KR20220152007A - Low power/high efficiency underwater communication system and method for underwater internet of things - Google Patents

Abstract

Disclosed are a low-power/high-efficiency underwater communication system for an underwater Internet-of-Things (IoT) and an underwater communication method thereof. According to the present invention, the low-power/high-efficiency underwater communication system for the underwater IoT comprises: a transmitter transmitting a bit having a length of L for each transmission symbol block, and distributing the bit with the length of L into bits of lengths smaller than L, and generating and transmitting a base band transmission signal block based on symbol modulation, chip spread spectrum (CSS) modulation, and random sequence selection by corresponding to each of the distributed bits; and a receiver detecting a bit with the length of L based on a base band reception signal block received from the transmitter.

Description

Low-power/high-efficiency underwater communication system for underwater IoT and its underwater communication method

The present invention relates to an underwater communication system and an underwater communication method thereof, and more particularly, uses a Chirp Spread Spectrum (CSS) modulation method based on pilot symbol transmission, scrambling, and superposition modulation techniques, and provides an underwater Internet of Things (IoT). It relates to a low-power / high-efficiency underwater communication system and an underwater communication method for underwater IoT, which can minimize power consumption in water and increase frequency efficiency.

In the case of underwater IoT, a wider coverage is required than land IoT, considering the wide sea area, device construction cost, and battery replacement cost. On the other hand, in the case of underwater environmental sensing data such as water temperature, salinity, and dissolved oxygen, the change over time is not large. Therefore, the transmission speed required for underwater acoustic communication for the underwater IoT is not very high.

Compared to terrestrial communication, the characteristic of underwater acoustic communication for underwater IoT is that the amount of change in the underwater channel is very large. The underwater environment has a large change over time due to various environmental factors such as tides, waves, and water temperature differences according to water depth.

The propagation speed of sound waves used in underwater acoustic communication in water is about 1500 m/s. Considering that the frequency band used for underwater acoustic communication is several kHz to several tens of kHz, it can be said that the propagation speed of sound waves is very slow. Due to the slow propagation speed of the sound wave, the amount of change in the underwater channel over time becomes relatively large, which greatly impedes the performance of underwater acoustic communication.

In underwater acoustic communication, a change in an underwater channel over time causes a Doppler phenomenon in a received signal. Furthermore, because of the slow propagation speed of sound waves, the start position of the received signal may rapidly change over time.

In the case of terrestrial communication, since the propagation speed of radio waves is the same as the speed of light, it can be assumed that the starting point of the signal received afterwards does not change if time synchronization is performed based on a known signal such as a preamble and the time error is compensated. have.

However, in the case of underwater acoustic communication, even if time synchronization is performed and the time error is compensated for, the starting point of a signal received thereafter may change due to a change in an underwater channel. If the changed starting point is not compensated for every predetermined received signal interval, the performance of the communication system can be greatly degraded.

Another characteristic of the underwater IoT is that it is very difficult to supply a separate power source. In the case of a device installed underwater, the cost and time required for installation and recovery are very high. Therefore, once installed, long-term operation is very important. To this end, it is necessary to minimize the power consumed in underwater acoustic communication.

In a communication system, the most power is consumed for signal amplification for transmitting a transmission signal. Therefore, if the frequency efficiency or transmission speed of the communication system can be increased, the number of signal transmissions can be reduced, and thus power consumption of the communication system can be greatly reduced.

Publication No. 10-2012-0062587 (published date: 2012.06.14)

The present invention was devised to solve the above problems, and uses a Chirp Spread Spectrum (CSS) modulation method based on pilot symbol transmission, scrambling, and superposition modulation techniques, and consumes water in water for the underwater Internet of Things. An object of the present invention is to provide a low-power / high-efficiency underwater communication system and an underwater communication method for underwater IoT that can minimize power consumption and increase frequency efficiency.

According to one aspect of the present invention for achieving the above object, a low-power / high-efficiency underwater communication system for underwater IoT transmits bits of length L in every transmission symbol block, and transmits bits of length L to the length L A transmitter for generating and transmitting baseband transmission signal blocks based on symbol modulation, CSS (Chirp Spread Spectrum) modulation, and random sequence selection in response to each of the distributed bits; and a receiver configured to detect the bit having the length L based on the baseband received signal block received from the transmitter.

Here, the transmitter may include a bit divider for distributing the bit of length L into three bits of length L1, length L2, and length L3, respectively.

In addition, the transmitter may include: a first converter for converting a bit having a length L1 among the three bits distributed by the bit divider into a decimal number; and a symbol modulator for converting the decimal number converted by the first converter into one of 2 ^L1 symbols.

In addition, the transmitter may include a second converter for converting a bit having a length L2 among the three bits distributed by the bit divider into a decimal number; and a CSS modulator for generating a CSS symbol according to the following equation based on the decimal number converted by the second converter.

는 n차 심블 블록의 십진수 β에 대해 생성된 CSS 심볼, M은

의 길이로서 2^L2, B는 CSS 심볼의 실제 대역폭, 그리고 Fs는 기저대역의 샘플링 주파수이다.here,

Is a CSS symbol generated for the decimal number β of the nth order symbol block, M is

2 as the length of ^L2 , B is the actual bandwidth of CSS symbols, and Fs is the baseband sampling frequency.

번째 시퀀스인

를 선택하는 랜덤 시퀀스 선택기;를 더 포함할 수도 있다.In addition, the transmitter includes a third converter for converting a bit having a length L3 among the three bits distributed by the bit divider into a decimal number; and among a total of 2 ^L3 sequences determined in advance.

the second sequence

A random sequence selector for selecting; may be further included.

In addition, the transmitter may generate a baseband transmission signal block according to the following equation based on signals and pilot signals generated by the symbol modulator, the CSS modulator, and the random sequence selector.

은 기저대역 송신신호 블록,

는 파일럿 심볼과 데이터 심볼 간의 전력을 조절하는 파라미터,

는 상기 파일럿 신호,

는 상기 심볼 변조기에 의해 생성되는 신호,

는 상기 CSS 변조기에 의해 생성되는 신호, 그리고

는 상기 랜덤 시퀀스 선택기에 의해 미리 결정된 총 2^L3개의 시퀀스 중에서 선택된

번째 시퀀스이다.here,

is a baseband transmission signal block,

Is a parameter for adjusting power between pilot symbols and data symbols,

is the pilot signal,

Is a signal generated by the symbol modulator,

is a signal generated by the CSS modulator, and

is selected from a total of 2 ^L3 sequences previously determined by the random sequence selector.

is the second sequence.

The receiver may include a time synchronization unit for synchronizing time based on a pilot signal of the baseband received signal block.

When the pilot symbol is a polyphase sequence, the time synchronization unit estimates the starting point of the received signal block through cross-correlation between the received signal and the pilot signal on the time axis.

In addition, when the pilot signal is a CSS symbol, the time synchronizer estimates a time error through a CSS demodulation process.

The receiver may further include a CSS demodulator that performs DFT (Discrete Fourier Transform) on each synchronized signal and detects transmission information using a value having the largest magnitude among DFT outputs of each signal and an index of the value. can

According to one aspect of the present invention for achieving the above object, a low-power / high-efficiency underwater communication method for the underwater Internet of Things is a low-power / high-efficiency underwater communication method for the underwater Internet of Things performed by an underwater communication system, The transmitter transmits bits of length L in every transmission symbol block, divides the bits of length L into bits of length less than the length L, and in response to each of the distributed bits, symbol modulation, CSS modulation, random sequence generating and transmitting a baseband transmission signal block based on the selection; and detecting, by a receiver, the bit having the length L based on the baseband received signal block received from the transmitter.

The above-described low-power/high-efficiency underwater communication method for the underwater Internet of Things may further include distributing, by the transmitter, the bit of length L into three bits of length L1, length L2, and length L3, respectively.

The low-power/high-efficiency underwater communication method for the above-described underwater Internet of Things includes: converting, by the transmitter, a bit having a length L1 among three bits distributed by the bit divider into a decimal number; and converting, by a symbol modulator, the converted decimal number of bits having a length L1 into one of 2 ^L1 symbols.

The above-described underwater communication method includes: converting, by the transmitter, a bit having a length L2 among three bits distributed by the bit divider into a decimal number; and generating, by the CSS modulator, a CSS symbol according to the following equation based on the converted decimal number of bits having the length L2.

는 n차 심블 블록의 십진수 β에 대해 생성된 CSS 심볼, M은

의 길이로서 2^L2, B는 CSS 심볼의 실제 대역폭, 그리고 Fs는 기저대역의 샘플링 주파수이다.here,

Is a CSS symbol generated for the decimal number β of the nth order symbol block, M is

2 as the length of ^L2 , B is the actual bandwidth of CSS symbols, and Fs is the baseband sampling frequency.

번째 시퀀스인

를 선택하는 단계;를 더 포함할 수도 있다.The above-described underwater communication method includes: converting, by the transmitter, a bit having a length L3 among three bits distributed by the bit divider into a decimal number; and among a total of 2 ^L3 sequences in which a random sequence selector is predetermined.

the second sequence

It may further include; step of selecting.

The transmitter may generate a baseband transmission signal block according to the following equation based on signals and pilot signals generated by the symbol modulator, the CSS modulator, and the random sequence selector.

은 기저대역 송신신호 블록,

는 파일럿 심볼과 데이터 심볼 간의 전력을 조절하는 파라미터,

는 상기 파일럿 신호,

는 상기 심볼 변조기에 의해 생성되는 신호,

는 상기 CSS 변조기에 의해 생성되는 신호, 그리고

는 상기 랜덤 시퀀스 선택기에 의해 미리 결정된 총 2^L3개의 시퀀스 중에서 선택된

번째 시퀀스이다.here,

is a baseband transmission signal block,

Is a parameter for adjusting power between pilot symbols and data symbols,

is the pilot signal,

Is a signal generated by the symbol modulator,

is a signal generated by the CSS modulator, and

is selected from a total of 2 ^L3 sequences previously determined by the random sequence selector.

is the second sequence.

The above-described underwater communication method may further include time synchronization based on a pilot signal of the baseband received signal block by the receiver.

Here, when the pilot symbol is a polyphase sequence, the receiver estimates the starting point of the received signal block through cross-correlation between the received signal and the pilot signal on the time axis.

In addition, when the pilot signal is a CSS symbol, the receiver estimates a time error through a CSS demodulation process.

In the above-described underwater communication method, the receiver performs Discrete Fourier Transform (DFT) on each synchronized signal, and detects transmission information using a value having the largest magnitude among DFT outputs of each signal and an index of the value. ; may be further included.

A low-power/high-efficiency underwater communication system and an underwater communication method for underwater IoT according to the present invention use a Chirp Spread Spectrum (CSS) modulation method based on pilot symbol transmission, scrambling, and superposition modulation techniques, For the Internet of Things, power consumption in water can be minimized and frequency efficiency can be increased.

1 is a diagram schematically showing the configuration of a low-power / high-efficiency underwater communication system for underwater IoT according to an embodiment of the present invention.
2 is a diagram schematically showing the configuration of the transmitter shown in FIG. 1;
3 is a diagram illustrating a bit of length L.
4 is a diagram illustrating bits of length L1, length L2, and length L3 distributed from bits of length L;
FIG. 5 is a diagram schematically illustrating the configuration of the receiver shown in FIG. 2 .
6 is a flowchart illustrating a low-power/high-efficiency underwater communication method for underwater IoT according to an embodiment of the present invention.
7 is a diagram comparing bit error rate performance of a CSS system to which a pilot-based symbol modulation and random sequence technique is applied according to an embodiment of the present invention with that of an existing CSS system.

Hereinafter, some embodiments of the present invention will be described through exemplary drawings. In describing the reference numerals for the components of each drawing, the same numerals indicate the same components as much as possible, even if they are displayed on different drawings. In addition, in describing an embodiment of the present invention, if it is determined that a detailed description of a related known configuration or function hinders understanding of the embodiment of the present invention, the detailed description will be omitted.

Also, terms such as first, second, A, B, (a), and (b) may be used to describe components of an embodiment of the present invention. These terms are only used to distinguish the component from other components, and the nature, order, or order of the corresponding component is not limited by the term. When an element is described as being “connected,” “coupled to,” or “connected” to another element, the element may be directly connected, coupled, or connected to the other element, but not between the element and the other element. It should be understood that another component may be “connected”, “coupled” or “connected” between elements.

1 is a diagram schematically showing the configuration of a low-power/high-efficiency underwater communication system for underwater IoT according to an embodiment of the present invention.

Referring to FIG. 1 , a low-power/high-efficiency underwater communication system for underwater IoT according to an embodiment of the present invention includes a transmitter 100 and a receiver 200.

At this time, the transmitter 100 transmits bits of length L for every transmission symbol block, distributes the bits of length L to bits of length less than length L, and in response to each of the distributed bits, symbol modulation, CSS ( Based on Chirp Spread Spectrum) modulation and random sequence selection, baseband transmission signal blocks are generated and transmitted.

Also, the receiver 200 detects a bit of length L based on the baseband received signal block received from the transmitter 100.

Here, as shown in FIG. 2, the transmitter 100 includes a bit divider 102, a first converter 104, a second converter 106, a third converter 108, a symbol modulator 110, and a CSS modulator. 112, a random sequence selector 114, a pilot signal generator 116, and a transmission signal generator 118.

The bit divider 102 divides bits of length L of every symbol block into three bits of length L1, length L2 and length L3, respectively. Here, a bit having a length L refers to a bit having L binary digits, as shown in FIG. 3 . That is, the length L bits is 2 ^L. In this case, the bit of length L may be a data bit or a result bit obtained by applying techniques such as a Cyclic Redundancy Check (CRC), an error-correction code, or interleaving to the data bit.

The bit divider 102 may distribute a bit having L digits into three bits having digits L1, L2, and L3, respectively, as shown in FIG. 4 . Here, L1, L2, and L3 are essential parameters for demodulation of the receiver 200, and L = L1 + L2 + L3. Here, bits of length L1, bits of length L2, and bits of length L3 correspond to symbol modulation, CSS modulation, and random sequence selection, respectively.

Values of L1, L2, and L3 may be transmitted to the receiver 200 through other signals in a physical or upper layer. For example, in the case of the physical layer, it can be included in the ID of the preamble, and the corresponding information can be included in a specific symbol. In addition, in the case of a higher layer, corresponding values may be transmitted to the receiver 200 in advance through a protocol of the corresponding layer prior to transmission of the corresponding symbol.

The bit divider 102 may reduce L1 and L3 when a high communication success rate is required according to system operation, and increase L1 and L3 appropriately when a high transmission rate is required. In this case, since the embodiment of the present invention is based on the chirp spread spectrum modulation method, L2 must be greater than or equal to at least 2. Here, L2 preferably has a value between 4 and 14. Also, L1 or L3 may be 0.

In the case of the existing CSS communication method, the transmission rate is determined according to L2. On the other hand, in the case of the present invention, since as many bits as L1 + L3 can be additionally transmitted during the same time period, the transmission rate can be increased. Considering that CSS communication is a technique that enables long-distance communication at the cost of transmission rate, the embodiment of the present invention can greatly improve the transmission rate of the existing CSS communication method. For example, considering a communication system having a bandwidth of 1 kHz and L2 = 8, the transmission rate is 31.25 bps in the case of the existing CSS communication method. The transmission rate of the communication system according to the embodiment of the present invention in which L1 = 3, L2 = 8, and L3 = 3 is 54.6875 bps, which is 75% higher than that of the existing CSS communication method.

Improving the transmission rate of the communication system according to the embodiment of the present invention enables improved high-speed communication compared to conventional CSS communication. Conversely, an increase in transmission rate means that a shorter time is required to transmit data of the same size. This means that power consumption can be greatly reduced due to the characteristics of underwater communication that depends on a battery.

라고 명명한다.The first converter 104 converts a bit having a length L1, a bit having a length L2, and a bit having a length L3 distributed by the bit divider 102 into a decimal number. At this time, the decimal number converted by the first converter 104

name it

라고 명명한다.The second converter 106 converts a bit having a length L1, a bit having a length L2, and a bit having a length L2 distributed by the bit divider 102 into a decimal number. At this time, the decimal number converted by the second converter 106

name it

라고 명명한다.The third converter 108 converts a bit having a length of L1, a bit having a length of L2, and a bit having a length of L3 distributed by the bit divider 102 into a decimal number. At this time, the decimal number converted by the third converter 104

name it

가 심볼 변조기(110)에 의해 변환된 값을

라고 명명한다.The symbol modulator 110 performs 2 ^L1 binary modulation of converting a decimal number corresponding to a bit of length L1 converted by the first converter 104 into one of 2 ^L1 symbols. In this case, the symbol modulator 110 may use representative modulation techniques such as binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), 16 quadrature amplitude modulation (16QAM), and 64QAM. where, the decimal number corresponding to the length L1 bits

The value converted by the symbol modulator 110

name it

The CSS modulator 112 generates a CSS symbol according to Equation 1 based on the decimal number converted by the second converter 106.

[Equation 1]

는 n차 심블 블록의 십진수 β에 대해 생성된 CSS 심볼, M은

의 길이로서 2^L2, B는 CSS 심볼의 실제 대역폭, 그리고 Fs는 기저대역의 샘플링 주파수이다.here,

is a CSS symbol generated for the decimal number β of the nth order symbol block, M is

2 as the length of ^L2 , B is the actual bandwidth of CSS symbols, and Fs is the baseband sampling frequency.

Equation 1 is an up-chirp CSS symbol whose frequency increases. Even if the CSS modulator 112 is a down-chirp CSS symbol generator whose frequency decreases, the present invention is not affected.

번째 시퀀스인

를 선택한다. 랜덤 시퀀스는 동일한 시퀀스 간의 자기 상관(autocorrelation)이 낮으며, 서로 다른 시퀀스 간의 상호 상관(crosscorrelation)이 낮은 특성을 가져야 한다. 이러한 특징을 갖는 이진 시퀀스(1 또는 -1)에는 gold code, hadamard code, maximal length sequence 등이 있으며, 잘 설계된 다항식(polynomial)에 의해 성성될 수 있다. 이와 같은 특성을 만족한다면, 이진 시퀀스가 아닌 Zadoff-Chu sequence와 같은 polyphase sequence가 사용될 수 있다. 이때, 수신기(200)의 구현 및 계산 복잡도를 고려하면 이진 시퀀스가 선호될 수 있다.The random sequence selector 114 selects from among a total of 2 ^L3 predetermined sequences.

the second sequence

Choose Random sequences should have low autocorrelation between identical sequences and low crosscorrelation between different sequences. Binary sequences (1 or -1) having these characteristics include gold codes, hadamard codes, maximal length sequences, and the like, and can be formed by well-designed polynomials. If these characteristics are satisfied, a polyphase sequence such as a Zadoff-Chu sequence rather than a binary sequence can be used. At this time, considering implementation and calculation complexity of the receiver 200, a binary sequence may be preferred.

The pilot signal generator 116 generates pilot symbols necessary for the receiver 200 to estimate and compensate a starting point for each symbol block. A random sequence or a CSS symbol may be used as the pilot symbol, and accordingly, a time error estimation method in the receiver 200 is changed.

As with the random sequence of data symbols, a binary sequence or a polyphase sequence may be used as the random sequence. When a CSS symbol is used as a pilot signal, a chirp signal in the opposite direction to the CSS symbol of the data symbol must be used. For example, if the CSS symbol of the data symbol is an up-chirp signal, the CSS symbol of the pilot signal must be a down-chirp signal. The pilot symbol can use the same signal regardless of the symbol block. In this case, since a peak-to-average power ratio (PAPR) may increase, different pilot signals may be used according to symbol block indexes. On the other hand, different pilot signals may be used for device/user identification purposes.

,

및

와, 파일럿신호 생성기(116)에서 생성된 파일럿 신호

을 이용하여 수학식 2를 통해 기저대역 송신신호 블록

을 생성한다.The transmission signal generator 118 is a signal generated by the symbol modulator 110, the CSS modulator 112 and the random sequence selector 114.

,

and

And, the pilot signal generated by the pilot signal generator 116

Using Equation 2, the baseband transmission signal block

generate

[Equation 2]

는 파일럿 심볼과 데이터 심볼 간의 전력을 조절하는 파라미터이다. 채널 변화가 작거나 미미해서 심볼 블록 별로 발생하는 시간 오차 변화가 적은 환경일 경우,

값을 증가시키거나 1로 설정하여 송신 전력을 데이터 심볼로 집중시킬 수 있다. here,

Is a parameter for adjusting power between pilot symbols and data symbols. In an environment where the change in time error for each symbol block is small because the channel change is small or insignificant,

By increasing the value or setting it to 1, transmit power can be concentrated on data symbols.

값을 감소시켜 송신 전력을 파일럿 심볼로 집중시키고, 이를 통해 수신기(200)에서의 시간 오차 추정 성능 향상을 꾀할 수 있다.If the channel change is large, the time error change occurring for each symbol block increases,

By reducing the value, transmission power is concentrated on pilot symbols, and through this, time error estimation performance in the receiver 200 can be improved.

를 입력 받으며, 시간 동기화부(202), 시간오차 보상부(204), 디스크램블러(206), CSS 복조기(208), 심볼 복조기(210) 및 비트 복조기(212)를 통해 각각 파일럿 신호 기반 시간 오차 추정 및 동기화, 시간 오차 보상, 디스크램블링, CSS 복조, 심볼 복조 및 비트 복조 과정을 거쳐 길이 L인 송신 비트를 검출한다.The receiver 200 is a baseband received signal block received from the transmitter 100

is received, and each pilot signal-based time error is passed through a time synchronization unit 202, a time error compensation unit 204, a descrambler 206, a CSS demodulator 208, a symbol demodulator 210, and a bit demodulator 212. Through the processes of estimation and synchronization, time error compensation, descrambling, CSS demodulation, symbol demodulation and bit demodulation, a transmission bit of length L is detected.

The pilot-based time synchronization method differs according to the type of pilot signal. If the pilot symbol is a polyphase sequence, the starting point of the received signal block can be estimated through cross-correlation between the received signal and the pilot signal on the time axis as shown in Equation 3.

[Equation 3]

에 대해 down-chirp 방식으로 생성한 CSS 심볼일 경우, CSS 복조 과정은 수학식 4와 같다.In addition, when the pilot signal is a CSS symbol, a time error can be estimated through a CSS demodulation process for the pilot signal. If the pilot signal is a decimal number

In the case of a CSS symbol generated by a down-chirp method for , the CSS demodulation process is as shown in Equation 4.

[Equation 4]

는 down-chirp 방식으로 생성하며, 십진수 0에 대한 CSS 심볼이다. 만일, 송신신호와 수신신호의 시작점이

샘플만큼 차이가 발생하면, CSS 복조에서

의 최대값의 위치가

가 아니라

만큼 차이가 생긴다. 따라서, 시작점 차이인

는 파일럿 신호에 대한 CSS 복조 과정에서의 최대값의 위치

와 송신 파일럿에 해당하는

의 비교를 통해 추정할 수 있다.here,

is created by down-chirp method and is a CSS symbol for decimal number 0. If the starting point of the transmission signal and the reception signal is

When a difference by sample occurs, CSS demodulation

is the position of the maximum value of

not

difference as much as Therefore, the starting point difference

is the position of the maximum value in the CSS demodulation process for the pilot signal

and corresponding to the transmit pilot

can be estimated through comparison.

를 추정하면, 시간오차 보상부(204)는 이를 이용하여 수신 심볼의 시작점을 재조정한다. 예를 들어, 시간오차 보상부(204)는 수신신호 버퍼 혹은 메모리에서 해당 수신 심볼을 처리할 때 해당 수신 심볼의 시작점 차이

를 감안하여 처리하며, 시작점 재조정 후 해당 수신 심볼의 복조를 수행한다.The time synchronization unit 202 uses a pilot to determine the starting point difference for each received symbol.

Estimating , the time error compensation unit 204 readjusts the starting point of the received symbol using this. For example, when the time error compensator 204 processes the corresponding received symbol in the received signal buffer or memory, the starting point difference of the corresponding received symbol

, and after readjusting the starting point, demodulation of the received symbol is performed.

를 검출하기 위해, 시작점이 재조정된 수신 심볼에 총 2^L3개의 시퀀스를 각각 곱하여 디스크램블링을 수행한다. The descrambler 206 transmits information corresponding to the scrambling sequence.

In order to detect , descrambling is performed by multiplying a total of 2 ^L3 sequences by the received symbol whose starting point is readjusted.

을 시작점이 재조정된 수신 심볼이라 할 때 상기의 과정은 수학식 5와 같이 나타낼 수 있다. The CSS demodulator 208 performs a CSS demodulation process on each of the descrambled signals with different sequences. That is, the CSS demodulator 208 performs Discrete Fourier Transform (DFT) on each signal and finds a value having the largest magnitude among DFT outputs of each signal and an index of the value. At this time, since the number of sequences is 2 ^L3 , there are also 2 ^L3 indexes of the maximum value and the maximum value.

Assuming that the starting point is a readjusted received symbol, the above process can be expressed as in Equation 5.

[Equation 5]

과 그 최대값의 인덱스

를 이용하여 송신정보

와

를 수학식 6과 같이 검출할 수 있다.2 ^L3 maximums

and the index of its maximum

Transmitted information using

Wow

can be detected as shown in Equation 6.

[Equation 6]

는 최대값

를 이용하여 검출할 수 있다. 이때, 수중 채널, 송수신간 오실레이터 차이 등으로 수신신호의 크기 및 위상이 달라질 수 있으나, 이는 이미 알고 있는 파일럿 신호를 이용하여 보상할 수 있다. 즉,

대신

을 기반으로 심볼 복조를 진행하면, 송신정보

를 검출할 수 있다.transmission information

is the maximum

can be detected using At this time, the magnitude and phase of the received signal may vary due to underwater channels, differences in oscillators between transmission and reception, etc., but this can be compensated for using a known pilot signal. in other words,

instead

If symbol demodulation is performed based on

can be detected.

,

,

를 검출 후 각 십진수를 이진수로 변환 후 송신기(100)에서 적용한 비트 분배방식을 역으로 수행하면, 길이 L인 비트를 검출할 수 있다.

,

,

After detecting , converting each decimal number into binary number and then performing the bit distribution method applied by the transmitter 100 inversely, it is possible to detect a bit of length L.

6 is a flowchart illustrating a low-power/high-efficiency underwater communication method for underwater IoT according to an embodiment of the present invention. A low-power/high-efficiency underwater communication method for underwater IoT according to an embodiment of the present invention can be performed by the underwater communication system 100 shown in FIG.

The transmitter 100 distributes bits of length L of each symbol block into three bits of length L1, length L2, and length L3 (S110). Here, a bit having a length L refers to a bit having L binary digits. That is, the length L bits is 2 ^L. In this case, the bit of length L may be a data bit or a result bit obtained by applying techniques such as a Cyclic Redundancy Check (CRC), an error-correction code, or interleaving to the data bit.

The transmitter 100 may distribute a bit having a digit of L into three bits having digits of L1, L2, and L3, respectively. Here, L1, L2, and L3 are essential parameters for demodulation of the receiver 200, and L = L1 + L2 + L3. Here, bits of length L1, bits of length L2, and bits of length L3 correspond to symbol modulation, CSS modulation, and random sequence selection, respectively.

Values of L1, L2, and L3 may be transmitted to the receiver 200 through other signals in a physical or upper layer. For example, in the case of the physical layer, it can be included in the ID of the preamble, and the corresponding information can be included in a specific symbol. In addition, in the case of a higher layer, corresponding values may be transmitted to the receiver 200 in advance through a protocol of the corresponding layer prior to transmission of the corresponding symbol.

Depending on the operation of the system, the transmitter 100 may decrease L1 and L3 when a high communication success rate is required, and appropriately increase L1 and L3 when a high transmission rate is required. In this case, since the embodiment of the present invention is based on the chirp spread spectrum modulation method, L2 must be greater than or equal to at least 2. Here, L2 preferably has a value between 4 and 14.

In the case of the existing CSS communication method, the transmission rate is determined according to L2. On the other hand, in the case of the present invention, since as many bits as L1 + L3 can be additionally transmitted during the same time period, the transmission rate can be increased. Considering that CSS communication is a technique that enables long-distance communication at the cost of transmission rate, the embodiment of the present invention can greatly improve the transmission rate of the existing CSS communication method. For example, considering a communication system having a bandwidth of 1 kHz and L2 = 8, the transmission rate is 31.25 bps in the case of the existing CSS communication method. The transmission rate of the communication system according to the embodiment of the present invention in which L1 = 3, L2 = 8, and L3 = 3 is 54.6875 bps, which is 75% higher than that of the existing CSS communication method.

Improving the transmission rate of the communication system according to the embodiment of the present invention enables improved high-speed communication compared to conventional CSS communication. Conversely, an increase in transmission rate means that a shorter time is required to transmit data of the same size. This means that power consumption can be greatly reduced due to the characteristics of underwater communication that depends on a battery.

라고 명명한다.The transmitter 100 converts a bit of length L1 among the distributed bits of length L1, bits of length L2, and bits of length L3 into decimal numbers (S120). At this time, the converted decimal number

name it

라고 명명한다.Also, the transmitter 100 converts a bit having a length L2 among the distributed bits having a length of L1, bits having a length of L2, and bits having a length of L3 into decimal numbers. At this time, the converted decimal number

name it

라고 명명한다.Also, the transmitter 100 converts a bit having a length L3 among the distributed bits having a length of L1, bits having a length of L2, and bits having a length of L3 into decimal numbers. At this time, the converted decimal number

name it

가 심볼 변조기(110)에 의해 변환된 값을

라고 명명한다.The transmitter 100 performs 2 ^L1 binary modulation of converting the decimal number corresponding to the converted length L1 bit into one of 2 ^L1 symbols (S130). In this case, the transmitter 100 may use representative modulation techniques such as binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), 16 quadrature amplitude modulation (16QAM), and 64QAM. where, the decimal number corresponding to the length L1 bits

The value converted by the symbol modulator 110

name it

In addition, the transmitter 100 generates a CSS symbol according to Equation 1 based on the converted decimal number.

[Equation 1]

는 n차 심블 블록의 십진수 β에 대해 생성된 CSS 심볼, M은

의 길이로서 2^L2, B는 CSS 심볼의 실제 대역폭, 그리고 Fs는 기저대역의 샘플링 주파수이다.here,

Is a CSS symbol generated for the decimal number β of the nth order symbol block, M is

2 as the length of ^L2 , B is the actual bandwidth of CSS symbols, and Fs is the baseband sampling frequency.

Equation 1 is an up-chirp CSS symbol whose frequency increases. Even if the CSS modulator is a down-chirp CSS symbol generator whose frequency decreases, the present invention is not affected.

번째 시퀀스인

를 선택한다. 랜덤 시퀀스는 동일한 시퀀스 간의 자기 상관(autocorrelation)이 낮으며, 서로 다른 시퀀스 간의 상호 상관(crosscorrelation)이 낮은 특성을 가져야 한다. 이러한 특징을 갖는 이진 시퀀스(1 또는 -1)에는 gold code, hadamard code, maximal length sequence 등이 있으며, 잘 설계된 다항식(polynomial)에 의해 성성될 수 있다. 이와 같은 특성을 만족한다면, 이진 시퀀스가 아닌 Zadoff-Chu sequence와 같은 polyphase sequence가 사용될 수 있다. 이때, 수신기(200)의 구현 및 계산 복잡도를 고려하면 이진 시퀀스가 선호될 수 있다.The transmitter 100 selects from among a total of 2 ^L3 predetermined sequences.

the second sequence

Choose Random sequences should have low autocorrelation between identical sequences and low crosscorrelation between different sequences. Binary sequences (1 or -1) having these characteristics include gold codes, hadamard codes, maximal length sequences, and the like, and can be formed by well-designed polynomials. If these characteristics are satisfied, a polyphase sequence such as a Zadoff-Chu sequence rather than a binary sequence can be used. At this time, considering implementation and calculation complexity of the receiver 200, a binary sequence may be preferred.

The transmitter 100 generates pilot symbols necessary for the receiver 200 to estimate and compensate a starting point for each symbol block. A random sequence or a CSS symbol may be used as the pilot symbol, and accordingly, a time error estimation method in the receiver 200 is changed.

As with the random sequence of data symbols, a binary sequence or a polyphase sequence may be used as the random sequence. When a CSS symbol is used as a pilot signal, a chirp signal in the opposite direction to the CSS symbol of the data symbol must be used. For example, if the CSS symbol of the data symbol is an up-chirp signal, the CSS symbol of the pilot signal must be a down-chirp signal. The pilot symbol can use the same signal regardless of the symbol block. In this case, since a peak-to-average power ratio (PAPR) may increase, different pilot signals may be used according to symbol block indexes. On the other hand, different pilot signals may be used for device/user identification purposes.

,

및

와, 생성된 파일럿 신호

을 이용하여 수학식 2를 통해 기저대역 송신신호 블록

을 생성하여 수신기(200)에 전송한다(S140).Transmitter 100 generates a signal

,

and

and the generated pilot signal

Using Equation 2, the baseband transmission signal block

is generated and transmitted to the receiver 200 (S140).

[Equation 2]

는 파일럿 심볼과 데이터 심볼 간의 전력을 조절하는 파라미터이다. 채널 변화가 작거나 미미해서 심볼 블록 별로 발생하는 시간 오차 변화가 적은 환경일 경우,

값을 증가시키거나 1로 설정하여 송신 전력을 데이터 심볼로 집중시킬 수 있다. here,

Is a parameter for adjusting power between pilot symbols and data symbols. In an environment where the change in time error for each symbol block is small because the channel change is small or insignificant,

By increasing the value or setting it to 1, transmit power can be concentrated on data symbols.

값을 감소시켜 송신 전력을 파일럿 심볼로 집중시키고, 이를 통해 수신기(200)에서의 시간 오차 추정 성능 향상을 꾀할 수 있다.If the channel change is large, the time error change occurring for each symbol block increases,

By reducing the value, transmission power is concentrated on pilot symbols, and through this, time error estimation performance in the receiver 200 can be improved.

를 입력 받으며, 파일럿 신호 기반 시간 오차 추정 및 동기화, 시간 오차 보상, 디스크램블링, CSS 복조, 심볼 복조 및 비트 복조 과정을 거쳐 길이 L인 송신 비트를 검출한다.The receiver 200 is a baseband received signal block received from the transmitter 100

, and detects a transmission bit of length L through pilot signal-based time error estimation and synchronization, time error compensation, descrambling, CSS demodulation, symbol demodulation, and bit demodulation.

The pilot-based time synchronization method differs according to the type of pilot signal. If the pilot symbol is a polyphase sequence, the starting point of the received signal block can be estimated and synchronized through cross-correlation between the received signal and the pilot signal on the time axis as shown in Equation 3 (S150).

[Equation 3]

에 대해 down-chirp 방식으로 생성한 CSS 심볼일 경우, CSS 복조 과정은 수학식 4와 같다.In addition, when the pilot signal is a CSS symbol, a time error may be estimated and synchronized through a CSS demodulation process for the pilot signal. If the pilot signal is a decimal number

In the case of a CSS symbol generated by a down-chirp method for , the CSS demodulation process is as shown in Equation 4.

[Equation 4]

는 down-chirp 방식으로 생성하며, 십진수 0에 대한 CSS 심볼이다. 만일, 송신신호와 수신신호의 시작점이

샘플만큼 차이가 발생하면, CSS 복조에서

의 최대값의 위치가

가 아니라

만큼 차이가 생긴다. 따라서, 시작점 차이인

는 파일럿 신호에 대한 CSS 복조 과정에서의 최대값의 위치

와 송신 파일럿에 해당하는

의 비교를 통해 추정할 수 있다.here,

is created by down-chirp method and is a CSS symbol for decimal number 0. If the starting point of the transmission signal and the reception signal is

When a difference by sample occurs, CSS demodulation

is the position of the maximum value of

not

difference as much as Therefore, the starting point difference

is the position of the maximum value in the CSS demodulation process for the pilot signal

and corresponding to the transmit pilot

can be estimated through comparison.

를 추정하면, 이를 이용하여 수신 심볼의 시작점을 재조정한다. 예를 들어, 수신기(200)는 수신신호 버퍼 혹은 메모리에서 해당 수신 심볼을 처리할 때 해당 수신 심볼의 시작점 차이

를 감안하여 처리하며, 시작점 재조정 후 해당 수신 심볼의 복조를 수행한다.The receiver 200 uses a pilot to determine the starting point difference for each received symbol.

If is estimated, the starting point of the received symbol is readjusted using this. For example, when the receiver 200 processes a corresponding received symbol in a received signal buffer or memory, the starting point difference of the corresponding received symbol

, and after readjusting the starting point, demodulation of the received symbol is performed.

를 검출하기 위해, 시작점이 재조정된 수신 심볼에 총 2^L3개의 시퀀스를 각각 곱하여 디스크램블링을 수행한다. The receiver 200 transmits information corresponding to the scrambling sequence.

In order to detect , descrambling is performed by multiplying a total of 2 ^L3 sequences by the received symbol whose starting point is readjusted.

을 시작점이 재조정된 수신 심볼이라 할 때 상기의 과정은 수학식 5와 같이 나타낼 수 있다. In addition, the receiver 200 performs a CSS demodulation process on each of the descrambled signals in different sequences. That is, the receiver 200 performs Discrete Fourier Transform (DFT) on each signal and finds a value having the largest magnitude among DFT outputs of each signal and an index of the value. At this time, since the number of sequences is 2 ^L3 , there are also 2 ^L3 indexes of the maximum value and the maximum value.

Assuming that the starting point is a readjusted received symbol, the above process can be expressed as in Equation 5.

[Equation 5]

과 그 최대값의 인덱스

를 이용하여 송신정보

와

를 수학식 6과 같이 검출할 수 있다(S160).2 ^L3 maximums

and the index of its maximum

Transmitted information using

Wow

Can be detected as in Equation 6 (S160).

[Equation 6]

는 최대값

를 이용하여 검출할 수 있다. 이때, 수중 채널, 송수신간 오실레이터 차이 등으로 수신신호의 크기 및 위상이 달라질 수 있으나, 이는 이미 알고 있는 파일럿 신호를 이용하여 보상할 수 있다. 즉,

대신

을 기반으로 심볼 복조를 진행하면, 송신정보

를 검출할 수 있다.transmission information

is the maximum

can be detected using At this time, the magnitude and phase of the received signal may vary due to underwater channels, differences in oscillators between transmission and reception, etc., but this can be compensated for using a known pilot signal. in other words,

instead

If symbol demodulation is performed based on

can be detected.

,

,

를 검출 후 각 십진수를 이진수로 변환 후 송신기(100)에서 적용한 비트 분배방식을 역으로 수행하면, 길이 L인 비트를 검출할 수 있다(S170).

,

,

After detecting and converting each decimal number to binary number, if the bit distribution method applied by the transmitter 100 is reversely performed, a bit having a length L can be detected (S170).

7 is a diagram comparing bit error rate (BER) performance of a CSS system to which a pilot-based symbol modulation and random sequence technique is applied according to an embodiment of the present invention with that of an existing CSS system. Performance analysis compared CSS system performance in a total of five cases.

Referring to FIG. 7, the first (1. CSS without pilot) is the performance of the existing CSS system without using any technique including pilot. In addition, the second (2. CSS + pilot) is the performance of a system in which only a pilot signal is applied to the existing CSS system. In addition, the third (3. CSS + pilot + scrambling) is the performance of applying a pilot signal and a random sequence to the existing CSS system. In addition, the fourth (4. CSS + pilot + modulation) is the performance of the system applying the pilot signal and symbol modulation technique to the existing CSS system. In addition, the fifth (5. CSS + pilot + scrambling + modulation) is the performance of a system in which pilot signal, random sequence, and symbol modulation techniques are applied to the existing CSS system.

Here, it is assumed that the bandwidth of the system is 1 kHz, L1 = 2, L2 = 8, and L3 = 2. At this time, the transmission rates of the aforementioned five systems are given as 31.25 bps, 31.25 bps, 39.0625 bps, 39.0625 bps, and 46.8750 bps, respectively.

In order to simulate an actual underwater communication channel, the delay time of the multi-path was changed randomly. In addition, to consider the temporal variability of the underwater channel, different Doppler effects were applied to each multipath.

7 shows the performance of the five systems described above when the relative velocity between the transmitter and receiver has a uniform distribution with a standard deviation of 0.1 m/s. As can be seen in the graph, in the case of the first method, the existing CSS system, when the Doppler effect occurs due to time variability, very severe performance degradation occurs, making communication impossible. On the other hand, the second to fifth methods proposed in the present invention show robust performance against the Doppler effect.

Comparing the second and fourth methods, performance degradation does not occur even when the symbol modulation technique is applied to the pilot signal. In addition, since the fourth method has a higher data rate than the second method, it means that the symbol modulation technique proposed in the present invention is an effective method for improving the data rate without performance degradation. In addition, in the case of the third method, although the data transmission rate increases through the random sequence, it can be seen that performance deterioration occurs compared to the second or fourth method.

Finally, the fifth method is a method in which a random sequence and a symbol modulation method are simultaneously applied. Compared to the third method, it can be confirmed that additional data rate improvement is obtained through the application of the symbol modulation technique and there is no performance degradation.

Through performance comparison analysis, it was found that if the method proposed in the present invention is applied, not only can stable performance be secured compared to the existing CSS system, but also the data transmission rate can be improved even in an environment where severe Doppler phenomenon occurs due to time variability of the underwater channel. can

Embodiments according to the present invention have been described above, but these are merely examples, and those skilled in the art will understand that various modifications and embodiments of equivalent range are possible therefrom. Therefore, the protection scope of the present invention should be defined by the following claims as well as those equivalent thereto.

Claims (20)

Bits of length L are transmitted in every transmission symbol block, and the bits of length L are divided into bits of length less than the length L, and symbol modulation and chirp spread spectrum (CSS) modulation are performed in response to each of the distributed bits. , a transmitter for generating and transmitting a baseband transmission signal block based on random sequence selection; and
a receiver for detecting the bit of length L based on the baseband received signal block received from the transmitter;
Characterized in that it comprises a low-power / high-efficiency underwater communication system for the underwater Internet of things. The method of claim 1, wherein the transmitter,
a bit divider dividing the bit of length L into three bits of length L1, length L2 and length L3, respectively;
Characterized in that it comprises a low-power / high-efficiency underwater communication system for the underwater Internet of things. The method of claim 2, wherein the transmitter,
a first converter converting a bit having a length L1 among the three bits distributed by the bit divider into a decimal number; and
a symbol modulator for converting the decimal number converted by the first converter into one of 2 ^L1 symbols;
Characterized in that it further comprises, a low-power / high-efficiency underwater communication system for the underwater Internet of things. The method of claim 3, wherein the transmitter,
a second converter converting a bit having a length L2 among the three bits distributed by the bit divider into a decimal number; and
a CSS modulator generating a CSS symbol according to the following equation based on the decimal number converted by the second converter;
Low-power / high-efficiency underwater communication system for underwater IoT, characterized in that it further comprises:

here,

Is a CSS symbol generated for the decimal number β of the nth order symbol block, M is

2 as the length of ^L2 , B is the actual bandwidth of CSS symbols, and Fs is the baseband sampling frequency. The method of claim 4, wherein the transmitter,
a third converter for converting a bit having a length L3 among the three bits distributed by the bit divider into a decimal number; and
Out of a total of 2 ^L3 sequences determined in advance

the second sequence

a random sequence selector for selecting;
Characterized in that it further comprises, a low-power / high-efficiency underwater communication system for the underwater Internet of things. The method of claim 5, wherein the transmitter,
Based on the signals and pilot signals generated by the symbol modulator, the CSS modulator, and the random sequence selector, a baseband transmission signal block is generated according to the following equation, characterized in that low power / high efficiency for underwater IoT Underwater communication system:

here,

is a baseband transmission signal block,

Is a parameter for adjusting power between pilot symbols and data symbols,

is the pilot signal,

Is a signal generated by the symbol modulator,

is a signal generated by the CSS modulator, and

is selected from a total of 2 ^L3 sequences previously determined by the random sequence selector.

is the second sequence. The method of claim 1, wherein the receiver,
a time synchronization unit for synchronizing time based on the pilot signal of the baseband received signal block;
Characterized in that it comprises a low-power / high-efficiency underwater communication system for the underwater Internet of things. According to claim 7,
The time synchronization unit estimates the starting point of the received signal block through cross-correlation of the received signal and the pilot signal on the time axis when the pilot symbol is a polyphase sequence, a low-power / high-efficiency underwater communication system for the underwater IoT . According to claim 7,
The time synchronization unit estimates a time error through a CSS demodulation process when the pilot signal is a CSS symbol. The method of claim 7, wherein the receiver,
A CSS demodulator that performs DFT (Discrete Fourier Transform) on each synchronized signal and detects transmission information using a value having the largest magnitude among DFT outputs of each signal and an index of the value;
Characterized in that it further comprises, a low-power / high-efficiency underwater communication system for the underwater Internet of things. In the low-power / high-efficiency underwater communication method for underwater IoT, performed by an underwater communication system,
The transmitter transmits bits of length L in every transmission symbol block, divides the bits of length L into bits of length less than the length L, and in response to each of the distributed bits, symbol modulation, CSS modulation, random sequence generating and transmitting a baseband transmission signal block based on the selection; and
detecting, by a receiver, a bit having the length L based on a baseband received signal block received from the transmitter;
Characterized in that it comprises, a low-power / high-efficiency underwater communication method for the underwater Internet of things. According to claim 11,
distributing, by the transmitter, the bit of length L into three bits of length L1, length L2 and length L3, respectively;
Characterized in that it further comprises, a low-power / high-efficiency underwater communication method for the underwater Internet of things. According to claim 12,
converting, by the transmitter, a bit having a length L1 among the three bits distributed by the bit divider into a decimal number; and
converting, by a symbol modulator, the decimal number of the converted length L1 bits into one of 2 ^L1 symbols;
Characterized in that it further comprises, a low-power / high-efficiency underwater communication method for the underwater Internet of things. According to claim 13,
converting, by the transmitter, a bit having a length L2 among the three bits distributed by the bit divider into a decimal number; and
generating, by a CSS modulator, a CSS symbol according to the following equation based on the converted decimal number of bits of length L2;
Low-power / high-efficiency underwater communication method for underwater IoT, characterized in that it further comprises:

here,

is a CSS symbol generated for the decimal number β of the nth order symbol block, M is

2 as the length of ^L2 , B is the actual bandwidth of CSS symbols, and Fs is the baseband sampling frequency. According to claim 14,
converting, by the transmitter, a bit having a length L3 among the three bits distributed by the bit divider into a decimal number; and
From a total of 2 ^L3 sequences for which a random sequence selector is predetermined

the second sequence

selecting;
Characterized in that it further comprises, a low-power / high-efficiency underwater communication method for the underwater Internet of things. The method of claim 15, wherein the transmitter,
Based on the signals and pilot signals generated by the symbol modulator, the CSS modulator, and the random sequence selector, a baseband transmission signal block is generated according to the following equation, characterized in that low power / high efficiency for underwater IoT Underwater communication system:

here,

is a baseband transmission signal block,

Is a parameter for adjusting power between pilot symbols and data symbols,

is the pilot signal,

Is a signal generated by the symbol modulator,

is a signal generated by the CSS modulator, and

is selected from a total of 2 ^L3 sequences previously determined by the random sequence selector.

is the second sequence. According to claim 11,
synchronizing, by the receiver, a time based on a pilot signal of the baseband received signal block;
Characterized in that it further comprises, a low-power / high-efficiency underwater communication method for the underwater Internet of things. According to claim 17,
When the pilot symbol is a polyphase sequence, the receiver estimates the starting point of the received signal block through cross-correlation of the received signal and the pilot signal on the time axis. According to claim 17,
Wherein the receiver estimates a time error through a CSS demodulation process when the pilot signal is a CSS symbol. According to claim 17,
performing DFT (Discrete Fourier Transform) on each synchronized signal by the receiver, and detecting transmission information using a value having the largest magnitude among DFT outputs of each signal and an index of the value;
Characterized in that it further comprises, a low-power / high-efficiency underwater communication method for the underwater Internet of things.

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