1. SignalEx: Linking environmental acoustics with the signaling schemes
Michael Porter
Ocean Sciences Division
Science Applications International
and
Keyko McDonald, Paul Baxley, Joseph Rice
Space and Naval Warfare Systems Center
San Diego, CA

2. Outline Motivation Case study: Front engineering test SignalEx tests
Telesonar testbeds
Sites b, c, d
Measured channel impulse response
Predicted channel impulse response
Performance of a DPSK/DSSS system

3. The National Oceanographic Partnership Program (NOPP) FRONT system is being installed by a consortium led by U. Conn
Cellular modems relay data to shore from the Montauk Point and Block Island USCG buoys
ADCP sensor nodes with trawl-resistant bottom frame design
Diver-free recovery: acoustic release holds ball floats, line packed in canister.
Acoustic modem (azimuthal omnidirectional 409 transducer) at apex; all other components below its lower plane.
Smooth outer surface to limit snaring of fishing gear.
9-km
spacing

4. Upward refraction in FRONT-1 caused strong dependence on the sea-surface boundary
SignalEx
BER=0 (%)
S/N (dB)
Wind (kts)
Depth (m)
Sound speed (m/s)
Range (m)
Year-day

5. Summary The environment can have a big effect on modem performance
SignalEx
Summary
The environment can have a big effect on modem performance
These effects are not well understood
SignalEx program
study a variety of modems in diverse environments
learn which work … and when
optimize modem parameters
develop and validate a channel model to provide a predictive capability for modem performance
Result: ’Smart Modem’ selects best operating mode for the channel

6. Modem schemes tested in SignalEx
type
Method
Analysis group a
Multi-frequency shift keyed (MFSK)
SAIC/SPAWARSSC b
Frequency-Hopped FSK (FH-MFSK)
Benthos x
Differential phase-shift keyed (DPSK)
Northeastern Univ. d
N-QAM (BPSK, QPSK, 16-QAM)
Northeastern Univ., Delphi, NUWC, Benthos e
Pulse-Position Modulation (PPM) g
Orthogonal Frequency Division Multiplexing (OFDM)
Polytechnic Univ. h
Multi-Carrier Code Division Multiple Access (MC-CDMA)

7. Telesonar testbeds Mk-1 SignalEx Mk-2, 2000-01 Mk-1, 1998-99 Mk-1
Sublink’98

8. SignalEx waveform LFM chirps (8-11 kHz) Type-a MFSK waveforms
7-tone comb
LFM chirps
(8-16 kHz)
Type-x DPSK waveforms

9. SignalEx spectrogram LFM chirps Type-a MFSK waveforms (8-11 kHz)
7-tone comb
LFM chirps
(8-16 kHz)
Type-x DPSK waveforms

10. SignalEx 2000 experiment locations
SX-D
Buzzard’s Bay
(in SeaWeb00)
August 10-11, 2000
SX-C
San Diego
(in SubLink00)
May 23-25, 2000
SX-B
New England Shelf
(in ForeFront)
April 17-20, 2000

11. SignalEx-B in ForeFRONT (New England Shelf)
April 17-20, 2000

12. SignalEx-C in Sublink (Point Loma) May 23-25, 2000

13. SignalEx-D (Buzzard’s Bay) August 10-11, 2000

14. Ray/beam trace and incoherent TL

15. CTD Record

16. Predicted Impulse Response

17. SX-B (New England Shelf) impulse response
SignalEx
SX-B (New England Shelf) impulse response

18. SX-C (San Diego) Eigenrays and impulse response

19. SX-D (Buzzard’s Bay) impulse response
Drift 1: km
Drift 2: km
Drift 3: km

20. Type-x (DPSK) bit error rates
SignalEx
Type-x (DPSK) bit error rates
Range = 5 km
Range = 7 km

21. MFSK BER

22. DSSS/DPSK (type-x) Transmitter
½ rate, contraint length 7 convolutional coder
(interleaver)
Gold sequence for spreading (4000 chips/sec)
BPSK on I/Q channels (QPSK out) (12 kHz carrier)
Shaping filter
Receiver
RAKE receiver, variable number of taps (or sparse)
Delay-locked loop
Viterbi decoder, 35 stage lookback
(John Proakis/Ethem Sozer Delphi/NEU)

23. SignalEx
DSSS/DPSK (type-x) bit errors in SX-B 400-bit transmissions 8 kHz bandwidth

24. DSSS/DPSK bit errors in SX-C 64-bit transmissions; 3 kHz bandwidth
SignalEx
R=3 km
R=5 km

25. DSSS/DPSK bit errors in SX-D (Drift 1) 500-bit transmissions; 8 kHz bandwidth
SignalEx
Channel errors
Convolutional coding

26. DSSS/DPSK bit errors in SX-D (Drift 3) 500-bit transmissions; 8 kHz bandwidth
SignalEx
Channel errors
Convolutional coding

27. Summary
Channel impulse response is well-predicted by classical multipath picture
Type-x multi-access DPSK performs reliably at 100 bps in all cases tested to date (ranges from 0-7 km)
Further SignalEx analysis will provide common-platform comparisons between many signaling schemes