Multicarrier Signal Generation via Frequency Offset and Sinusoidal Windowing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current multicarrier modulation techniques, such as OFDM, face limitations in spectral efficiency and the ability to handle time-dispersive channels due to the absence of a guard interval, which is necessary for echo absorption in radio transmissions.
Innovation Solution
A method for generating multicarrier signals that combines real and imaginary parts of source symbols with delayed versions of themselves, applying sinusoidal windowing in the frequency domain to improve spectral efficiency and allow for the insertion of a guard interval, while maintaining quadrature and simplicity in hardware implementation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If OFDM modulation is used, then simplicity of equalization and resistance to time-dispersive channels is improved, but spectral efficiency deteriorates
Solution Approach 1:
The invention segments the source symbols into real and imaginary parts, processing them separately through different modulation paths. This segmentation allows independent optimization of each part's spectral characteristics while maintaining the overall signal structure, thereby improving spectral efficiency without compromising resistance to time-dispersive channels.
Solution Approach 2:
The patent applies asymmetric modulation where the real and imaginary parts of the signal are modulated differently - the real part uses one set of carriers while the imaginary part uses another set with different frequency offsets. This asymmetric treatment enables better spectral confinement and efficiency while preserving the robustness against time-dispersive channels through the differentiated carrier structures.
2Reliability
If guard interval is inserted in OFDM, then echo absorption capability is improved, but spectral efficiency deteriorates
Solution Approach 1:
Instead of adding a guard interval to the time-domain signal as in conventional OFDM, the invention inverts the approach by using offset quadrature amplitude modulation in the frequency domain. The guard interval function is achieved through frequency offset between the real and imaginary carrier sets, eliminating the need for time-domain guard intervals and thus preserving spectral efficiency while maintaining echo absorption capability.
Solution Approach 2:
The patent introduces frequency offset as an intermediary mechanism between the real and imaginary signal components. This frequency offset acts as a mediator that provides the time separation equivalent to a guard interval, enabling echo absorption without the spectral penalty of traditional time-domain guard intervals. The frequency offset effectively translates the guard interval function into the frequency domain.
3Productivity
If OFDM/OQAM modulation is used, then spectral efficiency is improved, but ability to absorb echoes deteriorates
Solution Approach 1:
The invention applies preliminary frequency offset to the carrier sets before modulation. By pre-establishing the frequency separation between real and imaginary carrier components, the system proactively creates the time separation needed for echo absorption before the signal encounters time-dispersive channels. This preliminary action ensures both spectral efficiency and echo absorption capability are maintained simultaneously.
4Productivity
If sinusoidal windowing is applied in time domain, then spectral efficiency is improved, but hardware implementation complexity increases
Solution Approach 1:
The patent replaces the mechanical/time-domain sinusoidal windowing operation with a frequency-domain frequency offset mechanism. Instead of multiplying the time-domain signal by a sinusoidal window function (which requires complex hardware multiplication and synchronization), the invention achieves the same spectral confinement effect through simple frequency offset in the carrier modulation, dramatically reducing hardware implementation complexity while maintaining spectral efficiency.
Data Source
Figure 1~3a
Figure 2~3b
Figure 4A~4B
AI summary
The invention relates to a method for generating a multicarrier signal formed of multicarrier symbols comprising the following steps: acquiring (E200) N first modulating symbols and N second modulating symbols, from a sequence of source symbols, the acquisition comprising, for at least one of the source symbols of index k, a sub-step of: - linearly combining (E200a) a real part, respectively an imaginary part, of the source symbol of index k with a real part, respectively an imaginary part, of one of the source symbols of index k +/- R, where R is a nonzero integer, delivering at least one first, respectively second, combined symbol, time-frequency transforming (E210) the N first, respectively N second, modulating symbols, delivering a first, respectively second, block of N carriers; and generating (E220) said multicarrier symbol from the first and second blocks of N carriers.