Acoustic Communications ANCHOR Workshop Feb 27-Mar 1 2006 Lee Freitag Woods Hole Oceanographic Institution Woods Hole, Massachusetts

Outline Communications system design Applications and Results High frequency Medium Frequency Low Frequency Networking Interoperability Standardization Recommendations

Typical Communications Frequency Regimes VLF LF MF HF VHF Ambient Noise Studies Marine Mammals Typical Communications Band 1-50 kHz Long-Range Navigation Seismic Tomography 0.1 1 10 100 1k 10k 100k Frequency (Hz)

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

Typical Communications Frequency Regimes VLF LF MF HF VHF Ambient Noise Studies Marine Mammals Typical Communications Band 1-50 kHz Long-Range Navigation Seismic Tomography 0.1 1 10 100 1k 10k 100k Frequency (Hz)

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 Vehicle 2 Path: Re-Acquisition Missions with REMUS equipped with APL-UW Acoustic Lens Initial Holding Pattern Actual Missions Sent Using the Acoustic Modem

Typical Communications Frequency Regimes VLF LF MF HF VHF Ambient Noise Studies Marine Mammals Typical Communications Band 1-50 kHz Long-Range Navigation Seismic Tomography 0.1 1 10 100 1k 10k 100k Frequency (Hz)

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.

Typical Communications Frequency Regimes VLF LF MF HF VHF Ambient Noise Studies Marine Mammals Typical Communications Band 1-50 kHz Long-Range Navigation Seismic Tomography 0.1 1 10 100 1k 10k 100k Frequency (Hz)

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 Physical Layer: WHOI Frequency-Hopping Standard Low-rate (80 bps) standard for inter-operable modem communications. Application Layer: Compact Control Language (CCL) Standardized messages for TIME, POSITION, BATTERY, etc. Surf-Zone Crawler Cetus II Solar AUV: WHOI and Benthos Acoustic Modems Real-Time Data: Two different Modems REMUS Search-Classify-Map

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 Gateway Buoys Nekton Ranger REMUS AUVs Cetus II Bluefin Sea Lion

Compact Control Language Spec. Messages are documented in detail using C-language structures with example hex dumps for use in validation. 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 meters char heading_encoded; LATLON_COMPRESSED lat_start; // ack only, where started LATLON_COMPRESSED lon_start; char spare[3]; } MODEM_MSG_DATA_REDIRECT;

Table 1: Bathymetry Message Fields Example Message: Bathymetry Table 1: Bathymetry Message Fields Bytes Description 1 6 9 Message type indicator Spare byte Depth[3] Altitude[3] Latitude[3] Longitude[3] 32 Total bytes used

Table 2: Redirect Message Fields Example Message: Redirect Survey Table 2: Redirect Message Fields Bytes Description 1 3 2 Message type indicator Spare byte Latitude of center of search area Longitude of center of search area Speed/Depth Flags Depth goal encoded transit Speed encoded transit Device command transit Number of rows Row length (meters) Row spacing (odd rows) Row spacing (even rows) Heading Latitude 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 100 0 % Collided 100 Slow Fast Msg Rate Slow Fast Msg Rate Approach: Development of message-based protocol for shared channel communication and navigation Implementation of protocol in black-box translator units for existing systems Construction of firmware updates to implement protocol in newer systems Simple (Greedy) Algorithm 4-Way Handshake Algorithm

Modular Acoustic Communications Vision Acoustic Channel Proprietary Modulation N Types Standard M Types Acoustic Modem Manufacturer 1 Modem Interface & Driver Standard Acoustic Modem Software API Network Type 1 Type N Manufacturer P 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?