OAM Multiplexing Interference Suppression Using Concentric UCAs

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Solution Overview

Problem

In OAM multiplexing communication systems, inter-mode interference occurs due to deviations in the optical axis, tilt, or reflected waves between transmitting and receiving UCAs, leading to deteriorated communication quality.

Innovation Solution

The system employs a configuration with concentrically disposed uniform circular arrays (UCAs) at the transmitting and receiving stations, using discrete Fourier transform and inverse Fourier transform to generate and demultiplex OAM modes, and calculates weights based on channel estimation to suppress interference between OAM modes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single UCA is used for OAM mode transmission, then the system structure is simple, but inter-mode interference occurs due to optical axis deviation, tilt, or reflected waves

Engineering Contradiction:

Improveantenna structureVSAvoidcommunication quality

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The single UCA is divided into multiple concentric UCAs, each with its own DFT/IDFT processing. This segmentation allows independent optimization of each sub-array's contribution to OAM modes, enabling interference suppression through coordinated processing across multiple segments while maintaining overall system manageability

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system transitions from a two-dimensional single UCA plane to a three-dimensional concentric UCA structure with multiple radial layers. This dimensional expansion provides additional spatial degrees of freedom for beamforming and OAM mode generation, enabling better control over interference patterns and improved communication quality

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If multiple concentric UCAs are used to suppress inter-mode interference, then communication quality is improved, but device complexity increases

Engineering Contradiction:

Improvecommunication qualityVSAvoidantenna structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Each UCA in the concentric structure serves multiple functions: generating OAM modes, suppressing inter-mode interference through its specific radial position, and contributing to spatial diversity. This multi-functionality justifies the increased structural complexity by providing multiple benefits from each additional component

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent replaces complex mechanical alignment systems with signal processing-based interference suppression. Instead of precisely mechanically aligning a single UCA to eliminate interference from optical axis deviation or tilt, the system uses multiple UCAs with DFT/IDFT processing to computationally suppress inter-mode interference, trading mechanical simplicity for signal processing complexity

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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

This approach effectively suppresses inter-mode interference, improving communication quality by determining appropriate transmitting and receiving weights, even under non-ideal alignment conditions or with reflected waves.

Implementation Method 1

performing discrete Fourier transform on input signals, so as to output to the corresponding UCAs

Methodology Applied

Scientific EffectDiscrete Fourier transform:

Implementation Method 2

performing inverse Fourier transform on the input signals, so as to output by each of received signal sequences

Methodology Applied

Scientific EffectInverse Fourier transform:

Implementation Method 3

subjecting a radio signal to spatial multiplex transmission by using orbital angular momentum (OAM) of an electromagnetic wave

Methodology Applied

Scientific EffectOrbital angular momentum: Angular Momentum

Data Source

PatentEP3691150B1OAM multiplexing communication system and inter-mode interference elimination method

Publication Date: 2023.01.18 NIPPON TELEGRAPH & TELEPHONE CORP

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AI summary

Inter-mode interference occurring due to deviation of an optical axis, a tilt, or a reflected wave between a transmitting UCA and a receiving UCA is suppressed with low computational complexity. A transmitting station includes a plurality of transmitting weight multiplication units each inputting a plurality of transmission signal sequences and multiplying each of the transmission signal sequences by a transmitting weight, to be converted into MTX signals corresponding to UCAs forming an M-UCA so as to output the converted signals, and MTX transmitting OAM mode generation units inputting the signals corresponding to the UCAs and performing discrete Fourier transform on the input signals, so as to output to the corresponding UCA; and a receiving station includes MRX receiving OAM mode demultiplex units inputting signals from each of the UCAs forming the M-UCA and performing inverse Fourier transform on the input signals, so as to output by each of received signal sequences, and a plurality of receiving weight multiplication units multiplying for each of the received signal sequences by a receiving weight, so as to demultiplex the received signal sequences subjected to spatial multiplex transmission and to output the received signal sequence in which interference between spatially multiplexed OAM modes is suppressed.