DFT-Spread FBMC/OQAM Modulation for PAPR Reduction
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Solution Overview
Problem
The filter bank multi-carrier (FBMC) modulation technique, particularly FBMC/OQAM, suffers from high peak to average power ratio (PAPR) due to overlapping subcarrier signals, leading to performance degradation and increased out-of-band power when passing through nonlinear amplifiers, which hinders the achievement of a single carrier effect even with discrete Fourier transform (DFT) spreading.
Innovation Solution
A modulation apparatus and method that performs DFT on input data symbols, divides them into real and imaginary parts, multiplies by phase shift coefficients, and modulates using the FBMC/OQAM scheme to generate candidate transmission signals with identically time-shifted subcarriers, selecting the signal with the smallest PAPR for transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If FBMC/OQAM modulation is used to achieve multi-carrier transmission, then data transmission capacity is improved, but peak to average power ratio (PAPR) increases due to overlapping subcarrier signals
Solution Approach 1:
The patent applies DFT spreading to the input data symbols before FBMC/OQAM modulation. This preliminary transformation of the data symbols into DFT-spread symbols modifies the signal characteristics in advance, ensuring that when subcarriers are generated and overlapped during FBMC/OQAM modulation, the resulting signal has reduced PAPR while maintaining the multi-carrier transmission capacity.
2Object-generated harmful factors
If DFT spreading is applied to FBMC/OQAM, then PAPR is reduced, but single carrier effect cannot be achieved due to structural problems of OQAM
Solution Approach 1:
The patent introduces different time shifts for different subcarriers in the FBMC/OQAM modulation process. Specifically, even-indexed subcarriers are time-shifted by one symbol duration while odd-indexed subcarriers are time-shifted by half a symbol duration. This local differentiation in time shifting allows the system to achieve both PAPR reduction through DFT spreading and maintain single carrier effect by controlling the overlapping characteristics of subcarriers locally.
3Object-generated harmful factors
If multiple candidate transmission signals are generated and selected based on smallest PAPR, then PAPR reduction performance is improved, but device complexity increases
Solution Approach 1:
The patent generates multiple candidate transmission signals (typically 2 or 4 candidates) from the same DFT-spread symbols by applying different time shift patterns, then selects the candidate with the smallest PAPR. This partial action approach provides PAPR reduction performance improvement without requiring complete redesign of the modulation system, achieving a balance between performance enhancement and acceptable increase in device complexity.
Data Source
AI summary
A plurality of candidate transmission signals which are modulated according to a discrete Fourier transform (DFT)-spread filter-bank multi-carrier (FBMC)/offset quadrature amplitude modulation (OQAM) scheme and are capable of achieving a single carrier effect are generated. A candidate transmission signal having the smallest peak to average power ratio (PAPR) is selected and transmitted, so that a PAPR performance can be effectively improved.