AquaNode: A Solution for Wireless Underwater

Communication

Ryan KastnerDepartment of Electrical and Computer

EngineeringUniversity of California, Santa Barbara

CREON & GLEON WorkshopMarch 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

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

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: 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

lagoon

MOOREA

Lab

Aquanodes

Collection station withacoustic sensor array

Ad hoc networkbetween Aquanodesensors.

Underwater Acoustic Channel

AquaNodes with acoustic modems/routers, sensors.

Dock

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

WetNet using Aquanodes

Dock

Dockside acoustic/RF comms and signal processing.

Cabled hydrophone array

Wi-Fi or Wi-Max link

CTD, currents, nutrient data to Internet. Adaptive sampling commands to AquaNodes.

Data collection sites with acoustic modems/routers, sensors, mooring

and underwater floats

Float

SensorsBatteries

Transducer

Router

Software Defined Acoustic Modem

Sensor Interface

Modem Circuitry

Mooring

AquaNode

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

Reconfigurable Hardware Platform

TransducerCTDSensor

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

Reconfigurable Hardware Platform

TransducerCTDSensor

Communication Interface: Amplifiers, Transducers Signal modulation Hardware:

Software Defined Acoustic Modem (SDAM) Reconfigurable hardware known to provide,

flexible, high performance implementations for DSP applications

Complex, computationally intensive communication protocols Limited power/energy Ease of use: Good design tools, plug-n-play, reprogrammable

Acoustic Modem Requirements

Reconfigurable Hardware Platform

Transducer

Mapping

CTDSensor

Communication Protocol

Plug-N-Play

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…)

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?

AquaModem Data SheetSignal 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

Power Amp and Transducer Matching Network

TI 2812 DSP with CompactFlash, ADC, DAC

< 1 meterSonatech Transducer

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

Note: 112 Nyquist samples/symbol + 112 samples for channel clearing.

MatchingPursuitCore

MatchingPursuitCore

MatchingPursuitCore

MatchingPursuitCore

arg

min i

Generalized multiple hypothesis test (GMHT)

Acoustic Modem Performance

Nf: # paths assumed by MP estimation

N: Number of paths present

MP identifies major paths using one symbol of information

True multipath intensity profile (MIP)

Acoustic Modem Performance

14 15 16 17 18 19 20 21 2210

-4

10-3

10-2

10-1

Es/N

0

SE

R

AquaNode/GMHT-MP N =12 Nf =16

RAKE N =12 Nf =16

FSK/SFH N =12 Nf =16

Symbol Error Rate (SER)

Signal to noise ratio (Es/N0)

Nf: # paths assumed by MP estimation

N: Number of paths present

> 4 dB gain over FSK @ .5 x 10-3 SER

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

Required Transmit Power

Energy used while “asleep” < 10% of

total

Energy used per bit transceived ≈

constant

Energy Usage

For all links up to 400 meters, projected

energy use is ≤ 50 mJ per bit

In most cases CPU power dominates (when using low transmit power)

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 TestsUCSB Engineering 1 Hallway

233’

18’

7’

7’5’ 5’ 11’

6’

7’

10’

233’

18’7’

7’5’ 5’ 11’

6’

7’

10’

Transmitter Location

Receiver Location

233’

18’

7’

7’5’ 5’ 11’

6’

7’

10’

# Symbols Sent: 144# Packets Sent: 36Symbol Error: 1.4%Packet Error: 5.6%

# Symbols Sent: 360# Packets Sent: 90Symbol Error: 1.1%Packet Error: 4.4%

# Symbols Sent: 192# Packets Sent: 48Symbol Error: 10%Packet Error: 20.1%

Challenges 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? (< 100 US $)

Computation 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: