xiuzhen cheng [email protected] xiuzhen cheng [email protected] [email protected] csci332 mas networks –...
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Xiuzhen ChengXiuzhen Cheng [email protected]
CsciCsci332332 MAS Networks – Challenges MAS Networks – Challenges and State-of-the-Art Research and State-of-the-Art Research – – Underwater Sensor NetworksUnderwater Sensor Networks
Introduction
Underwater acoustic sensor networks consist of a variable number of sensors and vehicles that are deployed to perform collaborative monitoring tasks over a given area.
Acoustic communications are the typical physical layer technology
Radios propagate to long distance only at extra low frequencies, with a large antennae and high transmission power
Mica mote can transmit to 120cm at 433MHz in underwater
Applications
Ocean Sampling Networks
Environmental (chemical, biological, and nuclear) monitoring
Water quality in situ analysis
Undersea explorations (for oilfields, minerals, reservoirs, for determining routes for laying undersea cables, etc.)
Disaster prevention (earthquakes, etc.)
Assisted navigation
Distributed tactical surveillance
Mine reconnaissance
Challenges
Severely limited bandwidth
Severely impaired channel
Propagation delay is 5 times longer
High bit error rates, intermittent connectivity
Battery power
Underwater sensors are error-prone due to fouling and corrosion
Challenges to enable 3D monitoring
Sensing coverageNeed collaborative regulation on sensor depth
Communication coverageConnectivity requirement
Autonomous Underwater Vehicles
Can reach any depth in the ocean
The integration of fixed sensor networks and AUVs is an almost unexplored research area
Adaptive sampling (where to place sensors?)
Self-configuration (where there is a failure?)
Design Challenges (1/2)
Difference with terrestrial sensor networksCost (more due to complex transceivers and hardware protection), deployment (sparser due to cost), power (higher due to long transmission range and complex DSP), memory (larger due to intermittent connectivity), spatial correlation (less likely to happen due to sparser deployment)
Underwater sensorsProtecting frames, many underwater sensors exist
New design: Develop less expensive, robust, “nano-sensors”
Devise periodical cleaning mechanisms against corrosion and fouling
Design robust, stable sensors on a high range of temperatures
Design integrated sensors for synoptic sampling of physical, chemical, and biological parameters
Design Challenges (2/2)
A cross-layer protocol stackAll the layers in the TCP/IP model
Need a power management plane, a coordination plane, and a localization plane
Real-time vs. delay-tolerant networkingApplication driven
Basics of Acoustic Propagation
Available bandwidth for different ranges in UW-A channels
Range [km] Bandwidth [kHz] Very long 1000 <1 Long 10–100 2–5 Medium 1-10 around 10Short 0.1–1 20–50 Very short <0.1 >100
Underwater acoustic communications are mainly influenced by path loss, noise, multipath, Doppler spread, and high and variable propagation delay
Physical Layer
Evolution of modulation technique Type Year Rate [kbps] Band [kHz] Range [km]a FSK 1984 1.2 5 3s PSK 1989 500 125 0.06d FSK 1991 1.25 10 2d PSK 1993 0.3–0.5 0.3–1 200d–90s PSK 1994 0.02 20 0.9s FSK 1997 0.6–2.4 5 10d–5s DPSK 1997 20 10 1d PSK 1998 1.67–6.7 2–10 4d–2s 16-QAM 2001 40 10 0.3s
a The subscripts d and s stand for deep (>=100m) and shallow water (<100)
New development needed for inexpensive transceiver modems, filters, etc.
Data Link Layer
Challenges: low bandwidth and high/variable delayFDMA is not suitable due to low bandwidth
TDMA is not suitable due to the variable delay (long-term guards)
CSMA is not efficient since it only prevents collision at the transmitter side
Contention-based schemes that rely on RTS/CTS are not practical due to the long/variable delay
CDMA is promising due to its robustness again fading and Doppler spreading especially in shallow water
Challenges: Error control functionalities are neededARQ, FEC, etc.
Open research issuesOptimal data packet length for network efficiency optimization
CDMA code, encoders and decoders, etc.
Network Layer
From sensors to surface stations
3D routingExisting routing schemes (proactive, reactive, and geographical routing schemes) may be tailored for underwater sensor networks
ChallengesLong/variable delay
Intermittent connectivity
Accurate modeling of the dynamics of the data transmission
Route optimization
The integration of AUV and sensors
Location discovery techniques for geographical routing protocols
Transport LayerTotally unexplored area
Underwater sensor networks necessitate a new event transport reliability notion
Traditionally transport layer provides robust end-to-end approach
Challenges: long/variable delayNeeds flow control and congestion control
Most existing TCP implementations are unsuited due to the window-based flow/congestion control mechanisms (RTT is needed)
Rate-based transport protocols may not work due to the dependency on feedback control messages
Packet loss caused by high bit error rate
New strategies may be needed!
Open research issues: Abundant!
Application Layer
Largely unexplored
PurposesTo provide a network management protocol
To provide a language for query the sensor networks
To assign tasks and to advertise events/data
Experimental Implementations
The Front-Resolving Observational Network with Telemetry (FRONT) project at u Connecticut
Sensors, repeaters, and gateways
Sensors are connected to acoustic modems
Repeaters are acoustic modems to relay data
Gateways are surface buoys
Experiment conducted: 20 sensors and repeaters are deployed in shallow water
AOSN program at the Monterey Bay Aquarium Research Institute
To study the upwelling of cold, nutrient-rich water in the Monterey Bay.