UNDERWATER ACUSTIC SENSOR NETWORKS (UW-ASNs) Daladier Jabba Molinares Department of Computer Science and Engineering University of South Florida Tampa, FL 33620 daladier@cse.usf.edu

UNDERWATER ACUSTIC SENSOR NETWORKS (UW-ASNs) Introduction Communication architecture UW-ASN: Design challenges Principal layers MAC Layer Network Layer Transport Layer Clusters in Mobile Ad hoc Networks Minimum Cut problem applied to UW-ASN References Questions

INTRODUCTION

INTRODUCTION Group of sensors and vehicles deployed underwater and networked via acoustic links, performing collaborative tasks Equipment Autonomous Underwater Vehicles (AUVs) Underwater sensors (UW-ASN)

INTRODUCTION (Cont…) Objectives UW_ASNs AUVs To exploit multi hop paths To minimize the signaling overhead for building underwater paths AUVs Rely on local intelligence Less dependent on communications from online shores Control strategies (autonomous coordination obstacle avoidance)

INTRODUCTION (Cont…) Applications Environment monitoring Review how human activities affect the marine ecosystem Undersea explorations Detect underwater oilfields Disaster prevention Monitoring ocean currents and winds (Tsunamis) Assisted navigation Locate dangerous rocks in shallow waters Distributed tactical surveillance Intrusion detection (Navy)

INTRODUCTION (Cont…) Acoustic comms  physical layer technology in underwater networks High attenuation  radio waves propagation problems Links for underwater networks based on acoustic wireless communications (typically used)

INTRODUCTION (Cont…) Challenges Available bandwidth is limited Propagation delayUnderwater=5 x Radio Frequency(RF)ground High bit errors and temporary loss of connectivity Limited battery power Tendency of failure in the underwater sensors because of corrosion

COMMS ARCHITECTURE

COMMS ARCHITECTURE Two-dimensional Underwater Sensor Networks : for ocean bottom monitoring Three-dimensional Underwater Sensor Networks : for ocean-column monitoring Sensor Networks with Autonomous Underwater vehicles : for underwater explorations

COMMS ARCHITECTURE (Cont…) 1. Static two-dimensional UW-ASNs for ocean bottom monitoring Components: Gateway *: not necessary

COMMS ARCHITECTURE (Cont…) Satellite comms RF comms Comms with the surface station Acoustic link comms Comms. Intra clusters (using CH) anchored

Static two-dimensional UW-ASNs for ocean bottom monitoring (Cont…) Problems Long distances between gateways and UW-ASNs Power to transmit decay easy It is better multi hop paths Bandwidth limitations Greater bandwidth for a shorter transmission distance Increasing the UW-ASNs density generates routing complexity Solving the problems Energy savings Increase network capacity

COMMS ARCHITECTURE (Cont…) 2. Three-dimensional Underwater Sensor Networks Components: *: not necessary

COMMS ARCHITECTURE (Cont…) Satellite comms RF comms Comms with the surface station Acoustic link comms anchored

Three-dimensional Underwater Sensor Networks (Cont…) Problems If they are attached to a surface buoy They can be easily detected by enemies Floating buoys are vulnerable to the weather and pilfering ship navigations can be a problem Increasing the UW-ASNs density generates routing complexity Solving the problems Be anchored to the bottom of the ocean (to an anchors by wires) Energy savings Increase network capacity

COMMS ARCHITECTURE (Cont…) 3. Sensor Networks with Autonomous Underwater vehicles Components: AUV *: not necessary

COMMS ARCHITECTURE (Cont…) Satellite comms RF comms Comms with the surface station Acoustic link comms anchored

UW-ASN:DESIGN CHALLENGES

DESIGN CHALLENGES (Cont…) UWSNs vs Terrestrial Sensor Networks Cost Terrestrial sensor networks will be cheaper and cheaper with the time UWSNs are expensive Deployment Terrestrial SNs are densely deployed UWSNs are generally more sparse Power For UWSNs is higher Memory Terrestrial sensors have less capacity

DESIGN CHALLENGES (Cont…) Basics of acoustic propagation in UWSNs Radio waves propagation for long distances through sea water only at frequencies of 30-300 Hz High transmission power Large antennas Poor available Bandwidth * In 802.11b : between 2.412 GHz to 2.484 GHz

DESIGN CHALLENGES (Cont…) Some factors that affect the design Path loss Attenuation provoked by absorption due to conversion of acoustic energy into heat Because of the spreading sound energy as a result of the expansion of the wavefronts Noise Man-made noise Ambient noise High delay Propagation delayUnderwater=5 x Radio Frequency(RF)ground

MEDIUM ACCESS CONTROL LAYER Biomimetic Underwater Robot, Robolobster

MAC LAYER (Cont…) Multiple access techniques Code Division Multiple Access (CDMA) Carrier Sense Multiple Access (CSMA) Time Division Multiple Access (TDMA) Frequency Division Multiple Access (FDMA)

MAC LAYER (Cont…) Proposed MAC protocols Slotted Fama Applies control packets before starting transmission to avoid multiple transmissions at the same time Issue: handshaking process can generate low throughput

MAC LAYER (Cont…) Adapted MACA to underwater acoustic networks It uses CTS-RTS-DATA exchange and for Error detection STOP and WAIT ARQ Retransmitting packets because of timeout in receiving ACK The source drops the communication after K trials Problems Energy consumption because of repeating RTS several times before receiving a CTS Deadlock problems Solutions To add a WAIT commands (destination tells that is busy) Add an assignment priority to every packet

MAC LAYER (Cont…) Clustering and CDMA/TDMA multiple access For distributed UW-ASNs Communication intra cluster uses TDMA (time slots) CDMA by each cluster using a different code for transmission Problem Number of code is limited Solution proposed Reusable code (possible because the acoustic signal fades due to distance)

MAC LAYER (Cont…) Open research issues Design access codes for CDMA taking into account minimum interference among nodes Maximize the channel utilization Distributed protocols to save battery consumption

NETWORK LAYER

NETWORK LAYER (Cont…) Proactive routing protocols Dynamic Destination Sequenced Distance Vector (DSDV), Optimizing Link State Routing (OLSR) They are not suitable for UW-ASNs Large signaling overhead every time network topology has to be updated All nodes are able to establish a path with others and it is not necessary

NETWORK LAYER (Cont…) Reactive routing protocols Ad hoc On Demand Distance Vector (AODV) and Dynamic Source Routing (DSR) They are not suitable for UW-ASNs It requires flooding of control packets at the beginning to establish paths (excessive signaling overhead) High latency on establishment of paths Must of the reactive protocols rely in symmetrical links

NETWORK LAYER (Cont…) Geographical routing protocols Routing with Guaranteed Delivery in Ad Hoc Wireless Networks (GFG) and Optimal local topology knowledge for energy efficient geographical routing in sensor networks (PTKF) Establish source destination paths by leveraging localization information A node selects its next hop based on the position of its neighbors and of the destination node Problems They work with GPS (GPS uses waves in the 1.5 GHz band) It has not been improved the localization information in the underwater environment

NETWORK LAYER (Cont…) Solution proposed Network layer protocols specifically tailored to underwater environment Example A routing protocol was proposed that autonomously establishes the underwater network topology, control network resources and establishes the network flows using a centralized management

NETWORK LAYER (Cont…) Open research issues Develop algorithms that reduces the latency Handle loss of connectivity using mechanisms without generating retransmission Algorithms and protocols needs to improve the way to deal with disconnections because of failures of battery depletion How to integrate AUV with UW-ASNs and able communication among them

TRANSPORT LAYER

TRANSPORT LAYER (Cont…) Unexplored area It has to perform: Flow control To avoid that network devices with limited memory are overwhelmed by data transmissions Congestion control To prevent the network being congested TCP implementations are not suited The long Round Trip Time (RTT) in underwater environment affect the throughput

TRANSPORT LAYER (Cont…) A transport layer for UW-ASNs requieres: Reliability hop by hop In case of congestion, transport layer need to be adapted faster to decrease the response time Minimum energy consumption To avoid many feedbacks with the ACK mechanism that can utilize bandwidth unnecessarily

TRANSPORT LAYER (Cont…) Open research issues Flow control strategies to reduce not only the high delay but also delay variance of the control messages Efficient mechanisms to find the cause of packet loss To create solutions for handling the effect of losses of connectivity caused by shadow zones

Clusters in Mobile Ad hoc Networks

Clusters in Mobile Ad hoc Networks (Cont…) Reduce the overhead in the network Reduce power consumption Different type of nodes Cluster head Gateway Nodes in the cluster Communication Intra cluster Inter cluster

Clusters in Mobile Ad hoc Networks (Cont…) Problems Hidden Terminal problem Exposed Terminal problem

Clusters in Mobile Ad hoc Networks (Cont…) Topology control (Cluster Initialization) LIDCA algorithm lowest identifier HCCA algorithm high connectivity Minimum cut problem (graph theory) Contract nodes Routing protocols Maintenance

Challenge Minimum Cut problem applied to UW-ASN (Network layer) To reduce interference x a b c d e f b,c X,a,b,c D,e,f Connectivity

References I. F. Akyildiz, D. Pompili, and T. Melodia. Underwater Acoustic Sensor Networks: Research Challenges. Ad Hoc Networks (Elsevier), vol. 3(3), pp. 257–279, May 2005. K. Kredo and P. Mohapatra. Medium Access Control in Wireless Sensor Networks. to appear in Computer Networks (Elsevier), 2006. F. Salva-Garau and M. Stojanovic. Multi-cluster Protocol for Ad Hoc Mobile Underwater Acoustic Networks. In Proc. Of MTS/IEEE OCEANS. San Francisco, CA, Sep. 2003. Hayat DOUKKALI and Loutfi NUAYMI. Analysis of MAC protocols for Underwater Acoustic Data Networks. 0-7803-8887-9/05. (c)2005 IEEE Jim Partan, Jim Kurose Brian Neil Levine. A Survey of Practical Issues in Underwater Networks. Borja Peleato and Milica Stojanovic. A MAC Protocol for Ad Hoc Underwater Acoustic Sensor Networks. WUWNet’06, September 25, 2006. Ian F. Akyildiz, Dario Pompili, and Tommaso Melodia. State of the Art In Protocol Research for Underwater Acoustic Sensor Networks. WUWNet’06, September 25, 2006.

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