Edward A. Carlson

Location-Aware Routing Protocol for Underwater Acoustic Networks

Autonomous underwater vehicles (AUVs) are being used in ever larger numbers, and the rise in the simultaneous use of multiple AUVs is introducing challenging communication problems best addressed in the realm of mobile, ad hoc networking (MANET). This paper describes location-aware source routing (LASR), our modification of the dynamic source routing (DSR) protocol to add location awareness and link quality metrics. A new protocol is needed because of the unique difficulties of underwater networking: radio links do not work through water, and the acoustic links that are used instead have much lower data-rates and much higher latency. Specifically designed for use in underwater acoustic networks, LASR is explained, and initial simulation results are presented to show that the new protocol performs better than two existing techniques

HERMES - A high-speed acoustic modem for real-time transmission of uncompressed image and status transmission in port environment and very shallow water

A new generation of high-speed, high-frequency acoustic modem, named HERMES, has been developed. The acoustic communications link consists of a topside component and an underwater (wet-side) component. Together these components implement two underwater acoustic communication channels: a very high bit rate broadband data uplink and a low bit rate command downlink. The experimental results, obtained with the high-speed high-frequency acoustic uplink, demonstrate the systems ability to transmit high-resolution, uncompressed acoustic images with sufficient quality for any practical purposes. At the fastest data rate (mode 5), HERMES can transmit an uncompressed, high-resolution 400000-bit sonar image in 4.6 seconds. The results presented in this paper demonstrate that these data can be transmitted at a range of 120 m.

Simulating communication during multiple AUV operations

Communication between multiple autonomous underwater vehicles is challenging and best addressed by considering it as a networking problem. Treating the vehicles as the nodes of an ad hoc network consolidates much of the complexity of the communication system in the networks routing protocol. We discuss the many issues associated with the development of routing protocols and consider some existing protocols. The number and duration of in situ trials necessary during the development, testing, evaluation and refinement of these protocols makes a simulation tool invaluable. The requirements of such a simulator are compared with the capabilities of several existing simulators. We propose the design for a new simulator and discuss its implementation.

A Path planning control strategy for search-classify task using multiple cooperative underwater vehicles

This paper proposes to investigate the performance of a path planning controller for a search-classify mission using multiple cooperative underwater vehicles. We present a control strategy for multi-agent cooperative systems, namely the Grid-based Multi-Objective Optimal Problem (GMOOP) solving technique, to find the optimal solutions for a search-classify mission using an action determination map subject to certain constraints and objectives. This technique is based on an Interval Programming (IvP) algorithm introduced in for representing and optimizing over multiple competing objective functions. We made improvements in this GMOOP technique to suit the harsh underwater acoustic communication environment by taking advantages of the Location-Aware Source Routing (LASR) protocol for underwater Mobile Ad hoc Network (MANET). Preliminary simulation trials based on two simplified scenarios have been carried out. Results show that the demanded cooperative search task could be finished satisfactorily under harsh acoustic constraints, and the performance of the GMOOP model are studied in various aspects.

Task allocation and path planning for collaborative AUVs operating through an underwater acoustic network

Multiple cooperative vehicles, joined in an acoustic communication network, can perform time-critical, cooperative operations given a robust task allocation mechanism and an efficient path planning model. In this paper, we present solutions for the task-allocation and path-planning problems of the cooperative schema for multiple AUVs: a Location-Aided task Allocation Framework (LAAF) algorithm for multi-target task assignment and the Grid-based Multi-Objective Optimal Programming (GMOOP) mathematical model for finding an optimal vehicle command decision given a set of objectives and constraints. Our research is based on an existing mobile ad-hoc network underwater acoustic simulator and two routing protocols (blind flooding and dynamic source routing). The LAAF and GMOOP controllers combine within a “task-planact” structure to generate an optimized local system output in a timely manner to achieve fleet-wide cooperation. Our preliminary results demonstrate that the location-aided auction strategies perform significantly better than a generic auction algorithm in terms of task-allocation time and network bandwidth consumption. We also demonstrate that the GMOOP path planning technique provides an efficient method for multi-objective tasks by cooperative agents with limited communication capabilities with its results can be referenced in [7]. Prior to this work, existing multi-objective action selection methods were limited to robust networks where constant, reliable communication was available. Both the LAAF and GMOOP algorithms were robust to poor acoustic network conditions and ongoing changing environments. LAAF dynamic task allocation and the GMOOP path planning controller provide an effective solution for cooperative search-classify missions with multiple AUVs under marginal communication conditions.

Task Allocation and Path Planning for Collaborative Autonomous Underwater Vehicles Operating through an Underwater Acoustic Network

Dynamic and unstructured multiple cooperative autonomous underwater vehicle (AUV) missions are highly complex operations, and task allocation and path planning are made significantly more challenging under realistic underwater acoustic communication constraints. This paper presents a solution for the task allocation and path planning for multiple AUVs under marginal acoustic communication conditions: a location-aided task allocation framework (LAAF) algorithm for multitarget task assignment and the grid-based multiobjective optimal programming (GMOOP) mathematical model for finding an optimal vehicle command decision given a set of objectives and constraints. Both the LAAF and GMOOP algorithms are well suited in poor acoustic network condition and dynamic environment. Our research is based on an existing mobile ad hoc network underwater acoustic simulator and blind flooding routing protocol. Simulation results demonstrate that the location-aided auction strategy performs significantly better than the well-accepted auction algorithm developed by Bertsekas in terms of task-allocation time and network bandwidth consumption. We also demonstrate that the GMOOP path-planning technique provides an efficient method for executing multiobjective tasks by cooperative agents with limited communication capabilities. This is in contrast to existing multiobjective action selection methods that are limited to networks where constant, reliable communication is assumed to be available.

Location-aware source routing protocol for underwater acoustic networks of AUVs

Acoustic networks of autonomous underwater vehicles (AUVs) cannot typically rely on protocols intended for terrestrial radio networks. This work describes a new location-aware source routing (LASR) protocol shown to provide superior network performance over two commonly used network protocols--flooding and dynamic source routing (DSR)--in simulation studies of underwater acoustic networks of AUVs. LASR shares some features with DSR but also includes an improved link/route metric and a node tracking system. LASR also replaces DSRs shortest-path routing with the expected transmission count (ETX) metric. This allows LASR to make more informed routing decisions, which greatly increases performance compared to DSR. Provision for a node tracking system is another novel addition: using the time-division multiple access (TDMA) feature of the simulated acoustic modem, LASR includes a tracking system that predicts node locations, so that LASR can proactively respond to topology changes. LASR delivers 2-3 times as many messages as flooding in 72% of the simulated missions and delivers 2-4 times as many messages as DSR in 100% of the missions. In 67% of the simulated missions, LASR delivers messages requiring multiple hops to cross the network with 2-5 times greater reliability than flooding or DSR.

An Improved Location-Aware Routing Protocol for Mobile Underwater Acoustic Networks

A significant problem in missions employing multiple autonomous underwater vehicles (AUVs) is the difficulty of communicating effectively. This challenging communication problem is best addressed in the realm of mobile, ad hoc networking (MANET). This paper describes work towards improving location-aware source routing (LASR), our modification of the dynamic source routing (DSR) protocol to add location awareness and link quality metrics. Specifically designed for use in underwater acoustic networks, LASR is explained and results of investigations into the sensitivity of LASR to medium-model error, tracking error and compression of communicated routing data are shown.

Combined vehicle control, status check and high-resolution acoustic images retrieval using a high-frequency acoustic modem on a hovering AUV

Hermes is a two-way half-duplex underwater acoustic modem developed to transfer large amounts of information from an underwater asset to a surface operator, while being able to send command-and-control information to the underwater asset. In addition, this communication system must operate in very challenging environments such as busy ports and very shallow waters. Hermes must also provide the ability to transfer data from multiple sources simultaneously, without any impact on the source of information. To do so, the communication system uses a specific pipe architecture tailored for wireless underwater applications, combined with a multi-scale, parallel decision-feedback-equalizer technique. The authors show that Hermes can relay simultaneously and reliably high-resolution scan sonar images with target recognition, mosaics and vehicle status in various port environments, at a range of up to 130 m using high-frequency, omni-directional transducers. The fastest data rate tested is 87,768 bps. The main platform is the Bluefin Robotics HULS3. Experimental results are also presented using the WHOI Remus-100 Gudgeon.