Acoustic Modem Research Articles

Use of data hiding in aerial sounds for accessibility

This article reviews previous technologies for aerial acoustic data transmission, namely, audio data hiding, acoustic modems, and a hybrid of the two. These technologies can provide an information channel to convey index data for static text messages or data for text messages to assist people who are deaf or hard of hearing. The payload bitrate of these technologies ranges from several bits per second for long distances (>100 m) to hundreds of bits per second for short distances (<1 m). Previous studies have mainly focused on developing methods for embedding and encoding information into aerial sounds. However, few works have evaluated actual aerial transmission in the presence of various disturbances, such as reverberation and reflections, transfer functions of loudspeakers and microphones, nonlinear distortions in loudspeakers, background noise, and Doppler effects. Therefore, in this study, evaluation methods for these acoustic data transmission technologies are proposed and discussed. In addition, pra...

Experimental estimation of delivery success of navigation data packages transmitted via digital hydroacoustic communication channel

The paper reports the experimental research and provides the obtained quantitative and qualitative dependencies of underwater acoustic (UWA) modem performance, particularly, delivery success of navigation data packages on the main characteristics of hydroacoustic communication channel. Experiments were carried out at the sea shelf near the island of Palmaria (Italy, Mediterranean) during CommsNet13 marine expedition organized by the Center for Maritime Research and Experimentation (CMRE, La Spezia) using UWA S2C modems by Evologics, Germany.

A Multi‐Autonomous Underwater Vehicle System for Autonomous Tracking of Marine Life

This paper presents a multi-autonomous underwater vehicle system capable of cooperatively and autonomously tracking and following marine targets (i.e., fish) tagged with an acoustic transmitter. The AUVs have been equipped with stereo-hydrophones that receive signals broadcasted by the acoustic transmitter tags to enable real-time calculation of bearing-to-tag and distance-to-tag measurements. These measurements are shared between AUVs via acoustic modem and fused within each AUV's particle filter for estimating the target's position. The AUVs use a leader/follower multi-AUV control system to enable the AUVs to drive toward the estimated target state by following collision-free paths. Once within the local area of the target, the AUVs circumnavigate the target state until it moves to another area. The system builds on previous work by incorporating a new SmartTag package that can be attached to an individual's dorsal fin. The SmartTag houses a full inertial measurement unit (INU), video logger, acoustic transmitter, and timed release mechanism. After real-time AUV tracking experiments, the SmartTag is recovered. Logged IMU data are fused with logged AUV-obtained acoustic tag measurements within a particle filter to improve state estimation accuracy. This improvement is validated through a series of multi-AUV shark and boat tracking experiments conducted at Santa Catalina Island, California. When compared with previous work that did not use the SmartTag package, results demonstrated a decrease in mean position estimation error of 25–75%, tag orientation estimation errors dropped from 80° to 30° , the sensitivity of mean position error with respect to distance to the tag was less by a factor of 50, and the sensitivity of mean position error with respect to acoustic signal reception frequency to the tag was 25 times less. These statistics demonstrate a large improvement in the system's robustness when the SmartTag package is used.

FDCA: A Full-Duplex Collision Avoidance MAC Protocol for Underwater Acoustic Networks

Unlike terrestrial radio frequency communication, acoustic waves are major communication means in underwater networks. Unfortunately, acoustic waves incur long propagation delays that must be considered in the media access control (MAC) design to achieve a high throughput. Another major reason for low throughput is that almost all the acoustic modems operate under half-duplex mode. For increasing communication throughput, several full-duplex acoustic modems are proposed. However, most current MAC protocols are designed for half-duplex modems that are not suited for full-duplex modems. Toward a proper approach, this paper models and analyzes the impact of full-duplex modem characteristics on the Aloha protocol. We propose a full-duplex collision avoidance (FDCA) MAC protocol for underwater acoustic networks. It is a handshaking based protocol that designed for full-duplex modems to maximize network throughput. Collision avoidance schedule algorithm avoids the collisions at both the receiver and the sender by passively acquired local information (neighboring nodes' propagation delay and expected transmission schedules). Moreover, to cope with the channel's long propagation delay, it launches multiple simultaneous handshaking processes with neighbors to concurrently propagate multiple packets in the underwater channel. Our extensive simulation results have confirmed that the FDCA protocol outperforms the existing full-duplex MAC protocols in representative long propagation delay scenarios.

Underwater Acoustic Modems

Due to the growing interest using underwater acoustic networks, there are more and more research papers about underwater communications. These papers are mainly focused on deployments and studies about the constraints of the underwater medium. The underwater acoustic channel is highly variable and the signal transmission can change according to environmental factors, such as the temperature, pressure, or salinity of the water. For this reason, it is important to know how these devices are developed and the maximum distance and data transfer rates they can achieve. To this end, this paper presents an exhaustive study of existing underwater acoustic modems where their main features are highlighted. We also review the main features of their hardware. All presented proposals in the research literature are compared with commercial underwater acoustic modems. Finally, we analyze different programs and improvements of existing network simulators that are often used to simulate and estimate the behavior of underwater networks.

Underwater Acoustic Modems (S2CR Series) for Synchronization of Underwater Acoustic Network Clocks During Payload Data Exchange

Modern underwater acoustic modems, in addition to receiving and transmitting data, can measure signal propagation time and evaluate the distance between the transmitter and the receiver. These capabilities can be exploited to support the synchronization of underwater acoustic sensor networks, where sensing and actuation must be coordinated across multiple nodes. However, the problem of accurate propagation time measurement, especially in highly reverberant environments, and the evaluation of clock skew on acoustically interacting modems have been investigated rather poorly. In this paper, therefore, we conduct an experimental evaluation of stability/precision of propagation time measurements considering underwater acoustic modems communicating in reverberant environments. We also show how modem built-in tools can provide opportunities for precise estimation of the modems clock skews. Additionally, we demonstrate that payload data exchange can be used as a “comfortable” way for clock synchronization of underwater acoustic networks nodes. At-sea experiments have been carried out considering several modem pairs and node positions in conditions of reverberant underwater acoustic channels. These experiments have been conducted in collaboration with the NATO Centre for Maritime Research and Experimentation (CMRE, La Spezia, Italy) that we gratefully acknowledge.

Independent Benthic Microbial Fuel Cells Powering Sensors and Acoustic Communications with the MARS Underwater Observatory

AbstractMost oceanographic instruments on the seafloor have no connections with the surface and therefore have to run on batteries and store data until recovery. To demonstrate a developing technology, sensors and acoustic modems were powered with energy harvested from the seafloor, and data were relayed acoustically in near–real time to the Monterey Accelerated Research System (MARS) observatory in Monterey Bay, California, and to surface research vessels. MARS is a cabled observatory in deep water (~890 m) at the edge of Monterey Canyon. An acoustic modem was attached to the MARS node and configured to send out commands to, and relay data received from, remote modems. Two benthic microbial fuel cells (BMFCs) positioned approximately 0.5 km away from MARS supplied power to the remote modems and sensors. At their peak performance, these BMFCs produced continuous power densities of ~35 mW m−2 (footprint area). The modems utilized in this study contained an integrated power management platform (PMP) designed to manage and store the electrical energy generated by each BMFC and to record BMFC performance parameters and sensor data on an hourly basis. Temperature and either oxygen or conductivity sensors were chosen because of their common use and environmental relevance. Acoustically transmitted data records show that the BMFCs renewed energy stores and that the oceanographic sensors measured dissolved oxygen, temperature, and conductivity reliably throughout the operational life of each BMFC system (~6 months). These systems remained in place for more than 12 months.

Design of Low-Power Acoustic Modem for Underwater Communication

Design of Low-Power Acoustic Modem for Underwater Communication

Cooperation of coordinated teams of Autonomous Underwater Vehicles

This paper presents the initial stage of the development of an underwater localization system suitable for a flexible number of users. Multiple Autonomous Underwater Vehicles (AUVs) can work as a team and cooperate with other teams of AUVs without costly and acoustically active components, which saves energy and allows AUVs to remain silent. The main building blocks for such a system are: spiral wavefront beacon in conjunction with a standard (circular) acoustic modem, Chip Scale Atomic Clocks (CSAC), acoustic modems, state-of-the-art adaptive underwater networking and Cooperative Localization (CL) algorithms. Using the difference in time of arrival between the spiral wavefront and the modem circular wavefront, receivers will be able to determine the bearing to the source using only one hydrophone. Synchronizing vehicles Chip Scale Atomic Clocks (CSAC) with the beacon at the beginning of the mission and during the longer missions will ensure the vehicles ability to also calculate their distance from the beacon upon every message reception.

HydroCast: Pressure Routing for Underwater Sensor Networks

A Sensor Equipped Aquatic (SEA) swarm is a sensor cloud that drifts with water currents and enables 4-D (space and time) monitoring of local underwater events such as contaminants, marine life, and intruders. The swarm is escorted on the surface by drifting sonobuoys that collect data from the underwater sensors via acoustic modems and report it in real time via radio to a monitoring center. The goal of this study is to design an efficient anycast routing algorithm for reliable underwater sensor event reporting to any surface sonobuoy. Major challenges are the ocean current and limited resources (bandwidth and energy). In this paper, these challenges are addressed, and HydroCast, which is a hydraulic-pressure-based anycast routing protocol that exploits the measured pressure levels to route data to the surface sonobuoys, is proposed. This paper makes the following contributions: a novel opportunistic routing mechanism to select the subset of forwarders that maximizes the greedy progress yet limits cochannel interference and an efficient underwater dead end recovery method that outperforms the recently proposed approaches. The proposed routing protocols are validated through extensive simulations.

An Inductive Charging and Real-Time Communications System for Profiling Moorings

AbstractThis paper describes a system for providing power and communications to moored profiling vehicles. A McLane Moored Profiler (MP) was equipped with a rechargeable battery pack and an inductive charging system to allow it to move periodically to a charging dock at the top of a subsurface mooring. Power was provided from a large bank of alkaline batteries housed in two 0.94-m steel spheres. Data were transferred inductively from the profiler to a mooring controller, and from there back to shore via radio and Iridium satellite modems housed in a small surface communications float on an “L” tether. An acoustic modem provided backup communications to a nearby ship in the event of loss or damage to the surface float. The system was tested in a 180-m-deep fjord (Puget Sound, Washington) and at Station ALOHA (A Long-Term Oligotrophic Habitat Assessment), a 4748-m-deep open-ocean location north of Hawaii. Basic functionality of the system was demonstrated, with the profiler repeatedly recharging at about 225 W (with an overall efficiency of about 70%). Data were relayed back to shore via Iridium and to a nearby ship via the radio and acoustic modems. The system profiled flawlessly for the entire 6-week test in Puget Sound, but charging at the deep site stopped after only 9 days in the deep-ocean deployment owing to damage to the charging station, possibly by surface wave action.

Software-defined underwater acoustic networks: toward a high-rate real-time reconfigurable modem

We review and discuss the challenges of adopting software-defined radio principles in underwater acoustic networks, and propose a software-defined acoustic modem prototype based on commercial off-the-shelf components. We first review current SDR-based architectures for underwater acoustic communications. Then we describe the architecture of a new software-defined acoustic modem prototype, and provide performance evaluation results in both indoor (water tank) and outdoor (lake) environments. We present three experimental testbed scenarios that demonstrate the real-time reconfigurable capabilities of the proposed prototype and show that it exhibits favorable characteristics toward spectrally efficient cognitive underwater networks, and high data rate underwater acoustic links. Finally, we discuss open research challenges for the implementation of next-generation software-defined underwater acoustic networks.

Cooperative bathymetry-based localization using low-cost autonomous underwater vehicles

We present a cooperative bathymetry-based localization approach for a team of low-cost autonomous underwater vehicles (AUVs), each equipped only with a single-beam altimeter, a depth sensor and an acoustic modem. The localization of the individual AUV is achieved via fully decentralized particle filtering, with the local filter's measurement model driven by the AUV's altimeter measurements and ranging information obtained through inter-vehicle communication. We perform empirical analysis on the factors that affect the filter performance. Simulation studies using randomly generated trajectories as well as trajectories executed by the AUVs during field experiments successfully demonstrate the feasibility of the technique. The proposed cooperative localization technique has the potential to prolong AUV mission time, and thus open the door for long-term autonomy underwater.

High-frequency, vertically directional short-range underwater acoustic communications

The underwater acoustic channel is a challenging environment for achieving high data rate communications due to multipath, attenuation, noise, and propagation delay. Performing and maintaining adaptive channel equalization requires significant computational overhead, leading to costly and power-hungry devices. Here we describe a low-cost reconfigurable acoustic modem platform (RAMP) intended to facilitate a cable-less benthic hydrophone array made from inexpensive and replaceable nodes. The high data rate acoustic modem is modulated on a carrier frequency of 750 kHz via binary phase shift keying (BPSK). Each modem is spaced approximately 10 m from adjacent units. Due to the vertical directivity of the transducer the half-maximum envelope of the main lobe is approximately 3°, thereby mitigating multipath from the bottom. Data at rates of up to 125 kbps will be shown from at-sea experimental measurements made in Panama City Beach, Fl. [This work was supported by the Office of Naval Research.]

수중-육상 네트워크 연계용 게이트웨이 부이시스템 개발 및 실 해역 성능 검증

게이트웨이 부이시스템은 수중 어플리케이션 구현 시 수중-육상 간 네트워크 연계를 위한 시스템으로 수중노드와 육상국간 통신 연계, 수중 네트워크 모니터링 등을 수행한다. 본 논문에서는 다수의 수중노드로 수중 네트워크를 구현 시 취득된 데이터들을 육상국과 연계하여 실시간으로 모니터링이 가능한 게이트웨이 부이시스템 개발에 대해 소개한다. 개발된 게이트웨이 부이시스템은 수중음향통신모뎀, RF 통신시스템, 게이트웨이 운용시스템으로 구성되며, 게이트웨이 운용과 수중 네트워크 상태모니터링을 위한 육상국용 관제 프로그램을 구현하였다. 또한 실 해역 시험을 통해 실시간 수중 네트워크 모니터링, 게이트웨이 상태모니터링 등의 성능 검증을 수행하였다. A gateway buoy system connects a underwater network to a terrestrial network, which enables to efficiently monitor the underwater network on a land station. In this paper, we introduce an implemented gateway buoy system which relays gathered data from multiple underwater nodes to a land station in a real time. The gateway buoy hardware system is composed of a underwater acoustic modem system, a radio frequency modem system, and a gateway operating system. in additional, we have implemented a land operating program and a land monitoring program for gateway system and states of underwater network, respectively. We also perform real-sea experiments to verify the performance of the gateway buoy system which real-time monitors underwater network states and gateway system states.

Simple, affordable, and sustainable borehole observatories for complex monitoring objectives

Abstract. Seafloor drill rigs are remotely operated systems that provide a cost-effective means to recover sedimentary records of the upper sub-seafloor deposits. Recent increases in their payload included downhole logging tools or autoclave coring systems. Here we report on another milestone in using seafloor rigs: the development and installation of shallow borehole observatories. Three different systems have been developed for the MARUM-MeBo (Meeresboden-Bohrgerät) seafloor drill, which is operated by MARUM, University of Bremen, Germany. A simple design, the MeBoPLUG, separates the inner borehole from the overlying ocean by using o-ring seals at the conical threads of the drill pipe. The systems are self-contained and include data loggers, batteries, thermistors and a differential pressure sensor. A second design, the so-called MeBoCORK (Circulation Obviation Retrofit Kit), is more sophisticated and also hosts an acoustic modem for data transfer and, if desired, fluid sampling capability using osmotic pumps. In these MeBoCORKs, two systems have to be distinguished: the CORK-A (A stands for autonomous) can be installed by the MeBo alone and monitors pressure and temperature inside and above the borehole (the latter for reference); the CORK-B (B stands for bottom) has a higher payload and can additionally be equipped with geochemical, biological or other physical components. Owing to its larger size, it is installed by a remotely operated underwater vehicle (ROV) and utilises a hot-stab connection in the upper portion of the drill string. Either design relies on a hot-stab connection from beneath in which coiled tubing with a conical drop weight is lowered to couple to the formation. These tubes are fluid-saturated and either serve to transmit pore pressure signals or collect porewater in the osmo-sampler. The third design, the MeBoPUPPI (Pop-Up Pore Pressure Instrument), is similar to the MeBoCORK-A and monitors pore pressure and temperature in a self-contained manner. Instead of transferring data on command using an acoustic modem, the MeBoPUPPI contains a pop-up telemetry with iridium link. After a predefined period, the data unit with satellite link is released, ascends to the sea surface, and remains there for up to 2 weeks while sending the long-term data sets to shore. In summer 2012, two MeBoPLUGs, one MeBoCORK-A and one MeBoCORK-B were installed with MeBo on RV Sonne, Germany, in the Nankai Trough area, Japan. We have successfully downloaded data from the CORKs, attesting that coupling to the formation worked, and pressure records were elevated relative to the seafloor reference. In the near future, we will further deploy the first two MeBoPUPPIs. Recovery of all monitoring systems by a ROV is planned for 2016.

Balance Transmission Mechanism in Underwater Acoustic Sensor Networks

With the rapid development of underwater acoustic modem technology, underwater acoustic sensor networks (UWASNs) have more applications in long-term monitoring of the deployment area. In the underwater environment, the sensors are costly with limited energy. And acoustic communication medium poses new challenges, including high path loss, low bandwidth, and high energy consumption. Therefore, designing transmission mechanism to decrease energy consumption and to optimize the lifetime of UWASN becomes a significant task. This paper proposes a balance transmission mechanism, and divides the data transmission process into two phases. In the routing set-up phase, an efficient routing algorithm based on the optimum transmission distance is present to optimize the energy consumption of the UWASN. And then, a data balance transmission algorithm is introduced in the stable data transmission phase. The algorithm determines one-hop or multihop data transmission of the node to underwater sink according to the current energy level of adjacent nodes. Furthermore, detailed theoretical analysis evaluates the optimum energy levels in the UWASNs with different scales. The simulation results prove the efficiency of the BTM.

An efficient MAC protocol for underwater multi-user uplink communication networks

Multi-user uplink transmission has been proved to be a promising technique for spectrum-efficient communications. However, due to the unique features of underwater acoustic networks (UANs), such as the long propagation delay, low transmission rate and long preamble of acoustic modems, conventional medium access control (MAC) protocols proposed for terrestrial multi-user uplink communications need an overhaul to work efficiently in UANs. In this paper, we carefully consider these features and propose a new MAC protocol, called the competitive transmission MAC (CT-MAC), for underwater multi-user uplink networks. In CT-MAC, we aim to improve the channel utilization and energy efficiency of a network by using a parallel competition mechanism. With parallel competitions, the control packets produced by each user only need to reach the direct neighbors with a low transmission power to save energy. Meanwhile, the data generated by users in different time slots can join the competition transmission in parallel to improve the channel utilization. In addition, we propose two competition schemes for CT-MAC to achieve both the short-term and the long-term fairness in different network conditions. The theoretical analysis and simulation results illustrate that compared with the conventional multi-user uplink MAC protocols, CT-MAC can achieve higher channel utilization and much lower end-to-end delay in UANs, while maintaining comparable energy efficiency.

An Acoustic Modem Featuring a Multi-Receiver and Ultra-Low Power

Wireless technology for underwater communication possesses a wide range of potential application, but it is still a relatively unexplored area in many aspects concerning modems physical design. A step towards future deployment of underwater networks is the reduction of power consumption. Therefore, asynchronous wakeup systems need to be integrated within the physical layer design while avoiding the use of additional transducers. This paper offers a practical and generic solution to adapt data reception and transmission together with asynchronous wakeup sub-systems in acoustic underwater modem architectures using a low power and low cost solution. The proposal has been implemented in a real prototype with success.

A Study on the Characteristics of Underwater Sound Transmission by Short-term Variation of Sound Speed Profiles in Shallow-Water Channel with Thermocline

Underwater acoustic channel impulse responses (CIR) are influenced by sound speed profile (SSP), and the variation of CIR has significant effects on the performance of underwater acoustic communication systems. A significant change of SSP can occur within a short period, which must be considered during the design of underwater acoustic modems. This paper statistically analyzes the effect of the variation of SSP on the long-range acoustic signal propagation in shallow-water with thermocline using numerical modeling based on the data acquired from JACE13 experiment near Jeju island. The analysis result shows that CIR changes variously according to the SSP and the depth of the transmitter and receiver. We also found that when the transmitter and receiver are deeper, the variation of sound wave propagation pattern is smaller and signal level becomes higher. All CIR obtained in this study show that a series of bottom reflections due to downward refraction and small bottom loss in the shallow water with thermocline can be very important factor for long-range signal transmission and the performance of underwater acoustic communication system in time varying ocean environment can be very sensitive to the variation of SSP even for a short period of time.