karl nieman, kenneth perrine , terry henderson, keith lent, terry brudner, and brian evans
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
APPLIED RESEARCH LABORATORIES
THE UNIVERSITY OF TEXAS AT AUSTIN
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 SystemsOct. 8, 2010
APPLIED RESEARCH LABORATORIES
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Communicator(s)
Receiver
UUVsSeafloor
Instruments
Buoys
Divers
APPLIED RESEARCH LABORATORIES
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Reverberations are significant
-20 -10 0 10 20 30 40-70
-60
-50
-40
-30
-20
-10
0Representative Underwater Reverberation
Sample time (ms)
Sig
nal s
treng
th (d
B)
APPLIED RESEARCH LABORATORIES
THE UNIVERSITY OF TEXAS AT AUSTIN
APPLIED RESEARCH LABORATORIES
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Doppler effects can be horrendous
???Toward Away
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Phase with no Doppler effects
0 50 100 150 200 250-pi
-pi/2
0
pi/2
piQPSK Ideal
Sample time (ms)
Pha
se
00
01
10
11
APPLIED RESEARCH LABORATORIES
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Uncompensated Doppler effects
0 50 100 150 200 250-pi
-pi/2
0
pi/2
pi
Sample time (ms)
Pha
se
APPLIED RESEARCH LABORATORIES
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After gross Doppler compensation
0 50 100 150 200 250-pi
-pi/2
0
pi/2
pi
Sample time (ms)
Pha
se
00
01
10
11
!!
APPLIED RESEARCH LABORATORIES
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Doppler Detection: Carrier Recovery
t
f(t)
t
g(t) = f(t)2
Expected for
Zero-DopplerDoppler-inflicted
Observation
FFT
ω
|G(ω)| O(M ln M) for M samples
APPLIED RESEARCH LABORATORIES
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Doppler Detection: Replica Bank
…
Δf = 3.6 Hz
Δf = 3.4 Hz
Δf = 3.2 Hz…
……O(cM ln M) for M samples and c replicas
c replicas
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Doppler Detection: Marker Distances
O(M ln M) for M samples
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Static Equalizer
ΣFeed-forward taps
Feedback taps
x[t] y[t]
Decision
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Sparse Equalizer
ΣFeed-forward taps
Feedback taps
x[t] y[t]
Decision
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Fully Adaptive Equalizer
ΣFeed-forward taps
x[t] y[t]
Decision
Update
Feedback taps
–
Update: O(N) per symbol(N = total # of taps)
APPLIED RESEARCH LABORATORIES
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Single-Tap Adaptive Equalizer
ΣFeed-forward taps
x[t] y[t]
Decision
Update
Feedback taps
–
Update: O(1) per symbol
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Which is the best combination to use?
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- BPSK, 30 kHz carrier, 1 kHz symbol rate (1 kbit/sec)- QPSK, 25 kHz carrier, 32 kHz symbol rate (64 kbits/sec)
250 m
150 m
July, 2009
Start
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Results: Gross Doppler Detection
• Carrier recovery highest accuracy
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Results: BPSK (Narrowband) Packet
SNR at 150 m, Stationary SNR at 250 m, In Motion
# feedback taps1 4 8 16 32 64
# feedback taps1 4 8 16 32 64
Static EQSparse EQAdaptive (Single-Tap)Adaptive (Full)
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Results: QPSK Packet
SNR at 150 m, Stationary SNR at 250 m, In Motion
# feedback taps# feedback taps4 16 64 256 4 16 64 256
Static EQSparse EQAdaptive (Single-Tap)Adaptive (Full)
APPLIED RESEARCH LABORATORIES
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Adaptation rate (8 feedforward and 32 feedback taps)
Out
put S
NR
(dB
)
BPSK, stationaryBPSK, in motionQPSK, stationaryQPSK, in motion
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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
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Conclusions
• Fully adaptive equalizer:– Most sophisticated and most computationally expensive– Does not work in all cases
• Run multiple techniques and choose the best
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Dataset
http://users.ece.utexas.edu/~bevans/projects/underwater/datasets/index.html
• 5-element underwater dataset available:– 5 simultaneous receiver elements– 62.5 kHz center frequency, up to 31.25 kHz bandwidth– MATLAB format