Underwater acoustic communications is a global domain in which different manufacturers produce di... more Underwater acoustic communications is a global domain in which different manufacturers produce different devices and implement different (and usually incompatible) communication protocols. The myriad of vendor-specific protocols is not conducive to collaboration amongst different industry, academia and research partners. The need for interoperability drove the efforts of NATO Science and Technology Organization (STO) Centre for Maritime Research and Experimentation (CMRE) towards the establishment of a standard for digital underwater acoustic communications. The JANUS standard was recently published as a NATO Standardard (STANAG 4748) and has been implemented by an increasing number of vendors. To validate these implementations and ensure interoperability, CMRE organised the first JANUS Interoperability Fest in May 2018. This article details the tests performed and the main outcomes of the event. The success of this Fest led to the organisation of a second Fest in November 2019 with an increased number of participants.
2018 Fourth Underwater Communications and Networking Conference (UComms), 2018
We design a software modem for long range underwater acousticcommunications in ice-covered oceans... more We design a software modem for long range underwater acousticcommunications in ice-covered oceans. The modem is equipped with three coded modulation schemes achieving 1.8, 21.4 and 96.2 bps, respectively. In addition, we design a new large-scale underwater channel simulator and test the modem performance in the underwater environment of Baffin Bay. Our analysis shows that ranges of more than 200 km can be achieved during summer months provided that the link exploits the ducted sound propagation. During winter months, however, this performance may not be always possible and multiple hops will be needed to cover the same range. The results presented in this work are the basis for the study of adaptive routing solutions for data delivery in multi-hop networks [1].
The Journal of the Acoustical Society of America, 1999
Sound is the best form of energy for broadcasting communication signals in the ocean. However, th... more Sound is the best form of energy for broadcasting communication signals in the ocean. However, the physical channel is impaired by nonwhite noise, frequency-selective absorption, a refractive medium, a sloping seafloor, a dynamic sea-surface, and scattering at the boundaries. Temporal variability of these influences and motion of the link terminals introduce fluctuations in the received signal and noise fields. These oceanographic and geometric factors produce measurable effects on underwater acoustic communication systems. The relevant direct measures of these channel effects include multipath spreading, Doppler shifts and spreading, coherence time, and noise statistics. Measuring and understanding these effects support optimization of both modulation and demodulation parameters. Such channel adaptation strategies enhance quality of service for the communication link. Theory, simulation, and ocean experiment illustrate link improvements. [Work funded by ONR 32, the SSC-SD Independe...
There are three basic techniques commonly employed to extract data from an undersea sensor: 1. vi... more There are three basic techniques commonly employed to extract data from an undersea sensor: 1. via a fixed wired link to a surface expression. 2. via a pop-up buoy, usually incorporating an RF link. 3. via wireless undersea communications. We suggest that the first is impractical in deep or rough conditions (consider the recent oil platform disaster in the Gulf of Mexico). The second consumes considerable energy, especially when winching down the buoy, and it is susceptible for many reasons to mechanical failure. Wireless communications, which encompasses any or all of magnetic, RF, optical, and, especially acoustic methods, has distinct throughput constraints, but it overcomes the limitations of the first two. We focus on this third option, but consider systems in which the communications function and infrastructure is a tightly integrated component of the sensing system itself. The historical focus for wireless communications was primarily on developing assets to support existing sensors devices that themselves were designed for wired connectivity. This focus led directly to never-ending efforts to maximize communications data rate, even when the information content of the data might require only a modest signaling rate. High data rate signaling generally requires high SNR and/or a very limited multipath environment or highly complex and energy-demanding signal processing resources. We suggest that the focus of the discussion change to in situ data and signal processing and compression to support appropriate telemetry. This can provide savings in energy consumption and more appropriate allocation of resources. We describe intelligent, autonomous cross-over among several modes of underwater communications, each designed for an appropriate physical range, or data rate, or appropriate level of energy consumption. We discuss these issues through reference to three real-world examples: diver-based sensors and position tracking, a UUV-based data truck which relies on acoustic communications for precision navigation and data recovery, and long term deployment of ocean sensors. In the diver case, we describe a diver-borne integration of RF and acoustic communications (acomms) and the use of the latter for autonomous monitoring of diver location and status. The through-water RF link provides telemetry between a wristmount device, several diver-status monitors, and a backpack-mounted acomms modem. The Slocum Glider UUV is now integrated with an acomms modem which provides autonomous guidance to and through remote undersea networks linked by acomms. The UUV may visit any modem-equipped sensor, but in particular is used as a data truck with our Sonar Modem, a combined acomms modem and subsea surveillance sensor.
OCEANS 2000 MTS/IEEE Conference and Exhibition. Conference Proceedings (Cat. No.00CH37158)
Abstract-Seaweb '98, Seaweb '99, and Seaweb 2000 begin a series of annual experiments i... more Abstract-Seaweb '98, Seaweb '99, and Seaweb 2000 begin a series of annual experiments incrementally advancing telesonar underwater acoustic signaling and ranging technology for undersea wireless networks. The constraints imposed by acoustic transmission through ...
The counter-detectability of low-bit-rate frequency-hopped communications signals is explored. Ex... more The counter-detectability of low-bit-rate frequency-hopped communications signals is explored. Examples of waveforms received in selected channels are used to demonstrate that signal levels more than 10 dB above those required for error-free signaling are needed by an interceptor having knowledge of the telesonar type-B signal structure. Accompanying sound will be played for the audience to demonstrate the low detectability of these signals, TELESONAR TYPE B SIGNAL~G Telesonar type-B signaling is intended to provide robust communications in adverse channel conditions by accepting a relatively low bit rate in exchange for assured connectivity at low SNR. The technique involves powerful, non-binary convolutional coding for error correction, M~ary frequency-shift-keying (MFSK) modulation combined with sophisticated frequency hopping (FHNFSK), non-coherent demodulation and sequential decoding. Details of the method are contained in [ I]. A benefit of this signaling methodology is the an...
2018 Fourth Underwater Communications and Networking Conference (UComms), 2018
Well-defined terms and measurement procedures are important for transparency in communication and... more Well-defined terms and measurement procedures are important for transparency in communication and repro- ducibility of results. Underwater acoustic communications is a technology and research area populated by people with different backgrounds, using different vocabularies and practices. This paper discusses a few important terms which are known to confuse people.
The past 30 years have seen a growing interest in underwater acoustic communications because of i... more The past 30 years have seen a growing interest in underwater acoustic communications because of its applications in marine research, oceanography, marine commercial operations, the offshore oil industry and defense. Continued research over the years has resulted in improved performance and robustness as compared to the initial communication systems. In this paper, we aim to provide an overview of the key developments in point-to-point communication techniques as well as underwater networking protocols since the beginning of this decade. We also provide an insight into some of the open problems and challenges facing researchers in this field in the near future.
Proceedings of the 10th International Conference on Underwater Networks & Systems - WUWNET '15
This paper provides an overview of a NATO open-access protocol for underwater acoustic communicat... more This paper provides an overview of a NATO open-access protocol for underwater acoustic communications intended to facilitate interoperability among deployed marine assets. NATO has established an advisory committee with a mandate to review the technical specification and the considered applications as this scheme makes its way to a NATO Standardization Agreement (STANAG). The purpose of this paper is to acquaint the community with the technology and to use the international collaboration as an example of the process required to establish a Standard. Underwater (UW) communication capabilities are currently manufacturer-specific, with no international standards for digital coding protocols. Different manufacturers provide different UW communication capabilities, generally using proprietary digital coding technologies. Presently, there exists no general interoperable capability for digital UW communication between assets using modems from different manufacturers. An interoperability capability is essential as maritime operators seek to integrate an increasingly heterogeneous mix of maritime assets. Many autonomous Underwater Vehicles, surface craft, fixed- and rotary-wing aircraft, moored ocean sensing systems, gateway buoys and floats depend on underwater acoustic communications for command, control and information sharing. There is currently no existing capability for these to communicate UW with each other unless they carry matching equipment from the same manufacturer. There also are no existing means to discover other communicating assets to permit the formation of ad-hoc networks. Among the several manufacturers of UW digital modems, only a very few claim to be able to communicate with systems produced by other manufacturers. The establishment of an UW digital communications standard therefore has wide application in both military and civilian contexts. The requirement is for communication interoperability between UW military and civilian maritime assets to facilitate digital UW communication and, additionally, the ad-hoc networked coordination and sharing of information among underwater sensors, surface ships, submarines, AUVs, gateway buoys and sensor networks, covering the transmission and reception of many types of information and providing a communications service that compliments that offered by existing systems.
One of the major challenges in open-ocean deployment of unmanned underwater vehicles (UUVs) or un... more One of the major challenges in open-ocean deployment of unmanned underwater vehicles (UUVs) or unmanned surface vehicles (USVs) is collision avoidance with approaching surface shipping. Existing methods assume that the underwater robot carries a radar and/or has access via radio to commercial Automatic Identification System (AIS) information. However, radars are expensive and both radars and radio can only operate above the water. Moreover, AIS status is not always broadcast by passing shipping. An alternative solution may be found through the use of underwater acoustics whereby a sonar system determines the direction of arrival for a surface ship based upon the ship's radiated noise. The effectiveness of this method lies in the use of as much of the radiated frequency spectrum as is practically accessible, hence a broadband sonar is preferred. We refer to our device as the Passive Bearing Detector (PBD). Ultra-short baseline (USBL) is a well-known interferometric method for est...
The goals of this project were three-fold: 1) to power underwater instruments with energy harvest... more The goals of this project were three-fold: 1) to power underwater instruments with energy harvested from deep sea, organic poor sediments using Benthic Microbial Fuel Cells (BMFCs); 2) to relay instrument data acoustically -and in near-real time- through a cabled seafloor observatory or surface vessel, as appropriate; and 3) to characterize the operational performance of these interactive systems during in situ deployments. Two BMFC- underwater sensing/communications packages were demonstrated near the Monterey Accelerated Research System (MARS) observatory in Monterey Bay, California. MARS is a cabled observatory that resides in deep water (~890 m), about 37 km (23 miles) seaward of the Monterey Bay Aquarium Research Institute (MBARI). The BMFCs were constructed using a cylindrical chamber design with a 0.28 m2 footprint. Each BMFC was used to power an Aanderaa dissolved O2/temperature or conductivity/temperature sensor, as well as a Teledyne Benthos compact acoustic modem which co...
The past decades of development of underwater acoustic communications (acomms) have produced many... more The past decades of development of underwater acoustic communications (acomms) have produced many advances in physical layer algorithms, in hardware and firmware capabilities tailored to the underwater environment, and in concepts for networked sensors. In general, most deployed systems and most conceptual networks have assumed a strictly half duplex channel wherein all links must be shared over a bandwidth-constrained channel. This has led to an almost universal insistence on avoiding collisions among receptions, which might be achieved by TDMA schemes or by adapting other network concepts derived from (RF) mobile communications technology. For long duration deployment of underwater systems, any requirement for tight TDMA access forces the modem developer to use power-hungry high accuracy clocks, thus quickly draining precious battery resources. While networked acknowledgements at the speed of light make perfect sense, the latency of the acoustic channel demands excessive consumpti...
The Journal of the Acoustical Society of America, 2014
ABSTRACT Hydrophone arrays with spacing much less than an acoustic wavelength can be converted to... more ABSTRACT Hydrophone arrays with spacing much less than an acoustic wavelength can be converted to vector sensors. Subsequent vector sensor signal processing can then be applied. Two particular applications are presented: The first is converting very low frequency acoustic data to seismic type data that contain polarization information and the second is getting directional information from sub wavelength acoustic arrays. We start with a review of the simple theory followed by some illustrative simulation examples. We then apply these signal processing methods to ocean acoustic data.
— In this paper, we present our ongoing work on developing a reconfigurable underwater networking... more — In this paper, we present our ongoing work on developing a reconfigurable underwater networking testbed based on the Teledyne Benthos Telesonar SM-75 modem. The testbed is designed with the objective of allowing researchers and developers to advance research activities in the field of underwater networking and communications through a flexible testbed platform. We will first discuss the testbed architecture, with a particular emphasis on architectural considerations, software-hardware separation, and general capabilities. We will then present work in progress on enabling support for IPv6, custom-designed medium access control, and ad hoc routing protocols. Finally, we will discuss integration of the testbed with a channel emulator that allows performing laboratory controlled experiments where the user is able to configure transmission distance, channel effects, and underwater communication parameters. Emulation results for several different scenarios as well as actual experimental...
Underwater acoustic communications is today accomplished with a variety of modulation techniques,... more Underwater acoustic communications is today accomplished with a variety of modulation techniques, including both non-coherent and coherent methods, each shown to perform "best" under certain environmental and operational constraints. Coherent communications typically involve a form of M-ary phase shift keyed (MPSK) signaling, combined with one of a variety of channel equalization schemes at the receiver. The most common scheme is
Achieving effective through-water acoustic digital signaling (telesonar) requires an ability to a... more Achieving effective through-water acoustic digital signaling (telesonar) requires an ability to adaptively accommodate a complex and possibly time-varying acoustic channel. Variable combinations of noise, interference, multipath, and motion impair real-world telesonar channels. When considering any one of these factors individually, performance degradation may be predicted from theory. But the combination of these factors can confound our theoretical predictive capabilities. A computer simulation of the acoustic channel is useful for developing telesonar waveforms and modems. The simulation directly drives the modem receiver with a virtually propagated analog signal, enabling us to test the performance of the synthetic end-to-end telesonar link. We have observed a close correlation between simulation-based performance and observed performance in at-sea channels exhibiting similar characteristics. The fact that telesonar performance is now quite predictable in a wide variety of channels is due, in large measure, to the use of channel simulation. The simulation presented here does not rely on physical modeling of the channel. Rather, it is based on the combination of theoretical multipath models (e.g., a Rician channel) with rapidly time-varying impulse response functions, where the statistics are derived from at-sea experiments or governed by values derived from independent physics-based models (e.g., PC-SWAT, Bellhop, etc). Noise and other additive interference are combinations of theoretical and stored data, and range rate-induced compression and dilation are incorporated.
Underwater acoustic communications is a global domain in which different manufacturers produce di... more Underwater acoustic communications is a global domain in which different manufacturers produce different devices and implement different (and usually incompatible) communication protocols. The myriad of vendor-specific protocols is not conducive to collaboration amongst different industry, academia and research partners. The need for interoperability drove the efforts of NATO Science and Technology Organization (STO) Centre for Maritime Research and Experimentation (CMRE) towards the establishment of a standard for digital underwater acoustic communications. The JANUS standard was recently published as a NATO Standardard (STANAG 4748) and has been implemented by an increasing number of vendors. To validate these implementations and ensure interoperability, CMRE organised the first JANUS Interoperability Fest in May 2018. This article details the tests performed and the main outcomes of the event. The success of this Fest led to the organisation of a second Fest in November 2019 with an increased number of participants.
2018 Fourth Underwater Communications and Networking Conference (UComms), 2018
We design a software modem for long range underwater acousticcommunications in ice-covered oceans... more We design a software modem for long range underwater acousticcommunications in ice-covered oceans. The modem is equipped with three coded modulation schemes achieving 1.8, 21.4 and 96.2 bps, respectively. In addition, we design a new large-scale underwater channel simulator and test the modem performance in the underwater environment of Baffin Bay. Our analysis shows that ranges of more than 200 km can be achieved during summer months provided that the link exploits the ducted sound propagation. During winter months, however, this performance may not be always possible and multiple hops will be needed to cover the same range. The results presented in this work are the basis for the study of adaptive routing solutions for data delivery in multi-hop networks [1].
The Journal of the Acoustical Society of America, 1999
Sound is the best form of energy for broadcasting communication signals in the ocean. However, th... more Sound is the best form of energy for broadcasting communication signals in the ocean. However, the physical channel is impaired by nonwhite noise, frequency-selective absorption, a refractive medium, a sloping seafloor, a dynamic sea-surface, and scattering at the boundaries. Temporal variability of these influences and motion of the link terminals introduce fluctuations in the received signal and noise fields. These oceanographic and geometric factors produce measurable effects on underwater acoustic communication systems. The relevant direct measures of these channel effects include multipath spreading, Doppler shifts and spreading, coherence time, and noise statistics. Measuring and understanding these effects support optimization of both modulation and demodulation parameters. Such channel adaptation strategies enhance quality of service for the communication link. Theory, simulation, and ocean experiment illustrate link improvements. [Work funded by ONR 32, the SSC-SD Independe...
There are three basic techniques commonly employed to extract data from an undersea sensor: 1. vi... more There are three basic techniques commonly employed to extract data from an undersea sensor: 1. via a fixed wired link to a surface expression. 2. via a pop-up buoy, usually incorporating an RF link. 3. via wireless undersea communications. We suggest that the first is impractical in deep or rough conditions (consider the recent oil platform disaster in the Gulf of Mexico). The second consumes considerable energy, especially when winching down the buoy, and it is susceptible for many reasons to mechanical failure. Wireless communications, which encompasses any or all of magnetic, RF, optical, and, especially acoustic methods, has distinct throughput constraints, but it overcomes the limitations of the first two. We focus on this third option, but consider systems in which the communications function and infrastructure is a tightly integrated component of the sensing system itself. The historical focus for wireless communications was primarily on developing assets to support existing sensors devices that themselves were designed for wired connectivity. This focus led directly to never-ending efforts to maximize communications data rate, even when the information content of the data might require only a modest signaling rate. High data rate signaling generally requires high SNR and/or a very limited multipath environment or highly complex and energy-demanding signal processing resources. We suggest that the focus of the discussion change to in situ data and signal processing and compression to support appropriate telemetry. This can provide savings in energy consumption and more appropriate allocation of resources. We describe intelligent, autonomous cross-over among several modes of underwater communications, each designed for an appropriate physical range, or data rate, or appropriate level of energy consumption. We discuss these issues through reference to three real-world examples: diver-based sensors and position tracking, a UUV-based data truck which relies on acoustic communications for precision navigation and data recovery, and long term deployment of ocean sensors. In the diver case, we describe a diver-borne integration of RF and acoustic communications (acomms) and the use of the latter for autonomous monitoring of diver location and status. The through-water RF link provides telemetry between a wristmount device, several diver-status monitors, and a backpack-mounted acomms modem. The Slocum Glider UUV is now integrated with an acomms modem which provides autonomous guidance to and through remote undersea networks linked by acomms. The UUV may visit any modem-equipped sensor, but in particular is used as a data truck with our Sonar Modem, a combined acomms modem and subsea surveillance sensor.
OCEANS 2000 MTS/IEEE Conference and Exhibition. Conference Proceedings (Cat. No.00CH37158)
Abstract-Seaweb '98, Seaweb '99, and Seaweb 2000 begin a series of annual experiments i... more Abstract-Seaweb '98, Seaweb '99, and Seaweb 2000 begin a series of annual experiments incrementally advancing telesonar underwater acoustic signaling and ranging technology for undersea wireless networks. The constraints imposed by acoustic transmission through ...
The counter-detectability of low-bit-rate frequency-hopped communications signals is explored. Ex... more The counter-detectability of low-bit-rate frequency-hopped communications signals is explored. Examples of waveforms received in selected channels are used to demonstrate that signal levels more than 10 dB above those required for error-free signaling are needed by an interceptor having knowledge of the telesonar type-B signal structure. Accompanying sound will be played for the audience to demonstrate the low detectability of these signals, TELESONAR TYPE B SIGNAL~G Telesonar type-B signaling is intended to provide robust communications in adverse channel conditions by accepting a relatively low bit rate in exchange for assured connectivity at low SNR. The technique involves powerful, non-binary convolutional coding for error correction, M~ary frequency-shift-keying (MFSK) modulation combined with sophisticated frequency hopping (FHNFSK), non-coherent demodulation and sequential decoding. Details of the method are contained in [ I]. A benefit of this signaling methodology is the an...
2018 Fourth Underwater Communications and Networking Conference (UComms), 2018
Well-defined terms and measurement procedures are important for transparency in communication and... more Well-defined terms and measurement procedures are important for transparency in communication and repro- ducibility of results. Underwater acoustic communications is a technology and research area populated by people with different backgrounds, using different vocabularies and practices. This paper discusses a few important terms which are known to confuse people.
The past 30 years have seen a growing interest in underwater acoustic communications because of i... more The past 30 years have seen a growing interest in underwater acoustic communications because of its applications in marine research, oceanography, marine commercial operations, the offshore oil industry and defense. Continued research over the years has resulted in improved performance and robustness as compared to the initial communication systems. In this paper, we aim to provide an overview of the key developments in point-to-point communication techniques as well as underwater networking protocols since the beginning of this decade. We also provide an insight into some of the open problems and challenges facing researchers in this field in the near future.
Proceedings of the 10th International Conference on Underwater Networks & Systems - WUWNET '15
This paper provides an overview of a NATO open-access protocol for underwater acoustic communicat... more This paper provides an overview of a NATO open-access protocol for underwater acoustic communications intended to facilitate interoperability among deployed marine assets. NATO has established an advisory committee with a mandate to review the technical specification and the considered applications as this scheme makes its way to a NATO Standardization Agreement (STANAG). The purpose of this paper is to acquaint the community with the technology and to use the international collaboration as an example of the process required to establish a Standard. Underwater (UW) communication capabilities are currently manufacturer-specific, with no international standards for digital coding protocols. Different manufacturers provide different UW communication capabilities, generally using proprietary digital coding technologies. Presently, there exists no general interoperable capability for digital UW communication between assets using modems from different manufacturers. An interoperability capability is essential as maritime operators seek to integrate an increasingly heterogeneous mix of maritime assets. Many autonomous Underwater Vehicles, surface craft, fixed- and rotary-wing aircraft, moored ocean sensing systems, gateway buoys and floats depend on underwater acoustic communications for command, control and information sharing. There is currently no existing capability for these to communicate UW with each other unless they carry matching equipment from the same manufacturer. There also are no existing means to discover other communicating assets to permit the formation of ad-hoc networks. Among the several manufacturers of UW digital modems, only a very few claim to be able to communicate with systems produced by other manufacturers. The establishment of an UW digital communications standard therefore has wide application in both military and civilian contexts. The requirement is for communication interoperability between UW military and civilian maritime assets to facilitate digital UW communication and, additionally, the ad-hoc networked coordination and sharing of information among underwater sensors, surface ships, submarines, AUVs, gateway buoys and sensor networks, covering the transmission and reception of many types of information and providing a communications service that compliments that offered by existing systems.
One of the major challenges in open-ocean deployment of unmanned underwater vehicles (UUVs) or un... more One of the major challenges in open-ocean deployment of unmanned underwater vehicles (UUVs) or unmanned surface vehicles (USVs) is collision avoidance with approaching surface shipping. Existing methods assume that the underwater robot carries a radar and/or has access via radio to commercial Automatic Identification System (AIS) information. However, radars are expensive and both radars and radio can only operate above the water. Moreover, AIS status is not always broadcast by passing shipping. An alternative solution may be found through the use of underwater acoustics whereby a sonar system determines the direction of arrival for a surface ship based upon the ship's radiated noise. The effectiveness of this method lies in the use of as much of the radiated frequency spectrum as is practically accessible, hence a broadband sonar is preferred. We refer to our device as the Passive Bearing Detector (PBD). Ultra-short baseline (USBL) is a well-known interferometric method for est...
The goals of this project were three-fold: 1) to power underwater instruments with energy harvest... more The goals of this project were three-fold: 1) to power underwater instruments with energy harvested from deep sea, organic poor sediments using Benthic Microbial Fuel Cells (BMFCs); 2) to relay instrument data acoustically -and in near-real time- through a cabled seafloor observatory or surface vessel, as appropriate; and 3) to characterize the operational performance of these interactive systems during in situ deployments. Two BMFC- underwater sensing/communications packages were demonstrated near the Monterey Accelerated Research System (MARS) observatory in Monterey Bay, California. MARS is a cabled observatory that resides in deep water (~890 m), about 37 km (23 miles) seaward of the Monterey Bay Aquarium Research Institute (MBARI). The BMFCs were constructed using a cylindrical chamber design with a 0.28 m2 footprint. Each BMFC was used to power an Aanderaa dissolved O2/temperature or conductivity/temperature sensor, as well as a Teledyne Benthos compact acoustic modem which co...
The past decades of development of underwater acoustic communications (acomms) have produced many... more The past decades of development of underwater acoustic communications (acomms) have produced many advances in physical layer algorithms, in hardware and firmware capabilities tailored to the underwater environment, and in concepts for networked sensors. In general, most deployed systems and most conceptual networks have assumed a strictly half duplex channel wherein all links must be shared over a bandwidth-constrained channel. This has led to an almost universal insistence on avoiding collisions among receptions, which might be achieved by TDMA schemes or by adapting other network concepts derived from (RF) mobile communications technology. For long duration deployment of underwater systems, any requirement for tight TDMA access forces the modem developer to use power-hungry high accuracy clocks, thus quickly draining precious battery resources. While networked acknowledgements at the speed of light make perfect sense, the latency of the acoustic channel demands excessive consumpti...
The Journal of the Acoustical Society of America, 2014
ABSTRACT Hydrophone arrays with spacing much less than an acoustic wavelength can be converted to... more ABSTRACT Hydrophone arrays with spacing much less than an acoustic wavelength can be converted to vector sensors. Subsequent vector sensor signal processing can then be applied. Two particular applications are presented: The first is converting very low frequency acoustic data to seismic type data that contain polarization information and the second is getting directional information from sub wavelength acoustic arrays. We start with a review of the simple theory followed by some illustrative simulation examples. We then apply these signal processing methods to ocean acoustic data.
— In this paper, we present our ongoing work on developing a reconfigurable underwater networking... more — In this paper, we present our ongoing work on developing a reconfigurable underwater networking testbed based on the Teledyne Benthos Telesonar SM-75 modem. The testbed is designed with the objective of allowing researchers and developers to advance research activities in the field of underwater networking and communications through a flexible testbed platform. We will first discuss the testbed architecture, with a particular emphasis on architectural considerations, software-hardware separation, and general capabilities. We will then present work in progress on enabling support for IPv6, custom-designed medium access control, and ad hoc routing protocols. Finally, we will discuss integration of the testbed with a channel emulator that allows performing laboratory controlled experiments where the user is able to configure transmission distance, channel effects, and underwater communication parameters. Emulation results for several different scenarios as well as actual experimental...
Underwater acoustic communications is today accomplished with a variety of modulation techniques,... more Underwater acoustic communications is today accomplished with a variety of modulation techniques, including both non-coherent and coherent methods, each shown to perform "best" under certain environmental and operational constraints. Coherent communications typically involve a form of M-ary phase shift keyed (MPSK) signaling, combined with one of a variety of channel equalization schemes at the receiver. The most common scheme is
Achieving effective through-water acoustic digital signaling (telesonar) requires an ability to a... more Achieving effective through-water acoustic digital signaling (telesonar) requires an ability to adaptively accommodate a complex and possibly time-varying acoustic channel. Variable combinations of noise, interference, multipath, and motion impair real-world telesonar channels. When considering any one of these factors individually, performance degradation may be predicted from theory. But the combination of these factors can confound our theoretical predictive capabilities. A computer simulation of the acoustic channel is useful for developing telesonar waveforms and modems. The simulation directly drives the modem receiver with a virtually propagated analog signal, enabling us to test the performance of the synthetic end-to-end telesonar link. We have observed a close correlation between simulation-based performance and observed performance in at-sea channels exhibiting similar characteristics. The fact that telesonar performance is now quite predictable in a wide variety of channels is due, in large measure, to the use of channel simulation. The simulation presented here does not rely on physical modeling of the channel. Rather, it is based on the combination of theoretical multipath models (e.g., a Rician channel) with rapidly time-varying impulse response functions, where the statistics are derived from at-sea experiments or governed by values derived from independent physics-based models (e.g., PC-SWAT, Bellhop, etc). Noise and other additive interference are combinations of theoretical and stored data, and range rate-induced compression and dilation are incorporated.
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Papers by Dale Green