OFDM Orbital Angular Momentum Transmitter Bore-Sight Singularity
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Solution Overview
Problem
Current radio communication systems using Orbital Angular Momentum (OAM) face inefficiencies due to the need for large receiving antennas and precise antenna alignment, making them impractical for long-distance satellite communications, and they struggle with the phase singularity issue at the bore-sight direction.
Innovation Solution
A multidimensional space modulation technique that allows orthogonal RF OAM modes to be transmitted and received in the bore-sight direction using a single antenna, overcoming phase singularity by introducing supplementary phase modulation and simplifying antenna design, enabling efficient transmission and reception regardless of antenna element spacing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pure OAM modes are transmitted using pure tones, then transmission capacity is increased, but the receiving antenna dimensions become impractically large
Solution Approach 1:
The patent applies parameter changes by modulating the OAM modes with OFDM signals, transforming them from pure tones to complex modulated signals. This changes the frequency and phase parameters dynamically, allowing the transmission of multiple data streams while maintaining practical antenna dimensions. The OFDM modulation spreads the signal across multiple subcarriers, increasing transmission capacity without requiring impractically large receiving antennas.
Solution Approach 2:
The patent introduces another dimension by using multiple OAM modes (different topological charges) simultaneously. Instead of relying on a single frequency dimension, it exploits the spatial dimension of orbital angular momentum modes. This allows multiplexing multiple independent data streams in the OAM domain, significantly increasing transmission capacity while keeping antenna sizes practical.
2Productivity
If OAM modes are transmitted using pure tones, then transmission capacity is increased, but antenna alignment precision requirements become excessive
Solution Approach 1:
The patent applies dynamics by using OFDM modulation which creates time-varying phase and frequency characteristics. The cyclic prefix in OFDM provides temporal redundancy that helps maintain signal integrity despite alignment variations. This dynamic modulation scheme makes the system more robust to alignment errors compared to static pure tone transmission.
Solution Approach 2:
The patent implements beforehand cushioning through the cyclic prefix in OFDM signals. The cyclic prefix acts as a guard interval that compensates for timing and alignment variations before they affect the main signal. This pre-built redundancy cushions the system against alignment precision errors, allowing practical antenna implementations without excessive precision requirements.
3Device complexity
If standard antennas are used for OAM transmission, then device complexity is reduced, but phase singularity issues at bore-sight direction occur
Solution Approach 1:
The patent applies mechanics substitution by replacing the need for complex phased array antenna systems with standard single-element antennas. Instead of using multiple antenna elements with precise phase control (mechanical/electrical complexity), it uses a single antenna transmitting OFDM-modulated OAM modes. The phase singularity issue is addressed through signal processing rather than antenna array geometry.
Solution Approach 2:
The patent introduces an intermediary - the OFDM modulation scheme - between the antenna and the OAM mode transmission. The OFDM signal acts as an intermediary that carries the information while avoiding the direct phase singularity problem. The modulated signal structure provides redundancy and robustness that mediates against the harmful effects of phase singularities.
Data Source
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AI summary
Disclosed herein is a radio communications method that comprises carrying out, by a transmitter (7), the following steps: providing a digital time signal carrying digital symbols to be transmitted; and transmitting a radio frequency signal carrying said digital time signal. The method further comprises carrying out, by a receiver (8), the following steps: receiving the radio frequency signal transmitted by the transmitter (7); processing the received radio frequency signal so as to obtain a corresponding incoming digital signal; and extracting, from the incoming digital signal, the digital symbols carried by said incoming digital signal. Said digital time signal carrying the digital symbols to be transmitted results from an approximation of the Hilbert transform in frequency domain, which approximation is based on a frequency main mode and one or more frequency twisted modes, wherein said frequency main and twisted modes carry, each, respective digital symbols to be transmitted. The transmitted signal is produced by a bank of IFFT each devoted to one mode and consists in overlapped OFDM modes with growing bandwidths per modes.