Transcript Underwater Sensor Nets

Csci332 MAS Networks – Challenges
and State-of-the-Art Research
– Underwater Sensor Networks
Xiuzhen Cheng
[email protected]
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
Two-dimensional Sensor Networks
Two acoustic radios
RF
Three-dimensional sensor networks
floating
buoy
anchor
Challenges to enable 3D monitoring
Sensing coverage
Need collaborative regulation on sensor depth
Communication coverage
Connectivity 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 networks
Cost (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 sensors
Protecting 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 stack
All the layers in the TCP/IP model
Need a power management plane, a coordination plane, and a
localization plane
Real-time vs. delay-tolerant networking
Application driven
Basics of Acoustic Propagation
Underwater acoustic communications are mainly
influenced by path loss, noise, multipath, Doppler spread,
and high and variable propagation delay
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 10
Short
0.1–1
20–50
Very short
<0.1
>100
Physical Layer
New development needed for inexpensive transceiver modems, filters, etc.
Evolution of modulation technique
Type Year Rate [kbps] Band [kHz]
FSK 1984 1.2
5
PSK 1989 500
125
FSK 1991 1.25
10
PSK 1993 0.3–0.5
0.3–1
PSK 1994 0.02
20
FSK 1997 0.6–2.4
5
DPSK 1997 20
10
PSK 1998 1.67–6.7
2–10
16-QAM 2001
40
10
Range [km]a
3s
0.06d
2d
200d–90s
0.9s
10d–5s
1d
4d–2s
0.3s
a The subscripts d and s stand for deep (>=100m) and shallow water (<100)
Data Link Layer
Challenges: low bandwidth and high/variable delay
FDMA 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 needed
ARQ, FEC, etc.
Open research issues
Optimal data packet length for network efficiency optimization
CDMA code, encoders and decoders, etc.
Network Layer
From sensors to surface stations
3D routing
Existing routing schemes (proactive, reactive, and geographical
routing schemes) may be tailored for underwater sensor networks
Challenges
Long/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 Layer
Totally unexplored area
Underwater sensor networks necessitate a new event
transport reliability notion
Traditionally transport layer provides robust end-to-end approach
Challenges: long/variable delay
Needs 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
Purposes
To 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.