OFDM Signal Space Diversity Using I/Q Interleaving and Rotation
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Solution Overview
Problem
Current LTE wireless communication systems face challenges in maintaining robustness and spectral efficiency, particularly in high-multipath propagation conditions, due to the increased number of subcarriers used in OFDM symbols, which can lead to difficulty in demodulating data and requiring a higher signal-to-noise ratio to achieve a target bit error rate.
Innovation Solution
The implementation of signal space diversity through rotation and separate interleaving of the in-phase (I) and quadrature (Q) components of modulation symbols, combined with adaptive rotation angles and interleaving patterns, enhances the resilience of OFDM transmission in fading channels and improves the robustness of data detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of sub-carriers is increased to improve spectral efficiency, then spectral efficiency is improved, but demodulation robustness deteriorates
Solution Approach 1:
The patent segments the modulation symbol into in-phase (I) and quadrature (Q) components, treating them as separate entities that can be independently interleaved and transmitted. This segmentation allows the system to maintain high spectral efficiency while improving robustness by distributing these components across different sub-carriers, preventing simultaneous degradation of both components in fading conditions.
Solution Approach 2:
The patent introduces a new dimension of diversity by separating and independently interleaving the I and Q components of modulation symbols. This transforms the traditional single-dimension transmission into a two-dimensional approach where I and Q components experience different channel conditions, providing diversity gain without reducing spectral efficiency.
2Reliability
If signal space diversity with rotation is applied to improve robustness, then demodulation robustness is improved, but system complexity increases
Solution Approach 1:
The patent employs dynamic rotation angles that are adaptively selected based on the detected modulation scheme. Different rotation angles are applied for different modulation orders (e.g., QPSK, 16-QAM, 64-QAM), allowing the system to optimize robustness for each modulation type while keeping the complexity manageable through standardized angle sets.
Solution Approach 2:
The patent changes the rotation angle parameter according to the modulation scheme being used. By adapting this single parameter based on modulation detection, the system achieves improved robustness across different modulation orders without requiring complex reconfiguration of the entire signal processing chain.
Data Source
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AI summary
A transmitter transmits payload data using Orthogonal Frequency Division Multiplexed (OFDM) symbols, the transmitter comprising a frame builder configured to receive the payload data to be transmitted and to receive signalling data for use in detecting and recovering the payload data at a receiver, and to form the payload data into data-units for transmission. A modulator is configured to modulate a plurality of sub-carriers of one or more OFDM symbols with the signalling data and the payload data in accordance with a modulation scheme to provide for each of the plurality of sub- carriers a modulation symbol, a prefixing circuit prefixes a guard interval to the one or more OFDM symbols, and a transmission circuit transmits the one or more OFDM symbols. The modulator includes a I/Q interleaver which is configured to receive a real component of the modulation symbol of each of the one or more sub-carriers of the one or more OFDM symbols and to interleave the real component of the modulation symbols differently to the imaginary component. By interleaving the real and imaginary components of the modulation symbols differently for transmission there is a greater likelihood of recovering one or both of the signalling data and the payload data.