RU2645893C2 - Method of underwater communication - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: optoacoustic modem includes an optical generator (1), a modulator (2), an information message input device (3), a device for outputting modulated optical radiation into an aqueous medium (4), an optical radiation input device from an aqueous medium (5), a demodulator (6), an information message output device (7), an optical channel pointing error detector (8), an acoustic antenna (9), an acoustic modem (10), an acoustic channel guidance error detector (11), and a control unit for guidance and stabilization system (12). For direct high-speed optical underwater communication between various mobile or stationary and mobile objects, a call signal is pre-emitted using the acoustic antenna (9) and the acoustic modem (10).

EFFECT: simultaneous realization of a high-speed stabilised optical communication channel and an acoustic channel with a long range of action.

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Description

The method relates to the field of telecommunication systems using electromagnetic waves of the optical range and sound waves, where water acts as a transmission medium.

The main telecommunication channel between underwater objects is the acoustic channel, which provides sufficient performance and communication range for most applications. At the same time, in some applications, for example, real-time video transmission, requiring the exchange of megabit streams of information, the acoustic channel cannot fundamentally provide the required performance.

Currently underwater communication methods are being intensively developed, based on the use of electromagnetic radiation in the optical wavelength range. The defining advantage of the optical method is the potential possibility of creating a communication channel with a data transfer rate in water of several Mbit / s. However, a significant drawback of the optical method of underwater communication is its relatively low range. The most promising way to implement the method of optical underwater communication is the use of laser systems operating in the wavelength range (470-570 nm) [Vikrant, A.K., & Jha, R.S. Comparison of Underwater Laser Communication System with Underwater Acoustic Sensor Network // International Journal of Scientific & Engineering Research. - Volume 3. - Issue 10. - 2012. - P. 2]. The choice of this wavelength range is due to the smallest attenuation in the aquatic environment.

The known method according to patent US 2005/0232638 A1 "METHODS AND DEVICE FOR UNDERWATER WIRELESS OPTICAL COMMUNICATION" protects the method and device for underwater communication between stationary underwater systems for collecting information, where LEDs are used as the source of optical radiation, and the system is used as a receiving device based silicon photodiodes. Data transfer in a known solution is performed using the standard IRDA protocol. The maximum data transmission distance is 10 meters. The estimated maximum data rate is estimated at 4 Mbps.

The disadvantage of this method is the small communication range, limiting the scope of its application. In addition, there is no system provided for providing mutual spatial orientation of the radiation patterns of the transmitting and receiving modules.

There is also a known method and technical solution for organizing an optical communication channel using a complex optical signal obtained by modulating laser radiation with a pseudo-random sequence, which allowed transmitting data at a speed of 1 Gbit / s over a distance exceeding 2 m under water [Hanson F., Radic S. Broadband underwater optical communication // Applied optics. - 2008. - T. 47. - No. 2. - S. 277-283]. The disadvantage of this method is small for practical use of the communication distance.

It also does not provide a system for directing laser radiation to the active region of the receiving device, which, with a small angular divergence of the radiation beam, does not allow maintaining the necessary alignment of radiation patterns.

Closest to the claimed method of optical underwater communication, adopted as a prototype, is the method described in patent US 7,953,326 B2 "SYSTEMS AND METHODS FOR UNDERWATER OPTICAL COMMUNICATION". The known method allows for omnidirectional transmission and reception of optical signals under water at a distance of about 100 m, with a data transfer rate of more than 1 Mbit / s. The prototype provides several options for the implementation of optical communication channels and technical solutions for the main nodes and blocks of the communication channel.

Common to all given in the prototype implementation options and for the proposed method is the presence of devices and actions:

- a transmitter including a carrier frequency generator of the optical wavelength range, an input signal input device, a carrier frequency modulator and a device for outputting modulated optical radiation into the aquatic environment;

- a receiving device comprising a device for inputting optical radiation from an aqueous medium, a signal receiver of an optical wavelength range, a demodulator and an information message output device;

- the transmitter emits directly into the aquatic environment a signal modulated by an information message;

- the receiving device receives the transmitter signal that has passed through the aquatic environment, demodulates and displays the received information message.

The disadvantage of this method, adopted as a prototype, is the small communication range due to the use of diffusers that expand the radiation patterns on the emitting and receiving sides. Such expansion leads to a decrease in the energy density emitted by the transmitter and to an increase in the noise of third-party sources on the receiving side, as a result of which the system is not effective in providing long-distance communications. The use of a transmitter and a receiver with narrow radiation patterns in the prototype is impossible due to the lack of a system for guiding the axes of the radiation patterns of the transmitter and receiver towards each other. To communicate using narrow radiation patterns, a guidance system should be provided that allows the axes of the radiation patterns of the optical emitter and receiver to be reduced towards each other and to maintain this state throughout the entire communication session.

The technical problem to which the claimed method is directed is to eliminate these drawbacks, namely the creation of an effective range of action, high-speed optical communication channel between mobile or mobile and stationary underwater objects.

The stated technical problem is solved in that in the known method and device for underwater communication, comprising a transmitter, which includes an optical wave electromagnetic source, an information message input device, a modulator, a diffuser, a modulated optical signal output device to an aqueous medium; a receiver containing a diffuser, an optical radiation input system from an aqueous medium, a demodulator and an information message output device, in contrast to it, in order to increase the maximum range of an optical communication channel, an emitter and an optical signal receiver are made with a small angular divergence of radiation patterns, which allows to increase radiation energy flux density and reduce the noise exposure of the optical receiver; To ensure the operation of such a communication channel between moving or stationary and moving objects, an acoustic communication channel has been introduced into the system in order to detect, identify correspondents, determine the distance between them, point and stabilize the axes of the radiation-reception diagrams.

A block diagram of a device that implements the proposed method for underwater optoacoustic underwater communication is shown in Fig. one.

The block diagram of a device that implements the proposed method for underwater optoacoustic underwater communication includes: A, B - correspondents; 1 - optical generator; 2 - modulator; 3 - input device informational messages; 4 - a device for outputting modulated optical radiation into an aqueous medium; 5 - a device for inputting optical radiation from an aqueous medium; 6 - demodulator; 7 - device output informational messages; 8 - optical channel pointing error detector; 9 - acoustic antenna; 10 - acoustic modem; 11 - acoustic channel pointing error detector; 12 - control unit guidance system and stabilization.

The method works as follows.

The object initiating the communication session emits a ring signal using the acoustic antenna 9 of the acoustic modem 10. In the process of emitting a call signal, a water space is scanned by a variable or narrow radiation pattern of an acoustic antenna. The oncoming correspondent, having received a call signal, emits a response signal using an acoustic antenna 9 and a similar acoustic modem 10. After establishing acoustic contact, correspondents specify the mutual distance, relative position in space, the direction of movement, if approach is required, and combine the radiation / reception axis of the acoustic antennas. Approach is carried out to the distance necessary to establish optical communication. Prior to the establishment of an optical contact, guidance of the optical output / input devices 4.5 is controlled by the acoustic channel through the control unit of the guidance and stabilization system 12, according to the signal extracted by the guidance error detector of the acoustic channel 11, from the signal received by the acoustic modem 10. Control unit of the guidance system and stabilization supports the axis of the radiation patterns of the acoustic antenna, output devices and input modulated optical radiation into the aquatic environment, in collinear th position. The pointing error is contained in the pilot signal received by the acoustic modem emitted by the oncoming correspondent. The criterion for precise guidance of the receiving and radiating systems is the maximum modulus (power) of the received signal and / or the minimum of its phase delay, depending on the directional antennas on the accuracy of pointing to the signal source. After the optical contact is established and the orientation system is captured by the optical communication channel, the orientation control passes to the optical system. Here, the correspondents also exchange pilot signals, from which the guidance error detector of the optical channel 11 generates a control signal for the control unit of the guidance and stabilization system of error compensation 12. During the optical communication session, the guidance and stabilization system provides spatial orientation of the radiation-reception pair based on pointing error. In case of loss of optical contact, orientation control passes to the acoustic channel until the communication channel is captured by the optical orientation system.

The operation of the optical communication channel is as follows: the optical generator of the carrier frequency 1 generates electromagnetic oscillations of the optical wavelength range, which in the modulator 2 interact with the signal of the information message received from the input device information message 3. Next, the modulated carrier frequency is supplied to the output device of the modulated optical radiation into the aquatic environment 4, having a small angular divergence of the emitted signal. A certain fraction of the energy of the emitted signal, depending on the magnitude of absorption, scattering, and energy loss due to spherical wave divergence at a distance between the correspondents, enters the optical radiation input device from the aqueous medium 5, which has a narrow angular characteristic of the receive radiation pattern, and then to the demodulator 6, where the received message is allocated and issued through the output device of the information message 7 to the consumer.

Claims (1)

The method of communication between underwater objects, which consists in the fact that in the transmitting device containing the carrier frequency generator of the optical wavelength range, an information message input device, a carrier frequency modulator and a modulated optical radiation output device in an aqueous medium, the information message modulates the carrier frequency, which is then output a device for outputting modulated optical radiation into the aquatic environment; a receiving device comprising an optical radiation input device from an aqueous medium, an optical signal demodulator and an information message output device, receives an optical signal through an optical radiation input device from an aqueous medium, detects it in a demodulator and issues to a consumer via an information message output device, characterized in that a device for outputting modulated optical radiation into an aqueous medium and a device for inputting optical radiation from an aqueous medium are made with a small angular divergence of the radiation patterns, the optical communication system is supplemented by an acoustic two-way communication channel, as well as a guidance and stabilization system consisting of acoustic and optical guidance error detectors connected respectively to the acoustic modem and to the optical channel demodulator, the detector outputs are connected to the system control unit guidance and stabilization, which is associated with guidance systems of an acoustic antenna, a device for outputting modulated optical radiation in a single medium and a device for inputting optical radiation from an aqueous medium.

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