SignalEx: Linking environmental acoustics with the signaling schemes

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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

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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

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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
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Upward refraction in FRONT-1 caused strong
dependence on the sea-surface boundary
Range (m)
Year-day
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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

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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. SAIC/SPAWARSSC
d N-QAM (BPSK, QPSK, 16-QAM) Northeastern Univ., Delphi, NUWC, Benthos
e Pulse-Position Modulation (PPM) SAIC/SPAWARSSC
g Orthogonal Frequency Division Multiplexing (OFDM) Polytechnic Univ.
h Multi-Carrier Code Division Multiple Access (MC-CDMA) Polytechnic Univ.
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Mk-1
Telesonar testbeds
Mk-2, 2000-01
Mk-1, 1998-99
Mk-1 Sublink98
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SignalEx waveform
LFM chirps (8-11 kHz)
Type-a MFSK waveforms
7-tone comb
LFM chirps (8-16 kHz)
Type-x DPSK waveforms
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SignalEx spectrogram
LFM chirps (8-11 kHz)
Type-a MFSK waveforms
7-tone comb
LFM chirps (8-16 kHz)
Type-x DPSK waveforms
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SignalEx 2000 experiment locations
SX-D Buzzards 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
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SignalEx-B in ForeFRONT (New England Shelf) April
17-20, 2000
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SignalEx-C in Sublink (Point Loma)May 23-25, 2000
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SignalEx-D (Buzzards Bay)August 10-11, 2000
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Ray/beam trace and incoherent TL
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CTD Record
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Predicted Impulse Response
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SX-B (New England Shelf)impulse response
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SX-C (San Diego)Eigenrays and impulse response
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SX-D (Buzzards Bay) impulse response
Drift 1 0-3.5 km
Drift 2 2.2-4.2 km
Drift 3 1.4-3.8 km
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Type-x (DPSK) bit error rates
Range 7 km
Range 5 km
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MFSK BER
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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)

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DSSS/DPSK (type-x) bit errors in SX-B400-bit
transmissions8 kHz bandwidth
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DSSS/DPSK bit errors in SX-C64-bit
transmissions 3 kHz bandwidth
R3 km
R5 km
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DSSS/DPSK bit errors in SX-D (Drift 1)500-bit
transmissions 8 kHz bandwidth
Channel errors
Convolutional coding
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DSSS/DPSK bit errors in SX-D (Drift 3)500-bit
transmissions 8 kHz bandwidth
Channel errors
Convolutional coding
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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