Mobile Underwater Acoustic Communications via Double Differential Encoding

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Solution Overview

Problem

Mobile underwater acoustic communications face challenges such as low signal-to-noise ratios, significant Doppler shifts, and severe inter-symbol interference due to environmental factors and relative motion, making existing LRAC schemes complex and unreliable.

Innovation Solution

The method employs double differentially encoded signals with direct sequence spread spectrum (DD-SS), which eliminates the need for complicated signal processing like channel estimation and phase/Doppler tracking, increasing signal-to-noise ratio, suppressing multipath interference, and improving bandwidth efficiency through data multiplexing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional LRAC schemes are used in mobile applications, then communication capability is provided, but receiver processing becomes complicated requiring phase/Doppler tracking, channel estimation, and equalization

Engineering Contradiction:

Improvecommunication reliabilityVSAvoidreceiver processing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent transforms the communication signal parameters by applying double differential encoding and direct sequence spread spectrum modulation. This changes the signal representation from conventional phase-modulated signals to differentially encoded spread spectrum signals, which are inherently more robust to Doppler shifts and eliminate the need for complex phase tracking and channel estimation at the receiver

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent extracts and removes the problematic components from the receiver processing chain. By using double differential encoding, the need for phase/Doppler tracking and channel estimation is completely eliminated. The spread spectrum technique further simplifies reception by providing processing gain and inherent multipath rejection, removing the need for complex equalization

Inventive Principle:

Principle #2Taking out (Extraction)

2Adaptability or versatility

If mobile LRAC is implemented with conventional schemes, then communication is enabled, but performance deteriorates due to low signal-to-noise ratio, Doppler shifts, and inter-symbol interference

Engineering Contradiction:

Improvemobile communication capabilityVSAvoidcommunication performance

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent converts the harmful effects of mobile underwater acoustic channels into beneficial features. The double differential encoding transforms Doppler-induced phase variations from harmful distortions into useful frequency shifts that can be easily compensated. The spread spectrum technique converts multipath interference and low signal-to-noise ratio conditions into advantages through processing gain and inherent correlation properties that reject interference

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent applies preliminary signal processing at the transmitter through double differential encoding and spread spectrum modulation. This preliminary action pre-compensates for expected channel effects such as Doppler shifts and multipath interference, so that the receiver only needs simple correlation-based detection without complex tracking or equalization

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If fixed LRAC schemes are applied to mobile cases, then theoretical performance may be achieved, but practical sea-going experiments show frequent performance outage

Engineering Contradiction:

Improvetheoretical performanceVSAvoidpractical performance stability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent introduces dynamic adaptation through double differential encoding that automatically tracks and compensates for time-varying Doppler shifts without requiring explicit feedback or reconfiguration. The spread spectrum signal maintains its correlation properties dynamically throughout the transmission, adapting to changing channel conditions inherent in mobile applications

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS9030918B2Method for mobile underwater acoustic communications

Publication Date: 2015.05.12 THE GOVERNMENT OF THE UNITED STATES OF AMERICA AS REPRESENTED BY THE SECRETARY DEPARTMENT OF HEALTH & HUMAN SERVICES

AI summary

A method for mobile underwater acoustic communications includes double differentially (DD) encoding a communication signal to produce a DD-encoded communication signal, applying direct sequence spread spectrum (SS) to the DD-encoded signal to produce a DD-SS communication output signal, and transmitting the DD-SS communication output signal. The method i) increases the SNR via processing gain, ii) eliminates the ISI through multipath suppression, and iii) enables bandwidth efficiency improvement via data multiplexing. The method is shown capable of facilitating simple receiver processing and offering performance robustness against unpredictable channel fluctuations.