Marine Ecosystems Research Department - jamstec japan agency ...

JAMSTEC 2002 Annual Report
Marine Technology Department
ated vehicles and deployed observation systems using
acoustic signals.
This fiscal year, we created demodulation software
that applies multi-channel DFE (Decision Feedback
Equalizer), which can utilize the space diversity
effect, to facilitate communication under environments
that contains a large multi-path mix. Sea trials
carried out in Suruga Bay showed that demodulation
is possible using -QAM multi-channel DFE
demodulator, even when there is a large multi-path.
Figure shows the channel characteristics through
chirp pulse correlated value, and Figures and
Correlated value
110
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90
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10
Direct wave
Reflected wave
0
14 15 16 17 18 19 20
Time [ms]
Fig. 1 Channel characteristics measured using chirp pulse
Constelation in training mode
4
2
0
-2
-4
-4
-2 0 2 4
Constelation in decision oriented mode
4
2
0
-2
-4 -4 -2 0 2 4
show demodulation results. From Figure we can see
that a multi-path (in this sea trial, it is a bottom
reflected wave) of about % of the direct wave is
received about ms after the direct-path. Under such
environment, when using a single-channel receiver,
errors arise as indicated in figure . If data are
demodulated using a two-channel receiver, the space
diversity effect will enable error-free data to be
received as in Figure .
(d) Measurement and sensor technology
A great deal of effort is required by operators to
control AUV attitude in marine research. As AUVs
become more highly functional, there is a greater need
to incorporate various automatic functions using highprecision
sensors and powerful computers to enhance
control over their movement. In this research we are
developing sensors capable of measuring underwater
movement with a high degree of precision. For ring
laser gyros developed as a part of this research, we
adopted conditions used for aircraft in environmental
endurance. Conditions for aircraft require much
tougher environmental performance than conditions
used for ROVs, so in fiscal we improved the performance
of the gyros by modifying a part of the environmental
conditions so they conform with the condi-
Constelation in training mode Constelation in decision oriented mode
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-2
-4
-4 -2 0 2 4
4
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-2
-4 -4 -2 0 2 4
MSE [dB]
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-10
-20
MSE [dB]
0
-10
-20
-30
0 1000 2000 3000 4000 5000 6000 7000 8000
Time [symbols]
Fig. 2 Demodulation example (single element, error: 1.2x10 -3 )
-30
0 1000 2000 3000 4000 5000 6000 7000 8000
Time [symbols]
Fig. 3 Demodulation result (two elements, error free)
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