Title: AquaNode: A Solution for Wireless Underwater Communication
1AquaNode A Solution for Wireless Underwater
Communication
- Ryan Kastner
- Department of Electrical and Computer Engineering
- University of California, Santa Barbara
- CREON GLEON Workshop
- March 30, 2006
2Monitoring in Moorea
- Establish monitoring sites in lagoons and on fore
reefs surrounding Moorea - Response variables measured
- Weather
- Tides, Currents and Flows
- Ocean Temperature Color
- Salinity, Turbidity pH
- Nutrients
- Recruitment Settlement
- Size Age Structure
- Species Abundance
- Community Diversity
Underwater wireless enabling technology for Moorea
3Why Use Wireless Underwater?
- Wired underwater not feasible in all situations
- Temporary experiments
- Tampering/breaking of wires
- Significant cost for deployment
- Experiments over longer distances
- Ocean observatories
- ORION, LOOKING, MARS, NEPTUNE
- Not ideal for coral reefs, lakes
- AquaNode can easily be used in conjunction with
observatories - Why not use radios and buoys?
- Common use is buoy with mooring commercial
radio on buoy to satellite, shore, - Buoys/equipment get stolen
- Cable breakage, ice damage
Underwater wireless will enable new experiments
complement existing technologies
4Scenario for WetNet for Eco-Surveillance
- Deploy Ad hoc wireless (acoustic) network in
lagoon - Network consists of AquaNodes with Conductivity,
Temperature, Depth (CTD) sensors (and many
others) - Ad hoc network allows AquaNodes to relay data to
a dockside collector - AquaNode requirements
- Low cost, low power wireless modems
- Integral router
- Integral CTD sensor suite
- Additional nitrate, oxygen chemical sensors
- Real-time data from Moorea available on Web
5Underwater Acoustic Channel
- Severe multipath - 1 to 10 msec for shallow water
at up to 1 km range - Doppler Shifts
- Long latencies speed of sound underwater approx
1500 m/sec
Dock
AquaNodes with acoustic modems/routers, sensors.
6WetNet using Aquanodes
CTD, currents, nutrient data to Internet.
Adaptive sampling commands to AquaNodes.
Wi-Fi or Wi-Max link
Dockside acoustic/RF comms and signal processing.
Cabled hydrophone array
Dock
Data collection sites with acoustic
modems/routers, sensors, mooring and underwater
floats
7AquaNode
Software Defined Acoustic Modem
Transducer
Float
Router
Modem Circuitry
Batteries
Sensor Interface
Sensors
Mooring
8Hardware Platform
- Ideal One piece of hardware for all sensor nodes
- Hardware is wirelessly updatable no need to
retrieve equipment to update hardware for
changing communication protocols, sampling,
sensing strategies
Transducer
CTD Sensor
Reconfigurable Hardware Platform
9Hardware Platform Interfaces
- Sensor Interface
- Must develop common interface with different
sensors (CTD, chemical, optical, etc.) and
communication elements (transducer) - Wide (constantly changing) variety of sensors,
sampling strategies
- Communication Interface
- Amplifiers, Transducers
- Signal modulation
- Hardware
- Software Defined Acoustic Modem (SDAM)
- Reconfigurable hardware known to provide,
flexible, high performance implementations for
DSP applications
Transducer
CTD Sensor
Reconfigurable Hardware Platform
10Acoustic Modem Requirements
- Complex, computationally intensive communication
protocols - Limited power/energy
- Ease of use Good design tools, plug-n-play,
reprogrammable
Transducer
Communication Protocol
CTD Sensor
Reconfigurable Hardware Platform
Plug-N-Play
Mapping
11Design Considerations for SDAM
- Multipath Spread Range of 1 to 10 milliseconds
for shallow water at up to 1 km range - Larger bandwidths reduce frequency dependent
multipaths - Transducers
- Size/weight/cost proportional to wavelength
- Acceptable propagation losses at 100 meter ranges
- Waveform
- M-FSK signaling
- Datasonics/Benthos modems (used in Seaweb, FRONT)
- Narrowband thus sensitive to frequency-selective
fading. - Use more tones increasing sensitivity to
Doppler spread. - Walsh/m-sequence signaling (Direct-sequence)
- Provides frequency diversity due to wide
bandwidth - Can be detected noncoherently
12What about existing modems?
- Commercial modems (Benthos, Linkquest)
- Too expensive, power hungry for Eco-Sensing.
Proprietary algorithms, hardware. - M-FSK (Scussel, Rice 97, Proakis 00) does use
frequency diversity, but requires coding to
erase/correct fades. - Navy modems
- Need open architecture for international LTER
community precludes military products. - Direct-sequence, QPSK, QAM, coherent OFDM
- Great deal of work on DS, QPSK for underwater
comms. But equalization, channel estimation are
difficult. (Stojanovic 97, Freitag, Stojanovic
2001, 2003.) - MicroModem (WHOI)
- Best available solution for WetNet.
- FSK/Freq. Hopping relies on coding to correct bad
hops.
But can we do better? Less power? Wider
bandwidth?
13AquaModem Data Sheet
Sonatech Transducer
lt 1 meter
TI 2812 DSP with CompactFlash, ADC, DAC
Power Amp and Transducer Matching Network
14Walsh/m-Sequence Waveforms
Chip rate 5 kcps, approx. 5 kHz bandwidth.
Uses 25 kHz carrier. Use 7 chip m-sequence c per
Walsh symbol, 8 bits per Walsh symbol bi.
Composite symbol duration is thus T 11.2 msec.
(Longer than maximum multipath spread.) Symbol
rate is 266 bps, or 133 bps using 11.2 msec. time
guard band for channel clearing.
11 msec.
15Transmitted Signal
1
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1
16Walsh/m-sequence Signal Parameters
1
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178 Walsh Symbols
18UWA Walsh/m-sequence GMHT-MP Modem
Generalized multiple hypothesis test (GMHT)
19Acoustic Modem Performance
- True multipath intensity profile (MIP)
- Nf paths assumed by MP estimation
- N? Number of paths present
MP identifies major paths using one symbol of
information
20Acoustic Modem Performance
- Symbol Error Rate (SER)
- Signal to noise ratio (Es/N0)
- Nf paths assumed by MP estimation
- N? Number of paths present
21Required Transmit Power
- Transmit power control
- Adapt automatically to field conditions, Use only
enough to get reliable links - Often use small of amplifier capacity ?
Significant reduction in system energy use
22Energy Usage
In most cases CPU power dominates (when using low
transmit power)
For all links up to 400 meters, projected energy
use is 50 mJ per bit
23Battery life
- System example uses alkaline D cells
- (low self discharge, good J / )
- 16 or 32 cells 1.3 or 2.6 MJ respectively
- At 50 mJ per bit, with 16 cell battery,
- endurance days 300 / rate bps
24AquaModem Air Tests
UCSB Engineering 1 Hallway
7
6
Symbols Sent 144 Packets Sent 36 Symbol
Error 1.4 Packet Error 5.6
7
10
18
5
5
11
7
233
7
6
Symbols Sent 360 Packets Sent 90 Symbol
Error 1.1 Packet Error 4.4
7
10
18
5
5
11
7
233
7
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Symbols Sent 192 Packets Sent 48 Symbol
Error 10 Packet Error 20.1
7
10
18
5
5
11
7
233
Transmitter Location
Receiver Location
25Challenges
- Power
- Communication
- Transducer size/weight/cost proportional to
wavelength - Adaptive power control
- Computation
- Microprocessors extremely power hungry
- Move towards FPGA, ASIC
- Cost
- Communication
- Current transducer 3K US
- Fish finders? (lt 100 US )
- Computation
- Data rates arent particularly high ? simple
microprocessors - Communication protocols complex ? DSP, FPGAs
- Low power/energy will cost money ? FPGA, ASIC
- Ease of use
- Plug-n-play interfaces to sensors
- Change network/communication protocols
- Adjust sampling strategies
26Credits
- Investigators Ron Iltis, Hua Lee, Ryan Kastner
- ExPRESS Lab http//express.ece.ucsb.edu/
- Telemetry Lab http//telemetry.ece.ucsb.edu/
- AquaNode Research Team
- Research Tech Maurice Chin
- PhD Students Bridget Benson, Daniel Doonan,
Tricia Fu, Chris Utley - Undergrads Brian Graham
- http//aquanode.ece.ucsb.edu/
- Sponsor