Vincent Rigaud

Monte-Carlo-based channel characterization for underwater optical communication systems

We consider channel characterization for underwater wireless optical communication (UWOC) systems. We focus on the channel impulse response and, in particular, quantify the channel time dispersion for different water types, link distances, and transmitter/receiver characteristics, taking into account realistic parameters. We use the Monte Carlo approach to simulate the trajectories of emitted photons propagating in water from the transmitter towards the receiver. During their propagation, photons are absorbed or scattered as a result of their interaction with different particles present in water. To model angle scattering, we use the two-term Henyey-Greenstein model in our channel simulator. We show that this model is more accurate than the commonly used Henyey-Greenstein model, especially in pure sea waters. Through the numerical results that we present, we show that, except for highly turbid waters, the channel time dispersion can be neglected when working over moderate distances. In other words, under such conditions, we do not suffer from any inter-symbol interference in the received signal. Lastly, we study the performance of a typical UWOC system in terms of bit-error-rate using the simple on-off-keying modulation. The presented results give insight into the design of UWOC systems.

UNION: underwater intelligent operation and navigation

The main goal of the UNION ESPRIT Basic Research Action is to develop methods for increasing the autonomy and intelligence of underwater remotely operated vehicles (ROVs). The project focuses mainly on the development of coordinated control and sensing strategies for combined manipulator and vehicle systems. Both fundamental theories and methods for the design of these heterogeneous systems are investigated. A complex canonical mission in the field of offshore inspection maintenance and repair tasks was chosen as an integration guideline of all the results.

Channel modeling for underwater optical communication

We consider in this paper channel modeling for underwater optical channels. In particular, we focus on the channel impulse response and quantify the channel time dispersion under different conditions of water type, link distance, and transmitter/receiver parameters. We use the Monte Carlo approach to simulate the trajectories of emitted photons propagating in water towards the receiver. We show that in most practical cases, the time dispersion is negligible and does not induce any inter-symbol interference on the received symbols. Our results can be used to appropriately set different system design parameters.

Underwater wireless optical communication; recent advances and remaining challenges

Because of its ability of providing very high data transmission rates over distances up to several tens of meters, underwater wireless optical communication (UWOC) has attracted considerable interest during the past few years. The underwater channel is a challenging environment, especially because of its high attenuation. The difficulty of precise localization underwater also leads to unavoidable link misalignments that can have an important impact on the link availability and otherwise on the quality of signal transmission. In this paper, after a review of the recent research works on UWOC and the available commercialized systems, we present the performance study of a typical UWOC system under some simplifying assumptions for system modeling. We also address the open issues and the challenges that we are faced with in practice.

Map based underwater navigation using a multibeam echosounder

This paper describes a navigation system for underwater vehicles (UV) using bathymetric profiles. The UV localisation by matching a local bathymetry within a reference map aims to avoid the use of transponder-based positioning systems which need a costly preparation. Terrain based navigation concerns, using a vehicle-borne multibeam echosounder, to build a local map of the bottom and to match it to a previously constructed terrain map. Bathymetric image restoration and segmentation are necessary before extracting characteristic points from the two maps. These points are matched by the means of rotational and translational invariant attributes. An iterative algorithm estimates the position and the orientation of the local bathymetry and actualizes the set of matched points, The real time estimation of attribute variances allows the use of probabilistic tools like the Mahalanobis distance (threshold) and the Kalman filter (position estimation).

Real-time geo-referenced video mosaicking with the MATISSE system

This paper presents the MATISSE system: Mosaicking Advanced Technologies Integrated in a Single Software Environment. This system aims at producing in-line and off-line geo-referenced video mosaics of seabed given a video input and navigation data. It is based upon several techniques of image and signal processing which have been developed at Ifremer these last years in the fields of image mosaicking, camera self-calibration or correction and estimation of navigation data.

A terrain referenced underwater positioning using sonar bathymetric profiles and multiscale analysis

Terrain-based underwater navigation using sonar bathymetric profiles is presented. It deals with matching high resolution local depth maps against a large, onboard, low resolution reference map. The matching algorithm locates the local depth map within the a priori larger map to determine absolute position and heading of the vehicle. It uses cliff maps which are steep gradient contours extracted from both local and reference maps. This segmentation provides us with a means to extract critical points, which are defined as high curvature values. The problem is reduced to a singular point-based matching algorithm: given two point sets, find correspondences and estimate transformation between the two sets. In order to register maps at different scales, a part of this study will focus on partial differential equations based scale-space techniques. This approach is tested using real terrain data of the Var underwater canyon (France).

Performance oriented robust nonlinear control for subsea robots: experimental validation

This paper investigates the benefits of applying simple PID+nonlinear controller to subsea robot. This control structure has the advantage of only adding a supplementary nonlinear feedback loop to the existing linear PID-regulator and at the same time improving both the transient and stability margins. Several simulations and experiments have been performed on the experimental subsea robot (VORTEX) and have demonstrated the improvements of the PID+nonlinear controller over the simple PID.<<ETX>>

Segmentation of bathymetric profiles and terrain matching for underwater vehicle navigation

A terrain-based underwater navigation using sonar bathymetric profiles is presented. It deals with matching high-resolution local depth maps against a large on-board reference map. The matching algorithm locates the local depth map within the a priori known larger map to determine the absolute position and heading of the vehicle. Two separate approaches for this problem are presented. The first uses a contour-based representation of depth maps. Contours are extracted from both local and reference maps. Invariant attributes under rigid plane transformation are associated with each contour point, so that the problem is reduced to a point-based matching algorithm: given two point sets, find correspondences and estimate transformation between the two sets. We shall particularly focus on the formalism of partial differential equations, which is used to smooth depth maps in a morphologically invariant way and to obtain anisotropic contours. The second approach is also based on a correspondence algorithm. Here, ...

Investigation of suitable modulation techniques for underwater wireless optical communication

For an underwater wireless optical communication system, we consider the use of different intensity modulation techniques, and compare their performance by taking realistic system parameters into account. In particular, we contrast the performances of on-off keying, pulse position modulation, pulse width modulation, and digital pulse interval modulation, when a PIN or an avalanche photodiode is used at the receiver. We discuss the suitability of these modulation techniques to the underwater optical channel by considering the implementation issues.