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Self-Localization by Eavesdropping in Acoustic Underwater Sensor Networks
Abstract
Localization is a common problem in underwater
sensor networks. Since global navigation satellite systems do not work underwater, geo-referencing of underwater sensors requires other technologies. In this paper, we present an novel localization approach for nodes in an acoustic underwater sensor network. By combining pressure sensors with the functionality of modern acoustic USBL modems, the nodes are able to self-localize their position inside the network. This can be done in a passive manner, just by listening to the transmitted messages of other network nodes, thereby saving energy and sparing the communication channel from additional traffic. In order to evaluate the performance of the method, experiments have been conducted in simulation and under real conditions in the Middle Atlantic Ocean.
Navigation is a challenging task for underwater devices, as there is no global navigation system available. This often restricted Autonomous Underwater Vehicles (AUV) in their operations, either spatially because they depend on reference markers that need to be deployed on the mission side, or by dive time as they need to surface regularly to geo-reference themselves via satellite. For most applications the position and attitude information of an AUV is crucial for a meaningful interpretation of the collected data. In this paper, we present Deep Net Localization (DNL), a novel localization approach for stationary and mobile nodes in an acoustic underwater sensor network. For that purpose a communication protocol was developed that enables network nodes to self-localize their position and attitude in the network by eavesdropping on the communication of other nodes. This is achieved by combining modern acoustic USBL modems and pressure sensors with a Bayes estimator. Without the need to actively transmit acoustic signals, DNL saves energy and reduces
the overall workload of the communication channel. Furthermore this minimizes interference effects with other acoustic sensors, like multi-beam sonar, which are essential for the measurement purpose of a sensor node. In order to assess the approach we first tested the general functioning in a Monte-Carlo-Simulation.
Subsequently the method was evaluated with real data that was collected during a sea trial in the Middle Atlantic Ocean.
This report summarizes our research directions in un- derwater sensor networks. We highlight potential applica- tions to off-shore oilelds for seismic monitoring, equipment monitoring, and underwater robotics. We identify research directions in short-range acoustic communications, MAC, time synchronization, and localization protocols for high- latency acoustic networks, long-duration network sleeping, and application-level data scheduling.
Underwater sensor nodes will find applications in oceanographic data collection, pollution monitoring, offshore exploration, disaster prevention, assisted navigation and tactical surveillance applications. Moreover, unmanned or autonomous underwater vehicles (UUVs, AUVs), equipped with sensors, will enable the exploration of natural undersea resources and gathering of scientific data in collaborative monitoring missions. Underwater acoustic networking is the enabling technology for these applications. Underwater networks consist of a variable number of sensors and vehicles that are deployed to perform collaborative monitoring tasks over a given area.In this paper, several fundamental key aspects of underwater acoustic communications are investigated. Different architectures for two-dimensional and three-dimensional underwater sensor networks are discussed, and the characteristics of the underwater channel are detailed. The main challenges for the development of efficient networking solutions posed by the underwater environment are detailed and a cross-layer approach to the integration of all communication functionalities is suggested. Furthermore, open research issues are discussed and possible solution approaches are outlined.
This paper examines the main approaches and challenges in the design and implementation of underwater wireless sensor networks. We summarize key applications and the main phenomena related to acoustic propagation, and discuss how they affect the design and operation of communication systems and networking protocols at various layers. We also provide an overview of communications hardware, testbeds and simulation tools available to the research community.
Multipath propagation causes the transmitted signal to take numerous, time-varying different-length paths to the receiver. Exploitation of conventional frequency-constant carrier signals for communication over underwater acoustic channels typically shows that intricate mutual time variations of multipath arrivals create an extremely hard problem for equalizers to compensate for nonstable intersymbol interactions. Communication over such channels can be, however, substantially improved by using a new method based on the implementation of a sweep-spread carrier (S2C). Such a carrier consists of a succession of sweeps, which cause permanent rapid fluctuation of signal frequency. Apart from some additional useful effects such as providing multiuser access and reducing influence of narrow-band noise, the method provides significant processing improvement enabling clear separation of multipath arrivals by converting their time delays into their frequency reallocations--the steeper the sweeps, the better the multipath resolution that can be achieved. When converting the signal into constant intermediate frequencies, the best suitable multipath arrival can be separated not as traditionally in time domains, applying complex equalizers, but in frequency domains by means of usual band-pass filters. High transmission stability of this approach was confirmed in both computer simulations as well as in validation experiments carried out since summer 1999.
For deep-sea (robotic) applications, accurate acoustic localization is required, e.g. using USBL devices. Internal calculations for these devices usually assume a constant sound velocity within the deployment area ignoring refraction effects due to a depth-dependent sound velocity profile. This work presents the results of long-range deep-sea (5000m) USBL localization tests to estimate absolute positioning accuracy. The experiments lead to a correction approach by incorporating both the depth of acoustic participants as well as the full sound velocity profile. For bigger horizontal distances (> 800m), this approach can largely reduce the resulting (systematic) elevation angle error.
CLAWAR 2015: 18th International Conference on Climbing and Walking Robots and the Support Technologies for Mobile Machines
Zhejiang University, HangZhou, China, 6 – 9 September 2015
Edited by: Hongye Su ( Zhejiang University, China), Tianmiao Wang ( Beijing University of Aeronautics and Astronautics, China), Mohammad O Tokhi ( University of Sheffield, UK), Gurvinder S Virk ( University of Gävle, Sweden)
Successful deep-sea exploration (up to 6000m) performed by autonomous underwater vehicles (AUVs) depends heavily on accurate AUV localization. In the absence of GPS underwater, this requires acoustic communication, localization and geo-referencing underwater participants, e.g. by a GPS-positioned surface vehicle, which is necessary to periodically correct drift errors from deadreckoning. Within the SMIS project this is supposed to be achieved by a team of AUVs assisted by an unmanned surface vehicle (USV) and a sea-bed-station. In order to derive constraints for the team behaviour, the quality and stability of the acoustic localization needs to be examined thoroughly in advance. This delivers various constraints for later at-sea operation, e.g. the maximum distance between AUV and USV and the maximum horizontal distance to the USV for a given AUV depth. Additionally, heuristic estimates for reproducibility of long-range position measurements can be derived which indicate imminent errors based on acoustic localization only. This paper reports associated tests and their results using USBL modems in deep-sea trials performed in the Atlantic ocean.
This paper introduces a simple model for modeling inertial sensors and expands on this model to incorporate terms that model the errors associated with high dynamics. The paper uses the techniques of Allan Variance Charts, Monte Carlo Simulations, and Autocorrelation functions to characterize sensors through identification of the error statistics. The error growth of the position and heading navigation solution for two and six degree of freedom scenarios using static error parameters is developed. Analytical expressions for the error growth with wide-band noise are presented and used as an error baseline for investigating the effects of sensor drift, or walking bias. Experimental data is used to validate the error growth bounds in both scenarios. An advanced sensor model is developed for both an accelerometer and gyro with an explanation of the effects of the dynamic error parameters. A simple rocket trajectory simulation is used to illustrate the adverse effects of high dynamic sensor errors when dead-reckoning with a tactile-grade IMU. Analysis of the advanced model is concluded with an investigation into the relative effect of each error parameter on the trajectory target.
Underwater Wireless Sensor Networks (UWSNs) are expected to support a variety of civilian and military applications. In UWSNs, Medium Access Control (MAC) protocol has attracted strong attention due to its potentially large impact to the overall network performance. Unlike terrestrial networks, which mainly rely on radio waves for communications, UWSNs utilize acoustic waves, which pose a new research challenge in the design of MAC protocols. To present the development of MAC protocols in UWSNs, this paper surveys the current state-of-the-art MAC protocols for UWSNs. In the early development, the performance in terms of delay and throughput of the UWSNs has been the major concern of the MAC layer protocol design. Later, the design of energy-efficient MAC protocols becomes a new research focus because sensor nodes are generally powered by batteries which are less likely to be recharged. In this paper, we first describe the underwater acoustic environment and the challenges to the MAC protocols design in UWSNs. We then provide a comparative study of several types of MAC protocols according to current existing diverse implementations. Furthermore, open research issues will be summarized. Hopefully, this survey will inspire more active research in this area.
Autonomous underwater vehicle (AUV) navigation and localization in underwater environments is particularly challenging due to the rapid attenuation of Global Positioning System (GPS) and radio-frequency signals. Underwater communications are low bandwidth and unreliable, and there is no access to a global positioning system. Past approaches to solve the AUV localization problem have employed expensive inertial sensors, used installed beacons in the region of interest, or required periodic surfacing of the AUV. While these methods are useful, their performance is fundamentally limited. Advances in underwater communications and the application of simultaneous localization and mapping (SLAM) technology to the underwater realm have yielded new possibilities in the field. This paper presents a review of the state of the art of AUV navigation and localization, as well as a description of some of the more commonly used methods. In addition, we highlight areas of future research potential.
Underwater Wireless Sensor Networks (UWSNs) are expected to support a variety of civilian and military applications. Sensed data can only be interpreted meaningfully when referenced to the location of the sensor, making localization an important problem. While global positioning system (GPS) receivers are commonly used in terrestrial WSNs to achieve this, this is infeasible in UWSNs as GPS signals do not propagate through water. Acoustic communications is the most promising mode of communication underwater. However, underwater acoustic channels are characterized by harsh physical layer conditions with low bandwidth, high propagation delay and high bit error rate. Moreover, the variable speed of sound and the non-negligible node mobility due to water currents pose a unique set of challenges for localization in UWSNs. In this paper, we provide a survey of techniques and challenges in localization specifically for UWSNs. We categorize them into (i) range-based vs. range-free techniques; (ii) techniques that rely on static reference nodes vs. those who also rely on mobile reference nodes, and (iii) single-stage vs. multi-stage schemes. We compare the schemes in terms of localization speed, accuracy, coverage and communication costs. Finally, we provide an outlook on the challenges that should be, but have yet been, addressed.
A Kalman Filtering algorithm which is robust to observational outliers is developed by assuming that the measurement error may come from either one of two Normal distributions, and that the transition between these distributions is governed by a Markov Chain. The resulting algorithm is very simple, and consists of two parallel Kalman Filters having different gains. The state estimate is obtained as a weighted average of the estimates from the two parallel filters, where the weights are the posterior probabilities that the current observation comes from either of the two distributions. The large improvements obtained by this Robust Kalman Filter in the presence of outliers is demonstrated with examples.
In this paper, we present a silent positioning scheme termed UPS for underwater acoustic sensor networks. UPS relies on the time difference of arrivals locally measured at a sensor to detect range differences from the sensor to four anchor nodes. These range differences are averaged over multiple beacon intervals before they are combined to estimate the 3-D sensor location through trilateration. UPS requires no time synchronization and provides location privacy at underwater vehicles/sensors whose locations need to be determined. To study the performance of UPS, we model the underwater acoustic channel as a modified ultrawideband Saleh-Valenzuela model: The arrival of each path cluster and the paths within each cluster follow double Poisson distributions, and the multipath channel gain follows a Rician distribution. Based on this channel model, we perform both theoretical analysis and simulation study on the position error of UPS under acoustic fading channels. The obtained results indicate that UPS is an effective scheme for underwater vehicle/sensor self-positioning.
Localization in underwater sensor networks: survey and challenges
- Vijay Chandrasekhar
- K G Winston
- Yoo Sang Seah
- Choo