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Karl Nieman, Kenneth Perrine , Terry Henderson, Keith Lent, Terry Brudner, and Brian Evans

Multi-Stage and Sparse Equalizer Design for Communications Systems in Reverberant Underwater Channels. Karl Nieman, Kenneth Perrine , Terry Henderson, Keith Lent, Terry Brudner, and Brian Evans Applied Research Laboratories: The University of Texas at Austin

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Karl Nieman, Kenneth Perrine , Terry Henderson, Keith Lent, Terry Brudner, and Brian Evans

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  1. Multi-Stage and Sparse Equalizer Design for Communications Systems in Reverberant Underwater Channels Karl Nieman, Kenneth Perrine, Terry Henderson, Keith Lent, Terry Brudner,and Brian Evans Applied Research Laboratories: The University of Texas at Austin 2010 IEEE Workshop on Signal Processing Systems Oct. 8, 2010

  2. Buoys Receiver Divers Communicator(s) Seafloor Instruments UUVs

  3. Representative Underwater Reverberation 0 -10 -20 -30 Signal strength (dB) -40 -50 -60 -70 -20 -10 0 10 20 30 40 Sample time (ms) Reverberations are significant

  4. Doppler effects can be horrendous ??? Toward Away

  5. Phase with no Doppler effects QPSK Ideal pi 00 pi/2 01 0 Phase 10 -pi/2 11 -pi 0 50 100 150 200 250 Sample time (ms)

  6. Uncompensated Doppler effects pi pi/2 Phase 0 -pi/2 -pi 0 50 100 150 200 250 Sample time (ms)

  7. After gross Doppler compensation pi 00 pi/2 01 Phase 0 10 -pi/2 11 -pi 0 50 100 150 200 250 Sample time (ms) !!

  8. Doppler Detection: Carrier Recovery g(t) = f(t)2 t FFT |G(ω)| ω Expected for Zero-Doppler Doppler-inflicted Observation f(t) t O(M ln M) for M samples

  9. Doppler Detection: Replica Bank … … O(cM ln M) for M samples and c replicas Δf = 3.6 Hz c replicas Δf = 3.4 Hz Δf = 3.2 Hz … …

  10. Doppler Detection: Marker Distances O(M ln M) for M samples

  11. Static Equalizer Decision Feed-forward taps Σ x[t] y[t] Feedback taps

  12. Sparse Equalizer Decision Feed-forward taps Σ x[t] y[t] Feedback taps

  13. Fully Adaptive Equalizer Decision Feed-forward taps Σ x[t] y[t] – Update Feedback taps Update: O(N) per symbol (N = total # of taps)

  14. Single-Tap Adaptive Equalizer Decision Feed-forward taps Σ x[t] y[t] – Update Feedback taps Update: O(1) per symbol

  15. Which is the best combination to use?

  16. 250 m 150 m Start July, 2009 - BPSK, 30 kHz carrier, 1 kHz symbol rate (1 kbit/sec) - QPSK, 25 kHz carrier, 32 kHz symbol rate (64 kbits/sec)

  17. Results: Gross Doppler Detection • Carrier recovery  highest accuracy

  18. Results: BPSK (Narrowband) Packet SNR at 150 m, Stationary SNR at 250 m, In Motion 1 4 8 16 32 64 1 4 8 16 32 64 # feedback taps # feedback taps Static EQ Sparse EQ Adaptive (Single-Tap) Adaptive (Full)

  19. Results: QPSK Packet SNR at 150 m, Stationary SNR at 250 m, In Motion 4 16 64 256 4 16 64 256 # feedback taps # feedback taps Static EQ Sparse EQ Adaptive (Single-Tap) Adaptive (Full)

  20. BPSK, stationary BPSK, in motion QPSK, stationary QPSK, in motion Output SNR (dB) Adaptation rate (8 feedforward and 32 feedback taps)

  21. Conclusions • No single choice for EQ parameters • EQ type • Number of adaptive taps • Adaptation rate • Underwater channel changes quickly • Reverberation length • 150m to 250m • Underwater features • Thermocline

  22. Conclusions • Fully adaptive equalizer: • Most sophisticated and most computationally expensive • Does not work in all cases • Run multiple techniques and choose the best

  23. Dataset • 5-element underwater dataset available: • 5 simultaneous receiver elements • 62.5 kHz center frequency, up to 31.25 kHz bandwidth • MATLAB format http://users.ece.utexas.edu/~bevans/projects/underwater/datasets/index.html

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