1 underwater sensor networks: applications and challenges jun-hong cui computer science &...
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Underwater Sensor Networks:Applications and Challenges
Jun-Hong Cui
Computer Science & Engineering
University of Connecticut
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Why Underwater? The Earth is a water planet
– About 2/3 of the Earth covered by oceans• Uninhabited, largely unexplored• A huge amount of (natural) resources to discover
Many potential applications– Long-term aquatic monitoring
• Oceanography, marine biology, deep-sea archaeology, seismic predictions, pollution detection, oil/gas field monitoring …
– Short-term aquatic exploration• Underwater natural resource discovery, hurricane
disaster recovery, anti-submarine mission, loss treasure discovery …
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What are the Application Requirements?
Desired properties– Unmanned underwater exploration
– Localized and precise data acquisition for better knowledge
– Tetherless underwater networking for motion agility/flexibility
– Scalable to 100’s, 1000’s of nodes for bigger spatial coverage
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Underwater Sensor Networks (UWSNs)
The Ideal Technique:
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Application Scenario I
Submarine Detection
Buoys
Radio
Acoustic
Data Report
Sonar Transmitter
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Why UWSN for Submarine Detection? Existing Approaches
– Active or passive sonar– Cons: submarine anti-detection techniques (e.g.,
sonar absorption) make them less-effective Using UWSN
– Collaborative detection• Multiple sensors, and/or multi-modal data
– Large coverage– Timely reporting– High reusability
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Application Scenario II
Estuary Monitoring
Fresh
Salty
Fresh Water Current
Salty Water Current
BuoyancyControl
BuoyancyControl
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Why UWSN for Estuary Monitoring? Existing Approaches
– Ship tethered with chains of sensors moves from one end to the other
– Cons: no 4D data, either f(x, y, z, fixed t), or f(fixed (x, y, z), t); and cost is high
Using UWSN– Easily get 4D data, f(x, y, z, t), sensors move– Reduce cost significantly– Increase coverage– Have high reusability
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Research Issues (I)
Sensor node system design– Sensing, computing, communication integration – Power management: energy saving, life time
Autonomous network system design – Communication, multiple access– Routing, forwarding, reliable transfer– Localization, synchronization– Security, robustness– Energy efficiency
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Research Issues (II)
Applications and data management– Application classification & characterization– Data sampling, structure, storage
Collaborative estimation & detection– Data fusion, dissemination, tracking
Modeling, simulation, evaluation– Network simulator– Sensor node simulator
Hardware, middleware, software design
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Research Personnel Sensor Network and Systems research
– Jun-Hong Cui, Computer Science & Engineering (Director)– Yunsi Fei, Electrical & Computer Engineering– Jerry Zhijie Shi, Computer Science & Engineering– Bing Wang, Computer Science & Engineering– Peter Willett, Electrical & Computer Engineering– Shengli Zhou, Electrical & Computer Engineering (Co-director)
Algorithmic and Performance support– Reda Ammar, Computer Science & Engineering– Lanbo Liu, Civil & Environmental Engineering– Sanguthevar Rajasekaran, Computer Science & Engineering
Context and Applications consultation– Amvrossios Bagtzoglou, Civil & Environmental Engineering– Thomas Torgersen, Marine Sciences
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Networking Issues in UWSNs
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Underwater Transmission Characteristics
Narrow bandwidth channels– High-frequency waves rapidly absorbed by water
radio not applicable in water– Must use acoustic channels - low bandwidth, fading
High attenuation– Bandwidth X Range product = 40 Kbps x Km– Very low compared to RF channels (1:100)
• 802.11b/a/g yields up to 5Mbps x Km
Very slow acoustic signal propagation– 1.5x103 m / sec vs. 3x108 m / sec– Causes large propagation delay
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State-of-Art Underwater Acoustics
Reported by Modulation Method Bandwidth Bandwidth Carrier Data Rate Range
Kaya&Yauchi,Oceans'89 16QAM 125kHz 1000kHz 500kbps 60mJones et al.,Oceans'97 DPSK 10kHz 50kHz 20kbps 1kmCapellano et al.,Oceans'97 BPSK 0.2kHz 7kHz 0.2kbps 50km
Courtesy: Kilfoyle & Baggeroer
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Research Challenges UnderWater Acoustic (UW-A) channel:
– Narrow band: hundreds of kHZ at most– Huge propagation latency– High channel error rate
Random topology and sensor node mobility (1--1.5m/s due to water current)
– Existing protocols in terrestrial sensor networks assume stationary sensor nodes;
– In mobile sensor networks, these protocols weakened
Mobility & UW-A channel limitations open the door to very challenging networking issues
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UWSN Protocol Stack
UWSNs must require:– Reliable data transfer (tolerating high error-prone
acoustic channels)– Efficient data delivery (should be energy-efficient) – Localization (for geo-routing or meaningful data) – Time synchronization (for sleep cycle schedule, multiple
access protocol schedule, etc)– Efficient multiple access (sensors are densely deployed)
Design Objective: – Build efficient, reliable, and scalable UWSNs
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Reliable Data Transfer TCP like end-to-end approach does not work
– Large propagation delay large end-to-end delay large bandwidth x delay product– High error-prone acoustic channels high loss rate
Pure ARQ type (hop-by-hop) does not work well– Performance degraded because of frequent ACKs
Possible solutions: – FEC-based hop-by-hop approach with infrequent ACKs
• Have obtained some initial results
– Network coding utilizing multiple paths for robustness• Have started investigation on this
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Efficient Multi-Hop Routing Existing routing protocols in terrestrial WSNs do
not work well in UWSNs – Node mobility changes node neighborhood– Directed diffusion requires too frequent route
enforcement Existing routing protocols in terrestrial ad-hoc
networks do not work well in UWSNs– Proactive: too much overhead to maintain updated topo– Passive: flooding is not efficient, also causes contention
Possible solution: location-based routing– VBF: Vector-Based Forwarding (Networking’06)– More work to improve energy efficiency & robustness
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Localization & Time-Synchronization GPS-free and Mobility are main challenges Existing GPS-free localization & time-sync
schemes (range-based & range-free) – Nodes are usually immobile– Multi-hop schemes usually suffer from
• Poor precision due to high error probability & dynamic network topologies
Considering underwater GPS-like approach – Using multiple surface reference points
Range-based approaches are possible– Need dedicated devices to measure distances
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Efficient Multiple Access Challenges: Large prop. delay & low bandwidth Examine existing MAC protocols
– Scheduled protocols• TDMA: ? CDMA: ?• FDMA: not feasible due to narrow band
– Contention-based protocols• Random access: ALOHA/Slotted ALOHA ?• Carrier sensing access: CSMA (meaningless in UWSN) • Collision avoidance with handshaking: MACA/MACAW ?
Suggested solutions– A cluster architecture:
• CDMA between clusters, TDMA inside clusters
– An adaptive approach • Exploring random access & handshaking
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Acoustic Physical Layer The key is to increase bandwidth
– Current limit: range x rate < 40 kbps x km Explored approaches:
– FSK, PSK, QAM Advanced technologies to examine
– MIMO transmission– Multicarrier communication
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UWSN Lab Testbed @ UCONN
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Testbed Overview
Equipment List:
– Acoustic modem– Underwater speaker– Hydrophone– Sound mixer– Sound receiver– Speaker/microphone– Aquarium
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Micro-Modem Designed and Implemented by WHOI (Woods Hole
Oceanographic Institution)
A Low-power Acoustic Modem
Based on the TMS320C5416 DSP from TI
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Receivers/Speakers
Control-1 150 Watt Two-Way Loudspeaker System
– Good performs in recording studios– Low distortion reproduction – Frequency Range: 70 Hz - 20 kHz
Sony STRDE197 Stereo Receiver
Sennheiser MKE 300 Microphone
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Underwater Speakers
Frequency range: 200 Hz to 32 KHz
Directional at higher frequencies
A completely passive, non-powered device
Can be used as an air speaker or a receive hydrophone
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Aquarian Hydrophone
Output: – 300mW, short-circuit-proof– 3.5mm (mini) phone jack
Power Requirements: – 7mA quiescent current
Usable Frequency Response:
– 20Hz - 100KHz
Polar Response:
– Omni directional
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Behringer SL2442FXPRO Eurodesk 24-Channel Mixer
Ultra-Pure Sound and Crystal-Clear Audio
99 special sound effects: – Reverbs– Delays– Tube distortion– And More!
24 channels
Could simulate different underwater environments
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Water Test Setting Distance between the underwater speaker and hydrophone: 1 meter
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Conclusions and Future Work UWSN
– Is a challenging and promising new area– Requires interdisciplinary efforts from
• Acoustic communication• Signal processing• Network design
Future Work– A long to-do list …– Conducting research at different layers
• reliable transfer, routing, localization, multiple access, acoustic communication, …
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