Underwater sensor nodes will find applications in oceanographic data collection, pollution monitoring, offshore exploration, disaster prevention, assisted navigation and tactical surveillance applications. Moreover, unmanned or autonomous underwater vehicles (UUVs, AUVs), equipped with sensors, will enable the exploration of natural undersea resources and gathering of scientific data in collaborative monitoring missions. Underwater acoustic networking is the enabling technology for these applications. Underwater networks consist of a variable number of sensors and vehicles that are deployed to perform collaborative monitoring tasks over a given area. In this paper, several fundamental key aspects of underwater acoustic communications are investigated. Different architectures for two-dimensional and three-dimensional underwater sensor networks are discussed, and the characteristics of the underwater channel are detailed. The main challenges for the development of efficient networking solutions posed by the underwater environment are detailed and a cross-layer approach to the integration of all communication functionalities is suggested. Furthermore, open research issues are discussed and possible solution approaches are outlined. � 2005 Published by Elsevier B.V.

/pdf/underwater-acoustic-sensor-networks-research-challenges-15fjl1gvhc.pdf

Underwater acoustic sensor networks: research challenges

Traditionally, interference is considered harmful. Wireless networks strive to avoid scheduling multiple transmissions at the same time in order to prevent interference. This paper adopts the opposite approach; it encourages strategically picked senders to interfere. Instead of forwarding packets, routers forward the interfering signals. The destination leverages network-level information to cancel the interference and recover the signal destined to it. The result is analog network coding because it mixes signals not bits.So, what if wireless routers forward signals instead of packets? Theoretically, such an approach doubles the capacity of the canonical 2-way relay network. Surprisingly, it is also practical. We implement our design using software radios and show that it achieves significantly higher throughput than both traditional wireless routing and prior work on wireless network coding.

/pdf/embracing-wireless-interference-analog-network-coding-1vuvzsncu8.pdf

Embracing wireless interference: analog network coding

With the advances in acoustic modem technology that enabled high-rate reliable communications, current research focuses on communication between various remote instruments within a network environment. Underwater acoustic (UWA) networks are generally formed by acoustically connected ocean-bottom sensors, autonomous underwater vehicles, and a surface station, which provides a link to an on-shore control center. While many applications require long-term monitoring of the deployment area, the battery-powered network nodes limit the lifetime of UWA networks. In addition, shallow-water acoustic channel characteristics, such as low available bandwidth, highly varying multipath, and large propagation delays, restrict the efficiency of UWA networks. Within such an environment, designing an UWA network that maximizes throughput and reliability while minimizing the power consumption becomes a very difficult task. The goal of this paper is to survey the existing network technology and its applicability to underwater acoustic channels. In addition, we present a shallow-water acoustic network example and outline some future research directions.

https://www.mit.edu/~millitsa/resources/pdfs/joema.pdf

Underwater acoustic networks

This paper investigates two fundamental characteristics of a wireless multi -hop network: its minimum node degree and its k--connectivity Both topology attributes depend on the spatial distribution of the nodes and their transmission range Using typical modeling assumptions :--- :a random uniform distribution of the nodes and a simple link model :--- :we derive an analytical expression that enables the determination of the required range r0 that creates, for a given node density ρ, an almost surely k--connected network Equivalently, if the maximum r0 of the nodes is given, we can find out how many nodes are needed to cover a certain area with a k--connected network We also investigate these questions by various simulations and thereby verify our analytical expressions Finally, the impact of mobility is discussedThe results of this paper are of practical value for researchers in this area, eg, if they set the parameters in a network--level simulation of a mobile ad hoc network or if they design a wireless sensor network

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On the minimum node degree and connectivity of a wireless multihop network

This paper explores applications and challenges for underwater sensor networks. We highlight potential applications to off-shore oilfields for seismic monitoring, equipment monitoring, and underwater robotics. We identify research directions in short-range acoustic communications, MAC, time synchronization, and localization protocols for high-latency acoustic networks, long-duration network sleeping, and application-level data scheduling. We describe our preliminary design on short-range acoustic communication hardware, and summarize results of high-latency time synchronization

Research challenges and applications for underwater sensor networking

Underwater acoustic networks are generally formed by acoustically connected ocean bottom sensor nodes, autonomous underwater vehicles (AUVs), and surface stations that serve as gateways and provide radio communication links to on-shore stations. The quality of service of such networks is limited by the low bandwidth of acoustic transmission channels, high latency resulting from the slow propagation of sound, and elevated noise levels in some environments. The long-term goal in the design of underwater acoustic networks is to provide for a self-configuring network of distributed nodes with network links that automatically adapt to the environment through selection of the optimum system parameters. This article considers several aspects in the design of shallow water acoustic networks that maximize throughput and reliability while minimizing power consumption.

Shallow water acoustic networks

Underwater acoustic networks are generally formed by acoustically connected ocean bottom sensor nodes, autonomous underwater vehicles (AUVs), and surface stations that serve as gateways and provide radio communication links to on-shore stations. The QoS of such networks is limited by the low bandwidth of acoustic transmission channels, high latency resulting from the slow propagation of sound, and elevated noise levels in some environments. The long-term goal in the design of underwater acoustic networks is to provide for a self-configuring network of distributed nodes with network links that automatically adapt to the environment through selection of the optimum system parameters. This paper considers several aspects in the design of shallow water acoustic networks that maximize throughput and reliability while minimizing power consumption.


Keywords:

underwater;
acoustic;
communications;
network;
media access control (MAC);
routing;
ad hoc;
Seaweb

Shallow-Water Acoustic Networks†

An underwater acoustic communication system based on direct-sequence spread-spectrum signaling is presented. The method is intended for use in multiple-access underwater communication networks. In this paper, the transmitter and receiver designs are proposed, discussed, and demonstrated using real data. At the receiver, a RAKE filter is employed. The same signaling scheme is also used to obtain an adaptive estimate of the time-varying channel coefficients. The channel estimator performance is demonstrated using simulations and experimental data.

Direct sequence spread spectrum based modem for under water acoustic communication and channel measurements

There is a growing interest for underwater sensor networks where long term monitoring of water masses around the world for scientific, environmental, commercial, and military reasons is desired. In this paper we will present the concept of a highly flexible acoustic modem called the Reconfigurable Modem (rModem) that can be used for rapid testing and development of such networks.

/pdf/reconfigurable-acoustic-modem-for-underwater-sensor-networks-1fgsjz10fz.pdf

E.M. Sozer

Papers

Underwater acoustic networks

Shallow water acoustic networks

Shallow-Water Acoustic Networks†

Direct sequence spread spectrum based modem for under water acoustic communication and channel measurements

Reconfigurable acoustic modem for underwater sensor networks