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

2. 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

3. INTRODUCTION

4. 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)

5. 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)

6. 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)

7. 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)

8. 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

9. COMMS ARCHITECTURE

10. 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

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

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

13. 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

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

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

16. 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

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

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

19. UW-ASN:DESIGN CHALLENGES

20. 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

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

22. 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

23. MEDIUM ACCESS CONTROL LAYER
Biomimetic Underwater Robot, Robolobster

24. 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)

25. 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

26. 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

27. 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)

28. 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

29. NETWORK LAYER

30. 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

31. 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

32. 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

33. 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

34. 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

35. TRANSPORT LAYER

36. 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

37. 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

38. 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

39. Clusters in Mobile Ad hoc Networks

40. 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

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

42. 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

43. 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

44. 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
Hayat DOUKKALI and Loutfi NUAYMI. Analysis of MAC protocols for Underwater Acoustic Data Networks /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.

45. Questions ?
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