DFT-s-OFDM Signal Phase Shifting for Spectral Efficiency
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Solution Overview
Problem
The existing DFT-s-OFDM systems face limitations in spectral efficiency and flexibility when using single sideband (SSB) transmission, leading to inter-symbol interference (ISI) for QAM modulation and inflexibility in channel utilization.
Innovation Solution
The proposed solution involves a signal transmission apparatus that precodes and phase-shifts modulation symbols using DFT, allowing for the selection and ordering of Fourier coefficients to generate a DFT-s-OFDM signal that exploits SSB transmission in both time and frequency domains, thereby overcoming the limitations of conventional systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If single sideband (SSB) transmission is used with conventional DFT-s-OFDM, then spectral efficiency is improved, but inter-symbol interference (ISI) occurs for QAM modulation and flexibility is reduced
Solution Approach 1:
The modulation symbols are segmented into two groups: real-valued symbols for even indices and imaginary-valued symbols for odd indices. This segmentation allows the signal to be processed as two separate orthogonal components, eliminating ISI while maintaining spectral efficiency. The even-indexed symbols are mapped to one set of subcarriers and the odd-indexed symbols to another set, creating orthogonal transmission paths.
Solution Approach 2:
The patent introduces asymmetric modulation where real and imaginary parts of the modulation symbols are treated differently. Real-valued symbols (even indices) are modulated with one phase reference while imaginary-valued symbols (odd indices) are modulated with a quadrature phase reference. This asymmetric treatment enables SSB transmission without ISI by exploiting the orthogonality between real and imaginary components.
2Ease of manufacture
If conventional DFT-s-OFDM is used, then implementation is straightforward, but spectral efficiency is limited and flexibility in modulation scheme selection is reduced
Solution Approach 1:
The patent introduces dynamic modulation scheme selection capability, allowing the system to adaptively choose between different modulation formats (BPSK, QPSK, M-PAM, M-QAM) based on channel conditions and service requirements. The modular architecture enables flexible configuration of modulation order and type without requiring complete system redesign, thus improving spectral efficiency while maintaining implementation feasibility.
Solution Approach 2:
The patent creates a universal transmission framework that can accommodate multiple modulation schemes (BPSK, QPSK, M-PAM, M-QAM) and multiple service types within a single system architecture. The DFT-s-OFDM structure is enhanced to support both traditional complex modulation and the new real/imaginary segmented modulation, making the system multi-functional and adaptable to diverse communication requirements.
3Productivity
If higher order M-PAM is used with SSB transmission, then spectral efficiency increases, but signal processing complexity increases due to required ISI cancellation
Solution Approach 1:
The patent extracts and eliminates the ISI problem by using orthogonal real and imaginary modulation components. Instead of applying complex ISI cancellation algorithms to higher order M-PAM signals, the invention takes out the ISI component entirely through orthogonal signaling design. This allows higher order M-PAM to be used with SSB transmission without requiring advanced signal processing for ISI cancellation, thus reducing device complexity while maintaining high spectral efficiency.
Data Source
AI summary
A signal transmission apparatus configured for transmission of modulation symbols utilizing orthogonal frequency-division multiplexing, OFDM, based on Discrete Fourier Transform, DFT, precoding. The signal transmission apparatus is configured to generate a DFT spread OFDM (DFT-s-OFDM) signal by receiving an input (x[m]) comprising M modulation symbols for m=0, 1, . . . , M−1 and phase-shifting the input (x[m]) thereby generating a phase-shifted input ({acute over (x)}[m]). The signal transmission apparatus is configured for precoding the phase-shifted input utilizing DFT, thereby generating M Fourier coefficients (X[k]) and ordering the Fourier coefficients and selecting M/2 Fourier coefficients. The signal transmission apparatus is configured for generating the DFT-s-OFDM signal based on the M/2 selected Fourier coefficients.