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

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

3. 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)

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

5. 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)

6. UUVs and Scientific Applications

7. 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.

9. Previous Results

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

11. 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

12. 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)

13. 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.

14. 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.

15. 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)

18. 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, bps coded, depending on array.

19. 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, bps coded, depending on array.

20. 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

21. 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

22. 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;

23. 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

24. 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

25. 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.
% Collided
% Collided
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

26. 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.

27. 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

28. Questions?