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Publications

Publications by Nuno Cruz

2015

A Centralized Approach to the Coordination of Marine Robots

Authors
Ferreira, BM; Matos, AC; Cruz, NA; Moreira, AP;

Publication
CONTROLO'2014 - PROCEEDINGS OF THE 11TH PORTUGUESE CONFERENCE ON AUTOMATIC CONTROL

Abstract
This paper presents a centralized coordination scheme for multiple marine vehicles. The only requirements for proper operation of this method are the presence of bidirectional communication links with a virtual leader and bounded reference tracking errors. By relying on a, lower level, individual position tracking control, coordination is achieved by means of a centralized potential-field that uniquely defines the desired formation geometry as well as its position. The formation can be driven along a path that does not necessarily need to be predefined. Instead, a virtual leader defines the formation position at each instant of time. Furthermore, the possibility of setting stationary points over the path followed by the formation is guaranteed. The approach is illustrated in practice with autonomous surface vehicles in real environment, subjected to disturbances such as wind and waves.

2014

A mission programming system for an autonomous sailboat

Authors
Alves, JC; Cruz, NA;

Publication
2014 Oceans - St. John's, OCEANS 2014

Abstract
Robotic sailing vehicles can provide the support for carrying out long ocean sampling missions, using solely renewable energy for propulsion and for powering the computing, communication and electromechanical systems. The basic automatic sailing tasks required to visit a sequence of waypoints has already been correctly addressed by various teams. However, an effective system for specifying long term autonomous missions is necessary to fill the gap between the developers of the robotic platforms and the scientific end users, mainly interested in the data they can get. This paper presents a simple, flexible and easy to use mission programming system implemented in the autonomous sailing boat FASt. A mission is programmed by defining events and assigning to them sequences of high level actions. The support of conditional statements allows the implementation of a basic control flow mechanism to make route decisions during the deployment of the mission. Examples are presented to illustrate the construction of mission programs. © 2014 IEEE.

2015

AIS-Enabled Collision Avoidance Strategies for Autonomous Sailboats

Authors
Alves, JC; Cruz, NA;

Publication
Robotic Sailing 2015

Abstract

2015

Autonomous tracking of a horizontal boundary

Authors
Cruz, NA; Matos, AC;

Publication
2014 Oceans - St. John's, OCEANS 2014

Abstract
The ability to employ autonomous vehicles to find and track the boundary between two different water masses can increase the efficiency in waterborne data collection, by concentrating measurements in the most relevant regions and capturing detailed spacial and temporal variations. In this paper we provide a guidance mechanism to enable an autonomous vehicle to find and track the steepest gradient of a scalar field in the horizontal plane. The main innovation in our approach is the mechanism to adapt the orientation of the crossings to the local curvature of the boundary, so that the vehicle can keep tracking the gradient regardless of its horizontal orientation. As an example, we show how the algorithms can be used to find and track the boundary of a dredged navigation channel, using only altimeter measurements. © 2014 IEEE.

2016

BLUECOM plus : Cost-effective Broadband Communications at Remote Ocean Areas

Authors
Campos, R; Oliveira, T; Cruz, N; Matos, A; Almeida, JM;

Publication
OCEANS 2016 - SHANGHAI

Abstract
The ocean and the Blue Economy are increasingly top priorities worldwide. The immense ocean territory in the planet and its huge associated economical potential is envisioned to increase the activity at the ocean in the forthcoming years. The support of these activities, and the convergence to the Internet of Things paradigm, will demand wireless and mobile communications to connect humans and systems at remote ocean areas. Currently, there is no communications solution enabling cost-effective broadband Internet access at remote ocean areas in alternative to expensive, narrowband satellite communications. This paper presents the maritime communications solution being developed in the BLUECOM+ project. The BLUECOM+ solution enables cost-effective broadband Internet access at remote ocean areas using standard wireless access technologies, e.g., GPRS/UMTS/LTE and Wi-Fi. Its novelty lies on the joint use of TV white spaces for long range radio communications, tethered balloons for lifting communications nodes high above the ocean surface, multi-hop relaying techniques for radio range extension, and standard access networks at the ocean. Simulation results prove it is possible to reach radio ranges beyond 100 km and bitrates in excess of 3 Mbit/s using a two-hop land-sea communications chain.

2016

Characterization of Measurement Errors in a LBL Positioning System

Authors
Almeida, R; Melo, J; Cruz, N;

Publication
OCEANS 2016 - SHANGHAI

Abstract
There are several sources of error affecting the accuracy of underwater ranging using acoustic signals. These errors have a direct impact in the performance of Long Baseline (LBL) navigation system. This paper presents the results of experiments designed to characterize the most significant sources of errors in acoustic ranging. For the experiments, we use a set of acoustic devices and compare distances given by GPS differences with and acoustic ranges. We describe the experimental procedure and we process the results to provide a qualitative and quantitative analysis of the errors.

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