Underwater acoustic communication

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Example of multi-path propagation Vixar3.jpg
Example of multi-path propagation

Underwater acoustic communication is a technique of sending and receiving messages in water. [1] There are several ways of employing such communication but the most common is by using hydrophones. Underwater communication is difficult due to factors such as multi-path propagation, time variations of the channel, small available bandwidth and strong signal attenuation, especially over long ranges. Compared to terrestrial communication, underwater communication has low data rates because it uses acoustic waves instead of electromagnetic waves.

Contents

At the beginning of the 20th century some ships communicated by underwater bells as well as using the system for navigation. Submarine signals were at the time competitive with the primitive maritime radionavigation. [2] The later Fessenden oscillator allowed communication with submarines.

Types of modulation used for underwater acoustic communications

In general the modulation methods developed for radio communications can be adapted for underwater acoustic communications (UAC). However some of the modulation schemes are more suited to the unique underwater acoustic communication channel than others. Some of the modulation methods used for UAC are as follows:

The following is a discussion on the different types of modulation and their utility to UAC.

Frequency-shift keying

FSK is the earliest form of modulation used for acoustic modems. FSK usually employs two distinct frequencies to modulate data; for example, frequency F1 to indicate bit 0 and frequency F2 to indicate bit 1. Hence a binary string can be transmitted by alternating these two frequencies depending on whether it is a 0 or 1. The receiver can be as simple as having analogue matched filters to the two frequencies and a level detector to decide if a 1 or 0 was received. This is a relatively easy form of modulation and therefore used in the earliest acoustic modems. However more sophisticated demodulator using digital signal processors (DSP) can be used in the present day.

The biggest challenge FSK faces in the UAC is multi-path reflections. With multi-path (particularly in UAC) several strong reflections can be present at the receiving hydrophone and the threshold detectors become confused, thus severely limiting the use of this type of UAC to vertical channels. Adaptive equalization methods have been tried with limited success. Adaptive equalization tries to model the highly reflective UAC channel and subtract the effects from the received signal. The success has been limited due to the rapidly varying conditions and the difficulty to adapt in time.

Phase-shift keying

Phase-shift keying (PSK) is a digital modulation scheme that conveys data by changing (modulating) the phase of a reference signal (the carrier wave). The signal is impressed into the magnetic field x,y area by varying the sine and cosine inputs at a precise time. It is widely used for wireless LANs , RFID and Bluetooth communication.

Orthogonal frequency-division multiplexing

Orthogonal frequency-division multiplexing (OFDM) is a digital multi-carrier modulation scheme. OFDM conveys data on several parallel data channels by incorporating closely spaced orthogonal sub-carrier signals.

OFDM is a favorable communication scheme in underwater acoustic communications thanks to its resilience against frequency selective channels with long delay spreads. [3] [4] [5]

Continuous phase modulation

Continuous phase modulation (CPM) is a modulation technique, which is a continuous phase shift, where the phase of the carrier signal varies over time and avoids abrupt changes between successive symbols. This smooth phase trajectory reduces spectral side lobes. [6]

redusin spectral side lobes increases the spectral efficiency of CPM and enables it to transmit data within a narrower bandwidth. Notable variants of CPM include minimum shift keying (MSK) and Gaussian minimum shift keying (GMSK), which uses a Gaussian filter to smooth out phase shifts. [7] [8]

Since the underwater environment is highly scattered, it can cause multipath propagation and signal degradation. The CPM's continuous phase featur mitigates these effects and maintains signal integrity. Besides itss high spectral efficiency helps make optimal use of limited bandwidth underwater. [6]

Use of vector sensors

Compared to a scalar pressure sensor, such as a hydrophone, which measures the scalar acoustic field component, a vector sensor measures the vector field components such as acoustic particle velocities. Vector sensors can be categorized into inertial and gradient sensors. [9]

Vector sensors have been widely researched over the past few decades. [10] [11] Many vector sensor signal processing algorithms have been designed. [12]

Underwater vector sensor applications have been focused on sonar and target detection. [11] They have also been proposed to be used as underwater multi‐channel communication receivers and equalizers. [13] Other researchers have used arrays of scalar sensors as multi‐channel equalizers and receivers. [14] [15]

Applications

Underwater telephone

The underwater telephone, also known as UQC, AN/WQC-2, or Gertrude, was used by the U.S. Navy in 1945 [16] after in Kiel, Germany, in 1935 different realizations at sea were demonstrated. [17] The terms UQC and AN/WQC-2 follow the nomenclature of the Joint Electronics Type Designation System. [18] The type designation "UQC" stands for General Utility (multi use), Sonar and Underwater Sound and Communications (Receiving/Transmitting, two way). The "W" in WQC stands for Water Surface and Underwater combined. The underwater telephone is used on all crewed submersibles and many Naval surface ships in operation. Voice or an audio tone (morse code) communicated through the UQC are heterodyned to a high pitch for acoustic transmission through water. [19]

JANUS

In April 2017, NATO's Centre for Maritime Research and Experimentation announced [20] the approval of JANUS, a standardized protocol to transmit digital information underwater using acoustic sound (like modems and fax machines do over telephone lines). [21] Documented in STANAG 4748, it uses 900 Hz to 60 kHz frequencies at distances of up to 28 kilometres (17 mi). [22] [23] It is available for use with military and civilian, NATO and non-NATO devices; it was named after the Roman god of gateways, openings, etc.

The JANUS specification (ANEP-87) provides for a flexible plug-in-based payload scheme. A baseline JANUS packet consists of 64 bits to which further arbitrary data (Cargo) can be appended. [24] This enables multiple different applications such as Emergency location, Underwater AIS (Automatic Identification System), and Chat. An example of an Emergency Position and Status message is the following JSON representation: [25] [26] 

{"ClassUserID":0,"ApplicationType":3,"Nationality":"PT","Latitude":"38.386547","Longitude":"-9.055858","Depth":"16","Speed":"1.400000","Heading":"0.000000","O2":"17.799999","CO2":"5.000000","CO":"76.000000","H2":"3.500000","Pressure":"45.000000","Temperature":"21.000000","Survivors":"43","MobilityFlag":"1","ForwardingCapability":"1","TxRxFlag":"0","ScheduleFlag":"0"}

This Emergency Position and Status Message (Class ID 0 Application 3 Plug-in) message shows a Portuguese submarine at 38.386547 latitude -9.055858 longitude at a depth of 16 meters. It is moving north at 1.4 meters per second, and has 43 survivors on board and shows the environmental conditions.

Underwater messaging

Commercial hardware products have been designed to enable two-way underwater messaging between scuba divers. [27] [28] These support sending from a list of pre-defined messages from a dive computer using acoustic communication.

Research efforts have also explored the use of smartphones in water-proof cases for underwater communication, using acoustic modem hardware as phone attachments [29] as well as using a software app without any additional hardware. [30] The Android software app, AquaApp, from University of Washington uses the microphones and speakers on existing smartphones and smart watches to enable underwater acoustic communication. [31] It had been tested to send digital messages using smartphones between divers at distances of up to 100 m. [30]

See also

Related Research Articles

In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a separate signal called the modulation signal that typically contains information to be transmitted. For example, the modulation signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer.

<span class="mw-page-title-main">Orthogonal frequency-division multiplexing</span> Method of encoding digital data on multiple carrier frequencies

In telecommunications, orthogonal frequency-division multiplexing (OFDM) is a type of digital transmission used in digital modulation for encoding digital (binary) data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital communication, used in applications such as digital television and audio broadcasting, DSL internet access, wireless networks, power line networks, and 4G/5G mobile communications.

<span class="mw-page-title-main">Baseband</span> Range of frequencies occupied by an unmodulated signal

In telecommunications and signal processing, baseband is the range of frequencies occupied by a signal that has not been modulated to higher frequencies. Baseband signals typically originate from transducers, converting some other variable into an electrical signal. For example, the electronic output of a microphone is a baseband signal that is analogous to the applied voice audio. In conventional analog radio broadcasting, the baseband audio signal is used to modulate an RF carrier signal of a much higher frequency.

<span class="mw-page-title-main">Frequency-shift keying</span> Data communications modulation protocol

Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is encoded on a carrier signal by periodically shifting the frequency of the carrier between several discrete frequencies. The technology is used for communication systems such as telemetry, weather balloon radiosondes, caller ID, garage door openers, and low frequency radio transmission in the VLF and ELF bands. The simplest FSK is binary FSK, in which the carrier is shifted between two discrete frequencies to transmit binary information.

Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency carrier wave. The modulation is accomplished by varying the sine and cosine inputs at a precise time. It is widely used for wireless LANs, RFID and Bluetooth communication.

<span class="mw-page-title-main">Fading</span> Term in wireless communications

In wireless communications, fading is the variation of signal attenuation over variables like time, geographical position, and radio frequency. Fading is often modeled as a random process. In wireless systems, fading may either be due to multipath propagation, referred to as multipath-induced fading, weather, or shadowing from obstacles affecting the wave propagation, sometimes referred to as shadow fading.

Angle modulation is a class of carrier modulation that is used in telecommunications transmission systems. The class comprises frequency modulation (FM) and phase modulation (PM), and is based on altering the frequency or the phase, respectively, of a carrier signal to encode the message signal. This contrasts with varying the amplitude of the carrier, practiced in amplitude modulation (AM) transmission, the earliest of the major modulation methods used widely in early radio broadcasting.

Pulse-position modulation (PPM) is a form of signal modulation in which M message bits are encoded by transmitting a single pulse in one of possible required time shifts. This is repeated every T seconds, such that the transmitted bit rate is bits per second. It is primarily useful for optical communications systems, which tend to have little or no multipath interference.

<span class="mw-page-title-main">Power-line communication</span> Data network that uses electrical wiring

Power-line communication (PLC) is the carrying of data on a conductor that is also used simultaneously for AC electric power transmission or electric power distribution to consumers. The line that does so is known as a power-line carrier.

Continuous phase modulation (CPM) is a method for modulation of data commonly used in wireless modems. In contrast to other coherent digital phase modulation techniques where the carrier phase abruptly resets to zero at the start of every symbol, with CPM the carrier phase is modulated in a continuous manner. For instance, with QPSK the carrier instantaneously jumps from a sine to a cosine whenever one of the two message bits of the current symbol differs from the two message bits of the previous symbol. This discontinuity requires a relatively large percentage of the power to occur outside of the intended band, leading to poor spectral efficiency. Furthermore, CPM is typically implemented as a constant-envelope waveform, i.e., the transmitted carrier power is constant. Therefore, CPM is attractive because the phase continuity yields high spectral efficiency, and the constant envelope yields excellent power efficiency. The primary drawback is the high implementation complexity required for an optimal receiver.

Communication with submarines is a field within military communications that presents technical challenges and requires specialized technology. Because radio waves do not travel well through good electrical conductors like salt water, submerged submarines are cut off from radio communication with their command authorities at ordinary radio frequencies. Submarines can surface and raise an antenna above the sea level, or float a tethered buoy carrying an antenna, then use ordinary radio transmissions; however, this makes them vulnerable to detection by anti-submarine warfare forces.

<span class="mw-page-title-main">Bell 202 modem</span> Modem standard developed by Bell System in 1976

The Bell 202 modem was an early (1976) modem standard developed by the Bell System. It specifies audio frequency-shift keying (AFSK) to encode and transfer data at a rate of 1200 bits per second (bit/s), half-duplex. It has separate sets of circuits for 1200 bit/s and 300 bit/s rates. These signalling protocols, also used in third-party modems, are referred to generically as Bell 202 modulation, and any device employing it as Bell-202-compatible.

In digital modulation, minimum-shift keying (MSK) is a type of continuous-phase frequency-shift keying that was developed in the late 1950s by Collins Radio employees Melvin L. Doelz and Earl T. Heald. Similar to OQPSK, MSK is encoded with bits alternating between quadrature components, with the Q component delayed by half the symbol period.

In a digitally modulated signal or a line code, symbol rate, modulation rate or baud rate is the number of symbol changes, waveform changes, or signaling events across the transmission medium per unit of time. The symbol rate is measured in baud (Bd) or symbols per second. In the case of a line code, the symbol rate is the pulse rate in pulses per second. Each symbol can represent or convey one or several bits of data. The symbol rate is related to the gross bit rate, expressed in bits per second.

Multi-carrier code-division multiple access (MC-CDMA) is a multiple access scheme used in OFDM-based telecommunication systems, allowing the system to support multiple users at the same time over same frequency band.

IEC 61334, known as Distribution automation using distribution line carrier systems, is a standard for low-speed reliable power line communications by electricity meters, water meters and SCADA. It is also known as spread frequency-shift keying (S-FSK) and was formerly known as IEC 1334 before IEC's most recent renumbering. It is actually a series of standards describing the researched physical environment of power lines, a well-adapted physical layer, a workable low-power media access layer, and a management interface. Related standards use the physical layer, but not the higher layers.

Multiple-input, multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) is the dominant air interface for 4G and 5G broadband wireless communications. It combines multiple-input, multiple-output (MIMO) technology, which multiplies capacity by transmitting different signals over multiple antennas, and orthogonal frequency-division multiplexing (OFDM), which divides a radio channel into a large number of closely spaced subchannels to provide more reliable communications at high speeds. Research conducted during the mid-1990s showed that while MIMO can be used with other popular air interfaces such as time-division multiple access (TDMA) and code-division multiple access (CDMA), the combination of MIMO and OFDM is most practical at higher data rates.

Non-orthogonal frequency-division multiplexing (N-OFDM) is a method of encoding digital data on multiple carrier frequencies with non-orthogonal intervals between frequency of sub-carriers. N-OFDM signals can be used in communication and radar systems.

Stress wave communication is a technique of sending and receiving messages using host structure itself as the transmission medium. Conventional modulation methods such as amplitude-shift keying (ASK), frequency-shift keying (FSK), phase-shift keying (PSK), quadrature amplitude modulation (QAM), pulse-position modulation (PPM) and orthogonal frequency-division multiplexing (OFDM) could be leveraged for stress wave communication. The challenge to use stress wave as the carrier of the communication is the severe signal distortions due to the multipath channel dispersion. Compared with other communication techniques, it is a very reliable communication for special applications, such as within concrete structures, well drilling string, pipeline structures and so on.

Orthogonal Time Frequency Space (OTFS) is a 2D modulation technique that transforms the information carried in the Delay-Doppler coordinate system. The information is transformed in the similar time-frequency domain as utilized by the traditional schemes of modulation such as TDMA, CDMA, and OFDM. It was first used for fixed wireless, and is now a contending waveform for 6G technology due to its robustness in high-speed vehicular scenarios.

References

  1. ↑ I. F. Akyildiz, D. Pompili, and T. Melodia, "Underwater Acoustic Sensor Networks: Research Challenges," Ad Hoc Networks (Elsevier), vol. 3, no. 3, pp. 257-279, March 2005.
  2. ↑ "Submarine Signaling on Steamships". www.ggarchives.com. Retrieved 2016-01-18.
  3. ↑ E. Demirors, G. Sklivanitis, T. Melodia, S. N. Batalama, and D. A. Pados, "Software-defined Underwater Acoustic Networks: Toward a High-rate Real-time Reconfigurable Modem," IEEE Communications Magazine, vol. 53, no. 11, pp. 64 – 71, November 2015.
  4. ↑ S. Zhou and Z.-H. Wang, OFDM for Underwater Acoustic Communications. John Wiley and Sons, Inc., 2014.
  5. ↑ E. Demirors, G. Sklivanitis, G.E. Santagati, T. Melodia, and S. N. Batalama, "Design of A Software-defined Underwater Acoustic Modem with Real-time Physical Layer Adaptation Capabilities," in Proc. of ACM Intl. Conf. on Underwater Networks & Systems (WUWNet), Rome, Italy, November 2014.
  6. 1 2 "CONTINUOUS PHASE MODULATION (CPM)" (PDF).
  7. ↑ "Gaussian Minimum Shift Keying (GMSK) - Modulation and Demodulation" (PDF). 17 May 2014.
  8. ↑ "Minimum Shift Keying (MSK) - A Tutorial - Qasim Chaudhari".
  9. ↑ Gabrielson, T. B. (2001). Design problems and limitations in vector sensors (PDF). Workshop on Directional Acoustic Sensors. Newport, RI. p. 29.
  10. ↑ Proc. AIP Conf. Acoustic Particle Velocity Sensors: Design, Performance, and Applications, Mystic, CT, 1995.
  11. 1 2 A. Nehorai and E. Paldi, “Acoustic vector-sensor array processing,” IEEE Trans. Signal Process., vol. 42, pp. 2481–2491, 1994.
  12. ↑ K. T. Wong & H. Chi, "Beam Patterns of an Underwater Acoustic Vector Hydrophone Located Away from any Reflecting Boundary," IEEE Journal of Oceanic Engineering, vol. 27, no. 3, pp. 628-637, July 2002.
  13. ↑ A. Abdi and H. Guo, “A new compact multichannel receiver for underwater wireless communication networks,” IEEE Trans. Wireless Commun., vol. 8, pp. 3326‐3329, 2009.
  14. ↑ T. C. Yang, “Temporal resolutions of time-reversal and passive phase conjugation for underwater acoustic communications,” IEEE J. Oceanic Eng., vol. 28, pp. 229–245, 2003.
  15. ↑ M. Stojanovic, J. A. Catipovic, and J. G. Proakis, “Reduced-complexity spatial and temporal processing of underwater acoustic communication signals,” J. Acoust. Soc. Am., vol. 98, pp. 961–972, 1995.
  16. ↑ Quazi, A.; Konrad, W. (March 1982). "Underwater Acoustic Communications". IEEE Comm Magazine. pp. 24–29.
  17. ↑ Nissen, I. (March 2017). "GERTRUDE - 80 years underwater telephony". DAGA 2017. pp. 1–13.
  18. ↑ "Acoustic influence of underwater mobile survey vehicles on the soundscape of Pacific rockfish habitat". pubs.aip.org. Retrieved 2023-07-03.
  19. ↑ "How is sound used to communicate underwater?". Discovery of Sound in the Sea. University of Rhode Island. 2021.
  20. ↑ "A new era of digital underwater communications". NATO. 2017-04-27.
  21. ↑ "JANUS Community Wiki".
  22. ↑ Brown, Eric (2017-08-15). "The Internet of Underwater Things: Open Source JANUS Standard for Undersea Communications". Linux.com. The Linux Foundation.
  23. ↑ Nacini, Francesca (2017-05-04). "JANUS creates a new era for digital underwater communications". Robohub.
  24. ↑ "ANEP-87 Ed: A, Ver. 1, DIGITAL UNDERWATER SIGNALLING STANDARD FOR NETWORK NODE DISCOVERY & INTEROPERABILITY". NATO Standardization Office. March 2017.
  25. ↑ "Popoto User's Guide PMM5021" (PDF). p. 44.
  26. ↑ "JANUS Community Wiki | Class User Id: 002 Underwater AIS". JANUS Community Wiki. Retrieved 2023-07-15.
  27. ↑ "Israel's UTC brings text-messaging underwater [VIDEO]". ISRAEL21c. 2008-02-04. Retrieved 2022-08-30.
  28. ↑ "Ultrasonic dive computer lets divers communicate through "pings"". New Atlas. 2019-02-08. Retrieved 2022-08-30.
  29. ↑ Restuccia, Francesco; Demirors, Emrecan; Melodia, Tommaso (2017-11-06). "ISonar". Proceedings of the International Conference on Underwater Networks & Systems. Halifax NS Canada: ACM. pp. 1–9. doi:10.1145/3148675.3148710. ISBN   978-1-4503-5561-2. S2CID   11584770.
  30. 1 2 Chen, Tuochao; Chan, Justin; Gollakota, Shyamnath (2022-08-22). "Underwater messaging using mobile devices". Proceedings of the ACM SIGCOMM 2022 Conference. Amsterdam Netherlands: ACM. pp. 545–559. doi: 10.1145/3544216.3544258 . ISBN   978-1-4503-9420-8. S2CID   251496040.
  31. ↑ "Finally, an underwater messaging app". TechCrunch. 29 August 2022. Retrieved 2022-08-30.
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