Performance Of Acoustic Communication Research Articles

An experimental study of mobile underwater acoustic channels and their impacts on mobile acoustic communications

Most underwater acoustic communication schemes have implicitly assumed limited platform mobility and their performance tends to suffer considerably when the platform is in high motion. To gain insight into the effects of high platform mobility, a sea-going experiment was recently conducted. In the experiment, two channels are set up. One is a stationary channel between a fixed source and a fixed receiver. The other is a highly mobile channel between a fixed receiver and a source towed in a circle at a speed of 6 knots. The two channels are directly compared in terms of four key channel parameters changes that matter most to the performance of acoustic communications, namely, channel coherence, path loss, Doppler scaling factor and carrier frequency offsets. A channel probing signal is judiciously designed to enable reliable estimation of those parameters at high resolution in time. This paper will provide the details of this sea experiment, including its design, setups and execution, and report interesting findings.

2E3-3 Underwater acoustic communication performance of space-frequency diversity applying maximum ration combining with maximum likelihood estimation in time varying fading channel by the movement of underwater vehicle

2E3-3 Underwater acoustic communication performance of space-frequency diversity applying maximum ration combining with maximum likelihood estimation in time varying fading channel by the movement of underwater vehicle

Model-based learning of underwater acoustic communication performance for marine robots

Accurate prediction of acoustic communication performance is an important capability for marine robots. In this paper, we propose a model-based learning methodology for the prediction of underwater acoustic communication performance. The learning algorithm consists of two steps: (i) estimation of the covariance matrix by evaluating candidate functions with estimated parameters using detrended measurements;and (ii) prediction of communication performance. Covariance estimation is addressed with a multi-stage iterative training method that produces unbiased and robust results with nested models. The efficiency of the framework is validated with simulations and experimental data from field trials. The field trials involved a manned surface vehicle and an autonomous underwater vehicle.

Underwater acoustic communication performance by signal to noise plus interference ratio in BLAC18

In underwater acoustic communications, inter-symbol interference (ISI) caused by multipath propagation of underwater channel degrades communication performance significantly. Various techniques, such as time reversal combining and decision feedback equalization, have been developed to eliminate the influence of the interference. However, few studies have assessed the performance with the signal-to-noise (SNR) of received communication signals. In practical underwater acoustic systems, the channel must be accurately estimated for the channel equalization and the SNR is involved in the accuracy of the channel estimation. The effect of interference is dominant at short distances, but the effect of noise becomes dominant as distance increases. In this study, SNR, signal-to-interference ratio, and signal-to-noise plus interference ratio (SINR) are estimated as a function of the distance, and communication performances are examined. Communication data from BLAC18, conducted in East Sea of Korea in 2018, are used to analyze the communication performances. In the experiment, communication signals with a carrier frequency of 2.5 kHz were transmitted and received at horizontal distances of 30, 60, and 90 km. Data analysis results shows that communication performance is most correlated with SINR. [Work supported by the ADD(UD170022DD).]

Optimal Deployment of Vector Sensor Nodes in Underwater Acoustic Sensor Networks.

Underwater acoustic sensor networks have recently attracted considerable attention as demands on the Internet of Underwater Things (IoUT) increase. In terms of efficiency, it is important to achieve the maximum communication coverage using a limited number of sensor nodes while maintaining communication connectivity. In 2017, Kim and Choi proposed a new deployment algorithm using the communication performance surface, which is a geospatial information map representing the underwater acoustic communication performance of a targeted underwater area. In that work, each sensor node was a vertically separated hydrophone array, which measures acoustic pressure (a scalar quantity). Although an array receiver is an effective system to eliminate inter-symbol interference caused by multipath channel impulse responses in underwater communication environments, a large-scale receiver system degrades the spatial efficiency. In this paper, single-vector sensors measuring the particle velocity are used as underwater sensor nodes. A single-vector sensor can be considered to be a single-input multiple-output communication system because it measures the three directional components of particle velocity. Our simulation results show that the optimal deployment obtained using single-vector sensor nodes is more effective than that obtained using a hydrophone (three-channel vertical-pressure sensor) array.

Optimal Deployment of Sensor Nodes Based on Performance Surface of Underwater Acoustic Communication.

The underwater acoustic sensor network (UWASN) is a system that exchanges data between numerous sensor nodes deployed in the sea. The UWASN uses an underwater acoustic communication technique to exchange data. Therefore, it is important to design a robust system that will function even in severely fluctuating underwater communication conditions, along with variations in the ocean environment. In this paper, a new algorithm to find the optimal deployment positions of underwater sensor nodes is proposed. The algorithm uses the communication performance surface, which is a map showing the underwater acoustic communication performance of a targeted area. A virtual force-particle swarm optimization algorithm is then used as an optimization technique to find the optimal deployment positions of the sensor nodes, using the performance surface information to estimate the communication radii of the sensor nodes in each generation. The algorithm is evaluated by comparing simulation results between two different seasons (summer and winter) for an area located off the eastern coast of Korea as the selected targeted area.

Underwater acoustic channel characteristics and communication performance at 85 kHz.

A high frequency acoustic experiment was conducted in the northern portion of the Gulf of Mexico in August 2016 to examine the operating range, data rates, and performance of acoustic communication systems at the carrier frequency of 85 kHz. The received signal-to-noise ratios, channel coherence, and impulse responses were reported between two 85 kHz transducers and a five-element hydrophone array over multiple ranges up to 1500 m. Channel estimation based decision feedback equalizers (DFEs) were applied to process the communication measurements. A data rate of 27.2 kb/s was achieved for four tested ranges with a uniform set of receiver parameters.

Experimental Multipath Delay Profile of Underwater Acoustic Communication Channel in Shallow Water

<p>The shallow water channel is an environment that is of particular interest to many research fields. An underwater acoustic channel is characterized as a multipath channel. Time-varying multipath propagation is one of the major factors that limit the acoustic communication performance in shallow water. This study conducts two underwater acoustic experiments in Tanjung Balau, Johor, Malaysia. A transducer and a hydrophone are submerged at different depths and separated by different distances. Linear frequency modulated (LFM) pulses are chosen as the main transmit signal for the experiments. The cross-correlation between the transmitted and received signals represents the impulse response of the channel (multipath profile). The results show that the amplitude of the successive paths will not rapidly decline, and vice versa, when the distance between the sender and the receiver increases. Moreover, the time difference between the different paths will be small in the case of distance increase. In other words, the successive paths will converge in time.</p>

Proteus II: Design and Evaluation of an Integrated Power-Efficient Underwater Sensor Node

We describe the design and evaluation of an integrated low-cost underwater sensor node designed for reconfigurability, allowing continuous operation on a relatively small rechargeable battery for one month. The node uses a host CPU for the network protocols and processing sensor data and a separate CPU performs signal processing for the ultrasonic acoustic software-defined Modulator/Demodulator (MODEM). A Frequency Shift Keying- (FSK-) based modulation scheme with configurable symbol rates, Hamming error correction, and Time-of-Arrival (ToA) estimation for underwater positioning is implemented. The onboard sensors, an accelerometer and a temperature sensor, can be used to measure basic environmental parameters; additional internal and external sensors are supported through industry-standard interfaces (I2C, SPI, and RS232) and an Analog to Digital Converter (ADC) for analog peripherals. A 433 MHz radio can be used when the node is deployed at the surface. Tests were performed to validate the low-power operation. Moreover the acoustic communication range and performance and ToA capabilities were evaluated. Results show that the node achieves the one-month lifetime, is able to perform communication in highly reflective environments, and performs ToA estimation with an accuracy of about 1-2 meters.

Estimation of seabed bottom loss using wideband signal for underwater acoustic communication

Performance of acoustic communication through shallow underwater channel is affected by surface and bottom interaction, and the bottom loss has great importance for long-range signal transmission. In 2013, KRISO has performed a shallow-water communication experiment near Jeju island, South Korea, and the experiment aims at evaluating communication link budget as well as measuring the channel fading statistics. The measured sound velocity profiles show the existence of strong thermocline resulting in downward refraction and therefore its long-range signal propagation is strongly dependent on the seabed characteristics. We use a wideband signal, which was originally designed for channel impulse response estimation. The signals were recorded using a four-element receiver array with two different source depth configurations which enable observing the seabed at various grazing angles. The estimated bottom loss is used to estimate the transmission losses at longer ranges, and they are compared with the measured values to examine the estimated bottom loss.

Low frequency acoustic communication and the waveguide modal behavior during Shallow Water 2006 experiment

Low frequency (i.e., <500 Hz) acoustic intensity fluctuations in the presence of internal waves has been studied in some detail during the past two decades. However, not much has been reported on the relationship between the modal behavior of the waveguide and the potential for long-range communications. Previously, we have shown significant performance degradation at higher frequencies (i.e., 800 and 1600 Hz) while an internal wave packet travels through a source-receiver track. Here, we further examine the acoustic transmissions at lower frequencies (i.e., 100 and 200 Hz) during the same internal wave event. Significant intensity fluctuations at these frequencies can be explained by modal analysis. We also report acoustic communication performance at multiple frequencies (i.e., 100, 200, 800, and 1600 Hz). The frequency dependency is analyzed with the focus on modal behaviors to explain the performance variation of acoustic communication during the passage of the internal waves.

Influence of Underwater Channel Time-Variability on Communication Throughput Efficiency

Underwater acoustic channel has time-variability. Time varying channel which disturbs the continuous transmission of information data reduces the underwater acoustic communication performance. In this paper, we show the temporal coherence as time-variability of channel and indicate throughput efficiency in accordance with transmission time of information data. Then we analyzed influence of underwater channel time-variability on communication throughput efficiency. We confirmed that the throughput efficiency reduced when the time-variability of the channel increased via lake trial.

Underwater acoustic communication channel simulation using parabolic equation

High frequency acoustic communication (8–50 kHz) has attracted much attention recently. At these high frequencies, vaHigh frequency acoustic communication (8–50 kHz) has attracted much attention recently. At these high frequencies, various physical processes, including surface waves, subsurface bubbles, and ocean volume fluctuations, can significantly affect the communication channel. While there is an on-going work, however, the research community is still lacking adequate numerical models that can provide realistic representations of both deterministic and stochastic channel properties in the dynamic ocean. Advancements in underwater acoustic communication technologies mainly rely on at-sea experiments, which are very costly. Our studies show that it is possible to simulate realistic communication channels through parabolic equation (PE) modeling. The Monterey-Miami PE model with an evolving sea surface has been used to generate time-varying impulse responses. Data from our recent experiments are used to evaluate the model in predicting acoustic communication performance. [Work supported by ONR Code 322OA.]

Acoustic communication performance of impulse suppressing hearing protectors.

An array of hearing protection products having acoustic impulse suppression capabilities are currently on the market. Level‐dependent hearing protectors which suppress impulsive noise are already being issued for use in combat situations (i.e., by soldiers, law enforcement). The effects of this class of hearing protection on acoustic communication is a subject which merits research at the present time. An investigation was made focusing on the performance of several off‐the‐shelf electronic hearing protection products, in terms of features critical to acoustic communication. In particular, spatial awareness and speech intelligibility were looked at to better understand the impact of these devices and to predict the performance of the personnel they are issued to.

Relating acoustic communication performance in different shallow water environments.

Relating the performance of an underwater communication system with the signal/environmental characteristics under different environmental conditions is a subject of great interest. Consider a very‐shallow water channel, for example, with different wind speeds. The higher the wind speed, the more random the channel (due to sound‐scattering from the rough surface), and hence the less the channel coherence‐time and the higher the channel‐estimation error. For such a channel, one expects the output signal‐to‐noise (SNR) to decrease inversely with the channel‐estimation error; the latter reflects how much of the channel energy is random and treated like noise. On the other hand, the output SNR is expected to be unrelated between different environments where propagation conditions (the multipath arrivals) are significantly different. This paper shows, based on experimental data, that the output SNR (given the same input SNR) is correlated with the channel‐estimation error with the same functional relationship despite the environmental differences. The reason is the universal property of the so‐called Q function, the auto‐correlation of the received impulse responses summed over all receiver channels. The channel‐estimation error can thus serve as a metric for performance assessment in different shallow water environments. [Work supported by the Office of Naval Research.]

Ocean variability effects on high‐frequency coherent acoustic communications.

The variability of the ocean environment can cause fluctuations of acoustic channels and these fluctuations often pose serious difficulties for high rate digital communications. During a series of recent acoustic communications experiments conducted around Kauai Island, Hawaii (KauaiEx’03, MakaiEx’05, and KAM’08), coherent communication data with concurrent environmental measurements were collected under different experimental settings. The variability of the ocean parameters, mainly the water temperature profiles and the sea surface condition, has been studied in order to understand their impact on the performance of acoustic communications at high frequencies (greater than 10 kHz). It is shown that both the long‐term (in hours) changes in the ocean volume and the fast fluctuations (in seconds) of the sea surface have impact on the receiver design and on the receiver performance. Using time reversal combining followed by a single channel decision feedback equalizer, the ocean variability effects on the p...

Ocean surface degradation of shallow water acoustic communication.

The accurate prediction of underwater acoustic communication system performance at high frequencies is essential to system risk mitigation prior to deployment. The deterioration of acoustic coherence by ocean surface dynamics will be predicted via three dimensional (3‐D) ray tracing with the inclusion of interaction with a realistic dynamic ocean surface. Acoustic communication performance limits at high frequencies for most fixed platform systems are dominated by multipath interaction with the spectrally rich heaving ocean. The high‐fidelity Wave‐watch III surface spectra model is used here with a wave‐number integration approach for surface time series modeling. A fully 3‐D ray tracing model is used to model the propagation of sound under a dynamic surface boundary at the time and spatial scales that dominate coherence degrading effects for underwater acoustic communications. The proposed method will serve the rapid development of operating regimes for high‐frequency underwater acoustic communication systems. Proposed applications include distributed underwater sensor networks and persistent deployable low‐cost systems that meet a wide range of underwater sensing needs. This work seeks to solve problems in deploying advanced communication systems by predicting the degradation of signals due to ocean variability and automatically selecting appropriate signaling rates, schemes, and constants. [This work was supported by ONR.]

Effects of internal waves on acoustic coherent communications during SW06

During the SW06 experiment conducted east off the New Jersey continental shelf from July to September of 2006, internal wave surface expression and water temperature profiles were recorded when phase shift keying signals (PSK) were transmitted to study internal wave effects on coherent underwater acoustic communications at low to mid frequency bands. The collected communications data are processed using time reversal multichannel combining followed by a decision feedback equalizer. Due to the presence of internal waves, the acoustic channels show a time-varying property. Continuous channel updates prior to time reversal combining are required to combat fast channel fluctuations. The communications performance in terms of output signal-to-noise ratio exhibits significant change due to the internal waves. Further, the internal wave effects on the performance of coherent acoustic communications exhibit a frequency- and depth- dependency. The choices of receiver parameters also can be affected by the presence of internal waves.

Universal properties of the channel Q function: Applications to underwater acoustic communications

Channel Q function is, for a time-invariant channel, the sum of autocorrelation functions of the channel impulse response functions over multiple receivers [T. C. Yang, IEEE J. Oceanic Eng. 28, 229–245 (2003)]. It can be used to characterize the performance (output SNR) of acoustic communications using either passive-phase conjugation or decision feedback equalizer [T. C. Yang, IEEE J. Oceanic Eng. 29, 472–487 (2004)]. Channel Q function also determines the channel capacity for a single source and multiple receivers (SIMO). We analyze in this paper the properties of the channel Q function and show that it possesses universal and stable properties for underwater acoustic waveguides, irrespective of the channel sound-speed profiles, source and receiver range/depths. This property is examined with real data collected in various oceans with significant temporal variations in the propagation conditions and/or source-receiver range. Applications to underwater acoustic communications are discussed. [Work supported by the Office of Naval Research.]