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

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

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

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

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

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)

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

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

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

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

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

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

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

Ray/beam trace and incoherent TL

CTD Record

Predicted Impulse Response

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

SX-C (San Diego) Eigenrays and impulse response

SX-D (Buzzard’s Bay) impulse response Drift 1: 0-3.5 km Drift 2: 2.2-4.2 km Drift 3: 1.4-3.8 km

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

MFSK BER

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)

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

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

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

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

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