, for example, 50 to 150 kHz, the wave may be relatively less affected, and the distortion may be reduced compared to other waveforms.

As described above, since the liquor wave has less distortion due to the influence of the channel, the present invention uses the liquor wave as a pilot signal, transmits the liquor wave to the transmitting end at the receiving end, and receives the liquor wave at the transmitting end, thereby serving as an underwater channel. The pulse response can be obtained. In the digital communication, since the frequency band is limited, only the channel response of the frequency band used by the adopted digital communication technique needs to be found. Therefore, it is appropriate to use a liquor wave with a limited frequency band as a pilot signal.

In addition, a Gaussian pulse may be used as a pilot signal for channel measurement. Gaussian pulses are pulses in which the pulse waveform in the time domain has a Gaussian distribution function. The Gaussian pulse can be represented by Equation 11 below.

5A through 5B illustrate waveforms of an embodiment of a digital signal transmission method in an underwater channel according to the present invention.

A Ricker wave having a center frequency of 100 kHz is received as a pilot signal from the receiver (FIG. 5A), and a reverse impulse response is generated from the received pilot signal (FIG. 5B). A signal to be transmitted is generated (FIG. 5C) and a signal to be transmitted is precoded (FIG. 5D). The precoded signal is transmitted to the receiver, and the receiver receives the precoded signal (FIG. 5E).

5C and 5E, it can be seen that the signal to be transmitted and the signal received at the receiver are almost identical.

6 to 9 show the performance of the digital signal transmission method in the underwater channel according to the present invention in various indices.

There are two ways to influence the reconstruction of signals in digital signal communication using the precoding technique. The first is the Signal to Noise Ratio (SNR). In this specification, SNR is defined as the ratio of the power of the earliest arriving pulse to the background noise in the pilot signal response. The second time is the measurement of the pilot signal response. This is referred to herein as a measurement length of a pilot signal response (Pilot Response Duration: hereinafter referred to as PRD). The longer the PRD is, the better it is possible to reflect the multiple condensation. However, the signal recovery by the precoding is smooth, but the calculation time of the inverse impulse response may be long, and the memory may take up a lot of memory.

The SNR required for precoding can be taken as a reference by measuring the point where the BER becomes to some extent possible for digital communication. This may vary for each type of pilot signal. For example, if a digital communication that a certain amount of available BER is ^10-3, the BER can be based on the point at which the ^10-3.

The PRD transmits a pilot signal from a receiving end to a transmitting end, and causes the transmitted pilot signal to be completely attenuated for more than the time when no reverberation sound exists. For example, if the reverberation sound is present for 100 ms after the pilot signal is transmitted, more than 100 ms may be sufficient PRD. Since the reverberation time varies depending on the environment, the optimal PRD is applied differently according to the environment.

In the present specification, it is possible to determine the digital communication performance as a performance index, which is defined as the ratio of the power of the recovered signal and the power of noise generated due to precoding. The figure of merit is an indication of the reconstruction performance of the signal.

6A and 6B show graphs and tables of values of the performance index according to the signal-to-noise ratio (SNR) and the measured length (PRD) of the pilot signal response.

6A and 6B, the higher the SNR and the longer the PRD, the higher the performance index. If the PRD is longer than a certain time, the impact on improving the figure of merit decreases, because the measurement was made for enough time to reflect the multipath phenomena.

7 shows average error rate and standard deviation according to SNR and PRD.

In order to measure the bit error rate (hereinafter referred to as BER), after generating data of a constant, for example, 1000 bits, and transmitting data by using precoding, an error according to the change of the SNR and the PRD The number of bits was measured and shown in FIG. 7.

When the PRD is 4ms or 8ms, the change in SNR does not significantly affect the change in BER, and the error rate is maintained. This may be because the multipath phenomenon was not sufficiently reflected regardless of the signal strength. If the PRD exceeds 16ms, the error rate tends to decrease as the SNR increases.

8A and 8B illustrate graphs and tables showing lengths of data to be transmitted and error rates according to PRDs. Data of 500 bits, 1000 bits, and 2000 bits is transmitted by the precoding scheme, and respective BERs are obtained and shown in FIGS. 8A and 8B. Since the error value when the data is 500 bits and the PRD is 32 ms is 0, it is not shown in Fig. 8A.

8A and 8B, it appears that the error rate tends to increase as the amount of data increases.

9A and 9B show the BER according to PRD, averaging each BER.

Referring to FIGS. 9A and 9B, considering that the BER for transmitting satisfactory data is 10 ⁻³ , a predetermined degree of SNR is required to perform an appropriate level of digital communication, as can be seen from the BER result.

10 is a block diagram of an apparatus for transmitting digital signals in an underwater channel according to an embodiment of the present invention.

Referring to FIG. 10, the apparatus 100 for transmitting digital signals includes a receiver 101, a data encoder 103, a controller 102, a transmitter 105, and a precoding unit 104.

The receiver 101 receives the pilot signal transmitted from the receiver.

The data encoder 103 encodes data to generate a signal to be transmitted.

The controller 102 generates a channel impulse response using the pilot signal received by the receiver 101 to determine a channel characteristic, and generates a reverse impulse response. It also controls the signal processing of the entire transmitter.

The precoding unit 104 precodes a transmission signal generated by the data encoder 103 using the inverse impulse response generated by the control unit 104.

The transmitter 104 transmits a signal precoded by the precoder 104 to a receiver.

The detailed operation in each of the above blocks applies to the above description of the present specification.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

1 is a flowchart illustrating a digital signal transmission method according to an embodiment of the present invention.

2A to 2E show waveform diagrams in the case of transmitting a sine wave.

3A to 3E show waveform diagrams in the case of transmitting a square wave.

4A to 4E show waveform diagrams in the case of transmitting a leaker wave.

5A-5B show, in waveforms, an embodiment of a digital signal transmission method in an underwater channel according to the present invention.

6A and 6B show graphs and tables of values of the performance index according to the signal-to-noise ratio (SNR) and the measured length (PRD) of the pilot signal response.

7 shows average error rate and standard deviation according to SNR and PRD.

8A and 8B illustrate graphs and tables showing lengths of data to be transmitted and error rates according to PRDs.

9A and 9B show the BER according to PRD, averaging each BER.

10 is a block diagram of an apparatus for transmitting digital signals in an underwater channel according to an embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

100: digital signal transmission device 101: receiver

102 control unit 103 data encoder

104: precoding section 105: transmitting section

Claims (10)

Receiving a pilot signal from a receiving end for a predetermined time to generate a reverse impulse response of the underwater channel; Generating a signal to transmit to a receiving end; Precoding the signal to be transmitted with the generated inverse impulse response; Transmitting the precoded signal through the underwater channel to the receiving end; The precoded signal satisfies the following equation, wherein the digital signal transmission method in the underwater channel

Where s' (t) is the precoded signal, s (t) is a signal to be transmitted, S (f) is a signal obtained by Fourier transforming s (t), h (t) is the impulse response of the underwater channel, H (f) is the Fourier-converted signal of h (t), r (t) is the received signal at the receiving end, and R (f) is the signal obtained by Fourier transforming r (t). The method of claim 1, The pilot signal is a digital signal transmission method in the underwater channel, characterized in that for using a limited band (Ricker Wave) of the frequency band (Ricker Wave). The method of claim 2, The Ricker wave is a digital signal transmission method in the underwater channel, characterized in that the following formula

Where t is greater than 0 and less than 3 / fc (0 <t <3 / fc) fc is the center frequency). The method of claim 1, The pilot signal is a digital signal transmission method in an underwater channel using a Gaussian pulse, the pulse waveform of the time domain in the form of a Gaussian distribution function. The method of claim 1, The precoding of the signal to be transmitted includes distorting a signal to be transmitted in advance at a transmitting end, and converging a reverse impulse response to the signal to be transmitted. delete The method of claim 1, The predetermined time is a time for transmitting a pilot signal from a receiving end to a transmitting end, and the time when the transmitted pilot signal is completely attenuated so that there is no reverberation sound. A receiver which receives a pilot signal from a receiver for a predetermined time; A data encoder for encoding a data to be transmitted to a receiver and generating a signal to be transmitted; A controller configured to analyze the pilot signal received by the receiver and generate a reverse impulse response of the underwater channel; A precoding unit which precodes the signal to be transmitted by the inverse impulse response generated by the controller; And A transmitter which transmits a signal precoded by the precoding unit through an underwater channel, The precoded signal is a digital signal transmission apparatus in the underwater channel, characterized in that the following formula

Where s' (t) is the precoded signal, s (t) is a signal to be transmitted, S (f) is a signal obtained by Fourier transforming s (t), h (t) is the impulse response of the underwater channel, H (f) is the Fourier-converted signal of h (t), r (t) is the received signal at the receiving end, and R (f) is the signal obtained by Fourier transforming r (t). The method of claim 8, The control unit transmits a pilot signal from a receiving end to a transmitting end, and controls the receiving unit to receive the pilot signal for more than a time when the transmitted pilot signal is completely attenuated and there is no reverberation sound. Transmitting device. delete

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