Acoustic Communications ANCHOR WorkshopFeb 27-Mar 1 2006

Lee Freitag

Woods Hole Oceanographic InstitutionWoods Hole, Massachusetts

Outline• Communications system design

• Applications and Results• High frequency

• Medium Frequency

• Low Frequency

• Networking

• Interoperability

• Standardization

• Recommendations

Frequency Regimes

0.1 1 10 100 1k 10k 100k

Frequency (Hz)

Seismic Tomography

Typical Communications Band 1-50 kHz

Marine Mammals

Ambient Noise Studies

VLF MF VHF

Long-RangeNavigation

LF HF

Layered Architecture

From draft ASTM standard on communications developed by Committee F41, UUVs, with sponsorship from PMS-403 (US Navy).

Frequency Regimes

0.1 1 10 100 1k 10k 100k

Frequency (Hz)

Seismic Tomography

Typical Communications Band 1-50 kHz

Marine Mammals

Ambient Noise Studies

VLF MF VHF

Long-RangeNavigation

LF HF

UUVs and Scientific Applications

Very High-Rate – Shallow Water (15 m)

Test Parameters:• 1.5 km Range• 10 kHz BW• 4 bits per Hertz• 8 channel array (one meter)• 40,000 bps raw, 30,000 bps coded.

Previous Results

Compressed Pre-stored Sidescan Images Transmitted from REMUS at AUV Fest 2001

Two AUV Simultaneous Operation with Acoustic Re-direction for MCM Work

Initial HoldingPattern

Vehicle 2 Path: Re-Acquisition Missions with REMUS equipped with APL-UW Acoustic Lens

Actual Missions Sent Using the Acoustic Modem

Frequency Regimes

0.1 1 10 100 1k 10k 100k

Frequency (Hz)

Seismic Tomography

Typical Communications Band 1-50 kHz

Marine Mammals

Ambient Noise Studies

VLF MF VHF

Long-RangeNavigation

LF HF

Medium Frequency Example: 6 km

Test Parameters:• 6 km Range• 200 m depth• 1.25 kHz BW• 2 bits per Hertz• 8 channel, 8 m array• 2500 bps raw, 2,000 bps coded.

Medium Frequency Example: 44 km

Test Parameters:• 44 km Range• 200 m depth• 1.25 kHz BW• 2 bits per Hertz• 8 channel, 8 m array• 2500 bps raw, 2,000 bps coded.

Frequency Regimes

0.1 1 10 100 1k 10k 100k

Frequency (Hz)

Seismic Tomography

Typical Communications Band 1-50 kHz

Marine Mammals

Ambient Noise Studies

VLF MF VHF

Long-RangeNavigation

LF HF

VLF Example: AET Tomography Signal 3200 km

Test Parameters:• 3200 km Range• Pacific Ocean• 37.5 Hz BW• 1 bit per Hertz• 20 channel array• 37.5 bps max raw, 0.1-20 bps coded, depending on array.

VLF Example: AET Tomography Signal 3200 km

Test Parameters:• 3200 km Range• Pacific Ocean• 37.5 Hz BW• 1 bit per Hertz• 20 channel array• 37.5 bps max raw, 0.1-20 bps coded, depending on array.

Interoperability

Application Layer: Compact Control Language (CCL)

• Standardized messages for TIME, POSITION, BATTERY, etc.

Surf-Zone Crawler Cetus II

REMUS Search-Classify-Map

Physical Layer: WHOI Frequency-Hopping Standard

• Low-rate (80 bps) standard for inter-operable modem communications.

Solar AUV: WHOI and Benthos Acoustic Modems

Real-Time Data: Two different Modems

Multi-Vehicle Command and Control and Interoperability

Multi-vehicle operations using a common acoustic navigation network and common command and control structure at AUV Fest 2003 and 2005

Surf-Zone Crawlers

Cetus II

REMUS AUVs

Gateway Buoys

Bluefin Sea Lion

Nekton Ranger

Compact Control Language Spec.

Example Message Format (Re-Direct)

typedef struct { unsigned char mode; // MDAT_REDIRECT unsigned char

message_number;LATLON_COMPRESSED lat; // Center of search

LATLON_COMPRESSED lon; // Center of search char speed_depth_flags;

unsigned short depth_goal_encoded_transit; char speed_encoded_transit; unsigned char device_cmd_transit; //range. unsigned short depth_goal_encoded_survey; char speed_encoded_survey; unsigned char device_cmd_survey;unsigned char num_rows; // 0 if not rows. unsigned short row_length; // in meters unsigned char

spacing_0; // in meters unsigned char spacing_1; // in meterschar heading_encoded; LATLON_COMPRESSED lat_start; // ack only, where

started LATLON_COMPRESSED lon_start; char spare[3]; } MODEM_MSG_DATA_REDIRECT;

Messages are documented in detail using C-language structures with example hex dumps for use in validation.

Example Message: Bathymetry

Table 1: Bathymetry Message Fields

Bytes

Description

116699

Message type indicatorSpare byteDepth[3]Altitude[3]Latitude[3]Longitude[3]

32 Total bytes used

Example Message: Redirect Survey

Table 2: Redirect Message Fields

Bytes

Description

1133121121112111333

Message type indicatorSpare byteLatitude of center of search areaLongitude of center of search areaSpeed/Depth FlagsDepth goal encoded transitSpeed encoded transitDevice command transitDepth goal encoded transitSpeed encoded transitDevice command transitNumber of rowsRow length (meters)Row spacing (odd rows)Row spacing (even rows)HeadingLatitude of start (in acknowledgement)Longitude of start (in acknowledgement)Spare bytes

32 Total bytes used

Network Access Protocol Prof. J. Schindall & R. Kanthan

Objectives:• To allow all AUVs to cooperatively

communicate and navigate in the field without centralized access control.

• Create fair access protocol.• Allow “desperate” node to go first.Status: Thesis complete & available.

0 % Collided 100Slow

Fast

Msg

Rat

e

0 % Collided 100Slow

Fast

Msg

Rat

e

4-Way Handshake AlgorithmSimple (Greedy) Algorithm

Modular Acoustic Communications Vision

Acoustic Channel

Proprietary Modulation

N Types

Standard Modulation

M Types

Acoustic Modem

Manufacturer 1

Modem Interface & Driver

Standard Acoustic Modem Software API

NetworkType 1

NetworkType N

Standard Modulation

M Types

Acoustic Modem

Manufacturer P

Modem Interface & Driver

Proprietary Modulation

N Types

Different types of networks can be supported on top of multiple modems: Fixed, ad-hoc, etc.

Common API allows network development to be independent of modem

Modems Support open, proprietary and Navy-only protocols.

Recommendations• Confirm draft requirements vis-à-vis:

• Platform needs and capabilities (size, etc.)

• Development effort (risk)

• Infrastructure cost

• Operations and Maintenance

• Develop functional specification to capture requirements

• Describe notional implementation which is:

• Modular & Layered

• Standardized (interoperable at various levels)

• Isolates high-risk & developmental areas

Questions?