Localizing mobile nodes in underwater networks is a highly challenging endeavor due to range errors caused by the mobility and uncertainty of sound speed. We propose a novel localization approach, ...which incorporates time alignment and range bending compensation to meet this challenge. Given the lengthy and varied propagation delays to different anchor nodes, we use a Kalman filter to align different time instants and locations as a mobile node receives timestamps from different anchors during a localization period. Based on Snell's law, the ray tracing theory is applied to compensate for sound speed variations. These two steps minimize the errors caused by mobility and sound speed uncertainty. A penalty convex-concave procedure approach is also applied to accurately solve a nonconvex optimization problem to minimize localization errors. Deep sea trial results show that the final localization error for the mobile node is only 1.44 m (with the differential GPS as the true-value reference), marking a substantial improvement over existing state-of-the-art solutions.
Dear Editor, This letter proposes a high-precision seafloor transponder positioning method based on the correction of sound speed profile (SSP) temporal variation. In the proposed method, the ocean ...sound speed error is modeled as the temporal variation of a background SSP, and the linearized expression of the acoustic travel time with respect to the sound speed coefficient is derived based on the ray acoustic model. Moreover, the proposed method introduces the constraint of acoustic ranging observations between seafloor transponders and determines the weights of travel time and ranging observations using Akaike's Bayesian information criterion (ABIC) to reduce the positioning error caused by the correlation between sound speed and position parameters. The experimental results in the South China Sea show that the proposed method performs better than the global navigation satellite system-acoustic ranging combined positioning solver (GARPOS) 1, in terms of rigid distance errors and long baseline positioning accuracy.
The absolute position of an underwater target is difficult to pinpoint because the global positioning system (GPS) cannot penetrate water bodies. The long baseline (LBL) positioning system can extend ...GPS using high-precision calibrated underwater beacons as references. While traditional LBL systems give the target position without considering calibration error of deployed beacons. To solve this problem, we propose a method different from previous works, that combining all of the observations together. We use GPS outputs as true values to evaluate the localization performance. An LBL system with four beacons was installed in shallow water and deep sea to test the results. The positioning accuracy in shallow water and deep sea improves 0.06 m and 1.98 m respectively. The results suggest that beacon positioning errors have a great impact on localization precision, especially in
Large scale underwater wireless sensor networks (UWSNs) have great applications in ocean exploration. The basic localization scheme is the recursive position estimation with hierarchical steps. To ...achieve accurate localization for each node and a rather high localization coverage, the localized nodes to be chosen as reference nodes are one of the critical steps. This paper proposed a new method to define the confidence value of a reference node based on covariance law. With the measured distance between nodes, the estimated position is more accurate throughout the network and can give a comprehensive localization error. Localization coverage and localization error are used to evaluate the performance. Compared with the previous methods, the simulation results show that the proposed method have great advantage in controlling error accumulation, it is suitable for high precision large scale UWSNs.
For USBL (ultra-short baseline) positioning system, orthogonal receiving arrays with three elements distributed in `L'-shape or four elements forming a cross are generally used. With this ...configuration, the accuracy of the localization results depend on the accuracy of the coordinates of array elements, and sometimes the quadrant of the results may be significantly changed. Using redundant data measured by multi-element array can make the localization results robust. But, the calculation procedure to the multi-element array is based on geometry projections, which is complicated. And extra localization errors are generated because of model approximation. In order to overcome these problems, this article designed a novel underwater acoustic localization approach to an arbitrary multi-element array, such as a three-dimensional or two-dimensional array with multiple elements. Using coordinate rotation theory of surveying and mapping field, this approach establishes a reference coordinate system, so that the object's bearings in the reference coordinate system and the measured data can be combined with the help of rotation matrix, and the bearings can be determined by least square estimation. Taking the approach developed in this article, not only the complicated calculation procedure is simplified, but also the localization robustness is improved. Computer simulation and tank test results show the novel approach can work well.
Abstract For the underwater acoustic (UAC) positioning system based on continuous waveform signal, the time-delay estimation of the Line-of-sight (Los) is not robust under the UAC strongly ...time-varying multipath channel. So an anti-multipath time-delay detection algorithm based on dual-delta (DD) correlators is proposed in this paper to address the issue. The algorithm uses a differential processing code-phase discriminator model to improve the traditional delay-locked-loop (DLL) time-delay detection algorithm, and combines it with the signal tracking loop adapted to the UAC channel condition to estimate time-delay. Theoretical analysis indicates that due to the reduction of local code interval and the differential processing operation, the proposed algorithm effectively mitigates the effect of time-varying multipath signals on time-delay estimation compared with conventional methods. Simulation analysis further demonstrates that the proposed algorithm can robustly detect the Los and achieve high-precision time-delay estimation under the time-varying multipath channel. The algorithm shows great potential for practical applications.
For USBL (Ultra short Baseline), the positioning precision is a significant technical index. How to use the data gained in field trail to evaluate the precision has become an important problem that ...the USBL users pay more attention to. This paper used error ellipses theory to evaluate the USBL positioning precision, and after analyzing and computing, verified the conclusion that the error ellipse is equivalent to the statistical results corresponding to the 39.35% of the positioning points and then established a connection between the theoretical error model and the actual statistical results. Therefore, with the correct prior errors information, the USBL positioning precision evaluation can be performed with one of the USBL error ellipses. When the actual data is polluted by system errors, USBL theoretical error ellipse is not consistent with the statistical results of the scatter points. On this occasion, the error ellipse can be a criterion to evaluate system errors. In the last, according to the analysis for the results, this paper made a summary about the method used to evaluate USBL positioning precision combining error ellipse theory and actual positioning scatter points. That is, using the statistical value of the 39.95% of the positioning scatter points as the system precision and the theoretical error ellipse to evaluate the system error. Application has been achieved in the field trail to process data.
•Proposes a method for calibrating the transducer phase center that is applicable for outfield experiments.•Construct a virtual long baseline with the fixed beacon in the carrier coordinate ...system.•Solves the issue that acoustic phase center of the transducer does not coincide with the geometric center.
This paper proposes a high-precision transducer acoustic phase center calibration method based on outfield experiments, which solves the issue that the acoustic phase center of the transducer does not coincide with the geometric center. The developed method involves the construction of a virtual long baseline by transforming a fixed beacon into a moving point in the carrier coordinate system via coordinate conversion. Meanwhile, it reverse-calibrates the acoustic phase center of each transducer on the array. The lake trial results indicate that the positioning accuracy of the proposed method is improved from 0.56 m (for the uncalibrated acoustic phase center) to 0.29 m.
The absolute position of an underwater target is difficult to pinpoint because the global positioning system (GPS) cannot penetrate water bodies. The long baseline (LBL) positioning system can extend ...GPS using high-precision calibrated underwater beacons as references. While traditional LBL systems give the target position without considering calibration error of deployed beacons. To solve this problem, we propose a method different from previous works, that combining the errors of observations together. We use GPS outputs as true values to evaluate the localization performance. An LBL system with four beacons was installed in deep sea to test the results. The positioning accuracy in deep sea improves nearly 5m. The results suggest that beacon positioning errors have a great impact on localization precision, that is significant in high-precision positioning tasks.
This paper proposes a sound velocity correction method for underwater acoustic positioning systems (UAPSs) which suppresses the influence of heterogeneous sound velocity and achieves high-precision ...positioning for the real-time operations using the effective sound velocity (ESV). The method involves searching the optimal ESV from a sparse effective sound velocity table (S-ESVT) as-extracted from an effective sound velocity table (ESVT) by genetic algorithm (GA), which minimizes the burden on the hardware of the system and improves efficiency. Simulation results show that the proposed method performs faster and more accurately than traditional methods. Field trial results show that the reversed RMSE of localization can be improved from 5.02 m to 2.35 m using the proposed method, where GPS outputs serve as true values to evaluate the localization performance. The results altogether indicate that the proposed method is well applicable to high-precision real-time localization for UAPSs.
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