Matthew Grund

The WHOI micro-modem: an acoustic communications and navigation system for multiple platforms

The micro-modem is a compact, low-power, underwater acoustic communications and navigation subsystem. It has the capability to perform low-rate frequency-hopping frequency-shift keying (FH-FSK), variable rate phase-coherent keying (PSK), and two different types of long base line navigation, narrow-band and broadband. The system can be configured to transmit in four different bands from 3 to 30 kHz, with a larger board required for the lowest frequency. The user interface is based on the NMEA standard, which is a serial port specification. The modem also includes a simple built-in networking capability which supports up to 16 units in a polled or random-access mode and has an acknowledgement capability which supports guaranteed delivery transactions. The paper contains a detailed system description and results from several tests are also presented

Experimental Results in Synchronous-Clock One-Way-Travel-Time Acoustic Navigation for Autonomous Underwater Vehicles

This paper reports recent experimental results in the development and deployment of a synchronous-clock acoustic navigation system suitable for the simultaneous navigation of multiple underwater vehicles. The goal of this work is to enable the task of navigating multiple autonomous underwater vehicles (AUVs) over length scales of O(100 km), while maintaining error tolerances commensurate with conventional long-baseline transponder-based navigation systems (i.e., O(1 m)), but without the requisite need for deploying, calibrating, and recovering seafloor anchored acoustic transponders. Our navigation system is comprised of an acoustic modem-based communication/navigation system that allows for onboard navigational data to be broadcast as a data packet by a source node, and for all passively receiving nodes to be able to decode the data packet to obtain a one-way travel time pseudo-range measurement and ephemeris data. We present results for two different field experiments using a two-node configuration consisting of a global positioning system (GPS) equipped surface ship acting as a global navigation aid to a Doppler-aided AUV. In each experiment, vehicle position was independently corroborated by other standard navigation means. Initial results for a maximum-likelihood sensor fusion framework are reported.

Experiments in moving baseline navigation using autonomous surface craft

This paper describes an on-going research effort to achieve real-time cooperative localization of multiple autonomous underwater vehicles. We describe a series of experiments that utilize autonomous surface craft (ASC), equiped with undersea acoustic modems, GPS, and 802.11b wireless Ethernet communications, to acquire data and develop software for cooperative localization of distributed vehicle networks. Our experiments demonstrate the capability of the Woods Hole acoustic modems to provide accurate round-trip and one-way range measurements, as well as data transfer, for a fully mobile network of vehicles in formation flight. Finally, we present preliminary results from initial experiments involving cooperative operation of an Odyssey III AUV and two ASCs, demonstrating ranging and data transfer from the ASCs to the Odyssey III.

Integrated acoustic communication and navigation for multiple UUVs

Integrated acoustic communication and navigation for underwater vehicles provides dual functionality in a single system which reduces cost, size, power and potential acoustic interference. A combination of time and code division multiplexing is used to allow long baseline navigation and bidirectional communication for a number of vehicles operating simultaneously in the same area. The communication system uses multi-rate phase coherent modulation to maximize throughput for the uplink from a vehicle to a central node, and code-division multiple-access using a simple frequency-hopping scheme. The data rate and modulation methods are completely programmable and may be selected based on the application requirements and the propagation conditions present between the different vehicles in the network. While one or several vehicles may use time-multiplexed long-baseline (LBL) navigation, when the number of vehicles grows large, the time between fixes becomes unacceptably long. Thus in addition to LBL, a second mode of navigation is also available for use with swarms of vehicles such as the surf-zone crawlers proposed for mine counter-measure applications. This second mode employs navigation broadcasts initiated by the central controller and incorporates three additional fixed nodes that transmit in response. The time differences of arrival measured at the vehicle are used to determine its location.

Recent Advances in Synchronous-Clock One-Way-Travel-Time Acoustic Navigation

This paper reports recent results in the development and deployment of a synchronous-clock acoustic navigation system suitable for the simultaneous navigation of multiple underwater vehicles. The goal of this work is to enable the task of navigating multiple autonomous underwater vehicles (AUVs) over length scales of (D(100 km), while maintaining error tolerances commensurate with conventional long-baseline transponder-based navigation systems (O(1 m)), but without the requisite need for deploying, calibrating, and recovering seafloor anchored acoustic transponders. Our navigation system is comprised of an acoustic modem-based communication/navigation system that allows for onboard navigational data to be broadcast as a data packet by a source node, and for all passively receiving nodes to be able to decode the data packet to obtain a one-way travel time pseudo-range measurement and ephemeris data. We present field results for a two-node configuration consisting of a surface ship acting as a global navigation aid to a Doppler-aided AUV

A Compact Control Language for AUV acoustic communication

Acoustic communication with autonomous underwater vehicles (AUVs) implies low data rates and potentially high latency, depending on the range and the number of vehicles operating in one area. To efficiently use this limited resource the Compact Control Language (CCL) was developed for use with the WHOI REMUS AUV. CCL is a set of messages that includes commands for AUVs and data messages for typical sensors. Almost all of the messages are less than 32 bytes long. CCL commands include simple operations such as Abort Now and Abort to Mission End, but also complex commands such as re-direction with side scan sonar over areas of interest. When this simple command set is used with a telemetry system that includes network addressing (such as the WHOI Micro-Modem), sophisticated multi-vehicle operations may be carried out. The open nature of the specification allows vehicles developed at different research institutions or commercial companies to work together, thus promoting interoperability. CCL has been adopted by others working in the Office of Naval Research Very Shallow Water mine-countermeasure (VSW-MCM) program which includes multiple vehicles with different types of sensors.

Underwater Acoustic Navigation with the WHOI Micro-Modem

The WHOI Micro-Modem is a compact, low-power acoustic transceiver that can provide both acoustic telemetry and navigation. Its size and versatility make it ideal for integration in autonomous underwater vehicles (AUVs). The modem supports the use of both broadband and narrowband transponders for long baseline navigation systems, has a modem-to-modem ranging capability, and can be configured to provide synchronous oneway ranging, when integrated with a precision clock. This paper gives an overview of the different navigation systems supported by the Micromodem and presents the results from field tests conducted on the SeaBED AUV in deployments in Greece, the Bluefin AUV, and whale localizations in the Stellwagen Bank Marine Sanctuary

Multi-band acoustic modem for the communications and navigation aid AUV

An acoustic communications system with the capability to operate at multiple data rates in two frequency bands has been designed and developed for use in 21-inch AUVs. The system is specifically designed around the 21-inch diameter Bluefin Robotics AUV, though it could be adapted to smaller vehicles (12-inch), or similar free-flooded vehicles. The system includes both high (25 kHz) and mid-frequency (3 kHz) modems and supports data rates from 80 bps to more than 5000 bps. Both of the modems utilize four-channel arrays to increase reliability. The high-frequency modem is also used to support multi-vehicle navigation via one-way travel time measurements using synchronized clocks on all of the vehicles in a work group

Multi-objective optimization of sensor quality with efficient marine vehicle task execution

This paper describes the in-field operation of two interacting autonomous marine vehicles to demonstrate the suitability of interval programming (IvP), a novel mathematical model for multiple-objective optimization. Broadly speaking, IvP coordinates competing control needs such as primary task execution that depends on a sufficient position estimate, and vehicle maneuvers that will improve that position estimate. In this work, vehicles cooperate to improve their position estimates using a sequence of vehicle-to-vehicle range estimates from acoustic modems. Coordinating primary task execution and sensor quality maintenance is a ubiquitous problem, especially in underwater marine vehicles. This work represents the first use of multiobjective optimization in a behavior-based architecture to address this problem

The PLUSNet Underwater Communications System: Acoustic Telemetry for Undersea Surveillance

The Persistent Littoral Undersea Surveillance Network (PLUSNet) demonstrates multi-sensor and multi-vehicle anti-submarine warfare (ASW) by means of an underwater acoustic communications network. This ONR-funded multi-institution effort is part of a larger research and development framework which aims to provide autonomous detection and tracking of quiet submarines in support of the Navy Sea Power 21 concept. This paper describes the acoustic network implementation using the WHOI Micro-modem, and highlights the physical and messaging communication layers