KR101004364B1 - Communication apparatus method for underwater wireless communications - Google Patents

Abstract

Disclosed are a communication apparatus and method for underwater wireless communication. According to an aspect of the present invention, there is provided a communication apparatus for performing underwater wireless communication, comprising: a modulator for generating a transmission symbol including a modulation section in which an ultrasonic signal is input and modulated into a modulation signal and a protection section inserted at a front end or a rear end of the modulation section An amplifier for amplifying the ultrasonic signal includes an ultrasonic sensor for transmitting and receiving the ultrasonic signal using an underwater channel and a demodulator for demodulating the modulated signal into an original signal. According to the present invention, it is possible to increase the efficiency of information transmission by minimizing signal interference along multiple paths that can occur underwater.

Ultrasound, underwater communication

Description

Communication device and method for underwater wireless communication {COMMUNICATION APPARATUS METHOD FOR UNDERWATER WIRELESS COMMUNICATIONS}

The present invention relates to underwater wireless communication, and more particularly, to an underwater wireless communication method and apparatus that can improve the transmission efficiency considering the underwater environment.

Since oceans are a treasure trove of natural resources and an unexplored field of humanity, research on marine development has been conducted for a long time. Underwater exploration robots have been researched and developed to collect deep sea mineral resources. Underwater wireless communication has been studied to efficiently control them. In addition, as the interest in marine development and disaster prevention system has recently increased, research on underwater sensor networks has been actively conducted, and the necessity of a high speed, low cost, low power underwater ultrasonic communication modem for managing multiple nodes efficiently is increasing. have.

In general, underwater wireless channels have the property of scattering and absorbing radio waves, so they cannot communicate using radio frequency, which is widely used on the ground, and must communicate using ultrasonic waves. Due to the narrow bandwidth, the data rate is low.

As a preceding study for underwater ultrasonic communication, research on underwater channel characteristics and limitations of underwater ultrasonic communication has been conducted. Based on the above research, a study on the development of high power and expensive ultrasonic communication modem applying various modulation / demodulation techniques and signal processing algorithms Was performed. In addition, practical researches on sensor network system design, physical layer (PHY layer) and media access control layer (MAC layer) for various applications in the water have been conducted.

However, the above-mentioned underwater sensor network systems are all implemented using an expensive ultrasonic communication modem, and when a system using a plurality of sensor nodes needs to be constructed, a low-cost, high-performance underwater communication modem is required.

In addition, there is a case of implementing an ultrasonic communication modem using a speaker and a microphone based on the conventional Mica2 sensor node, but has a problem that the application to underwater communication is not suitable because the communication distance is short and the communication environment is limited to the ground.

In addition, although underwater communication experiment was performed using hardware called CORAL manufactured based on the conventional microcontroller unit (hereinafter referred to as 'MCU'), the maximum communication possible by the bit error rate and transmission power according to the communication frequency is possible. Only the distance is mentioned but the maximum transmission speed is not presented.

The present invention is to provide a method and apparatus for improving the efficiency of information transmission by minimizing signal interference due to multiple paths that can occur underwater.

In addition, the present invention can provide a transmission symbol in consideration of the underwater environment that can improve the transmission efficiency in underwater wireless communication.

In addition, the present invention is to provide a method and apparatus that can reduce the error of information transmission and reception by giving a guard time to the transmission symbol.

In addition, the present invention is to provide a method and apparatus for efficiently transmitting information in underwater wireless communication by using the proposed frame format.

In addition, the present invention is to provide a method and apparatus for increasing the reliability of transmission and reception by selectively using channel coding in underwater wireless communication.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

According to an aspect of the present invention, the present invention provides a communication device for performing underwater wireless communication, comprising: a transmission section including a modulation section in which an ultrasonic signal is received and modulated into a modulation signal and a protection section inserted at the front or rear end of the modulation section; A modulator for generating a symbol; an amplifier for amplifying the ultrasonic signal; and a communication device including an ultrasonic sensor for transmitting and receiving the ultrasonic signal using an underwater channel and a demodulator for demodulating the modulated signal into an original signal. Can provide.

According to another aspect of the present invention, the present invention provides a method for performing underwater wireless communication in the underwater wireless communication device, the modulation period and the guard interval inserted into the front end or the rear end of the modulation period and modulated signal received by the ultrasonic signal Generating a transmission symbol including amplifying the ultrasonic signal; transmitting and receiving the ultrasonic signal using an underwater channel; and demodulating the modulated signal into an original signal. Can be provided.

According to the present invention, it is possible to provide a method and apparatus for improving the efficiency of information transmission by minimizing signal interference due to multiple paths that can occur underwater.

In addition, the present invention can provide a transmission symbol in consideration of the underwater environment that can improve the transmission efficiency in underwater wireless communication.

In addition, the present invention can provide a method and apparatus that can reduce the error of information transmission and reception by giving a guard time to the transmission symbol.

In addition, the present invention can provide a method and apparatus for efficiently transmitting information in underwater wireless communication by using the proposed frame format.

In addition, the present invention can provide a method and apparatus for increasing the reliability of transmission and reception by selectively using channel coding in underwater wireless communication.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all transformations, equivalents, and substitutes included in the spirit and scope of the present invention. In the following description of the present invention, if it is determined that the detailed description of the related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 illustrates hardware related to an ultrasonic communication modem implementation according to an embodiment of the present invention.

In this embodiment, the high-speed underwater communication modem is designed and implemented using an MCU and a low-cost general-purpose ultrasonic sensor, and the performance of the underwater communication modem manufactured by performing communication experiments in various environments is provided. For this reason, the present invention discusses the design and implementation method of the ultrasonic communication modem and the transmission and reception signal processing, and confirms the performance of the implemented modem through experiments.

FIG. 1A illustrates an ultrasonic sensor 110 and FIG. 1B illustrates a communication device 120 performing underwater wireless communication, and FIG. 1C illustrates a waterproof process of the communication device 120. It is a figure which shows the state.

The ultrasonic sensor 110 is a sensor that detects distance, thickness, motion, etc. using ultrasonic characteristics or generates ultrasonic waves, and transmits ultrasonic waves for underwater communication. In this embodiment, a low-cost drip-type ultrasonic sensor 110 widely used for distance measurement is used in consideration of the use of a large node, which is a characteristic of the sensor network.

In this embodiment, since the modem is implemented mainly for the performance of underwater ultrasonic communication, the discussion about power supply voltage and power consumption management will not be described.

Hereinafter, the communication modem shown in FIG. 1 (b) will be described in detail as a technology applicable to the physical layer of underwater wireless communication.

2 is a functional block diagram of a communication device according to an embodiment of the present invention and a schematic configuration diagram for performing underwater wireless communication.

Referring to FIG. 2, in the present embodiment, the communication devices 120 and 120 ′ serve as transmitting and receiving devices, and each communication device 120 and 120 ′ is an amplifier 210 and 210 ′ and a modulator 220. , 220 '), demodulators 230 and 230', channel coding units 240 and 240 ', and ultrasonic sensors 110 and 110'.

When the communication device 120 or 120 'serves as a transmitter 120, the information to be transmitted is modulated by the modulator 220, and then an amplifier that detonates the frequency and power of the modulated signal. Via 210, it is output underwater through the ultrasonic sensor 110.

The amplifiers 210 and 210 'amplify the analog signals received by the other communication devices 120 and 120' or amplify the analog signals output to the other communication devices 120 and 120 '.

The modulator 220 converts the ultrasonic signal into a modified ultrasonic signal that can be sent to the transmission link by performing an analog / digital conversion. In the present embodiment, the modulation scheme used in the modulator 220 may adopt binary pulse modulation, which is relatively easy to receive signal processing in consideration of the computational power of the MCU.

In addition, in the present embodiment, the modulators 220 and 220 'may set a modulation signal generation period to discontinuously generate the modulated signal. That is, the modulators 220 and 220 'generate a modulated signal for a predetermined time (modulation time), and do not generate a modulated signal for a predetermined time (protection time) so that the communication device 120 does not output a signal. Do this. This is to minimize signal interference due to multiple paths in an underwater wireless communication environment.

Hereinafter, the roles of the modulators 220 and 220 'and the demodulators 230 and 230' may be described as being performed by an MCU (not shown).

In the transmission, the main frequency is useful when the sensor used in the implementation uses the frequency in water, and it is useful that the intensity of the received signal is the greatest.

In addition, when the communication device 120 or 120 'serves as a receiver 120', the signal input to the ultrasonic sensor 110 'is received by the demodulator 230' via the amplifier 210 '. do.

The demodulator 230 'is an envelope detector that detects an envelope using a diode and a low frequency filter to detect the waveform of an amplitude modulated input signal, and improves the interference by frequency component before modulation to be less susceptible to interference. Contains filters that play a role. This corresponds to a processing method for normalizing that the signal strength is reduced and distorted due to the influence of the underwater channel.

The channel coding units 240 and 240 'selectively channel-code packets transmitted and received through the underwater channel. For example, in the case of a transmitting device, a PPDU (original text) is channel-encoded and then converted into a digitally modulated signal. In the case of a receiving device, the original PPDU is decoded by channel decoding the demodulated signal.

In addition, in the present embodiment, in order to further reduce the signal interference due to the multipath of the underwater wireless communication, the configuration of the transmission symbol transmitted on the underwater channel is as follows.

3 is a diagram illustrating a configuration of a transmission symbol according to an embodiment of the present invention.

The transmission symbol according to the present embodiment includes a modulation section for generating a predetermined modulation signal and a guard band inserted at the front or rear end thereof.

Referring to FIG. 3, T _s denotes a symbol duration transmitted by ultrasonic communication, and the symbol period T _s leaves a guard time of b after modulation for as long as a. In this case, the symbol period during the guard time, that is, the guard period is an area between the modulation periods and a period in which no modulated signal is generated. If the guard interval includes these features, the guard interval may be generated by any technique.

In the underwater channel environment, delay spread due to multi-path causes ISI (Inter Symbol Interference) that affects adjacent symbols, which distorts transmitted symbols and becomes a serious obstacle in underwater communication. However, according to the present embodiment, it is possible to reduce errors in data transmission by reducing signal interference that may occur due to the multipath of underwater wireless communication. In order to prove this effect, the following experiment was conducted.

4 is a graph illustrating signal processing during transmission in a communication device according to an embodiment of the present invention.

In this embodiment, the communication apparatuses 120 and 120 'set the main frequency to 30 kHz at the time of transmission. That is, when the transmission bit is 1, the square wave signal of 18Vp-p having the peak voltage twice the power supply voltage is output at the frequency of 30kHz across the ultrasonic sensors 110 and 110 ', and the square wave signal is output when the transmission bit is 0. It is designed not to.

In addition, when the information to be transmitted is input to the communication device 120, the communication device 120 reads one bit from the most significant bit (MSB) according to the transmission speed of the information, and if the bit value is 1, a predetermined time according to the main frequency While inverting the signal output pin. On the other hand, if the bit value is not 1, nothing is done during 1 symbol transmission time.

Thereafter, the output of the communication device 120 is divided into a signal having an inverted phase and an uninverted signal through a NOT logic gate, and outputs a voltage of 9Vp-p to both ends of the sensor through the amplifier 210, respectively. do. The input across the sensor can achieve the same effect as the voltage of 18Vp-p is applied by the instantaneous phase difference.

4 shows an example of a voltage across the transmitter sensor that transmits 1-byte information of 0xAC at 1 kbps as an example of transmission signal processing. Here, T ₁ denotes a transmission time per symbol, that is, 1 / T ₁ denotes a transmission rate, and T ₂ denotes an inverse of the main frequency.

Referring to FIG. 3, T ₁ corresponds to a symbol period T _s . In addition, the modulation time a is T ₃ , and the protection time b corresponds to (T ₁ -T ₃ ). That is, in the present embodiment, a square wave is output for transmission bit 1 for T ₃ hours, and a guard interval is provided for (T ₁ -T ₃ ) time, which is an important factor affecting the data rate and the communication distance according to the communication environment. This can be called.

5 is a graph illustrating signal processing upon reception in a communication device according to an embodiment of the present invention.

That is, FIG. 5 illustrates a signal processing process when the communication device 120 'receives a signal. Each waveform measures an output voltage with an oscilloscope at a specific position of a receiving circuit.

5 (a) shows a waveform obtained by firstly amplifying a signal input to a reception sensor, and it can be seen that a multi-path signal due to a channel environment is mixed with a signal determined as an estimate of a transmission signal. . Multipath signal has a big difference according to the underwater channel environment, which is one of the important factors affecting the information transmission rate of underwater ultrasonic communication.

5B shows a waveform in which the first amplified signal is changed into a low frequency signal by an envelope detector.

FIG. 5 (c) shows a second amplified signal after the noise signal generated in the channel is removed by the filter. In this example, the amplification ratio is set to almost 1 in consideration of the large output signal strength of the envelope detector, but the amplification ratio may vary depending on the channel environment or the distance between the modems. In addition, when an automatic gain controller (AGC) is applied later, it is expected that flexible and reliable signal processing can be performed.

The waveform (d) of FIG. 5 shows that the second narrowly amplified signal is changed into a high or low stabilized signal by Schmitt-trigger hysteresis. This signal is connected to the interrupt pin of the MCU. When the first rising edge of the data packet is input, it generates an interrupt to the MCU to start sampling the received signal. .

Sampling is performed three times at 50us intervals after the initial interrupt is generated, and sampling is performed in the same manner every T ₁ hour. Finally, a majority voting is performed on the sampled values to determine the received bit.

On the other hand, to measure the strength of the received signal, the output of the second amplified signal is input to the analog-to-digital converter (ADC) pin of the MCU and converts the analog signal into a digital signal at about the same time as the sampling is performed. .

The measured reception strength is a kind of received signal strength indicator (RSSI) value indicating a distance between modems and a current channel state, and is expected to be used for resource allocation in the AGC implementation and the media access control layer.

6 is a diagram illustrating a packet format for performing wireless underwater communication according to an embodiment of the present invention.

Referring to FIG. 6, in this embodiment, the packet format includes a synchronization field (Preamble field), a packet length field, and an information data field. This embodiment simply configures the packet format because the present embodiment performs the experiment mainly on the communication performance between the ultrasonic communication modems.

Here, the synchronization field (Preamble field) performs communication synchronization, the packet length field (packet length field) represents the size of the information data included in the packet, the information data section (information data field) includes the information to be transmitted do.

In the present embodiment, the preamble value uses 0xAC out of arbitrary 1 byte data having the MSB of 1 due to received signal processing characteristics. In addition, the packet length section indicates the number of bytes of information data carried in the packet, which is also used as information for measuring received signal strength. That is, in this embodiment, since the information data per packet is fixed to 127 bytes, the packet length section always has a value of 0x7F.

Since the communication device 120 ′ knows this value in advance when performing the role of a receiver, the communication device 120 ′ defines an average value of reception strength for 7 bits having a value of 1 as the reception signal strength of one packet.

According to another embodiment of the present invention, a PHY Protocol Data Unit (PPDU) includes a synchronization field (Preamble field), a Start of Frame Delimiter field (SFD), a frame length field, and a reserved field. ) And PSDU interval (PHY Service Data Unit field).

In the configuration of the PPDU, a synchronization field (Preamble field) is used to synchronize the transmitting side and the receiving side, and the SFD section (Start of Frame Delimiter field) indicates that the synchronization is completed, and also indicates the start of packet data.

The frame length field is a section indicating the length of the payload (PSDU), the reserved field is inserted to be used for additional purposes, and the PSDU section (PHY Service Data Unit field) is a higher layer. The payload passed in. Here, each field may have a specific length.

As such, the packet format according to the present embodiment may vary depending on the application.

7 is a table illustrating a change in received signal strength according to a change in a square wave signal output time T ₃ in a communication device according to an embodiment of the present invention.

Referring to FIG. 7, T ₂ means an inverse of the main frequency, and the square wave signal output time T ₃ is selected as multiples of T ₂ . In addition, the received signal strength is that the packet length field signal of the data packet among the output signals of the secondary amplifiers 210 and 220 'of the receiver is converted into a linear 256 level from 0x00 to 0xFF by the ADC of the MCU.

Experimental results show that as the T ₃ increases, the received signal strength increases, while the increase rate of the signal strength decreases gradually. In addition, when T ₃ is 1 · T ₂ , the signal strength is weak and information loss increases.In the case of 10 · T ₂ , the received signal strength increases, but the interference between multipaths and symbols increases due to the narrow experimental environment. I could confirm it.

This means that when the communication device transmits a signal, the smaller the modulation time, that is, the greater the protection time, the higher the intensity of the received signal received by the other communication device.

On the other hand, after fixing the square wave signal output time to 2 · T ₂ , a communication performance test was performed while varying the distance between the two communication devices 120 and 120 ′. As the communication distance increases, the strength of the received signal decreases drastically. I could confirm it. The results indicate that the measured value of the received signal strength can be used as important information for estimating the state of the channel or the distance between the communication devices 120 and 120 '.

8 is a table illustrating a bit error rate (BER) according to a change in data rate and a square wave signal output time T ₃ per symbol in a communication device according to an embodiment of the present invention.

Referring to FIG. 8, when the data rates of the communication devices 120 and 120 'were fixed at 1 kbps and T ₃ was set to 2 · T ₂ and 3 · T ₂ , a BER performance of 10 ⁻⁶ was obtained. _{When 3} is less than 2 · T ₂ or greater than 3 · T ₂ , the bit error rate (BER) is significantly higher.

Similar characteristics were also observed when the data rate was fixed at 1.2 kbps or 1.5 kbps. In the case that T ₃ is 3 · T ₂ , bit error rate is about 10 times higher than that of 2 · T ₂ . It can be inferred that the effects of multiple paths in the current experimental environment are significant. This means that as the guard interval of the transmission symbol transmitted from the communication device increases, the bit error rate decreases.

The method of performing underwater wireless communication in the apparatus according to the present invention may be implemented in the form of program instructions that can be executed by various computer means and recorded in a computer readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. Program instructions recorded on the media may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of computer-readable recording media include magnetic media, such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks, 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. The medium may be a transmission medium such as an optical or metal wire, a waveguide, or the like including a carrier wave for transmitting a signal specifying a program command, a data structure, and the like. Examples of program instructions include not only machine code generated by the compiler, but also high-level language code that can be executed by a computer using an interpreter. The hardware device described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art to which the present invention pertains without departing from the spirit and scope of the present invention as set forth in the claims below It will be appreciated that modifications and changes can be made.

1 illustrates hardware related to an ultrasonic communication modem implementation in accordance with one embodiment of the present invention.

2 is a functional block diagram of a communication device according to an embodiment of the present invention and a schematic configuration diagram for performing underwater wireless communication.

3 is a diagram illustrating a configuration of a transmission symbol according to an embodiment of the present invention.

4 is a graph illustrating signal processing during transmission in a communication device according to an embodiment of the present invention.

5 is a graph illustrating signal processing upon reception in a communication device according to an embodiment of the present invention.

6 illustrates a packet format for performing wireless underwater communication according to another embodiment of the present invention.

7 is a table illustrating a change in received signal strength according to a change in a square wave signal output time T ₃ in a communication device according to an embodiment of the present invention.

8 is a table illustrating a bit error rate (BER) according to a change in data rate and square wave signal output time (T ₃ ) per symbol in a communication device according to an embodiment of the present invention.

Claims (12)

A communication device for performing underwater wireless communication, A modulator for generating a transmission symbol including a modulation period in which an ultrasonic signal is modulated into a modulation signal and a guard period inserted at a front end or a rear end of the modulation period; An amplifier for amplifying the ultrasonic signal; An ultrasonic sensor for transmitting and receiving the amplified ultrasonic signal using an underwater channel; And A demodulator for demodulating the modulated signal, The guard period is a communication device for performing underwater wireless communication, characterized in that the area is not modulated. delete The method of claim 1, The format of the packet transmitted and received through the underwater channel is Underwater comprising a synchronization field (Preamble field), SFD section (Start of Frame Delimiter field), Frame length field (Reserved field), PSDU section (PHY Service Data Unit field) Communication device that performs wireless communication. The method of claim 1, And a strength of a signal received by the communication device increases as a modulation time for outputting a modulation signal transmitted from the communication device increases. The method of claim 1, And a bit error rate decreases as the guard interval of the transmission symbol increases. The method of claim 1, A communication apparatus for performing underwater wireless communication, characterized in that the channel coding selectively transmitted and received through the underwater channel. A method of performing underwater wireless communication in an underwater wireless communication device, Generating a transmission symbol including a modulation period in which an ultrasonic signal is modulated into a modulation signal and a guard period inserted at a front end or a rear end of the modulation period; Amplifying the ultrasonic signal; Transmitting and receiving the ultrasonic signal using an underwater channel; And Demodulating the modulated signal into an original signal; The guard period is a method of performing underwater wireless communication, characterized in that the data or time domain is not modulated. delete The method of claim 7, wherein The format of the packet transmitted and received through the underwater channel is Underwater comprising a synchronization field (Preamble field), SFD section (Start of Frame Delimiter field), Frame length field (Reserved field), PSDU section (PHY Service Data Unit field) How to perform wireless communication. The method of claim 7, wherein And the intensity of a signal received at the communication device increases as the modulation time for outputting the modulated signal transmitted from the communication device increases. The method of claim 7, wherein And the larger the guard interval of the transmission symbol, the lower the bit error rate. The method of claim 7, wherein A method for performing underwater wireless communication, characterized in that the channel coding selectively transmitted and received through the underwater channel.

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