CN105553572A - Underwater communication system - Google Patents

Abstract

The present invention relates to an underwater communication system, including a sensor, a transmitting subsystem and a receiving subsystem, wherein: the sensor is used to perceive the external environment, and help the underwater wireless communication node to automatically select a suitable communication mode and corresponding modulation and demodulation standard; the transmitting subsystem is composed of a coding unit, an adaptive modulation unit and a transmitting unit, and the transmitting subsystem sends the signal to be transmitted to the The corresponding channel of the transmitting unit converts the electrical signal into an acoustic signal or an optical signal for transmission; the receiving subsystem is composed of a receiving unit, an adaptive demodulation unit and a decoding unit, and the corresponding channel of the receiving unit receives the acoustic signal or optical signal and convert it into an electrical signal, after being demodulated by the adaptive demodulation unit, the original signal is finally demodulated by the decoder of the decoding unit, so as to realize the transmission of data or instructions within the scope of the communication network Reliable transmission.

Description

An underwater communication system

technical field

The invention relates to the field of underwater communication, in particular to an underwater communication system.

Background technique

At present, with the continuous development of underwater applications such as communication, exploration, and monitoring, the use of large-volume sensing devices represented by sensors such as video and sonar is becoming more and more frequent. The requirements of the system are also becoming more and more urgent. However, due to the complexity of the underwater environment, underwater wireless communication (sound and light) channels are different in different waters, different water depths, different transmission distances, horizontal and vertical directions, and the transmission media such as sound and light are different in the underwater environment. The speed, available frequency, and transmission distance are also very different. Therefore, the current underwater wireless communication is still dominated by a single medium communication method, either underwater acoustic communication, wireless optical communication, or other methods. Underwater acoustic communication and wireless optical communication are the main communication methods used in underwater communication, especially underwater acoustic communication.

With the advantages of long transmission distance and reliable performance, underwater acoustic communication technology still firmly occupies the dominant position of underwater wireless communication technology. However, as an important underwater communication medium, sound waves, whose underwater propagation speed is 5 orders of magnitude lower than the speed of electromagnetic waves, have a great impact on the communication protocol of the system, thereby greatly reducing the throughput of the communication network; at the same time, due to the Reflection from the ocean surface and the bottom of the sea, as well as the sound velocity of seawater in the depth direction approximately change according to the horizontal layer, and the underwater multipath is complex, which all reduce the transmission rate and increase the bit error rate; moreover, the noise source in the ocean has a great impact Randomness, which severely limits the bandwidth and range of reliable communication. These phenomena have led to the insurmountable defects of low transmission rate, long delay, and high power consumption in underwater acoustic communication technology.

Compared with underwater acoustic communication, light waves have a higher frequency and a stronger ability to carry information, making it easier to realize large-capacity underwater data transmission; moreover, light waves have better directionality than sound waves. Users can find out that the communication link is intercepted in time, so the security and confidentiality are higher. However, the transmission of light beams in seawater is much more complicated than that in the atmosphere, which is mainly affected by the water medium, dissolved substances and suspended substances in seawater. The absorption characteristics of seawater in the same water area at different times, at different depths, and in different water areas vary with space and time. Moreover, in the shallow sea area and the deep sea area, the turbidity of the sea water is different, and the absorption and attenuation effects on the light beam are also different. The minimum attenuation coefficient band of ocean water is 480-500nm, and the minimum attenuation coefficient band of coastal sea water is 530-580nm. It can be seen that , the best window of the beam in seawater only exists in the 480-580nm band, and the transmission distance is much shorter than that of the sound wave.

Obviously, the current underwater communication system for a single transmission medium can no longer meet the current needs of people for underwater fast communication. In addition, in the prior art, only one modulation and demodulation method is used for one communication method, so it cannot be based on the underwater communication system. Under the conditions to give full play to the respective advantages of underwater acoustic communication and wireless optical communication.

Contents of the invention

The technical problem to be solved by the present invention is to provide an adaptive underwater communication system, at least partly solving the problems existing in the underwater communication in the prior art.

According to one aspect of the present invention, an underwater communication system is provided, wherein the system includes a sensor, a transmitting subsystem and a receiving subsystem, wherein:

The sensor is used to sense the external environment and help the underwater wireless communication node to automatically select a suitable communication mode and a corresponding modulation and demodulation mode;

The transmission subsystem is composed of a coding unit, an adaptive modulation unit and a transmission unit, and the transmission subsystem sends the signal to be transmitted to the transmission after being encoded by the coding unit and modulated by the adaptive modulation unit. The corresponding channel of the unit converts the electrical signal into an acoustic signal or an optical signal for transmission;

The receiving subsystem is composed of a receiving unit, an adaptive demodulation unit and a decoding unit. After the corresponding channel of the receiving unit receives an acoustic signal or an optical signal and converts it into an electrical signal, it passes through the adaptive demodulation unit demodulation, and finally the original signal is demodulated by the decoder of the decoding unit, so as to realize reliable transmission of data or instructions within the scope of the communication network.

Further, the sensing of the external environment includes but is not limited to sensing the depth of water, the complexity of the environment, channel conditions, the size of data transmission, and the distance of reliable communication.

Further, the automatic selection of an appropriate communication mode by the underwater wireless communication node refers to: when the distance between the underwater wireless communication nodes is relatively short and there is a large amount of data that needs to be transmitted in one direction, the underwater wireless communication node Use the underwater acoustic communication device to realize positioning, and then automatically select the optical communication method to transmit a large amount of data; when command transmission, network initialization, routing establishment, long-distance or small amount of data transmission, the underwater wireless communication node automatically selects the underwater Communication by means of acoustic communication.

Further, the system includes a transmitting end, an adaptive modulation and demodulation mechanism and a receiving end, and the transmitting end is used for transmitting signals; the adaptive modulation and demodulation mechanism implements different modulation and demodulation modes through feedback from the receiving end switching; the receiving end is used to receive signals; the transmitting end and the receiving end divide the channel signal-to-noise ratio into different levels according to agreement, and each level corresponds to a certain range of signal-to-noise ratio values.

Further, the modulation and demodulation process of the adaptive modulation and demodulation mechanism includes:

Step S110, when requesting a link connection, the sending end first sends the handshake signal RTS in MFSK modulation mode, and the receiving end receives the data packet from the source node for the first time after the set threshold, it is considered as the handshake signal RTS, Use the MFSK system for demodulation. If the demodulation is correct, send a reply handshake signal CTS to the sending end in the MFSK system. The reply handshake signal CTS contains the signal-to-noise ratio level and bit error rate of the channel state tested by the training word, such as demodulation If it is wrong or it is not the handshake signal RTS, it will be discarded and ignored. After receiving the reply handshake signal CTS, the receiving end sets the modulation system according to the signal-to-noise ratio level;

Step S120, the sending end still sends the debugging mode definition signal M-RTS signal in the original modulation system, indicating the modulation type, and after receiving the debugging mode definition signal M-RTS, the receiving end sends the agreed modulation mode response signal to the sending end according to the latest standard M-CTS, indicating that the sender is ready;

Step S130, the sending end demodulates the agreed modulation mode in the sent debugging mode definition signal M-RTS, and after confirming receipt of the agreed modulation mode response signal M-CTS, considers that the receiving end is ready, and then sends the data packet;

Step S140, the receiving end calculates the signal-to-noise ratio, bit error rate, and channel capacity while receiving data, and sends a channel change signal M-ARQ to the sending end when the signal-to-noise ratio and bit error rate exceed a preset threshold, And add the accumulated signal-to-noise ratio level value of each data packet in the channel change signal M-ARQ signal frame load;

Step S150, after receiving the channel change signal M-ARQ, the sending end looks up the SNR average value of the corresponding range according to the additional SNR level value, and uses it to estimate the future SNR value, and resets accordingly modulation format;

Step S160, jump to step S120, and repeat the sending-receiving process. When the data packet is sent and the receiving end receives it correctly, the receiving end uses the MFSK modulation system to send the end signal ACK to notify the sending end and other nodes that the reception is complete. The send-receive process ends.

Further, the adaptive modulation process of the adaptive modulation and demodulation mechanism includes:

In step S210, the transmitter uses MFSK modulation to send the handshake signal RTS, and waits for the receiver to reply with the handshake signal CTS. If within the specified time, the transmitting end does not receive the reply handshake signal CTS, then resend the handshake signal RTS, if the number of times the handshake signal RTS is sent exceeds the predetermined value, the link is considered unreachable;

Step S220, after receiving the reply handshake signal CTS, the transmitting end calculates the distance and signal-to-noise ratio between communication nodes according to the delay and signal strength between the RTS and CTS signals, and selects an appropriate communication method in combination with the amount of data to be transmitted ;

Step S230, the transmitting end uses the MFSK modulation method to send the debugging mode definition signal M-RTS, notifies the receiving end of the debugging mode used for subsequent data, and waits for the receiving end to respond at the same time, if no response is received within the predetermined time, resend the M-RTS RTS signal, if the number of M-RTS signals sent exceeds a predetermined value, then proceed to step S210, and resend the RTS signal;

In step S240, after receiving the reply signal from the receiving end, the transmitter demodulates the received reply signal with the agreed modulation method and judges whether it is the agreed modulation method reply signal M-CTS. If it is not the agreed modulation response signal M-CTS, then proceed to step S230, and wait for the receiving end to send the response signal again;

Step S250, if it is confirmed after demodulation that it is the agreed modulation mode response signal M-CTS, then use the agreed modulation mode to send the data packet, each time a data is sent, wait for the channel change signal M-ARQ replied by the receiving end, if within the predetermined time After receiving the M-ARQ signal, estimate the signal-to-noise ratio according to the mean value of the signal-to-noise ratio added to the M-ARQ signal by the receiving end, and reselect the modulation method accordingly, and then go to step S230;

Step S260, if the M-ARQ signal is not received within the predetermined time, it is considered that the channel state has not changed, and it is judged whether the data transmission is completed, and if not, it is transferred to step S250 to continue sending data, and if the transmission is completed, it is judged whether it is received by the receiving end The error frame signal ARQ that sends, if receive ARQ signal, then forward to step S250 to resend error frame according to the error frame number attached to sending ARQ signal;

Step S270, if the ARQ signal is not received, then judge whether the receiving end signal ACK is received, if the ACK signal is not received within the predetermined time, then it is considered that the link is faulty, and then go to step S210 to re-initiate the communication link, if the ACK signal is received signal, the communication ends successfully and the communication is exited.

Further, the adaptive demodulation process of the adaptive modulation and demodulation mechanism includes:

Step S310, the receiving end receives the signal from the sending node for the first time, demodulates with MFSK, and judges whether to transmit the handshake signal RTS, if it does not transmit the handshake signal RTS, then sends the end signal ACK, and exits, if it is to transmit the handshake signal RTS, then use The MFSK system sends the handshake signal CTS to be received to the transmitter. The CTS signal contains the signal-to-noise ratio level and bit error rate of the channel state tested by the training word, and waits for the debugging mode to define the signal M-RTS. If within the predetermined time If no M-RTS signal is received, the communication will be exited.

Step S320, after receiving the M-RTS signal, the receiving end sends a modulation response signal M-CTS according to the modulation method defined by the M-RTS signal, and waits to receive data;

Step S330, the receiving end calculates the signal-to-noise ratio and the bit error rate each time a piece of data is received, and if it exceeds the threshold, sends the channel change signal M-ARQ, if it does not exceed the threshold, then judges whether the transmission is over, if not, continues to wait for reception If there is an error frame, the error frame signal ARQ will be sent, and the sending end will be notified to resend the data packet with the specified frame number using the current modulation system. If there is no error frame, the end signal ACK will be sent. , notify the transmitter that this communication is over and exit the communication link.

Further, the circuit structure of the self-adaptive modulation and demodulation mechanism includes: ARM, DSP, FPGA, ADC, DAC, amplifier and drive circuit, wherein, the amplifier and drive circuit are mainly responsible for the amplification of analog signals, and driving underwater sound The transmitting and receiving system and the wireless optical communication photoelectric conversion system work; the ADC circuit and DAC circuit mainly complete the conversion of analog signals and digital signals; the ARM processor, as the central processing unit, is responsible for drive management, memory management, transaction management, interrupt Processing, network communication protocol stack management, application program operation, human-computer interaction and other functions; the DSP processor performs baseband signal processing on the signal respectively; the FPGA is used for peripheral digital logic circuit and intermediate frequency signal processing respectively.

Further, the DSP processor is composed of a DSP1 processor and a DSP2 processor, and the DSP1 processor is mainly responsible for random processing, channel coding, quadrature phase shift keying (QPSK) modulation, quadrature amplitude modulation ( QAM), multi-ary frequency shift keying (MFSK) modulation, adaptive resource allocation, adaptive modulation, physical layer applications of space-time coding, and the underlying MAC functions of encryption/decryption and authentication; the DSP2 is responsible for the receiving side Functions of channel decoding, QPSK demodulation, QAM demodulation, MFSK demodulation, de-randomization, channel estimation, and channel equalization.

Further, the FPGA is composed of FPGA1, FPGA2 and FPGA3, wherein the FPGA1 is mainly used for OFDM modulation and demodulation, digital filtering, up-down conversion, and framing operation control; the FPGA2 completes high-speed bus logic control, and peripheral Interface circuits, systems and other equipment interface interaction functions; the FPGA3 is responsible for the functions of serial-to-parallel conversion, space-time encoding, and space-time decoding.

The invention has built-in multiple modulation and demodulation schemes, so that the system can self-adaptively select a suitable modulation and demodulation mode according to the characteristics of the underwater channel, which can give full play to the advantages of various modulation schemes and reduce the bit error rate and system power consumption.

Description of drawings

FIG. 1 is a schematic diagram of the structure and principle of an underwater communication system according to an embodiment of the present invention.

Fig. 2 is a schematic flowchart of an adaptive modulation process of an underwater communication system according to an embodiment of the present invention.

Fig. 3 is a schematic flowchart of an adaptive demodulation process of an underwater communication system according to an embodiment of the present invention.

Fig. 4 is a schematic structural diagram of the frame format of each handshake signal in an underwater communication system according to an embodiment of the present invention.

FIG. 5 is a schematic diagram of a hardware platform implementation of an underwater communication system according to an embodiment of the present invention.

detailed description

In order to facilitate a further understanding of the present invention, the technical solutions of the present invention will be further explained below in conjunction with the drawings and specific embodiments, and each embodiment does not constitute a limitation to the embodiments of the present invention.

According to an embodiment of the present invention, a multi-mode adaptive underwater communication system 10 based on software radio technology is provided. As shown in FIG. 1 , the system 10 includes a sensor 11, a transmitting subsystem 12 and a receiving subsystem 13, wherein , the sensor 11 is used to perceive the external environment, such as the depth of the perception of water, the complexity of the environment, the channel situation, the size of the data transmission, and the distance of reliable communication, to help the underwater wireless communication node to automatically select the appropriate communication mode (underwater acoustic or wireless optical communication) and corresponding modulation and demodulation; the transmitting subsystem 12 is composed of a coding unit 121, an adaptive modulation unit 122 and a transmitting unit 123, and the transmitting subsystem 12 passes the coding and adaptive coding of the signal to be transmitted by the coding unit 121 After the modulation by the modulation unit 122, it is sent to the corresponding channel of the transmitting unit 123, and the electrical signal is converted into an acoustic signal or an optical signal for transmission; the receiving subsystem 13 is composed of a receiving unit 131, an adaptive demodulation unit 132 and a decoding unit 133, After the corresponding channel of the receiving unit 131 receives the acoustic signal or optical signal and converts it into an electrical signal, it is demodulated by the adaptive demodulation unit 132, and finally the original signal is demodulated by the decoder of the decoding unit 133, which realizes Reliable transmission of data or instructions within a communication network. For example: when the distance between communication nodes is relatively short and there is a large amount of data that needs to be transmitted in one direction, the node uses the underwater acoustic communication device to achieve positioning, and then automatically selects the optical communication method to transmit a large amount of data; while in command transmission, network initialization, When establishing a route, long-distance or small amount of data transmission, the node automatically selects the underwater acoustic communication method for communication.

The state of underwater wireless acoustic and optical channels is greatly affected by changes in environmental factors, such as organic and inorganic particles in water, temperature, salinity, density, water depth, internal waves, water masses, reflections on the sea surface and the bottom of the sea, etc. , the establishment of an adaptive modulation and demodulation system that can perceive the channel environment and adaptively select the communication mode (wireless optical communication or wireless underwater acoustic communication) and modulation system according to the amount of communication data will be very important for underwater wireless communication. s help.

Therefore, according to another aspect of the present invention, the present invention also provides an underwater communication system, including a transmitting end, an adaptive modulation and demodulation mechanism, and a receiving end. The establishment of the adaptive modulation and demodulation mechanism can be achieved through feedback from the receiving end Realize the switching of different modulation and demodulation modes, and track this change, so that the system can adaptively determine the modulation mode, frequency band, bit power allocation, etc. in one communication according to the channel characteristics of the test, and maximize the use of limited bandwidth to achieve different modulations The multi-data rate transmission mode of different frequency bands and different carrier numbers enables the communication system to transmit at the highest data rate under different distances and different channel environments. By establishing an adaptive modulation and demodulation mechanism, the sending end and the receiving end will divide the channel SNR into M different levels according to the agreement, and each level corresponds to a certain range of SNR values.

The modulation and demodulation process of the adaptive modulation and demodulation mechanism is:

Step S110, when the sending end requests a link connection, it first sends the handshake signal RTS (including 10 bytes of training words, used to test the channel state) in MFSK modulation mode, and the receiving end Threshold) after receiving the data packet from the source node for the first time, it is considered to be a handshake signal RTS, which is demodulated using the MFSK system. If the demodulation is correct, a reply handshake signal CTS is sent to the sender in the MFSK system, and the handshake signal is replied The CTS contains the signal-to-noise ratio level and the bit error rate of the channel state tested by the training word. If there is a demodulation error or it is not the handshake signal RTS, it will be discarded. After receiving the reply handshake signal CTS, the receiving end sets the modulation system according to the SNR level.

Step S120, the sending end still sends the debugging mode definition signal M-RTS signal in the original modulation system, indicating the modulation type, and after receiving the debugging mode definition signal M-RTS, the receiving end sends the agreed modulation mode response signal to the sending end according to the latest standard M-CTS, indicating that the sender is ready.

Step S130, the sending end demodulates with the agreed modulation mode in the sent debugging mode definition signal M-RTS, and after confirming receipt of the agreed modulation mode response signal M-CTS, considers that the receiving end is ready, and then sends the data packet.

Step S140, the receiving end calculates the signal-to-noise ratio, bit error rate, and channel capacity while receiving data, and sends a channel change signal M-ARQ to the sending end when the signal-to-noise ratio and bit error rate exceed a preset threshold, And the accumulated signal-to-noise ratio level value of each data packet is added to the frame load of the channel change signal M-ARQ signal.

Step S150, after receiving the channel change signal M-ARQ, the sending end looks up the SNR average value of the corresponding range according to the additional SNR level value, and uses it to estimate the future SNR value, and resets accordingly modulation format.

Step S160, jump to step S120, and repeat the sending-receiving process. When the data packet is sent and the receiving end receives it correctly, the receiving end uses the MFSK modulation system to send the end signal ACK to notify the sending end and other nodes that the reception is complete. The send-receive process ends.

Specifically, the adaptive modulation process of the adaptive modulation and demodulation mechanism is shown in Figure 2, including:

In step S210, the transmitter uses MFSK modulation (multi-ary digital frequency modulation) to send the handshake signal RTS, and waits for the receiver to reply with the handshake signal CTS. If within the specified time (such as 1 second), the transmitter does not receive the reply handshake signal CTS, then resend the handshake signal RTS, if the number of times the handshake signal RTS is sent exceeds the predetermined value (such as the predetermined value is 4 times), it is considered The link is down.

Step S220, after receiving the reply handshake signal CTS, the transmitting end calculates the distance and signal-to-noise ratio (SNR) between communication nodes according to the delay and signal strength between the RTS and CTS signals, and selects an appropriate one based on the amount of data to be transmitted. communication mode (MODE(n)).

Step S230, the transmitting end uses the MFSK modulation method to send the debugging mode definition signal M-RTS, notifies the receiving end of the debugging mode used for subsequent data, and waits for the receiving end to respond at the same time, if no response is received within the predetermined time, resend the M-RTS For the RTS signal, if the number of times the M-RTS signal is sent exceeds the predetermined value, go to step S210 and resend the RTS signal.

Step S240, after receiving the response signal replied by the receiving end, the transmitter demodulates the received response signal with the agreed modulation mode (MODE(n)) and judges whether it is the agreed modulation mode response signal M-CTS. If it is not the agreed modulation mode response signal M-CTS, go to step S230 and wait for the receiving end to send the response signal again.

Step S250, if it is confirmed after demodulation that it is the agreed modulation mode response signal M-CTS, then use the agreed modulation mode to send the data packet, each time a data is sent, wait for the channel change signal M-ARQ replied by the receiving end, if within the predetermined time After receiving the M-ARQ signal, estimate the signal-to-noise ratio according to the average value of the signal-to-noise ratio added by the receiving end to the M-ARQ signal, and reselect the modulation method accordingly, and then go to step S230.

Step S260, if the M-ARQ signal is not received within the predetermined time, it is considered that the channel state has not changed, and it is judged whether the data transmission is completed, and if not, it is transferred to step S250 to continue sending data, and if the transmission is completed, it is judged whether it is received by the receiving end Sending the error frame signal ARQ, if the ARQ signal is received, go to step S250 to resend the error frame according to the error frame number attached to the sending ARQ signal.

Step S270, if the ARQ signal is not received, then judge whether the receiving end signal ACK is received, if the ACK signal is not received within the predetermined time, then it is considered that the link is faulty, and then go to step S210 to re-initiate the communication link, if the ACK signal is received signal, the communication ends successfully and the communication is exited.

Specifically, the adaptive demodulation process of the adaptive modulation and demodulation mechanism is shown in Figure 3, including:

Step S310, the receiving end receives the signal from the sending node for the first time (that is, receives the first packet from the source node), demodulates with MFSK mode, and judges whether to transmit the handshake signal RTS, if the handshake signal RTS is not transmitted, then sends the end signal ACK, and Exit, if the handshake signal RTS is to be transmitted, the handshake signal CTS to be received is sent to the transmitter in MFSK format, and the CTS signal contains the signal-to-noise ratio level and bit error rate of the channel state tested by the training word, and waits for the debugging mode Define the signal M-RTS, if the M-RTS signal is not received within the predetermined time, the communication will be exited.

Step S320, after receiving the M-RTS signal, the receiving end sends a modulation response signal M-CTS according to the modulation method defined by the M-RTS signal, and waits to receive data;

Step S330, the receiving end calculates the signal-to-noise ratio and the bit error rate each time a piece of data is received, and if it exceeds the threshold, sends the channel change signal M-ARQ, if it does not exceed the threshold, then judges whether the transmission is over, if not, continues to wait for reception If there is an error frame, the error frame signal ARQ will be sent, and the sending end will be notified to resend the data packet with the specified frame number using the current modulation system. If there is no error frame, the end signal ACK will be sent. , notify the transmitter that this communication is over and exit the communication link.

In the real-time process, you can customize the handshake signal MAC identifier value table and the frame format of each handshake signal. As shown in Table 1, it is an embodiment of the handshake signal MAC identification value table provided by the present invention; as shown in FIG. 4, it is an embodiment of the frame format of each handshake signal provided by the present invention.

signal type MAC identifier value reserve 0000 RTS 0001 CTS 0010 M-ARQ 0011 M-RTS 0100 M-CTS 0101 ARQ 0110 ACK 0111 TSA 1000 DATA 1001 reserve 1010-1111

Table 1

The main purpose of using software radio technology in multi-mode adaptive software underwater wireless communication network is to realize underwater acoustic communication and optical communication in underwater wireless communication through software programming based on a general, standard and modular hardware platform. Such as automatic switching of communication modes, adaptive selection of modulation system according to communication distance, channel status, etc., adaptive selection of resource allocation and other functions according to signal-to-noise ratio, bit error rate, etc., so as to maximize the use of a unified hardware platform and adapt to underwater complex communication environment. The schematic diagram of the hardware platform of the underwater communication system is shown in Figure 5:

The hardware platform of adaptive modulation and demodulation mechanism consists of one ARM processor, two DSP processors, three FPGAs (Field-Programmable Gate Array, Field Programmable Gate Array), ADC, DAC, amplifier and driving circuit. Among them, the amplifier and the driving circuit are mainly responsible for the amplification of the analog signal, as well as driving the underwater acoustic emission and receiving system, and the photoelectric conversion system for wireless optical communication. ADC and DAC mainly complete the conversion of analog signal and digital signal.

As the central processing unit, the ARM processor is responsible for driver management, memory management, transaction management, interrupt processing, network communication protocol stack management, application program operation, human-computer interaction and other functions. Two DSP processors perform baseband signal processing on the signal respectively, among which DSP1 is mainly responsible for random processing, channel coding, quadrature phase shift keying (QPSK) modulation, quadrature amplitude modulation (QAM) and multi-ary frequency shift on the sending side Physical layer applications such as keying (MFSK) modulation, adaptive resource allocation, adaptive modulation, and space-time coding, as well as some underlying MAC functions such as encryption/decryption and authentication; DSP2 is responsible for channel decoding, QPSK demodulation, and QAM at the receiving side Demodulation, MFSK demodulation, de-randomization, channel estimation, channel equalization and other functions.

Three FPGAs are used for peripheral digital logic circuit and intermediate frequency signal processing respectively. FPGA1 is mainly used for operation control such as OFDM modulation and demodulation, digital filtering, up-down conversion, and framing; FPGA2 completes high-speed bus logic control, and peripheral interface circuits such as RJ45, RS232, USB, etc. Other equipment interface interaction functions; FPGA3 is mainly responsible for serial-to-parallel conversion, space-time encoding, space-time decoding and other functions.

In summary, due to the complexity of the underwater environment, different water depths, different transmission distances, horizontal and vertical directions, etc. are applicable to different communication methods. In order to automatically adapt to different underwater environments, the present invention proposes to use software radio technology, that is On the hardware platform, using software to integrate the external environment perceived by the sensor, the underwater wireless communication node automatically selects the appropriate communication mode according to the channel conditions to establish a communication link, which can allocate resources reasonably and realize data or communication within the communication network. Reliable delivery of instructions. The present invention borrows the advantages of software radio and has a variety of modulation and demodulation schemes built in, so that the system can adaptively select a suitable modulation and demodulation mode according to the characteristics of the underwater channel, so as to give full play to the advantages of various modulation schemes, reduce the bit error rate and system power consumption.

The present invention proposes a multi-mode self-adaptive underwater wireless communication network system. Aiming at the characteristics of underwater wireless optical communication channels and underwater acoustic communication channels, an adaptive encoding and decoding solution is proposed. The main advantages of the present invention are as follows:

(1) Develop communication system based on software radio technology, relying on a general, open, standard and modular hardware platform, use software to define and realize various underwater communication functions, which is convenient for developers to carry out secondary development.

(2) The system has the ability to adapt to the underwater communication environment. According to the complexity of the underwater environment, according to different water depths, different transmission distances, different transmission directions (horizontal or vertical), and different data volumes (commands, small data volumes, large data volume) and so on to adaptively select an appropriate communication method for processing.

(3) With multiple underwater wireless communication methods, the system automatically selects the corresponding communication method according to different environments.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of changes or modifications within the technical scope disclosed in the present invention. Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (10)

1. An underwater communication system, characterized in that: the system includes a sensor, a transmitting subsystem and a receiving subsystem, wherein: The sensor is used to sense the external environment and help the underwater wireless communication node to automatically select a suitable communication mode and a corresponding modulation and demodulation mode; The transmission subsystem is composed of a coding unit, an adaptive modulation unit and a transmission unit, and the transmission subsystem sends the signal to be transmitted to the transmission after being encoded by the coding unit and modulated by the adaptive modulation unit. The corresponding channel of the unit converts the electrical signal into an acoustic signal or an optical signal for transmission; The receiving subsystem is composed of a receiving unit, an adaptive demodulation unit and a decoding unit. After the corresponding channel of the receiving unit receives an acoustic signal or an optical signal and converts it into an electrical signal, it passes through the adaptive demodulation unit demodulation, and finally the original signal is demodulated by the decoder of the decoding unit, so as to realize reliable transmission of data or instructions within the scope of the communication network. 2. The underwater communication system according to claim 1, characterized in that: said perceiving the external environment includes but is not limited to perceiving the depth of water, the complexity of the environment, channel conditions, the size of data transmission, and reliable communication distance. 3. The underwater communication system according to claim 1, wherein: the automatic selection of a suitable communication mode by the underwater wireless communication node refers to: when the distance between the underwater wireless communication nodes is relatively close, and there is When a large amount of data needs one-way transmission, the underwater wireless communication node uses the underwater acoustic communication device to realize positioning, and then automatically selects the optical communication method to transmit a large amount of data; When transmitting mass data, the underwater wireless communication node automatically selects the underwater acoustic communication mode for communication. 4. An underwater communication system, characterized in that: the system includes a transmitting end, an adaptive modulation and demodulation mechanism and a receiving end, and the transmitting end is used for transmitting signals; the adaptive modulation and demodulation mechanism is passed from the The feedback of the receiving end realizes the switching of different modulation and demodulation modes; the receiving end is used to receive signals; the transmitting end and the receiving end divide the channel signal-to-noise ratio into different levels according to the agreement, and each level corresponds to a certain range The signal-to-noise ratio value. 5. The underwater communication system according to claim 4, characterized in that: the modulation and demodulation process of the adaptive modulation and demodulation mechanism comprises: Step S110, when requesting a link connection, the sending end first sends the handshake signal RTS in MFSK modulation mode, and the receiving end receives the data packet from the source node for the first time after the set threshold, it is considered as the handshake signal RTS, Use the MFSK system for demodulation. If the demodulation is correct, send a reply handshake signal CTS to the sending end in the MFSK system. The reply handshake signal CTS contains the signal-to-noise ratio level and bit error rate of the channel state tested by the training word, such as demodulation If it is wrong or not the handshake signal RTS, it will be discarded; after receiving the reply handshake signal CTS, the receiving end will set the modulation system according to the signal-to-noise ratio level; Step S120, the sending end still sends the debugging mode definition signal M-RTS signal in the original modulation system, indicating the modulation type, and after receiving the debugging mode definition signal M-RTS, the receiving end sends the agreed modulation mode response signal to the sending end according to the latest standard M-CTS, indicating that the sender is ready; Step S130, the sending end demodulates the agreed modulation mode in the sent debugging mode definition signal M-RTS, and after confirming receipt of the agreed modulation mode response signal M-CTS, considers that the receiving end is ready, and then sends the data packet; Step S140, the receiving end calculates the signal-to-noise ratio, bit error rate, and channel capacity while receiving data, and sends a channel change signal M-ARQ to the sending end when the signal-to-noise ratio and bit error rate exceed a preset threshold, And add the accumulated signal-to-noise ratio level value of each data packet in the channel change signal M-ARQ signal frame load; Step S150, after receiving the channel change signal M-ARQ, the sending end looks up the SNR average value of the corresponding range according to the additional SNR level value, and uses it to estimate the future SNR value, and resets accordingly modulation format; Step S160, jump to step S120, and repeat the sending-receiving process. When the data packet is sent and the receiving end receives it correctly, the receiving end uses the MFSK modulation system to send the end signal ACK to notify the sending end and other nodes that the reception is complete. The send-receive process ends. 6. The underwater communication system according to claim 4, characterized in that: the adaptive modulation process of the adaptive modulation and demodulation mechanism comprises: Step S210, the transmitter uses MFSK modulation to send the handshake signal RTS, and waits for the receiver to reply the handshake signal CTS; if the transmitter does not receive the reply handshake signal CTS within the specified time, then resend the handshake signal RTS, if the handshake signal is sent If the number of RTS exceeds the predetermined value, the link is considered unreachable; Step S220, after receiving the reply handshake signal CTS, the transmitting end calculates the distance and signal-to-noise ratio between communication nodes according to the delay and signal strength between the RTS and CTS signals, and selects an appropriate communication method in combination with the amount of data to be transmitted ; Step S230, the transmitting end uses the MFSK modulation method to send the debugging mode definition signal M-RTS, notifies the receiving end of the debugging mode used for the subsequent data, and waits for the receiving end to respond at the same time, if no response is received within the predetermined time, resend the M-RTS RTS signal, if the number of M-RTS signals sent exceeds a predetermined value, then proceed to step S210, and resend the RTS signal; Step S240, after receiving the reply signal from the receiving end, the transmitter demodulates the received reply signal with the agreed modulation method and judges whether it is the agreed modulation method reply signal M-CTS; if it is not the agreed modulation method reply signal M-CTS -CTS, then proceed to step S230, and wait for the receiving end to send a response signal again; Step S250, if it is confirmed after demodulation that it is the agreed modulation mode response signal M-CTS, then use the agreed modulation mode to send the data packet, each time a piece of data is sent, wait for the channel change signal M-ARQ replied by the receiving end, if within the predetermined time After receiving the M-ARQ signal, estimate the signal-to-noise ratio according to the mean value of the signal-to-noise ratio added to the M-ARQ signal by the receiving end, and reselect the modulation method accordingly, and then turn to step S230; Step S260, if the M-ARQ signal is not received within the predetermined time, it is considered that the channel state has not changed, and it is judged whether the data transmission is completed, and if not, it is transferred to step S250 to continue sending data, and if the transmission is completed, it is judged whether it is received by the receiving end The error frame signal ARQ that sends, if receive ARQ signal, then forward to step S250 to resend error frame according to the error frame number attached to sending ARQ signal; Step S270, if the ARQ signal is not received, then judge whether the receiving end signal ACK is received, if the ACK signal is not received within the predetermined time, then it is considered that the link is faulty, and then go to step S210 to re-initiate the communication link, if the ACK signal is received signal, the communication ends successfully and the communication is exited. 7. The underwater communication system according to claim 4, characterized in that: the adaptive demodulation process of the adaptive modulation and demodulation mechanism comprises: Step S310, the receiving end receives the signal from the sending node for the first time, demodulates with MFSK, and judges whether to transmit the handshake signal RTS, if it does not transmit the handshake signal RTS, then sends the end signal ACK, and exits, if it is to transmit the handshake signal RTS, then use The MFSK system sends the handshake signal CTS to be received to the transmitter. The CTS signal contains the signal-to-noise ratio level and bit error rate of the channel state tested by the training word, and waits for the debugging mode to define the signal M-RTS. If within the predetermined time If the M-RTS signal is not received, exit the communication; Step S320, after receiving the M-RTS signal, the receiving end sends a modulation response signal M-CTS according to the modulation method defined by the M-RTS signal, and waits to receive data; Step S330, the receiving end calculates the signal-to-noise ratio and the bit error rate each time a piece of data is received, and if it exceeds the threshold, sends the channel change signal M-ARQ, if it does not exceed the threshold, then judges whether the transmission is over, if not, continues to wait for reception If there is an error frame, the error frame signal ARQ will be sent, and the sending end will be notified to resend the data packet with the specified frame number using the current modulation system. If there is no error frame, the end signal ACK will be sent. , notify the transmitter that this communication is over and exit the communication link. 8. The underwater communication system according to claim 4, characterized in that: the circuit structure of the adaptive modulation and demodulation mechanism includes: ARM, DSP, FPGA, ADC, DAC, amplifier and drive circuit, wherein the The amplifier and the driving circuit are mainly responsible for amplifying the analog signal, and driving the underwater acoustic transmission and receiving system, and the photoelectric conversion system for wireless optical communication; the ADC circuit and the DAC circuit mainly complete the conversion of the analog signal and the digital signal; the ARM processor serves as The central processing unit is responsible for driver management, memory management, transaction management, interrupt processing, network communication protocol stack management, application program operation, human-computer interaction and other functions; the DSP processor performs baseband signal processing on the signal respectively; the FPGA respectively For peripheral digital logic circuits and intermediate frequency signal processing. 9. The underwater communication system according to claim 8, characterized in that: the DSP processor is made up of a DSP1 processor and a DSP2 processor, and the DSP1 processor is mainly responsible for the random processing, channel coding, and normalization of the sending side. Physical layer applications of quadrature phase shift keying (QPSK) modulation, quadrature amplitude modulation (QAM), multiple frequency shift keying (MFSK) modulation, adaptive resource allocation, adaptive modulation, space-time coding, and encryption/ The underlying MAC function of decryption and authentication; the DSP2 is responsible for the functions of channel decoding, QPSK demodulation, QAM demodulation, MFSK demodulation, de-randomization, channel estimation, and channel equalization at the receiving side. 10. The underwater communication system according to claim 8, characterized in that: said FPGA is made up of FPGA1, FPGA2 and FPGA3, wherein said FPGA1 is mainly used for OFDM modulation and demodulation, digital filtering, frequency conversion up and down, and framing operation control; the FPGA2 completes the high-speed bus logic control, and the peripheral interface circuit, system and other equipment interface interaction functions; the FPGA3 is responsible for the functions of serial-to-parallel conversion, space-time encoding, and space-time decoding.