Underwater OAM Optical Communication System
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Solution Overview
Problem
Undersea optical communication systems face limitations in data rate and range due to turbidity, multipath interference, and lack of low probability of intercept (LPI), which restricts connectivity and robustness against eavesdropping.
Innovation Solution
An underwater communication system utilizing orbital angular momentum (OAM) with pre-coding and power adaptation based on channel conditions, incorporating orthogonal frequency division multiplexing (OFDM) and singular value decomposition (SVD) to maximize data rate and mitigate turbidity effects, while providing LPI and protection against eavesdropping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If acoustic communication is used for undersea communication, then propagation loss is reduced and connectivity is improved, but data rate becomes much lower due to lower acoustic frequencies
Solution Approach 1:
The patent replaces acoustic wave propagation with optical wave propagation. Instead of using acoustic pressure waves that travel slowly through water, the system uses laser beams to carry information optically through the water column, enabling much higher data rates while maintaining undersea connectivity.
Solution Approach 2:
The patent changes the fundamental parameter of wave propagation from acoustic frequency to optical frequency. By using laser light instead of acoustic waves, the system achieves data rates in the gigabit per second range compared to the much lower data rates of acoustic communication, while operating in the same undersea environment.
2Productivity
If RF communication is used for undersea communication, then data rate can be higher, but electro-magnetic waves are rapidly absorbed in conductive seawater
Solution Approach 1:
The patent changes the electromagnetic spectrum parameter from RF frequencies to optical frequencies. Laser light at optical frequencies experiences much lower absorption in seawater compared to RF waves, enabling signal propagation over practical distances while maintaining high data rates.
3Productivity
If laser communication is used to achieve high data rates, then data rate increases to Gbps, but range is limited to about 100-200 meters due to attenuation
Solution Approach 1:
The patent implements adaptive power allocation that dynamically adjusts the transmit power for each OAM mode based on real-time channel conditions. When channel conditions are favorable, higher power is allocated to maintain high data rates over extended ranges. The system also adapts the modulation and coding schemes for each sub-carrier to optimize the trade-off between data rate and range.
Solution Approach 2:
The patent transitions from single-mode optical communication to multi-mode OAM communication. By utilizing multiple orthogonal OAM modes simultaneously, the system creates parallel communication channels that increase overall capacity and extend effective range through spatial diversity, allowing data to be transmitted through multiple independent paths.
4Reliability
If optical communication is used to provide LPI and directionality, then low probability of intercept is improved, but scattering increases beam divergence and requires wider field-of-view at receiver
Solution Approach 1:
The patent segments the optical signal into multiple orthogonal OAM modes, each carrying independent data streams. This segmentation allows the receiver to use narrower field-of-view for each mode while maintaining overall system performance, as each mode can be detected independently with more focused optical collectors.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves a significant increase in data rate and range, enhances connectivity, and provides robustness against turbidity and eavesdropping by optimizing power allocation and bit loading across OAM modes and OFDM subcarriers, effectively addressing the limitations of existing undersea communication technologies.
Implementation Method 1
modulate the data streams onto an optical signal corresponding to an orthogonal OAM mode
Implementation Method 2
Scattering also increases the divergence of a transmitted laser beam. Scattering decreases the received signal level
Implementation Method 3
Attenuation occurs due to losses from absorption and scattering
Data Source
AI summary
A system for providing underwater communication using orbital angular momentum (OAM) includes a transmitter that processes input data to be transmitted using pre-coding information based on current transmission channel conditions to maximize data rate based on channel conditions. A receiver receives a transmitted multiplexed OAM optical signal and analyzes the received signal for channel state information. The channel state information is used to determine a set of pre-coding values that allow the transmitter to pre-code the input data to maximize the data rate based on current channel conditions. The pre-coding values are mapped to a codebook entry which identifies the pre-coding values. The codebook entry is transmitted from the receiver to the transmitter. The transmitter uses the received codebook entry to identify pre-coding values used to process subsequent input data to be transmitted in order to enhance data rate across the transmit channel.