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63
A discrete-time channel simulator driven by measured scattering functions
- IEEE J. Select. Areas Commun
"... Abstract—In-situ measurements of the scattering function are used to drive a channel simulator developed in the context of underwater acoustic telemetry. Two operation modes of the simulator are evaluated. A replay mode is accomplished by interpolation of measured impulse responses. A second, stocha ..."
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Cited by 11 (5 self)
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Abstract—In-situ measurements of the scattering function are used to drive a channel simulator developed in the context of underwater acoustic telemetry. Two operation modes of the simulator are evaluated. A replay mode is accomplished by interpolation of measured impulse responses. A second, stochastic mode delivers multiple realizations of a given scattering function. The initial assumption of wide-sense stationary uncorrelated scattering is violated by strong phase correlations between taps. It is shown that time-varying Doppler shifts due to platform motion must be eliminated from measured scattering functions in order to provide the stochastic tap gains with the true Doppler spectrum of the channel. The simulator is validated through a comparison of acoustic data measured at sea, and emulated data, governed by the same scattering function. This comparison is based on scattering and coherence functions, multipath phase measurements, and application of a decisionfeedback equalizer. After the Doppler correction, the synthetic data are indistinguishable from the acoustic data in terms of delay-Doppler spread, temporal coherence, phase behavior, equalizer mean square error, and bit error ratio. Index Terms—Time-varying channels, discrete-time filters, underwater acoustic communication, acoustic signal processing. I.
System design considerations for undersea networks: Link and multiple access protocols
- IEEE J. Sel. Areas Commun
"... Abstract—We address several inter-related aspects of underwater network design within the context of a cross-layer approach. We first highlight the impact of key characteristics of the acoustic propagation medium on the choice of link layer parameters; in turn, the consequences of these choices on d ..."
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Cited by 9 (2 self)
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Abstract—We address several inter-related aspects of underwater network design within the context of a cross-layer approach. We first highlight the impact of key characteristics of the acoustic propagation medium on the choice of link layer parameters; in turn, the consequences of these choices on design of a suitable MAC protocol and its performance are investigated. Specifically, the paper makes contributions on the following fronts: a) Based on accepted acoustic channel models, the pointto-point (link) capacity is numerically calculated, quantifying sensitivities to factors such as the sound speed profile, power spectral density of the (colored) additive background noise and the impact of boundary (surface) conditions for the acoustic channel; b) It provides an analysis of the Micromodem-like linklayer based on FH-FSK modulation; and finally c) it undertakes performance evaluation of a simple MAC protocol based on ALOHA with Random Backoff, that is shown to be particularly suitable for small underwater networks. Index Terms—Underwater acoustic communications, Information rate, Access protocols. I.
Robust deployment of dynamic sensor networks for cooperative track detection
- IEEE SENSORS
, 2009
"... The problem of cooperative track detection by a dynamic sensor network arises in many applications, including security and surveillance, and tracking of endangered species. Several authors have recently shown that the quality-of-service of these networks can be statically optimized by placing the s ..."
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Cited by 7 (3 self)
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The problem of cooperative track detection by a dynamic sensor network arises in many applications, including security and surveillance, and tracking of endangered species. Several authors have recently shown that the quality-of-service of these networks can be statically optimized by placing the sensors in the region of interest (ROI) via mathematical programming. However, if the sensors are subject to external forcing, such as winds or currents, they may be rapidly displaced, and their quality-of-service may be significantly deteriorated over time. The novel approach presented in this paper consists of placing the sensors in the ROI based on their future displacement, which can be estimated from environmental forecasts and sensor dynamic models. The sensor network deployment is viewed as a new problem in dynamic computational geometry, in which the initial positions of a family of circles with time-varying radii and positions are to be optimized subject to sets of algebraic and differential equations. When these equations are nonlinear and time-varying, the optimization problem does not have an exact solution, or global optimum, but can be approximated as a finite-dimensional nonlinear program by discretizing the quality-of-service and the dynamic models with respect to time. Then, a near-optimal solu-tion for the initial sensor positions is sought by means of sequential quadratic programming. The numerical results show that this approach can improve quality-of-service by up to a factor of five compared to existing techniques, and its performance is robust to propagated modeling and deployment errors.
Optimal Control of an Underwater Sensor Network for Cooperative Target Tracking
- IEEE JOURNAL OF OCEANIC ENGINEERING
, 2009
"... Optimal control (OC) is a general and effective ap-proach for trajectory optimization in dynamical systems. So far, however, it has not been applied to mobile sensor networks due to the lack of suitable objective functions and system models. In this paper, an integral objective function representin ..."
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Cited by 6 (4 self)
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Optimal control (OC) is a general and effective ap-proach for trajectory optimization in dynamical systems. So far, however, it has not been applied to mobile sensor networks due to the lack of suitable objective functions and system models. In this paper, an integral objective function representing the quality of service of a sensor network performing cooperative track detec-tion over time is derived using a geometric transversals approach. A set of differential equations modeling the sensor network’s dynamics is obtained by considering three dependent subsystems, i.e., underwater vehicles, onboard sensors, and oceanographic fields. Each sensor-equipped vehicle is modeled as a bounded subset of a Euclidian space, representing the sensor’s field of view (FOV), which moves according to underwater vehicle dynamics. By this approach, the problem of generating optimal sensors’ trajectories is formulated as an OC problem in computational geometry. The numerical results show that OC significantly improves the network’s quality of service compared to area-coverage and path-planning methods. Also, it can be used to incorporate sensing and energy constraints on the sensors’ state and control vectors, and to generate fronts of Pareto optimal trajectories.
Geoacoustic Inversion of Tow-Ship Noise via Near-Field–Matched-Field Processing
"... Abstract—This paper discusses geoacoustic inversion from tow-ship noise data acquired via a horizontal towed array. Through simulations and experimental results, it is shown that even very quiet ships radiate sufficient noise power to enable self-noise inversion of basic geoacoustic parameters such ..."
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Cited by 5 (5 self)
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Abstract—This paper discusses geoacoustic inversion from tow-ship noise data acquired via a horizontal towed array. Through simulations and experimental results, it is shown that even very quiet ships radiate sufficient noise power to enable self-noise inversion of basic geoacoustic parameters such as effective bottom velocity. The experimental results presented are particularly encouraging in view of the high level of interference shown to be tolerated from nearby shipping. Index Terms—Geoacoustic inversion, self-noise, tow ship. I.
A Smart Sensor Web for Ocean Observation: Integrated Acoustics, Satellite Networking, and Predictive Modeling
"... change research, there is a need for near real-time integration of data from heterogeneous and spatially distributed sensors, in particular in-situ and space-based sensors. The data integration, as provided by a smart sensor web, enables numerous improvements, namely, 1) adaptive sampling for more e ..."
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Cited by 2 (2 self)
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change research, there is a need for near real-time integration of data from heterogeneous and spatially distributed sensors, in particular in-situ and space-based sensors. The data integration, as provided by a smart sensor web, enables numerous improvements, namely, 1) adaptive sampling for more efficient use of expensive space-based sensing assets, 2) higher fidelity information gathering from data sources through integration of complementary data sets, and 3) improved sensor calibration. The specific purpose of the smart sensor web to be demonstrated as part of the development presented here is to provide for adaptive sampling and calibration of space-based data via in-situ data. Our ocean-observing smart sensor web presented herein is composed of both mobile and fixed underwater in-situ ocean sensing assets and Earth Observing System (EOS) satellite sensors providing larger-scale sensing.
Virtual Battle Experiment to Investigate Coalition Data Sharing
- Unclassified, Proceedings of the 9th International Command and Control Research and Technology Symposium
, 2004
"... There is a supposition in net-centric warfare that the effectiveness of a coalition will increase with the amount of shared data. This supposition presumes that the shared data contributes positively to the situational awareness and effectiveness of the recipient platform. In the limiting cases, the ..."
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Cited by 2 (0 self)
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There is a supposition in net-centric warfare that the effectiveness of a coalition will increase with the amount of shared data. This supposition presumes that the shared data contributes positively to the situational awareness and effectiveness of the recipient platform. In the limiting cases, the resource cost to the recipient platform may exceed the potential value of the contributed information. In the ideal situation, shared data at appropriate levels of refinement improves the effectiveness of the entire command team. A series of Virtual Battle Experiments (VBEs) has been initiated with which to investigate the influence of sharing broadband passive sonar data and how this influence changes with the level at which the data is shared. The experiments use different operators in multiple sessions to make statistically relevant measurements. In the baseline experiment, VBE CA-1, the shared data was provided in a purely visual format. Operator effectiveness was evaluated by analyzing the speed and accuracy with which sonar track segments were manually associated. Also of interest in this experiment was the decision rationale that was used by the operators to associate or disassociate track segments. This paper summarizes the results of this trial and outlines our plans for extending these experiments.
Underwater acoustic communications performance modeling in support of ad hoc network design
- Proc. IEEE Oceans Conference
"... Abstract—This paper discusses a methodology for predicting underwater acoustic communications performance using high fidelity acoustic time series simulation and acoustic modem processing emulation. Multiple source/receiver combinations can be simultaneously simulated, so that aspects of a complete ..."
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Abstract—This paper discusses a methodology for predicting underwater acoustic communications performance using high fidelity acoustic time series simulation and acoustic modem processing emulation. Multiple source/receiver combinations can be simultaneously simulated, so that aspects of a complete underwater network can be studied. Here, the fundamental modeling and emulation capability will be described, with examples of the propagation modeling, time series simulation, and modem processing over multiple realizations of example communications channels. The results show the dependence of source and receiver location in the water column with respect to the sound speed profile on communications performance. The utility of such simulations for ad hoc network design in the presence of moving communications nodes will be discussed. I.
Active Detection With A Barrier Sensor Network Using A Scan Statistic
"... Abstract—The cooperation of an active acoustic source and a large number of distributed passive sensors offers an opportunity for active sonar detection. The system works as follows: first, each sensor compares its matched filter output with a given threshold to obtain a binary local decision—‘0 ’ o ..."
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Cited by 1 (0 self)
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Abstract—The cooperation of an active acoustic source and a large number of distributed passive sensors offers an opportunity for active sonar detection. The system works as follows: first, each sensor compares its matched filter output with a given threshold to obtain a binary local decision—‘0 ’ or ‘1’; then a fusion center collects them to make a system-level inference. How effectively to combine these local results—distributed detection fusion—is the concentration of this paper. Suppose that the sensor network is unaware of the target’s reflection model. Then the local detection probabilities cannot be obtained; therefore, the optimal fusion rule is unavailable. The obvious detection strategy is a counting rule test (CRT), which simply counts the total number of 1’s and compares it to a threshold. This approach does not require the knowledge of sensor locations, and equally considers all network subareas. However, the reflected signal from some targets, such as a submarine, can be highly aspect dependent, and in many instances only sensors in a particular zone can receive its echoes. This paper focuses on the scan statistic, which slides a window across the sensor field, and selects the subarea with the largest number of 1’s to make a decision. The scan statistic integrates the aspect-dependence characteristic of the target into detection fusion. With a proper window size, it may suppress the subarea interference, and improve the system-level performance. Index Terms—Detection, multistatic, detection fusion, scan statistic, counting rule test, sensor network, sonar, submarine. I.
Analysis of Shallow-Water Experimental Acoustic Data Including a Comparison With a Broad-Band Normal-Mode-Propagation Model
- IEEE Journal of Oceanic Engineering, Vol
, 2001
"... Abstract—Channel temporal variability, resulting from fluctuations in oceanographic parameters, is an important issue for reliable communications in shallow-water-long-range acoustic propagation. As part of an acoustic model validation exercise, audio-band acoustic data and oceanographic data were c ..."
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Cited by 1 (0 self)
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Abstract—Channel temporal variability, resulting from fluctuations in oceanographic parameters, is an important issue for reliable communications in shallow-water-long-range acoustic propagation. As part of an acoustic model validation exercise, audio-band acoustic data and oceanographic data were collected from shallow waters off the West Coast of Scotland. These data have been analyzed for temporal effects. The average impulse response for this channel has been compared with simulations using a fast broad-band normal-mode propagation model. In this paper, we also introduce a novel technique for estimating and removing the bistatic reverberation contribution from the data. As propagation models do not necessarily account for reverberation, it has to be extracted from the signals when comparing measured and modeled transmission loss. Index Terms—Geo-acoustic parameters, impulse response,
