AquaNode: 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
Monitoring 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
Lagoon
Fore reef
Underwater wireless enabling technology for Moorea
Why Use Wireless Underwater?

Wired underwater not feasible in all situations





Ocean observatories




Temporary experiments
Tampering/breaking of wires
Significant cost for deployment
Experiments over longer distances
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
Scenario 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:





Aquanodes
Lab
MOOREA
Ad hoc network
between Aquanode
sensors.
Low cost, low power wireless
modems
Integral router
Collection station with
Integral CTD sensor suite
Additional nitrate, oxygen chemical acoustic sensor array
sensors
Real-time data from Moorea
available on Web
lagoon
Underwater 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.
WetNet 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.
Dock
Cabled hydrophone array
Data collection sites with acoustic
modems/routers, sensors, mooring
and underwater floats
AquaNode
Transducer
Router
Software
Defined
Acoustic
Modem
Float
Modem
Circuitry
Sensor
Interface
Batteries
Sensors
Mooring
Hardware 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

CTD
Sensor
Transducer
Reconfigurable
Hardware Platform
Hardware 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
CTD
Sensor
Transducer
Reconfigurable
Hardware Platform
Acoustic Modem Requirements



Complex, computationally intensive communication protocols
Limited power/energy
Ease of use: Good design tools, plug-n-play, reprogrammable
Communication Protocol
Transducer
CTD
Sensor
Mapping
Reconfigurable
Hardware Platform
Design 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
What about existing modems?

Commercial modems: (Benthos, Linkquest…)



Navy modems:


Need open architecture for international LTER community – precludes
military products.
Direct-sequence, QPSK, QAM, coherent OFDM


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.
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?
AquaModem Data Sheet
Signal and Data Parameters
Data rate: 133 bps
Chip duration Tc = .2 msec.
Symbol duration Tsym = 11.2 msec.
Time guard interval Tc = 11.2 msec.
M-sequence length Lpn = 7 chips.
Walsh sequence length Nw = 8
Bandwidth = 5 kHz
Carrier Frequency fc = 25 kHz
Nominal range 100 – 300 m.
Power Consumption Overview
Load
Tx State Rx State Sleep State
CPU
440 mW 440 mW .30 mW
CPU I/O
420 mW 420 mW .15 mW
Flash Memory 165 mW 165 mW .10 mW
Power Amp.
7.2 W
.05 mW .05 mW
Battery Total
9.3 W
2.1 W
10 mW
Battery Life (Based on 20 amp-hours)
Tx Duty Cycle
Rx Duty Cycle Days
.1%
.2 %
624
.5%
1%
189
1%
2%
101
Sonatech
Transducer
TI 2812 DSP with CompactFlash, ADC, DAC
Power Amp and Transducer Matching Network
Walsh/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.
Transmitted Signal



  
1
1
-1 1
-1 -1 -1 -1
-1
1 -1
1
1 1
1
1
-1 1
-1 -1 -1
Walsh/m-sequence Signal Parameters



  
1
1
-1 1
-1 -1 -1 -1
-1
1 -1
1
1 1
1
1
-1 1
-1 -1 -1
8 Walsh Symbols
UWA Walsh/m-sequence
GMHT-MP Modem
Matching
Pursuit
Core
arg min
i
Matching
Pursuit
Core
Matching
Pursuit
Core
Note: 112 Nyquist
samples/symbol +
112 samples for
channel clearing.
Matching
Pursuit
Core
Generalized multiple hypothesis test (GMHT)
Acoustic 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
Acoustic Modem Performance
 Symbol
-1
10
-2
10
> 4 dB gain over
FSK @ .5 x 10-3 SER
SER
Error
Rate (SER)
 Signal to noise
ratio (Es/N0)
 Nf: # paths
assumed by MP
estimation
 N: Number of
paths present
-3
10
AquaNode/GMHT-MP N =12 Nf =16
RAKE N =12 Nf =16
FSK/SFH N =12 Nf =16
-4
10
14
15
16
17
18
Es /N0
19
20
21
22
Required Transmit Power
10dB = 90% reduction in
amplifier power for all links
less than 450 meters
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
Energy 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
Energy used per bit
transceived ≈ constant
Energy used while
“asleep” < 10% of total
Battery 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]
AquaModem Air Tests
7’
UCSB Engineering 1 Hallway
7’
18’
5’
10’
5’
6’
# Symbols Sent: 144
# Packets Sent: 36
Symbol Error: 1.4%
7’
Packet Error: 5.6%
6’
# Symbols Sent: 360
# Packets Sent: 90
7’ Symbol Error: 1.1%
Packet Error: 4.4%
11’
233’
7’
7’
18’
5’
10’
5’
11’
233’
7’
7’
18’
233’
Transmitter Location
Receiver Location
5’
10’
6’
5’
11’
# Symbols Sent: 192
# Packets Sent: 48
7’ Symbol Error: 10%
Packet Error: 20.1%
Challenges

Power

Communication



Computation



Microprocessors extremely power hungry
Move towards FPGA, ASIC
Cost

Communication



Current transducer ~ 3K US $
Fish finders? (< 100 US $)
Computation




Transducer size/weight/cost proportional to wavelength
Adaptive power control
Data rates aren’t 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
Credits
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: