Underwater Acoustic Communication Using Synchronized Symbol Sequences
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Solution Overview
Problem
Underwater communication systems face challenges due to high acoustic noise levels, multi-path effects, limited frequency bandwidth, and complexity, which result in poor signal-to-noise ratios and reduced data rates, making it difficult to maintain reliable and efficient data transmission in harsh marine environments.
Innovation Solution
The system uses symbols with two components - a distinctive bit code and a character that changes through a predetermined sequence, synchronized between the transmitter and receiver, employing correlator and amplitude detection to enhance signal detection and mitigate interference, with phase shift keying and frequency hopping, and optimal correlation processing to achieve robust data transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If time or frequency domain equalisation is used to remove interference, then signal quality is improved, but system complexity increases and data transfer time increases
Solution Approach 1:
The patent applies preliminary action by using a training sequence (preamble) of known data transmitted before the actual data. The receiver uses this preliminary sequence to determine optimal equalizer coefficients and adjust its parameters in advance, so that when the actual data arrives, the system is already optimized for the current channel conditions, eliminating the need for complex real-time equalisation during data transfer.
2Reliability
If symbols with long time duration are used to avoid inter-symbol interference, then signal reliability is improved, but data rate decreases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the equalizer coefficients based on the received training sequence to optimize the equalization filter parameters for current channel conditions. This allows the system to maintain signal reliability through adaptive equalisation while using shorter symbol durations to achieve higher data rates, resolving the contradiction between symbol duration and data rate.
3Use of energy by moving object
If system complexity is reduced to lower power consumption in battery-powered devices, then energy efficiency is improved, but ability to handle multi-path effects and noise deteriorates
Solution Approach 1:
The patent applies preliminary action by performing channel estimation and equalizer training during the preamble phase before actual data transmission. This preliminary adaptation allows the receiver to be pre-configured for the specific channel conditions, enabling simpler subsequent processing during data transmission while maintaining the ability to handle multi-path effects and noise effectively.
Solution Approach 2:
The patent uses a known training sequence (preamble) that is essentially a copy of predetermined data pattern. By comparing the received preamble with the expected pattern, the system can extract channel characteristics without needing complex real-time processing, thus reducing power consumption while maintaining reliability in handling adverse channel conditions.
4Productivity
If bandwidth is increased to improve data rate, then productivity is improved, but signal absorption increases and range capability deteriorates
Solution Approach 1:
The patent applies parameter changes by using adaptive equalisation with coefficients dynamically adjusted based on channel conditions determined from the training sequence. This allows efficient utilization of available bandwidth for high data rates while the adaptive equalizer compensates for frequency-dependent absorption effects, maintaining communication reliability across the bandwidth.
Data Source
AI summary
A robust underwater communication system, for communication between an acoustic signal transmitter and a remotely positioned acoustic signal receiver, wherein transmitted data is carried by a plurality of symbols each having two components one of which comprises a distinctive bit code and the other of which appertains to the character of the symbol as a whole wherein the character of successive symbols is stepped through a predetermined continuously repeating sequence of distinctive steps each of which occurs once in the sequence, the signal receiver being operated synchronously with the signal transmitter and comprising a correlator arrangement responsive both to the bit code and to the character of received signals for effecting demodulation and having a plurality of outputs one for each symbol, so that as each symbol is detected a signal on the output to which it corresponds pre-dominates and amplitude detector means responsive to the outputs from the correlator arrangement for providing an output signal corresponding to the data transmitted.