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|Title: ||Spread-spectrum techniques for environmentally-friendly underwater acoustic communications|
|Authors: ||Sherlock, Benjamin|
|Issue Date: ||2018 |
|Publisher: ||Newcastle University|
|Abstract: ||Anthropogenic underwater noise has been shown to have a negative impact on marine life.
Acoustic data transmissions have also been shown to cause behavioural responses in marine
mammals. A promising approach to address these issues is through reducing the power of
acoustic data transmissions. Firstly, limiting the maximum acoustic transmit power to a safe limit
that causes no injury, and secondly, reducing the radius of the discomfort zone whilst maximising
the receivable range. The discomfort zone is dependent on the signal design as well as the signal
power. To achieve these aims requires a signal and receiver design capable of synchronisation
and data reception at low-received-SNR, down to around −15 dB, with Doppler effects. These
requirements lead to very high-ratio spread-spectrum signaling with efficient modulation to
maximise data rate, which necessitates effective Doppler correction in the receiver structure.
This thesis examines the state-of-the-art in this area and investigates the design, development
and implementation of a suitable signal and receiver structure, with experimental validation in
a variety of real-world channels. Data signals are designed around m-ary orthogonal signaling
based on bandlimited carrierless PN sequences to create an M-ary Orthogonal Code Keying
(M-OCK) modulation scheme. Synchronisation signal structures combining the energy of
multiple unique PN symbols are shown to outperform single PN sequences of the same bandwidth
and duration in channels with low SNR and significant Doppler effects.
Signals and receiver structures are shown to be capable of reliable communications with band
of 8 kHz to 16 kHz and transmit power limited to less than 170.8 dB re 1 μPa @ 1m, or 1W of
acoustic power, over ranges of 10 km in sea trials, with low-received-SNR below −10 dB, at
data rates of up to 140.69 bit/s. Channel recordings with AWGN demonstrated limits of signal
and receiver performance of BER 10−3 at −14 dB for 35.63 bit/s, and −8.5 dB for 106.92 bit/s.
Piloted study of multipath exploitation showed this performance could be improved to −10.5 dB
for 106.92 bit/s by combining the energy of two arrival paths.
Doppler compensation techniques are explored with experimental validation showing synchronisation
and data demodulation at velocities over ranges of ±2.7m/s.
Non-binary low density parity check (LDPC) error correction coding with M-OCK signals is
investigated showing improved performance over Reed-Solomon (RS) coding of equivalent code
rate in simulations and experiments in real underwater channels.
The receiver structures are implemented on an Android mobile device with experiments
showing live real-time synchronisation and data demodulation of signals transmitted through an
|Description: ||PhD Thesis|
|Appears in Collections:||School of Engineering|
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